Body sound acquisition device

Abstract

This biological sound acquisition device (10) comprises a housing (100), a first acceleration sensor (210) and a second acceleration sensor (220). The first acceleration sensor (210) is disposed inside the housing (100). In addition, the first acceleration sensor (210) is mechanically connected to the housing (100) with a first vibration damping member (410) therebetween. The second acceleration sensor (220) is disposed inside the housing (100).

Description

[Technical field]

[0001] The present invention relates to a body sound acquiring device. [Background technology]

[0002] Currently, various body sound acquisition devices for use in body sound auscultation devices such as electronic stethoscopes have been developed. Such body sound acquisition devices may acquire not only body sounds but also external noise. Therefore, the body sound acquisition devices are required to suppress external noise.

[0003] Patent Document 1 describes a structure for suppressing external noise in a body sound acquisition device. In this structure, a sensor module is supported on a main body by a damper. In this structure, even if noise propagates from the main body to the sensor module via the damper, the noise propagation is suppressed by the damper. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2017-23595 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a body sound acquisition device, it is required to suppress external noise. In order to suppress external noise, a sensor may be supported by a damper, as described in, for example, Patent Document 1. However, simply supporting the sensor by the damper may not be enough to suppress external noise.

[0006] One example of a problem to be solved by the present invention is to suppress external noise in a body sound acquisition device. [Means for solving the problem]

[0007] The invention described in claim 1 is A housing and a first acceleration sensor disposed within the housing and mechanically connected to the housing via a first vibration damping member; A second acceleration sensor disposed within the housing; The body sound acquisition device includes:

[0008] The invention described in claim 9 is A housing and a first vibration sensor disposed within the housing and mechanically connected to the housing via a first vibration damping member; A second vibration sensor disposed within the housing; The body sound acquisition device includes: [Brief description of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a body sound acquisition device according to an embodiment. FIG. [Diagram 2] FIG. 2 is an enlarged view of a region α shown in FIG. [Diagram 3] FIG. 2 is an exploded view of the body sound acquiring device shown in FIG. [Figure 4] FIG. 1 is a diagram showing a multi-mass model for explaining the propagation of external noise in a body sound acquisition device according to an embodiment. [Diagram 5] FIG. 2 is a diagram showing a multi-mass model for explaining propagation of body sounds in the body sound acquisition device according to the embodiment. [Figure 6] 11 is a graph showing frequency characteristics of relative acceleration detected by a first acceleration sensor of the body sound acquisition device according to the embodiment when a body vibration, which is an input signal, is used as a reference. [Figure 7] FIG. 11 is a cross-sectional view of a body sound acquisition device according to a first modified example. [Figure 8] FIG. 8 is an exploded view of the body sound acquiring device shown in FIG. 7. [Figure 9] FIG. 13 is a diagram showing a multi-mass model of a body sound acquisition device according to a first modified example. [Figure 10]This is a graph showing the frequency characteristics of the relative acceleration detected by the second acceleration sensor of the body sound acquisition device of variant example 1 when the input signal, which is the body vibration, is used as a reference, and the frequency characteristics of the relative acceleration detected by the second acceleration sensor of the body sound acquisition device of the embodiment when the input signal, which is the body vibration, is used as a reference. [Figure 11] FIG. 11 is a cross-sectional view of a body sound acquisition device according to a second modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same components are denoted by the same reference numerals, and the description thereof will be omitted as appropriate.

[0011] Fig. 1 is a cross-sectional view of a body sound acquiring device 10 according to an embodiment. Fig. 2 is an enlarged view of an area α shown in Fig. 1. Fig. 3 is an exploded view of the body sound acquiring device 10 shown in Fig. 1. Figs. 1 and 2 show a cross section passing through the center of a first housing member 110 (described later) along the height direction of the first housing member 110. The second housing member 120 of Fig. 1 is not shown in Figs. 2 and 3.

[0012] The body sound acquisition device 10 acquires body sounds, i.e., body vibrations. In this embodiment, body sounds or body vibrations are emitted as vibrations when sounds or vibrations generated inside the body of the subject propagate through the subcutaneous tissue of the subject, and are emitted as sounds when sounds or vibrations generated inside the body of the subject propagate to the outside air. For example, the body sound acquisition device 10 acquires vibrations that appear on the body surface of the subject.

[0013] The body sound acquisition device 10 includes a housing 100, a first acceleration sensor 210, a second acceleration sensor 220, a first holder 310, a second holder 320, a first vibration damping member 410, and a substrate 500.

[0014] The housing 100 has a first housing member 110 and a second housing member 120. The first housing member 110 is the lower member of the housing 100, that is, the base. The second housing member 120 is the upper member of the housing 100. The first acceleration sensor 210, the first holder 310, the second acceleration sensor 220, the second holder 320, the first vibration damping member 410, and the substrate 500 are disposed in the housing 100. As shown in FIG. 1 and FIG. 3, in this embodiment, the first housing member 110, the first holder 310, the first acceleration sensor 210, the first vibration damping member 410, the second holder 320, the second acceleration sensor 220, the substrate 500, and the second housing member 120 are stacked in this order.

[0015] The first acceleration sensor 210 is housed in the first holder 310. When the body sound acquisition device 10 acquires body sound, the first holder 310 comes into contact with a measurement target such as skin tissue via a biocompatible material such as silicone. The first acceleration sensor 210 is a one-axis acceleration sensor. The first acceleration sensor 210 is capable of detecting vibration in one axis direction. In this embodiment, the first acceleration sensor 210 is capable of detecting vibration in a direction substantially perpendicular to a tangent plane of the measurement target. The first acceleration sensor 210 may be a multi-axis, for example, three-axis, acceleration sensor.

[0016] The second acceleration sensor 220 is accommodated in the second holder 320. When the body sound acquisition device 10 acquires body sound, the second holder 320 is separated from the measurement target such as skin tissue. That is, when the body sound acquisition device 10 acquires body sound, the second holder 320 does not contact the measurement target such as skin tissue. The second acceleration sensor 220 is a one-axis acceleration sensor. The second acceleration sensor 220 is capable of detecting vibration in one axis direction. In this embodiment, the second acceleration sensor 220 is capable of detecting vibration in a direction substantially perpendicular to the tangent plane of the measurement target. The second acceleration sensor 220 may be a multi-axis, for example, three-axis, acceleration sensor.

[0017] The sensitivity axis of the first acceleration sensor 210 and the sensitivity axis of the second acceleration sensor 220 are substantially parallel. "Substantially parallel" means not only that the sensitivity axis of the first acceleration sensor 210 and the sensitivity axis of the second acceleration sensor 220 are strictly parallel, but also that one of the sensitivity axes of the first acceleration sensor 210 and the second acceleration sensor 220 is tilted within a range of ±15 degrees with respect to the other of the sensitivity axes of the first acceleration sensor 210 and the second acceleration sensor 220. In this case, as described later, by calculating the difference between the detection signal detected by the first acceleration sensor 210 and the signal detected by the second acceleration sensor 220, the noise included in the detection signal detected by the first acceleration sensor 210 and the noise included in the detection signal detected by the second acceleration sensor 220 can at least partially cancel each other out. Note that the sensitivity axis of the first acceleration sensor 210 is an axis in a direction in which the first acceleration sensor 210 can detect vibration. Similarly, the sensitivity axis of the second acceleration sensor 220 is the axis in the direction in which the second acceleration sensor 220 can detect vibrations.

[0018] Even if the sensitivity axis of the first acceleration sensor 210 and the sensitivity axis of the second acceleration sensor 220 are not parallel to each other, when noise components contained in the detection results of the first acceleration sensor 210 and the second acceleration sensor 220 can be extracted by signal processing of the detection results of the first acceleration sensor 210 and the second acceleration sensor 220, the noise contained in the detection signal detected by the first acceleration sensor 210 and the noise contained in the detection signal detected by the second acceleration sensor 220 can be at least partially canceled out by each other using the extracted noise components.

[0019] The first vibration damping member 410 is a viscoelastic body such as a damper, etc. Depending on its hardness, the first vibration damping member 410 functions as a low-pass filter that blocks relatively high frequency vibrations and passes relatively low frequency vibrations.

[0020] The first acceleration sensor 210 is mechanically connected to the housing 100 via the first vibration damping member 410. The first acceleration sensor 210 being mechanically connected to the housing 100 via the first vibration damping member 410 means, for example, that the first acceleration sensor 210 is disposed relative to the first vibration damping member 410 so that vibrations of a predetermined frequency of the first acceleration sensor 210, for example, noise propagated from the housing 100, are attenuated by the first vibration damping member 410. For example, the first acceleration sensor 210 or the first holder 310 that houses the first acceleration sensor 210 may be in contact with the first vibration damping member 410. Note that the first acceleration sensor 210 being mechanically connected to the housing 100 via the first vibration damping member 410 may mean, for example, that the first acceleration sensor 210 is elastically connected to the housing 100 via the first vibration damping member 410.

[0021] Since the first acceleration sensor 210 is mechanically connected to the housing 100 via the first vibration damping member 410, when the biological sound is transmitted to the first holder 310, the first acceleration sensor 210 vibrates due to the biological sound as if it were separated from the housing 100 by the first vibration damping member 410. In general, according to the second law of motion, the acceleration of an acceleration sensor decreases as the mass of a vibrating object increases when the force of vibration is constant. Therefore, if the housing 100 vibrates together with the first acceleration sensor 210 due to biological vibration, this may lead to a loss or reduction of the biological vibration. In contrast, according to this embodiment, the loss or reduction of the biological vibration can be suppressed by the first vibration damping member 410, and the biological vibration can be accurately detected by the first acceleration sensor 210.

[0022] The second acceleration sensor 220 is mechanically connected to the housing 100 without the first vibration damping member 410. The second acceleration sensor 220 is mechanically connected to the housing 100 without the first vibration damping member 410 means, for example, that the second acceleration sensor 220 is disposed with respect to the first vibration damping member 410 so that vibrations of a predetermined frequency of the second acceleration sensor 220, for example, noise propagated from the housing 100, are not attenuated by the first vibration damping member 410. Note that the second acceleration sensor 220 is mechanically connected to the housing 100 without the first vibration damping member 410 may also mean that the second acceleration sensor 220 is rigidly connected to the housing 100 without the first vibration damping member 410.

[0023] Fig. 4 is a diagram showing a multi-mass model for explaining the propagation of external noise in the body sound acquisition device 10 according to the embodiment. The acquisition unit 510 shown in Fig. 4 is shown as a functional block diagram. The acquisition unit 510 is realized by, for example, an integrated circuit mounted on the board 500 shown in Figs. 1 to 3.

[0024] In this model, first, noise N as external noise propagates to the second housing member 120. For example, the noise N is generated when the second housing member 120 is gripped. do Muscle noise generated from the hand. Muscle noise is sound generated by muscle activity in the human body, such as the hand.

[0025] As indicated by the arrow extending from the second housing member 120 through the first housing member 110, the second holder 320, the first vibration damping member 410, and the first holder 310 to the first acceleration sensor 210, the noise N propagated to the second housing member 120 reaches the first acceleration sensor 210 through the second housing member 120, the first housing member 110, the second holder 320, the first vibration damping member 410, and the first holder 310. In this case, the first acceleration sensor 210 detects the noise N filtered for a certain frequency by the first vibration damping member 410.

[0026] The first vibration damping member 410 blocks relatively high frequency components of the noise N. For this reason, in order to block the noise N over a wide frequency band using the first vibration damping member 410, it is desirable to set the natural frequency of the first vibration damping member 410 to a low frequency. However, there is a limit to how low the natural frequency of the first vibration damping member 410 can be set to for the following reason. That is, the natural frequency of the first vibration damping member 410 is (k / m) 1 / 2 / 2π. Here, k is the spring constant of the first vibration damping member 410, and m is the mass of the first acceleration sensor 210 and the first holder 310 supported by the first vibration damping member 410. The larger the mass m, the smaller the natural frequency. However, the larger the mass m, the greater the loss or reduction of biological vibration due to the weight of the first acceleration sensor 210 and the first holder 310. For this reason, the first vibration damping member 410 alone cannot sufficiently remove the relatively low frequency components of the noise N. In this embodiment, as described later, the detection result of the second acceleration sensor 220 is used to remove the relatively low frequency components of the noise N.

[0027] As shown by the arrow extending from the second housing member 120 via the first housing member 110 and the second holder 320 to the second acceleration sensor 220, the noise N propagated to the second housing member 120 reaches the second acceleration sensor 220 via the second housing member 120, the first housing member 110 and the second holder 320.

[0028] The acquiring unit 510 acquires the difference between the detection signal detected by the first acceleration sensor 210 and the detection signal detected by the second acceleration sensor 220. Specifically, the detection signals of the first acceleration sensor 210 and the second acceleration sensor 220 are output as electric signals. The acquiring unit 510 calculates the difference between the electric signal output from the first acceleration sensor 210 and the electric signal output from the second acceleration sensor 220. This makes it possible to remove components of the noise N that cannot be sufficiently removed by the first vibration damping member 410 alone, that is, relatively low frequency components of the noise N.

[0029] When reducing noise N by the difference between the detection signal detected by the first acceleration sensor 210 and the detection signal detected by the second acceleration sensor 220, it is desirable that the level and phase of the electrical signal output from the first acceleration sensor 210 are equal to or similar to the level and phase of the electrical signal output from the second acceleration sensor 220. For example, by filtering the electrical signal output from the second acceleration sensor 220 with an electrical filter having filter characteristics equal to or similar to the filter characteristics of the first vibration damping member 410, the level and phase of the electrical signal output from the first acceleration sensor 210 can be made equal to or similar to the level and phase of the electrical signal output from the second acceleration sensor 220.

[0030] FIG. 5 is a diagram showing a multi-mass model for explaining propagation of body sound in the body sound acquisition device 10 according to the embodiment.

[0031] In this model, first, the body sound S propagates to the first holder 310.

[0032] As shown by the arrow extending from the first holder 310 to the first acceleration sensor 210, the body sound S propagated to the first holder 310 reaches the first acceleration sensor 210. The first acceleration sensor 210 detects the body sound S that has reached the first acceleration sensor 210. That is, the body sound S propagates to the first acceleration sensor 210 without passing through the first vibration damping member 410. If the body sound S propagates to the first acceleration sensor 210 through the first vibration damping member 410, the body sound S is lost or reduced by the first vibration damping member 410. In contrast, in this embodiment, it is possible to prevent the body sound S propagating to the first acceleration sensor 210 from being lost or reduced by the first vibration damping member 410.

[0033] As shown by the arrow extending from the first holder 310 through the first vibration damping member 410 and the second holder 320 to the second acceleration sensor 220, the body sound S propagated to the first holder 310 reaches the second acceleration sensor 220 through the first vibration damping member 410 and the second holder 320. The second acceleration sensor 220 detects the body sound S that has reached the second acceleration sensor 220. That is, the body sound S propagates to the second acceleration sensor 220 through the first vibration damping member 410. Therefore, the body sound S propagating to the second acceleration sensor 220 can be lost or reduced by the first vibration damping member 410.

[0034] From the viewpoint of reducing attenuation or loss of the body sound S detected by the first acceleration sensor 210 due to propagation of the body sound S to the second acceleration sensor 220 after propagating to the first holder 310, the total mass of the second acceleration sensor 220, the second holder 320, and the body sound acquisition device 10 including the housing 100 excluding the first acceleration sensor 210 and the first holder 310 can be made sufficiently larger than the total weight of the first acceleration sensor 210 and the first holder 310. More specifically, the mass of the second acceleration sensor 220 and the second holder 320 including the housing 100 can be made 30 times or more the mass of the first acceleration sensor 210 and the first holder 310.

[0035] FIG. 6 is a graph showing frequency characteristics of the relative acceleration detected by the first acceleration sensor 210 of the body sound acquisition device 10 according to the embodiment when the body vibration, which is an input signal, is used as a reference.

[0036] In Fig. 6, the horizontal axis of the graph indicates the vibration frequency [Hz]. The vertical axis of the graph indicates the relative acceleration [dB] detected by the first acceleration sensor 210 when the input signal, which is the biological vibration, is used as a reference. In the graph, frequency characteristics of the first vibration damping member 410 at nine spring constants are shown. The peaks in the frequency band of 1000 Hz to 10000 Hz for these nine frequency characteristics decrease in the order of the spring constants of 500 N / m, 1000 N / m, 1500 N / m, 2000 N / m, 3000 N / m, 5000 N / m, 10000 N / m, 20000 N / m, and 30000 N / m.

[0037] For the graph in Figure 6, the simulation was performed under the following conditions: (mass) Measured object: 0.2kg First acceleration sensor 210: 0.001 kg Second acceleration sensor 220: 0.001 kg Second housing member 120: 0.1 kg (Spring constant) Measured object: 1000N / m First acceleration sensor 210: 100000N / m Second acceleration sensor 220: 100000N / m Second housing member 120: 3000N / m (damping coefficient) Measured object: 4.242641Ns / m First acceleration sensor 210: 2 Ns / m Second acceleration sensor 220: 2Ns / m Second housing member 120: 14.69694 Ns / m

[0038] In this simulation, it is assumed that the object to be measured is skin tissue. Skin tissue is generally called a soft elastic body, and the reaction force from the skin tissue differs between a thick part of the skin tissue and a thin part of the skin tissue when the skin tissue is pressed with the same area and the same pressing force. In this simulation, it is assumed that the skin tissue is 4.5 mm thick. The spring constant of skin tissue with a thickness of 4.5 mm is estimated to be approximately 1000 N / m.

[0039] As shown in the graph of Fig. 6, the larger the spring constant, the more prominent the resonance and anti-resonance of the frequency characteristics at frequencies below 100Hz, particularly for spring constants of 30000N / m, 20000N / m, and 10000N / m, whose frequency characteristics are shown by dashed lines. Also, the larger the spring constant, the smaller the peak of the frequency characteristics at frequencies above 1000Hz, particularly for spring constants of 30000N / m, 20000N / m, and 10000N / m, whose frequency characteristics are shown by dashed lines. This suggests that as the first vibration damping member 410 hardens, the sensing target of the first acceleration sensor 210 shifts from the vibration of the skin tissue to the vibration of the second housing member 120.

[0040] From the graph of FIG. 6, when the spring constant of the first vibration damping member 410 is equal to or less than the spring constant of the skin tissue, i.e., the spring constant of the object to be measured, the resonance of the frequency characteristic of a frequency of 100 Hz or less, i.e., the peak where the relative acceleration is greater than 0 dB, and the anti-resonance, i.e., the peak where the relative acceleration is less than 0 dB, are hardly observed, and the peak of the frequency characteristic of a frequency of 1000 Hz or more is relatively prominent. The resonance and anti-resonance of the frequency of 1000 Hz or less in the graph of FIG. 6 are due to the natural frequency of the housing 100. In addition, when the natural frequency of the first vibration damping member 410, i.e., the natural frequency, approaches the natural frequency of the housing 100, the housing 100 and the first vibration damping member 410 are likely to resonate with each other. Therefore, in order to suppress the resonance between the housing 100 and the first vibration damping member 410, it is preferable to make the natural frequency of the first vibration damping member 410 lower than the natural frequency of the housing 100. Furthermore, it is preferable that the resonant frequency band of the housing 100 and the resonant frequency band of the first vibration damping member 410 do not overlap.

[0041] (Variation 1) Fig. 7 is a cross-sectional view of the body sound acquisition device 10 according to the first modification. Fig. 8 is an exploded view of the body sound acquisition device 10 shown in Fig. 7. Fig. 7 shows a cross section passing through the center of the housing 100 in the height direction of the housing 100. The body sound acquisition device 10 according to the first modification is similar to the body sound acquisition device 10 according to the embodiment, except for the following points.

[0042] The body sound acquisition device 10 further includes a second vibration damping member 420 and a third holder 330. The second vibration damping member 420 is, for example, a viscoelastic body such as a damper. As shown in Fig. 8, the first housing member 110, the first holder 310, the first acceleration sensor 210, the first vibration damping member 410, the second holder 320, the third holder 330, the second acceleration sensor 220, the second vibration damping member 420, and the second housing member 120 are stacked in this order. The second acceleration sensor 220 is accommodated in the third holder 330. In addition, the second holder 320 is mechanically connected to the housing 100.

[0043] The second acceleration sensor 220 is mechanically connected to the housing 100 via the second vibration damping member 420. The second acceleration sensor 220 being mechanically connected to the housing 100 via the second vibration damping member 420 means, for example, that the second acceleration sensor 220 is disposed relative to the second vibration damping member 420 so that vibrations of a predetermined frequency of the second acceleration sensor 220, for example, noise propagated from the housing 100, are attenuated by the second vibration damping member 420. For example, the second acceleration sensor 220 or the second holder 320 that houses the second acceleration sensor 220 may be in contact with the second vibration damping member 420. The second acceleration sensor 220 being mechanically connected to the housing 100 via the second vibration damping member 420 may mean, for example, that the second acceleration sensor 220 is elastically connected to the housing 100 via the second vibration damping member 420.

[0044] FIG. 9 is a diagram showing a multi-mass model of the body sound acquisition device 10 according to the first modification.

[0045] When noise such as muscle sound noise propagates to the second housing member 120, the noise travels from the second housing member 120 through the first housing member 110, the second holder 320, the first vibration damping member 410, and the first holder 310 to reach the first acceleration sensor 210, and also travels from the second housing member 120 through the first housing member 110, the second holder 320, the second vibration damping member 420, and the third holder 330 to reach the second acceleration sensor 220.

[0046] As in the embodiment, the acquisition unit 510 acquires the difference between the detection signal detected by the first acceleration sensor 210 and the detection signal detected by the second acceleration sensor 220. In this modification, the mass point system from the second housing member 120 to the first acceleration sensor 210 is the same as or similar to the mass point system from the first acceleration sensor 210 to the second acceleration sensor 220. Therefore, the noise detected by the first acceleration sensor 210 and the noise detected by the second acceleration sensor 220 can at least partially cancel each other out in the entire frequency band of the body sound, for example, from 20 Hz to 2 kHz.

[0047] When the body sound propagates to the first holder 310, the body sound propagates from the first holder 310 to the first acceleration sensor 210, and also from the first holder 310 to the second acceleration sensor 220 via the first vibration damping member 410, the second holder 320, the second vibration damping member 420, and the third holder 330. That is, the body sound propagates to the first acceleration sensor 210 without passing through the first vibration damping member 410 and the second vibration damping member 420. In contrast, the body sound propagates to the second acceleration sensor 220 via the first vibration damping member 410 and the second vibration damping member 420.

[0048] Figure 10 is a graph showing the frequency characteristics of the relative acceleration detected by the second acceleration sensor 220 of the body sound acquisition device 10 of variant example 1 when the input signal, which is the body vibration, is used as a reference, and the frequency characteristics of the relative acceleration detected by the second acceleration sensor 220 of the body sound acquisition device 10 of the embodiment when the input signal, which is the body vibration, is used as a reference.

[0049] In Fig. 10, the horizontal axis of the graph indicates the vibration frequency [dB]. The vertical axis of the graph indicates the relative acceleration [dB] detected by the second acceleration sensor 220 when the biological vibration, which is the input signal, is used as a reference. The solid line in the graph indicates the frequency characteristic of the relative acceleration detected by the second acceleration sensor 220 of the biological sound acquisition device 10 according to the first modification example when the biological vibration, which is the input signal, is used as a reference. The dashed line in the graph indicates the frequency characteristic of the relative acceleration detected by the second acceleration sensor 220 of the biological sound acquisition device 10 according to the embodiment when the biological vibration, which is the input signal, is used as a reference.

[0050] In the embodiment, as shown in Fig. 5, the body sound reaching the second acceleration sensor 220 from the first holder 310 passes through only one vibration damping member, i.e., the first vibration damping member 410. In contrast, in this modification, as shown in Fig. 9, the body sound reaching the second acceleration sensor 220 from the first holder 310 passes through two vibration damping members, i.e., the first vibration damping member 410 and the second vibration damping member 420. Therefore, in this modification, the body sound reaching the second acceleration sensor 220 from the first holder 310 can be damped by more vibration damping members than in the embodiment.

[0051] Also, as shown in Fig. 10, when two vibration damping members are used, the frequency at which the resonant frequency band, i.e., the frequency band where the relative acceleration is higher than 0 dB, changes to the anti-resonant frequency band, i.e., the frequency band where the relative acceleration is lower than 0 dB, is about 65 Hz. In contrast, when one vibration damping member is used, the frequency at which the resonant frequency band changes to the anti-resonant frequency band is about 91 Hz. Furthermore, when two vibration damping members are used, the relative acceleration peaks at about 35 Hz in the resonant frequency band. In contrast, when one vibration damping member is used, the relative acceleration peaks at about 60 Hz in the resonant frequency band.

[0052] As described above, the acquisition unit 510 acquires the difference between the detection signal detected by the first acceleration sensor 210 and the detection signal detected by the second acceleration sensor 220. Therefore, in FIG. 10, the loss of the detection signal of the first acceleration sensor 210 for the difference in the frequency band where the relative acceleration is higher than 0 dB is larger than the loss of the detection signal of the first acceleration sensor 210 for the difference in the frequency band where the relative acceleration is lower than 0 dB. From FIG. 10, within the body sound frequency band of approximately 20 Hz to 2 kHz, the frequency band where the relative acceleration is higher than 0 dB when two vibration damping members are used is narrower than the frequency band where the relative acceleration is higher than 0 dB when one vibration damping member is used. Therefore, the loss of the detection signal of the first acceleration sensor 210 for the above difference when two vibration damping members are used is smaller than the loss of the detection signal of the first acceleration sensor 210 for the above difference when one vibration damping member is used.

[0053] (Variation 2) Fig. 11 is a cross-sectional view of the body sound acquisition device 10 according to the modified example 2. Fig. 11 shows a cross section passing through the center of the housing 100 in the height direction of the housing 100. The body sound acquisition device 10 according to the modified example 2 is similar to the body sound acquisition device 10 according to the embodiment, except for the following points.

[0054] The first acceleration sensor 210 and the second acceleration sensor 220 are aligned in a direction perpendicular to the height direction of the housing 100. In the second modification, external noise such as muscle sound noise can be suppressed in the same manner as in the embodiment.

[0055] Although the embodiment and modified examples have been described above with reference to the drawings, these are merely examples of the present invention, and various configurations other than those described above can also be adopted.

[0056] For example, in the embodiment and the modified example, the first acceleration sensor 210 and the second acceleration sensor 220 are used as vibration sensors for detecting body sounds or noise. However, the vibration sensor may be a vibration sensor different from the acceleration sensor, such as a speed sensor.

[0057] Furthermore, for example, in the embodiment and the modified example, the noise N is reduced by calculating the difference between the detection signal detected by the first acceleration sensor 210 and the detection signal detected by the second acceleration sensor 220, but before calculating the difference, a filter may be applied to the detection signal by the second acceleration sensor 220. More specifically, a high-pass filter may be applied and then subtraction processing may be performed so as to attenuate signals in a frequency band where the relative acceleration in Fig. 10 is higher than 0 dB.

[0058] This application claims priority based on Japanese Patent Application No. 2020-057855, filed on March 27, 2020, the disclosure of which is incorporated herein in its entirety. [Explanation of symbols]

[0059] 10. Body sound acquisition device 100 Case 110 First housing member 120 Second housing member 210 First acceleration sensor 220 Second acceleration sensor 310 First Holder 320 Second Holder 330 3rd Holder 410 First vibration damping member 420 Second vibration damping member 500 boards 510 Acquisition Department N Noise S Body Sound

Claims

1. A housing and a first acceleration sensor disposed within the housing and mechanically connected to the housing via a first vibration damping member; A second acceleration sensor disposed within the housing; Equipped with A body sound is propagated to the first acceleration sensor without passing through the first vibration damping member, A body sound acquiring device, wherein body sound is transmitted to the second acceleration sensor via the first vibration damping member.

2. The body sound acquisition device according to claim 1 , A body sound acquisition device, wherein a sensitivity axis of the first acceleration sensor and a sensitivity axis of the second acceleration sensor are substantially parallel to each other.

3. The body sound acquisition device according to claim 1 , The first vibration damping member has a natural frequency lower than a natural frequency of the housing.

4. The body sound acquisition device according to any one of claims 1 to 3, The second acceleration sensor is mechanically connected to the housing via a second vibration damping member.

5. The body sound acquisition device according to any one of claims 1 to 4, The body sound acquiring device further includes a first holder that houses the first acceleration sensor and is in contact with a subject to be measured.

6. The body sound acquisition device according to any one of claims 1 to 5, The body sound acquiring device further includes a second holder that houses the second acceleration sensor and is spaced apart from the subject to be measured.

7. The body sound acquisition device according to any one of claims 1 to 6, The body sound acquiring device further includes an acquiring unit that acquires a difference between a detection signal of the first acceleration sensor and a detection signal of the second acceleration sensor.

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