Thermal Response of Human Skin to Microwave Energy: A Critical Review

AbstractThis is a review/modeling study of heating of tissue by microwave energy in the frequency range from 3 GHz through the millimeter frequency range (30–300 GHz). The literature was reviewed to identify studies that reported RF-induced increases in skin temperature. A simple thermal model, based on a simplified form of Pennes’ bioheat equation (BHTE), was developed, using parameter values taken from the literature with no further adjustment. The predictions of the model were in excellent agreement with available data. A parametric analysis of the model shows that there are two heating regimes with different dominant mechanisms of heat transfer. For small irradiated areas (less than about 0.5–1 cm in radius) the temperature increase at the skin surface is chiefly limited by conduction of heat into deeper tissue layers, while for larger irradiated areas, the steady-state temperature increase is limited by convective cooling by blood perfusion. The results support the use of this simple thermal model to aid in the development and evaluation of RF safety limits at frequencies above 3 GHz and for millimeter waves, particularly when the irradiated area of skin is small. However, very limited thermal response data are available, particularly for exposures lasting more than a few minutes to areas of skin larger than 1–2 cm in diameter. The paper concludes with comments about possible uses and limitations of thermal modeling for setting exposure limits in the considered frequency range.

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

[2]  M C Ziskin,et al.  Local heating of human skin by millimeter waves: A kinetics study , 2003, Bioelectromagnetics.

[3]  Subhash C. Mishra,et al.  Conventional and newly developed bioheat transport models in vascularized tissues: A review , 2013 .

[4]  John M. Johnson,et al.  Local thermal control of the human cutaneous circulation. , 2010, Journal of applied physiology.

[5]  P. A. Mason,et al.  COMPARISON OF BLOOD PRESSURE AND THERMAL RESPONSES IN RATS EXPOSED TO MILLIMETER WAVE ENERGY OR ENVIRONMENTAL HEAT , 2006, Shock.

[6]  K. Lomas,et al.  A computer model of human thermoregulation for a wide range of environmental conditions: the passive system. , 1999, Journal of applied physiology.

[7]  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.

[8]  J W Hunt,et al.  Experimental evaluation of two simple thermal models using transient temperature analysis. , 1998, Physics in medicine and biology.

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

[10]  J. Baish.  Microvascular Heat Transfer , 1999 .

[11]  E. Adair,et al.  Thermoregulatory responses to RF energy absorption , 2003, Bioelectromagnetics.

[12]  F. Gustrau,et al.  W-band investigation of material parameters, SAR distribution, and thermal response in human tissue , 2002 .

[13]  H. Shirai,et al.  Dosimetry Using a Localized Exposure System in the Millimeter-Wave Band for in vivo Studies on Ocular Effects , 2014, IEEE Transactions on Microwave Theory and Techniques.

[14]  R. Leggett,et al.  Reference values for resting blood flow to organs of man. , 1989, Clinical physics and physiological measurement : an official journal of the Hospital Physicists' Association, Deutsche Gesellschaft fur Medizinische Physik and the European Federation of Organisations for Medical Physics.

[15]  E Atalar,et al.  A Green's function approach to local rf heating in interventional MRI. , 2001, Medical physics.

[16]  Jeffrey G. Andrews,et al.  What Will 5G Be? , 2014, IEEE Journal on Selected Areas in Communications.

[17]  S. Weinbaum,et al.  A new fundamental bioheat equation for muscle tissue: Part I--Blood perfusion term. , 1997, Journal of biomechanical engineering.

[18]  Soichi Watanabe,et al.  Parameter variation effects on temperature elevation in a steady-state, one-dimensional thermal model for millimeter wave exposure of one- and three-layer human tissue , 2010, Physics in medicine and biology.

[19]  Kenneth R Foster,et al.  Modeling thermal responses in human subjects following extended exposure to radiofrequency energy , 2004, Biomedical engineering online.

[20]  D. Colombi,et al.  Implications of EMF Exposure Limits on Output Power Levels for 5G Devices Above 6 GHz , 2015, IEEE Antennas and Wireless Propagation Letters.

[21]  M C Ziskin,et al.  Local heating of human skin by millimeter waves: Effect of blood flow , 2005, Bioelectromagnetics.

[22]  W. C. Randall,et al.  Regional differences in the basal and maximal rates of blood flow in the skin. , 1948, Journal of applied physiology.

[23]  C. P. Burger,et al.  Thermal modeling , 1975 .

[24]  Roland Glaser,et al.  THERMAL MECHANISMS OF INTERACTION OF RADIOFREQUENCY ENERGY WITH BIOLOGICAL SYSTEMS WITH RELEVANCE TO EXPOSURE GUIDELINES , 2007, Health physics.

[25]  Margarethus M. Paulides,et al.  Temperature simulations in hyperthermia treatment planning of the head and neck region , 2014, Strahlentherapie und Onkologie.

[26]  Kenneth R. Foster,et al.  THERMAL MODELING OF MILLIMETER WAVE DAMAGE TO THE PRIMATE CORNEA AT 35 GHz AND 94 GHz , 2003, Health physics.

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

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

[29]  E. Wissler,et al.  Pennes' 1948 paper revisited. , 1998, Journal of applied physiology.

[30]  Keith A. Seffen,et al.  Mathematical Modeling of Skin Bioheat Transfer , 2009 .

[31]  Kenneth R Foster,et al.  Thermal aspects of exposure to radiofrequency energy: Report of a workshop , 2011, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

[32]  E R Adair,et al.  Human exposure to 2450 MHz CW energy at levels outside the IEEE C95.1 standard does not increase core temperature. , 2001, Bioelectromagnetics.

[33]  E. Neufeld,et al.  IT’IS Database for Thermal and Electromagnetic Parameters of Biological Tissues , 2012 .

[34]  D. Savitz,et al.  INTERNATIONAL COMMISSION ON NON-IONIZING RADIATION PROTECTION , 2011 .

[35]  R. Treede,et al.  Heat‐evoked vasodilatation in human hairy skin: axon reflexes due to low‐level activity of nociceptive afferents. , 1996, The Journal of physiology.

[36]  T J Walters,et al.  INTER-SPECIES EXTRAPOLATION OF SKIN HEATING RESULTING FROM MILLIMETER WAVE IRRADIATION: MODELING AND EXPERIMENTAL RESULTS , 2003, Health physics.

[37]  P M Corry,et al.  Application of the time-dependent Green's function and Fourier transforms to the solution of the bioheat equation. , 1995, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

[38]  O. Fujiwara,et al.  Computational verification of anesthesia effect on temperature variations in rabbit eyes exposed to 2.45 GHz microwave energy , 2006, Bioelectromagnetics.

[39]  A. Ahlbom.  Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz) , 1998 .

[40]  Douglas H. K. Lee,et al.  Handbook of Physiology, Section 9: Reactions to Environmental Agents , 1979 .

[41]  J. Werner,et al.  Use of vascular and non-vascular models for the assessment of temperature distribution during induced hyperthermia. , 1995, International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group.

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