JP2023111693A - Pulse wave measuring apparatus - Google Patents

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

The present invention relates to a pulse wave measuring device.

2. Description of the Related Art A pulse wave sensor is known that detects a pulse wave generated as the heart pumps out blood. One example is a pulse wave sensor provided with a pressure-receiving plate serving as a strain-generating body supported flexibly by the action of an external force, and piezoelectric conversion means for converting the flexure of the pressure-receiving plate into an electrical signal. In this pulse wave sensor, the flexible region of the pressure receiving plate is formed in a dome shape with a convex curved surface facing outward, and a pressure detecting element is provided on the inner surface of the top of the pressure receiving plate as piezoelectric conversion means (for example, , see Patent Document 1).

Japanese Unexamined Patent Application Publication No. 2002-78689

Since a pulse wave sensor needs to detect minute signals, a pulse wave measuring device using a pulse wave sensor needs to bring the pulse wave sensor into close contact with the subject in order to improve measurement accuracy.

However, in the above-described pulse wave sensor, the pressure receiving plate is made of a material such as SUS or copper and is formed with a thickness of several tens of μm to several hundreds of μm. , there is a risk of plastic deformation due to the repulsive force from blood vessels.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a pulse wave measuring device capable of suppressing plastic deformation of a pulse wave sensor.

The present pulse wave measuring device is a pulse wave measuring device that can be worn by a subject, and has a housing and a pulse wave sensor fixed to the housing, and the pulse wave sensor is provided with a strain gauge. The strain body is fixed to the housing in a state in which the strain body can contact the subject, and the sensor surface, which is the subject side surface of the strain body, is the sensor of the housing. It is recessed in the direction away from the subject with respect to the surface positioned around the surface.

According to the disclosed technique, it is possible to provide a pulse wave measuring device capable of suppressing plastic deformation of the pulse wave sensor.

1 is a perspective view illustrating a pulse wave measuring device according to a first embodiment; FIG. 1 is a front side perspective view illustrating a pulse wave measuring device according to a first embodiment; FIG. FIG. 2 is a back side perspective view illustrating the pulse wave measuring device according to the first embodiment; 1 is a side view illustrating a pulse wave measuring device according to a first embodiment; FIG. 1 is a perspective view illustrating a pulse wave sensor according to a first embodiment; FIG. 1 is a plan view illustrating a pulse wave sensor according to a first embodiment; FIG. 1 is a cross-sectional view illustrating a pulse wave sensor according to a first embodiment; FIG. 1 is a plan view illustrating a strain gauge according to a first embodiment; FIG. 1 is a cross-sectional view (part 1) illustrating a strain gauge according to a first embodiment; FIG. FIG. 2 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings. In each drawing, the same components are denoted by the same reference numerals, and redundant description may be omitted.

<First embodiment>
[Pulse wave measuring device 1]
FIG. 1 is a perspective view illustrating the pulse wave measuring device according to the first embodiment, showing how the pulse wave measuring device is worn on 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;

An arrow N in FIG. 4 indicates the normal direction of the sensor surface 40 s of the pulse wave sensor 40 . 1 to 4, for the sake of convenience, the starting point (root) side of the arrow N will be referred to as the "upper side", and the ending point (arrowhead) side of the arrow N will be referred to as the "lower side". Further, the surface located above each part is called "upper surface", and the surface located below each part is called "lower surface". However, the pulse wave measuring device 1 can also be used upside down. Also, the pulse wave measuring device 1 can be arranged at any angle. In addition, the term “planar view” refers to viewing an object in the direction of the arrow N. As shown in FIG. The planar shape refers to the shape of the object when the object is viewed in the direction of the arrow N. As shown in FIG.

With reference 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. ing.

The pulse wave measuring device 1 is worn on the subject's wrist, for example, so that the pulse wave sensor 40 is placed near the subject's radial artery. A pulse wave is a waveform obtained by capturing a change in the volume of a blood vessel that occurs as the heart pumps out blood, and the pulse wave measurement device 1 can monitor the change in the volume of the blood vessel.

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

For example, a battery or electronic components may be mounted inside the upper portion 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, or a semiconductor for wireless communication that transmits the result of signal processing to the outside. When pulse wave measuring device 1 and an external circuit or the like are connected by wire, a connector may be arranged on the side surface of upper portion 11 or the like, or a cable may be pulled out from the side surface of upper portion 11 or the like.

A through-hole 12x having a substantially circular planar shape and penetrating in the direction of the arrow N is provided in substantially the center of the lower portion 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 portion 12 while 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 and the lower part 12 together.

Pulse wave sensor 40 is fixed to lower portion 12 of housing 10 . Specifically, the pulse wave sensor 40 includes a strain body 42 (described later) in which a strain gauge 100 (described later) is arranged. there is The sensor surface 40s, which is the subject-side surface of the strain body 42, is recessed in the direction away from the subject with respect to the lower surface 12a of the lower portion 12, which is the surface positioned around the sensor surface 40s of the housing 10. FIG.

That is, the sensor surface 40s of the pulse wave sensor 40 is recessed toward the base of the arrow N from the lower surface of the housing 10 . The recess amount D of the sensor surface 40s from the lower surface of the housing 10 can be, for example, about 1 mm or more and 2 mm or less when measured in the arrow N direction. In addition, the surface of the pulse wave sensor 40 opposite to the sensor surface 40 s may be accommodated in the lower portion 12 or protrude into the upper portion 11 .

Note that the sensor surface 40s is, for example, parallel to a surface located around the sensor surface 40s of the housing 10 (the lower surface 12a of the lower portion 12 of the housing 10). The parallelism here allows an error of ±5 degrees.

The belt portion 90 has, for example, a belt body 91 , a first connection portion 92 and a second connection portion 93 . The belt main body 91 is made of, for example, resin, rubber, cloth, or the like, and has elasticity. By using the stretchable belt body 91, it is possible to ensure the pressing force of the pulse wave sensor 40 on the subject's radial artery. The first connection portion 92 and the second connection 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 resin, rubber, or the like, for example.

In the illustrated example, one end of the belt body 91 is inserted into and fixed to a groove provided at one end of the first connection portion 92 . The other end of the first connection portion 92 is provided with protrusions that protrude on both sides in the width direction of the belt body 91 . The two protrusions of the first connecting portion 92 are attached to a pair of opposed through holes of a notch provided on one end side of the lower portion 12 so as to be uniaxially swingable.

The other end of the belt main body 91 is inserted into a groove provided at one end of the second connection portion 93 and fixed. The other end of the second connection portion 93 is provided with protrusions that protrude on both sides in the width direction of the belt body 91 . The two protrusions of the second connection portion 93 are attached to a pair of opposing through holes of a cut portion provided on the other end side of the lower portion 12 so as to be uniaxially swingable.

The first connecting portion 92 and the second connecting portion 93 can be provided as required. That is, the belt portion 90 is composed only of the belt body 91 , one end of the belt body 91 is directly attached to one end of the lower portion 12 of the housing 10 so as to be swingable, and the other end of the belt body 91 is directly attached to the lower portion 12 of the housing 10 . It may be attached to the other end of the so as to be swingable.

The belt body 91 may be a single continuous structure as in the illustrated example, or may be composed of a plurality of structures. For example, a first strip having one end fixed to the first connecting portion 92 and a second strip having one end fixed to the second connecting portion 93 are provided, and the other end of the first strip and the second strip are provided. may be detachably connected to the other end of the terminal by means of a hook-and-loop fastener or the like. In this case, depending on the position where the other end of the first band-shaped body and the other end of the second band-shaped body are connected, the tightening strength when attaching the pulse wave measuring device 1 to the subject can be changed. In other words, by adjusting the length of the belt main body 91, the adhesion between the subject's radial artery and the pulse wave sensor 40 can be improved, and a constant pressure can be continuously applied.

By obtaining highly accurate pulse waves with the pulse wave measuring device 1, it is possible to monitor blood sugar levels, blood pressure, and the like. In addition, it becomes possible to predict arteriosclerosis and the like.

If, in the pulse wave measuring device 1, the sensor surface 40s of the pulse wave sensor 40 protrudes from the lower surface of the housing 10 (lower surface 12a of the lower part 12), the pulse wave measuring device 1 is worn on the arm of the subject. At that time, the sensor surface 40s may contact the subject's arm and be plastically deformed, making it impossible to accurately measure the pulse wave. In addition, since the pressing force when the pulse wave measuring device 1 is attached to the subject's arm for measurement is increased, the sensor surface 40s is plastically deformed by the repulsive force from the skin, muscles, blood vessels, etc. of the wrist, and the pulse wave is measured. Accurate measurements may not be possible.

However, in the pulse wave measuring device 1 according to the present embodiment, the sensor surface 40s of the pulse wave sensor 40 is recessed in the direction away from the subject with respect to the surfaces of the housing 10 located around the sensor surface 40s. Accordingly, when the pulse wave measuring device 1 is worn on the subject's arm, the sensor surface 40s does not come into contact with the subject's arm, so there is no risk of plastic deformation of the sensor surface 40s. In addition, since the pressing force when the pulse wave measuring device 1 is attached to the subject's arm and measured is not too strong, the repulsive force from the skin, muscles, blood vessels, etc. of the wrist can be reduced, and the sensor surface 40s is plastically deformed. can be suppressed.

Furthermore, if the sensor surface 40s protrudes from the lower surface of the housing 10 or is flush with the lower surface of the housing 10, the sensor surface 40s and the subject's skin are always in contact. According to the pulse wave measuring device 1 according to the embodiment, the sensor surface 40s does not actively touch the skin unless pressure is applied by tightening a belt or the like during measurement. Therefore, it leads to protection of the pulse wave sensor 40 and countermeasure against metal allergy.

A biasing mechanism that biases the pulse wave sensor 40 toward the subject may be provided between the pulse wave sensor 40 and the lid portion 13 . For example, the urging mechanism may be composed only of a spring, may be configured to include a spring and an adjustment section for adjusting the urging force of the spring, or may be configured in some other manner. By having an urging mechanism that urges 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.

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

5 to 7, the pulse wave sensor 40 has a housing 41, a strain body 42, and a strain gauge 100. FIG.

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

In the description of the pulse wave sensor 40 in FIGS. 5 to 7, for convenience, the side of the strain-generating body 42 on which the load portion 42c is provided is referred to as the [upper side], and the side on which the load portion 42c is not provided is referred to as " called "lower side". Further, the surface located above each part is called "upper surface", and the surface located below each part is called "lower surface". However, the pulse wave sensor 40 can be used upside down. Also, the pulse wave sensor 40 can be arranged at any angle. Further, the term "planar view" refers to viewing an object in the direction normal to the sensor surface 40s of the strain-generating body 42 from the upper side to the lower side. The planar shape refers to the shape of the object when the object is viewed in the normal direction.

In pulse wave sensor 40 , housing 41 is a portion that holds strain-generating body 42 . The housing 41 is cylindrical, closed on the bottom side and open on the top side. The housing 41 can be made of metal, resin, or the like, for example. A substantially disk-shaped strain-generating body 42 is fixed with an adhesive or the like so as to block the opening on the upper surface side of the housing 41 . The strain-generating body 42 is a portion where the strain gauge 100 is arranged and which detects a pulse wave.

In the strain generating body 42, the base portion 42a is a circular frame-shaped (ring-shaped) region outside the circular dashed line shown in FIGS. Note that the area inside the circular dashed line may be referred to as a circular opening. That is, 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 (that is, the diameter of the circular opening) is, for example, 5 mm or more and 40 mm or less.

The beam portion 42b is provided so as to bridge the inside of the base portion 42a. The beam portion 42b has, for example, two beams that intersect in a cross shape in a plan view, and the intersecting area of the two beams includes the center of the circular opening. In the example of FIG. 6, one beam forming the cross has its longitudinal direction in the X direction, and another beam forming the cross has its longitudinal direction in the Y direction, and they are orthogonal to each other. Each of the two orthogonal beams is preferably inside the inner diameter d (the diameter of the circular opening) of the base 42a and is as long as possible. That is, the length of each beam is preferably approximately equal to the diameter of the circular opening. The width _w2 of each beam constituting the beam portion 42b is constant except for the intersecting region, and is, for example, 1 mm or more and 5 mm or less. Although it is not essential that the width _w2 is constant, it is preferable in that the strain can be detected linearly by making the width _w2 constant.

The load portion 42c is provided on the beam portion 42b. The load portion 42c is provided, for example, in an area where two beams forming the beam portion 42b intersect. The load portion 42c protrudes from the upper surface of the beam portion 42b. The amount of protrusion of the load portion 42c based on 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 portion 42c.

The four extending portions 42d are fan-shaped portions extending from the inside of the base portion 42a toward the beam portion 42b in plan view. A gap of about 1 mm is provided between each extending portion 42d and beam portion 42b. If the gap is set to, for example, about 0.05 to 0.2 mm, it is possible to prevent contaminants from entering the housing 41 from the outside. The extending portion 42d does not contribute to the sensing of the pulse wave sensor 40, so it does not have to be provided. The pulse wave sensor 40 has a shielded cable, a flexible substrate, and the like (not shown) for inputting and outputting electrical signals with the outside.

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 plane.

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 side of the beam portion 42b. Since the beam portion 42b has a flat plate shape, the strain gauge can be easily attached. One or more strain gauges 100 may be provided, but four strain gauges 100 are provided in this embodiment. By providing four strain gauges 100, strain can be detected by a full bridge.

Two of the four strain gauges 100 are arranged so as to face the load portion 42c in plan view on the side near the load portion 42c of the beam whose longitudinal direction is the X direction (center side of the circular opening). are placed. The other two of the four strain gauges 100 are arranged on the side near the base portion 42a of the beam whose longitudinal direction is the Y direction so as to face each other across the load portion 42c in plan view. Such an arrangement allows effective detection of compressive and tensile forces to provide greater power output from the full bridge.

The pulse wave sensor 40 is used by being fixed to the subject's arm so that the load portion 42c contacts the subject's radial artery. When a load is applied to the load portion 42c according to the subject's pulse wave and the beam portion 42b is elastically deformed, the resistance value of the resistor of the strain gauge 100 changes. The pulse wave sensor 40 can detect a pulse wave based on a change in the resistance value of the resistor of the strain gauge 100 accompanying deformation of the beam portion 42b. A pulse wave is output as a periodic change in voltage from a measurement circuit connected to the electrodes of the strain gauge 100, for example.

[Strain gauge 100]
FIG. 8 is a plan view illustrating a strain gauge according to the first embodiment; FIG. FIG. 9 is a cross-sectional view (part 1) illustrating the strain gauge according to the first embodiment, showing a cross section along line BB in FIG. 8 and 9, the strain gauge 100 has a substrate 110, a resistor 130, wiring 140, electrodes 150, and a cover layer 160. As shown in FIG. In addition, in FIG. 8, only the outer edge of the cover layer 160 is shown with a dashed line for convenience. Note that the cover layer 160 can be provided as necessary.

8 and 9, in the strain gauge 100, the side of the base material 110 on which the resistor 130 is provided is referred to as the "upper side" for convenience, and the resistor 130 is not provided. The side will be referred to as the "lower side". Further, the surface located above each part is called "upper surface", and the surface located below each part is called "lower surface". However, the strain gauge 100 can also be used upside down. Also, the strain gauge 100 can be arranged at any angle. For example, in FIG. 7, the strain gauge 100 is affixed to the beam portion 42b in a state inverted from that in FIG. That is, the base material 110 in FIG. 9 is attached to the lower surface of the beam portion 42b with an adhesive or the like. In addition, the term “planar view” refers to viewing an object in the normal direction from the upper side to the lower side with respect to the upper surface 110a of the base material 110 . The planar shape refers to the shape of the object when the object is viewed in the normal direction.

The base material 110 is a member that serves as a base layer for forming the resistor 130 and the like. Base material 110 has flexibility. The thickness of the base material 110 is not particularly limited, and may be appropriately determined according to the purpose of use of the strain gauge 100 or the like. For example, the thickness of the base material 110 may be about 5 μm to 500 μm. Considering the transmission of strain from the outer surface of the strain-generating body 42 to the sensing part and the dimensional stability against environmental changes, the thickness of the base material 110 should be in the range of 5 μm to 200 μm. preferable. Moreover, from the viewpoint of insulation, the thickness of the base material 110 is preferably 10 μm or more.

The substrate 110 is made of, for example, PI (polyimide) resin, epoxy resin, PEEK (polyetheretherketone) resin, PEN (polyethylene naphthalate) resin, PET (polyethylene terephthalate) resin, PPS (polyphenylene sulfide) resin, LCP (liquid crystal It is formed from an insulating resin film such as polymer) resin, polyolefin resin, or the like. In addition, the film refers to a member having a thickness of about 500 μm or less and having flexibility.

When the base material 110 is formed of an insulating resin film, the insulating resin film may contain fillers, impurities, and the like. For example, the base material 110 may be formed from an insulating resin film containing filler such as silica or alumina.

Materials other than the resin of the base material 110 include, for example, SiO ₂ , ZrO ₂ (including YSZ), Si, Si ₂ N ₃ , Al ₂ O ₃ (including sapphire), ZnO, perovskite ceramics (CaTiO ₃ , crystalline materials such as BaTiO ₃ ). In addition to the crystalline material described above, amorphous glass or the like may be used as the material of the base material 110 . As the material of the base material 110, a metal such as aluminum, an aluminum alloy (duralumin), or titanium may be used. When using metal, an insulating film is provided on the base material 110 made of metal.

The resistor 130 is a thin film formed in a predetermined pattern on the upper side of the base material 110 . In the strain gauge 100, the resistor 130 is a sensing part that receives strain and produces a resistance change. The resistor 130 may be formed directly on the upper surface 110a of the base material 110, or may be formed on the upper surface 110a of the base material 110 via another layer. In addition, in FIG. 8, the resistor 130 is shown with a dark pear-skin pattern for the sake of convenience.

In the resistor 130, a plurality of elongated portions are arranged in the same longitudinal direction (the X direction in the example of FIG. 8) at predetermined intervals, and the ends of adjacent elongated portions are alternately connected to form an overall structure. It is a structure that folds in a zigzag as The longitudinal direction of the plurality of elongated portions is the grid direction, and the direction perpendicular to the grid direction is the grid width direction (the Y direction in the example of FIG. 8).

In the resistor 130, the X− side end of the elongated portion located closest to the Y+ side is bent in the Y+ direction and reaches one end _130e1 of the resistor 130 in the grid width direction. Also, the X-side end of the elongated portion located closest to the Y-side bends in the Y-direction and reaches the other end _130e2 of the resistor 130 in the grid direction. Each termination 130e ₁ and 130e ₂ is electrically connected to an electrode 150 via a wire 140 . In other words, the wiring 140 electrically connects the ends 130e ₁ and 130e ₂ of the resistor 130 in the grid width direction and each electrode 150 .

The resistor 130 can be made of, 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 made of a material containing at least one of Cr and Ni. Materials containing Cr include, for example, a Cr mixed phase film. Materials containing Ni include, for example, Cu—Ni (copper nickel). Materials containing both Cr and Ni include, for example, Ni—Cr (nickel chromium).

Here, the Cr mixed phase film is a film in which Cr, CrN, Cr ₂ N and the like are mixed. The Cr mixed phase film may contain unavoidable impurities such as chromium oxide.

The thickness of the resistor 130 is not particularly limited, and may be appropriately determined according to the purpose of use of the strain gauge 100 or the like. For example, the thickness of the resistor 130 may be about 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 (for example, the crystallinity of α-Cr) forming the resistor 130 is improved. In addition, when the thickness of the resistor 130 is 1 μm or less, (i) cracks in the film and (ii) warpage of the film from the base material 110 due to internal stress of the film constituting the resistor 130 are reduced. be done.

In consideration of making it difficult for lateral sensitivity to occur and taking measures against disconnection, the width of the resistor 130 is preferably 10 μm or more and 100 μm or less. Furthermore, the width of the resistor 130 is preferably 10 μm or more and 70 μm or less, more preferably 10 μm or more and 50 μm or less.

For example, when the resistor 130 is a Cr mixed phase film, the stability of gauge characteristics can be improved by using α-Cr (alpha chromium), which is a stable crystal phase, as the main component. Further, for example, when the resistor 130 is a Cr mixed phase film, the strain gauge 100 has a gauge factor of 10 or more and a gauge factor temperature coefficient TCS and a resistance temperature coefficient TCR by making the resistor 130 mainly composed of α-Cr. can be in the range of -1000 ppm/°C to +1000 ppm/°C. Here, the "main component" means a component that accounts for 50% by weight or more of the total substance constituting the resistor. From the viewpoint of improving gauge characteristics, the resistor 130 preferably contains 80% by weight or more of α-Cr. Furthermore, from the same point of view, it is 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).

Also, when the resistor 130 is a Cr mixed phase film, CrN and Cr ₂ N contained in the Cr mixed phase film are preferably 20% by weight or less. When CrN and Cr ₂ N contained in the Cr mixed phase film are 20% by weight or less, a decrease in the gauge factor of the strain gauge 100 can be suppressed.

Also, the ratio of CrN and Cr ₂ N in the Cr mixed phase film is preferably such that the ratio of Cr ₂ N is 80% by weight or more and less than 90% by weight with respect to the total weight of CrN and Cr ₂ N. . More preferably, the ratio of Cr ₂ N to the total weight of CrN and Cr ₂ N is 90% by weight or more and less than 95% by weight. Cr ₂ N has semiconducting properties. Therefore, by setting the ratio of Cr ₂ N to 90% by weight or more and less than 95% by weight, the decrease in TCR (negative TCR) becomes even more pronounced. Furthermore, by setting the ratio of Cr ₂ N to 90% by weight or more and less than 95% by weight, it is possible to reduce the use of ceramics in the resistor 130 . Therefore, brittle fracture of the resistor 130 can be made difficult to occur.

On the other hand, CrN also has the advantage of being chemically stable. By including more CrN in the Cr mixed phase film, the possibility of generating unstable N can be reduced, so a stable strain gauge can be obtained. Here, “unstable N” means a trace amount of N ₂ or atomic N that may exist in the Cr mixed-phase film. These unstable N may leak out of the film depending on the external environment (for example, high temperature environment). When unstable N escapes out of the film, the film stress of the Cr mixed phase film can change.

The wiring 140 is provided on the base material 110 . The wiring 140 is electrically connected with the resistor 130 and the electrode 150 . The wiring 140 is not limited to a straight line, and may have any pattern. Also, the wiring 140 can be of any width and any length. In addition, in FIG. 8, the wiring 140 is shown with a pear-skin pattern that is thinner than the resistor 130 for the sake of convenience.

Electrode 150 is provided on substrate 110 . Electrode 150 is electrically connected to resistor 130 via wiring 140 . The electrode 150 is wider than the wiring 140 and formed in a substantially rectangular shape in plan view. The electrodes 150 are a pair of electrodes for outputting to the outside the change in the resistance value of the resistor 130 caused by strain. A lead wire for external connection, for example, is joined to the electrode 150 . A metal layer with low resistance such as copper or a metal layer with good solderability such as gold may be laminated on the upper surface of the electrode 150 . Although the resistor 130, the wiring 140, and the electrode 150 are given different symbols for convenience, they can be integrally formed from the same material in the same process. In FIG. 8, the electrodes 150 are shown in the same pear-skin pattern as the wiring 140 for the sake of convenience.

A cover layer 160 is optionally provided on the substrate 110 . The cover layer 160 is provided on the upper surface 110 a of the base material 110 so as to cover the resistors 130 and the wirings 140 and expose the electrodes 150 . Examples of materials for the cover layer 160 include insulating resins such as PI resins, epoxy resins, PEEK resins, PEN resins, PET resins, PPS resins, and composite resins (eg, silicone resins and polyolefin resins). Note that the cover layer 160 may contain a filler or a pigment. 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, it is possible to prevent the resistor 130 from being mechanically damaged. Also, by providing the cover layer 160, the resistor 130 can be protected from moisture and the like.

In the strain gauge 100, when a Cr mixed phase film is used as the material of the resistor 130, it is possible to achieve high sensitivity and miniaturization. For example, while the output of a conventional strain gauge was about 0.04 mV/2 V, when a Cr mixed phase film is used as the material of the resistor 130, an output of 0.3 mV/2 V or more can be obtained. . In addition, while the size of the conventional strain gauge (gauge length x gauge width) was about 3 mm x 3 mm, the size (gauge length x gauge width) can be reduced to about 0.3 mm×0.3 mm.

Therefore, the strain gauge 100 using a Cr mixed-phase film as the material of the resistor 130 must be arranged in a narrow portion of the strain-generating body 42, and it is necessary to detect extremely minute fluctuations occurring in the radial artery. It can be used particularly preferably for the measuring device 1 . Moreover, the strain gauge 100 using a Cr mixed phase film as the material of the resistor 130 has a higher resistance than the conventional strain gauge. Therefore, when driven by a battery, power consumption can be reduced, and the battery life can be extended.

[Manufacturing method of strain gauge]
A method of manufacturing the strain gauge 100 will be described below. In order to manufacture the strain gauge 100 , first, the base material 110 is prepared, and a metal layer (referred to as metal layer A for convenience) is formed on the upper surface 110 a of the base material 110 . The metal layer A is a layer that is finally patterned to become the resistor 130 , the wiring 140 and the electrode 150 . Therefore, the material and thickness of the metal layer A are the same as those of the resistor 130, the wiring 140, and the electrode 150 described above.

The metal layer A can be formed, for example, by magnetron sputtering using a raw material capable of forming the metal layer A as a target. The metal layer A may be formed using a reactive sputtering method, a vapor deposition method, an arc ion plating method, a pulse laser deposition method, or the like instead of the magnetron sputtering method.

Note that the metal layer A may be formed after forming a base layer on the upper surface 110a of the base material 110 . For example, on the upper surface 110a of the substrate 110, a functional layer having a predetermined film thickness may be vacuum-formed by conventional sputtering. By providing the base layer in this manner, the gauge characteristics of the strain gauge 100 can be stabilized.

In the present application, the functional layer refers to a layer having a function of promoting crystal growth of at least the upper metal layer A (resistor 130). The functional layer further has a function of preventing oxidation of the metal layer A due to oxygen or moisture contained in the base material 110 and/or a function of improving adhesion between the base material 110 and the metal layer A. is preferred. The functional layer may also have other functions.

The insulating resin film forming the base material 110 may contain oxygen and moisture, and Cr may form a self-oxidized film. Therefore, especially when the metal layer A contains Cr, it is preferable to form a functional layer having a function of preventing the metal layer A from being oxidized.

In this way, by providing the functional layer under the metal layer A, it becomes possible to promote the crystal growth of the metal layer A, and the metal layer A having a stable crystal phase can be produced. As a result, in the strain gauge 100, the stability of gauge characteristics is improved. In addition, the material forming the functional layer diffuses into the metal layer A, so that the gauge characteristics of the strain gauge 100 are improved.

FIG. 10 is a cross-sectional view (part 2) illustrating the strain gauge according to the first embodiment. FIG. 10 shows the cross-sectional shape of the strain gauge 100 when the functional layer 120 is provided as a base layer for the resistor 130, the wiring 140, and the electrode 150. FIG.

The planar shape of the functional layer 120 may be patterned to be substantially the same as the planar shape of the resistor 130, the wiring 140, and the electrode 150, for example. However, the planar shapes of the functional layer 120, the resistor 130, the wiring 140, and the electrode 150 may not be substantially the same. For example, when the functional layer 120 is made of an insulating material, the functional layer 120 may be patterned into a shape different from the planar shape of the resistor 130 , the wiring 140 and the electrode 150 . In this case, the functional layer 120 may be formed solidly in the region where the resistor 130, the wiring 140, and the electrode 150 are formed, for example. Alternatively, the functional layer 120 may be formed all over the top surface of the substrate 110 .

Next, by patterning the metal layer A by photolithography, a planar resistor 130, two wirings 140, and two electrodes 150 shown in FIG. 8 are formed.

A cover layer 160 may be formed on the upper surface 110 a of the substrate 110 after forming the resistor 130 , the wiring 140 , and the electrodes 150 . Cover layer 160 covers resistor 130 and wiring 140 , but electrode 150 may be exposed from cover layer 160 . For example, a semi-cured thermosetting insulating resin film is laminated on the upper surface 110a of the substrate 110 so as to cover the resistor 130 and the wiring 140 and expose the electrode 150, and then the insulating resin film is laminated. The cover layer 160 can be formed by heating and curing. Through the above steps, the strain gauge 100 is completed.

Although the preferred embodiments and the like have been described in detail above, the present invention is not limited to the above-described embodiments and the like, and various modifications and substitutions can be made to the above-described embodiments and the like without departing from the scope of the claims. can be added.

1 Pulse wave measuring device 10 Case 11 Upper part 12 Lower part 12a Lower surface 12x Through hole 13 Lid part 40 Pulse wave sensor 41 Case 42 Strain body 42a Base part 42b Beam part 42c Load Part 42d Extension 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 Upper surface 130 Resistor 130e ₁ , 130e ₂ terminations, 140 wiring, 150 electrodes, 160 cover layer

Claims (8)

A pulse wave measuring device attachable to a subject,
a housing;
and a pulse wave sensor fixed to the housing,
The pulse wave sensor includes a strain body in which a strain gauge is arranged, and the strain body is fixed to the housing so as to be in contact with the subject,
A pulse wave measuring device, wherein a sensor surface, which is a surface of the strain body on the side of the subject, is recessed in a direction away from the subject with respect to a surface of the housing located around the sensor surface. The pulse wave measuring device according to claim 1, wherein the sensor surface is flat. 3. The pulse wave measuring device according to claim 2, wherein said sensor surface is parallel to a surface of said housing surrounding said sensor surface. a belt-shaped body having 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 belt-like body has stretchability. The strain-generating body is
a base with a circular opening;
a beam that bridges the inside of the base;
and a load portion provided on the beam portion,
5. The pulse wave measuring device according to any one of claims 1 to 4, wherein the pulse wave is detected based on a change in the resistance value of the strain gauge that accompanies deformation of the strain body. The beam portion has two beams that intersect in a cross shape in a plan view,
the area of intersection of the beams includes the center of the circular opening;
6. The pulse wave measuring device according to claim 5, wherein said load section is provided in an area where said beams intersect. Equipped with four strain gauges,
Two of the four strain gauges are arranged on a side of the beam having a first direction as a longitudinal direction and close to the load section so as to face each other across the load section in a plan view,
The other two of the four strain gauges are opposed to the side of the beam near the base portion whose longitudinal direction is the second direction orthogonal to the first direction, with the load portion interposed therebetween in a plan view. 7. The pulse wave measuring device according to claim 6, arranged to: The pulse wave measuring device according to any one of claims 1 to 7, wherein said strain gauge has a resistor formed of a Cr mixed phase film.

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