將聲音聚焦於特定目標對象之聚光燈形式的聲場已發展多年。其中發射波束的基本概念是基於高頻聲音的高指向特性，將欲傳送的音訊透過載波傳遞，藉由一組超音波陣列便可發射出人耳無法感知的超音波束，在抵達私密聆聽區後經過空氣中的調變成可聽音。基於高頻定向的特性，可聽音可輕易地只傳遞給該區的聆聽者，而周遭的人卻無法感知。現今大多數的文獻資料都著重於聲音的調變技術來減少失真，卻較少探討聲學傳遞以及超音波輻射的現象。

在本文中，將透過聲學模型建立超音波陣列的指向性圖樣。首先介紹聲學的理論，其中定義了波的傳遞與輻射現象，接著描述從發射器產生的波束在空氣中擴散的情況，模擬的結果將用於顯示指向性圖樣以及後續的量測。實驗量測將超音波發射器單體排列成陣列形式做為聲源，並紀錄產生的波束輻射。之後再將量測結果與模擬內容藉由指向性圖樣相互比較，驗證實驗模擬中的指向性與精確度。由結果可以得知增加效率的超音波陣列配置方式，並依據相關模擬所顯示的資訊提出改善建議。

A spotlight-like sound field to the target audiences has been developed for years. The fundamental idea of sound beams is based on the high directivity of high-frequency sound, which is used as the carrier for delivering messages. The private listening zone could be created by projecting the inaudible ultrasound via a set of emitters. Based on this directional property, sound proximity can also be conveniently placed near the listener. Most of the literatures focus on the sound modulation techniques for reducing distortion, whereas place few emphasis on the study of acoustic transmission and radiation. In this work, we establish the directivity pattern of an ultrasound array by acoustic models. This acoustic transfer function is modeled for enhancing the directivity patterns, and then the radiation beam is generated for measuring and fitting. We try several emitter arrangements for improving the configuration efficiency and reducing the development cost. As a result, the radiation evaluation and numerical design are provided to verify the directivity and precision of the proposed system.

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