JPS6126834A - Electrostatic capacity type pressure sensor - Google Patents

Abstract

PURPOSE:To reduce an electrostatic capacity pressure sensor in size by arranging a coil which constitutes an LC tank circuit at a pressure signal conversion part spirally on almost the same plane with a fixed electrode on a base. CONSTITUTION:The LC tank circuit is constituted by connecting the plane spiral coil 10 is connected to the series type electrostatic capacity composed of a plane electrode 6 and two divided parts 8-1, and 8-2 of the fixed electrode 8. When pressure is applied, a pressure receiving film 2 flexes an the electrostatic capacity C between the electrodes 6 and 8 varies, so the resonance frequency also varies with the applied pressure, showing 1:1 correspondence ralation between the applied pressure and resonance frequency. This resonance frequency is led out of the external coil 12 coupled inductively with the spiral coil 10 through a base 4. The coil 10 constituting said LC tank circuit is formed on almost the same plane with the fixed electrode 8, so the total capacity is reduced.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention is applicable to aircraft air data computers, etc.
The present invention relates to pressure sensors used for various systems, and particularly to capacitance type pressure sensors. (Prior Art) Most conventional capacitive pressure sensors convert pressure into low-level analog signals.

However, low-level analog signals have low resolution and are susceptible to noise.

Therefore, an electrode is provided on the pressure-receiving membrane, and by applying pressure, the gap between this electrode and a fixed electrode provided opposite to it is changed, and the applied pressure value is detected as a change in capacitance based on the change in the gap. Digital capacitive pressure sensors have been developed.

In this digital capacitive pressure sensor, the pressure signal converter consists of an electrode of the pressure-receiving membrane, a fixed electrode, and a normal coil connected to the fixed electrode to form two LC meta circuits. It is sealed in a vacuum container. The resonant frequency of the tank circuit of the pressure signal converter is extracted by a coil wound so as to be inductively coupled to the external side surface of the vacuum container housing the tank circuit.

(Problems to be Solved by the Invention) Conventional digital capacitance pressure sensors have a complicated structure, and the tank circuit is constructed using an ordinary coil, resulting in a large volume. There is.

An object of the present invention is to miniaturize a digital capacitive pressure sensor that can detect with high resolution and is less susceptible to noise.

(Means for Solving the Problems) The present invention provides a pressure signal converter in which a coil constituting an LC tank circuit is arranged in a planar spiral shape on substantially the same plane as a fixed electrode on a base, and the LC tank circuit An external coil for inductively extracting the resonant frequency is provided on the surface of the base opposite to the surface on which the coil of the LC tank circuit is provided.

That is, in the capacitive pressure sensor of the present invention, the pressure-receiving membrane 2 and the base 4 are arranged facing each other with a small interval, and the planar electrode 6 is provided on the pressure-receiving membrane 2 side of the opposing surfaces, and the flat electrode 6 is provided on the pressure-receiving membrane 2 side of the opposing surfaces. A fixed electrode 8 divided into two parts is provided at a position facing the planar electrode 6 to form a series capacitance, and a planar spiral shape is provided on almost the same plane as the fixed electrode 8 of the base 4. A coil 10 is disposed, and both ends of the planar spiral coil 10 are connected to two parts of the fixed electrode 8 to form a tank circuit.
A coil 12 that is inductively coupled to the spiral coil 10 is provided on the back side of the surface on which the spiral coil 10 is provided, and this coil 12 converts the tank circuit of the pressure signal converter. The resonant frequency is configured to be detected.

(effect) FIG. 2 shows an equivalent circuit of the pressure sensor of the present invention.

A portion 8- which is divided into two parts, a plane electrode 6 and a fixed electrode 8.
The planar spiral coil 10 is connected to the series capacitance formed by 1.8-2 to form an LC tank circuit. The resonant frequency f of the LC tank circuit is expressed as f=1/2πr "♂ (1).

Here, L is the self-inductance of the spiral coil 10,
C is the capacitance due to the electrodes 6 and 8.

When pressure is applied, the pressure-receiving membrane 2 bends and the capacitance C between the electrodes 6° and 8 changes, so the resonance frequency f according to equation (1) also changes according to the applied pressure, and the applied pressure and resonance frequency change. f indicates a one-to-one correspondence.

This resonant frequency f is transmitted to the spiral coil 10 via the base 4.
The external coil 12 is provided to be inductively coupled to the coil 12.
is extracted and converted into a digital signal.

Since the coil 10 constituting the LC tank circuit is formed on substantially the same plane as the fixed electrode 8, the overall volume is small.

(Example) FIG. 1 represents one embodiment.

The pressure-receiving membrane 2 is made of fused silica, which has low hysteresis and high dimensional stability, and the central part that receives pressure is set to have a thickness of, for example, 0.3 to 0.5 mm, depending on the applied pressure, and the one peripheral part is made of fused silica. It is thickened so that it is joined to the base 4 to form an internal space.

A flat electrode 6 is provided inside the pressure-receiving membrane 2 .

The base 4 is also made of fused silica and has a concave portion in the center corresponding to the S pressure receiving film 2. A planar fixed electrode 8 divided into two parts is provided in the center of the recess at a position facing the planar electrode 6 of the pressure-receiving membrane 2, and a planar spiral coil 10 is fixed around the fixed electrode 8. It is formed on substantially the same plane as the electrode 8 and connected to two parts of the fixed electrode 8. A spiral coil 12 is also provided on the opposite surface of the base 4 and is inductively coupled to the spiral coil 10 in the recess.

The pressure-receiving membrane 2 and the base 4 are opposed to each other so as to form a space inside, and are joined at their respective peripheral edges. At this time, although not shown, the interior can be evacuated through a glass tube, and the glass tube can be sealed to make the interior space evacuated.

It is preferable that the distance between the flat electrode 6 of the pressure-receiving membrane and the fixed electrode 8 of the base in the joined state as shown in FIG. 1 be set to be, for example, about 10 to 20 μm.

An example of the fixed electrode 8 and the spiral coil 10 formed on the four parts of the base 4 is shown in FIG.

The fixed electrode 8 is formed in the same circular shape as the plane electrode 6 of the opposing pressure-receiving membrane, and is separated into two semicircular parts 8-1 and 8-2. A spiral coil 10 is formed around the fixed electrode 8, and both ends of the spiral coil 10 are connected to two parts 8-1, 8-2 of the fixed electrode 8, respectively.

This fixed electrode 8 (8-1, 8-2) and spiral coil 1
0 has an intersection 14, so the process of forming a metal layer and patterning it by photolithography or the like is required twice.
This can be obtained by forming an insulating layer of the intersection portion 14 between them.

FIG. 4 shows another example of the fixed electrode 8 and spiral coil 10 formed in the recess of the base 4.

In this example, the fixed electrode 8 is composed of a central circular part 8-3 and a ring-shaped part 8-4 on the outer periphery, and both ends of the spiral coil 10 formed on the outer periphery of the ring-shaped part 8-4 are two parts 8-3 and 8-4 of fixed electrode 8, respectively;
It is connected to the.

In addition, in the example, the pressure-receiving membrane was explained as fused silica, but
Materials such as alumina can also be used.

(Effects of the Invention) According to the present invention, it is possible to downsize a digital capacitance pressure sensor that can detect pressure with high resolution and is less susceptible to noise.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing one embodiment of the present invention, FIG. 2 is an equivalent circuit diagram for explaining the present invention in detail, and FIGS.
The figures are cross-sectional views taken along the line A-B in FIG. 1, showing examples of patterns of fixed electrodes and spiral coils on the base, respectively. 2...Pressure membrane, 4...Base, 6
...Planar electrode, 8...Fixed electrode,
10... Spiral coil, 12...
...External coil.

Claims (1)

[Claims] (1) A pressure-receiving membrane and a base are arranged facing each other with a small interval, a flat electrode is provided on the pressure-receiving membrane side of both opposing surfaces, and two portions are provided on the base side at positions facing the flat electrode. Divided fixed electrodes are provided to form a series capacitance, and a planar spiral coil is arranged approximately on the same plane as the fixed electrode on the base side, and both ends of this planar spiral coil are connected to the fixed electrode. are connected to the two parts of the base to form a tank circuit, and a surface of the base that is opposite to the surface on which the spiral coil is provided is inductively connected to the spiral coil. A capacitive pressure sensor characterized by being provided with a coil to be coupled.