Cancellation technique of external noise inside a magnetically shielded room used for biomagnetic measurements

Akihiko Kandori, Tsuyoshi Miyashita, Keiji Tsukada

Research output: Contribution to journalArticle

14 Citations (Scopus)

Abstract

First-order gradiometers inside a magnetically shielded room (MSR) were used to cancel magnetic-field noise. However, the magnetic field inside a MSR is distorted when the amount of external noise is large. This distortion is caused by the low-pass filter property of the MSR. Therefore, the time constants of the frequency-dependent attenuation of the MSR vary spatially and this variation must be taken into account. To investigate noise cancellation, we used a multichannel superconducting quantum interference device consisting of four gradiometers measuring a source signal and two gradiometers as a reference. To compensate for the different magnitudes of the gradiometer wave forms, which differed because of slight differences in their pickup-coil cancel rates, we calculated a fitting parameter. The noise-cancellation method consisted of two processes: reduction of ambient noise caused by the differences in the cancel rate of the gradiometers and a gradient magnetic field inside the MSR, and cancellation of wave-form distortion caused by the spatial variation of the time constants inside the MSR. This cancellation method provides additional attenuation of over 20-30 dB in addition to the balance (>46 dB) of a first-order gradiometer. However, the remaining noise, especially a spike (

Original languageEnglish
Pages (from-to)2184-2190
Number of pages7
JournalReview of Scientific Instruments
Volume71
Issue number5
Publication statusPublished - May 2000
Externally publishedYes

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gradiometers
cancellation
rooms
Magnetic fields
Pickups
SQUIDs
Low pass filters
time constant
attenuation
magnetic fields
low pass filters
spikes
coils
interference
gradients
sensors

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)
  • Instrumentation

Cite this

Cancellation technique of external noise inside a magnetically shielded room used for biomagnetic measurements. / Kandori, Akihiko; Miyashita, Tsuyoshi; Tsukada, Keiji.

In: Review of Scientific Instruments, Vol. 71, No. 5, 05.2000, p. 2184-2190.

Research output: Contribution to journalArticle

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