Patent ID: 7705598

Claim:
Apparatus for determining presence of an object, comprising: a. an emitter adapted to produce and propagate a time varying primary electromagnetic field, the primary electromagnetic field including a plurality of primary electric field cycles, the emitter including a clock circuit; b. at least one sensor, the sensor adapted to receive a secondary electromagnetic field, the secondary electromagnetic field produced by the object as a function of the primary electromagnetic field and containing a plurality of secondary field cycles; c. the sensor coupled to a receiver, the receiver adapted to determine differences in phase between the primary electromagnetic field and the secondary electromagnetic field at a plurality of points in the primary field cycles and the secondary field cycles and to provide information corresponding to identification of the material forming the object as a function of said phase differences; and d. in which the emitter is adapted to pulse width modulate the emitter at a high frequency in order to generate at least one smooth lower frequency waveform in the primary electromagnetic field; e. in which the at least one sensor uses the emitter clock circuit.