JPWO2016027613A1 - Piezoelectric film laminate and bending detection sensor - Google Patents

Abstract

Provided is a piezoelectric film laminate in which charges are generated only by displacement in the normal direction of the surface of the detection object, and are less likely to be generated by displacement in the surface direction of the surface of the detection object. In the biosensor (100), the film (3) and the film (4) are converted into the film (4) by displacing the skin (901) where the sensor element (10) is mounted in the surface direction (width direction and depth direction). 1) and the film (2) are stretched more and more, the charge directions of the film (3) and the film (4) are opposite to each other, and the charge directions of the film (1) and the film (2) are opposite to each other. Therefore, the potential difference between the signal electrode (6) and the reference potential electrode (7) becomes small, and the expansion and contraction in the surface direction of the surface of the skin (901) is mistaken as being raised or settled on the surface of the skin (901). Detection can be prevented.

Description

  The present invention relates to a piezoelectric film laminate in which a plurality of films each including a piezoelectric resin are laminated.

  2. Description of the Related Art In recent years, there has been known a piezoelectric film laminate in which a plurality of films (hereinafter simply referred to as piezoelectric films) including, for example, a polyvinylidene fluoride that is a piezoelectric resin are laminated.

  For example, Patent Document 1 discloses a piezoelectric element in which a piezoelectric film made of polyvinylidene fluoride is disposed on both main surfaces of a signal electrode via an adhesive layer, and a reference potential electrode is disposed on each outermost layer from each piezoelectric film. Piezoelectric film laminates) are disclosed.

  For example, when the piezoelectric film is strained to expand and contract in a predetermined direction, an electric charge is generated. In the piezoelectric element described in FIG. 10 of Patent Document 1, each piezoelectric film is arranged so that the polarization directions applied to the piezoelectric film are the same. When the piezoelectric element described in FIG. 10 of Patent Document 1 expands and contracts in the direction orthogonal to the stacking direction, each piezoelectric film is strained to expand and contract in the direction orthogonal to the stacking direction. As a result, the electric charges generated by one piezoelectric film are offset by the electric charges generated by the other piezoelectric film because the polarization directions of the piezoelectric films are the same.

  When the entire piezoelectric element described in FIG. 10 of Patent Document 1 is curved in a projecting manner in the stacking direction, a strain that expands in the projecting piezoelectric film and a strain that contracts in the other piezoelectric film occur. As a result, the charge generated in one piezoelectric film and the charge generated in the other piezoelectric film are added.

  Therefore, if the piezoelectric element shown in FIG. 10 of Patent Document 1 is attached to the detection target so that the reference potential electrode of the outermost layer and the surface of the detection target are parallel, the signal electrode and the reference potential electrode When the surface of the detected object is displaced in the normal direction and the piezoelectric element is displaced in the bending direction (the same direction as the stacking direction), a potential difference is generated, and the surface of the detected object is displaced in the plane direction. When the piezoelectric element is displaced in the expansion / contraction direction (the same direction as the direction orthogonal to the stacking direction), no potential difference occurs. Thus, the piezoelectric element described in Patent Document 1 is mounted on the detection object, and only the displacement in the normal direction of the surface of the detection object is detected by detecting the potential difference between the signal electrode and the reference potential electrode, And it becomes realizable not to detect the displacement of the surface direction of the surface of a detected object.

JP-A-6-216422

  In the piezoelectric element described in FIG. 10 of Patent Document 1, when the surface of the detection object is displaced in the surface direction, the piezoelectric film on the side opposite to the mounting side is not fixed. The amount of expansion and contraction of the piezoelectric film increases. As a result, the charges generated by the piezoelectric film on the detected object side are not completely offset by the charges generated by the piezoelectric film on the opposite side to the detected object side. Therefore, when the piezoelectric element described in Patent Document 1 is used, the displacement in the surface direction of the surface of the detection object may be erroneously detected as the displacement in the normal direction of the surface of the detection object.

  In addition, since the piezoelectric element described in Patent Document 1 has an adhesive layer interposed between each piezoelectric film and the signal electrode, the adhesive layer that is more elastically deformed than the electrode allows an amount of expansion / contraction between the piezoelectric films. Differences are likely to occur. The greater the difference in the amount of expansion / contraction, the greater the amount of charge that is not offset when the surface of the detection object is displaced in the surface direction.

  Accordingly, an object of the present invention is to provide a piezoelectric film laminate in which charges are generated only by displacement in the normal direction of the surface of the detection object and charges are not easily generated by displacement in the surface direction of the surface of the detection object. There is to do.

  The laminate of the piezoelectric film of the present invention includes a first reference potential electrode, a first film partially including a piezoelectric resin, a second film partially including a piezoelectric resin, a signal electrode, A third film including a piezoelectric resin, a fourth film partially including a piezoelectric resin, and a second reference potential electrode are sequentially arranged in the stacking direction, and the first film, the second film, The third film and the fourth film generate charges on one main surface and the other main surface when a stretching strain occurs, and the polarity of the charge generated by the first film with respect to the same stretching direction. The charge direction, which is a direction, is opposite to the charge direction of the second film, the charge direction of the third film is opposite to the charge direction of the fourth film, and the charge of the first film Direction of the fourth film Is the same as the load direction.

  The operation of the piezoelectric film laminate of the present invention will be described using two deformation modes.

(First deformation mode)
For example, when a laminated body of piezoelectric films is attached to the surface of a detection object on the first reference potential electrode side and the surface of the detection object expands in the plane direction, each film is strained to expand in a direction perpendicular to the lamination direction. Occurs. Since the first film and the second film are closer to the surface of the detection object than the third film and the fourth film, the extension amount is larger than that of the third film and the fourth film. Since the first film and the second film are arranged close to each other without the signal electrode, the extension amounts are substantially the same. Similarly, since the third film and the fourth film are arranged close to each other without the signal electrode, the extension amounts are substantially the same.

  Accordingly, the charges generated in the first film are offset by the charges generated in the second film because the charge directions of the first film and the second film are opposite to each other. Similarly, the charge generated in the third film is offset by the charge generated in the fourth film because the charge directions of the third film and the fourth film are opposite to each other. Since the charge is canceled between the first film and the second film, and between the third film and the fourth film between the signal electrode and the first reference potential electrode, a potential difference is unlikely to occur. This action and effect can be obtained even when a laminated body of piezoelectric films is mounted on the surface of the detection object on the second reference potential electrode side.

(Second deformation mode in which the whole is curved in the stacking direction)
In this mode, each film curves in a projecting manner in the stacking direction of the stack. Then, for example, the first film is distorted with respect to the second film. In other words, the second film is distorted with respect to the first film. That is, the first film and the second film are distorted with displacements opposite to each other. Then, the charge direction of the first film and the charge direction of the second film are aligned.

  Similarly, the third film is strained to stretch with respect to the fourth film. In other words, the fourth film is distorted with respect to the third film. Then, the charge direction of the third film is aligned with the charge direction of the fourth film.

  In the second mode, for example, the first film has a stretching strain, and the fourth film having the same charge direction as the first film has a shrinking strain. Therefore, the charge direction aligned in the first film and the second film and the charge direction aligned in the third film and the fourth film are opposite to each other with the signal electrode as a boundary. Accordingly, the charges generated in the first film and the second film are added to the charges generated in the third film and the fourth film. Thereby, a potential difference is generated between the signal electrode and the first reference potential electrode.

  As described above, when the piezoelectric film laminate of the present invention is mounted on the surface of the detection object, a charge is generated by the displacement in the normal direction of the surface of the detection object, and the surface of the detection object is It is possible to make it difficult to generate charges by the displacement in the surface direction.

  In order to configure the charge direction as described above, for example, each film is configured as follows.

  One of the first film and the second film is made of L-type polylactic acid, the other film is made of D-type polylactic acid, and the first film and the second film are co-extruded. After being integrally formed into a laminated shape, it is stretched integrally, and one of the third film and the fourth film is made of L-type polylactic acid, and the other film is made of D-type polylactic acid, The third film and the fourth film are integrally formed in a laminated shape in the co-extrusion step, and then are integrally stretched.

  In the coextrusion step, for example, an extruder that extrudes molten L-type polylactic acid (PLLA; Poly-L-Latic Acid) and an extruder that extrudes molten PDLA (PDLA; Poly-D-Lacy Acid) are stacked. In the state, the first film and the second film are integrally formed into a laminated shape by extruding PLLA and PDLA to the cooling drum.

  PLLA and PDLA are in an enantiomeric relationship. When each polylactic acid is stretched in a predetermined direction, molecules are oriented in the same direction. Since PLLA and PDLA are enantiomers, the charge directions are opposite to each other if the orientation direction of the molecules is the same.

  In the co-extrusion step, the first film and the second film are integrally formed, and thus are disposed closer to each other without using the adhesive layer. As a result, in the first film and the second film, the first film and the second film are less likely to cause a difference in expansion and contraction when expanding and contracting in the direction orthogonal to the stacking direction. Thereby, the first film and the second film are less likely to cause a difference in the amount of charge generated in the first deformation mode. Therefore, since the difference in charge amount is reduced, the charge amount remaining without being canceled between the first film and the second film is further reduced. Similarly, between the third film and the fourth film, the amount of electric charge remaining without being canceled out is further reduced in the deformation of the first mode.

  In the coextrusion step, PDLA may be formed thicker than PLLA. In this case, in view of the following third mode deformation, it is desirable to dispose a film made of thick PDLA on the outside. That is, an embodiment in which the first film and the fourth film are made of PDLA is desirable. Moreover, PLLA may be formed thicker than PDLA. In this case, in view of the following deformation of the third mode, it is desirable to dispose a film made of a thick PLLA on the outside. That is, an embodiment in which the first film and the fourth film are made of PLLA is desirable.

  The third mode deformation occurs simultaneously with the second mode deformation in which the film laminate is curved in the laminating direction.

(Third deformation mode)
In this mode, for example, when the first film and the second film are based on the signal electrode, the third film and the fourth film are strained to expand. In other words, when the third film and the fourth film are based on the signal electrode, the first film and the second film are distorted to contract.

  When the first film is thicker than the second film, the charge generated in the first film is not completely offset by the charge generated in the second film, and a part of the charge remains. The direction of the remaining charge coincides with the charge direction aligned between the first film and the second film in the second deformation mode. Thereby, the potential difference between the signal electrode and the first reference potential electrode in the second deformation mode is increased. Similarly, when the fourth film is thicker than the third film, the charge generated in the fourth film is not completely offset by the charge generated in the third film, and a part of the charge remains. The direction of the remaining charge coincides with the charge direction aligned between the third film and the fourth film in the second deformation mode. Thereby, the potential difference between the signal electrode and the first reference potential electrode in the second deformation mode is increased.

  Further, the charge direction of each film of the present invention can be configured using the same material without using a material different from PLLA and PDLA.

  For example, each of the first film, the second film, the third film, and the fourth film is made of L-type polylactic acid, and the orientation direction of the molecules of the L-type polylactic acid in the first film is The alignment direction of the molecules of the L-type polylactic acid of the third film is orthogonal to the alignment direction of the second film, and the alignment direction of the molecules of the L-type polylactic acid of the third film is orthogonal to the alignment direction of the fourth film.

  When films of PLLA whose molecular orientation directions are orthogonal to each other are laminated, the charge directions of the respective films are opposite to each other. Of course, not only PLLA but also four films of PDLA may be arranged so that the orientation directions of molecules are orthogonal to each other.

  Preferably, the signal electrode is made of a copper foil, and the first reference potential electrode and the second reference potential electrode are made of a soft conductive material such as a silver paste or a conductive nonwoven fabric.

  Since the silver paste material has a Young's modulus smaller than that of the copper foil, a strain larger than that of the copper foil is caused by the same stress. By arranging hard copper as a signal electrode in the center and soft silver as the first reference potential electrode and the second reference potential electrode in the outermost layer in this way, the laminate of piezoelectric films is easily deformed in the lamination direction. However, it is difficult to deform in the direction perpendicular to the stacking direction. As a result, the piezoelectric film laminate is more likely to generate charges only by displacement in the normal direction of the surface of the detection target, and is less likely to generate charges by displacement in the surface direction of the surface of the detection target. .

  Furthermore, when a bias voltage is applied to the signal electrode, if the signal electrode is formed of copper, copper is less likely to be ionized than silver, so that migration of the signal electrode can be prevented.

  Moreover, the laminated body of a piezoelectric film may be provided with an insulating dielectric film instead of the third film and the fourth film.

  Even if the film is arranged only on one main surface side of the signal electrode, the laminate of the piezoelectric film can generate an electric charge only when it is curved in the laminating direction. In this configuration, a capacitance is formed between the signal electrode sandwiching the dielectric film and the second reference potential electrode. This capacitance can be used, for example, in a detection circuit that detects a potential difference between the signal electrode and the first reference potential electrode.

  The piezoelectric film laminate includes a detection circuit that is electrically connected to the signal electrode and the first reference potential electrode and detects a potential difference between the signal electrode and the first reference potential electrode. It becomes a bending sensor for detecting the displacement in the normal direction of the surface of the body. For example, a bending sensor is attached to the skin of a living body and used as a living body sensor that detects displacement in the normal direction of the skin (for example, due to pulsation or the like under the skin).

  According to this invention, even when the surface of the object to be detected is displaced in the plane direction and the pair of films between the surface and the signal electrode has a larger amount of expansion / contraction than the other pair of films, When the charge between each pair of films cancels out, the surface of the object to be detected is displaced in the normal direction, and all the films are curved in the laminating direction, the charges generated in each film are added. Therefore, the piezoelectric film laminate of the present invention can generate charges only by displacement in the normal direction of the surface of the detection object.

(A) is a perspective view of the biosensor which concerns on Embodiment 1, (B) is a figure for demonstrating the usage example of a biosensor. It is a side view of the sensor element viewed in the depth direction. It is a block diagram which shows a part of structure of a biometric sensor. (A) is a top view of the first film, and (B) is a top view of the second film. It is the side view of the sensor element seen in the depth direction when the surface of the skin is extended in the width direction. (A) And (B) is a side view of the sensor element viewed in the depth direction when the surface of the skin is raised. It is the side view seen in the depth direction of the sensor element which concerns on Embodiment 2. FIG. It is the side view of the sensor element seen in the depth direction when the surface of skin protrudes. It is the side view seen in the depth direction of the sensor element which concerns on Embodiment 3. FIG. (A) is a top view of the first film, and (B) is a top view of the fourth film. It is the side view seen in the depth direction of the sensor element which concerns on Embodiment 4.

  A biosensor 100 according to Embodiment 1 will be described with reference to FIGS. 1A, 1B, 2, 3, 4A, and 4B. 1A is a perspective view of the biosensor 100, and FIG. 1B is a diagram for explaining an example of use of the biosensor 100. FIG. FIG. 2 is a side view of the sensor element 10 viewed in the depth direction. FIG. 3 is a block diagram showing a part of the configuration of the biosensor 100. 4A is a top view of the first film (film 1), and FIG. 4B is a top view of the second film (film 2).

  The biological sensor 100 is mounted on the surface of the skin of a living body, for example, and detects only the displacement in the normal direction of the skin surface due to pulsation or the like, and does not detect the displacement in the surface direction of the skin surface due to skin stretching or the like It is.

  As shown in FIG. 1A, the biosensor 100 includes a sensor element 10 and a detection unit 20. The sensor element 10 and the detection unit 20 are electrically connected via a signal line 21 and a signal line 22. However, the detection unit 20 may have a structure directly connected to the sensor element 10 without using a signal line.

  The sensor element 10 has a thin film shape in the height direction compared to the width direction and the depth direction.

  As shown in FIG. 1B, the biosensor 100 has the upper surface (surface in the height direction) or the lower surface (surface in the direction opposite to the height direction) of the sensor element 10 in contact with the surface of the skin 901 of the living body 900. To be fitted. For example, the sensor element 10 is mounted by winding the band 30 so that the sensor element 10 is sandwiched between the surface of the skin 901.

  As shown in FIG. 2, in the sensor element 10, the reference potential electrode 7, the film 4, the film 3, the signal electrode 6, the film 2, the film 1, and the reference potential electrode 5 are sequentially arranged in the height direction. The actual sensor element 10 has an adhesive layer for bonding each electrode and each film, but the description and illustration of each adhesive layer are omitted. In the actual sensor element 10, an insulating material that insulates the reference potential electrode 5 and the reference potential electrode 7 is disposed in the outermost layer, but description and illustration of these insulating materials are omitted.

  The signal electrode 6 is a thin film made of, for example, copper (Cu). A signal line 22 is electrically connected to an end of the signal electrode 6 in the width direction.

  Each of the reference potential electrode 5 and the reference potential electrode 7 is made of, for example, silver (Ag). However, copper (Cu), aluminum (Al), indium tin oxide (ITO), or the like can be used as a material for the reference potential electrode 5 and the reference potential electrode 7.

  The reference potential electrode 5 and the reference potential electrode 7 are electrically connected via a connecting portion 8 at an end portion in a direction opposite to the width direction. The reference potential electrode 5, the reference potential electrode 7, and the connecting portion 8 are formed by, for example, bending a urethane film coated with a silver paste. A signal line 21 is electrically connected to the end of the reference potential electrode 7 in the width direction. However, the reference potential electrode 5, the reference potential electrode 7, and the connecting portion 8 are not limited to being formed by bending a urethane film coated with silver paste, but may be formed by bending a conductive nonwoven fabric. Good.

  Further, the reference potential electrode 5 and the reference potential electrode 7 may not be provided with the connecting portion 8 and may be electrically connected by the detection circuit 23 (see FIG. 3) of the detection portion 20. However, if the reference potential electrode 5 and the reference potential electrode 7 are electrically connected by the connecting portion 8, it is not necessary to separately provide a signal line for electrically connecting the reference potential electrode 5 and the reference potential electrode 7. Thereby, the connection failure of the signal line does not occur. Furthermore, the structure provided with the connection part 8 can electrically connect the reference potential electrode 5 and the reference potential electrode 7 simply by bending the urethane film coated with the silver paste.

  Further, by making the length of the connecting portion 8 equal to the length of the signal electrode 6 in the width direction, the signal electrode 6 is suppressed from being affected by noise from the outside in the width direction.

  The sensor element 10 is attached to the surface of the skin 901 at the reference potential electrode 5 side or the reference potential electrode 7 side. Since the silver paste material constituting the reference potential electrode 5 and the reference potential electrode 7 has a Young's modulus smaller than that of the copper foil, a larger strain than that of the copper foil is caused by the same stress. In the sensor element 10, the reference potential electrode 5 and the reference potential electrode 7 made of a silver paste that is easily distorted are arranged in the outermost layer, and the signal electrode 6 made of a copper foil that is hardly distorted is arranged in the center. Thereby, the sensor element 10 is less likely to be expanded and contracted in the width direction and the depth direction while being easily curved in a protruding manner in the height direction and the opposite direction.

  Furthermore, copper constituting the signal electrode 6 is less ionized than silver, and migration is less likely to occur. Therefore, the sensor element 10 can prevent deterioration due to migration of the signal electrode 6 when a bias voltage is applied to the signal electrode 6.

  As shown in FIG. 3, the reference potential electrode 7 is connected to the detection circuit 23 of the detection unit 20 via the signal line 21. The signal electrode 6 is connected to the detection circuit 23 via the signal line 22. The detection circuit 23 detects a potential difference between the reference potential electrode 7 and the signal electrode 6 and outputs a detection result based on the potential difference. For example, if the absolute value of the potential difference is greater than or equal to a predetermined value, the detection circuit 23 outputs a detection result that the surface of the skin 901 is displaced in the normal direction, and if the absolute value of the potential difference is less than the predetermined value. The detection result that the surface of the skin 901 is not displaced in the normal direction is output.

  Film 1, film 2, film 3, and film 4 are each made of polylactic acid, which is a piezoelectric resin. Film 1, film 2, film 3, and film 4 have substantially the same thickness (length in the height direction). The film 1 and the film 2 are integrated with no adhesive layer. The film 3 and the film 4 are integrated with no adhesive layer.

  However, the film 1 and the film 2 may be bonded together with an adhesive having substantially the same elastic modulus as that of the film 1 and the film 2. The film 3 and the film 4 may also be bonded together with an adhesive having substantially the same elastic modulus as that of the film 3 and the film 4.

  Moreover, the film 1, the film 2, the film 3, and the film 4 should just include a piezoelectric resin in part, respectively. For example, a combination of a piezoelectric body and a resin may be used as the film 1, the film 2, the film 3, and the film 4.

  Since the film 1, the film 2, the film 3 and the film 4 are each made of a piezoelectric resin, an electric charge is generated when a distortion in a predetermined direction on the main surface occurs. However, if each film has the same thickness, the same amount of charge is generated with the same amount of strain. Hereinafter, in each film, the direction from one main surface where negative charges are generated due to distortion to the other main surface where positive charges are generated is referred to as a charge direction.

  The charge direction of each film depends on the direction of strain (elongation or shrinkage), the orientation direction of polylactic acid molecules, and the composition of polylactic acid. The directions of strain are the same, the orientation directions of the polylactic acid molecules are the same, and the composition of the polylactic acid is D-type polylactic acid (PDLA (Poly-D-Lactic Acid)) and L-type polylactic acid (PLLA (PLLA ( Poly-L-Lictic Acid)), the charge directions of the films are opposite to each other.

  In this embodiment, the film 1, film 2, film 3, and film 4 have the same orientation direction of the polylactic acid molecules, but the charge direction is changed as follows by changing the composition of the polylactic acid. It is set.

  More specifically, in the film 1, the film 2, the film 3, and the film 4, the polylactic acid molecules are oriented in a 45 ° direction counterclockwise from the width direction when the sensor element 10 is viewed from above. . In order to orient the polylactic acid molecules in this direction, the film 1 and the film 2 are 45 ° counterclockwise from the width direction as shown by the arrow 911 in FIG. 4A and the arrow 912 in FIG. 4B. It only needs to be stretched in the direction. Similarly, films 3 and 4 that are stretched in the direction of 45 ° counterclockwise from the width direction are used.

  However, the width direction and the orientation direction of the polylactic acid molecules may be approximately 45 °, and if it is in the range of 35 ° to 55 °, the effect of charge generation can be sufficiently obtained.

  In the present embodiment, the film 1 and the film 4 are each made of PDLA. The film 2 and the film 3 are each made of PLLA. PLLA and PDLA are in an enantiomeric relationship. Therefore, when the orientation directions of the molecules are the same, the direction of the charges generated in the film made of PLLA and the film made of PDLA are opposite to each other when distortion (elongation or shrinkage) in the same direction occurs.

  A film made of PLLA may be used as the film 1 and the film 4, and a film made of PDLA may be used as the film 2 and the film 3.

  The charge direction of the film 1 is the downward direction (the direction opposite to the height direction). The film 2 with the same orientation direction of polylactic acid molecules and a different composition of polylactic acid with respect to the film 1 has an upward charge direction (height direction). The film 4 is in the same charge direction (downward) as the film 1. The film 3 has an upward direction in which the charge direction is opposite to the charge direction of the film 4. That is, the charge direction of the film 3 is the same as the charge direction of the film 2. However, these charge directions are directions of charges generated by the strain in which each film extends in the width direction.

  The relationship between the strain generated in the sensor element 10 and the direction of the charge generated in each film will be described with reference to FIG. FIG. 5 is a side view of the sensor element 10 viewed in the depth direction when the skin 901 extends in the width direction. Further, in FIG. 5, the reference potential electrode 5 and the reference potential electrode 7 are not illustrated for explaining each film. FIG. 5 exaggerates the deformation of each film. In FIG. 5, the sizes of the black arrow and the white arrow indicate the stretch amount of the film and the charge amount generated in the film.

(First deformation mode)
As shown by the black arrows in FIG. 5, when the skin 901 is stretched in the width direction, the film 1, the film 2, the film 3, and the film 4 are distorted in the width direction. Since the film 3 and the film 4 are closer to the skin 901 than the film 1 and the film 2, the film 3 and the film 4 are stretched more than the film 1 and the film 2.

  Since the film 1 and the film 2 are integrated with each other without the signal electrode 6, the extension amounts are substantially the same. Similarly, since the film 3 and the film 4 are integrated with each other without the signal electrode 6, the stretch amount is substantially the same.

  Since the film 1 is distorted in the width direction, the charge direction is downward as indicated by the white arrow 801 in FIG. When the film 2 is strained to extend in the width direction, the charge direction is opposite to the charge direction of the film 1, so that the charge direction is upward as shown by the white arrow 802 in FIG. 5. Since the film 1 and the film 2 are equal in thickness and have substantially the same amount of extension, substantially the same amount of charge is generated. Accordingly, the charge amount generated in the film 1 is offset by the charge amount generated in the film 2 because the charge directions of the film 1 and the film 2 are opposite to each other.

  Since the film 3 is distorted to expand in the width direction, the charge direction is upward as indicated by the white arrow 803 in FIG. When the film 4 is strained to extend in the width direction, the charge direction is opposite to the charge direction of the film 3, so that the charge direction is downward as indicated by the white arrow 804 in FIG. 5. Since the film 3 and the film 4 are equal in thickness and have substantially the same amount of extension, substantially the same amount of charge is generated. Accordingly, the charge amount generated in the film 3 is offset by the charge amount generated in the film 3 because the charge directions of the film 3 and the film 4 are opposite to each other.

  Even if there is a difference between the shrinkage amount of the film 1 and the film 2 and the shrinkage amount of the film 3 and the film 4, the skin 901 at the mounting location of the sensor element 10 shrinks in the width direction. The charge is canceled between the two, and the charge is canceled between the film 3 and the film 4.

  Even if the skin 901 at the mounting position of the sensor element 10 expands and contracts in the depth direction and there is a difference between the expansion amount of the film 1 and the film 2 and the expansion amount of the film 3 and the film 4, The charge is canceled between the two, and the charge is canceled between the film 3 and the film 4.

(Second deformation mode)
Next, regarding the relationship between the strain generated in the sensor element 10 and the direction of the charge generated in each film when the surface of the skin 901 is displaced in the height direction with respect to the sensor element 10, FIG. This will be described with reference to FIG. FIGS. 6A and 6B are side views of the sensor element 10 viewed in the depth direction when the skin 901 is raised in a protruding shape in the height direction. FIG. 6A separately shows a set of film 1 and film 2 and a set of film 3 and film 4 for explanation.

  As shown in FIG. 6A, when the surface of the skin 901 rises in the height direction with respect to the sensor element 10, the film 1 and the film 2 are integrally curved in a protruding shape in the height direction. As a result, the film 1 is distorted with respect to the film 2 when the bonding surface of the film 1 and the film 2 shown in FIG. In other words, the film 2 is distorted to shrink with respect to the film 1. Then, as shown in a white arrow 811, the charge direction of the film 1 is downward. The film 2 has a downward charge direction as indicated by the white arrow 812. Therefore, the charge generated in the film 1 is added to the charge generated in the film 2.

  Similarly, the film 3 and the film 4 are integrally curved in a projecting manner in the height direction. Accordingly, the film 3 is distorted to expand with respect to the film 4 when the bonding surface of the film 3 and the film 4 shown in FIG. In other words, the film 4 is distorted to shrink with respect to the film 3. Then, as shown by the white arrow 813, the charge direction of the film 3 is upward. In the film 4, the charge direction is the upward direction as indicated by the white arrow 814. Therefore, the charge generated in the film 3 is added to the charge generated in the film 4.

  The charge added by the film 1 and the film 2 raises the potential of the signal electrode 6 with respect to the reference potential electrode 5. The charge added by the films 3 and 4 raises the potential of the signal electrode 6 with respect to the reference potential electrode 7. Therefore, the detection circuit 23 of the detection unit 20 detects the potential difference between the signal electrode 6 and the reference potential electrode 7 and detects that the skin 901 on which the sensor element 10 is mounted has been raised in the height direction.

  When the surface of the skin 901 where the sensor element 10 is mounted sinks in a projecting shape in the direction opposite to the height direction, the film 1 and the film 2 are integrally bent in a projecting shape in the direction opposite to the height direction, and the film 3 and The film 4 is integrally bent in a protruding shape in the direction opposite to the height direction. Then, also in this case, charges are added between the film 1 and the film 2, and charges are added between the film 3 and the film 4, so that a potential difference is generated between the signal electrode 6 and the reference potential electrode 7. .

  As described above, in the biosensor 100 according to the present embodiment, the film 3 and the film 4 are the film 1 when the skin 901 at the mounting position of the sensor element 10 is displaced in the surface direction (width direction and depth direction). Even if the film 2 expands or contracts more, the charge directions of the film 3 and the film 4 are opposite to each other, and the charge directions of the film 1 and the film 2 are opposite to each other. The potential difference between the two is reduced, and it is possible to prevent erroneous detection of expansion and contraction in the surface direction of the surface of the skin 901 as a rise or settling of the surface of the skin 901. Therefore, the biosensor 100 according to the present embodiment can prevent the erroneous detection and can detect only the bulging and sinking of the surface of the skin 901 where the sensor element 10 is attached. The action and effect of the sensor element 10 can be obtained even when the sensor element 10 is attached to the surface of the skin 901 on the reference potential electrode 5 side.

  Moreover, since the film 1 and the film 2 are united without an adhesive layer, they are disposed closer to each other than when the adhesive layer is interposed. Since the film 1 and the film 2 are arranged closer to each other, the amount of expansion and contraction when they expand and contract with each other is substantially the same. Thereby, the film 1 and the film 2 have substantially the same amount of charge generated in the first deformation mode. Therefore, the film 1 and the film 2 are opposite in charge direction and have substantially the same amount of generated charge, so that the potential difference between the signal electrode 6 and the reference potential electrode 7 is approximately 0 (V). Since the film 3 and the film 4 are also arranged closer to each other than when the adhesive layer is interposed, the potential difference between the signal electrode 6 and the reference potential electrode 7 becomes approximately 0 (V). Therefore, the biosensor 100 can more reliably prevent erroneous detection of the expansion and contraction of the surface of the skin 901 as the rise or sink of the surface of the skin 901.

  In addition, unlike the ferroelectric polymer such as polyvinylidene fluoride, polylactic acid contained in each film of the sensor element 10 has no pyroelectric effect and does not generate charges due to temperature changes. Therefore, a film made of polylactic acid is suitable as a configuration of the sensor element 10 that transmits the temperature of the living body. In addition, since the film made of polylactic acid has translucency, if the other components such as the signal electrode 6 and the reference potential electrode 7 are formed of a translucent material, the entire sensor element 10 is made transparent. It is possible to make the surface of the skin 901 visible while wearing the sensor element 10.

  In addition, in order to integrally mold the film made of PLLA and the film made of PDLA, for example, a coextrusion process is used. In the co-extrusion step, an extruder in which PLLA is melted and an extruder in which PDLA is melted are stacked so that the extruded resin is layered, and PLLA and PDLA are simultaneously extruded onto the peripheral surface of the rotating cooling drum.

  However, in the biosensor 100 of the present embodiment, the film 1, the film 2, the film 3, and the film 4 may be formed from polyvinylidene fluoride (PVDF). In the film made of PVDF, the charge direction is set by the direction of the electric field applied in poling (polarization treatment).

  In addition, the effect | action and effect of the sensor element 10 of this embodiment are acquired even if it is a case where arrangement | positioning of the film 1 and the film 2 is replaced, and arrangement | positioning of the film 3 and the film 4 is replaced.

  Actually, when the sensor element 10 is deformed in the second deformation mode shown in FIG. 6A, the sensor element 10 is also deformed in the following third deformation mode.

(Third deformation mode)
As shown in FIG. 6B, the film 1 and the film 2 are distorted in the width direction with respect to the film 3 and the film 4 with respect to the signal electrode 6. In other words, in the third deformation mode, the film 3 and the film 4 are distorted in the width direction with respect to the film 1 and the film 2, respectively.

  Similarly to the first deformation mode shown in FIG. 5, the charge generated in the film 1 (the charge direction is the direction shown by the white arrow 821 in FIG. 6B) is the charge generated in the film 2 (the charge direction is the figure). 6 (B), the direction indicated by the white arrow 822). Similarly, the charge generated in the film 3 (the charge direction is the direction indicated by the white arrow 823 in FIG. 6B) is the charge generated in the film 4 (the charge direction is the white arrow 824 in FIG. 6B). Offset by the direction shown).

  Even if the sensor element 10 is deformed in the third deformation mode due to the displacement of the skin 901 in the height direction shown in FIGS. 6 (A) and 6 (B), the potential difference between the signal electrode 6 and the reference potential electrode 7. Is not affected. That is, when displacement in the height direction of the skin 901 shown in FIGS. 6A and 6B occurs, the potential difference between the signal electrode 6 and the reference potential electrode 7 is the second deformation mode of the sensor element 10. Only affected by deformation due to.

  Next, FIG. 7 is a side view of the sensor element 10A according to the second embodiment viewed in the depth direction. In the sensor element 10, the deformation in the third deformation mode does not affect the potential difference between the signal electrode 6 and the reference potential electrode 7, but the sensor element 10 </ b> A uses the third deformation mode. The sensitivity is improved by increasing the potential difference between the signal electrode 6 and the reference potential electrode 7 in the second deformation mode.

  More specifically, the sensor element 10A is different from the sensor element 10 according to the first embodiment in that the film 1A and the film 4A are thicker than the film 1 and the film 4 according to the first embodiment. That is, the film 1A and the film 4A are thicker than the film 2 and the film 3, respectively. For example, the film 1 </ b> A and the film 4 </ b> A are approximately 10% thicker with respect to the thickness of the film 2 and the film 3, respectively.

  The operation and effect of the sensor element 10A will be described with reference to FIG. FIG. 8 is a side view of the sensor element 10A viewed in the depth direction when the surface of the skin 901 is raised.

  As described above, when the sensor element 10A is curved in a projecting manner in the height direction, the sensor element 10A is deformed in the second deformation mode and simultaneously in the third deformation mode.

(Third deformation mode)
The film 1A and the film 2 are distorted in the width direction with respect to the film 3 and the film 4A with respect to the signal electrode 6. In other words, in the third deformation mode, the film 3 and the film 4A are distorted in the width direction with respect to the film 1A and the film 2, respectively.

  Since the film 1 </ b> A is thicker than the film 2, the amount of charge generated is larger than the amount of charge generated in the film 2. Accordingly, in the third deformation mode, the amount of charge generated in the film 1A (generated in the direction indicated by the white arrow 821) is the amount of charge generated in the film 2 (generated in the direction indicated by the white arrow 822). All are not offset and some remain. The direction of the remaining charge coincides with the charge direction in the second deformation mode (the direction indicated by the white arrow 811 and the white arrow 812).

  Similarly, since the film 4 </ b> A is thicker than the film 3, the amount of charge generated is larger than the amount of charge generated in the film 3. Accordingly, in the third deformation mode, the amount of charge generated in the film 4A (generated in the direction indicated by the white arrow 824) is the amount of charge generated in the film 3 (generated in the direction indicated by the white arrow 823). All are not offset and some remain. The direction of the remaining charge coincides with the charge direction in the second deformation mode (the direction indicated by the white arrow 813 and the white arrow 814).

  In the sensor element 10A, the charge amount in the second deformation mode and the charge amount in the third deformation mode are added. Therefore, the sensor element 10A has a larger potential difference between the signal electrode 6 and the reference potential electrode 7 with respect to the bulging or sinking of the surface of the skin 901, and is sensitive to the bulging or sinking of the surface of the skin 901 at the mounting location. improves.

  Similarly, even if the film 1A and the film 2 are distorted in the width direction with respect to the film 3 and the film 4A with respect to the signal electrode 6, the charges remaining in the film 1A and the film 4A are This is added to the charge amount in the two deformation modes.

  In addition, the sensor element 10A is made from the film 1A and the film 4A by increasing the content of polylactic acid in the film 1A and the film 4A as compared with the film 2 and the film 3 while keeping the thickness of each film equal. A larger amount of charge may be generated.

  In the above example, the charge direction of each film was set by changing the composition of polylactic acid contained in the film, but each film was changed without changing the composition of polylactic acid contained in the film as follows. The charge direction can also be set.

  FIG. 9 is a side view of the sensor element 10B according to the third embodiment viewed in the depth direction. FIG. 10A is a top view of the first film (film 1B), and FIG. 10B is a top view of the fourth film (film 4B).

  The sensor element 10B is different from the sensor element 10 in that it includes the film 1B and the film 4B. The description of the overlapping configuration is omitted.

  The film 1B and the film 4B are made of PLLA like the film 2 and the film 3. Although illustration is omitted, the film 1B and the film 2 are bonded to each other via an adhesive layer. The film 3 and the film 4B are bonded together through an adhesive layer.

  The film 1B and the film 4B are different from the film 2 and the film 3 in the cut-out direction with respect to the stretching direction in the original film. More specifically, the film 1B and the film 4B are 45 ° clockwise with respect to the width direction, as indicated by the white arrow 913 in FIG. 10A and the white arrow 914 in FIG. Each is cut out from the original film so that the direction is the stretching direction. Therefore, in the films 1B and 4B, the orientation directions of the PLLA molecules contained in the films 1B and 4B are orthogonal to the orientation directions of the PLLA molecules contained in the films 2 (see FIG. 4B) and the film 3, respectively. Thereby, the charge directions of the film 1B and the film 2 are opposite to each other. Similarly, the charge directions of the film 3 and the film 4B are opposite to each other.

  In the configuration of the sensor element 10B, each film can be prepared from a film original made of one PLLA. Accordingly, the thicknesses of the respective films are more equal, and the remaining charge amount due to the difference in thickness can be further prevented in the first mode deformation.

  Next, FIG. 11 is a side view of the sensor element 10C according to the fourth embodiment viewed in the depth direction.

  The sensor element 10 </ b> C is different from the sensor element 10 in that the piezoelectric element 1 and the film 2 are provided only on one main surface side of the signal electrode 6 and the insulating body 9 is provided on the other main surface side. The description of the configuration overlapping with the sensor element 10 is omitted.

  As shown in FIG. 11, an insulator (film) 9 is disposed between the signal electrode 6 and the reference potential electrode 7. For example, a dielectric film can be used as the insulator 9.

  The insulator 9 is formed, for example, by applying an acrylic pressure-sensitive adhesive to both main surfaces of a PET (Polyethylene terephthalate) base material. The insulator 9 has a thickness smaller than the total thickness of the film 1 and the film 2. The insulator 9 has a higher dielectric constant ε (F / m) than the film 1 and the film 2. Thereby, a capacitance is formed between the signal electrode 6 and the reference potential electrode 7. This capacity is larger than the capacity formed when the film 1 and the film 2 are sandwiched between the reference potential electrode 5 and the signal electrode 6.

  The capacitance formed between the signal electrode 6 and the reference potential electrode 7 is electrically connected in parallel to the piezoelectric element including the signal electrode 6, the film 1, the film 2, and the reference potential electrode 5 in the detection circuit 23. . Therefore, the detection circuit 23 does not need to include a capacitor separately.

  Even if the sensor element 10C includes the film 1 and the film 2 only on one main surface side of the signal electrode 6, the charge is canceled between the film 1 and the film 2 with respect to expansion and contraction in the surface direction, and in the height direction. A charge is added between the film 1 and the film 2 with respect to the curvature of the film. Therefore, the sensor element 10 </ b> C can form a capacitance (capacitance) while generating a charge only by displacement of the surface of the skin 901 in the normal direction.

DESCRIPTION OF SYMBOLS 1,1A, 1B, 2,3,4A, 4B ... Film 5, 7 ... Reference potential electrode 6 ... Signal electrode 8 ... Connection part 9 ... Insulator 10, 10A, 10B, 10C ... Sensor element 20 ... Detection part 21, 22 ... Signal line 23 ... Detection circuit 30 ... Band 100 ... Biosensor

Claims (7)

A first reference potential electrode;
A first film partially containing a piezoelectric resin;
A second film partially containing a piezoelectric resin;
A signal electrode;
A third film partially containing a piezoelectric resin;
A fourth film partially containing a piezoelectric resin;
A second reference potential electrode;
Are arranged in the stacking direction in order,
The first film, the second film, the third film, and the fourth film generate charges on one main surface and the other main surface when a stretching strain occurs.
For the same stretch direction, the charge direction, which is the direction of the polarity of the charge generated by the first film, is opposite to the charge direction of the second film,
The charge direction of the third film is opposite to the charge direction of the fourth film;
The charge direction of the first film is the same as the charge direction of the fourth film;
A laminate of piezoelectric films. One of the first film and the second film is made of L-type polylactic acid, and the other film is made of D-type polylactic acid,
The first film and the second film are integrally formed in a laminated shape in a co-extrusion step, and then stretched integrally.
One of the third film and the fourth film is made of L-type polylactic acid, and the other film is made of D-type polylactic acid.
The third film and the fourth film are integrally formed in a laminated shape in a co-extrusion step, and then stretched integrally.
A laminate of the piezoelectric film according to claim 1. The first film and the fourth film are each made of the D-type polylactic acid,
The first film and the fourth film are thicker than the second film and the third film, respectively.
A laminate of the piezoelectric film according to claim 2. The first film, the second film, the third film, and the fourth film are each made of L-type polylactic acid,
The orientation direction of the molecules of the L-type polylactic acid of the first film is orthogonal to the orientation direction of the second film,
The orientation direction of the L-type polylactic acid molecules of the third film is orthogonal to the orientation direction of the fourth film.
A laminate of the piezoelectric film according to claim 1. The signal electrode is made of copper,
The first reference potential electrode and the second reference potential electrode are each made of silver.
The laminated body of the piezoelectric film in any one of Claim 1 thru | or 4. A first reference potential electrode;
A first film partially containing a piezoelectric resin;
A second film partially containing a piezoelectric resin;
A signal electrode;
An insulating dielectric film;
A second reference potential electrode;
Are arranged in the stacking direction in order,
The first film and the second film generate charges on one main surface and the other main surface when a stretching strain occurs.
For the same stretch direction, the charge direction, which is the direction of the polarity of the charge generated by the first film, is opposite to the charge direction of the second film.
A laminate of piezoelectric films. A laminate of the piezoelectric film according to any one of claims 1 to 6,
A detection circuit that is electrically connected to the signal electrode and the first reference potential electrode and detects a potential difference between the signal electrode and the first reference potential electrode;
Bending detection sensor with

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