A real-time fuzzy control laser system to control tissue temperature during hyperthermia in fresh pig liver samples is presented in this paper. The technical difficulties of this study lie in two facts: laser tissue heating is a highly nonlinear time-varying dynamic process; and the output power of the 810 nm diode laser that we used is not adjustable during operation. We have overcome the difficulties by regulating the laser via variable ON-OFF signal sequence, which is computed at each sampling time, by our novel nonlinear time-varying fuzzy controller. The structure of the fuzzy controller is analytically analyzed and the result is related to the PD controller. The average of the absolute values of the maximum temperature derivations for six hyperthermia experiments using the fuzzy control system is 0.44/spl deg/C. These satisfactory results indicate that our fuzzy control system could be useful for clinical applications.
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