Since 1972 Mettler Electronics has produced an affordable shortwave diathermy (SWD) unit that produces comforting deep heat in muscle tissues. Shortwave diathermy is used when the clinician needs to provide deep heat to a larger area than normally covered by ultrasound. The illustration below shows the relative penetration of various heating modalities.
Comparison of heat distribution with inductive coil SWD applicator, capacitive plate SWD applicator, microwave diathermy and ultrasound Reprinted from Physical Agents in Rehabilitation, from Research to Practice, Michelle H. Cameron. Chapter 10–Electromagnetic Radiation, page 325, Copyright 1999, with permission from Elsevier Science.