模擬聲波干涉

科展類別
臺灣國際科展
屆次
2004年
科別
物理科
學校名稱
臺北市立麗山高級中學
指導老師
吳明德
作者
戚禎庭
關鍵字
聲波,相位延遲

摘要或動機

在高中光學裡,介紹了許多有關光波之特性,而聲波與光波皆具有波動性,因此聲波應具有如干涉、反射、聚焦等特性,但在物理課本上並未詳加敘述,所以我們開始了本項的研究,希望可以籍由改變聲源及邊界的各項條件,而探討其發生之現象。在本研究中,我們利用聲波之基本原理在電腦上進行聲場的模擬並加以改變其變因(頻率、相位、聲源數、聲源間距、強度、邊界反射),進而明瞭聲場之各項特性及應用與控制方式。經電腦模擬聲場圖中,我們觀察到,兩聲源干涉所形成之圖形為多組雙曲線所組成,近似於光學之雙狹縫干涉,增加聲音頻率與聲源間距離皆可使腹(節)線數目增加。如同現實世界中所知的,隨著頻率的增加,將會具有指向性的產生並且在聲源數目越多時越明顯,但發現頻率增加至一定值之後,指向性反而會降低而形成冠狀面。在延遲了多點聲源間相位之後,聲場分佈有偏轉之現象,利用相位延遲的方法,在多聲源中,將兩旁之聲音偏向中央將可造成聲音的聚焦。在兩聲源干涉中,調整其中一聲源之強度,將可完全消除兩音源連線間一點之聲音,可適當的應用在工業上消除噪音。聲場分佈在具有邊界的環境下,我們試著找出聲源位置及邊界條件對聲場分佈的影響與關係以模擬室內聲場,但在簡化的數學模式下,即無法有我們所希望之最均勻聲場分佈產生。最後我們將實驗中的結果與文獻上的實驗數據加以比較,以探討其誤差。 The optical course in senior high school , which introduced many characteristics of optical wave. However, both of sound and light have the characters of wave; therefore, sound wave should have the characteristics, such as interference, reflection and focalizing. Nevertheless, there are not many details of sound wave in the section of acoustic on our textbook. So we began this research, and discuss the different phenomena by changing many kinds of variables. In our research, we simulated the sound field on the computer, based on sound wave’s principle, furthermore we change many variables, which like frequency, phase, source number, distance, intensity and reflection. It helps us understand the characteristics of\r
sound, how to control sound and how to apply these findings. According to the result of computer simulation, we discovered that the graph of two acoustic source’s interference comprised by many pairs of hyperbola, just like optical double slit interference. As the frequency or the sound source distance increased, acoustic direction became more and more obvious. But when the frequency was high enough to over the extreme, instead increasing, the acoustic direction would lower down like a crown. After we make phase differences on one of the two sound sources, sound field generated\r
deviation. So if we use this method in multiple sound source, and delay the middle source, the sound field might be converged. In such two-sound-source interference pattern, when we control the intensity of one, a certainly point on the line of the two sources disappeared When the sound field enclose by borderline, the standing wave appear, and we discovered many funny phenomena. We put large amount of source in a narrow slit, the phenomenon of diffraction appeared. Finally, we discussed the discrepancies between interference pattern previously done by others experiments and the simulated one conducted by us.


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