Evaluating Permissive Change Compliance Paths for Potted RF Transmitter Modules
Adding potting compound to an unpotted RF module demands Class II permissive change re-testing if dielectric loading increases radiated spurious emissions.
RF Exposure Boundary
Meaning
Spatial limits define the minimum safe distance that must be maintained between a radiating transmitter antenna and the human body to ensure compliance with radio frequency exposure standards. The calculation of the RF exposure boundary depends on the transmitter’s output power, antenna gain, and operating frequency. This boundary becomes irrelevant for devices that operate with very low power, below the threshold where formal SAR testing is required.
Spatial Separation
Distance requirements are determined using mathematical models of electromagnetic radiation in the far-field region. In the case of an RF exposure boundary, the goal is to identify the contour where the power density drops below the maximum permissible exposure limit. This information must be clearly stated in the product manual to instruct the installer on safe positioning.
If the device is intended for mobile or fixed installations, this boundary must be verified through physical measurement or numerical simulation.
Calculation Model
Power density equations are used to predict the field strength at varying distances from the antenna surface. These calculations are verified by accredited laboratories during the regulatory approval process.
Safety Margin
Operating limits are set to ensure that even under worst-case transmitter configurations, the public remains protected. This conservative approach accounts for reflections from nearby conductive surfaces.