Christoph Becker, Alexander Steppke, Torsten Koettig, Joachim Gerster,
Lars Dörrer, Matthias Thürk, Frank Schmidl and Paul Seidel

Institut für Festkörperphysik, Friedrich-Schiller-Universität Jena,
Helmholtzweg 5, 07743 Jena, Germany;
E-mail: paul.seidel@uni-jena.de

Abstract - A planar high-T_c DC-SQUID gradiometer has been operated with a specially developed low-noise pulse tube refrigerator. The cold finger of the refrigerator consists only of non-metallic and non-magnetic materials. During the operation of both the sensor and the refrigerator, the noise generated by the cryocooler is below the noise level of the SQUID-gradiometer. We demonstrate the potential of this non-metallic pulse tube refrigerator by measuring the magnetic field originating from a human heart (magnetocardiogram), without additional suppression of the intrinsic refrigerator noise.

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Manuscript received Dec. 14, 2007; accepted January 11, 2008. Reference No. ST25; Category 4 and Category 11.
Paper submitted to Proceedings of EUCAS 2007; published in JPCS 98 (2008), paper # 012039