Adaptive Temperature Control Applied to a 900-MHz In Vitro Exposure Setup for Nonthermal Effects of a High-Level SAR

Abstract

Adaptive temperature control is proposed to increase the nonthermal exposure level of in vitro experiments. By regulating an air temperature to cancel the exposure-induced temperature elevation in cells, the maximum specific absorption rate (SAR) is at least doubled to trigger and characterize nonthermal effects. The air temperature is prescribed by an iteration algorithm to balance the maximum and minimum cell temperature levels while preventing them from exceeding a nonthermal threshold. Adaptive temperature control is applied to a 900-MHz exposure setup based on a TEM cavity. An air temperature regulator was installed to the TEM cavity loaded with cell monolayers in two 35-mm-diameter Petri dishes. SAR and temperature distributions in the culture medium were calculated by the finite-difference time-domain algorithm and validated by | S₁₁| and temperature measurements. Using a properly regulated air temperature, adaptive temperature control suppressed the temperature variances in cells within the 0.1 °C threshold through a 60-min exposure with a 6.10-W/kg average SAR. The SAR is 2.43 times as much as that of conventional temperature control using a stable air temperature. An air temperature regulator for adaptive temperature control is a simple addition to upgrade a conventional exposure setup and increase the exposure level in search of nonthermal effects.