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 micro-thermocouples. 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. © 2019 Bioelectromagnetics Society.

中文翻译：

---

体外研究中的毫米波加热：连续和脉冲调制方式下的对流效应。

毫米波（MMW）的浅穿透和体外实验中的不均匀照明导致比吸收率（SAR）的不均匀分布。这些SAR梯度会触发液体中的对流，从而影响瞬态和稳态温度分布。我们使用微热电偶分析了连续波（CW）和脉冲波（PW）振幅调制方案中MMW暴露期间对流对温度动态的影响。温升动力学的特征是，随着MMW暴露SAR的增加，温度峰的出现会移到较短的时间，并在大量对流开始之前发生。此外，我们证明了液体量会影响对流。增大体积会导致对流提前触发，并在暴露结束后提高冷却速度。在PW模式下，对流在很大程度上取决于影响热脉冲幅度和冷却速率的脉冲持续时间。后者导致PW方案中平均温度的变化。生物电磁学。2019; 40：553-568。©2019生物电磁学会。