Description:TECHNICAL FIELD
The present disclosure relates generally to the field of density and viscosity sensors and fluid mechanics and more specifically, to a droplet-based oscillation system for sensing physical properties of fluids using a droplet as test fluid.
BACKGROUND
In the field of fluid mechanics, determination of physical properties of a fluid is important in a variety of applications, such as biomedical, food processing, chemical processing, and monitoring of lubrication or oil condition, and the like. In such applications, viscosity and density of the fluid are important physical parameters, which are used to determine effect of physical properties of the fluid. Currently, there are various viscosity density sensors used to determine the viscosity and the density of the fluid together. Some conventional viscosity-density sensors include bulk acoustic wave (BAW) sensors, surface acoustic wave (SAW) sensors, or cantilever and diaphragm-based sensors in which a cantilever is vibrated inside the test fluid, to estimate the viscosity and the density of the test fluid, and the like. There are many other types of viscosity sensors, such as wire, spiral, or spring-based sensors. Most of the conventional systems involve submerging a resonator inside a test fluid medium.
Currently, one of the major technical problems associated with the conventional viscosity-density sensors is that such conventional systems and sensors are unable to decouple the measurement of viscosity and density (i.e., unable to separately determine the viscosity and density of the test fluid). Certain attempts have been made to develop the viscosity density sensors, which decouple the measurement of viscosity and density by using a single resonator frequency response. However, such attempts have limited use in practice, manifest system complexity, and further do not provide accurate results for fluids having a viscosity more than 18 mPa-s. Thus, there exists a technical problem of how to decouple the measurement of viscosity and density in the viscosity density estimation during measurement of the test fluids having a wide range of viscosity using a same system.
Therefore, in light of the foregoing discussion, there exists a need to overcome the aforementioned drawbacks associated with the conventional viscosity density sensors.
SUMMARY
The present disclosure provides a droplet-based oscillation system for sensing physical properties of fluids. The present disclosure provides a solution to the technical problem of how to decouple the measurement of physical properties of fluids, such as viscosity and density, using a same system and how to develop a system that is suitable for testing fluids having a wide range of viscosity. An aim of the present disclosure is to provide a solution that overcomes at least partially the problems encountered in the prior art and provide an improved droplet-based oscillation system that separately measures the viscosity and density during measurement of physical properties of fluids. Additionally, the present disclosure provides an improved droplet-based oscillation system that is capable of measuring the viscosity and density of test fluid having a wide range of viscosity (i.e., with improved sensing range).
One or more objectives of the present disclosure is achieved by the solutions provided in the enclosed independent claims. Advantageous implementations of the present disclosure are further defined in the dependent claims.
In one aspect, the present disclosure provides a droplet-based oscillation system for sensing physical properties of fluids. The droplet-based oscillation system comprises a first mechanical structure and a second mechanical structure. Moreover, a droplet of a known volume of a test fluid is placed between the first mechanical structure and the second mechanical structure. Furthermore, the droplet-based oscillation system comprises an actuator configured to vibrate the first mechanical structure. Moreover, the second mechanical structure is passive and vibrates due to vibrational energy transferred through the droplet. In addition, the droplet-based oscillation system comprises a velocity detector, which is configured to monitor velocity of the first mechanical structure and the second mechanical structure, and a processor configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure and the second mechanical structure.
The droplet-based oscillation system not only determines the density and viscosity of the test fluid distinct with each other (i.e., decoupled with each other) but also improves the sensing range covering a wide range of different viscosity and density of test fluids. Unlike the conventional systems where resonators need to be partially or completely submerged inside a test fluid medium to measure the density or viscosity, the present disclosure uses a droplet as the test fluid for the measurement of the physical properties of fluids, such as the density and viscosity. Further, as the droplet is used as a mechanical coupling between the first mechanical structure and the second mechanical structure, the sensing range of the droplet-based oscillation system is significantly improved as compared to conventional systems and sensors.
In another aspect, the present disclosure provides a droplet-based oscillation system for sensing physical property of fluids. The droplet-based oscillation system comprises a first mechanical structure and a droplet of a known volume of a test fluid is placed on the first mechanical structure. Furthermore, the droplet-based oscillation system comprises an actuator configured to vibrate the first mechanical structure and a velocity detector configured to monitor a velocity of the first mechanical structure when the first mechanical structure vibrates on actuation by the actuator. In addition, the droplet-based oscillation system comprises a processor configured to determine a density and a viscosity of the test fluid as distinct parameters based on the monitored velocity of the first mechanical structure. Moreover, the droplet is an added mass and an added damping to the first mechanical structure used in the determination of the viscosity and the density of the test fluid.
Advantageously, as the droplet of the test fluid acts as an added mass and an added damping to the first mechanical structure, the sensing range of the droplet-based oscillation system is significantly improved. In this embodiment, only a single mechanical structure (i.e., the first mechanical structure) is used to estimate the viscosity and density of the test fluid in the form of the droplet, due to which the complexity of the droplet-based oscillation system in setup is reduced.
In yet another aspect, the present disclosure provides a droplet-based oscillation system for sensing physical properties of fluids. The droplet-based oscillation system comprises a first mechanical structure and a second mechanical structure. Moreover, a droplet of a known volume of a test fluid is placed between the first mechanical structure and the second mechanical structure. Furthermore, the droplet-based oscillation system comprises a first actuator configured to vibrate the first mechanical structure and a second actuator configured to vibrate the second mechanical structure, and a velocity detector configured to monitor velocity of the first and second mechanical structure and the second mechanical structure. In addition, the droplet-based oscillation system comprises a processor configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure and second mechanical structure.
The droplet-based oscillation system uses a small volume of droplet as test fluid for determining the viscosity and density of the test fluid, which improves the sensing range of the droplet-based oscillation system. Further, the droplet-based oscillation system enables determination of the density and viscosity of the test fluid decoupled with each other.
It is to be appreciated that all the aforementioned implementation forms can be combined. All steps which are performed by the various entities described in the present application as well as the functionalities described to be performed by the various entities are intended to mean that the respective entity is adapted to or configured to perform the respective steps and functionalities. It will be appreciated that features of the present disclosure are susceptible to being combined in various combinations without departing from the scope of the present disclosure as defined by the appended claims.
Additional aspects, advantages, features and objects of the present disclosure would be made apparent from the drawings and the detailed description of the illustrative implementations construed in conjunction with the appended claims that follow.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a diagram that depicts a droplet-based oscillation system for sensing physical properties of fluids, in accordance with an embodiment of the present disclosure;

FIG. 1B is a diagram that depicts a droplet-based oscillation system for sensing physical property of fluids, in accordance with an alternative embodiment of the present disclosure.
FIG. 1C is a diagram that depicts a droplet-based oscillation system for sensing physical properties of fluids, in accordance with yet another embodiment of the present disclosure.
FIG. 1D a diagram that depicts two mechanical structures in a cantilever arrangement in a droplet-based oscillation system, in accordance with another embodiment of the present disclosure;
FIG. 1E is a diagram that depicts a first mechanical structure of a droplet-based oscillation system with hydrophilic and hydrophobic areas, in accordance with an embodiment of the present disclosure;
FIG. 1F is a diagram that depicts an arrangement of two mechanical structures in a droplet-based oscillation system, in accordance with an alternative embodiment of the present disclosure;
FIG. 2 is an exploded isometric view that depicts an assembly of a first mechanical structure and a second mechanical structure in a droplet-based oscillation system, in accordance with another embodiment of the present disclosure;
FIG. 3 is a diagram that depicts graphical representations related to signal processing during determination of density of a test fluid in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 4 is a diagram that depicts a graphical representation of amplitude against frequency determined by a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 5 is a diagram that depicts a graphical representation of a frequency response of a cantilevered first mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 6 is a diagram that depicts a graphical representation of a quality factor against viscosity of a test fluid in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 7 is a diagram that depicts a graphical representation that represents variation of a resonant frequency against density in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 8 is a diagram that depicts graphical representations of a frequency responses of two mechanical structures in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 9 is a diagram that depicts graphical representations of a frequency response of a second mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure;
FIG. 10 is a diagram that depicts graphical representations of a frequency response of a first mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure; and
FIG. 11 is a diagram that depicts a graphical representation of a Fast Fourier Transform (FFT) of a second mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure.
The summary above, as well as the following detailed description of illustrative embodiments, is better understood when read in conjunction with the appended drawings. For the purpose of illustrating the present disclosure, exemplary constructions of the disclosure are shown in the drawings. However, the present disclosure is not limited to specific methods and instrumentalities disclosed herein. Moreover, those skilled in the art will understand that the drawings are not to scale. Wherever possible, like elements have been indicated by identical numbers.
Embodiments of the present disclosure will now be described, by way of example only, with reference to the following diagrams wherein:
In the accompanying drawings, an underlined number is employed to represent an item over which the underlined number is positioned or an item to which the underlined number is adjacent. A non-underlined number relates to an item identified by a line linking the non-underlined number to the item. When a number is non-underlined and accompanied by an associated arrow, the non-underlined number is used to identify a general item at which the arrow is pointing.
DETAILED DESCRIPTION OF EMBODIMENTS
The following detailed description illustrates embodiments of the present disclosure and ways in which they can be implemented. Although some modes of carrying out the present disclosure have been disclosed, those skilled in the art would recognize that other embodiments for carrying out or practicing the present disclosure are also possible.
FIG. 1A is a diagram that depicts a droplet-based oscillation system for sensing physical properties of fluids, in accordance with an embodiment of the present disclosure. With reference to FIG. 1, there is shown a diagram that depicts a droplet-based oscillation system 100A for sensing physical properties of fluids, which includes a first mechanical structure 102A, a second mechanical structure 102B, an actuator 106, a velocity detector 108, and a processor 110. There is further shown a signal generator 120 and a data acquisition (DAQ) system 118. In an implementation, the physical properties of the fluids is to be measured by the droplet-based oscillation system 100A are viscosity and density. In another implementation, the droplet-based oscillation system 100A determines the surface tension of the fluids along with the viscosity and the density.
The droplet-based oscillation system 100A includes the first mechanical structure 102A and the second mechanical structure 102B, where a droplet 104 of a known volume of a test fluid is placed between the first mechanical structure 102A and the second mechanical structure 102B. Each of the first mechanical structure 102A and the second mechanical structure 102B refers to a structure that is capable of oscillating or vibrating when actuated by an actuating means. Moreover, the second mechanical structure 102B is arranged above the first mechanical structure 102A. Furthermore, each of the first mechanical structure 102A and the second mechanical structure 102B is a beam structure, specifically a fixed-fixed beam structure. In addition, the first mechanical structure 102A and the second mechanical structure 102B are flat beam structures that run parallel to each other and in which both ends are fixed. In an example, each of the first mechanical structure 102A and the second mechanical structure 102B includes a first end and a second end. For example, the first mechanical structure 102A includes a first end 102C and a second end 102D that are fixed on rigid supports. Similarly, the second mechanical structure 102B includes a first end 102E and a second end 102F that are fixed on rigid supports.
In an implementation, the test fluid is a fluid of which the physical properties are to be measured by the droplet-based oscillation system 100A. In an example, the known volume of the droplet 104 may range from 1-500 microlitres, preferably 1-50 microliters. Furthermore, the droplet 104 is placed between the first mechanical structure 102A and the second mechanical structure 102B so that the droplet 104 is coupled between the first mechanical structure 102A and the second mechanical structure 102B. Beneficially, as compared to conventional viscosity density sensors, instead of using a bulk quantity of the test fluid, the use of the droplet 104 enables the droplet-based oscillation system 100A for the determination of viscosity of the test fluid that is having large values of viscosity.
The droplet-based oscillation system 100A includes the actuator 106 configured to vibrate the first mechanical structure 102A. Moreover, the second mechanical structure 102B is passive and vibrates due to vibrational energy transferred through the droplet 104. The actuator 106 refers to a linear actuator, which is configured to produce a linear motion upon receiving an actuation signal. Moreover, the actuator 106 is operatively coupled to the first mechanical structure 102A. Furthermore, the actuator 106 is configured to vibrate the first mechanical structure 102A upon receiving an actuation signal from the processor 110. Examples of the actuator 106 may include but are not limited to an electromagnetic actuator, a piezoelectric actuator, a capacitive actuator, a thermal actuator, an acoustic actuator, a magnetic actuator, and the like.
In an implementation, the first mechanical structure 102A is an active structure, which directly receives vibrational motion from the actuator 106. In addition, the second mechanical structure 102B is a passive structure, which vibrates due to the transfer of vibrational energy from the first mechanical structure 102A through the droplet 104. Moreover, the droplet 104 acts as a mechanical coupling between the first mechanical structure 102A and the second mechanical structure 102B. Therefore, the height of the droplet 104 affects the transmission of vibrational energy from the first mechanical structure 102A (i.e., active structure) to the second mechanical structure 102B (i.e., passive structure). Furthermore, due to the mechanical coupling between the first mechanical structure 102A and the second mechanical structure 102B, the transmission of the vibrational energy from the first mechanical structure 102A to the second mechanical structure 102B is increased with a decrease in height of the droplet 104. In addition, the vibrational energy from the first mechanical structure 102A to the second mechanical structure 102B results in the production of a velocity.
The droplet-based oscillation system 100A includes the velocity detector 108 that is configured to monitor velocity of the first mechanical structure 102A and the second mechanical structure 102B. The velocity detector 108 is a velocity sensor, which is configured to detect the velocity of the first mechanical structure 102A and the second mechanical structure 102B. Examples of the velocity detector 108 may include but are not limited to a laser doppler velocimeter (LDV), a magnetic velocity sensor, an ultrasonic velocity sensor, a capacitive velocity sensor, a piezoresistive velocity sensor, a piezoelectric velocity sensor, an optical velocity sensor and the like. In an example, the velocity of the first mechanical structure 102A and of the second mechanical structure 102B is produced during the transmission of the vibration energy from the first mechanical structure 102A to the second mechanical structure 102B. In addition, the velocity detector 108 is operatively connected to both the first mechanical structure 102A and the second mechanical structure 102B. In an implementation, the velocity detector 108 is configured to detect the amplitude of vibration of the first mechanical structure 102A and the second mechanical structure 102B and further determines the time taken by the first mechanical structure 102A and the second mechanical structure 102B to achieve corresponding amplitude. Further, in such implementation, the corresponding data of amplitude and time is transmitted to the processor 110 that is configured to calculate the velocity of the first mechanical structure 102A and the second mechanical structure 102B.
The droplet-based oscillation system 100A includes the processor 110 that is configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure 102A and the second mechanical structure 102B. The processor 110 refers to a computational element that is operable to respond to and processes instructions that drive the droplet-based oscillation system 100A. The processor 110 is operatively connected to the velocity detector 108 that transmits the monitored velocity of the first mechanical structure 102A and the second mechanical structure 102B to the processor 110, which is configured to separately determine the density and the viscosity of the test fluid based on the calculated velocity. The processor 110 may refer to one or more individual processors, processing devices, and various elements associated with a processing device that may be shared by other processing devices. Additionally, the one or more individual processors, processing devices, and elements are arranged in various architectures for responding to and processing the instructions that drive the droplet-based oscillation system 100A. Examples of the processor 110 may include but are not limited to, a hardware processor, a digital signal processor (DSP), a microprocessor, a microcontroller, a complex instruction set computing (CISC) processor, an application-specific integrated circuit (ASIC) processor, a reduced instruction set (RISC) processor, a very long instruction word (VLIW) processor, a state machine, a data processing unit, a graphics processing unit (GPU), and other processors or control circuitry.
Before the operation of the droplet-based oscillation system 100A, the droplet 104 is placed between the first mechanical structure 102A and the second mechanical structure 102B. During the operation of the droplet-based oscillation system 100A, the actuator 106 provides vibrational motion to the first mechanical structure 102A with a definite frequency. In an implementation, the actuator 106 is an electromagnetic actuator. In an implementation, the electromagnetic actuator is a linear actuator, which is operated based on the principle of electromagnetism, where an electrical current passing through a coil of wire generates a magnetic field, which is used to create a force that vibrates the first mechanical structure 102A. The electromagnetic actuator is advantageous to achieve a significant displacement of the first mechanical structure 102A. Moreover, the vibrations of the first mechanical structure 102A get transferred to the second mechanical structure 102B through the droplet 104 and the second mechanical structure 102B starts vibrating. Furthermore, the velocity detector 108 monitors the velocities of both the first mechanical structure 102A and the second mechanical structure 102B. Thereafter, the velocity detector 108 is configured to transmit the data of monitored velocity to the processor 110. Further, the processor 110 is configured to determine the density and the viscosity of the test fluid based on the monitored velocities.
In an exemplary implementation, the droplet-based oscillation system 100A may include three or more numbers of mechanical structures. In such a case, one or more droplets of a known volume of a test fluid can be placed between the first mechanical structure 102A and the second mechanical structure 102B without limiting the scope of the present disclosure. Therefore, in such an example, the processor 110 can be configured to determine the density and the viscosity of the test fluid from the one or more droplets (i.e, multiple sample test fluid droplets at the same time).
In accordance with an embodiment, each of the first mechanical structure 102A and the second mechanical structure 102B may be a cantilever structure, a beam structure, a shell element, a flat plate, or other resonators. In an implementation, the shell element is a curved structure with thin walls. In an implementation, the first mechanical structure 102A and the second mechanical structure 102B are resonators, which are adapted to resonate or vibrate at specific frequencies. In such implementation, the first mechanical structure 102A and the second mechanical structure 102B are non-identical structures.
In accordance with an embodiment, the first mechanical structure 102A has a higher spring constant than the second mechanical structure 102B. The spring constant refers to a characteristic of a material, which defines an external force required to compress or stretch a spring made from the corresponding material. Furthermore, as the spring constant of the first mechanical structure 102A is higher than the spring constant of the second mechanical structure 102B, thus the first mechanical structure 102A is stiffer as compared to the second mechanical structure 102B. In addition, the stiffness of the second mechanical structure 102B is maintained lesser than the first mechanical structure 102A to increase the sensitivity of the second mechanical structure 102B. The stiffness of the first mechanical structure 102A is greater than the surface tension of the droplet 104 to avoid bending of the first mechanical structure due to inertial forces exerted by the droplet 104 during the operation of the droplet-based oscillation system 100A. In an example, the first mechanical structure 102A is made up of 100-µm thick stainless steel, and the second mechanical structure 102B is made up of 50-µm thick plastic.
In an implementation, the test fluid may be a Newtonian fluid or a non-Newtonian fluid. In an implementation, a puddle of the test fluid is placed between the first mechanical structure 102A and the second mechanical structure 102B. The puddle is a small accumulation of liquid between the first mechanical structure 102A and the second mechanical structure 102B, which may be created either by pooling in a depression on the first mechanical structure 102A or by surface tension upon the first mechanical structure 102A. In an implementation, the stiffness of the second mechanical structure 102B is comparable to the stiffness of the droplet 104 to receive vibrational energy transferred through the droplet 104. In an implementation, an array of droplets is positioned between the first mechanical structure 102A and the second mechanical structure 102B. In another implementation, a stack of multiple mechanical structures forms the first mechanical structure 102A and another stack of mechanical structures (different from the first mechanical structure) forms the second mechanical structure 102B.
In accordance with an embodiment, the second mechanical structure 102B is arranged at a defined distance (D1) from the first mechanical structure 102A creating an air gap between the first mechanical structure 102A and the second mechanical structure 102B. Moreover, the droplet 104 mechanically couples the first mechanical structure 102A and the second mechanical structure 102B to transfer a vibrational energy from the first mechanical structure 102A to the second mechanical structure 102B. In an example, the value of the D1 is 1mm. Moreover, the air gap between the first mechanical structure 102A and the second mechanical structure 102B provides a space for the accommodation of the droplet and the value of the D1 is dependent on the known volume of the droplet 104. In an implementation, the magnitude of the D1 is lesser than the height of the droplet 104. Moreover, a contact area between the droplet 104, the first mechanical structure 102A, and the second mechanical structure 102B changes depending on the height of the droplet 104. The first mechanical structure 102A, the droplet 104, and the second mechanical structure 102B act as a rigid link, which transfers vibrational motion from the first mechanical structure to the second mechanical structure 102B. In accordance with an embodiment, the droplet 104 is arrested at a predefined location (L1) on the first mechanical structure 102A. In an implementation, the L1 is a location over the first mechanical structure 102A and the second mechanical structure 102B over which the droplet is placed to estimate the physical properties of the test fluid. Optionally, the value of the L1 can vary without limiting the scope of the present disclosure.
In an implementation, the magnitude of the velocity of the first mechanical structure 102A and the second mechanical structure 102B detected by the velocity detector 108 is transferred to the data acquisition (DAQ) system 118. In an example, the DAQ system 118 refers to an electronic system, which is configured to capture, measure, and analyze the data received from the velocity detector 108. In an implementation, the DAQ system 118 includes a signal conditioning circuitry, which amplifies or filters the electric signals to improve quality, and a data acquisition module, which samples and digitizes the electric signals before transmitting to the processor 110. In an implementation, the output of the processor 110 is further received by the signal generator 120 that is configured to provide electric signals to the actuator 106 for providing vibrational motion to the first mechanical structure 102A. Moreover, an amplitude of vibration of the first mechanical structure 102A may be varied by controlling the magnitude of the electric signals provided by the signal generator 120.
In accordance with an embodiment, based on the monitored velocity of the first mechanical structure 102A, the processor 110 is further configured to track a frequency response of the first mechanical structure 102A to determine the density of the test fluid. In an implementation, the frequency response of the first mechanical structure 102A refers to the frequency of vibration of the first mechanical structure 102A at a definite velocity (or variation of the frequency of vibration of the first mechanical structure 102A with respect to the velocity of the first mechanical structure 102A). Moreover, the processor 110 is configured to determine the frequency of vibrations of the first mechanical structure 102A based on the monitored velocity of the first mechanical structure 102A. In an implementation, the frequency of the first mechanical structure 102A with the droplet 104 at a definite velocity is more than the frequency of the first mechanical structure 102A without the droplet 104 at the same velocity. Therefore, the difference (or shift) between the frequency response of the first mechanical structure 102A with the droplet 104 and the frequency response of the first mechanical structure 102A without the droplet 104 is used by the processor 110 to configured to determine the density of the test fluid. The droplet 104 acts as an added mass and an added damping to the first mechanical structure 102A, which causes a shift in the frequency response of the first mechanical structure 102A.
In accordance with an embodiment, a resonant frequency of the second mechanical structure 102B that is passively actuated through the droplet 104 is lesser than the first mechanical structure 102A. The resonant frequency refers to a frequency at which a mechanical structure vibrates with maximum amplitude (i.e., maximum velocity). In such implementation, the actuator 106 vibrates the first mechanical structure 102A (i.e., with the droplet 104) and increases the frequency of vibration up to the resonant frequency of the first mechanical structure 102A. In an implementation, the processor 110 is configured to determine the frequency response of the first mechanical structure 102A at the resonant frequency of the first mechanical structure 102A. Moreover, when the frequency of vibration of the first mechanical structure 102A reaches the resonant frequency, then the processor 110 receives the monitored velocity of the first mechanical structure 102A at the resonant frequency and the corresponding monitored velocity is used to determine the density of the test fluid. In addition, due to the lesser spring constant of the second mechanical structure 102B as compared to the first mechanical structure 102A, the frequency at which the first mechanical structure 102A achieves resonance is more as compared to the second mechanical structure 102B. In an implementation, the thickness of the second mechanical structure 102B is comparable to the thickness (or height) of the droplet and is kept lesser than the first mechanical structure 102A to avoid overlapping of resonance between the first mechanical structure 102A and the second mechanical structure 102B. Furthermore, the resonant frequency of the first mechanical structure 102A decreases due to the virtually added mass effect of the droplet 104, which acts as a factor to determine the density of the test fluid. In addition, the processor 110 is configured to correlate the resonant frequency of the first mechanical structure 102A with the density of the test fluid. Moreover, the frequency of vibration of the first mechanical structure 102A with the droplet 104 reaches up to a natural frequency of the first mechanical structure 102A with the droplet 104 to form a resonance. Furthermore, the natural frequency of the first mechanical structure 102A with the droplet 104 is given by an equation (1) as follows:
𝜔 = √(k/(m+Δm)) (1)
Where, 𝜔 refers to a natural frequency of the first mechanical structure 102A, 𝑚 refers to an effective mass of the first mechanical structure 102A, 𝑘 corresponds to an effective stiffness of the first mechanical structure 102A and Δ𝑚 corresponds to mass of the droplet 104. The value of the 𝑚 and the 𝑘 are predetermined and stored in the processor 110, whereas the value of the 𝜔 is determined by the processor 110 based on the monitored velocity of the first mechanical structure 102A and the value of the Δ𝑚 is estimated to determine the density of the test fluid. Moreover, a change in mass represents a change in density, as the volume of the droplet 104 of the test liquid is fixed.
In accordance with an embodiment, based on the monitored velocity of the second mechanical structure 102B, the processor 110 is further configured to determine a quality factor associated with the second mechanical structure 102B to determine the viscosity of the test fluid. In an implementation, the quality factor (also known as Q factor) refers to a dimensionless parameter, which is a ratio of the energy stored in the second mechanical structure 102B to an energy lost per cycle due to damping of the second mechanical structure 102B. Furthermore, a higher quality factor indicates lower damping of the second mechanical structure 102B and improved energy efficiency, while a lower quality factor indicates higher damping of the second mechanical structure 102B and lower energy efficiency.
The droplet 104 introduces an added damping to both the first mechanical structure 102A and the second mechanical structure 102B, which is reflected in the quality factor. In an implementation, the second mechanical structure 102B is 35% more sensitive to vibrations than the first mechanical structure 102A, due to the lesser stiffness of the second mechanical structure 102B as compared to the first mechanical structure 102A. Therefore, the quality factor of the second mechanical structure 102B is used to estimate the viscosity of the test fluid. Moreover, the quality factor is determined by the processor 110 based on the resonance frequency of the second mechanical structure 102B. The processor 110 is further configured to determine the density of the test fluid based on the frequency response of the first mechanical structure 102A and determines the viscosity of the test fluid based on the frequency response of the second mechanical structure 102B.
In accordance with an embodiment, the quality factor is inversely proportional to the damping as well as the viscosity, and an amplitude at which the droplet 104 starts sloshing is attributed to the viscosity of the droplet 104 that is further utilized to determine the viscosity of the test fluid. In other words, the actuator 106 increases the frequency of vibration of the first mechanical structure 102A until the droplet 104 between the first mechanical structure 102A and the second mechanical structure 102B sloshes. In addition, the corresponding amplitude (or velocity) is detected by the velocity detector 108, which is used by the processor 110 to determine the viscosity of the test fluid. The use of the quality factor of the second mechanical structure 102B and the frequency response of the first mechanical structure 102A provides an improved linear relationship for a larger range of the viscosity and the density as compared to conventional viscosity density sensors. In accordance with an embodiment, the density and the viscosity of the test fluid as distinct parameters are determined in a range of 996 - 1200 kilogram per cubic metre and 0.8 - 66 centipoise respectively. Moreover, the range of the viscosity as determined by the droplet-based oscillation system 100A is more than the conventional viscosity density sensor (which is up to 17 centipoise) due to the small volume of the droplet 104. In an implementation, the quality factor of the second mechanical structure 102B is determined by detecting the frequency of vibration of the second mechanical structure 102B at a first mode of vibration. In an implementation, the first mode of vibration refers to a lowest frequency at which the second mechanical structure 102B can vibrate. The quality factor of the first mode of vibration of the second mechanical structure 102B is 35% more sensitive than the first mechanical structure 102A. In an implementation, a display module is configured with the processor 110. The display module displays the values of the density, viscosity, and surface tension determined by the processor 110.
In accordance with an embodiment, the processor 110 is configured to determine a surface tension of the droplet 104 of the test fluid when a spring constant parameter of the second mechanical structure 102B is comparable to the surface tension of the droplet 104. In such embodiment, the processor 110 is configured to determine the surface tension separately similar to the viscosity and density of the test fluid. Moreover, the spring constant parameter is indicative of the stiffness of the second mechanical structure 102B. Furthermore, the comparable spring constant parameter of the second mechanical structure 102B with respect to the surface tension of the droplet 104 is advantageous for the accurate determination of the quality factor and the viscosity of the test fluid. Moreover, a resonance of the droplet 104 is captured by the second mechanical structure 102B to determine the surface tension. In other words, the frequency of the vibration of the second mechanical structure 102B is detected by the velocity detector 108 when the second mechanical structure 102B achieves resonance. Moreover, the frequency of the vibration of the second mechanical structure 102B with the droplet 104 becomes equal to the natural frequency of the second mechanical structure 102B with the droplet 104. Moreover, a change in the resonance or the monitored velocity of the second mechanical structure 102B is indicative of a change in the surface tension of the droplet 104. In an implementation, the natural frequency of the second mechanical structure 102B with the droplet is different from the natural frequency of the second mechanical structure 102B without droplet 104. Therefore, the change in the resonant frequency of the second mechanical structure 102B (due to added damping of the droplet 104) is attributed to a change in the surface tension of the droplet 104 and such change is correlated with the surface tension of the test fluid by the processor 110. Moreover, the droplet-based oscillation system 100A determines the accurate surface tension of the test fluid having surface tension lesser than 30Nm.
In an example, the natural frequency of the second mechanical structure 102B is given by following equation (2), as shown below:
ω=√((k+Δk)/m) (2)
Where, ω corresponds to a natural frequency of the second mechanical structure 102B, m corresponds to a mass of the second mechanical structure 102B, k corresponds to a stiffness of the second mechanical structure 102B, and Δk corresponds to a surface tension of the droplet 104. In addition, the natural frequency of the second mechanical structure 102B is estimated by the processor 110 based on the frequency response of the second mechanical structure 102B and the magnitude of the m, such as the value of the k is predefined in the processor 110. Moreover, the processor 110 is configured to determine the value of the Δk, that is, the surface tension of the test fluid.
The droplet-based oscillation system 100A is configured to determine the density as well as the viscosity of the test fluid distinct with each other (i.e., decoupled with each other) but also improves the sensing range covering a wide range of different viscosity and density of test fluids. Unlike the conventional systems where resonators need to be partially or completely submerged inside a test fluid medium to measure the density or viscosity, the present disclosure uses the droplet 104 as the test fluid for measurement of the physical properties of fluids, such as the density and viscosity. Further, as the droplet 104 is used as a mechanical coupling between the first mechanical structure 102A and the second mechanical structure 102B, the sensing range of the droplet-based oscillation system 100A is significantly improved as compared to conventional systems and sensors. Further, the droplet-based oscillation system 100A is advantageous to estimate the viscosity, density, and surface tension of the droplet with a single system. The droplet-based oscillation system 100A is applicable as an inline sensor for monitoring properties of lubricant in gearboxes, process control industries, biomedical applications, such as hemoglobin monitoring sensor, point of care coagulation sensor, and the like.
FIG. 1B is a schematic diagram that depicts a droplet-based oscillation system for sensing physical property of fluids, in accordance with a different embodiment of the present disclosure. With reference to FIG. 1B, there is shown a schematic diagram that depicts a droplet-based oscillation system 100B for sensing physical property of fluids, which includes the first mechanical structure 102A, the actuator 106, the velocity detector 108, the processor 110, the signal generator 120, and the data acquisition (DAQ) system 118.
The droplet-based oscillation system 100B is configured to sense the physical properties of the fluids, such as density and viscosity. The droplet-based oscillation system 100B includes the first mechanical structure 102A. Moreover, the droplet 104 of a known volume of a test fluid is placed on the first mechanical structure 102A. Furthermore, in this implementation, the first mechanical structure 102A is a cantilever structure, which is fixed at one end and free at the other end. In an implementation, the droplet 104 is positioned at the predefined location (L1). In an implementation, the predefined location (L1) may be closer to the free end of the first mechanical structure 102A, although this is not essential. In another implementation, the predefined location (L1) corresponds to a central location over the first mechanical structure 102A (i.e., equidistant from both ends of the first mechanical structure 102A). Furthermore, the test fluid is a fluid of which the physical properties are to be measured by the droplet-based oscillation system 100B. Beneficially as compared to conventional viscosity density sensors where a bulk quantity of the test fluid was implemented, the use of droplet 104 enables the determination of the viscosity of a test fluid having large values of viscosity.
The droplet-based oscillation system 100B includes the actuator 106 that is configured to vibrate the first mechanical structure 102A. The actuator 106 is operatively coupled with the first mechanical structure 102A. Moreover, the actuator 106 is a linear actuator, which is operatively coupled with the first mechanical structure 102A and provides a linear motion to the first mechanical structure 102A. Examples of the actuator 106 may include but are not limited to an electromagnetic actuator, a piezoelectric actuator, a capacitive actuator, a thermal actuator, an acoustic actuator, a magnetic actuator, and the like. In an implementation, the signal generator 120 is configured to provide electrical signals to the actuator 106 for providing vibrational motion to the first mechanical structure 102A.
The droplet-based oscillation system 100B includes the velocity detector 108 configured to monitor a velocity of the first mechanical structure 102A when the first mechanical structure 102A vibrates on actuation by the actuator 106. The velocity detector 108 is a velocity sensor, which is configured to monitor the velocity of the first mechanical structure 102A. Moreover, the velocity detector 108 is operatively connected with the first mechanical structure 102A. In addition, the actuator 106 provides linear vibrational motion to the first mechanical structure 102A, and the velocity detector 108 monitors the corresponding velocity of vibration of the first mechanical structure 102A. In an example, the velocity detector 108 is a laser doppler velocimeter (LDV), which emits a laser beam towards the first mechanical structure 102A and measures doppler shift in the laser beam to determine the velocity of the first mechanical structure 102A.
The droplet-based oscillation system 100B includes the processor 110 is configured to receive the monitored velocity of the first mechanical structure 102A from the velocity detector 108 and determine a density and a viscosity of the test fluid as distinct parameters based on the monitored velocity of the first mechanical structure 102A. The processor 110 is operatively connected to the velocity detector 108. The processor 110 is configured to correlate the velocity of the monitored velocity of the first mechanical structure 102A with the density and viscosity of the test fluid. Moreover, the droplet 104 is an added mass and an added damping to the first mechanical structure 102A used in the determination of the viscosity and the density of the test fluid. In an implementation, the added mass refers to an increase in an effective mass of the first mechanical structure 102A, which is correlated to the density of the first mechanical structure 102A by the processor 110. In another implementation, the added damping refers to an increase in damping (i.e., reduction in vibrations) of the first mechanical structure 102A, which is correlated to the viscosity of the first mechanical structure 102A by the processor 110.
In accordance with an embodiment, the processor 110 is further configured to track the frequency response of the first mechanical structure 102A before and after placement of the droplet on the first mechanical structure 102A based on the monitored velocity of the first mechanical structure 102A. In an example, the velocity detector 108 monitors the velocity of the first mechanical structure 102A before placement of the droplet 104 on the first mechanical structure 102A. Moreover, based on the monitored velocity, the processor 110 is configured to determine the frequency response of the first mechanical structure 102A without placement of the droplet 104. Further, the droplet 104 is placed on the first mechanical structure 102A at the predefined location (L1) and the velocity detector 108 is further configured to monitor the velocity of the first mechanical structure 102A. Thereafter, based on the monitored velocity, the processor 110 is configured to determine the frequency response of the first mechanical structure 102A with the placement of the droplet 104.
In accordance with an embodiment, the processor 110 is further configured to determine a quality factor associated with the first mechanical structure 102A for the determination of the viscosity of the test fluid, based on the monitored velocity of the first mechanical structure 102A. The velocity detector 108 is configured to monitor the velocity of the first mechanical structure 102A after the placement of the droplet 104. Thereafter, the value of the velocity is transmitted to the processor 110 that is configured to determine the frequency response of the first mechanical structure 102A and further, determines the quality factor of the first mechanical structure 102A based on the determined frequency response. Both the density and the viscosity of the test fluid are separately calculated based on the frequency response of the first mechanical structure 102A. In accordance with an embodiment, the density and the viscosity of the test fluid as distinct parameters are determined in a range of 996-1257-Y kilogram per cubic metre and 1-1972 centipoise respectively. Furthermore, the droplet-based oscillation system 100A is advantageous to determine the viscosity of test fluids having a viscosity of more than 18 cP, which is not possible in the case of conventional viscosity density sensors.
In an implementation, the first mechanical structure 102A includes a hydrophilic area and hydrophobic areas to arrest the droplet 104 at the predefined location (L1), such as at the hydrophilic area on the first mechanical structure 102A. In such implementation, a hydrophobic substance is coated over the first mechanical structure 102A at one side on which the droplet 104 is positioned to form the hydrophobic areas barring a portion corresponding to the hydrophilic area to arrest the droplet 104 at the predefined location (L1) of the hydrophilic area. The hydrophilic area and the hydrophobic areas contrast over the first mechanical structure 102A that are advantageous to restrict the droplet 104 to the predefined location (L1) and ensure only a definite volume (i.e., the known volume) of the droplet 104. In an example, based on the hydrophilic area, one or more droplets can be arranged on the first mechanical structure 102A without limiting the scope of the present disclosure. An exemplary implementation of the hydrophilic area and the hydrophobic areas is further shown and described in FIG. 1E.
Advantageously, as the droplet of the test fluid acts as the added mass and the added damping to the first mechanical structure 102A, thus the sensing range of the droplet-based oscillation system 100B is significantly improved. Further, in the droplet-based oscillation system 100B, only a single mechanical structure (i.e., the first mechanical structure) is used to estimate the viscosity and density of the test fluid in the form of the droplet 104, and the complexity of the droplet-based oscillation system 100B in setup is reduced.
FIG. 1C is a schematic diagram that depicts a droplet-based oscillation system for sensing physical properties of fluids, in accordance with a different embodiment of the present disclosure. With reference to FIG. 1C, there is shown a schematic diagram that depicts a droplet-based oscillation system 100C for sensing physical properties of fluids, which includes a first actuator 106A and a second actuator 106B. There is further shown the first mechanical structure 102A, the second mechanical structure 102B, the velocity detector 108, the processor 110, the signal generator 120, and the data acquisition (DAQ) system 118.
The droplet-based oscillation system 100C is configured to sense the physical properties of the fluids, such as density and viscosity of the fluids. The droplet-based oscillation system 100C includes the first mechanical structure 102A and the second mechanical structure 102B. Moreover, the droplet 104 of a known volume of a test fluid is placed between the first mechanical structure 102A and the second mechanical structure 102B. The first mechanical structure 102A and the second mechanical structure 102B are fixed-fixed beams, which are supported over both ends. In an implementation, the first mechanical structure 102A and the second mechanical structure 102B are cantilevered structures. In an implementation, the known volume of the droplet 104 ranges from 1-500 microlitres. In another implementation, the second mechanical structure 102B is arranged at a defined distance (D1) from the first mechanical structure 102A creating an air gap between the first mechanical structure 102A. The droplet 104 is arrested at the predefined location (L1) on the first mechanical structure 102A.
The droplet-based oscillation system 100C includes the first actuator 106A that is configured to vibrate the first mechanical structure 102A. The droplet-based oscillation system 100C further includes the second actuator 106B that is configured to vibrate the second mechanical structure 102B. The first actuator 106A is operatively connected to the first mechanical structure 102A and the second actuator 106B is operatively connected to the second mechanical structure 102B. In an implementation, the first actuator 106A and the second actuator 106B are linear actuators, which are operatively coupled with the first mechanical structure 102A and the second mechanical structure 102B and provide a linear motion to the first mechanical structure 102A and the second mechanical structure 102B respectively. Examples of the first actuator 106A and the second actuator 106B may include, but are not limited to a piezoelectric actuator, a capacitive actuator, a thermal actuator, an acoustic actuator, a magnetic actuator, and the like.
The droplet-based oscillation system 100C further includes the velocity detector 108 that is configured to monitor the velocity of the first mechanical structure 102A and the second mechanical structure 102B. The velocity detector 108 is operatively connected to both the first mechanical structure 102A and the second mechanical structure 102B. Further, the droplet-based oscillation system 100C includes the processor 110 that is configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure 102A and the second mechanical structure 102B. In an implementation, the processor 110 is configured to determine the frequency response of the first mechanical structure 102A based on the monitored velocity and based on the frequency response and determines the density of the test fluid. In such implementation, the processor 110 is configured to determine the quality factor of the second mechanical structure 102B based on the monitored velocity and based on the quality factor. Thereafter, the processor 110 is configured to determine the viscosity of the test fluid.
In accordance with an embodiment, when the first mechanical structure 102A and the second mechanical structure 102B undertake in-phase and out-of-phase motion during vibration and two different frequency responses are obtained for the droplet 104 of the test fluid. In an implementation, an in-phase vibrational motion takes place when vibrational motions of both the first mechanical structure 102A and the second mechanical structure 102B are synchronized and move in the same direction at the same frequency during vibration. In an implementation, an out of phase vibrational motion takes place when vibrational motions of both the first mechanical structure 102A and the second mechanical structure 102B are not synchronized and move in the opposite direction at the different frequency during vibration. In an implementation, the frequency response of the first mechanical structure 102A and the second mechanical structure 102B is used by the processor 110 to determine the density and viscosity of the test fluid.
In an implementation, the first mechanical structure 102A includes a hydrophilic area and hydrophobic areas on either side of the hydrophilic area to arrest the droplet 104 at the predefined location (L1) that corresponds to the hydrophilic area on the first mechanical structure 102A. Moreover, the first mechanical structure 102A is coated with a hydrophobic substance at one side that faces the second mechanical structure 102B to form the hydrophobic areas barring a portion corresponding to the hydrophilic area to arrest the droplet 104 at the predefined location (L1) of the hydrophilic area.
The droplet-based oscillation system 100C uses a small volume of the droplet 104 as a test fluid to determine the viscosity and the density of the test fluid, which improves the sensing range of the droplet-based oscillation system 100C. Further, the droplet-based oscillation system 100C enables the determination of the density and viscosity of the test fluid decoupled with each other.
FIG. 1D a diagram that depicts two mechanical structures arranged in a cantilever arrangement in a droplet-based oscillation system, in accordance with another embodiment of the present disclosure. With reference to FIG. 1D, there is shown the first mechanical structure 102A in the droplet-based oscillation system 100A, which is a flat cantilevered structure with the first end 102C and the second end 102D, where the first end 102C is fixed in a rigid support 102G and the second end 102D is free. With reference to FIG.2, there is further shown the second mechanical structure 102B in the droplet-based oscillation system 100A, which is a flat cantilevered structure with the first end 102E and the second end 102F, where the first end 102E is fixed in the rigid support 102G and the second end 102F is free. Furthermore, the droplet 104 is positioned closer to the free ends (i.e., close to the second end 102D and the second end 102F).
FIG. 1E is a diagram that depicts a first mechanical structure of a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 1E, there is shown a top view of the first mechanical structure 102A that includes a hydrophilic area 112 and hydrophobic areas 114A, and 114B coated with a hydrophobic substance 116 in the droplet-based oscillation system 100A.
In accordance with an embodiment, the hydrophilic area 112 and the hydrophobic areas 114A, and 114B that are configured on either side of the hydrophilic area 112 to arrest the droplet 104 at the predefined location (L1) that corresponds to the hydrophilic area 112 on the first mechanical structure 102A. In an implementation, the hydrophilic area 112 is a region over the first mechanical structure 102A, which is having an affinity for the test fluid. In other words, the hydrophilic area 112 is enabled to attract the droplet 104 of the test fluid and provides a location for the droplet 104 to rest during the operation of the droplet-based oscillation system 100A. In an implementation, the hydrophobic areas 114A and 114B are regions over the first mechanical structure 102A, which are having zero affinity for the test fluid. In an example, a Teflon tape is coated over a definite portion of the first mechanical structure 102A, which acts as the hydrophobic areas 114A, and 114B. Furthermore, the area of the first mechanical structure 102A is not coated with the Teflon tape and acts as the hydrophilic area 112.
In accordance with an embodiment, the first mechanical structure 102A is coated with the hydrophobic substance 116 at one side that faces the second mechanical structure 102B to form the hydrophobic areas 114A, 114B barring a portion corresponding to the hydrophilic area 112 to arrest the droplet 104 at the predefined location (L1) of the hydrophilic area 112. In an implementation, the hydrophobic substance 116 corresponds to a substance, which is repelled by the test fluid and does not mix with the test fluid. Moreover, the hydrophobic areas 114A and 114B are enabled to repel the droplet 104 of the test fluid and restrict the location of the droplet 104 to the predefined location (L1). Examples of hydrophobic substance 116 may include, but are not limited to fats, oils, waxes, greases, and the like. Furthermore, the amount of the hydrophilic area 112 and the hydrophobic areas 114A and 114B are determined based on the known volume of the droplet 104. In an implementation, the first mechanical structure 102A and the second mechanical structure 102B are dipped inside a sample of fluid and the known volume of the droplet 104 gets trapped between the first mechanical structure 102A and the second mechanical structure 102B at the predefined location (L1). In addition, the hydrophilic area 112 and the hydrophobic areas 114A, 114B are contrast over the first mechanical structure 102A and advantageous to restrict the droplet 104 to the predefined location (L1), such as to ensure only a definite volume (i.e., the known volume) of the droplet 104 that is retained over the first mechanical structure 102A. In an implementation, the predefined location (L1) is determined to be positioned at a tip of the first mechanical structure 102A. In another implementation, the predefined location (L1) is determined to be positioned at a centre position of the two beams the first mechanical structure 102A and the second mechanical structure 102B.
FIG. 1F is a diagram that depicts an arrangement of two mechanical structures in a droplet-based oscillation system, in accordance with an alternative embodiment of the present disclosure. With reference to FIG. 1F, there is shown an arrangement of the first mechanical structure 102A and the second mechanical structure 102B in the droplet-based oscillation system 100A during the measurement of surface tension of the test fluid. Moreover, the arrangement shown in FIG. 1F is configured for measuring the surface tension of the test fluid having viscosity of more than 30 Nm. With reference to FIG.1F, there is shown a piston 122 that is configured with the second mechanical structure 102B, and a cylinder 124 that is configured with the first mechanical structure 102A. In addition, the droplet 104 of the test fluid is placed within the cylinder 124 and the piston 122 that is arranged in contact with the droplet 104. Furthermore, during the operation of the droplet-based oscillation system 100A, the vibrations from the first mechanical structure 102A are transferred to the second mechanical structure 102B through the piston 122. Thereafter, the processor 110 is configured to determine the surface tension of the test fluid based on the frequency response of the second mechanical structure 102B.
FIG. 2 is an exploded isometric view that depicts an assembly of the first mechanical structure and the second mechanical structure in a droplet-based oscillation system, in accordance with another embodiment of the present disclosure. With reference to FIG. 2, there is shown an exploded isometric view 200 that depicts an assembly of the first mechanical structure 102A and the second mechanical structure 102B in the droplet-based oscillation system 100A. The assembly includes a top fixture 202, one or more connecting brackets 206, a bottom fixture 204, and a plurality of guide holes 208 over the bottom fixture 204. There is further shown the second mechanical structure 102B, the first mechanical structure 102A, and the actuator 106, such as the actuator 106 is positioned in a central cavity of the bottom fixture 204. Further, the first mechanical structure 102A is positioned over the bottom fixture 204 in contact with the actuator 106 through the connecting brackets 206. In addition, the second mechanical structure 102B is fitted with the top fixture 202 through the connecting brackets 206. Moreover, the connecting brackets 206 are fitted with the second mechanical structure 102B through a plurality of screws. Further, a plurality of guide holes 208 are configured over the bottom fixture 204 for accommodating screw heads of the plurality of screws to provide a rigid connection between the top fixture 202 and the bottom fixture 204. During assembly, the actuator 106 is fitted over the bottom fixture 204. Further, the first mechanical structure 102A is fitted over the bottom fixture 204 through the connecting brackets 206 so that the first mechanical structure 102A gets operatively connected with the actuator 106. Further, the second mechanical structure is fitted to the bottom fixture 204 through the connecting brackets 206 so that the second mechanical structure 102B is positioned at the predefined distance (D1) from the first mechanical structure 102A. Further, the top fixture 202 is fitted over the second mechanical structure 102B to form a complete assembly.
FIG. 3 is a diagram that depicts graphical representations of signal processing during determination of the density of the test fluid in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG 3, there is shown a first graphical representation 302 that depicts a voltage (V) vs time (s) characteristic of an in phase electric signal provided by the signal generator 120 to the actuator 106 for vibrating the first mechanical structure 102A in the droplet-based oscillation system 100A. Further, with reference to FIG 3, there is shown a second graphical representation 304 depicts a variation of the monitored velocity (in mm/s) of the first mechanical structure 102A (i.e., an input velocity) and the second mechanical structure 102B (i.e., an output velocity) with respect to a plurality of data points.
In an implementation, the data regarding the monitored velocity from the velocity detector 108 (shown by the second graphical representation 304) and the data regarding the electric signal provided by the signal generator 120 (shown by the first graphical representation 302) are captured by the data acquisition (DAQ) system 118 that is further configured to perform signal processing on the data received from the velocity detector and the signal generator 120. With reference to FIG 3, there is shown a third graphical representation 306 that depicts the signal processing on the data received from the velocity detector 108 and the signal generator 120. Moreover, the data represented through the third graphical representation 306 is a combination of the data from the first graphical representation 302 and the second graphical representation 304. The signal processing involves the determination of a Fast Fourier Transform (FFT) of the electric signal provided by the signal generator 120 and that of the data regarding the monitored velocity of the first mechanical structure 102A. The FFT is an algorithm, which is used by the DAQ system 118 to perform Fourier transformation over electrical signals received from the signal generator 120 and the velocity detector 108. Further, the processor 110 is configured to determine a Frequency Response Function (FRF) by using equation (3), as shown below:
(3)
The FRF is indicative of how a system responds to a sinusoidal input of different frequencies. Based on the FRF, the processor 110 is configured to determine the frequency response and the quality factor of the first mechanical structure 102A.
FIG. 4 is a diagram that depicts a graphical representation of amplitude against frequency in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 4, there is shown a graphical representation 400 that includes an X-axis 402 that depicts frequency (in Hz) and a Y-axis 404 that depicts an amplitude in decibels (dB). There is further shown a first line 406 depicts a variation in the amplitude (dB) of vibration of the second mechanical structure 102B with respect to variation in the frequency. For example, with the increase in the frequency, there is an increment in the corresponding amplitude of the, which is further used in the determination of the quality factor of the second mechanical structure 102B. There is further shown that the second mechanical structure 102B vibrates at maximum amplitude at a center frequency, that is, the resonant frequency (denoted by f0) and thereafter, the amplitude of the second mechanical structure 102B decreases with an increase in the value of frequency. Furthermore, the processor 110 is configured to determine the resonant frequency (e.g., based on the amplitude) and determines a bandwidth (BW), which corresponds to a difference between frequencies that are at 3dB from the resonant frequency (e.g., denoted as BW= f2 – f1). In other words, a 3dB bandwidth is determined by the processor 110 that is further used to determine the quality factor of the second mechanical structure 102B based on equation (4), as shown below:
Q=f_0/(f_2- f_1 ) (4)
Therefore, based on the quality factor (Q) determined from the above invention, the processor 110 is configured to determine the viscosity of the test fluid. In an example, the higher the quality factor, the lower the damping. In an implementation, the droplet introduces an added damping to the droplet-based oscillation system 100A. Moreover, the source of such damping is the damping of fluid, which is viscosity. In addition, the change in damping can be attributed to the change in viscosity, such as the quality factor is the inverse of the damping. Therefore, a higher quality factor lowers the viscosity and vice versa.
FIG. 5 is a diagram that depicts a graphical representation of a frequency response of a cantilevered first mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 5, there is shown a graphical representation 500 that includes an X-axis 502 that depicts frequency (in Hz) and a Y-axis 504 that depicts velocity (in mm/s). The graphical representation 500 depicts sa variation of the velocity (in mm/s) of the first mechanical structure 102A with respect to variation in the frequency (in Hz) of the first mechanical structure 102A of the droplet 104 in the droplet-based oscillation system 100A. In other words, the graphical representation 500 represents a frequency response of the droplet on a cantilever tip for various concentrations of glycerol water mixture (GWM), such as on a tip of the first mechanical structure 102A. For example, a first line 506 represents a frequency response of the droplet on a tip of the first mechanical structure 102A for 0% concentration of the GWM. Similarly, a second line 508 represents a frequency response of the droplet on a tip of the first mechanical structure 102A for 20% concentration of the GWM. Moreover, a third line 510 represents a frequency response of the droplet on a tip of the first mechanical structure 102A for 40% concentration of the GWM. Furthermore, a fourth line 512 represents a frequency response of the droplet on a tip of the first mechanical structure 102A for 60% concentration of the GWM. In addition, a fifth line 514 represents a frequency response of the droplet on a tip of the first mechanical structure 102A for 80% concentration of the GWM. The graphical representation 500 further depicts that the monitored velocity decreases with an increase in the concentration of the glycerol water mixture.
FIG. 6 is a diagram that depicts a graphical representation of a quality factor against viscosity of a test fluid in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 6, there is shown a graphical representation 600 that includes an X-axis 602 that depicts viscosity (cP) and a Y-axis 604 that depicts the quality factor. The graphical representation 600 depicts a first line 606 that represents an experimental data, which denotes values of the viscosity for multiple values of the quality factor, which decreases with the increase in the values of the viscosity. The values of viscosity and corresponding the quality factor are predefined in the processor 110 (in the form of the graphical representation 600). In an implementation, the processor 110 is configured to determine the quality factor of the first mechanical structure 102A or the second mechanical structure 102B by tracing the corresponding quality factor in the graphical representation 600 to determine the viscosity of the test fluid.
FIG. 7 is a diagram that depicts a graphical representation that represents variation of a resonant frequency against density in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 7, there is shown a graphical representation 700 that includes an X-axis 702 that depicts density (Kg/m3) and a Y-axis 704 that depicts resonant frequency (Hz). The graphical representation 700 depicts a first line 706 that represents an experimental data, which denotes values of the density (in kg/m3) for multiple values of the resonant frequency (in Hz) in the droplet-based oscillation system 100A. The values of the density and the corresponding resonant frequencies are predefined in the processor 110 The processor 110 is configured to determine the resonant frequency of the first mechanical structure 102A by tracing the corresponding resonant frequencies in the graphical representation 700 to determine density of the test fluid.
FIG. 8 is a diagram that depicts graphical representations of a frequency responses of two mechanical structures in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 8, there is shown a first graphical representation 800A that includes a first X-axis 802 that depicts the frequency (Hz) of the first mechanical structure 102A and a first Y-axis 804 that depicts the velocity (mm/s) of the first mechanical structure 102A. In addition, the first graphical representation 800A depicts five curves that represent the frequency responses of the first mechanical structure 102A at different concentrations (0%, 20%, 40%, 60%, and 80%) of the test fluid, such as glycerol water mixture in the droplet-based oscillation system 100A.
Further, with reference to FIG. 8, there is shown a second graphical representation 800B that includes a second X-axis 806 that depicts the frequency (Hz) of the second mechanical structure 102B and a second Y-axis 808 that depicts the velocity (mm/s) of the second mechanical structure. In addition, the second graphical representation 800B depicts five curves that represent the frequency responses of the second mechanical structure 102B at different concentrations (0%, 20%, 40%, 60%, and 80%) of the test fluid, such as glycerol water mixture in the droplet-based oscillation system 100A, 100B or 100C. With reference to the second graphical representation 800B, the frequency response of the second mechanical structure 102B shows additional peaks in the monitored velocity corresponding to the resonance of the second mechanical structure 102B at frequencies at 400Hz, 700Hz, and 1100 Hz frequency of vibration of the second mechanical structure 102B.
FIG. 9 is a diagram that depicts graphical representations of a frequency response of a second mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 9, there is shown a first graphical representation 900A that includes a first X-axis 902 that depicts the frequency (Hz) of the second mechanical structure 102B and a first Y-axis 904 that depicts the velocity (mm/s) of the second mechanical structure 102B. In addition, the first graphical representation 900A depicts five curves that represent the frequency responses of the second mechanical structure 102B at different concentrations (0%, 20%, 40%, 60%, and 80%) of the test fluid, such as glycerol water mixture in the droplet-based oscillation system 100A, the droplet-based oscillation system 100B or the droplet-based oscillation system 100C.
Further, with reference to FIG. 9, there is shown a second graphical representation 900B with a second X-axis 906 that depicts the viscosity (mPa.s) of the test fluid and a second Y-axis 908 that depicts the quality factor of the second mechanical structure 102B. Further, there is shown a first line 910 that represents an experimental data, which denotes values of the quality factors for multiple values of the viscosity (in mPa.s) of the test fluid represented on a logarithmic scale (y = - 11.11*log(x) + 23.13). The second graphical representation 900B depicts that the quality factor of the second mechanical structure 102B is inversely proportional to the viscosity of the test fluid. In an implementation, the processor 110 is configured to determine the viscosity of the test fluid from a first mode of frequency of the second mechanical structure 102B.
FIG. 10 is a diagram that depicts graphical representations of a frequency response of a first mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 10, there is shown a first graphical representation 900A that includes a first X-axis 1002 that depicts the frequency of the first mechanical structure 102A and a first Y-axis 1004 that depicts the velocity (mm/s) of the first mechanical structure 102A. Further, the first graphical representation 1000A depicts five lines that depict the variation of the monitored velocity with respect to the frequency of vibration of the first mechanical structure 102A at multiple concentrations (0%, 20%, 40%, 60%, and 80%) of the test fluid, such as glycerol water mixture. Further, with reference to FIG. 10, there is further shown a second graphical representation 1000B, which includes a second X axis 1006 that depicts the density (kg/mm3) of the test fluid and a second Y axis 1008 that depicts the velocity (mm/s) of the first mechanical structure 102A. In addition, the second graphical representation 1000B includes a first line 1010 that depicts an experimental data, which denotes values of the densities of the test fluid for multiple values of the monitored velocities (mm/s) of the first mechanical structure 102A represented on a logarithmic scale (y = - 1.48E-4x + 0.08258). In an implementation, the processor 110 is configured to determine the density of the test fluid through the monitored velocity, that is, the amplitude of the first mechanical structure 102A in an off-resonance region. In an example, the off-resonance region is determined by the processor 110 corresponding to the amplitude of the first mechanical structure 102A at the frequency of 398 Hz. Further, the processor 110 is configured to determine the density of the test fluid from the corresponding amplitude. The use of the amplitude (i.e., monitored velocity) of the first mechanical structure 102A provides an improved linearity than using the resonant frequency for the determination of the density of the test fluid.
FIG. 11 is a diagram that depicts a graphical representation of Fast Fourier Transform (FFT) of a second mechanical structure in a droplet-based oscillation system, in accordance with an embodiment of the present disclosure. With reference to FIG. 11, there is shown a graphical representation 1100 that depicts an X-axis 1102 that denotes frequency (Hz) of the second mechanical structure 102B and a Y-axis 1104 that denotes the velocity (mm/s) of the second mechanical structure 102B. The graphical representation 1100 denotes the frequency response of the second mechanical structure 102B in the droplet-based oscillation system 100A. In addition, with reference to FIG. 11, there are shown two curves, such as a first curve 1106 and a second curve 1108 that denotes an experimental data, which depicts frequency responses of the second mechanical structure 102B for the test fluids, such as glycerol water mixture (GWM) at 0% and 20% concentration respectively. In the droplet-based oscillation system 100A, the stiffness of the second mechanical structure 102B is lower than the surface tension of the droplet 104. Moreover, if the stiffness of the second mechanical structure 102B is lower than the surface tension of the droplet 104, then an additional resonance peak, that is a second resonance peak 1112 due to the droplet 104 is observed alongside a first resonance peak 1110 of the second mechanical structure 102B. The first resonance peak 1110 appears at a frequency range of 75 to 80 Hz and the second resonance peak 1112 appears at a frequency of around 100 Hz. Moreover, the density and viscosity of the test fluid is estimated using the resonant frequency and the quality factor of the second mechanical structure 102B at the second resonance peak 1112. The second resonance peak 1112 further represents the resonance frequency of the droplet 104 that is calculated using equation (5), as shown below:
f=c√(2πγ/ρ) (5)
where c is the constant, 𝛾 is the surface tension, and 𝜌 is the density. The value of f is determined by the processor 110 from the graphical representation 1100 at the resonance peak 1110. Further, if the value of the c and the 𝜌 are known, then the surface tension can be determined by the processor 110 using the above equation (5).
Modifications to embodiments of the present disclosure described in the foregoing are possible without departing from the scope of the present disclosure as defined by the accompanying claims. Expressions such as "including", "comprising", "incorporating", "have", "is" used to describe and claim the present disclosure are intended to be construed in a non-exclusive manner, namely allowing for items, components or elements not explicitly described also to be present. Reference to the singular is also to be construed to relate to the plural. The word "exemplary" is used herein to mean "serving as an example, instance or illustration". Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments. The word "optionally" is used herein to mean "is provided in some embodiments and not provided in other embodiments". It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable combination or as suitable in any other described embodiment of the disclosure.
, C , Claims:1. A droplet-based oscillation system (100A) for sensing physical properties of fluids, the droplet-based oscillation system (100A) comprising:
a first mechanical structure (102A) and a second mechanical structure (102B), wherein a droplet (104) of a known volume of a test fluid is placed between the first mechanical structure (102A) and the second mechanical structure (102B);
an actuator (106) configured to vibrate the first mechanical structure (102A), wherein the second mechanical structure (102B) is passive and vibrates due to vibrational energy transferred through the droplet (104);
a velocity detector (108) configured to monitor velocity of the first mechanical structure (102A) and the second mechanical structure (102B); and
a processor (110) configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure (102A) and the second mechanical structure (102B).
2. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the known volume of the droplet (104) ranges from 1-500 microlitres.
3. The droplet-based oscillation system (100A) as claimed in claim 1, wherein a resonant frequency of the second mechanical structure (102B) that is passively actuated through the droplet (104) is lesser than the first mechanical structure (102A).
4. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the second mechanical structure (102B) is arranged at a defined distance (D1) from the first mechanical structure (102A) creating an air gap between the first mechanical structure (102A) and the second mechanical structure (102B), and wherein the droplet (104) mechanically couples the first mechanical structure (102A) and the second mechanical structure (102B) to transfer the vibrational energy from the first mechanical structure (102A) to the second mechanical structure (102B).

5. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the first mechanical structure (102A) has a higher spring constant than the second mechanical structure (102B).
6. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the droplet (104) is arrested at a predefined location (L1) on the first mechanical structure (102A).
7. The droplet-based oscillation system (100A) as claimed in claim 6, wherein the first mechanical structure (102A) comprises a hydrophilic area (112) and hydrophobic areas (114A, 114B) on either side of the hydrophilic area (112) to arrest the droplet (104) at the predefined location (L1) that corresponds to the hydrophilic area (112) on the first mechanical structure (102A).
8. The droplet-based oscillation system (100A) as claimed in claim 7, wherein the first mechanical structure (102A) is coated with a hydrophobic substance (116) at one side that faces the second mechanical structure (102B) to form the hydrophobic areas (114A,114B) barring a portion corresponding to the hydrophilic area (112) to arrest the droplet (104) at the predefined location (L1) of the hydrophilic area (112).
9. The droplet-based oscillation system (100A) as claimed in claim 1, wherein, based on the monitored velocity of the first mechanical structure (102A), the processor (110) is further configured to track a frequency response of the first mechanical structure (102A) to determine the density of the test fluid.
10. The droplet-based oscillation system (100A) as claimed in claim 1, wherein, based on the monitored velocity of the second mechanical structure (102B), the processor (110) is further configured to determine a quality factor associated with the second mechanical structure (102B) to determine the viscosity of the test fluid.
11. The droplet-based oscillation system (100A) as claimed in claim 10, wherein the quality factor is inversely proportional to the damping as well as the viscosity, and wherein an amplitude at which the droplet (104) starts sloshing is attributed to the viscosity of the droplet (104) that is further utilized to determine the viscosity of the test fluid.

12. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the processor (110) is further configured to determine a surface tension of the droplet (104) of the test fluid when a spring constant parameter of the second mechanical structure (102B) is comparable to the surface tension of the droplet (104), and wherein a resonance of the droplet (104) is captured by the second mechanical structure (102B) to determine the surface tension, and wherein a change in the resonance or the monitored velocity of the second mechanical structure (102B) is indicative of a change in the surface tension of the droplet (104).
13. The droplet-based oscillation system (100A) as claimed in claim 1, wherein each of the first mechanical structure (102A) and the second mechanical structure (102B) is at least one of: a cantilever, a beam structure, a shell element, a flat plate, or other resonators.
14. The droplet-based oscillation system (100A) as claimed in claim 1, wherein the density and the viscosity of the test fluid as distinct parameters are determined in a range of 996 1200 kilogram per cubic metre and 0.8 - 66 centipoise respectively.
15. A droplet-based oscillation system (100B) for sensing physical property of fluids, the droplet-based oscillation system (100B) comprising:
a first mechanical structure (102A), wherein a droplet (104) of a known volume of a test fluid is placed on the first mechanical structure (102A);
an actuator (106) configured to vibrate the first mechanical structure (102A);
a velocity detector (108) configured to monitor a velocity of the first mechanical structure (102A) when the first mechanical structure (102A) vibrates on actuation by the actuator (106); and
a processor (110) configured to determine a density and a viscosity of the test fluid as distinct parameters based on the monitored velocity of the first mechanical structure (102A), wherein the droplet (104) is an added mass and an added damping to the first mechanical structure (102A) used in the determination of the viscosity and the density of the test fluid.
16. The droplet-based oscillation system (100B) as claimed in claim 15, wherein the processor (110) is further configured to track frequency response of the first mechanical structure (102A) before and after placement of the droplet on the first mechanical structure (102A) based on the monitored velocity of the first mechanical structure (102A).
17. The droplet-based oscillation system (100B) as claimed in claim 15, wherein the processor (110) is further configured to determine a quality factor associated with the first mechanical structure (102A) for the determination of the viscosity of the test fluid, based on the monitored velocity of the first mechanical structure (102A).
18. The droplet-based oscillation system (100B) as claimed in claim 15, wherein the density and the viscosity of the test fluid as distinct parameters are determined in a range of 996-1257 kilogram per cubic metre and 1-1972 centipoise respectively.
19. A droplet-based oscillation system (100C) for sensing physical properties of fluids, the droplet-based oscillation system (100C) comprising:
a first mechanical structure (102A) and a second mechanical structure (102B), wherein a droplet (104) of a known volume of a test fluid is placed between the first mechanical structure (102A) and the second mechanical structure (102B);
a first actuator (106A) configured to vibrate the first mechanical structure (102A) and a second actuator (106B) configured to vibrate the second mechanical structure (102B);
a velocity detector (108) configured to monitor velocity of the first mechanical structure (102A) and the second mechanical structure (102B); and
a processor (110) configured to determine a density and a viscosity of the test fluid as distinct parameters decoupled from each other, based on the monitored velocity of the first mechanical structure (102A) and second mechanical structure (102B).
20. The droplet-based oscillation system (100C) as claimed in claim 19, wherein when the first mechanical structure (102A) and the second mechanical structure (102B) undertake in phase and out of phase motion during vibration, two different frequency responses are obtained for the droplet (104) of the test fluid.