Transient or time-domain electromagnetic (TEM) method is one of major geophysical exploration techniques. A TEM system employing a multilayer HTS-SQUID sensor, SQUITE3, was developed by ISTEC and MINDECO in commission by JOGMEC in 2010-2012.1) In SQUITEM3, a SQUID sensor is simply cooled by liquid nitrogen in a glass Dewar accompanied with an appropriate low-pass electromagnetic shield. SQUITEM3 is more compact than the former SQUID-based TEM system (SQUITEM2) and exhibits one order of magnitude higher slew rate (10.5 mT/s). 2) Its superior exploration depth was confirmed in a field test in Australia. Since 2013 SQUITEM3 has been used for accrual exploration of metal resources. Recently, an improved SQUID-based TEM system with three component HTS-SQUID sensors has also been developed in commission by JOGNEC.
2) T. Hato et al., Supercond. Sci. Technol. 26, 115003 (2013).
Principle of electromagnetic exploration based on TEM method.
Actual exploration using SQUITEM3 in Peru