Patent ID: 8063814

Claim:
A beat-product radio imaging method (RIM) system, comprising: a matched continuous wave (CW) transmitter and receiver for electronically imaging material in between them, wherein signal attenuation measurements can be collected from a number of different transmitter and receiver perspectives around the material; a pair of crystal oscillators, one of which is disposed in the transmitter and the other of which is disposed in the receiver, and each crystal oscillator having the same rating for frequency uncertainty better than ten parts per million (10-ppm); and a local oscillator disposed in the receiver that uses a reference frequency obtained from the receiver one of the pair of crystal oscillators, and configured to produce a local oscillator signal that can beat-down the transmitter's carrier frequency to baseband; wherein, the frequency error between the local oscillator and the transmitter carrier frequencies produces a beat product of less than one Hertz in frequency and its magnitude is inversely proportional to the path attenuation between the transmitter and receiver; and wherein, a low-pass filter is used to remove everything above one Hertz in the detector to produce an output signal for tomographic processing and display of the material characteristics.