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研究生:吳欣樺
研究生(外文):Sin-Hua Wu
論文名稱:使用寬頻波束形成技術於水下超音波成像
論文名稱(外文):Underwater Ultrasonic Imaging with Wide-band Beamforming Technology
指導教授:林俊華林俊華引用關係
指導教授(外文):Jiun-Hwa Lin
學位類別:碩士
校院名稱:國立臺灣海洋大學
系所名稱:電機工程學系
學門:工程學門
學類:電資工程學類
論文種類:學術論文
論文出版年:2004
畢業學年度:92
語文別:中文
論文頁數:57
中文關鍵詞:波束形成功率波束場型寬頻十字形陣列
外文關鍵詞:beamformingbeam power patternwide-bandMill's cross array
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本論文於超音波成像是使用波束形成技術,所謂波束形成(beamforming)儼然是一種空間性濾波器(spatial filtering),可增強操作方向的訊號,消除其它方向的干擾,有效地將想要信號予以接收。儘管如此,仍然有許多問題待於克服,諸如不佳的指向性導致粗糙的解析度;太高的旁波瓣(side lobe)讓雜訊無法有效地排除…等,因此首要之任務是探討超音波陣列的各種參數對功率波束場型(beam power pattern)之影響,以利設計高性能的超音波陣列。
另外在減少陣列元素,以便降低電路複雜度的情況下,為了縮窄主波寬度,提高發射頻率或拉寬陣列元素間距是必要之手段,但接踵而來的是grating lobe的出現,因此我們應用寬頻(wide-band)波束形成技術,減少脈衝訊號週期個數,壓制grating lobe對成像品質的干擾,並利用十字形陣列(Mill’s cross array)之架構,讓兩發射/接收一維線性陣列互相垂直,來等效二維陣列成像出3D影像,大幅減少陣列元素個數,企圖以稀疏陣列(sparse array)達到高解析度、高品質之超音波成像圖。
This thesis uses beamforming in ultrasonic imaging. Beamforming is a kind of spatial filtering, which strengthen the signal of steering direction and suppress the interference of other directions. Nevertheless, there are a lot of questions have to overcome, such as poor directivity leads to coarse resolution; the noise is unable to reject efficiently due to high side lobe. Hence, in order to design the high performance of ultrasonic array, primary task is research of ultrasonic array, which can influence all kinds of parameters on beam power pattern (BPP).
In the situation of lower number of array element and lower circuit complexity, it is essential to raise center frequency or extend interelement spacing for reduction main’s width. Unfortunately, the grating lobe will be occurred when interelement spacing is larger than . Hence, we use the wide-band beamforming technology to suppress grating lobe. Besides, we design architecture of Mill’s cross array to equal 2D array and create tree dimension imaging. We attempt to reach high resolution and high quality ultrasonic imaging with sparse array.
目錄
摘要………………………………………………………………………Ⅰ
Abstract…………………………………………………………………Ⅱ
第一章 緒論………………………………………………………………1
1.1 研究動機與目的…………………………………………………….1
1.2 文獻回顧…………………………………………………………….1
1.3章節概要………………………………………………………………2
第二章 數值理論分析與公式……………………………………………3
2.1聲壓之基本理論………………………………………………………3
2.1.1聲壓波動方程式………………………………………………….3
2.1.2聲壓散射場……………………………………………………….4
2.1.3聲壓入射場……………………………………………………….6
2.1.4換能器接收之訊號……………………………………………….8
2.2水下超音波成像原理…………………………………………………9
2.2.1超音波成像技術……………………………………………….9
2.2.2窄頻波束場型…………………………………………………10
2.2.3成像系統之解析度……………………………………………13
2.3寬頻波束形成技術………………………………………………….15
2.3.1寬頻波束場型定義……………………………………………15
2.3.2寬頻波束場型準近似公式……………………………………16
2.3.3寬歲波束場型分析……………………………………………19
2.4 多波束成像系統……………………………………………………21
2.4.1跳頻訊號之定義………………………………………………22
2.4.2訊號相關性質…………………………………………………23
2.4.3跳頻場型之建立………………………………………………24
第三章 數值程式實作………………………………………………….26
3.1空間脈衝響應……………………………………………………….26
3.1.1空間脈衝響應之計算方法………………………………………26
3.1.2空間脈衝響應之計算流程………………………………………28
3.2超音波陣列之設計………………………………………………….30
3.2.1一維陣列之設計…………………………………………………30
3.2.2十字形陣列之設計………………………………………………30
3.3程式架構與流程…………………………………………………….33
3.3.1功率波束場型程式之建構……………………………………33
3.3.2水下超音波成像程式之建構…………………………………34
第四章 數值結果分析與探討………………………………………….38
4.1一維陣列功率波束場型之分析比較………………………….38
4.2一維陣列成像結果…………………………………………….40
4.3十字形陣列成像結果………………………………………….44
4.4四種陣列架構之分析………………………………………….46
4.5四種陣列架構成像結果……………………………………….50
第五章 結論與未來發展方向………………………………………….54
5.1結論…………………………………………………………….54
5.2未來發展方向………………………………………………….55
參考文獻…………………………………………………………………56
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