| Summary: | 碩士 === 國立彰化師範大學 === 車輛科技研究所 === 98 === Inside the car, each passenger can hear the music or information he wants, other passenger would not feel bothered. A directional audible sound system could be used in order to achieve the performance mentioned above. The array of ultrasonic transducers may be employed for the audible sound reproduction in air through the self-demodulation of finite-amplitude sound beams.
The objective of this thesis is to design a directional audible sound system which uses optimisation methods to investigate the weighting distribution of uniform linear array composed of eight transducers, and the influence on the spreading angle of the sound beam. Compared with Chebyshev method, it is found that the optimisation method can control the sidelobe in a more effective way. Lastly, we built up our own uniform linear array composed of eight transducers, measuring the distribution of the audible sound in the far field, and comparing the experimental results with the theoretical simulation. According to the experimental results, a better transducer is required to produce audible sound with 100dB or higher in order to exhibit the sidelobe difference with or without the weighting factor. The directional audible sound system can also be applied to electric vehicles. It can warn the pedestrians and other vehicles in front of electric vehicles, without noise pollution.
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