A device designed to make visible enemy aeroplanes at night or through fog is the subject of an American patent, states, the New York "Times." Patent rights to the instrument. which is also said to permit pilots to make safe landings, and ships to become visible in fog, are assigned to the Radio Corporation of America.
The device comprises a supersensitive infrared ray detector, which makes objects visible fy the infra-red rays or "heat waves" which emanate from motors. The ordinarily invisible Object reveals itself as a glowing image on fluorescent or luminescent screen. The screen comprises a "pane" of quartz on which is a coating of a luminescent substance such as zinc or magnesium sulphate.
Between the coating and quartz pane are fine parelld wires. When an electric current is passed through the wires, the screen gives off a faint, uniform glow due to the gradual release of energy stored in the coating In this condition the screen is highly sensitized to infra-red rays.
In detecting the presence of aeroplanes at might the screen is faced skyward. Since the exhaust manifolds of motors give off infra-red rays, when such rays strike the sensitized detector they cause a sudden increased release of light energy from the fluorescent screen. The area struck by the rays reveals itself as a glowing image of the plane, which is brighter than the remaining areas of the screen.
In the same way, it is said, infra-red ray generators placed along airfields and on ships would permit pilots in fogs to see on the de-rector the outline of the airport or a ship, whichever the case may be, since infra-red rays penetrate fog. Instead of sensitizing the detector by electric current, it can also be sensitized to infra-red rays by focusing invisible ultra-violet rays on it, the patent reveals.
Sound Detector "Spots" Planes A selective sound wave receiver which picks up sounds coming only from certain directions and thus may locate the direction in which enemy planes are heading has been developed by the Bell Telephone Laboratories, Inc, it is revealed, Because it eliminates sounds coming from other directions than toward which it is pointed, the device is said to have directional sensitivity It comprises a cluster of open-ended tubes of progressively varying lengths, stacked close together so that the open ends, from the shortest to the longest tube, form an ascending spiral. The longest tube has a length aqua] fo the wave length of the lowest frequency of sound {c be picked up. In one example the sound de-rector comprises 49 such tubes.
The tubes are mounted on a cone-shaped device which funnels the sound waves toward e diaphragm of a microphone. Pressure of the waves causes the diaphragm to vibrate, setting up electric currents, These are amplified, then sent to a loud-speaker. Only sound waves coming directly toward the tubes and parallel thereto are picked up, Thus, extraneous ground noises which might interfere are eliminated.
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