Why do exposure limits vary with frequency?

Exposure limits vary with frequency because the human body interacts with radio frequency (RF) energy differently depending on the frequency of the signal. Some frequencies are more readily absorbed by body tissues, particularly water and fat, which can lead to increased exposure levels and potential biological effects.

At specific frequencies, the resonance effects can enhance absorption, meaning that these frequencies can lead to greater energy deposition within the tissues. For example, the human body can effectively absorb RF energy in the range of 30 MHz to 300 MHz, which is why there are stricter exposure limits set for those frequencies.

This dynamic explains why it is crucial to establish varying exposure limits, as they take into account the differing levels of energy absorption by the body at different frequencies, aiming to protect users from potentially harmful effects.