Matching new peizo elements to existing ultrasonic driver

[rbm]

I'm planning on replacing piezo elements in an older Whaledent BioSonic UC1-110 ultrasonic cleaner that I own.  The driver circuit uses the elements as part of a LRC oscillator.  When measured, the original piezo elements are wired in parallel and read 13.3nF.  The new piezo elements I bought measure 7.23nF when paralleled.

I believe the replacements should match the capacitance of the OEM elements to keep the oscillator characteristics.  Would it be OK to parallel an additional 6nF across the new elements to raise the apparent capacitance of the driven elements?

[Conrad Hoffman]

Not sure, but I think you need both electrical and mechanical resonance in the same vicinity. You could add some low loss high voltage caps to get the capacitance back where the driver needs it, but do you know the mechanical resonance of the replacement system?

[rbm]

Thank you for that.  I believe the mechanical resonance is 44KHz - 45KHz.  I know the driver is capable of 100W of power delivery to the elements and was concerned that any matching capacitors I may introduce into the system needed to withstand this power.   I can obtain 4.7nF 1000V polypropylene film capacitors readily.  Will these be low loss?