Question
Why are there separate electric (E) and magnetic (H) MPE limits at frequencies below 300 MHz?
Answer Options
- A) The body reacts to electromagnetic radiation from both the E and H fields
- B) Ground reflections and scattering cause the field strength to vary with location
- C) E field and H field radiation intensity peaks can occur at different locations
- D) All these choices are correct
Correct Answer: D
Explanation
In the ‘far field’ (away from the antenna), the electric (E) and magnetic (H) fields of a radio wave are related by the impedance of free space, and measuring one is sufficient. However, at frequencies below 300 MHz, near the antenna (the ‘near field’), this relationship breaks down, and the fields are largely independent.
At these low frequencies and short distances, the E field and H field radiation intensity peaks can occur at different locations, and the body reacts to electromagnetic radiation from both the E and H fields. Furthermore, the interaction of the signal with local objects (ground/scattering) means that the fields can vary independently. Therefore, to ensure complete safety, All these choices are correct, requiring that both the E-field and H-field MPE limits must be checked independently.
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