# US 4,393,434 A · Capacitance humidity sensor

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- Number: US 4,393,434 A
- Document ID: US4393434A
- Status: Granted
- Kind: A
- Application number: 06/323,586
- Filed: 1981-11-20
- Granted: 1983-07-12
- Earliest claimed: 1980-12-16
- Assignees: Yoshio Imai
- Inventors: Yoshio Imai; Yoichi Nabeta; Tadao Inuzuka
- Web page: https://patentgrep.com/patent/US4393434A

## CPC

- G01N 27/225: {by using hygroscopic materials}
- G01R 27/2605: {Measuring capacitance (capacitive sensors G01D5/24)}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)

## Abstract

A capacitance humidity sensor according to the disclosure a non-conductive base plate, electrodes oppositely arranged on the base plate, a metal compound membrane formed by ion-plating independently on the electrodes, the metal compound membrane being roughened on its surface by plasma etching and being active to the humidity, and a moisture permeable metal skin formed on the metal compound membrane. The metal compound is preferably an oxide or nitride of aluminum or magnesium.

## Claims

### Claim 1

A capacitance humidity sensor which comprises a non-conductive base plate, electrodes oppositely arranged on the base plate, a metal compound membrane formed by ion-plating independently on the electrodes, said metal compound membrane being roughened at its surface by plasma etching and being active to the humidity, and a moisture permeable metal skin formed on the roughened surface of the metal compound membrane.

### Claim 2 (depends on 1)

The capacitance humidity sensor according to claim 1, wherein the non-conductive base plate is a glass plate.

### Claim 3 (depends on 1)

The capacitance humidity sensor according to claim 1 wherein the metal compound membrane consists of metal oxide or nitride.

### Claim 4 (depends on 1)

The capacitance humidity sensor according to claim 1, wherein the electrodes are formed in a comb shape and are arranged oppositely so as to mesh with but not contact with each other.

### Claim 5 (depends on 3)

The capacitance humidity sensor according to claim 3, wherein the metal of the oxide or nitride is aluminum or magnesium.