Computational modeling investigation of pulsed high peak power microwaves and the potential for traumatic brain injury

2021 · Unclear · Insufficient evidence

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UnclearInsufficient evidencePaper 976

Study snapshot

Publicationmanual · 2021

Study typeother

Reported directionUnclear

Evidence ratingInsufficient

Abstract

Computational modeling investigation of pulsed high peak power microwaves and the potential for traumatic brain injury Amy M Dagro, Justin W Wilkerson, Thaddeus P Thomas, Benjamin T Kalinosky, Jason A Payne. Computational modeling investigation of pulsed high peak power microwaves and the potential for traumatic brain injury. Sci Adv. 2021 Oct 29;7(44):eabd8405. doi: 10.1126/sciadv.abd8405. Amy Dagro and Thaddeus Thomas are with the U.S. Army Research Laboratory, Aberdeen Proving Ground, MD; Benjamin Kalinosky is with General Dynamics Information Technology, JBSA Fort Sam Houston, San Antonio, TX; and Jason Payne is with U.S, Air Force Research Laboratory, 711th Human Performance Wing, Airman Systems Directorate, Bioeffects Division, Radio Frequency Bioeffects Branch, JBSA Fort Sam Houston, San Antonio, TX. Abstract When considering safety standards for human exposure to radiofrequency (RF) and microwave energy, the dominant concerns pertain to a thermal effect. However, in the case of high-power pulsed RF/microwave energy, a rapid thermal expansion can lead to stress waves within the body. In this study, a computational model is used to estimate the temperature profile in the human brain resulting from exposure to various RF/microwave incident field parameters. The temperatures are subsequently used to simulate the resulting mechanical response of the brain. Our simulations show that, for certain extremely high-power microwave exposures (permissible by current safety standards), very high stresses may occur within the brain that may have implications for neuropathological effects. Although the required power densities are orders of magnitude larger than most real-world exposure conditions, they can be achieved with devices meant to emit high-power electromagnetic pulses in military and research applications. Excerpts "The bulk of scientific literature uses continuous waves and moderate field strengths (typical of real-life scenarios), with less emphasis on pulsed fields of very high peak strength that may occur with ultrawideband pulse generators or EM pulse simulators (4). It is worth investigating whether extremely high peak power sources applied with a slow repetition frequency, or low duty cycle, can induce injurious effects without thermal buildup greater than a few degrees Celsius." "With the exception of low intracranial absorption at 1400 MHz, the highest ratio of peak average intracranial SAR* to peak average skin SAR* occurs between 1 to 1.8 GHz." "The MAE, also referred to as “microwave hearing” or the “Frey effect” due to its discovery by Allan Frey in 1961 (7, 8), was initially observed when subjects standing up to hundreds of feet away from a radar transponder could hear an audible tonal noise (e.g., chirping, buzzing, or clicking). The scientific underpinnings of the MAE were controversial for the first several years (9–11). After more than a decade of investigations, it became generally accepted that the perceived sound is due to the cochlea detecting stress waves that result from a rapid temperature rise in tissues within the head due to pulsed RF/microwave exposure (11, 12)." "Typically, relatively low-average powers and small temperature changes (10−6°C) are required to elicit the MAE (12). Although adverse health effects from the MAE have not been previously established, one study on rodents suggests that very high–peak power pulsed microwaves can result in cognitive deficits (13)." "This study uses a two-simulation approach to investigate whether an HPM source could theoretically induce adverse mechanical responses within the brain." "This study has shown that, by applying a small temperature increase (<0.0005°C) in a very short amount of time (less than several microseconds), potentially injurious stress waves are created." "For frequencies between 400 MHz to 2 GHz, the IEEE C95.1 RF exposure guidelines limit the exposure reference limit (ERL) to fmhz/200 (W/m2) over an averaging time of 30 min. For 1-GHz exposures, the IEEE C95.1 ERL of 5 W/m2 over 30 min would equate to an average energy density of 9000 J/m2. Our computational model shows that, for sufficiently high incident power densities, a single pulse could potentially result in biologically meaningful pressures. For example, large pressures may occur following 1-GHz frequency, a pulse duration of 5 μs, and incident power densities of at least 1.5 × 107 W/m2. The energy density associated with such a pulse would be equal to PIN×τd or 75 J/m2 (significantly less than the ERL standard)." " Note that the proposed HPM power densities in this study are extremely large and several orders of magnitude larger than power densities typically experienced by the public. As an illustrative example, at around 200 feet from a cell phone base station, a person will be exposed to a power density of only 0.001 mW/cm2 or less (36). This study establishes a testable hypothesis between potential neurocognitive effects and the thermoelastic mechanism from HPM systems. To date, however, adverse effects from HPM systems have not been established in the scientific literature." Open access paper: ncbi.nlm.nih.gov

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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 typeother

Effect directionunclear

PopulationComputational human brain model (simulations)

Sample sizeNot supplied

ExposureRF · pulse duration example: 5 μs; mentions very short time (< several microseconds) and low duty cycle/slow repetition frequency

Evidence strengthInsufficientConfidence: 74% · Peer reviewed: yes

Main findings

Using a two-step computational approach (temperature modeling followed by mechanical simulation), the authors report that certain extremely high-power pulsed RF/microwave exposures (stated as permissible by current safety standards) could generate very high stresses/pressures in the brain via rapid thermoelastic expansion. They note the required power densities are orders of magnitude above most real-world public exposures and that adverse effects from HPM systems have not been established in the scientific literature.

Outcomes measured

Brain temperature profile from RF/microwave exposure (modeled)
Mechanical response/stress waves/pressures in brain tissue (modeled)
Potential implications for traumatic brain injury/neuropathological or neurocognitive effects (hypothesized)
Microwave auditory effect (MAE/Frey effect) mechanism context (stress waves from rapid temperature rise)

Limitations

Computational modeling/simulation study (no direct human or animal outcome data reported in the abstract/excerpts)
Exposure scenarios involve extremely large power densities stated to be orders of magnitude above typical public exposures
Authors state adverse effects from HPM systems have not been established in the scientific literature

View raw extracted JSON

{
  "study_type": "other",
  "exposure": {
    "band": "RF",
    "source": "high-power pulsed microwave (HPM) source / pulsed RF/microwave incident fields",
    "frequency_mhz": null,
    "sar_wkg": null,
    "duration": "pulse duration example: 5 μs; mentions very short time (< several microseconds) and low duty cycle/slow repetition frequency"
  },
  "population": "Computational human brain model (simulations)",
  "sample_size": null,
  "outcomes": [
    "Brain temperature profile from RF/microwave exposure (modeled)",
    "Mechanical response/stress waves/pressures in brain tissue (modeled)",
    "Potential implications for traumatic brain injury/neuropathological or neurocognitive effects (hypothesized)",
    "Microwave auditory effect (MAE/Frey effect) mechanism context (stress waves from rapid temperature rise)"
  ],
  "main_findings": "Using a two-step computational approach (temperature modeling followed by mechanical simulation), the authors report that certain extremely high-power pulsed RF/microwave exposures (stated as permissible by current safety standards) could generate very high stresses/pressures in the brain via rapid thermoelastic expansion. They note the required power densities are orders of magnitude above most real-world public exposures and that adverse effects from HPM systems have not been established in the scientific literature.",
  "effect_direction": "unclear",
  "limitations": [
    "Computational modeling/simulation study (no direct human or animal outcome data reported in the abstract/excerpts)",
    "Exposure scenarios involve extremely large power densities stated to be orders of magnitude above typical public exposures",
    "Authors state adverse effects from HPM systems have not been established in the scientific literature"
  ],
  "evidence_strength": "insufficient",
  "confidence": 0.74,
  "peer_reviewed_likely": "yes",
  "keywords": [
    "pulsed microwaves",
    "high peak power",
    "HPM",
    "radiofrequency",
    "microwave",
    "thermoelastic mechanism",
    "stress waves",
    "brain",
    "traumatic brain injury",
    "IEEE C95.1",
    "microwave auditory effect",
    "Frey effect"
  ],
  "suggested_hubs": [
    {
      "slug": "occupational-exposure",
      "weight": 0.42,
      "reason": "Mentions military and research applications with devices emitting high-power electromagnetic pulses; relevance to non-public/operational exposures."
    },
    {
      "slug": "who-icnirp",
      "weight": 0.3,
      "reason": "Discusses safety standards/exposure guidelines (IEEE C95.1) and implications for standards focused on thermal effects."
    }
  ]
}

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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: 10.1126/sciadv.abd8405
PubMed: Not supplied

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