Aural non-detectability of portable HOT infrared imagers Alexander Veprik RICOR, Cryogenic & Vacuum Systems, En Harod Ihud, 18960, Israel ABSTRACT Further shrinking size, weight, power consumption of the High Operating Temperature (HOT) infrared (IR) Integrated Detector-Dewar-Cooler Assemblies (IDDCA) eventually calls for development of high-speed cryocoolers. In case of integral rotary design, the immediate penalty is the more intensive slapping of compression and expansion pistons along with intensification of micro collisions inherent for the operation of crank-slide linkages featuring ball bearings. Resulting from this is the generation of impulsive vibration export, the spectrum of which features the driving frequency along with numerous high-order harmonics covering the entire range of audible frequencies. In a typical design of an infrared imager, the metal light-weight enclosure accommodates a directly mounted IDDCA and an optical train, thus serving as an optical bench and heat sink. This usually results in excitation of structural resonances in the said enclosure and, therefore, in excessive noise generation compromising the aural stealth, especially during the cooldown (boost) phase of operation. The author presents the complex approach to a design of aural undetectable infrared imagers in which the IDDCA is mounted upon the imager enclosure through a silent pad. Special attention is paid to resolving the line of sight stability and heat sinking issues. The demonstration imager relying on Ricor K562S based IDDCA meets the most stringent requirement to 10 meters aural non-detectability distance (per MIL-STD 1474D, Level II) even during boost cooldown phase of operation. Keywords: infrared imager, cryogenic cooler, aural nondetectability, vibration, noise, structural resonance, vibration mounting, silent pad. 1. INTRODUCTION In spite of the recent advances and widespread use of uncooled IR technology it is still generally acknowledged that the “best technology for true IR heat detection is the cooled detectors” [1]. They are superior to the uncooled rivals in terms of working ranges, resolution and ability to detect/track fast moving objects in dynamic infrared scenes. The superior performance of such imagers is achieved by using advanced optronic technologies along with maintaining the IR detector at cryogenic temperatures (77K, typically) using mechanical closed-cycle Stirling cryogenic coolers. Unfortunately, such imagers appear to be too expensive in buying and use, too bulky, too power thirsty, too noisy for a massive deployment. Along with these lines, additional preventing factor is awkward batteries supply/recharge logistics. Over the past few years the industrial progress has led to the development of a new Mercury Cadmium Telluride (MCT) n/p and p/n technology [2,3] offering an attractive opportunity to operate IR detectors at essentially higher temperatures (up to 200K) at extremely low rate of defective pixels and dark currents without compromising performance in a middle wavelength (MW) and long wavelength (LW). More complex nBn infrared detector architecture is a relatively new concept. It was first introduced by Maimon and Wicks [4] and has surprised many with both simplicity and level of performance [2,3]. This technology shows good potential to operate at even higher temperatures. It is not a surprise, therefore, that major market players (DRS Technologies, Raytheon, Teledyne, Sofradir, Selex Galileo, AIM and SCD) continue exploring existing and future MCT opportunities. The direct benefits of using such HOT IR detectors are the lowering the optical, cooling and heat sinking constraints. This eventually results in simplified and more compact night vision instruments allowing using, in particular, rotary integral cryocoolers with improved size, weight and power consumption (SWAP) indices. These improvements are attainable by improving thermodynamic performance, lowering parasitic (conductance and radiation) losses and increasing operational speed leading to more compact design and improving performance of rotary drivers. The unfortunate penalty of increasing driving speed during both the boost cooldown and temperature regulation operational modes is the more intensive slapping of compression and expansion pistons along with intensification of
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Aural non-detectability of portable HOT infrared imagers
Alexander Veprik
RICOR, Cryogenic & Vacuum Systems, En Harod Ihud, 18960, Israel
ABSTRACT
Further shrinking size, weight, power consumption of the High Operating Temperature (HOT) infrared (IR)
Integrated Detector-Dewar-Cooler Assemblies (IDDCA) eventually calls for development of high-speed cryocoolers. In
case of integral rotary design, the immediate penalty is the more intensive slapping of compression and expansion
pistons along with intensification of micro collisions inherent for the operation of crank-slide linkages featuring ball
bearings. Resulting from this is the generation of impulsive vibration export, the spectrum of which features the driving
frequency along with numerous high-order harmonics covering the entire range of audible frequencies.
In a typical design of an infrared imager, the metal light-weight enclosure accommodates a directly mounted
IDDCA and an optical train, thus serving as an optical bench and heat sink. This usually results in excitation of structural
resonances in the said enclosure and, therefore, in excessive noise generation compromising the aural stealth, especially
during the cooldown (boost) phase of operation.
The author presents the complex approach to a design of aural undetectable infrared imagers in which the IDDCA
is mounted upon the imager enclosure through a silent pad. Special attention is paid to resolving the line of sight
stability and heat sinking issues.
The demonstration imager relying on Ricor K562S based IDDCA meets the most stringent requirement to 10
meters aural non-detectability distance (per MIL-STD 1474D, Level II) even during boost cooldown phase of operation.