Method and apparatus for tuning a megasonic transducer

A method for selecting an optimum frequency for driving a transducer comprising the steps of:

• selecting a plurality of frequency values that span a frequency range containing an optimum frequency for driving a piezoelectric crystal;
• determining a reflected power at each frequency value, thereby generating a data set of ordered pairs of the reflected power and the frequency value;
• fitting the data set to a function;
• obtaining the first derivative equation of the function;
• finding the roots of the first derivative equation to yield a set of roots;
• and
• selecting the optimum frequency from the set of roots.

A method for selecting an optimum frequency for driving a transducer comprising the steps of:

• selecting a plurality of frequency values FN that span a frequency range containing an optimum frequency for driving a piezoelectric crystal;
• determining a reflection coefficient “ρ” at each frequency value FN, where “ρ” is the reflected power divided by the forward power, thereby generating a data set of ordered pairs of the reflection coefficient and the frequency value;
• fitting the data set to a polynomial to obtain the coefficients A, B, C and D in a third degree polynomial equation f(ω)=Aω3+Bω2+Cω+D;
• obtaining the first derivative of the third degree polynomial to yield the equation f(ω)=3Aω2+2Bω+C;
• finding the roots of the first derivative equation to yield a set of roots;
• and
• selecting the optimum frequency from the set of roots.

A system for selecting a frequency for driving a transducer comprising:

• a microprocessor;
• a radio frequency (RF) frequency generator for generating an RF excitation signal at a specific frequency, the specific frequency being somewhere in the frequency range of approximately 10.0 KHz to 10.0 MHz;
• a transducer means for converting the RF excitation signal into acoustic energy;
• a directional coupler/decoupler means for separating the RF excitation signal from an RF reflected signal, the RF reflected signal arising, at least in part, from the RF excitation signal interacting with the transducer means;
• an analog to digital converter means connected to the directional coupler/decoupler means for converting the RF excitation signal into a digital excitation signal that can be processed by the microprocessor and for converting the RF reflected signal into a digital reflected signal that can be processed by the microprocessor;
• and
• software means running on the microprocessor for using the digital excitation signal and the digital reflected signal to calculate a reflection coefficient at the specific frequency, and for using a plurality of reflection coefficients measured at a plurality of specific frequency values to determine an optimum drive frequency.