NONDESTRUCTIVE EVALUATION BY QUANTITATIVE DIELECTRIC IMAGING

A TECHNIQUE OF NON-DESTRUCTIVE TESTING AND EVALUATION (NDT&E) BY THREE-DIMENSIONAL QUANTITATIVE IMAGING OF DIELECTRIC PERMITTIVITY IS PROPOSED. DIELECTRIC IMAGE OF A TARGET IS RECONSTRUCTED BY MEASURING THE MICROWAVE SCATTERING FIELD AND UTILIZING A SCATTERING INVERSION ALGORITHM. IT IS EXPECTED TO YIELD A RESOLUTION UNLIMITED BY WAVELENGTH, BUT ONLY LIMITED BY SIGNAL-TO-NOISE RATIO. TO OVERCOME WAVELENGTH LIMITATION, SCATTERING EQUATION IS DIGITIZED INTO A MATRIX FORM WITHOUT FAR-FIELD APPROXIMATION. TO STABILIZE THE INVERSION AND REDUCE ITS SENSITIVITY TO NOISES, THE NUMBER OF NEAR-FIELD SCATTERING DATA IS INCREASED TO MORE THAN THE NUMBER OF PIXELS IN THE TARGET AND A LEAST-MEAN-SQUARE METHOD IS USED TO FIT THE EQUATIONS. THE RESEARCH IS EXPECTED TO LEAD TO DEVELOPMENT OF A LOW-COST AND TRANSPORTABLE QUANTITATIVE NDT&E EQUIPMENT. OWING TO THE SENSITIVITY OF DIELECTRIC PERMITTIVITY TO VARIOUS MATERIALS, IT WILL PROVIDE SHARPER CONTRAST THAN EXISTING DEVICES. THE IMAGING PROCESSING TIMEIS EXPECTED TO BE IN MILLISECONDS, THE EXPOSURE TIME IN THE ORDER OF MICROSECONDS, WITH MICROWAVE DOSE IN THE ORDER OF MICROWATT PER GRAM TO TENS OF MICROWATT PER GRAM, WHICH IS TWO TO THREE ORDERS OF MAGNITUDE BELOW THE SAFETY LEVEL OF CONTINUOUS EXPOSURE.