| Summary: | 碩士 === 國立陽明大學 === 生物醫學工程學系 === 104 === Energy transfer is very important to achieve the best performance of ultrasonic transducer. The internal impedance of most ultrasonic pulser / receiver is 50Ω, so we need to make the impedance of ultrasonic needle transducer to be 50Ω. Because of the production process and environmental differences, each batch of ultrasonic needle transducer have different impedances and efficacy. To achieve the best performance, we need to use impedance matching network make the resistance of ultrasonic needle transducer to be 50Ω. After evaluating the cost, effect and usage scenario, we use L-type matching network. In this study, we used 3 ultrasonic needle transducer which made by PMN-PT (lead magnesium niobate-lead titanate) to verify the effect of impedance matching. The frequency of each transducer is 21.3MHz, 21.9MHz and 22MHz, and impedance 137.1∠-66.3˚,108.7∠-65.2˚ and 99.5∠-69.3˚. We used Pspice to simulate the peak to peak voltage at transducer, and measured echo amplitude with a steel block. The result of simulation, the peak to peak voltage increase more than 25%. The result of measured echo amplitude increase at least 35%. We used the ultrasonic transducer to detect the position of epidural. Because the noise ratio raise, we can easily distinguish relatively weak signals.
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