Which factor is not typically used to compute the thermal index?

• A. Transmit power
• B. Exposure duration
• C. Frequency
• D. Receiver gain

Answer: (D)

The thermal index is about how much RF energy could raise tissue temperature, so it depends on energy that is actually emitted and deposited: the transmitter’s power (how strong the signal is), how long the energy is delivered (exposure duration), and how tissue absorbs energy at a given frequency (frequency affects absorption and heating rate). Receiver gain, which describes how a receiving system amplifies incoming signals, doesn’t influence how much energy enters the body during transmission. It sits on the receiving side and doesn’t affect heating potential, so it isn’t used to compute the thermal index. In short, higher transmit power, longer exposure, and appropriate frequency-related absorption drive heating risk, which the thermal index estimates; receiver gain does not.