Magneto-inductive phase-shifters and interferometers

Abstract

Controllable phase shifting of magneto-inductive waves is demonstrated by ferrite loading of magneto-inductive waveguides, which consist of simple linear arrangements of magnetically coupled L–C resonators. It is shown that ferrite loading reduces the resonant frequency in isolated resonators and lowers the pass-band in waveguides. Simple theory is presented to estimate the dependence of the phase shift on the perturbed waveguide parameters and wavelength, and confirmation is provided using experiments carried out using thin film L–C resonators and thin-film magneto-inductive cable operating near 100 MHz frequency. Phase shifts are converted into amplitude changes by interference of magneto-inductive waves in Mach–Zehnder interferometer structures analogous to those used in guided wave optics, using conventional RF components for beam splitting and recombination. Modulation and space switching are both demonstrated, and in each case the variation of output power with phase shift follows the conventional sinusoidal characteristic.