Microwave burn

Microwave burns are burn injuries caused by thermal effects of microwave radiation absorbed in a living organism. In comparison with radiation burns caused by ionizing radiation, where the dominant mechanism of tissue damage is internal cell damage caused by free radicals, the primary damage mechanism of microwave radiation is thermal, by dielectric heating.

Microwave damage can manifest with a delay; pain and/or signs of skin damage can show some time after microwave exposure.

The depth of penetration depends on the frequency of the microwaves and the tissue type. The Active Denial System ("pain ray") is a less-lethal directed energy weapon that employs a microwave beam at 95 GHz; a two-second burst of the 95 GHz focused beam heats the skin to a temperature of 130 °F (54 °C) at a depth of 1/64th of an inch (0.4 mm) and is claimed to cause skin pain without lasting damage. Conversely, lower frequencies penetrate deeper; at 5.8 GHz the depth most of the energy is dissipated in the first millimeter of the skin; the 2.45 GHz frequency microwaves commonly used in microwave ovens can deliver energy deeper into the tissue; the generally accepted value is 17 mm for muscle tissue.

As lower frequencies penetrate deeper into the tissue, and as there are only few nerve endings in deeper-located parts of the body, the effects of the radio frequency waves (and the damage caused) may not be immediately noticeable. The lower frequencies at high power densities present a significant risk.

The microwave absorption is directed by the dielectric constant of the tissue. At 2.5 GHz, this ranges from about 5 for adipose tissue to about 56 for the cardiac muscle. As the speed of electromagnetic waves is proportional to the reciprocial value of the square root of the dielectric constant, the resulting wavelength in the tissue can drop to a fraction of the wavelength in air; e.g. at 10 GHz the wavelength can drop from 3 cm to about 3.4 mm.

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