Presentation 2009-10-22
Biomagnetic field measurements and EMI : Active magnetic shielding, and observation and reduction methods of conducted EMI
Ichiro SASADA,
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Abstract(in Japanese) (See Japanese page)
Abstract(in English) Magnetic fields from a human heart and a human brain are very small. They are on the order of several tens of pT for the former and sub-pT for the latter. They are time-varying signals having main frequency spectra less than 30Hz in which range there are relatively strong low-frequency environment magnetic noises as interferences. Magnetic shielding rooms are widely used for their measurements. However, not only they are heavy and expensive, but also there is a hight barrier at the door way of such rooms. In this report, active magnetic shielding methods are presented in which unlike a conventional active magnetic shielding highly permeable shells are combined with it in order to obtain a wide shielded volume with high shielding efficiency and holding an easy access way to the shielded space. Another topic in this report is conducted EMI problem encountered in operating a SQUID sensor used to measure biomagnetic fields with a cryocooler for cooling. The cold head of a cryocooler where a SQUID is located is linked to an inverter-driven valve motor with conducting horses, and the valve motor is further linked to an electrically noisy compressor housing with conducting horse and with a power line. We have analyzed conducting passes of noise currents by observing their waveforms simultaneously at several points using current transformers we made. Through the simultaneous observation of noises, we could easily locate the cause of conducted EMI and succeed to operate a SQUID after reduction of the influence of the EMI.
Keyword(in Japanese) (See Japanese page)
Keyword(in English) Active magnetic shielding / Biomagnetic fields / SQUID / Cryocooler / conducted EMI / Current transformer
Paper # EMCJ2009-44,MW2009-93
Date of Issue

Conference Information
Committee EMCJ
Conference Date 2009/10/15(1days)
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Paper Information
Registration To Electromagnetic Compatibility (EMCJ)
Language JPN
Title (in Japanese) (See Japanese page)
Sub Title (in Japanese) (See Japanese page)
Title (in English) Biomagnetic field measurements and EMI : Active magnetic shielding, and observation and reduction methods of conducted EMI
Sub Title (in English)
Keyword(1) Active magnetic shielding
Keyword(2) Biomagnetic fields
Keyword(3) SQUID
Keyword(4) Cryocooler
Keyword(5) conducted EMI
Keyword(6) Current transformer
1st Author's Name Ichiro SASADA
1st Author's Affiliation Department of Applied Science for Electronics and Materials, Kyushu University()
Date 2009-10-22
Paper # EMCJ2009-44,MW2009-93
Volume (vol) vol.109
Number (no) 241
Page pp.pp.-
#Pages 6
Date of Issue