A HTS SQUID Gradiometer Using Superconducting Coplanar Resonators for Operation in Unshielded Environment

Y. Zhang ； G. Panaitov ； S. G. Wang ； N. Wolters ； R. Otto ； J. Schubert ； W. Zander ； H.-J. Krause ； H. Bousack

《Chinese Journal of Physics》 38卷2S期 (2000/04) Pp. 330-338

並列摘要

We have developed a simple second-order gradiometer with high temperature superconducting quantum interference devices (SQUIDs) suitable for magnetocardiography (MCG) in unshielded environment. The gradiometer consists of three radio frequency SQUIDs with superconducting coplanar resonators, mounted in axial direction with base line of 7.5 cm. The SQUIDs have a pickup area of 8 X 8 mm^2 The gradiometer is only balanced electronically, no mechanical trimming is used. The system achieves a rejection of common mode fields in axial direction of 10^4, and a field sensitivity better than 130 fT/√Hz at 77 K. We have performed a 36-point MCG mapping over the chest of a healthy subject with a recording bandwidth up to 130 Hz. The measurement demonstrates the potential of applying the system for clinical diagnosis of the human heart. We have also demonstrated a potential application of the first-order gradiometer for Non-destructive Evaluation: the detection of small magnetic particles.