Pulse wave measurement device

Abstract

To provide a pulse wave measuring apparatus capable of suppressing the plastic deformation of a pulse wave sensor.SOLUTION: The pulse wave measuring apparatus, which is attachable to a subject, comprises a casing and a pulse wave sensor affixed to the casing. The pulse wave sensor comprises a strain-inducing body where a strain gage is placed. The strain-inducing body is affixed to the casing in a state of being capable of making contact with the subject. A sensor face being the subject-side face of the strain-inducing body is concaved in a direction of separating from the subject, with respect to a face positioned around the sensor face of the casing.SELECTED DRAWING: Figure 4

Description

Technical Field

[0004]

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

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 to be deflectable by the action of an external force, and piezoelectric conversion means for converting the deflection of the pressure receiving plate into an electric signal. This pulse wave sensor has a dome shape in which the deflectable region of the pressure receiving plate is formed as 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, in a pulse wave measuring device using a pulse wave sensor, in order to improve the measurement accuracy, it is necessary to appropriately attach the pulse wave sensor to a subject.

[0005] However, in the above-described pulse wave sensor, since the pressure receiving plate is formed of a material such as SUS or copper to a thickness of about several tens of μm to several hundreds of μm, when pressed against the radial artery, there is a risk of plastic deformation due to the repulsive force from a person's skin, muscle, and blood vessel.

[0006] The present invention has been made in view of the above points, and an object thereof is to provide a pulse wave measuring device capable of suppressing plastic deformation of a pulse wave sensor.

Means for Solving the Problems

[0007] This pulse wave measuring device is a pulse wave measuring device that can be worn on a subject, and comprises a housing and a pulse wave sensor fixed to the housing, wherein the pulse wave sensor includes a strain generating body on which strain gauges are arranged, the strain generating body is fixed to the housing in a manner that allows it to contact the subject, and the sensor surface, which is the surface of the strain generating body facing the subject, is ,before Located around the sensor surface and the lower surface of the housing that can come into contact with the subject In contrast, there is a depression in the direction away from the subject. fruit , The strain generating body has a base with a circular opening, a flat plate-shaped beam bridging the inside of the base, and a load portion provided on the beam portion and protruding from a surface that constitutes a part of the sensor surface of the beam portion. It detects pulse waves based on the change in the resistance value of the strain gauges due to the deformation of the strain generating body. The beam portion has two beams that intersect in a cross shape in plan view, the region where the beams intersect includes the center of the circular opening, the load portion is provided in the region where the beams intersect, and it has four strain gauges. Two of the four strain gauges are arranged on the beam whose longitudinal direction is in the first direction, so as to face the load portion in a plan view, and the other two of the four strain gauges are arranged on the beam whose longitudinal direction is in the second direction perpendicular to the first direction, so as to face the load portion in a plan view. . [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to provide a pulse wave measuring device that can suppress plastic deformation of the pulse wave sensor. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 2] This is a surface-side perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 3] This is a rear-side perspective view illustrating a pulse wave measuring device according to the first embodiment. [Figure 4] This is a side view illustrating a pulse wave measuring device according to the first embodiment. [Figure 5] This is a perspective view illustrating a pulse wave sensor according to the first embodiment. [Figure 6] This is a plan view illustrating a pulse wave sensor according to the first embodiment. [Figure 7] This is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment. [Figure 8] This is a plan view illustrating a strain gauge according to the first embodiment. [Figure 9] This is a cross-sectional view (part 1) illustrating a strain gauge according to the first embodiment. [Figure 10] This is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment.

Best Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same reference numerals are assigned to the same components, and redundant descriptions may be omitted.

[0011] 〈First Embodiment〉 [Pulse Wave Measuring Device 1] FIG. 1 is a perspective view illustrating a pulse wave measuring device according to the first embodiment, showing the state in which the pulse wave measuring device is attached to the wrist of a subject. FIG. 2 is a front side perspective view illustrating the pulse wave measuring device according to the first embodiment. FIG. 3 is a back side perspective view illustrating the pulse wave measuring device according to the first embodiment. FIG. 4 is a side view illustrating the pulse wave measuring device according to the first embodiment.

[0012] In addition, the arrow N in FIG. 4 indicates the normal direction of the sensor surface 40s of the pulse wave sensor 40. In the description of FIGS. 1 to 4, for convenience, the starting point (base) side of the arrow N is referred to as the "upper side", and the ending point (arrowhead) side of the arrow N 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 measuring device 1 can also be used in an upside-down state. Also, the pulse wave measuring device 1 can be arranged at an arbitrary angle. Also, a plan view refers to viewing an object in the direction of the arrow N. And the planar shape refers to the shape of an object when viewed in the direction of the arrow N.

[0013] Referring to FIGS. 1 to 4, the pulse wave measuring device 1 is a wristwatch-type wearable device that can be worn by a subject, and mainly includes a housing 10, a pulse wave sensor 40, and a belt portion 90.

[0014] The pulse wave measuring device 1 is attached to the wrist of a subject, for example, so that the pulse wave sensor 40 is disposed near the radial artery of the subject. A pulse wave is a waveform obtained by capturing the volume change of blood vessels that occurs as the heart pumps out blood, and the pulse wave measuring device 1 can monitor the volume change of blood vessels.

[0015] The housing 10 has an upper part 11, a lower part 12, and a lid part 13. The upper part 11 is a hollow box with a substantially rectangular planar shape and is open at the upper side. The lower part 12 has a substantially rectangular planar shape that is smaller than the upper part 11 and protrudes downward from the lower surface of the upper part 11. The lid part 13 closes the upper opening of the upper part 11. The lid part 13 can be removably fixed to the upper part 11 and / or the lower part 12, for example, at the four corners, by screws 70. The upper part 11, the lower part 12, and the lid part 13 can be formed from, for example, metal, resin, or the like. Note that the upper part 11 and the lower part 12 may be integrally formed or may be joined as separate bodies by an adhesive, welding, or the like.

[0016] For example, a battery or electronic components may be mounted inside the upper part 11. The electronic components mounted on the upper part 11 may include, for example, a semiconductor for signal processing that processes the signal measured by the pulse wave sensor 40 and a semiconductor for wireless communication that transmits the result of signal processing to the outside. When the pulse wave measuring device 1 is wired-connected to an external circuit or the like, a connector may be arranged on the side surface or the like of the upper part 11, or a cable may be drawn out from the side surface or the like of the upper part 11.

[0017] A through-hole 12x having a substantially circular planar shape that penetrates in the direction of arrow N is provided at substantially the center of the lower part 12. The through-hole 12x is a hole for fixing the pulse wave sensor 40, and the pulse wave sensor 40 is fixed to the lower part 12 in a state of being inserted into the through-hole 12x. Any method such as screwing or press-fitting can be used to fix the pulse wave sensor 40 to the lower part 12.

[0018] The pulse wave sensor 40 is fixed to the lower part 12 of the housing 10. Specifically, the pulse wave sensor 40 includes a strain generating body 42 (described later) in which a strain gauge 100 (described later) is arranged, and the strain generating body 42 is fixed to the housing 10 in a state where it can contact the subject. The sensor surface 40s, which is the surface of the strain generating body 42 on the subject side, is recessed in a direction away from the subject with respect to the lower surface 12a of the lower part 12, which is the surface located around the sensor surface 40s of the housing 10.

[0019] In other words, the sensor surface 40s of the pulse wave sensor 40 is recessed from the bottom surface of the housing 10 towards the base of arrow N. The amount of recess D of the sensor surface 40s from the bottom surface of the housing 10 can be, for example, about 1 mm to 2 mm when measured in the direction of arrow N. The surface of the pulse wave sensor 40 opposite to the sensor surface 40s may be contained within the lower part 12 or may protrude within the upper part 11.

[0020] The sensor surface 40s is parallel to, for example, the surface of the housing 10 located around the sensor surface 40s (the lower surface 12a of the lower part 12 of the housing 10). Here, parallelism is permitted to have an error of ±5 degrees.

[0021] The belt portion 90 includes, for example, a belt body 91, a first connecting portion 92, and a second connecting portion 93. The belt body 91 is made of, for example, resin, rubber, cloth, etc., and is elastic. By using an elastic belt body 91, it is possible to ensure sufficient pressure on the radial artery of the subject by the pulse wave sensor 40. The first connecting portion 92 and the second connecting portion 93 are members for connecting the belt body 91 to both ends of the lower portion 12 of the housing 10. The first connecting portion 92 and the second connecting portion 93 can be made of, for example, resin, rubber, etc.

[0022] In the illustrated example, one end of the belt body 91 is inserted into and fixed in a groove provided at one end of the first connecting portion 92. The other end of the first connecting portion 92 is provided with protrusions that extend from both sides of the belt body 91 in the width direction. The two protrusions of the first connecting portion 92 are pivotably attached on one axis to a pair of opposing through holes in a notch provided at one end of the lower portion 12.

[0023] Furthermore, the other end of the belt body 91 is inserted into and fixed in a groove provided at one end of the second connecting portion 93. The other end of the second connecting portion 93 is provided with protrusions that extend from both sides of the belt body 91 in the width direction. The two protrusions of the second connecting portion 93 are pivotably attached on one axis to a pair of opposing through holes in a notch provided at the other end of the lower portion 12.

[0024] The first connecting portion 92 and the second connecting portion 93 can be provided as needed. That is, the belt portion 90 may consist only of the belt body 91, with one end of the belt body 91 pivotably attached directly to one end of the lower part 12 of the housing 10, and the other end of the belt body 91 pivotably attached directly to the other end of the lower part 12 of the housing 10.

[0025] The belt body 91 may be a single continuous structure as shown in the illustrated example, or it may be composed of multiple structures. For example, it may be provided with a first belt-shaped body with one end fixed to a first connecting part 92 and a second belt-shaped body with one end fixed to a second connecting part 93, and the other end of the first belt-shaped body and the other end of the second belt-shaped body may be detachably connected by hook-and-loop fasteners or the like. In this case, the tightness applied when attaching the pulse wave measuring device 1 to the subject can be changed by adjusting the position where the other end of the first belt-shaped body and the other end of the second belt-shaped body are connected. In other words, by adjusting the length of the belt body 91, the contact between the subject's radial artery and the pulse wave sensor 40 can be improved, and a constant pressure can be maintained.

[0026] By obtaining highly accurate pulse waves with the pulse wave measurement device 1, blood glucose levels, blood pressure, etc., can be monitored. Furthermore, it becomes possible to predict conditions such as arteriosclerosis.

[0027] If, in the pulse wave measurement device 1, the sensor surface 40s of the pulse wave sensor 40 protrudes from the lower surface of the housing 10 (the lower surface 12a of the lower part 12), then when the pulse wave measurement device 1 is attached to the subject's arm, the sensor surface 40s may come into contact with the subject's arm and undergo plastic deformation, potentially making accurate measurement of the pulse wave impossible. Furthermore, because the pressing force when the pulse wave measurement device 1 is attached to the subject's arm becomes strong, the sensor surface 40s may undergo plastic deformation due to the repulsive force from the skin, muscles, blood vessels, etc. of the wrist, potentially making accurate measurement of the pulse wave impossible.

[0028] However, in the pulse wave measuring device 1 according to this embodiment, the sensor surface 40s of the pulse wave sensor 40 is recessed in a direction away from the subject with respect to the surface of the housing 10 that is located around the sensor surface 40s. As a result, when the pulse wave measuring device 1 is attached to the subject's arm, the sensor surface 40s does not come into contact with the subject's arm, and therefore there is no risk of plastic deformation of the sensor surface 40s. In addition, since the pressing force when measuring with the pulse wave measuring device 1 attached to the subject's arm does not become too strong, the repulsive force from the skin, muscles, blood vessels, etc. of the wrist can be reduced, and plastic deformation of the sensor surface 40s can be suppressed.

[0029] Furthermore, if the sensor surface 40s protrudes from the bottom surface of the housing 10 or is flush with the bottom surface of the housing 10, the sensor surface 40s is constantly in contact with the subject's skin. In contrast, with the pulse wave measuring device 1 according to this embodiment, the sensor surface 40s does not actively come into contact with the skin unless pressure is applied by tightening a belt or the like during measurement. This also contributes to the protection of the pulse wave sensor 40 and measures against metal allergies.

[0030] Furthermore, a biasing mechanism may be provided between the pulse wave sensor 40 and the lid portion 13 to bias the pulse wave sensor 40 toward the subject. The biasing mechanism may consist of, for example, only a spring, or it may include a spring and an adjustment part for adjusting the biasing force of the spring, or it may have any other configuration. By having a biasing mechanism that biases the pulse wave sensor 40 toward the subject, the sensor surface 40s of the pulse wave sensor 40 can be stably pressed against the subject's wrist.

[0031] [Pulse wave sensor 40] Figure 5 is a perspective view illustrating a pulse wave sensor according to the first embodiment. Figure 6 is a plan view illustrating a pulse wave sensor according to the first embodiment. Figure 7 is a cross-sectional view illustrating a pulse wave sensor according to the first embodiment, showing a cross-section along line AA in Figure 6. Note that Figures 5 to 7 are viewed from a different direction than Figure 4, etc. In Figure 4, the sensor surface 40s of the pulse wave sensor 40 is on the lower side, but in Figures 5 to 7 it is on the upper side.

[0032] Referring to Figures 5 to 7, the pulse wave sensor 40 comprises a housing 41, a strain generating body 42, and a strain gauge 100.

[0033] The strain generating body 42 has a base portion 42a, a beam portion 42b, a load portion 42c, and an extension portion 42d. The strain generating body 42 has a shape that is four-fold symmetrical in plan view, for example. As the material of the strain generating body 42, for example, stainless steel (SUS), copper, and aluminum can be used. However, the material of the strain generating body 42 is not limited to metal; non-metals such as glass may also be used. The strain generating body 42 is, for example, in the shape of a flat plate, and each component is integrally formed by, for example, a press working method. The thickness t of the strain generating body 42, excluding the load portion 42c, is, for example, constant. The thickness t is, for example, 0.01 mm or more and 0.25 mm or less.

[0034] In the explanation of the pulse wave sensor 40 in Figures 5 to 7, for convenience, the side of the strain generating body 42 on which the load portion 42c is provided will be referred to as the "upper side," and the side on which the load portion 42c is not provided will be referred to as the "lower side." Also, the surface located above each part will be referred to as the "upper surface," and the surface located below each part will be referred to as the "lower surface." However, the pulse wave sensor 40 can be used upside down. Also, the pulse wave sensor 40 can be positioned at any angle. Furthermore, a planar view refers to viewing the object in the direction of the normal from above to below with respect to the sensor surface 40s of the strain generating body 42. And the planar shape refers to the shape of the object when viewed in the aforementioned normal direction.

[0035] In the pulse wave sensor 40, the housing 41 is the part that holds the strain generating body 42. The housing 41 is cylindrical, with the bottom side closed and the top side open. The housing 41 can be made of, for example, metal or resin. A roughly disc-shaped strain generating body 42 is fixed to the housing 41 with adhesive or the like so as to close the opening on the top side. The strain generating body 42 is the part that detects pulse waves and has a strain gauge 100 positioned on it.

[0036] In the strain generating body 42, the base portion 42a is the circular frame-shaped (ring-shaped) region outside the circular dashed line shown in Figures 5 and 6. The region inside the circular dashed line is sometimes referred to as the circular opening. In other words, the base portion 42a of the strain generating body 42 has a circular opening. The width w1 of the base portion 42a is, for example, 1 mm or more and 5 mm or less. The inner diameter d of the base portion 42a (i.e., the diameter of the circular opening) is, for example, 5 mm or more and 40 mm or less.

[0037] The beam section 42b is provided so as to bridge the inside of the base section 42a. The beam section 42b has, for example, two beams that intersect in a cross shape in a plan view, and the region where the two beams intersect includes the center of the circular opening. In the example of Figure 6, one beam forming the cross has its longitudinal direction in the X direction, and the other beam forming the cross has its longitudinal direction in the Y direction, and the two are orthogonal. It is preferable that each of the two orthogonal beams is located inside the inner diameter d (diameter of the circular opening) of the base section 42a and is as long as possible. In other words, it is preferable that the length of each beam is approximately equal to the diameter of the circular opening. In each beam forming the beam section 42b, the width w2 outside the intersecting region is constant, for example, 1 mm or more and 5 mm or less. It is not essential that the width w2 is constant, but it is preferable that the width w2 is constant so that strain can be detected linearly.

[0038] The load-bearing portion 42c is provided on the beam portion 42b. The load-bearing portion 42c is provided, for example, in the region where two beams constituting the beam portion 42b intersect. The load-bearing portion 42c protrudes from the upper surface of the beam portion 42b. The amount of protrusion of the load-bearing portion 42c relative to the upper surface of the beam portion 42b is, for example, about 0.1 mm. The beam portion 42b is flexible and elastically deforms when a load is applied to the load-bearing portion 42c.

[0039] The four extensions 42d are fan-shaped portions that extend from the inside of the base 42a toward the beam 42b in a plan view. A gap of about 1 mm is provided between each extension 42d and the beam 42b. If this gap is set to, for example, 0.05 to 0.2 mm, it is possible to prevent contamination from entering the housing 41 from the outside. The extensions 42d do not contribute to the sensing of the pulse wave sensor 40 and therefore do not need to be provided. The pulse wave sensor 40 has a shielded cable, a flexible circuit board, etc. (not shown) for inputting and outputting electrical signals to and from the outside.

[0040] The sensor surface 40s of the strain generating body 42 is composed of the upper surface of the base portion 42a, the upper surface of the beam portion 42b, and the upper surface of the extension portion 42d. The load portion 42c protrudes from the sensor surface 40s. The sensor surface 40s is, for example, a flat surface.

[0041] The strain gauge 100 is provided on the strain generating body 42. The strain gauge 100 can be provided, for example, on the lower surface of the beam portion 42b. Since the beam portion 42b 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.

[0042] Two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the X direction that is closer to the load section 42c (towards the center of the circular opening), facing each other in a plan view, with the load section 42c in between. The other two of the four strain gauges 100 are positioned on the side of the beam with its longitudinal direction in the Y direction that is closer to the base section 42a, facing each other in a plan view, with the load section 42c in between. This arrangement allows for effective detection of compressive and tensile forces, enabling greater output from the full bridge.

[0043] The pulse wave sensor 40 is used by fixing it to the subject's arm so that the load portion 42c is in contact with the subject's radial artery. When a load is applied to the load portion 42c in response to the subject's pulse wave, causing the beam portion 42b to elastically deform, the resistance value of the resistor of the strain gauge 100 changes. The pulse wave sensor 40 can detect the pulse wave based on the change in the resistance value of the resistor of the strain gauge 100 accompanying the deformation of the beam portion 42b. The pulse wave is output, for example, as a periodic change in voltage from a measurement circuit connected to the electrodes of the strain gauge 100.

[0044] [Strain Gauge 100] Figure 8 is a plan view illustrating a strain gauge according to the first embodiment. Figure 9 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 8. Referring to Figures 8 and 9, the strain gauge 100 includes a base material 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. In Figure 8, for convenience, only the outer edge of the cover layer 160 is shown with a dashed line. The cover layer 160 can be provided as needed.

[0045] In the explanation of the strain gauge 100 in Figures 8 and 9, for convenience, the side of the base material 110 on which the resistor 130 is provided will be referred to as the "upper side," and the side on which the resistor 130 is not provided will be referred to as the "lower side." Also, the surface located above each part will be referred to as the "upper surface," and the surface located below each part will be 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. For example, in Figure 7, the strain gauge 100 is attached to the beam section 42b in an inverted state compared to Figure 9. That is, the base material 110 in Figure 9 is attached to the lower surface of the beam section 42b with adhesive or the like. Also, a plan view refers to viewing the object in the direction of the normal from the top to the bottom with respect to the upper surface 110a of the base material 110. Furthermore, the planar shape refers to the shape of the object when viewed in the direction of the normal vector.

[0046] 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 outer surface of the strain generating body 42 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.

[0047] 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.

[0048] 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.

[0049] 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 is used, an insulating film is provided on the metallic substrate 110.

[0050] 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. For convenience, in Figure 8, the resistor 130 is shown with a dark, textured pattern.

[0051] 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 8), and the ends of adjacent elongated sections are connected alternately, so that the whole structure folds back 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 8).

[0052] 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.

[0053] 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).

[0054] Here, a Cr multiphase film is a film in which Cr, CrN, and Cr2N are mixed together. The Cr multiphase film may contain unavoidable impurities such as chromium oxide.

[0055] 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 crystal 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.

[0056] 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.

[0057] 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).

[0058] 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.

[0059] 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, 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, the ceramicization of the resistor 130 can be reduced. Therefore, brittle fracture of the resistor 130 can be made less likely.

[0060] On the other hand, CrN also 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.

[0061] 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. For convenience, in Figure 8, the wiring 140 is shown with a textured surface that is thinner than the resistor 130.

[0062] 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 substantially 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 8, for convenience, the electrode 150 is shown with the same textured pattern as the wiring 140.

[0063] The cover layer 160 is provided on the substrate 110 as needed. The cover layer 160 is provided on the upper surface 110a of the substrate 110 so as to cover the resistor 130 and wiring 140 and expose 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 about 2 μm to 30 μm. By providing the cover layer 160, mechanical damage to the resistor 130 can be suppressed. In addition, by providing the cover layer 160, the resistor 130 can be protected from moisture and the like.

[0064] 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.

[0065] Therefore, the strain gauge 100, which uses a Cr multiphase film as the material for the resistor 130, is particularly suitable for use in a pulse wave measuring device 1 that needs to be positioned in a narrow area of ​​the strain generating body 42 and that needs to detect extremely minute fluctuations occurring in the radial artery. Furthermore, the strain gauge 100, which uses a Cr multiphase film as the material for the resistor 130, has higher resistance than conventional strain gauges. Therefore, when powered by a battery, it is possible to reduce power consumption and extend battery life.

[0066] [Method of manufacturing strain gauges] 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.

[0067] 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, or pulsed laser deposition instead of magnetron sputtering.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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.

[0072] Figure 10 is a cross-sectional view (part 2) illustrating a strain gauge according to the first embodiment. Figure 10 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.

[0073] 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.

[0074] Next, the metal layer A is patterned using photolithography to form the planar resistor 130, two wirings 140, and two electrodes 150 shown in Figure 8.

[0075] After forming the resistor 130, wiring 140, and electrode 150, a cover layer 160 may be formed on the upper surface 110a of the base material 110. 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.

[0076] Although preferred embodiments have been described in detail above, the invention is not limited to the embodiments described above, and various modifications and substitutions can be made to the embodiments described above without departing from the scope of the claims. [Explanation of symbols]

[0077] 1 Pulse wave measuring device, 10 Housing, 11 Top, 12 Bottom, 12a Bottom surface, 12x Through hole, 13 Cover, 40 Pulse wave sensor, 41 Housing, 42 Strain generating body, 42a Base, 42b Beam, 42c Load part, 42d Stretching part, 40s Sensor surface, 70 Screw, 90 Belt part, 91 Belt body, 92 First connection part, 93 Second connection part, 100 Strain gauge, 110 Base material, 110a Top surface, 130 Resistor, 130e1, 130e2 Termination, 140 Wiring, 150 Electrode, 160 Cover layer

Claims

1. A pulse wave measuring device that can be worn on a subject, The casing and The housing includes a pulse wave sensor fixed to the housing, The pulse wave sensor comprises a strain generating body on which strain gauges are arranged, and the strain generating body is fixed to the housing in a manner that allows it to come into contact with the subject. The sensor surface, which is the side of the strain-generating body facing the subject, is located around the sensor surface and is recessed in a direction away from the subject relative to the lower surface of the housing that can contact the subject. The strain-generating body is A base with a circular opening, A flat plate-shaped beam portion that bridges the inside of the base, The beam portion is provided and has a load portion that protrudes from a surface that constitutes a part of the sensor surface of the beam portion, A pulse wave is detected based on the change in the resistance value of the strain gauge accompanying the deformation of the strain-generating body. The aforementioned beam section has two beams that intersect in a cross shape in a plan view. The region where the beams intersect includes the center of the circular opening, The load-bearing section is provided in the region where the beams intersect. The aforementioned strain gauge is equipped with four of the above-mentioned strain gauges. Two of the four strain gauges are positioned on the beam, whose longitudinal direction is the first direction, so as to face each other in a plan view, with the load portion in between. A pulse wave measuring device in which the other two of the four strain gauges are arranged on the beam, whose longitudinal direction is perpendicular to the first direction, so as to face the load section in a plan view.

2. The pulse wave measuring device according to claim 1, wherein the sensor surface is planar.

3. The pulse wave measuring device according to claim 2, wherein the sensor surface is parallel to the lower surface of the housing.

4. It has a strip-shaped body with one end connected to one side of the housing and the other end connected to the other side of the housing, The pulse wave measuring device according to any one of claims 1 to 3, wherein the band-shaped body is stretchable.

5. Two of the four strain gauges are arranged on the side of the beam with the first direction as the longitudinal direction that is closer to the load portion, so as to face each other in a plan view, with the load portion in between. The pulse wave measuring device according to any one of claims 1 to 4, wherein the other two of the four strain gauges are arranged on the side of the beam with the second direction as its longitudinal direction, closer to the base, so as to face each other in a plan view, sandwiching the load portion.

6. The pulse wave measuring device according to any one of claims 1 to 5, wherein the strain gauge has a resistor formed from a Cr multiphase film.

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