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当感应参数很低时,可以将电磁场(EM)看作是自由空间内的静电场。在这种情况下,测量的EM场中将含有磁化率的信息。随着发射频率的提高,测量的EM场将受到感应现象(其中包含有电阻率的资料)更多的影响。本文提出一种利用多频和多分量EM数据采集系统为场地的磁化率和电阻率两种参数成象的层析方法。为了评价本方法,分别做了比例模型、数字模拟和现场测量试验。为了能较快地计算,在磁化率的正演模型试验中我们采用了Born一阶近似算法。比例模型试验证实了这种近似算法的有效性。为了调查场地内由于磁化率分布而引起的有意义的二次场,以及验证反演方法的有效性,我们分别做了数字模拟试验。这些成果指出,磁化率成象是可行的。我们研制了一种多频和多分量EM数据采集系统。在现场做了实际试验,验证我们的数据采集系统是否能准确地测出EM场,因为试验场地的磁化率较低,所以在低频段测量的振幅与计算的自由空间磁场的振幅相一致。在高频段测量值与计算EM感应现象所做的正演模拟成果一致,这说明我们的数据采集系统可以采集电阻率成象所需要的资料。这些试验研究指出,多频和多分量EM层析可能成为对场地的磁化率和电阻率两种参数成象的有效方法。
When the sensing parameters are low, the electromagnetic field (EM) can be considered as an electrostatic field in free space. In this case, the measured EM field will contain information on susceptibility. As the firing frequency increases, the measured EM field will be more affected by the induced phenomenon, which contains the resistivity data. In this paper, a multi-frequency and multi-component EM data acquisition system for the site of magnetic susceptibility and resistivity of two kinds of imaging imaging tomography method. In order to evaluate this method, a proportional model, numerical simulation and field measurement experiments were respectively conducted. In order to be able to calculate faster, we used the Born first-order approximation algorithm in the forward model test of susceptibility. Proportional model tests confirm the validity of this approximation algorithm. In order to investigate the significance of the second field due to the magnetic susceptibility distribution in the site and to verify the validity of the inversion method, we have done numerical simulations separately. These results indicate that magnetic susceptibility imaging is feasible. We developed a multi-frequency and multi-component EM data acquisition system. A practical test was done in the field to verify whether our data acquisition system can accurately measure the EM field because the magnetic susceptibility at the test site is low so the amplitude measured in the low frequency band is consistent with the amplitude of the calculated free space magnetic field. The measured values at high frequencies are consistent with the forward simulations performed to calculate the EM-induced phenomena, indicating that our data acquisition system can capture the data needed for resistivity imaging. These experimental studies indicate that multi-frequency and multi-component EM tomography may be an effective method of imaging both the susceptibility and the resistivity of a site.