A Compact Microwave Heating Platform Complemented by Nonlinear Model-Based Closed-Loop Temperature Control

This paper presents a compact and standalone 2.4 GHz/10 W microwave heating (MWH) device, along with the details of its interconnections and specifications. The device is useful for non-invasive superficial heating for diagnostic purposes (e.g., measuring blood perfusion), mild superficial hyperthermia, or small animal studies, with a target temperature of 40–45 °C. The device is accompanied by a front-end unit that houses an antenna and a temperature-regulation circuitry to minimize the temperature gradient between the body surface and the antenna for accurate MWH planning. This paper also introduces a nonlinear autoregressive exogenous (NL-ARX) modelling approach to accurately predict the MWH closed-loop response. The model was obtained by fitting open-loop measurements at five different power levels performed on a phantom. The phantom baseline temperature was around the body temperature. The NL-ARX models’ goodness of fit ranged from 90.7 to 96.5 % for a temperature rise of up to ∼18 °C from the baseline. The obtained model was then used as part of a closed-loop simulation with proportional-integral-differential (PID) feedback control. Appropriate choices of the PID gains were identified by an iterative approach, where the NL-ARX model was used as a surrogate to predict the closed-loop response. A desired system response had minimum overshoot and steady-state error. The simulation results were compared to closed-loop phantom measurements. A very good agreement between the measurements and simulations is observed for the initial rise time (within 12 s) and the steady-state (within ∼0.05 °C), indicating that the NL-ARX can accurately predict nonlinear MWH behavior.