Real time ultrasonic phase conjugation

A novel time ultrasonic phase-conjugate mirror is described. The system is based on a transducer array that samples an incident wavefront in space. The signals collected from each array element are electronically mixed with a second harmonic signal using an array of mixers. The phase of the difference frequency signal obtained is conjugate with the incident wavefront. The transducer array then retransmits the conjugated signals, leading to a phase-conjugated wavefront which is reconstructed in front of the transducer aperture and is transmitted back into the medium. Experiments at 300 kHz are described and phase conjugation is demonstrated by a 20-element array. It is shown that efficient phase conjugation is possible for angles of incidence extending up to ±80°