Abstract: A transducer and interrogator device is disclosed in which the interrogator provides power and information to the transducer via a magnetic field. The transducer is a passive actuator device that includes an inductive pickup coil that, when subjected to the interrogator's magnetic field, powers the passive actuator and an external electrical device. The magnetic field produced by the interrogator can be modulated in such a manner as to provide identification, commands, or other information to the passive actuator without substantially reducing the power transferred to the passive actuator. Modulation can be by amplitude, phase, frequency, pulse width, or pulse position. An antiphase magnetic field can also be generated to cancel far field radiation. The passive actuator can include a logic circuit to demodulate any received data from the interrogator via the magnetic field, which data can be used to control the operation of the external device.

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 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.