Appearance of Sign Reversal in Geophysical Transient Electromagnetics With a SQUID Due to Stacking

Abstract

. Although the step function inductive response for many TEM targets decays monotonically and is positive at all times, instances of sign reversal do occur. We postulate that this sign reversal is due to the typical bipolar waveform of the TEM transmitter and the stacking procedure. In this contribution, we systematically extend our analysis to binary and ternary power-law expressions for the step function response, modeling measured responses for typical ground structures. The conditions are determined under which sign reversals appear. It is shown that the effect occurs mainly in the case where a shallow slope response is followed by a rapidly decaying response at late times. Such a signal is typically measured on a resistive overburden over a conducting medium. As an example, data are presented from a location where a sign reversal was measured with a SQUID whereas none was found in the coil data. A deconvolution procedure for determining the single pulse response from measured SQUID data is proposed.

A food contaminant detection system based on high-TcSQUIDs

“…This suggests that the signal is proportional to the volume of each sample. In contrast, stainless steel balls (open circles), which are nominally austenitic stainless, produced signals which deviated from expected values because their magnetism depends on the martensitic phase content which is affected by the mechanical history of the material [5].…”

“…However, maintenance costs for x-ray equipment are high, and the lower detection limit for practical x-ray usage is of the order of 1 mm. Along with others, the authors have proposed the development of a detection system using a SQUID magnetic sensor to circumvent the difficulties outlined above [1][2][3][4][5]. The detection technique is based on recording the remanent magnetic field of contaminant by SQUID sensors.…”

Development of Contaminant Detection System using HTS SQUIDs

“…Therefore, to detect metal contaminants, food manufacturers have implemented eddy-current inspection systems, x-ray imaging inspection systems, and metal contaminant inspection systems that use superconducting quantum interference devices (SQUIDs) [1][2][3][4] in their production lines.…”

“…We develop and propose a contaminant inspection system that uses the RF SQUIDs to circumvent the reported difficulties [1][2][3][4] in metal contaminant detection.…”

Development of HTS-SQUID magnetometer system with high slew rate for exploration of mineral resources

“…To improve the sensitivity of the geophysical survey, TEM systems utilizing a superconducting quantum interference device (SQUID) have been developed in several laboratories in Australia and Germany [2][3][4][5][6]. Japan Oil Gas Metals National Corporation (JOGMEC) and Sumitomo Electrical Industry have also developed TEM systems utilizing an HTS-SQUID, called 'SQUITEM'.…”