Method and apparatus for examining a solid

Abstract

An apparatus and method for examining the structure of and in particular detecting flaws within a solid are disclosed. The transmitting source directs pseudo-random coded, phase modulated, interrogation signals, at a plurality of frequencies, toward the object being examined. At the receiver, the returning interrogation signals, reflected by structure within the solid object, are demodulated, employing a delayed replica of the pseudo-random code, and are thereafter processed to provide, preferably, both the phase and magnitude of the returning signals relative to the transmitted interrogation signals. The delayed replica of the pseudo-random code provided to the receiver is delayed by selected time increments to provide a range gate. Thus, the data provided by the receiver represents the amplitude and phase of returning signals as a function of both transit time and frequency. By maintaining a sufficiently small transmitting beam or field of view, the resolution of the beam can be made quite small; and for each source transducer position, the transit time can be related to a known examination cell of the solid. The preferred method of the invention further comprises forming determinants based upon at least the phase and magnitude signals to provide an analysis of the solid structure. In preferred embodiments, the frequency may be sequentially varied according to a predetermined pattern, or a plurality of frequencies can be directed toward the object simultaneously. In either circuit configuration, switches and narrow band filters may be provided for separating the received returning signals.