# US 4,393,403 A · Rotating diaphragm for a dynamic pick-up device having a pyroelectric layer

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- Number: US 4,393,403 A
- Document ID: US4393403A
- Status: Granted
- Kind: A
- Application number: 06/267,215
- Filed: 1981-05-26
- Granted: 1983-07-12
- Earliest claimed: 1980-09-18
- Assignees: U.S. Philips Corporation
- Inventors: Hans P. Geis; Holger Helber
- Web page: https://patentgrep.com/patent/US4393403A

## CPC

- G03B 9/06: Two or more co-operating pivoted blades, e.g. iris type (shutters functioning as diaphragms by limiting extent of opening movement G03B9/08)
- G01J 5/0805: Means for chopping radiation
- H04N 23/23: from thermal infrared radiation
- G03B: APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR (optical parts of such apparatus G02B; photosensitive materials or processes for photographic purposes G03C; apparatus for processing exposed photographic materials G03D)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)
- H04N: PICTORIAL COMMUNICATION, e.g. TELEVISION

## Abstract

By rotating a diaphragm in front of a pickup device, for example a pyroelectric vidicon, eddy currents are generated in the diaphragm if the diaphragm is made of a metal. These eddy currents are generated as a result of the interaction between the moving diaphragm and the magnetic field of the deflection coils of the vidicon. If the diaphragm is instead made of an insulating material, separation of charges occurs on it as a result electrostatic generation, due to the interaction between the diaphragm and the electrostatic field of the vidicon. Compensation of the charge separation causes interference in the video signal. According to the invention a diaphragm of an insulating material is used which is covered with a pattern of electrically conductive tracks or a very high resistance layer. As a result of this no eddy currents and no noteworthy electrostatic charges can occur, so that an interference-free video signal is obtained.

## Claims

### Claim 1

A rotating diaphragm for a pickup device having a pyroelectric target, in operation said diaphragm rotating about an axis and periodically interrupting thermal radiation which is incident on the pyroelectric target, characterized in that said diaphragm comprises:
an electrically insulating material; and
a layer of electrically conductive material on the electrically insulating material, said electrically conductive layer being in the form of a pattern of electrically conductive tracks in which substantially no eddy currents are generated on rotation of the diaphragm in a magnetic field.

### Claim 2 (depends on 1)

A rotating diaphragm as claimed in claim 1, characterized in that in operation all of the conductive tracks are connected to a single reference potential.

### Claim 3 (depends on 2)

A rotating diaphragm as claimed in claim 2, characterized in that:
the diaphragm is disc-shaped;
the conductive tracks are arranged in a radial pattern; and
the diaphragm has an electrically conductive shaft which is electrically connected to each conductive track.

### Claim 4 (depends on 3)

A rotating diaphragm as claimed in claim 3, characterized in that the pickup device is a pyroelectric vidicon.

### Claim 5

A rotating diaphragm for a pickup device having a pyroelectric target, in operation said diaphragm rotating about an axis and periodically interrupting thermal radiation which is incident on the pyroelectric target, characterized in that said diaphragm comprises:
an electrically insulating material; and
a layer of a material having a high electrical resistance provided on the electrically insulating material, said resistive material having a sheet resistance of between 5.times.10.sup.4 and 10.sup.6 ohms.

### Claim 6 (depends on 5)

A rotating diaphragm as claimed in claim 5, characterized in that in operation the resistive material is connected to a reference potential.

### Claim 7 (depends on 6)

A rotating diaphragm as claimed in claim 6, characterized in that the resistive material has a sheet resistance of approximately 10.sup.5 ohms.

### Claim 8 (depends on 7)

A rotating diaphragm as claimed in claim 7, characterized in that the pickup device is a pyroelectric vidicon.