Abstract: An identification system comprising a transponder having receiver means adapted to extract powering energy from a surrounding electromagnet field, transponder transmitter means adapted to transmit at least one unique signal from the transponder, frequency generating means for generating a plurality of pre-determined frequencies, each frequency adapted to carry the signal from the transmitter means to an interrogator receiver means adapted to receive said signals to achieve identification of said transponder, said transponder transmitting signals successively or repetitively using at each successive or repetitive transmission a newly selected frequency or set of newly selected frequencies.

Abstract: An apparatus for radiating a magnetic field of substantially uniform magnitude along an axis in a volume of space having width, height and depth directions includes a first coil arranged in the width and height directions and has a first imaginary point as its center. A second coil is arranged in the width and height directions with a second imaginary point at its center and is spaced from the first coil. The first and second coils each have a side and a predetermined configuration and are positioned adjacent each other, in opposite and facing configuration. The first and second coils are spaced by a distance in the range of 2.0 to 0.1 times the length of one of the coil sides. The first and second coils provide in response to a current applied to the coils, a substantially uniform field within the volume of space being located between first and second imaginary points and extending in the depth direction.

Abstract: A concentrator adapted to concentrate signals for reception by a receiver, said concentrator comprising a conductive portion juxtaposed with said receiver, said concentrator being aligned so as to receive said signals and cause further signals to impinge on said receiver and thereby enhance reception of said signals by said receiver. Also disclosed is a shield for substantially eliminating magnetic field radiation from within a predetermined area, the field being diverted from the area via a conductive strip.

Abstract: A portable passive transponder utilizes a single inductive coil transmission and reception system along with a single component rectifying means that is integratable on a single chip. The single coil is adapted to receive a power and/or information signal from an interrogator and transmit another signal simultaneously and independently of the power and/or information signal. A phase coherent frequency multiplier is also utilized which allows higher frequencies than the power signal to be generated, transmitted, and coherently detected.