I guess a 40kHz
How would one get a sine wave through transistors etc?
QuoteHow would one get a sine wave through transistors etc?No need, just hit it with a square wave and let the natural resonance of the transducer turn it into a sin wave.
Saw a construction article long ago in Radio Electronics magazine, I think, for an ultrasonic parts cleaner. I seem to recall that they made the piezo transducers part of a tuned LC circuit, with added capacitors.
At 40kHz? How long are your traces?
The wavelength of 40kHz ultrasound in water is about 8.5mm. If you have all the transducers driven at exactly the same frequency and with zero (or constant) phase difference, then you will get standing waves caused by interference between them. This will result in areas on the object to be cleaned that have little or no ultrasonic waves, and therefore do not get cleaned. To get thorough cleaning, I think you will need to either selectively turn some transducers off, or selectively adjust the phase - possibly just by having the option to drive each transducer in-phase or 180 degrees out of phase with respect to its neighbours.
Would this explain why when you watch a cheap cleaner, you get waves 'standing' on the surface constantly around that size peak to peak, (or more or less depending upon working frequency), yet with the more expensive units the water is perfectly flat - as they must be as you say, varying the phase of the transducers to ensure the whole part gets cleaned?