Pulse wave sensor

Abstract

To provide a pulse wave sensor having both sensitivity and rigidity.SOLUTION: A pulse wave sensor includes: a strain-inducing body having a circular opening; a resin layer that coats one surface of the strain-inducing body; and a strain gage which is provided on the other surface positioned opposite the one surface of the strain-inducing body and which uses a Cr mixed phase film as a resistor. Assuming that a diameter of the circular opening is d[mm] and a thickness of the strain-inducing body is t[mm], dimensions of d and t are defined for a case where a material of the strain-inducing body is SUS, copper or aluminum. A pulse wave is detected based on a change in a resistance value of the resister associated with deformation of the strain-inducing body.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a pulse wave sensor.

Background Art

[0002] A pulse wave sensor for detecting a pulse wave generated as the heart pumps blood is known. As an example, there is a pulse wave sensor provided with a pressure receiving plate serving as a strain generating body that is supported so as to be bendable by the action of an external force, and piezoelectric conversion means for converting the bending of the pressure receiving plate into an electric signal. This pulse wave sensor has a dome shape in which the flexible region of the pressure receiving plate is formed into a convex curved surface facing outward, and a pressure detection element is provided on the inner surface of the top of the pressure receiving plate as the piezoelectric conversion means (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since a pulse wave sensor needs to detect a minute signal, a thin strain generating body is used to ensure the required sensitivity. On the other hand, since durability is also required, it is necessary to be compatible with rigidity. However, in conventional pulse wave sensors, the compatibility between sensitivity and rigidity has not been sufficiently studied.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a pulse wave sensor that achieves both sensitivity and rigidity.

Means for Solving the Problems

[0006] This pulse wave sensor comprises a strain-generating body with a circular opening, a resin layer covering one surface of the strain-generating body, and a strain gauge with a Cr multiphase film as a resistor, provided on the other surface of the strain-generating body opposite to the one surface. When the diameter of the circular opening is d [mm] and the thickness of the strain-generating body is t [mm], the following values ​​apply: If the material of the strain-generating body is SUS and d=32, then 0.059 ≤ t ≤ 0.124; if the material is SUS and d=22, then 0.046 ≤ t ≤ 0.099; if the material is SUS and d=13, then 0.030 ≤ t ≤ 0.067; if the material is SUS and d=7, then 0.026 ≤ t ≤ 0.034; and if the material is copper and d=32, then 0.084 If t ≤ 0.166, and the material is copper with d=22, then 0.066 ≤ t ≤ 0.132; if the material is copper with d=13, then 0.044 ≤ t ≤ 0.088; if the material is copper with d=7, then 0.032 ≤ t ≤ 0.050; if the material is aluminum with d=32, then 0.097 ≤ t ≤ 0.212; if the material is aluminum with d=22, then 0.079 ≤ t ≤ 0.168; if the material is aluminum with d=13, then 0.050 ≤ t ≤ 0.107; and if the material is aluminum with d=7, then 0.038 ≤ t ≤ 0.063. The pulse wave is detected based on the change in the resistance value of the resistor accompanying the deformation of the strain-generating body. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a pulse wave sensor that achieves both sensitivity and rigidity. [Brief explanation of the drawing]

[0008] [Figure 1] This is a perspective view illustrating a pulse wave sensor according to the first embodiment. [Figure 2] This is a plan view illustrating a pulse wave sensor according to the first embodiment. [Figure 3] This is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment, showing a cross-section along line AA in Figure 2. [Figure 4] This is a graph (part 1) of experimental results using SUS as the material for the strain-generating body. [Figure 5] This is a graph (part 2) of the experimental results using SUS as the material for the strain-generating body. [Figure 6] This is a graph (part 3) of experimental results using SUS as the material for the strain-generating body. [Figure 7] This is a graph (part 4) of experimental results using SUS as the material for the strain-generating body. [Figure 8] This is a graph (part 1) of experimental results using copper as the material for the strain-generating body. [Figure 9] This is a graph (part 2) of the experimental results using copper as the material for the strain-generating body. [Figure 10] This is a graph (part 3) of the experimental results using copper as the material for the strain-generating body. [Figure 11] This is a graph (part 4) of the experimental results using copper as the material for the strain-generating body. [Figure 12] This is a graph (part 1) of experimental results using aluminum as the material for the strain-generating body. [Figure 13] This is a graph (part 2) of the experimental results using aluminum as the material for the strain-generating body. [Figure 14] This is a graph (part 3) of the experimental results using aluminum as the material for the strain-generating body. [Figure 15] This is a graph (part 4) of experimental results using aluminum as the material for the strain-generating body. [Figure 16] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 17] This is a cross-sectional view illustrating a strain gauge according to the first embodiment. [Figure 18] This is a cross-sectional view (part 1) illustrating a pulse wave sensor according to a modified example of the first embodiment. [Figure 19] This is a cross-sectional view (part 2) illustrating a pulse wave sensor according to a modified example of the first embodiment. [Figure 20] This is a cross-sectional view (part 3) illustrating a pulse wave sensor according to a modified example of the first embodiment. [Figure 21]It is a plan view and a sectional view showing an example of a detection element included in the strain gauge according to the second embodiment. [Figure 22] It is a perspective view, a plan view, and a sectional view showing an example of a detection element included in the strain gauge according to the third embodiment. [Figure 23] It is a perspective view, a plan view, and a sectional view showing another example of a detection element included in the strain gauge according to the third embodiment. [Figure 24] It is a perspective view, a plan view, and a sectional view showing still another example of a detection element included in the strain gauge according to the third embodiment.

Mode for Carrying Out the Invention

[0009] Hereinafter, modes for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are given to the same components, and redundant descriptions may be omitted.

[0010] 〈First Embodiment〉 FIG. 1 is a perspective view illustrating a pulse wave sensor according to the first embodiment. FIG. 2 is a plan view illustrating the pulse wave sensor according to the first embodiment. FIG. 3 is a sectional view illustrating the pulse wave sensor according to the first embodiment, showing a section along the line A-A in FIG. 2. In FIG. 2, the resin layer 50 is not shown, but the resin layer 50 exists at the same position as shown in FIG. 1 in FIG. 2 as well.

[0011] Referring to FIGS. 1 to 3, the pulse wave sensor 1 has a housing 10, a strain generating body 20, a wire 30, a resin layer 50, and a strain gauge 100.

[0012] The strain generating body 20 has a base portion 21, a beam portion 22, a load portion 23, and an extension portion 24. The strain generating body 20 is in a flat plate shape, and each component is integrally formed by, for example, a press working method or the like. The strain generating body 20 is, for example, a shape that is rotationally symmetric four times in a plan view. The thickness t of the strain generating body 20 excluding the load portion 23 is constant. The preferred range of the thickness t will be described later.

[0013] In this embodiment, for convenience, the side of the pulse wave sensor 1 on which the load portion 23 of the strain generating body 20 is provided is referred to as the upper side or one side, and the side on which the load portion 23 is not provided is referred to as the lower side or the other side. Furthermore, the surface on which the load portion 23 of each part is provided is referred to as one surface or the upper surface, and the surface on which the load portion 23 is not provided is referred to as the other surface or the lower surface. However, the pulse wave sensor 1 can be used upside down or positioned at any angle. Moreover, "plan view" refers to viewing the object from the direction normal to the upper surface of the strain generating body 20, and "planar shape" refers to the shape of the object viewed from the direction normal to the upper surface of the strain generating body 20.

[0014] In the pulse wave sensor 1, the housing 10 is the part that holds the strain generating body 20. The housing 10 is hollow and cylindrical, with its bottom closed and its top open. The housing 10 can be made of, for example, metal or resin. The roughly disc-shaped strain generating body 20 is fixed to the housing 10 with adhesive or the like so as to close the opening on the top side.

[0015] In the strain generating body 20, the base portion 21 is the circular frame-shaped (ring-shaped) region outside the circular dashed line shown in Figures 1 and 2. The region inside the circular dashed line is sometimes referred to as the circular opening. In other words, the base portion 21 of the strain generating body 20 has a circular opening. The width w1 of the base portion 21 is, for example, 1 mm or more and 5 mm or less. The preferred range for the inner diameter d of the base portion 21 (i.e., the diameter of the circular opening) will be described later.

[0016] The beam section 22 is provided to bridge the inside of the base section 21. The beam section 22 has, for example, two beams that intersect in a cross shape in a plan view, and the region where the two beams intersect includes the center of the circular opening. In the example in Figure 2, one beam forming the cross has its longitudinal direction in the X direction, and the other beam forming the cross has its longitudinal direction in the Y direction, and the two are orthogonal. It is preferable that each of the two orthogonal beams is located inside the inner diameter d (diameter of the circular opening) of the base section 21 and is as long as possible. In other words, it is preferable that the length of each beam is approximately equal to the diameter of the circular opening. In each beam forming the beam section 22, the width w2 outside the intersecting region is constant, for example, 1 mm or more and 5 mm or less. It is not essential that the width w2 is constant, but it is preferable that the width w2 is constant so that strain can be detected linearly.

[0017] The load-bearing section 23 is provided on the beam section 22. The load-bearing section 23 is provided, for example, in the region where two beams constituting the beam section 22 intersect. The load-bearing section 23 protrudes from the upper surface of the beam section 22. The amount of protrusion of the load-bearing section 23 relative to the upper surface of the beam section 22 is, for example, about 0.1 mm. The beam section 22 is flexible and elastically deforms when a load is applied to the load-bearing section 23.

[0018] The four extensions 24 are fan-shaped portions that extend from the inside of the base 21 toward the beam 22 in a plan view. A gap of about 1 mm is provided between each extension 24 and the beam 22. The extensions 24 do not contribute to the sensing of the pulse wave sensor 1 and therefore may not be provided.

[0019] The wire 30 is a cable that transmits and receives electrical signals between the pulse wave sensor 1 and the outside. The wire 30 may be a shielded cable, a flexible circuit board, or the like.

[0020] The resin layer 50 covers one surface of the strain-generating body 20. In this embodiment, the one surface is the upper surface 20m. The resin layer 50 may cover the entire upper surface 20m of the strain-generating body 20, or it may cover a part of the upper surface 20m. The resin layer 50 is also formed over the gap between the beam portion 22 and the extension portion 24. Therefore, the gap between the beam portion 22 and the extension portion 24 is not exposed to the outside of the pulse wave sensor 1. The resin layer 50 may penetrate the gap between the beam portion 22 and the extension portion 24, filling part or all of the gap between the beam portion 22 and the extension portion 24.

[0021] It is preferable to use a resin material with an elastic modulus of 10 GPa or less for the resin layer 50. Examples of such resin materials include epoxy resin and silicone resin. By using a resin material with an elastic modulus of 10 GPa or less, even if the resin material constituting the resin layer 50 penetrates the gap between the beam portion 22 and the stretched portion 24, it will not hinder the elastic deformation of the beam portion 22.

[0022] The resin layer 50 may be formed, for example, by molding a resin material onto the upper surface 20m of the strain body 20 using a mold, or by laminating a resin film onto the upper surface 20m of the strain body 20. The thickness of the resin layer 50 can be, for example, about 10 μm to 500 μm. Since the resin layer 50 is formed along the upper surface 20m of the strain body 20, a load portion 53 that covers the load portion 23 is formed on the resin layer 50. The load portion 53 protrudes from the upper surface of the resin layer 50. The amount of protrusion of the load portion 53 relative to the upper surface of the resin layer 50 is, for example, about 0.1 mm.

[0023] The strain gauge 100 is an example of a detection unit for detecting pulse waves in this disclosure. The strain gauge 100 is provided on the other side of the strain generating body 20, which is located opposite to one of the other sides. In this embodiment, the other side is the lower surface 20n. The strain gauge 100 can be provided, for example, on the lower side of the beam portion 22. Since the beam portion 22 is flat, the strain gauge can be easily attached to it. One or more strain gauges 100 are sufficient, but in this embodiment, four strain gauges 100 are provided. By providing four strain gauges 100, strain can be detected by full bridge.

[0024] Two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the X direction that is closer to the load section 23 (towards the center of the circular opening), facing each other in a plan view, with the load section 23 in between. The other two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the Y direction that is closer to the base section 21, facing each other in a plan view, with the load section 23 in between. This arrangement allows for effective detection of compressive and tensile forces, enabling greater output from the full bridge.

[0025] The pulse wave sensor 1 is used by fixing it to the subject's arm so that the load portion 53 covering the load portion 23 is in contact with the subject's radial artery. When a load is applied to the load portion 23 via the load portion 53 in response to the subject's pulse wave, causing the beam portion 22 to elastically deform, the resistance value of the resistor of the strain gauge 100 changes. The pulse wave sensor 1 can detect the pulse wave based on the change in the resistance value of the resistor of the strain gauge 100 accompanying the deformation of the beam portion 22. The pulse wave is output, for example, as a periodic change in voltage from a measurement circuit connected to the electrodes of the strain gauge 100.

[0026] In the pulse wave sensor 1, the upper surface 20m of the metal strain-generating body 20 is covered with a resin layer 50, so the metal strain-generating body 20 does not come into direct contact with the subject's skin. Therefore, it is possible to avoid skin inflammation and metal allergies caused by the metal in the subject's skin.

[0027] Furthermore, if the gap between the beam portion 22 and the extension portion 24 were open to the outside of the pulse wave sensor 1, dust and foreign matter could get trapped in the gap, potentially preventing the beam portion 22 from elastically deforming. However, in the pulse wave sensor 1, the resin layer 50 is also formed on top of the gap between the beam portion 22 and the extension portion 24, so the gap between the beam portion 22 and the extension portion 24 is not exposed to the outside of the pulse wave sensor 1. As a result, dust and foreign matter cannot get trapped in the gap between the beam portion 22 and the extension portion 24, enabling more reliable and stable measurement of pulse waves by the pulse wave sensor 1.

[0028] For the pulse wave sensor 1 to detect a subject's pulse wave, it is necessary to achieve both sensitivity and rigidity. In the pulse wave sensor 1, the required sensitivity is that the output of the strain gauge 100 is 0.1 mV / V or higher when a 1 g load is applied to the load section 23. Below this sensitivity, the pulse wave cannot be clearly measured due to a decrease in the signal-to-noise ratio during measurement. Furthermore, since a load of about 50 g is applied when attaching the pulse wave sensor 1 to the subject, the required rigidity is that the beam section 22 does not undergo plastic deformation when a 50 g load is applied to the load section 23 with a safety factor of 2. If these conditions are not met, it will be difficult to use the pulse wave sensor continuously.

[0029] The inventors discovered that the above-mentioned sensitivity and rigidity can be achieved simultaneously when the material of the strain generating body 20, its thickness t [mm], and the diameter d [mm] of the circular opening satisfy certain conditions. Specifically, the inventors experimentally determined the value of t [mm] that allows for a balance between sensitivity and rigidity when using SUS (stainless steel), copper, and aluminum as the material of the strain generating body 20, and setting the diameter d to 32 mm, 22 mm, 13 mm, and 7 mm.

[0030] The shape of the strain-generating body 20 is as shown in Figures 2 and 3, with w1=w2=3mm. However, in this experiment, no resin layer 50 covering the strain-generating body 20 was provided. In addition, four strain gauges 100 using the Cr multiphase film described later as resistors were attached to the positions shown in Figures 2 and 3.

[0031] The experimental results are graphed in Figures 4 to 15. Figures 4 to 7 show the results when SUS was used as the material for the strain body 20, Figures 8 to 11 show the results when copper was used as the material for the strain body 20, and Figures 12 to 15 show the results when aluminum was used as the material for the strain body 20. In each graph, the left side of the vertical axis shows the sensitivity, and the right side of the vertical axis shows the maximum stress when a 50g load is applied to the load section 23 with a safety factor of 2. The horizontal axis represents the thickness t [mm] of the strain body 20.

[0032] In each graph, as t decreases, sensitivity increases but rigidity decreases. The range of t where sensitivity is 0.1 mV / V or higher and the maximum stress is less than or equal to the yield strength represents the range of t that balances sensitivity and rigidity. In each graph, the range of t that balances sensitivity and rigidity is shown in white. The yield strength of SUS is 1275 MPa, the yield strength of copper is 675 MPa, and the yield strength of aluminum is 490 MPa.

[0033] [Table 1] Table 1 summarizes the range of t that balances sensitivity and rigidity, as read from each graph. From Table 1, when the diameter of the circular opening is d [mm] and the thickness of the strain body 20 is t [mm], if the material of the strain body 20 is SUS and d=32, the requirement for balancing sensitivity and rigidity is 0.059 ≤ t ≤ 0.124. If the material of the strain body 20 is SUS and d=22, the requirement is 0.046 ≤ t ≤ 0.099. If the material of the strain body 20 is SUS and d=13, the requirement is 0.030 ≤ t ≤ 0.067. If the material of the strain body 20 is SUS and d=7, the requirement is 0.026 ≤ t ≤ 0.034.

[0034] Furthermore, if the material of the strain body 20 is copper and d=32, the requirement is 0.084≦t≦0.166. Furthermore, if the material of the strain body 20 is copper and d=22, the requirement is 0.066≦t≦0.132. Furthermore, if the material of the strain body 20 is copper and d=13, the requirement is 0.044≦t≦0.088. Furthermore, if the material of the strain body 20 is copper and d=7, the requirement is 0.032≦t≦0.050.

[0035] Furthermore, if the material of the strain body 20 is aluminum and d=32, the requirement is 0.097≦t≦0.212. Furthermore, if the material of the strain body 20 is aluminum and d=22, the requirement is 0.079≦t≦0.168. Furthermore, if the material of the strain body 20 is aluminum and d=13, the requirement is 0.050≦t≦0.107. Furthermore, if the material of the strain body 20 is aluminum and d=7, the requirement is 0.038≦t≦0.063.

[0036] Thus, when the material, thickness t [mm], and diameter d [mm] of the circular opening of the strain-generating body 20 meet certain conditions, the required sensitivity and rigidity can be achieved simultaneously. However, if a Cr multiphase film is not used as the resistive element of the strain gauge 100, it may not be possible to achieve both the required sensitivity and rigidity, or even if they can be achieved, the allowable range of t will be significantly narrowed.

[0037] Now, let's explain strain gauge 100.

[0038] Figure 16 is a plan view illustrating a strain gauge according to the first embodiment. Figure 17 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 16. Referring to Figures 16 and 17, the strain gauge 100 includes a base material 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. In Figure 16, for convenience, only the outer edge of the cover layer 160 is shown with a dashed line. The cover layer 160 may be provided as needed.

[0039] In Figures 16 and 17, for convenience, the side of the strain gauge 100 on which the resistor 130 is provided is referred to as the upper side or one side, and the side on which the resistor 130 is not provided is referred to as the lower side or the other side. Also, the side of each part on which the resistor 130 is provided is referred to as one side or the upper surface, and the side on which the resistor 130 is not provided is referred to as the other side or the lower surface. However, the strain gauge 100 can be used upside down or positioned at any angle. For example, in Figure 2, the strain gauge 100 is attached to the beam section 22 in an inverted state compared to Figure 17. That is, the base material 110 in Figure 17 is attached to the lower surface of the beam section 22 with adhesive or the like. Furthermore, "plan view" refers to viewing the object from the direction normal to the upper surface 110a of the base material 110, and "planar shape" refers to the shape of the object viewed from the direction normal to the upper surface 110a of the base material 110.

[0040] The base material 110 is a member that serves as a base layer for forming the resistor 130, etc., and is flexible. The thickness of the base material 110 is not particularly limited and can be appropriately selected depending on the purpose, but for example it can be about 5 μm to 500 μm. In particular, a thickness of 5 μm to 200 μm for the base material 110 is preferable in terms of the transmission of strain from the surface of the strain-generating body joined to the lower surface of the base material 110 via an adhesive layer, etc., and dimensional stability against the environment, and a thickness of 10 μm or more is even preferable in terms of insulation.

[0041] The base material 110 can be formed from an insulating resin film such as PI (polyimide) resin, epoxy resin, PEEK (polyether ether ketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal polymer) resin, or polyolefin resin. Note that "film" refers to a flexible component with a thickness of approximately 500 μm or less.

[0042] Here, "formed from an insulating resin film" does not prevent the base material 110 from containing fillers or impurities in the insulating resin film. For example, the base material 110 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0043] Other materials for the substrate 110 besides resin include crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3), as well as amorphous glass. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 110. In this case, an insulating film is formed on the metallic substrate 110.

[0044] The resistor 130 is a thin film formed on the substrate 110 in a predetermined pattern, and is a sensitive part that undergoes a change in resistance when strained. The resistor 130 may be formed directly on the upper surface 110a of the substrate 110, or it may be formed on the upper surface 110a of the substrate 110 via another layer. For convenience, in Figure 16, the resistor 130 is shown with a dark, textured pattern.

[0045] The resistor 130 has a structure in which multiple elongated sections are arranged at predetermined intervals with their longitudinal directions aligned in the same direction (the direction of the BB line in Figure 16), and the ends of adjacent elongated sections are connected alternately, resulting in a zigzag folding pattern overall. The longitudinal direction of the multiple elongated sections becomes the grid direction, and the direction perpendicular to the grid direction becomes the grid width direction (the direction perpendicular to the BB line in Figure 16).

[0046] The longitudinal ends of the two elongated portions located on the outermost side in the grid width direction are bent in the grid width direction, forming the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction. Each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction is electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects each of the respective ends 130e1 and 130e2 of the resistor 130 in the grid width direction to each of the electrode 150.

[0047] The resistor 130 can be formed from, for example, a material containing Cr (chromium), a material containing Ni (nickel), or a material containing both Cr and Ni. That is, the resistor 130 can be formed from a material containing at least one of Cr and Ni. An example of a material containing Cr is a Cr multiphase film. An example of a material containing Ni is Cu-Ni (copper nickel). An example of a material containing both Cr and Ni is Ni-Cr (nickel chromium).

[0048] Here, a Cr multiphase film is a film in which Cr, CrN, Cr2N, etc., are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0049] The thickness of the resistor 130 is not particularly limited and can be appropriately selected depending on the purpose, but for example, it can be about 0.05 μm to 2 μm. In particular, a thickness of 0.1 μm or more of the resistor 130 is preferable because it improves the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr). Furthermore, a thickness of 1 μm or less of the resistor 130 is even preferable because it can reduce cracks in the film caused by internal stress in the film constituting the resistor 130 and warping from the substrate 110. The width of the resistor 130 can be optimized for the required specifications such as resistance value and lateral sensitivity, and also takes into account measures to prevent wire breakage, for example, it can be about 10 μm to 100 μm.

[0050] For example, if the resistor 130 is a Cr multiphase film, the stability of the gauge characteristics can be improved by making α-Cr (alpha-chromium), a stable crystalline phase, the main component. Furthermore, by making α-Cr the main component of the resistor 130, the gauge factor of the strain gauge 100 can be set to 10 or higher, and the temperature coefficient of gauge factor TCS and the temperature coefficient of resistance TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Here, "main component" means that the substance in question accounts for 50% by weight or more of the total substances constituting the resistor. From the viewpoint of improving gauge characteristics, it is preferable that the resistor 130 contains 80% by weight or more of α-Cr, and more preferably 90% by weight or more. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0051] Furthermore, if the resistor 130 is a Cr multiphase film, it is preferable that the amount of CrN and Cr2N contained in the Cr multiphase film be 20% by weight or less. By having CrN and Cr2N contained in the Cr multiphase film at 20% by weight or less, the decrease in gauge factor can be suppressed.

[0052] Furthermore, the proportion of Cr2N in CrN and Cr2N is preferably 80% by weight or more and less than 90% by weight, and more preferably 90% by weight or more and less than 95% by weight. When the proportion of Cr2N in CrN and Cr2N is 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced due to the semiconducting properties of Cr2N. In addition, brittle fracture is reduced by reducing the ceramicization.

[0053] On the other hand, if trace amounts of N2 or atomic N are mixed into the film, external environmental factors (such as high temperatures) can cause them to escape from the film, resulting in changes in film stress. By creating chemically stable CrN, the generation of the aforementioned unstable N is avoided, and a stable strain gauge can be obtained.

[0054] The wiring 140 is formed on the substrate 110 and is electrically connected to the resistor 130 and the electrode 150. The wiring 140 has a first metal layer 141 and a second metal layer 142 laminated on the upper surface of the first metal layer 141. The wiring 140 is not limited to a straight line and can be in any pattern. Also, the wiring 140 can have any width and any length. For convenience, in Figure 16, the wiring 140 and the electrode 150 are shown with a matte finish that is thinner than the resistor 130.

[0055] The electrode 150 is formed on the substrate 110 and is electrically connected to the resistor 130 via the wiring 140. For example, it is wider than the wiring 140 and formed in a roughly rectangular shape. The electrode 150 is a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 130 caused by strain, and for example, lead wires for external connection are joined to it.

[0056] The electrode 150 has a pair of first metal layers 151 and a second metal layer 152 laminated on the upper surface of each first metal layer 151. The first metal layers 151 are electrically connected to the ends 130e1 and 130e2 of the resistor 130 via the first metal layers 141 of the wiring 140. The first metal layers 151 are formed in a substantially rectangular shape in plan view. The first metal layers 151 may be formed to the same width as the wiring 140.

[0057] Although the resistor 130, the first metal layer 141, and the first metal layer 151 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the resistor 130, the first metal layer 141, and the first metal layer 151 have approximately the same thickness. Similarly, although the second metal layer 142 and the second metal layer 152 are given different reference numerals for convenience, they can be integrally formed from the same material in the same process. Therefore, the second metal layer 142 and the second metal layer 152 have approximately the same thickness.

[0058] The second metal layers 142 and 152 are formed from a material with lower resistance than the resistor 130 (first metal layers 141 and 151). The material of the second metal layers 142 and 152 is not particularly limited as long as it has lower resistance than the resistor 130, and can be appropriately selected according to the purpose. For example, if the resistor 130 is a Cr multiphase film, the material of the second metal layers 142 and 152 can be Cu, Ni, Al, Ag, Au, Pt, etc., or an alloy of any of these metals, a compound of any of these metals, or a laminated film in which any of these metals, alloys, or compounds are appropriately stacked. The thickness of the second metal layers 142 and 152 is not particularly limited and can be appropriately selected according to the purpose, but can be, for example, about 3 μm to 5 μm.

[0059] The second metal layers 142 and 152 may be formed on a portion of the upper surface of the first metal layers 141 and 151, or on the entire upper surface of the first metal layers 141 and 151. One or more additional metal layers may be laminated on the upper surface of the second metal layer 152. For example, the second metal layer 152 may be a copper layer, and a gold layer may be laminated on top of the copper layer. Alternatively, the second metal layer 152 may be a copper layer, and a palladium layer and a gold layer may be sequentially laminated on top of the copper layer. By making the uppermost layer of the electrode 150 a gold layer, the solder wettability of the electrode 150 can be improved.

[0060] Thus, the wiring 140 has a structure in which a second metal layer 142 is laminated on a first metal layer 141 made of the same material as the resistor 130. Therefore, since the wiring 140 has lower resistance than the resistor 130, it is possible to suppress the wiring 140 from functioning as a resistor. As a result, the accuracy of strain detection by the resistor 130 can be improved.

[0061] In other words, by providing wiring 140 with lower resistance than the resistor 130, the effective sensitive area of ​​the strain gauge 100 can be limited to the local region where the resistor 130 is formed. Therefore, the accuracy of strain detection by the resistor 130 can be improved.

[0062] In particular, in a highly sensitive strain gauge with a gauge factor of 10 or higher using a Cr multiphase film as the resistor 130, reducing the resistance of the wiring 140 to that of the resistor 130 and limiting the effective sensitive area to the local region where the resistor 130 is formed has a remarkable effect on improving the accuracy of strain detection. Furthermore, reducing the resistance of the wiring 140 to that of the resistor 130 also has the effect of reducing lateral sensitivity.

[0063] The cover layer 160 is formed on the substrate 110 and covers the resistor 130 and wiring 140, while exposing the electrode 150. A portion of the wiring 140 may be exposed from the cover layer 160. By providing the cover layer 160 that covers the resistor 130 and wiring 140, mechanical damage to the resistor 130 and wiring 140 can be prevented. In addition, the cover layer 160 can protect the resistor 130 and wiring 140 from moisture and other elements. The cover layer 160 may be provided so as to cover the entire portion excluding the electrode 150.

[0064] The cover layer 160 can be formed from an insulating resin such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, or composite resin (e.g., silicone resin, polyolefin resin). The cover layer 160 may contain fillers or pigments. There are no particular restrictions on the thickness of the cover layer 160, and it can be appropriately selected depending on the purpose, but for example, it can be about 2 μm to 30 μm.

[0065] To manufacture the strain gauge 100, first, a base material 110 is prepared, and a metal layer (for convenience, referred to as metal layer A) is formed on the upper surface 110a of the base material 110. Metal layer A is the layer that will ultimately be patterned to become the resistor 130, the first metal layer 141, and the first metal layer 151. Therefore, the material and thickness of metal layer A are the same as those of the resistor 130, the first metal layer 141, and the first metal layer 151.

[0066] Metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming metal layer A. Alternatively, metal layer A may be deposited using reactive sputtering, evaporation, arc ion plating, pulsed laser deposition, or other methods instead of magnetron sputtering.

[0067] From the viewpoint of stabilizing gauge characteristics, it is preferable to vacuum-deposit a functional layer of a predetermined thickness as an underlayer on the upper surface 110a of the substrate 110, for example, by conventional sputtering, before depositing the metal layer A.

[0068] In this application, the functional layer refers to a layer that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130). Preferably, the functional layer further has the function of preventing oxidation of the metal layer A by oxygen and moisture contained in the substrate 110, and the function of improving the adhesion between the substrate 110 and the metal layer A. The functional layer may further have other functions.

[0069] Since the insulating resin film that makes up the base material 110 contains oxygen and moisture, and especially when the metal layer A contains Cr, Cr forms an oxidized film, it is effective for the functional layer to have a function that prevents oxidation of the metal layer A.

[0070] The material of the functional layer is not particularly limited as long as it is a material that has the function of promoting crystal growth of at least the upper metal layer A (resistor 130), and can be appropriately selected according to the purpose. For example, Cr (chromium), Ti (titanium), V (vanadium), Nb (niobium), Ta (tantalum), Ni (nickel), Y (yttrium), Zr (zirconium), Hf (hafnium), Si (silicon), C (carbon), Zn (zinc), Cu (copper), Bi (bisulfite). Examples include one or more metals selected from the group consisting of M(Os), Fe (iron), Mo (molybdenum), W (tungsten), Ru (ruthenium), Rh (rhodium), Re (rhenium), Os (osmium), Ir (iridium), Pt (platinum), Pd (palladium), Ag (silver), Au (gold), Co (cobalt), Mn (manganese), and Al (aluminum), an alloy of any of these metals, or a compound of any of these metals.

[0071] Examples of the alloys mentioned above include FeCr, TiAl, FeNi, NiCr, and CrCu. Examples of the compounds mentioned above include TiN, TaN, Si3N4, TiO2, Ta2O5, and SiO2.

[0072] When the functional layer is formed from a conductive material such as a metal or alloy, the thickness of the functional layer is preferably 1 / 20 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor can flow into the functional layer, preventing a decrease in strain detection sensitivity.

[0073] When the functional layer is formed from a conductive material such as a metal or alloy, it is more preferable that the thickness of the functional layer be 1 / 50 or less of the thickness of the resistor. Within this range, the crystal growth of α-Cr can be promoted, and a portion of the current flowing through the resistor flows into the functional layer, further preventing a decrease in strain detection sensitivity.

[0074] When the functional layer is formed from a conductive material such as a metal or alloy, it is even more preferable that the thickness of the functional layer be 1 / 100 or less of the thickness of the resistor. Within this range, it is possible to further prevent a decrease in strain detection sensitivity due to some of the current flowing through the resistor flowing into the functional layer.

[0075] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is preferably 1 nm to 1 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be easily formed without cracking.

[0076] When the functional layer is formed from an insulating material such as an oxide or nitride, the thickness of the functional layer is more preferably 1 nm to 0.8 μm. Within this range, the crystal growth of α-Cr can be promoted, and the functional layer can be formed more easily without cracking.

[0077] When the functional layer is formed from an insulating material such as an oxide or nitride, it is even more preferable that the thickness of the functional layer be 1 nm to 0.5 μm. Within this range, the crystal growth of α-Cr can be promoted, and the film can be formed more easily without cracking in the functional layer.

[0078] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 16, for example. However, the planar shape of the functional layer is not limited to being substantially the same as the planar shape of the resistor. When the functional layer is formed from an insulating material, it does not need to be patterned to be the same as the planar shape of the resistor. In this case, the functional layer may be formed as a solid block at least in the region where the resistor is formed. Alternatively, the functional layer may be formed as a solid block over the entire upper surface of the substrate 110.

[0079] Furthermore, when the functional layer is formed from an insulating material, forming the functional layer relatively thick, such as 50 nm to 1 μm, and forming it in a solid form increases the thickness and surface area of ​​the functional layer, allowing the heat generated when the resistor heats up to be dissipated towards the base material 110. As a result, the decrease in measurement accuracy due to self-heating of the resistor can be suppressed in the strain gauge 100.

[0080] The functional layer can be deposited using a conventional sputtering method, for example, by targeting a raw material capable of forming a functional layer and introducing Ar (argon) gas into a chamber. By using the conventional sputtering method, the functional layer is deposited while etching the upper surface 110a of the substrate 110 with Ar, thus minimizing the amount of functional layer deposited and achieving improved adhesion.

[0081] However, this is just one example of a method for forming a functional layer, and the functional layer may be formed by other methods. For example, the upper surface 110a of the substrate 110 may be activated by plasma treatment using Ar or the like before forming the functional layer to improve adhesion, and then the functional layer may be formed in a vacuum by magnetron sputtering.

[0082] There are no particular restrictions on the combination of materials for the functional layer and the metal layer A, and they can be appropriately selected according to the purpose. For example, it is possible to use Ti as the functional layer and deposit a Cr multiphase film mainly composed of α-Cr (alpha-chromium) as the metal layer A.

[0083] In this case, for example, metal layer A can be formed by targeting a raw material capable of forming a Cr multiphase film and using a magnetron sputtering method with Ar gas introduced into the chamber. Alternatively, metal layer A may be formed by targeting pure Cr and using a reactive sputtering method with an appropriate amount of nitrogen gas introduced into the chamber along with Ar gas. In this case, the ratio of CrN and Cr2N in the Cr multiphase film, as well as the ratio of Cr2N within CrN and Cr2N, can be adjusted by changing the amount and pressure (partial pressure of nitrogen) of nitrogen gas introduced or by adjusting the heating temperature by providing a heating step.

[0084] In these methods, a functional layer made of Ti dictates the growth surface of the Cr multiphase film, enabling the formation of a Cr multiphase film primarily composed of α-Cr, which has a stable crystalline structure. Furthermore, the diffusion of Ti constituting the functional layer into the Cr multiphase film improves the gauge characteristics. For example, the gauge factor of a strain gauge of 100 can be set to 10 or higher, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / °C to +1000 ppm / °C. Note that if the functional layer is formed from Ti, the Cr multiphase film may contain Ti or TiN (titanium nitride).

[0085] Furthermore, when metal layer A is a Cr multiphase film, the functional layer made of Ti has all of the following functions: promoting crystal growth of metal layer A, preventing oxidation of metal layer A by oxygen and moisture contained in the substrate 110, and improving adhesion between the substrate 110 and metal layer A. The same applies when Ta, Si, Al, or Fe are used instead of Ti as the functional layer.

[0086] In this way, by providing a functional layer beneath the metal layer A, crystal growth in the metal layer A can be promoted, and a metal layer A consisting of a stable crystalline phase can be fabricated. As a result, the stability of the gauge characteristics of the strain gauge 100 can be improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A can improve the gauge characteristics of the strain gauge 100.

[0087] Next, a second metal layer 142 and a second metal layer 152 are formed on the upper surface of metal layer A. The second metal layer 142 and the second metal layer 152 can be formed, for example, by photolithography.

[0088] Specifically, first, a seed layer is formed to cover the upper surface of metal layer A, for example, by sputtering or electroless plating. Next, a photosensitive resist is formed over the entire upper surface of the seed layer, and exposure and development are performed to create openings that expose the areas for forming the second metal layer 142 and the second metal layer 152. At this time, the pattern of the second metal layer 142 can be made into any shape by adjusting the shape of the openings in the resist. For example, a dry film resist can be used as the resist.

[0089] Next, for example, a second metal layer 142 and a second metal layer 152 are formed on the seed layer exposed within the opening by an electroplating method using the seed layer as the power supply path. The electroplating method is preferable because it has a high cycle time and can form low-stress electroplated layers as the second metal layer 142 and the second metal layer 152. By making the thick electroplated layer low-stress, warping of the strain gauge 100 can be prevented. The second metal layer 142 and the second metal layer 152 may also be formed by an electroless plating method.

[0090] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0091] Next, a photosensitive resist is formed on the entire upper surface of the seed layer, exposed and developed to pattern it into a planar shape similar to the resistor 130, wiring 140, and electrode 150 in Figure 16. For example, a dry film resist can be used as the resist. Then, the resist is used as an etching mask to remove the metal layer A and seed layer exposed from the resist, forming the resistor 130, wiring 140, and electrode 150 with the planar shape shown in Figure 16.

[0092] For example, unwanted portions of metal layer A and seed layer can be removed by wet etching. If a functional layer is formed beneath metal layer A, etching will pattern the functional layer into the planar shape shown in Figure 16, similar to the resistor 130, wiring 140, and electrode 150. At this point, seed layers are formed on resistor 130, first metal layer 141, and first metal layer 151.

[0093] Next, the second metal layers 142 and 152 are used as etching masks, and the unwanted seed layers exposed from the second metal layers 142 and 152 are removed to form the second metal layers 142 and 152. Note that the seed layers directly beneath the second metal layers 142 and 152 remain. For example, the unwanted seed layers can be removed by wet etching using an etching solution that etches the seed layers but not the functional layers, resistors 130, wiring 140, and electrodes 150.

[0094] Subsequently, if necessary, a cover layer 160 is provided on the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, thereby completing the strain gauge 100. The cover layer 160 can be made, for example, by laminating a semi-cured thermosetting insulating resin film onto the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it. Alternatively, the cover layer 160 may be made by applying a liquid or paste-like thermosetting insulating resin to the upper surface 110a of the base material 110 to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing it.

[0095] <Variations of the first embodiment> A modified example of the first embodiment shows a pulse wave sensor using a non-metallic strain-generating body. In this modified example of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0096] Figure 18 is a cross-sectional view (part 1) illustrating a modified pulse wave sensor according to the first embodiment. The pulse wave sensor 1A shown in Figure 18 includes a strain-generating body 20A formed from a non-metallic material. For example, ceramics or glass can be used as the material for the strain-generating body 20A. The strain-generating body 20A is the same as the strain-generating body 20 except that it is made of a non-metallic material. Unlike the pulse wave sensor 1, the pulse wave sensor 1A does not include a resin layer 50.

[0097] The strain-generating body 20A may be formed from a non-metallic material, as in the pulse wave sensor 1A. In this case, even if the strain-generating body 20A comes into direct contact with the subject's skin, no inflammation of the subject's skin or metal allergy will occur due to the metal, and therefore, a resin layer 50 does not need to be provided.

[0098] Figure 19 is a cross-sectional view (part 2) illustrating a modified pulse wave sensor according to the first embodiment. When a non-metallic strain body 20A is used, as in the pulse wave sensor 1B shown in Figure 19, a resin layer 50 covering the upper surface 20m of the strain body 20A may be provided, similar to the pulse wave sensor 1 shown in Figure 3. The resin layer 50 is also formed on the gap between the beam portion 22 and the extension portion 24, so that the gap between the beam portion 22 and the extension portion 24 is not exposed to the outside of the pulse wave sensor 1B. As a result, dust and foreign matter cannot get trapped in the gap between the beam portion 22 and the extension portion 24, making the pulse wave sensor 1B more reliable and enabling more stable measurement of pulse waves.

[0099] Figure 20 is a cross-sectional view (part 3) illustrating a modified pulse wave sensor according to the first embodiment. When a non-metallic strain body 20A is used, as in the pulse wave sensor 1C shown in Figure 20, a resin layer 50A covering the lower surface 20n of the strain body 20A may be provided instead of a resin layer 50 covering the upper surface 20m of the strain body 20A. The material and thickness of the resin layer 50A are the same as those of the resin layer 50. In the pulse wave sensor 1C, the resin layer 50A fits into the gap between the beam portion 22 and the extension portion 24, filling the gap between the beam portion 22 and the extension portion 24. As a result, dust and foreign matter cannot get trapped in the gap between the beam portion 22 and the extension portion 24, thus increasing the reliability of the pulse wave sensor 1C and enabling more stable measurement of pulse waves. In addition, the resin layer 50A, together with the cover layer 160, protects the strain gauge 100 from moisture and the like.

[0100] Furthermore, a resin layer 50 may be provided to cover the upper surface 20m of the strain-generating body 20A, and a resin layer 50A may be provided to cover the lower surface 20n of the strain-generating body 20A. Alternatively, a resin layer 50A may be provided on the lower surface 20n of the strain-generating body 20 as shown in Figures 1 to 3. In this case, the resin layer 50A, together with the cover layer 160, protects the strain gauge 100 from moisture and other elements.

[0101] <Second Embodiment> In the embodiments and modifications described above, an example was given in which the detection unit according to the present disclosure is a strain gauge using a resistor. That is, in the above embodiments, the case in which the detection unit according to the present disclosure is an electrical resistance type metal strain gauge was described. However, the detection unit according to the present disclosure is not limited to a metal strain gauge. For example, the detection unit according to the present disclosure may be a strain gauge that detects magnetic changes caused by strain in a strain-generating body (or a structure equivalent to a strain-generating body) using a detection element included in the strain gauge.

[0102] Specifically, the detection unit according to this disclosure may be a strain gauge including a detection element that utilizes the Villari phenomenon (described later). Alternatively, the detection unit according to this disclosure may be a strain gauge including a detection element having a magnetic tunnel junction structure (described later). In the second embodiment below, a strain gauge including a detection element that utilizes the Villari phenomenon will be described. In the third embodiment, a strain gauge including a detection element having a magnetic tunnel junction structure will be described.

[0103] In each embodiment of this specification, components having similar functions will be given the same name and component number, and their descriptions will not be repeated. Furthermore, the directions of the x, y, and z axes in the drawings of each embodiment thereafter (drawings from Figure 21 onwards) are the same as the directions of the x, y, and z axes shown in Figures 2 and 3. In the following description, the positive direction of the z axis will be referred to as "up," and the negative direction of the z axis will be referred to as "down." That is, in the following description, "upper side" refers to the side in the positive direction of the z axis, and "upper surface" refers to the surface on the positive direction of the z axis. Similarly, "lower side" refers to the side in the negative direction of the z axis, and "lower surface" refers to the surface on the negative direction of the z axis.

[0104] Figure 21 shows an example of a detection element 300 included in a strain gauge according to the second embodiment. Figure 21(a) is a plan view of the detection element 300 as seen from the negative z-axis to the positive z-axis (i.e., from the bottom surface to the top surface). On the other hand, Figure 21(b) shows a cross-sectional view of the detection element 300 shown in Figure 21(a) along the α-α' line. Note that the wiring extending from the detection element 300 is not shown in Figures 21(a) and (b). However, the detection element 300 may be connected to wiring that connects the drive coil 320 and the power supply, which will be described later, and to wiring that transmits the current detected by the sensing coil 380.

[0105] As shown in Figure 21(a), the detection element 300 includes a drive coil 320, a sensing coil 380, and a base layer 310. The base layer 310 is the core layer for the drive coil 320 and the sensing coil 380. The sensing coil 380 is a coil for detecting the magnetization strength of the base layer 310 (more precisely, the base metal 370 described later). The drive coil 320 is a coil for generating a magnetic field. The detection element 300 has a double structure with the base layer 310 as the core material, with the sensing coil 380 wound on the inside and the drive coil 320 wound on the outside. The materials for the drive coil 320 and the sensing coil 380 are preferably conductive metals such as Cu, Ag, Al, and Au, or alloys of these metals. The number of turns and the size of the cross-sectional area of ​​the drive coil 320 and the sensing coil 380 may be appropriately designed according to the strain detection sensitivity required for the detection element 300.

[0106] As will be explained in detail later, when stress is applied to the base layer 310, the magnetization strength of the base metal 370 (described later) contained in the base layer 310 changes. The detection element 300 can determine the strength of the stress (i.e., the degree of strain) applied to the base layer 310 by detecting this change in magnetization strength with the sensing coil 380.

[0107] The configuration of the detection element 300 will be further explained with reference to the cross-sectional view in Figure 21(b). In Figure 21(b), the drive coil 320, the sensing coil 380, and the three insulating layers 340, 350, and 360 are each formed to surround the core material, the base metal 370. That is, the layers with the same component number in Figure 21(b) are connected and surround the base metal 370.

[0108] The base metal 370 is a core material for various coils and insulating layers. The base metal 370 may be, for example, a substantially flat metal plate. The base metal 370 is covered so as to surround it with the insulating layer 360. Preferably, the base metal 370 is made of a soft magnetic material such as an Fe-Si-Al alloy such as Sendust, or a Ni-Fe alloy such as Permalloy. The aforementioned base layer 310 consists of this base metal 370 and the insulating layer 360, as shown in Figure 21(b).

[0109] Outside the insulating layer 360, an insulating layer 350 is formed so as to surround the insulating layer 360. Further outside the insulating layer 350, an insulating layer 340 is formed. The insulating layer 350 is a layer containing the sensing coil 380, and the gaps around the sensing coil 380 are filled with insulating material. The insulating layer 340 is a layer containing the drive coil 320, and the gaps around the drive coil 320 are filled with insulating material. It is preferable that the insulating layers 340, 350, and 360 are made of a dry film that is not affected by the magnetic field or a resist-cured material such as a photosensitive polyimide.

[0110] One side of the detection element 300 may be attached to the base material 110, as shown in Figure 21(b). The base material 110 is a member that fixes the detection element 300. For example, the base material 110 may be a flexible substrate made of plastic film or the like. The detection element 300 is attached to the strain-generating body 20 or 20A via the base material 110. The detection element 300 may be a flat plate or a thin film as a whole. If the detection element 300 is a flat plate or a thin film, the detection element 300 can be easily attached to the base material 110. Furthermore, the base material 110 is not an essential component of the detection element 300. For example, the detection element 300 may be used without a base material 110, by directly attaching the upper surface of the detection element 300 to the strain-generating body 20 or 20A.

[0111] The strain-generating bodies 20 and 20A according to this embodiment may have basically the same configuration and materials as the strain-generating bodies 20 and 20A according to the first embodiment. However, it is more desirable that the strain-generating bodies 20 and 20A be made of a non-magnetic material. The strain-generating bodies 20 and 20A according to this embodiment can be made from, for example, non-magnetic stainless steel.

[0112] Next, the principle of detecting strain using the detection element 300 will be outlined. The detection element 300 includes a base metal 370, which is a magnetic material. When an alternating current is supplied from the power source to the drive coil 320, the drive coil 320 generates an alternating magnetic field around it. This generates a magnetic field, and the base metal 370 is magnetized. When the strain-generating body 20 or 20A deforms in this state, strain occurs. The strain is transmitted through the substrate 110, and stress is applied to the base metal 370. If the detection element 300 is attached to the strain-generating body 20 or 20A without going through the substrate 110, the stress is transmitted directly from the strain-generating body 20 or 20A to the base metal 370 (and the insulating layers 340-360 covering it).

[0113] When stress is applied to the base metal 370, the permeability of the base metal 370 changes according to that stress. Consequently, the magnetization strength (degree of magnetization) of the base metal 370 changes. This phenomenon, in which the permeability and magnetization strength of a magnetic material change when stress is applied to it, is called the "Villari phenomenon." According to the configuration of the detection element 300, an AC voltage corresponding to the magnetization strength of the base metal 370 is induced in the sensing coil 380, which is the pickup coil. Therefore, based on the principle of the Villari phenomenon, the stress applied to the base metal 370 can be calculated from the value of this AC voltage. Then, from the calculated stress, the degree of strain in the strain-generating bodies 20 and 20A can be determined. Note that if the detection element 300 has the shape shown in Figures 21(a) and (b), the grid direction of the detection element 300 is equal to the α-α' direction in Figure 21(a). Based on the principle described above, the detection element 300 can detect the strain in the strain-generating bodies 20 and 20A. In other words, the detection element 300 functions as a detection element for strain gauges.

[0114] Furthermore, it is desirable that the drive coil 320 be wound as uniformly as possible around the outside of the sensing coil 380 and over the entire region in which the sensing coil 380 is present. This allows for a more uniform application of the alternating magnetic field to the entire region of the base metal 370 in which the sensing coil 380 is present. As a result, changes in the magnetization strength of the base metal 370 due to the vilari phenomenon can be detected more precisely. Therefore, the performance of the detection element 300 is improved.

[0115] Furthermore, the insulating layer 360 may be formed on only a part of the base metal 370, rather than the entirety of it. For example, the portion of the base metal 370 around which the sensing coil 380 and the drive coil 320 are wound may be covered with the insulating layer 360, the insulating layer 360 may be covered with an insulating layer 350 including the sensing coil 380, and the insulating layer 350 may be further covered with an insulating layer 340 including the drive coil 320.

[0116] Furthermore, if the base metal 370 is substantially flat, the insulating layer 360 may be formed to surround the base metal 370 only in the direction in which the coil is wound. That is, in Figure 21(b), both ends of the base metal 370 in the y-direction do not need to be covered by the insulating layer 360.

[0117] In the pulse wave sensor according to this embodiment, when the strain-generating body 20 or 20A deforms (i.e., strain occurs in the strain-generating body), the base material 110 of the strain gauge (or the detection element 300 itself) is strained. The detection element 300 can detect the magnetic change caused by this strain based on the principle of the Villari phenomenon described above.

[0118] The strain gauge including the detection element 300 according to this embodiment can be arranged on the strain bodies 20 and 20A in any arrangement pattern shown in the first embodiment and the modified version of the first embodiment. That is, the strain of the strain bodies 20 and 20A can be detected using the detection element 300 according to this embodiment, in the same way as when an electrical resistance type strain gauge is used. Therefore, the strain gauge according to this embodiment has the same effects as the strain gauge 100 according to the first embodiment and the modified version of the first embodiment.

[0119] <Third Embodiment> Figure 22 shows a detection element 500, which is an example of a detection element included in the strain gauge according to the third embodiment. Figure 23 shows a detection element 600, which is another example of a detection element according to the third embodiment. Figure 24 shows a detection element 700, yet another example of a detection element according to the third embodiment. Figures 22 to 24(a) are perspective views of the detection elements 500, 600, and 700, respectively. Figures 22 to 24(b) are plan views of the detection elements 500, 600, and 700 viewed from the negative z-axis to the positive z-axis, respectively. Figures 22 to 24(c) are cross-sectional views of the detection elements 500, 600, and 700 in a plane parallel to the zy-plane. Note that wiring extending from the detection elements is not shown in any of the figures 22 to 24. However, these detection elements 500, 600, and 700 may also be connected to wiring that connects the upstream electrode 510 to the power supply and wiring that connects the downstream electrode 520 to the power supply, as described later.

[0120] As shown in Figures 22 to 24(a), the detection elements 500, 600, and 700 include an upstream electrode 510, a downstream electrode 520, a magnetic film 530, and an insulating film 540. The insulating film 540 is sandwiched between the magnetic film 530 as shown in the figure. A magnetic tunnel junction is formed by this magnetic film 530 and insulating film 540. In other words, the detection elements 500, 600, and 700 have a structure in which electrodes are connected to a magnetic tunnel junction structure.

[0121] The upper surfaces of the detection elements 500, 600, and 700 may be attached to a substrate similar to the substrate 110 of the second embodiment. The detection element 500 may be attached to the strain-generating body 20 or 20A via the substrate. The detection elements 500, 600, and 700 may be flat plates or thin films as a whole. If the detection elements 500, 600, and 700 are flat plates or thin films, they can be easily attached to the substrate or strain-generating body 20 or 20A. Alternatively, for example, the upper surfaces of the detection elements 500, 600, and 700 may be directly attached to the strain-generating body 20 or 20A for use.

[0122] The magnetic film 530 is a magnetic nanothin film. The insulating film 540 is an insulating nanothin film. The materials of the magnetic film 530 and the insulating film 540 are not particularly limited, as long as a magnetic tunnel junction structure can be formed. For example, cobalt iron boron, or 3d transition metal ferromagnets such as Fe, Co, and Ni, and alloys containing them can be used as the magnetic film 530. Also, silicon oxide, silicon nitride, aluminum oxide, magnesium oxide, etc. can be used as the insulating film 540.

[0123] The upstream electrode 510 and the downstream electrode 520 are electrodes for applying a voltage to the magnetic tunnel junction structure. In the examples in Figures 22-24, the current flows from the upstream electrode 510 to the downstream electrode 520. For example, in Figure 22(c), when a voltage is applied between the upstream electrode 510 and the downstream electrode 520, electrons flow from the lower (negative z-axis) magnetic film 530, across the insulating film 540, to the upper (positive z-axis) magnetic film 530. This phenomenon is called the "tunneling effect," and the electrical resistance when electrons pass through the insulating film 540 is called the "tunneling resistance." In the examples in Figures 22-24, the junctions of each part of the electrodes are treated at the ends to prevent current from short-circuiting the magnetic tunnel junction structure.

[0124] Incidentally, when strain is applied to the detection element 500 via the substrate 110, a magnetic change occurs in the tunnel junction structure. More specifically, the magnetization directions of the upper and lower magnetic films 530 are misaligned. When the magnetization directions of the upper and lower magnetic films 530 are misaligned in this way, the tunnel resistance increases compared to when the magnetization directions are parallel (tunnel magnetoresistance effect). Therefore, in the detection element 500 having the above configuration, the current flowing between the electrodes decreases in proportion to the magnitude of the strain in the detection element 500 (more precisely, the magnetic tunnel junction portion). That is, as the strain increases, the electrical resistance increases. In this way, the detection element 500 can detect strain based on the current value in relation to the applied voltage. Therefore, by attaching the detection element 500 to the strain generating body 20 or 20A, the strain applied to the strain generating body 20 or 20A can be measured.

[0125] The detection element having a magnetic tunnel junction structure is not limited to the example shown in Figure 22. For example, detection elements 600 and 700 as shown in Figures 23 and 24 can also be used. Both the detection element 600 shown in Figure 23 and the detection element 700 shown in Figure 24 are composed of an upstream electrode 510, a downstream electrode 520, a magnetic film 530, and an insulating film 540, and the principle of detecting strain by these components is the same as that of the detection element 500. The basic operation of the detection elements 600 and 700 is also the same as that of the detection element 500. The grid direction of the detection elements 500, 600, and 700 corresponds to the y-axis direction (positive y-axis and negative y-axis direction) in Figures 22 to 24, respectively. As shown in the figure, the detection element 600 shown in Figure 23 has a structure in which the upper magnetic film 530 and the lower magnetic film 530 are partially connected. In other words, a magnetic tunnel junction structure is formed only in a portion of the magnetic film 530, and a tunnel magnetoresistance effect occurs in this structure. On the other hand, the detection element 700 shown in Figure 24 is attached to the substrate 110 via the substrate 710. As shown in Figures 22 to 24, the design of the detection element may be modified as appropriate according to the required size, durability, and magnitude of stress to be detected, as long as it does not exceed the aforementioned principle.

[0126] The strain generators 20 and 20A according to this embodiment may have basically the same configuration and materials as the strain generators 20 and 20A according to the first embodiment. However, it is more desirable that the strain generators 20 and 20A be made of a non-magnetic material. For example, the strain generators 20 and 20A according to this embodiment can be made from non-magnetic stainless steel. The detection elements 500, 600, and 700 as a whole may have a substantially flat plate shape, such as a film type. This allows the detection elements 500 to be easily attached to the strain generators 20 and 20A. The detection elements 500, 600, and 700 may also have a structure for applying a weak magnetic field to the structural parts of the magnetic tunnel junction, such as a drive coil. By applying a magnetic field to the structural parts of the magnetic tunnel junction, the tunnel magnetoresistance effect can be measured more stably, and thus strain can be detected stably.

[0127] Furthermore, the terms "upstream electrode" and "downstream electrode" in the detection elements 500, 600, and 700 are merely convenient names, and the direction of current flow may be reversed. In other words, in the detection elements 500, 600, and 700 shown in Figures 22 to 24, the design may be such that current flows from the downstream electrode 520 to the upstream electrode 510.

[0128] In the pulse wave sensor according to this embodiment, when the strain-generating body 20 or 20A deforms (i.e., strain occurs in the strain-generating body), the base material of the strain gauge (or the detection element 500, 600, or 700 itself) is strained. The detection element 500, 600, or 700 can detect the magnetic change caused by this strain based on the principle of the tunnel magnetoresistance effect described above.

[0129] The strain gauges including the detection elements 500, 600, and 700 according to this embodiment can be placed on the strain bodies 20 and 20A at any of the arrangement positions shown in the first embodiment and the modified examples of the first embodiment. That is, the strain of the strain bodies 20 and 20A can be detected using the detection elements 500, 600, and 700 according to this embodiment, in the same way as when using an electrical resistance type strain gauge. Therefore, the strain gauges according to this embodiment have the same effects as the strain gauge 100 according to the first embodiment and the modified examples of the first embodiment.

[0130] <Fourth Embodiment> The detection unit according to this disclosure may be a semiconductor strain gauge, a capacitive pressure sensor, or an optical fiber strain gauge. Alternatively, the detection unit may be a mechanical pressure sensor, a vibratory pressure sensor, or a piezoelectric pressure sensor. The principles of various strain gauges and pressure sensors will be explained below.

[0131] (Semiconductor strain gauge) Semiconductor strain gauges are strain gauges that detect strain by utilizing the pressure-resistive effect of semiconductors. In other words, semiconductor strain gauges are strain gauges that use semiconductors as strain detection elements.

[0132] It is known that when stress is applied to a semiconductor, strain occurs in the semiconductor's crystal lattice, changing the number and mobility of carriers in the semiconductor, and consequently changing its electrical resistance. Semiconductor strain gauges can be used by directly attaching them to the strain body 20 or 20A, similar to electrical resistance metal strain gauges. In this case, when the strain body 20 or 20A expands or contracts, the attached semiconductor (more specifically, the semiconductor's crystal lattice) is strained, and its electrical resistance changes. Therefore, the amount of strain in the strain body 20 or 20A can be determined by measuring this electrical resistance.

[0133] Furthermore, semiconductor strain gauges can also be configured as strain sensors equipped with a diaphragm structure. In this case, the strain sensor includes, for example, a non-metallic diaphragm (or a metal diaphragm with an electrically insulating layer formed on it) and a semiconductor (for example, a silicon thin-film semiconductor) formed on the diaphragm. In this structure including a diaphragm, when the diaphragm is strained by a normal stress applied to it, the electrical resistance of the semiconductor changes. Therefore, by measuring this electrical resistance, the amount of strain in the diaphragm (and consequently, the amount of strain in the strain-generating body 20 or 20A) can be determined.

[0134] (Capacitive pressure sensor) A capacitive pressure sensor is a pressure sensor that measures the pressure applied to a diaphragm as a change in the capacitance of a pair of electrodes. In other words, a capacitive pressure sensor is a pressure sensor that uses a pair of electrodes as detection elements. A capacitive pressure sensor comprises, for example, a diaphragm as a movable electrode and one or more fixed electrodes. The diaphragm is formed of, for example, silicon containing impurities (i.e., silicon that functions as a conductor).

[0135] When pressure is applied to a diaphragm, the diaphragm is displaced, and the distance between the fixed electrode and the movable electrode changes. It is known that the capacitance between electrodes is determined by the distance between the electrodes, provided that the dielectric constant of the interelectrode medium and the area of ​​the electrodes are constant. Therefore, by measuring the capacitance, the amount of diaphragm displacement (i.e., the magnitude of the pressure) can be determined.

[0136] (Optical fiber strain gauge) An optical fiber strain gauge is a strain gauge that detects strain using an optical fiber on which a fiber Bragg grating (FBG) is formed. In other words, an optical fiber strain gauge is a strain gauge that uses an optical fiber as a strain detection element. The FBG is a diffraction grating that causes different light reflections in the optical fiber than in other parts of the optical fiber, and each of these gratings is formed at a constant interval. When the optical fiber is strained and stretched, the grating spacing of the FBG widens, so the wavelength of the reflected light of light incident on the optical fiber (e.g., laser light) changes. Conversely, when the optical fiber is strained and contracted, the grating spacing of the FBG narrows, so the wavelength of the reflected light of light incident on the fiber (e.g., laser light) changes.

[0137] By attaching an optical fiber having such characteristics to a strain-generating body 20 or 20A and measuring the wavelength spectrum of the reflected light from the optical fiber, the amount of strain in the optical fiber (i.e., the amount of strain in the strain-generating body 20 or 20A) can be determined. Alternatively, an optical fiber strain gauge may be one that determines the amount of strain in the optical fiber from the change in the frequency of the Brillouin scattered light generated within the optical fiber.

[0138] (Mechanical pressure sensor) A mechanical pressure sensor is a sensor that determines the pressure acting on a mechanical structure by measuring the displacement of that structure. A mechanical pressure sensor, for example, is equipped with a spring or a bent tube, and measures the amount of expansion or contraction of the spring or the bent tube. These amounts of expansion or contraction (i.e., displacement) change according to the magnitude of the pressure acting on the spring or bent tube. Therefore, by measuring these amounts of expansion or contraction, the pressure acting on the spring or bent tube can be determined. The shape and size of the spring or bent tube may be appropriately determined according to the size and shape of the object to which the mechanical pressure sensor is attached.

[0139] (Vibration-type pressure sensor) A vibration pressure sensor is a sensor that detects pressure by utilizing the phenomenon that the natural frequency of an elastic beam changes due to the pressure (i.e., axial force) generated along the axis of the elastic beam. Like electrical resistance type metal strain gauges, the vibration pressure sensor can be used by directly attaching it to the strain generating bodies 20 and 20A. Alternatively, for example, the vibration pressure sensor may be a pressure sensor composed of a diaphragm formed on a substrate and a beam-shaped vibrator formed on the surface of the diaphragm.

[0140] In either case, when the strain-generating body 20 or 20A is strained, the pressure is transmitted directly or indirectly to the oscillator, generating an axial force in the oscillator. The natural frequency of the oscillator changes in accordance with the axial force. Therefore, by measuring the natural frequency of the oscillator, the magnitude of the pressure on the strain-generating body 20 or 20A can be determined.

[0141] (Piezoelectric pressure sensor) A piezoelectric pressure sensor is a sensor that contains a piezoelectric element (also called a piezo element) and detects pressure using the properties of this piezoelectric element. A piezoelectric element has the property of generating an electromotive force corresponding to the force applied and deforming (straining) when force is applied to it. In addition, a piezoelectric element has the property of expanding and contracting by generating a force corresponding to the voltage applied to it.

[0142] A piezoelectric pressure sensor can determine the force applied to a piezoelectric element (i.e., the amount of strain on the piezoelectric element) by measuring the electromotive force of the piezoelectric element. Therefore, by attaching a piezoelectric pressure sensor to the strain-generating body 20 or 20A, the amount of strain on the strain-generating body 20 or 20A can be determined.

[0143] As described above, even when using semiconductor, capacitive, optical fiber, vibration, mechanical, and piezoelectric pressure sensors, the same effects as the strain gauge 100 according to the first embodiment and its modified form can be obtained.

[0144] Preferred embodiments have been described in detail above. However, the pulse wave sensor according to this disclosure is not limited to the embodiments and modifications described above. For example, various modifications and substitutions can be made to the pulse wave sensor according to the embodiments described above without departing from the scope described in the claims. [Explanation of Symbols]

[0145] 1,1A,1B,1C Pulse wave sensor, 10 Housing, 20,20A Strain generating body, 20m Top surface, 20n Bottom surface, 21 Base, 22 Beam, 23,53 Loading part, 24 Stretching part, 30 Wire, 50,50A Resin layer, 100 Strain gauge, 110 Substrate, 110a Top surface, 130 Resistor, 140 Wiring, 150 Electrode, 160 Cover layer, 130e1,130e2 Termination, 300,500,600,700 Detection element, 310 Base layer, 320 Drive coil, 340,350,360 Insulating layer, 370 Base metal, 380 Sensing coil, 510 Upstream electrode, 520 Downstream electrode, 530 Magnetic film, 540 Insulating film, 710 Substrate

Claims

1. a strain-generating body having a circular opening; a resin layer covering one surface of the strain generating element; a strain gauge having a Cr mixed phase film as a resistor, the strain gauge being provided on the other surface of the strain generating element opposite to the one surface of the strain generating element; and When the diameter of the circular opening is d [mm] and the thickness of the strain generating element is t [mm], When the material of the strain generating element is SUS and d=32, 0.059≦t≦0.124, When the material is SUS and d=22, 0.046≦t≦0.099; When the material is SUS and d=13, 0.030≦t≦0.067; When the material is SUS and d=7, 0.026≦t≦0.034; When the material is copper and d=32, 0.084≦t≦0.166; When the material is copper and d=22, 0.066≦t≦0.132; When the material is copper and d=13, 0.044≦t≦0.088; When the material is copper and d=7, 0.032≦t≦0.050; When the material is aluminum and d=32, 0.097≦t≦0.212; When the material is aluminum and d=22, 0.079≦t≦0.168; When the material is aluminum and d=13, 0.050≦t≦0.107; If the material is aluminum and d=7, 0.038≦t≦0.063; A pulse wave sensor that detects a pulse wave based on a change in the resistance value of the resistor accompanying the deformation of the strain body.

2. A strain-generating body, a resin layer covering one surface of the strain generating element; a strain gauge having a Cr mixed phase film as a resistor, the strain gauge being provided on the other surface of the strain generating element that is located on the opposite side to the one surface of the strain generating element, The strain body is a base with a circular opening; A beam portion bridging the inside of the base portion; a load portion provided on the beam portion, The strain element is flat, A pulse wave sensor that detects a pulse wave based on a change in the resistance value of the resistor accompanying the deformation of the strain body.

3. a non-metallic strain element; a strain gauge provided on the strain generating element and having a Cr mixed phase film as a resistor, The strain body is a base with a circular opening; A beam portion bridging the inside of the base portion; a load portion provided on the beam portion, The strain element is flat, A pulse wave sensor that detects a pulse wave based on a change in the resistance value of the resistor accompanying the deformation of the strain body.

4. a resin layer covering one surface of the strain generating element; 4. The pulse wave sensor according to claim 3, wherein the strain gauge is provided on the other surface of the strain generating element that is located opposite to the one surface of the strain generating element.

5. The strain body is a base having the circular opening; A beam portion bridging the inside of the base portion; The pulse wave sensor according to claim 1 , further comprising: a load portion provided on the beam portion.

6. The pulse wave sensor according to claim 5 , wherein the strain generating element is in the form of a flat plate.

7. The beam portion has two beams that intersect in a cross shape in a plan view, the intersecting region of the beams includes the center of the circular opening; The pulse wave sensor according to claim 2 , wherein the load portion is provided in an area where the beams intersect.

8. The strain gauge is provided in four pieces, Two of the four strain gauges are arranged on a side of the beam having a longitudinal direction in the first direction that is closer to the load portion so as to face each other across the load portion in a plan view, 8. The pulse wave sensor according to claim 7, wherein the other two of the four strain gauges are arranged on a side closer to the base of the beam, whose longitudinal direction is a second direction perpendicular to the first direction, so as to face each other across the load portion in a plan view.

9. The pulse wave sensor of claim 7 , wherein the length of each of the beams is approximately equal to the diameter of the circular opening.

10. The pulse wave sensor according to claim 7 , wherein the width of each beam is constant except for the intersecting region.

11. 7. The pulse wave sensor according to claim 1, further comprising a second resin layer provided on the other surface of the strain generating element and covering the strain gauge.

12. a strain-generating body having a circular opening; a resin layer covering one surface of the strain generating element; a detection unit provided on the other surface of the strain generating body that is located opposite to the one surface of the strain generating body; and When the diameter of the circular opening is d [mm] and the thickness of the strain generating element is t [mm], When the material of the strain generating element is SUS and d=32, 0.059≦t≦0.124, When the material is SUS and d=22, 0.046≦t≦0.099; When the material is SUS and d=13, 0.030≦t≦0.067; When the material is SUS and d=7, 0.026≦t≦0.034; When the material is copper and d=32, 0.084≦t≦0.166; When the material is copper and d=22, 0.066≦t≦0.132; When the material is copper and d=13, 0.044≦t≦0.088; When the material is copper and d=7, 0.032≦t≦0.050; When the material is aluminum and d=32, 0.097≦t≦0.212; When the material is aluminum and d=22, 0.079≦t≦0.168; When the material is aluminum and d=13, 0.050≦t≦0.107; If the material is aluminum and d=7, 0.038≦t≦0.063; the detection unit detects deformation of the strain-generating body and / or pressure applied to the strain-generating body, detecting a pulse wave based on the change in the deformation and / or the change in the pressure detected by the detection unit; Pulse wave sensor.

13. A strain-generating body, a resin layer covering one surface of the strain generating element; a detection unit provided on the other surface of the strain generating body that is located opposite to the one surface of the strain generating body, The strain body is a base with a circular opening; A beam portion bridging the inside of the base portion; a load portion provided on the beam portion, The strain element is flat, the detection unit detects deformation of the strain-generating body and / or pressure applied to the strain-generating body, detecting a pulse wave based on the change in the deformation and / or the change in the pressure detected by the detection unit; Pulse wave sensor.

14. a non-metallic strain element; a detection unit provided on the strain generating body, The strain body is a base with a circular opening; A beam portion bridging the inside of the base portion; a load portion provided on the beam portion, The strain element is flat, the detection unit detects deformation of the strain-generating body and / or pressure applied to the strain-generating body, detecting a pulse wave based on the change in the deformation and / or the change in the pressure detected by the detection unit; Pulse wave sensor.

15. a resin layer covering one surface of the strain generating element; The pulse wave sensor according to claim 14, wherein the detection portion is provided on the other surface of the strain generating element that is located opposite to the one surface of the strain generating element.

16. The strain body is a base having the circular opening; A beam portion bridging the inside of the base portion; The pulse wave sensor according to claim 12 , further comprising: a load portion provided on the beam portion.

17. The pulse wave sensor according to claim 16, wherein the strain element is in the shape of a flat plate.

18. The beam portion has two beams that intersect in a cross shape in a plan view, the intersecting region of the beams includes the center of the circular opening; The pulse wave sensor according to claim 13 , wherein the load portion is provided in an area where the beams intersect.

19. The detector includes four detectors, Two of the four detection units are arranged on a side of the beam having a longitudinal direction in the first direction that is closer to the load portion so as to face each other across the load portion in a plan view, 19. The pulse wave sensor according to claim 18, wherein the other two of the four detection units are arranged on a side closer to the base of the beam whose longitudinal direction is a second direction orthogonal to the first direction, so as to face each other across the load unit in a planar view.

20. The pulse wave sensor of claim 18 , wherein the length of each of the beams is approximately equal to the diameter of the circular opening.

21. The pulse wave sensor according to claim 18 , wherein the width of each beam is constant except for the intersecting region.

22. The pulse wave sensor according to claim 12 , further comprising a second resin layer provided on the other surface of the strain generating element and covering the detection portion.

23. The pulse wave sensor according to claim 12 , wherein the detection unit includes a detection element that detects a magnetic change caused by deformation of the strain-generating body.

24. the detection element includes a magnetic material, 24. The pulse wave sensor according to claim 23, wherein the detection element detects a change in the intensity of magnetization of the magnetic body when pressure is applied to the magnetic body due to deformation of the strain body.

25. the detection element includes a magnetic tunnel junction structure in which an insulating film is sandwiched between magnetic films, 24. The pulse wave sensor according to claim 23, wherein the detection element detects a magnetic change generated in the structure due to deformation of the strain-generating body.

26. The pulse wave sensor according to claim 12 , wherein the detection unit is a semiconductor strain gauge.

27. The pulse wave sensor according to claim 12 , wherein the detection unit is a capacitance type pressure sensor.

28. The pulse wave sensor according to claim 12 , wherein the detecting unit is an optical fiber strain gauge.

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