DESC:FIELD OF INVENTION
The present invention generally relates to the field of acoustic vector sensors, which employ light-based transduction for sound detection and directional analysis.
The present system focuses on tracking light source movements and utilizes advanced signal processing techniques or machine learning to derive information about the sound field.
BACKGROUND OF THE INVENTION
An acoustic vector sensor is a device capable of measuring both the direction of sound and the acoustic pressure. The direction information is usually obtained by measuring either the pressure gradient or the particle velocity associated with the sound. Vector sensors, that operate on the principle of pressure gradient, measure the acoustic pressure gradient in 3 directions using closely placed phase-matched hydrophones. The spacing between the hydrophones should be very small compared to the wavelength of the hydrophone to achieve satisfactory operation, thus, the frequency range of operation vastly depends on the size of the hydrophones employed.
Measurement of particle velocity is largely performed based on the response of unconstrained rigid objects when subjected to acoustic plane waves. The size of the object used for the particle velocity measurement should be very small compared to the wavelength of the maximum acoustic frequency of interest to achieve meaningful measurements.
Although an immense amount of research has been carried out in the past to develop signal-processing techniques for acoustic vector sensor arrays, a very limited number of practical sensors are available. The application of fiber optic sensing technology for underwater acoustic sensing has been steadily increasing momentum over the past decade, driven by numerous advantages such as remote sensing, ease of multiplexing, and improved reliability due to the absence of wet-end electronics. While this trend can also be observed in vector sensor development, many research programs have followed a conventional approach where fiber laser-based accelerometers mounted in a neutrally buoyant sphere are used to measure the acoustic particle velocity. However, the neutrally buoyant construction of such acoustic vector sensors tends to be bulky and requires specialized suspension mechanisms. This, combined with the requirement of a vibration isolation arrangement, limits the practicality of deploying these sensors or their arrays in field applications. In the realm of underwater surveillance, one of the most formidable challenges lies in accurately detecting low-frequency underwater sound and estimating its direction. Submarines and other underwater autonomous vehicles often emit significant noise in low-frequency bands. However, conventional array processing techniques demand huge sensor apertures or sizes to achieve direction estimation.
To address these challenges, the present invention proposes a configuration designed to measure the acoustic particle velocity for obtaining both direction and amplitude information. The present invention introduces a system and method for sensing sound and its direction using a light-based acoustic vector sensor. The present system enables point measurement of the sound signal and its direction, offering a wide range of applications in underwater surveillance. The sensing scheme of the present system exploits the principle that when a freely floating neutrally buoyant object is placed in a sound field, its motion follows the particle velocity of the water. The present invention includes a light source capable of emitting a highly collimated beam of light. This device will be configured so that the light source moves with acoustic particle velocity in the medium due to the propagating sound wave. If required, the motion of the light source can be further amplified by adjusting the effective buoyancy of the packaging surrounding it. The light emitted from the light source will be captured by a high-speed camera. The collimated beam will excite only one or a small collection of closely located pixels in the imaging sensor. The motion of the light source will result in a corresponding change in the pixels that get excited. Signal processing on the intensity pattern or the image information read out from the camera will yield acoustic particle velocity information. The magnitude of the shift in the intensity pattern will be proportional to the magnitude of the acoustic particle velocity and the direction of the shift will give information about the direction of the sound.
VARIOUS PRIOR ARTS HAVE DISCLOSED SIMILAR SYSTEMS AND METHODS
US Patent Application US11867539B2 discloses acoustic methods and systems for providing digital data. The technique employed in this prior art is distributed fiber optic sensing, which operates based on backscattered signals or changes occurring within the fiber. Although it represents an active research area and existing undersea communication infrastructure could potentially be utilized for sound detection, it is not directly related to the present invention. Furthermore, the referenced prior art doesn’t involve point measurement of the sound field whereas the present invention allows for precisely measuring the sound signal and its direction using light-based transduction. As a result, the present system offers a broader spectrum of applications in underwater surveillance.
US Patent Application US9527403B2 describes a fiber optic directional acoustic sensor, designed for detecting sound waves and determining their direction. This sensor consists of a light-emitting diode (LED), a fiber optic probe with transmitting and receiving optical fibers, and a cantilever with an edge reflector. The cantilever is a rod that can move in response to sound waves, and the edge reflector is positioned to reflect light from the transmitting fiber to the receiving fiber. The movement of the cantilever, caused by sound waves, changes the amount of light received by the receiving fiber, which can be detected and analyzed to determine the direction and intensity of the sound. It is significantly different from the present invention as it uses multiple fibers to transmit the reflected signal back. The cantilever is part that responds to the sound signal and there is no scope for array processing of intensity data in this referenced prior art. Additionally, it lacks the capability for array processing of intensity data, which is a key feature of the present invention.
A research paper entitled “A Vector Sensing Scheme for underwater acoustics based on Particle Velocity Measurements” published in OCEANS 2015 - MTS/IEEE Washington deals with the amplification of the acoustic sound field using acoustic horns. These acoustic horns have inherent directionality, hence use of two or more horns could yield the direction measurement of acoustic signals. While it mentions various techniques including coherent sensing with interferometers that could be used to detect the amplified particle velocity, it does not talk about specific measurement configurations for measuring the particle velocity sensing. The present invention directly gives the direction of the sensor in a plane, but it becomes irrelevant in the horn as sound field information gets distorted by the horn.
To solve the aforementioned challenges in the prior arts, the present invention introduces a system and method for sensing sound and its direction using a light-based acoustic vector sensor. The present system’s ability to precisely measure sound signals and their direction offers a wide range of applications in underwater surveillance and beyond. Its versatility makes it suitable for various scenarios where accurate sound detection and directional analysis are essential, providing a broader spectrum of potential use cases compared to some existing systems. In contrast to prior art, which may lack the capability of point measurement of the sound field, the present invention enables point measurement of both the sound signal and its direction through light-based transduction. The present invention offers a more streamlined and compact design, distinguishing it from prior arts utilizing fiber optic technology, which often requires bulky construction and specialized suspension mechanisms. This enhances practicality, facilitating deployment in various field applications with greater ease and efficiency.
OBJECTS OF THE INVENTION
It is the main object of the present invention to provide a system and method for sensing sound and its direction using a light-based acoustic vector sensor.
It is the primary objective of this invention to provide a system and method employing optical sensing techniques to measure acoustic particle velocity, facilitating the determination of the direction and intensity of the sound.
It is another object of the present invention to provide a system and method that facilitates precise point measurement of both sound signals and their direction through light-based transduction, wherein particle motion induced by sound is converted into optical signals.
It is another object of the present invention to provide a system and method capable of array processing of intensity data, facilitating advanced analysis and interpretation of sound signals and their direction.
It is another object of the present invention to provide a system and method that employs the high-speed camera to capture and analyze the images of optical signals.
It is another object of the present invention to provide a system and method that integrates machine learning techniques in particle velocity captured data to derive/ interpret the information on the direction and intensity of the sound.
It is another object of the present invention to provide a system and method that offers a more streamlined and compact design, suitable for a wide range of applications.
SUMMARY OF THE INVENTION
The present invention introduces a system and method for sensing sound and its direction using a light-based acoustic vector sensor. The present invention offers a system and method that employs an optical sensing technique to measure acoustic particle velocity. This particle velocity measurement aids in determining the direction and intensity of the sound.
The present invention comprises a floating, neutrally buoyant object, a light source, a collimator, and a high-speed camera/ imaging sensor. The buoyant object, such as a single-mode or multi-mode optical fiber, is suspended in the medium (water), provided the characteristic dimension of the object should be significantly smaller than the wavelength of the acoustic wave. At the free end of the optical fiber, a light collimator is attached. The collimator ensures the creation of focused beams of light. An optional deflection amplifier like an optical lever can be incorporated between the collimator and the camera to amplify the optical beam deflections. The high-speed camera is positioned at a predefined distance from the tip of the optical fiber to capture the optical signals.
When the sound propagates through the water, it induces a small motion of the suspended optical fiber. These subtle movements cause minute variations in the light spot, which are then captured by a high-speed camera. It detects changes in the position or intensity of the light spot over time. Based on the detected variations, the image will be processed using Machine Learning and AI models to measure the amplitude and direction of the sound signal. Multiple fiber lines or multiple light beam arrays can be used for similar measurements, allowing for more comprehensive sensing.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 provides a schematic illustration of Vector sensing of a low-frequency underwater acoustic sensing system in accordance with the present invention.
Figure 2 provides a schematic illustration of Vector sensing of a low-frequency underwater acoustic sensing system with optical beam deflection amplifier in accordance with the present invention.

Figure 3 provides a snapshot of the instant showing change in intensity pattern due to acoustic wave in accordance with the present invention.
Provided below is the list of components of the present invention along with its reference numerals:
PART DESCRIPTION / COMPONENT REFERENCE NUMERAL
Buoyant Object 100
Light Source 102
Collimator 104
High-speed Camera/ Imaging Sensor 106
Light Beam/ Light Spot 108
Optical beam deflection amplifier (eg. Optical lever) 110
While the invention is amendable to various modifications and alternative forms, specifics thereof have been shown by way of examples in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to this, terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms. The present invention should be construed as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined. Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiments of the present invention and do not represent all the technical ideas of the present invention. Therefore, it should be understood that equivalents and modifications are possible.
DETAILED DESCRIPTION OF THE INVENTION WITH RESPECT TO THE DRAWINGS
The present invention as embodied by "A system and method for sensing sound and its direction using light-based acoustic vector sensor" succinctly fulfils the above-mentioned need(s) in the art. The present invention has objective(s) arising as a result of the above-mentioned need(s), said objective(s) being enumerated below. In as much as the objective(s) of the present invention are enumerated, it will be obvious to a person skilled in the art that, the enumerated objective(s) are not exhaustive of the present invention in its entirety and are enclosed solely for the purpose of illustration. Further, the present invention encloses within its scope and purview, any structural alternative(s) and/or any functional equivalent(s) even though, such structural alternative(s) and/or any functional equivalent(s) are not mentioned explicitly herein or elsewhere, in the present disclosure. The present invention therefore encompasses also, any improvisation(s)/ modification(s) applied to the structural alternative(s)/functional alternative(s) within its scope and purview. The present invention may be embodied in other specific form(s) without departing from the spirit or essential attributes thereof.
Throughout this specification, the use of the word "comprise" and variations such as "comprises" and "comprising" may imply the inclusion of an element or elements not specifically recited.
The present invention discloses a system and method for sensing sound and its direction using a light-based acoustic vector sensor. The present invention offers a system and method that employs an optical sensing technique to measure acoustic particle velocity. This particle velocity measurement aids in determining the direction and intensity of the sound.
In the preferred embodiment of the present invention, as shown in Figure 1, the system consists of a buoyant object (100), a light source (102), a collimator (104), and a high-speed camera/ imaging sensor (106), and an optional deflection amplifier (110). These components are arranged in a manner that enables the detection and interpretation of acoustic signals based on optical variations, as described below:
(i) Buoyant Object (100):
The buoyant object (100), such as a single-mode or multi-mode optical fiber, is suspended in the medium (water or any suitable medium based on impedance matching requirements associated with the implementation of various embodiments disclosed by the present invention), provided the characteristic dimension of the object should be significantly smaller than the wavelength of the acoustic wave.

(ii) Light Source (102):
The present invention consists of a light source (102) that is externally connected to one end of the optical fiber (100). The light source (102) emits a light spot or beam (108). The system is configured such that the fiber and/or collimator will move with the acoustic particle velocity in the medium due to the propagating sound wave, and it will result in the deflection of the light beam (108). If required, additional amplification of the light source motion can be achieved by adjusting the effective buoyancy on the fiber and/or collimator, which effectively performs the function of the light source (102).

Any generic light source like LEDs or Lasers diodes could act as a light source. Light sources (102) could also be selected based on the light sensitivity of the imaging sensor selected for the implementation of various embodiments disclosed by the present invention. This light (108) will be carried into the sensor (106) using an optical fiber (100).

(iii) Collimator (104):
At the other end of the optical fiber (100), a light collimator (104) is attached to ensure the creation of focused beams of light. The collimator (104) is a device that narrows or aligns a beam of particles or waves, typically light, into parallel rays. Its main purpose is to reduce the divergence of the beam, so it travels in a straight and consistent path.

(iv) High-speed Camera/ Imaging Sensor (106): A high-speed camera (106) is positioned at a predefined distance from the tip of the optical fiber (100) to capture the optical signals. The camera (106) could be selected based on the frequency and intensity range of interest of the sound signals. The sensor dimensions and pixel density etc., could be chosen carefully to address various operation requirements. In some cases, very high-speed operation of the camera could be achieved by limiting the readout to the active region of the imaging sensor.
(v) Optional Deflection Amplifier (110): In another embodiment of the present invention, wherein the system is provided with an optical beam deflection amplifier like optical lever which is incorporated between the collimator (104) and the camera (106) to amplify the optical beam deflections.
In the preferred embodiment of the present invention, wherein the method for sensing sound and its direction using light-based acoustic vector sensor, comprises of:
i. As sound waves propagate through water, they induce a slight displacement in the suspended optical fiber (100);
ii. These minor displacements of the optical fiber (100) result in subtle variations in the light spot (108), which are captured by a high-speed camera (106);
iii. The camera (106) detects changes in the position or intensity of the light spot (108) over time;
iv. Based on the detected variations, the image will be processed using machine learning techniques to measure the amplitude and direction of the sound signal;
v. Multiple fiber lines or multiple light beam arrays can be used for similar measurements, allowing for more comprehensive sensing.
KEY FEATURES OF THE PRESENT INVENTION:
Some of the important aspects of the present invention include:
1) Light-Based Transduction: The present invention offers a system operating on the principle of light-based transduction. Light-based transduction means converting or transducing the particle motion induced by sound into optical signals. These optical signals are then captured and interpreted using light sensors (106) /optical detectors.
2) Image-Based Sensing of Particle Velocity: The present system incorporates a method of sensing acoustic particle velocity by capturing and analyzing images of particle motion by means of employing high-speed, high-resolution cameras. It measures the variations in collimated beams affected by the particle motions due to sound propagation.
3) Machine Learning Techniques for Particle Velocity Sensing: The present invention further integrates machine learning techniques in particle velocity captured data. The image captured by the high-speed camera, be processed using Machine learning to derive/ interpret the information on the direction and intensity of the sound. The present invention is configured to process the changes using machine learning techniques to measure an amplitude and direction of a sound signal, thereby determining a direction and intensity of the sound.

Enhanced Beam Deflection Mechanisms:
The present invention can be further enhanced through additional mechanisms that improve the system's sensitivity and performance. These enhancements focus on amplifying the deflection of the light beam to improve detection capabilities:
1. Multiple Deflection Mechanisms
• Buoyant Forces: As previously disclosed, neutrally buoyant objects can follow particle motion in acoustic fields. Optimized buoyancy configurations can be designed where the effective mass of the sensing element precisely balances with the displaced fluid, creating maximum sensitivity to acoustic particle motion.
• Viscous Drag Implementation: In addition to buoyant forces, the system can leverage viscous drag forces for enhanced beam deflection. When properly implemented, viscous drag can significantly improve the sensor's response to acoustic waves, particularly in low-frequency applications. The fiber's response to acoustic fields can be enhanced through specialized coatings or structural modifications that maximize viscous interaction with the surrounding medium.
• Mechanical Configuration Enhancements: Intelligent mechanical geometries can be devised to enhance beam deflection sensitivity. These may include:
a. Tapered fiber structures that optimize flexibility at strategic points.
b. Specialized attachment mechanisms that amplify motion at the fiber tip.
c. Custom damping elements that improve signal-to-noise ratio by filtering mechanical noise while preserving desired acoustic response.

2. Optical Lever Implementation
• Beam Path Modification: Introducing optical levers between the collimator and camera can significantly amplify small deflections in the fiber. This operates on the principle that small angular changes at the reflection point translate to larger displacements at the detector plane.
• Multi-Stage Amplification: Cascaded optical lever systems can be implemented to achieve multiplicative amplification effects, allowing detection of extremely small acoustic signals.
• Adaptive Optics Integration: Dynamic optical elements can be incorporated to provide adjustable amplification based on signal characteristics, optimizing detection across varying acoustic conditions.
System Integration Considerations
These enhancements can be implemented without significantly altering the core design principles of the present invention. These additions maintain compatibility with the machine learning and signal processing approaches while substantially improving the system's ability to detect low-amplitude acoustic signals. The combination of both mechanical (buoyancy and viscous) effects with optical amplification techniques creates a highly sensitive measurement system that maintains the compact form factor advantages of the original design while addressing detection threshold limitations.
EXAMPLE
The present invention discloses a system and method for sensing sound and its direction using a light-based acoustic vector sensor. The present invention offers a system and method that employs an optical sensing technique to measure acoustic particle velocity. This particle velocity measurement aids in determining the direction and intensity of the sound. The system consists of a Buoyant object (100), a light source (102), a collimator (104), and a high-speed camera/ imaging sensor (106). The system is configured to detect changes in a position or intensity of the light spot (108) over time due to the propagation of acoustic waves through the sensing medium, wherein the changes are caused by minor displacements of the optical fiber (100) resulting in subtle variations in the light spot (108).
The method for sensing sound and its direction using light-based acoustic vector sensors comprises the following steps:
i. As sound waves propagate through water, they induce a slight displacement in the suspended optical fiber (100);
ii. These minor displacements of the optical fiber (100) result in subtle variations in the light spot (108), which are captured by a high-speed camera (106);
iii. The camera (106) detects changes in the position or intensity of the light spot (108) over time;
iv. Based on the detected variations, the image will be processed using machine learning techniques to measure the amplitude and direction of the sound signal;
v. Multiple fiber lines or multiple light beam arrays can be used for similar measurements, allowing for more comprehensive sensing.
TEST RESULTS
As illustrated in Figure 2, the present invention provides a snapshot of the instant showing change in intensity pattern due to acoustic waves. The light coming out from the light source (102) will be detected by a high-speed camera (106). The collimated beam will excite only one or a small collection of closely located pixels in the imaging sensor (106). The motion of the light source (102) will result in a corresponding change in the pixels that get excited. Signal processing on the intensity pattern or the image information read out from the camera (106) will yield acoustic particle velocity information. The magnitude of the shift in the intensity pattern will be proportional to the magnitude of the acoustic particle velocity, and the direction of the shift will give information about the direction of the sound.
ADVANTAGES OF THE PRESENT INVENTION
1. Real-time Monitoring: The present system offers real-time monitoring capabilities by enabling precise point measurement of both sound signals and their direction.
2. Enhanced Sensitivity: By utilizing a light-based sensing scheme, the invention offers enhanced sensitivity to acoustic particle velocity. This allows for more accurate measurement of sound direction and amplitude, even in low-frequency sound environments.
3. Compact Design: Unlike conventional neutrally buoyant sphere-based sensors, the present invention's configuration is compact, eliminating the need for bulky construction and special suspension mechanisms. This makes it more suitable for various field applications where space constraints are a concern.
4. High-Speed Measurement: The incorporation of a high-speed camera enables rapid detection and processing of changes in the intensity pattern caused by the motion of the light source. This allows for real-time measurement and analysis of acoustic signals.
5. Versatility: The present invention's configuration is versatile and adaptable to different acoustic environments and applications. It can be easily adjusted and optimized for various frequency ranges and sound field conditions, enhancing its flexibility in diverse underwater surveillance scenarios.
6. Reduced Cost and Complexity: By utilizing light-based sensing technology and compact design, the present invention potentially reduces the overall cost and complexity associated with traditional acoustic vector sensor systems. This makes it more accessible and practical for widespread deployment in underwater surveillance applications.
Although the proposed concept has been described as a way of example with reference to various models, it is not limited to the disclosed embodiment, and that alternative designs could be constructed without deviating from the scope of invention as defined above.
It will be apparent to a person skilled in the art that the above description is for illustrative purposes only and should not be considered as limiting. Various modifications, additions, alterations, and improvements without deviating from the scope of the invention may be made by a person skilled in the art. ,CLAIMS:We Claim,
1. A system for sensing sound and its direction using light-based acoustic vector sensor, comprising of:
i. A buoyant object which is a single-mode or multi-mode optical fiber (100) which is suspended in a medium;
ii. A light source (102) emitting light (108) that is externally connected to one end of the optical fiber (100);
iii. A collimator (104) attached to the other end of the optical fiber (100), which ensures the creation of focused beams of light, wherein the collimator (104) narrows or aligns a beam of particles or waves of light into parallel rays;
iv. A high-speed camera/ imaging sensor (106) positioned at a predefined distance from a tip of the optical fiber (100) to capture optical signals,
wherein the system is configured such that the fiber (100) and/or collimator (104) will move with the acoustic particle velocity in the medium due to the propagating sound wave and it will result in deflection of the light beam (108);
wherein the system is configured to detect changes in a position or intensity of the light spot (108) over time due to the propagation of acoustic waves through the sensing medium, wherein the changes are caused by minor displacements of the optical fiber (100) resulting in subtle variations in the light spot (108).

2. The system as claimed in claim 1, wherein the medium is water or any suitable medium wherein the characteristic dimension of the object (100) should be significantly smaller than the wavelength of the acoustic wave.

3. The system as claimed in claim 1, wherein additional amplification of the light source motion is achieved by adjusting the effective buoyancy on the fiber (100) and/or collimator (104) which effectively perform the function of the light source (102).

4. The system as claimed in claim 1, wherein the deflection of the optical beam in response to acoustic waves is enhanced by viscous drag forces, achieved through coatings or structural modifications of the optical fiber (100) that increase viscous interaction with the surrounding medium.

5. The system as claimed in claim 1, wherein the light spot (108) is carried into the imaging sensorX (106) using the optical fiber (100).

6. The system as claimed in claim 1, wherein the light source (102) is an LED or a laser diode.

7. The system as claimed in claim 1, wherein the collimator (104) reduces the divergence of the light source (102) beam, so it travels in a straight and consistent path.

8. The system as claimed in claim 1, wherein an optical beam deflection amplifier (110) such as optical lever is incorporated between the collimator (104) and the camera (106) to amplify the optical beam deflections.
9. The system as claimed in claim 1, wherein the system comprises a method for sensing sound and its direction using light-based acoustic vector sensor, comprising:
i. Inducing a slight displacement in the suspended optical fiber (100), as sound waves propagate through water;
ii. These minor displacements of the optical fiber (100) result in subtle variations in the light spot (108), which are captured by the high-speed camera/ image sensor (106);
iii. The camera (106) detects changes in the position or intensity of the light spot (108) over time;
iv. Based on the detected variations, the image will be processed to measure the amplitude and direction of the sound signal,
Wherein the acoustic particle velocity is sensed by capturing and analyzing images of particle motion by the image sensor (106) and the variations in collimated beams affected by the particle motions due to sound propagation is measured.