Diathermy is the controlled production of “deep heating” beneath the skin in the subcutaneous tissues, deep muscles and joints for therapeutic purposes. There are basically two types of diathermy devices on the market today: radio or high frequency and microwave. Ultrasonic or ultrasound therapy is also a form of diathermy, and is sometimes combined with electrical stimulation. Radio frequency (r.f.) diathermy is assigned an operating frequency of 27.12MH Z (short wave) by the Federal Communications Commission. Older radio frequency units were assigned an operating frequency of 13.56MH Z. Microwave diathermy is assigned 915MH Z and 2450MH Z as operating frequencies (these are also Microwave oven frequencies).