Development of TDEM Data Acquisition System Based on High T_c SQUIDs for Mineral Exploration(SQUIDs, <Special Section>Superconducting Electronic Devices and Their Applications)

概要

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The Time Domain Electromagnetic Method (TDEM) survey is one of the several geophysical exploration methods. In the conventional TDEM survey, an induction coil is used as the magnetometer. However, the measurement depth is limited to about 500 m. Using high T_c SQUIDs, there are expectations of large bandwidth and high sensitivity for the TDEM. We developed the high T_c SQUID TDEM system. We have reduced the system noise by developing a 20 mm×20 mm step-edge type direct coupled SQUID and a low noise direct readout flux locked loop (FLL) circuit. We have also improved the slew rate, optimizing the parameter of the FLL circuit. Consequently, the system noise of less than 0.2 pT/Hz^<1/2> at 1 kHz was achieved in the earth's magnetic field. The slew rate was 7.3 mT/sec. We conducted field trials and confirmed that the TDEM using high T_c SQUIDs obtains information of deeper region with high precision compared with the TDEM using induction coils.
社団法人電子情報通信学会の論文
2005-02-01