Time‐Reversal Imaging

Time‐reversal mirror (TRM) properties can be used not only to locate active sources; that is, to solve an inverse source problem, but also to detect passive targets in the frame of inverse scattering problems. Since the time‐domain signal can be expressed as a linear superposition of its Fourier components, this chapter focuses on frequency‐domain representation. This choice is convenient when discussing spatial resolution of imaging in terms of wavelength. The chapter presents TRM for active sources that radiate by themselves, and discusses the implementation steps and fundamental theory. It presents the scalar wave first, followed by the vectorial wave. The chapter discloses the application of TRM for target detections, where targets are illuminated by other active sources and consequently secondary sources are induced on targets. It also discusses several topics, such as the application of TRM in a random medium and the properties of time‐domain TRM.