JP2013096816A - Piezoelectric characteristic measurement system and piezoelectric characteristic measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric characteristic measurement system and its method capable of accurately finding out piezoelectric characteristics even for a dynamic load.SOLUTION: Information (target output voltage information) on a voltage generated from a piezoelectric substance S to be a measuring target and information (pedestal output voltage information) on a voltage generated from a pedestal piezoelectric substance 26 superposed to the piezoelectric substance S in a direction of an axis C to be a direction for applying pressure are acquired and the piezoelectric characteristics of the piezoelectric substance S is found out based on both of the target output voltage information and the pedestal output voltage information, so that the characteristics of the piezoelectric substance S against dynamic pressure can be highly accurately measured.

Description

  The present invention relates to a piezoelectric characteristic measuring system and a piezoelectric characteristic measuring method.

  For example, piezoelectric sensors using piezoelectric elements are used in various applications, such as measuring the pressure of an automobile fuel injection device. The piezoelectric element generates a voltage having a predetermined relationship with the applied pressure. In order to evaluate the measurement result of the pressure by the piezoelectric sensor with high accuracy, it is necessary to measure the predetermined relationship representing the characteristics of the piezoelectric element with high accuracy in advance.

  In Patent Document 1, in order to measure the characteristics of a piezoelectric element, the biasing force of a spring whose spring coefficient is known in advance and the force applied to the piezoelectric element are balanced, and the amount of bending of the spring is determined by the capacitance of the variable capacitor. Patent Document 1 discloses a measuring apparatus that precisely measures the characteristics of a piezoelectric body by using this method, in which a method for accurately measuring the applied force and calculating the applied force is disclosed. . In this apparatus, force is applied to the piezoelectric element by manually pressing the probe against the piezoelectric element.

JP 2004-235589 A

  For example, in-vehicle pressure sensors, etc. have high measurement accuracy not only for statically applied pressure (static pressure) but also for time-varying pressure (dynamic pressure) caused by vibration. It is also important. In an in-vehicle piezoelectric element, it is important to know in detail not only a characteristic for a static pressure but also a characteristic for a dynamic pressure as a characteristic of the piezoelectric element itself.

  However, with the conventional measuring device described in Patent Document 1, it is difficult to accurately measure the characteristic against dynamic pressure. For example, the pressure value calculated by the measuring device is superimposed with various time delays and errors such as an error due to a change in the spring constant, a time delay in capacitance change, and a time delay in spring deflection. For this reason, in the measuring apparatus as described in Patent Document 1, it is difficult to measure the magnitude of the applied dynamic pressure itself with high accuracy with a small time delay, and the characteristics of the piezoelectric element with respect to the dynamic pressure. It was difficult to know. The present invention aims to solve this problem.

  The present invention is a piezoelectric characteristic measurement system for measuring an output voltage from the piezoelectric body that is generated when a pressure is applied among the piezoelectric characteristics of the piezoelectric body that is a measurement object. A placement measuring unit having a placement surface to be placed, and a contact surface parallel to the placement surface disposed opposite to the placement surface, and the placement surface and the contact surface. A pressure application unit that applies a pressure along one orthogonal axial direction to the piezoelectric body via the contact surface, information on the applied pressure, and an output voltage from the piezoelectric body that is generated according to the pressure. An information acquisition unit that acquires information; and a calculation unit that calculates a piezoelectric characteristic value of the piezoelectric body using the pressure information and the output voltage information. A plate-like body having a pair of parallel principal surfaces with the mounting surface as one principal surface; A pedestal member having a pedestal surface orthogonal to the uniaxial direction, disposed opposite to the other main surface, and the other main surface of the plate-like body placed on the pedestal surface of the pedestal member The pedestal piezoelectric body is disposed between the pedestal surface and the other main surface, and is disposed at a position overlapping the piezoelectric body along the uniaxial direction. The pedestal output voltage is generated according to the pressure along the line, the information acquisition unit acquires information on the pedestal output voltage generated according to the applied pressure, and the calculation unit is information on the pedestal output voltage. And a piezoelectric characteristic measurement system for calculating a piezoelectric characteristic of the piezoelectric body that is a measurement object using the output voltage information from the piezoelectric body.

  The present invention also relates to a piezoelectric characteristic measuring method for measuring an output voltage from the piezoelectric body that is generated when pressure is applied among the piezoelectric characteristics of a target piezoelectric body that is a measurement object, the uniaxial direction And a step of periodically applying a pressure along the uniaxial direction to the target piezoelectric body from a side opposite to the measurement piezoelectric body, and a step of applying the pressure to the target piezoelectric body. Obtaining information and information on the output voltage from the target piezoelectric body generated according to the pressure, and calculating a piezoelectric characteristic value of the measurement piezoelectric body using the pressure information and the output voltage information In the acquiring step, the information on the output voltage from the piezoelectric body for measurement generated according to the pressure along the uniaxial direction is acquired together as the information on the applied pressure. The piezoelectric characteristics measuring method according to symptoms, together provide.

  The piezoelectric characteristic measuring system and the piezoelectric characteristic measuring method of the present invention are based on a voltage generated by a piezoelectric body that is a measurement object and an applied pressure calculated from a pressure detecting pedestal piezoelectric body that is arranged on the piezoelectric body. Therefore, the piezoelectric characteristics can be accurately measured even with respect to dynamic pressure.

1 is a schematic configuration diagram of a piezoelectric characteristic measurement system according to an embodiment of the present invention. It is a schematic perspective view which shows an example of the measuring object measured with the measuring system of FIG. It is a schematic sectional drawing of one Embodiment of the current collection head of the measuring system of FIG. It is a schematic sectional drawing of other embodiment of the current collection head of the measurement system of FIG. It is a schematic sectional drawing which expands and shows the vicinity of the base member of the measurement system of FIG. It is a flowchart of the measuring method which concerns on one Embodiment of this invention.

  FIG. 1 is a schematic configuration diagram of a measurement system 1 which is an embodiment of the piezoelectric characteristic measurement system of the present invention. In FIG. 1, a part is shown in cross section. This is a piezoelectric characteristic measurement system for measuring an output voltage from the piezoelectric body S generated when a dynamic pressure is applied, among the piezoelectric characteristics of the piezoelectric body S as a measurement object. A mounting measurement unit 20 having a mounting surface 22A on which the piezoelectric body S is mounted, a pressure applying unit 30 for applying pressure to the piezoelectric body S, and information on the applied pressure and the piezoelectric generated in accordance with the pressure The information acquisition unit 40 that acquires information on the output voltage from the body S, and the calculation unit 50 that calculates the piezoelectric characteristic value of the piezoelectric body S using the pressure information and the output voltage information acquired by the information acquisition unit 40. And an applied pressure control unit 53 for controlling the magnitude and cycle of the dynamic pressure applied to the piezoelectric body S.

  The placement measurement unit 20 is disposed to face the plate-like body 22 having a pair of parallel principal surfaces with the placement surface 22A as one principal surface, and the other principal surface 22B of the plate-like body 22. A pedestal member 24 having a pedestal surface 24A orthogonal to the axis C, and a pedestal piezoelectric body 26 placed on the pedestal surface 24A of the pedestal member 24 and sandwiched between the other main surface 22B of the plate-like body 22 I have.

  The pedestal piezoelectric body 26 is arranged at a position overlapping the piezoelectric body S along the axis C, and a pedestal output corresponding to the pressure along the axis C received from the pedestal surface 24A and the other main surface 22B of the plate-like body 22. Generate voltage. The pedestal piezoelectric body 26 is connected to the information acquisition unit 40 via the low noise cable L1.

  The measurement system 1 includes a pedestal piezoelectric element that is superposed on the piezoelectric body S along the axis C, which is a direction in which pressure is applied, in addition to information on the voltage (target output voltage information) generated by the piezoelectric body S that is a measurement target Information on the voltage generated by the body 26 (pedestal output voltage information) is obtained, and the piezoelectric characteristics of the piezoelectric body S are obtained based on both the information on the output voltage and the information on the pedestal output voltage. The characteristics of the piezoelectric body S can be measured with high accuracy. Hereinafter, the configuration of each part of the measurement system 1 will be described.

  For example, as shown in FIG. 2, the piezoelectric body S has a cylindrical shape with a through hole Sa formed in the center. In the present embodiment, the center of the through hole Sa of the piezoelectric body S is arranged on the mounting surface 22A so as to coincide with the axis C shown in FIG.

  The pressure application unit 30 includes an actuator 34 and a current collecting head 35 provided with an abutment surface 35A parallel to the placement surface 22 and disposed opposite the placement surface 22A. The actuator 34 includes a piezoelectric device in which a plurality of piezoelectric elements are stacked, and is a pressure generating unit that generates a pressure to be applied to the piezoelectric body S. The actuator 34 is configured to expand or contract along the axial direction of the cylindrical body 13 by an amount corresponding to the applied voltage. As the piezoelectric element constituting the actuator 34, a piezoelectric element such as a piezo actuator that can accurately follow a high frequency fluctuation and generate pressure can be used. The actuator 34 is connected to the piezo driver 52 of the applied pressure control unit 53 via the low noise cable L3.

  The actuator 34 is disposed inside the cylindrical body 13 supported by the support body 11. The actuator 34 is accommodated inside the first cylindrical body 13 via a linear guide bush 17 for reducing sliding resistance. The linear guide bush 17 constitutes a so-called linear ball bearing or ball spline. The support 11 is a frame-like member having a side plate 11a, a top plate 11b, and a bottom plate 11c that are arranged to face each other. The cylindrical body 13 is fixed to the top plate 11b, and the central axis of the cylindrical body 13 coincides with the axis C.

  A female screw hole 11α having a central axis coinciding with the axis C is formed in the top plate 11b of the support body 11. A first preload application screw (male screw) 37 is screwed into the female screw hole 11α. ing. A preload pressure sensor 39 including a piezoelectric element is provided below the first preload application screw 37. The preload pressure sensor 39 is a sensor that converts pressure into an electrical signal. The preload pressure sensor 39 follows the preload application screw 37 and moves up and down in the cylindrical body 13. The preload pressure sensor 39 is provided with a reference surface 38 orthogonal to the axis C at the lower end. The reference surface 38 moves up and down in the cylindrical body 13 in accordance with the rotation of the preload application screw 37. The preload application screw 37 is a reference plane moving means. The actuator 34 has an upper end surface 34A orthogonal to the axis C, and the reference surface 38 is in contact with the upper end surface 34A.

  The applied pressure control unit 53 includes a function generator 51 that creates a voltage waveform to be sent to the actuator 34, and a piezo driver 52 that amplifies the generated waveform and operates the actuator 34. A measurement voltage is applied to the actuator 34 from the applied pressure control unit 53, and the actuator 34 is configured to expand or contract along the axial direction of the cylindrical body 13 by an amount corresponding to the applied voltage. ing.

  In the current collecting head 35, the contact surface 35 </ b> A comes into contact with the piezoelectric body S, collects (collects) electric charges generated from the piezoelectric body S, and outputs it as a voltage signal. As shown in an enlarged view in FIG. 3, the current collecting head 35 has an alumina ball 68 sandwiched between a cylindrical upper jig 66 and a lower jig 57, and a load is applied to the piezoelectric body S via the ball 68. And a voltage signal (target output voltage information) output from the piezoelectric body S corresponding to the charge generated by the piezoelectric body S is sent to the information acquisition unit 40 via the low noise cable L2.

  Conical recesses 66 a and 67 a for supporting the balls 68 are formed on the opposing surfaces of the upper jig 66 and the lower jig 67, respectively. The recesses 66a and 67a are filled with a soft resin 69 such as a silicone adhesive or a silicone sealant that prevents the ball 68 from falling off and absorbs an impact. By adopting a configuration in which the ball 68 is supported on the opposing surfaces of the upper jig 66 and the lower jig 67, even when the parallelism of the upper and lower surfaces of the piezoelectric body S varies, the entire contact surface 35A can be obtained. It can abut on the upper surface of the piezoelectric body S, and can efficiently transmit the pressure along the C-axis direction to the piezoelectric body S. In the measurement system 1, the entire support 11 is placed on the vibration isolation mechanism unit 70 so that excessive vibration is not transmitted to the piezoelectric body S.

  FIG. 4 is a diagram illustrating a different embodiment of the current collecting head. In the current collecting head 60 shown in FIG. 4, the upper jig 61 has a disk shape and the lower surface is flat as compared with the current collecting head 35 in FIG. The lower jig 62 is cylindrical and has a conical recess 62a formed at the center of the upper surface, and an alumina ball 63 is placed in the recess. Between the upper and lower jigs 61 and 62, a silicone adhesive 64 is provided in an annular shape to prevent the ball 63 from falling off and for a damper. At the center of the silicone-based adhesive 64, a space 65 is provided such that the ball 63 is not touched by cutting off after curing. Also in the embodiment shown in FIG. 4, the entire contact surface 35 </ b> A contacts the upper surface of the piezoelectric body S, and the pressure along the C-axis direction can be efficiently transmitted to the piezoelectric body S.

  The pedestal member 24 of the mounting measurement unit 20 includes a rail guide 41. The side plate 11a of the support 11 is provided with rails 13. The rail guide 41 of the pedestal member 24 is mounted on the rail 13, and the entire pedestal member 24 is moved in the C-axis direction by moving the rail guide 41 in the vertical direction (direction along the axis C) along the rail 13. It is possible to move along. The pedestal member 24 includes a hole 27 extending along the direction of the axis C, having an open end 27a opened on the surface opposite to the pedestal surface 24A and a bottom surface 27B orthogonal to the axis C. The bottom plate 11c of the support 11 is provided with a female screw hole 11β having a central axis coinciding with the axis C, and a rod member 25 is inserted into the female screw hole 11β. The rod member 25 has a male screw shape having irregularities on the outer peripheral surface, and is screwed into the female screw hole 11β of the bottom plate 11c. The rod member 25 has an end surface 25A orthogonal to the axis C, and the end surface 25A is in contact with the bottom surface 27B of the hole 27. The end surface 25 </ b> A varies in the amount of protrusion from the bottom plate portion 11 c according to the rotation of the rod member 25. The position of the pedestal member 24 along the axis C is changed according to the position of the end surface 25A of the rod member 25.

  In the measurement system 1, the position along the axis C of the reference surface 38 is adjusted by the first preload application screw (male screw) 37, and along the axis C of the pedestal member 24 and consequently the mounting surface 22 </ b> A by the rod member 25. The position can be adjusted. That is, in the measurement system 1, the distance between the reference surface 38 and the placement surface 22A can be changed. In the measurement system 1, the interval between the reference surface 38 and the mounting surface 22 </ b> A is changed, a static pressure having a predetermined size is applied to the piezoelectric body S, and a static pressure having a predetermined size is applied. Can be measured. The actuator 34 outputs an output voltage corresponding to the applied dynamic pressure. The response of the output voltage from the actuator 34 to the applied pressure is a state in which a certain static pressure is applied ( Preload state) may be higher. By changing the distance between the reference surface 38 and the mounting surface 22A and applying a predetermined static pressure to the actuator 34 in advance, the dynamic characteristics of the piezoelectric body S can be detected with high accuracy. A preload pressure sensor 39 that detects the pressure applied by the first preload application screw 37 is connected to a monitor (not shown) that displays the measured pressure. The measurement operator applies a static pressure of a predetermined size to the piezoelectric body by rotating the preload application screw 37 while confirming the display value (measurement value by the preload pressure sensor 39) displayed on the monitor. be able to.

  The pedestal piezoelectric body 26 also outputs a voltage corresponding to the applied pressure, but the responsiveness of the output voltage from the pedestal piezoelectric body 26 is also higher when a static pressure is applied to some extent. There is a case. FIG. 5 is an enlarged schematic sectional view showing the vicinity of the base member 24. In the measuring apparatus 1, a base piezoelectric body 26 having a shape in which a through hole 26 a is provided at the center is used. A concave portion 21 is formed in the center portion of the bottom surface 27 b of the hole portion 27 of the base member 24, and a through hole 21 a is formed in the bottom surface of the concave portion 21. Further, a female screw-like recess 23 is provided at the center of the other main surface 22B of the plate-like body 22 having the mounting surface 22A. In the measurement system 1, a second preload application screw (male screw) 29 is inserted into the through hole 21 a of the recess 21 and the through hole 26 a of the base piezoelectric body 26 and fastened to the recess 23 of the plate-like body 22. By fastening the preload application screw 29, the pedestal piezoelectric body 26 can be in a state (preload state) where a static pressure of a predetermined magnitude is applied. By adjusting the fastening strength of the second preload application screw 29, the magnitude of the static pressure applied to the pedestal piezoelectric body can be adjusted, and the voltage according to the dynamic pressure can be output satisfactorily. It is possible to apply a static pressure.

  The information acquisition unit 40 acquires information on the pedestal output voltage generated according to the applied pressure. The calculation unit 50 calculates the piezoelectric characteristics of the piezoelectric body S, which is the measurement object, using information on the pedestal output voltage and information on the output voltage from the piezoelectric body. The information acquisition unit 40 includes an output charge charge amplifier 56 connected to the current collecting head 35 via a low noise cable 55, and an applied pressure monitor charge amplifier 58 connected to the base piezoelectric body 26 via a low noise cable. And a data logger 59 connected to the charge amplifier 56 and the charge amplifier 58. The data logger 59 is connected to the calculation unit 50. The calculation unit 50 is a known personal computer (information processing unit). The outputs of both charge amplifiers 56 and 58 can be confirmed in real time during measurement by a monitor 59 such as an oscilloscope.

  Next, an embodiment of the measurement method of the present invention for measuring the piezoelectric characteristics of the piezoelectric body S with such a measurement system 1 will be described with reference to FIG.

  First, each part of the measurement system 1 and the piezoelectric body S are arranged so as to be in the state shown in FIG. 1 (step S1). In this step, the piezoelectric body S and the pedestal piezoelectric body, which is a measurement piezoelectric body, are arranged so as to overlap along the direction of the axis C, and the actuator 34, the first preload application means 27, the rod member 25, etc. Are arranged so that the central axis of the axis coincides with the axis C.

  Next, a static pressure is applied to the target piezoelectric body S to make a preload state (step S2). Specifically, the piezoelectric body S to be measured is sandwiched between the current collecting head 35 and the plate-like body 22, and the position of the reference plane 38 is adjusted by turning the first preload application screw 27 to obtain a predetermined size. Is applied to the piezoelectric body S. For example, a relatively high pressure of 4 to 6 kN is applied as a preloading static pressure. At this time, the position of the mounting surface 22A can also be adjusted by adjusting the rotation of the rod member 25. The first preload application means 27 and the rod member 25 are arranged so that their central axes coincide with the axis C, and a static pressure along the axis C is efficiently applied to the piezoelectric body S.

  Next, application of dynamic pressure to the piezoelectric body S is started (step S3). In this step, the applied pressure control unit 53 applies a voltage for measuring the actuator 34, and the actuator 34 expands or contracts along the axial direction of the cylindrical body 13 by an amount corresponding to the applied voltage, so that piezoelectric Dynamic pressure is applied to the body S.

  Subsequently, the information acquisition unit 40 overlaps the piezoelectric body S along the information on the voltage (target output voltage information) generated by the piezoelectric body S that is the measurement target and the direction of the axis C that is the direction in which the pressure is applied. Information on the voltage generated by the base piezoelectric body 26 (base output voltage information) is acquired (step S4). The pressure applied to the piezoelectric body S can be estimated from the voltage generated by the function generator 51 and the voltage obtained by amplification by the piezo driver 52. However, such an estimated value often differs greatly from the pressure actually applied to the piezoelectric body S. The pedestal piezoelectric body 26 is disposed immediately below the piezoelectric body S to be measured, and directly receives dynamic pressure along the axis C applied to the piezoelectric body S. It can be said that the information on the voltage output from the base piezoelectric body 26 accurately corresponds to the magnitude of the dynamic pressure applied to the piezoelectric body S.

  Next, the calculation unit 50 calculates the piezoelectric characteristic value of the piezoelectric body S using the target output voltage information and the pedestal output voltage information acquired by the information acquisition unit 40 (step S5). For example, the voltage waveform in the pedestal output voltage information is regarded as a waveform representing the time series change of the dynamic pressure input to the piezoelectric body S, and the voltage waveform in the target output voltage information is determined according to the time series change of the dynamic pressure. As the voltage information generated from the object S, a parameter representing the response characteristic of the piezoelectric body S with respect to the applied dynamic pressure is calculated. Examples of the parameter to be calculated include a piezoelectric strain constant called d33, but are not particularly limited.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention are not particularly limited, and it is needless to say that various improvements and modifications may be made without departing from the gist of the present invention.

S Piezoelectric body 11 Support body 11a Side plate 11b Top plate 11c Bottom plate 13 Tubular body 22A Placement surface 20 Placement measurement unit 22 Plate-like body 22A Placement surface 22B The other main surface 24 Base member 24A Base surface 25 Rod member 26 Base Piezoelectric body 30 Pressure application unit 34 Actuator 35 Current collecting head 35A Contact surface 37 First preload application screw 38 Reference surface 40 Information acquisition unit 50 Calculation unit 52 Piezo driver 53 Applied pressure control unit 56, 58 Charge amplifier

Claims (6)

Among the piezoelectric characteristics of a piezoelectric body that is a measurement object, a piezoelectric characteristic measurement system for measuring an output voltage from the piezoelectric body that is generated when pressure is applied,
A mounting measurement unit having a mounting surface on which the piezoelectric body is mounted;
The contact surface is disposed opposite to the placement surface, and has a contact surface parallel to the placement surface, and the pressure along the uniaxial direction perpendicular to the placement surface and the contact surface is A pressure application unit for applying to the piezoelectric body via,
An information acquisition unit that acquires information on the applied pressure and information on an output voltage from the piezoelectric body that is generated according to the pressure;
A calculation unit that calculates a piezoelectric characteristic value of the piezoelectric body using the pressure information and the output voltage information;
The mounting measurement unit is a plate having a pair of parallel main surfaces with the mounting surface as one main surface, and the uniaxially arranged to face the other main surface of the plate. A pedestal member having a pedestal surface orthogonal to the direction, and a pedestal piezoelectric body placed on the pedestal surface of the pedestal member and sandwiched between the other main surface of the plate-like body,
The pedestal piezoelectric body is disposed at a position overlapping the piezoelectric body along the uniaxial direction, and generates a pedestal output voltage corresponding to the pressure along the uniaxial direction received from the pedestal surface and the other main surface. ,
The information acquisition unit acquires information on the pedestal output voltage generated according to the applied pressure,
The calculation unit calculates a piezoelectric characteristic of the piezoelectric body, which is a measurement object, using information on the pedestal output voltage and information on the output voltage from the piezoelectric body. . A cylindrical body having a central axis along the uniaxial direction; and a support body for supporting the cylindrical body,
The pressure application unit is disposed inside the cylindrical body, and generates pressure to be applied to the piezoelectric body, and is disposed between the pressure generation means and the mounting surface. Comprising a plate for pressure application having a contact surface;
2. The piezoelectric characteristic measuring system according to claim 1, wherein the pressure generating means applies a pressure along the uniaxial direction to the pressure applying plate-like body. The cylindrical body includes a reference surface orthogonal to the central axis inside,
The pressure generating means includes a piezoelectric device that is arranged between the reference surface and the pressure applying plate and adjusts the magnitude of pressure along the uniaxial direction according to an applied voltage. The piezoelectric characteristic measuring system according to claim 2, wherein   The piezoelectric characteristic measurement system according to claim 3, further comprising a pedestal surface movable unit that varies a relative position of the pedestal surface with respect to the cylindrical body along the uniaxial direction. The pedestal member includes an opening extending along the uniaxial direction, having an open end opened on a surface opposite to the pedestal surface and a bottom surface orthogonal to the uniaxial direction,
The pedestal surface moving means includes a rod member having an end surface orthogonal to the uniaxial direction, and a rod member variation mechanism that varies the position of the end surface along the uniaxial direction,
The rod member is inserted into the hole, and the end surface is in contact with the bottom surface of the hole,
5. The piezoelectric characteristic according to claim 4, wherein the pedestal surface moving unit varies the relative position of the pedestal surface with respect to the cylindrical body by varying the position of the end surface by the rod member variation mechanism. Measuring system. Among the piezoelectric characteristics of the target piezoelectric body that is the measurement object, a piezoelectric characteristic measurement method for measuring an output voltage from the piezoelectric body that is generated when pressure is applied,
Arranging the target piezoelectric body and a measurement piezoelectric body that generates a voltage in accordance with an applied pressure, along one axis direction; and
Periodically applying a pressure along the uniaxial direction to the target piezoelectric body from a side opposite to the measurement piezoelectric body;
Obtaining information on the applied pressure and information on an output voltage from the target piezoelectric body generated in response to the pressure;
Calculating the piezoelectric characteristic value of the measurement piezoelectric body using the pressure information and the output voltage information,
In the obtaining step, information on the output voltage from the piezoelectric body for measurement generated according to the pressure along the uniaxial direction is also obtained as information on the applied pressure. Method.

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