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.

[1]  A. Guy,et al.  Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models , 1976, IEEE Transactions on Biomedical Engineering.

[2]  P. A. Mason,et al.  Recent Advancements in Dosimetry Measurements and Modeling , 2000 .

[3]  T. Walters,et al.  Heating and pain sensation produced in human skin by millimeter waves: comparison to a simple thermal model. , 2000, Health physics.

[4]  G. D. Lapin,et al.  Requirements for accurate anatomical imaging of the rat for electromagnetic modeling , 1997, Proceedings of the 19th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. 'Magnificent Milestones and Emerging Opportunities in Medical Engineering' (Cat. No.97CH36136).

[5]  John M. Ziriax,et al.  Variability in EMF permittivity values: implications for SAR calculations , 2000, IEEE Transactions on Biomedical Engineering.

[6]  H. F. Bowman,et al.  Theory, measurement, and application of thermal properties of biomaterials. , 1975, Annual review of biophysics and bioengineering.

[7]  C Gabriel,et al.  The dielectric properties of biological tissues: I. Literature survey. , 1996, Physics in medicine and biology.

[8]  P. Dimbylow.  FDTD calculations of the whole-body averaged SAR in an anatomically realistic voxel model of the human body from 1 MHz to 1 GHz. , 1997, Physics in medicine and biology.

[9]  A Comparison of Sar Values Determined Empirically and by FD-TD Modeling , 2000 .

[10]  C. Heaps,et al.  Physiological responses of rhesus monkeys to exercise at varied temperatures. , 1995, Aviation, space, and environmental medicine.

[11]  B. Wilson,et al.  Investigations of large vessel cooling during interstitial laser heating. , 1995, Medical physics.

[12]  R. K. Gilbert,et al.  Characterization and Evaluation of a Prototype Forward-Looking Automotive Radar (FLAR): Final Report , 1997 .

[13]  M. Kolka,et al.  Thermoregulation in Erythrocebus patas: a thermal balance study. , 1983, Journal of applied physiology: respiratory, environmental and exercise physiology.

[14]  H. F. Bowman,et al.  Limitations and significance of thermal washout data obtained during microwave and ultrasound hyperthermia. , 1990, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

[15]  K R Foster,et al.  Heating of tissues by microwaves: a model analysis. , 1998, Bioelectromagnetics.

[16]  T J Walters,et al.  Thresholds of microwave-evoked warmth sensations in human skin. , 1997, Bioelectromagnetics.

[17]  W F Pickard,et al.  On the assumption of negligible heat diffusion during the thermal measurement of a nonuniform specific absorption rate. , 1999, Radiation research.

[18]  K. Foster,et al.  Effect of Surface Cooling and Blood Flow on the Microwave Heating of Tissue , 1978, IEEE Transactions on Biomedical Engineering.

[19]  Y. Akyel,et al.  Current state and implications of research on biological effects of millimeter waves: a review of the literature. , 1998, Bioelectromagnetics.

[20]  O.P. Gandhi,et al.  Calculation of electric fields and currents induced in a millimeter-resolution human model at 60 Hz using the FDTD method with a novel time-to-frequency-domain conversion , 1996, IEEE Antennas and Propagation Society International Symposium. 1996 Digest.

[21]  K R Foster,et al.  Thermal models for microwave hazards and their role in standards development. , 1999, Bioelectromagnetics.

[22]  P. A. Mason,et al.  Radio frequency radiation of millimeter wave length: potential occupational safety issues relating to surface heating. , 2000, Health physics.

[23]  Cooper Te,et al.  Correlation of thermal properties of some human tissue with water content. , 1971 .

[24]  R C Eberhart,et al.  Influence of hypothermia and circulatory arrest on cerebral temperature distributions. , 1985, Journal of biomechanical engineering.

[25]  A finite-difference electromagnetic deposition/thermoregulatory model: comparison between theory and measurements. , 1987, Bioelectromagnetics.

[26]  D. Nelson,et al.  Brain temperature and limits on transcranial cooling in humans: quantitative modeling results , 1998, European Journal of Applied Physiology and Occupational Physiology.

[27]  R. W. Lau,et al.  The dielectric properties of biological tissues: II. Measurements in the frequency range 10 Hz to 20 GHz. , 1996, Physics in medicine and biology.

[28]  R. Eberhart,et al.  Influences of hypothermia and tissue perfusion on temperature distributions in simulated cranial surgery , 1993 .

[29]  P. A. Mason,et al.  Database created from magnetic resonance images of a Sprague‐Dawley rat, rhesus monkey, and pigmy goat , 1995, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[30]  R. Goodman,et al.  Direct intraoperative measurement of human brain temperature. , 1997, Neurosurgery.

[31]  R. W. Lau,et al.  The dielectric properties of biological tissues: III. Parametric models for the dielectric spectrum of tissues. , 1996, Physics in medicine and biology.

[32]  H. H. Pennes.  Analysis of tissue and arterial blood temperatures in the resting human forearm. 1948. , 1948, Journal of applied physiology.

[33]  P Moffa,et al.  DEVELOPMENT OF PERFORMANCE SPECIFICATIONS FOR COLLISION AVOIDANCE SYSTEMS FOR LANE CHANGE, MERGING, AND BACKING. TASK 5: CRASH COUNTERMEASURE TECHNOLOGY INVESTIGATION , 1996 .