Ultrasensitive Superconducting Magnetic Gradiometer.
Abstract
A compact battery-operated superconducting magnetic gradiometer with 10 to the minus 11th power gauss/cm (Hz to the 1/2 power) sensitivity has been built. It has been balanced to better than 50 ppm of the projected axial area in all three orthogonal directions. The sensor SQUID is a multihole 'fractional turn' type, coupled to multi-turn pickup loops made of fine wire to minimize flux trapping and jumping. The cryostat is a light-weight, non-metallic dewar with vapor-cooled radiation shields which holds one liter of liquid helium and operates in excess of 24 hours on one filling. An uhf (300 MHz) low-noise bias system has been developed which can provide a considerable increase of sensitivity when it is incorporated into the system. A data recording system is described which utilizes a battery-operated tape recorder with frequency modulation and demodulation circuits to improve the linearity. A new type of SQUID has been developed for use in the gradiometer and other applications. It combines the reliability of a Nb thin-film microbridge with the low inductance of a bulk Nb ring. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 31, 1972
- Accession Number
- AD0742794
Entities
People
- James E. Zimmerman
- Nolan V. Frederick
Organizations
- National Institute of Standards and Technology