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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

开发低频极低磁场测量系统-引入高性能磁屏蔽和自适应振动噪声消除机制

基本信息

批准号：
06555122
负责人：
SASADA Ichiro
金额：
$ 8.77万
依托单位：
KYUSHU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1996
项目状态：
已结题

项目摘要

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.

在本研究中，以下两个主题进行了调查，以发展;（1）应用磁振动技术，研制了一个人体大小、重量轻、两端开口的圆柱形磁屏蔽罩;（2）研制了一个自适应消除振动磁噪声的系统（直径= 52 cm，长度= 120 cm），使用Metalloy 2705 M非晶带，总计15 kg，呈五壳结构，其间具有窄间距（小于1cm）。横向施加交变磁场的屏蔽因子在1Hz时为90900，在10 Hz时为21000。它显示了高值的相对磁导率获得磁振动有助于多壳工作，尽管窄间距。然后，我们开发了一个人体大小的，四壳圆柱形屏蔽（直径= 90厘米，长度= 250厘米），具有相同的70公斤的非晶带和40公斤的坡莫合金带，其螺旋缠绕形成用于防止震动场不必要地泄漏到屏蔽空间中的最内层的壳。使用SQUID磁力计测量屏蔽中的背景磁噪声，在1Hz下为54 fT/（Hz）^<-1/2>，在10 Hz下为23 fT/（Hz）^<-1/2>。采用线性梯度交流磁场作为参考系，建立了一个二阶自由度振动的模型系统，研究了一种消除振动引起的非平稳磁噪声的算法。噪声抑制比为20 dB。该系统被实现为人体大小的圆柱形磁屏蔽。最后，将该屏蔽系统应用于心脏磁场测量，成功地实现了SQUID磁强计和一阶梯度计对人体心脏磁场的测量。