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Thin Film Pick-Up Coil Magnetometer Using High Temperature Super Conducting Material

IP.com Disclosure Number: IPCOM000036044D
Original Publication Date: 1989-Aug-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 3 page(s) / 55K

Publishing Venue

IBM

Related People

Tesche, CD: AUTHOR

Abstract

The overwhelming majority of SQUID magnetometer systems involve the use of superconducting pick-up coils connected through superconducting contacts to planar DC SQUIDs. These devices must, in turn, be connected through low resistance leads to superconducting impedance matching tuned or transformer circuits. This requires a fully elaborated superconducting technology (junctions, multilayer structures, wire, bulk shielding, superconducting contacts and low resistance contacts to the superconducting bulk and film). The advantage of such a system is that liquid helium can be eliminated as the coolant. The (Image Omitted) disadvantage is that the energy resolution scales with the ambient temperature.

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Thin Film Pick-Up Coil Magnetometer Using High Temperature Super Conducting Material

The overwhelming majority of SQUID magnetometer systems involve the use of superconducting pick-up coils connected through superconducting contacts to planar DC SQUIDs. These devices must, in turn, be connected through low resistance leads to superconducting impedance matching tuned or transformer circuits. This requires a fully elaborated superconducting technology (junctions, multilayer structures, wire, bulk shielding, superconducting contacts and low resistance contacts to the superconducting bulk and film). The advantage of such a system is that liquid helium can be eliminated as the coolant. The

(Image Omitted)

disadvantage is that the energy resolution scales with the ambient temperature. The latter is not of great importance for many applications provided all of the required superconducting structures can be fabricated, including low noise superconducting junctions with noise characteristics determined by the intrinsic Johnson noise terms. The absence of any one of these superconducting structures can seriously degrade the performance of the entire system, even though the performance of an isolated single layer SQUID may have been adequately achieved. Furthermore, the elaboration of all these structures presents a considerable challenge which may take some time to achieve.

The most important commercial application for SQUID magnetometers is in magnetoencephalographic systems for brain research and as a diagnostic tool. The state of the art is now 5 fT/root Hz. It is unlikely that systems with less resolution will be greeted with much enthusiasm in the future due to the extremely weak signal strength and the necessity to reduce the measurement time on patients. This places a severe requirement on the emerging high Tc technology. However, an advantage is gained by the use of only a few of the necessary superconducting structures in a system in which most of the elements are fabricated from conventional superconducting materials.

High temperature pick-up coils coupled to a conventional 4.2oK SQUID and impedance matching circuit will not degrade the energy resolution and can be fabricated. These pick-up coils can be placed in close proximity to the source. The signal for a localized current source falls off as the inverse square of the distance to the source. For a 4.2oK coil, the minimum separation is determined by the thickness of the cryostat wall to about 15 mm. A coil at 100oK could be maintained at a few millimeters from the source. This could provide a substantial increase in the signal strength. For planar samples such as tissue slices and small animal brains, or for planar structures such as films or materials which need to be maintained at temperatures in excess of 4.2oK, the increase could be as large as a factor of 1000.

The properties of the cryogenic shield between the coils and the sample can be altered. In the present magnetome...