Development of advanced measuring instruments based on SQUID sensors for laboratory and industrial applications

The design and development of Superconducting QUantum Interference Devices (SQUID)-based measuring systems using the indigenously developed SQUID sensors and the associated readout electronics is described in detail. The high-field SQUID magnetometer has a sensitivity of 1.2 x 10(-7) emu of magnetic moment. It incorporates several novel features such as a variable temperature regulator based on impedance capillary for achieving excellent temperature control, and the use of a novel input circuit that utilizes two SQUID sensors with different strengths of input signal coupling in order to allow a user-selectable trade-off between high-resolution measurements with a lower dynamic range and low-resolution measurements with a higher dynamic range to permit measurement of magnetization of samples with low as well as high values of magnetic moment. SQUID-based system for nondestructive evaluation of materials harnesses the low-frequency sensitivity of the SQUID sensors for the detection of deep subsurface defects not detectable by the conventional eddy current techniques owing to skin depth limitations. The system is based on a precision X-Y-theta scanner with a position resolution of 50 mu m, custom designed indigenously for this application and has been extensively used for studies on the frequency and depth dependence of the magnetic anomalies associated with the perturbation of the flow of eddy currents in the vicinity of the defects.