Radiant energy – With infrared or thermal pattern recording
Patent
1987-11-12
1989-08-29
Anderson, Bruce C.
Radiant energy
With infrared or thermal pattern recording
350350R, 350350S, G03C 516
Patent
active
048619922
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to thermal imager testing devices.
2. Description of Related Art
Thermal imager testing devices are used in the testing of thermal imagers so as to avoid the necessity of field trials for the imagers. This application requires that the device present to the thermal imager pictures sufficiently similar to those actually seen in the field for the test to be realistic.
One example of a known thermal imager testing device uses a vanadium dioxide thin film having a thermodynamic phase transition at a predetermined temperature which causes the film to switch from having high infrared transmission to low infrared transmission. The existence of a hysteresis in this phase transition enables the film to be used as an optical storage medium, such that by heating portions of the film above the transition temperature, and placing the film in an optical projector operating in the infrared, scene information written on the film may be projected into the field of view of a thermal imager to be tested.
Such a device suffers the disadvantages however of lack of accuracy and the inability to incorporate a grey scale.
Another example of a known thermal imager testing device comprises a nematic liquid crystal cell incorporating a photoconductive layer. An image shone on the photoconductive layer causes the molecules within selected areas of the liquid crystal to change their orientation within the cell, thus changing the transmission characteristics of incident infrared light through the cell.
Such a device suffers the disadvantage however that the response time of the liquid crystal to changes in the image is relatively slow.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermal imager testing device in which some of the problems inherent in known thermal imager testing devices are at least alleviated.
According to the present invention a thermal imager testing device comprises: a quantity of a smectic liquid crystal material; means for heating selected portions of the quantity such that the material in the selected portions changes from a state in which it is transparent to incident infrared radiation to a state in which it scatters incident infrared radiation; and means for directing infrared radiation onto the quantity so as to produce an indication of the pattern of selected portions across the quantity.
The material suitably has a homeotropic texture in said state in which it is transparent, and a focal conic texture in said state in which it scatters.
The device suitably includes means for applying a voltage across the quantity effective to cause at least some of the material to adopt said state in which it is transparent.
Preferably the device includes a plurality of said quantities, and means for sequentially exposing said quantities to said means for heating and to said means for directing infrared radiation.
BRIEF DESCRIPTION OF THE DRAWINGS
One thermal imager testing device in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawing in which:
FIG. 1 is a schematic plan view of the device; and
FIG. 2 is a schematic diagram of a section along the line II--II of one of the liquid crystal cells incorporated in the device of FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring firstly to FIG. 1, the device includes a number of liquid crystal cells only two such cells 2, 3 being shown in the drawing for the sake of simplicity. The cells 2, 3 are attached to a framework, indicated as 4, the framework being rotatable about a pivot 5. The framework 4 together with the cells 2, 3 are located in a temperature controlled enclosure, indicated as 7, each cell 2, 3 being provided with a backing plate 8 held at a required temperature corresponding to the lowest temperature of a thermal image to be synthesized by the device.
Referring now also to FIG. 2, each cell 2, 3 comprises a quantity of the smectic A phase liquid crystal 9 known as
REFERENCES:
patent: 3796999 (1974-03-01), Kahn
patent: 4040047 (1977-08-01), Hareng et al.
patent: 4059340 (1977-11-01), Kahn
patent: 4263515 (1981-04-01), Runciman
patent: 4639722 (1987-01-01), Urabe
patent: 4659502 (1987-04-01), Fearon et al.
patent: 4693557 (1987-09-01), Fergason
APIE vol. 98, Assessment of Imaging Systems (Sira Nov. 1976 London), "The Laboratory Evaluation of Thermal Imaging Systems", by A. R. Newbery & R. Worswick, pp. 96-104.
Appl. Phys. Lett., vol. 22, No. 3, 1 Feb. 1973, "Ir-Laser-Addressed Thermo-Optic Smectic Liquid-Crystal Storage Displays", by Frederick J. Kahn, pp. 111-113.
Clark Michael G.
Wiltshire Michael C.
Anderson Bruce C.
The General Electric Company p.l.c.
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