Sensor and method for manufacturing sensor

Abstract

This sensor is provided with a base material that is flexible and that has a first main surface and a second main surface facing each other, and a first piezoelectric element including a first piezoelectric film. The first main surface is provided with a first protrusion. The first piezoelectric element is in contact with the first protrusion. The first piezoelectric film is stretched under tension so as to be extended from the natural length of the film. When viewed in a second direction orthogonal to a first direction extending from the second main surface toward the first main surface, a central part of the first piezoelectric film is positioned farther in the first direction than an end part of the first piezoelectric film.

Description

Sensor and method for manufacturing the same

[0001] The present invention relates to a sensor.

[0002] A known example of a conventional invention related to a sensor is an operating device described in Patent Document 1. The operating device described in Patent Document 1 includes a flat membrane-shaped piezoelectric element and a rectangular parallelepiped housing. The piezoelectric element includes a piezoelectric film and electrodes formed on both main surfaces of the piezoelectric film. The housing has a front wall, a back wall, longitudinal side walls, and lateral side walls. The front wall and the back wall face each other with a gap between them. The longitudinal side walls and lateral side walls are formed along the outer periphery of the front wall and the outer periphery of the back wall. This structure gives the housing an internal space.

[0003] The piezoelectric element is provided in the internal space, approximately in the center of the longitudinal direction and near the end of the lateral direction when the housing is viewed from above. When the front or rear wall of the housing is pressed, the piezoelectric film deforms and generates a voltage.

[0004] International Publication No. 2012 / 137897

[0005] In the operation device described in Patent Document 1, the deformation direction of the piezoelectric film may differ depending on the location of pressure. Specifically, when the approximate center of the front wall is pressed, the piezoelectric film deforms so as to protrude from the front wall toward the back wall. On the other hand, when the vicinity of a short-side side wall of the front wall is pressed, the piezoelectric film deforms so as to protrude from the back wall toward the front wall. Because the deformation directions of the piezoelectric film differ, the polarity of the voltage generated by the piezoelectric film may differ, which may make it difficult to use the voltage signal generated by the piezoelectric film for various control signals.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a sensor and a method for manufacturing the sensor that can prevent the deformation direction of the piezoelectric film from varying depending on the location of pressure applied.

[0007] A sensor according to one embodiment of the present invention comprises: a flexible substrate having opposing first and second main surfaces; and a first piezoelectric element including a first piezoelectric film, wherein a first protrusion is provided on the first main surface, the first piezoelectric element is in contact with the first protrusion, the first piezoelectric film is stretched from its natural length by tension, and when viewed in a second direction perpendicular to a first direction from the second main surface toward the first main surface, a central portion of the first piezoelectric film is positioned further in the first direction than the end portion of the first piezoelectric film.

[0008] According to the present invention, it is possible to prevent the deformation direction of the piezoelectric film from varying depending on the pressed location.

[0009] FIG. 1 is a perspective view of sensor 1. FIG. 2 is a plan view of sensor 1. FIG. 3 is a cross-sectional view of sensor 1. FIG. 4 is an exploded perspective view of piezoelectric element 3 in a flat state. FIG. 5 is a cross-sectional view of sensor 1 when viewed in the front-to-rear direction, in which protrusion P is trapezoidal. FIG. 6 is a perspective view of sensor 1a. FIG. 7 is a plan view of sensor 1a. FIG. 8 is a cross-sectional view of sensor 1a and base 4. FIG. 9 is a cross-sectional view showing a method of manufacturing sensor 1a by countersinking with an end mill 5. FIG. 10 is a cross-sectional view showing an example of a method of manufacturing sensor 1a by countersinking with a ball end mill 6. FIG. 11 is a cross-sectional view showing another example of a method of manufacturing sensor 1a. FIG. 12 is a cross-sectional view of sensor 1b. FIG. 13 is a cross-sectional view of sensor 1c. FIG. 14 is a plan view of sensor 1c.

[0010] [First embodiment] A sensor 1 according to a first embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a perspective view of the sensor 1. Fig. 2 is a plan view of the sensor 1. Fig. 3 is a cross-sectional view of the sensor 1. Fig. 4 is an exploded perspective view of the piezoelectric element 3 in a state in which it is developed on a plane. Fig. 5 is a cross-sectional view of the sensor 1 when the protrusion P is trapezoidal as viewed in the front-to-rear direction.

[0011] In the sensor 1, directions are defined as follows, for example. As shown in FIG. 1 , the direction in which the long side of the upper main surface US2 extends is defined as the left-right direction. The direction in which the short side of the upper main surface US2 extends is defined as the front-rear direction. The direction in which the upper main surface US2 and the lower main surface DS2 are aligned is defined as the up-down direction. The left-right direction, front-rear direction, and up-down direction are perpendicular to each other. However, the left-right direction, front-rear direction, and up-down direction in this specification are defined for the convenience of explanation and may not coincide with the left-right direction, front-rear direction, and up-down direction when the sensor 1 is in use. Furthermore, in each drawing, the left direction and the right direction may be interchanged, the front direction and the rear direction may be interchanged, and the up-down direction may be interchanged.

[0012] As shown in FIG. 1 , the sensor 1 includes a substrate 2 and a piezoelectric element 3. The substrate 2 is flexible. The substrate 2 is made of, for example, polyimide, PET (Poly Ethylene Terephthalate), or a liquid crystal polymer. The substrate 2 has opposing upper and lower principal surfaces US2 and DS2. The upper and lower principal surfaces US2 and DS2 each have a rectangular shape with two long sides extending in the left-right direction and two short sides extending in the front-to-back direction when viewed in the vertical direction. The piezoelectric element 3 corresponds to the first piezoelectric element according to the present invention. The upper principal surface US2 corresponds to the second principal surface according to the present invention. The lower principal surface DS2 corresponds to the first principal surface according to the present invention. The downward direction, which is the direction from the upper principal surface US2 toward the lower principal surface DS2, corresponds to the first direction according to the present invention. The upper and lower principal surfaces US2 and DS2 do not necessarily have a rectangular shape when viewed in the vertical direction.

[0013] A protrusion P is provided on the lower main surface DS2. The protrusion P has a shape that protrudes downward. In this embodiment, the protrusion P is provided in the center of the lower main surface DS2. As shown in FIG. 2, in this embodiment, the protrusion P has a rectangular shape when viewed in the up-down direction. Also, as shown in FIG. 3, the protrusion P has an isosceles triangular shape when viewed in the front-to-back direction. That is, in this embodiment, the protrusion P has an isosceles triangular prism shape extending in the front-to-back direction. In this embodiment, the protrusion P is included in the base material 2. That is, the base material 2 and the protrusion P are a single member. The protrusion P corresponds to the first protrusion according to the present invention. Note that the protrusion P does not have to be provided in the center of the lower main surface DS2. Also, the shape of the protrusion P is not limited to the shape shown in this embodiment.

[0014] The piezoelectric element 3 is flexible. The piezoelectric element 3 is in the form of a flat film. As shown in Fig. 4, the piezoelectric element 3 includes a piezoelectric film 31, a reference electrode 32, and a signal electrode 33. The piezoelectric film 31 corresponds to the first piezoelectric film according to the present invention. The piezoelectric element 3 in a state where it is unfolded on a plane will be described below.

[0015] The piezoelectric film 31 is flat. When unfolded on a plane, the piezoelectric film 31 has an upper principal surface US31 and a lower principal surface DS31 that are aligned in the vertical direction. In this embodiment, the upper principal surface US31 and the lower principal surface DS31 are rectangular, each having a front side and a rear side that are long sides extending in the left-right direction, and a left side and a right side that are short sides extending in the front-to-back direction. Note that the shapes of the upper principal surface US31 and the lower principal surface DS31 are not limited to those shown in this embodiment.

[0016] The piezoelectric film 31 is polarized by deformation, generating a voltage between the upper principal surface US31 and the lower principal surface DS31. The voltage generated between the upper principal surface US31 and the lower principal surface DS31 depends on the amount of deformation of the piezoelectric film 31.

[0017] The piezoelectric film 31 is, for example, a film formed from a chiral polymer. The chiral polymer is, for example, polylactic acid (PLA), such as poly-L-lactic acid (PLLA) or poly-D-lactic acid (PDLA). The main chain of PLA has a helical structure. PLA has piezoelectricity due to the orientation of its molecules after uniaxial stretching. The piezoelectric film 31 has a piezoelectric constant of d14.

[0018] The PLA is stretched at least in the orientation direction OD. In this embodiment, the orientation direction OD of the PLA forms an angle of 45 degrees with respect to each of the left-right direction and the front-back direction. Note that the 45 degrees may be within a range of approximately 45 degrees ±10 degrees. When the piezoelectric film 31 is stretched or compressed along the left-right direction, a voltage is generated between the upper principal surface US31 and the lower principal surface DS31. The polarity of the voltage generated by stretching along the left-right direction is opposite to the polarity of the voltage generated by compression along the left-right direction. Similarly, when the piezoelectric film 31 is stretched or compressed along the front-back direction, a voltage is generated between the upper principal surface US31 and the lower principal surface DS31. The polarity of the voltage generated by stretching along the front-back direction is opposite to the polarity of the voltage generated by compression along the front-back direction. Note that, for example, the orientation direction OD of the PLA may form an angle of 0 degrees or 90 degrees with respect to the left-right direction. The angles 0 degrees and 90 degrees may be within the ranges of approximately 0 degrees ±10 degrees and 90 degrees ±10 degrees, respectively.

[0019] The reference electrode 32 is conductive. The material of the reference electrode 32 is, for example, copper. The reference electrode 32 is in the form of a flat film. The reference electrode 32 is provided on the upper principal surface US31. The reference electrode 32 covers the entire upper principal surface US31. The reference electrode 32 is connected to a ground potential, thereby functioning as a reference electrode and a shield conductor. The shape of the reference electrode 32 is not limited to the shape shown in this embodiment.

[0020] The signal electrode 33 is conductive. The material of the signal electrode 33 is, for example, copper. The signal electrode 33 is in the form of a flat film. The signal electrode 33 is provided on the lower main surface DS31. The signal electrode 33 covers the entire lower main surface DS31. The signal electrode 33 functions as a signal electrode for outputting a voltage generated by the piezoelectric film 31. The shape of the signal electrode 33 is not limited to the shape shown in this embodiment. The signal electrode 33 may be provided on the upper main surface US31, and the reference electrode 32 may be provided on the lower main surface DS31.

[0021] As shown in FIG. 1 , the piezoelectric element 3 is in contact with the protrusion P. In this embodiment, the piezoelectric element 3 is fixed to the protrusion P. As shown in FIG. 3 , when viewed in the front-to-rear direction, the center of the piezoelectric film 31 is located lower than the left and right ends of the piezoelectric film 31. The front-to-rear direction is an example of a second direction according to the present invention. The piezoelectric film 31 is stretched from its natural length due to tension. In this embodiment, the piezoelectric film 31 is stretched from its natural length in the left-to-right direction due to tension. Therefore, the piezoelectric film 31 is deformed so as to protrude downward. Tension is generated in the piezoelectric film 31 in the left-to-right direction. Note that as long as the piezoelectric element 3 is in contact with the protrusion P, the piezoelectric element 3 may be fixed to the lower main surface DS2.

[0022] The sensor 1 can prevent the deformation direction of the piezoelectric film 31 from varying depending on the location of pressure. More specifically, the piezoelectric element 3 is fixed to the protrusion P. As a result, the center of the piezoelectric film 31 is located lower than the left and right ends of the piezoelectric film 31 when viewed in the front-to-back direction. Furthermore, the piezoelectric film 31 is stretched in the left-to-right direction from its natural length due to tension. Therefore, when not pressed, the piezoelectric film 31 is deformed so as to protrude downward.

[0023] Even when the approximate center of the upper principal surface US31 is pressed, the deformation direction of the piezoelectric film 31 remains downward. Moreover, even when the left end or right end of the upper principal surface US31 is pressed, the deformation direction of the piezoelectric film 31 remains downward. Therefore, even if the pressing location is different, the deformation direction of the piezoelectric film 31 remains downward, and it is possible to prevent differences in the polarity of the voltage generated by the piezoelectric film 31 due to differences in the pressing location.

[0024] The protrusion P is not limited to an isosceles triangular prism extending in the front-rear direction. The protrusion P may also be a triangular prism, elliptical cylinder, triangular tube, or elliptical tube extending in the front-rear direction. Alternatively, as shown in FIG. 5 , the protrusion P may be trapezoidal when viewed in the front-rear direction. However, when the protrusion P is trapezoidal when viewed in the front-rear direction, when the side of the trapezoid that is in contact with the lower main surface DS2 is taken as the upper base, the two base angles at both ends of the lower base are obtuse angles. As a result, the piezoelectric film 31 is stretched in the left-right direction from its natural length due to tension even when not pressed.

[0025] The direction in which the protrusions P extend is not limited to the front-to-rear direction. Furthermore, the protrusions P do not have to extend in a specific direction. It is sufficient that the piezoelectric film 31 is stretched from its natural length by tension, and that the center of the piezoelectric film 31 is located lower than the ends of the piezoelectric film 31 when viewed in a direction perpendicular to the up-down direction. The direction perpendicular to the up-down direction corresponds to the second direction according to the present invention.

[0026] [First Modification] A sensor 1a according to a first modification of the present invention will be described below with reference to the drawings. Fig. 6 is a perspective view of the sensor 1a. Fig. 7 is a plan view of the sensor 1a. Fig. 8 is a cross-sectional view of the sensor 1a and the base 4. Note that with regard to the sensor 1a, only the parts that are different from the sensor 1 will be described, and the rest will be omitted.

[0027] Sensor 1a differs from sensor 1 in that a first support portion 2b1 is provided on the lower main surface DS2. In this modification, the first support portion 2b1 is included in the substrate 2. That is, the substrate 2 and the first support portion 2b1 are a single member. Therefore, in this modification, the substrate 2 includes the plate portion 2a, the first support portion 2b1, and the protrusion P. Note that the substrate 2 and the first support portion 2b1 may be separate members. The plate portion 2a, the protrusion P, and the piezoelectric element 3 in this modification are the same as the substrate 2, the protrusion P, and the piezoelectric element 3 in the first embodiment, and therefore will not be described here.

[0028] As shown in Fig. 6, in this modification, the first support portion 2b1 has a frame shape that surrounds the piezoelectric element 3. As shown in Fig. 7, when viewed in the vertical direction, the inner edge and outer edge of the first support portion 2b1 each have a rectangular shape. When viewed in the vertical direction, the first support portion 2b1 does not overlap with the piezoelectric element 3. Note that when viewed in the vertical direction, the inner edge of the first support portion 2b1 may have an elliptical shape, etc. Furthermore, the first support portion 2b1 does not have to have a frame shape.

[0029] 8 , the length L2b1 of the first support portion 2b1 in the vertical direction is longer than the maximum distance LM31 in the vertical direction between the lower main surface DS2 and the piezoelectric film 31. In this modification, the maximum distance LM31 in the vertical direction between the lower main surface DS2 and the piezoelectric film 31 is the distance in the vertical direction between the center of the lower main surface DS2 and the center of the piezoelectric film 31.

[0030] The sensor 1a also achieves the same effect as the sensor 1. Furthermore, since the length L2b1 in the vertical direction of the first support portion 2b1 is longer than the maximum distance LM31 in the vertical direction between the lower main surface DS2 and the piezoelectric film 31, even if the sensor 1a is placed on a stand 4 or the like, the piezoelectric element 3 does not come into contact with the stand 4 or the like. Therefore, the sensor 1a can prevent the stand 4 or the like from hindering the deformation of the piezoelectric film 31.

[0031] (Method for Manufacturing Sensor 1a) Hereinafter, a method for manufacturing the sensor 1a will be described with reference to the drawings.

[0032] The substrate 2 is produced by, for example, countersinking with an end mill, countersinking with a ball end mill, press working, electroforming, casting, sputtering, injection molding, laser processing, electric discharge processing, or a 3D printer, etc. A method for producing the sensor 1a will be described below.

[0033] First, a method for manufacturing the sensor 1a by countersinking using an end mill will be described. FIG. 9 is a cross-sectional view showing a method for manufacturing the sensor 1a by countersinking using an end mill 5. As shown in FIG. 9, first, a flexible, plate-shaped substrate 21 is prepared. Next, the upper main surface of the substrate 21 is countersunk using an end mill 5. The tip of the end mill 5 has a concave shape. Therefore, the substrate 2 including the first support portion 2b1 and the protrusion P can be manufactured by countersinking using the end mill 5. That is, the protrusion P and the first support portion 2b1 are formed by countersinking using the end mill 5. After the substrate 2 is manufactured, the piezoelectric element 3 is fixed to the protrusion P. According to the method for manufacturing the sensor 1a by countersinking using an end mill, the sensor 1a can be easily manufactured.

[0034] Next, a method for manufacturing the sensor 1a by countersinking using a ball end mill will be described. FIG. 10 is a cross-sectional view showing an example of a method for manufacturing the sensor 1a by countersinking using a ball end mill 6. As shown in FIG. 10, first, a flexible, plate-shaped substrate 21 is prepared. Next, the upper main surface of the substrate 21 is countersunk using a ball end mill 6. The tip of the ball end mill 6 is hemispherical. This allows the surface of the protrusion P to be smooth. The substrate 2 including the first support portion 2b1 and the protrusion P is manufactured by countersinking using the ball end mill 6. That is, the protrusion P and the first support portion 2b1 are formed by countersinking using the ball end mill 6. After the substrate 2 is manufactured, the piezoelectric element 3 is fixed to the protrusion P.

[0035] Next, another example of a manufacturing method for the sensor 1a will be described. FIG. 11 is a cross-sectional view showing another example of a manufacturing method for the sensor 1a. As shown in FIG. 11 , first, a flexible, plate-like substrate 22, a first member 23 in the shape of an isosceles triangular prism extending in the front-rear direction, and rectangular parallelepiped second and third members 24 and 25 are prepared. When viewed in the front-rear direction, the vertical lengths of the second and third members 24 and 25 are longer than the distance between the apex and base of the first member 23. The first member 23 is attached to the upper main surface of the substrate 22. The second and third members 24 and 25 are attached to the left and right ends of the upper main surface of the substrate 22, respectively. The plate portion 2a is made of the substrate 22. The protrusion P is made of the first member 23. The first support portion 2b1 is made of the second and third members 24 and 25. After the substrate 2 is prepared, the piezoelectric element 3 is fixed to the protrusion P. In other examples of the method for manufacturing the sensor 1a, the order of the steps is not limited to the above-described order and may be arbitrary.

[0036] [Second Modification] A sensor 1b according to a second modification of the present invention will be described below with reference to the drawings. Fig. 12 is a cross-sectional view of sensor 1b. Note that only the differences between sensor 1b and sensor 1a will be described, and the rest will be omitted.

[0037] Sensor 1b differs from sensor 1a in that it includes two protrusions P and a piezoelectric element 3. Hereinafter, the two protrusions P will be referred to as a first protrusion P1 and a second protrusion P2. The two piezoelectric elements 3 will be referred to as a first piezoelectric element 3a and a second piezoelectric element 3b. The piezoelectric film 31 of the second piezoelectric element 3b corresponds to the second piezoelectric film according to the present invention. As shown in FIG. 12 , the first piezoelectric element 3a is fixed to the first protrusion P1. The second piezoelectric element 3b is fixed to the second protrusion P2. The method of fixing the first piezoelectric element 3a to the first protrusion P1 and the method of fixing the second piezoelectric element 3b to the second protrusion P2 are the same as the methods of fixing the piezoelectric elements 3 to the protrusions P according to sensors 1 and 1a, and therefore will not be described here. The number of protrusions P and piezoelectric elements 3 may be three or more.

[0038] A second support portion 2b2 is provided on the lower main surface DS2. In this modification, the second support portion 2b2 is included in the base material 2. That is, the base material 2 and the second support portion 2b2 are a single member. Note that the base material 2 and the second support portion 2b2 may be separate members.

[0039] In this modification, the second support portion 2b2 has a rectangular parallelepiped shape that connects the front and rear edges of the inner edge of the first support portion 2b1. Therefore, the second support portion 2b2 is located between the first protrusion P1 and the second protrusion P2. Note that the second support portion 2b2 only needs to be located between the first protrusion P1 and the second protrusion P2, and does not have to connect the front and rear edges of the inner edge of the first support portion 2b1. Furthermore, the second support portion 2b2 does not have to have a rectangular parallelepiped shape.

[0040] The length L2b2 of the second support portion 2b2 in the vertical direction is approximately equal to the length L2b1 of the first support portion 2b1 in the vertical direction. Therefore, the length L2b2 of the second support portion 2b2 in the vertical direction is longer than the maximum distance LM31a in the vertical direction between the lower main surface DS2 and the piezoelectric film 31 of the first piezoelectric element 3a. Furthermore, the length L2b2 of the second support portion 2b2 in the vertical direction is longer than the maximum distance LM31b in the vertical direction between the lower main surface DS2 and the piezoelectric film 31 of the second piezoelectric element 3b.

[0041] Sensor 1b also achieves the same effect as sensor 1a. Furthermore, in sensor 1b, the vertical length L2b2 of second support portion 2b2 is substantially equal to the vertical length L2b1 of first support portion 2b1. Therefore, when sensor 1b is placed on a stand or the like, first support portion 2b1 and second support portion 2b2 support sensor 1b. Furthermore, since the vertical length L2b2 of second support portion 2b2 is longer than the maximum vertical distance LM31b between the lower main surface DS2 and the piezoelectric film 31 of second piezoelectric element 3b, even when sensor 1b is placed on a stand or the like, second piezoelectric element 3b does not come into contact with stand 4 or the like. Therefore, sensor 1b can prevent the stand or the like from interfering with the deformation of the piezoelectric film 31 of first piezoelectric element 3a and the piezoelectric film 31 of second piezoelectric element 3b.

[0042] In sensor 1b, second support portion 2b2 is located between first protrusion P1 and second protrusion P2. Even if a portion of upper principal surface US31 located directly above first support portion 2b1 and second support portion 2b2 is pressed, piezoelectric film 31 of first piezoelectric element 3a and piezoelectric film 31 of second piezoelectric element 3b do not deform. When a portion of upper principal surface US31 located to the left of second support portion 2b2 and not overlapping with first support portion 2b1 and second support portion 2b2 in the up-down direction is pressed, piezoelectric film 31 of second piezoelectric element 3b does not deform, but piezoelectric film 31 of first piezoelectric element 3a deforms. On the other hand, when a portion of the upper main surface US31 located to the right of the second support portion 2b2 and not overlapping with the first support portion 2b1 and the second support portion 2b2 in a vertical view is pressed, the piezoelectric film 31 of the first piezoelectric element 3a does not deform, but the piezoelectric film 31 of the second piezoelectric element 3b deforms. In other words, the piezoelectric elements 3 that react can be made different depending on the location of the pressure. Therefore, each piezoelectric element 3 can be given a different role.

[0043] [Third Modification] A sensor 1c according to a third modification of the present invention will be described below with reference to the drawings. Fig. 13 is a cross-sectional view of sensor 1c. Fig. 14 is a plan view of sensor 1c. Regarding sensor 1c, only the differences from sensor 1 will be described, and the rest will be omitted.

[0044] As shown in Fig. 13, the sensor 1c further includes a fourth member 7 provided on the lower main surface DS2 of the substrate 2. The fourth member 7 forms a protrusion P. That is, in this modification, the substrate 2 and the protrusion P are separate members. As shown in Figs. 13 and 14, in this modification, the fourth member 7 has a cylindrical shape extending in the front-rear direction. The material of the fourth member 7 may be the same as or different from the material of the substrate 2.

[0045] Furthermore, if the piezoelectric film 31 is stretched from its natural length due to tension and the center of the piezoelectric film 31 is located lower than the end of the piezoelectric film 31 when viewed in a direction perpendicular to the up-down direction, the sensor 1c does not need to be equipped with the fourth member 7.

[0046] The sensor 1c also has the same effect as the sensor 1.

[0047] Other Embodiments The sensor according to the present invention is not limited to the sensors 1, 1a to 1c, and can be modified within the scope of the gist thereof. In addition, the structures of the sensors 1, 1a to 1c may be combined arbitrarily.

[0048] The method for manufacturing a sensor according to the present invention is not limited to the method for manufacturing the sensor 1a, and can be modified within the scope of the gist thereof.

[0049] The present invention has the following configuration.

[0050] (1) A sensor comprising: a flexible substrate having opposing first and second principal surfaces; and a first piezoelectric element including a first piezoelectric film, wherein a first protrusion is provided on the first principal surface, the first piezoelectric element is in contact with the first protrusion, the first piezoelectric film is stretched from its natural length by tension, and when viewed in a second direction perpendicular to a first direction from the second principal surface toward the first principal surface, a central portion of the first piezoelectric film is positioned further in the first direction than an end of the first piezoelectric film.

[0051] (2) The sensor according to (1), wherein the base material and the first projections are a single member.

[0052] (3) The sensor according to (1), wherein the base material and the first projections are separate members.

[0053] (4) The sensor according to any one of (1) to (3), wherein a first support portion is provided on the first main surface, and a length of the first support portion along the first direction is longer than a maximum distance along the first direction between the first main surface and the first piezoelectric film.

[0054] (5) The sensor according to (4), wherein the base material and the first support portion are a single member.

[0055] (6) The sensor according to (4), wherein the base material and the first support portion are separate members.

[0056] (7) The sensor according to any one of (4) to (6), further comprising a second piezoelectric element including a second piezoelectric film, wherein a second protrusion and a second support portion are provided on the first main surface, the second piezoelectric element is fixed to the second protrusion, the second piezoelectric film is stretched from its natural length by tension, when viewed in the second direction, a central portion of the second piezoelectric film is positioned in the first direction further than an end portion of the second piezoelectric film, the second support portion is positioned between the first protrusion and the second protrusion, and the length along the first direction of the second support portion is approximately equal to the length along the first direction of the first support portion and is longer than the maximum distance along the first direction between the first main surface and the second piezoelectric film.

[0057] (8) The method for manufacturing the sensor according to (5), wherein the first protrusion is formed by countersinking using an end mill.

[0058] 1, 1a to 1c: Sensor 2, 21, 22: Base 2a: Plate portion 2b1: First support portion 2b2: Second support portion 3: Piezoelectric element 3a: First piezoelectric element 3b: Second piezoelectric element 4: Base 5: End mill 6: Ball end mill 7: Fourth member 23: First member 24: Second member 25: Third member 31: Piezoelectric film 32: Reference electrode 33: Signal electrode DS2, DS31: Lower main surface LM31, LM31a, LM31b: Maximum distance OD: Orientation direction P: Protrusion P1: First protrusion P2: Second protrusion US2, US31: Upper main surface

Claims

1. A sensor comprising: a flexible substrate having opposing first and second principal surfaces; and a first piezoelectric element including a first piezoelectric film, wherein a first protrusion is provided on the first principal surface, the first piezoelectric element is in contact with the first protrusion, the first piezoelectric film is stretched from its natural length by tension, and when viewed in a second direction perpendicular to a first direction from the second principal surface toward the first principal surface, a central portion of the first piezoelectric film is located further in the first direction than the ends of the first piezoelectric film.

2. The sensor according to claim 1, wherein the substrate and the first projection are a single member.

3. The sensor according to claim 1, wherein the substrate and the first projection are separate members.

4. A sensor as described in any one of claims 1 to 3, wherein a first support portion is provided on the first main surface, and the length of the first support portion along the first direction is longer than the maximum distance along the first direction between the first main surface and the first piezoelectric film.

5. The sensor according to claim 4, wherein the substrate and the first support are a single member.

6. The sensor according to claim 4, wherein the base material and the first support portion are separate members.

7. A sensor as described in any of claims 4 to 6, further comprising a second piezoelectric element including a second piezoelectric film, wherein a second protrusion and a second support portion are provided on the first main surface, wherein the second piezoelectric element is fixed to the second protrusion, wherein the second piezoelectric film is stretched from its natural length by tension, wherein, as viewed in the second direction, a central portion of the second piezoelectric film is located further in the first direction than an end portion of the second piezoelectric film, wherein the second support portion is located between the first protrusion and the second protrusion, and wherein the length of the second support portion in the first direction is approximately equal to the length of the first support portion in the first direction and is longer than the maximum distance in the first direction between the first main surface and the second piezoelectric film.

8. A method for manufacturing a sensor according to claim 5, wherein the first protrusion is formed by countersinking using an end mill.

Images