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ABSTRACT: The utilization of single-stage micromachined Joule-Thomson (JT) coolers for cooling small optical detectors is investigated. A design of a micromachined JT cold stage-detector system is made that focuses on the interface between a JT cold stage and detector, and on the wiring of the detector. Among various techniques, adhesive bonding is selected as most suitable technique for integrating the detector with the JT cold stage. Also, the optimum wiring of the detector is discussed. In this respect, it is important to minimize the heat conduction through the wiring. Therefore, each wire should be optimized in terms of acceptable impedance and thermal heat load. It is shown that, given a certain impedance, the conductive heat load of electrically bad conducting materials is about twice as high as that of electrically good conducting materials. A micromachined JT cold stage is designed and integrated with a dummy detector. The JT cold stage is operated at 100 K with nitrogen as the working fluid and at 140 K with methane. Net cooling powers of 143 mW and 117 mW are measured, respectively. Taking into account a radiative heat load of 40 mW, these measured values make the JT cold stage suitable for cooling a photon detector with a power dissipation up to 50 mW, allowing for another 27 to 53 mW heat load arising from the electrical leads.
The Review of scientific instruments 04/2012; 83(4):045117. · 1.52 Impact Factor
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ABSTRACT: At the University of Twente, a 15 K hydrogen‐based sorption cooler is under development, which has no moving parts and, therefore, is essentially vibration‐free. Moreover, it has the potential of a very long life. Although the cooler may operate standalone, it is designed to precool a helium‐based sorption cooler thats establishes 5 mW at 4.5 K, requiring a cooling power of 25 mW at the hydrogen stage. Both coolers use microporous activated carbon as the adsorption material. The combination of these two cooler stages needs a total of 5.4 W of input power and is heat sunk at two passive radiators at temperatures of about 50 K and 90 K (1.9 W and 3.5 W, respectively). We developed and built a demonstrator of the helium cooler under a previous ESA‐TRP contract, and in 2008 we started a new ESA‐sponsored project aiming at the development of the hydrogen stage. In the paper, the preliminary design of this hydrogen‐cooler is presented, along with introductory experiments on its Joule‐Thomson cold stage.
AIP Conference Proceedings. 04/2010; 1218(1):396-403.
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ABSTRACT: Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80 K, delivering a cooling power of 10 mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5 MPa and compression volume of about 22.6 mm(3) when operating the actuator with a peak-to-peak sinusoidal voltage of 100 V at a frequency of 1 kHz. The electrical power input was 2.73 W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.
Review of Scientific Instruments 05/2008; 79(4):045103. · 1.37 Impact Factor
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ABSTRACT: Micro cryogenic coolers can be used to cool small circuitry and improve their performance. The authors present a variety of micro coolers which are fabricated using MEMS technology production processes only. The typical dimension of a micro cold stage is 30 × 2.2 × 0.5 mm. It cools down to 96 K, applying Joule–Thomson expansion in a 300 nm high flow restriction and has a cooling power ranging from 10 mW to 25 mW. This paper discusses the operation of the micro cold stage and the characterization measurements done.
Journal of Micromechanics and Microengineering 09/2007; 17(10):1956. · 2.11 Impact Factor
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ABSTRACT: A breadboard 4.5 K helium sorption cooler for use in vibration-sensitive space missions was developed and successfully tested. This type of cooler has no moving parts and is, therefore, essentially vibration-free. The absence of moving parts also simplifies scaling down of the cooler to small sizes, and it contributes to achieving a very long lifetime. In addition, the cooler operates with limited dc's so that hardly any electromagnetic interference is generated. This cooler is a favorite option for future missions such as ESA's Darwin mission, a space interferometer in which the sensitive optics and detectors can hardly accept any vibration. The system design consists of a hydrogen stage cooling from 80 to 14.5 K and a helium stage establishing 5 mW at 4.5 K. Both stages use microporous activated carbon as the adsorption material. The two cooler stages need about 3.5 W of total input power and are heat sunk at two passive radiators at temperatures of about 50 and 80 K-radiators which are constructed at the cold side of the spacecraft. We developed, built, and tested a demonstrator of the helium cooler. This demonstrator has four sorption compressor cells in two compressor stages. Test experiments on this cooler showed that it performs within all specifications imposed by ESA. The cooler delivered 4.5 mW at 4.5 K with a long-term temperature stability of 1 mK and an input power of 1.96 W. So far, the cooler has operated continuously for a period of 2.5 months and has not shown any sign of performance degradation.
Review of Scientific Instruments 07/2007; 78(6):065102. · 1.37 Impact Factor
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ABSTRACT: The pressure drop of gas flows in a microchannel filled with a dense pillar matrix was investigated with specific attention to a pillar shape. Pillars of height 250 µm and aspect ratio of about 10 were etched in silicon using an optimized Bosch deep reactive ion etching process. The pressure drop head-loss coefficient due to compression and expansion of gas at the inlet and outlet of the pillar matrix was estimated to be about 1.4 for an opening ratio of 10. A comparison of friction factor correlations for circular pillar cross-sections agreed rather well with the correlations proposed for the macroscale. Experimentally determined friction factor correlations for several pillar cross-sections for Reynolds numbers in the range of 50–500 are presented. Among the various pillar cross-sections considered, sine-shaped pillars have the lowest friction factor. These pillar structures with low pressure drop but a rather large wetted area can be used quite effectively as regenerative materials enabling the development of microcryocoolers.
Journal of Micromechanics and Microengineering 06/2007; 17(7):1381. · 2.11 Impact Factor
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ABSTRACT: Cryogenic microcoolers can be used to cool small electronic devices to improve their performance. The authors present a micro-cold-stage of only 0.05 cm3 that cools to 96 K, applying Joule-Thomson expansion in a 300 nm high flow restriction. Critical in such a microcooler is the deposition of water molecules that migrate to the restriction and block the flow. Because the microcooler is made of glass the authors had the unique opportunity to monitor this phenomenon and combine this visualization with experimental data. This provides significant insight in the way this clogging develops and opens possibilities to realize stable operation.
Applied Physics Letters 02/2007; 90(6):064102-064102-3. · 3.84 Impact Factor
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J. F. Burger,
H. J. M. ter Brake, H. J. Holland,
G. Venhorst,
E. Hondebrink,
R. J. Meijer,
T. T. Veenstra,
H. Rogalla,
M. Coesel,
D. Lozano-Castello,
A. Sirbi
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ABSTRACT: ESA’s Darwin mission is a future space interferometer that consists of six free-flying telescopes. To guarantee a proper mechanical
stability of this system, hardly any vibration of the optical system with integrated cryocoolers can be tolerated. This paper
presents the system design of a 4.5 K, 10 mW vibration-free sorption cooler chain, of which the helium stage is currently
in development under an ESA-TRP contract. A sorption cooler is a favorite option because it has no moving parts and it is,
therefore, essentially vibration-free. A two-stage helium/hydrogen cooler is proposed which needs 5 Watts of input power and
which applies two passive radiators at 50 K and 80 K. The paper includes the following aspects: system modelling, radiator
configurations, activated carbons, different multi-stage cooler options, and integration aspects of the compressor cells with
the radiators.
12/2004: pages 503-512;
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ABSTRACT: A single sorption compressor cell that is thermally cycled provides an intermittent flow. For a Joule-Thomson expansion stage,
a more or less continuous flow is required. The standard method to obtain a continuous flow out of a sorption compressor is
to use three or more compressor cells that are operated out of phase. This paper presents an alternative compressor concept
that uses only one compressor cell, two buffer volumes and two check valves. Such a compressor is easier to construct and
to operate and has a higher reliability at the expense of a slight variation in the cooler’s cold-end temperature. The principle
was demonstrated using a sorption compressor cell that is equipped with a gas-gap heat-switch, is filled with Maxsorb activated
carbon, and uses xenon as a working fluid. A flow of 0.5 mg/s was achieved with a low pressure of 2.0 bar and a high pressure
of 12.6 bar. The compression ratio can be increased by reduction of the void volume and by optimization of the compressor
control system.
12/2004: pages 513-522;
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ABSTRACT: At the University of Twente, research on the development of a sorption-based micro cooler is in progress. Because of the absence
of moving parts, such a cooler is virtually vibration free and highly durable, which potentially results in a long lifetime.
A miniature cryogenic cooler with these properties would be appealing in a wide variety of applications including the cooling
of vibration-sensitive detectors in space missions, low-noise amplifiers and semi- and superconducting circuitry.
The objective of the present project is to scale down a Joule-Thomson (JT) cold stage to a total volume of a few hundredths
of a cm3. This size reduction introduces many problems. The proposed cold stage volume results in a restriction cross-sectional area
of about a thousandth of a mm2 which may cause clogging problems. Flow channels with a cross-sectional area of a few hundredths of a mm2 will produce high pressure drops influencing the JT cycle. Furthermore, the micro channels must be capable of withstanding
high pressures and maintaining a large temperature gradient over a relatively short length.
The project aim is to develop a reliable micro JT cold stage that is fabricated out of one material with a relatively simple
and reproducible fabrication method. The length of the cold stage is calculated at about 20 mm with a width of 1.7 mm and
height of about 0.3 mm. The mass flow is in the order of one mg per second to create a net cooling power of 10 mW at 96 K.
The final objective of the project is to integrate the cold stage, vacuum chamber and device into one compact design. This
paper discusses possible solutions to the problems mentioned and presents a concept design of such a miniature JT cold stage.
12/2004: pages 489-496;
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ABSTRACT: A sorption compressor requires heat switches to thermally isolate the cells during heating, and to connect them to a heat
sink during cooling. The requirements for these heat switches are discussed and related to important compressor parameters.
It is shown that under certain conditions a sorption compressor can be operated without heat switches at all. Furthermore,
the static heat transfer behaviour of a gas gap is modelled in detail and compared with experiments on a 300 μm gas gap. Finally,
the dynamics that limit the switching speed are discussed.
12/2001: pages 565-574;
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ABSTRACT: The sorption/Joule-Thomson cycle is a promising cycle for microscale cooling of low-temperature electronic devices because
the cycle lacks moving parts. This facilitates scaling down to small sizes, eliminates interferences, and contributes to achieving
a long life time. A thermodynamic analysis is presented in which the behaviour of compressor and cold stage are analysed separately,
leading to a better understanding of sorption coolers. Some fundamental possibilities to improve the thermodynamic efficiency
are discussed, and as a part of this a novel two stage compressor concept is proposed.
12/2001: pages 553-563;
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ABSTRACT: A heart scanner that can be equipped with up to 25 high-Tc SQUID magnetometers was designed at the University of Twente. In this design the mechanical cooler interference is reduced
by operating two coolers in counterphase. The magnetic cooler interference diminished by positioning the coolers and the SQUIDs
in a coplanar arrangement, and by separating the SQUIDs from the cold tips of the cryocoolers with a solid conducting thermal
interface.
In the present paper the construction of this cryogen-free high-Tc SQUID system is described and test results are presented. A SQUID plate temperature of 60 K was realized in about 2 hours.
The corresponding heat load to the coolers is roughly 0.9 W. With a preliminary magnetic shield around the compressors a noise
level of 0.6 pT/√Hz was measured in the frequency band 10 to 100 Hz and magnetocardiograms were recorded inside a magnetically shielded room.
A further reduction of the noise level is expected after optimizing the mumetal shielding of the compressors.
12/2001: pages 837-846;
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ABSTRACT: We investigated the feasibility of a high-Tc SQUID system for fetal magnetocardiography aiming at a system without a magnetically shielded room and cooled by a cryocooler.
For demonstration purposes, we have selected the APD-Cryotiger, a gas-mixture Joule-Thomson type cooler. We use an alumina
SQUID holder that contains three high-Tc primary measurement SQUIDs and two reference SQUIDs. The three primary SQUIDs can be combined electronically into a second-order
gradiometer with 6 cm baseline. Test experiments performed in a magnetically shielded room revealed a significant noise contribution
arising from the cooler. Because this noise contribution decreases with increasing distance to the cooler cold head, we expect
the source to be located in this cold head, most probably due to remanent magnetization. Because of the large field gradient
in this remanent field, a second-order gradiometer configuration is dominated by the cooler noise. As an alternative, we formed
a first-order gradiometer of the bottom SQUID and the middle SQUID, and corrected for the cooler noise in it by means of the
first-order gradiometer output obtained from the middle SQUID and the top SQUID. In this set up, adult magnetocardiograms
were successfully recorded. Outside the magnetically shielded room, however, second-order gradiometer operation is required.
Therefore, we attempt to identify the source of the noise contribution in order to be able to remove it from the system.
In the paper, the demonstrator set-up is described and experimental results are presented and discussed.
12/2001: pages 789-797;
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ABSTRACT: This paper presents the integration and testing of a 165 K microcooler that operates with a sorption compressor and a micromachined
cold stage. Attractive features of this combination are the lack of vibration and a long lifetime for a potentially very small
cryocooler. The developed cold stage works with the vapor compression cycle and consists of a silicon condenser and flow restriction/
evaporator, which are combined with two miniature glass-tube counterflow heat exchangers. The thermal compressor consists
of five miniature cells filled with adsorption material that are sequenced between ad- and desorption — thus providing a continuous
pressure difference. The system was tested with ethylene gas operating between 14 and 1.5 bar, and produced a cooling power
of 200 mW around 170 K with an input power of about 20 W.
12/2001: pages 643-649;
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ABSTRACT: This paper presents a check valve with integrated filter that can
stand gas pressures of more than 100 bar in the closed direction and
which has a very low pressure drop at low absolute gas pressures in the
forward direction. The check valve is designed as a part of a check
valve unit for application In a miniature cooler for cryogenic
temperatures (<120 K). This cooling system, which utilizes several
micromachined components, will in this paper be introduced to the MEMS
field
Micro Electro Mechanical Systems, 1999. MEMS '99. Twelfth IEEE International Conference on; 02/1999
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H J M ter Brake,
R Karunanithi, H J Holland,
J Flokstra,
D Veldhuis,
L Vargas,
J W M Hilgenkamp,
W Jaszczuk,
N Janssen,
F J G Roesthuis,
H Rogalla
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ABSTRACT: We have fabricated a seven-channel magnetometer, equipped with packaged high- SQUIDs. These inductively shunted SQUIDs have a noise level of typically 120 fT down to 1 Hz. A packaging method has been developed and proved to be reliable over a one-year period with at least 25 thermal cycles. The performance of the system was demonstrated by the wide-band recording of seven-channel magnetocardiograms inside a magnetically shielded room.
Measurement Science and Technology 12/1998; 8(8):927. · 1.49 Impact Factor
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ABSTRACT: A multichannel high-T<sub>c</sub>-SQUID-based heart scanner for unshielded environments is under development, Outside a magnetically shielded room, sensitive SQUID measurements are possible using gradiometers. However, it is difficult to realize large-baseline gradiometers in high-T<sub>c</sub> materials, Therefore, the authors developed two active noise compensation techniques. In the Total Field Compensation technique, a Helmholtz type coil set is placed around the sensors. One magnetometer is used as a zero detector controlling the compensation current through the coil set. For Individual Flux Compensation, the reference signal is sent to the separate SQUIDs (or their flux transformer circuits) to compensate the local environmental noise fluxes, The latter technique was tested on low-T<sub>c</sub> rf-SQUID magnetometers, each sensor set to a field resolution SQUID magnetometers, i.e. 0.1 pT<sub>RMS</sub>/√Hz. The authors were able to suppress the environmental disturbances to such an extent that magnetocardiograms could be recorded in an ordinary environment. Here the two suppression techniques are described and experimental results are presented.
IEEE Transactions on Appiled Superconductivity 07/1995; · 1.04 Impact Factor
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ABSTRACT: In order to achieve turnkey operation, we plan to use cryocoolers to cool a SQUID magnetometer system. To minimize the mag-netical and mechanical interference from the coolers, we intend to switch them off during the actual measurements. Consequently, a thermal storage unit (TSU) is required with sufficient capacity at an appropriate temperature (<77 K). In a feasibility study, we con-sider a load of 0.5 W from the SQUID sensor unit and an operating time of 10 h. To account for an increased load caused by the TSU itself, an overall capacity of 15 Wh is aimed at. The nitrogen triple-point is chosen because of the large latent heat involved in the transition from solid to liquid and the corresponding well-suited temperature (63 K). Furthermore, any safety risks involved with the use of nitrogen are small compared to alternatives. To contain the nitrogen, highly porous alumina is used. A structure was made in which layers of copper and porous material alternate, thus establishing a good thermal contact between the nitrogen and the cas-ing of the TSU. Experiments show an overall capacity of the system around 85% of the expected theoretical value. Suggestions for improvements are given so as to arrive at a TSU capacity of 15 Wh.
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ABSTRACT: A Cryotiger® gas-mixture cooler was applied for cooling of three high-Tc SQUID magnetometers. These SQUID magnetometers were mounted on an alumina holder in an axial gradiometer configuration. From 20 Hz upward, the system noise was about 0.1 pT/√Hz. Below this frequency, the noise gradually increased to a level of 10 pT/√Hz at 1 Hz. This low-frequency excess noise appeared to be due to remnant magnetization of the Cryotiger cold head. Movement of magnetic cold-head parts with respect to the SQUIDs are induced by pressure fluctuations in the heat exchanger lines. By using one SQUID as a reference for the cooler noise, a first-order gradiometer can be formed in which the cooler noise is eliminated. To establish a proper second-order gradiometer either a fourth SQUID has to be added, or the spatial separation between cold head and SQUIDs has to be increased significantly.
Cryogenics 45(4):317-322. · 0.67 Impact Factor
