US Patent 7116202 Inductor circuit with a magnetic interface

An inductor circuit includes a magnetic interface generator that generates a magnetic interface at a center frequency f0. The magnetic interface generator is a passive array of spirals that are deposited on one layer of a multi-layer substrate. The magnetic interface is generated in a plane at a distance Z above the surface of the substrate layer that it is printed on, where the antenna is printed on a second layer of the multi-layer substrate. The distance Z where the magnetic interface is created is determined by the cell size of the spiral array, where the cell size is based on the spiral arm length and the spacing S between the spirals. The center frequency of the magnetic interface is determined by the average track length DAV of the spirals in the spiral array. The spacing S of the spiral array is chosen to project the magnetic interface to the second layer in the multi-layer substrate so as to effect performance of an inductor that printed on the second layer.