LTS-SQUID Microscopy: A new technology for high resolution imaging of Magnetic Fields
Abstract
We have developed a scanning superconducting quantum interference device (SQUID) microscope for imaging magnetic fields of room-temperature samples with sub-millimeter resolution. The SQUID microscope can be easily configured with different low temperature superconducting (LTS) sensors, ranging from hand-wound Niobium (Nb) pickup coils for submillimeter resolution to custom designed monolithic thin film Nb SQUIDs with integrated pickup loop structures for higher spatial resolutions or minimum detectable dipole moments. The SQUID sensor and the pickup coil are in the vacuum space of the cryostat separated typically less than 50 μ m by a thin sapphire window from the room-temperature sample. The SQUID is cooled by a high thermal conductivity link to a cryogen reservoir in the same vacuum space. A computerized non-magnetic scanning stage with sub-micron resolution in combination with a tripod leveling system allows samples to be scanned below the sapphire window. For a 500 μ m diameter pickup coil we achieved a field sensitivity of 330fT/Hz1/2 and a 250 μ m diameter coil 850 fT/Hz1/2 for frequencies above 1 Hz. For our first generation monolithic SQUID sensors we used bare washer SQUID with diameters of 40, 60 and 80 μ m and achieved a field sensitivity of 11.9, 8.8 and 5.6 pT/Hz1/2 respectively for frequencies above 1 Hz. The resolution of the instrument can be improved by an order of magnitude by using a fractional turn design. The SQUID microscope will provide new capabilities for imaging of the magnetic fields produced by cardiac action and injury currents, and developmental currents, remnant magnetization, and magnetic susceptibility in isolated living tissue, experimental animal preparations, and algae at the scale of 100 μ m to 1 mm.
- Publication:
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AGU Spring Meeting Abstracts
- Pub Date:
- May 2002
- Bibcode:
- 2002AGUSMGP51A..04B
- Keywords:
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- 1505 Biomagnetism;
- 1594 Instruments and techniques