臺灣博碩士論文加值系統

本論文研究目的，是建構出一套應用時間反轉法與微麥克風陣列於3G手機上之抗噪系統。時間反轉法(Time reversal method, TRM)為基礎的聲源分離與辨識技術，TRM主要是利用回傳時間反轉之聲波訊號，藉由聲波之互易性原理(Principle of reciprocity)及線性波動方程式的不變性，補償因多重路徑傳遞與傳遞介質不均勻所造成的訊號失真，使訊號得以聚焦於原聲源位置。近年來廣泛應用於光學、超音波、非破壞檢測及水下通訊領域。本研究主要分成理論推導、數值模擬與實驗分析。理論推導中，包含TRM理論推導與環境脈衝響應函數求解。如何準確預估出環境脈衝響應函數，是本研究重點。數值模擬則是利用不同環境條件參數，模擬出TRM聚焦的效果，並使用相關度係數與訊雜比作為量化分析。在實驗分析部分，則是使用微麥克風陣列進行量測，並於時間域下對聲源進行分離與辨識。經過實際測試，可以消除由非主要聲源所產生的雜訊干擾，提高主要聲源訊號之訊雜比與相關性係數。證實本研究所建構的抗噪系統是有成效的，提升訊雜比幅度可達到目標值5dB~10dB，大幅提升聲音的品質與清晰度。

The purpose of this paper is to construct a noise control system in the 3G cell phones that combines time reversal method and MEMS array microphones. Time reversal method (TRM) is based on principle of reciprocity of sound by propagating of a reversal signal in time series to compensate distortion due to path effect in propagation and to focus the signal at origin. In recent years, the technique has been applied in optics, ultrasound and underwater acoustic communication. This research mainly divides into theoretical derivation, numerical simulation and experiment. Theory derivation includes TRM theory and solution of impulse response function of the path. The key point of this research is how to estimate accurately the impulse response function. Numerical simulation is to verify the effect of focusing by using TRM in the different environmental conditions and parameters. Also, it uses correlation coefficient and signal-to-noise ratio to analyze the result of TRM. In the experiment, MEMS array microphones are used to receive the signals. Then, the source signal is separated from the received signals in time domain. As the results of the experiment, the technique is to separate a specific source from a combination signal of multiple sources and to reduce noise effectively. The results indicate that TRM increases value of the correlation coefficient and signal-to-noise ratio of the source of interest. The results also confirm that the anti-noise system in this research is effective to enhance the signal-to-noise ratio by 5dB to 10dB, which significantly enhances the sound quality and clarity.

摘要................................................................................................................................ I
英文摘要....................................................................................................................... II
誌謝.............................................................................................................................. III
圖目錄.......................................................................................................................... IV
表目錄........................................................................................................................... X
第一章 緒論.................................................................................................................. 1
1-1研究背景與動機................................................................................................ 1
1-2文獻回顧............................................................................................................ 3
1-3研究內容與章節架構........................................................................................ 7
第二章 時間反轉法理論與模擬.................................................................................. 9
2-1時間反轉法理論推導........................................................................................ 9
2-2環境脈衝響應函數.......................................................................................... 12
2-3時間反轉法模擬.............................................................................................. 17
2-3-1相關性係數(correlation coefficient)....................................................... 17
2-3-2訊雜比(signal to noise ratio，SNR)........................................................ 18
2-3-3不同條件下之時間反轉法模擬............................................................. 21
2-3-4時間反轉法模擬之成效討論................................................................. 32


第三章 實驗架構介紹................................................................................................ 33
3-1前言.................................................................................................................. 33
3-2實驗架構.......................................................................................................... 33
3-3實驗儀器與設備.............................................................................................. 34
3-3-1微型麥克風(MEMS Microphone).......................................................... 34
3-3-2放大器電路設計..................................................................................... 36
3-3-3及時控制與量測介面............................................................................. 41
第四章 實驗步驟與數據分析.................................................................................... 44
4-1實驗步驟.......................................................................................................... 44
4-2實驗數據分析與比較...................................................................................... 48
4-2-1時間反轉法之抗噪性測試...................................................................... 48
4-2-2聲壓值差異與相關度比較...................................................................... 58
第五章 結論與未來展望............................................................................................ 69
5-1結論.................................................................................................................. 69
5-2未來展望.......................................................................................................... 71
參考文獻...................................................................................................................... 72

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