I've identified 7 components for the project: four electronics functions (in one package, presumably on one board) and three physical pieces, as shown in the diagram. My initial requirements are:

High Voltage DC supply:

• Supply (TBD) volts
• Capable of 200 watts power
• Galvanically isolated
• Inexpensive/easily made
• (Optional) Low voltage output to power electronics

Switcher:

• Self-resonant (ie - automatically finds resonant frequency)
• Can control power of transducer
• Can measure transducer power

Power control:

• Measure power level of transducer
• Control power level delivered by switcher
• On/Off control of DC supply
• Timed on/off control of transducer
• (optional) Remote computer control
• (optional) Auxiliary relays for control of other equipment

Display/User Input:

• Show current settings
• Show timer countdown
• Allow user to set power
• Allow timed pulses

Piezoezoelectric transducer:

• Easily available
• Inexpensive

Horn/Sonotrode:

• Tuned to transducer resonant frequency
• Easily made (as easy as possible)

Mounting bracket:

• Electrically insulated from transducer/horn

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I found this site describing making an ultrasonic drill... which is exactly what I plan to do! Woot!

His description is a little thin at places, so I will document the build process separately and in a different manner so that others will have both his and my descriptions for guidance.

I think his power supply circuit needs some changes, though (ie - as an instrument buildable/usable by others). It's fine for his uses, but I'd like something a little more automated and then I got an absolutely awful idea...

a perfectly wonderful, awful idea... and I need to do some experiments to see if it works and my inner Slytherin keeps saying "Bwa ha ha!" in the back of my mind.

There may be an easy, inexpensive way to build the HVDC supply using parts everyone has access to.

Stay tuned.