| Summary: | 碩士 === 國立臺灣大學 === 工程科學及海洋工程學研究所 === 100 === Improving the material property and manufacture process of porous electret were the main research targets in this thesis. With the application of ultra-thin flexible electret-speaker in mind, we identified the optimal parameters of using multiple-needle corona discharge system to enhance the production efficiency of large-area thin electret-speakers. The Parylene C was deposited in a particular pattern on the ePTFE substrate to modify the shortcomings of ePTFE such as medium charge storage stability and easy plastic deformation at low stress when adopted as ultra-thin flexible electret-speaker. The experimental results confirmed that the hybrid electret diaphragm can effectively increase the sound pressure level of electret loudspeaker 2dB and maintain the low-frequency response to form a wide bandwidth loudspeaker. In addition, we presented a novel method to form the porous structure of P(VDF-TrFE) by coating the solution of P(VDF-TrFE) onto the ePTFE substrate for developing flexible skin-like sensors and ultrasonic transducers. Comparing to the traditional chemical solution process, this newly developed method can easily produce porous structure of P(VDF-TrFE) to form large-area film. The ePTFE/P(VDF-TrFE) composite film is a suitable material for ultrasound transducer and film type sensor as its porous structure make the acoustic impedance of the film matched well with that of the air. It should be noted that porous ePTFE/P(VDF-TrFE) composite film is also softer, which makes it even more suitable for flexible ultrasonic or skin transducers. Finally, we combined the spatial dipole of porous electret and the dipole charge of dipole electret to enhance the piezoelectric effect and quadruple piezoelectric constant with an attempt to improve the sensor pressure directional sensitivity. This behavior can reduce the cross-axis sensitivity and thus enhance the potential of sensor applications.
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