A 2-channel wideband SQUID system for high-frequency geophysical applications

Author

Drung, D. ; Radic, T. ; Matz, H. ; Koch, H. ; Knappe, S. ; Menkel, S. ; Burkhardt, H.

Author_Institution

Phys. Tech. Bundesanstalt, Berlin, Germany

Volume

7

Issue

2

fYear

1997

fDate

6/1/1997 12:00:00 AM

Firstpage

3283

Lastpage

3286

Abstract

A prototype radiomagnetic sounding system for measuring the conductivity of the shallow subsoil down to some 10 m depth was built. With this system, the horizontal magnetic field and field gradient of radio transmitters in the frequency range 10-2000 kHz are detected in small bore-holes of /spl lsim/1 m depth using two wideband SQUIDs. The SQUIDs are operated at 4.2 K in a flux-locked loop having a bandwidth of 11 MHz, a white flux noise level of 1.6/spl times/10/sup -6/ /spl Phi//sub 0///spl radic/(Hz), a feedback range of /spl plusmn/610 /spl Phi//sub 0/, and a maximum slew rate of 2/spl times/10/sup 6/ /spl Phi//sub 0//s above 500 kHz increasing to 5/spl times/10/sup 7/ /spl Phi//sub 0//s at 13 kHz. The system was successfully tested in a first field measurement under urban environmental conditions. The system design allows one in principle to use nitrogen-cooled sensors.

Keywords

SQUID magnetometers; geomagnetism; geophysical techniques; soil; 10 to 2000 kHz; 4.2 K; conductivity measurement; feedback; flux-locked loop; high-frequency geophysical application; magnetic field gradient; nitrogen-cooled sensor; radio transmitter; radiomagnetic sounding; shallow subsoil; slew rate; two-channel wideband SQUID; urban environment; white noise; Bandwidth; Conductivity measurement; Frequency; Geophysical measurements; Magnetic field measurement; Noise level; Prototypes; Radio transmitters; SQUIDs; Wideband;

fLanguage

English

Journal_Title

Applied Superconductivity, IEEE Transactions on

Publisher

ieee

ISSN

1051-8223

Type

jour

DOI

10.1109/77.622054

Filename

622054