Magnetic field exposure to wireless charging stations for mobile phones

2017 · Mixed · Low evidence

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MixedLow evidencePaper 2333

Study snapshot

Publicationmanual · 2017

Study typeexposure_assessment

Reported directionMixed

Evidence ratingLow

Abstract

Magnetic field exposure to wireless charging stations for mobile phones Fröhlich, J., Zahner, M. and Dürrenberger, G. (2017), Magnetic field exposure to wireless charging stations for mobile phones. Bioelectromagnetics. doi:10.1002/bem.22087 No Abstract Excerpts This brief communication presents measurement and simulation data about magnetic field levels of, and human exposure to, wireless charging devices for smart phones, respectively. Most transmitters for inductive charging operate within a frequency window from 110 up to 205 kHz. The highest instantaneous field levels can be measured in stand-by mode. Peak and rms values amount to a few 100 µT, which is above the reference level. However, simulation results showed that the basic restrictions (defined in terms of electric field levels, V/m, in tissue and power absorption, specific absorption rate [SAR]), were met. From a regulatory point of view, inductive charging systems for small electronic devices like cell phones comply with safety standards, but worst- case induced electrical fields may come close to basic restrictions. Therefore, maximum currents for all specific implementations have to be restricted. Currently, inductive charging is the only commercialized wireless charging technology. In the near future, devices for resonant power transfer will be available, too. Two standards for inductive charging exist: Qi and AirFuel. Qi is dominating the market. Some key technical characteristics of the Qi inductive charging standard are given in Table 1. Conclusion The dosimetric characterization showed that inductive charging stations comply with basic restrictions recommended by ICNIRP and IEEE, albeit the incident magnetic flux densities exceed the reference values by factors of tens, roughly. For internal electric fields, the margin was below a factor of 10. For SAR, in contrast, the margin amounted to three orders of magnitude. The study (i) affirmed that checking basic restrictions in case of local exposures that exceed reference values is necessary; (ii) showed that exposure levels of current smartphone wireless charging systems may exploit ICNIRP basic restrictions on induced electric fields up to 30%, roughly, and are far from recommended maximum SAR levels; and (iii) indicated that increasing the allowed maximum power for charging systems (as already outlined in the standard) has to be carefully evaluated regarding instantaneous values of induced electric fields. onlinelibrary.wiley.com

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AI evidence extraction

Structured fields below were generated from the paper’s abstract and metadata to make the evidence easier to inspect. Automated extraction may be incomplete or incorrect; verify important details against the original paper.

Study typeexposure_assessment

Effect directionmixed

PopulationNot supplied

Sample sizeNot supplied

ExposureELF

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Measurements and simulations for smartphone inductive wireless charging (typically 110–205 kHz) found peak and rms magnetic flux densities of a few hundred µT, with highest instantaneous levels in stand-by mode, exceeding reference levels by factors of tens. Simulations indicated basic restrictions were met (internal electric fields and SAR), though worst-case induced electric fields could come close to basic restrictions (reported up to ~30% of ICNIRP basic restrictions), while SAR margins were about three orders of magnitude below recommended maximum levels.

Outcomes measured

Magnetic flux density (instantaneous, peak, rms; µT) near wireless charging transmitters
Compliance with reference levels vs basic restrictions (internal electric fields in tissue, V/m; SAR)
Regulatory compliance with ICNIRP and IEEE limits

View raw extracted JSON

{
  "study_type": "exposure_assessment",
  "exposure": {
    "band": "ELF",
    "source": "wireless charging station (inductive charging) for mobile phones",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Magnetic flux density (instantaneous, peak, rms; µT) near wireless charging transmitters",
    "Compliance with reference levels vs basic restrictions (internal electric fields in tissue, V/m; SAR)",
    "Regulatory compliance with ICNIRP and IEEE limits"
  ],
  "main_findings": "Measurements and simulations for smartphone inductive wireless charging (typically 110–205 kHz) found peak and rms magnetic flux densities of a few hundred µT, with highest instantaneous levels in stand-by mode, exceeding reference levels by factors of tens. Simulations indicated basic restrictions were met (internal electric fields and SAR), though worst-case induced electric fields could come close to basic restrictions (reported up to ~30% of ICNIRP basic restrictions), while SAR margins were about three orders of magnitude below recommended maximum levels.",
  "effect_direction": "mixed",
  "limitations": [],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "wireless charging",
    "inductive charging",
    "Qi",
    "AirFuel",
    "magnetic field",
    "magnetic flux density",
    "110–205 kHz",
    "exposure assessment",
    "dosimetry",
    "ICNIRP",
    "IEEE",
    "basic restrictions",
    "reference levels",
    "induced electric fields",
    "SAR"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.78,
      "reason": "Discusses compliance with ICNIRP (and IEEE) reference levels and basic restrictions for induced fields and SAR."
    }
  ]
}

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AI-extracted fields are generated from the abstract and metadata and may be incomplete or incorrect. This material is for informational purposes and is not medical advice.

Identifiers and source

DOI: 10.1002/bem.22087
PubMed: Not supplied

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