Hello all. I would like to receive clarification and opinions on driving bolt clamped (Langevin) piezoelectric transducers. These transducers are most abundantly found in ultrasonic cleaning equipment. The same transducers are also used in industrial tank, reservoir, and boat hull anti-fouling applications (this latter application is what I'm interested in).
I have acquired transducers spec'd at a 40khz resonate frequency and 50w operating power consumption. The specifications also state that at resonance, this transducer presents a 10-20 ohm impedance (this is pretty much the average resonant impedance for most of these transducers). In determination of the drive voltage required, and conservatively using the 20 ohm upper-end of the rated resonate impedance, Watts Law states that the voltage required to drive the transducer at 50w is just under 32v. And this is where my concerns begin...
I had originally determined to step-up the voltage to 36v and then use an H-Bridge gate driver IC to drive a transducer at resonance with a 40khz square wave.
However, after much time spent on Google, I'm beginning to second guess this approach and am more confused than ever. Nearly all of the circuits I've found, and all the applications I've found (for both ultrasonic cleaners and anti-fouling) are using transformers to directly drive a transducer at (as quoted from one source) "250VAC (about 700V peak-to-peak)".
Forgive me but I have no experience with piezoelectric transducers or AC circuits in general, and it frankly seems I'm overlooking something. I've calculated 32v to drive a 50w 20ohm impedance load, but in most applications, the same or similar transducers with equally matched specifications are driven at nearly 10x that voltage.
What am I missing?