Kuc R
Department of Electrical Engineering, Yale University, New Haven, CT 06520-8284, USA.
IEEE Trans Biomed Eng. 1996 Nov;43(11):1125-7. doi: 10.1109/10.541255.
A criterion for determining the maximum spacing between magnetometers for measuring the magnetic field is derived. A two-dimensional (2-D) filter model is employed to determine the maximum spatial frequency component present in the magnetic field that is above the spectral noise level. This maximum frequency component is then sampled at a rate greater than twice per period as indicated by the Nyquist criterion, yielding the required magnetometer spacing. It is shown that the rule-of-thumb employed in current clinical biomagnetic array systems, that the spacing between the coils should be approximately equal to the depth of the source, is adequate when the signal-to-noise power ratio is less than 28.4 (14.5 dB). The analysis also quantitatively demonstrates that reducing the separation between the measurement and source planes has a greater effect on the resolution than decreasing the noise level by the same factor. This result is important for employing high Tc superconductor magnetometers that allow thinner thermal insulating layers at the cost of higher thermal noise.
推导了确定用于测量磁场的磁力计之间最大间距的标准。采用二维（2-D）滤波器模型来确定磁场中高于频谱噪声水平的最大空间频率分量。然后，按照奈奎斯特准则的要求，以高于每周期两倍的速率对该最大频率分量进行采样，从而得出所需的磁力计间距。结果表明，当信噪功率比小于28.4（14.5 dB）时，当前临床生物磁阵列系统所采用的经验法则（即线圈之间的间距应近似等于源的深度）是合适的。分析还定量地证明，减小测量平面与源平面之间的间距对分辨率的影响比将噪声水平降低相同倍数的影响更大。这一结果对于采用高温超导磁力计很重要，因为这种磁力计允许使用更薄的热绝缘层，但代价是热噪声更高。
