JP2022035144A - Piezo element and motion sensor - Google Patents

Abstract

To provide an acceleration sensor using a piezo-ion effect with an ionic liquid, which enables high functionality and versatile extension of the sensor on the basis of an elastomer matrix design.SOLUTION: A flexible accelerometer 11 contains a mixture of liquid and polymeric material. A gel layer formed in the form of a sheet forms a three-dimensional polymer network inside by heat or light. In addition, stretchable electrodes 2-1, 2-2 independently laminated on both sides of the ionic liquid-polymer material gel layer are included. The electric charge generated in the ionic liquid-polymer material gel layer is output in response to the acceleration applied to the ionic liquid-polymer material gel layer.SELECTED DRAWING: Figure 1

Description

Application for application of Article 30, Paragraph 2 of the Patent Act was submitted. The 67th JSAP Spring Meeting (Cancelled) Proceedings was published on February 28, 2nd year of Reiwa. Proceedings of the Annual Meeting of the Japan Society of Applied Physics (Cancelled) published on the WEB

The present invention relates to a piezo element and a motion sensor, and more particularly to a piezo element used for a flexible accelerometer having elasticity and a motion sensor using the piezo element.

The Internet of Things IoT, which is a system that connects people to things and things to things through the Internet, is drawing attention. For example, there are health monitoring using a heart rate sensor, remote control of home appliances using a wearable device, walking sensing using a sole sensor, and the like.

Patent Document 1 discloses a technique relating to a wearable biological information collecting device capable of collectively collecting a wide variety of biological information of the human body.
Wearable electronics are indispensable for the realization of IoT and its application to the real world, and its key device is a flexible sensor. However, it is said that 1 trillion sensors are used in the social implementation of IoT, and the power supply to each sensor becomes a big issue. Therefore, research on piezosensors using piezoelectric polymers that do not require power supply from the outside or power storage devices and energy harvesting by triboelectric charging is attracting attention. However, although the voltage generation in the above-mentioned existing technology is instantaneous and excellent in detecting acceleration, it is not suitable for measuring slow motion that requires output on a longer time scale. For example, since the response frequency of the muscle is as slow as 10 Hz or less, it can be seen that the detection of displacement is more suitable than the acceleration for the application of the flexible sensor.

As the flexible sensor, for example, an extension sensor technique as in Patent Document 2 is disclosed.
Flexible sensors are required to have moldability, elasticity, and wearability. As a report on elastic electrodes, as in Patent Document 3, elasticity with improved electrical conductivity and cutting elongation by adding polyglycerin to a colloidal aqueous dispersion of PEDOT: PSS, which is a conductive polymer. A technique using an electrode for an actuator is disclosed. The physical information such as the ionic liquid transport number and the ionic volume disclosed in the actuator of Patent Document 3 is disclosed in Non-Patent Document 1.

There are various types of accelerometers, but a typical piezoelectric accelerometer has a sensitivity of about 0.035 nC / (m / s ² ) at the highest.
As an acceleration sensor using the piezoion effect of an ionic liquid, an example of using a thermoplastic polyurethane as an elastomer matrix as in Patent Document 4 is disclosed.

JP-A-2015-070917 Japanese Unexamined Patent Publication No. 2014-228507 Japanese Unexamined Patent Publication No. 2011-05233 Japanese Unexamined Patent Publication No. 2018-031680

"Driving Mechanisms of Ionic Polymer Actuators Having Electric DoubleLayer Capacitor Structures", S.Imaisumi et al., J.Phys.chem. B, 116, 5080 (2012)

Of the various wearable biometric information collection devices and sensors currently proposed, the accelerometer using the piezoion effect of the ionic liquid is a wearable sensor that requires formability, elasticity, and wearability, and is an element. It is useful as a flexible accelerometer that easily detects acceleration without monitoring changes in resistance value. On the other hand, the influence of the polymer structure of the elastomer matrix forming the accelerometer on the piezoion effect is limited, and when oriented to social implementation, the physical properties of the sensor can be controlled based on the design of the elastomer matrix, and the electrical output can be improved. Versatility expansion is needed.

The piezo element of the present invention contains a polymer material layer containing a mixture of an ionic liquid and a polymer material, which is formed into a sheet and forms a three-dimensional polymer network inside the piezo element by heat or light, and further. The polymer material layer is provided with elastic electrodes independently laminated on both sides thereof, and the electric charge generated in the polymer material layer is output according to the force applied to the polymer material layer.

Further, the motion sensor of the present invention has a plurality of the piezo elements, includes a calculation unit for calculating a measured value by the plurality of piezo elements, and is further provided with a piezo element according to the calculation result of the calculation unit. It is equipped with a quantification unit that quantifies the movement of objects.

The piezo element of the present invention can easily construct a flexible acceleration sensor capable of easily detecting acceleration and controlling the electrical and physical functions of the sensor.

It is sectional drawing of an example of the flexible accelerometer which concerns on Example 1 of this invention. It is a top view of the flexible accelerometer shown in FIG. 1. It is a figure which shows the manufacturing flow of an example of the flexible accelerometer which concerns on Example 1 of this invention. It is a figure which showed the relationship with respect to the temperature of the storage elastic modulus for each different initiator amount. It is a figure which showed the relationship between the initiator amount and the cross-linking density. It is a figure which shows the measuring apparatus which measures the sensor response characteristic. It is a figure which shows the time response of the generated charge and the generated voltage when the sensor is distorted. It is a figure explaining the consideration of the operation of a sensor. It is a figure which showed the behavior of the generated charge and voltage with respect to time for each different cross-linking density. It is a figure which shows the value of charge, capacitance, and voltage with respect to the cross-linking density.

The piezo element of the present invention functions as a flexible accelerometer. The flexible accelerometer includes the piezo element of the present invention.
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

(Structure of flexible accelerometer)
FIG. 1 is a cross-sectional view of a flexible accelerometer 11 which is an example of a flexible accelerometer including the piezo element of the present invention. As shown in FIG. 1, the flexible accelerometer 11 includes a polymer material layer 1 formed in a sheet shape, elastic electrodes 2-1 independently laminated on both surfaces of the polymer material layer 1, and elasticity. The piezo element 10 including the electrode 2-2 is included. Further, FIG. 2 is a view (top view) of the flexible acceleration sensor 11 shown in FIG. 1 as viewed from the stretchable electrode 2-1 side.

The polymer material layer 1 is composed of a mixture of an ionic liquid (IL) and a polymer material. The polymer material layer 1 is composed of a mixture of an ionic liquid and acrylonitrile-butadiene rubber (NBR) (hereinafter, also referred to as IL-NBR). Suitable examples of IL-NBR include 1-methyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([EMI] [TFSI]), which is an ionic liquid, and acrylonitrile-butadiene rubber (NBR), which is a polymer material. (Ionic liquid-polymer material gel) can be mentioned.

The elastic electrode 2-1 and the elastic electrode 2-2 are independently laminated so as to cover both sides of the polymer material layer 1. The thickness of the polymer material layer is not particularly limited, but may be, for example, 50 to 300 μm. The stretchable electrode 2-1 and the stretchable electrode 2-2 may be thin films. In FIG. 1, the elastic electrode 2-1 side is a positive electrode, and the elastic electrode 2-2 side is a negative electrode. Here, the elastic electrode 2-1 and the elastic electrode 2-2 are, for example, a mixture of polyglycerin (PG) and PEDOT: PSS (Poly (3,4-ethylenedioxythiophene): Poly (4-stylelensulphonicacid)). It is a film (hereinafter referred to as PEDOT: PSS-PG film) composed of PEDOT: PSS-PG).

In this example, the ionic liquid (IL) preferably contains at least one selected from the group consisting of an imidazolium salt, a piperidinium salt, a pyridinium compound, and a pyrrolidinium salt, and specifically, 1-methyl-3. -Methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-hexyl-3-methylimidazole Rium tetrafluoroborate, 1-ethyl-3-methylimidazolium 2- (2-methoxyethoxy) -ethylsulfate, 1-butyl-1-methylpyrrolidinium bis (trifluoromethanesphonyl) imide, etc. Be done. Among these, 1-methyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide has a relatively high ionic conductivity, is soluble in methyl ethyl ketone, and has good compatibility with acrylonitrile and butadiene rubber. Especially preferable from the viewpoint.

Further, as the polymer material, acrylonitrile-butadiene rubber (NBR) is used. The content ratio of the structural unit derived from acrylonitrile contained in NBR is preferably 15 to 50% by mass, more preferably 18 to 45% by mass, because a high output device can be obtained. Although NBR is used as the polymer material, a material in which a part of NBR is replaced with another polymer material capable of containing an ionic liquid can be used. Examples of such polymer materials include polyacrylamide, polyvinyl alcohol, polyvinyl chloride, polyacrylic acid, polymethacrylic acid, N-isopropylacrylamide, acrylic rubber, and styrene-butadiene rubber latex (emulsion SBR) obtained by emulsion polymerization. ), Hydroponic Styrene-butadiene rubber (hydrogenated SBR), styrene / ethylenebutylene / olefin crystal block polymer (SEBC), olefin crystal / ethylene / olefin crystal block polymer (CEBC), styrene / ethylene / styrene block polymer (SEBS) Can be mentioned.

As the stretchable electrode 2-1 and the stretchable electrode 2-2, a PEDOT: PSS film, an aluminum thin film, or the like is used in addition to the PEDOT: PSS-EG film in which ethylene glycol (EG) is contained in PEDOT: PSS. You can also. The PEDOT: PSS-EG film is particularly preferable from the viewpoint of imparting high conductivity and flexibility to the stretchable electrode 2-1 and the stretchable electrode 2-2.

Further, as shown in FIG. 1, the flexible acceleration sensor 11 has the elastic electrode 2-1 and the elastic electrode 2- on a part or all of the surfaces of the elastic electrode 2-1 and the elastic electrode 2-2, respectively. A lead wire 4-1 for connecting the 2 and an external measurement system (not shown), a connection terminal 3-1 of the lead wire 4-2, and a connection terminal 3-2 may be provided.

(experiment)
1. 1. Manufacture of Flexible Accelerometer FIG. 3 shows an example of the manufacturing flow of the flexible sensor 11 shown in FIG. The flexible sensor 11 was manufactured as follows.

1.1 Preparation of IL-NBR gel Acrylonitrile-butadiene rubber (NBR, JSR N220S, acrylonitrile 41.5% by mass) is dissolved in methyl ethyl ketone (MEK) to make a uniform solution, which is an ionic liquid (IL). -Methyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([EMI] [TFSI]), phenylbis (2,4,6-trimethylbenzoyl) phosphinoxide (Irgacure819), which is a photoinitiator (PI). Was added to prepare a mixed solution of NBR, IL, and PI. The amounts of NBR, IL, and PI used were such that NBR was 10% by mass, IL was 20% by mass, and PI was 0 to 9% by mass. A photograph of the mixed solution in the container is shown in the lower left of FIG. The upper left of FIG. 3 shows a photograph and a chemical formula of NBR. The upper middle of FIG. 3 shows the chemical formulas of [EMI] and [TFSI].
The prepared mixture was cast on a Teflon petri dish and dried at room temperature for 12 hours to remove MEK and obtain a self-supporting membrane. An IL-NBR gel was prepared by irradiating this with ultraviolet rays (ELC-500, Fusionet LLC) having a wavelength of 365 nm for 40 minutes and then drying in an oven at 100 ° C. for 30 minutes. A photograph of the IL-NBR gel in the container is shown in the lower middle of FIG.

1.2 Preparation of PEDOT / PSS / EG dispersion PEDOT: Ammonia, a neutralizing agent, was added dropwise to the PSD aqueous dispersion until the pH reached 7, while measuring with a pH meter (F-50, HORIBA). Further, the solid component of the neutralized PEDOT: PSS aqueous dispersion was measured with a moisture meter (MOC-120H, Shimadzu Corporation). PEDOT: PSS aqueous dispersion (pH 7, neutralizer: ammonia) was used to remove water so that the solid component was 2.5% by mass, and after adding 10% by mass of EG, Awatori Rentaro (AR-100, PEDOT / PSS / EG dispersion was prepared by stirring and defoaming with Shinky Co., Ltd. for about 5 minutes. The upper right of FIG. 3 shows the chemical formula of PEDOT: PSS.

1.3 Formation of IL-NBR / PEDOT / PSS / EG electrode by spin coating method The prepared PEDOT / PSS / EG dispersion was prepared by pasting IL-NBR gel on a glass substrate, and opticoat (MS-A150, MIKASA (MS-A150, MIKASA) Co., Ltd.) was used to spin coat both sides of the IL-NBR gel. Each side was dried in air at 100 ° C. for 3 minutes using a moisture meter (Moisture Balance MOC-120H, Shimadzu Corporation). After that, in order to improve the electrical conductivity of the PEDOT / PSS / EG electrode, heat treatment is performed at 120 ° C. in the air for 30 minutes while monitoring the residual water content using a moisture meter to perform IL-NBR / PEDOT / PSS /. An EG electrode was prepared. As a result, the flexible accelerometer 11 was manufactured. A photograph of the flexible accelerometer 11 is shown in the lower right of FIG.

2. 2. Measurement of sample characteristics 2.1 Measurement of cross-linking density of IL-NBR gel Thermomechanical analyzer (TMA / SS6200, Hitachi High-Tech Science, SS control mode: Lsin control mode, temperature rise rate: 2 ° C / min, sampling time: 1s, Dynamic viscoelasticity measurements (DMA) of IL-NBR gels were performed using a temperature range: 20-100 ° C., tensile strain: 10%, amplitude: 1%, frequency: 0.1 Hz). The IL-NBR gel sample used for the measurement was cut out to a length of 15 mm and a width of 1 mm using a cutter blade, sandwiched between chucks so that the distance between the chucks was 5 mm, and set in the apparatus. The sample width, film thickness, and chuck distance were measured using a tool microscope (TM-500, Mitutoyo). FIG. 4 shows the relationship between the storage elastic modulus and the temperature at different photoinitiator amounts used. The horizontal axis of FIG. 4 indicates the temperature, the vertical axis indicates the storage elastic modulus, and the numerical values in the figure indicate the concentration of the photoinitiator (PI).

From the storage elastic modulus (E') obtained by the above measurement and the slope of the temperature plot, the crosslink density ν _e was calculated using the following equation (1).

ν_e: 架橋密度（／ｃｍ³）
ＮＡ：アボガドロ定数（６．０２×１０２３ ／ｍｏｌ）
Ｅ’：貯蔵弾性率（Ｐａ）
Ｒ： 気体定数（８．３１４ Ｊ／Ｋ／ｍｏｌ）
Ｔ： 温度（Ｋ）

ν _e : Crosslink density (/ cm ³ )
NA: Avogadro constant (6.02 × 1023 / mol)
E': Storage modulus (Pa)
R: Gas constant (8.314 J / K / mol)
T: Temperature (K)

The storage elastic modulus of the IL-NBR gel prepared by changing the photoinitiator concentration increases with increasing temperature, and the gradient and the cross-linking density ν _e of the IL-NBR gel obtained from the formula (1) are photoinitiated. It increased in proportion to the agent concentration, and was about 2 × 10 ²⁰ pieces / cm ³ at a photoinitiator concentration of 9% by mass. FIG. 5 is a plot of the crosslink density ν _s with respect to the amount of photoinitiator.

2.2 Measurement of sensor response FIG. 6A is a diagram showing a measuring device 30 for measuring the sensor response characteristic of the flexible acceleration sensor 11. FIG. 6A shows a state in which the flexible acceleration sensor 11 including the sample piezo element 10 is mounted on the sample holder 36. FIG. 6B is a photograph of an example of an actual measuring device. Each sample of the flexible accelerometer 11 has a polymer material layer 1 formed into a sheet as shown in FIG. 1, and elastic electrodes 2-1 and elastic electrodes 2 laminated on both sides thereof. Includes a piezo element 10 with -2.

Here, the flexible accelerometer 11 and the sample holder 36, which are samples, are set as shown in FIG. 6 (B), and the detailed settings of the measuring device 30 are set as shown in FIG. 6 (A). First, as shown in FIGS. 6A and 6B, a flexible accelerometer 11 including a sample piezo element 10 is placed on a PET film 35, and each elastic electrode of the sample is mounted on a sample holder 36. One end of the sample was sandwiched between the gold electrodes 31 so as to be connected to the gold electrode 31, and the measuring device 30 was set.

As described above, the piezo element 10 can be provided with a laminated portion made of a non-conductive material such as a PET film on the whole or a part of the surface. By providing the piezo element 10 with such a laminated portion, durability can be improved and stable acceleration can be measured.

The response characteristics of the flexible accelerometer 11 (IL-NBR / PEDOT / PSS / EG sensor) configured as shown in FIGS. 6A and 6B are the constant temperature and humidity chamber (SH-241, ESPEC Co., Ltd.). In the environment where the temperature is set to 25 ° C and the humidity is set to 30%, one end of the sample is not fixed by the position controller (CP-100, COMS Co., Ltd.) 37 installed in the high temperature and high humidity tank. The sensor was bent by pressing, and the charge and voltage output at this time were measured for evaluation.

The charge signal was amplified by a charge amplifier (NR-CA04) and collected in real time by a data acquisition unit (NR-500, KEYENCE). In addition, the voltage signal was directly collected by the same data acquisition unit as the charge measurement after AD conversion. Furthermore, the response at that time was analyzed by WAVEROGGER, which is software on a personal computer. The sensor characteristics were evaluated by directly measuring the charge signal with a charge amplifier and the voltage signal with a data collection unit. The measurement conditions of the sensor are shown below.
Bending speed: 100 mm / min
Bending displacement: 7 mm
Hold time: 30s
Sampling time: 500 μs

FIG. 7 is an example showing the time response of the generated voltage and the electric charge when the flexible acceleration sensor 11 is bent. In highlight A in FIG. 7, the position controller is operated and the distortion applied to the sensor is continuously relaxed in highlight B while the position controller is operated in the opposite direction and the distortion applied to the sensor is continuously applied. The time from the right end of highlight A to the left end of highlight B indicates the period during which the position controller is stopped and the sensor maintains a constant distortion.

As shown in FIG. 7, when the sensor starts to bend, an electric charge is suddenly generated, and when the bending is stopped, a reverse charge is generated. Therefore, the flexible accelerometer 11 functions as a typical acceleration sensor. I understand. Furthermore, when the strain was returned to the original state from the bent state (during restoration), the response opposite to that at the time of bending was shown.

The capacitance (C) of the flexible acceleration sensor (IL-NBR / PEDOT / PSS / EG sensor) uses an electrochemical measurement system (1255WB, Solartron, applied voltage: 0 to 1.0V, voltage scanning speed: 10mV / s). Cyclic voltammetry (CV) was measured, and the result was calculated by capacitance analysis software (CorrView, Solartron) using the following equation (2).

3. 3. Explanation of sensor operation 3.1 Piezoion effect The mechanism by which an ionic liquid generates an electric charge is called the piezoion effect, and unlike a general piezoelectric phenomenon, a large electric charge is generated by the movement of ions. In this example, 1-methyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide ([EMI] [TFSI]) is used as the ionic liquid. As is clarified in Non-Patent Document 1, the ionic volumes of the ionic liquid [EMI] + (cation) and [TFSI]-(anion) in this example are similar, but [EMI] + is larger. It is known to show a high transport rate (Transfer Number). FIG. 8 (A) shows the transport numbers (Transfer Number) and molar ion conductivity (Molar Ionic Conductivity) of [EMI] + and [TFSI]-. FIG. 8B shows a schematic cross-sectional view of a piezo element having an IL-NBR gel and a PEDOT: PSS-EG electrode. [EMI] + and [TFSI]-are present in the IL-NBR gel. In the case of this embodiment, when the sensor is bent, a strain difference of about 1% is generated on both sides, and [EMI] +, which has a high transport number, is the + pole side first (the electrode side having a larger curvature in FIG. 8B). A positive charge is generated by moving to. On the other hand, since the anion ([TFSI]-) also moves with a delay, the charge becomes small. At this time, if the total charge Q + associated with the movement of the cation and the total charge Q− associated with the movement of the anion are not equal, the charge of ΔQ remains in the bent state, which is considered to be the mechanism of voltage generation. FIG. 8C illustrates this relationship. Cross-linking the IL-NBR gel forms a three-dimensional network of polymer chains, which is expected to change the movement of ions within the gel.

3.2 Effect of IL-NBR gel cross-linking density on electrical output FIG. 9 is a diagram showing the results of plotting the cross-linking density of IL-NBR gel and the behavior of the generated charge and voltage of the sensor over time. The upper figure of FIG. 9 is a diagram showing the generated charge with respect to time for each different cross-linking density, and the lower figure of FIG. 9 is a diagram showing the generated voltage with respect to time for each different cross-linking density. The magnitude, speed, and time of the distortion applied to the sensor were constant. The upper figure of FIG. 10 is a diagram showing the relationship between the crosslink density and the electric charge. The middle figure of FIG. 10 is a diagram showing the relationship between the crosslink density and the capacitance. The lower figure of FIG. 10 is a diagram showing the relationship between the crosslink density and the voltage. The black square plot shows the measured voltage value, and the white square plot shows the calculated voltage value.

The result in the upper figure of FIG. 10 means that both [EMI] + and [TFSI]-difficult to move in the gel because all of Q +, Q-, and δQ decrease as the crosslink density increases. .. Further, as shown in the middle figure of FIG. 10, the capacitance of the IL-BR gel also drops sharply due to cross-linking. It is considered that this is because the degree of freedom of movement of the polymer chain was reduced by the cross-linking, and the movement of the ionic liquid was reduced accordingly, so that the polarization was suppressed. Interestingly, as shown in the lower figure of FIG. 10, it was found that the generated voltage increased by about 1.5 times due to the cross-linking and reached about 6 mV. This is because the value of ΔQ is lowered by the crosslinked structure, but the capacitance (C) is further lowered, so that the generated voltage is increased as shown in the following equation (3). This generated voltage is an order of magnitude higher than the output (0.2 mV) when a Nafion membrane (perfluoroalkyl sulfonic acid polymer) generally used as a polymer electrolyte is used.

Since the measured value of the generated voltage and the calculated value obtained by the charge (C), the capacitance (F) and the equation 3 are in good agreement, it is considered that the increase in the generated voltage is caused by the remarkable decrease in the capacitance. Thus, it is clear that cross-linking of polymer chains plays an important role in the piezoion effect.

In addition, cross-linking to the IL-NBR gel can impart physical strength to the gel, particularly rubber elasticity, and can impart higher durability to the sensor.
Therefore, in the piezo element of the present invention, it is preferable that the acrylonitrile-butadiene rubber contained in the polymer material layer has a crosslinked structure. When the acrylonitrile-butadiene rubber has a crosslinked structure, the crosslinked density is not particularly limited, but is preferably 10 ¹⁸ to 10 ²¹ / cm ³ .

The piezo element of the present invention can directly measure the force as described above. Further, since the velocity and the displacement can be calculated by integration outside the piezo element based on the measured value measured by the piezo element, the motion sensor can be manufactured by using the piezo element of the present invention. As such a motion sensor, for example, the piezo element is provided by a plurality of the piezo elements, a calculation unit for calculating a value measured by the piezo element, and a plurality of calculation results calculated by the calculation unit. A motion sensor including a quantifying unit for quantifying the movement of the object to be measured can be mentioned.

1 Polymer material layer 2-1 and 2-2 Elastic electrodes 3-1 and 3-2 Connection electrodes 4-1 and 4-2 Lead wire 10 Piezo element 30 Measuring device 31 Gold electrode 35 PET film 36 Sample holder 37 Position controller

Claims (9)

A piezo element including a polymer material layer made of a mixture of an ionic liquid and acrylonitrile / butadiene rubber, and elastic electrodes independently laminated on both sides of the polymer material layer. The piezo element according to claim 1, wherein the acrylonitrile-butadiene rubber has a content ratio of a structural unit derived from acrylonitrile of 15 to 50% by mass. The piezo element according to claim 1 or 2, wherein the acrylonitrile-butadiene rubber has a crosslinked structure. The piezo element according to any one of claims 1 to 3, wherein the ionic liquid comprises at least one selected from the group consisting of an imidazolium salt, a piperidinium salt, a pyridinium compound, and a pyrolidinium salt. The ionic liquid is 1-methyl-3-methylimidazolium bis (trifluoromethylsulfonyl) imide, 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium tetrafluoroborate. , 1-Hexyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium 2- (2-methoxyethoxy) -ethylsulfate, and 1-butyl-1-methylpyrrolidinium. The piezo element according to any one of claims 1 to 4, which is at least one compound selected from the group consisting of bis (trifluoromethanesphonyl) imide. The stretchable electrode is an electrode made of PEDOT: PSS-PG, which is a mixture of polyglycerin (PG) and PEDOT: PSS (Poly (3,4-ethylenedioxythiophene): Poly (4-styrenesulfonic acid)). The piezo element according to any one of 5 to 5. The piezo element according to any one of claims 1 to 6, wherein a laminated portion made of a non-conductive material is provided on the whole or a part of the surface. The plurality of piezo elements according to any one of claims 1 to 7.
An arithmetic unit that calculates the measured value by the piezo element,
A motion sensor including a quantification unit for quantifying the movement of an object to be measured provided with the piezo element based on a plurality of calculation results calculated by the calculation unit. A flexible accelerometer including the piezo element according to any one of claims 1 to 7.

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