Subject(s)
Infrared Rays , Thermography/instrumentation , Varicose Veins/diagnostic imaging , Female , Humans , Male , RadiographySubject(s)
Body Temperature Regulation/physiology , Face , Respiration , Skin Temperature/physiology , Adult , Aged , Female , Humans , Male , Middle Aged , Respiratory Physiological Phenomena , Time FactorsSubject(s)
Body Temperature Regulation/physiology , Eye/metabolism , Body Temperature , Computer Simulation , Eye/anatomy & histology , Female , Humans , Male , TemperatureABSTRACT
Convection in liquids caused by 53-78 GHz millimeter wave irradiation with incident power density that ranged from 10 microW/cm2 to 1 W/cm2 was studied. Infrared thermography was used as an artifact-free method for recording surface-temperature dynamics during irradiation. It was found that continuous (nonmodulated) waves can produce a relaxation-type temperature oscillation in liquids with a relatively high stability of the period between temperature spikes. The temperature oscillation is due to the repetitive formation and dissipation of a torroidal type of convection vortex. When the vortex became stable during irradiation, we observed a temperature decrease following the initial temperature-rise phase, even though the irradiation was constantly maintained. This result constitutes a new process that can play a significant role in producing microwave bioeffects, including some so-called "nonthermal" effects and some effects that are inversely related to heating. Also, it can be considered as a newly discovered potential artifact in microwave bioeffects studies.
Subject(s)
Electromagnetic Phenomena , Microwaves , Biophysical Phenomena , Biophysics , Hot Temperature , Microwaves/adverse effects , Temperature , WaterABSTRACT
Distribution of millimeter wavelength electromagnetic energy absorption in surface layers of biological tissue models was studied using methods of Infrared Thermography. 0.1 mm thin-layer phantoms were irradiated in the near field using different types of horn antennas in the 37-78 GHz frequency range. Heating patterns were recorded during microwave irradiation, and surface SAR distributions were calculated. The temperature resolution was better than 0.05 K. It was found that horn antennas produced nonuniform heating patterns in irradiated objects. These nonuniform patterns were due to a geometrical resonance resulting from a secondary wave-mode interaction between an irradiated object and the corresponding critical cross-section of the horn antenna. Local SAR values in hot spots exceeded the spatially averaged values by over 10 times, and the widths of these hot spots at 5 times the average SAR were often 1 mm or less. The location, quantity, number and size of the local field absorption maxima of irradiated objects strongly depended on the frequency of electromagnetic irradiation, with equivalent Q-factors of 500 or more. These findings provide an explanation for a number of frequency-dependent effects of millimeter wave electromagnetic irradiation.
