Pulse wave sensor

Abstract

To provide a pulse wave sensor having a strain inducer with a structure prone to strain.SOLUTION: A pulse wave sensor includes: a strain inducer including multiple slender slits that bend in the same direction; and a strain gage provided in the strain inducer and using a Cr mixed phase film as a resistor. In each of the multiple slits, a distance from a gravity center of the strain inducer to one end of the slit is different from a distance from the gravity center of the strain inducer to the other end of the slit, and a pulse wave is detected based on a change in a resistance value of the resister associated with deformation of the strain inducer.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 that serves as a strain generating body supported so as to be bendable by the action of an external force, and a piezoelectric conversion means for converting the bending of the pressure receiving plate into an electric signal. In this pulse wave sensor, the flexible region of the pressure receiving plate is formed in a dome shape that is convex 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] A pulse wave sensor needs to detect a minute signal, but with the structure of the strain generating body of a conventional pulse wave sensor, it has been difficult to generate a strain of sufficient magnitude.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a pulse wave sensor having a strain generating body with a structure that easily generates strain.

Means for Solving the Problems

[0006] This pulse wave sensor comprises a strain-generating body having multiple elongated slits that curve in the same direction, and a strain gauge provided on the strain-generating body, the strain gauge having a Cr multiphase film as a resistor. In each of the multiple slits, the distance from the center of gravity of the strain-generating body to one end of the slit is different from the distance from the center of gravity of the strain-generating body to the other end of the slit. The pulse wave is detected based on the change in the resistance value of the resistor due to the deformation of the strain-generating body. [Effects of the Invention]

[0007] According to the disclosed technology, a pulse wave sensor can be provided that has a strain-generating body with a structure that is prone to strain. [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 bottom view illustrating a pulse wave sensor according to the first embodiment. [Figure 4] This is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment. [Figure 5] This figure illustrates the simulation results. [Figure 6] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 7] This is a cross-sectional view illustrating a strain gauge according to the first embodiment. [Figure 8] This is a cross-sectional view (part 1) illustrating a pulse wave sensor according to a modified example of the first embodiment. [Figure 9] This is a cross-sectional view (part 2) illustrating a pulse wave sensor according to a modified example of the first embodiment. [Figure 10] These are a plan view and a cross-sectional view showing an example of a detection element included in a strain gauge according to the second embodiment. [Figure 11] These are perspective views, plan views, and cross-sectional views showing an example of a detection element included in a strain gauge according to the third embodiment. [Figure 12] These are perspective views, plan views, and cross-sectional views showing another example of a detection element included in a strain gauge according to the third embodiment. [Figure 13] These are perspective views, plan views, and cross-sectional views showing yet another example of a detection element included in a strain gauge according to the third embodiment. [Modes for carrying out the invention]

[0009] The embodiments for carrying out the invention will be described below with reference to the drawings. In each drawing, identical components may be denoted by the same reference numeral. In each drawing, mutually orthogonal X, Y, and Z directions may be defined. In this case, in the X direction, the starting point (root) of the arrow may be referred to as the X- side, and the ending point (arrowhead) of the arrow may be referred to as the X+ side. The same applies to the Y and Z directions. In addition, in the description of each drawing, the description of components that are the same as those already described may be omitted.

[0010] <First Embodiment> Figure 1 is a perspective view illustrating a pulse wave sensor according to the first embodiment. Figure 2 is a plan view illustrating a pulse wave sensor according to the first embodiment. Figure 3 is a bottom view illustrating a pulse wave sensor according to the first embodiment. Figure 4 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. Here, a view from the direction in which the load portion 29 protrudes is considered a plan view, and a view from the direction in which the strain gauge 100 is provided is considered a bottom view.

[0011] Referring to Figures 1 to 4, the pulse wave sensor 1 comprises a housing 10, a strain generating body 20, a wire 30, and a strain gauge 100.

[0012] In the description of the pulse wave sensor 1 in FIGS. 1 to 4, for the sake of convenience, in the pulse wave sensor 1, the side surface of the distortion generating body 20 that contacts the radial artery of the subject is referred to as the "upper side", and the opposite side surface is referred to as the "lower side". Also, the surface located on the upper side of each part is referred to as the "upper surface", and the surface located on the lower side of each part is referred to as the "lower surface". However, the pulse wave sensor 1 can also be used in an upside-down state. Also, the pulse wave sensor 1 can be arranged at an arbitrary angle. Also, the plan view refers to viewing the object in the normal direction from the upper side to the lower side with respect to the upper surface 20m of the distortion generating body 20. And the planar shape refers to the shape of the object when viewed in the normal direction.

[0013] The housing 10 is a part that holds the distortion generating body 20. The housing 10 is, for example, a hollow cylindrical shape, with the lower surface side closed and the upper surface side open. The housing 10 can be formed from, for example, metal, resin, or the like. A substantially disk-shaped distortion generating body 20 is fixed, for example, by an adhesive or the like so as to close the opening on the upper surface side of the housing 10.

[0014] The distortion generating body 20 is used such that the upper surface 20m side contacts the radial artery of the subject. When a load is applied to the distortion generating body 20 according to the pulse wave of the subject, the distortion generating body 20 elastically deforms according to the magnitude of the load.

[0015] The distortion generating body 20 is, for example, a flat plate shape. The distortion generating body 20 is, for example, made of metal. Examples of the metal constituting the distortion generating body 20 include stainless steel, phosphor bronze, aluminum, and the like. Among these, it is preferable to use stainless steel from the viewpoints of corrosion resistance and high strain. The distortion generating body 20 can be formed, for example, by a press working method or the like. The distortion generating body 20 is, for example, a shape that is symmetric about two axes in a plan view.

[0016] The thickness t of the distortion generating body 20 is preferably 0.02 mm or more and 0.2 mm or less. If the thickness t of the distortion generating body 20 becomes thinner, the sensitivity increases but the rigidity decreases, and if the thickness t of the distortion generating body 20 becomes thicker, the rigidity increases but the sensitivity decreases. By setting the thickness t of the distortion generating body 20 to be 0.02 mm or more and 0.2 mm or less, both rigidity and sensitivity can be achieved.

[0017] The shape of the strain generating body 20 may be any shape, such as a circle, ellipse, or rectangle. However, a circular shape is preferable for the strain generating body 20 in order to provide the slit 20s described later and to miniaturize the entire strain generating body 20. Hereafter, the explanation will be given using the case where the shape of the strain generating body 20 is circular as an example.

[0018] The strain-generating body 20 is provided with a plurality of elongated slits 20s that curve in the same direction. At each position in the longitudinal direction, the width of the slits 20s may or may not be constant. Here, "elongated" refers to a shape in which the ratio of width to length is 1:3 or greater. The width is defined as the average value of the width at each position in the longitudinal direction. The length is defined as the length of the line connecting the points where the width is halfway at each position in the longitudinal direction.

[0019] Furthermore, curving in the same direction means that each slit 20s curves such that, when a point is defined on the circumference of the second virtual circle 20o (described later) that is closest to the longitudinal center of each slit 20s, it becomes a convex portion on the side of that point.

[0020] In each of the multiple slits 20s, the distance from the center of gravity G of the strain generating body 20 to one end of the slit 20s is different from the distance from the center of gravity G of the strain generating body 20 to the other end of the slit. In other words, each slit 20s is not shaped to lie along the circumference of a virtual circle of arbitrary radius centered at the center of gravity G of the strain generating body 20. In the strain generating body 20, the region sandwiched between the slits 20s functions as a beam. By providing multiple slits 20s of this shape, a pulse wave sensor 1 having a strain generating body 20 with a structure that easily generates strain can be realized.

[0021] Note that the centroid G referred to here is the centroid in a planar view, that is, the centroid of a planar figure without considering thickness. For example, since the strain-generating body 20 shown in Figures 1 to 4 has a circular planar shape, the centroid G of the strain-generating body 20 coincides with the center of the circle that makes up the strain-generating body 20.

[0022] In Figure 2, 20i represents a first virtual circle centered at the centroid G of the strain-generating body 20. 20o represents a second virtual circle centered at the centroid G of the strain-generating body 20. The second virtual circle 20o has a larger diameter than the first virtual circle 20i. It is preferable that the multiple slits 20s are arranged in the region R between the circumference of the first virtual circle 20i and the circumference of the second virtual circle 20o.

[0023] In this way, by arranging each slit 20s in the region R of the strain generating body 20, excluding the central and outer edges, the necessary rigidity can be ensured for the strain generating body 20 as a whole, while also making the region R where the slits 20s are located easier to deform. For example, the diameter of the first virtual circle 20i can be about 1 / 5 to 1 / 4 of the diameter of the strain generating body 20. Also, the diameter of the second virtual circle 20o can be about 3 / 4 to 4 / 5 of the diameter of the strain generating body 20.

[0024] Preferably, the multiple slits 20s include two or more slits, one end of which is located on the circumference of the first virtual circle 20i and the other end of which is located on the circumference of the second virtual circle 20o. This allows the length of the slits 20s to be increased. As a result, the region that functions as a beam, sandwiched between the slits 20s, becomes longer, making it easier to deform the entire region R in which the slits 20s are located. In the example in Figure 2, there are four such slits.

[0025] The multiple slits 20s may include one or more inner slits, one end of which is located on the circumference of the first virtual circle 20i and the other end of which is separated from the circumference of the second virtual circle o. The multiple slits 20s may also include one or more outer slits, one end of which is separated from the circumference of the first virtual circle 20i and the other end of which is located on the circumference of the second virtual circle 20o. In the example in Figure 2, the multiple slits 20s include inner slits 21 and 22 and outer slits 23 and 24.

[0026] In this way, by including inner and outer slits in the multiple slits 20s, a region for placing strain gauges 100 can be secured on one surface of the strain generating body 20. The number of inner and outer slits should be determined by considering the number of strain gauges 100 to be placed.

[0027] Furthermore, if the strain gauge 100 is sufficiently small, it is not necessary to provide inner and outer slits. In other words, all of the multiple slits 20s may be slits in which one end is located on the circumference of the first virtual circle 20i and the other end is located on the circumference of the second virtual circle 20o.

[0028] When inner and outer slits are provided, one or more slits 20s may be provided between the inner and outer slits. In this case, the imaginary straight line connecting the other end of the inner slit and one end of the outer slit intersects with one or more slits 20s. This makes it easier to secure a region for placing the strain gauge 100. In the example in Figure 2, one slit 20s is provided between the other end of the inner slit 21 and one end of the outer slit 23, and one slit 20s is provided between the other end of the inner slit 22 and one end of the outer slit 24.

[0029] In the example shown in Figure 2, the strain-generating body 20 is provided with eight slits 20s, including inner slits 21 and 22 and outer slits 23 and 24. In the example shown in Figure 2, the eight slits 20s are twofold symmetric with respect to the centroid G of the strain-generating body 20.

[0030] When the strain-generating body 20 is circular, as in the example in Figure 2, the length of each slit 20s is preferably between 0.5 and 1.2 times the diameter of the strain-generating body 20. When the length of each slit 20s is within this range, the region R in which the slits 20s are located can be easily deformed. Furthermore, it becomes easier to place the resonant frequency of the strain-generating body 20 within the range of 500 Hz to 2 kHz.

[0031] The width w of each slit 20s is preferably between 0.025 mm and 0.1 mm. When the width of each slit 20s is within this range, the region R in which the slits 20s are arranged can be easily deformed. In addition, it becomes easier to place the resonant frequency of the strain-generating body 20 within the range of 500 Hz to 2 kHz.

[0032] The main frequency components of the pulse wave measured by the pulse wave sensor 1 are less than 500 Hz. Therefore, it is preferable that the resonance frequency of the strain-generating body 20 be 500 Hz or higher. This suppresses a decrease in the measurement accuracy of the pulse wave sensor 1 due to the influence of the resonance frequency of the strain-generating body 20. On the other hand, if the resonance frequency of the strain-generating body 20 is higher than 2 kHz, high-frequency noise may be superimposed on the signal measured by the pulse wave sensor 1. Therefore, it is preferable that the resonance frequency of the strain-generating body 20 be between 500 Hz and 2 kHz. To improve the measurement accuracy of the pulse wave sensor 1, it is more preferable that the resonance frequency of the strain-generating body 20 be between 800 Hz and 1.5 kHz, and particularly preferable that it be between 900 Hz and 1.1 kHz.

[0033] The strain generating body 20 may have a load portion 29 protruding from its upper surface 20m, which is the surface that contacts the subject. The load portion 29 can be provided inside the first virtual circle 20i. The load portion 29 may also be provided over the entire first virtual circle 20i. The diameter of the load portion 29 can be, for example, about 1 / 5 to 1 / 4 of the diameter of the strain generating body 20. The amount of protrusion of the load portion 29 relative to the upper surface 20m of the strain generating body 20 can be, for example, about 0.1 mm. By providing the strain generating body 20 with a load portion 29 protruding from its upper surface 20m, the load corresponding to the subject's pulse wave can be more easily transmitted to the strain generating body 20.

[0034] 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.

[0035] The strain gauge 100 is an example of a detection unit for detecting pulse waves in this disclosure. The strain gauge 100 is provided in region R of the strain generating body 20. The strain gauge 100 can be provided, for example, on the lower surface 20n side of the strain generating body 20. Since the strain generating body 20 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.

[0036] In the example shown in Figure 3, two strain gauges 100 are positioned opposite each other on the strain generating body 20, with a slit 20s that intersects a virtual straight line connecting the other end of the inner slit 21 and one end of the outer slit 23 in between. Additionally, two strain gauges 100 are positioned opposite each other on a slit 20s that intersects a virtual straight line connecting the other end of the inner slit 22 and one end of the outer slit 24.

[0037] Two of the four strain gauges 100 are positioned closer to the first virtual circle 20i (inside) in region R, while the other two are positioned closer to the second virtual circle 20o (outside) in region R. This arrangement allows for effective detection of compressive and tensile forces, enabling greater output from the full bridge.

[0038] Figure 5 is an illustrative diagram of the simulation results, showing the magnitude of strain in the strain body 20 when a load is applied to the center of the strain body 20, which has the shape shown in Figures 1 to 4. The simulation conditions are as follows: The material of the strain body 20 is phosphor bronze, the diameter of the strain body 20 is 8.4 mm, the thickness t of the strain body 20 is 0.025 mm, there are 8 slits 20s, the length of the slits 20s is adjusted within the range of 0.5 times to 1.2 times the diameter of the strain body 20, and the width w of the slits 20s is 0.025 mm.

[0039] In Figure 5, black areas indicate regions with little to no strain, while gray areas indicate regions with significant strain. From Figure 5, it can be seen that large strain occurs in region R where multiple slits 20s are provided. The resonant frequency of the strain-generating body 20 at this time was approximately 1 kHz.

[0040] The pulse wave sensor 1 is used by fixing it to the subject's arm so that the upper surface 20m of the strain generating body 20 is in contact with the subject's radial artery. When a load is applied to the strain generating body 20 in accordance with the subject's pulse wave, the region R provided with multiple slits 20s elastically deforms as shown in Figure 5, and the resistance value of the resistor of the strain gauge 100 placed in region R changes accordingly. In other words, 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 region R of the strain generating body 20. The pulse wave is output as a periodic voltage change from a measurement circuit connected to the electrodes of the strain gauge 100, for example.

[0041] Now, let's explain strain gauge 100.

[0042] Figure 6 is a plan view illustrating a strain gauge according to the first embodiment. Figure 7 is a cross-sectional view illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 6. Referring to Figures 6 and 7, the strain gauge 100 includes a base material 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. In Figure 6, 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.

[0043] In Figures 6 and 7, 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 3, the strain gauge 100 is attached to the strain generating body 20 in an inverted state compared to Figure 7. That is, the base material 110 in Figure 7 is attached to the lower surface 20n of the strain generating body 20 with adhesive or the like. Furthermore, a plan view refers to viewing the object from the direction normal to the upper surface 110a of the base material 110, and a planar shape refers to the shape of the object viewed from the direction normal to the upper surface 110a of the base material 110.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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. In Figure 6, for convenience, the resistor 130 is shown with a dark, textured pattern.

[0049] 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 6), 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 6).

[0050] 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.

[0051] 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).

[0052] 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.

[0053] 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.

[0054] 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).

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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 6, the wiring 140 and the electrode 150 are shown with a matte finish that is thinner than the resistor 130.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] The planar shape of the functional layer is patterned to be substantially the same as the planar shape of the resistor shown in Figure 6. 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 in at least 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.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] 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).

[0089] 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.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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.

[0094] Next, remove the resist. The resist can be removed, for example, by immersing it in a solution that can dissolve the resist material.

[0095] 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 6. 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 6.

[0096] 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 6, 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.

[0097] 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.

[0098] 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.

[0099] <Variations of the first embodiment> A modified example of the first embodiment shows a pulse wave sensor having a resin layer covering a strain-generating body. In the modified example of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0100] Figure 8 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 8 differs from the pulse wave sensor 1 (see Figure 4, etc.) in that it is provided with a resin layer 50.

[0101] 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 portion of the upper surface 20m. The resin layer 50 is also formed on each slit 20s. Therefore, each slit 20s is not exposed to the outside of the pulse wave sensor 1A. The resin layer 50 may penetrate each slit 20s and fill part or all of each slit 20s.

[0102] 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, the elastic deformation of the strain-generating body 20 is not hindered even if the resin material constituting the resin layer 50 enters the gaps of each slit 20s.

[0103] 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 59 that covers the load portion 29 is formed on the resin layer 50. The load portion 59 protrudes from the upper surface of the resin layer 50. The amount of protrusion of the load portion 59 relative to the upper surface of the resin layer 50 is, for example, about 0.1 mm.

[0104] In the pulse wave sensor 1A, the upper surface 20m of the strain-generating body 20 is covered with a resin layer 50, so the strain-generating body 20 does not come into direct contact with the subject's skin. Therefore, if the strain-generating body 20 is made of metal and the subject using the pulse wave sensor is prone to developing skin inflammation or metal allergies caused by metal, using the pulse wave sensor 1A can prevent the subject from developing skin inflammation or metal allergies caused by metal.

[0105] Furthermore, if each slit 20s were to open to the outside of the pulse wave sensor 1, dust or foreign matter could get trapped in each slit 20s, potentially preventing the strain-generating body 20 from elastically deforming. However, in the pulse wave sensor 1A, the resin layer 50 is also formed on top of each slit 20s, so that each slit 20s is not exposed to the outside of the pulse wave sensor 1. As a result, dust or foreign matter cannot get trapped in each slit 20s, enabling more reliable and stable measurement of pulse waves by the pulse wave sensor 1A.

[0106] Figure 9 is a cross-sectional view (part 2) illustrating a modified pulse wave sensor according to the first embodiment. The pulse wave sensor 1B shown in Figure 9 differs from the pulse wave sensor 1 (see Figure 4, etc.) in that it is provided with a resin layer 50A.

[0107] As shown in Figure 9, the pulse wave sensor 1B may be provided with a resin layer 50A covering the lower surface 20n of the strain-generating body 20, instead of the resin layer 50 covering the upper surface 20m of the strain-generating body 20. The material and thickness of the resin layer 50A are the same as those of the resin layer 50. In the pulse wave sensor 1B, the resin layer 50A fits into the gaps of each slit 20s, filling the gaps of each slit 20s. As a result, dust and foreign matter cannot get trapped in the gaps of each slit 20s, thus increasing the reliability of the pulse wave sensor 1B 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 other elements.

[0108] Furthermore, a resin layer 50 may be provided to cover the upper surface 20m of the strain generating body 20, and a resin layer 50A may be provided to cover the lower surface 20n of the strain generating body 20.

[0109] <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.

[0110] 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.

[0111] 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 are the same as the directions of the x, y, and z axes shown in Figures 2 and 3.

[0112] Figure 10 shows an example of a detection element 300 included in the strain gauge 100 according to the second embodiment. Figure 10(a) is a plan view of the strain gauge 100 when it is attached to the strain generating body 20 as shown in Figures 1 to 3, and is a plan view of the detection element 300 as seen from the bottom surface (i.e., the surface opposite to the attachment surface of the strain gauge 100) to the top surface (i.e., the attachment surface of the strain gauge 100). On the other hand, Figure 10(b) shows a cross-sectional view of the detection element 300 shown in Figure 10(a) in the α-α' plane. Note that the wiring of the detection element 300 is not shown in any of the figures in Figure 10. However, the detection element 300 may also have wiring to connect the drive coil 320 and the power supply, which will be described later, and wiring to transmit the current detected by the sensing coil 380.

[0113] As shown in Figure 10(a), the detection element 300 includes a drive coil 320, a sensing coil 380, and a base layer 310. The sensing coil 380 is a coil with the base layer 310 as its core material. The drive coil 320 is also a coil with the base layer 310 as its core material, and is wound on the outside of the sensing coil. In this way, the drive coil 320 and the sensing coil 380 form a double structure with the drive coil 320 on the outside and the sensing coil 380 on the inside. By winding the sensing coil 380 inside the drive coil 320 in this way, an alternating magnetic field (described later) can be applied uniformly to the entire sensing coil 380. This improves the performance of the detection element 300.

[0114] The drive coil 320 is a coil for generating a magnetic field. When alternating current is supplied to the drive coil 320 from the power source, the drive coil 320 generates an alternating magnetic field around it. The base layer 310 is a substantially flat metal plate (base metal 370, described later) covered with an insulating layer (insulating layer 360, described later). The metal plate of the base layer 310 is the magnetic material in the detection element 300. The metal plate of the base layer 310 is magnetized by the alternating magnetic field generated by the drive coil 320. The sensing coil 380 is a coil for detecting the strength of the magnetization of the base metal 370. The materials of the drive coil 320 and the sensing coil 380 are preferably conductive metals such as Cu, Ag, Al, and Au, and 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.

[0115] The detection element 300 will be described in more detail with reference to the cross-sectional view in Figure 10(b). The layers 340 to 360 described below are wrapped around the core material, the base metal 370. Therefore, in Figure 10(b), the layers with the same component number are connected and surround the base metal 370.

[0116] As described above, the detection element 300 has a structure in which a sensing coil 380 and a drive coil 320 are wound around a base layer 310. The base layer 310 has a structure in which an insulating layer 360 covers a base metal 370. An insulating layer 350 is formed so as to surround the insulating layer 360. The insulating layer 350 is a layer that includes the sensing coil 380 and is a layer in which the gaps of the sensing coil 380 are filled with insulating material. Furthermore, an insulating layer 340 is formed so as to surround the insulating layer 350. The insulating layer 340 is a layer that includes the drive coil 320 and is a layer in which the gaps of the drive coil 320 are filled with insulating material.

[0117] Furthermore, the base metal 370 is preferably composed of a soft magnetic material such as an Fe-Si-Al alloy like Sendust, or a Ni-Fe alloy like Permalloy. In addition, the insulating layers 340, 350, and 360 are preferably dry films that are not affected by magnetic fields or resist-cured products such as photosensitive polyimide.

[0118] As shown in the cross-sectional view in Figure 10(b), the adhesive side of the detection element 300 is attached to the base material 110. The detection element 300 may be a flat plate or a thin film overall. If the detection element 300 is a flat plate or a thin film, it can be attached to the base material 110 more easily. The base material 110 is then attached to the strain generating body 20. The strain generating body 20 according to this embodiment may have basically the same configuration and materials as the strain generating body 20 according to the first embodiment. However, it is more desirable that the strain generating body 20 be made of a non-magnetic material. The strain generating body 20 according to this embodiment can be made from, for example, non-magnetic stainless steel.

[0119] As described above, the detection element 300 according to this embodiment includes a base metal 370, which is a magnetic material. When current flows through the drive coil 320, a magnetic field is generated, and the base metal 370 is magnetized. When the strain-generating body 20 deforms in this state, strain occurs as a result. The strain is transmitted through the substrate 110, and stress is applied to the base metal 370. When stress is applied to the base metal 370, the permeability of the base metal 370 changes according to that stress, and the strength of magnetization (degree of magnetization) changes. This phenomenon, in which the permeability and strength of magnetization of a magnetic material change due to the application of stress to the magnetic material, is called the "Villari phenomenon." According to the configuration of the detection element 300, an AC voltage corresponding to the strength of magnetization of the base metal 370 is induced in the sensing coil 380, which is a pickup coil. Therefore, based on the principle of the Villari phenomenon, the stress applied to the base metal 370 (i.e., the degree of strain in the substrate 110) can be calculated from the value of this AC voltage. In the example shown in Figure 10(a), the grid direction of the detection element 300 is the α-α' direction in the same figure.

[0120] Based on this principle, the detection element 300 can detect the strain applied to the substrate 110 attached to the strain generating body 20. In other words, the detection element 300 functions as a detection element of the strain gauge 100.

[0121] The pulse wave sensor 1 according to this embodiment is used by fixing it to the arm of a subject so that the upper surface 20m side of the strain generating body 20 is in contact with the subject's radial artery, similar to the pulse wave sensor 1 according to the first embodiment. When a load is applied to the strain generating body 20 in accordance with the subject's pulse wave, the region R provided with multiple slits 20s elastically deforms as shown in Figure 5, and the base material 110 of the strain gauge 100 placed in region R is strained accordingly. The detection element 300 of the strain gauge 100 can detect the magnetic change caused by this strain based on the principle of the Villari phenomenon described above.

[0122] Furthermore, the strain gauge 100 including the detection element 300 according to this embodiment can be placed in any of the arrangement positions shown in the first embodiment and the modified examples of the first embodiment. Therefore, the strain of the strain generating body 20 can be detected using the detection element 300 that utilizes the Villari phenomenon, in the same way as when a resistor strain gauge is used. Thus, the strain gauge 100 according to this embodiment has the same effects as the strain gauge 100 according to the first embodiment and the modified examples of the first embodiment.

[0123] Note that the base material 110 is not an essential component of the detection element 300. For example, the detection element 300 may be used without the base material 110, by directly attaching the upper surface of the detection element 300 to the strain generating body 20. If the detection element 300 is attached to the strain generating body 20 without the base material 110, stress is directly transmitted from the strain generating body 20 to the base metal 370 (and the insulating layers 340-360 covering it).

[0124] 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.

[0125] 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.

[0126] 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 10(b), both ends of the base metal 370 in the y-direction do not need to be covered by the insulating layer 360.

[0127] <Third Embodiment> Figure 11 shows an example of a detection element 500 included in the strain gauge 100 according to the third embodiment. Figure 12 shows another example of the detection element according to the third embodiment. Figure 13 shows yet another example of the detection element according to the third embodiment. In the description of Figures 11 to 13, "upper side" and "lower side" refer to the same directions as "upper side" and "lower side" in Figures 1 to 4. That is, the positive direction of the z-axis is the "upper side" in Figures 1 to 4, and the negative direction of the z-axis is the "lower side" in Figures 1 to 4. Figures 11 to 13(a) are perspective views of the detection elements 500, 600, and 700, respectively. Figures 11 to 13(b) are plan views of the detection elements 500, 600, and 700 viewed from the negative direction of the z-axis to the positive direction (i.e., from the lower side to the upper side in Figures 1 to 4), respectively. Figures 11-13(c) show cross-sectional views of the detection elements 500, 600, and 700 in a plane parallel to the zy-plane. The surface on which the detection elements 500, 600, and 700 are attached to the substrate 110 is the upper plane (parallel to the xy-plane). Note that none of the figures 11-13 show the wiring of the detection elements. However, these detection elements 500, 600, and 700 may have wiring connecting the upstream electrode 510 to the power supply and wiring connecting the downstream electrode 520 to the power supply, which will be described later.

[0128] As shown in Figures 11-13(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 element 500 has a structure in which electrodes are connected to a magnetic tunnel junction structure.

[0129] Furthermore, a flexible substrate made of plastic film or the like may be provided above the upstream electrode 510 and / or the downstream electrode 520. This substrate may also serve as the base material 110.

[0130] 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.

[0131] 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 11-13, the current flows from the upstream electrode 510 to the downstream electrode 520. For example, in Figure 11(c), when a voltage is applied between the upstream electrode 510 and the downstream electrode 520, electrons flow from the lower magnetic film 530, across the insulating film 540, to the upper 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 11-13, the junctions of each part of the electrodes are treated at the ends to prevent current from flowing through the magnetic tunnel junction structure.

[0132] 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 substrate 110, the strain applied to the strain-generating body 20 can be measured.

[0133] The detection element having a magnetic tunnel junction structure is not limited to the example shown in Figure 11. For example, detection elements 600 and 700 as shown in Figures 12 and 13 can also be used. Both the detection element 600 shown in Figure 12 and the detection element 700 shown in Figure 13 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 and negative y-axis directions) in Figures 11 to 13, respectively. As shown in the figure, the detection element 600 shown in Figure 12 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 13 is attached to the substrate 110 via the substrate 710. As shown in Figures 11 to 13, 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.

[0134] The strain generating body 20 according to this embodiment may have basically the same configuration and materials as the strain generating body 20 according to the first embodiment. However, it is more desirable that the strain generating body 20 be made of a non-magnetic material. For example, the strain generating body 20 according to this embodiment can be made from non-magnetic stainless steel. Also, 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 element 500 to be easily attached to the base material 110. Furthermore, the detection elements 500, 600, and 700 may 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.

[0135] Furthermore, the terms "upstream electrode" and "downstream electrode" in the detection elements 500, 600, and 700 are merely convenient designations, and the direction of current flow may be reversed. In other words, in the detection elements 500, 600, and 700 shown in Figures 11 to 13, the design may be such that current flows from the downstream electrode 520 to the upstream electrode 510.

[0136] The pulse wave sensor 1 according to this embodiment is used by fixing it to the arm of a subject so that the upper surface 20m side of the strain generating body 20 is in contact with the subject's radial artery, similar to the pulse wave sensor 1 according to the first embodiment. When a load is applied to the strain generating body 20 in accordance with the subject's pulse wave, the region R provided with multiple slits 20s elastically deforms as shown in Figure 5, and the base material 110 of the strain gauge 100 placed in region R is strained accordingly. The detection elements 500, 600, or 700 of the strain gauge 100 can detect the magnetic change caused by this strain based on the principle of the Villari phenomenon described above.

[0137] Furthermore, the strain gauge 100, including the detection elements 500, 600, and 700 according to this embodiment, can be positioned at any of the arrangement locations shown in the first embodiment and the modified examples of the first embodiment. Therefore, the strain of the strain-generating body 20 can be detected using the detection elements 500, 600, and 700 that utilize the magnetic tunneling effect, in the same way as when using a resistive strain gauge. Thus, the strain gauge 100 according to this embodiment provides the same effects as the strain gauge 100 according to the first embodiment and the modified examples of the first embodiment.

[0138] Furthermore, the base material 110 is not an essential component for detection elements 500, 600, and 700. For example, the upper surfaces of detection elements 500, 600, and 700 may be directly attached to the strain generating body 20 or 20A.

[0139] 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.

[0140] <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.

[0141] (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.

[0142] 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 a strain-generating body 20, similar to electrical resistance-type metal strain gauges. In this case, when the strain-generating body 20 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-generating body 20 can be determined by measuring this electrical resistance.

[0143] 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 a structure including a diaphragm in this way, 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) can be determined.

[0144] (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).

[0145] 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.

[0146] (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.

[0147] By attaching an optical fiber having such characteristics to the strain-generating body 20 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) 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.

[0148] (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.

[0149] (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, vibration pressure sensors can be used by directly attaching them to the strain generating body 20. Alternatively, for example, a 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.

[0150] In either case, when the strain-generating body 20 is deformed, 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 can be determined.

[0151] (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.

[0152] 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 the piezoelectric pressure sensor to the strain generating body 20, the amount of strain on the strain generating body 20 can be determined.

[0153] As described above, even when using semiconductor strain gauges, capacitive pressure sensors, optical fiber strain gauges, mechanical pressure sensors, vibratory pressure sensors, and piezoelectric pressure sensors, the same effects as the strain gauge 100 according to the first embodiment and its modified form can be obtained.

[0154] 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]

[0155] 1,1A,1B Pulse wave sensor, 10 Housing, 20 Strain generating body, 20i First virtual circle, 20m Top surface, 20n Bottom surface, 20o Second virtual circle, 20s Slit, 21,22 Inner slit, 23,24 Outer slit, 29,59 Load section, 30 Wire, 50,50A Resin layer, 100 Strain gauge, 110 Base material, 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 Insulation 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 plurality of elongated slits curved in the same direction; a strain gauge provided on the strain generating element and having a Cr mixed phase film as a resistor, In each of the plurality of slits, a distance from the center of gravity of the strain body to one end of the slit is different from a distance from the center of gravity of the strain body to the other end of the slit, A pulse wave sensor that detects a pulse wave based on a change in the resistance value of the resistor accompanying deformation of the strain generating body.

2. the plurality of slits are arranged in a region between the circumference of a first imaginary circle whose center is the center of gravity of the strain body and the circumference of a second imaginary circle whose diameter is larger than that of the first imaginary circle whose center is the center of gravity of the strain body, 2. The pulse wave sensor according to claim 1, wherein the plurality of slits include two or more slits each having one end located on the circumference of the first imaginary circle and the other end located on the circumference of the second imaginary circle.

3. The plurality of slits are one or more inner slits, one end of which is located on the circumference of the first imaginary circle and the other end of which is spaced apart from the circumference of the second imaginary circle; 3. The pulse wave sensor according to claim 2, further comprising one or more outer slits, one end of which is spaced apart from the circumference of the first imaginary circle and the other end of which is located on the circumference of the second imaginary circle.

4. The pulse wave sensor according to claim 3 , wherein an imaginary line connecting the other end of the inner slit and one end of the outer slit intersects with one of the slits.

5. The pulse wave sensor according to claim 4 , wherein two of the strain gauges are arranged to face each other across the slit that intersects with the imaginary straight line.

6. The pulse wave sensor according to claim 2 , wherein the plurality of slits are arranged in dyad symmetry with respect to the center of gravity of the strain body.

7. The pulse wave sensor according to claim 2 , wherein the strain element has a load portion that protrudes from a surface that comes into contact with the subject, the load portion being located inside the first imaginary circle.

8. The pulse wave sensor according to claim 2 , wherein the strain element is a circle having a diameter larger than that of the second imaginary circle.

9. 9. The pulse wave sensor according to claim 8, wherein the length of each of the slits is 0.5 to 1.2 times the diameter of the strain-generating element.

10. The pulse wave sensor according to claim 1 , wherein the width of each of the slits is not less than 0.025 mm and not more than 0.1 mm.

11. 6. The pulse wave sensor according to claim 1, wherein the strain element has a thickness of 0.025 mm or more and 0.2 mm or less.

12. 6. The pulse wave sensor according to claim 1, wherein the resonant frequency of the strain generating element is 900 Hz or more and 1.1 kHz or less.

13. a resin layer covering one surface of the strain generating element; 6. The pulse wave sensor according to claim 1, wherein the strain gauge is provided on one surface of the strain generating element, the other surface being opposite to the one surface of the strain generating element.

14. 6. 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.

15. a strain generating body having a plurality of elongated slits curved in the same direction; a detection unit provided on the strain generating body, In each of the plurality of slits, a distance from the center of gravity of the strain body to one end of the slit is different from a distance from the center of gravity of the strain body to the other end of the slit, 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.

16. the plurality of slits are arranged in a region between the circumference of a first imaginary circle whose center is the center of gravity of the strain body and the circumference of a second imaginary circle whose diameter is larger than that of the first imaginary circle whose center is the center of gravity of the strain body, 16. The pulse wave sensor according to claim 15, wherein the plurality of slits include two or more slits each having one end located on the circumference of the first imaginary circle and the other end located on the circumference of the second imaginary circle.

17. The plurality of slits are one or more inner slits, one end of which is located on the circumference of the first imaginary circle and the other end of which is spaced apart from the circumference of the second imaginary circle; 17. The pulse wave sensor according to claim 16, further comprising one or more outer slits, one end of which is spaced apart from the circumference of the first imaginary circle and the other end of which is located on the circumference of the second imaginary circle.

18. The pulse wave sensor according to claim 17 , wherein an imaginary line connecting the other end of the inner slit and one end of the outer slit intersects with one of the slits.

19. The pulse wave sensor according to claim 18 , wherein the two detection units are arranged to face each other across the slit that intersects with the imaginary straight line.

20. 20. The pulse wave sensor according to claim 16, wherein the plurality of slits are arranged in dyad symmetry with respect to the center of gravity of the strain body.

21. 20. The pulse wave sensor according to claim 16, wherein the strain element has a load portion that protrudes from a surface that comes into contact with the subject, the load portion being located inside the first imaginary circle.

22. The pulse wave sensor according to claim 16 , wherein the strain element is a circle having a diameter larger than that of the second imaginary circle.

23. 23. The pulse wave sensor according to claim 22, wherein the length of each of the slits is not less than 0.5 times and not more than 1.2 times the diameter of the strain element.

24. 20. The pulse wave sensor according to claim 15, wherein the width of each of the slits is not less than 0.025 mm and not more than 0.1 mm.

25. 20. The pulse wave sensor according to claim 15, wherein the strain element has a thickness of 0.025 mm or more and 0.2 mm or less.

26. 20. The pulse wave sensor according to claim 15, wherein the resonant frequency of the strain generating element is equal to or higher than 900 Hz and equal to or lower than 1.1 kHz.

27. a resin layer covering one surface of the strain generating element; 20. The pulse wave sensor according to claim 15, wherein the detection unit is provided on the other surface of the strain generating element that is located opposite to the one surface of the strain generating element.

28. 20. The pulse wave sensor according to claim 15, further comprising a second resin layer provided on the other surface of the strain generating body and covering the detection portion.

29. The pulse wave sensor according to claim 15 , wherein the detection unit includes a detection element that detects a magnetic change caused by deformation of the strain-generating body.

30. the detection element includes a magnetic material, 30. The pulse wave sensor according to claim 29, wherein the detection element detects a change in intensity of magnetization of the magnetic body when pressure is applied to the magnetic body due to deformation of the strain body.

31. the detection element includes a magnetic tunnel junction structure in which an insulating film is sandwiched between magnetic films, 30. The pulse wave sensor according to claim 29, wherein the detection element detects a magnetic change generated in the structure due to deformation of the strain-generating body.

32. 20. The pulse wave sensor according to claim 15, wherein the detection unit is a semiconductor strain gauge.

33. The pulse wave sensor according to claim 15 , wherein the detection unit is a capacitance type pressure sensor.

34. 20. The pulse wave sensor according to claim 15, wherein the detection unit is an optical fiber strain gauge.

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