Abstract: 4. A signal-reconstitution method for signals transmitted through a bounded medium comprising the steps of:Propagating a first signal from one point in said bounded medium;Receiving the propagated signal at another point in said bounded medium;Propagating the received signal from one of said points;Receiving the second propagated signal at the other of said points;Reversing the second received signal with respect to time;Propagating said reversed signal from one of said points in said bounded medium; and,When a reflecting object is present at the other of said points, receiving an echo signal at the point at which the reversed signal was propagated, the form of said echo signal approximating the form of said first signal.