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The use of electromagnetic (EM) power for therapeutic applications has existed since EM sources have been available to man. Physical medicine has been a major user of both shortwave (27.33 MHz) and microwave (2450 MHz) diathermy over the decades in which the EM power has been used to heat deep tissues for stimulating various medically beneficial physiologic responses in the relief of certain pathological conditions. Experimental and clinical research indicates that these responses will occur as a result of elevating the tissue temperatures in the range 41° to 45°C requiring absorbed power densities from 50 to 170 W/kg in the deep tissues where treatment is desired. The combination of pain responses and a large reserve of blood cooling capacity seems to be sufficient for limiting the heating to safe, but therapeutic levels in vasculated and innervated tissue. Recent research has shown that the use of the industrial, scientific, and medical (ISM) frequency of 915 MHz is more efficient than the currently used 2450-MHz microwave frequency in terms of maximum power transfer to deep tissues. The results also show that in addition to thermal applications, microwave energy can be used for the controlled transcutaneous stimulation of nerve action potentials via implanted miniature microwave diodes.