Bends in magneto-inductive waveguides

Magneto-inductive (MI) waveguides are periodic structures that operate by magnetic coupling between a set of lumped-element L-C resonators. The effect of waveguide bending on the propagation of MI waves is investigated, and it is shown that discontinuities in axis curvature will typically generate reflections. Changes in the equivalent circuit parameters of two types of MI waveguides (formed from discrete elements and continuous cable, respectively) at abrupt bends are identified, and simple formulae are developed for the reflection and transmission coefficients in each case. It is shown that thin-film MI cable can outperform MI waveguides formed using separate elements, due to the inherent stability of the mutual inductance, and can tolerate extremely tight bends. The theory is confirmed using experiments carried out using thin-film cable operating at ca. 100 MHz frequency.