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 report ed. A deviation of the carrier frequency in a sequence of incident ultrasou nd bursts and in a proper sequence of electromagnetic Dumping is applied. T he deviation avoids amplification of the reverberation noise in the active medium when the repetition time of the conjugation is short enough to be co mparable with the relaxation time of acoustic reverberations. As a result, a decrease of repetition time and a correspondent increase of the average o utput power of a phase conjugator becomes available. The advantage of the n ew operation mode is demonstrated on an example of supercritical phase conj ugation in magnetoacoustic ceramics.