Regensburg 2007 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 8: Superconductivity - Poster Session

TT 8.40: Poster

Montag, 26. März 2007, 14:00–17:45, Poster A

Electromagnetic Exploration with SQUID magnetometers — •Andreas Chwala, Ronny Stolz, Nikolai Uhkansky, Frank Bauer, and Hans-Georg Meyer — Institute for Physical High Technology, Albert-Einstein-Straße 9, D-07745 Jena, Germany

Electromagnetic methods are widely used in geophysical exploration to detect conductivity anomalies, which are a marker for a variety of ore deposits. Transient ElectroMagnetics (TEM) is a standard method for ground based and airborne exploration: A rectangular-like excitation field (primary signal) generates eddy currents in the ground and the corresponding secondary field of the decaying eddy is measured after the primary field is switched off. By this means, an apparent resistivity depth profile can be calculated.

Since SQUIDs are much more sensitive than coils at low frequencies and measure the B field directly they can extend the exploration depth in TEM significantly. IPHT Jena has developed HTS and LTS SQUID systems for TEM. One major demand for such a system is a high slew rate of several milli-Tesla/second since the Flux Locked Loop has to follow the steep transients of the primary signal. The systems are designed to be robust and easy to handle. A ruggedised, water proof box holds the control unit and power supply, the cryostat is placed in a shock absorbing container, the working points of the SQUIDs are tuned automatically by using a microprocessor. The magnetic field resolution is 20fT/√Hz for the LTS SQUID system. The HTS SQUID system uses an ac bias technique to reach a noise floor of 30fT/√Hz above 100Hz and 100fT/√Hz at 1Hz. The superiority of the SQUIDs compared to conventional induction coil type and fluxgate sensors has been demonstrated on many targets. The LTS SQUID systems are now used in routine exploration work.