Passive gasket type pressure sensor based on parametric negative resistance self-excitation and monitoring method

Abstract

The application discloses a passive gasket type pressure sensor based on parametric negative resistance self-excitation and a monitoring method, and belongs to the technical field of bolt loosening state monitoring. The sensor is improved based on a standard metal flat gasket, and a piezoelectric sensing unit, an out-of-frequency response passive network and a passive thermal-induced drift suppression circuit are embedded in the improved sensor. The embedded area is filled with organic silicone glue. The out-of-frequency response passive network utilizes parametric reactance modulation to generate active negative resistance through strong nonlinearity, realizes self-excitation of weak radio frequency energy, maps bolt axial load changes into echo frequency sideband drift, and the thermal-induced drift suppression circuit eliminates temperature drift. The monitoring further determines the environmental temperature through the temperature echo, matches the frequency-load curve, and then determines the bolt loosening state through the bolt loosening state echo. The application realizes passive wireless, maintenance-free and high-precision monitoring, and solves the problems of high starting threshold, short communication distance and poor integration of the prior art.

Description

Technical Field

[0001] This application relates to the field of bolt loosening condition monitoring technology, and in particular to a passive gasket-type pressure sensor and monitoring method based on parametric negative resistance self-excitation. Background Technology

[0002] In the fields of equipment manufacturing and maintenance, such as aerospace, rail transportation, bridges and tunnels, and large precision machinery, bolted connections are the most basic and critical structural fastening method. The stability of the bolt loosening state directly affects the overall operational safety and service life of the equipment. During long-term service, bolts are affected by complex factors such as environmental vibration, impact loads, temperature fluctuations, and material creep, making them prone to loosening or even falling off, which can lead to catastrophic accidents. Therefore, real-time, online monitoring of bolt loosening status is of great significance.

[0003] Currently, the main methods for monitoring bolt loosening include traditional manual inspection, wired monitoring, active wireless monitoring, and existing passive wireless monitoring. Traditional monitoring methods rely on torque wrenches or small hammers for periodic manual inspections, which suffers from low efficiency, easy omissions and false positives, and difficulty in capturing the dynamic loosening process of bolts. Wired monitoring schemes based on resistance strain gauges or fiber optic sensors have high measurement accuracy, but they have inherent problems such as cumbersome wiring, high power requirements, and alteration of the original tightening performance of bolts. Active wireless sensing technology based on micro-batteries, which has emerged in recent years, has solved the wiring problem, but it is limited by battery life and cannot achieve maintenance-free monitoring of bolts throughout their entire life cycle.

[0004] Among existing passive wireless sensing technologies, surface acoustic wave (SAW) sensors have achieved passivity, but their piezoelectric substrate processing technology is complex and costly, and they have extremely high requirements for reader signal processing. RFID passive tag sensors based on integrated circuit chips (ICs) are limited by the chip's start-up threshold voltage, resulting in technical bottlenecks such as short communication distance, low analog sensing accuracy, difficulty in effectively starting oscillation in confined metal spaces, and inability to deeply integrate with standard gasket structures.

[0005] Specifically, firstly, passive wireless solutions based on diodes, varactor diodes, or single-channel transistors (transistors or field-effect transistors) have high oscillation thresholds and are extremely sensitive to excitation power, resulting in low system output signal amplitude and limited communication distance and reliability. Furthermore, this principle is highly temperature-dependent, causing measurement failures in environments with significant temperature differences. Secondly, UHF RFID-based passive wireless pressure sensing systems heavily rely on integrated circuit chips, exhibiting high rectification start-up thresholds, preventing oscillation under weak energy, thus limiting communication distance. Additionally, silicon-based chips are inherently fragile and difficult to embed directly into bolt washers that withstand high bolt preload, making them prone to encapsulation failure or pin breakage in industrial high-pressure and high-vibration environments. Thirdly, LC resonant-based passive wireless pressure sensing systems rely on near-field electromagnetic induction coupling, where magnetic field energy decays with distance to the sixth power, limiting effective read / write distance to the centimeter level, making far-field non-contact monitoring difficult. Moreover, in environments with dense metal elements such as bolts, they are highly susceptible to parasitic capacitance and eddy current interference, leading to resonant frequency drift and low measurement signal-to-noise ratio.

[0006] In summary, existing monitoring technologies cannot simultaneously meet the requirements of passive wireless, long-distance communication, high sensitivity, integrated structure and function, low cost, and adaptability and compensation capability to environmental variables. There is an urgent need for a new passive sensing design scheme to achieve maintenance-free and high-precision monitoring of bolt loosening status throughout its entire life cycle. Summary of the Invention

[0007] To address the limitations of existing bolt loosening condition monitoring technologies in simultaneously achieving passive, wireless, and maintenance-free operation while also ensuring long communication distances, integration with standard gasket structures for high bolt preload conditions, and high-precision monitoring, this invention provides a passive gasket-based pressure monitoring method based on parametric negative resistance self-excitation. The technical solution is as follows:

[0008] On the one hand, a passive pad-type pressure sensor based on parametric negative resistance self-excitation is provided, including a pad area, a piezoelectric sensing unit (20) and a different frequency response passive network (30).

[0009] The gasket area includes a pressure gasket (09) and a gasket substrate (10);

[0010] The pressure pad (09) is aligned and installed with the pad base (10) by setting a plurality of pressure crosses (091), and the piezoelectric sensing unit (20) is sandwiched between the installation.

[0011] The gasket substrate (10) is based on a standard metal flat washer, and the piezoelectric sensing unit (20) and the frequency response passive network (30) are embedded therein, and the embedded area is filled with backing material.

[0012] The passive network (30) with different frequency response is connected to the piezoelectric sensing unit (20) and is used to receive an external radio frequency wireless activation energy field and generate a modulated echo signal carrying information about the loosening state of the bolts.

[0013] Optionally, at least one shallow cylindrical groove (111) is provided at the gasket substrate (10).

[0014] The piezoelectric sensing unit (20) is a piezoelectric perovskite transducer and is provided with a channel (211). The piezoelectric sensing unit (20) is fixed in the shallow cylindrical groove (111). The channel (211) serves as a connection between the various piezoelectric sensing units (20) to achieve series or parallel connection.

[0015] The gasket substrate (10) is also provided with an annular fan-shaped groove (121) for embedding a custom-designed circuit board. The groove wall is insulated and meets the preset roughness requirements.

[0016] The frequency response passive network (30) is encapsulated on the circuit board. The circuit board is fixed in the annular fan-shaped groove (121) by the backing material and is provided with a number of limiters (213) for limiting the position of the embedded frequency response passive network (30).

[0017] Optionally, the frequency response passive network (30) includes a miniature antenna (31), an impedance matching system (32), and a high-frequency inductor L. S The system includes a semiconductor parametric reactance modulation core (33), an elastic electromagnetic resonant cell (34), and a passive thermally induced drift suppression circuit (35). The impedance matching system (32) includes common π-shaped, T-shaped, and inverted L-shaped types. The parametric reactance modulation core (33) includes a combination of silicon-germanium heterojunction bipolar transistors (HBT), silicon-based enhancement-mode MOSFETs (MOSFETs), and gallium arsenide enhancement-mode (pHEMT). The passive thermally induced drift suppression circuit (35) is used to generate an echo signal carrying ambient temperature information.

[0018] The parametric reactance modulation core (33) is connected to the passive thermally induced drift suppression circuit (35);

[0019] The miniature antenna (31) serves as the radio frequency input / output terminal, and the impedance matching system (32) and the high-frequency inductor L are connected in series in sequence. S It is then connected to the input terminal of the parametric reactance modulation core (33), and the output terminal of the parametric reactance modulation core (33) is connected to the elastic electromagnetic resonant pool (34) and the impedance matching system (32);

[0020] The impedance matching system (32) is designed for 50Ω;

[0021] The passive network (30) with different frequency response adopts an integrated configuration structure of "one channel and two transistors". By integrating the parametric reactance modulation core (33) composed of two-by-two silicon-germanium heterojunction bipolar transistors (HBT), silicon-based enhancement-mode MOSFETs (MOSFETs) and gallium arsenide enhancement-mode (pHEMT) with the passive thermally induced drift suppression circuit (35) in the same circuit path, a single circuit is formed to realize the dual-function configuration of bolt loosening status signal sensing and ambient temperature signal acquisition. The "one channel and two transistors" configuration structure is used to reduce the circuit oscillation conditions, reduce the power of the required external radio frequency wireless activation energy field, and at the same time increase the output amplitude of the sideband frequency signal carrying bolt loosening status information and ambient temperature information.

[0022] Optionally, the parametric reactance modulation core (33) is of the type adapted to radio frequency operation. Under the drive of an external strong radio frequency wireless activation energy field, it operates in a strong nonlinear capacitance region. Its nonlinear charge-voltage relationship satisfies the Taylor series expansion characteristics, and the time-varying capacitance changes periodically with the frequency of the pump signal of the external radio frequency excitation.

[0023] The equivalent capacitance of the parametric reactance modulation core (33) changes with the high-frequency AC voltage, and the capacitance change is correlated with the high-frequency inductance L. S The coupling effect of the inductance value generates an active negative resistance, the absolute value of which is proportional to the square of the capacitance change and the high-frequency inductance L. S The inductance value is positively correlated and is used to offset the circuit loss by generating the active negative resistance to meet the oscillation condition; wherein, the steps of the parametric negative resistance calculation algorithm of the parametric reactance modulation core (33) are as follows:

[0024] Step 301: Define physical parameters and set the static capacitance of the parametric reactance modulation core. First-order nonlinear coefficients angular frequency of external radio frequency excitation pump signal ( =2πf 0， f0 represents the frequency and amplitude of the external radio frequency wireless activation energy field. The inductance value of the high-frequency inductor LS, and the angular frequency of the weak low-frequency disturbance current in the circuit. (i.e., the local oscillator frequency of the LC resonant circuit);

[0025] Step 302, Time-varying capacitance calculation, based on the characteristics of Taylor series expansion, using the formula Calculate the time-varying capacitance and substitute it into the pump signal. (t)= We obtain C(t) = C0 + ΔCcos( ), where ΔC is proportional to the pump amplitude. ;

[0026] Step 303: Active negative resistance is generated through the coupling effect of capacitance change ΔC and high-frequency inductance LS, based on the formula... The absolute value of the active negative resistance is positively correlated with the square of the capacitance change and the inductance of the high-frequency inductor LS.

[0027] Step 304, Determine the oscillation start-up conditions, and set the parallel LC circuit at the resonant frequency. Equivalent loss resistance at the point According to the Backhausen criterion, through the formula Determine the oscillation state, among which For input impedance, The real part of the input impedance (i.e., the real part contribution corresponding to the active negative resistance) is the active negative resistance. When this condition is met, the active negative resistance cancels out the loop loss and achieves self-excitation.

[0028] Optionally, the elastic electromagnetic resonant cell (34) includes a fixed inductor L. P and the piezoelectric sensing unit (20), the piezoelectric sensing unit (20) serving as a piezoresistive capacitor C piezo The connection circuit is connected to the fixed inductor L. P Parallel connection forms an LC resonant circuit; where,

[0029] The local angular frequency of the LC resonant circuit is determined by the fixed inductance L. P The inductance and the varistor C piezo The capacitance value is determined by both factors, and the local oscillator angular frequency has a monotonic mapping relationship with the state of bolt loosening;

[0030] The number of the piezoelectric sensing units (20) is one or more, and the multiple piezoelectric sensing units (20) are connected in series or in parallel to improve the mapping sensitivity between the capacitance change and the bolt loosening state.

[0031] The varistor C piezo The steps of the algorithm for mapping bolt loosening status are as follows:

[0032] Step 401: Define physical parameters, set the total bolt preload applied by the bolt as F, the force diversion coefficient k (k<1), the cross-sectional area A and thickness h of the piezoelectric crystal, the piezoelectric constant d, and the dielectric constant ε of the piezoelectric material;

[0033] Step 402, stress calculation, using the formula Calculate the actual pressure exerted on a single piezoelectric crystal, and then use the formula... Calculate the internal stress of the crystal;

[0034] Step 403, charge calculation, based on the piezoelectric effect principle, using the formula The total surface charge of the crystal was derived and simplified by substituting it into the stress formula. This achieves a proportional mapping between the amount of charge and the state of bolt loosening;

[0035] Step 404, equivalent capacitance calculation, based on the parallel plate capacitor model, using the formula Calculate the equivalent capacitance of the piezoelectric sensing unit;

[0036] Step 405, Capacitor-bolt loosening state mapping, combining charge Q and equivalent capacitance. The relationship between capacitance changes and bolt axial load changes is indirectly reflected by capacitance changes, providing a physical basis for subsequent frequency mapping.

[0037] Optionally, the parametric reactance modulation core (33) with semiconductor also has a convolution function, which is used to frequency couple the pump signal of external radio frequency excitation with the local oscillator signal of LC resonant circuit to generate a sideband frequency signal containing the sum frequency and difference frequency of the pump signal and the local oscillator signal. The sideband frequency also includes the relevant frequency of the passive thermally induced drift suppression circuit (35).

[0038] The sideband frequency signal is reflected and transmitted through a miniature antenna (31), and the offset of the sideband frequency is linearly related to the change in the axial load of the bolt, which is used to reversely determine the loose state of the bolt.

[0039] Optionally, the resonant frequency variation ranges of the elastic electromagnetic resonant pool (34) and the passive thermally induced drift suppression circuit (35) belong to different frequency bands forming range differences, and the range differences are used to avoid signal confusion.

[0040] Optionally, the backing material is silicone, which, after filling, is flush with the original surface of the gasket substrate (10);

[0041] The installation method of the piezoelectric sensing unit (20) includes:

[0042] The piezoelectric sensing unit (20) is fixed by the inner frustum (112) of the silicone mating pad substrate groove. The piezoelectric sensing unit (20) is not in contact with the groove wall of the shallow cylindrical groove (111). The inner frustum (112) of the pad substrate groove is used for positioning and does not contact the piezoelectric sensing unit (20). It is also used for force transmission. Specifically, it is used to engage with the pressure cross (091) of the pressure pad (09) and the shallow cylindrical groove (111) and transmit force through the silicone mating pad.

[0043] Optionally, the gasket base (10) is compatible with bolts of M12-M27 specifications;

[0044] The standard metal flat washer can be installed by directly replacing a regular flat washer or by placing it on top of the original metal washer.

[0045] On the other hand, a method for monitoring bolt loosening condition is provided, the method comprising:

[0046] Receive the echo signal carrying temperature information sent by the passive thermally induced drift suppression circuit in the passive frequency response network to determine the current ambient temperature;

[0047] The corresponding frequency-load relationship spectrum is selected based on the ambient temperature, wherein the frequency-load relationship curve is obtained by laboratory temperature-load coupling experiment calibration, covering the sensor's operating temperature and load range;

[0048] The sideband frequency signal reflected by the passive network with different frequency response is received, the sum frequency or difference frequency component is extracted, and the current loosening state of the bolt is determined based on the frequency-load spectrum relationship curve.

[0049] Therefore, compared with the prior art, this application achieves at least the following technical effects.

[0050] It achieves passive wireless and maintenance-free operation throughout the entire life cycle, eliminating the dependence on batteries and integrated circuit chips. By using an external radio frequency wireless activation energy field through a parametric negative resistance self-excitation mechanism, it can complete signal acquisition and transmission without the need for additional power supply, thus meeting the maintenance-free monitoring requirements of bolts throughout their entire life cycle.

[0051] It combines long-distance communication with high signal amplitude. Specifically, it adopts a "one-channel dual-tube" integrated setting structure, which reduces the circuit oscillation energy threshold, reduces the required radio frequency activation power, and at the same time increases the output amplitude of the sideband frequency signal carrying bolt loosening status and temperature information. This significantly breaks through the communication distance limitation of traditional passive sensing and realizes far-field non-contact monitoring.

[0052] By using a parallel design of piezoelectric sensing units, the mapping sensitivity between capacitance change and bolt loosening state is improved. Combined with a passive thermally induced drift suppression circuit, measurement errors caused by environmental parameters such as temperature are accurately compensated, ensuring high-precision monitoring under complex working conditions.

[0053] Based on the improved design of standard metal flat washers, there is no need to modify the original bolt connection structure. It supports direct replacement or stacking installation, realizing the deep integration of fastening and sensing functions. Moreover, the core components are universally selected and the processing technology is mature, reducing industrialization costs.

[0054] It has strong adaptability to harsh environments. Specifically, the embedded area is filled with highly insulating and temperature-resistant organic silicone. The circuit and sensing unit adopt an insulating and vibration-proof encapsulation design, which can resist complex and harsh environments such as vibration, impact, and temperature changes, and ensure long-term stable operation. Attached Figure Description

[0055] Figure 1 This diagram illustrates the structure of a pressure pad;

[0056] Figure 2 A schematic diagram of a gasket substrate is shown.

[0057] Figure 3 A schematic diagram of the topology of a frequency response passive network is shown.

[0058] Figure 4 It indicates about Figure 3 Detailed circuit connection diagram Figure 1 ;

[0059] Figure 5 It indicates about Figure 3 Detailed circuit connection diagram Figure 2 ;

[0060] Figure 6 It indicates about Figure 3 Detailed circuit connection diagram Figure 3 ;

[0061] Figure 7 It indicates about Figure 3 Detailed circuit connection diagram Figure 4 ;

[0062] Figure 8 It indicates about Figure 3 Detailed circuit connection diagram Figure 5 ;

[0063] Figure 9 It indicates about Figure 3 Detailed circuit connection diagram Figure 6 ;

[0064] Figure 10 This diagram illustrates the assembly of a washer and a bolt and nut.

[0065] Figure 11 A schematic diagram showing the relationship between frequency and torque under different ambient temperatures is presented. Detailed Implementation

[0066] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0067] In this article, "multiple" refers to two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A alone, A and B simultaneously, or B alone. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0068] Example 1

[0069] like Figure 1 and Figure 2 The overall structure of the passive pad pressure sensor based on parametric negative resistance self-excitation is shown in the figure. This embodiment discloses a passive pad pressure sensor based on parametric negative resistance self-excitation. Its core structure includes a pad area, a piezoelectric sensing unit 20 and a different frequency response passive network 30.

[0070] The gasket area includes the pressure gasket 09 and the gasket substrate 10.

[0071] The pressure pad 09 is installed by aligning it with the pad base 10 through several pressure cross-shaped platforms 091, and a piezoelectric sensing unit 20 is sandwiched between the installation points. Figure 2 As shown, S111 is the area used to embed the piezoelectric sensing unit 20. The piezoelectric sensing unit 20 is, for example, a piezoelectric perovskite transducer. During installation, several pressure crosses 091 at the pressure pad 09 are aligned with the shallow cylindrical grooves 111 at the pad base 10 and installed, with a piezoelectric perovskite transducer sandwiched in the middle.

[0072] The gasket substrate 10 is an improvement upon the GB / T97.1-2002 standard metal flat washer. The embedded area is filled with silicone rubber as a backing material, and after filling, it is flush with the original surface of the gasket substrate 10 to ensure that it does not affect the tightening effect after bolt assembly. The gasket substrate 10 embeds a piezoelectric sensing unit 20 and a frequency response passive network 30 to modulate the bolt loosening state signal and the ambient temperature signal, respectively.

[0073] The passive network 30 with different frequency response is connected to the piezoelectric sensing unit 20 by wires. The wire routing path is embedded in the backing material through grooves, and the solder joints are wrapped and protected by epoxy glue.

[0074] like Figure 3 The diagram shows the topology of a passive frequency response network. An external signal transceiver transmits a 200MHz-2GHz radio frequency wireless activation energy field f0. The miniature antenna 31 receives this wireless activation energy field, which is then transmitted through an impedance matching system 32 (e.g., a 50Ω design) and a high-frequency inductor L. S The signal is transmitted to the input terminal of the parametric reactance modulation core 33.

[0075] The output terminal of the parametric reactance modulation core 33 in this application is connected to the elastic electromagnetic resonant cell 34. The parametric reactance modulation core 33 is a combination of two silicon-germanium heterojunction bipolar transistors (HBTs), silicon-based enhancement-mode MOSFETs (MOSFETs), or gallium arsenide enhancement-mode (pHEMTs), with one of its terminals grounded to achieve operating state regulation.

[0076] Among them, the piezoelectric perovskite transducer C piezo As a piezoelectric sensing unit and a fixed inductor L qAn elastic electromagnetic resonant cell is formed, and its capacitance changes with the axial load of the bolt, causing the resonant frequency f1 to change. The parametric reactance modulation core 33 convolves f0 and f1 to generate a modulated echo signal of (f0±f1) and transmits it through the miniature antenna 31.

[0077] The passive thermally induced drift suppression circuit 35 is connected to the parametric reactance modulation core 33, and its temperature-sensitive capacitor C T Unaffected by the looseness of the bolts, the resonant frequency of this circuit only changes with the ambient temperature and differs from f1 by 30-100MHz, thus avoiding confusion between the two signals.

[0078] As can be seen, the embodiments of this application, through the partitioned design and deep integration of the gasket substrate, achieve the integration of fastening and sensing functions without reducing the mechanical strength of the gasket or changing the bolt fastening performance; based on the parametric negative resistance self-excitation mechanism, it completely eliminates the dependence on batteries and chips, solves the pain points of high start-up threshold and short communication distance of existing passive sensing technologies, and has the ability to monitor the bolt throughout its entire life cycle in harsh environments.

[0079] Example 2

[0080] This embodiment, based on embodiment 1, further supplements the content on gasket substrate design, passive network parameters for different frequency responses, characteristics of thermally induced drift suppression circuit, selection of backing material, and gasket compatibility and installation method, as detailed below.

[0081] Regarding the compatibility and installation method of the gasket base, the gasket base 10 is compatible with bolts of M12-M27 specifications. This embodiment uses M20 bolts as the application object. The type of standard metal flat washer can be selected according to the current standards. It can be a Class A flat washer conforming to GB / T97.1-2002, a Class A large washer conforming to GB / T96.1-2002, or a washer that meets the requirements of other national standards, or a custom-made improved flat washer in use, etc. This embodiment does not limit this.

[0082] The installation method supports the following two scenarios.

[0083] It can directly replace the existing bolted connection structure without altering the original bolted connection, and directly replace ordinary round metal flat washers, such as... Figure 10 As shown, Figure 10This diagram illustrates an assembly of a washer and bolt / nut. Utilizing the built-in frustum 112 within the annular washer base groove of bolt 114 and nut 113, the bolt preload is applied only to the washer base. A partially enlarged area on the right side of the diagram shows the mating structure of the smart washer with nuts 113 and bolt 114. The frustum 112 within the washer base groove of the smart washer mates with the corresponding parts of nuts 113 and bolt 114, ensuring that the bolt preload is applied only to the corresponding embedded area within the washer base, preventing external pressure. This assembly method can directly replace ordinary round flat metal washers without altering the original bolt connection structure.

[0084] In the case of stacked installation, it is placed on top of the original metal washer and transmits part of the preload through the original metal washer to ensure that the piezoelectric sensing unit 20 can accurately sense the axial load without affecting the overall fastening performance of the bolt (the preload of the M20 bolt can reach 100KN, far exceeding the requirements of conventional low load scenarios).

[0085] Furthermore, such as Figure 2 As shown, several shallow cylindrical grooves 111 are formed at the gasket substrate 10, and are evenly distributed along the part shown in the figure.

[0086] For example, in the shallow cylindrical groove 111, laser processing is used, with a dimensional tolerance of ±0.05mm. The groove wall is insulated (to prevent the metal gasket substrate from conducting electricity and interfering with the circuit), and the groove opening is chamfered (to avoid the concentrated axial load of the bolt causing the groove wall to crack).

[0087] It is necessary to emphasize the role of the frustum 112 inside the gasket substrate groove in this application. First, it is used for positioning, as the frustum 112 inside the gasket substrate groove is used for positioning without contacting the piezoelectric sensing unit 20; second, it is used for force transmission, as it works in conjunction with the pressure cross 091 of the pressure gasket 09 and the shallow cylindrical groove 111 to engage and transmit force through the silicone.

[0088] The piezoelectric sensing unit 20 uses a piezoelectric perovskite transducer and is provided with a channel 211. The piezoelectric sensing unit 20 is fixed in a shallow cylindrical groove 111, and the channel 211 serves as a connection between the various piezoelectric sensing units 20 to achieve series or parallel connection. In the figure, the area marked by the frustum 112 in the gasket substrate groove is also indicated by bright blue to show the channel 211, which is the connection between the piezoelectric ceramic and the crystal in series or parallel connection.

[0089] The piezoelectric sensing unit 20 is installed by fixing it to the inner frustum 112 of the substrate groove with silicone mating pad, and the piezoelectric sensing unit 20 is not in contact with the groove wall of the shallow cylindrical groove 111.

[0090] In addition, such as Figure 2As shown, within the annular fan-shaped groove 121 of the gasket base 10, two small shafts are illustrated as limiters 213, used to restrict the position of the embedded circuit board for easy installation. The red arrows indicate the installation method of the pressure gasket 09 and the gasket base 10; the pressure gasket 09 is at the top, and its pressure frustum aligns with the shallow cylindrical groove 111 of the gasket base 10. It should be noted that after installation, the pressure frustum will not contact the piezoelectric perovskite transducer; the force is transmitted through the silicone rubber.

[0091] In addition, such as Figure 2 As shown, a ring-shaped groove 121 is also provided at the gasket substrate 10, with an example central angle of 60 degrees, a radial width of 6 mm, and a depth of 1.5 mm. The exemplary groove wall roughness Ra≤1.6μm (to ensure smooth potting), and the groove wall is insulated (e.g., using a polyimide coating with a thickness of 50μm).

[0092] A custom-designed circuit board is embedded in the annular fan-shaped slot 121. The passive frequency response network 30 and the passive thermally induced drift suppression circuit 35 are independently packaged in two areas of the circuit board (to avoid electromagnetic interference between circuits). The circuit board is fixed by filling with silicone. After filling, the upper surface of the circuit board is flush with the original surface of the pad substrate 10.

[0093] Furthermore, such as Figure 3 As shown, the frequency response passive network 30 includes a miniature antenna 31, an impedance matching system 32, and a high-frequency inductor L. S The system includes a semiconductor parametric reactance modulation core 33, an elastic electromagnetic resonant cell 34, and a passive thermally induced drift suppression circuit 35. The impedance matching system 32 includes common π-type, T-type, and inverted L-type transistors. The parametric reactance modulation core 33 includes a combination of silicon-germanium heterojunction bipolar transistors (HBTs), silicon-based enhancement-mode MOSFETs, and gallium arsenide enhancement-mode pHEMTs. The passive thermally induced drift suppression circuit (35) is used to generate an echo signal carrying ambient temperature information.

[0094] The parametric reactance modulation core 33 is connected to the passive thermally induced drift suppression circuit 35.

[0095] The miniature antenna 31 is a loop antenna integrated on the edge of the circuit board. It is used to receive external 200MHz-2GHz radio frequency wireless activation energy field f0 and reflect modulated echo signals.

[0096] The impedance matching system 32 is designed with a characteristic impedance of 50Ω (using a π-type matching circuit, 0402 packaged NP0 capacitors, and multilayer inductors) to ensure efficient energy transmission between the antenna and subsequent circuits.

[0097] High-frequency inductor L SA high-frequency multilayer inductor is selected, with its inductance value adapted to the frequency of the wireless activation energy field, and is connected in series between the impedance matching system 32 and the input terminal of the parametric reactance modulation core 33.

[0098] Furthermore, if the parametric reactance modulation core 33 with semiconductor is a transistor or field-effect transistor, its control electrode is grounded to achieve operation state regulation. Moreover, the parametric reactance modulation core 33 is selected to be suitable for radio frequency operation. Under the drive of an external strong radio frequency wireless activation energy field, it operates in a strong nonlinear capacitance region. Its equivalent capacitance changes drastically with the high-frequency AC voltage, generating an active negative resistance to offset the loop loss.

[0099] The elastic electromagnetic resonant cell 34 is composed of a fixed inductor LP (e.g., 100nH) connected in parallel with a piezoelectric sensing unit 20, where the piezoelectric sensing unit 20 acts as a piezoresistive capacitor C. piezo Access.

[0100] Furthermore, Figures 4 to 9 It shows about Figure 3 The specific circuit connection diagram is a "one-channel dual-transistor" circuit connection diagram of a different frequency response passive network, containing six "one-channel dual-transistor" sub-diagrams—corresponding to the pairwise combinations of three types of devices: silicon-germanium heterojunction bipolar transistors (HBTs), silicon-based enhancement-mode MOSFETs (MOSFETs), and gallium arsenide enhancement-mode pHEMTs (six sub-diagrams are derived due to different device connection orders, with a total of nine arrangements; the order of different types of devices can be interchanged, so six are shown). Each sub-diagram adopts a single-channel integration method of "two devices sharing one pole": the two devices are connected to a high-frequency inductor. Between the elastic electromagnetic resonant cell or the passive thermally induced drift suppression circuit, the control terminals of some devices are grounded to regulate the operating state.

[0101] The advantages of this design are as follows: by increasing circuit nonlinearity through the collaborative work of dual devices, the energy threshold for circuit oscillation is significantly reduced, and the power requirement for external radio frequency wireless activation energy field is reduced; at the same time, the integrated design of "one channel, two tubes" simplifies the circuit structure, reduces the space occupied by the devices, and adapts to the compact size requirements of the pad-type sensor; it also reduces redundant components and lowers costs and failure risks by integrating passive sensing of bolt loosening status and passive sensing of ambient temperature; it can further reduce signal transmission loss and significantly improve the amplitude of the sideband frequency signal carrying preload and temperature information, which not only enhances the signal stability in harsh environments and reduces the impact of environmental variables on detection parameters, but also breaks through the communication distance limitations of existing passive sensors and realizes far-field non-contact monitoring.

[0102] In one possible implementation, this embodiment uses two piezoelectric perovskite transducers connected in parallel (to increase the capacitance change and enhance sensitivity), with the capacitance value changing linearly with the state of bolt loosening.

[0103] Furthermore, the varistor Cpiezo The steps of the mapping algorithm to the bolt loosening state are as follows.

[0104] Step 401: Define physical parameters, set the total bolt preload applied to the bolt as F (F directly determines the bolt loosening state), force diversion coefficient k (k<1), cross-sectional area A and thickness h of the piezoelectric crystal, piezoelectric constant d, and dielectric constant ε of the piezoelectric material;

[0105] Step 402, stress calculation, using the formula Calculate the actual pressure exerted on a single piezoelectric crystal, and then use the formula... Calculate the internal stress of the crystal;

[0106] Step 403, charge calculation, based on the piezoelectric effect principle, using the formula The total surface charge of the crystal was derived and simplified by substituting it into the stress formula. This achieves a proportional mapping between the amount of charge and the state of bolt loosening;

[0107] According to the principle of piezoelectric effect, when a piezoelectric material is subjected to pressure, a charge density is generated on its surface. The charge density is equal to the piezoelectric constant multiplied by the stress.

[0108] Therefore, the total charge on the entire crystal surface (charge density multiplied by area):

[0109]

[0110] In the first step Substituting the formula into the above equation:

[0111]

[0112] As can be seen, cross-sectional area This is eliminated from both the numerator and denominator, resulting in the simplified formula for charge:

[0113]

[0114] It can be proven that the amount of charge generated is directly proportional to the bolt preload and is independent of the crystal area.

[0115] Step 404, equivalent capacitance calculation, based on the parallel plate capacitor model, using the formula Calculate the equivalent capacitance of the piezoelectric sensing unit;

[0116] Step 405, Capacitor-bolt loosening state mapping, combining charge Q and equivalent capacitance. The relationship between capacitance changes and bolt axial load changes is indirectly reflected by capacitance changes, providing a physical basis for subsequent frequency mapping.

[0117] Specifically, a crystal can be considered as a capacitor. And charge has accumulated on this capacitor. Then the potential difference across the equivalent capacitor is: Substitute and : After simplification, the final relationship between voltage and force is obtained: .

[0118] It should also be noted that the resonant frequency variation ranges of the elastic electromagnetic resonant cell 34 and the passive thermally induced drift suppression circuit 35 belong to different frequency band formation range differences, which are used to avoid signal confusion.

[0119] Furthermore, the backing material is made of silicone (such as model E-51, which has high insulation and temperature resistance), which is filled into the shallow cylindrical groove 111 and the annular fan-shaped groove 121. After filling, it is smoothed with a scraper to ensure that it is flush with the original surface of the pad substrate 10. The wire routing path of the piezoelectric sensing unit 20 is embedded in the fine groove milled on the outside of the pad substrate 10. The wires and solder joints are all wrapped with silicone, which is used to achieve insulation, fixation and protection, and to prevent vibration from causing the wires to fall off or the solder joints to oxidize.

[0120] As can be seen, the detailed design disclosed above not only ensures the structural integrity and parameter determinism of the sensor, but also further optimizes its performance. These improvements include: the area ratio of the shallow cylindrical groove and the chamfer design ensure mechanical strength; the anti-adhesion fixation of the piezoelectric unit prevents damage; impedance matching and parametric reactance modulation core improve energy utilization; the frequency difference design of the thermally induced drift suppression circuit eliminates temperature drift interference; and the flexible installation method and compatible specifications enhance engineering applicability. In summary, this design comprehensively solves the problems of difficult integration of sensing elements and gaskets, high oscillation threshold of passive circuits, and susceptibility to interference in measurements in existing technologies, achieving high-precision and high-reliability monitoring of bolt loosening status.

[0121] Example 3

[0122] This embodiment provides a method for monitoring bolt loosening, which is applied to the passive gasket-type pressure sensor based on parametric negative resistance self-excitation in Embodiments 1 and 2. The specific steps are as follows.

[0123] Step 1: The external signal transceiver continuously transmits a 200MHz-2GHz radio frequency wireless activation energy field f0 to the sensor. The passive thermally induced drift suppression circuit 35 of the sensor generates self-excited oscillation under the radio frequency excitation and transmits an echo signal carrying temperature information (corresponding to its resonant frequency).

[0124] After receiving the echo signal, the external signal transceiver extracts the resonant frequency value and, in conjunction with a frequency-temperature data mapping table obtained in advance through numerous constant-temperature experiments in the laboratory, determines the current ambient temperature (e.g., if the echo frequency is f). t (The corresponding data corresponds to 25℃ in the table).

[0125] Step 2: Based on the ambient temperature (25℃) determined in Step 1, select the matching curve from a set of preset frequency-load relationship curves (each set of frequency-load spectrum relationship curves corresponds to a specific temperature, and the frequency-load spectrum relationship curves are obtained by laboratory temperature-load coupling experiments, covering the sensor's operating temperature and load range).

[0126] Step 3: Receive the sideband frequency signal reflected by the passive network with different frequency response, extract the sum frequency or difference frequency component, substitute it into the "frequency-load" relationship curve corresponding to 25℃ selected in Step 2, and calculate the current bolt loosening state.

[0127] Therefore, by first obtaining the ambient temperature and matching the corresponding frequency-load curve through a passive thermally induced drift suppression circuit, the interference of temperature changes on the measurement of bolt loosening status is effectively eliminated, and the measurement error problem caused by temperature drift is solved. The quantitative monitoring method based on frequency sideband drift has a stronger ability to resist parasitic parameters and electromagnetic interference in the metal environment compared with traditional signal strength (RSSI) or simple LC resonant frequency detection, ensuring real-time, online high-precision monitoring of bolt loosening status under complex working conditions.

[0128] Example 4

[0129] To further disclose the core working mechanism of the passive network with different frequency response in the above embodiments, the theoretical calculation process of parametric negative resistance self-excitation, bolt loosening state-frequency mapping and signal modulation is further disclosed below, providing a basis for the feasibility of the technical solution. At the same time, in order to better provide the implementation principle, the parametric reactance modulation core is used as a MOS transistor as an example. The input terminal of the parametric reactance modulation core corresponds to the drain of the MOS transistor, the output terminal of the parametric reactance modulation core corresponds to the source of the MOS transistor, and the ground terminal of the parametric reactance modulation core is grounded, corresponding to the gate of the MOS transistor.

[0130] In the above embodiments, the parametric reactance modulation core is mentioned as being adapted for radio frequency operation. Under the drive of an external strong radio frequency wireless activation field, it operates in a strongly nonlinear capacitive region. In one example, its nonlinear charge-voltage relationship satisfies the Taylor series expansion characteristic, and the time-varying capacitance changes periodically with the frequency of the external radio frequency excitation pump signal. In the specific calculation logic, the nonlinear charge-voltage relationship of the MOS transistor under strong signal drive is defined. Taylor series expansion:

[0131] ,in, It is a static capacitor. This is a first-order nonlinear coefficient. The resulting time-varying capacitance... for: ;

[0132] When a strong pump signal is input When applied to a MOSFET, the time-varying capacitance can be approximated as: ,in, It is the angular frequency of the pump signal (external radio frequency wireless activation energy field), i.e. =2πf 0， f0 is the frequency of the external radio frequency wireless activation energy field; Proportional to pump amplitude Assume there is a weak, low-frequency disturbance current in the circuit. The frequency is Due to the nonlinear mixing of the system, there will be three main frequency components in the circuit, namely the signal frequency. Pump frequency Idle frequency (Note: It also exists, but for the sake of simplifying the calculation, we mainly consider the difference frequency, where This is the angular frequency of the weak, low-frequency disturbance current (i.e., the local oscillator angular frequency of the LC resonant circuit, which is related to the looseness of the bolts). Therefore, it can be seen that the local oscillator angular frequency of the LC resonant circuit is determined by the fixed inductor L. P The inductance and the varistor C piezo The capacitance value is determined by the oscillator frequency, and the local oscillator frequency has a monotonically varying relationship with the state of bolt loosening. According to Kirchhoff's voltage law, the voltage across the MOSFET... With current The relationship is described by the following formula:

[0133] .

[0134] Write the voltage and current components of each frequency component in phasor form:

[0135] , ,use By expanding and extracting the frequency components, we can establish and The coupling matrix equation between them:

[0136] ,in, For signal frequency The corresponding voltage phasor (characterized by) (Voltage amplitude and phase at frequency) For idle frequency ( = - The corresponding voltage phasor (characterized by) (Voltage amplitude and phase at frequency) * indicates idle frequency voltage phasor The conjugate of complex numbers, For signal frequency The corresponding current phasor (characterized by) (Amplitude and phase of current at frequency), I i For signal frequency The corresponding current phasor (characterized by) (Amplitude and phase of current at frequency), with * indicating I. i The conjugate of complex numbers.

[0137] The calculation of input impedance and parametric negative resistance is further explained below.

[0138] For signal frequency current : ,in, The conjugate of the idler frequency voltage originates from... The feature parameter convolution response term.

[0139] For idle frequency current (Taking the conjugate form): In the idle frequency At this point, the external circuit must be closed to form a loop. Series inductor For idle frequency The presented impedance is Therefore, in the idler circuit, the voltage... With current The relationship is constrained by external impedance constraints: ,in, This refers to the idle frequency Below, the "total impedance of the external circuit" is measured from the two ends of the nonlinear capacitor of the MOSFET.

[0140] To simplify mathematical calculations, we assume the external circuit is primarily inductive and neglect resistance. Use directly To approximate equality, substitute this constraint into the above current equations and eliminate it through algebraic operations. Solve and The ratio of the two values ​​yields the input impedance. After calculation, the input impedance is approximately:

[0141] .

[0142] When considering series inductance When the idler circuit approaches resonance or exhibits inductive behavior, we can derive a formula based on the real part of the impedance: Perform real part extraction, where, The quality factor (Q factor), representing the idler circuit, is a parameter used to characterize the loss of the idler circuit. A higher Q value indicates lower idler circuit loss. This is expressed as taking the imaginary part of a complex number. Observing the above equation, in series inductors... Under the condition of existence, and > When the real part of the impedance is negative, an active negative resistance will appear.

[0143] .

[0144] The above formula shows that the stronger the nonlinearity, The larger the value, the greater the absolute value of the negative resistance, which can offset the circuit loss.

[0145] The calculation of the minimum starting power threshold will be explained below.

[0146] The equivalent capacitance of the parametric reactance modulation core changes with the high-frequency AC voltage, and this change in capacitance is correlated with the high-frequency inductance L. S The coupling effect of the inductance generates an active negative resistance. The absolute value of the active negative resistance is proportional to the square of the capacitance change and the high-frequency inductance L. S The inductance value is positively correlated and used to offset loop losses by generating active negative resistance to meet the oscillation start-up conditions. In the specific calculation logic, the calculated active negative resistance is combined with the parallel LC load for stability analysis. Assume the parallel LC circuit at the resonant frequency... The equivalent loss resistance at the point is According to the Barkhausen criterion, the system's starting condition is that the total damping ≤ 0. Substituting into the aforementioned negative resistance formula, we get: ,in, For input RF power, proportional to , The product of the frequency ratio term and the idler impedance term in the formula is derived from the real part of the impedance, which simplifies the process. , Where η is the input RF power. With (ΔC) 2 The proportionality coefficient between them (i.e.) With (ΔC) 2 (a multiple constant), used to convert (ΔC) 2 The change corresponds to the input RF power The value of this value is then used in the calculation of κ (a parameter related to the oscillation condition) (i.e., the corresponding value). By changing the above formula, we get:

[0147]

[0148] That is, there exists a minimum starting power threshold.

[0149] This formula is theoretically proven to be true as long as the nonlinearity of the MOSFET is strong enough (i.e., Large enough) and inductance With proper parameter selection, the oscillation threshold can be reduced to an extremely low energy level.

[0150] Next, we perform bolt loosening state-frequency mapping and signal convolution calculation.

[0151] In the above embodiments, the parametric reactance modulation kernel with semiconductor also has a convolution function, which is used to frequency couple the pump signal of external radio frequency excitation with the local oscillator signal of LC resonant circuit to generate a sideband frequency signal containing the sum frequency and difference frequency of the pump signal and the local oscillator signal. The sideband frequency also includes the relevant frequency of the passive thermally induced drift suppression circuit 35. The sideband frequency signal is reflected and transmitted through a micro antenna, and the offset of the sideband frequency is linearly related to the change in the axial load of the bolt, which is used to reversely determine the loosening state of the bolt.

[0152] Specifically, once the above oscillation conditions are met, a stable low-frequency voltage self-excited oscillation is established in the circuit, which is expressed as: .in, It is directly related to the state of bolt looseness. This is the amplitude of the low-frequency voltage self-oscillation signal (characterizing the intensity of the oscillation signal). At this time, the MOSFET not only acts as a negative resistance generator but also functions as a characteristic parameter convolution. The output current of the MOSFET... This includes the product of the pump signal and the self-excitation signal. Assume the MOSFET's transfer characteristic follows a square-law approximation:

[0153] ,in, It is the minimum gate-source voltage required for a MOSFET to transition from the "off" state to the "on" state. It is a constant determined by the manufacturing process and physical dimensions of the MOSFET. Substituting the superimposed pump signal and self-oscillation signal into the MOSFET input voltage... :

[0154] Then bring it into In the middle, expand the squared terms and focus on the cross-product terms:

[0155]

[0156]

[0157] Using the product-to-sum formula of trigonometric functions:

[0158] ,set up That is, the main frequency of the wireless activation energy field is ; That is, the frequency at which new information about the loosening of bolts is generated in the circuit is Based on the above calculations, a signal located at [location missing] must be observed in the spectrum of the reflected echo. and The sideband components at that location, and these frequency components are emitted through the pad antenna. Therefore, by monitoring... The echo signal can be used to achieve passive wireless sensing of bolt loosening status information.

[0159] Furthermore, the logic for suppressing heat-induced drift is disclosed.

[0160] In actual testing, it was found that... The frequency value does not only change with bolt load, but also with temperature. Therefore, relying solely on... The current value cannot uniquely determine the bolt's looseness state; the current temperature needs to be known, and temperature compensation based on experimental data is required. The passive thermally induced drift suppression circuit, with the same structure as the aforementioned passive network for heterogeneous response, does not bear the bolt's axial load. Therefore, its capacitance value is only related to the current temperature; that is, the resonant frequency of its parallel LC circuit changes with the current temperature. Furthermore, the frequency range of the parallel resonant LC circuit in this circuit does not overlap with the frequency range of the passive network for heterogeneous response, preventing the inability to distinguish between echoes carrying load information and temperature information.

[0161] The applicant conducted numerous experiments in the laboratory and obtained data on the frequency variation with temperature, as shown in the figure. Figure 11 A schematic diagram showing the relationship between frequency and torque under different ambient temperatures is presented.

[0162] Figure 11 In the diagram, the horizontal axis represents torque (unit: ...). The vertical axis represents frequency (unit: MHz). The different styles of curves in the graph correspond to the relationship between frequency and torque at different ambient temperatures, such as -20℃, -10℃, 0℃, 10℃, 20℃, 30℃, 40℃, 50℃, 60℃, and 70℃. It can be seen that in actual measurement, the applicant's operation process is to first determine the ambient temperature, then select the corresponding frequency-load change relationship curve according to the ambient temperature, and confirm the current accurate bolt loosening status based on the curve and the echo carrying the bolt loosening status information.

[0163] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0164] It should be noted that the core calculation principles of the parametric negative resistance self-excitation mechanism, the bolt loosening state-frequency mapping relationship, and the thermally induced drift suppression logic upon which this invention relies have been fully implemented through the aforementioned specific technical solutions. Specifically, through the partitioned integrated design of the gasket substrate, the selection of components (parametric reactance modulation core, high-frequency inductor, resonant load, etc.) and topology connection of the heterogeneous frequency response passive network, the application of the varistor characteristics of the piezoelectric sensing unit, and the step-by-step process for monitoring the bolt loosening state (temperature calibration, frequency extraction, load matching), a reproducible technical solution has been formed. The technical implementation path, circuit structure, and monitoring method supported by the aforementioned calculation principles are all fully covered by the technical features defined in the claims of this invention, and the industrialization implementation methods of the related technical solutions and core principles are all within the protection scope of this invention.

[0165] Those skilled in the art will understand that all or part of the steps of the above embodiments can be implemented by hardware, or by a program instructing related hardware. The program can be stored in a computer-readable storage medium, such as a read-only memory, a disk, or an optical disk. The above descriptions are merely optional embodiments of this application and are not intended to limit the application. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A passive pad-type pressure sensor based on parametric negative resistance self-excitation, characterized in that, It includes a gasket area, a piezoelectric sensing unit (20), and a frequency response passive network (30). The gasket area includes a pressure gasket (09) and a gasket substrate (10); The pressure pad (09) is aligned and installed with the pad base (10) by setting a plurality of pressure crosses (091), and the piezoelectric sensing unit (20) is sandwiched between the installation. The gasket substrate (10) is based on a standard metal flat washer, and the piezoelectric sensing unit (20) and the frequency response passive network (30) are embedded therein, and the embedded area is filled with backing material. The passive network (30) with different frequency response is connected to the piezoelectric sensing unit (20) and is used to receive an external radio frequency wireless activation energy field and generate a modulated echo signal carrying information about the loosening state of the bolts. At least one shallow cylindrical groove (111) is provided at the gasket substrate (10); The piezoelectric sensing unit (20) is a piezoelectric perovskite transducer and is provided with a channel. The piezoelectric sensing unit (20) is fixed in the shallow cylindrical groove (111). The channel serves as a connection between the various piezoelectric sensing units (20) to achieve series or parallel connection. The gasket substrate (10) is also provided with an annular fan-shaped groove (121) for embedding a custom-designed circuit board. The groove wall is insulated and meets the preset roughness requirements. The frequency response passive network (30) is encapsulated on the circuit board. The circuit board is fixed in the annular fan-shaped groove (121) by the backing material and is provided with several limiters to limit the position of the embedded frequency response passive network (30). The frequency response passive network (30) includes a miniature antenna (31), an impedance matching system (32), and a high-frequency inductor L. S The system includes a parametric reactance modulation core (33) with semiconductors, an elastic electromagnetic resonant cell (34), and a passive thermally induced drift suppression circuit (35). The impedance matching system (32) includes π-shaped, T-shaped, and inverted L-shaped types. The parametric reactance modulation core (33) includes a combination of silicon-germanium heterojunction bipolar transistors (HBT), silicon-based enhancement-mode MOSFETs (MOSFETs), and gallium arsenide enhancement-mode (pHEMT). The passive thermally induced drift suppression circuit (35) is used to generate an echo signal carrying ambient temperature information. The parametric reactance modulation core (33) is connected to the passive thermally induced drift suppression circuit (35); The miniature antenna (31) serves as the radio frequency input / output terminal, and the impedance matching system (32) and the high-frequency inductor L are connected in series in sequence. S It is then connected to the input terminal of the parametric reactance modulation core (33), and the output terminal of the parametric reactance modulation core (33) is connected to the elastic electromagnetic resonant pool (34) and the impedance matching system (32).

2. The sensor according to claim 1, characterized in that, The impedance matching system (32) is designed for 50Ω; The passive network (30) with different frequency response adopts an integrated configuration structure of "one channel and two transistors". By integrating the parametric reactance modulation core (33) composed of two-by-two silicon-germanium heterojunction bipolar transistors (HBT), silicon-based enhancement-mode MOSFETs (MOSFETs) and gallium arsenide enhancement-mode (pHEMT) with the passive thermally induced drift suppression circuit (35) in the same circuit path, a single circuit is formed to realize the dual-function configuration of bolt loosening status signal sensing and ambient temperature signal acquisition. The "one channel and two transistors" configuration structure is used to reduce the circuit oscillation conditions, reduce the power of the required external radio frequency wireless activation energy field, and at the same time increase the output amplitude of the sideband frequency signal carrying bolt loosening status information and ambient temperature information.

3. The sensor according to claim 2, characterized in that, The parametric reactance modulation core (33) is adapted to radio frequency operation. Under the drive of an external strong radio frequency wireless activation energy field, it operates in a strong nonlinear capacitance region. Its nonlinear charge-voltage relationship satisfies the Taylor series expansion characteristics. Its equivalent capacitance changes periodically with the periodic action of the pump signal of the external radio frequency wireless activation energy field. The equivalent capacitance of the parametric reactance modulation core (33) changes with the high-frequency AC voltage, and the capacitance change is correlated with the high-frequency inductance L. S The coupling effect of the inductance value generates an active negative resistance, the absolute value of which is proportional to the square of the capacitance change and the high-frequency inductance L. S The inductance value is positively correlated and is used to offset the circuit loss by generating the active negative resistance to meet the oscillation condition; wherein, the steps of the parametric negative resistance calculation algorithm of the parametric reactance modulation core (33) are as follows: Step 301: Define physical parameters and set the static capacitance of the parametric reactance modulation core. First-order nonlinear coefficients angular frequency of external radio frequency excitation pump signal Amplitude High-frequency inductor L S The inductance value, the angular frequency of the weak low-frequency disturbance current in the circuit. The angular frequency Let be the local oscillator frequency of the LC resonant circuit, where =2πf 0， f0 is the frequency of the external radio frequency wireless activation energy field; Step 302, Time-varying capacitance calculation, based on the characteristics of Taylor series expansion, using the formula Calculate the time-varying capacitance and substitute it into the pump signal. (t)= We obtain C(t) = C0 + ΔCcos( ), where ΔC is proportional to the pump amplitude. ; Step 303: Active negative resistance is generated, through the capacitance change ΔC and the high-frequency inductance L. S The coupling effect of inductance, based on the formula The absolute value of the active negative resistance is positively correlated with the square of the capacitance change and the inductance of the high-frequency inductor LS. Step 304, Determine the oscillation start-up conditions, and set the parallel LC circuit at the resonant frequency. Equivalent loss resistance at the point According to the Backhausen criterion, through the formula Determine the oscillation state, among which For input impedance, The real part of the input impedance is the contribution of the real part corresponding to the active negative resistance. When this condition is met, the active negative resistance cancels out the loop loss and achieves self-excitation.

4. The sensor according to claim 2, characterized in that, The elastic electromagnetic resonant cell (34) includes a fixed inductor L P and the piezoelectric sensing unit (20), the piezoelectric sensing unit (20) serving as a piezoresistive capacitor C piezo The connection circuit is connected to the fixed inductor L. P Parallel connection forms an LC resonant circuit; where, The local angular frequency of the LC resonant circuit is determined by the fixed inductance L. P The inductance and the varistor C piezo The capacitance value is determined by both factors, and the local oscillator angular frequency has a monotonic mapping relationship with the state of bolt loosening; The number of the piezoelectric sensing units (20) is one or more, and the multiple piezoelectric sensing units (20) are connected in series or in parallel to improve the mapping sensitivity between the capacitance change and the bolt loosening state. The varistor C piezo The steps of the algorithm for mapping bolt loosening status are as follows: Step 401: Define physical parameters, set the total bolt preload applied by the bolt as F, the force diversion coefficient k, k<1, the cross-sectional area A and thickness h of the piezoelectric crystal, the piezoelectric constant d, and the dielectric constant ε of the piezoelectric material; Step 402, stress calculation, using the formula Calculate the actual pressure exerted on a single piezoelectric crystal, and then use the formula... Calculate the internal stress of the crystal; Step 403, charge calculation, based on the piezoelectric effect principle, using the formula The total surface charge of the crystal was derived and simplified by substituting it into the stress formula. This achieves a proportional mapping between the amount of charge and the state of bolt loosening; Step 404, equivalent capacitance calculation, based on the parallel plate capacitor model, using the formula Calculate the equivalent capacitance of the piezoelectric sensing unit; Step 405, Capacitor-bolt loosening state mapping, combining charge Q and equivalent capacitance. The relationship between capacitance changes and bolt axial load changes is indirectly reflected by capacitance changes, providing a physical basis for subsequent frequency mapping.

5. The sensor according to claim 3, characterized in that, The semiconductor-based parametric reactance modulation core (33) also has a convolution function, which is used to frequency couple the external RF excitation pump signal with the local oscillator signal of the LC resonant circuit to generate a sideband frequency signal containing the sum frequency and difference frequency of the pump signal and the local oscillator signal. The sideband frequency also includes the relevant frequency of the passive thermally induced drift suppression circuit (35). The sideband frequency signal is reflected and transmitted through a miniature antenna (31), and the offset of the sideband frequency is linearly related to the change in the axial load of the bolt, which is used to reversely determine the loose state of the bolt.

6. The sensor according to claim 2, characterized in that, The resonant frequency variation ranges of the elastic electromagnetic resonant pool (34) and the passive thermally induced drift suppression circuit (35) belong to different frequency bands forming range differences, and the range differences are used to avoid signal confusion.

7. The sensor according to claim 1, characterized in that, The backing material is silicone, which, after filling, is flush with the original surface of the gasket substrate (10); The installation method of the piezoelectric sensing unit (20) includes: The piezoelectric sensing unit (20) is fixed by the inner frustum (112) of the silicone mating pad substrate groove. The piezoelectric sensing unit (20) is not in contact with the groove wall of the shallow cylindrical groove (111). The inner frustum (112) of the pad substrate groove is used for positioning and does not contact the piezoelectric sensing unit (20). It is also used for force transmission. Specifically, it is used to engage with the pressure cross (091) of the pressure pad (09) and the shallow cylindrical groove (111) and transmit force through the silicone mating pad.

8. The sensor according to claim 1, characterized in that, The gasket base (10) is compatible with bolts of M12-M27 specifications; The standard metal flat washer can be installed by directly replacing a regular flat washer or by placing it on top of the original metal washer.

9. A method for monitoring bolt loosening status, applied to the passive gasket-type pressure sensor based on parametric negative resistance self-excitation as described in any one of claims 1-8, characterized in that, The method includes: Receive the echo signal carrying temperature information sent by the passive thermally induced drift suppression circuit in the passive frequency response network to determine the current ambient temperature; The corresponding frequency-load relationship spectrum is selected based on the ambient temperature, wherein the frequency-load relationship curve is obtained by laboratory temperature-load coupling experiment calibration, covering the sensor's operating temperature and load range; The sideband frequency signal reflected by the passive network with different frequency response is received, the sum frequency or difference frequency component is extracted, and the current loosening state of the bolt is determined based on the frequency-load spectrum relationship curve.

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