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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/6775

Title: 使用基因演算法最佳化超音波陣列之寬頻功率波束場形
Using the Genetic Algorithm to Optimize Wide-band Beam Power Pattern of Ultrasonic Arrays
Authors: Kun-Lung Wu
Contributors: NTOU:Department of Electrical Engineering
Keywords: T字形陣列;基因演算法;最佳化;寬頻;功率波束場形
T-shaped array;genetic algorithm;optimize;wide-band;beam power pattern
Date: 2006
Issue Date: 2011-06-22T08:55:57Z
Abstract: 摘要 本論文對於超音波陣列應用在水中成像,由於陣列元素的形狀為矩形,中心元素無法作為發射與接收共同使用,故將原本十字形陣列(Mill’s cross array)架構的陣列,發射陣列與接收陣列錯開一段距離,形成一T字形陣列( T-shaped array)之架構,應用來成像出3D影像。如此陣列個數可由 個減少至 個。並利用T形陣列架構於水中進行實際成像試驗。 另ㄧ方面,為了使成像的橫向解析度(lateral resolution)提升,必須增加元素的個數,電路設計的複雜度也接著增加。故本論文中對於超音波陣列進行最佳化,擬利用基因演算法(genetic algorithm; GA ),所謂基因演算法是一種隨機最佳化的方法,它根據自然演化找尋最佳解。它會傳承先前的收尋經驗,以作為下一次收尋方向的諮詢,可避開掉入區域極值(local extremum)的危險,而得到全域的最佳解。 故最佳化超音波陣列之寬頻(wide-band)功率波束場形(beam power pattern;BPP),設計一個具有不同元素位置分佈與不同權值比重的超音波陣列,如此可在一維線性陣列上依不同需求,控制元素的ON/OFF與權值比重來得到所要的波束場形。可以減少陣列元素的使用個數與降低電路設計之複雜度。 並以最佳化後之一維陣列架構成T字形陣列,進行模擬成像3D影像,以提供往後實際超音波陣列製作簡化之參考依據。
Abstract This thesis uses the ultrasonic arrays to image objects under water. Because the element at the center of the array is rectangular. It cannot be used to transmit and receive at the same time. The transmitters and receivers in the Mill’s cross-array are displaced a distance to form a T-shaped array used to image three-dimensional objects. In this manner the number of array elements is reduced from to . We use the so-designed T-shaped array to measure data, from which under-water images are formed. On the other hand, to increase the lateral resolution, the number of array elements must be increased, which then exasperates the circuit complexity. Hence, this thesis aims to use the genetic algorithm (GA) to optimize the ultrasonic arrays. The genetic algorithm is a stochastic optimization approach, and it approaches the optimum solution according to the nature evolution. It determines the searching direction for the next step according to the previous experience, is free from falling in the local extrema, and then arrives at the global optimum solution. Hence, we will optimize the wide-band beam power pattern (BPP) of the ultrasonic array by adjusting the element position and assigning appropriate weights to elements. The array element can be switched on with appropriate weighting or switched off being inactive in order to meet the prescribed BPP for a one-dimensional linear array. At the same time the element number is one of the designing parameters under the constraint of less elements and hence less circuit complexity. Employing these optimized arrays in the T-shaped array, we simulate imaging 3D underwater objects. This serves the purpose of the basis on which the underwater ultrasonic arrays are built.
URI: http://ethesys.lib.ntou.edu.tw/cdrfb3/record/#G0M93530061
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