One of the problems I’m having with powder-bed processes in the ceramic studio is that fine powders, whether quartz, feldspar, or glass, are clumpy. I’m thinking I can vibrate a tool to break them up. I’ve ascertained that some commercial ultrasonic vibrating sieves use about 200 watts of power per kilogram of vibrating mass; I think I can get by with 10 grams of apparatus and powder (really more like 100mg of powder) and thus 2 watts, and I'm wondering if piezoelectric speakers are a plausible way to deliver that vibration.
Digi-Key’s most popular "buzzer element/piezo bender" is the CUI CEB-20D64, a US$1.38 6.5kHz piezo buzzer element that takes 30 volts peak-to-peak at an impedance of 350 ohms, which I guess works out to 2.6 watts.
So the answer is yes, cheap piezoelectric speakers have enough power to do the job. How about reaching ultrasonic frequencies?
The Murata MA40S4S is a US$6.80 40kHz ultrasonic transmitter; it takes a 20-volt peak-to-peak square wave input and delivers 120 dB SPL output at 30cm with a 10Vrms sine wave. It claims a 2550 pF capacitance at 1kHz. Unfortunately, this is not enough information to estimate its power output, since the SPL (20 Pa) depends on its directionality, which is not specified.
The next most popular ultrasonic transmitter is the US$4.95 PUI UT-1240K-TT-R, 40kHz with a 70° -6dB beam angle, running on 30V peak-to-peak. It claims 2100pF and 115dB.
(I could totally calculate how much power gets stored in and paid back from that capacitance at a given frequency and voltage, but what I'm interested in is the fraction that doesn’t get paid back because it’s emitted as sound.)
In the "Alarms, Buzzers, and Sirens" Digi-Key category, I find the much more popular TDK PS1240P02BT, a 33¢ 3V 4kHz single-tone “piezoelectronic buzzer without oscillator circuit” that TDK markets for, among other things, “speech synthesis output”; they plot its frequency response curve out to 10kHz in the 70–80 dBA range at 10cm and 3V, but it takes up to 30V input.
These are probably in the same power range as the first buzzer, though, just less directional.