A dual piezoelectric acoustic emission sensor with self-checking function and system

Abstract

The application discloses a double piezoelectric acoustic emission sensor with self-checking function and a system thereof, and belongs to the technical field of sensors, which comprises a sealed shell, a backing layer arranged at the bottom of the sealed shell, a first layer of a supporting table arranged above the backing layer and used for mounting a first piezoelectric ceramic sheet, the first piezoelectric ceramic sheet used as a transmitting end of a self-checking signal, a first matching layer arranged above the first layer of the supporting table, a second layer of a supporting table arranged above the first matching layer and used for mounting a second piezoelectric ceramic sheet, the second piezoelectric ceramic sheet used as a receiving end of a signal, used for detecting the self-checking signal transmitted by the first piezoelectric ceramic sheet and detecting a vibration signal generated when a detected object is fractured, a second matching layer arranged above the second layer of the supporting table and used for being in contact with the detected object, performing acoustic impedance matching, and transmitting the vibration signal generated when the detected object is fractured to the second piezoelectric ceramic sheet.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of electronic circuits, civil engineering and sensors, and relates to a double piezoelectric acoustic emission sensor with a self-checking function and a system. BACKGROUND

[0002] As a key node of the traffic network, the safety of a bridge is directly related to the safety of public life and property. With the increase of the service life of the bridge and the increasing traffic load, bridge health detection has become a necessary means to ensure the safe operation of the bridge. An acoustic emission sensor can collect vibration sound signals released when cracks in the material expand, concrete cracks or steel structures fatigue, and plays an important role in bridge detection. However, the internal piezoelectric ceramic sheet is easily damaged by physical impact, and has low tolerance to high humidity, corrosion or extreme temperature, so the sensitivity and accuracy of the sensor will gradually decrease or be damaged. SUMMARY

[0003] To solve the above problems, the technical scheme adopted by the application is: a double piezoelectric acoustic emission sensor with a self-checking function, comprising

[0004] a sealed shell;

[0005] a backing layer is arranged at the bottom of the sealed shell;

[0006] a first layer of a supporting platform is arranged above the backing layer and is used for mounting a first piezoelectric ceramic sheet;

[0007] the first piezoelectric ceramic sheet is used as a transmitting end of a self-checking signal;

[0008] a first matching layer is arranged above the first layer of the supporting platform and is used for stable transmission of vibrations generated by the first piezoelectric ceramic sheet in the self-checking process, so as to maximize the utilization rate of vibration energy;

[0009] a second layer of a supporting platform is arranged above the first matching layer and is used for mounting a second piezoelectric ceramic sheet;

[0010] the second piezoelectric ceramic sheet is used as a receiving end of a signal and detects the self-checking signal transmitted by the first piezoelectric ceramic sheet and the vibration signal generated when the detected object breaks;

[0011] a second matching layer is arranged above the second layer of the supporting platform and is used for contact with the detected object, acoustic impedance matching and transmission of the vibration signal generated when the detected object breaks to the second piezoelectric ceramic sheet.

[0012] Further, the first layer of the supporting platform and the second layer of the supporting platform both adopt a stepped double layer of supporting platforms; the stepped double layer of supporting platforms comprises a first supporting platform and a second supporting platform, and the first supporting platform and the second supporting platform are arranged in parallel.

[0013] Further: the backing layer adopts epoxy resin and tungsten powder mixed material as material;

[0014] The first matching layer and the second matching layer adopt epoxy resin and glass microbead mixed material as material;

[0015] Further: the determination process of the resonance frequency of the first piezoelectric ceramic sheet is as follows:

[0016] Different frequency sinusoidal excitation signals are applied to the first piezoelectric ceramic sheet, and the output signal amplitude of the second piezoelectric ceramic sheet is monitored; the frequency of the input signal is gradually scanned, and the change of the received signal amplitude is recorded;

[0017] When the signal amplitude of the second piezoelectric ceramic sheet reaches the maximum, that is, the sensor is in resonance state, the corresponding excitation frequency is the resonance frequency of the first piezoelectric ceramic sheet.

[0018] According to any one of the detection systems of the dual piezoelectric acoustic emission sensor with self-checking function, comprising:

[0019] Signal generation module: for generating alternating signals of different frequencies;

[0020] Dual piezoelectric acoustic emission sensor: for receiving the vibration signals generated by the signal generation module and the vibration signals generated by the detected object, and converting the vibration signals into electrical signals for transmission;

[0021] Pre-signal conditioning module: for amplifying and filtering the signals transmitted by the dual piezoelectric acoustic emission sensor;

[0022] Signal acquisition module: for receiving and collecting the amplified and filtered signals transmitted by the pre-signal conditioning module;

[0023] Master module: for driving the signal generation module to generate alternating signals of different frequencies, and simultaneously processing the electrical signals transmitted by the signal acquisition module in time domain and frequency domain, and judging whether the detected object is abnormal and whether the dual piezoelectric acoustic emission sensor is in working state based on the processed time domain and frequency domain information.

[0024] Further: the process of processing the electrical signals in time domain and frequency domain is as follows:

[0025] The electrical signals are processed in time domain and frequency domain by sliding window to obtain the time domain energy integral And frequency domain energy integral The time domain energy integral And frequency domain energy integral of the first window signal and the second window signal; the first window signal and the second window signal are adjacent signal segments in time.

[0026] Further, the process of judging whether the detected object is abnormal and whether the dual piezoelectric acoustic emission sensor is in working state based on the processed time domain and frequency domain information is as follows:

[0027] The time domain energy integral and the frequency domain energy integral of the first section window signal and the second section window signal are compared respectively to obtain the time domain energy change value of the first section window signal and the second section window signal And the frequency domain energy change value ;

[0028] The time domain energy integral and the frequency domain energy integral of the second section window signal and the third section window signal are compared respectively to obtain the time domain energy change value of the second section window signal and the third section window signal , the frequency domain energy change value ,

[0029] When And , is a jump alarm threshold value, it is judged that the dual piezoelectric acoustic emission sensor has a large energy fluctuation, and an alarm signal is sent out.

[0030] After sending out the self-check signal, the second piezoelectric ceramic sheet signal of the receiving end is analyzed, if the second piezoelectric ceramic sheet signal of the receiving end is consistent with the time and frequency domain signal of the first piezoelectric ceramic sheet of the transmitting end, and the main frequency of the collected signal is consistent with the signal frequency sent out by the signal generating module, it is judged that the dual piezoelectric acoustic emission sensor is intact, otherwise it is judged that the dual piezoelectric acoustic emission sensor is damaged.

[0031] The dual piezoelectric acoustic emission sensor and system provided by the application have the functions of self-checking, monitoring the state of the sensor itself, detecting the bridge and steel cable fracture signals, and specifically are a bridge health detection device based on dual piezoelectric ceramic sheets and having a sensor self-checking function. The positive piezoelectric effect and the inverse piezoelectric effect of the piezoelectric ceramic sheet are combined, the vibration signals generated by the bridge structure fracture can be collected and analyzed, and the sensor structure can be detected by outputting the transmitting end excitation signal and judging the collected signal of the receiving end.

[0032] The application can be used for the structural health monitoring of bridges, steel cables and other key infrastructures, can effectively avoid the abnormal situation of missing alarm caused by the damage of the sensor structure due to the uncontrollable factors, and improves the reliability and real-time performance of the bridge monitoring.

[0033] Compared with the traditional acoustic emission detection scheme, the scheme has higher signal quality and anti-interference ability, and has a self-checking function, which can exclude false alarms caused by sensor damage when encountering uncontrollable factors such as earthquakes. It has higher signal excitation control precision, the main control module drives the signal generation module to generate a frequency stable and amplitude adjustable sine wave signal to complete the sensor state self-checking, and improves the accuracy and reliability of the detection device. BRIEF DESCRIPTION OF DRAWINGS

[0034] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0035] Figure 1 It is a structure diagram of a double piezoelectric acoustic emission sensor with self-checking function;

[0036] Figure 2 It is a schematic diagram of a system of a double piezoelectric acoustic emission sensor with self-checking function.

[0037] Reference signs: 1, backing layer, 2, first matching layer, 3, first piezoelectric ceramic sheet, 4, second matching layer, 5, second piezoelectric ceramic sheet, 6, signal generation module, 7, double piezoelectric acoustic emission sensor, 8, pre-signal conditioning module, 9, signal acquisition module, 10, main control module. DETAILED DESCRIPTION

[0038] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict, and the present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0040] Figure 1 It is a structure diagram of a double piezoelectric acoustic emission sensor with self-checking function;

[0041] A double piezoelectric acoustic emission sensor with self-checking function, comprising the following steps:

[0042] The sealed shell is made of aluminum alloy;

[0043] A backing layer 1 is arranged at the bottom of the sealed shell to reduce the influence of excess vibration and effectively reduce the bottom noise detected by the sensor;

[0044] A first layer of support is arranged above the backing layer 1 for mounting a first piezoelectric ceramic sheet 3;

[0045] The first piezoelectric ceramic sheet 3 is used as a transmitting end of a self-checking signal;

[0046] A first matching layer 2 is arranged above the first layer of support for stable transmission of the vibration generated by the first piezoelectric ceramic sheet 3 during the self-checking process, maximizing the utilization rate of vibration energy;

[0047] A second layer of support is arranged above the first matching layer 2 for mounting a second piezoelectric ceramic sheet 5;

[0048] The second piezoelectric ceramic sheet 5 is used as a receiving end of a vibration signal to detect the self-checking signal emitted by the first piezoelectric ceramic sheet 3 and the vibration signal generated when the detected object breaks;

[0049] A second matching layer 4 is arranged above the second layer of support for contact with the detected object, acoustic impedance matching, and transmission of the vibration signal generated when the detected object breaks to the second piezoelectric ceramic sheet 5.

[0050] The first layer of support and the second layer of support are both stepped double-layer supports, which include a first support and a second support arranged in parallel. The height difference between the first support and the second support is 10mm;

[0051] The stepped double-layer support structure ensures that the first piezoelectric ceramic sheet 3 at the transmitting end and the second piezoelectric ceramic sheet 5 at the receiving end are strictly aligned to ensure stable transmission of the signal.

[0052] The second support is filled with a mixture of glass beads and epoxy resin to reduce impedance mismatch, improve signal coupling efficiency, and improve the signal-to-noise ratio of the received signal. The first support is part of the sealed shell;

[0053] The backing layer 1 is made of a mixture of epoxy resin and tungsten powder to reduce signal reflection;

[0054] The first matching layer 2 and the second matching layer 4 are both made of a mixture of epoxy resin and glass beads.

[0055] The first matching layer 2 adopts an epoxy resin and glass bead mixed material to ensure effective transmission of vibration energy, complete acoustic impedance matching of the transmitting end and the receiving end, and maximize the utilization rate of vibration energy.

[0056] The second matching layer 4 adopts a glass bead and epoxy resin mixture as a material to perform acoustic impedance matching on the second piezoelectric ceramic sheet 5 of the receiving end and the object to be measured, optimize the vibration characteristics, and further improve the detection sensitivity and reliability of the sensor.

[0057] The second matching layer 4 is used for vibration signal coupling,

[0058] The sensor of the present application is suitable for detecting bridge and steel cable fracture signals.

[0059] The double piezoelectric ceramic sheet sensor of the present application adopts the same specification piezoelectric ceramic sheet for the first piezoelectric ceramic sheet 3 and the second piezoelectric ceramic sheet 5, utilizes the positive piezoelectric effect and inverse piezoelectric effect of the piezoelectric ceramic, applies an excitation signal to the first piezoelectric ceramic sheet 3 to generate vibration, transmits the vibration to the receiving end piezoelectric ceramic sheet through the first matching layer 2, and when the excitation signal frequency is equal to the resonance frequency of the first piezoelectric ceramic sheet 3, the vibration amplitude reaches the maximum value. Since the piezoelectric ceramic sheets are of the same specification, the response of the receiving end (second piezoelectric ceramic sheet 5) to the generated vibration also reaches the maximum value.

[0060] A signal generation module 6 is used to apply a series of alternating signals of different frequencies to the transmitting end first piezoelectric ceramic sheet 3, and an oscilloscope is used to observe the voltage change of the receiving end piezoelectric ceramic sheet, so as to find the maximum response frequency (i.e. the resonance frequency). According to the expected working frequency range of the piezoelectric ceramic sheet, the start frequency, end frequency and frequency step value of the signal generation module 6 are set. The output frequency of the signal generator is gradually changed at the set frequency step value, and the response of the receiving end piezoelectric ceramic sheet at each frequency is recorded. The recorded data is analyzed to find the resonance frequency of the piezoelectric ceramic sheet.

[0061] The determination process of the resonance frequency of the first piezoelectric ceramic sheet 3 is as follows:

[0062] The resonance frequency of the transmitting end first piezoelectric ceramic sheet 3 is measured to ensure that the excitation signal matches the optimal working frequency.

[0063] A sinusoidal excitation signal of different frequencies is applied to the first piezoelectric ceramic sheet 3 of the packaged double piezoelectric acoustic sensor, and the output signal amplitude of the second piezoelectric ceramic sheet 5 is monitored; the frequency of the input signal is gradually scanned, and the change of the receiving signal amplitude is recorded.

[0064] When the signal amplitude of the second piezoelectric ceramic sheet 5 reaches the maximum value, the sensor is in a resonant state, and the corresponding excitation frequency is the resonance frequency of the first piezoelectric ceramic sheet 3.

[0065] The matching layer of the present application is the first matching layer 2 between the transmitting piezoelectric ceramic and the receiving piezoelectric ceramic and the second matching layer 4 between the receiving second piezoelectric ceramic 5 and the object to be measured. According to the acoustic impedance matching characteristics, the composite structure of epoxy resin and glass beads is adopted to ensure efficient transmission of signals. The acoustic impedance calculation formula of the matching layer is as follows:

[0066] wherein, Zm is the acoustic impedance of the matching layer, Zp is the acoustic impedance of the piezoelectric ceramic, Zt is the acoustic impedance of the transmission medium (such as air or water). In order to optimize the matching layer characteristics, reduce the acoustic impedance mismatch, and improve the energy coupling efficiency. According to the target acoustic impedance of the matching layer , the volume fraction of glass beads can be determined by the following formula :

[0067] wherein, Zr is the acoustic impedance of the epoxy resin, Zb is the acoustic impedance of the glass beads. The optimal amount of glass beads is calculated to ensure the performance of the matching layer.

[0068] The present application adopts epoxy resin and tungsten powder mixed material as the backing layer 1, which is filled between the transmitting piezoelectric ceramic and the shell to effectively enhance the back energy absorption, reduce signal reflection, and improve detection sensitivity. The attenuation coefficient of the backing layer 1 is calculated as follows:

[0069] wherein, a is the attenuation coefficient, f is the driving frequency (100 kHz), v is the propagation speed of the acoustic wave in the backing material (about 5000-6000 m / s), Q is the internal friction factor of the material (about 0.001-0.005). In order to optimize the performance of the backing layer 1, the proportion of tungsten powder added is calculated based on the density of the composite material as follows:

[0070]

[0071] wherein, D is the density after mixing, D1 is the density of the epoxy resin, D2 is the density of the tungsten powder, V is the volume fraction of the tungsten powder. By adjusting the value of , the density and damping characteristics of the backing layer 1 can be controlled to optimize the acoustic wave attenuation effect.

[0072] Figure 2 ​It is a schematic diagram of a double piezoelectric acoustic emission sensor system with self-checking function.

[0073] According to any one of the detection systems of the double piezoelectric acoustic emission sensor with self-checking function, comprising:

[0074] The signal generation module 6 is used to generate alternating signals of different frequencies.

[0075] The signal generation module 6 comprises a DAC module for converting digital signals into analog signals.

[0076] The double piezoelectric acoustic emission sensor 7 is used to receive the vibration signals generated by the signal generation module 6 and the vibration signals generated by the object, and convert the vibration signals into electrical signals for transmission.

[0077] The pre-signal conditioning module 8 is used to amplify and filter the signals transmitted by the double piezoelectric acoustic emission sensor 7.

[0078] The signal acquisition module 9 is used to receive the amplified and filtered signals transmitted by the pre-signal conditioning module 8 for acquisition.

[0079] The signal acquisition module 9 comprises an ADC conversion module for acquiring the amplified and filtered vibration signals.

[0080] The main control module 10 is used to drive the signal generation module 6 to generate alternating signals of different frequencies, and simultaneously process the signals transmitted by the signal acquisition module 9 in time domain and frequency domain, and judge whether the detection object has an abnormality and whether the double piezoelectric acoustic emission sensor 7 is in working state based on the processed time domain and frequency domain information.

[0081] The abnormal conditions include bridge and steel cable rupture, etc.

[0082] The signal generation module 6 generates a sinusoidal signal matching the resonance frequency of the first ceramic sheet at the transmitting end, which is converted by DAC and amplified to drive the first piezoelectric ceramic sheet 3 at the transmitting end to vibrate. The physical vibration is transmitted to the second piezoelectric ceramic sheet 5 at the receiving end through the first matching layer 2, and the second piezoelectric ceramic sheet 5 at the receiving end converts the mechanical vibration into an electrical signal. The electrical signal is transmitted to the acquisition module after the pre-signal conditioning module 8, and is converted by ADC to enter the main control module 10 for time domain analysis and frequency domain analysis to obtain the time domain characteristics and maximum frequency value of the received signal. The characteristics are matched with the signal generated by the signal generation module 6. If they do not match, it is determined that the sensor is damaged, an alarm signal is sent, online self-checking is realized, and the reliability of the sensor is ensured.

[0083] The main control module 10 drives the signal generation module to generate digital sine wave signal data, and then generates an analog sine signal through a DAC module. After power amplification, the analog sine signal is input into the transmitting end first piezoelectric ceramic piece 3 in the dual piezoelectric acoustic emission sensor 7 to generate mechanical vibration, thereby causing the receiving end piezoelectric ceramic piece to vibrate to generate an electric signal. The sensor self-checking is completed by collecting and analyzing the signal of the receiving end second piezoelectric ceramic piece 5.

[0084] The frequency calculation formula of the signal generation module 6 generating a sine wave signal is as follows:

[0085] wherein is a system clock frequency (50 MHz in this case), is a frequency control word, is the number of phase accumulator bits (32 in this case).

[0086] First, the time domain analysis and frequency domain analysis of the environmental noise received by the receiving end second piezoelectric ceramic piece 5 are performed to obtain the time energy integral and the frequency energy integral of the signal of the receiving end piezoelectric ceramic piece under normal working conditions. The time interval is set to ten minutes for self-checking once. When the self-checking starts, the self-checking signal flag bit is pulled high. During this period, the signal duration of 500 ms is set to high level 1, and the signal duration of 500 ms is set to low level 0. The self-checking signal is set to 11011011. After the excitation signal is sent out, the main control module 10 performs time domain analysis and frequency domain analysis on the signal of the receiving end second piezoelectric ceramic piece 5, and the time energy integral and the frequency energy integral are obtained within a time interval of 500 ms. The time energy integral and the frequency energy integral are obtained, and the main frequency of the collected signal is obtained. The time energy integral and the frequency energy integral are compared. If , the main frequency is consistent with the signal frequency of the signal generation module 6, and if the signal of the receiving end second piezoelectric ceramic piece 5 is consistent with the time domain signal and the frequency domain signal of the transmitting end first piezoelectric ceramic piece 3, and the main frequency is consistent, it is determined that the dual piezoelectric acoustic emission sensor 7 is intact.

[0087] If , the sensor is damaged.

[0088] If the signal of the second piezoelectric ceramic piece 5 is inconsistent with the time domain signal or the frequency domain signal of the first piezoelectric ceramic piece 3, the dual piezoelectric acoustic emission sensor is damaged.

[0089] The main control module 10 drives the signal generating module 6, and processes the output signal of the receiving end piezoelectric ceramic piece after the pre-signal conditioning module 8 in time and frequency domains, so as to realize effective judgment on the fracture condition of the bridge structure.

[0090] The process of processing the electric signal in time and frequency domains is as follows:

[0091] The time domain energy integral and the frequency domain energy integral of the first window signal are obtained by processing the electric signal in time and frequency domains in a sliding window manner and The time domain energy integral and the frequency domain energy integral of the second window signal are obtained by processing the electric signal in time and frequency domains in a sliding window manner and The first window signal and the second window signal are adjacent signal segments.

[0092] The process of judging whether the detected object is abnormal and whether the dual piezoelectric acoustic emission sensor 7 is in a working state based on the processed time domain and frequency domain information is as follows:

[0093] The time domain energy integral and the frequency domain energy integral of the first window signal and the second window signal are compared respectively, and the time domain energy change value and the frequency domain energy change value of the first window signal and the second window signal are obtained.

[0094] The time domain energy integral and the frequency domain energy integral of the second window signal and the third window signal are compared respectively, and the time domain energy change value and the frequency domain energy change value of the second window signal and the third window signal are obtained.

[0095] When and , is a jump alarm threshold value, it is judged that the dual piezoelectric acoustic emission sensor 7 has a large energy fluctuation, and an alarm signal is sent.

[0096] After sending the self-check signal, the signal of the receiving end second piezoelectric ceramic piece 5 is analyzed, if , and whether the main frequency of the collected signal is consistent with the signal frequency sent by the signal generating module, if the time domain and frequency domain signals of the receiving end second piezoelectric ceramic piece 5 and the transmitting end first piezoelectric ceramic piece 3 are consistent, and the main frequency of the collected signal is consistent with the signal frequency sent by the signal generating module, it is judged that the dual piezoelectric acoustic emission sensor is intact, otherwise the dual piezoelectric acoustic emission sensor is damaged.

[0097] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A dual piezoelectric emission sensor with self-testing function, characterized in that: include Sealed housing; A backing layer is provided at the bottom of the sealed housing; A first support is provided above the backing layer for mounting the first piezoelectric ceramic sheet; The first piezoelectric ceramic sheet serves as the transmitter of the self-test signal. A first matching layer is provided above the first layer support to stabilize the transmission of vibrations generated by the first piezoelectric ceramic sheet during the self-test process and maximize the utilization rate of vibration energy. A second support is provided above the first matching layer for mounting the second piezoelectric ceramic sheet; The second piezoelectric ceramic sheet is used as a signal receiving end to detect the self-test signal emitted by the first piezoelectric ceramic sheet and to detect the vibration signal when the tested object breaks. A second matching layer is provided above the second layer support, which is used to contact the object being tested, perform acoustic impedance matching, and transmit the vibration signal generated by the breakage of the object being tested to the second piezoelectric ceramic sheet.

2. The dual piezoelectric emission sensor with self-testing function according to claim 1, characterized in that: Both the first and second layer support platforms adopt a stepped double-layer support platform; The stepped double-layer support platform includes a first support platform and a second support platform, which are arranged in parallel.

3. A dual piezoelectric emission sensor with self-testing function according to claim 1, characterized in that: The backing layer is made of a mixture of epoxy resin and tungsten powder. The first matching layer and the second matching layer are made of a mixture of epoxy resin and glass microspheres.

4. A dual piezoelectric emission sensor with self-testing function according to claim 1, characterized in that: The process for determining the resonant frequency of the first piezoelectric ceramic sheet is as follows: Sinusoidal excitation signals of different frequencies are applied to the first piezoelectric ceramic sheet, while the amplitude of the output signal of the second piezoelectric ceramic sheet is monitored; the frequency of the input signal is gradually scanned, and the changes in the amplitude of the received signal are recorded. When the signal amplitude of the second piezoelectric ceramic sheet reaches its maximum, the sensor is in a resonant state, and the corresponding excitation frequency is the resonant frequency of the first piezoelectric ceramic sheet.

5. A detection system for a dual piezoelectric emission sensor with self-testing function according to any one of claims 1-4, characterized in that: include: Signal generation module: Used to generate AC signals of different frequencies; Dual piezoelectric emission sensor: used to receive vibration signals generated by the signal generation module and vibration signals generated by the detected object, and convert the vibration signals into electrical signals for transmission; Pre-signal conditioning module: used to amplify and filter the signal transmitted by the dual piezoelectric emission sensor; Signal acquisition module: used to receive and acquire the amplified and filtered signal transmitted by the pre-signal conditioning module; Main control module: Used to drive the signal generation module to generate AC signals of different frequencies. At the same time, it performs time-domain and frequency-domain processing on the electrical signals transmitted by the signal acquisition module. Based on the processed time-domain and frequency-domain information, it determines whether the detected object has an anomaly and whether the dual piezoelectric emission sensor is in working condition.

6. The detection system of a dual piezoelectric emission sensor with self-testing function according to claim 5, characterized in that: The process of processing the electrical signal in the time and frequency domains is as follows: The electrical signal is processed by sliding windowing in the time and frequency domains to obtain the time-domain energy integral of the first window signal. Frequency domain energy integral Time-domain energy integral with the second window signal Frequency domain energy integral The first window signal and the second window signal are time-adjacent signal segments.

7. The detection system of a dual piezoelectric emission sensor with self-testing function according to claim 5, characterized in that: The process of determining whether the detected object is abnormal and whether the dual piezoelectric emission sensor is in working condition based on the processed time-domain and frequency-domain information is as follows: By comparing the time-domain energy integral and frequency-domain energy integral of the first and second window signals respectively, the time-domain energy change values ​​of the first and second window signals are obtained. and frequency domain energy change value ; By comparing the time-domain energy integral and frequency-domain energy integral of the second and third window signals respectively, the time-domain energy change values ​​of the second and third window signals are obtained. Frequency domain energy change value , when and hour, If the alarm threshold is exceeded, it is determined that there is a large energy fluctuation in the dual piezoelectric emission sensor, and an alarm signal is issued. After a self-test signal is emitted, the signal from the second piezoelectric ceramic element at the receiving end is analyzed. If the signal from the second piezoelectric ceramic element at the receiving end is consistent with the time and frequency domain signal from the first piezoelectric ceramic element at the transmitting end, and the main frequency of the acquired signal is... The frequency of the signal emitted by the signal generation module If the results are consistent, the dual piezoelectric emission sensor is considered to be intact; otherwise, the dual piezoelectric emission sensor is considered to be damaged.

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