Electromagnetic tunnel detection is studied numerically using a 3D analytic infinite lossy homogeneous space solution to magnetic dipole radiation and scattering from an infinite cylinder, in a crosshole context. At low frequencies, this serves as a model for a transmit coil radiating a time-varying magnetic field that is then detected from the open-circuit voltage induced on a receive coil. Numerical simulations illustrate how various parameters influence the signal strength and the ability to discern the scattered signal. Tunnel detection is achieved at relatively high frequencies (but below typical ground-penetrating radar frequencies) for fresh water-saturated sand and for weathered granite, which are lower loss media; for the coil and tunnel parameters used here, the optimum frequencies appear to be between 100 kHz and 1 MHz. Tunnel detection for fresh water-saturated clay, a much more lossy medium, can be achieved at a quite low frequency, with an optimum frequency between 1 and 10 kHz. These results suggest that, when a resonant coil system is used, tunnel detection may be possible in a wider range of earth media than previously reported, when the best-suited choice of frequency is used.

中文翻译：

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井间电磁隧道探测的数值研究

使用3D解析无限无损均匀空间解决方案对电磁偶极子的辐射和来自无限圆柱体的散射（在交叉孔环境中）进行了数值研究。在低频下，它用作发射线圈辐射时变磁场的模型，然后从接收线圈上感应的开路电压中检测出时变磁场。数值模拟说明了各种参数如何影响信号强度以及辨别散射信号的能力。对于淡水饱和的沙子和风化的花岗岩，在相对较高的频率（但低于典型的穿透地面的雷达频率）下实现隧道检测，这是损耗较低的介质；对于此处使用的线圈和隧道参数，最佳频率似乎在100 kHz到1 MHz之间。可以以非常低的频率（在1至10 kHz之间的最佳频率）实现对淡水饱和粘土（一种损耗更大的介质）的隧道检测。这些结果表明，当使用谐振线圈系统时，当使用最合适的频率选择时，在比以前报道的更广泛的地球介质中，隧道检测是可能的。