Theoretical & numerical assessment of maximally allowable power-density averaging area for EMF exposure assessment above 6 GHz

2018 · Unclear · Low evidence

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UnclearLow evidencePaper 1963

Study snapshot

Publicationmanual · 2018

Study typeengineering

Reported directionUnclear

Evidence ratingLow

Abstract

Theoretical & numerical assessment of maximally allowable power-density averaging area for EMF exposure assessment above 6 GHz Neufeld E, Carrasco E, Murbach M, Balzano Q, Christ A, Kuster N.Theoretical and numerical assessment of maximally allowable power-density averaging area for conservative electromagnetic exposure assessment above 6 GHz. Bioelectromagnetics. 01 November 2018. doi.org Abstract The objective of this paper is to determine a maximum averaging area for power density (PD) that limits the maximum temperature increase to a given threshold for frequencies above 6 GHz. This maximum area should be conservative for any transmitter at any distance >2 mm from the primary transmitting antennas or secondary field-generating sources. To derive a generically valid maximum averaging area, an analytical approximation for the peak temperature increase caused by localized exposure was derived. The results for a threshold value of 1 K temperature rise were validated against simulations of a series of sources composed of electrical and magnetic elements (dipoles, slots, patches, and arrays) that represented the spectrum of relevant transmitters. The validation was successful for frequencies in which the power deposition occurred superficially (i.e., >10 GHz). In conclusion, the averaging area for a PD limit of 10 W/m2 that conservatively limits the temperature increase in the skin to less than 1 K at any distance >2 mm from the transmitters is frequency dependent, increases with distance, and ranges from 3 cm2 at <10 GHz to 1.9 cm2 at 100 GHz. In the far‐field, the area depends additionally on distance and the antenna array aperture. The correlation was found to be worse at lower frequencies (<10 GHz) and very close to the source, the systematic evaluation of which is part of another study to investigate the effect of different coupling mechanisms in the reactive near-field on the ratio of temperature increase to incident power density. The presented model can be directly applied to any other PD and temperature thresholds. Excerpts Standardization The results presented herein have important consequences for safety standards, as they demonstrate a need to use smaller and potentially frequency-dependent averaging areas. The maximal area at a source distance of 2 mm ranges from <2 cm2 at 100 GHz to ≥3 cm2 at <10 GHz. These conditions could be relaxed, should a temperature threshold >1 K be selected or for larger distances from the source. The suggested areas are smaller but comparable to the 4 cm2 previously suggested by Hashimoto et al. [2017] based on computational modeling of localized exposure-induced heating. Further Investigations The current investigation assumed stationary exposure. However, time-averaged limits are foreseen by the standards to allow for pulsed exposures. The presented investigation can be readily extended to transient exposures by application of 4D rather than 3D Green's functions [Yeung and Atalar, 2001]. In the absence of a steady‐state temperature increase, the 1 K criterion could be replaced, for example, with a criterion based on thermal dose [Van Rhoon et al., 2013]. CONCLUSIONS Analytical relationships for localized exposure in the 5G frequency range that permit estimation of temperature increase and of conservative limits on the acceptable power density averaging area have been established, ensuring exposure safety for devices positioned as close as 2 mm from the body. The predictions have been validated against simulations of conservative layered skin configurations exposed to a range of single antennas and antenna arrays in the frequency range of 10-100 GHz. For frequencies >30 GHz, the analytical predictions of temperature increase generally deviated from the simulation results by less than 25%. The results demonstrate that a conservative averaging area can be expressed as function of frequency, distance from the transmitter, and-in the far-field-antenna aperture (see Eq. for a simple approximation at a distance of 2 mm from the source). 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 typeengineering

Effect directionunclear

PopulationNot supplied

Sample sizeNot supplied

ExposuremmWave

Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

The paper derives analytical approximations and validates them with simulations to determine a conservative, frequency- and distance-dependent maximum PD averaging area that limits peak skin temperature increase to 1 K for frequencies above 6 GHz and distances >2 mm from transmitters. For a PD limit of 10 W/m2, the conservative averaging area is reported to range from about 3 cm2 at <10 GHz to 1.9 cm2 at 100 GHz, with validation described as successful when power deposition is superficial (>10 GHz) and generally within 25% deviation for >30 GHz.

Outcomes measured

Power-density (PD) averaging area for exposure assessment
Modeled peak skin temperature increase (threshold 1 K)
Conservative exposure assessment parameters above 6 GHz

Limitations

Validation described as worse at lower frequencies (<10 GHz) and very close to the source; systematic evaluation of these conditions is deferred to another study.
Assumed stationary exposure; notes that standards foresee time-averaged limits for pulsed exposures and that extension to transient exposures is not performed here.
Results are based on analytical modeling and simulations (e.g., layered skin configurations and representative antenna/source models), not empirical measurements in humans.

View raw extracted JSON

{
  "study_type": "engineering",
  "exposure": {
    "band": "mmWave",
    "source": "other",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": null
  },
  "population": null,
  "sample_size": null,
  "outcomes": [
    "Power-density (PD) averaging area for exposure assessment",
    "Modeled peak skin temperature increase (threshold 1 K)",
    "Conservative exposure assessment parameters above 6 GHz"
  ],
  "main_findings": "The paper derives analytical approximations and validates them with simulations to determine a conservative, frequency- and distance-dependent maximum PD averaging area that limits peak skin temperature increase to 1 K for frequencies above 6 GHz and distances >2 mm from transmitters. For a PD limit of 10 W/m2, the conservative averaging area is reported to range from about 3 cm2 at <10 GHz to 1.9 cm2 at 100 GHz, with validation described as successful when power deposition is superficial (>10 GHz) and generally within 25% deviation for >30 GHz.",
  "effect_direction": "unclear",
  "limitations": [
    "Validation described as worse at lower frequencies (<10 GHz) and very close to the source; systematic evaluation of these conditions is deferred to another study.",
    "Assumed stationary exposure; notes that standards foresee time-averaged limits for pulsed exposures and that extension to transient exposures is not performed here.",
    "Results are based on analytical modeling and simulations (e.g., layered skin configurations and representative antenna/source models), not empirical measurements in humans."
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "power density",
    "averaging area",
    "temperature increase",
    "skin heating",
    "mmWave",
    "above 6 GHz",
    "10-100 GHz",
    "5G",
    "exposure assessment",
    "safety standards",
    "near-field",
    "far-field",
    "antenna arrays"
  ],
  "suggested_hubs": [
    {
      "slug": "5g-policy",
      "weight": 0.72,
      "reason": "Discusses exposure assessment and conservative PD averaging areas in the 5G frequency range (10–100 GHz) with implications for safety standards."
    }
  ]
}

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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.22147
PubMed: Not supplied

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