Since more than 15 years, AIM is developing and fabricating dual opposed piston linear coolers with moving magnet motors. Key advantage of such coolers are high MTTF and thus low total cost of ownership, low exported vibration and modular and geometrical flexibility.
SX035 compressor and 6mm standard coldfinger are in serial production for several production programs.
AIM will report on recent product improvements with regard to harsh environments (high ambient temperatures, random vibrations and constant accelerations) and performance enhancements. These changes include compressor, regenerator and cooler drive electronics.
In 2007 AIM introduced SF100 Moving-Magnet Flexure-Bearing compressor suitable for Stirling and Pulse Tube coldfinger.
In this paper there will be an update on several improvements for SF100 Stirling-Type Cooler suitable for SADA-applications.
The improvements to both compressor and regenerator focus on improvements regarding:
- Compliance with harsh environments
- Reliability
- Efficiency
- Increase in power density, i.e. max. input power
- Fast cooldown, especially at high ambient temperatures
Design approach and performance data as well as qualification results will be shown.
Over the past decade, AIM has developed a family of compact, highly reliable cryocoolers to meet the demands of various customers and its products. These developments mainly focused on the improvement and optimization of size, weight, power consumption and cost (SWaP,C). In particular, efforts have been made to meet the requirements for ultra-compact camera cores using high operating temperature (HOT)-IR sensors as well as for high performance IR-modules using the latest digital ROIC technology. Design features and performance data of the most recent cryocooler and cooler electronics developments will be presented. Technical details introduced to meet demanding customer requirements will be discussed.
Minimum size, weight and power (SWaP) is a key requirement for state-of-the-art high performance IR Integrated Detector Cooler Assemblies (IDCA). In the past, the cryocooler was predominantly impact all of the three SWaP characteristics. High operating temperature (HOT) detectors allowed the development for dedicated HOT cryocoolers with significantly improved SWaP. Power consumption for instance, can now be in the same order of magnitude as the detector electronics.
AIM developed a family of linear cryocoolers to meet the demands for HOT, SWaP applications. The coolers are also optimized to meet Harsh Environments. Methods to meet such requirements will be discussed for different designs like single and dual piston compressors. Performance data for new cooler models will be presented.
To meet the increasing demand for compact cryocoolers for commercial applications, AIM developed the MCC cooler family. A key requirement for such applications is long MTTF life as mostly a 24/7 operation is needed. Further technical solutions have been investigated and implemented in the cooler design to comply with common industrial standards and regulations. Cooler types, technical solutions and performance data will be presented.
Significantly increased FPA temperatures for both Mid Wave and Long Wave IR detectors, i.e. HOT detectors, which have been developed in recent years are now leaving the development phase and are entering real application. HOT detectors allowing to push size weight and power (SWaP) of Integrated Detectors Cooler Assemblies (IDCA’s) to a new level. Key component mainly driving achievable weight, volume and power consumption is the cryocooler. AIM cryocooler developments are focused on compact, lightweight linear cryocoolers driven by compact and high efficient digital cooler drive electronics (DCE) to also achieve highest MTTF targets. This technology is using moving magnet driving mechanisms and dual or single piston compressors. Whereas SX030 which was presented at SPIE in 2012 consuming less 3 WDC to operate a typical IDCA at 140K, next smaller cooler SX020 is designed to provide sufficient cooling power at detector temperature above 160K. The cooler weight of less than 200g and a total compressor length of 60mm makes it an ideal solution for all applications with limited weight and power budget, like in handheld applications. For operating a typical 640x512, 15μm MW IR detector the power consumption will be less than 1.5WDC. MTTF for the cooler will be in excess of 30,000h and thus achieving low maintenance cost also in 24/7 applications. The SX020 compressor is based on a single piston design with integrated passive balancer in a new design achieves very low exported vibration in the order of 100mN in the compressor axis. AIM is using a modular approach, allowing the chose between 5 different compressor types for one common Stirling expander. The 6mm expander with a total length of 74mm is now available in a new design that fits into standard dewar bores originally designed for rotary coolers. Also available is a 9mm coldfinger in both versions. In development is an ultra-short expander with around 35mm total length to achieve highest compactness. Technical solutions and key performance data for AIM’s HOT cryocoolers will be presented.
State of the art Mid Wave IR-technology has the potential to rise the FPA temperature from 77K to 130-150K (High
Operation Temperature, HOT). Using a HOT FPA will significantly lower SWaP and keep those parameters finally
dominated by the employed cryocooler. Therefore, compact high performance cryocoolers are mandatory.
AIM has developed the SX040 cooler, optimized for FPA temperatures of about 95K (presented at SPIE 2010). The
SX040 cooler incorporates a high efficient dual piston driving mechanism resulting in a very compact compressor of less
than 100mm length.
Higher compactness - especially shorter compressors - can be achieved by change from dual to single piston design. The
new SX030 compressor has such a single piston Moving Magnet driving mechanism resulting in a compressor length of
about 60mm. Common for SX040 and SX030 family is a Moving Magnet driving mechanism with coils placed outside
the helium vessel. In combination with high performance plastics for the piston surfaces this design enables lifetimes in
excess of 20,000h MTTF.
Because of the higher FPA temperature and a higher operating frequency also a new displacer needs to be developed.
Based on the existing 1/4" coldfinger interface AIM developed a new displacer optimized for an FPA temperature of
140K and above.
This paper gives an overview on the development of this new compact single piston cryocooler. Technical details and
performance data will be shown.
State of the art high performance cooled IR systems need to have more than just excellent E/O performance. Minimum
size weight and power (SWaP) are the design goals to meet our forces' mission requirements. Key enabler for minimum
SWaP of IR imagers is the operation temperature of the focal plane array (FPA) employed. State of the art MCT or
InAsSb nBn technology has the potential to rise the FPA temperature from 77 K to 130-150 K (high operation
temperature HOT) depending on the specific cut-off wavelength. Using a HOT FPA will significantly lower SWaP and
keep those parameters finally dominated by the employed cryocooler. Therefore compact high performance cryocoolers
are mandatory.
For highest MTTF life AIM developed its Flexure Bearing Moving Magnet product family "SF". Such coolers achieve
more than 20000 h MTTF with Stirling type expander and more than 5 years MTTF life with Pulse Tube coldfinger (like
for Space applications).
To keep the high lifetime potential but to significantly improve SWaP AIM is developing its "SX" type cooler family.
The new SX040 cooler incorporates a highly efficient dual piston Moving Magnet driving mechanism resulting in very
compact compressor of less than 100mm length. The cooler's high lifetime is also achieved by placing the coils outside
the helium vessel as usual for moving magnet motors.
The mating ¼" expander is extremely compact with less than 63 mm length. This allows a total dewar length from
optical window to expander warm end of less than 100 mm even for large cold shields. The cooler is optimized for HOT
detectors with operating temperatures exceeding 95 K.
While this kind of cooler is the perfect match for many applications, handheld sights or targeting devices for the
dismounted soldier are even more challenging with respect to SWaP. AIM therefore started to develop an even smaller
cooler type with single piston and balancer.
This paper gives an overview on the development of this new compact cryocooler. Technical details and performance
data will be shown.
Highest efficiency states a crucial requirement for modern tactical IR cryocooling systems. For enhancement of overall
efficiency, AIM cryocooler designs where reassessed considering all relevant loss mechanisms and associated
components. Performed investigation was based on state-of-the-art simulation software featuring magnet circuitry
analysis as well as computational fluid dynamics (CFD) to realistically replicate thermodynamic interactions. As a result,
an improved design for AIM linear coolers could be derived. This paper gives an overview on performance enhancement
activities and major results.
An additional key-requirement for cryocoolers is reliability. In recent time, AIM has introduced linear coolers with full
Flexure Bearing suspension on both ends of the driving mechanism incorporating Moving Magnet piston drive. In
conjunction with a Pulse-Tube coldfinger these coolers are capable of meeting MTTF's (Mean Time To Failure) in
excess of 50,000 hours offering superior reliability for space applications. Ongoing development also focuses on
reliability enhancement, deriving space technology into tactical solutions combining both, excelling specific performance with space like reliability. Concerned publication will summarize the progress of this reliability program and give further prospect.
For different IR application specific cooler requirements are needed to achieve best performance on system level.
Handheld applications require coolers with highest efficiency and lowest weight. For application with continuous
operation, i.e. border surveillance or homeland security, a very high MTTF is mandatory. Space applications
additionally require extremely high reliability. In other application like fighter aircraft sufficient cooling capacity even
at extreme high reject temperatures has to be provided. Meeting all this requirements within one cooler design is
technically not feasible.
Therefore, different coolers designs like integral rotary, split rotary or split linear are being employed. The use of
flexure bearings supporting the driving mechanism has generated a new sub-group for the linear coolers; also, the
coolers may either use a motor with moving magnet or with moving coil.
AIM has mainly focussed on long life linear cooler technology and therefore developed a series of moving magnet
flexure bearing compressors which meets MTTF's exceeding 20,000h (up to 50,000h with a Pulse-Tube coldfinger).
These compressors have a full flexure bearing support on both sides of the driving mechanism. Cooler designs are being
compared in regard to characteristic figures as described above.
For high performance IR detectors the split linear cooler is a preferred solution. High reliability, low induced vibration
and low audible noise are major benefits of such coolers. Today, most linear coolers are qualified for MTTF of 8,000h or
above. It is a strong customer desire to further reduce the maintenance costs on system level with significantly higher
cooler lifetime. Increased cooler MTTF figures are also needed for IR applications with high lifetime requirements like
missile warning applications, border surveillance or homeland security applications.
AIM developed a Moving Magnet Flexure Bearing compressor to meet a MTTF of minimum 20,000h. The compressor
has a full flexure bearing support on both sides of the driving mechanism. In the assembly process of the compressor an
automated alignment process is used to achieve the necessary accuracy. Thus, side-forces on the pistons are minimized
during operation, which significantly reduces the wear-out. In order to reduce the outgassing potential most of the
internal junctions are welded and the use of all non-metallic components is minimized.
The outline dimensions comply with the SADA2 requirements in length and diameter. Further, when operated with a 1/2"
SADA type coldfinger, the cooler meets all specified performance data for SADA2.
The compressor can be combined with different Stirling type coldfingers and also with the AIM Pulse Tube coldfinger,
which gives increased lifetime potential up to 50,000h MTTF.
Technical details and performance data of the new compressor are shown.
Remote sensing from space is an emerging market for applications in security, climate research, weather forecast, and global environmental monitoring, to mention a few. In particular, next generation systems demand for large, two-dimensional arrays in the short (SWIR, 0.9-2.5 μm) and the very long wavelength infrared (VLWIR) spectral range up to 15 μm. AIM's developments for space applications benefit from AIM's experiences in high-performance thermal imaging and seeker-head applications. AIM has delivered a 13 μm cut-off demonstrator for a high resolution Fourier-transform imaging spectrometer in limb geometry. For this 256 x 256 VLWIR sensor we measured a responsivity of 100 LSB/K and a noise equivalent temperature difference of 22 mK with 14 bit ADCs at 880 Hz full frame-rate. The substrate and epitaxial layer grown at AIM exhibit very good uniformity and low dark currents. Currently, AIM develops a 1024 x 256 SWIR detector (0.9-2.5 μm) with a capacitance transimpedance amplifier (CTIA) for hyperspectral imaging. The radiation hardness of AIM's FPA technology (MCT sensor and Silicon read-out integrated circuit) has been successfully tested by a total ionization dose (TID) experiment using ESTEC's 60Co γ-source. Our reference module withstands 30 krad TID. For enhanced reliability of the IDCA, AIM has developed a compact 1 W pulse-tube cooler with flexure bearing compressor, which induces also a very low vibration output. In summary, AIM will be able to supply space qualified detector modules covering the spectral range from 0.9 to 13 μm in the near future.
Pulse tube cryocoolers (PTC) can be regarded as the next step in the development of the Stirling cooler. The major advantage vs. the Stirling cooler is the omission of any moving part in the cold head, resulting in significantly increased MTTF. Further advantages are higher mechanical robustness and stability and the potential for cost reduction. AIM developed PTC's for several years in close cooperation with the University of Giessen. As a recent result at AIM, Coaxial PTC cold head are available within the outline dimension of typical IR Stirling cold head of 13mm diameter. The achieved performance data are comparable to the serial data of the Stirling cold head. This PTC cold head is designed to be operated in the orifice mode without a double inlet which is known to cause instabilities. Technical details and performance data represent the current technical status at AIM.
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