The smoke-ring concept is a useful device for understanding how the electromagnetic fields induced in a 1D earth propagate and diffuse through a medium. Aside from facilitating a physical understanding of field propagation, the smoke-ring concept has been used to interpret behavior of vertical and radial magnetic fields at the surface and used to estimate depth of penetration for conductivity-depth transforms. Past studies have focused on the current distribution during the off-time. We have calculated the current in a half-space from a half-sine excitation (which provides a continuous induction). In comparison, the current pattern from a continuously excited waveform is more densely distributed in the near surface than the off-time current system, suggesting that measurements during a continuously excited on time are more sensitive to shallow targets. For airborne applications, in which the primary field coupling changes and is an important noise source, a primary field-stripping algorithm affects the current distribution but does not deleteriously affect near-surface sensitivity.

中文翻译：

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有源发射器激励期间半空间中的瞬态电磁烟环

烟圈概念是用于了解一维地球中感应的电磁场如何通过介质传播和扩散的有用设备。除了促进对场传播的物理理解之外，烟圈概念还用于解释表面垂直和径向磁场的行为，并用于估计电导率-深度转换的穿透深度。过去的研究集中在非工作时间的当前分布。我们已经从半正弦激励（提供连续感应）计算出了半空间中的电流。相比之下，来自连续激励波形的电流模式比截止时间电流系统更密集地分布在近地表中，这表明在连续激发时间内的测量对浅层目标更敏感。对于主场耦合发生变化并且是重要噪声源的机载应用，主场剥离算法会影响电流分布，但不会有害地影响近地表灵敏度。