JP7542996B2 - Piezoelectric sensor and pressure detection device - Google Patents

Description

The present invention relates to a piezoelectric sensor and pressure detection device that utilizes a piezoelectric element, and, for example, to improvements in a piezoelectric sensor and pressure detection device that are suitable for measuring the human body's pulse (pulse rate or pulse wave) and respiration.

A conventional piezoelectric sensor and pressure detection device is described, for example, in Patent Document 1 below. This is intended to measure minute pressure fluctuations occurring in a measured object with high accuracy, and the pressure detection device 12 is provided with an input chamber 35 whose wall surface is made up of a piezoelectric body 17, and air is introduced into this input chamber 35 from an introduction section 21 in a direction inclined relative to the piezoelectric body 17. Patent Document 2 below discloses a "biological information measuring device," and Figure 2 shows an example of a signal processing device.

Figure 2 (B) of the present invention shows an example of a pressure detection device 900 that takes into account the background technology described above, in which pressure fluctuations detected by air pads 912 of a measurement unit 910 are converted to voltage by piezoelectric elements 922 of a piezoelectric sensor 920, amplified by an amplifier 924, and sent to a gain setting unit 932 of a processing device 930. The gain setting unit 932 adjusts the gain, and then processing such as frequency band filtering is performed by a processing unit 934. The results are stored in a memory unit 936, and the data is displayed on a display unit 938.

JP 2017-219341 A JP 2005-110969 A

However, in the background art of the above-mentioned patent document, when there is a large pressure fluctuation, the measured value becomes saturated. In order to prevent this saturation phenomenon, the following process is carried out.
Gain adjustment is performed in the gain setting unit 932 of FIG. 2B of the present invention, and the gain is lowered so that the measurement value by the piezoelectric sensor 920 does not become saturated, or the gain is raised so that the measurement value does not become too small, thereby allowing measurement of respiration and pulse to continue.

However, even if the gain is adjusted using the above method, sudden body movements such as turning over in bed can occur, and a signal that momentarily saturates the measurement value can be input. In this case, if the gain is adjusted using auto gain control, for example, a time lag occurs until the appropriate value is reached. This makes it impossible to measure respiration or pulse. When the measurement value becomes small, the gain must be increased again using auto gain control, but in this case a time lag occurs until the appropriate value is reached, resulting in the problem that the pulse wave, which is a small signal component, cannot be detected accurately.

The present invention has been made in consideration of the above problems, and aims to improve measurement accuracy by enabling biometric information to be continuously measured even when saturation of the measurement signal occurs.

The piezoelectric sensor of the present invention is characterized by having a first piezoelectric element having a first piezoelectric body on one side, a first chamber having the front surface of the first piezoelectric element as its inner wall, an inlet attached to the first chamber, a second piezoelectric element having a second piezoelectric body on one side, and a second chamber having the back surface of the first piezoelectric element and the second piezoelectric element as its inner walls.

According to one of the main aspects, the second piezoelectric element has a front surface that forms the inner wall of the second chamber, a back surface, and further has a third chamber that forms the back surface of the second piezoelectric element as its inner wall. According to another aspect, the first piezoelectric element and the piezoelectric element are characterized by having a vibration plate made of metal, and the piezoelectric body provided in a partial area of one surface of the vibration plate.

According to yet another embodiment, the first piezoelectric element and the second piezoelectric element have the same shape. For example, the length, width, and thickness of the first piezoelectric body are the same as the length, width, and thickness of the second piezoelectric body, and the length, width, and thickness of a first vibration plate of the first piezoelectric element are the same as the length, width, and thickness of a second vibration plate of the second piezoelectric element . According to yet another embodiment, the piezoelectric device further includes an amplifier for amplifying the output from the second piezoelectric body.

The pressure measuring device of the present invention is a pressure measuring device using any one of the piezoelectric sensors, and is characterized by comprising first and second gain setting units that perform gain adjustment on the output electric signals of the first and second piezoelectric bodies, respectively, and a control means that performs gain control in the corresponding one of the first and second gain setting units to make the electric signals non-saturated when the output electric signals of the first and second piezoelectric bodies are saturated. According to a main aspect, the pressure measuring device is characterized by comprising a measuring means that performs frequency band filtering on the electric signal of at least one of the first and second piezoelectric bodies that has been subjected to the gain control to obtain biological information of a measurement subject. The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

According to the present invention, the first and second piezoelectric elements are arranged with a space between them, so that even if the output signal of one piezoelectric element becomes saturated, the measurement can be continued using the output signal of the other piezoelectric element, thereby improving the measurement accuracy.

1A and 1B are diagrams illustrating a structure of a piezoelectric sensor according to a first embodiment of the present invention. 1A is a diagram showing the configuration of a pressure detection device using the piezoelectric sensor of the embodiment, and FIG. 1B is a diagram showing the configuration of a pressure detection device in the background art. 4 is a graph showing an example of a detected waveform according to the embodiment.

The present invention is described in detail below.

FIG. 1 shows a cross-sectional structure of a piezoelectric sensor 100 according to this embodiment.
The piezoelectric sensor 100 has piezoelectric elements 110 and 120 provided at the upper and lower stages inside. These piezoelectric elements 110 and 120 are formed by stacking an upper cover 130, an intermediate cover 140, a lower cover 150, and a bottom cover 160, and the outer shape and the internal space are configured to be cylindrical.

Piezoelectric elements 110, 120 have piezoelectric bodies PE1, PE2 formed on a metal plate MP made of brass, for example. Note that this embodiment has the same configuration as a known piezoelectric speaker (piezoelectric microphone), and one electrode of piezoelectric bodies PE1, PE2 is the metal plate MP. That is, one electrode of piezoelectric body PE1 is connected to solder EA, and the other electrode is the metal plate MP, which is connected to solder EB. The lead wire for drawing out is electrically connected to solder EA, EB, so that the electrical signal of piezoelectric body PE1 is output. Note that when solder is used, depending on the type of metal plate MP, a copper coating that has good solder wettability may be formed.

The piezoelectric elements 110 and 120 may have the same shape. Specifically, the length, width, and thickness of the first piezoelectric body are the same as the length, width, and thickness of the second piezoelectric body, and the length, width, and thickness of the first vibration plate of the first piezoelectric element are the same as the length, width, and thickness of the second vibration plate of the second piezoelectric element, and so on.

The bottom cover 160 is provided with a circuit board CB, on which circuit components such as amplifiers 112, 122 (described later) are provided. Lead wires (not shown) are connected to the solders EA, EB, and electrically connected to the amplifiers provided on the circuit board CB. The circuit board CB may be connected to a processing device 220 (see FIG. 2) provided outside the piezoelectric sensor 100 via the lead wires.

A ring-shaped engagement protrusion 162 is provided on the inside of the upper surface of the bottom cover 160. The engagement protrusion 162 engages with the lower end opening of the lower cover 150. The upper part of the lower cover 150 is provided with an expanded diameter portion 152 formed wide from the installation area of the metal plate MP toward the outside. The intermediate cover 140 is installed on a step 154 of this expanded diameter portion 152, and a seal 156 is formed between the step 154 and the intermediate cover 140. This seal 156 is for improving adhesion. Furthermore, the piezoelectric element 120 is sandwiched between the step 154 and the seal 156. The seal 156 is provided around the entire circumference of the piezoelectric element 120. An inner peripheral flange 142 is provided on the lower side of the intermediate cover 140 protruding inward, and an installation area for the seal 144 is between this inner peripheral flange 142 and the periphery of the piezoelectric element 120. Meanwhile, the piezoelectric element 110 is placed on the step 146 on the upper side of the inner flange 142, sandwiching a sealing 148 between them.

The upper cover 130 is provided above the intermediate cover 140 via a spacer 132. This spacer 132 improves the airtightness between the upper cover 130 and the intermediate cover 140.

An introduction tube 134 is provided at the center of the upper side of the upper cover 130. The introduction tube 134 is connected to the air pad via a tube that serves as an air passage. Air pressure changes due to vibrations received by the air pad are transmitted to the piezoelectric element 110 via the introduction tube. On the other hand, the lower side of the upper cover 130 is expanded in diameter, and the expanded diameter portion 136 covers the expanded diameter portion 152 of the lower cover 150. A protrusion 138 is provided on the inner tip of the expanded diameter portion 136 of the upper cover 130, so that the upper cover 130 and the lower cover 150 are tightly engaged with each other with good airtightness, sandwiching the intermediate cover 140. With the above configuration, the piezoelectric sensor 100 has spaces 102, 104, and 106 formed in this order from the introduction tube 134 side. The space 102 and the piezoelectric element 110 form a first room, and the space 104 and the piezoelectric element 120 form a second room.

The air pressure change caused by the vibration transmitted from the introduction tube 134 is received by the piezoelectric element 110 through the space 102, and the air pressure change is transmitted from the back surface of the piezoelectric element 110 through the space 104 to the piezoelectric element 120. The air pressure change transmitted by the piezoelectric element 110 is weakened. Since this vibration is transmitted mechanically, even minute vibrations can be transmitted. As described in the prior art, it is believed that a saturation signal is generated by the circuit processing after the piezoelectric body, but in the present invention, by using multiple piezoelectric elements, the vibration is mechanically attenuated, so even signals that have been removed by the saturation signal can be extracted.

2A shows a pressure measuring device 200 that uses the piezoelectric sensor 100. In the figure, the air pressure output side of the air pad 212 of the measuring unit 210 is connected to the space 102 of the piezoelectric sensor 100 via the introduction tube 134, so that the air pressure change is transmitted to the piezoelectric element 110. As a result, the piezoelectric body PE1 is deformed. When the piezoelectric element 110 is deflected, an air pressure change occurs in the space 104, so that the deflection of the piezoelectric element 110 is transmitted to the piezoelectric element 120 via the space 104, and the piezoelectric body PE2 is deformed. In the piezoelectric bodies PE1 and PE2 provided on the piezoelectric elements 110 and 120, respectively, the change in air pressure is converted into a voltage signal, and the converted signal is input to the gain setting units 222 and 232 of the processing device 220 via the amplifiers 112 and 122, respectively. The output side of these gain setting units 222, 232 is connected to a processing unit 224, which is connected to a memory unit 226 and a display unit 228.

Of these, the amplifiers 112 and 122 are used to amplify or attenuate the input electrical signal. The gain setting units 222 and 232 are used to amplify or attenuate the input electrical signal, and the amount of gain adjustment is controlled by the processing unit 224. In addition to the gain adjustment, the processing unit 224 has the function of performing processing such as frequency band filtering of the input signal. The memory unit 226 stores the control processing program, various setting values, measured values, etc., and the display unit 228 displays the measurement results.

Next, the overall operation of this embodiment will be described. The air pad 212 is placed on, for example, a bed or a chair, and acquires the subject's biological information, such as pulse waves and respiratory vibrations. Air pressure fluctuations in the air pad 212 are transmitted as air pressure fluctuations to the space 102 of the piezoelectric sensor 100 through the introduction tube 134. The air pressure fluctuations then cause the piezoelectric element 110 to bend and the piezoelectric body PE1 to deform, and the air pressure fluctuations are converted into a voltage signal. Meanwhile, the bending of the piezoelectric element 110 causes air pressure fluctuations in the space 104, which causes the piezoelectric element 120 to bend and the piezoelectric body PE2 to deform, and the air pressure fluctuations are converted into a voltage signal.

The electric signals output from the piezoelectric elements 110 and 120 are amplified or attenuated by the amplifiers 112 and 122, and then undergo gain adjustment by the gain setting units 222 and 232 before being input to the processing unit 224. The processing unit 224 performs the following on the input signals:
a. When saturation occurs, the gain is decreased, and when saturation is eliminated, the gain is increased.
b) Processing such as filtering, peak detection, and peak counting is performed to obtain necessary data such as pulse waves and respiration.
c) The measurement results are stored in the memory unit 226 and displayed on the display unit 228.
Such an operation is carried out.

Figure 3 shows an example of the measurement results of the above embodiment. In Figure 3 (A), the output signal strength of the piezoelectric elements 110 and 120 is shown, with the horizontal axis representing frequency. This figure shows a comparison of the signals of the piezoelectric elements 110 and 120 when the amplification degree of the amplifiers 112 and 122 and the gain setting values of the gain setting units 222 and 232 are all the same, and although the strength is different, the frequency characteristics are almost the same. The upper piezoelectric element 110 is directly affected by the air pressure fluctuation from the air pad 212 through the space 102, while the lower piezoelectric element 120 is affected through the piezoelectric element 110 and the space 104, so the upper piezoelectric element 110 has a higher signal strength than the lower piezoelectric element 120.

Figure 3B shows an example of the time change of the output signal voltage of the piezoelectric elements 110 and 120. In the example of the figure, the air pressure fluctuation from the air pad 212 due to the living body is strong, and the signal of the upper piezoelectric element 110 shown by the dotted line is saturated, but the lower piezoelectric element 120 is not saturated. In such a case, the processing unit 224 controls the gain of the gain setting unit 222 to be in a non-saturated state for the output signal of the upper piezoelectric element 110. On the other hand, since the signal of the lower piezoelectric element 120 is not saturated, pulse and respiration data can be obtained by referring to this signal. Specifically, in the solid line graph of the lower piezoelectric element 120, the low frequency change represents respiration, and the pulse-like waveform represents the pulse, so that the two can be separated by performing processing such as filtering, and the number of peaks can be counted to obtain the pulse rate and respiration rate.

As described above, according to this embodiment, by providing the piezoelectric elements 110 and 120, even if the output signal of the upper piezoelectric element 110 becomes saturated and a waiting time is required until the gain is adjusted to become non-saturated, it is possible to continue measurement based on the output signal of the lower piezoelectric element 120, and furthermore, it is possible to improve the measurement accuracy overall.

Other Examples The present invention is not limited to the above-described examples, and various modifications can be made without departing from the spirit and scope of the present invention. For example, the following modifications are also included.
(1) In the above embodiment, the signal strength of the upper piezoelectric element 110 is set to be greater than the signal strength of the lower piezoelectric element 120, but the signal strength of the piezoelectric elements 110, 120 may be set to the same strength by adjusting the gain of the gain setting units 222, 232, and biological information may be measured using the signals of both the piezoelectric elements 110, 120. In that case, for example, by applying different filters, for example, a BPF (band pass filter) to the upper piezoelectric element 110 to obtain respiratory information and an LPF (low pass filter) to the lower piezoelectric element 120 to obtain pulse information, it is possible to obtain signals of different purposes with high accuracy.
(2) In addition, under normal circumstances, pulse and respiration can be measured using the output signal of the upper piezoelectric element 110, which has a high signal strength, and when a strong air pressure fluctuation occurs and the signal becomes saturated as shown in Figure 3 (B), pulse and respiration can be measured using the output signal of the lower piezoelectric element 120.
(3) The structure of the piezoelectric sensor shown in FIG. 1 is one example, and the shape and dimensions may be appropriately set so as to achieve the same function.
(4) In the above embodiment, pulse and respiration are measured as vital signs, but the present invention may be applied to the measurement of various air pressure fluctuations.
(5) In the above embodiment, the fluctuation in air pressure is measured. However, gases other than air or fluids such as various liquids may also be used.

According to the present invention, the first and second piezoelectric elements are arranged with a space between them. Therefore, even if the output signal of one piezoelectric element becomes saturated, the measurement can be continued using the output signal of the other piezoelectric element, improving the measurement accuracy, which is suitable for measuring biological information such as pulse and respiration.

100: Piezoelectric sensor 102, 104, 106: Space 110, 120: Piezoelectric element 112, 122: Amplifier 130: Upper cover 132: Spacer 134: Inlet tube 136: Enlarged diameter portion 138: Protrusion 140: Middle cover 142: Inner peripheral flange 144: Sealing 146: Step 148: Sealing 150: Lower cover 152: Enlarged diameter portion 154: Step 156: Sealing 160: Bottom cover 162: Engagement protrusion 200: Pressure measurement Pressure detection device 210: Measurement unit 212: Air pad 220: Processing device 222, 232: Gain setting unit 224: Processing unit 226: Memory unit 228: Display unit 900: Pressure detection device 910: Measurement unit 912: Air pad 920: Piezoelectric sensor 922: Piezoelectric element 924: Amplifier 930: Processing device 932: Gain setting unit 934: Processing unit 936: Memory unit 938: Display unit EA, EB: Electrode CB: Circuit board MP: Metal plate PE1, PE2: Piezoelectric body

Claims (8)

a first piezoelectric element having a first piezoelectric body provided on at least one surface;
a first chamber having an inner wall formed on a front surface of the first piezoelectric element;
an inlet attached to the first chamber; a second piezoelectric element having a second piezoelectric body provided on at least one surface thereof;
a second chamber having inner walls including a rear surface of the first piezoelectric element and the second piezoelectric element;
A piezoelectric sensor having a the second piezoelectric element has a front surface that forms an inner wall of the second chamber and a back surface,
2. The piezoelectric sensor according to claim 1, further comprising a third chamber having a rear surface of the second piezoelectric element as an inner wall thereof. The first piezoelectric element includes a vibration plate made of a metal, and the first piezoelectric body is provided in a partial area of one surface of the vibration plate.
The piezoelectric sensor according to claim 1 or claim 2, characterized in that the second piezoelectric element has a vibration plate made of metal, and the second piezoelectric body is provided in a partial area of one surface of the vibration plate . The piezoelectric sensor according to any one of claims 1 to 3, wherein the first piezoelectric element and the second piezoelectric element have the same shape. The length, width, and thickness of the first piezoelectric body are the same as the length, width, and thickness of the second piezoelectric body, respectively;
5. The piezoelectric sensor of claim 4, wherein the length, width, and thickness of the first vibration plate of the first piezoelectric element are the same as the length, width, and thickness of the second vibration plate of the second piezoelectric element. The piezoelectric sensor according to any one of claims 1 to 5, further comprising an amplifier that amplifies the output from the second piezoelectric body. A pressure measuring device using the piezoelectric sensor according to any one of claims 1 to 6,
a first gain setting unit and a second gain setting unit which adjust the gains of the output electrical signals of the first and second piezoelectric bodies, respectively;
a control means for performing gain control in a corresponding one of the first and second gain setting sections when the output electrical signals of the first and second piezoelectric elements become saturated, thereby bringing the electrical signals into a non-saturated state. The pressure measuring device according to claim 7, further comprising a measuring means for filtering a frequency band from the electrical signal of at least one of the first and second piezoelectric bodies that has been subjected to the gain control according to claim 7 to obtain biological information of the subject to be measured.

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