Patent ID: 8035400

Claim:
A method for nondestructively detecting one or more features within a bulk dielectric material, said method comprising the steps of: (a) generating microwaves from a microwave source, wherein the microwaves have substantially constant frequency; (b) directing a first portion of the generated microwaves to the material, to create a standing wave; wherein the standing wave is a function of the wavelength of the microwaves, of the distance from the source to the material, and of the reflection of microwaves from one or more features within the bulk dielectric material, features that are characterized by at least one interface between different dielectric constants; (c) mixing the reflected microwaves with a second portion of the generated microwaves to produce an interference pattern that is a function of the position, size, shape, and composition of the features within the bulk dielectric material; (d) repeating steps (a), (b), and (c) with a plurality of different standing waves; wherein the standing waves differ from one another due to differing distances between the microwave source and the bulk dielectric material, or due to differing microwave frequencies, or both; and wherein the repetitions of steps (a), (b), and (c) with a plurality different standing waves may occur simultaneously, or consecutively, or both; (e) comparing the interference patterns derived from two or more different standing waves; and inferring the position of one or more features from the locations where the interference pattern changes from one standing wave to another; wherein features at a selected depth range within the bulk dielectric material are detected by selecting at least some of the standing waves such that, at the selected depth range, the rate of change of the standing wave, as a function of distance from the microwave source, is at or near a local maximum, whereby changes in the interference pattern between incrementally close standing waves are enhanced for features at the selected depth range within the bulk dielectric material; and wherein the dimensions of the features detected are substantially smaller than the wavelength of the microwaves; and (f) repeating steps (a) through (e) for a plurality of locations within the bulk dielectric material, and forming an image that displays graphically the difference between interference patterns at the plurality of locations, whereby the image depicts features within the bulk dielectric material visually.