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Dynamic impedance matching network based on real-time measurement of transducer impedance for high-intensity focused ultrasound

High-intensity focused ultrasound (HIFU) has been widely used for treatment of uterine fibroids. The mismatch of impedance of transducer with that of HIFU driver source can limit the output of acoustic power, which would impact treatment efficacy. In addition, the impedance of transducer could fluctuate during operation. To address this issue, a dynamic impedance matching network (IMN) has been proposed based on real-time measurement of transducer impedance. Both the voltage and current of the excitation signal of transducer are measured in real time and converted into frequency domain for impedance analysis. Impedance matching is carried out by controlling switches in dynamic IMN. After adding the dynamic IMN, with the input voltage of Class-AB power amplifier (PA) set at 30mVrms, 40mVrms and 50mVrms, the mean active power has been increased by 25.00%, 24.58% and 18.33%, respectively, and the mean power factor has been increased by 40.31%, 44.36% and 41.50%; with the supply voltage of Class-E PA set at 5V and 7V, the mean active power has been increased respectively by 66.33% and 59.15%, and the mean power factor has been increased by 53.00% and 45.61%. The improvement of active power and power factor has verified the efficacy of the proposed dynamic IMN, which can be used in different classes of PA.