AbstractUltrasonic surgical instruments actuated by piezoelectric transducers are usually driven at relatively high power levels to generate high vibration amplitude at the probe, which interact with biological tissues to achieve the desired effects. In operation, the high power level introduces nonlinearities into the behaviours of the piezoelectric transducer and the biological tissues place a load onto the transducer. Both the nonlinearities and the load result in variations in resonant frequency and electric impedance, which negatively affect the performance of the ultrasonic surgical instrument. The aim of this work was to develop an adaptive driving system to address the issue of the resonant frequency shift and impedance variation and to study its effectiveness in optimising the performance of ultrasonic surgical instruments.
An ultrasonic planar tool based on piezocrystal PMN-PT was designed with various configurations as an alternative to the existing ultrasonic scalpels. To address the problem of resonant frequency shift and impedance variation observed on the planar tools in characterisation stage, an adaptive driving system was developed to track the resonant frequency and stabilise the vibration velocity. The system was carefully calibrated, and its effectiveness in optimising the performance of unloaded transducers in a broad frequency range was validated. The performance variation of the planar tool under the combined influence of high power level and external tissue loads was then investigated. The capacity of the adaptive driving system to optimise the performance of the planar tool under such conditions was then accessed by performing soft tissue penetrating test. Furthermore, a needle actuating device was designed to increase the visibility of medical needles in ultrasound guided percutaneous procedures. Its modal behaviour was studied in finite element analysis and verified by experimental characterisation. The ability of the adaptive driving system to improve the performance of the needle actuating device was accessed in pre-clinical trials.
The results demonstrate that the adaptive driving system developed can track the resonant frequency and stabilise the vibration velocity of ultrasonic surgical instruments in frequency up to 5 MHz and power up to 300 W. By using the adaptive driving system, optimal performance of the planar tool and needle actuating device can be achieved in both unloaded and loaded conditions. The ultrasonic planar tool with PMN-PT is potentially useful in surgical operations. However, its performance is limited by the intensive heat generated in the joint area and the low Curie point of PMN-PT. The needle actuating device can increase the visibility of standard medical needles in colour Doppler imaging.
|Date of Award
|China Scholarship Council
|Zhihong Huang (Supervisor) & Sandy Cochran (Supervisor)