1996 Fiscal Year Final Research Report Summary
Development of a measuring system for low-frequency, extremely low-level magnetic field-Introduction of high-performance magnetic shield and a adaptive vibratory noise cancelling mechanism
| Project/Area Number |
06555122
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 試験 |
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| Research Field |
計測・制御工学
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
SASADA Ichiro Kyushu Univ.Electrical and Electronic Systems Engng, Asso.Prof., 大学院・システム情報科学研究科, 助教授 (20117120)
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| Co-Investigator(Kenkyū-buntansha) |
MATSUBA Hironori Hurukawa Electric Applied Physics Research Division, Division Manager, 応用物理研究部, 部長
YAMADA Satoshi Kanazawa Univ.Electrical and Computer Engng, Prof., 工学部, 教授 (80019786)
MIYAZAKI Akio Kyushu Univ.Intelligent Systems, Asso.Prof., 大学院・システム情報科学研究科, 助教授 (70192763)
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| Project Period (FY) |
1994 – 1996
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| Keywords | magnetic shield / magnetic shaking / cylindrical magnetic shield / SQUID magnetometer / biomagnetism / brain magnetic field / heart magnetic field |
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| Research Abstract |
In this study, the following two themes were investigated to develop ; (1) a human-size, light-weight, cylindrical magnetic shield with open ends by applying magnetic shaking technique, and (2) a system canceling vibratory magnetic noise adaptively.
We first constructed half-sized model (diameter=52cm, length=120cm) using Metglas 2705M amorphous ribbons amounting to 15kg in a five-shell structure with narrow spacing (less than 1cm) in-between. The shielding factor for transversely applied alternating magnetic field was 90900 at 1 Hz and 21000 at 10 Hz. It shows high value for relative permeability obtained with magnetic shaking helps multi-shell to work well despite narrow spacings. We then developed a human-size, four-shell cylindrical shield (diameter=90cm, length=250cm) with the same amorphous ribbon of 70kg and Permalloy tapes of 40kg which was wound helically to form the innermost shell used to prevent unwanted leak of the shaking field into the shielded space. Background magnetic noise in the shield was measured using a SQUID magnetometer as 54 fT/ (Hz)^<-1/2> at 1 Hz and 23 fT/ (Hz)^<-1/2> at 10 Hz. The residual dc magnetic field was only 1-2nT.An algorithm to cancel nonstationary magnetic noise due to vibration was evaluated using a model system in which vibration of two order of freedom was assumed and linear gradient ac magnetic fields were used as a reference frame. Noise rejection ratio was 20dB.This system was then implemented to the human-size cylindrical magnetic shield. The rejection ratio was 10dB.Finally, the shielding system was used for a heart magnetic field measurement, showing magnetic field from a human heart was successfully measured by both a SQUID magnetometer and a first-order gradiometer.
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