Been playing along with this new motherboard and plugged in a Raspberry Pi W, along with its high-speed ADC board (here for the hackaday page) - you will note that the power use of 2W is somehow not bad for a whole ultrasound system - without motors):

In smallish (but better quality here), I've done the tests on cheap (2$) piezos without backing, for which I didn't know the frequency. The central frequency was around 1.9MHz, and the shield was enough to do some FFT'ing !