Draft Updates to Wireless Power Transfer Applications

The Federal Communications Commission (FCC) of the United States provides a draft of the updates clarifying compliance limits for devices using low-power, closely coupled, inductive power transfer techniques.

Wireless power transfer (WPT) devices operating at frequencies above 9 kHz are intentional radiators and are subject to either Part 15 and/or Part 18 of the FCC rules. The specific applicable rule part depends on how the device operates, and if there is communication between the charger and device being charged.

Intentional radiators transmitting information must be certified under the appropriate Part 15 Rules and will generally require an equipment certification.

The RF exposure requirements must be determined in conjunction with the device's operating characteristics, according to the FCC mobile and portable exposure requirements (Sections 2.1091 and 2.1093)

  • SAR limits do not cover wireless power transfer applications operating below 100 kHz
  • MPE limits do not cover wireless power transfer applications operating below 300 kHz

A KDB inquiry for Part 18 inductive wireless power transfer devices up to 1 meter distance that contains supporting field strength results and that meets all of the following requirements is not required:

  • The power transfer frequency is below 1 MHz.
  • The output power from each primary coil is less than or equal to 15 watts.
  • Each client device is placed directly in contact with the transmitter.
  • Only mobile exposure conditions apply
  • The aggregate H-field strength anywhere at or beyond 15 cm surrounding the device, and 20 cm away from the surface from all coils that by design can simultaneously transmit, and while those coils are simultaneously energized, are demonstrated to be less than 50% of the applicable MPE limit.
  • For systems with more than one primary coil, the conditions specified in (5) must be met when the system is fully loaded and all coils are powered at the same time.

For beyond one, meter the following additional conditions must be satisfied:

  • RF field in all locations anywhere at or beyond one meter is at or below the level that would be present within 1 meter when all devices being charged are within 1 meter of the transmitter.
  • The devices may only operate indoors
  • The maximum fundamental and unwanted radiated emissions of the Part 18 device on any non-ISM frequency meet the limits in Part 15 of the Commissionโ€™s rules when measured outdoors
  • Devices are professionally installed

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