Pulse wave sensor

Abstract

To provide a pulse wave sensor that enhances adhesion to the skin of a subject, and has good strain transmissibility.SOLUTION: A pulse wave sensor can be fitted to a subject, and comprises: a supporting body; a strain generator comprising a first surface that is a surface in contact with the body of the subject when the subject is fitted with the pulse wave sensor, and a second surface on the side opposite to the first surface, and fixed to the supporting body in such a manner that the first surface is exposed from the supporting body; and a strain gage fixed to the second surface. The first surface is provided with a plurality of protruding parts.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 piezoelectric conversion means for converting the bending of the pressure receiving plate into an electric signal. This pulse wave sensor has a dome shape in which the flexible region of the pressure receiving plate is formed into a convex curved surface facing outward, and a pressure detection element is provided on the inner surface of the top of the pressure receiving plate as the piezoelectric conversion means (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Since a pulse wave sensor needs to detect a minute signal, it is necessary to appropriately attach the pulse wave sensor to a subject in order to improve the measurement accuracy. In addition, the pulse wave sensor requires a strain generating body that can efficiently transmit strain.

[0005] The present invention has been made in view of the above points, and an object thereof is to provide a pulse wave sensor that improves the adhesion to the skin of a subject and has good strain transmission properties.

Means for Solving the Problems

[0006] A pulse wave sensor according to one embodiment of the present disclosure is a pulse wave sensor that can be worn on a subject, comprising a support, a first surface which is the surface that comes into contact with the subject's body when the pulse wave sensor is worn by the subject, and a second surface opposite to the first surface, a strain generating body fixed to the support such that the first surface is exposed from the support, and a strain gauge fixed to the second surface, wherein the first surface is provided with a plurality of protrusions. [Effects of the Invention]

[0007] According to the disclosed technology, it is possible to provide a pulse wave sensor that improves adhesion to the subject's skin while also having good strain transmission capabilities. [Brief explanation of the drawing]

[0008] [Figure 1] This is a plan view illustrating a pulse wave sensor according to the first embodiment. [Figure 2] This is a partial cross-sectional view illustrating a pulse wave sensor according to the first embodiment. [Figure 3] This is a bottom view illustrating the strain-generating body of a pulse wave sensor according to the first embodiment. [Figure 4] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 5] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 6] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. [Figure 7] This is a plan view illustrating a pulse wave sensor according to a modified example 1 of the first embodiment. [Figure 8] This is a bottom view (part 1) illustrating the strain-generating body of a pulse wave sensor according to a modified example 2 of the first embodiment. [Figure 9] This is a bottom view (part 2) illustrating the strain-generating body of a pulse wave sensor according to a modified example 2 of the first embodiment. [Figure 10] This is a plan view illustrating a pulse wave sensor according to the second embodiment. [Figure 11]This is a partial cross-sectional view illustrating a pulse wave sensor according to the second embodiment. [Figure 12] 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 third embodiment. [Figure 13] 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 fourth embodiment. [Figure 14] 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 fourth embodiment. [Figure 15] 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 fourth 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> [Pulse wave sensor 1] Figure 1 is a plan view illustrating a pulse wave sensor according to the first embodiment. Figure 2 is a partial cross-sectional view illustrating a pulse wave sensor according to the first embodiment, showing a cross-section along line AA in Figure 1.

[0011] Referring to Figures 1 and 2, the pulse wave sensor 1 is a wearable device that can be attached to a subject, and mainly comprises a support 10, a strain generating body 20, a strain gauge 100, and a housing 200.

[0012] The pulse wave sensor 1 is worn on the wrist of a subject, for example, such that the strain body 20 is disposed near the radial artery of the subject. A pulse wave captures the volume change of a blood vessel generated as the heart pumps blood as a waveform, and the pulse wave sensor 1 can monitor the volume change of the blood vessel.

[0013] In the pulse wave sensor 1, the support 10 is an elongated belt that is worn on the wrist of the subject and can be wrapped around the wrist of the subject. Here, the elongated shape refers to a shape in which the longitudinal direction and the lateral direction can be clearly distinguished. The support 10 can be formed of a material that is easily curved, such as resin or rubber. The support 10 preferably has elasticity in order to be easily and securely worn by the subject. In FIGS. 1 and 2, the longitudinal direction of the support 10 is the X direction.

[0014] The support 10 includes a back surface 10m and a front surface 10n. For example, a pair of surface fasteners are provided on the back surface 10m side of one end of the support 10 and the front surface 10n side of the other end of the support 10, and the support 10 can be detachably worn on the wrist of the subject by this surface fastener. When wearing the support 10 on the wrist of the subject, it is worn such that the back surface 10m contacts the body of the subject (for example, contacts the skin of the wrist of the subject).

[0015] As shown in FIG. 2, the back surface 10m of the support 10 is recessed in the Z+ direction. This portion is referred to as the attachment portion 10x for convenience. Further, a part of the attachment portion 10x has a portion that is further recessed in the Z+ direction. This further recessed portion is referred to as the recess 10y. The attachment portion 10x and the recess 10y are portions for attaching the strain gauge 100 and the strain body 20 to the support 10.

[0016] An adhesive layer 30 is provided on the bottom surface of the mounting portion 10x (a surface on the XY plane in Figure 2). The strain generating body 20 is fixed to the support 10 by this adhesive layer 30. The strain generating body 20 has a first surface 20m, which is the surface that comes into contact with the subject's body when the pulse wave sensor 1 is attached to the subject's arm, and a second surface 20n, which is the surface opposite to the first surface 20m. The strain generating body 20 is attached to the mounting portion 10x such that the first surface 20m is exposed from the back surface 10m of the support 10. Furthermore, it is desirable that the strain generating body 20 be provided so as to seal the recess 10y with the second surface 20n.

[0017] The material of the adhesive layer 30 is not particularly limited as long as it is a material that has the function of bonding the support 10 and the strain-generating body 20. For example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used as the adhesive layer 30. Alternatively, a bonding sheet or the like may be used as the adhesive layer 30. The thickness of the adhesive layer 30 is not particularly limited. For example, the thickness of the adhesive layer 30 can be about 0.1 μm to 50 μm.

[0018] The strain generating body 20 is a component that generates strain when subjected to a load. When a load is applied to the strain generating body 20, strain occurs in the strain generating body 20, and the resistance value of the strain gauge 100 bonded to the strain generating body 20 changes. The shape of the strain generating body 20 is not particularly limited. For example, the strain generating body 20 may be a flat rectangular plate. As the material of the strain generating body 20, for example, SUS (stainless steel), copper, aluminum, etc. can be used. If the strain generating body 20 is flat, it can be formed by a press working method or the like. The thickness t of the strain generating body 20 is, for example, 0.01 mm or more and 0.25 mm or less. Note that the thickness t of the strain generating body 20 does not include the projection 21 described later.

[0019] Multiple protrusions are provided on the first surface 20m of the strain-generating body 20. In this embodiment, as an example, six protrusions 21 are provided on the first surface 20m of the strain-generating body 20. When the first surface 20m is viewed from above, the protrusions 21 have a straight line or rectangular shape extending in the Y-axis direction, as shown in the figure. The amount p of each protrusion 21 protruding from the first surface 20m is, for example, 0.01 mm or more and 0.25 mm or less. Each protrusion 21 may be provided so that its width w and spacing i are constant. In this case, the width w of each protrusion 21 is, for example, about 0.5 mm to 1 mm. The spacing i of each protrusion 21 is, for example, about 1 mm to 2 mm.

[0020] A strain gauge 100 is fixed to the second surface 20n of the strain generating body 20 by an adhesive layer 40. The strain gauge 100 is an example of a detection unit in this disclosure. As shown in Figure 2, the strain gauge 100 is housed, for example, in the space formed by the recess 10y and the second surface 20n of the strain generating body 20. The strain gauge 100 is a sensor that detects pulse waves based on the change in the resistance value of the resistor 130 caused by the strain of the strain generating body 20.

[0021] Furthermore, it is preferable that the strain gauge 100 is positioned within the recess 10y, separated from the support 10. When the strain gauge 100 is positioned separated from the support 10, the support 10 does not hinder the expansion and contraction of the resistance element 130 of the strain gauge 100. Therefore, this arrangement improves the accuracy of strain detection by the strain gauge 100. Consequently, the pulse wave sensor 1 can detect pulse waves with high accuracy.

[0022] The material of the adhesive layer 40 is not particularly limited as long as it is a material that has the function of bonding the strain body 20 and the strain gauge 100. For example, epoxy resin, modified epoxy resin, silicone resin, modified silicone resin, urethane resin, modified urethane resin, etc. can be used as the adhesive layer 40. Alternatively, a bonding sheet or the like may be used as the adhesive layer 40. The thickness of the adhesive layer 40 is not particularly limited. For example, the thickness of the adhesive layer 40 can be about 0.1 μm to 50 μm.

[0023] The housing 200 is fixed, for example, to the surface 10n of the support 10. The output of the strain gauge 100 is electrically connected to a circuit located inside the housing 200, for example, by wire or a flexible circuit board. Inside the housing 200, for example, a bridge circuit, an A / D conversion circuit, a memory unit, a communication unit, a battery, etc. are arranged.

[0024] The output of the strain gauge 100 is connected, for example, to a bridge circuit in the housing 200, and an analog pulse wave signal, which is a periodic voltage change corresponding to the resistance value of the resistor 130, is obtained as the output of the bridge circuit. The analog pulse wave signal is converted to a digital signal by an A / D conversion circuit and then stored in a memory unit. The memory unit is, for example, a non-volatile memory such as flash memory. The data stored in the memory unit is transmitted to the outside of the pulse wave sensor 1 by, for example, a communication unit. Alternatively, the communication unit may not be placed inside the housing 200, and the data stored in the memory unit may be transmitted to the outside of the pulse wave sensor 1 by wire or the like.

[0025] Figure 3 is a bottom view illustrating the strain-generating body of the pulse wave sensor according to the first embodiment. As shown in Figure 3, in the strain-generating body 20 of the pulse wave sensor 1, the longitudinal direction of each projection 21 is approximately perpendicular to the longitudinal direction of the support 10. That is, while the longitudinal direction of the support 10 is the X-axis direction, the longitudinal direction of each projection 21 is the Y-axis direction. Here, "approximately perpendicular" means that the longitudinal direction of the projection 21 is at an angle of approximately 90 degrees ± 5 degrees with respect to the longitudinal direction of the support 10.

[0026] By providing at least two protrusions 21 on the strain generating body 20, the necessary rigidity of the strain generating body 20 as a whole can be ensured while reducing the thickness of the strain generating body 20 in areas where no protrusions 21 are provided (for example, the area between the protrusions 21). Therefore, when the support 10 is attached to the subject's wrist, the portion of the strain generating body 20 between the protrusions 21 becomes more flexible, allowing the strain generating body 20 to bend flexibly to conform to the shape of the subject's wrist. Thus, when the subject wears the pulse wave sensor 1, the tip surface 21a of the protrusions 21 shown in Figure 2 can be brought into close contact with the subject's radial artery. As a result, the pulse wave sensor 1 can detect the strain occurring in the subject's radial artery with high accuracy.

[0027] While it is sufficient for at least two protrusions 21 to be placed on the first surface 20m, it is preferable that more protrusions 21 be arranged across the entire first surface 20m with a certain regularity. This makes it even easier to bend the entire strain-generating body 20 to conform to the shape of the subject's wrist. Note that having a certain regularity does not mean a random state, but rather that there is some kind of regularity, and the nature of that regularity is not limited. Examples of a certain regularity include arranging protrusions 21 of the same shape at equal intervals in one direction, arranging protrusions 21 of the same shape in a matrix, or repeatedly repeating the same arrangement.

[0028] Furthermore, in the pulse wave sensor 1, multiple protrusions 21 are provided on the first surface 20m of the strain generating body 20, and the tip surfaces 21a of the protrusions 21 are in contact with the subject's skin. This reduces the contact area between the strain generating body 20 and the subject's skin compared to the case where the protrusions 21 are not provided, i.e., when the entire first surface 20m of the strain generating body 20 is in contact with the subject's skin. As a result, the pressure received by the strain generating body 20 from the radial artery becomes greater, allowing the pulse wave sensor 1 to detect minute strains occurring in the subject's radial artery with high accuracy.

[0029] Furthermore, it is preferable that the strain gauge 100 is positioned so that the resistor 130 does not overlap with the protrusions 21 when viewed from a direction perpendicular to the first surface 20m of the strain generating body 20 (viewed from the Z- side to the Z+ side). The portion of the strain generating body 20 between the protrusions 21 is thinner than the protrusions 21 and therefore prone to strain. By positioning the strain gauge 100 so that the resistor 130 can receive the strain in this portion, the strain generated in the strain generating body 20 can be detected with high accuracy.

[0030] [Strain Gauge 100] Figure 4 is a plan view illustrating a strain gauge according to the first embodiment. Figure 5 is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment, showing a cross-section along line BB in Figure 4.

[0031] Referring to Figures 4 and 5, the strain gauge 100 comprises a base material 110, a resistor 130, wiring 140, an electrode 150, and a cover layer 160. The cover layer 160 can be provided as needed. For convenience, in Figures 4 and 5, only the outer edge of the cover layer 160 is shown with a dashed line. First, the various parts constituting the strain gauge 100 will be described in detail.

[0032] In this embodiment, for convenience, the side of the strain gauge 100 on which the resistor 130 is provided on the base material 110 is referred to as the "upper side," and the side on which the resistor 130 is not provided is referred to as the "lower side." Furthermore, the surface located above each part is referred to as the "upper surface," and the surface located below each part is referred to as the "lower surface." However, the strain gauge 100 can also be used upside down. Furthermore, the strain gauge 100 can be positioned at any angle. Moreover, a planar view refers to viewing the object in the direction normal to the upper surface 110a of the base material 110 from top to bottom. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0033] The base material 110 is a component that serves as a base layer for forming the resistor 130, etc. The base material 110 is flexible. The thickness of the base material 110 is not particularly limited and may be appropriately determined according to the intended use of the strain gauge 100, etc. For example, the thickness of the base material 110 may be about 5 μm to 500 μm. However, from the viewpoint of strain transmission from the second surface 20n of the strain generating body 20 to the sensing part, and dimensional stability against environmental changes, the thickness of the base material 110 is preferably in the range of 5 μm to 200 μm. Furthermore, from the viewpoint of insulation, the thickness of the base material 110 is preferably 10 μm or more.

[0034] The base material 110 is 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. The term "film" refers to a flexible material with a thickness of approximately 500 μm or less.

[0035] When the base material 110 is formed from an insulating resin film, the insulating resin film may contain fillers, impurities, etc. For example, the base material 110 may be formed from an insulating resin film containing fillers such as silica or alumina.

[0036] Other materials for the substrate 110 besides resin include, for example, crystalline materials such as SiO2, ZrO2 (including YSZ), Si, Si2N3, Al2O3 (including sapphire), ZnO, and perovskite ceramics (CaTiO3, BaTiO3). In addition to the aforementioned crystalline materials, amorphous glass or the like may also be used as the material for the substrate 110. Furthermore, metals such as aluminum, aluminum alloys (duralumin), and titanium may be used as the material for the substrate 110. When a metal substrate 110 is used, an insulating film is provided so as to cover the upper surface 110a.

[0037] The resistor 130 is a thin film formed in a predetermined pattern on the upper side of the substrate 110. In the strain gauge 100, the resistor 130 is a sensitive part that receives strain and causes a change in resistance. 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 4, for convenience, the resistor 130 is shown with a dense, textured pattern.

[0038] 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 X direction in the example of Figure 4), and the ends of adjacent elongated sections are connected alternately, so that the whole structure is folded in a zigzag pattern. 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 Y direction in the example of Figure 4).

[0039] In the resistor 130, the X-side end of the elongated portion located furthest to the Y+ side bends in the Y+ direction and reaches one end 130e1 in the grid width direction of the resistor 130. Similarly, the X-side end of the elongated portion located furthest to the Y- side bends in the Y- direction and reaches the other end 130e2 in the grid direction of the resistor 130. Each end 130e1 and 130e2 is electrically connected to the electrode 150 via the wiring 140. In other words, the wiring 140 electrically connects each end 130e1 and 130e2 in the grid width direction of the resistor 130 to each electrode 150.

[0040] 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).

[0041] Here, a Cr multiphase film is a film in which Cr, CrN, and Cr2N are mixed. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0042] The thickness of the resistor 130 is not particularly limited and may be determined appropriately depending on the intended use of the strain gauge 100. For example, the thickness of the resistor 130 may be approximately 0.05 μm to 2 μm. In particular, when the thickness of the resistor 130 is 0.1 μm or more, the crystallinity of the crystals constituting the resistor 130 (for example, the crystallinity of α-Cr) is improved. Also, when the thickness of the resistor 130 is 1 μm or less, (i) cracks in the film and (ii) warping of the film from the substrate 110, caused by internal stress in the film constituting the resistor 130, are reduced.

[0043] Considering the need to minimize lateral sensitivity and prevent wire breakage, the width of the resistor 130 is preferably 10 μm or more and 100 μm or less. More specifically, the width of the resistor 130 is preferably 10 μm or more and 70 μm or less, and more preferably 10 μm or more and 50 μm or less.

[0044] 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. Also, for example, if the resistor 130 is a Cr multiphase film, 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 more, and the gauge factor temperature coefficient TCS and resistance temperature coefficient TCR can be set within the range of -1000 ppm / ℃ to +1000 ppm / ℃. Here, "main component" means a component that accounts for 50% by weight or more of the total material 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. Furthermore, from the same viewpoint, it is even more preferable that the resistor 130 contains 90% by weight or more of α-Cr. Note that α-Cr is Cr with a bcc structure (body-centered cubic lattice structure).

[0045] 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 be 20% by weight or less, the decrease in the gauge factor of the strain gauge 100 can be suppressed.

[0046] Furthermore, in the Cr multiphase film, it is preferable that the ratio of CrN to Cr2N is such that the proportion of Cr2N is 80% or more and less than 90% by weight relative to the total weight of CrN and Cr2N. More preferably, the ratio is such that the proportion of Cr2N is 90% or more and less than 95% by weight relative to the total weight of CrN and Cr2N. Cr2N has semiconducting properties. Therefore, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the decrease in TCR (negative TCR) becomes even more pronounced. Moreover, by setting the proportion of Cr2N to 90% or more and less than 95% by weight as described above, the ceramicization of the resistor 130 is reduced, making brittle fracture of the resistor 130 less likely to occur.

[0047] On the other hand, CrN has the advantage of being chemically stable. By including more CrN in the Cr multiphase film, the possibility of unstable nitrogen generation can be reduced, thus enabling the creation of a stable strain gauge. Here, "unstable nitrogen" refers to trace amounts of N2 or atomic nitrogen that may be present in the Cr multiphase film. These unstable nitrogen atoms may escape from the film depending on the external environment (e.g., high temperature environment). When unstable nitrogen atoms escape from the film, the film stress of the Cr multiphase film may change.

[0048] In the strain gauge 100, using a Cr multiphase film as the material for the resistor 130 makes it possible to achieve both high sensitivity and miniaturization. For example, while the output of a conventional strain gauge was about 0.04mV / 2V, using a Cr multiphase film as the material for the resistor 130 makes it possible to obtain an output of 0.3mV / 2V or higher. Furthermore, while the size (gauge length × gauge width) of a conventional strain gauge was about 3mm × 3mm, using a Cr multiphase film as the material for the resistor 130 makes it possible to miniaturize the size (gauge length × gauge width) to about 0.3mm × 0.3mm.

[0049] The wiring 140 is provided on the base material 110. The wiring 140 is electrically connected to the resistor 130 and the electrode 150. 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. In Figure 4, for convenience, the wiring 140 is shown with a matte pattern that is less dense than the resistor 130.

[0050] The electrode 150 is provided on the substrate 110. The electrode 150 is electrically connected to the resistor 130 via the wiring 140. In a plan view, the electrode 150 is wider than the wiring 140 and is 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. For example, lead wires for external connection are joined to the electrode 150. A layer of a metal with low resistance, such as copper, or a layer of a metal with good solderability, such as gold, may be laminated on the upper surface of the electrode 150. For convenience, the resistor 130, wiring 140, and electrode 150 are given different reference numerals, but they can all be formed integrally from the same material in the same process. In Figure 4, for convenience, the electrode 150 is shown with a textured pattern of the same density as the wiring 140.

[0051] The cover layer 160 (protective layer) is provided on the upper surface 110a of the substrate 110 as needed, covering the resistor 130 and wiring 140 and exposing the electrodes 150. Examples of materials for the cover layer 160 include insulating resins such as PI resin, epoxy resin, PEEK resin, PEN resin, PET resin, PPS resin, and composite resins (e.g., silicone resin, polyolefin resin). The cover layer 160 may also contain fillers and pigments. The thickness of the cover layer 160 is not particularly limited and can be appropriately selected according to the purpose. For example, the thickness of the cover layer 160 can be approximately 2 μm to 30 μm. By providing the cover layer 160, mechanical damage to the resistor 130 can be suppressed. Furthermore, by providing the cover layer 160, the resistor 130 can be protected from moisture and other elements.

[0052] [Manufacturing method for strain gauge 100] In the strain gauge 100 according to this embodiment, a resistor 130, wiring 140, electrodes 150, and a cover layer 160 are formed on a base material 110. Note that another layer (such as a functional layer described later) may be formed between the base material 110 and these layers.

[0053] The manufacturing method for the strain gauge 100 is described below. 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, wiring 140, and electrode 150. Therefore, the material and thickness of metal layer A are the same as those of the resistor 130, wiring 140, and electrode 150 described above.

[0054] The metal layer A can be deposited, for example, by a magnetron sputtering method targeting a raw material capable of forming the metal layer A. Alternatively, the metal layer A may be deposited using reactive sputtering, vapor deposition, arc ion plating, or pulsed laser deposition instead of magnetron sputtering. After depositing the metal layer A on the upper surface 110a of the substrate 110, the metal layer A is patterned into a planar shape similar to the resistor 130, wiring 140, and electrode 150 in Figure 4 using a well-known photolithography method.

[0055] Alternatively, a base layer may be formed on the upper surface 110a of the substrate 110 before forming the metal layer A. For example, a functional layer of a predetermined thickness may be vacuum-deposited on the upper surface 110a of the substrate 110 by conventional sputtering. By providing a base layer in this way, the gauge characteristics of the strain gauge 100 can be stabilized.

[0056] 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 or moisture contained in the substrate 110, and / or the function of improving the adhesion between the substrate 110 and the metal layer A. The functional layer may further have other functions.

[0057] The insulating resin film constituting the base material 110 may contain oxygen and moisture, and Cr may form an oxidized film. Therefore, especially when metal layer A contains Cr, it is preferable to form a functional layer that has the function of preventing oxidation of metal layer A.

[0058] 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 is improved. Furthermore, the diffusion of the material constituting the functional layer into the metal layer A improves the gauge characteristics of the strain gauge 100.

[0059] Examples of materials for the functional layer include one or more metals selected from the group consisting of 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 (bismuth), 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.

[0060] Figure 6 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 6 shows the cross-sectional shape of the strain gauge 100 when a functional layer 120 is provided as a base layer for the resistor 130, wiring 140, and electrode 150.

[0061] The planar shape of the functional layer 120 may be patterned to be substantially the same as the planar shapes of, for example, the resistor 130, the wiring 140, and the electrodes 150. However, the planar shapes of the functional layer 120 and the resistor 130, the wiring 140, and the electrodes 150 do not have to be substantially the same. For example, if the functional layer 120 is formed from an insulating material, the functional layer 120 may be patterned to be a different shape from the planar shapes of the resistor 130, the wiring 140, and the electrodes 150. In this case, the functional layer 120 may be formed as a solid in the region where the resistor 130, the wiring 140, and the electrodes 150 are formed. Alternatively, the functional layer 120 may be formed as a solid over the entire upper surface of the substrate 110.

[0062] After forming the resistor 130, wiring 140, and electrode 150, a cover layer 160 is formed on the upper surface 110a of the base material 110, if necessary. The cover layer 160 covers the resistor 130 and wiring 140, but the electrode 150 may be exposed from the cover layer 160. For example, the cover layer 160 can be formed by laminating a semi-cured thermosetting insulating resin film onto the upper surface 110a of the base material 110 so as to cover the resistor 130 and wiring 140 and expose the electrode 150, and then heating and curing the insulating resin film. Through the above steps, the strain gauge 100 is completed.

[0063] <Variation 1 of the First Embodiment> Modification 1 of the first embodiment shows an example of a pulse wave sensor in which the housing 200 is not provided on the support 10. In Modification 1 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0064] Figure 7 is a plan view illustrating a pulse wave sensor according to modification 1 of the first embodiment. Referring to Figure 7, the pulse wave sensor 1A differs from the pulse wave sensor 1 shown in Figure 1 in that it does not have a housing 200.

[0065] Since the pulse wave sensor 1A does not have a housing 200, the output of the strain gauge 100 is connected by wire or the like to a memory unit located away from the pulse wave sensor 1A. For example, an external connection lead wire is attached to the electrode 150 of the strain gauge 100 and connected to the memory unit.

[0066] Thus, the housing 200, including the memory unit, may be placed on the support 10 or at a location separate from the support 10. The type, size, and shape of the memory unit are not particularly limited. For example, the pulse wave sensor 1A may have wiring for connecting to a portable recording medium (i.e., a memory unit) that is small enough to fit in a subject's pocket. Furthermore, the present invention may be configured such that the pulse wave data detected by the pulse wave sensor 1 is stored in the recording medium.

[0067] Furthermore, in this modified example, the pulse wave sensor 1A and the memory unit may be wirelessly connected. That is, the pulse wave sensor 1A may transmit the measurement data of the strain gauge 100 to an external memory device via its own communication unit.

[0068] <Modification 2 of the First Embodiment> Modification 2 of the first embodiment shows other examples of the shape of the protrusion and the shape of the strain-generating body. In Modification 2 of the first embodiment, descriptions of components that are the same as those described in the previously described embodiment may be omitted.

[0069] Figure 8 is a bottom view (part 1) illustrating the strain-generating body of a pulse wave sensor according to Modification 2 of the First Embodiment. Figure 9 is a bottom view (part 2) illustrating the strain-generating body of a pulse wave sensor according to Modification 2 of the First Embodiment.

[0070] In the example shown in Figure 8, the strain-generating body 20A has a rectangular, flat structure. A rectangular projection 22 is formed on the first surface 20m of the strain-generating body 20A. Here, the projection 22 is a structure that protrudes from the first surface 20m in the Z-direction. Therefore, in three dimensions, the projection 22 can be said to have the shape of a rectangular prism. The projections 22 are arranged at equal intervals in the X-axis and Y-axis directions on the first surface 20m. In the example shown in Figure 9, the strain-generating body 20B has a circular, flat structure. On the first surface 20m of the strain-generating body 20B, rectangular prism projections 22 are arranged at equal intervals in the X-axis and Y-axis directions. Note that the shape of the projections 22 is not limited to rectangular prisms. For example, the projections 22 may be various columnar shapes such as triangular prisms, cylinders, and elliptical prisms.

[0071] Furthermore, the shape of the first surface 20m of the strain-generating body is not particularly limited. For example, the first surface 20m may be a rectangle as shown in Figure 8, a circle as shown in Figure 9, or other shapes such as a triangle or an ellipse. Also, the first surface 20m of the strain-generating body may have elongated rectangular protrusions (for example, protrusion 21 in Figure 3) or columnar protrusions (for example, protrusions 22 in Figures 8 and 9). By providing at least two or more protrusions on the strain-generating body, the strain-generating body can be made thinner in the parts between the protrusions while ensuring the necessary rigidity of the strain-generating body as a whole.

[0072] <Second Embodiment> In the second embodiment, an example of a bandage-type pulse wave sensor is shown. In the second embodiment, descriptions of components that are the same as those described in the previously described embodiments may be omitted.

[0073] Figure 10 is a plan view illustrating a pulse wave sensor according to the second embodiment. Figure 11 is a partial cross-sectional view illustrating a pulse wave sensor according to the second embodiment, showing a cross-section along the CC line in Figure 10.

[0074] Referring to Figures 10 and 11, the pulse wave sensor 2 is a wearable device that can be attached to a subject and mainly comprises a support 50, a strain generating body 20, and a strain gauge 100. The pulse wave sensor 2 may also have a housing 200, similar to the pulse wave sensor 1.

[0075] In the pulse wave sensor 2, the support 50 is a circular patch that is attached to the subject's wrist and can be adhered to the subject's skin. The support 50 can be made from, for example, resin, paper, cloth, nonwoven fabric, etc., or a combination thereof. The support 50 may be a color close to skin tone, for example, like an adhesive bandage. In the example in Figure 10, the support 50 is circular in plan view, but is not limited to this, and may be elliptical, square, rectangular, etc.

[0076] The structure of the support 50 around the strain generating body 20 and strain gauge 100 is the same as that of the support 10. That is, the support 50 has a back surface 50m and a front surface 50n, and when a subject wears the pulse wave sensor 2, the back surface 50m of the support 50 comes into contact with the subject's skin. The back surface 50m of the support 50 is provided with a mounting portion 50x, which has the same configuration as the mounting portion 10x. The mounting portion 50x also has a recess 50y, which is a portion that is further recessed in the Z+ direction. The strain generating body 20 is fixed to the support 50 via an adhesive layer 30. The strain generating body 20 is attached to the mounting portion 50x such that its first surface 20m is exposed from the back surface 50m of the support 50. The strain gauge 100 is housed in the space formed by the recess 50y and the second surface 20n.

[0077] The support 50 differs from the support 10 in that an adhesive layer 60 is provided on its back surface 50m. More specifically, an adhesive layer 60, to which an adhesive is attached, is provided on at least a portion of the back surface 50m of the support 50, excluding the area where the first surface 20m of the strain-generating body 20 is exposed. The adhesive layer 60 has the property of adhering to human skin. The adhesive layer 60 is formed, for example, by applying an adhesive to the support 50. Alternatively, the adhesive layer 60 may be formed by laminating the adhesive layer 60 to the support 50. Specific examples of adhesives that form the adhesive layer 60 include, for example, acrylic adhesives, rubber adhesives, silicone adhesives, etc. A release sheet 70 may be attached to the side of the adhesive layer 60 that comes into contact with the subject's body (the subject's skin). The release sheet 70 is, for example, paper that has undergone a release treatment or a resin sheet that has undergone a release treatment.

[0078] When using the pulse wave sensor 2, the user of the pulse wave sensor 2 peels off the release sheet 70 and then directly attaches the exposed adhesive layer 60 to the skin near the radial artery of the person whose pulse wave is to be measured. The support body 50 is provided with a strain generating body 20 having two or more protrusions 21, similar to the first embodiment. Therefore, the pulse wave sensor 2, like the pulse wave sensor 1, can bend the strain generating body 20 to conform to the shape of the subject's wrist, and the tip surfaces 21a of the protrusions 21 can be brought into close contact with the subject's radial artery. As a result, the pulse wave sensor 2, like the pulse wave sensor 1, can detect the strain occurring in the subject's radial artery with high accuracy.

[0079] In addition, the pulse wave sensor 2 may be provided with a columnar projection 22 instead of a linear projection 21.

[0080] <Third Embodiment> In the embodiments and their modifications described above, examples were given in which the detection unit according to the present disclosure is a strain gauge using a resistor. That is, in each of the embodiments described above, 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.

[0081] 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 third embodiment below, a strain gauge including a detection element that utilizes the Villari phenomenon will be described. In the fourth embodiment, a strain gauge including a detection element having a magnetic tunnel junction structure will be described.

[0082] In each embodiment of this specification, components having similar functions will be given the same name and component number, and their descriptions will not be repeated. Furthermore, the directions of the x, y, and z axes in the drawings of each embodiment thereafter (drawings from Figure 12 onwards) are the same as the directions of the x, y, and z axes shown in Figures 1 to 11. In the following description, the positive direction of the z axis will be referred to as "up," and the negative direction of the z axis will be referred to as "down." That is, in the following description, "upper side" refers to the side in the positive direction of the z axis, and "upper surface" refers to the surface on the positive direction of the z axis. Similarly, "lower side" refers to the side in the negative direction of the z axis, and "lower surface" refers to the surface on the negative direction of the z axis.

[0083] Figure 12 shows an example of a detection element 300 included in a strain gauge according to the third embodiment. Figure 12(a) is a plan view of the detection element 300 when viewed from the positive z-axis to the negative z-axis (i.e., from the top surface to the bottom surface). On the other hand, Figure 12(b) shows a cross-sectional view of the detection element 300 shown in Figure 12(a) along the α-α' line. Note that the wiring extending from the detection element 300 is not shown in Figures 12(a) and (b). However, the detection element 300 may be connected to wiring that connects the drive coil 320 and the power supply, which will be described later, and to wiring that transmits the current detected by the sensing coil 380.

[0084] As shown in Figure 12(a), the detection element 300 includes a drive coil 320, a sensing coil 380, and a base layer 310. The base layer 310 is the core layer for the drive coil 320 and the sensing coil 380. The sensing coil 380 is a coil for detecting the magnetization strength of the base layer 310 (more precisely, the base metal 370 described later). The drive coil 320 is a coil for generating a magnetic field. The detection element 300 has a double structure with the base layer 310 as the core material, with the sensing coil 380 wound on the inside and the drive coil 320 wound on the outside. The materials for the drive coil 320 and the sensing coil 380 are preferably conductive metals such as Cu, Ag, Al, and Au, or alloys of these metals. The number of turns and the size of the cross-sectional area of ​​the drive coil 320 and the sensing coil 380 may be appropriately designed according to the strain detection sensitivity required for the detection element 300.

[0085] As will be explained in detail later, when stress is applied to the base layer 310, the magnetization strength of the base metal 370 (described later) contained in the base layer 310 changes. The detection element 300 can determine the strength of the stress (i.e., the degree of strain) applied to the base layer 310 by detecting this change in magnetization strength with the sensing coil 380.

[0086] The configuration of the detection element 300 will be further explained with reference to the cross-sectional view in Figure 12(b). In Figure 12(b), the drive coil 320, the sensing coil 380, and the three insulating layers 340, 350, and 360 are each formed to surround the core material, the base metal 370. That is, the layers with the same component number in Figure 12(b) are connected and surround the base metal 370.

[0087] The base metal 370 is a core material for various coils and insulating layers. The base metal 370 may be, for example, a substantially flat metal plate. The base metal 370 is covered so as to surround it with the insulating layer 360. Preferably, the base metal 370 is made of a soft magnetic material such as an Fe-Si-Al alloy such as Sendust, or a Ni-Fe alloy such as Permalloy. The aforementioned base layer 310 consists of this base metal 370 and the insulating layer 360, as shown in Figure 12(b).

[0088] Outside the insulating layer 360, an insulating layer 350 is formed so as to surround the insulating layer 360. Further outside the insulating layer 350, an insulating layer 340 is formed. The insulating layer 350 is a layer containing the sensing coil 380, and the gaps around the sensing coil 380 are filled with insulating material. The insulating layer 340 is a layer containing the drive coil 320, and the gaps around the drive coil 320 are filled with insulating material. It is preferable that the insulating layers 340, 350, and 360 are made of a dry film that is not affected by the magnetic field or a resist-cured material such as a photosensitive polyimide.

[0089] One side of the detection element 300 may be attached to the base material 110, as shown in Figure 12(b). The base material 110 is a member that fixes the detection element 300. For example, the base material 110 may be a flexible substrate made of plastic film or the like. The detection element 300 is attached to the strain generating body 20, 20A, or 20B via the base material 110. The detection element 300 may be a flat plate or a thin film as a whole. If the detection element 300 is a flat plate or a thin film, the detection element 300 can be easily attached to the base material 110. Furthermore, the base material 110 is not an essential component of the detection element 300. For example, the detection element 300 may be used without a base material 110, by directly attaching the bottom surface of the detection element 300 to the strain generating body 20, 20A, or 20B.

[0090] The strain-generating bodies 20, 20A, and 20B according to this embodiment may have basically the same configuration and materials as the strain-generating bodies 20, 20A, and 20B according to the first and second embodiments. However, in this embodiment, it is more desirable that the strain-generating bodies 20, 20A, and 20B be made of a non-magnetic material. The strain-generating bodies 20, 20A, and 20B according to this embodiment can be manufactured, for example, from non-magnetic stainless steel.

[0091] Next, the principle of detecting strain using the detection element 300 will be outlined. The detection element 300 includes a base metal 370, which is a magnetic material. When an alternating current is supplied from the power source to the drive coil 320, the drive coil 320 generates an alternating magnetic field around it. This generates a magnetic field, and the base metal 370 is magnetized. When the strain-generating body 20, 20A, or 20B deforms in this state, strain occurs. The strain is transmitted through the base material 110, and stress is applied to the base metal 370. If the detection element 300 is attached to the strain-generating body 20, 20A, or 20B without going through the base material 110, the stress is transmitted directly from the strain-generating body 20, 20A, or 20B to the base metal 370 (and the insulating layers 340-360 covering it).

[0092] When stress is applied to the base metal 370, the permeability of the base metal 370 changes according to that stress. Consequently, the magnetization strength (degree of magnetization) of the base metal 370 changes. This phenomenon, in which the permeability and magnetization strength of a magnetic material change when stress is applied to it, is called the "Villari phenomenon." According to the configuration of the detection element 300, an AC voltage corresponding to the magnetization strength of the base metal 370 is induced in the sensing coil 380, which is the pickup coil. Therefore, based on the principle of the Villari phenomenon, the stress applied to the base metal 370 can be calculated from the value of this AC voltage. Then, from the calculated stress, the degree of strain of the strain-generating bodies 20, 20A, and 20B can be determined. Note that if the detection element 300 has the shape shown in Figures 12(a) and (b), the grid direction of the detection element 300 is equal to the α-α' direction in Figure 12(a). Based on the principle described above, the detection element 300 can detect the strain of the strain-generating bodies 20, 20A, and 20B. In other words, the detection element 300 functions as a detection element for a strain gauge.

[0093] 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.

[0094] 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.

[0095] 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 12(b), both ends of the base metal 370 in the x direction do not need to be covered by the insulating layer 360.

[0096] In the pulse wave sensor according to this embodiment, when the strain-generating body 20, 20A, or 20B deforms (i.e., strain occurs in the strain-generating body), the base material 110 of the strain gauge (or the detection element 300 itself) is strained. The detection element 300 can detect the magnetic change caused by this strain based on the principle of the Villari phenomenon described above.

[0097] The strain gauge including the detection element 300 according to this embodiment can be arranged on the strain bodies 20, 20A, and 20B in any arrangement pattern shown in the first and second embodiments and their variations. That is, the strain of the strain bodies 20, 20A, and 20B can be detected using the detection element 300 according to this embodiment, in the same way as when using an electrical resistance type strain gauge. Therefore, the strain gauge according to this embodiment has the same effects as the strain gauge 100 according to the first and second embodiments and their variations.

[0098] <Fourth Embodiment> Figure 13 shows a detection element 500, which is an example of a detection element included in the strain gauge according to the fourth embodiment. Figure 14 shows a detection element 600, which is another example of a detection element according to the fourth embodiment. Figure 15 shows a detection element 700, yet another example of a detection element according to the fourth embodiment. Figures 13 to 15(a) are perspective views of the detection elements 500, 600, and 700, respectively. Figures 13 to 15(b) are plan views of the detection elements 500, 600, and 700 viewed from the positive z-axis to the negative z-axis. Figures 13 to 15(c) are cross-sectional views of the detection elements 500, 600, and 700 in a plane parallel to the zx-plane. Note that wiring extending from the detection elements is not shown in any of the figures 13 to 15. However, these detection elements 500, 600, and 700 may also be connected to wiring that connects the upstream electrode 510 to the power supply and wiring that connects the downstream electrode 520 to the power supply, as described later.

[0099] As shown in Figures 13-15(a), the detection elements 500, 600, and 700 include an upstream electrode 510, a downstream electrode 520, a magnetic film 530, and an insulating film 540. The insulating film 540 is sandwiched between the magnetic film 530 as shown in the figure. A magnetic tunnel junction is formed by this magnetic film 530 and insulating film 540. In other words, the detection elements 500, 600, and 700 have a structure in which electrodes are connected to a magnetic tunnel junction structure.

[0100] The lower surfaces of the detection elements 500, 600, and 700 may be attached to a substrate similar to the substrate 110 of the first and second embodiments. The detection element 500 may be attached to the strain-generating body 20, 20A, or 20B via the substrate. The detection elements 500, 600, and 700 may be flat plates or thin films as a whole. If the detection elements 500, 600, and 700 are flat plates or thin films, they can be easily attached to the substrate or the strain-generating body 20, 20A, or 20B. Alternatively, for example, the lower surfaces of the detection elements 500, 600, and 700 may be directly attached to the strain-generating body 20, 20A, or 20B for use.

[0101] 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.

[0102] 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 13-15, the current flows from the upstream electrode 510 to the downstream electrode 520. For example, in Figure 13(c), when a voltage is applied between the upstream electrode 510 and the downstream electrode 520, electrons flow from the upper (positive z-axis) magnetic film 530, across the insulating film 540, to the lower (negative z-axis) magnetic film 530. This phenomenon is called the "tunneling effect," and the electrical resistance when electrons pass through the insulating film 540 is called the "tunneling resistance." In the examples in Figures 13-15, the junctions of each part of the electrodes are treated at the ends to prevent current from short-circuiting the magnetic tunnel junction structure.

[0103] Incidentally, when strain is applied to the detection element 500 via the substrate 110, a magnetic change occurs in the tunnel junction structure. More specifically, the magnetization directions of the upper and lower magnetic films 530 are misaligned. When the magnetization directions of the upper and lower magnetic films 530 are misaligned in this way, the tunnel resistance increases compared to when the magnetization directions are parallel (tunnel magnetoresistance effect). Therefore, in the detection element 500 having the above configuration, the current flowing between the electrodes decreases in proportion to the magnitude of the strain in the detection element 500 (more precisely, the magnetic tunnel junction portion). That is, as the strain increases, the electrical resistance increases. In this way, the detection element 500 can detect strain based on the current value in relation to the applied voltage. Therefore, by attaching the detection element 500 to the strain generating body 20, 20A, or 20B, the strain applied to the strain generating body 20, 20A, or 20B can be measured.

[0104] The detection element having a magnetic tunnel junction structure is not limited to the example shown in Figure 13. For example, detection elements 600 and 700 as shown in Figures 14 and 15 can also be used. Both the detection element 600 shown in Figure 14 and the detection element 700 shown in Figure 15 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 x-axis direction (positive and negative x-axis directions) in Figures 13 to 15, respectively. As shown in the figure, the detection element 600 shown in Figure 14 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 15 is attached to the substrate 110 via the substrate 710. As shown in Figures 13 to 15, 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.

[0105] The strain generators 20, 20A, and 20B according to this embodiment may have basically the same configuration and materials as the strain generators 20, 20A, and 20B according to the first embodiment. However, in this embodiment, it is more desirable that the strain generators 20, 20A, and 20B be made of a non-magnetic material. For example, the strain generators 20, 20A, and 20B according to this embodiment can be made from non-magnetic stainless steel. Furthermore, the detection elements 500, 600, and 700 as a whole may have a substantially flat plate shape, such as a film type. This allows the detection elements 500 to be easily attached to the strain generators 20, 20A, and 20B. In addition, 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.

[0106] 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 13 to 15, the design may be such that current flows from the downstream electrode 520 to the upstream electrode 510.

[0107] In the pulse wave sensor according to this embodiment, when the strain-generating body 20, 20A, or 20B deforms (i.e., strain occurs in the strain-generating body), the base material of the strain gauge (or the detection element 500, 600, or 700 itself) is strained. The detection element 500, 600, or 700 can detect the magnetic change caused by this strain based on the principle of the tunnel magnetoresistance effect described above.

[0108] The strain gauges including the detection elements 500, 600, and 700 according to this embodiment can be placed on the strain generating bodies 20, 20A, and 20B at any of the arrangement positions shown in the first and second embodiments and their modified examples. That is, the strain of the strain generating bodies 20, 20A, and 20B can be detected using the detection elements 500, 600, and 700 according to this embodiment, in the same way as when using an electrical resistance type strain gauge. Therefore, the strain gauges according to this embodiment have the same effects as the strain gauges 100 according to the first and second embodiments and their modified examples.

[0109] <Fifth 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.

[0110] (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.

[0111] 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 strain bodies 20, 20A, or 20B, similar to electrical resistance metal strain gauges. In this case, when the strain bodies 20, 20A, or 20B expand or contract, 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 bodies 20, 20A, or 20B can be determined by measuring this electrical resistance.

[0112] Furthermore, semiconductor strain gauges can also be configured as strain sensors equipped with a diaphragm structure. In this case, the strain sensor includes, for example, a non-metallic diaphragm (or a metal diaphragm with an electrically insulating layer formed on it) and a semiconductor (for example, a silicon thin-film semiconductor) formed on the diaphragm. In this structure including a diaphragm, when the diaphragm is strained by a normal stress applied to it, the electrical resistance of the semiconductor changes. Therefore, by measuring this electrical resistance, the amount of strain in the diaphragm (and consequently, the amount of strain in the strain-generating bodies 20, 20A, or 20B) can be determined.

[0113] (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).

[0114] 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.

[0115] (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.

[0116] By attaching an optical fiber having such characteristics to a strain-generating body 20, 20A, or 20B 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, 20A, or 20B) 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.

[0117] (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.

[0118] (Vibration-type pressure sensor) A vibration pressure sensor is a sensor that detects pressure by utilizing the phenomenon that the natural frequency of an elastic beam changes due to the pressure (i.e., axial force) generated along the axis of the elastic beam. Like electrical resistance type metal strain gauges, the vibration pressure sensor can be used by directly attaching it to the strain generating bodies 20, 20A, and 20B. Alternatively, for example, the vibration pressure sensor may be a pressure sensor composed of a diaphragm formed on a substrate and a beam-shaped vibrator formed on the surface of the diaphragm.

[0119] In any case, when the strain-generating body 20, 20A, or 20B is strained, the pressure is transmitted directly or indirectly to the oscillator, generating an axial force in the oscillator. The natural frequency of the oscillator changes in accordance with the axial force. Therefore, by measuring the natural frequency of the oscillator, the magnitude of the pressure on the strain-generating body 20, 20A, or 20B can be determined.

[0120] (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.

[0121] A piezoelectric pressure sensor can determine the force applied to a piezoelectric element (i.e., the amount of strain on the piezoelectric element) by measuring the electromotive force of the piezoelectric element. Therefore, by attaching a piezoelectric pressure sensor to the strain-generating body 20, 20A, or 20B, the amount of strain on the strain-generating body 20, 20A, or 20B can be determined.

[0122] 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 and second embodiments and their modified versions can be obtained.

[0123] 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]

[0124] 1,1A,2 Pulse wave sensor, 10,50 Support, 10m,50m Back surface, 10n,50n Front surface, 10x,50x Mounting part, 10y,50y Recess, 20,20A,20B Strain generating body, 20m First surface, 20n Second surface, 21,22 Protrusion, 21a Tip surface, 30,40 Adhesive layer, 60 Adhesive layer, 70 Release sheet, 100 Strain gauge, 110 Substrate, 110a Top surface, 120 Functional layer, 130 Resistor, 130e1,130e2 Termination, 140 Wiring, 150 Electrode, 160 Cover layer, 200 Housing, 300,500,600,700 Detection element, 310 Base layer, 320 Drive coil, 340,350,360 370 Insulating layer, 380 Base metal, 510 Sensing coil, 510 Upstream electrode, 520 Downstream electrode, 530 Magnetic film, 540 Insulating film, 710 Substrate

Claims

1. A pulse wave sensor that can be worn by a subject, A support; a strain generating body including a first surface that is a surface that contacts the body of the subject when the subject wears the pulse wave sensor, and a second surface opposite to the first surface, the strain generating body being fixed to the support body such that the first surface is exposed from the support body; a strain gauge fixed to the second surface, The pulse wave sensor has a plurality of protrusions provided on the first surface.

2. The pulse wave sensor according to claim 1 , wherein the plurality of protrusions are arranged with a certain regularity over the entire first surface.

3. The pulse wave sensor according to claim 1 , wherein each of the protrusions has a linear or rectangular shape when the first surface is viewed in plan, and is arranged with its longitudinal direction facing in the same direction.

4. The support is elongated, The pulse wave sensor according to claim 3 , wherein a longitudinal direction of each of the protrusions is substantially perpendicular to a longitudinal direction of the support body.

5. The pulse wave sensor according to claim 1 , wherein the protrusion is columnar.

6. the support has a recessed portion on a surface that contacts the body of the subject, the strain element is provided so as to close the recess, 3. The pulse wave sensor according to claim 1, wherein the strain gauge is disposed in a space defined by the recess and the second surface of the strain generating element, and is spaced apart from the support.

7. 3. The pulse wave sensor according to claim 1, wherein the strain gauge has a resistor, and the resistor is arranged so as not to overlap the protrusion when viewed from a direction perpendicular to the first surface.

8. The pulse wave sensor according to claim 1 , wherein an adhesive layer is provided on at least a portion of the surface of the support that contacts the body of the subject, excluding an area where the first surface is exposed.

9. The pulse wave sensor according to claim 8 , wherein a release sheet is attached to a surface of the adhesive layer that comes into contact with the body of the subject.

10. The strain gauge is made of Cr, CrN, and Cr ２ 3. The pulse wave sensor according to claim 1, further comprising a resistor formed from a film containing N.

11. A pulse wave sensor that can be worn by a subject, A support; a strain generating body including a first surface that is a surface that contacts the body of the subject when the subject wears the pulse wave sensor, and a second surface opposite to the first surface, the strain generating body being fixed to the support body such that the first surface is exposed from the support body; a detection unit fixed to the second surface, the detection unit detects deformation of the strain-generating body and / or pressure applied to the strain-generating body, The first surface is provided with a plurality of protrusions, A pulse wave sensor that detects a pulse wave based on the change in the deformation and / or the change in the pressure detected by the detection unit.

12. The pulse wave sensor according to claim 11 , wherein the plurality of protrusions are arranged with a certain regularity over the entire first surface.

13. The pulse wave sensor according to claim 11 or 12, wherein each of the protrusions has a linear or rectangular shape when the first surface is viewed in plan, and is arranged with its longitudinal direction facing in the same direction.

14. The support is elongated, The pulse wave sensor according to claim 13 , wherein a longitudinal direction of each of the protrusions is substantially perpendicular to a longitudinal direction of the support body.

15. The pulse wave sensor according to claim 11 or 12, wherein the protrusion is columnar.

16. the support has a recessed portion on a surface that contacts the body of the subject, the strain element is provided so as to close the recess, The pulse wave sensor according to claim 11 or 12, wherein the detection unit is disposed apart from the support body in a space formed by the recess and the second surface of the strain generating element.

17. The pulse wave sensor according to claim 11 or 12, wherein an adhesive layer is provided on at least a portion of the surface of the support that contacts the body of the subject, excluding an area where the first surface is exposed.

18. The pulse wave sensor according to claim 17 , wherein a release sheet is attached to a surface of the adhesive layer that comes into contact with the body of the subject.

19. The pulse wave sensor according to claim 11 or 12, wherein the detection unit has a detection element that detects a magnetic change caused by deformation of the strain-generating body.

20. the detection element includes a magnetic material, 20. The pulse wave sensor according to claim 19, 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.

21. the detection element includes a magnetic tunnel junction structure in which an insulating film is sandwiched between magnetic films, 20. The pulse wave sensor according to claim 19, wherein the detection element detects a magnetic change generated in the structure due to deformation of the strain-generating body.

22. 13. The pulse wave sensor according to claim 11, wherein the detection unit is a semiconductor strain gauge.

23. The pulse wave sensor according to claim 11 or 12, wherein the detection unit is a capacitance type pressure sensor.

24. 13. The pulse wave sensor according to claim 11, wherein the detection unit is an optical fiber strain gauge.

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