Fastener with surface acoustic wave sensor and processing technology

Abstract

The invention belongs to the technical field of sensors, and particularly relates to a fastener with a surface acoustic wave sensor and a processing technology. The surface acoustic wave sensor comprises a piezoelectric layer and an electrode layer, the piezoelectric layer grows on the upper end face of the fastener base body in an in-situ mode, the electrode layer comprises an interdigital electrode and reflecting gratings, the interdigital electrode and the reflecting gratings both grow on the surface of the piezoelectric layer in an in-situ mode, and the reflecting gratings are located on the two opposite sides of the interdigital electrode. Compared with the prior art, under the condition that the structure of the fastener base body is not damaged, the in-situ strain information of the end face of the head of the fastener base body is accurately detected, so that sensing of the pre-tightening force is achieved, permanent residence of the surface acoustic wave sensor in the fastener base body can be achieved, and the service life of the sensor with the pre-tightening force detection function is prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and in particular relates to a fastener with a surface acoustic wave sensor and a processing technology thereof. Background Art

[0002] A surface acoustic wave (SAW) sensor is a device that uses acoustic waves excited by an alternating electric field on the surface of a piezoelectric material to sense physical information.

[0003] CN117723636A proposes a sensor based on a delay line surface acoustic wave device to address the problems of existing preload sensors, such as high cost, susceptibility to environmental influences, and complex data processing. The specific implementation method is as follows: the bolt head is embedded in a cantilever beam fixture, and a pair of interdigital transducers are arranged at both ends of the cantilever beam. When the surface acoustic wave passes through the cantilever beam, it couples the preload force information contained in the bolt into the surface wave, which is transmitted to the host computer through the electrical signal processing circuit to identify the fastener status. However, this method embeds a larger cantilever beam structure in the bolt, limiting its use scenarios and making it difficult to use in some flat surfaces and small-scale locations.

[0004] CN113739978A proposes a wireless preload sensor based on surface acoustic waves (SAWs) to address the limitations of current preload measurement methods in engineering. The specific implementation method involves placing a SAW sensor in the gap between the bolt head and the shank. This sensor couples the strain information on the bolt into the SAWs, and transmits the signal to a data processing terminal via leads and a sensor antenna. However, this method disrupts the load-bearing structure of the bolt itself, making it prone to breakage when subjected to heavy loads or high-temperature creep.

[0005] CN113029420A proposes an embedded passive wireless monitoring system for bolt tightness based on surface acoustic waves. The system consists of a sensitive end (including a matching network and a surface acoustic wave resonator) and a measurement module (antenna and device terminal). The sensitive end of this sensor is prefabricated within the bolt body and connected to the sensitive end by one end of the antenna. However, this placement within the bolt body affects the bolt body's load-bearing performance. Furthermore, the manufacturing process is complex, and each bolt sensor needs to be individually calibrated for use (consistent placement cannot be guaranteed in experiments), resulting in low versatility.

[0006] The present invention is proposed to address the above problems of sensors based on surface acoustic waves. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to overcome the shortcomings of the existing technology and provide a fastener with a surface acoustic wave sensor and a processing technology to solve the technical problems in the related technology that the use scenarios are limited due to the method of embedding the bolt into the cantilever beam, the bearing performance of the bolt is affected by arranging the surface acoustic wave sensor in the narrow gap between the screw and the screw head, and the preparation process is complicated and the versatility is not high due to placing the surface acoustic wave sensor inside the bolt.

[0008] A first aspect of the present invention provides a fastener having a surface acoustic wave sensor, the fastener comprising:

[0009] Fastener base;

[0010] A surface acoustic wave sensor includes a piezoelectric layer and an electrode layer, wherein the piezoelectric layer is in-situ grown on the upper end surface of the fastener substrate; the electrode layer includes interdigitated electrodes and a reflection grating, wherein both the interdigitated electrodes and the reflection grating are in-situ grown on the surface of the piezoelectric layer, and the reflection grating is located on opposite sides of the interdigitated electrodes.

[0011] Optionally, the fastener base includes a head and a stem, the head includes the upper end surface and the lower end surface, and the stem is connected to the lower end surface;

[0012] The electrode layer is arranged in an annular region with a center located at the central axis of the rod, an inner diameter L1 and an outer diameter L2, and a radius of the projection of the rod on the upper end surface is R, L1≤R≤L2;

[0013] The annular area is connected to the projection of the rod portion on the upper end surface, or the annular area and the projection of the rod portion on the upper end surface at least partially overlap.

[0014] Optionally, the projection of the rod on the upper end surface includes a contour line, the distance between the inner ring of the annular area and the contour line is L3, the distance between the outer ring of the annular area and the contour line is L4, L3≤0.5R, and / or, L4≤0.5R.

[0015] Optionally, the electrode layer is located on the contour line.

[0016] Optionally, the interdigitated electrode includes a plurality of electrode fingers, the electrode layer includes an edge portion perpendicular to the plurality of electrode fingers, and the diameter of the rod portion projected on the upper end surface is perpendicular to the edge portion.

[0017] Optionally, the surface acoustic wave sensor further includes a PCB board and an impedance matching circuit, wherein the PCB board is provided on the piezoelectric layer, the impedance matching circuit is provided on the PCB board, and the impedance matching circuit is electrically connected to the interdigital electrodes;

[0018] Alternatively, the surface acoustic wave sensor further includes a PCB board and a transceiver antenna, the PCB board is provided on the piezoelectric layer, the transceiver antenna is provided on the PCB board, and the transceiver antenna is directly electrically connected to the interdigital electrodes or indirectly electrically connected to the interdigital electrodes via a circuit on the PCB board;

[0019] Alternatively, the surface acoustic wave sensor further includes a PCB board, an impedance matching circuit and a transceiver antenna, the PCB board is arranged on the piezoelectric layer, the impedance matching circuit and the transceiver antenna are both arranged on the PCB board, and the interdigital electrodes, the impedance matching circuit and the transceiver antenna are sequentially connected in series.

[0020] Optionally, the real value of the impedance of the impedance matching circuit is the same as the real value of the impedance of the surface acoustic wave sensor, and the complex value of the impedance of the impedance matching circuit is opposite to the complex value of the impedance of the surface acoustic wave sensor;

[0021] And / or, the frequency of the transceiver antenna matches the resonant frequency of the surface acoustic wave sensor.

[0022] Optionally, the fastener further comprises a sealing cover, the sealing cover being provided on the surface of the piezoelectric layer, and the functional structure provided on the surface of the piezoelectric layer being encapsulated in the sealing cover;

[0023] The functional structure includes at least the electrode layer.

[0024] In a second aspect, the present application provides a process for processing a fastener having a surface acoustic wave sensor. The process is used to process the fastener having a surface acoustic wave sensor provided in the first aspect of the embodiment of the present application. The process includes:

[0025] In-situ growing a piezoelectric layer on the upper end surface of the fastener base head;

[0026] spraying photoresist on the surface of the piezoelectric layer to form a photoresist layer;

[0027] Placing a mask on the photoresist layer, the mask having a light-transmitting area corresponding to the electrode layer, exposing the photoresist layer using a photolithography machine, removing the mask, and placing the exposed fastener substrate in a developer to remove the exposed photoresist;

[0028] The electrode layer material is in-situ grown on the head surface of the developed fastener substrate, and then the photoresist layer and the electrode layer material deposited on the surface of the photoresist layer are removed, and the electrode layer material on the surface of the piezoelectric layer is retained.

[0029] Optionally, the fastener processing process with a surface acoustic wave sensor further includes:

[0030] Arranging a PCB board on the piezoelectric layer, designing an impedance matching circuit and arranging a transceiver antenna on the PCB board, and connecting the interdigital electrodes, the impedance matching circuit and the transceiver antenna in series;

[0031] The impedance matching circuit must meet the following requirements: the real value of the impedance of the impedance matching circuit is the same as the real value of the impedance of the surface acoustic wave sensor, and the complex value of the impedance of the impedance matching circuit is opposite to the complex value of the impedance of the surface acoustic wave sensor; and the antenna frequency of the transceiver antenna is adapted to the resonant frequency of the surface acoustic wave sensor.

[0032] After adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art:

[0033] This application achieves preload sensing by in-situ growing a surface acoustic wave sensor on the head of the fastener substrate without damaging the fastener substrate structure. This allows for precise in-situ strain detection of the end face of the fastener substrate, ensuring the fastener substrate's load-bearing performance. Furthermore, the fasteners described in this application have unlimited usage scenarios, a simple manufacturing process, and high versatility. Compared to traditional strain detection methods, this allows for the permanent retention of the surface acoustic wave sensor on the fastener substrate, extending the service life of fasteners with preload detection capabilities.

[0034] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The accompanying drawings are part of the present invention and are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but do not constitute an undue limitation of the present invention. Obviously, the drawings described below are only some embodiments. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without inventive effort. In the accompanying drawings:

[0036] Figure 1 It is a front view of a fastener having a surface acoustic wave sensor according to an embodiment of the present application.

[0037] Figure 2 A top view of a fastener with a surface acoustic wave sensor according to an embodiment of the present application with the sealing cover removed is shown.

[0038] Figure 3 This is a cross-sectional view of a fastener having a surface acoustic wave sensor according to an embodiment of the present application.

[0039] Figure 4 Schematic diagram of the arrangement position of the electrode layer of the fastener with the surface acoustic wave sensor according to an embodiment of the present application.

[0040] Figure 5This is a linear diagram of the strain field distribution of an M8 bolt under different pre-tightening forces, shown as an exemplary embodiment of the present application.

[0041] Figure 6 The strain contour diagram of an M8 bolt is shown as an exemplary embodiment of the present application.

[0042] Figure 7 This is a schematic diagram showing the connection between an impedance matching circuit and interdigital electrodes according to an exemplary embodiment of the present application.

[0043] Figure 8 This is a process flow chart of a fastener with a surface acoustic wave sensor according to an embodiment of the present application.

[0044] Wherein: 1, fastener base; 11, head; 111, upper end surface; 112, lower end surface; 12, rod;

[0045] 2. Piezoelectric layer; 3. Electrode layer; 31. Interdigital electrode; 32. Reflection grid; 33. First pad; 34. Edge; 4. Transceiver antenna; 5. Bonding gold wire; 6. Impedance matching circuit; 7. Second pad; 8. Sealing cover; 9. Inductor; 10. Capacitor; 101. PCB board.

[0046] It should be noted that these drawings and textual descriptions are not intended to limit the conceptual scope of the present invention in any way, but rather to illustrate the concept of the present invention for those skilled in the art by referring to specific embodiments. DETAILED DESCRIPTION

[0047] In the description of the present invention, it should be noted that the terms "inside" and "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 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 operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0048] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connected," "in contact," and "connected" should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; and direct or indirect connections through an intermediary. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0049] First, the principle of surface acoustic wave sensor is explained:

[0050] A surface acoustic wave (SAW) sensor is a device that uses acoustic waves excited by an alternating electric field on the surface of a piezoelectric material to sense physical information. There are two types of SAW devices: delay line SAW devices and resonant SAW devices. The delay line type uses the change in the propagation time of the surface acoustic wave to parse physical information from the time domain. The physical quantity to be measured causes a change in the time required for the receiving end to receive the signal by causing a change in the propagation speed or transmission distance of the surface wave, and the size of the physical quantity to be measured is calibrated by the time length. The resonant type is that after an electrical signal consistent with the intrinsic frequency of the device is input through two interdigital ports, the surface acoustic wave propagates from the interdigital electrodes to both sides and the reflection grating returns the acoustic wave to the interdigital electrodes to form a standing wave. After the interdigital electrodes collect the standing wave frequency, they convert the wave energy into an electrical signal through the piezoelectric effect and output it to the receiving end. The standing wave frequency has a linear relationship with the surface wave velocity, and the surface wave velocity has a linear relationship with the strain of the material. Both delay line SAW devices and resonant SAW devices can be passively wirelessized to become a terminal node in WSN. Delay line SAW devices have a wider linear region, while resonant SAW devices have smaller insertion loss and higher signal strength in wireless transmission.

[0051] The technical solution of this embodiment is described in detail below with reference to the accompanying drawings. The following implementation modes and examples may be combined with each other unless there is any conflict.

[0052] This embodiment provides a fastener having a surface acoustic wave sensor, such as Figure 1-Figure 4 As shown, the fastener includes a fastener base 1 and a surface acoustic wave sensor.

[0053] The fastener body 1 includes a head 11 and a stem 12. The head 11 includes an upper end surface 111 and a lower end surface 112. The stem 12 is connected to the lower end surface 112. The surface acoustic wave sensor includes a piezoelectric layer 2 and an electrode layer 3, which are stacked layer by layer from the inside to the outside on the upper end surface 111.

[0054] The material of the fastener base 1 includes, but is not limited to, stainless steel, titanium alloy, aluminum alloy, and high-temperature alloy. Exemplarily, the fastener base 1 is a bolt base. The upper end surface 111 of the head 11 is a flat surface to allow the mask plate to adhere to the piezoelectric layer with photoresist during the photolithography process. Preferably, the piezoelectric layer 2 completely covers the upper end surface 111. The piezoelectric layer 2 can be directly disposed on the upper end surface 111 of the head 11, or indirectly disposed on the upper end surface 111 of the head 11 through other structures. In one example, after the upper end surface 111 of the head 11 of the fastener base 1 is polished, the piezoelectric layer 2 material is directly grown in situ on the upper end surface 111 of the head 11. In another example, a transition layer is grown in situ on the upper end surface 111 of the head 11 of the fastener base 1. The material of the transition layer includes, but is not limited to, Ti or Al. The transition layer has the ability to reduce the contact stress between the piezoelectric layer 2 and the fastener base 1. The piezoelectric layer 2 is in situ disposed on the upper end surface 111 through the transition layer. In another example, the piezoelectric layer 2 is in-situ grown on a flexible metal substrate, such as a metal foil, which is bonded to the upper end surface 111 of the head 11 , and the piezoelectric layer 2 is disposed on the upper end surface 111 through the flexible metal substrate.

[0055] The piezoelectric layer 2 is one of the key parts of the surface acoustic wave device and plays the role of acoustic-to-electrical / electroacoustic conversion. The quality, type, thickness and other parameters of the piezoelectric layer 2 directly affect the performance of the surface acoustic wave device. The materials of the piezoelectric layer 2 include but are not limited to zinc oxide ZnO, aluminum nitride AlN, lead zirconate titanate PZT, lithium niobate LNO, and tantalum oxide Ta2O5. The piezoelectric layer 2 can be a layer structure formed by a single material, or a multi-layer composite structure formed by multiple materials, such as ZnO / AlN, ZnO / LNO, etc. Due to the working characteristics of the surface acoustic wave sensor, the piezoelectric layer 2 does not need to be very thick, as long as it has sufficient piezoelectricity and dielectric properties. Exemplarily, the thickness of the piezoelectric layer 2 is 0 to 5 microns, but not 0.

[0056] The electrode layer 3 includes interdigitated electrodes 31 and reflective gratings 32. The interdigitated electrodes 31 and the reflective gratings 32 are both grown in situ on the surface of the piezoelectric layer 2, and the reflective gratings 32 are located on opposite sides of the interdigitated electrodes 31. The interdigitated electrodes 31 also include two first pads 33, and the two interdigitated ports of the interdigitated electrodes 31 are connected to the two first pads 33 in a one-to-one correspondence. The interdigitated electrodes 31 include two groups of finger electrodes, each group of finger electrodes consisting of a series of slender electrode fingers, which usually have uniform width and spacing. The length of the electrode fingers can be designed according to specific application requirements, and is generally micron-sized in width and millimeter-sized in length. The electrode fingers of the two groups of finger electrodes are arranged crosswise, with a certain spacing between the two groups of electrode fingers, and each electrode finger is interlaced with the opposite group of electrode fingers. The two reflective gratings 32 are located on both sides of the interdigitated electrodes 31 perpendicular to the direction of the electrode fingers.

[0057] The material of the electrode layer 3 includes but is not limited to Cu, Al, Mo, and Ag. The electrode layer 3 is another key part of the surface acoustic wave device, which plays the role of applying a periodic electric potential to the piezoelectric layer 2 and confining the surface acoustic wave to the inside of the device to form a standing wave. The material type, finger width, and thickness of the interdigitated electrode 31 will affect the eigenfrequency of the surface acoustic wave device, and the thickness, finger width, electrical continuity (divided into open-circuit reflective grating 32 and short-circuit reflective grating 32), and material type of the reflection grating 32 will affect the phase and intensity of the surface wave reflected to the interdigitated electrode 31 area. In actual applications, the material type, finger width, and thickness of the interdigitated electrode 31 and the thickness, finger width, electrical continuity, and material type of the reflection grating 32 can be flexibly selected based on comprehensive considerations of the performance, usage scenario, and production cost of the preload force sensor. Exemplarily, the thickness of the electrode layer 3 is 0 to 1 micron, but not 0.

[0058] In an optional embodiment, the piezoelectric material is in-situ grown on the upper end surface 111 of the head 11 by PVD (physical vapor deposition) or CVD (chemical vapor deposition) process. And / or, the electrode layer 3 material is grown on the surface of the piezoelectric layer 2 by magnetron sputtering or thermal evaporation.

[0059] In an alternative embodiment, if Figure 4 As shown, the electrode layer 3 is arranged in an annular area with its center located at the central axis of the rod 12, an inner diameter L1, and an outer diameter L2. The radius of the projection of the rod 12 on the upper end surface 111 is R, and L1≤R≤L2.

[0060] Since the rod 12 is a columnar structure, the projection of the rod 12 on the upper end surface 111 is a circle. The central axis of the rod 12 passes through the center of the projection of the rod 12 on the upper end surface 111. The projection of the rod 12 on the upper end surface 111 is a circle. Figure 4 The shaded portion in FIG. In one embodiment, the annular area is connected to the projection of the rod portion 12 on the upper end surface 111. For example, the outer ring of the annular area is connected to the outline of the projection, in which case R = L2, or the inner ring of the annular area is connected to the outline of the projection, in which case R = L1. In another embodiment, the annular area at least partially overlaps with the projection of the rod portion 12 on the upper end surface 111, that is, the annular area and the projection of the rod portion 12 on the upper end surface 111 have an overlapping area, in which case L1 < R < L2.

[0061] When the fastener is subjected to an axial preload, the head 11 of the fastener will have corresponding deformation and strain field distribution, and the deformation / strain has a highly linear relationship with the magnitude of the preload.

[0062] Figure 5 The linear relationship diagram of the strain and preload of the M8 bolt is shown. Figure 6 The strain contours under the same preload are shown. Figure 5The horizontal axis is the distance between the two opposite ends of the bolt head 11, and the vertical axis is the strain field size. Figure 5 It can be seen that as the preload increases, the deformation and strain field of the bolt head 11 will also increase accordingly. Figure 5 and Figure 6 It can be seen that under the same preload force, as the distance from one end to the other of the two opposite ends of the bolt head 11 increases, the equivalent elastic strain tends to first increase and then decrease.

[0063] Because the strain field and preload at all locations on the end surface of the fastener head 11 are quasi-linear, and the region of the fastener head 11 where the strain field varies significantly is an annular region, placing electrode layer 3 in this annular region significantly increases the variation in the preload force detected by the preload sensor, resulting in more accurate preload detection results. For example, for an M8 bolt, electrode layer 3 is placed within an annular region 4 cm from the central axis of the shank 12.

[0064] Preferably, the projection of the rod portion 12 on the upper end surface 111 includes a contour line, and the contour line refers to Figure 2 and Figure 4 The dashed line in the annular region indicates that the distance between the inner ring and the contour line is L3, and the distance between the outer ring and the contour line is L4. L3 < 0.5R, and / or L4 < 0.5R. The change in the fastener strain field is most pronounced within this annular region. Further preferably, electrode layer 3 is located on the contour line. Placing electrode layer 3 there enables strain detection along an isostrain ring. Compared to other locations, the strain at the contour line is greater, further improving the accuracy of the detection results.

[0065] In an optional embodiment, the interdigitated electrode 31 includes a plurality of electrode fingers, the electrode layer 3 includes an edge 34 perpendicular to the plurality of electrode fingers, and the diameter of the rod portion 12 projected on the upper end surface 111 is perpendicular to the edge 34 .

[0066] Since the projection of the rod 12 on the upper end surface 111 is circular, the diameter of the projection of the rod 12 on the upper end surface 111 is perpendicular to the edge 34, which means: the projection of the rod 12 on the upper end surface 111 has such a diameter that is perpendicular to the edge 34. The edge 34 perpendicular to the finger electrode is referred to as Figure 4 The middle part represents the long side of the rectangle of the electrode layer 3. The side portion 34 is perpendicular to the diameter of the projection of the rod portion 12 on the upper end surface 111, so that the surface acoustic wave sensor can detect the preload force under a uniform strain field, ensuring the accuracy of the detection result.

[0067] This embodiment also proposes a fastener with a surface acoustic wave sensor. The fastener of this embodiment is based on the fastener proposed above, and adds a PCB board 101, and an impedance matching circuit 6 and / or a transceiver antenna 4 is provided on the PCB board 101.

[0068] The PCB is provided on the piezoelectric layer 2 and is used to carry the impedance matching circuit 6 and / or the transceiver antenna 4. The PCB board 101 includes a plurality of second pads 7, which are used to achieve electrical connections between different components, and the connection methods include bonding and soldering.

[0069] Impedance matching circuit 6 reduces transmission reflections and increases transmission power. The type of impedance matching circuit 6 is not particularly limited; it only requires that the real impedance value of impedance matching circuit 6 be the same as the real impedance value of the SAW sensor, and the complex impedance value of impedance matching circuit 6 be opposite to the complex impedance value of the SAW sensor. This allows more power to be transmitted to the SAW sensor, thereby increasing the SAW sensor's transmission power.

[0070] In one example, the impedance matching circuit 6 can be an L-type circuit. Figure 7 The impedance matching circuit 6 is a schematic diagram of the connection between the interdigital electrodes 31 . The impedance matching circuit 6 includes a capacitor 10 and an inductor 9 . The capacitor 10 is connected in series with the interdigital electrodes 31 , and the inductor 9 is connected in parallel with the interdigital electrodes 31 .

[0071] The transceiver antenna 4 receives and transmits electromagnetic waves from space, providing energy and information to the surface acoustic wave sensor. The antenna frequency of the transceiver antenna 4 must match the operating frequency of the surface acoustic wave device to maximize the amount of electromagnetic energy received from space that can be delivered to the sensor. Common antenna frequencies include 6765 kHz and 433 MHz.

[0072] The following are implementations of different combinations of the PCB board 101 , the impedance matching circuit 6 , and the transceiver antenna 4 .

[0073] In one embodiment, the surface acoustic wave sensor further includes a PCB 101 and an impedance matching circuit 6. The PCB 101 is disposed on the piezoelectric layer 2, and the impedance matching circuit 6 is disposed on the PCB 101. The impedance matching circuit 6 is electrically connected to the interdigital electrodes 31. Specifically, one port of the impedance matching circuit 6 is connected to a second pad 7. This second pad 7, connected to the impedance matching circuit 6, is electrically connected to a first pad 33 via a gold bonding wire 5. The gold bonding wire 5 can be prepared using a gold ball bonder. A floating potential is provided between the interdigital port corresponding to the other first pad 33 and the other port of the impedance matching circuit for connection to a test instrument, such as a vector network analyzer.

[0074] In one embodiment, the surface acoustic wave sensor further includes a PCB 101 and a transceiver antenna 4. The PCB 101 is disposed on the piezoelectric layer 2, and the transceiver antenna 4 is disposed on the PCB 101. The transceiver antenna 4 is directly electrically connected to the interdigital electrodes 31 or indirectly electrically connected via a circuit on the PCB 101. For example, the transceiver antenna 4 is electrically connected to a second pad 7 on the PCB 101, which is electrically connected to a first pad 33 of the interdigital electrode 31. Alternatively, the second pad 7 of the interdigital electrode 31 is electrically connected to one end of a circuit provided on the PCB 101, and the other end of the circuit provided on the PCB is electrically connected to the transceiver antenna 4.

[0075] In one embodiment, Figure 2 and Figure 3 As shown, the surface acoustic wave sensor further includes a PCB board 101, an impedance matching circuit 6, and a transceiver antenna 4. The PCB board 101 is disposed on the piezoelectric layer 2. The impedance matching circuit 6 and the transceiver antenna 4 are both disposed on the PCB board 101. The interdigital electrodes 31, the impedance matching circuit 6, and the transceiver antenna 4 are sequentially connected in series. Specifically, the impedance matching circuit 6 is connected in series between one port of the transceiver antenna 4 and one interdigital port of the interdigital electrode 31. The other port of the transceiver antenna 4 is electrically connected to the other interdigital port of the interdigital electrode 31. Specifically, the series connection between the interdigital electrodes 31, the impedance matching circuit 6, and the transceiver antenna 4 is achieved by an electrical connection between a first pad 33 and a second pad 7 located on the PCB board 101.

[0076] In one embodiment, Figure 1 and Figure 3 As shown, the fastener also includes a sealing cover 8, which is provided on the surface of the piezoelectric layer 2. The functional structure provided on the surface of the piezoelectric layer 2 is encapsulated within the sealing cover 8 to protect the functional structure. The functional structure includes at least the electrode layer 3. When a transceiver antenna 4 and / or an impedance matching circuit 6 are also provided on the piezoelectric layer 2, the functional structure also includes the transceiver antenna 4 and / or the impedance matching circuit 6, and the transmitting antenna and / or the impedance matching circuit 6 are also encapsulated within the sealing cover 8. The sealing cover 8 needs to be fixedly connected to the piezoelectric layer 2, for example, by bonding the lower end of the sealing cover 8 to the surface of the piezoelectric layer 2 to ensure the reliability of the connection between the sealing cover 8 and the piezoelectric layer 2.

[0077] This embodiment also proposes a processing technology for a fastener with a surface acoustic wave sensor, which is used to process the fastener with a surface acoustic wave sensor proposed above, referring to Figure 8 The process includes the following steps:

[0078] Step 1: In-situ growth of the piezoelectric layer 2 on the upper end surface 111 of the head 11 of the fastener base 1.

[0079] Specifically, the upper end surface 111 of the head 11 of the fastener is first polished to a quasi-idealized plane, facilitating subsequent coating and photolithography. The fastener is then cleaned multiple times with a cleaning solution to remove impurities from the head 11 and ensure reliable bonding between the piezoelectric layer 2 and the upper end surface 111. The cleaning solution may be, for example, an alcohol solution.

[0080] Next, the piezoelectric layer 2 is in situ grown on the upper end surface 111 of the head 11. For example, aluminum nitride is used as the material for the piezoelectric layer 2. The fastener is placed in a magnetron sputtering chamber. After the pressure is evacuated to 8E-4 Pa, 110 sccm of high-purity nitrogen and 70 sccm of high-purity argon are introduced. At a working pressure of 0.6 Pa and a power of 3000 W, aluminum is sputtered onto the upper end surface 111 of the head 11. The aluminum reacts with the nitrogen to form an aluminum nitride film. The deposition takes 3 hours, resulting in a 3-micron-thick aluminum nitride film on the upper end surface 111 of the head 11. The surface wave velocity of this AlN film is between 4600 and 5000 m / s.

[0081] Step 2: spraying photoresist on the surface of the piezoelectric layer 2 to form a photoresist layer.

[0082] Specifically, the fastener substrate 1, on which the piezoelectric layer 2 has been deposited, is first cleaned to remove dust particles attached to the surface. For example, a mixture of acetone and alcohol is used to clean the fastener substrate 1. The substrate 1, on which the piezoelectric layer 2 has been deposited, is then air-dried and placed in a photoresist sprayer. Photoresist is ultrasonically sprayed onto the surface of the piezoelectric layer 2 and then dried. For example, a 1.5-micron thick layer of photoresist is ultrasonically sprayed onto the surface of the piezoelectric layer 2 and then baked at 110°C for 3 minutes.

[0083] Step 3: Place a mask on the photoresist layer, the mask having a hollow pattern corresponding to the electrode layer 3, use a photolithography machine to expose the photoresist layer, remove the mask, and place the exposed fastener substrate 1 in a developer to remove the exposed photoresist.

[0084] Specifically, a mask with a hollowed-out pattern corresponding to the electrode layer 3 is first placed on the surface of the photoresist layer. The shape of the mask matches the shape of the upper end surface 111 of the head 11. For example, if the upper end surface 111 of the fastener head 11 is hexagonal, the mask is a hexagonal mask. This allows the mask to align with the edges of the upper end surface 111, improving the versatility of the mask.

[0085] Then, an ultraviolet lithography machine is used to expose the photoresist by contact exposure, and the area of ​​the photoresist layer corresponding to the light-transmitting area of ​​the mask is exposed.

[0086] Next, the mask is separated from the surface of the photoresist layer, which now includes exposed and unexposed areas. The fastener substrate 1 is placed in a developer to remove the exposed photoresist. After the exposed photoresist is removed, a portion of the piezoelectric layer 2 is exposed from the photoresist layer, which is used for the subsequent deposition of the electrode layer 3. For example, the fastener substrate 1 is placed in a 2.38 wt% tetramethylammonium hydroxide developer and developed for 70 seconds to remove the exposed photoresist.

[0087] Step 4: In-situ grow the electrode layer 3 material on the surface of the head 11 of the developed fastener substrate 1, then remove the photoresist layer and the electrode layer 3 material deposited on the surface of the photoresist layer, and retain the electrode layer 3 material on the surface of the piezoelectric layer 2.

[0088] Specifically, the developed fastener substrate 1 is placed back into the vacuum chamber, and the electrode layer 3 material is in-situ grown on the surface of the head 11. For example, Al is used as the material for the electrode layer 3. After the developed fastener substrate 1 is placed into the vacuum chamber, the pressure is evacuated to 8E-4 Pa, and then 100 sccm of high-purity argon gas is introduced. The butterfly valve is adjusted to sputter Al onto the head 11 of the fastener substrate 1 at a working pressure of 0.6 Pa and a power of 1500 W.

[0089] Since the electrode layer 3 material is deposited both on the surface of the piezoelectric layer 2 exposed to the photoresist layer and on the surface of the photoresist layer during sputtering, the photoresist layer and the electrode layer 3 material deposited on the surface of the photoresist layer must be removed to retain only the electrode layer 3 material in the area where the electrode layer 3 is to be formed. For example, the fastener substrate 1, having the electrode layer 3 prepared thereon, is placed in acetone and ultrasonically treated for 30 minutes to strip away the electrode layer 3 material and the photoresist deposited on the photoresist.

[0090] Optional, continue to refer to Figure 8 Flowchart, after the electrode layer is formed on the fastener substrate 1, it is necessary to detect whether the two interdigital ports of the interdigital electrode 31 of the electrode layer 3 are connected. If not, it means that the quality of the electrode layer 3 is qualified.

[0091] Specifically, after the fasteners with the photoresist layer stripped off are dried, the two interdigital ports of the interdigital electrode 31 are checked for connectivity. If not, it indicates that the quality of the electrode layer 3 is qualified. If connected, it indicates that the quality of the electrode layer 3 is unqualified. There are two ways to detect whether the two interdigital ports are connected. One is to use a microscope to assist in naked eye observation. Since the electrode layer 3 and the piezoelectric layer 2 are different colors, taking the material of the electrode layer 3 as aluminum and the material of the piezoelectric layer 2 as an example, aluminum is a metal and appears white under a microscope, while aluminum nitride is an inorganic material and appears light blue under a microscope, and does not have a metallic luster. By adjusting the position of the device under the microscope, it is determined whether the structure of all electrode layers 3 conforms to the expected structure of the photolithography pattern to determine whether the two interdigital ports are connected. The second is to use a multimeter to detect. In the resistance mode, use two test leads to touch the two first pads 33 of the interdigital electrode 31. If the resistance is in the 10,000 ohm level or above, it can be determined that there is no connectivity.

[0092] Optional, continue to refer to Figure 8 The processing technology also includes:

[0093] Step 5: Set up a PCB board 101 on the piezoelectric layer, design an impedance matching circuit 6 and set up a transceiver antenna 4 on the PCB board 101, and connect the interdigital electrodes 31, the impedance matching circuit 6 and the transceiver antenna 4 in series.

[0094] Specifically, the resonant frequency and impedance of the fastener base 1 with the piezoelectric layer 2 and the electrode layer 3 formed on the head 11 need to be determined first, and then the resonant frequency and Q value are measured using a vector network analyzer and a Smith chart is drawn to obtain the impedance of the surface acoustic wave sensor.

[0095] Select a suitable impedance matching circuit 6 and solder it to PCB 101. The impedance matching circuit 6 must meet the following requirements: the real impedance value of the impedance matching circuit 6 is the same as the real impedance value of the SAW sensor, and the complex impedance value of the impedance matching circuit 6 is opposite to the complex impedance value of the SAW sensor. This allows more power to be transmitted to the SAW sensor, thereby increasing the SAW sensor's transmission power. Then, electrically connect one of the two first solder pads 33 of the interdigital electrode 31 to one port of the impedance matching circuit 6.

[0096] Then, a transceiver antenna 4 whose antenna frequency is adapted to the resonant frequency of the surface acoustic wave sensor is selected and soldered to the PCB board 101, and one port of the transceiver antenna 4 is electrically connected to another port of the impedance matching circuit 6, and the other port of the transceiver antenna 4 is electrically connected to another interdigital port of the interdigital electrode 31.

[0097] Finally, the sealing cover 8 is placed on the surface of the piezoelectric layer 2 , and the electrode layer 3 , the impedance matching circuit 6 and the transceiver antenna 4 are encapsulated in the sealing cover 8 to protect the electrode layer 3 , the impedance matching circuit 6 and the transceiver antenna 4 .

[0098] After the fasteners with surface acoustic wave sensors are manufactured, a vector network analyzer is used with four transceiver antennas to perform passive wireless testing of the surface acoustic wave sensors under different tensile loads to calibrate the device (bolts of the same model and material only need to be calibrated once). Once the linear relationship between tension and SAW resonator spectrum displacement is obtained, the fasteners can be used.

[0099] In summary, this embodiment provides a surface acoustic wave sensor on the surface of the head 11 of the fastener base 1. Without damaging the structure of the fastener base 1, the fastener base 1 can be precisely detected by in-situ strain information on the end face of the head to achieve preload sensing and ensure the load-bearing performance of the fastener base 1.

[0100] In this embodiment, the piezoelectric layer 2 of the surface acoustic wave sensor is in-situ grown on the upper end surface 111 of the head 11 of the fastener base 1, so that the surface acoustic wave sensor can be permanently stationed on the fastener base 1, thereby improving the service life of the fastener with a preload detection function.

[0101] This embodiment improves the accuracy of preload force detection results by arranging the electrode layer 3 of the surface acoustic wave sensor in an annular area where the strain field changes significantly. By ensuring that the edge 34 perpendicular to the finger-shaped electrodes of the electrode layer 3 is perpendicular to the radius of the projection of the rod portion 12 of the fastener base 1 onto the upper end surface 111 of the head 11, the surface acoustic wave sensor can detect the preload force under a uniform strain field, thereby ensuring the accuracy of the detection results.

[0102] In this embodiment, an impedance matching circuit 6 is added to the surface of the piezoelectric layer 2 to improve the transmission power of the surface acoustic wave sensor; and a transceiver antenna 4 is added to the surface of the piezoelectric layer 2 to power the entire surface acoustic wave sensor and realize wireless transmission of information.

[0103] The fastener with the surface acoustic wave sensor of this embodiment has no restrictions on usage scenarios, a simple preparation process, high versatility, broad application prospects and strong market competitiveness.

[0104] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above technical content without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A fastener having a surface acoustic wave sensor, characterized in that: The fastener comprises: Fastener base; A surface acoustic wave sensor includes a piezoelectric layer and an electrode layer, wherein the piezoelectric layer is in-situ grown on the upper end surface of the fastener substrate; the electrode layer includes interdigitated electrodes and a reflection grating, wherein both the interdigitated electrodes and the reflection grating are in-situ grown on the surface of the piezoelectric layer, and the reflection grating is located on opposite sides of the interdigitated electrodes.

2. The fastener having a surface acoustic wave sensor according to claim 1, wherein: The fastener base includes a head and a stem, the head includes the upper end surface and the lower end surface, and the stem is connected to the lower end surface; The electrode layer is arranged in an annular area with a center located at the central axis of the rod, an inner diameter of L1 and an outer diameter of L2. The radius of the projection of the rod on the upper end surface is R, and L1≤R≤L2.

3. The fastener having a surface acoustic wave sensor according to claim 2, wherein: The projection of the rod portion on the upper end surface includes a contour line, the distance between the inner ring of the annular area and the contour line is L3, the distance between the outer ring of the annular area and the contour line is L4, L3≤0.5R, and / or L4≤0.5R.

4. The fastener having a surface acoustic wave sensor according to claim 3, wherein: The electrode layer is located on the contour line.

5. The fastener having a surface acoustic wave sensor according to claim 2, wherein: The interdigitated electrode includes a plurality of electrode fingers, the electrode layer includes a side portion perpendicular to the plurality of electrode fingers, and the diameter of the rod portion projected onto the upper end surface is perpendicular to the side portion.

6. The fastener having a surface acoustic wave sensor according to any one of claims 1 to 5, characterized in that: The surface acoustic wave sensor further includes a PCB board and an impedance matching circuit, wherein the PCB board is provided on the piezoelectric layer, the impedance matching circuit is provided on the PCB board, and the impedance matching circuit is electrically connected to the interdigital electrodes; Alternatively, the surface acoustic wave sensor further includes a PCB board and a transceiver antenna, the PCB board is provided on the piezoelectric layer, the transceiver antenna is provided on the PCB board, and the transceiver antenna is directly electrically connected to the interdigital electrodes or indirectly electrically connected to the interdigital electrodes via a circuit on the PCB board; Alternatively, the surface acoustic wave sensor further includes a PCB board, an impedance matching circuit and a transceiver antenna, the PCB board is arranged on the piezoelectric layer, the impedance matching circuit and the transceiver antenna are both arranged on the PCB board, and the interdigital electrodes, the impedance matching circuit and the transceiver antenna are sequentially connected in series.

7. The fastener having a surface acoustic wave sensor according to claim 6, wherein: The real value of the impedance of the impedance matching circuit is the same as the real value of the impedance of the surface acoustic wave sensor, and the complex value of the impedance of the impedance matching circuit is opposite to the complex value of the impedance of the surface acoustic wave sensor; And / or, the frequency of the transceiver antenna matches the resonant frequency of the surface acoustic wave sensor.

8. The fastener having a surface acoustic wave sensor according to claim 1, wherein: The fastener further comprises a sealing cover, the sealing cover being arranged on the surface of the piezoelectric layer, and the functional structure arranged on the surface of the piezoelectric layer being encapsulated in the sealing cover; The functional structure includes at least the electrode layer.

9. A process for processing a fastener having a surface acoustic wave sensor, characterized in that: The processing technology is applied to the fastener with a surface acoustic wave sensor according to any one of claims 1 to 8, and the processing technology includes: In-situ growing a piezoelectric layer on the upper end surface of the fastener base head; spraying photoresist on the surface of the piezoelectric layer to form a photoresist layer; Placing a mask on the photoresist layer, the mask having a light-transmitting area corresponding to the electrode layer, exposing the photoresist layer using a photolithography machine, removing the mask, and placing the exposed fastener substrate in a developer to remove the exposed photoresist; The electrode layer material is in-situ grown on the head surface of the developed fastener substrate, and then the photoresist layer and the electrode layer material deposited on the surface of the photoresist layer are removed, and the electrode layer material on the surface of the piezoelectric layer is retained.

10. The process for processing a fastener having a surface acoustic wave sensor according to claim 9, characterized in that: The processing technology also includes: A PCB board is set on the piezoelectric layer, an impedance matching circuit is designed and a transceiver antenna is set on the PCB board, and the interdigital electrodes, the impedance matching circuit and the transceiver antenna are connected in series in sequence; wherein, the impedance matching circuit must meet the following requirements: the real value of the impedance of the impedance matching circuit is the same as the real value of the impedance of the surface acoustic wave sensor, and the complex value of the impedance of the impedance matching circuit is opposite to the complex value of the impedance of the surface acoustic wave sensor; the antenna frequency of the transceiver antenna is adapted to the resonant frequency of the surface acoustic wave sensor.

Images