A high-temperature in-situ piezoelectric property detection system and method for eliminating the influence of pyroelectric effect

Abstract

The present invention discloses a high-temperature in-situ piezoelectric property detection system and method for eliminating the influence of the pyroelectric effect. The detection system includes a first control circuit and a second control circuit; the first control circuit includes a first signal processing module and a filtering charge conversion module; the first control circuit strips the original signal containing the temperature signal and the piezoelectric source signal, screens out the piezoelectric source signal, and converts the piezoelectric source signal into a piezoelectric signal for output; the second control circuit includes a second signal processing module, a low-pass filter and an output unit; the second control circuit strips the original signal containing the temperature signal and the piezoelectric source signal, screens out the temperature signal, and amplifies the temperature signal after low-pass filtering to form an effective pyroelectric signal for output.

Description

Technical Field

[0001] The present invention relates to the field of performance testing of piezoelectric materials, and particularly to a high-temperature in-situ piezoelectric performance detection system and method for eliminating the influence of pyroelectric effect. Background Art

[0002] Piezoelectric materials are an important class of functional materials that can generate net charges on the material surface under the action of external forces. In recent years, piezoelectric materials have been increasingly widely used in fields such as aerospace, space technology, medical treatment, and weaponry. The operating temperature range of piezoelectric materials has also been extended to a wider temperature range. In particular, the performance of piezoelectric materials in the high-temperature range has become the top priority of research. However, most of the current testing methods for the piezoelectric performance of piezoelectric materials are limited to room temperature and cannot meet the requirements of high-temperature in-situ piezoelectric performance testing. Although a few methods have achieved high-temperature in-situ piezoelectric performance testing, the accuracy of the test results still needs to be improved. The reason is that: in addition to the piezoelectric effect, piezoelectric materials also have a pyroelectric effect, that is, net charges will also be generated on the material surface when the temperature changes. When piezoelectric materials are subjected to in-situ high-temperature testing, the charges generated by the pyroelectric effect will be mixed with the charges generated by the piezoelectric effect, seriously interfering with the test results. However, if the influence of pyroelectricity is not considered, it will be difficult to ensure the accuracy of the high-temperature in-situ piezoelectric performance test results. If the pyroelectric signal and the piezoelectric signal can be separated, then studying the pyroelectric parameters of piezoelectric materials during the high-temperature process will be an important parameter for exploring the high-temperature effects of samples. Summary of the Invention

[0003] In view of the above problems, the present invention proposes a high-temperature in-situ piezoelectric performance detection system and method for eliminating the influence of pyroelectric effect, which can improve the test accuracy and precision of high-temperature in-situ piezoelectric performance and truly and accurately reflect the piezoelectric performance and pyroelectric parameters of piezoelectric materials under high-temperature conditions.

[0004] In a first aspect, the present invention provides a high-temperature in-situ piezoelectric performance detection system for eliminating the influence of the pyroelectric effect. The detection system includes a first control circuit and a second control circuit; the first control circuit includes a first signal processing module and a filter charge conversion module; the first signal processing module has a filter differential amplification unit, a frequency-locked phase discrimination unit, a phase delay unit, and a phase-locked loop unit that form a closed loop; the filter charge conversion module has a filter and a charge converter; the first control circuit strips the original signal containing the temperature signal and the piezoelectric power source signal, screens out the piezoelectric power source signal, and converts the piezoelectric power source signal into a piezoelectric signal for output; the second control circuit includes a second signal processing module, a low-pass filter, and an output unit; the second signal processing module has an input amplification unit, a band-pass filter, a reference trigger unit, a phase shift unit, and a mixing phase discrimination unit; the second control circuit strips the original signal containing the temperature signal and the piezoelectric power source signal, screens out the temperature signal, and amplifies the temperature signal after low-pass filtering to form an effective pyroelectric signal for output.

[0005] Preferably, the original signal containing the temperature signal and the piezoelectric power source signal is divided into one of two paths after passing through the filter of the filter differential amplification unit and given to the phase delay unit, and the signal after the phase delay unit eliminates the phase difference is given to the phase-locked loop unit for natural frequency screening to form a basic measurement signal.

[0006] Preferably, the other of the two paths after the original signal passes through the filter of the filter differential amplification unit is given to the differential amplifier, and the frequency-locked phase discrimination unit uses the basic measurement signal provided by the phase-locked loop unit as a reference signal, and uses the phase and frequency of the basic measurement signal as screening conditions to strip out the piezoelectric power source signal from the signal processed by the differential amplification unit.

[0007] Preferably, the filter of the filter charge conversion module is connected to the frequency-locked phase discrimination unit of the first signal processing module.

[0008] Preferably, the input signal of the second signal processing module has two paths, one of the input signals is the original signal containing the temperature signal and the piezoelectric power source signal, and the original signal is amplified and selectively filtered by the input amplification unit and the band-pass filter connected to the input amplification unit and then provided to the mixing phase discrimination unit.

[0009] Preferably, the other input signal of the second signal processing module is the input signal provided by the dynamic force reference signal processing module. The input signal provided by the dynamic force reference signal processing module is converted into a standard digital square wave by the reference trigger unit, and then phase compensation is performed by the phase shift unit and used as the reference signal of the mixing phase discrimination unit to frame out the piezoelectric power source signal and extract the temperature signal.

[0010] Preferably, the mixing and phase discrimination unit obtains the temperature signal by excluding the voltage power supply signal with a reference signal whose phase is opposite to that of the original signal as the identification condition.

[0011] Preferably, the low-pass filter is connected to the mixing and phase discrimination unit of the second signal processing module.

[0012] Preferably, the detection system further includes a dynamic force reference signal generation module connected to the reference trigger unit, and the dynamic force reference signal generation module has a phase-inverting amplification unit and a zero-crossing detection unit.

[0013] Preferably, the voltage power supply signal of the original signal is input to the phase-inverting amplification unit for inverting amplification, and then the inverted amplified signal is given to the zero-crossing detection unit to be converted into a square wave signal at the zero-crossing point and input to the reference trigger unit of the second signal processing module.

[0014] Preferably, the detection system further includes a signal processing module for processing the piezoelectric signal and the pyroelectric signal, and the signal processing module has an analog-to-digital conversion unit, a high-speed data processing unit and a micro control unit.

[0015] In a second aspect, the present invention provides a detection method using the high-temperature in-situ piezoelectric property detection system for eliminating the influence of the pyroelectric effect described in any one of the above. The detection method includes the following steps:

[0016] Step S1. Apply a dynamic force F to the surface of the sample to be measured under variable temperature conditions;

[0017] Step S2. After removing the pyroelectric signal caused by the temperature change in Step S1, measure the surface charge density Q generated by the positive piezoelectric effect caused by the dynamic force;

[0018] Step S3. Calculate the piezoelectric coefficient d of the sample to be measured according to the formula d = Q / F.

[0019] Preferably, according to the loading direction of the dynamic force F, the piezoelectric signal includes d 33 signal, d 31 signal or d 15 signal. Description of the Drawings

[0020] Figure 1 is a schematic structural diagram of the first control circuit and the second control circuit;

[0021] Figure 2 is a schematic structural diagram of the dynamic force reference signal generation module;

[0022] Figure 3 is a schematic structural diagram of the signal processing module;

[0023] Figure 4It is a schematic structural diagram of a measurement condition control module;

[0024] Figure 5 It is a schematic circuit diagram of a static force control unit;

[0025] Figure 6 It is a schematic circuit diagram of a temperature control unit;

[0026] Figure 7 It is a schematic circuit diagram of a dynamic force control unit;

[0027] Figure 8 It is a Q-F curve with a static clamping force of 0 to 10 N;

[0028] Figure 9 It is a Q-F curve with a static clamping force of 8 N;

[0029] Figure 10 It is a Q-F curve with a static clamping force of 6.5 N;

[0030] Figure 11 It is a Q-F curve with a static clamping force of 4.3 N;

[0031] Figure 12 It is a Q-F curve with a static clamping force of 1.36 N;

[0032] Figure 13 It is a Q-F curve with a static clamping force of 0.61 N;

[0033] Figure 14 It is the piezoelectric coefficient d of the sample to be measured 33 The changing trend with the increase of static clamping force. Specific implementation mode

[0034] The present invention is further illustrated by the following implementation modes. It should be understood that the following implementation modes are only used to illustrate the present invention and do not limit the present invention.

[0035] The high-temperature in-situ piezoelectric performance detection system includes a first control circuit and a second control circuit. By adopting a special circuit design, synchronous measurement of piezoelectric signals and pyroelectric signals is realized in a variable-temperature environment.

[0036] The first control circuit includes a first signal processing module and a filtering charge conversion module. The first control circuit strips the original signal containing temperature signals and piezoelectric source signals, screens out the piezoelectric source signals, and converts the piezoelectric source signals into piezoelectric signals for output.

[0037] The first signal processing module has a filtering differential amplification unit, a frequency-locked phase discrimination unit, a phase delay unit, and a phase-locked loop unit (PLL unit) that form a closed loop. The first signal processing module strips and extracts the piezoelectric source signals from the input original signals.

[0038] From Figure 1 It can be seen that the filtering differential amplification unit has a filter and a differential amplifier. The filter of the filtering differential amplification unit receives the input original signal and denoises it, thereby removing the noise generated by the power supply and other circuits. The denoised original signal is amplified by a low-noise operational amplifier through the differential amplifier connected to the filter, thereby avoiding interference from high-frequency radiation interference signals and 50HZ power frequency. The other end of the filter is connected to the phase delay unit. The phase delay unit eliminates the phase difference caused by mechanical reaction. The phase delay unit can also eliminate the phase shift caused by the time difference brought by the transmission of the piezoelectric power signal generated by the sample to be measured in a dynamic force environment. The signal processed by the phase delay unit will be transmitted to the PLL unit. The PLL unit screens the inherent frequency of the signal containing clutter and completes the basic signal screening. The basic measurement signal completed by the PPL unit screening is given to the frequency-locked phase discrimination unit. The frequency-locked phase discrimination unit uses the basic measurement signal provided by the PLL unit as a reference signal, uses the phase and frequency of the basic measurement signal as a reference, discriminates and tracks the signal of the sample to be measured containing clutter signals in the signal processed by the differential amplification unit, and strips out the piezoelectric power signal. In this way, a closed loop is formed.

[0039] The filtering charge conversion module has a filter and a charge converter. The other end of the frequency-locked phase discrimination unit is connected to the filtering charge converter. The filter filters the stripped piezoelectric power signal to eliminate burrs and further optimize the signal purity. The processed piezoelectric power signal is collected and integrated by the charge converter to convert the weak piezoelectric power signal into a piezoelectric signal for output. The piezoelectric signal is a related signal reflecting the piezoelectric coefficient. According to the loading direction of the dynamic force, the piezoelectric signal includes d 33 signal, d 31 signal or d 15 signal, etc.

[0040] The piezoresponse signal is essentially an electrical signal formed by the release of charges generated when the sample under test is subjected to an external force. When the sample under test is subjected to an external dynamic force, electrons are released, forming a weak piezoresponse signal. Therefore, the piezoresponse signal is in the same frequency as the vibration source. The piezoresponse signal also contains some interference signals and circuit radiation signals. The temperature signal is a direct current signal generated when the electrons of the sample under test are shifted due to the temperature difference in a variable temperature environment (which can be a heating environment or a cooling environment). That is, whether the positive phase or the negative phase of the temperature signal increases depends on the temperature difference between the sample under test and the environment. When the temperature of the sample under test is higher than the ambient temperature, the pyroelectric effect grows in the negative phase, and vice versa. The present invention designs a special frequency-locking and phase discrimination technique for the weak piezoresponse signal. Through the frequency-locking and phase discrimination technique, the piezoresponse signal can be specifically stripped, other invalid signals can be filtered out, and the measurement accuracy and accuracy of the piezoelectric coefficient can be improved. Among them, the inherent frequency screening condition of the PLL unit is the same frequency and phase as the piezoelectric signal (dynamic force signal) as the screening condition to screen the original signal to obtain the basic measurement signal. In addition, the frequency-locking and phase discrimination unit uses the basic measurement signal provided by the PLL unit as the screening condition based on the frequency and phase of this signal to eliminate the pyroelectric signal caused by temperature change, and strip the piezoresponse signal from the original signal, thereby achieving the purpose of frequency-locking and phase discrimination.

[0041] As can be seen from the above, the original signal first passes through the filter of the filter differential amplifier unit to remove the power supply and interference noise of the original signal. The processed signal is divided into two paths, one path is given to the phase delay unit, and the other path is given to the differential amplifier. The differential amplifier amplifies the original signal with a low-noise operational amplifier to avoid interference from high-frequency radiation interference signals and 50HZ power frequency. The phase delay unit eliminates the phase difference caused by mechanical reaction, and the signal with the phase difference eliminated will be given to the PLL unit to complete the basic signal screening by following the inherent frequency screening. The completed basic signal is given to the frequency-locking and phase discrimination unit as a reference signal. The frequency-locking and phase discrimination unit uses the phase and frequency of the basic signal as a reference to identify and track the signal of the sample under test containing clutter signals in the signal processed by the differential amplifier unit and strip out the piezoresponse signal. The piezoresponse signal is given to the filter charge conversion unit. The filter further improves the purity of the piezoresponse signal, and then gives it to the charge converter to collect and integrate the piezoresponse signal, and finally obtains the piezoelectric signal.

[0042] From Figure 1 It can also be seen that the second control circuit includes a second signal processing module, a low-pass filter, and an output unit. The second signal processing module has an input amplification unit, a band-pass filter, a reference trigger unit, a phase shift unit, and a mixing and phase discrimination unit. The second signal processing module does not form a closed loop.

[0043] The second signal processing module of the second control circuit has two input signals. One of the input signals is the original signal. After passing through the input amplification unit and the band-pass filter connected to the input amplification unit, the original signal is amplified and selectively filtered. In this process, the original signal of the sample to be measured is amplified, and then the signals of ineffective high frequencies and ineffective low frequencies are removed. The other end of the band-pass filter is connected to the mixing and phase discrimination unit. The other input signal is the input signal provided by the dynamic force reference signal processing module. The input signal provided by the dynamic force reference signal processing module is converted into a standard digital square wave by the reference trigger unit, and then phase compensation is performed by the phase shift unit and used as the final reference signal to cancel the voltage supply signal and extract the temperature signal. That is, the mixing and phase discrimination unit uses the digital square wave processed by the phase shift unit as the reference. Specifically, the mixing and phase discrimination unit uses the reference (square wave) signal with the opposite phase to the original signal as the recognition condition. When the original signal is on the positive half-axis, the reference signal is exactly on the negative half-axis, achieving the purpose of canceling the voltage supply signal. The signal finally output by the mixing and phase discrimination unit is the temperature signal without the voltage supply signal.

[0044] The mixing and phase discrimination unit is connected to the low-pass filter. The function of the low-pass filter is to retain the low-frequency temperature signal and filter out the high-frequency interference signals. The other end of the low-pass filter is connected to the output unit. The output unit amplifies the temperature signal after stripping the dynamic force signal and outputs it as a pyroelectric signal. The stripped temperature signal is low-pass filtered to eliminate high-frequency clutter and interference signals, and the processed temperature signal is amplified and finally the pyroelectric signal is output.

[0045] The signal path of the second signal processing module is that the original signal is amplified by the input amplification unit, and then selectively filtered by the band-pass filter, and the processed original signal is given to the mixing and phase discrimination unit. The reference signal provided by the dynamic force reference signal processing module is converted into a standard digital square wave by the reference trigger unit, and then after phase compensation, it is used as the final reference signal of the mixing and phase discrimination unit to cancel the voltage supply signal and extract the temperature signal. The temperature signal is low-pass filtered to eliminate high-frequency interference signals and then given to the amplification output unit to amplify and output the pyroelectric signal.

[0046] From Figure 2It can be seen that the dynamic force reference signal generation module has an in-phase amplification unit and a zero-crossing detection unit. The dynamic force signal is provided by the dynamic force control unit of the measurement condition control module. The original dynamic force signal is input to the in-phase amplification unit, which inverts and amplifies the original dynamic force signal, and then the inverted and amplified signal is given to the zero-crossing detection unit to convert the inverted signal into a square wave signal with a zero-crossing point. The square wave signal is the input signal provided by the dynamic force reference signal processing module to the reference trigger unit of the second signal processing module. As described above, the reference trigger unit of the second control circuit converts the square wave signal with a zero-crossing point into a standard digital square wave signal to facilitate the generation of a trigger by the digital circuit, and gives the processed square wave signal to the phase shift unit to compensate for the phase difference caused by different hardware batches.

[0047] It can be seen that Figure 3 the detection system may further include a signal processing module. The signal processing module has an analog-to-digital conversion unit (ADC), a high-speed data processing unit (FPGA), and a micro-control unit (MCU). The analog-to-digital conversion unit is used to convert the processed piezoelectric signal and pyroelectric signal into digital signals. The analog-to-digital conversion unit and the high-speed data processing unit are connected through a 16-bit parallel transmission port. The high-speed data processing unit is used to process the calculated signals that have been measured and control the measurement. The high-speed data processing unit and the micro-control unit are connected through a 16-bit parallel transmission port. The micro-control unit is used for display communication, human-computer interaction, and external communication control, and provides an external communication port. The external communication port includes, but is not limited to, a USB communication port, a communication serial port, and a communication network port.

[0048] The measurement condition control module provides a test environment for the sample to be measured. The measurement condition control module is not the innovative point of the present invention. It can be seen that Figure 4 the measurement condition control module mainly includes a temperature control module, a dynamic force control module, and a static force control module. The static force control module includes a static force clamping motor, a static force sensor, and a static force control unit. The static force clamping motor can perform rotational motion and / or linear motion. When the static force clamping motor moves linearly up and down in the vertical direction, the static force sensor detects the clamping pressure and feeds it back to the static force control unit to adjust the rotation direction and speed of the motor. The temperature control module includes a heating furnace, a temperature control unit, and a furnace temperature sensor. The furnace temperature sensor senses the furnace ambient temperature and feeds it back to the temperature control unit, so that the furnace ambient temperature is adjusted through the temperature control unit to change the temperature environment of the sample to be measured. The dynamic force control module includes an oscillator, a dynamic force sensor, and a dynamic force control unit. The dynamic force sensor is connected to the oscillator. The oscillator can provide dynamic forces of different magnitudes. The dynamic force sensor detects the magnitude of the dynamic force and feeds it back to the dynamic force control unit to regulate the amplification (reduction) factor of the dynamic force.

[0049] The temperature control module, dynamic force control module, and static force control module respectively provide a test temperature environment, dynamic force, and static clamping force for the sample to be tested, so that the sample to be tested is in a charge release condition for subsequent measurement. The sample to be tested requires a certain static clamping force for pre-tightening during the measurement and then the piezoelectric properties are measured. The sample to be tested is clamped between the upper electrode of the static force clamping motor and the lower electrode of the dynamic force control unit. After the static clamping is stable, the dynamic force control unit generates a dynamic force, and surface charge density Q is rapidly generated on the upper and lower surfaces of the sample to be tested. When the wire conducts the upper and lower electrodes clamping the sample, the original signal of the sample to be tested is output. This signal is provided to the control circuit of the detection system for piezoelectric property detection. Since different static force magnitudes will cause different deformations of the sample to be tested. The magnitude of this deformation may cause a change in the amount of charge generated by the sample to be tested under the drive of the dynamic force, thus affecting the test accuracy of the piezoelectric properties of the sample. Therefore, by changing the magnitude of the static clamping force through the static force control unit, the change trend of the piezoelectric properties of the sample to be tested with the change of the static clamping force is statistically analyzed, providing an effective way for simulating the performance test of piezoelectric materials under actual working conditions.

[0050] Figure 5 It is a schematic circuit diagram of the static force control unit. Its function is to provide the (downward pressure) static clamping force required by the sample to be tested. The control signal is sent from the high-speed data processing unit (FPGA) to the stepping motor control signal conversion circuit unit, which converts the digital control signal into a pulse signal that the stepping motor can recognize, and then sent to the actuator motor unit. After the motor receives the pulse signal, it moves downward or upward to achieve the action of controlling the downward pressure static force. The state after the motor executes will be reflected to the static force sensing circuit unit. The static force sensing circuit will constantly detect the downward pressure static force of the motor and feedback the detected downward pressure static force to the force sensor acquisition circuit unit. The force sensor acquisition circuit unit first amplifies the analog signal given by the static force sensing circuit unit, and then converts the analog signal into a digital signal through the ADC acquisition part and sends it to the high-speed data processing unit for downward pressure static force control adjustment, forming a closed-loop circuit to achieve the purpose of accurately controlling the downward pressure static clamping force.

[0051] Figure 6It is a schematic diagram of the circuit structure of the temperature control unit. The high-speed data processing unit (FPGA) inputs a heating control signal (such as heating by 60 °C). After receiving the control signal, the PID control unit will control the high-power control unit to start working. The high-power control unit will supply the current to the heating wire unit according to the instructions of the PID control unit. The heating wire intermittently heats according to the control instructions to generate a temperature reaching the controlled temperature. The temperature sensor unit will feedback the real-time temperature status to the amplification and acquisition unit. The amplification and acquisition unit first amplifies the temperature signal of the temperature sensor unit and then converts it into a digital signal through the ADC acquisition part and gives it to the PID control unit to form a closed-loop circuit to achieve precise temperature control.

[0052] Figure 7 It is a schematic diagram of the circuit structure of the dynamic force control unit. First, the high-speed data processing unit (FPGA) inputs a control signal (such as: it is required to generate an AC waveform with 60 Hz and an amplitude of 0.7 V). The DDS unit of the programmable dynamic force generation circuit unit generates a corresponding signal according to the control instruction. Then the generated signal is amplified and given to the dynamic force power amplification unit and the dynamic force reference signal processing module respectively. The dynamic force power amplification unit further amplifies the original dynamic force signal to a power that can drive the dynamic force excitation unit. The dynamic force excitation unit generates an upward vibration dynamic force according to the signal. The dynamic force will be reflected to the dynamic force sensor in real time. The dynamic force sensor feedbacks the sensed upward vibration force to the filter amplification unit in the form of an analog electrical signal. The filter amplification unit first filters the received signal to remove the interference signal and the clutter signal, and then amplifies the signal and gives it to the AD acquisition unit. The AD acquisition unit performs analog-to-digital conversion on the processed analog signal and converts it into a digital signal that can be recognized by the FPGA to achieve the control detection loop. The FPGA adjusts the output signal with the feedback dynamic force signal to further achieve the purpose of precise control.

[0053] It should be noted here that Figures 5 to 7 the high-speed data processing units are the same unit, and the high-speed data processing unit of the signal processing module and the high-speed data processing unit of the measurement condition control module are independent of each other.

[0054] In summary, the detection system described in the present invention introduces a frequency-locked phase discrimination unit in the first control circuit to discriminate the original signal, track and amplify the effective signal, and remove the invalid interference signal and the temperature electrical signal, so as to extract the dynamic force signal; a mixing phase discrimination unit is introduced in the second control circuit to process the original signal, perform the peeling process of the dynamic force signal and amplify the temperature signal.

[0055] Next, the detection method of using the high-temperature in-situ piezoelectric performance detection system described in the present invention will be described.

[0056] The composition and structure of the sample to be measured are not limited. Preferably, the sample to be measured has strong piezoelectric properties. The sample to be measured includes but is not limited to piezoelectric ceramic wafers, ceramic columns, PVDF piezoelectric films, soft ceramics, hard ceramic materials, single crystal materials, etc. The shape of the sample to be measured can be a wafer, a film, a square column, a cylinder, etc. In a specific embodiment, a wafer-shaped sample to be measured is used. The size of the sample to be measured can also be adaptively changed according to actual needs. In order to reduce the non-linear piezoelectric effect caused by the static clamping force, the thickness of the wafer-shaped sample to be measured is preferably not less than 1 mm. As an example, the size of the sample to be measured is a diameter of 20 mm × a thickness of 1 mm. The sample to be measured is a polarized piezoelectric sample. The polarization process is a conventional operation in the art and will not be elaborated here.

[0057] Apply a dynamic force F to the surface to be measured under variable temperature conditions. It can be a continuous variable temperature condition, that is, heating from room temperature to a certain temperature above 100 °C or cooling from a certain temperature above 100 °C to room temperature at a certain rate. The heating rate or the cooling rate can be 1 - 2 °C / min. Preferably, the heating rate or the cooling rate is 2 °C / min. It can also adopt a mode of segmented heating. The heating rate can be 3 - 8 °C / min. After reaching the target temperature, it is preferably kept at a constant temperature for 10 min. The maximum temperature can be lower than 800 °C.

[0058] In some technical solutions, the frequency of the dynamic force is lower than the resonance frequency of the sample to be measured. Preferably, the frequency of the dynamic force is much lower than the resonance frequency of the sample to be measured. The resonance frequency of the piezoelectric sample is measured by an automatic balance bridge. The resonance frequency of the sample to be measured is usually relatively high. When the frequency of the dynamic force is relatively high, the working performance of the vibration table fails to reach its resonance frequency and becomes ineffective. In some embodiments, the application frequency of the dynamic force is 20 - 300 HZ.

[0059] The direction of the dynamic force can be adaptively changed according to requirements. For example, the direction of the dynamic force is perpendicular or parallel to the polarization direction of the sample to be measured. Or, the direction of the dynamic force has a tangent angle relationship with the polarization direction.

[0060] Measure the surface charge density Q generated by the direct piezoelectric effect. Specifically, eliminate the pyroelectric signal generated due to temperature change, and then measure the remaining surface charge density Q generated by the direct piezoelectric effect. The principle of eliminating the pyroelectric signal is as described above. The piezoelectric source signal is an AC signal in phase with the dynamic force signal, and the pyroelectric signal is a monotonically increasing or decreasing signal. The piezoelectric source signal and the pyroelectric signal are distinguished through circuit design and phase-locked technology to achieve the elimination of the pyroelectric signal.

[0061] Calculate the piezoelectric coefficient of the sample to be measured according to the formula d = Q / F. d is the piezoelectric coefficient, Q is the surface charge density, and F is the dynamic force. As an example, d 33: For the test sample of the wafer, electrodes are coated on both end faces of the test sample, polarized along the thickness direction, the dynamic force application direction is parallel to the polarization direction, and a dynamic force F3 is applied and the electric charge amount Q3 at both ends of the electrode surface is measured. d 31 : For the rectangular thin sheet sample, electrodes are coated on the two larger end faces of the sample, polarized along the thickness direction, the dynamic force application direction is perpendicular to the polarization direction, a dynamic force F1 is applied in this direction, and charge collection test Q3 is performed on the coated electrode surface. d 15 : For the rectangular thin sheet sample, it is polarized along the length direction of the test sample, electrodes are coated on the larger cross-section parallel to the polarization direction, a tangential force F1 is applied on the narrower surface in the length direction, and charge Q5 is collected on the coated electrode surface.

[0062] The method of the present invention comprehensively considers the piezoelectric effect and pyroelectric effect in the process of high-temperature in-situ piezoelectric property testing. By eliminating the pyroelectric effect and retaining the charge generated by the pure piezoelectric effect, the accuracy and precision of the high-temperature in-situ piezoelectric property testing are improved.

[0063] Example 1

[0064] Specifically, the high-temperature in-situ piezoelectric property measurement method for eliminating the influence of the pyroelectric effect includes:

[0065] Step S1. Under continuous temperature change conditions, a dynamic force F is applied to the test sample. The test sample is a thin wafer. Electrode materials are coated on both the upper surface and the lower surface of the test sample, and the polarization direction of the test sample is perpendicular to the upper surface and the lower surface. The continuous temperature change condition is to heat from room temperature to 400 °C at a rate of 2 °C / min. The magnitude of the dynamic force is 0.25 N, the frequency is 110 Hz, and the action direction of the dynamic force is parallel to the polarization direction.

[0066] Step S2. Eliminate the pyroelectric signal generated due to temperature change in Step S1, and then measure the remaining charge density Q generated by the direct piezoelectric effect on the electrode surface of the above-mentioned test sample.

[0067] S3. Calculate the piezoelectric coefficient d of the test sample according to the formula d = Q / F 33 。

[0068] The test sample needs a certain static clamping force for pre-tightening during the measurement process and then the piezoelectric property is measured. Different magnitudes of static force will cause different deformations of the test sample. The magnitude of this deformation may cause a change in the Q value generated by the test sample under the drive of the dynamic force F, thereby affecting the piezoelectric coefficient d 33 value of the sample. Therefore, by changing the magnitude of the static clamping force multiple times and recording the Q-F curve under this static clamping force condition, the change trend of the static clamping force and the d 33 value of the test sample is obtained.

[0069] For example, while maintaining a certain constant static clamping force, by changing the magnitude of the dynamic force, the electric charge amounts under different dynamic forces are obtained, and d is calculated. 33 In the present invention, a series of dynamic forces are applied to the sample to be measured, a series of corresponding electric charge amounts Q are obtained, and the slope of a linear function is taken as the d value of the sample. 33 Compared with the ratio of the electric charge amount to the dynamic force of a single measurement of the sample to be measured, this value has a higher accuracy in the test result. Verification shows that the piezoelectric coefficient d of the sample to be measured 33 = Q / F can be represented by the slope of a linear function and has a high accuracy.

[0070] Figure 8 is the Q-F curve with a static clamping force of 10 N. Figure 9 is the Q-F curve with a static clamping force of 8 N. Figure 10 is the Q-F curve with a static clamping force of 6.5 N. Figure 11 is the Q-F curve with a static clamping force of 4.3 N. Figure 12 is the Q-F curve with a static clamping force of 1.36 N. Figure 13 is the Q-F curve with a static clamping force of 0.61 N. It can be seen that within a certain range of static clamping forces, the piezoelectric coefficient d value of the sample to be measured 33 changes with the change of the static clamping force.

[0071] Figure 14 is the piezoelectric coefficient d of the sample to be measured 33 The change trend with the increase of the static clamping force. For some piezoelectric ceramic materials, when the static clamping force is different, the actual piezoelectric d 33 coefficient values of the sample are different, and when the static clamping force exceeds a certain value, the d 33 of the sample basically no longer changes, which provides an effective way for simulating the performance test of materials under actual working conditions.

[0072] Although the above describes the implementation embodiments of the present invention, the present invention is not limited to the above specific implementation embodiments and application fields. The above specific implementation embodiments are merely illustrative and guiding, rather than restrictive. Those of ordinary skill in the art can also make many forms under the inspiration of this specification and without departing from the scope protected by the claims of the present invention, and these all belong to the scope of protection of the present invention.

Claims

1. A high-temperature in-situ piezoelectric property detection system, characterized in that, The detection system includes a first control circuit and a second control circuit; the first control circuit includes a first signal processing module and a filter charge conversion module; the first signal processing module has a filter differential amplification unit, a frequency-locked phase discrimination unit, a phase delay unit, and a phase-locked loop unit that form a closed loop; the filter charge conversion module has a filter and a charge converter; the first control circuit strips the original signal containing the temperature signal and the piezoelectric power supply signal, screens out the piezoelectric power supply signal, and converts the piezoelectric power supply signal into a piezoelectric signal for output; the second control circuit includes a second signal processing module, a low-pass filter, and an output unit; the second signal processing module has an input amplification unit, a band-pass filter, a reference trigger unit, a phase shift unit, and a mixing phase discrimination unit; The second control circuit strips the original signal containing the temperature signal and the piezoelectric power supply signal, screens out the temperature signal, low-pass filters the temperature signal and then amplifies it to form an effective pyroelectric signal for output.

2. The detection system according to claim 1, wherein The original signal containing the temperature signal and the piezoelectric power supply signal is divided into one of two paths after passing through the filter of the filter differential amplification unit and given to the phase delay unit. The signal after the phase delay unit eliminates the phase difference is given to the phase-locked loop unit for natural frequency screening to form a basic measurement signal; the original signal is divided into the other of the two paths after passing through the filter of the filter differential amplification unit and given to a differential amplifier. The frequency-locked phase discrimination unit uses the basic measurement signal provided by the phase-locked loop unit as a reference signal, and uses the phase and frequency of the basic measurement signal as screening conditions to strip out the piezoelectric power supply signal from the signal processed by the differential amplification unit.

3. The detection system according to claim 1, characterized in that, The filter of the filter charge conversion module is connected to the frequency-locked phase discrimination unit of the first signal processing module.

4. The detection system according to claim 1, wherein The input signal of the second signal processing module has two paths. One of the input signals is the original signal containing the temperature signal and the piezoelectric power supply signal. The original signal is amplified and selectively filtered by the input amplification unit and the band-pass filter connected to the input amplification unit and then provided to the mixing phase discrimination unit; the other input signal of the second signal processing module is the input signal provided by the dynamic force reference signal processing module. The input signal provided by the dynamic force reference signal processing module is converted into a standard digital square wave by the reference trigger unit, and then phase compensation is performed by the phase shift unit and used as the reference signal of the mixing phase discrimination unit to frame out the piezoelectric power supply signal and extract the temperature signal.

5. The detection system according to claim 4, wherein The mixing phase discrimination unit frames out the piezoelectric power supply signal with a reference signal having a phase opposite to that of the original signal as the identification condition to obtain the temperature signal.

6. The detection system according to claim 1, wherein The low-pass filter is connected to the mixing phase discrimination unit of the second signal processing module.

7. The detection system according to claim 1, wherein The detection system further includes a dynamic force reference signal generation module connected to the reference trigger unit, and the dynamic force reference signal generation module has an in-phase amplification unit and a zero-crossing detection unit.

8. The detection system according to claim 7, wherein The piezoelectric power supply signal of the original signal is input to the in-phase amplification unit for inverting amplification, and then the signal after inverting amplification is given to the zero-crossing detection unit to be converted into a square wave signal at the zero-crossing point and input to the reference trigger unit of the second signal processing module.

9. The detection system according to claim 1, wherein, The detection system further includes a signal processing module for processing piezoelectric signals and pyroelectric signals, and the signal processing module has an analog-to-digital conversion unit, a high-speed data processing unit, and a micro-control unit.

10. A detection method using the high-temperature in-situ piezoelectric property detection system according to any one of claims 1 to 9, characterized in that, It includes the following steps: Step S1. Apply a dynamic force F to the surface of the sample to be measured under variable temperature conditions; Step S2. After removing the pyroelectric signals caused by temperature changes in Step S1, measure the surface charge density Q generated by the positive piezoelectric effect caused by the dynamic force; Step S3. Calculate the piezoelectric coefficient d of the sample to be measured according to the formula d = Q / F.

11. The detection method using the high-temperature in-situ piezoelectric property detection system according to claim 10, characterized in that, According to the loading direction of the dynamic force F, the piezoelectric signal includes d 33 signal, d 31 signal or d 15 signal.

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