Patent ID: 7679375

Claim:
A system for detecting a change in material composition in a product, said system comprising: at least one microwave transmitter, arranged so as to emit a microwave signal at a predetermined microwave frequency composition, and at least one ultrasonic transmitter, arranged so as to emit an ultrasonic signal at a predetermined ultrasonic frequency composition into at least a part of said product to create a propagating density displacement within the product, said microwave and ultrasonic transmitters are arranged so as to cause a local interaction between said microwave and ultrasonic signals in at least a part of said product, and said system further comprises: receiver means to receive at least one of: a) the microwave signal(s) emitted by the microwave transmitter(s) having passed through said part of said product, b) the ultrasonic signal(s) emitted by the ultrasound transmitter(s) having passed through said part of said product, measurement means to measure the attenuation and/or runtime between each emitted signal and each received signal, respectively, under the influence of said propagating density displacement and the associated interaction, and comparison means to compare the measured attenuation and/or runtime with a previously determined attenuation and/or runtime to determine a change in material composition.