Megasonic multifrequency apparatus with matched transducers and mounting plate
A megasonic processing apparatus matches the fundamental resonant or higher-level harmonic frequencies of megasonic thickness-mode transducers to the fundamental resonant or higher-level harmonic frequencies of a plate or other mounting structure upon which the transducers are mounted. The multifrequency transducers are piezoelectric transducers operating in thickness mode at different operating frequencies. The thickness of the mounting plate at the transducer locations is selected to provide a resonant or harmonic frequency matched to that of its corresponding transducer. Two or more megasonic transducers are bonded to the same radiating surface.
1. A megasonic processing apparatus comprising:
a first piezoelectric transducer operating in thickness mode and having a fundamental resonant frequency of at least 300 KHz and having a first operating frequency;
a second piezoelectric transducer operating in thickness mode and having a fundamental resonant frequency of at least 300 KHz and having a second operating frequency different from the first operating frequency;
a rectangular mounting plate upon which the first and second transducers are mounted, wherein the mounting plate has an area available for mounting transducers, wherein each first and second transducer is in the shape of a rectangle having a long side and a short side that is shorter than the long side, wherein the first and second transducers are arranged with the long sides parallel to each other and each transducer extends across one dimension of the mounting plate, wherein transducers cover at least 80% of the area of the mounting plate, wherein at the location of the first transducer the mounting plate has a first thickness and has a fundamental resonant or harmonic frequency substantially equal to the first operating frequency, and wherein at the location of the second transducer the mounting plate has a second thickness different from the first thickness and has a fundamental resonant or harmonic frequency substantially equal to the second operating frequency;
a tank adapted to contain fluid and one or more parts to be processed, wherein said mounting plate is operatively coupled to the tank so that the transducers provide vibrations to the tank and its contents; and
a generator coupled to the transducers for supplying driving signals at the first and second operating frequencies.
2. An apparatus as recited in claim 1 wherein the first operating frequency of the first transducer is its fundamental resonant frequency, and wherein the second operating frequency of the second transducer is its third harmonic frequency.
3. An apparatus as recited in claim 1 wherein the first operating frequency of the first transducer is its fundamental resonant frequency, wherein the second operating frequency of the second transducer is its fundamental resonant frequency, and wherein the fundamental resonant frequencies of the first and second transducers are different.
4. An apparatus as recited in claim 3 wherein the first thickness of the mounting plate has a fundamental resonant frequency substantially equal to the fundamental resonant frequency of the first transducer, and wherein the second thickness of the mounting plate has a fundamental resonant frequency substantially equal to the fundamental resonant frequency of the second transducer.
5. An apparatus as recited in claim 4 wherein the second thickness of the mounting plate is less than the first thickness of the mounting plate, and wherein the second thickness is formed by removing material from the mounting plate.
6. An apparatus as recited in claim 4 wherein the second thickness of the mounting plate is less than the first thickness of the mounting plate, and wherein the first thickness is formed by adding material to the mounting plate.
7. An apparatus as recited in claim 3 further comprising a plurality of first transducers and a plurality of second transducers, said transducers arranged on the mounting plate in alternating sequence.
8. An apparatus as recited in claim 1 further comprising a third piezoelectric transducer mounted on the mounting plate and having a fundamental frequency of at least 300 KHz, wherein the fundamental frequency of the third transducer is different from the fundamental frequencies of the first and second transducers, wherein the third transducer is in the shape of a rectangle having a long side and a short side shorter than the long side, and wherein the third transducer is arranged with its long side parallel to the long sides of the first and second transducers.
9. An apparatus as recited in claim 8 wherein the transducers are arranged in a sequence starting with the lowest operating frequency and progressing to the highest operating frequency.
10. An apparatus as recited in claim 8 further comprising a transport mechanism for moving the parts to be processed through the tank to subject the parts to vibrations provided by each transducer.
11. An apparatus as recited in claim 1 wherein the mounting plate is incorporated into the tank.
12. An apparatus as recited in claim 11 wherein the mounting plate is integral with the tank.
13. An apparatus as recited in claim 11 wherein the mounting plate is attached to the tank.
14. An apparatus as recited in claim 1 wherein the mounting plate is immersed in the tank.
15. An apparatus as recited in claim 1 wherein the generator supplies the driving signals at a variable frequency throughout a frequency range that includes the operating frequencies of the transducers.