Progress in Superconductivity

The Korean Superconductivity Society (한국초전도학회)
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Characteristics of Superconductive Pb shield for a Whole Head MEG System

헬멧형 뇌자도 장치로의 활용을 위한 Pb 초전도 차폐의 특성

  • Yu, K.K. (Korea Research Institute of Standards and Science) ;
  • Kim, K. (Korea Research Institute of Standards and Science) ;
  • Lee, Y.H. (Korea Research Institute of Standards and Science) ;
  • Kwon, H. (Korea Research Institute of Standards and Science)
  • Published : 2009.10.30
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Abstract

We have investigated the characteristics of a superconductive Pb shield for hemispherical shape and plate to improving signal-to-noise ratio(SNR) of biomagnetism. We measured the shielding factor for the position of helmet shape Pb and for changing the distance from Pb surface. To make a uniform magnetic field, a $1.5m{\times}1.5m$ set of the helmholtz coils activated at several frequencies. The shielding factor of hemispherical shape Pb was from 20 to 57 dB and of Pb plate was about $6{\sim}26dB$ as a function of distance from the lead surface. The shielding factor was rapidly reduced as increasing the distance from Pb surface. The white noise of superconductive quantum interference device(SQUID) with a superconductive shield was about $12fT/Hz^{1/2}$ at 1 Hz, $7fT/Hz^{1/2}$ at 100 Hz. The white noise was more increased about two times than conventional SQUID system without Pb shielding. An auditory signal was measured by first order gradiometer and magnetometer with Pb superconductive shield and compared the SNR. The SQUID system with Pb shield had better performance at low frequency noise level.

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References

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