本論文為研究ITO (indium tin oxide)靜電揚聲器(直徑60 mm)和雙層壓電圓板複合薄膜揚聲器(直徑73 mm)的共振模態和聲壓，我們以理論計算靜電圓形薄膜的聲壓，以及壓電圓形薄板的特徵頻率，並規劃四項測量方法，包括集中參數測量法(lumped parameter measurement，LPM)、分佈參數測量法(distributed parameter measurement，DPM)、全像式電子斑點干涉術(amplitude-fluctuation electronic speckle pattern interferometry，ESPI)和聲學測量(acoustic measurement，AM)，測量範圍為20–20k Hz。先使用LPM和DPM方法測量振膜的位移振幅和模態，並預估聲壓，再以AM方法測量聲壓曲線來驗證之。實驗結果顯示在沒有聲學網的聲學阻尼影響下，聲壓曲線呈現許多鋸齒狀的共振頻率，LPM、DPM和AM方法分別測得的對稱模態頻率非常接近；在對稱模態圖形上，ESPI測量全像的條紋數與DPM的節圓數相符合。另外，靜電揚聲器的聲壓曲線整體較壓電揚聲器平滑，其模態(0,1)的品質因子(Q)為9.8；當使用145 [ray1]特定聲阻的聲學網，易受到聲學阻尼影響，Q值降至1.8。相反地，壓電揚聲器的模態(0,1)–(0,4)無論是否有聲學網，皆不受聲學阻尼影響，Q值皆維持10至11之間。故「靜電薄膜」和「壓電薄板」揚聲器有截然不同的振動機制和聲壓特性，在實際產品的應用上，前者相當適合用於音樂用耳機，後者則可用在音頻訊號裝置。無論ITO孔極板或圓板複合薄膜的新想法，藉由不同的光學測量特性，可有效鑑別出揚聲器的振動和聲輻射行為。

To investigate the resonance modes and sound pressure of an ITO (indium tin oxide) push-pull electrostatic speaker (60-mm diameter) and free-edge-like piezoelectric speakers (73-mm diameter), we calculated the sound pressure of an electrostatic circular membrane and the eigenfrequencies of piezoelectric circular plates, as well as employed four evaluation methods. In this study, lumped parameter measurement (LPM), distributed parameter measurement (DPM), amplitude-fluctuation electronic speckle pattern interferometry (ESPI) and acoustic measurement (AM) were employed from 20 Hz to 20 kHz. Measurements of displacement amplitude and vibrating mode were used to predict sound pressure levels (SPLs) based on LPM and DPM results. Comparisons with measured SPL values of AM were used to verify our predictions. The experimental results demonstrate the electrostatic and piezoelectric speakers, without additional acoustic mesh damping, both produced numerous resonant frequencies. The LPM, DPM and AM produced the SPL values of each mode that were in good agreement. Under linear operations, the DPM and ESPI techniques proved effective in determining the visualization of axisymmetric mode shapes. The piezoelectric speakers produced jagged SPL curves with peaks steeper than those of the electrostatic speaker. At mode (0,1), the electrostatic speaker was affected by acoustic resistance, which resulted in the following quality factor (Q) values: Q = 9.8 without mesh and Q = 1.8 using a mesh with specific acoustic resistance of 145 [rayl]. By contrast, the piezoelectric speakers at modes (0,1)–(0,4) were unaffected by acoustic resistance, which resulted in Q values of 10–11, regardless of whether mesh was applied. These characteristics make electrostatic speakers suitable for headphones and piezoelectric speakers suitable for audio signaling devices.

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