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

Abstract

Shallow penetration of millimeter waves (MMW) and non-uniform illumination in in vitro experiments result in a non-uniform distribution of the specific absorption rate (SAR). These SAR gradients trigger convective currents in liquids affecting transient and steady-state temperature distributions. We analyzed the effect of convection on temperature dynamics during MMW exposure in continuous-wave (CW) and pulsed-wave (PW) amplitude-modulated regimes using microthermocouples. Temperature rise kinetics are characterized by the occurrence of a temperature peak that shifts to shorter times as the SAR of the MMW exposure increases and precedes initiation of convection in bulk. Furthermore, we demonstrate that the liquid volume impacts convection. Increasing the volume results in earlier triggering of convection and in a greater cooling rate after the end of the exposure. In PW regimes, convection strongly depends on the pulse duration that affects the heat pulse amplitude and cooling rate. The latter results in a change of the average temperature in PW regime. Bioelectromagnetics. 2019;40:553-568.

Millimeter-Wave Heating In Vitro: Local Microscale Temperature Measurements Correlated to Heat Shock Cellular Response

“…The exposure system used in this study is presented in Fig. 1 and described in detail in [24]. A WR15 waveguide (WG) aperture antenna, operating at 58.4 GHz, was used to drive the MMW radiation toward one well of the 12-well tissue culture plate set 5 mm from it (inset of Fig.…”

“…Temperature measurements and cell exposures were performed in separate experiments to avoid possible cellular damage or contamination as well as local increase of SAR in the cell monolayer due to the presence of the µTC (see sections A and B of Results). Indeed, the presence of the cells induces an approximatively 1% drop of the incoming energy absorbed by the culture medium [30], that affects only slightly the temperature dynamics [24] (differences < 1% compared to measurements with cells). Temperature measurements were repeated 4 times to ensure reproducibility.…”

“…3, filled with 2 ml of culture medium (corresponding to the height of 5.2 mm), and the WG (Fig. 3) as we previously detailed [24], [30]. The effects of a thin metallic µTC on the SAR and temperature in the exposed liquid were computed using the EM and T • solvers of CST.…”

“…Its expression is an indicator of thermotolerance that must be minimized to guarantee the success of the thermal treatment. CW-induced heating has been generated at the cellular level through a specific MMW-generator setup [12], [24]. A micro-thermocouple (µTC) has been used to measure temperature elevation at the level of the exposed cell monolayer.…”

Effects of Radiofrequency Radiation on Gene Expression: A Study of Gene Expressions of Human Keratinocytes From Different Origins

“…The cells were exposed in the corresponding culture medium supplemented with 10 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) for primary keratinocyte cultures and 4.6 mM HEPES for HaCaT cells for 3 h. For each experiment 4 ml of medium was used. Note that the volume does not influence either the SAR or the IPD [Orlacchio et al, 2019]. Two exposure conditions (unexposed [Sham] and MMW-exposed [Expo]) were used under the same cell culture conditions.…”