Surface acoustic wave strain sensor with sensibilization and protection structure

Abstract

The invention relates to a surface acoustic wave strain sensor with a sensibilization and protection structure, and belongs to the field of surface acoustic wave sensors. The sensor comprises a surface acoustic wave device, a matching circuit, an antenna, a sensitization substrate and a protective cover. Wherein the sensitization substrate is provided with a sensitive area and stepped non-sensitive areas which are symmetrically distributed on the two sides of the sensitive area, and the non-sensitive area on each side is provided with at least three steps. And the surface acoustic wave device is fixed in the sensitive area of the sensitization substrate. And the matching circuit is arranged on steps except the first step and the last step in the non-sensitive area on any side, and is used for realizing impedance matching between the surface acoustic wave device and the antenna. The antenna is fixed on the matching circuit. The two ends of the protective cover are fixed on the first steps of the non-sensitive areas on the two sides and completely cover the surface acoustic wave device. The strain sensitivity can be enhanced by amplifying the strain of the measured object through the sensitive area of the sensitizing substrate, and the surface acoustic wave device is protected from being interfered by the external environment by adopting the protective cover.

Description

Technical Field

[0001] The invention belongs to the field of surface acoustic wave sensors and relates to a surface acoustic wave strain sensor with a sensitivity enhancement and protection structure. Background Art

[0002] Strain measurement plays an important role in engineering. By measuring the tiny deformation of materials when they are subjected to stress, strain measurement technology can reveal the stress state of the structure under actual working conditions, which is crucial to preventing potential structural damage and failures in engineering. For example, in oil and gas pipelines, strain measurement can monitor the stress level of the pipeline in real time, and promptly detect tiny cracks and deformations caused by corrosion, fatigue or external environmental influences, thereby preventing leakage and breakage, or embed or adhere SAW sensors to key stress parts of scaffolding (such as connection nodes and load-bearing rods). The sensor can sense the strain distribution of the scaffolding under different loads in real time. Prevent the occurrence of scaffolding breakage or collapse accidents. Strain monitoring can extend the life of the facility and reduce losses. Therefore, strain measurement is one of the key technologies to ensure public safety, improve the reliability of engineering structures and economic benefits.

[0003] Existing strain measurement methods include resistive and fiber optic strain sensors. Resistive strain sensors detect material strain by measuring changes in resistance. They require external power supply and their resistance value is affected by temperature. Fiber optic sensors use the propagation characteristics of light in optical fibers to detect strain. They do not require external power supply, but the optical fiber itself may be prone to breakage. At the same time, the manufacturing and installation costs of fiber optic sensors are relatively high, which limits their use in certain special environments, such as replacement of power supplies, difficulty in maintaining wiring harnesses, flammable and explosive environments, high temperatures and high pressures, and complex wiring.

[0004] The surface acoustic wave (SAW) sensor processed by MEMS technology has the advantages of passive wireless, high sensitivity, compact size, strong anti-interference ability, and good consistency. This feature makes it very suitable for scenes where it is difficult to wire or replace batteries in extreme environments such as scaffolding and oil and gas pipelines. At the same time, the use of wireless radio frequency for remote data reading reduces the risk of manual inspection in complex environments such as high altitude, so that it can work reliably in various complex environments, thus playing a key role in some extreme environments such as high temperature and high pressure, flammable and explosive.

[0005] In order to improve the strain sensitivity of the existing surface acoustic wave strain sensor, a flexible strain sensor is made. This method leads to more sensor process steps and increases the production cost. At the same time, due to improper packaging method, the packaging shell affects the device measurement, resulting in low strain sensitivity. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a surface acoustic wave strain sensor with a sensitivity enhancement and protection structure, which takes the surface acoustic wave device as the core, receives and sends electromagnetic wave signals through an antenna, and at the same time, sets a protection structure in the non-sensitive area to protect the surface acoustic wave device from interference from the external environment.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A surface acoustic wave strain sensor with a sensitivity enhancement and protection structure comprises a surface acoustic wave device, a matching circuit, an antenna, a sensitivity enhancement substrate and a protection cover.

[0009] Wherein, the sensitization substrate has a sensitive area, and non-sensitive areas in a stepped shape symmetrically distributed on both sides of the sensitive area, and the non-sensitive area on each side has at least three steps. The surface acoustic wave device is fixed to the sensitive area of ​​the sensitization substrate. The matching circuit is arranged on the steps except the first and last steps in the non-sensitive area on either side, and is used to achieve impedance matching between the surface acoustic wave device and the antenna, thereby realizing passive wireless of the sensor. The antenna is fixed on the matching circuit. The two ends of the protective cover are fixed on the first step of the non-sensitive area on both sides, and completely cover the surface acoustic wave device. Wherein, the surface acoustic wave device is fixed to the sensitive area by bonding with organic glue.

[0010] Furthermore, the protective cover has two fixed ends and a cavity opened at the bottom. The two fixed ends are respectively fixed on the first step of the non-sensitive area on both sides, and the cavity at the bottom completely covers the surface acoustic wave device, thereby preventing the surface acoustic wave device from being contaminated by the external environment.

[0011] Furthermore, the material of the sensitization substrate is beryllium bronze, which has excellent mechanical properties and can meet the material requirements of the sensitization substrate such as strong plasticity, corrosion resistance, fatigue resistance, etc. In the sensitization substrate, the sensitive area is a cavity structure composed of a beryllium bronze sheet and a cavity under the sheet.

[0012] Furthermore, the matching circuit is an LC series-parallel circuit, preferably a T-type network or a π-type network.

[0013] Furthermore, the antenna is a monopole or dipole antenna.

[0014] Furthermore, the surface acoustic wave device adopts a resonant structure or a delay line structure, which includes a piezoelectric functional layer, interdigital electrodes on the surface of the piezoelectric functional layer, and reflective gratings on both sides of the interdigital electrodes. The piezoelectric functional layer can be a piezoelectric crystal or a piezoelectric thin film material, the piezoelectric crystal can be a quartz crystal, lithium niobate, lithium tantalate, etc., and the piezoelectric thin film material can be a piezoelectric ceramic (PZT), zinc oxide (ZnO), aluminum nitride (AlN), etc.

[0015] The beneficial effects of the present invention are as follows: the present invention proposes a sensitization substrate, and fixes the surface acoustic wave device in the sensitive area of ​​the sensitization substrate. When the sensor is placed on the object to be measured and the object to be measured is strained, the strain can be amplified and transmitted to the surface acoustic wave device through the sensitive area of ​​the sensitization substrate, thereby achieving the effect of enhancing strain sensitivity. In addition, the present invention also uses a protective cover to protect the surface acoustic wave device from interference from the external environment, while also reducing the impact of the sensor package on the strain. When used, the present invention can be directly pasted or welded on the surface of the object to be measured, or can be bound to the object to be measured through the steps of the non-sensitive area of ​​the sensitization substrate. The method of use is simple and repeatable.

[0016] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0018] Figure 1 A surface acoustic wave strain sensor provided by an embodiment of the present invention;

[0019] Figure 2 It is a schematic diagram of the cross section of the sensitized substrate;

[0020] Figure 3 It is a schematic diagram of the protective cover structure;

[0021] Figure 4 It is a schematic diagram of the structure of a surface acoustic wave device;

[0022] Figure 5 For the experimental model designed by finite element analysis method;

[0023] Figure 6 Schematic diagram of the strain comparison between the sensitized substrate and the traditional substrate.

[0024] Figure numerals: 1 - sensitization substrate; 2 - matching circuit; 3 - surface acoustic wave device; 4 - antenna; 5 - protective cover. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0026] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0027] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0028] like Figure 1 to Figure 3 As shown, a surface acoustic wave strain sensor with a sensitivity enhancement and protection structure provided by an embodiment of the present invention includes: a sensitivity enhancement substrate 1, a matching circuit 2, a surface acoustic wave device 3, an antenna 4 and a protective shell 5, wherein the surface acoustic wave device 3 is arranged in the sensitive area of ​​the sensitivity enhancement substrate 1, the matching circuit 2 is arranged in the non-sensitive area, and the matching circuit 2 is connected to the surface acoustic wave device 3 and the antenna 4.

[0029] The surface acoustic wave strain sensor uses the surface acoustic wave device 3 as the core, and receives and sends electromagnetic wave signals through the antenna 4. Its working principle is as follows: the surface acoustic wave device 3 converts the electromagnetic wave signal transmitted by the antenna 4 into a surface acoustic wave, and forms resonance on the device; when the object under test is strained, the strain is amplified through the sensitive area of ​​the sensitization substrate 1, and the surface acoustic wave device 3 senses the strain, causing the wavelength or phase velocity of the surface acoustic wave device 3 to change, affecting the resonance frequency; the surface acoustic wave device 3 converts the changed surface acoustic wave signal into an electromagnetic wave signal, and transmits it to the antenna 4 through the matching circuit 2, uses the reader to obtain the signal of the antenna 4, and demodulates the signal sent by the antenna 4 to obtain the strain information, thereby realizing passive wireless measurement.

[0030] The sensitization substrate 1 needs to meet the material requirements of strong plasticity, corrosion resistance, fatigue resistance, etc. Beryllium bronze is a copper alloy with beryllium as the main alloying element. It has excellent mechanical properties, a density of 8.3g / cm3, a hardness range of usually between 36 and 46HRC, and wear resistance and fatigue resistance. Therefore, the sensitization substrate 1 is made of beryllium bronze. Figure 2 As shown, the sensitization substrate 1 has a sensitive area and non-sensitive areas symmetrically distributed on both sides of the sensitive area in a stepped shape. The sensitive area is a cavity structure composed of a 0.1 mm thick beryllium bronze sheet and the cavity below it. The non-sensitive areas are distributed on both sides of the sensitive area, and each side has at least three steps. This embodiment takes three steps as an example.

[0031] The matching circuit 2 can adopt a π-type, T-type or other LC series-parallel circuit. The matching circuit 2 is respectively connected to the interdigital electrodes in the surface acoustic wave device 3 and the antenna 4 to achieve impedance matching between the surface acoustic wave device 3 and the antenna 4, thereby reducing the loss of the electromagnetic wave signal during propagation. The matching circuit 2 is installed on the second step of the non-sensitive area on one side of the sensitization substrate 1.

[0032] In actual use, the surface acoustic wave device 3 in the sensitive area of ​​the sensitization substrate 1 is easily polluted by the external environment, and the traditional protective packaging structure is easy to affect the strain measurement, so the following is introduced: Figure 3 The step-type protective cover 5 shown in the figure uses organic glue or welding to fix the two fixed ends of the protective cover 5 on the first step of the non-sensitive area of ​​the sensitivity-enhancing substrate 1, and the cavity opened at the bottom of the protective cover 5 covers the surface acoustic wave device 3, which can reduce the influence of the protective cover 5 on the device measurement and prevent the surface acoustic wave device 3 from being polluted by the external environment. Among them, the protective cover 5 needs to be made of high temperature resistant and tough material.

[0033] like Figure 4As shown, the surface acoustic wave device 3 used in this embodiment, its basic structure is composed of interdigital electrodes, left and right reflective grids, and piezoelectric functional layers. The surface acoustic wave device 3 uses the inverse piezoelectric effect and the piezoelectric effect to realize the conversion of electrical signals to surface acoustic waves and then to electrical signals. The interdigital electrodes are metal film materials prepared by magnetron sputtering and electron beam evaporation processes, such as aluminum (Al), copper (Cu), platinum (Pt) and molybdenum (Mo). The surface acoustic wave device 3 needs to be attached to the sensitive area of ​​the sensitization substrate 1 using organic glue, for example, CC-33A, a special glue for strain gauges, can be used, and its operating temperature range is -196 to 120°C.

[0034] In the surface acoustic wave strain sensor, the increased sensitivity of the sensitization substrate 1 can be explained by the following formula:

[0035]

[0036] Wherein, L1 and L2 represent the distance between the original measuring point and the neutral layer of the object under test, L1′ and L2′ represent the distance between the measuring point and the neutral layer of the object under test after bending, y represents the distance between the measuring point and the neutral layer of the object under test, and K=1 / R represents the curvature of the neutral layer after bending.

[0037] This embodiment uses the finite element analysis method to design an experimental model. Figure 5 As shown, the sensitized substrate 1 and the traditional substrate are placed at the same horizontal position of the cantilever beam to ensure that the two have the same mechanical conditions. The strain data of the traditional substrate and the sensitized substrate are extracted, and the strain conditions are compared and analyzed. The comparison results are shown in Figure 6 As shown, it can be seen that the strain amount of the sensitive area of ​​the sensitized substrate 1 proposed by the present invention is significantly higher than that of the traditional substrate ( Figure 6 In the figure, the left side is the traditional substrate, and the right side is the sensitization substrate proposed in the present invention), which can verify the effectiveness of the sensitization structure proposed in the present invention.

[0038] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A surface acoustic wave strain sensor with a sensitivity enhancement and protection structure, comprising a surface acoustic wave device, a matching circuit and an antenna, characterized in that: Also included are a sensitizing base and protective cover; The sensitization substrate has a sensitive area and non-sensitive areas in a stepped shape symmetrically distributed on both sides of the sensitive area, and each side of the non-sensitive area has at least three steps; The surface acoustic wave device is fixed to the sensitive area; The matching circuit is arranged on the steps other than the first and last steps in the non-sensitive area on either side, and is used to achieve impedance matching between the surface acoustic wave device and the antenna; The antenna is fixed on the matching circuit; The two ends of the protective cover are fixed on the first step of the non-sensitive area on both sides and completely cover the surface acoustic wave device.

2. The surface acoustic wave strain sensor according to claim 1, characterized in that: The protective cover has two fixed ends and a cavity opened at the bottom, the two fixed ends are respectively fixed on the first step of the non-sensitive area on both sides, and the cavity completely covers the surface acoustic wave device.

3. The surface acoustic wave strain sensor according to claim 1, characterized in that: The surface acoustic wave device is fixed to the sensitive area by means of organic glue.

4. The surface acoustic wave strain sensor according to claim 1, characterized in that: The material of the sensitization substrate is beryllium copper.

5. The surface acoustic wave strain sensor according to claim 1 or 4, characterized in that: In the sensitization substrate, the sensitive area is a cavity structure formed by a beryllium bronze sheet and a cavity below the sheet.

6. The surface acoustic wave strain sensor according to claim 1, characterized in that: The matching circuit is a T-type network or a π-type network.

7. The surface acoustic wave strain sensor according to claim 1, characterized in that: The antenna is a monopole or a dipole antenna.

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