September 23, 2004Univeristy of Twente6 UWA (van Kann et.al. 2002) Noise level: 0.5 E/Hz CMRR (ang.): >10 4 (10 6 ) CMRR (lin.): 10 9 (310 10 )
September 23, 2004Univeristy of Twente7 Gravitec (Veryaskin 2000) Noise level: 3 E/Hz CMRR: ?
September 23, 2004Univeristy of Twente8 Univ. Kharkov (verozub 1996) F = 0 for I 1 = 0. Magnetic levitation of proof mass Low intrinsic noise level… Lateral stability… Potential for miniaturization…
September 23, 2004Univeristy of Twente9 High-Tc High-Tc conceptual design study on basis of Maryland device 1 Predicted sensitivity 4 mE/ Hz @ 1 Hz and 77 K 2.5 mE/ Hz @ 0.1 Hz and 28 K 1 C.S. Jacobsen et. al., Conceptual Design of a Gravity Gradient sensor based on high Tc superconducting technology, ESA contract 9031/90/NL/PB CCN2 final report May 1995
September 23, 2004Univeristy of Twente10 Key technologies: materials Low-Tc Nb @ 4 K High-Tc YBCO @ 77 K Bi, Tl, Hg families MgB 2 Tc of 39 K, operating temp. 35 K Test masses High quality Nb or Si
September 23, 2004Univeristy of Twente11 Key technologies: SQUIDS Low-Tc Nb: improved sensitivity Well developed technology High-Tc YBCO: limited progress since 1995 Lifetime: no significant improvement Coupling coils: still difficult (T) MgB 2 Research in full swing At present no sophisticated junction technology More work needed
September 23, 2004Univeristy of Twente12 Key technologies: levitation coils Nb Fulfils requirements BSCCO Joining still a problem Tapes 0.2x5 mm 2 (big) Geometry: react after wind, limited strain Other materials not suitable MgB 2 First results wit powder in tube, but improvement in properties needed Joints not yet realised
September 23, 2004Univeristy of Twente13 Key technologies: electronics SQUID electronics for both low-Tc and high-Tc has improved in sensitivity and speed Modulation techniques are available for improved signal to noise ratios at low frequencies
September 23, 2004Univeristy of Twente14 Key technologies: cooling 1 Cooler mass 4K 100 kg 35K 10 kg 77K 1 kg Recent overview for cryocoolers in space: ISEC, 6-9 september 2005, Noordwijkerhout
September 23, 2004Univeristy of Twente15 Key technologies: cooling Efficiency: P in @ 0.3W 2kW @ 4K 20W @ 40K 7W @ 77K
September 23, 2004Univeristy of Twente16 Key technologies: cooling Mass vs. volume
September 23, 2004Univeristy of Twente17 Conclusions Low-Tc: possible, size reduction possible, cooler has large mass and requires a lot of power MgB 2 : research is underway, has to prove itself, cooling hast intermediate mass and power requirements High-Tc: looks possible when several practical issues have been solved (maybe hybrid structure with MEMS), cooler has acceptable mass and power requirement
September 23, 2004Univeristy of Twente18 High-Tc Mechanical No specific improvements (Q) Thermal Cooling technology improving, but reliability and lifetime insufficient
September 23, 2004Univeristy of Twente19 Noise in small Gradiometer: Thermal gradiometer noise M=0.1kg; T=4K; Q=10 5 ; f 0 =1Hz; b=0.1m; Miniaturization
September 23, 2004Univeristy of Twente20 M=1 kg, b=1 m, Q=10 5 M=1 kg, b=0.1 m, Q=10 5 M=1 g, b=0.1 m, Q=10 5 M=1 g, b=0.01 m, Q=10 5 Miniaturization
September 23, 2004Univeristy of Twente21 Miniaturization High-T c Coils, squids and cooling make a superconducting High-Tc SGGM not feasible Low T c Maryland/Oxford approach… Kharkov approach…
September 23, 2004Univeristy of Twente22 Reduced mass smaller dimensions everything closer together Coils geometry problems increase stray couplings increase Mechanical alignment etc. more difficult Miniaturization Maryland/Oxford approach
September 23, 2004Univeristy of Twente23 Miniaturization Maryland/Oxford approach Thermal Liq.-He bath not suitable for planetary mission: long lived 4K mechanical cooler? Technical Problems are already conside- rable without miniaturization The technical challenge of realizing a low-Tc Maryland/Oxford-type SGG is considerable. Miniaturization will be difficult and a reliable ‘low mass’ 4K cooler is not yet available.
September 23, 2004Univeristy of Twente24 L1I1L1I1 L2I2L2I2 M Miniaturization Kharkov approach Reduced mass smaller dimensions Coils 2-D coil arrangement possible that can easily be scaled down Mechanical Magnetic spring determined by electrical currents alignment of measurement axis
September 23, 2004Univeristy of Twente25 L1I1L1I1 L2I2L2I2 M Miniaturization Kharkov approach Thermal Liq.-He bath not suitable for planetary mission: long lived 4K mechanical cooler? Realization of a miniature Kharkov-type SGG seems feasible in low-Tc. A reliable ‘low mass’ 4K cooler is not yet available
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