Multirate output feedback controller for multielement array hyperthermia systems

Modeling, control and analysis of an automatic control system for managing the power output of large multielement hyperthermia applicator heated by microwave applied to tissue equivalent phantom is simulated. The modeling of tissue equivalent phantom is done by Pennes bioheat transfer equation. Classical implicit method is used to arrive at the state space model of the system. In hyperthermia it is important to maintain a uniform and stable temperature profile over a large surface area of the tissue regardless of surrounding thermal load. An automatic feedback controller is to be designed for this purpose. A control objective for the controller design is framed with rise time, overshoot and settling time specifications. As also after reaching the steady state, the controller should maintain a stable set temperature by adapting to changes in the body blood perfusion rate. To satisfy the above requirements a Fast Output sampling control algorithm is designed such that desired closed loop behavior and closed loop stability is achieved. The performance of the system is analyzed for varying blood perfusion and power levels. A desired trajectory that meets the control objective of hyperthermia is formed and the closed loop error norm between desired and achieved trajectory is minimized through controller tuning. Simulations are performed to show the effects of blood perfusion variation and power level variation.