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Wireless charging standards and exposure limits

Qi phone charging typically runs at 87–205 kHz, and Qi2’s Magnetic Power Profile at 360 kHz. SAE J2954 EV charging uses 85 kHz (79–90 kHz band), and AirFuel Resonant uses the 6.78 MHz ISM band. For exposure, ICNIRP 2010 sets a 27 µT general-public reference level from 3 kHz to 10 MHz.

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Last updated: By: the AirInduct Sim engineering team

Which wireless charging standards matter for coil design?

Three standards families cover most commercial inductive and resonant charging. Each fixes the operating frequency band, and with it the coil inductance, capacitor values and losses a design can use. The table summarises what the public documents say; the full specifications define much more (coil geometries, foreign-object detection, communication and test methods).

StandardApplicationOperating frequencyPower
Qi BPP / EPP (WPC)Phones, accessoriesTypically 87–205 kHzBPP ≤ 5 W; EPP up to 15 W
Qi2 MPP (WPC, Qi v2.0+)Phones with magnetic alignment360 kHz15 W; up to 25 W from Qi v2.2
SAE J2954 (current: J2954_202408)Light-duty electric vehicles85 kHz nominal, 79–90 kHz bandWPT1 3.7, WPT2 7.7, WPT3 11.1 kVA
AirFuel ResonantMulti-device, spatial freedom6.78 MHz ISM band (6.765–6.795 MHz)Varies by device class

What frequency and power does Qi use?

The Wireless Power Consortium’s Qi v1.3 introduction describes an operating frequency that is typically in the 87–205 kHz range, with the system resonance near the low end. It defines the Baseline Power Profile (BPP) for up to 5 W and the Extended Power Profile (EPP) for up to 15 W. Qi v2.0 (2023) added the Magnetic Power Profile (MPP), which uses magnets to align phone and charger and operates at 360 kHz; the WPC’s specification history notes that MPP was based on a contribution from Apple. Qi v2.2 (2025) raised MPP to up to 25 W, marketed as Qi2 25W.

For coil design this means inductances in the microhenry range, litz or multi-strand windings to control AC resistance (copper skin depth is about 0.21 mm at 100 kHz and 0.11 mm at 360 kHz), and tight coupling at a few millimetres. Qi specifies its transmitter designs in detail, so a compliant product starts from the specification’s coil definitions rather than a free design.

What does SAE J2954 specify for EV wireless charging?

SAE J2954 covers wireless power transfer for light-duty plug-in and electric vehicles and an alignment methodology. The current revision is J2954_202408. ITU-R Report SM.2303-4 summarises the October 2020 edition: an 85 kHz band spanning 79–90 kHz and three power classes, WPT1 at 3.7 kVA, WPT2 at 7.7 kVA and WPT3 at 11.1 kVA. SAE’s own summary describes charging levels up to 11 kVA, with higher power left for future revisions. The standard also defines ground-clearance (Z) classes and interoperability between ground and vehicle assemblies from different suppliers.

ITU-R Recommendation SM.2110-2 (2025) lists 79–90 kHz and 19–21 kHz as frequency ranges for wireless power transfer to electric vehicles. At 85 kHz the copper skin depth is about 0.23 mm, and vehicle pads commonly combine litz windings with ferrite and an aluminium back plate; Covic and Boys review these pad designs.

Why does AirFuel Resonant use 6.78 MHz?

The AirFuel Alliance’s resonant specification operates at 6.78 MHz, in the 6.765–6.795 MHz industrial, scientific and medical (ISM) band also covered by ITU-R Report SM.2303. At this frequency coils can be small and loosely coupled while still reaching useful kQ, which supports charging several devices at once with more positional freedom. The trade-offs are higher conductor loss per unit length (skin depth about 25 µm), sensitivity to self-resonance and parasitic capacitance, and stricter attention to emissions.

Standards fix the frequency band and power level, and the coil designer works inside them. A practical first step is to compute, for a candidate geometry, the coupling coefficient over the expected gap and misalignment range, the self-inductances that set the compensation capacitors at the standard’s frequency, and the peak magnetic field the coils produce at the design current. AirInduct Sim reports M, L_tx, L_rx, k, induced voltage and peak H for eight air-core coil topologies, with 3D, heatmap and contour plots of the field, which makes it a fast way to screen geometries before building one. It does not certify compliance: interoperability tests come from the standard itself, and exposure compliance for a product follows assessment procedures such as IEC/IEEE 63184, with the real enclosure, ferrite and shielding in place. Treat the simulated field map as a guide to where those measurements should focus.

What are the magnetic field exposure limits for wireless chargers?

Three documents set the limits most regulators reference:

  • ICNIRP 2010 (scope 1 Hz–100 kHz, with nerve-stimulation protection applying up to 10 MHz). The basic restriction is the internal electric field, 1.35 × 10⁻⁴·f V/m for the general public between 3 kHz and 10 MHz (f in Hz). The corresponding reference level is B = 27 µT (H = 21 A/m) for the general public and 100 µT (80 A/m) for workers, flat from 3 kHz to 10 MHz.
  • ICNIRP 2020 (100 kHz–300 GHz) addresses heating. For the general public between 0.1 and 30 MHz the whole-body reference level for incident magnetic field is H = 2.2/f_M A/m (f_M in MHz, 30-minute average) and the local level is 4.9/f_M A/m. ICNIRP states that the 2010 nerve-stimulation restrictions still apply from 100 kHz to 10 MHz, so both sets must be met in that range.
  • IEEE C95.1-2019 covers 0 Hz to 300 GHz and replaced C95.1-2005 and C95.6-2002. Its electrostimulation limits apply from 0 Hz to 5 MHz and its thermal limits from 100 kHz to 300 GHz.

At 6.78 MHz the ICNIRP 2020 general-public values work out to H = 0.324 A/m whole-body (B = 408 nT) and 0.723 A/m local (B = 908 nT), far below the 27 µT stimulation level. At 0.1 MHz the whole-body value is 22 A/m (B ≈ 27.6 µT), close to the stimulation level, and at 0.36 MHz it is 6.11 A/m (B ≈ 7.68 µT). The thermal levels are averaged over the body and over time, whereas the stimulation levels are not averaged in time, so above 100 kHz both checks are needed. In the United States, the FCC’s KDB 680106 explains how wireless power devices are authorised under Parts 15 and 18 and how RF exposure is evaluated.

Worked example: screening a coil against 27 µT

A circular transmitter coil, radius 40 mm, 10 turns, carrying 2 A RMS. The on-axis field from the Biot–Savart law, B(z) = μ₀NIR² / (2(R² + z²)^(3/2)), computed on this page:

Distance from coil plane on axisB (RMS)vs 27 µT
0 mm314 µT12 ×
50 mm76.6 µT2.8 ×
100 mm16.1 µT0.6 ×
200 mm2.37 µT0.088 ×
B falls to 27 µT at z ≈ 81.3 mm on the axis.

This is a screening calculation for the coil alone, in air, with no receiver, ferrite or shield. The field near a small coil is highly non-uniform, and ICNIRP reference levels assume exposure averaged over the body, so exceeding 27 µT at a point close to the coil does not by itself mean the basic restriction is exceeded. It does tell you where a proper assessment (IEC/IEEE 63184, or the method a regulator requires) must focus. The coil design guide shows where this check fits in the overall design, and the Biot–Savart vs FEM article covers when induced-field and SAR modelling needs a body model.

References

  1. Wireless Power Consortium, “Qi Specification version 1.3: Introduction” (PDF), operating frequency and power profiles. www.wirelesspowerconsortium.com/media/cd4ljryt/qi-v13-introduction.pdf
  2. Wireless Power Consortium, “History of the Qi specifications” (knowledge base). www.wirelesspowerconsortium.com/knowledge-base/qi-specification/history-of-the-qi-specifications/
  3. Wireless Power Consortium, news release on Qi2 25W (Qi v2.2), July 2025 (PDF). www.wirelesspowerconsortium.com/media/wvsmia32/qi2-25w-news-release-v72.pdf
  4. SAE International, J2954_202408, “Wireless Power Transfer for Light-Duty Plug-in/Electric Vehicles and Alignment Methodology” (2024). saemobilus.sae.org/standards/j2954_202408-wireless-power-transfer-light-duty-plug-electric-vehicles-alignment-methodology
  5. G. A. Covic and J. T. Boys, “Inductive power transfer,” Proceedings of the IEEE 101(6), 1276–1289 (2013). doi.org/10.1109/JPROC.2013.2244536
  6. ITU-R, Report SM.2303-4, “Wireless power transmission using technologies other than radio frequency beam” (06/2023). www.itu.int/dms_pub/itu-r/opb/rep/R-REP-SM.2303-4-2023-PDF-E.pdf
  7. ITU-R, Recommendation SM.2110-2, “Frequency ranges for operation of non-beam wireless power transmission systems for electric vehicles” (09/2025), Table 1. www.itu.int/dms_pubrec/itu-r/rec/sm/R-REC-SM.2110-2-202509-I!!PDF-E.pdf
  8. AirFuel Alliance, “Frequency choice” (AirFuel Resonant at 6.78 MHz). airfuel.org/frequency-choice/
  9. ICNIRP, “Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz),” Health Physics 99(6), 818–836 (2010). doi.org/10.1097/HP.0b013e3181f06c86
  10. ICNIRP, Guidelines for limiting exposure to time-varying electric and magnetic fields (1 Hz to 100 kHz), full text (PDF), Tables 2–4. www.icnirp.org/cms/upload/publications/ICNIRPLFgdl.pdf
  11. ICNIRP, “Guidelines for limiting exposure to electromagnetic fields (100 kHz to 300 GHz),” Health Physics 118(5), 483–524 (2020). doi.org/10.1097/HP.0000000000001210
  12. ICNIRP, Guidelines for limiting exposure to electromagnetic fields (100 kHz to 300 GHz), full text (PDF), Tables 5–6. www.icnirp.org/cms/upload/publications/ICNIRPrfgdl2020.pdf
  13. IEEE Std C95.1-2019, IEEE Standard for Safety Levels with Respect to Human Exposure to Electric, Magnetic, and Electromagnetic Fields, 0 Hz to 300 GHz (2019). doi.org/10.1109/IEEESTD.2019.8859679
  14. IEC/IEEE 63184:2025, Assessment methods of the human exposure to electric and magnetic fields from wireless power transfer systems (3 kHz to 30 MHz). Supersedes IEC PAS 63184:2021. standards.ieee.org/ieee/63184/10156/
  15. U.S. FCC Office of Engineering and Technology, KDB 680106, “Wireless Power Transfer” (updated October 2023). apps.fcc.gov/oetcf/kdb/forms/FTSSearchResultPage.cfm?switch=P&id=41701

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Frequently asked questions

What frequency does Qi wireless charging use?

Qi Baseline and Extended Power Profile chargers typically operate between 87 and 205 kHz, according to the Wireless Power Consortium’s Qi v1.3 introduction. The Qi2 Magnetic Power Profile, added in Qi v2.0, operates at 360 kHz.

What frequency does SAE J2954 use for EV wireless charging?

SAE J2954 uses a nominal 85 kHz in the 79–90 kHz band for light-duty vehicles. ITU-R Recommendation SM.2110-2 lists 79–90 kHz (and 19–21 kHz) as frequency ranges for wireless power transfer to electric vehicles.

What is the ICNIRP magnetic field limit for wireless chargers?

For the general public between 3 kHz and 10 MHz, the ICNIRP 2010 reference level is 27 µT (21 A/m), to protect against nerve stimulation. Above 100 kHz the ICNIRP 2020 guidelines add thermal limits. Reference levels are screening values: exceeding one means the basic restrictions must be assessed, not that they are exceeded.

Why does AirFuel Resonant use 6.78 MHz?

AirFuel Resonant operates in the 6.78 MHz industrial, scientific and medical (ISM) band, 6.765–6.795 MHz. The higher frequency supports loosely coupled, spatially free charging with small coils, at the cost of tighter emission and efficiency challenges.