US Patent 7598654 Megasonic processing apparatus with frequency sweeping of thickness mode transducers

A megasonic processing apparatus and method has one or more piezoelectric transducers operating in thickness mode at fundamental resonant frequencies of at least 300 KHz. A generator powers the transducers with a variable-frequency driving signal that varies or sweeps throughout a predetermined sweep frequency range. The generator repeatedly varies or sweeps the frequency of the driving signal through a sweep frequency range that includes the resonant frequencies of all the transducers.