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.

在这项研究中，研究了以下两个主题以发展。（1）通过应用磁性摇动技术，一种人体大小的，轻巧的圆柱磁屏蔽，带有开放端的末端，以及（2）一种取消振动磁噪声的系统。我们首先构建了半尺寸的模型（直径= 52厘米，长度= 120cm，长度= 120cm），使用metglas 2705m的无晶型织布型（五脚架）在较近的五-Shell结构中，该结构较小，该结构是五-Shell的结构（比15ke）（五-Shell）（五-Shornell）（五-Shell）结构（比15ke）。中间。横向应用交替磁场的屏蔽因子在1 Hz时为90900，在10 Hz时为21000。它显示出具有磁摇动获得的相对渗透性的高价值，有助于多壳，尽管间距狭窄。然后，我们开发了一个人类大小的四壳圆柱形盾牌（直径= 90厘米，长度= 250厘米），具有相同的70kg的无定形色带和40千克的薄饼胶带，呈螺旋形成螺旋状的螺旋，形成用于防止不必要渗出的弹药漏水的壳壳。使用鱿鱼磁力计为54 ft/（hz）^<-1/2>在1 Hz时和23 ft/（hz）^<-1/2>在10 Hz时测量盾牌中的背景磁噪声。残留的直流磁场仅为1-2nt。使用模型系统评估了由于振动而取消非平稳磁噪声的算法，其中假定两个自由度的振动，并将线性梯度AC磁场用作参考框架。噪声排斥比为20dB。然后将该系统实现到人尺寸的圆柱磁屏蔽。排斥比为10dB。在最后，屏蔽系统用于心脏磁场测量，显示了人心脏的磁场，通过squid磁力计和一阶渐变仪成功测量了人类心脏的磁场。