David Nelson

Skin heating effects of millimeter-wave irradiation-thermal modeling results

Millimeter microwaves (MMWs) are a subset of RF in the 30-300-GHz range, The proliferation of devices that operate in the MMW range has been accompanied by increased concern about their safety. As MMW irradiation has a very shallow penetration in tissue, the specific absorption rate is not a relevant parameter for dosimetry purposes. A thermal modeling program was used to investigate the tissue heating effects of MMW irradiation (100 GHz nominal) on the primate head. The objectives were to determine the extent to which the surface and subsurface tissue temperatures depend on applied energy density and the effects of blood flow and surface cooling on tissue temperatures. Two power ranges were considered: short-duration exposure to high power microwaves (HPMs), with power densities of 1.0, 1.5, 2.0, 2.5, or 3.0 W cm/sup -2/ for 3 s, and longer duration exposure to low-power microwaves (LPMs), with power densities of 0.1, 0.15, 0.2, 0.25, 0.3 W cm/sup -2/ for 30 s. The applied energies were comparable for both HPM and LPM exposures. The authors found both surface and subsurface temperatures increase as the energy level increases, with HPMs having a higher peak temperature than the LPMs for similar exposure energy densities. The surface temperature increase is linear with energy density for the HPMs, except under combined conditions of high blood flow (blood-flow rate of 8/spl times/10/sup -3/ g s/sup -1/ cm/sup -3/) and high-energy density (greater than 7.5 J cm/sup -2/), The LPM surface temperatures are not linear with incident energy. The peak surface temperature is affected by environmental conditions (convection coefficient, sweat rate). The magnitude of the temperature increase due to MMW exposure did not change with environmental conditions. The subsurface temperature increases are considerably damped, compared to the surface temperatures.

Recent Advancements in Dosimetry Measurements and Modeling

Whole-body specific absorption rate (SAR) values provide useful information about energy deposition resulting from exposure to radio frequency radiation (RFR). However, whole-body SAR values do not reveal possible localized “hot spots”. Although differences in regional temperatures have been measured in animals during RFR exposure [1–3], the use of temperature probes to make empirical measurements of these “hot spots” can be extremely time consuming and are invasive in nature [4].

Determining localized garment insulation values from manikin studies: computational method and results

The localized thermal insulation value expresses a garment’s thermal resistance over the region which is covered by the garment, rather than over the entire surface of a subject or manikin. The determination of localized garment insulation values is critical to the development of high-resolution models of sensible heat exchange. A method is presented for determining and validating localized garment insulation values, based on whole-body insulation values (clo units) and using computer-aided design and thermal analysis software. Localized insulation values are presented for a catalog consisting of 106 garments and verified using computer-generated models. The values presented are suitable for use on volume element-based or surface element-based models of heat transfer involving clothed subjects.

A Comparison of Sar Values Determined Empirically and by FD-TD Modeling

Specific absorption rate (SAR) is defined by the National Council on Radiation Protection and Measurements as “…the time derivative of the incremental energy absorbed by (dissipated in) an incremental mass contained in a volume of a given density” (NRCP, 1981). The whole-body and partial-body SAR form the basis of permissible exposure limits for radio frequency radiation (RFR). The whole-body SAR provides very useful information regarding the influence of frequency, polarization, and orientation on RFR absorption[1,2]. However, RFR is not absorbed uniformly throughout a biological system. Numerous factors contribute to the heterogeneity of SAR values in biological system, including differences in electrical properties of different tissues, impedance mismatches at tissue boundaries, and the complex geometry of individual organs and structures [1,2]. Due to these factors, local SAR must be used to reveal the distribution of RFR absorption within the animal. Without this information, bioeffects data obtained from one species cannot be meaningfully extrapolated to another.

An Investigation on Driver Behaviors and Eye-Movement Patterns at Grade Crossings Using a Driving Simulator

Collisions at grade crossings are often attributed to driver failure to detect warnings, to comprehend their meaning, or to react appropriately. One of the solutions to tackling these problems is the development of various visual signs. We designed three types of visual warnings at virtual grade crossings: a gate with lights and crossbuck, a gate with a crossbuck, and a crossbuck alone. Study 1 shows that vehicle speeds of 18 participants in the period 20 seconds before approaching the crossing (critical zone) decreased in comparison to the baseline (pre-critical zone) for visual warning type 1, a gate with lights. Additionally, participants, who were exposed to a train early in the scenario, showed more defensive driving behaviors than the other case. In study 2, we considered drivers’ eye movement pattern in the pre-critical and the critical zone for 17 participants. Design applications of warnings in vehicles and on roads and further research directions are discussed.Copyright

Driver Behavior at Simulated Railroad Crossings

Highway-rail grade crossing collisions and fatalities have been in decline for several decades, but a recent ‘plateau’ has spurred additional interest in novel safety research methods. With the support of Federal Railroad Administration (FRA), Michigan Tech researchers have performed a large-scale study that utilizes the SHRP2 Naturalistic Driving Study (NDS) data to analyze how various crossing warning devices affect driver behavior and to validate the driving simulation data. To this end, representative crossings from the NDS dataset were recreated in a driving simulator. This paper describes driver behavior at simulated rail crossings modeled after real world crossings included in the NDS dataset. Results suggest that drivers may not react properly to crossbucks and active warnings in the off position. Participants performed the safest behaviors in reaction to STOP signs. The majority of participants also reported an increase in vigilance and compliant behaviors after repeated exposure to RR crossings, which was supported by the results of a linear regression analysis. Participants used the presence of active RR warnings (in the off position) as a cue that there is no oncoming train and it is safe to cross without preparing to yield (operationalized as visually scanning for a train and active speed reduction). Drivers react the most appropriately to STOP signs, but it is unclear whether or not these behaviors would lead to a decrease in train-vehicle collisions.

Getting active with passive crossings: Investigating the use of in-vehicle auditory alerts for highway-rail grade crossings

This paper investigates the plausibility of a novel in-vehicle auditory alert system to warn drivers of the presence of railroad crossings. Train-Vehicle collisions at highway-rail grade crossings continue to be a major issue despite improvements over the past several decades. In 2014 there were 2,286 highway-rail incidents leading to 852 injuries and 269 fatalities. This marked the first time in the past decade that incident rates increased from the previous year. To prevent the overall trend in safety improvement from plateauing, interest is shifting towards novel warning devices that can be applied to all crossings at minimal cost. These novel warnings are intended to complement but not replace the primary visual warnings that are already in place at both active and passive crossings. Few in-vehicle warning systems have been described and tested in the rail safety literature. The ones that have been described only manipulate the modality or reliability of the warning message, and pay little attention to message content, timing of presentation, mappings between crossing events and warning logic, and driver habituation associated with long term use. To this end, a line of research has been being carried out to design in-vehicle auditory alerts and measure subjective preference and driver behavior in response to in-vehicle auditory alerts. The first study included a subjective evaluation of potential auditory cues. Cues rated as most effective and appropriate were included in the design of prototype systems in the follow up study. The second study will measure compliance rates in a driving simulator with and without in-vehicle auditory alerts. The results of first study and the study design for the second study are discussed.Copyright

Microwave-Induced Temperature Gradients In The Rat Brain

The ability to mathematically describe the relationship between radiofrequency (RF) exposure conditions and tissue temperature distributions is important to extrapolating animal data to man, and to establishing safe exposure conditions. Exposure to hgh-powered microwave (HPM) fields is known to produce non-uniform heating in . laboratory animals. The temperature fields which result from exposure depend on a number of variables, including the RF power density and frequency, subject orientation with respect to the field, time duration and mode (CW, pulsed or modulated). In addition, anatomical factors such as tissue permittivity, thermal diffusivity, and local blood perfusion, may profoundly affect the temperature field. Temperature measurements in the brains of rats exposed to 2.45 GHz irradiation over a 30-minute period demonstrated significant tissue heating (Ward, et al., 1986). However, the brain temperature elevation was fairly uniform, with no observable ‘hot spots’ despite the fact that the energy absorption patterns are highly nonuniform at that frequency. The temperature Uniformity was attributed to the brain’s high perfusion rate which makes it difficult to sustain large temperature gradients .