Is it true that ultrasound generates heat? If so, how much heat can be generated in say, a glass of water? How long would it take to reach the boiling point? What kind of drive would have to do this? I do not think a speaker can’t be used I hope to build a device for heating water using ultrasonic waves. Do you know how long it would take for a device to heat water using ultrasound waves? Do you have a device that can be used to heat a glass?”]
Source: http://mick-hoo-mas.blogspot.com/2009/12/ultrasonic-speaker-diy-is-it-true-that.html