Multi-frequency parametric phase conjugation of ultrasound beams in magnetic ceramics

A new operation mode of a parametric phase conjugation of ultrasound waves above the threshold of absolute parametric instability of phonons is reported. A deviation of the carrier frequency in a sequence of incident ultrasound bursts and in a proper sequence of electromagnetic pumping is applied. The deviation avoids amplification of the reverberation noise in the active medium when the repetition time of the conjugation is short enough to be comparable with the relaxation time of acoustic reverberations. As a result, a decrease of repetition time and a correspondent increase of the average output power of a phase conjugator becomes available. The advantage of the new operation mode is demonstrated on an example of supercritical phase conjugation in magnetoacoustic ceramics.