The wavelength of MWD is between infrared radiations and short wave diathermy. It is also known as decimeter wave. The commonly used therapeutic wavelength is 12.25 cm and frequency is 2,450 cycles/second.

Production of MWD:High frequency is passed through the special valve (Magnetron) producing microwave diathermy. The output is carried into air and microwaves are emitted (produced).

Physiological effects:

When the electromagnetic energy of the microwave radiation is absorbed in the tissue, it provokes ionic movements, rotation of the dipoles and causes distortion of the molecules of the insulators. The amount of heat produce inside the tissue depends upon the fluid contents. The microwave penetrates deeper than infrared rays. The affective depth of penetration of MWD is 4.3 cm. The half value depth of MWD is 3cm. As Microwaves are more absorbed by the water so those tissues which have good blood supply like muscle are heated mostly while those tissues which have low fluid contents like fat produces less heat. The depth of penetration of MWD is frequency dependent. As the frequency decreases the depth of penetration increase i.e. MWD has two therapeutic frequencies 915 MHz and 2,450 MHz, The depth of penetration of 915 MHz is greater than 2,450 MHz.
Note: The therapeutic effects of MWD are same as those of SWD