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 vanes or sweeps the frequency of the driving signal through a sweep frequency range that includes the resonant frequencies of all the transducers.
1. A megasonic processing method comprising:
providing two or more piezoelectric transducers, each having a fundamental resonant frequency of at least 300 KHz, wherein the fundamental resonant frequency of one piezoelectric transducer defines a maximum fundamental resonant frequency and the fundamental resonant frequency of another piezoelectric transducer defines a minimum fundamental resonant frequency;
providing a tank adapted to contain fluid wherein said two or more transducers are coupled to the tank and adapted for providing vibrations to the tank and its contents; and
generating and simultaneously supplying a driving signal to the transducers, wherein the driving signal has a frequency that sweeps throughout a frequency range that ranges from a maximum drive frequency that exceeds the maximum fundamental resonant frequency and a minimum drive frequency that is less than the minimum fundamental resonant frequency,
further including determining the maximum fundamental resonant frequency and minimum fundamental resonant frequency of the transducers and defining the maximum drive frequency and minimum drive frequency such that the amount that the maximum drive frequency exceeds the maximum fundamental resonant frequency is substantially equal to the amount that the minimum drive frequency is less than the minimum fundamental resonant frequency.
2. A method for operating a megasonic processing apparatus, the method comprising the steps of:
providing a tank adapted to contain fluid;
providing two or more piezoelectric transducers, each having a fundamental resonant frequency of at least 300 KHz, wherein said transducers are adapted for providing megasonic energy to the tank and its contents;
providing a generator coupled to the transducers for supplying to all transducers a driving signal having a frequency that sweeps continuously throughout a frequency range;
determining a maximum fundamental resonant frequency and a minimum fundamental resonant frequency of the transducers;
setting the generator for a maximum drive frequency that exceeds the maximum fundamental resonant frequency and for a minimum drive frequency that is less than the minimum fundamental resonant frequency;
generating the driving signal by sweeping the frequency of the driving signal between the minimum drive frequency and maximum drive frequency.
3. A method as recited in claim 2 , wherein the step of setting the generator includes setting the amount by which the maximum drive frequency exceeds the maximum fundamental resonant frequency to be substantially equal to the amount by which the minimum drive frequency is less than the minimum fundamental resonant frequency.
4. A method as recited in claim 2 , wherein the generator has a controller with a user interface that is used in the step of setting the maximum drive frequency and minimum drive frequency of the generator.
5. A method as recited in claim 2 , further comprising a step of setting a sweep rate for the driving signal.
6. A method as recited in claim 2 , further comprising grouping the transducers according to similar fundamental resonant frequencies, determining a maximum resonant frequency and a minimum resonant frequency of each group of transducers, and supplying a separate driving signal to each group of transducers, wherein each separate driving signal varies within a frequency range that exceeds the maximum and minimum fundamental resonant frequencies of the transducers of its associated group.
7. A megasonic processing method comprising:
providing two or more piezoelectric transducers, each having a fundamental resonant frequency of at least 300 KHz;
determining a maximum fundamental resonant frequency and a minimum fundamental resonant frequency of the transducers;
providing a tank adapted to contain fluid, wherein the transducers provide megasonic energy to the contents of the tank;
providing a generator coupled to the transducers for supplying a driving signal to the transducer;
generating and supplying the driving signal to the transducers, wherein the frequency of the driving signal sweeps throughout a range that exceeds the maximum and minimum fundamental resonant frequencies of the transducers.