超聲波指向性喇叭陣列波束之高頻寬自動量測系統

本論文針對超聲波指向性喇叭陣列之聲學特性，建構一套高頻寬、高動態範圍之自動檢測平台。超聲波指向性喇叭陣列之工作原理係以壓電陣列發射高聲壓超聲波為載波之調變波，於空氣中傳遞時藉由空氣介質本身之非線性，將低頻可聽聲波解調於超聲波的波束範圍中。從頻域上分析，此種聲波由高聲壓之超聲波載波與旁波及低聲壓之低頻可聽聲波所組成。此高頻寬與高動態範圍的量測需求限制了解調訊號的量測精準度。為了精確地研究此超聲波指向性喇叭陣列之聲學表現，本論文以標準麥克風系統接收調變聲波，並利用低通濾波的方法將高聲壓高頻載波衰減，以壓縮量測所需之動態範圍，提升量測之可靠度與精準度。同時，以1/3八度音程來分析訊號，配合自動化儀器控制，達到同步量測超聲波指向性喇叭陣列產生之超聲波與解調聲波波束。

關鍵字

非線性解調；波束量測；指向性量測；高頻寬量測；大動態範圍量測

並列摘要

We developed an automated measurement platform possessing both high bandwidth and high dynamic range to investigate acoustic characteristic of an ultrasonic directive loudspeaker array. An ultrasonic directive loudspeaker works by an amplitude-modulated ultrasonic beam with high intensity reproduced by a piezoelectric ceramic based ultrasonic array and then demodulated as a highly directive audible beam by the inherently non-linearity of air, which is confined within the beam pattern of its ultrasonic carrier. In frequency domain analysis, this highly directive beam was composed of ultrasonic carrier and sideband with high sound level and demodulated audible sound with low sound level. The broad bandwidth and wide dynamic range requirement limits the detection accuracy of the testing system. In order to precisely study the acoustic performance of the ultrasonic directive loudspeaker array, a low-filtering method was introduced to decay the high sound level carrier and sideband detected by a standard microphone system so as to decrease wide dynamic range need and to increase reliability and accuracy of detections. In addition, a one-third octave analysis and an automated instrument control were integrated to our testing platform. The beam patterns of both carrier and demodulated audible beam reproduced by the non-linear demodulation based ultrasonic directive loudspeaker were precisely detected through our measurement system.

並列關鍵字

non-linear demodulation ； beam pattern measurement ； directivity measurement ； high bandwidth measurement ； wide dynamic range measurement

國際替代計量

超聲波指向性喇叭陣列波束之高頻寬自動量測系統

全文下載

主題瀏覽