Claims:1. A sensor (A) comprising a stainless steel integrated structure having circular diaphragm (6) integrated with cellulose material embedded with reduced graphene oxide nanosheets (5).
2. The sensor as claimed in claim 1, wherein the cellulose material is filter paper.
3. The sensor as claimed in claim 1, wherein the reduced graphene oxide nanosheets are of size ranging from about 300nm to about 500nm.
4. The sensor as claimed in claim 1, wherein the sensor (A) is enclosed in a coating selected from a group comprising parylene, room temperature vulcanized silicone compound (RTV); preferably parylene.
5. The sensor as claimed in claim 1 and 4, wherein sensor is provided with electrical leads (8) for sensing.
6. A method of fabrication of sensor (A), said method comprising acts of
a) preparation of cellulose embedded with reduced graphene oxide nanosheets; said preparation comprising acts of-
i. oxidising graphite powder using potassium permanganate, hydrogen peroxide and deionized water in presence of sulphuric acid to obtain graphite oxide;
ii. purifying the graphite oxide using hydrochloric acid and deionized water;
iii. grinding the graphene oxide sheets to a powder , diluting it with de-ionized water and ultra-sonicating the diluted mixture to obtain mixture containing nanosheets;
iv. exfoliating the graphite oxide to obtain graphene oxide sheets;
v. reducing the mixture containing nanosheets with hydrazine hydrate solution to obtain reduced graphene oxide nanosheets;
vi. preparing and coating the reduced graphene oxide nanosheets solution and filtering under vacuum over cellulose material;
vii. annealing the cellulose material coated with reduced graphene oxide solution at a temperature ranging from about 75°C to about 85°C, preferably 80°C to obtain a film wherein thickness of film is about 2 µm;
viii.encapsulating the cellulose material coated with reduced graphene oxide and annealing at 55 °C- 65 °C; preferably 60 °C; and
viii. providing electrical leads through an electrode.
and
b) integration of the cellulose embedded with reduced graphene oxide nanosheets onto the parylene coated stainless steel diaphragm to obtain sensor (A).
7. A transducer (B) comprising, sensor (A) of claim 1; wherein the sensor (A) is integrated with the pressure port (2) to sense pressure in the transducer (B).
8. The transducer as claimed in claim 7, wherein the transducer is for sensing a parameter selected from a group comprising pressure, movement, flow, speed, acoustics, impact, shock, force and shear.
, Description:TECHNICAL FIELD

The present invention is in relation to sensor technology. In particular to Piezoresistive based thin films for Temperature, Pressure, and Humidity Sensors Technology. The invention specifically provides sensor element for transducer application. The sensor element is based on reduced Graphene oxide nanosheets coated on paper and method of its preparation for application as sensor in a transducer and transducer thereof.

BACKGROUND OF INVENTION

Sensors are emerging as an integral part of our daily life. Various types of sensors based on temperature, pressure, humidity, chemical, proximity, optical activity and the like have been developed and the research to ameliorate such sensors is consistently going on to accommodate the current trend and need in various domains.
Pressure sensor have a wide range of applications in the fields of automotive industry, aviation, touch screen devices, medical field and the like. Over the years many potential improvements in sensor performance are realized by using structures and sensing elements complementary to each other, like flat diaphragm, boss diaphragm, embossed diaphragm and cantilever beam structures to name a few. Structures and sensing materials have played a very important role in realizing non linearity, hysteresis, sensitivity, repeatability, and accuracy characteristics of these pressure sensors.
Currently most pressure sensing applications are based on the piezoresistive type of excitation and detection is based on the thin film metal strain gauges, diffused semiconductor and graphene. Most of the piezoresistive metals and thin film based strain gauges exhibit gauge factor between 1 to 5, strain gauges involving polycrystalline silicon material, graphene and diffused semiconductor is around 30, between 2 to 12 and between 80 to 200 respectively.
The technologies are expensive due to inherent characteristics of the materials adopted for example, semiconductor based technology are to be processed and assembled in a clean (Class 100/1000) environment making it expensive and tedious to produce.
The reduced graphene oxide material is of interest because at nano scale it displays unique electrical, mechanical, thermal and optical properties with the advantage of low cost manufacturing and processing. The properties of reduced graphene oxide offers it as an ideal candidate for pressure sensing applications.
Sung Il Ahn in has reported in Scientific Reports 6, 2016; titled “Self-assembled and intercalated film of reduced graphene oxide for a novel vacuum pressure sensor” describes about RGO films containing various amounts of a water-soluble polymer, poly-vinyl-alcohol (PVA), were prepared using the RSA method. They were then characterized and their electrical behavior is examined under changing vacuum pressure to determine their potential sensor applications.
Rouzbeh Kazemzadeh in the document titled “Piezo-resistive Pressure Sensor Array with Photo-thermally Reduced Graphene Oxide” in MRS Online Proceeding Library Archive, 1798; 2015 discusses about pressure sensor fabricated by photo-thermally reduced Graphene oxide (GO) with silver nano wires (AgNWs).
The challenges associated with the present art are being currently addressed with the proposed sensor element and transducer thereof without comprising the key characteristics of the sensor element. The sensors of the present invention can be widely used in corrosive environments and find a variety of applications in the fields of civil, nuclear plants, oil and natural gas lines.

Summary of invention
Accordingly the present invention provides a sensor comprising reduced graphene oxide nanosheets on cellulose material integrated on a stainless steel diaphragm for detecting various parameters like pressure, temperature, movement, stress, heat and the like. The graphene oxide is reduced by adopting modified Hummer’s method and filtered using onto cellulose material, preferably filter paper and later the filter paper embedded with reduced graphene oxide is used to fabricate the sensor by a simple and cost effective way.
The sensor is adopted in a transducer to for the ease of detection of the aforesaid parameters.

Brief description of drawings

The features of the present invention can be understood in detail with the aid of appended figures. It is to be noted however, that the appended figures illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope for the invention.

Figure 1: XRD phases of GO and RGO nanosheets on filter paper based films.
Figure 2: FE-SEM images of RGO based films: (a) The dimensions of filter paper pores structure, (b) Surface view of the RGO nanosheets stacked on the filter paper, (c) The cross sectional view of RGO sheets filled onto the filter paper, (d) The thickness of multilayered single RGO nanosheets.
Figure 3: Raman Spectroscopy of (a) GO sheets, (b) RGO nanosheets.
Figure 4: Simulation of diaphragm at different beam locations to achieve optimum stress distribution on it.
Figure 5: Drawing of the primary structure.
Figure 6: Drawing of the pressure port.
Figure 7: 3D drawing of the complete assembly of the pressure transducer assembly.
Figure 8: The fabricated Pressure transducer assembly.

Figure 9: Schematic integrated standard / RGO sensing elements on pressure transducer assembly.
Figure 10: Sensor calibration using hydraulic dead weight calibrator.

Figure 11: Input –output characteristics of pressure versus strain by simulation, standard strain gauge experimental and RGO strain gauge experimental.
Figure 12: Input –output characteristics of pressure versus resistance, (a) Three trials, (b) The combined Non-linear and Hysteresis on for three trials.
Figure 13: Pressure sensor temperature calibration.

Figure 14: The typical linear response of the sensor in terms of change in resistance with respect to temperature, (a) R-T curve represents the linear relationship for two trials, (b) The combined effect of Non-linearity and Hysteresis, (c) The relative resistance with respect to temperature (TCR).

Detailed description of invention

The foregoing description of the embodiments of the invention has been presented for the purpose of illustration. It is not intended to be exhaustive or to limit the invention to the precise form disclosed as many modifications and variations are possible in light of this disclosure for a person skilled in the art in view of the figures, description and claims. It may further be noted that as used herein and in the appended claims, the singular forms "a", "an", and "the" include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by person skilled in the art.

The present invention is in relation to a sensor (A) comprising a stainless steel integrated structure having circular diaphragm (6) integrated with cellulose material embedded with reduced graphene oxide nanosheets (5).
In another embodiment of the invention, the cellulose material is filter paper.
In another embodiment of the invention, the reduced graphene oxide nanosheets are of size ranging from about 300nm to about 500nm.
In another embodiment of the invention, the sensor (A) is enclosed in a coating selected from a group comprising parylene, room temperature vulcanized silicone compound (RTV); preferably parylene.
In another embodiment of the invention, the sensor is provided with electrical leads (8) for sensing.
In another embodiment, a method of fabrication of sensor (A), said method comprising acts of
preparation of cellulose embedded with reduced graphene oxide nanosheets; said preparation comprising acts of-
oxidising graphite powder using potassium permanganate, hydrogen peroxide and deionized water in presence of sulphuric acid to obtain graphite oxide;
purifying the graphite oxide using hydrochloric acid and deionized water;
grinding the graphene oxide sheets to a powder , diluting it with de-ionized water and ultra-sonicating the diluted mixture to obtain mixture containing nanosheets;
exfoliating the graphite oxide to obtain graphene oxide sheets;
reducing the mixture containing nanosheets with hydrazine hydrate solution to obtain reduced graphene oxide nanosheets;
preparing and coating the reduced graphene oxide nanosheets solution and filtering under vacuum over cellulose material;
annealing the cellulose material coated with reduced graphene oxide solution at a temperature ranging from about 75°C to about 85°C, preferably 80°C to obtain a film wherein thickness of film is about 2 µm;
encapsulating the cellulose material coated with reduced graphene oxide and annealing at 55 °C- 65 °C; preferably 60 °C; and
providing electrical leads through an electrode.
and
integration of the cellulose embedded with reduced graphene oxide nanosheets onto the parylene coated stainless steel diaphragm to obtain sensor (A).
The present invention is also in relation to a transducer (B) comprising, sensor (A); wherein the sensor (A) is integrated with the pressure port (2) to sense pressure in the transducer (B).
In another embodiment of the invention, the transducer is for sensing a parameter selected from a group comprising pressure, movement, flow, speed, acoustics, impact, shock, force and shear.
The present invention provides economical sensing elements based on reduced graphene oxide (RGO) nanosheet films for pressure transducer application. The sensing element (A) comprises reduced graphene oxide nanosheets on cellulose material, preferably filter paper. Figure 8 & 9 show the schematic representation and photograph image of fabricated reduced graphene oxide nanosheets based strain sensing films for pressure transducer application and a transducer (B) thereof.
The RGO nanomaterials when integrated with different structures can be used to sense and respond to external input like mechanical, electrical, chemical, thermal parameters. An uncomplicated and simple method for the fabrication of RGO nanosheets is demonstrated on the filter paper that possesses better and easier measurable macroscopic electrical properties for adoption in a transducer.
In another embodiment, the sensing elements of the present invention are fabricated involving two steps.
Synthesis of RGO nanosheets
Oxidation of graphite powder by Modified Hummer’s method to obtain graphite
oxide sheets.
Exfoliation of graphite oxide into individual sheets.
Reduction of exfoliated graphene oxide sheets by hydrazine hydrate at about 95º C for 4 hrs.
Filtration of reduced graphene oxide sheets by vacuum filtration method.
Annealing process for the cellulose filtered paper.
Design and preparation of micro pattern structure for sensing element in sensors development.
Bonding of micro structured RGO nanosheets based filter paper sensing films onto the diaphragms/beams made of stainless steel.
Electrode preparation.
Copper leads attachment.

Fabrication of the integrated structure which forms the primary sensing element of the sensor comprises below mentioned steps which are further described in the below sections.
Processing flow of the sensor manufacturing process
Preparation of the RGO strain gauge material
Characterization of the material
Design and development of the structure
Fabrication of the structure
Assembly
Testing and calibration
Thus in an embodiment, the present invention is also in relation to a stainless steel integrated structure fabricated using Reduced Graphene oxide (RGO) strain gauges as transducer in pressure sensing application.

In an embodiment, the RGO nanosheets solution is synthesized through modified Hummer’s method and filtered by vacuum filtration process. The synthesized RGO nanosheets are on a filter paper, with the thickness of the film around 2 µm. Both graphene oxide and reduced graphene oxide nanosheets (of size 300nm-500nm) are characterized all through the preparation using XRD, FE-SEM and Raman spectroscopy techniques for comparison of the properties. The RGO nanosheets based films annealed at a temperature ranging from about 55 ºC – 65 ºC temperature, preferably at about 60 ºC shows good sensing performance. The sensing RGO nanomaterial displays an excellent gauge factor of 124, considerably a very significant number as compared to the 2-14. The filter paper comprising reduced graphene oxide is integrated on stainless steel diaphragm. In particular, the integrated structure of 17-4 PH steel, also displays good nonlinearity and displacement characteristic making this combination an excellent pair for pressure transducer applications. The RGO nanomaterial and the integrated structure complement each other thereby giving excellent output characteristics.

After the realization of the RGO nanosheets based strain sensing films, it respond to the pressure and temperature studies with respect to the resistance change variations and the typical responses obtained from the RGO sensing films are shown in figures 14 to 15.

Specifically, it uses an integrated structure which includes a circular diaphragm and a fixed guided beam as a primary sensing element with RGO strain gauge as a secondary sensing element. The resulting strain on the fixed guided beam due to applied pressure is sensed by the sensing element and the output is measured by the change in resistance.

Procedure for the fabrication of RGO nanosheets filter paper based films as strain gauge sensing elements in the pressure transducer is described hereunder.

A) Processing of the RGO strain gauge material:
Synthesis of Graphene Oxide (GO):
Graphene Oxide (GO) is synthesized by Modified Hummer’s method as fine graphite powder exfoliating through chemical route. Typically, the graphite powder (2gm) is oxidized using strong acidic environment H2SO4 (54 ml) through constant magnetic stirring maintained at below 5°C. The KMnO4 (6gm) is slowly added to the (H2SO4) solution over a period of 20 minutes. Then the concentrated solution is rigorously stirred up for about 40 min and deionized water (100 ml) is added dropwise to the solution on stirring for 90 min. Later, the deionized water (200 ml) is again added to complete the oxidation reaction. The entire oxidation process is completed by adding 30 ml of hydrogen peroxide (H2O2) to the mixture. After few minutes, the colour of the reaction mixture changes from black to reddish brown indicating the end of the reaction process. The mixture is washed two to three times with Hydrochloric acid (HCl) solution and deionized water (DI) in order to remove metal ions and un-oxidized graphite from the reaction mixture. The mixture is filtered through Whatman filter paper by using vacuum filtration method to separate the unreacted components from the mixture and the filtration cake residue is collected at the end of the process. Finally, GO sheets powder is annealed at 90°C for 8 hours and grinding the GO sheets for further purification process.

2. Procedure for the synthesis of RGO sheets on filter paper films for sensing elements in sensors:
The GO powder (0.3gm; 1 mgml-1) is added to DI water in 300 ml (De-ionized water) mixture at weight ratio of 1:1 to form suspension. The diluted suspension is ultra-sonicated for 90 min. The flakes are split into individual nano sheets. The entire mixture is reduced using reducing agent as Hydrazine hydrate solution (0.1gm; 3ml) is added to the mixture under constant stirring at 95o C for 4 hours. The mixture is filtered through Whatman filter paper by using vacuum filtration method to separate the unreacted components from the mixture and the filtration cake residue is collected at the end of the process. The RGO sheets are annealed at about 80°C for 2 hours and grinding the RGO sheets for further purification process. Finally, it is separated from the cellulose filter paper. Due to the bigger lateral sizes of RGO compared with the size of the filter paper pores, some are retained to form a stack on the filter paper surface. The filter paper embedded with films of RGO is used for making sensing elements for various sensors applications with minor fabrication steps.

Characterizing the material:

X-ray diffraction (XRD) patterns are recorded on the synthesized GO sheets and RGO nanosheets filter paper based films for their structural analysis. The existence of XRD peak at 2? =25.61° corresponding to the (002) plane of crystalline nature of GO nanosheets, which arises from stack of graphene layers before exfoliation of graphite. The same peak is shifted to 11.2°, corresponding to the (001) plane after oxidation treatment, indicating that the interlayer spacing in the Graphite Oxide (GO) increases. The diffraction peak at 42.82º corresponding to the (100) plane, represents the graphite microcrystals nature in the GO system. In the RGO, after chemical reduction, the fact that nearly all peaks disappears indicates that the efficient exfoliation of multilayers during the chemical reduction process of GO. However, the end of the reaction a new wide diffraction peak appeared at 23.5° which corresponds to an interlayer spacing of 0.38 nm as shown in Fig.1. This indicates the formation of the RGO nanosheets from the reduction. The shoulder peak appearing at 42.82° which is fingerprint peak for graphite due to (100) diffraction indicates that the reformation of graphite microcrystals on reduced graphene oxide plane because of chemical reduction of the Graphene Oxide (GO).

The surface morphology analysis is carried out for as-synthesized RGO nanosheets on the filter paper based films by field emission- scanning electron microscopy (FE-SEM (Carl Zeiss), ULTRA 55). Fig.2 (a) shows the porous nature of bare filter paper having dimensions around in between 300 - 500 nm in different positions of locations. Fig.2 (b) - (d) shows the RGO nanosheets are used to fill the porous nature of the filter paper films for making functional conductive structure. The prepared RGO nanosheets surface morphology shows confirming the loosely bound sheet like structure in Fig.2 (b). Fig 2(c) shows the cross sectional view of the RGO nanosheets filled filter paper having dimension around 2.5 -3.5 µm. The multilayered single RGO nanosheets having the thickness 300 nm to 500 nm is observed on the RGO sheets filter paper film as shown in fig.2 (d). Also, the RGO nanosheets are uniformly inter linking sheets are expected for the insulating filter paper becomes electrically conductive.

Moreover, another important tool for the structural characteristics and properties of graphene based materials information is obtained from Raman spectroscopy. The spectrum of GO sheets and RGO nanosheets based filter paper films are shown in Fig.3, which shows the existence of the D, G and 2D bands. In the GO, the demonstration of a two sharp peaks corresponding to D- band (1347.22 cm-1) and G- band (1585.42 cm-1) which indicate the presence of structural defects in GO as shown in Fig.3. The 2D band (2717.17 cm-1) originate from second order double resonant Raman Scattering, which varies based on the number of layers. The peak position of 2D band is similar to the monolayer graphene prepared from the mechanical cleavage method. The intensity of 2D-band is sensitive to doping of graphene by either holes or electrons. In GO, G-band is located at (1585.42 cm-1), while for graphene (RGO), the G-band moves (1581.66 cm-1) which is closer to the value of the pristine graphite and confirms the reduction of the GO during chemical treatment. However, the existence of the D band at (1347.22 cm-1) and (1340.28 cm-1) corresponding to GO and graphene (RGO) also predict the defects of the sample. The peak position of 2D (2703.33 cm-1) represents graphitic nature in the RGO nanosheets system.

D) Design and development of transducer structure:

The geometry and dimensions of the Stainless Steel (17-4 PH) integrated structure is optimized considering the available machining capabilities and tolerance. The landing position of the fixed guided beam on the diaphragm is optimized using simulation software for maximum stress, yielding high tensile and compressive strain values of close magnitudes, as shown in the Fig.4. The figure 4 is a simulation of diaphragm at different beam locations to achieve optimum stress distribution on it.

E) Fabrication of the structure:

The guided fixed beam (1) is designed and fabricated using 17-4 PH (Precipitation-hardening) stainless steel as the structural element, due to its high strength coupled with good corrosion resistance and excellent toughness, which are desirable properties of a pressure transducer. The material is machined to the designed dimensions to match with the pressure port, which has a M14 X 1.5 adaptor as shown in Fig.5 and Fig.6 respectively. The sensor and the pressure port (2) are laser welded (3) together forming the primary sensing element of the device module. The actual 3D view of welded joint structure of device is as shown in Fig.8. Further, the fabricated device is encapsulated with Parylene coating (4) (thickness of ? 1.5 µm) in order to insulate between RGO sensing elements (5) and body of the diaphragm to avoid shorting of the diaphragm to the sensing elements.

The schematic 3D view representations of integrated structure having circular diaphragm (6) and photograph images of the developed reduced graphene oxide nanosheets on filter paper as sensing elements for pressure transducer are shown in Fig.7 and Fig.8. The area of the strain gauge is around 3 mm x 1.5 mm x 0.1 mm, which is bonded over the beam with the help of thermally conductive epoxy (H72) (7) as shown in Fig.9. This assembly is cured at about 60° C for 60 min. The electrical leads were taken out with thin double enameled copper wires (140 µm) (8) using silver epoxy on top side respective locations of the nanosheets patterned paper films. Also, the fully fabricated sensing film is post cured at 60º C for 30 min.

Assembly:

The integrated structure having circular diaphragm and the pressure port were laser welded together forming the primary sensing element and the RGO strain gauge as the secondary sensing element completing the assembly of pressure transducer. The photograph of the fabricated sensor is as shown in Fig.8.

Testing and calibration:

The experimental set up used for the pressure transducer (9) and its performance study of the RGO nanosheets based strain gauges are shown in Fig.10 and Fig.12 respectively. The sensor is subjected to strain due to the applied pressure range of 0 to 20 bar using a Fluke dead weight hydraulic calibrator, (Make: FLUKE, Model: P3125-BAR) and corresponding resistance variations are noted using digital voltmeter GW-INSTEK, Model GDM-8255A. The typical response of the sensor is linearly varied the change in resistance with respect to the applied pressure. The sensor’s critical parameters such as sensitivity, nonlinearity and hysteresis are studied. The sensor is also calibrated against the standard strain gauge with a known gauge factor, to determine the unknown gauge factor of the RGO strain gauge.

The strain on the fixed guided beam is determined experimentally by mounting standard strain gauges of known gauge factor on to the structure and calculating the strain as given by the equation (1) is shown in the Fig.11. Where ?R is the change in resistance due to the applied pressure, R is the original resistance and gauge factor as given in the data sheet of the strain gauge.

Strain (e) =?R/(R x G.F )…………………………………….. (1)

The unknown gauge factor (GF) of the RGO sensor is determined by replacing the standard strain gauges by RGO based strain gauge and calculating the gauge factor using equation (2) as given below, where ?R is the change in resistance due to the applied pressure, R is the original resistance and strain e derived experimentally using standard strain gauges. The calculated gauge factor of the fabricated pressure senor is found to be around 124 at a pressure of 20 bar.

Gauge factor (G.F)=?R/(R x ? )…………………………….. (2)

The sensor is pressurized to study the input-output characteristics namely sensitivity, non-linearity and hysteresis. Fig.12 (a) shows the sensitivity of the sensor, which is about 1.19 ?/ bar. The test results shows the combined effect of nonlinearity and hysteresis is 1.219% FSO (Full Scale Output) as shown in the Fig.12 (b). The gauge factor of RGO strain gauge based pressure transducer is found to be 124 as shown in the Fig.12(c).

In addition to above, the temperature sensing capability of the sensor is also studied using hot and cold chamber with temperature ranging between 0 ºC to 60 ºC in increments of 10 ºC as shown in Fig.13. The real time temperature is captured using Pt 100 temperature sensor. The typical response of sensor shows the negative temperature coefficient of resistance (NTC).

The TCR value of the sensor is calculated using the following equation

TCR(a)=(R_T-R_T0)/(?(T-T?_0)R_T0 )=?R/R?T ? / ? / K………………………………………………. (3)
Where a is the Temperature Coefficient of Resistance of the sensor, ?R is the change in resistance, R is the initial resistance and ?T is the change in temperature.
The sensor is also tested for temperature characteristics to verify the sensitivity, non-linearity and hysteresis. Fig.14 (a) shows the temperature sensitivity of the sensor is about 0.212 O / ºC. The calculated combined effect of non-linearity and hysteresis of the sensor is of about 1.291% FSO (Full Scale Output) as in the Fig.14 (b). The tested results shows NTC value of around -1.12 x 10-3 ? / ?/ ºC as shown in Fig.14 (c).

The Pressure transducer (B, 9) and Hot & Cold temperature measurement experimental setups (10), dead weight pressure calibrator (11) and 6 ½ digital multimeter (12) are used. Structure design, stress values obtained on the fixed beam for this geometry and Gauge factor of the RGO strain gauge of a typical prototype of the present invention is given below.

Table -1 typical sensor and transducer characteristics of present invention

Parameter Specification
Type of sensing film RGO based films
Dimensions (Diameter & length) 28 mm X 45 mm
Active Area for strain sensing 3 mm x 1.5 mm x 0.1mm
Thickness of RGO ~ 3.5 µm
Weight ~ 110 grams
Pressure Range 0- 20 Bar
Temperature range 0-60º C
Encapsulation of RGO Parylene
Application Pressure Transducer
Type of nanostructures 2D nanosheets
Type of material Graphene on filter paper
Deposition process Vacuum filtration method

The as fabricated Graphene nanosheets filter paper based films can alsobe adopted for many potential applications including but not limitng to Movement sensor, Flow sensor, Speed sensor, Acoustic sensor, Impact sensor, Shock sensor, Force sensor and Shear sensor.

The aforesaid description is enabled to capture the nature of the invention. It is to be noted however that the aforesaid description and the appended figures illustrate only a typical embodiment of the invention and therefore not to be considered limiting of its scope for the invention may admit other equally effective embodiments.
It is an object of the appended claims to cover all such variations and modifications as can come within the true spirit and scope of the invention.