Ultrasonic processing method and apparatus with multiple frequency transducers

An ultrasonic processing apparatus comprising:

• multiple ultrasonic devices operable for supplying ultrasonic energy, wherein a first group of the ultrasonic devices has a first resonant frequency and a second group of the ultrasonic devices has a second resonant frequency that is different from the first resonant frequency, and wherein there is an excluded subrange between the first and second resonant frequencies in which none of the ultrasonic devices has a resonant frequency;
• and
• a generator for supplying a driving signal to the ultrasonic devices, wherein the driving signal varies in frequency throughout a range that includes the excluded subrange and the resonant frequencies of the ultrasonic devices.

An ultrasonic processing method comprising the steps of:

• providing multiple ultrasonic devices operable for supplying ultrasonic energy, wherein a first group of the ultrasonic devices has a first resonant frequency and a second group of the ultrasonic devices has a second resonant frequency that is different from the first resonant frequency, and wherein there is an excluded subrange between the first and second resonant frequencies in which none of the ultrasonic devices has a resonant frequency;
• and
• supplying a driving signal to the ultrasonic devices, wherein the driving signal varies in frequency throughout a range that includes the excluded subrange and the resonant frequencies of the ultrasonic devices.