An In Vitro Experimental System for 5G 3.5 GHz Exposures

In this study, an in vitro experimental system is developed for fifth-generation (5G) 3.5 GHz exposures. A radial transmission line (RTL) housed in an incubator can support the single-mode propagation at a 3.5 GHz band. A conical antenna is also placed at the center of an RTL to ensure field symmetries. A 5G signal generator along with a customized power amplifier can create 5G new radio time division duplex (TDD) waveforms. Additionally, a feedback scheme implemented by employing a directional coupler and power meter allows power control to ensure a steady output power. The system is evaluated based on temperature measurements using the initial temperature slope and nonlinear curve fitting to determine the specific absorption rate (SAR) values. Comparing SARs obtained from a "worst-case" signal of a maximum power condition with the values obtained from a "TDD" signal of an actual 5G TDD transmission gives the initial slope ratio of 0.741, which is very similar to the theoretical duty cycle of 0.743. It is also shown that the average output power, water temperature, incubator air temperature, and CO2 density are adequately controlled for appropriate in vitro experiments.