Meaning
Regulatory provisions that exempt low-power or body-worn wireless devices from routine Specific Absorption Rate testing simplify the compliance and certification process. The sar exclusion applies to devices whose radiated output power falls below a calculated threshold determined by the separation distance from the human body. This exemption allows developers of wearable devices to avoid expensive and time-consuming laboratory testing of radio frequency energy absorption.
Threshold Calculation
Exclusion limits are calculated based on the operating frequency of the transmitter and the minimum physical separation distance to the user’s body. If the device’s maximum output power, including antenna gain and manufacturing tolerances, is below the calculated threshold, a sar exclusion can be claimed. This calculation must be documented in the technical construction file submitted for regulatory approval.
If the power exceeds the limit, the device must undergo full laboratory testing to measure the energy absorbed by human tissue.
Antenna Design
The physical placement of the antenna within the product enclosure is a critical factor in determining the separation distance. In a typical wearable device, the antenna is positioned as far from the skin-contact surface as possible to maximize this distance and ensure sar exclusion compliance. Even a difference of a few millimeters can determine whether the product is exempt from testing or must undergo the full test sequence.
Consequently, antenna routing must be coordinated with the mechanical design team early in the project.
Certification Strategy
Securing an exclusion reduces the overall certification costs and avoids the risk of failing the complex absorption tests. This strategy is essential for bringing compact, low-power consumer devices to market quickly.
