Catherine P. Foley

Airborne TEM surveying with a SQUID magnetometer sensor

Traditionally airborne time-domain electromagnetic (AEM) survey systems use induction coils as the sensor (receiver). We have replaced the induction coil in a transient electromagnetic (TEM) system with a liquid-nitrogen cooled superconducting quantum interference device (SQUID) magnetometer sensor. Using this prototype system, we aimed to improve performance in detecting conductive mineralization, particularly where the conductive mineralization of interest is covered by a conductive regolith. We successfully demonstrated one- and three-component SQUID sensors in airborne TEM surveying, and achieved performance comparable to the induction-coil systems.Implementation of the SQUID system required development of devices capable of operating in magnetically unshielded environments with low noise, high slew rate, and wide bandwidth. Operation of the SQUID sensor in the highly dynamic environment of a towed bird was also necessary, and this implies a high dynamic range and high level of noise associated with t...

Application of high-temperature superconductor SQUIDs for ground-based TEM

Superconducting quantum interference devices (SQUIDs) are intrinsically very sensitive detectors of magnetic flux. Flux sensitivities of one millionth of a flux quantum per root Hz (1μφ0/√Hz) may typically be realized in low-temperature superconductor (LTS) materials, while sensitivities of ∼5μφ0/√Hz may be realized in high-temperature superconductor (HTS) materials. LTS devices are typically cooled with liquid helium (4 K) while HTS devices are typically cooled with liquid nitrogen (77 K). Coupling the magnetic field into a SQUID via a flux-transformer can result in a very sensitive magnetometer with, depending on the type of superconducting material used and the effective area of the flux-coupling transformer, achievable magnetic field sensitivities ranging from fT/√Hz to pT/√Hz over typical bandwidths that span hundreds of kHz. SQUID applications include NDE, biomagnetism and magnetic microscopes.

Comparison of YBCO thin films and SQUIDs prepared by ion beam deposition and RF and DC unbalanced magnetron sputtering

Results obtained with DC SQUIDs prepared by ion beam deposited films of YBa/sub 2/Cu/sub 3/O/sub x/ on substrates of

Experimental determination of HTS dc-SQUID amplifier inductance and noise performance

The inductance L/sub sq/, transimpedance Z, transfer function V/sub /spl Phi// and flux noise S/sub /spl Phi// have been experimentally determined, in open loop mode, for a series of simple dc-SQUID amplifiers which varied only in the length of the loop. The SQUID design had no input flux transformer but included a current path for directly injecting flux into the loop. Correlations between these parameters were obtained which compare favorably with theoretical estimates. We confirm that the best device performance (small S/sub /spl Phi//) is obtained if L/sub sq/ is kept small whilst V/sub /spl Phi// is maximized; the latter was achieved in one device by a novel ion-beam trimming technique.

Preparation and properties of YBa2Cu3O7-x thin-film SQUIDs

Thin films of YBa2Cu3O7_ deposited by ion-beam sputtering on yttria-stabilised zirconia (YSZ) substrates at room temperature have been lithographically patterned to form dc SQUID structures. Weak links are formed by naturally-occurring grain boundaries during annealing f the previously patterned films. These devices function either by he collective action of an array of weak links or by the action of a few dominating ones. Using a flux-locked-loop feedback circuit, we have obtained an upper limit for the SQUID noise of 1.5 x iO of the flux quantum per root Hz at 100 Hz in a SQUID of inductance 60 pH perating in liquid nitrogen. Critical currents averaged over the weak link cross-section are greater than iO A/cm2 at 77 K. The performance of these devices is strongly dependent on temperature in the range 64-80 K. In this paper, we describe the preparation and properties of YBa2Cu3O7_ thin ifims and SQUID devices, and discuss further developments needed to improve the operating characteristics of these devices.