Piezo sensor

Abstract

The present invention provides a piezoelectric sensor that allows for accurate measurement of muscle contraction activity, etc., while increasing the degree of freedom in the mounting direction of the piezoelectric sensor when measuring muscle contraction activity, etc., of a subject using a piezoelectric sensor with a simple configuration. [Solution] The piezo sensor 2 is equipped with multiple piezoelectric elements 21, each having a single directional orientation. Each piezoelectric element 21 is elongated, and the multiple piezoelectric elements 21 are arranged independently such that the directional orientations of each piezoelectric element 21 are in different directions from each other.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a piezo sensor. BACKGROUND ART

[0002] Patent Document 1 discloses a transparent conductive piezoelectric film configured by stacking a fluororesin-made transparent piezoelectric film, a transparent coating layer, and a transparent electrode in this order. PRIOR ART DOCUMENTS PATENT DOCUMENTS

[0003] PATENT DOCUMENT 1 Japanese Patent No. 7434598 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION

[0004] In recent years, for the purpose of disease detection and the like, development of techniques for measuring muscle contraction activity and the like of a subject using a piezo sensor has been advanced. However, since the piezoelectric element provided in the piezo sensor has directivity, in order to accurately measure the muscle contraction activity and the like of the subject using the piezo sensor, the mounting direction of the piezo sensor on the subject needs to be aligned with a predetermined direction (appropriate direction). In this respect, conventional piezo sensors have room for improvement.

[0005] An object of the present disclosure is to provide a piezo sensor capable of accurately measuring muscle contraction activity and the like while increasing the degree of freedom in the mounting direction of the piezo sensor when measuring the muscle contraction activity and the like of a subject using the piezo sensor with a simple configuration. MEANS FOR SOLVING THE PROBLEMS

[0006] A piezo sensor according to one aspect for achieving the above object is: comprising a plurality of piezoelectric elements each having one directivity direction, each of the piezoelectric elements is elongated, The plurality of piezoelectric elements are arranged independently such that the directional directions of each piezoelectric element are in different directions from each other. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a piezoelectric sensor that can accurately measure muscle contraction activity, etc., while increasing the degree of freedom in the mounting direction of the piezoelectric sensor when measuring muscle contraction activity, etc., of a subject using a piezoelectric sensor with a simple configuration. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a diagram illustrating a sensor system according to the first embodiment. [Figure 2] Figure 2 is a diagram illustrating a piezoelectric sensor and detection circuit according to the first embodiment. [Figure 3] Figure 3 illustrates a piezoelectric sensor and detection circuit according to the first embodiment. [Figure 4] Figure 4 illustrates a piezoelectric sensor and detection circuit according to the second embodiment. [Figure 5] Figure 5 shows an example of a piezoelectric sensor. [Modes for carrying out the invention]

[0009] Hereinafter, an example of an embodiment of the present disclosure will be described with reference to the drawings. In the description of this embodiment, for the sake of convenience, the terms "left-right direction," "up-down direction," and "front-back direction" may be referred to as appropriate. These directions are relative directions set for the piezo sensor 2 exemplified in Figure 1 or the piezo sensor 2A exemplified in Figure 4. Here, the "left-right direction" includes the "left direction" and the "right direction." The "up-down direction" includes the "up direction" and the "down direction." In each figure, the symbol U shown in the figure indicates the up direction. The symbol D indicates the down direction. The symbol L indicates the left direction. The symbol R indicates the right direction. Here, the "left-right direction" includes the "left direction" and the "right direction." The "up-down direction" includes the "up direction" and the "down direction." The "front-back direction" includes the "forward direction" and the "backward direction." In each figure, the symbol U shown in the figure indicates the up direction. The symbol D indicates the down direction. The symbol L indicates the left direction. The symbol R indicates the right direction. The symbol F indicates the forward direction. The symbol B indicates the backward direction.

[0010] (First Embodiment) The sensor system 100 will be described with reference to Figures 1 to 3. Figure 1 is an illustrative diagram of the sensor system 100. Figures 2 and 3 are illustrative diagrams of the piezo sensor 2 and detection circuit 4. The sensor system 100 is used, for example, in medical facilities such as hospitals. The sensor system 100 is used to evaluate the step phenomenon and excitation-contraction coupling time (ECCT). The step phenomenon and excitation-contraction coupling time are evaluated, for example, based on the temporal change in the amplitude of the motor evoked waveform (MRP) or the latency difference between the compound muscle action potential (CMAP) and the motor evoked waveform. The compound muscle action potential is the sum of the action potentials emitted from individual muscle fibers of the subject in response to nerve stimulation, and is proportional to the number of firing muscle fibers. The motor evoked waveform reflects the mechanical strength of muscle contraction generated by a stimulus that induces muscle contraction in the subject. As illustrated in Figure 1, the sensor system 100 includes an electromyograph electrode unit 1, a piezo sensor 2, an electrical stimulation electrode 3, and a detection circuit 4.

[0011] The electromyograph electrode unit 1 is positioned below the piezo sensor 2 (on the back side of the piezo sensor 2). The electromyograph electrode unit 1 is configured to detect minute changes in electrical potential. The electromyograph electrode unit 1 includes multiple electromyograph electrodes. These multiple electromyograph electrodes are attached to the subject's skin at predetermined distances along the subject's muscles.

[0012] The piezoelectric sensor 2 is a piezoelectric sensor that utilizes the piezoelectric effect and is used to measure the muscle contraction activity of a subject. A piezoelectric sensor is a sensor that uses a piezoelectric material, which is a substance that converts mechanical energy into electrical energy or electrical energy into mechanical energy, to generate a voltage signal when stress such as pressure is applied. Piezoelectric sensors can detect a wide range of vibrations, from impacts to minute vibrations of the human body. The piezoelectric effect is a phenomenon in which a voltage proportional to the pressure is generated when pressure is applied to a substance. In this embodiment, the piezoelectric sensor 2 is used to measure the amplitude of a movement-induced waveform based on the voltage signal. The user attaches the piezoelectric sensor 2 to the muscle on the subject's body surface whose contraction activity is to be measured (for example, the abductor pollicis brevis muscle). As illustrated in Figures 2 and 3, the piezoelectric sensor 2 comprises a piezoelectric element 21, a first electrode 22, a second electrode 23, a first insulating film 24, and a second insulating film 25. In this embodiment, the piezo sensor 2 is equipped with eight piezoelectric elements 21 (piezoelectric elements 21A to 21H), but the number of piezoelectric elements 21 equipped in the piezo sensor 2 does not need to be limited to eight, but rather two or more.

[0013] Each of the piezoelectric elements 21 is elongated. When an external force (in this embodiment, an external force from the subject's skin) is applied to the piezoelectric element 21 and pressure is generated, the piezoelectric element 21 generates a voltage within the piezoelectric element 21. The piezoelectric elements 21 are formed from, for example, a polyvinylidene fluoride (PVDF) film. Since polyvinylidene fluoride film has excellent piezoelectric properties, the piezo sensor 2, which has multiple piezoelectric elements 21, has excellent piezoelectric properties.

[0014] Each piezoelectric element 21 has a single directional orientation. For example, if the surface of the subject's skin deforms vertically in a cross-sectional view passing through the front, back, top, and bottom in Figure 2 (a vertical cross-sectional view perpendicular to the plane of Figure 2) (specifically, if the cross-section bends in a roughly V-shape when viewed from the left or right), piezoelectric elements 21A and 21E detect the deformation (compression or extension). Also, for example, if the surface of the subject's skin deforms vertically in a cross-sectional view passing through the left, right, top, and bottom in Figure 2 (a horizontal cross-sectional view perpendicular to the plane of Figure 2) (specifically, if the cross-section bends in a roughly V-shape when viewed from the front or back), piezoelectric elements 21C and 21G detect the deformation. As illustrated in Figure 2, the multiple piezoelectric elements 21 are arranged independently such that the directional orientations of each piezoelectric element 21 are different from each other. Specifically, the multiple piezoelectric elements 21 are arranged radially from the center of the piezo sensor 2 and spaced apart from each other.

[0015] As illustrated in Figure 3, a first electrode 22 is attached to the upper surface of the piezoelectric element 21, and a second electrode 23 is attached to the lower surface of the piezoelectric element 21. The first electrode 22 and the second electrode 23 are, for example, needle electrodes or dish electrodes. The first electrode 22 and the second electrode 23 are formed from, for example, a conductive material. Such materials include, for example, conductive fibers, conductive polymers, and metal particles. The first electrode 22 and the second electrode 23 are elongated in shape. The first electrode 22 and the second electrode 23 are configured to detect the voltage generated within the piezoelectric element 21. A first insulating film 24 is attached to the upper surface of the first electrode 22, and a second insulating film 25 is attached to the lower surface of the second electrode 23. In this embodiment, a wire 20 is connected to the end 220 of the first electrode 22, and a wire 40 is connected to the end 230 of the second electrode 23. That is, as illustrated in Figures 2 and 3, the positive electrode of each piezoelectric element 21 is short-circuited with a conductor 10 and connected to the detection circuit 4 via the wire 20. Furthermore, the negative terminals of each piezoelectric element 21 are short-circuited by a conductor 30 and connected to the detection circuit 4 via a wire 40.

[0016] The first insulating film 24 and the second insulating film 25 have insulating properties. Further, although the first electrode 22 and the second electrode 23 are connected via the piezoelectric element 21, the piezoelectric elements 21 are not in direct contact with each other, so the voltage generated in each piezoelectric element 21 can be detected by the first electrode 22 and the second electrode 23 attached to the corresponding piezoelectric element 21. Therefore, each of the piezoelectric elements 21 is electrically insulated from the other piezoelectric elements 21.

[0017] The piezo sensor 2 transmits a voltage signal (electrical signal) indicating the voltage detected by the first electrode 22 and the second electrode 23 to the detection circuit 4. The voltage signal transmitted from the piezo sensor 2 to the detection circuit 4 may be an analog signal or a digital signal.

[0018] The electrical stimulation electrode 3 will be described with reference to Figure 1. The electrical stimulation electrode 3 is attached to the body surface of a subject. The electrical stimulation electrode 3 is connected to the detection circuit 4. The electrical stimulation electrode 3 is configured to output, to the subject, electrical stimulation controlled by the detection circuit 4 (for example, a biological signal amplifier such as an electromyograph).

[0019] The detection circuit 4 will be described with reference to FIG. 1 to FIG. 3. The detection circuit 4 can be, for example, a biological signal amplifier such as an electromyograph. The detection circuit 4 may perform signal processing such as amplification, noise removal, and filtering on the voltage signal from the piezo sensor 2. In particular, since the voltage signal from the piezo sensor 2 is weak, the detection circuit 4 is preferably configured to amplify the voltage signal from the piezo sensor 2. In the present embodiment, from the viewpoint of minimizing the loss of the voltage signal, the electric wire 20 and the electric wire 40 are used for the connection between the detection circuit 4 and the piezo sensor 2. When the voltage signal transmitted from the piezo sensor 2 to the detection circuit 4 is an analog signal, the detection circuit 4 converts the voltage signal into a digital signal by performing digitization, for example. The detection circuit 4 (for example, an electromyograph) can measure myoelectric potential by measuring the potential difference between the electromyograph electrodes included in the electromyograph electrode unit 1. Specifically, the detection circuit 4 measures the myoelectric potential by measuring the potential difference between the anode and the cathode of a certain electromyograph electrode. In the present embodiment, the detection circuit 4 measures the compound muscle action potential amplitude based on the myoelectric potential. The detection circuit 4 also measures the movement-evoked waveform amplitude based on the voltage signal received from the piezo sensor 2.

[0020] By the way, when measuring the contractile activity or the like of the muscle of a subject using a piezo sensor, the user attaches the piezo sensor onto the muscle whose contractile activity or the like is desired to be measured on the body surface of the subject. For this reason, depending on the position where the piezo sensor is attached, it may be desired to change the attachment direction of the piezo sensor. However, in order to accurately measure the contractile activity or the like of the muscle of the subject using the piezo sensor, it is necessary to align the attachment direction of the piezo sensor relative to the subject with a predetermined direction (appropriate direction).

[0021] In contrast, the piezoelectric sensor 2 with the above configuration has a long piezoelectric element 21 with a single directional orientation, and the multiple piezoelectric elements 21 are arranged independently such that the directional orientations of each piezoelectric element 21 are different from each other. In other words, although each long piezoelectric element 21 has a single directional orientation, the directional orientations of each piezoelectric element 21 are different. For example, if the skin surface of the subject deforms in the vertical direction in a cross-sectional view passing through the front, back, top, and bottom in Figure 2, piezoelectric elements 21A and 21E will detect the deformation. Also, for example, if the skin surface of the subject deforms in the vertical direction in a cross-sectional view passing through the left, right, top, and bottom in Figure 2, piezoelectric elements 21C and 21G will detect the deformation. Thus, the piezoelectric sensor 2 equipped with multiple piezoelectric elements 21A to 21H can accurately detect deformation in any direction, with any of the multiple piezoelectric elements 21A to 21H detecting the deformation. Therefore, in the piezo sensor 2, the multiple piezoelectric elements 21 are arranged independently such that the directional directions of each piezoelectric element 21 are different from those of the others. Consequently, the piezo sensor 2, despite its simple configuration, allows for greater freedom in the direction in which the piezo sensor 2 is attached when measuring the muscle contraction activity of a subject, and also enables accurate measurement of muscle contraction activity.

[0022] Furthermore, in the piezoelectric sensor 2 with the above configuration, the multiple piezoelectric elements 21 are arranged radially from the center of the piezoelectric sensor 2 and spaced apart from each other, thus having multiple directional orientations. Also, in the piezoelectric sensor 2, since the piezoelectric elements 21 do not overlap, the piezoelectric sensor 2 can be made relatively thin. Therefore, for example, when the piezoelectric sensor 2 is attached to a subject, it is possible to prevent it from hindering the movement of the subject's muscle tissue.

[0023] Furthermore, with the piezoelectric sensor 2 according to the above configuration, each piezoelectric element 21 is electrically insulated from other piezoelectric elements 21, so there is no electrical conduction between the piezoelectric elements 21. Therefore, with the piezoelectric sensor 2, the potentials generated in each piezoelectric element 21 do not interfere with each other, and the accuracy of the sensor can be improved.

[0024] Furthermore, in the piezoelectric sensor 2 with the above configuration, the piezoelectric element 21 is formed from a polyvinylidene fluoride (PVDF) film, and therefore, the piezoelectric sensor 2 equipped with such a piezoelectric element 21 has excellent piezoelectric properties.

[0025] (Second embodiment) Next, the piezoelectric sensor 2A according to the second embodiment will be described with reference to Figure 4. In this embodiment, parts similar to those in the first embodiment will be described using the same reference numerals as in the first embodiment, and descriptions of overlapping parts will be omitted as appropriate. As illustrated in Figure 4, the piezoelectric sensor 2A includes a first piezoelectric element 211 and a second piezoelectric element 212. Each of the first piezoelectric element 211 and the second piezoelectric element 212 has one directional orientation. Also, similar to the first embodiment, a first electrode 22 is attached to the upper surface of the first piezoelectric element 211 and the second piezoelectric element 212, and a second electrode 23 is attached to the lower surface of the first piezoelectric element 211 and the second piezoelectric element 212. In this embodiment as well, a first insulating film 24 is attached to the upper surface of the first electrode 22, and a second insulating film 25 is attached to the lower surface of the second electrode 23. A part of the first piezoelectric element 211 overlaps with a part of the second piezoelectric element 212. Specifically, the central part 211A of the first piezoelectric element 211 and the central part 212A of the second piezoelectric element 212 overlap. In this respect, the piezo sensor 2A according to this embodiment differs from the piezo sensor 2 according to the first embodiment.

[0026] The first piezoelectric element 211 and the second piezoelectric element 212 are arranged in a roughly cross shape in a plan view. The upper surface of the upper end 221A of the first electrode 221, which is attached to the upper surface of the first piezoelectric element 211, and the upper surface of the right end 222A of the first electrode 222, which is attached to the upper surface of the second piezoelectric element 212, are short-circuited by a conductor 50 and connected to the detection circuit 4 via a wire 60. In addition, the lower surface of the lower end 231A of the second electrode 231, which is attached to the lower surface of the first piezoelectric element 211, and the lower surface of the right end 232A of the second electrode 232, which is attached to the lower surface of the second piezoelectric element 212, are short-circuited by a conductor 70 and connected to the detection circuit 4 via a wire 80.

[0027] In the piezoelectric sensor 2A according to this embodiment, the first piezoelectric element 211 and the second piezoelectric element 212 are arranged in a substantially cross shape in a plan view. Therefore, even with the simple configuration of the piezoelectric sensor 2A, it is possible to increase the degree of freedom in the mounting direction of the piezoelectric sensor 2 when measuring the muscle contraction activity of a subject, and to accurately measure the muscle contraction activity.

[0028] Furthermore, with the piezoelectric sensor 2A according to the above configuration, a portion of the first piezoelectric element 211 overlaps with a portion of the second piezoelectric element 212. Therefore, compared to, for example, a case where each piezoelectric element 21 is arranged so as not to overlap, it is possible to suppress the increase in size of the piezoelectric sensor 2A.

[0029] The embodiments described above are provided to facilitate understanding of this disclosure and do not limit it. This disclosure may be modified or improved without departing from its intent.

[0030] In the above embodiment, the detection circuit 4 may be, for example, a biosignal amplifier other than an electromyograph. Such other biosignal amplifiers include, for example, a vital signs monitor, an amplifier capable of amplifying electrocardiogram signals, an amplifier capable of amplifying electroencephalogram signals, and so on. A vital signs monitor is a medical device that can acquire various biosignals such as electrocardiogram signals, blood pressure signals, and respiratory signals, and amplify these biosignals.

[0031] In the second embodiment, the piezo sensor 2A includes a first insulating film 24 and a second insulating film 25, but it does not necessarily have to include the first insulating film 24 and the second insulating film 25. In this case, it is preferable that an insulating layer 26 is provided between the first piezoelectric element 211 and the second piezoelectric element 212 (more precisely, between the first electrode 221 attached to the first piezoelectric element 211 and the second electrode 232 attached to the second piezoelectric element 212), for example, as illustrated in Figure 5.

[0032] In the second embodiment, the piezo sensor 2A includes a first piezoelectric element 211 and a second piezoelectric element 212, but it may also include three or more piezoelectric elements 21.

[0033] In the second embodiment, the central portion 211A of the first piezoelectric element 211 and the central portion 212A of the second piezoelectric element 212 overlap, but the first piezoelectric element 211 and the second piezoelectric element 212 may overlap in other portions.

[0034] As explained above, this specification discloses the matters described in the following clauses. <Clause 1> It comprises multiple piezoelectric elements having a single directional orientation, Each of the piezoelectric elements is elongated, A piezoelectric sensor in which a plurality of piezoelectric elements are arranged independently such that the directional directions of each of the piezoelectric elements are in different directions from each other. <Clause 2> The piezoelectric sensor according to Clause 1, wherein the plurality of piezoelectric elements are arranged radially from the center of the piezoelectric sensor and spaced apart from each other. <Clause 3> The piezoelectric sensor according to Clause 1, wherein a portion of the piezoelectric element overlaps with a portion of another piezoelectric element. <Clause 4> A piezoelectric sensor according to any one of the three clauses, wherein each of the piezoelectric elements is electrically insulated from the other piezoelectric elements. <Clause 5> The piezoelectric element is formed from a polyvinylidene fluoride film, as described in any one of the piezo sensor according to any one of the clauses 1 to 4. [Explanation of Symbols]

[0035] 1: Electrode unit for electromyograph, 2,2A: Piezo sensor, 3: Electrode for electrical stimulation, 4: Detection circuit, 10,30,50,70: Conductor, 20,40,60,80: Wire, 21: Piezoelectric element, 22,221,222: First electrode, 23,231,232: Second electrode, 24: First insulating film, 25: Second insulating film, 26: Insulating layer, 100: Sensor system, 211: First piezoelectric element, 211A: Center of the first piezoelectric element, 212: Second piezoelectric element, 212A: Center of the second piezoelectric element, 220: End of the first electrode, 221A: Upper end of the first electrode, 222A: Right end of the first electrode, 230: End of the second electrode, 231A: Lower end of the second electrode, 232A: Right end of the second electrode

Claims

1. It comprises multiple piezoelectric elements having a single directional orientation, Each of the piezoelectric elements is elongated, A piezoelectric sensor in which a plurality of piezoelectric elements are arranged independently such that the directional directions of each of the piezoelectric elements are in different directions from each other.

2. The piezoelectric sensor according to claim 1, wherein the plurality of piezoelectric elements are arranged radially from the center of the piezoelectric sensor and spaced apart from each other.

3. The piezoelectric sensor according to claim 1, wherein a portion of the piezoelectric element overlaps with a portion of another piezoelectric element.

4. The piezoelectric sensor according to any one of claims 1 to 3, wherein each of the piezoelectric elements is electrically insulated from the other piezoelectric elements.

5. The piezoelectric element is formed from a polyvinylidene fluoride film, as described in any one of claims 1 to 3.

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