Time Reversal for Energy Focusing in Fluid and Elastic Media

Brian E. Anderson
Department of Physics and Astronomy
Brigham Young University

Time reversal is a method of focusing wave energy to a specific location in space and/or to locate and characterize an unknown source of wave energy. It has been used in acoustics for secure underwater communications, biomedical applications (e.g. acoustic lithotripsy), and for nondestructive evaluation of structures and mechanical parts. The later application was developed by Anderson’s team at Los Alamos National Laboratory. Time reversal techniques require that a calibration signal (i.e. Green’s function, impulse response, transfer function, etc.) be obtained between a source and a receiver location. Assuming that conditions do not change, the calibration signal(s) may be used to send wave energy back to the target location to provide a coherent reconstruction of a source or to provide a coherent focus of energy at that selected location. This presentation will introduce time reversal techniques and then review some specific experimental results.