RF Safe

Human exposure to pulsed fields in the frequency range from 6 to 100 GHz

2017 · Unclear · Low evidence

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UnclearLow evidencePaper 2354

Finite-difference time-domain and bioheat modelling of far-field exposure of the human face to pulses <10 s at 6–100 GHz found that temperature rise depends on frequency, polarization, exposure duration, and depth, with hotspots often in/around fine structure…

Study snapshot

Publicationmanual · 2017
Study typeengineering
Reported directionUnclear
Evidence ratingLow

Abstract

Human exposure to pulsed fields in the frequency range from 6 to 100 GHz Laakso I, Morimoto R, Heinonen J, Jokela K, Hirata A. Human exposure to pulsed fields in the frequency range from 6 to 100 GHz. Phys Med Biol. 2017 Aug 9;62(17):6980-6992. doi: 10.1088/1361-6560/aa81fe. Abstract Restrictions on human exposure to electromagnetic waves at frequencies higher than 3-10 GHz are defined in terms of the incident power density to prevent excessive temperature rise in superficial tissue. However, international standards and guidelines differ in their definitions of how the power density is interpreted for brief exposures. This study investigated how the temperature rise was affected by exposure duration at frequencies higher than 6 GHz. Far-field exposure of the human face to pulses shorter than 10 s at frequencies from 6 to 100 GHz was modelled using the finite-difference time-domain method. The bioheat transfer equation was used for thermal modelling. We investigated the effects of frequency, polarization, exposure duration, and depth below the skin surface on the temperature rise. The results indicated limitations in the current human exposure guidelines and showed that radiant exposure, i.e. energy absorption per unit area, can be used to limit temperature rise for pulsed exposure. The data are useful for the development of human exposure guidelines at frequencies higher than 6 GHz. ncbi.nlm.nih.gov Excerpts Figure 2 shows that the hotspot locations depend on the frequency and polarization and often appear in and around fine structures such as the eyelids. However, they can also appear in other locations, most notably in the eyes and cheeks. Future studies should investigate the differences in the absorption pattern and temperature rise in multiple anatomically different individuals. The investigation should also take into account the extent of opening between the eyelids, .. our results showed that relatively long exposure averaging times used in current ICNIRP guidelines may not provide adequate protection in the case of brief, intense pulsed exposure (figure 4). An additional limit defined for the maximum radiant exposure could provide protection from short pulse exposure. It is important to note that the effect of exposure duration diminishes as the frequency decreases (figure 5). Therefore, separate consideration for pulsed exposure is relevant only at frequencies higher than 10 GHz. In conclusion, this study addressed the issue of pulsed exposure, which is currently treated differently in different international guidelines and standards. The results showed the effects of non-uniform energy absorption, exposure duration, and frequency on the temperature rise, and are useful for the development of human exposure guidelines at frequencies higher than 6 GHz.

Machine Enhanced Logic

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
PopulationHuman face (modelled)
Sample sizeNot supplied
ExposuremmWave · pulses shorter than 10 s
Evidence strengthLowConfidence: 74% · Peer reviewed: yes

Main findings

Finite-difference time-domain and bioheat modelling of far-field exposure of the human face to pulses <10 s at 6–100 GHz found that temperature rise depends on frequency, polarization, exposure duration, and depth, with hotspots often in/around fine structures such as eyelids (also eyes and cheeks). The authors report that current guideline averaging times may not adequately protect against brief, intense pulsed exposure and suggest a maximum radiant exposure (energy per unit area) limit to constrain temperature rise, particularly at frequencies >10 GHz.

Outcomes measured

  • Temperature rise in superficial tissue/skin
  • Hotspot location (spatial distribution of absorption/temperature rise)
  • Implications for exposure guideline metrics (incident power density vs radiant exposure)

Limitations

  • Computational modelling study (no direct measurements in humans reported)
  • Modelled exposure scenario limited to far-field exposure of the human face
  • No sample size / number of anatomical models specified; excerpt notes need to study multiple anatomically different individuals and eyelid opening extent
View raw extracted JSON
{
  "study_type": "engineering",
  "exposure": {
    "band": "mmWave",
    "source": null,
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "pulses shorter than 10 s"
  },
  "population": "Human face (modelled)",
  "sample_size": null,
  "outcomes": [
    "Temperature rise in superficial tissue/skin",
    "Hotspot location (spatial distribution of absorption/temperature rise)",
    "Implications for exposure guideline metrics (incident power density vs radiant exposure)"
  ],
  "main_findings": "Finite-difference time-domain and bioheat modelling of far-field exposure of the human face to pulses <10 s at 6–100 GHz found that temperature rise depends on frequency, polarization, exposure duration, and depth, with hotspots often in/around fine structures such as eyelids (also eyes and cheeks). The authors report that current guideline averaging times may not adequately protect against brief, intense pulsed exposure and suggest a maximum radiant exposure (energy per unit area) limit to constrain temperature rise, particularly at frequencies >10 GHz.",
  "effect_direction": "unclear",
  "limitations": [
    "Computational modelling study (no direct measurements in humans reported)",
    "Modelled exposure scenario limited to far-field exposure of the human face",
    "No sample size / number of anatomical models specified; excerpt notes need to study multiple anatomically different individuals and eyelid opening extent"
  ],
  "evidence_strength": "low",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "pulsed fields",
    "6–100 GHz",
    "millimeter wave",
    "incident power density",
    "radiant exposure",
    "temperature rise",
    "finite-difference time-domain",
    "bioheat transfer",
    "exposure guidelines",
    "ICNIRP"
  ],
  "suggested_hubs": [
    {
      "slug": "who-icnirp",
      "weight": 0.78,
      "reason": "Discusses limitations of current ICNIRP guideline averaging times for brief pulsed exposures and implications for guideline development."
    },
    {
      "slug": "5g-policy",
      "weight": 0.62,
      "reason": "Addresses human exposure metrics and guideline development for >6 GHz (mmWave) frequencies relevant to 5G."
    }
  ]
}
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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: 10.1088/1361-6560/aa81fe
PubMed: Not supplied

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