Coupling between coils in the presence of conducting medium

The authors have studied analytically by simulation and by experiment the impact of a conducting medium on the mutual inductance between two coils, in particular as related to the attenuation of magneto-inductive (MI) waves. To illustrate the physics, the distributions of both the magnetic field and the Poynting vector are determined. They show that the plane wave approach used in the literature for the theoretical description of MI attenuation has only limited validity. It is further found that the mutual inductance becomes a complex quantity, its modulus declining monotonically as a function of conductivity or medium thickness. Their results will be relevant for the design and optimisation of MI waveguide links in conducting media, in general, and particularly when the attenuation is caused by soil conductivity. The results can also be useful for practical applications including in vivo communication and wireless power transfer for medical implants.