TEMPERATURE OSCILLATIONS IN LIQUID-MEDIA CAUSED BY CONTINUOUS (NONMODULATED) MILLIMETER WAVELENGTH ELECTROMAGNETIC IRRADIATION

Convection in liquids caused by 53-78 GHz millimeter wave irradiation with incident power density that ranged from 10 mu W/cm(2) to 1 W/cm(2 ) was studied. Infrared thermography was used as an artifact-free meth od for recording surface-temperature dynamics during irradiation. It w as found that continuous (nonmodulated) waves can produce a relaxation -type temperature oscillation in liquids with a relatively high stabil ity of the period between temperature spikes. The temperature oscillat ion is due to the repetitive formation and dissipation of a torroidal type of convection vortex. When the vortex became stable during irradi ation, we observed a temperature decrease following the initial temper ature-rise phase, even though the irradiation was constantly maintaine d. This result constitutes a new process that can play a significant r ole in producing microwave bioeffects, including some so-called ''nont hermal'' effects and some effects that are inversely related to heatin g. Also, it can be considered as a newly discovered potential artifact in microwave bioeffects studies. (C) 1996 Wiley-Liss, Inc.