碩士 / 國立臺灣大學 / 物理學研究所 / 90 / Using high-Tc SQUID, we setup a single channel agnetocadiography measuring system in unshielded environment. The measuring device is a 2nd-order off-axis electronic gradiometer consisting of three rf SQUID magnetometers with one as the sensor SQUID and the other two as reference SQUIDs. We use an electronic subtraction circuit to combine the three outputs of the magnetometers by multiplying different coefficients in order to reduce the ambient noise in unshielded environment. We also developed an approach to find a set of coefficients to combine the three signals so that the level of noise spectrum in the frequency band we concerned is the lowest, i.e. the ambient noise is much suppressed in the frequency band we assign. In additional, as the power line interference is so strong to suppress effectively, we use a notch filter and a low-pass filter with cutoff frequency of 30 Hz to further filter out such interference and the unwanted noise. By means of electronic subtraction, the peak-to-peak value of the background noise is reduced from 60 nT to 25 pT and the field spectrum of ambient noise is reduced to about 1 pT/Hz1/2 at 10 Hz. As this noise level is lower than the typical value of MCG signals, we can perform the MCG measurement without magnetic shielding.
| Identifer | oai:union.ndltd.org:TW/090NTU00198012 |
| Date | January 2002 |
| Creators | Shu-Yun Wang, 王姝云 |
| Contributors | H. C. Yang, 楊鴻昌 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | en_US |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 51 |
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