Temperature oscillations in liquid media caused by continuous (nonmodulated) millimeter wavelength electromagnetic irradiation

Abstract

Convection in liquids caused by 53–78 GHz millimeter wave irradiation with incident power density that ranged from 10 μW/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. © 1996 Wiley‐Liss, Inc.

Millimeter‐Wave Heating in In Vitro Studies: Effect of Convection in Continuous and Pulse‐Modulated Regimes

“…This moment precedes the initiation of convection in bulk [Kaviany, ; Tanasawa, ; Kohl et al, ]. At MMW frequencies, a similar effect was observed by Khizhnyak and Ziskin [] during exposure of 0.5–3.0‐mm‐thick layers of NaCl solution, in the 53–78 GHz range at SAR levels up to 80 kW/kg. For exposure durations exceeding 70 s, the temperature rise in the liquid samples is noticeably lower than that in the agar gel due to convection.…”

“…The initiation of convection in liquids by MMW and MW exposures has been described in several studies [Sharov et al, ; Khizhnyak and Ziskin, ; Betskii et al, ; Cueille et al, ; Paffi et al, ; Zhadobov et al, ]. Convection during in vitro bioelectromagnetic experiments affects the temperature dynamics and distribution [Sandblom and Theander, ; Pickard et al, ], causing the formation of a toroidal vortex [Khizhnyak and Ziskin, ] and temperature drop in the irradiated spot [Wessapan and Rattanadecho, ; Zhadobov et al, ]. Additionally, liquid motion caused by convective currents may perturb the local concentration of oxygen and nutrients near the surface of the cells [Paffi et al, ].…”

The influence of millimeter waves on the physical properties of large and giant unilamellar vesicles

“…Assuming that δ ranges from about 0.35 mm up to about 0.40 mm in the frequency range studied [9], it can be calculated that 90% of the power density is absorbed within the first 0.4 mm of the suspension. However, as the presence of the sensor in the liquid could perturb the MMW field distribution [40], a remote temperature recording is desirable in order to obtain correct surface-temperature dynamics data on the convection process during MMW irradiation [41]. Therefore, a second measurement of potential heating patterns on the surface of the suspension was performed by using a noncontact, MMW-immune infrared thermometer.…”

Microscale temperature and SAR measurements in cell monolayer models exposed to millimeter waves

“…The initiation of convection in liquid by MMW exposure was described in a number of papers [Sharov et al, ; Khizhnyak and Ziskin, ]. It is known that background laminar convection develops in liquid due to a non‐uniform temperature distribution.…”

“…Therefore, the best candidates for a local temperature monitoring inside a sample in in vitro experiments are FO thermometers and TC. They were used for temperature monitoring in several in vitro studies [Khizhnyak and Ziskin, ; Logani and Ziskin, ; Szabo et al, ; Zhadobov et al, ; Habauzit et al, ]. Some reports also addressed the problem of temperature measurements during high intensity pulsed exposures at microwaves (for carrier frequencies ranging from 9 to 10 GHz) [Pakhomov et al, ,; Pakhomov, ].…”