A method and device for measuring the piezoelectric constant of a piezoelectric film

Abstract

The present invention belongs to the technical field of piezoelectric constant measurement, and provides a method and device for measuring the piezoelectric constant of a piezoelectric film, wherein the strain signal of the first strain gauge and the charge output signal of the piezoelectric film during the deformation of the test strip are collected; the strain signal and the charge output signal are processed to obtain the piezoelectric constant of the piezoelectric film; in each cycle of the force application process, the maximum amplitude of the strain signal and the charge output signal of the piezoelectric film are calculated to obtain the piezoelectric constant of the piezoelectric film; by not using or using as few theoretical values ​​of material parameters as possible, the measuring method can measure the piezoelectric constant in real time and more realistically and accurately.

Description

Technical Field

[0001] The invention belongs to the technical field of piezoelectric constant measurement, and in particular relates to a method and a device for measuring the piezoelectric constant of a piezoelectric film. Background Art

[0002] Piezoelectric film is a crystalline material that generates a voltage between its two end surfaces when subjected to pressure. The piezoelectric constant of a piezoelectric film can be expressed from different perspectives. There are four forms, namely, d ij 、e ij , g ij and h ij , where i = 1, 2, 3; j = 1, 2, 3, 4, 5, 6. At present, the methods for measuring the piezoelectric constant (piezoelectric constant) of piezoelectric films include: direct force measurement method, laser interferometry, laser Doppler vibrometer and piezoelectric force microscope. Among them, laser interferometry, laser Doppler vibrometer and piezoelectric force microscope all measure the piezoelectric constant through the inverse piezoelectric effect, that is, by applying a voltage signal to cause the material to produce a deformation effect. Although the measurement accuracy is high, the equipment is expensive and has high requirements for the measurement environment.

[0003] The direct force measurement method uses the positive piezoelectric effect, that is, the piezoelectric constant is measured by applying force to generate electric charge in the material. Although this method is not as accurate as the other three measurement methods, the measurement device is cheap and easy to use. For thin film materials, the parameters i=3, j=1 or 3 are commonly used. At present, most direct force measurement methods on the market are used to measure the piezoelectric constant d 33 , for measuring the piezoelectric constant e 31 There are very few methods.

[0004] The piezoelectric constant e is commonly used 31 The measurement method is to process the material into a tiny long cantilever beam structure with an output electrode. One end of the cantilever beam is fixed, and the cantilever beam is bent by applying force at the other end of the cantilever beam. Then, the force-applied end is suddenly released, and the cantilever beam will continue to vibrate attenuated for a period of time. Before the force is released, the strain of the cantilever beam can be theoretically calculated based on the bending of the cantilever beam; then, by recording the vibration frequency of the cantilever beam and the peak-to-peak amplitude change of the output voltage signal after the force is released, the piezoelectric constant e of the material can be inferred using the measured electrode size. 31. However, in the calculation process of the above measurement method, the measured material is set as a homogeneous material, and the calculation parameters are mostly public bulk material parameters. For thin film materials, due to the preparation process, there is usually a large stress inside the thin film material, and many parameters are different from those of the bulk material. This will inevitably lead to differences between the obtained results and the actual values, and when the thin film material has a multi-layer structure, the difference will be even greater. In addition, the above measurement method is calculated through the change relationship of the amplitude between multiple cycles, which means that the result must be an overall average effect, and cannot truly reflect the real-time relationship between the strain and the charge. Summary of the invention

[0005] The purpose of the present invention is to provide a method and device for measuring the piezoelectric constant of a piezoelectric film, so as to solve one or more technical problems existing in the prior art and at least provide a beneficial choice or create conditions.

[0006] In order to achieve the above object, the present invention provides a method for measuring the piezoelectric constant of a piezoelectric film, which specifically comprises the following steps:

[0007] A first strain gauge is provided on one side of the test strip, and a piezoelectric film is correspondingly provided on the other side;

[0008] Fixing one end of the test strip and applying force to the test strip at the other end to deform the test strip;

[0009] collecting a strain signal of the first strain gauge and a charge output signal of the piezoelectric film during deformation of the test bar;

[0010] The strain signal and the charge output signal are processed to obtain the piezoelectric constant of the piezoelectric film.

[0011] Furthermore, the collected strain signal and the charge output signal are processed to obtain the piezoelectric constant of the piezoelectric film by: acquiring the strain signal (strain) and the charge output signal (charge amount) of the piezoelectric film at the collection time to calculate the piezoelectric constant at the collection time.

[0012] Preferably, the process of applying force to the test strip is periodic;

[0013] In each cycle of the force application process, the maximum amplitude of the strain signal (strain amount) and the charge output signal (charge amount) of the piezoelectric film is calculated to obtain the piezoelectric constant of the piezoelectric film.

[0014] The piezoelectric constant is calculated as:

[0015] When a piezoelectric material is subjected to an external force, bound charges will be induced on its surface due to the piezoelectric effect, and its charge density σ3 is: σ3 = e 31 ×S1; where e 31 is the piezoelectric constant, which represents the ability of the strain parallel to the material plane to generate charge in the direction perpendicular to the material plane. S1 is the strain in a certain direction in the material plane. Therefore, as long as the strain S1 of the material and the charge Q3 generated on the surface electrode area A under the action of external force are measured, where Q3 = σ3A, the corresponding piezoelectric constant e can be obtained. 31 , (i.e. e 31 =σ3÷S1,σ3=Q3÷A).

[0016] Preferably, the test strip is a single homogeneous material; the test strip is in the shape of a long strip; and the deformation of the test strip is within the elastic strain range of the material.

[0017] Preferably, the test strip is an aluminum strip with a width of 15 mm, a length of 200 mm and a thickness of 2 mm.

[0018] Preferably, the piezoelectric film material has a Si / SiO2 / Pt / PZT / Pt structure, wherein Si / SiO2 is the substrate layer, PZT is the piezoelectric film layer, and the upper and lower electrodes are both made of Pt material.

[0019] Furthermore, the measuring method further comprises:

[0020] A third strain gauge is provided on one side of the reference strip, and a reference strip and a second strain gauge are provided on the other side (the second strain gauge is measured to obtain a strain correction coefficient corresponding to the variable and to correct the piezoelectric constant); the third strain gauge and the second strain gauge are strain gauges of the same model; the reference strip and the test strip are of the same specification;

[0021] Fixing one end of the reference bar and applying force to the reference bar at the other end to deform the reference bar;

[0022] collecting and processing the strain signal of the third strain gauge and the strain signal of the second strain gauge during the deformation of the reference bar to obtain a strain correction coefficient;

[0023] The piezoelectric constant is processed according to the strain correction coefficient to obtain a corrected piezoelectric constant.

[0024] Preferably, the reference strip is an aluminum strip with a width of 15 mm, a length of 200 mm and a thickness of 2 mm.

[0025] Preferably, the first strain gauge, the second strain gauge and the third strain gauge are strain gauges of the same model.

[0026] Furthermore, one side of the reference sheet is connected to the reference bar, and the other side is connected to the second strain gauge.

[0027] Furthermore, the specification of the reference sheet is the same as the specification of the piezoelectric film.

[0028] Preferably, the reference sheet is a Si / SiO2 sheet having the same size as the piezoelectric film.

[0029] The present invention also provides a device for measuring the piezoelectric constant of a piezoelectric film, the device comprising:

[0030] A force applying unit; the force applying unit is used to apply force to the test strip and / or reference strip in a method for measuring a piezoelectric constant of a piezoelectric film so that the test strip is deformed;

[0031] A fixing unit; the fixing unit is used to fix one end of the test strip and / or the reference strip in a method for measuring a piezoelectric constant of a piezoelectric film;

[0032] A charge conversion unit, which is electrically connected to the piezoelectric film in a method for measuring a piezoelectric constant of a piezoelectric film, and is used to collect the charge of the piezoelectric film and convert it into an output signal;

[0033] A control unit, which is electrically connected to the first strain gauge and / or the second strain gauge and / or the third strain gauge in a method for measuring a piezoelectric constant of a piezoelectric film, and is used to collect strain signals of the first strain gauge and / or the second strain gauge and / or the third strain gauge;

[0034] The control unit is also electrically connected to the charge conversion unit, and is used to receive the output signal and process it in combination with the strain signal to obtain a piezoelectric constant;

[0035] The control unit is also electrically connected to the force applying unit and is used to control the operation of the force applying unit.

[0036] Furthermore, the force-applying unit has a reciprocating motion structure, which includes a motor, an output wheel, an eccentric shaft, a transmission rod, a push rod, a guide sleeve and a bracket. The guide sleeve is horizontally arranged on the bracket. One end of the push rod can be hinged to the force-bearing end of the test strip. The other end of the push rod passes through the guide sleeve and is hinged to one end of the transmission rod. The other end of the transmission rod is installed on the eccentric shaft through a bearing. The eccentric shaft is arranged on the end face of the output wheel. The output wheel is installed on the output shaft of the motor. The speed of the motor is adjusted and controlled by the controller.

[0037] The beneficial effects of the present invention are as follows: the present invention provides a method for measuring the piezoelectric constant of a piezoelectric film, and by not using or using as few theoretical values ​​of material parameters as possible, the method can measure the piezoelectric constant e in real time and more realistically and accurately. 31 . BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and other features of the present invention will become more obvious by describing in detail the embodiments shown in the accompanying drawings. The same reference numerals in the accompanying drawings of the present invention represent the same or similar elements. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other accompanying drawings can be obtained based on these accompanying drawings without creative work. In the accompanying drawings:

[0039] Figure 1 is a graph of the voltage output of the strain gauge and the charge-to-voltage converter;

[0040] Figure 2 is the strain and piezoelectric constant e of the material in one cycle of the test 31 A real-time changing graph;

[0041] Figure 3 This is a structural diagram of the measuring device of Example 1;

[0042] Figure 4 This is a structural diagram of the measuring device of Example 2. DETAILED DESCRIPTION

[0043] The following will be combined with the embodiments and drawings to clearly and completely describe the concept, specific structure and technical effects of the present invention, so as to fully understand the purpose, scheme and effect of the present invention. It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other without conflict. The same reference numerals used throughout the drawings indicate the same or similar parts.

[0044] according to Figure 1 , Figure 2 , Figure 3 A method for measuring the piezoelectric constant of a piezoelectric film according to Example 1 of the present invention is described below, and a preferred embodiment is described in detail.

[0045] Example 1

[0046] like Figure 3 , a piezoelectric constant e 31 The measurement method comprises the following steps:

[0047] Step A: Use the fixing mechanism 20 to fix one end of the long strip pressure plate 51 (also called the test strip in Example 1), and use glue to fix the first strain gauge 52 on one side of the long strip pressure plate 51; the long strip pressure plate 51 is made of an aluminum (Al) strip with a width of 15 mm, a length of 200 mm, and a thickness of 2 mm.

[0048] Step B: Use glue to fix the sample 53 to the back of the Al strip 51 corresponding to the position of the first strain gauge 52; the sample 53 to be tested is a piezoelectric film with a Si / SiO2 / Pt lower electrode / PZT / Pt upper electrode structure. Among them, Si is 560um thick, SiO2 is 500nm thick, Pt lower electrode is 150nm thick, PZT is 1.5um thick, and Pt upper electrode is 100nm thick. The sample material to be tested is cut into small pieces of 7*10mm. The upper electrode at the measured position on the surface of the material is a circle with a diameter of 2mm, located in the center of the small piece. The first strain gauge is a strain gauge with a size of 7*4.5mm and an effective area of ​​3*3.5mm.

[0049] Step C: Start the force-applying unit 10 to apply force to the long strip pressure plate 51 to deform it, and perform periodic reciprocating motion within a horizontal displacement distance of 5 mm, and this displacement range is within the allowable range of elastic deformation of the Al strip. Because the Al strip is a single homogeneous material, when deformation occurs, the front and back sides of the Al strip can produce compressive strain and tensile strain of the same magnitude. The controller 40 reads the strain of the first strain gauge 52 in real time as the strain of the sample under test 53; the charge generated on the surface of the sample under test is converted into a voltage signal by using the charge-voltage converter 30. After the controller 40 collects the voltage signal of the charge-voltage converter 30, the charge corresponding to the voltage signal is obtained according to the charge-voltage relationship modulated by the charge-voltage converter 30; the voltage output of the strain gauge (first strain gauge) and the charge-voltage converter 30 obtained by the controller 40 is as follows: Figure 1 In the figure, the voltage of the strain gauge (first strain gauge) output (strainometer output) is represented by a dotted line, and the voltage of the charge-to-voltage converter 30 (piezo output) is represented by a solid line.

[0050] Among them, the modulation process of the charge-to-voltage converter is as follows: the relationship between the charge amount and the output voltage is first generated by using a standard charge generating device, and then a certain relationship is formed between the charge amount and the output voltage by adjusting and matching the parameters of the electronic components in the conversion device. For example, for a charge of 1pC, the converted output voltage is 10mV.

[0051] Step D: According to the strain and charge collected by the controller 40, the piezoelectric constant e of the sample to be tested is obtained by calculation. 31 value.

[0052] Figure 2 is the strain and piezoelectric constant e of the material in one cycle of the test 31 The real-time change curve of piezoelectric constant e 31 In most cases, it is at a relatively stable value, but when the strain is very small, there is a large change. This change trend is consistent with the change characteristics of piezoelectric materials.

[0053] Preferably, the process of applying force to the test strip is periodic;

[0054] In each cycle of the force application process, the maximum amplitude of the strain signal (strain amount) and the charge output signal (charge amount) of the piezoelectric film is calculated to obtain the piezoelectric constant of the piezoelectric film.

[0055] The piezoelectric constant is calculated as:

[0056] When a piezoelectric material is subjected to an external force, bound charges will be induced on its surface due to the piezoelectric effect, and its charge density σ3 is: σ3 = e 31 ×S1; where e 31 is the piezoelectric constant, which represents the ability of the strain parallel to the material plane to generate charge in the direction perpendicular to the material plane. S1 is the strain in a certain direction in the material plane. Therefore, as long as the strain S1 of the material and the charge Q3 generated on the surface electrode area A under the action of external force are measured, where Q3 = σ3A, the corresponding piezoelectric constant e can be obtained. 31 , (i.e. e 31 =σ3÷S1,σ3=Q3÷A).

[0057] Because there will be friction and gaps between the mechanical parts during the movement of the force-applying unit, non-uniform changes are sometimes inevitable; the electrical signal will also be affected by external noise signals and sometimes fluctuate. Therefore, although real-time one-to-one signal acquisition can understand the changes of the material in the whole process, the error fluctuation is relatively large and cannot accurately represent the performance of the material.

[0058] If the maximum amplitude of the strain signal and the piezoelectric signal output in one cycle is used for calculation, then from the strain point of view, the mechanical structure is in the maximum deformation state, and is turning from one direction to the opposite direction, and the position is relatively static, which can avoid the influence of errors caused by mechanical movement. The piezoelectric signal takes the maximum amplitude, and the influence of external noise signals can be suppressed by improving the signal-to-noise ratio. Moreover, in theory, the maximum amplitude of the piezoelectric signal also occurs at the moment of maximum strain. Therefore, the value obtained in this way should be the most accurate value that can represent the performance of the piezoelectric material. As shown by Figure 1 The e of the material is calculated from the four peak data shown. 31 3.21C / m2 , 3.21C / m 2 , 3.23C / m 2 , 3.20C / m 2 The average value is 3.21C / m 2 , the error is less than ±1%.

[0059] The above only takes the Si / SiO2 / Pt / PZT / Pt structure as an example, and other structures or piezoelectric materials may also be used.

[0060] Example 2

[0061] like Figure 4 As shown, after step C, a step of detecting the strain correction coefficient is also included.

[0062] The materials pasted on both sides of the Al strip are different, and the stress and strain on the material surface will also be different. In this structure, the thickness of the Al strip is the thickest, and metals generally have a higher Young's modulus. The strain generated in this system will be mainly determined by the characteristics of the Al strip. Although there is no correction, the obtained values ​​will not differ much in order of magnitude, and similar materials can also be compared. However, in order to obtain accurate values, the precise strain size of the measured film surface must be known.

[0063] The steps of strain correction coefficient detection are as follows: a second strain gauge 64 and a reference sheet 63 are prepared. A Si / SiO2 sheet of the same size as the above materials is selected for the reference sheet 63, with a thickness of 560um for Si and a thickness of 500nm for SiO2. The size is also 7*10mm. First, the second strain gauge 64 and the reference sheet 63 are glued together, and then the second strain gauge 64 and the reference sheet 63 are glued to one side of the Al bar 61 so that the reference sheet 63 is in contact with the Al bar 61; then the third strain gauge 62 is fixed at the corresponding position on the other side of the Al bar with glue. Then, one end of the long strip pressure plate (also called the reference bar in Example 2, i.e., the Al bar 61) is fixed with a fixing device 20, and the force unit 10 is started to push the other end of the Al bar 61 to make a reciprocating motion; finally, the controller 40 is used to collect the strain of the second strain gauge 64 and the third strain gauge 62 in real time.

[0064] Because the voltage output of the strain gauge is proportional to the strain, that is:

[0065] ΔU~ε;

[0066] Among them, ΔU is the voltage output by the strain gauge when strain occurs, and ε is the strain amount. Therefore, the ratio of the output voltage of the second strain gauge 64 on the reference gauge 63 to the output voltage of the third strain gauge 62 on the other side of the Al bar is the ratio of the strain magnitude of the second strain gauge (i.e., the strain magnitude on the surface of the reference gauge 63) to the strain magnitude at the third strain gauge 62 on the other side of the Al bar.

[0067] According to the corresponding multiple groups of strain information, it is obtained that under this condition, the output voltage of the second strain gauge 64 is only 70% of the output voltage of the strain gauge 62, that is, the strain correction coefficient is 70%, so that the strain on the surface of the reference photo 63 is 70% of the strain on the contact surface between the reference photo 63 and the Al strip. This may be due to the existence of the Si sheet, which weakens the effect of the Al strip deformation on the second strain gauge 64. Because the PZT film is formed on the surface of the above-mentioned Si sheet, the result of the strain gauge 62 is closer to the strain of the PZT film. This result is the actual strain value of the piezoelectric film layer that we directly obtain, rather than calculating a theoretical value through formulas and various physical parameters of the assumed film material. Therefore, this method also makes the measured e of the piezoelectric film 31 The piezoelectric coefficient is more accurate.

[0068] Among them, ΔU is the voltage output by the strain gauge when strain occurs, and ε is the strain amount.

[0069] Furthermore, the method of collecting and processing the strain signal of the third strain gauge and the strain signal of the second strain gauge during the deformation of the reference bar to obtain the strain correction coefficient is:

[0070] collecting a strain signal of the third strain gauge and a strain signal of the second strain gauge during deformation of the reference bar;

[0071] The ratio of the strain magnitude generated by the second strain gauge (ie, the strain magnitude generated on the surface of the reference gauge 63 ) to the strain magnitude at the third strain gauge 62 is used as the strain correction coefficient.

[0072] Preferably, in order to achieve the above effects and eliminate the problem of loss of measurement accuracy caused by inevitable non-uniform changes, the present application also proposes the following piezoelectric constant calculation method:

[0073] Preferably, the method of collecting and processing the strain signal of the third strain gauge and the strain signal of the second strain gauge during the deformation of the reference bar to obtain the strain correction coefficient is:

[0074] Start the force applying unit 10 to push the other end of the Al bar 61 to make a reciprocating motion;

[0075] The time of one reciprocating motion cycle is t;

[0076] When the output voltage of the second strain gauge 64 on the reference gauge 63 and the output voltage of the third strain gauge 62 on the other side of the Al bar are respectively the maximum values ​​of the most recent reciprocating motion cycle, the strain amount MAXε1 of the second strain gauge 64 and the strain amount MAXε2 of the third strain gauge 62 are respectively obtained; when the output voltage of the second strain gauge 64 on the reference gauge 63 and the output voltage of the third strain gauge 62 on the other side of the Al bar are respectively the minimum values ​​of the most recent reciprocating motion cycle, the strain amount MINε1 of the second strain gauge 64 and the strain amount MINε2 of the third strain gauge 62 are obtained;

[0077] In the time t of the next reciprocating motion cycle (at the current moment), the strain magnitudes of the second strain gauge at each moment are obtained, and the strain magnitude having the largest difference with MINε1 among the strain magnitudes is recorded as G1, the strain magnitude having the largest difference with MAXε1 among the strain magnitudes is recorded as G2, and the strain magnitude having the largest value between G1 and G2 is recorded as REMax2;

[0078] In the time t of the next reciprocating motion cycle (at the current moment), the strain magnitudes of the third strain gauge at each moment are obtained, and the strain magnitude having the largest difference with MINε2 among the strain magnitudes is recorded as G3, the strain magnitude having the largest difference with MAXε2 among the strain magnitudes is recorded as G4, and the strain magnitude having the largest value between G3 and G4 is recorded as REMax3;

[0079] The ratio of REMax2 and REMax3 is used as the strain correction coefficient.

[0080] Beneficial effect: The above method solves the problem that metals generally have a high Young's modulus. The local limit of the measured value of the effective strain size of the two strain gauges within the time t of the reciprocating motion cycle is used to obtain the strain correction coefficient through the limit value, so that the value obtained by correcting the piezoelectric constant after the correction coefficient is corrected under the limit of the output voltage will not have too much difference in order of magnitude, so that similar materials can be compared, further improving the accurate piezoelectric constant value obtained, and avoiding the problem of loss of piezoelectric constant measurement accuracy caused by non-uniform motion.

[0081] Furthermore, the piezoelectric constant is processed according to the strain correction coefficient to obtain a corrected piezoelectric constant by multiplying the strain correction coefficient by the piezoelectric constant of the piezoelectric material to obtain the corrected piezoelectric constant.

[0082] Thus, the strain correction coefficient is multiplied by the strain of the sample obtained in step D, and the product is used as the final strain of the sample. In this embodiment 2, the strain correction coefficient of 70% is used to correct the result of Example 1. 31The piezoelectric constant e of the PZT film is obtained by correcting it to 3.21C / m2. 31 4.59C / m 2 .

[0083] Although the description of the present invention has been quite detailed and has been described in particular with respect to several described embodiments, it is not intended to be limited to any of these details or embodiments or any particular embodiment, so as to effectively cover the intended scope of the present invention. In addition, the present invention is described above with the embodiments foreseeable by the inventors, and its purpose is to provide a useful description, and those non-substantial changes to the present invention that are not currently foreseen may still represent equivalent changes of the present invention.

Claims

1. A method for measuring the piezoelectric constant of a piezoelectric film, characterized in that: The method comprises the following steps: A first strain gauge is provided on one side of the test strip, and a piezoelectric film is correspondingly provided on the other side; Fixing one end of the test strip and applying force to the test strip at the other end to deform the test strip; collecting a strain signal of the first strain gauge and a charge output signal of the piezoelectric film during deformation of the test bar; Processing the strain signal and the charge output signal to obtain the piezoelectric constant of the piezoelectric film; The measuring method further comprises: A third strain gauge is provided on one side of the reference strip, and a reference strip and a second strain gauge are provided on the other side accordingly; Fixing one end of the reference bar and applying force to the reference bar at the other end to deform the reference bar; The strain signal of the third strain gauge and the strain signal of the second strain gauge during the deformation of the reference bar are collected and processed to obtain a strain correction coefficient, wherein the ratio of the strain magnitude of the second strain gauge to the strain magnitude at the third strain gauge is used as the strain correction coefficient; Processing the piezoelectric constant according to the strain correction coefficient to obtain a corrected piezoelectric constant; One side of the reference sheet is connected to the reference bar, and the other side is connected to the second strain gauge.

2. The method for measuring the piezoelectric constant of a piezoelectric film according to claim 1, characterized in that: The method for processing the collected strain signal and the charge output signal to obtain the piezoelectric constant of the piezoelectric film is as follows: acquiring the strain signal and the charge output signal of the piezoelectric film at the collection time to calculate the piezoelectric constant at the collection time.

3. The method for measuring the piezoelectric constant of a piezoelectric film according to claim 1, characterized in that: The process of applying force to the test strip is periodic; In a cycle of a force application process, the maximum amplitude of the strain signal and the charge output signal of the piezoelectric film are calculated to obtain the piezoelectric constant of the piezoelectric film.

4. The method for measuring the piezoelectric constant of a piezoelectric film according to claim 1, characterized in that: The test strip is a single homogeneous material; the test strip is in the shape of a long strip; and the deformation of the test strip is within the elastic strain range of the material.

5. The method for measuring the piezoelectric constant of a piezoelectric film according to claim 1, characterized in that: Specifically, the third strain gauge and the second strain gauge are strain gauges of the same model.

6. The method for measuring the piezoelectric constant of a piezoelectric film according to claim 1, characterized in that: The specifications of the reference sheet are the same as those of the piezoelectric film.

7. A device for measuring the piezoelectric constant of a piezoelectric film, characterized in that: The measuring device comprises: A force applying unit; the force applying unit is used to apply force to the test strip and / or the reference strip in the method for measuring the piezoelectric constant of a piezoelectric film according to any one of claims 3 to 6 to cause the test strip to deform; A fixing unit; the fixing unit is used to fix one end of the test strip and / or the reference strip in the method for measuring the piezoelectric constant of a piezoelectric film according to any one of claims 3 to 6; A charge conversion unit, which is electrically connected to the piezoelectric film in the method for measuring the piezoelectric constant of a piezoelectric film according to any one of claims 1 to 6, and is used to collect the charge of the piezoelectric film and convert it into an output signal; A control unit, which is electrically connected to the first strain gauge and / or the second strain gauge and / or the third strain gauge in the method for measuring the piezoelectric constant of a piezoelectric film according to any one of claims 1 to 6, and is used to collect strain signals of the first strain gauge and / or the second strain gauge and / or the third strain gauge; The control unit is also electrically connected to the charge conversion unit, and is used to receive the output signal and process it in combination with the strain signal to obtain a piezoelectric constant; The control unit is also electrically connected to the force applying unit and is used to control the operation of the force applying unit.

8. The device for measuring the piezoelectric constant of a piezoelectric film according to claim 7, characterized in that: The force-applying unit has a reciprocating motion structure, which includes a motor, an output wheel, an eccentric shaft, a transmission rod, a push rod, a guide sleeve and a bracket. The guide sleeve is horizontally arranged on the bracket. One end of the push rod can be hinged to the force-bearing end of the test strip. The other end of the push rod passes through the guide sleeve and is hinged to one end of the transmission rod. The other end of the transmission rod is installed on the eccentric shaft through a bearing. The eccentric shaft is arranged on the end face of the output wheel. The output wheel is installed on the output shaft of the motor. The speed of the motor is adjusted and controlled by the controller.

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