Patent ID: 7355409
Filing Date: 2008-04-08
Classification: G01V

Abstract:
1. Apparatus for determining presence of an object, comprising: a. an emitter adapted to produce and propagate a time varying primary electromagnetic field; 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; 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 and to provide information corresponding to identification of the material forming the object as a function of said phase differences; d. in which the primary electromagnetic field contains at least one code and the at least one sensor uses the code of said primary electromagnetic field to determine said phase differences; and e. wherein the coded primary electromagnetic field is propagated in time segments, each time segment including at least one continuous waveform of at least one frequency, and wherein the phase of said at least one frequency of each time segment always changes value between successive time segments.