Surface acoustic wave temperature strain composite sensor and preparation, testing and implementation method thereof

Abstract

The present invention provides a surface acoustic wave temperature strain composite sensor and a preparation, testing and implementation method, including a first SAW resonator, a second SAW resonator and a SAW resonator, wherein: the first SAW resonator and the second SAW resonator are cut using a substrate material that is sensitive to external strain, and the periods of the interdigital transducers of the first SAW resonator and the second SAW resonator are different; the third SAW resonator is cut using a substrate material that is sensitive to temperature; the first SAW resonator is in the same direction as the strain, and the second SAW resonator and the third SAW resonator are perpendicular to the strain direction; the three SAW resonators are all connected in parallel using gold wires for circuit connection. The present invention solves the problem that the temperature or strain cannot be accurately measured due to the cross-coupling of SAW temperature and strain. The present invention can achieve simultaneous measurement of external temperature and strain within the temperature and strain range that the substrate material can withstand.

Description

[0001] The present invention claims priority to Chinese patent application number 202311062958.9, filed on August 22, 2023, entitled “Surface Acoustic Wave Temperature Strain Composite Sensor and Preparation, Testing, and Implementation Methods”, the entire text of which is hereby incorporated by reference. Technical Field

[0002] The present invention relates to the field of sensor technology, and in particular to a surface acoustic wave temperature-strain composite sensor and a preparation, testing and implementation method thereof, and more particularly to a surface acoustic wave temperature-strain composite sensor using three-resonator differential compensation. Background Art

[0003] With the increasing demand for health monitoring of structural components in complex environments such as high temperature, high pressure and strong radiation in various fields, as well as the increasing need for health detection of structural components in rotating mechanical systems such as automobile engines, marine diesel engines and gas turbines, new requirements have been put forward for temperature and strain sensors. It is hoped that the sensors can withstand high temperature and high pressure, and can withstand electromagnetic radiation, and will not change the electromagnetic environment of the measured object. Most importantly, they should be wireless, passive and not affected by the rotating environment. Surface acoustic wave temperature sensors and surface acoustic wave strain sensors based on surface acoustic wave sensing technology can meet the above detection requirements.

[0004] SAW (Surface Acoustic Wave) refers to elastic waves generated on the surface of a piezoelectric medium and propagating along its free surface or interface. SAW sensors are devices that can sense external signals and are composed of a piezoelectric substrate and an IDT (Interdigital Transducer).

[0005] The piezoelectric substrate is formed by special cutting of piezoelectric materials. It is an important carrier for SAW sensors to convert energy and transmit signals. The material type and cutting type of the piezoelectric substrate are two important factors that determine the characteristics of SAW sensors. Quartz crystal is a material with small dielectric constant and piezoelectric constant. Its frequency characteristics depend on the shape or cutting method. Under special Euler angles, quartz can show zero TCF (Temperature Coefficient of Frequency).

[0006] IDT is the core of the surface acoustic wave sensor, and its function is to excite and receive surface acoustic waves. When an electrical signal is input to the IDT end, the piezoelectric substrate converts the electrical signal into mechanical energy through the inverse piezoelectric effect, thereby exciting the surface acoustic wave, and propagating the surface of the piezoelectric substrate in the form of a surface acoustic wave; when the surface acoustic wave is transmitted back through the reflection grating, the IDT can convert the surface acoustic wave vibration into an electrical signal through the piezoelectric effect, thereby receiving the surface acoustic wave. The surface acoustic sensor senses changes in the external environment through the difference in the received surface acoustic wave signal.

[0007] The SAW temperature sensor is a sensor that characterizes temperature changes through the frequency offset of the SAW resonator. The SAW strain sensor is a sensor that characterizes the magnitude of external stress and strain through the resonant frequency offset of the SAW resonator. Because the SAW resonator has mechanical and thermal coupling, differential compensation is required to obtain linear frequency-temperature response and frequency-strain response. Summary of the invention

[0008] In view of the defects in the prior art, an object of the present invention is to provide a surface acoustic wave temperature-strain composite sensor and a preparation, testing and implementation method thereof.

[0009] A surface acoustic wave temperature-strain composite sensor provided by the present invention includes: a first SAW resonator, a second SAW resonator and a third SAW resonator;

[0010] The first SAW resonator and the second SAW resonator are cut using a substrate material that is sensitive to external strain, and the periods of the interdigital transducers of the first SAW resonator and the second SAW resonator are different; the third SAW resonator is cut using a substrate material that is sensitive to temperature;

[0011] The first SAW resonator is in the same direction as the strain direction, and the second SAW resonator and the third SAW resonator are perpendicular to the strain direction;

[0012] The three SAW resonators are connected in parallel by gold wires.

[0013] In one embodiment, the three SAW resonators are all made of quartz as a substrate material and are fabricated on a stainless steel packaging structure.

[0014] In one embodiment, the first SAW resonator is fixed on the stainless steel packaging structure by using hard glue, and the second SAW resonator and the third SAW resonator are fixed on the stainless steel packaging structure by using soft glue.

[0015] In one embodiment, the frequency-temperature response of the first SAW resonator and the second SAW resonator are the same.

[0016] In one embodiment, the Euler angles of the first SAW resonator and the second SAW resonator substrate are both (0, 126, 0).

[0017] In one embodiment, the Euler angle of the third SAW resonator substrate is (0, 90, 0).

[0018] In one embodiment, the frequency-strain response of the second SAW resonator and the third SAW resonator are the same.

[0019] In one embodiment, a method for preparing a surface acoustic wave temperature-strain composite sensor for preparing a surface acoustic wave temperature-strain composite sensor comprises the following steps:

[0020] SAW resonator preparation steps: using electron beam evaporation technology in micro-nano electronic lithography to grow a 200nm thick aluminum electrode on the cut piezoelectric substrate, and then washing away the glue on the surface to make a SAW resonator;

[0021] Fixing step: fix the first SAW resonator on the stainless steel packaging structure with hard glue, and the propagation direction of its surface acoustic wave is in the same direction as the strain direction; fix the second SAW resonator and the third SAW resonator on the stainless steel packaging structure with soft glue, and the propagation direction of their surface acoustic waves is perpendicular to the strain direction;

[0022] Baking and heating steps: After fixing the three SAW resonators, place them in an oven at 150 degrees Celsius and bake them for 2 hours, then add the surface protection shell and antenna.

[0023] In one embodiment, a calibration test method for a surface acoustic wave temperature-strain composite sensor for calibrating and testing a surface acoustic wave temperature-strain composite sensor comprises the following steps:

[0024] Fixing steps: Fix the surface acoustic wave temperature-strain composite sensor on a standard cantilever beam, and fix a standard strain gauge at the same position as a reference;

[0025] Test steps: Place the entire surface acoustic wave temperature-strain composite sensor in a temperature chamber for calibration tests under different temperature conditions;

[0026] Fitting steps: Determine the sensitivity Kt of the frequency-strain response at each temperature by linear fitting, and determine the Kt-T relationship within the sensor temperature range by fitting temperature T and Kt.

[0027] In one embodiment, a method for implementing a surface acoustic wave temperature-strain composite sensor includes the following steps:

[0028] Installation steps: install the surface acoustic wave temperature strain composite sensor on the surface of the object to be measured;

[0029] Strain measurement steps: When the temperature and strain change, the surface acoustic wave temperature-strain composite sensor obtains the temperature T1 through differential compensation of the second SAW resonator and the third SAW resonator, that is, the sensitivity Kt1 at the temperature T1 is obtained through the Kt-T relationship, and then the frequency offset △f under the external strain after the first SAW resonator and the second SAW resonator is combined to determine the size of the external strain disturbance S to achieve strain measurement.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. Aiming at the problem that the temperature or strain cannot be accurately measured due to the cross-coupling of SAW temperature and strain, the present invention proposes a SAW temperature-strain composite sensor that obtains linear frequency-temperature and frequency-strain responses through differential compensation of three SAW resonators with different structures and positions. This solves the problem that the temperature or strain cannot be accurately measured due to the cross-coupling of SAW temperature and strain.

[0032] 2. The present invention can eliminate the interference of temperature on strain measurement and the interference of strain on temperature measurement by differential compensation, and realize the simultaneous measurement of external temperature and strain within the temperature and strain range borne by the substrate material. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Other features, objects and advantages of the present invention will become more apparent from the detailed description of non-limiting embodiments made with reference to the following drawings:

[0034] Figure 1 A schematic diagram of the structure of a SAW temperature-strain composite sensor in one embodiment;

[0035] Figure 2 Schematic diagram of a process for preparing a SAW temperature-strain composite sensor in one embodiment;

[0036] Figure 3 A schematic diagram of a flow chart of a calibration test method for a SAW temperature-strain composite sensor in one embodiment;

[0037] Figure 4 FIG. 4 is a flow chart of an implementation method of a SAW temperature-strain composite sensor in one embodiment. DETAILED DESCRIPTION

[0038] The present invention is described in detail below in conjunction with specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can also be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0039] In one embodiment, Figure 1 As shown, a surface acoustic wave temperature strain composite sensor is provided, which includes at least three different SAW resonators, namely a first SAW resonator, a second SAW resonator and a third SAW resonator. There are differences in the base materials and the periods of the interdigital transducers of the three SAW resonators. Specifically, the first SAW resonator and the second SAW resonator adopt a base material cut that is sensitive to external strain, and the third SAW resonator adopts a base material cut that is sensitive to temperature. The periods of the interdigital transducers of the first SAW resonator and the second SAW resonator are different.

[0040] The three SAW resonators are all fixed on the stainless steel packaging structure, the first SAW resonator is in the same direction as the strain direction, and the second SAW resonator and the third SAW resonator are perpendicular to the strain direction; wherein, strain is a concept in continuous medium mechanics, used to quantitatively describe the deformation of an object, such as expansion and contraction and torsion, and the strain itself is not directional, and the strain direction refers to the direction of deformation of the object. The strain direction in this embodiment can be a preset direction, which is only used to indicate the fixed direction of the first SAW resonator.

[0041] The three SAW resonators are connected in parallel by gold wires.

[0042] In one embodiment, the present invention uses three SAW resonators with quartz as the base material, which only differ in cut type ((0,126,0) and (0,90,0)) and period. Due to the difference in the sensitive characteristics to temperature and strain, a SAW temperature-strain composite sensor is proposed to obtain linear frequency-temperature and frequency-strain response through differential compensation of three SAW resonators, which aims to solve the problem that the temperature and strain cross-coupling of SAW leads to the inability to accurately measure temperature or strain. The SAW temperature-strain composite sensor proposed by the present invention can eliminate the interference of temperature on strain measurement and the interference of strain on temperature measurement by differential compensation, and realize the simultaneous measurement of external temperature and strain within the temperature and strain range borne by the base material.

[0043] To further explain in detail, the SAW temperature-strain composite sensor of the present invention includes a first SAW resonator, a second SAW resonator and a third SAW resonator, wherein the three resonators all use quartz as the base material, the Euler angles of the bases of the first SAW resonator and the second SAW resonator are both (0,126,0), the periods of the interdigital transducers of the first SAW resonator and the second SAW resonator are different, and the Euler angle of the base of the third SAW resonator is (0,90,0). The three SAW resonators are made on a stainless steel packaging structure, wherein the first SAW resonator is in the same direction as the strain and is fixed with hard glue, the second SAW resonator is perpendicular to the strain direction and is fixed with soft glue, and the third SAW resonator is perpendicular to the strain direction and is fixed with soft glue. The three SAW resonators are all connected in parallel using gold wires for circuit connection.

[0044] The present invention is composed of a SAW resonator, and its core is the relationship between the resonant frequency of the SAW resonator and the change of strain and temperature. According to the SAW device bias field theory and perturbation theory, the calculation formula for the relative change of the resonant frequency of the SAW resonator under the influence of temperature and strain is:

[0045] ;

[0046] in, is the SAW frequency offset; is the flat rate when there is no eccentric load; u is the SAW displacement; is the device volume; is the density without biasing load field; is the angular frequency of SAW; When the external disturbance is applied, the effective elastic constant of the substrate material of the SAW resonator is expressed as:

[0047] ;

[0048] in, , and are the stress component, strain component and displacement component of the substrate surface caused by external stress or temperature eccentric load respectively; is the second-order elastic constant, is the third-order elastic constant, is the Dirac operator.

[0049] Specifically, the frequency-strain response and frequency-temperature response can be obtained by substituting the SAW resonator substrate material parameters into the above expressions (1) and (2) in combination with the elastic strain, stress and thermal strain of the external bias field after angle transformation.

[0050] In an optional embodiment, the first SAW resonator and the second SAW resonator of the present invention are cut with a substrate material that is sensitive to external strain (Euler angle: 0,126,0), and their frequency-temperature responses are the same. The first SAW resonator is in the same direction as the external strain, and the second SAW resonator is perpendicular to the external strain. After differential compensation, the influence of temperature on the frequency-strain response can be eliminated, and a linear frequency-strain response can be obtained, thereby realizing the measurement of the external strain. The third SAW resonator is cut with a substrate material that is sensitive to temperature (Euler angle: 0,90,0), and is rotated in the same direction as the second SAW resonator, and is fixed with the same soft glue. Its frequency-strain response is the same. After differential compensation, the influence of external strain on the frequency-temperature response can be eliminated, and a linear frequency-temperature response can be obtained to realize the measurement of temperature.

[0051] In summary, the SAW temperature-strain composite sensor of the present invention can obtain linear frequency-temperature response and frequency-strain response through the differential compensation structure of three SAW resonators, and realize simultaneous measurement of external temperature and strain within the temperature and strain range borne by the substrate material.

[0052] In one embodiment, Figure 2 As shown, the preparation method of the SAW temperature-strain composite sensor of the present invention is as follows:

[0053] S201, using electron beam evaporation technology in micro-nano electronic lithography process to grow a 200nm thick aluminum electrode on the cut piezoelectric substrate, and then wash away the glue on the surface to make a SAW resonator.

[0054] Among them, electron beam evaporation technology is a type of physical vapor deposition. It can use electromagnetic fields to accurately bombard the target material in the crucible with high-energy electrons, causing it to melt and then deposit on the substrate. Electron beam evaporation technology can be used to deposit high-purity and high-precision thin films.

[0055] In this embodiment, the 200 nm thick aluminum electrode is the piezoelectric film, and correspondingly, the piezoelectric substrate is the substrate on which the piezoelectric film is generated.

[0056] The first SAW resonator, the second SAW resonator and the third SAW resonator can all be manufactured in this manner.

[0057] S202, fix the first SAW resonator on the stainless steel packaging structure by using hard glue, and the propagation direction of the surface acoustic wave thereof is the same as the strain direction.

[0058] Among them, surface acoustic wave is an elastic wave propagating along the surface of an object, and the strain direction refers to the direction in which the object deforms.

[0059] S203, the second SAW resonator and the third SAW resonator are fixed on the stainless steel packaging structure by using soft glue, and the surface acoustic wave propagation direction thereof is perpendicular to the strain direction.

[0060] It is understandable that after curing, the hard glue will become very hard and almost inflexible, and can provide a high degree of rigidity and structural strength, while the soft glue can maintain a certain degree of flexibility and elasticity after curing, absorb shock and stress, and maintain good adhesion. Therefore, for the first SAW resonator whose propagation direction of the surface acoustic wave is the same as the strain direction, the hard glue can be used to fix it, and for the second and third SAW resonators whose propagation directions of the surface acoustic wave are perpendicular to the strain direction, the soft glue can be used to fix them.

[0061] S204, after fixing, bake in an oven at 150 degrees Celsius for 2 hours, add a surface protection shell and an antenna, and a SAW temperature-strain composite sensor is developed.

[0062] In one embodiment, Figure 3 As shown, the calibration test of the SAW temperature-strain composite sensor of the present invention includes:

[0063] S301, fix the developed SAW temperature-strain composite sensor on the standard cantilever beam, and fix a standard strain gauge at the same position for reference. Put the entire strain calibration test device in a temperature box for calibration tests under different temperature conditions.

[0064] In other words, the developed SAW temperature-strain composite sensor is fixed on a standard cantilever beam, and a standard strain gauge is fixed at the same position for reference, thus forming a strain calibration test device, which is then placed in a temperature box for calibration tests under different temperature conditions.

[0065] Among them, the standard strain gauge is a sensor that measures strain by measuring the relative change in length. The standard strain gauge can use polyimide as the substrate, and the constantan wire is adhered to it.

[0066] Optionally, place the entire strain calibration test device in a temperature box, change the temperature point of the temperature box, and record the frequency-strain response sensitivity K of the strain calibration test device at each temperature point. t ,.

[0067] S302, determine the sensitivity K of the frequency-strain response at each temperature by linear fitting t , because K t It is inversely proportional to the temperature and can be determined by the temperature T and K t The fitting determines the sensor temperature range K t —T relationship.

[0068] Optionally, generate temperature T and sensitivity K t The curve between temperature T and sensitivity K t The correlation relationship between them.

[0069] In one embodiment, Figure 4 As shown, the implementation process of the SAW temperature-strain composite sensing of the present invention is as follows:

[0070] S401, installing the SAW temperature-strain composite sensor on the surface of the object to be measured. When the temperature and strain change, the SAW temperature-strain composite sensor obtains the temperature T through differential compensation of the second SAW resonator and the third SAW resonator. 1 When Kt-T relationship is obtained, T 1 Sensitivity at temperature Kt 1 .

[0071] S402, combining the frequency offset Δf under the external strain after the first SAW resonator and the second SAW resonator to determine the size of the external strain disturbance S, thereby achieving strain measurement.

[0072] Optionally, the magnitude of the external strain disturbance S is determined by combining the frequency offset Δf under the external strain after the first SAW resonator and the third SAW resonator, thereby achieving strain measurement.

[0073] In the description of the present application, it should be understood that the terms "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0074] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art can make various changes or modifications within the scope of the claims, which does not affect the essence of the present invention. In the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other arbitrarily.

Claims

1. A surface acoustic wave temperature-strain composite sensor, characterized in that: include: a first surface acoustic wave (SAW) resonator, a second SAW resonator, and a third SAW resonator; The first SAW resonator and the second SAW resonator are cut using a substrate material that is sensitive to external strain, and the periods of the interdigital transducers of the first SAW resonator and the second SAW resonator are different; the third SAW resonator is cut using a substrate material that is sensitive to temperature; The first SAW resonator is in the same direction as the strain direction, and the second SAW resonator and the third SAW resonator are perpendicular to the strain direction; the first SAW resonator and the second SAW resonator have the same frequency-temperature response; the second SAW resonator and the third SAW resonator have the same frequency-strain response; The three SAW resonators are connected in parallel by gold wires.

2. The surface acoustic wave temperature-strain composite sensor according to claim 1, characterized in that: The three SAW resonators all use quartz as the substrate material and are manufactured on a stainless steel packaging structure.

3. The surface acoustic wave temperature-strain composite sensor according to claim 2, characterized in that: The first SAW resonator is fixed on the stainless steel packaging structure by using hard glue, and the second SAW resonator and the third SAW resonator are fixed on the stainless steel packaging structure by using soft glue.

4. The surface acoustic wave temperature-strain composite sensor according to claim 1, characterized in that: The Euler angles of the first SAW resonator and the second SAW resonator substrates are both (0, 126, 0).

5. The surface acoustic wave temperature-strain composite sensor according to claim 1, characterized in that: The Euler angle of the third SAW resonator substrate is (0, 90, 0).

6. The surface wave temperature-strain composite sensor according to claim 1, characterized in that: The surface wave temperature-strain composite sensor obtains linear frequency-temperature response and frequency-strain response through a differential compensation structure of three SAW resonators.

7. A method for preparing a surface acoustic wave temperature-strain composite sensor, characterized in that: For preparing the surface acoustic wave temperature-strain composite sensor according to any one of claims 1 to 6, the preparation method comprises the following steps: SAW resonator preparation steps: using electron beam evaporation technology in micro-nano electronic lithography to grow a 200nm thick aluminum electrode on the cut piezoelectric substrate, and then washing away the glue on the surface to make a SAW resonator; Fixing step: fix the first SAW resonator on the stainless steel packaging structure with hard glue, and the propagation direction of its surface acoustic wave is in the same direction as the strain direction; fix the second SAW resonator and the third SAW resonator on the stainless steel packaging structure with soft glue, and the propagation direction of their surface acoustic waves is perpendicular to the strain direction; Baking and heating steps: After fixing the three SAW resonators, place them in an oven at 150 degrees Celsius and bake them for 2 hours, then add the surface protection shell and antenna.

8. A calibration test method for a surface acoustic wave temperature-strain composite sensor, characterized in that: Used for calibration testing of the surface acoustic wave temperature-strain composite sensor according to any one of claims 1 to 6, the calibration testing method comprises the following steps: Fixing steps: Fix the surface acoustic wave temperature-strain composite sensor on a standard cantilever beam, and fix a standard strain gauge at the same position as a reference; Test steps: Place the entire surface acoustic wave temperature-strain composite sensor in a temperature chamber for calibration tests under different temperature conditions; Fitting steps: Determine the sensitivity Kt of the frequency-strain response at each temperature by linear fitting, and determine the Kt-T relationship within the sensor temperature range by fitting temperature T and Kt.

9. A method for implementing a surface acoustic wave temperature-strain composite sensor, characterized in that: Used to implement the surface acoustic wave temperature-strain composite sensor according to any one of claims 1 to 6, the implementation method comprises the following steps: Installation steps: install the surface acoustic wave temperature strain composite sensor on the surface of the object to be measured; Strain measurement steps: When the temperature and strain change, the surface acoustic wave temperature-strain composite sensor obtains the temperature T1 through differential compensation of the second SAW resonator and the third SAW resonator, that is, the sensitivity Kt1 at the temperature T1 is obtained through the Kt-T relationship, and then the frequency offset △f under the external strain after the first SAW resonator and the second SAW resonator is combined to determine the size of the external strain disturbance S to achieve strain measurement; wherein, the Kt-T relationship within the temperature range of the sensor is determined by fitting the temperature T and the sensitivity Kt.

Images