Thin-film magneto-inductive cables

Magneto-inductive cables for low (ca 100 MHz) radio frequencies are demonstrated in thin-film form. 20 cm long resonant elements are formed using double-sided patterning of copper-clad polyimide, based on single-turn inductors and parallel-plate capacitors that use the substrate as an interlayer dielectric. Continuous cables are formed by overlaying elements, in an arrangement that allows a high, positive coupling coefficient (kappa > 0.6) to be achieved despite the use of a planar geometry. Equivalent circuit parameters are extracted from experiments on integrated coupling transducers, and propagation characteristics are compared with simple theory. Low propagation loss (4 dB m(-1) at 55 MHz, falling to 2.3 dB m(-1) at 130 MHz) is demonstrated near the operating frequencies of magnetic resonance imaging, for a potential application as patient-safe cable in internal imaging.