臺灣博碩士論文加值系統

本論文目的在於設計一套量測水下銅球體散射強度(Strength)與型態(Pattern)之實驗測試機構與量測流程，並且以銅球理論散射解為基準，檢證本設計之可行性。本研究在大小為1.8 m × 1.8 m × 1 m的中型水槽中，以窄頻聲波訊號入射在直徑6 cm 的銅球目標物上，測量其產生的散射聲場。所使用的聲源為具指向性之 iTP 192 kHz 換能器，配合函數產生器與功率放大器，發射64個脈衝正弦波。在理論方面，以R. Hickling（JASA, 34, 1962, pp.1582-1592）所發展出的解析解為依據。本研究利用滾珠圓環搭配鋁擠型自行設計一套高強度且高精度量測機構，可每一度等距離量測 360度銅球的散射訊號。量測之銅球的散射強度與已完成之理論值經相關性係數分析後得出量測之偏差角度誤差在兩度之內，故所設計的機構是可行的。而實驗結果與理論值比較後發現，在逆散射部分誤差約為3∼4 dB且有相同之趨勢；而在前散射區因直達波與散射波的距離差距甚小造成干擾，所以測得之結果較差。故目前採用的設計機構與實驗方法在逆散射量測具有一定的可行性及實用性，未來可供作量測其他目標物散射聲場之用。整體而言，本論文分為基本理論推導、先期測試、機構設計、散射場量測及數據分析等部分，重點為散射實驗之設計與觀察、資料誤差分析、檢討與改進等。

The aims of this research are to design an experimental testing mechanism and process for measuring the scattering strength and the pattern induced by an underwater target. The experimental data are to compare with existing theoretical results to insure the integrity of experimental design. The experiment is conducted in a water tank of dimension 1.8 m x 1.8 m x 1 m. The main work is to measure the sound field scattered by a copper sphere of diameter 60mm. There is one type of directive source employed in this analysis: 192 kHz iTP-192k transducer as the receiver and projector. The transducer transmits sine waves with the pulse duration roughly equal to 0.143 msec (equivalent to 64 waves). The scattering field theory is based on the formulation developed by Hickling (JASA, 1962, pp.1582-1592). In order to get more precise measurement results, this research designs a high strength and accurate mechanism with a ball-ring and aluminum workpieces. The mechanism can be used to measure target scattering signals circularly with same radius. The experimental process has demonstrated that it is more difficult to measure the forward scattering field than the backward scattering field, due to the fact that the forward scattering field is likely to be mingled with the direct waves. The comparison between experimental and theoretical results shows that the discrepancy in the backward scattering sector is within 3 to 4 dB; however, generally speaking, the variation of the curves show a good agreement. These results indicate that the design of this experiment is basically practicable, and with further improvements, it could be applied to measure other underwater targets. As a whole, the thesis is composed by basic theory deduction, experimental instrumentation, mechanism design, and experiment data analysis. The emphases place on the design and observation of the scattering experiment, data analysis, and further improvement.The aims of this research are to design an experimental testing mechanism and process for measuring the scattering strength and the pattern induced by an underwater target. The experimental data are to compare with existing theoretical results to insure the integrity of experimental design. The experiment is conducted in a water tank of dimension 1.8 m x 1.8 m x 1 m. The main work is to measure the sound field scattered by a copper sphere of diameter 60mm. There is one type of directive source employed in this analysis: 192 kHz iTP-192k transducer as the receiver and projector. The transducer transmits sine waves with the pulse duration roughly equal to 0.143 msec (equivalent to 64 waves). The scattering field theory is based on the formulation developed by Hickling (JASA, 1962, pp.1582-1592). In order to get more precise measurement results, this research designs a high strength and accurate mechanism with a ball-ring and aluminum workpieces. The mechanism can be used to measure target scattering signals circularly with same radius. The experimental process has demonstrated that it is more difficult to measure the forward scattering field than the backward scattering field, due to the fact that the forward scattering field is likely to be mingled with the direct waves. The comparison between experimental and theoretical results shows that the discrepancy in the backward scattering sector is within 3 to 4 dB; however, generally speaking, the variation of the curves show a good agreement. These results indicate that the design of this experiment is basically practicable, and with further improvements, it could be applied to measure other underwater targets. As a whole, the thesis is composed by basic theory deduction, experimental instrumentation, mechanism design, and experiment data analysis. The emphases place on the design and observation of the scattering experiment, data analysis, and further improvement.

一、緒論
1.1 研究動機
1.2 文獻回顧
1.3 研究目的
1.4 論文架構
二、理論模式
2.1 簡介
2.2 推導條件之假定
2.3 理論公式推導整理
2.3.1 流體介質中波動方程
2.3.2 彈性體內波動方程
2.3.3 待定係數求解
2.4 理論公式討論
三、量測基本概念
3.1 窄頻訊號定義
3.2 彈性球體的材質選擇
3.3 反射與透射
3.4 換能器工作原理
3.5 近場與遠場
3.6 換能器指向性
3.7 菲涅耳區域
3.8 AST換能器參數
3.9 散射聲場定義
3.10 訊號發射與接收
3.11 操作型量測公式
3.12 靈敏度
四、窄頻訊號量測目標物散射-先期測試
4.1 前言
4.2 實驗機構設計與架設
4.3 實驗設備
4.4 實驗流程與訊號處理
4.4.1實驗流程
4.4.2訊號處理
4.5 銅球散射場量測實驗
4.5.1 聲源強度定義實驗
4.5.2 銅球散射場實驗-以換能器接收
4.5.3 銅球散射場強度實驗-以水下麥克風接收
4.6 討論
4.6.1 偏移角度判定
4.6.2 誤差判定實驗
4.7 結論與建議
五、銅球散射場量測機構設計
5.1 機構基本概念
5.2 機構的設計概念
5.2.1 機構的功能要求
5.2.2 圓盤的選用
5.2.3 支架選用
5.2.4 實驗環境
5.3 機構設計
5.3.1 機架
5.3.2 延伸臂
5.3.3 滾珠圓環與壓克力圓板
5.3.4 聲源角度調整設計
5.3.5 換能器固定盒設計
5.3.6 角度指向裝置
5.3.7 角度判讀裝置
5.3.8 銅球固定裝置
5.4 機構組裝
5.5 機構測試
六、銅球散射場量測
6.1 前言
6.2 實驗架設與流程
6.3 實驗儀器設定與角度定義
6.4 實驗流程
6.5 背景噪音量測
6.5.1 水聲錄音裝置
6.5.2 儀器架設與實驗結果
6.6 聲源軸向判定實驗
6.7 換能器固定方式
6.8 換能器穩態分析
6.9 銅球散射場量測
6.10 鉛錘散射場量測
6.11 結論
七、討論與結論
7.1 討論
7.2 結論
7.3 未來展望
附錄A AST-Sonar
附錄B AST-Sonar聲學實驗系統之元件效能評估
附錄C 研討會論文

1.劉金源 (2001) "水中聲學—水聲系統之基本操作原理"，中山大學出版社。
2.Ding, Li (1997) “A method for acoustic scattering by slender bodies.II. Comparison with laboratory measurements”J. Acoust. Soc. Am., Vol 102, pp.1977-1981.
3.Ding, Li (1997) ”Direct laboratory measurement of forward scattering by individual fish”J. Acoust. Soc. Am.,Vol 101 ,pp.3398-3404.
4.Faran, J. J. (1951) “Sound scattering by Solid Cylinders and Spheres,” J. Acoust. Soc. Am., Vol. 23, pp. 405--418, 1951.
5.Foote, K. G. (1982) “Optimizing copper spheres for precision calibration of hydroacoustic equipment,” J. Acoust. Soc. Am., Vol. 71, pp. 742--747.
6.Hickling, R. (1962) “Analysis of Echoes from a Solid Elastic Sphere in Water,” J. Acoust. Soc. Am., Vol. 34, pp. 1582--1592.
7.Morse, P. M. (1948) Vibration and Sound, McGraw-Hill, New York.
8.Morse, P. M. and H. Feshbach (1953) Methods of Theoretical Physics, McGraw-Hill, New York.
9.Medwin, H. and C.S. Clay (1998) Fundamentals of acoustical oceanography, Academic Press, Boston.