Identification of Hidden Objects in Layered Media With Shadow Projection Near-Field Microwave Imaging

A shadow projection approach for near-field microwave imaging is developed to distinguish the size and shape of objects embedded in layered media. An ordinary microwave image may only present a small portion of the front surface of an object due to the lensing effect of refraction at the boundary between two adjacent layers with a high dielectric contrast. Therefore, instead of looking at the primary image, the projection onto the interface behind the object is investigated to better discern the object’s true size and shape. A diffraction tomographic algorithm is modified to accentuate the shadow image. The efficacy of this shadow projection method is demonstrated by 3-D numerical simulations of air voids in a dense dielectric slab.