| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所碩博士班 === 90 === Abstract
The viscoelastic properties are critical to specific function for each living organ and fundamental in biomechanical modeling of tissue behavior. Currently invasive methods are often used to measure biomechanical properties in vitro, which are deviated from those in living status and difficult to be applied in practice. During the last decade, sonoelasticity has being studied by the Doppler ultrasonic technology with low frequency tissue vibration. It seems to be prospective in developing non-invasive, in vivo measuring technology for viscoelasticity. The RF power amplifier, which is high frequency, power output and cost, is improperly applied to excite the ultrasonic transducers (UTS) with frequency at MHz order. The purpose of this research is to design a power transmitter system specified for a pulsed Doppler ultrasonic measuring system.
The system design consists of interface control (IC), burst signal generator (BSG), power amplifier (PA) and isolated limiter (IL) modules. The IC unit is developed for signal frequency, pulse repetitive frequency and number setting. The BSG is to generate pre-stage excited signal for the UTS, according to the setup from IC unit. Then the PA is designed for output voltage and power amplification to directly excite the UTS. The IL circuit design is used diodes to isolate the input transmitting signal to and the reflective signal from the UTS.
The prototyped power transmitter system has been developed completely with system component calibration. The IC unit has provided functions with keyboard input, LCDM display, PRF signal generation and output relay control. The PA provides maximally output signal of 270VP-P with 3.5, 5 and 7.5 MHz to excite the UTS. The calibration results show that there is signal distortion appearing in the forward and backward parts of each PRF signal. An improved method is to look into better IC component. The calibration of whole system indicates that the output standard error of central frequencies of 3.5, 5 and 7.5 MHz is within 0.1 MHz range. The results also show that maximal SNR (signal to noise ratio) is 53dB with minimal at 26dB. The system SNR is expected to be improved by circuit design.
The future system research and development are recommended as following: (1) improved BSG design to provide adjustable frequency setting; (2) to implement the system in the pulsed Doppler ultrasonic measuring system (replace the conventional RF power amplifier) to non-invasive, in vivo measuring for soft tissue’ viscoelasticity; and (3) to expand system design and development for the application of conventional ultrasonic instrumentation.
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