Question: Has the FCC issued RF exposure guidance for an on-body device equipped with motion sensors to control its conducted power?
Answer: On August 24, 2023 the FCC posted under KDB 447498 the following interim guidance applicable only on a case-by-case basis, for RF devices that use motion sensors to detect “on-body” use conditions to control the RF conducted power in order to maintain RF exposure compliance:
For these cases, it is also necessary to address "off-body, but close" use conditions, such as the device on a stationary surface (e.g., a table), with the motion sensors not triggered and therefore operating at maximum power, while close enough to a person's body to pose RF exposure compliance concerns.
Accordingly, it is possible to consider that if the particular device under test (DUT) is shown to be RF exposure-compliant at 25 mm without any power reduction, then any “off-body” use will also lead to an exposure that, on average, is within the compliance threshold. This argument is based on the fact that, for this particular DUT under consideration, operations at distances closer than 25 mm will likely lead to contact with the DUT, even temporary or accidental, thus triggering the motion sensor-based power reduction feature.
This consideration cannot be generalized, nor provide a precedent to support similar applications/ devices, and therefore can only be leveraged after the related application for certification has been approved for the Pre-Approval Guidance List item "PWRDYN" through the Pre-Approval Guidance Procedure.