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Proceedings Paper

Portable cryogenically cooled infrared imager: how silent it might be?
Author(s): Alexander Veprik; Herman Vilenchik; Ramon Broyde; Nachman Pundak; Andrew Struckhoff
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Paper Abstract

For the sake of weight and compactness, the enclosures of the modern portable cryogenically cooled infrared (IR) imagers are made in the form of a light metal (aluminium, magnesium, titanium) thin-walled shell, serving as an optical bench, accommodating a telescope, an optical train and an Infrared Detector Dewar Cooler Assembly (IDDCA). Such IDDCAs normally rely on miniature rotary Stirling cryogenic coolers, which are known as powerful sources of wideband vibration giving rise to the inherently lightly damped structural resonances in the imager enclosure thus causing loud structure-borne noise. This may lead to an increased range for aural detectability of forward observers who must remain undetected, potentially for long periods of time. Consequently, the aural nondetectability distance becomes one of the crucial figures of merit (along with the overall weight, battery life, imagery quality, etc) characterising the modern portable IR imager. In the novel approach, the IDDCA is mounted within the enclosure using a special silencing pad; effectively attenuating vibration export over the typical high frequency range that contains the relevant structural resonances of the enclosure. The residual noise radiation from the imager enclosure is then attenuated practically to a background level by reshaping the radiation modes thus cancelling the overall volume velocity. This is achieved by finding the "critical point" and affixing there the optimally sized correction mass. The authors report on a successful attempt to develop a cooled imager that is inaudible at greater than 10 meters (even during the cool down phase) per MIL-STD-1774D (Level II).

Paper Details

Date Published: 14 May 2007
PDF: 12 pages
Proc. SPIE 6542, Infrared Technology and Applications XXXIII, 65422P (14 May 2007); doi: 10.1117/12.719280
Show Author Affiliations
Alexander Veprik, RICOR, Cryogenic & Vacuum Systems (Israel)
Herman Vilenchik, RICOR, Cryogenic & Vacuum Systems (Israel)
Ramon Broyde, RICOR, Cryogenic & Vacuum Systems (Israel)
Nachman Pundak, RICOR, Cryogenic & Vacuum Systems (Israel)
Andrew Struckhoff, KOLLSMAN, Inc. (United States)

Published in SPIE Proceedings Vol. 6542:
Infrared Technology and Applications XXXIII
Bjørn F. Andresen; Gabor F. Fulop; Paul R. Norton, Editor(s)

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