Warm effect: human tissues have great absorption capacity for ultrasonic energy, so when ultrasonic waves propagate in human tissues, their energy is continuously absorbed by tissues and converted into heat, and as a result, the temperature of the tissues themselves rises.
The process of heat production is not only an energy conversion process in which mechanical energy is converted into heat energy in a medium. Namely endogenous heat. Ultrasonic hyperthermia can increase blood circulation, accelerate metabolism, improve local tissue nutrition and enhance enzyme activity. Generally speaking, the thermal effect of ultrasound is significant in bones and connective tissues, while fat and blood are the least.
Extended data:
Two main parameters of ultrasound:
Frequency: f≥20KHz (in practical application, sound waves with f≥ 10KHz are usually called ultrasonic waves because of their similar effects).
Power density: defined as p= emission power (W)/ emission area (cm? ), usually p≥0.3W/cm? . Ultrasonic wave propagating in liquid can clean dirt on the surface of objects, and its principle can be explained by "cavitation" phenomenon: when the sound wave pressure of ultrasonic vibration propagating in liquid reaches one atmosphere, its power density is 0.35W/cm? .
At this time, the peak pressure of ultrasonic wave can reach vacuum or negative pressure, but there is actually no negative pressure, so great pressure is generated in the liquid, which splits the liquid molecules into cavities-cavitation nuclei. This cavity is very close to vacuum, and it will rupture when the ultrasonic pressure is reversed to the maximum.
Baidu encyclopedia-ultrasound