Skin Heating Effects frequency range?

• A. 100 kHz-3 GHz
• B. 3 kHz-5 MHz
• C. 3 Hz-3 kHz
• D. 3 GHz-300 GHz

Answer: (D)

As frequency increases, electromagnetic energy is absorbed more and more near the surface of the skin because the skin depth gets smaller. Skin depth is roughly δ ≈ sqrt(2/(ω μ σ)), where ω = 2πf, μ is tissue permeability, and σ is electrical conductivity. When f rises, δ shrinks, so most of the energy is deposited in a very thin surface layer. That surface-focused absorption is what we call skin heating.

This makes the microwave to millimeter-wave range the one where skin heating is the dominant thermal effect—roughly from a few gigahertz up to a few hundred gigahertz. In the lower frequency bands, energy penetrates deeper into the body, producing heating that isn’t confined to the surface and is governed by different exposure characteristics.