The use of Heat therapy for deep-seated tissue can be treated with shortwave, microwave, and ultrasonic waves. This produces a high temperature that penetrates deeper. Shortwave produces a 27 MHz current, microwaves use 915 and 2456 MHz, and ultrasound is an acoustic vibration of 1 MHz. The way ultrasonic waves work is they selectively superimpose the incoming wave and increase the energy for absorption, and the significant part of the longitudinal compression gets converted into shear waves. When they are rapidly absorbed, the interface between soft tissue and bone is selectively heated.