In this paper the concept of time-reversal signal processing is briefly reviewed and its evolution is motivated as a viable technique to ``focus'' energy on a source through an inhomogeneous medium using an array of transducers. Discussed (briefly) are the underlying mathematics of this process and how it is a natural extension of the concept of phase conjugate mirrors, based on monochromatic waves (as in optics) to temporally broadband waves, which occur in ultrasonics or any pulse-echo based application such as ground penetrating radar. Once the basic theory and principles motivating this tantalizingly simple (algorithmically) approach have been developed some simulations to motivate the processing are developed. Shown here, this approach can be applied to ``detect'' anomalies, or more appropriately, scatterers in a medium and an optimization technique to sequentially remove the dominant (strongest) to detect even the weakest scatterer is discussed. This approach is similar to the CLEAN algorithm utilized in radio astronomy.