Generally, ultrasound is a mechanical wave generated by oscillations of a crystal placed in the ultrasound applicator. The oscillations are transferred from the applicator to the body surface and deeper into the tissue using a contact means, such as gel. The main effects include tissue heating and in-depth micro massage. 

The ultrasound frequency can be selected based on the targeted tissue. The 1 MHz frequency is typically used to treat deeper injuries while the 3 MHz frequency is ideal for the treatment of superficial tissues. 

BTL-4000 Smart & Premium enable alternating frequency treatment. When using the alternating frequency, the system automatically change the frequency from 1 to 3 MHz in preset intervals.