JP2013130421A - Oscillation sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a capacitance change that occurs in a movable structure by oscillation, equal to or greater than 100 femto Farad, without thickening the movable structure.SOLUTION: An oscillation sensor comprises a fixed electrode which is comprised of a plurality of band-like electrodes formed on a support substrate, and a movable electrode which is supported through a strut and a spring to the support substrate and is comprised of a plurality of electrodes confronted with the band-like electrodes of the fixed electrode. In accordance with oscillation from the outside, the movable electrode is made movable in an in-plane direction of the fixed electrode, and in accordance with displacement of a crossing area of the fixed electrode and the movable electrode, electrostatic capacitance is displaced. The plurality of band-like electrodes of the fixed electrode are electrically connected with each other alternately and connected to a sensor circuit part as two differential outputs.

Description

  The present invention relates to a vibration sensor that detects vibration by a change in capacitance generated in a movable structure.

FIG. 5 shows a configuration example of a sensor node system that performs vibration detection (Patent Documents 1 and 2).
In FIG. 5, the sensor node system includes a sensor node 50 and a receiving device 60. The vibration detection data detected by the sensor node 50 is transmitted to the receiving device 60 via a radio wave. A radio wave is a relatively weak radio signal and can communicate over a distance of several tens of centimeters to several tens of meters.

The sensor node 50 includes a vibration sensor 51, a sensor circuit unit 52, an A / D conversion unit 53, a control unit 54, a memory unit 55, a wireless unit 56, and a power supply unit 57. Power is supplied from the power supply unit 57 to each block. Supplied. The power supply unit 57 includes, for example, a power generation mechanism that converts vibration energy into electric energy, a secondary battery, and the like, and can operate for a long time.
The differential voltage signal obtained by the vibration sensor 51 is differentially detected by the sensor circuit unit 52, then A / D converted by the A / D conversion unit 53 in the subsequent stage, and data processed by the control unit 54 Detection data is stored in the memory unit 55. Thereafter, the vibration detection data is read from the memory unit 55 at a predetermined timing by the processing of the control unit 54 and transmitted from the wireless unit 56 to the receiving device 60 by wireless radio waves.

FIG. 6 shows a configuration example of a conventional vibration sensor 51.
In FIG. 6, the vibration sensor 51 has a fine comb-tooth structure formed on a silicon chip by a MEMS (Micro Electro Mechanical System) process, and is supported between two fixed electrodes 51P and 51N via a spring. The supported movable electrode 51M vibrates. With this configuration, a variable capacitor CP is formed between the movable electrode 51M and the fixed electrode 51P, and a variable capacitor CN is formed between the movable electrode 51M and the fixed electrode 51N. The capacitances of the two variable capacitors CP and CN change differentially.

FIG. 7 shows a configuration example of a conventional sensor circuit unit 52.
In FIG. 7, the sensor circuit unit 52 has a diode D1 whose input terminal is connected to the power supply potential VDD and whose output terminal is connected to one differential output terminal of the vibration sensor 51, and whose input terminal is the output terminal of the diode D1. The diode D2 is connected to one differential output terminal of the vibration sensor 51, the output terminal is connected to the other differential output terminal of the vibration sensor 51, and the input terminal is the output terminal of the diode D2 and the other of the vibration sensor 51. A diode D3 connected to the differential output terminal, the output terminal of which is connected to the output terminal OUT of the sensor circuit 52; a capacitive element C1 connected between the output terminal OUT of the sensor circuit unit 52 and the ground potential; And an initialization switch SW for setting the voltage of the output terminal OUT to the ground potential.

FIG. 8 shows an operation example of the sensor circuit unit 52 and the sensor node 50.
In FIG. 8, when the sensor node 50 is initialized before time T0, the initialization switch SW is turned on by an initialization signal supplied from a control circuit (not shown) to the initialization terminal RST, and the charge of the capacitive element C1 is discharged. Thereafter, the control circuit turns off the initialization switch SW, and the sensor circuit unit 52 waits for input.

  When vibration is applied to the sensor node 50 at time T0, the capacitances of the two variable capacitors CP and CN of the vibration sensor 51 change in a differential manner. At this time, the movable electrode 51M of the variable capacitor CP approaches the fixed electrode 51P or moves away from the fixed electrode 51P in response to the vibration, so that the capacitance of the variable capacitor CP repeats increasing and decreasing alternately. Therefore, the detection signal BP output from one differential output terminal of the vibration sensor 51 is a signal that alternately repeats increasing and decreasing as shown in FIG. Similarly, the detection signal BN output from the other differential output terminal of the vibration sensor 51 is a signal that alternately repeats increasing and decreasing as shown in FIG. As described above, since the capacitances of the variable capacitors CP and CN change differentially, the phases of the detection signals BP and BN differ by 180 °.

  When the detection signal BP is High and the detection signal BN is Low, the diode D1 and the diode D3 are turned off. When the detection signal BP is Low and the detection signal BN is High, the diode D1 and the diode D3 are turned on. On the other hand, when the detection signal BP is High and the detection signal BN is Low, the diode D2 is turned on, and when the detection signal BP is Low and the detection signal BN is High, the diode D2 is turned off. In this manner, the pair of the diode D1 and the diode D3 and the diode D2 are alternately turned on by the detection signals BP and BN, and electric charges are gradually accumulated in the capacitive element C1, and the output signal SO of the sensor circuit unit 52 is The voltage rises (FIG. 8 (C)).

  The A / D converter 53 of the sensor node 50 shown in FIG. 5 performs threshold processing on the output signal SO of the sensor circuit 52 and outputs a control signal as shown in FIG. In the example of FIGS. 8C and 8D, the output signal SO of the sensor circuit unit 52 becomes equal to or greater than the threshold at time T1 after ΔT1 from time T0, so that the control output from the A / D conversion unit 53 is performed. The signal becomes High.

  As described above, the pair of the diode D1 and the diode D3 and the diode D2 are alternately turned on according to the output of the vibration sensor 51, so that the direct current flowing from the power supply potential VDD to the ground potential can be reduced. The leakage current can be reduced to about the diode leakage current (sub-microamperes or less). Therefore, if such a vibration sensor 51 and sensor circuit unit 52 are used, the power consumption of the sensor node 50 on which the vibration sensor 51 and sensor circuit unit 52 are mounted can be reduced to the nanowatt level limit.

JP 2010-281761 A JP 2011-160612 A

  As shown in FIG. 6, the vibration sensor 51 is configured such that the movable electrode 51M vibrates between the fixed electrodes 51P and 51N. Here, the movable electrode 51M is connected to the support via a spring, and a capacitance change depending on vibration occurs between the fixed electrodes 51P and 51N. When vibration is detected using the sensor circuit unit 52 of FIG. 7, it is necessary to secure 100 femtofarads or more for the capacitance change generated in the movable structure including the movable electrode 51M and the fixed electrodes 51P and 51N.

  Here, assuming that the size of the movable electrode 51M is a millimeter level and the minimum distance between the movable electrode 51M and the fixed electrodes 51P and 51N is 10 μm, a capacitance change of 100 femtofarads or more is secured with respect to the magnitude of vibration. In order to achieve this, the thickness of the movable structure needs to be several hundred μm or more. However, when the movable structure is formed by a plating process, a huge processing time (for example, 100 hours or more) is required to secure the thickness, which raises a problem of an increase in manufacturing cost.

  An object of the present invention is to provide a vibration sensor that can increase the capacitance change caused by vibration to 100 femtofarads or more without increasing the thickness of the movable structure.

  The vibration sensor according to the present invention includes a fixed electrode formed of a plurality of strip-shaped electrodes formed on a support substrate, and a plurality of electrodes that are supported on the support substrate via struts and springs and that are opposed to the strip-shaped electrodes of the fixed electrode. The movable electrode is movable in the in-plane direction of the fixed electrode in response to external vibration, and the capacitance is displaced by the displacement of the crossing area of the fixed electrode and the movable electrode. The plurality of strip-like electrodes are electrically connected alternately and connected to the sensor circuit unit as two differential outputs.

  In the vibration sensor of the present invention, the movable electrode is configured to be supported on the support substrate by at least one pair of springs and support columns perpendicular to the arrangement direction of the fixed electrodes.

  In the vibration sensor of the present invention, the movable electrode is configured to be supported on the support substrate by a pair of springs and support columns perpendicular to the arrangement direction of the fixed electrodes. Is arranged along a trajectory that moves in a circular arc shape.

  In the vibration sensor of the present invention, the spring has a configuration in which the height of the support substrate in the vertical direction is increased with respect to the width.

  As described above, if the vibration sensor of the present invention is used, the fixed electrode and the movable electrode are made to face each other and move close to each other, so that the capacitance generated in the movable structure can be achieved without increasing the thickness of the movable structure. Changes can be over 100 femtofarads. Therefore, an increase in manufacturing cost can be suppressed while reducing the size of the vibration sensor.

  In addition, by using the vibration sensor of the present invention, the size of a sensor node having a vibration detection function can be reduced to a sub-centimeter or less. Therefore, downsizing of the sensor node is achieved, and the sensor node can be embedded in a part of a person or a person that could not be embedded due to size restrictions.

It is a figure which shows the structure of Example 1 of the vibration sensor of this invention. It is a figure which shows the circuit structural example of Example 1 of the vibration sensor of this invention. It is a figure which shows the structure of Example 2 of the vibration sensor of this invention. It is a figure which shows the three-dimensional structural example of the spring 4 used for the vibration sensor of Example 2. FIG. It is a figure which shows the structural example of the sensor node system which performs a vibration detection. It is a figure which shows the structural example of the conventional vibration sensor 51. FIG. It is a figure which shows the structural example of the conventional sensor circuit. FIG. 6 is a diagram illustrating an operation example of a sensor circuit 52 and a sensor node 50.

FIG. 1 shows a configuration of a vibration sensor according to a first embodiment of the present invention.
In FIG. 1, the vibration sensor of Example 1 is a movable electrode supported by a support substrate via a support 3 and a spring 4, and a fixed electrode 1 composed of a plurality of strip electrodes patterned on a support substrate (not shown). It is constituted by the electrode 2.

  As shown in FIG. 1 (A) as a stationary state, the movable electrode 2 has a plurality of strip-like electrodes of the fixed electrode 1 and every other strip-like electrode opposed to each other in an electrically integrated structure. Yes. Here, the movable electrode 2 is supported by four sets of support columns 3 and springs 4 and is arranged in parallel with the fixed electrode 1. The spring 4 is deflected by the vibration of the movable electrode 2, and the in-plane direction of the fixed electrode 1 (the left-right direction in the drawing) ) To move. That is, the four springs 4 are attached to the four corners of the movable electrode 2 at a position opposed to the four springs 4 at right angles to the vibration direction. Two or more springs 4 may be provided at opposing positions. FIG. 1B shows a state in which the position of the movable electrode 2 is displaced by vibration. With this configuration, the capacitance between the fixed electrode 1 and the movable electrode 2 changes according to the change in the crossing area.

FIG. 2 shows a circuit configuration example of the first embodiment of the vibration sensor of the present invention.
In FIG. 2, the plurality of strip-shaped electrodes of the fixed electrode 1 are electrically connected alternately, and are connected to a sensor circuit unit 52 having the same configuration as that shown in FIG. 7 via two differential output terminals. The sensor circuit unit 52 includes diodes D1, D2, and D3 connected in cascade between the power supply VDD and the output terminal OUT, a capacitor C1, and an initialization switch that sets the voltage of the output terminal OUT to the ground potential at the time of initialization. SW includes two differential output terminals of the vibration sensor connected to the anode and the cathode of the diode D2. The plurality of strip-like electrodes of the movable electrode 2 are electrically connected and grounded via the support column 3 and the spring 4 shown in FIG. The operation of the sensor circuit 52 is the same as that of the conventional circuit described with reference to FIGS.

  With this configuration, the capacitance change caused by vibration can be increased to 100 femtofarads or more without increasing the thickness of the fixed electrode 1 and the movable electrode 2.

FIG. 3 shows a configuration of a vibration sensor according to a second embodiment of the present invention.
In FIG. 3, the vibration sensor of Example 2 is supported by a fixed electrode 1 composed of a plurality of strip-like electrodes patterned on a support substrate (not shown), and a support substrate 3 via a column 3 and a single spring 4. It is comprised by the movable electrode 2 made.

  In the movable electrode 2, a plurality of strip-shaped electrodes opposed to every other strip-shaped electrode of the fixed electrode 1 have an electrically integrated structure. Here, one movable electrode 2 coupled to the notch is used. It is supported on the support substrate via the spring 4 and the column 3. The spring 4 is bent by the vibration of the movable electrode 2, and the movable electrode 2 is movable in the arc direction and in the in-plane direction of the fixed electrode 1 starting from the column 3.

FIG. 4 shows a three-dimensional configuration example of the spring 4 used in the vibration sensor of the second embodiment.
In FIG. 4, when the support substrate is a horizontal plane, the spring height T is increased with respect to the spring width W. Thereby, the displacement of the movable electrode 2 in the vertical direction can be suppressed, and the movable electrode 2 and the fixed electrode 1 can be brought close to each other. By using the spring 4 for the vibration sensor of the first embodiment, the movable electrode 2 and the fixed electrode 1 can be brought close to each other in the vibration sensor of the first embodiment.

  Since the vibration sensor of the second embodiment has a configuration in which the movable electrode 2 is supported by one spring 4 as compared with the first embodiment, the spring constant of the entire vibration sensor can be reduced and the resonance frequency is lowered. be able to. In general, the frequency of vibration generated in the environment is about 100 Hz. By using the vibration sensor of the second embodiment, most of vibration generated in the environment can be detected.

  The movable electrode 2 of the second embodiment vibrates in the arc direction starting from the support column 3, but the fixed electrode 1 may be arranged in an arc shape in accordance with the vibration locus. Thereby, the change amount of the crossing area of the fixed electrode 1 and the movable electrode 2 can be increased, and the capacitance change generated in the vibration sensor can be increased.

  The vibration sensor of the first to third embodiments is used as the vibration sensor 51 shown in FIG. 5, and the vibration sensor 51 and the sensor circuit 52 are connected as shown in FIG. A sensor node that can be operated with energy charged in the element can be realized. In the sensor node, the power consumption required for vibration detection can be reduced to the sub-nanowatt level, so that the operation time of the sensor node can be increased.

DESCRIPTION OF SYMBOLS 1 Fixed electrode 2 Movable electrode 3 Support | pillar 4 Spring 50 Sensor node 51 Vibration sensor 52 Sensor circuit part 53 A / D conversion part 54 Control part 55 Memory part 56 Radio | wireless part 57 Power supply part 60 Receiver

Claims (4)

A fixed electrode comprising a plurality of strip-shaped electrodes formed on a support substrate;
A movable electrode comprising a plurality of electrodes that are supported by the support substrate via struts and springs and are opposed to the band-like electrode of the fixed electrode, and the movable electrode is arranged on the surface of the fixed electrode in response to vibration from the outside. It is movable inward, and the capacitance is displaced by the displacement of the crossing area of the fixed electrode and the movable electrode.
A vibration sensor characterized in that a plurality of strip-like electrodes of the fixed electrode are alternately electrically connected and connected to a sensor circuit unit as two differential outputs. The vibration sensor according to claim 1,
The movable sensor is configured to be supported on the support substrate by at least one pair of springs and support columns perpendicular to the arrangement direction of the fixed electrodes. The vibration sensor according to claim 1,
The movable electrode is configured to be supported on the support substrate by a pair of springs and support columns perpendicular to the arrangement direction of the fixed electrodes.
The vibration sensor, wherein the plurality of strip-like electrodes of the fixed electrode are arranged along a trajectory in which the movable electrode moves in an arc shape starting from the support column. The vibration sensor according to claim 1,
The vibration sensor is characterized in that the height of the support substrate in the vertical direction is larger than the width.

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