李百祺臺灣大學：電機工程學研究所王文道Wang, Weng-TaoWeng-TaoWang2007-11-262018-07-062007-11-262018-07-062007http://ntur.lib.ntu.edu.tw//handle/246246/53588現今的臨床超音波影像系統，多數使用陣列形式，陣列探頭和單一探頭相比較，藉由電子掃描，不僅提供良好的動態聚焦，也加速擷取影像速率，有助於即時成像。 為了進一步提昇影像解析度，高頻(≧ 20 MHz)陣列探頭廣泛被提出研究與製作。高頻陣列探頭在製作上最大的問題之一是切割精密度的限制。傳統的陣列探頭是利用刀具切割來區隔陣列單元，為了要避免衍生瓣的出現，陣列探頭相鄰陣列單元的間距理論上必須小於二分之一波長，這在高頻製作時成為一個很大的挑戰。另外，壓電材料的厚度亦正比於波長，故在高頻時由於材料太薄而使得切割易造成碎裂。因應上述問題，一個不經切割的陣列探頭可以有效避免相關問題，但缺點是由於壓電片互相連接，增加了陣列單元間之cross-talk，對影像品質造成了影響。因此，如何製作一個無切割陣列探頭，再利用後端訊號處理的方式減輕cross-talk，是本論文之主要研究內容。 我們首先利用軟體來模擬無切割陣列探頭cross-talk的情形，接著製作一個20 MHz的無切割陣列探頭。使用的壓電材料為鈮酸鋰，厚度須磨至184μm。陣列單元間距為75μm，分別為電極寬度65μm以及10μm的kerf。固定聚焦深度在9mm，後端的電路連接則是採用軟性電路板。最終此無切割陣列探頭成功的製作出來，發射訊號頻率確實落在20 MHz附近，而單一陣列單元的發射訊號在20 dB的放大下有0.7 V的峰對峰值，SNR為23 dB。此外也利用水聽筒量測cross-talk的強度，量測結果在鄰近三個陣列單元內的平均cross-talk強度為-3 dB。Linear arrays have been widely used in medical ultrasonic imaging systems due to the abilities of dynamic focusing and electronic scanning. In order to improve image resolution, high frequency (≧20 MHz) array transducers have also been fabricated. One of the most critical problems when fabricating a high frequency array is the limitation of current dicing technologies. To avoid grating lobes, the interelement spacing needs to be less than half a wavelength. At higher frequencies, the spacing is small and this in turns limits the kerf width between two adjacent channels. Additionally, thickness of the piezoelectric material is also proportional to wavelength. At high frequencies, the piezoelectrical material becomes fragile particularly during dicing. In order to alleviate these problems, a kerfless linear array is proposed in this research. Because the piezoelectric material remains one piece, cross talk becomes significant and this lowers the image quality. To alleviate the cross talk problem, a signal processing method is also investigated. Both PZFlex and Field II simulations are performed. A 20 MHz kerfless linear array is also fabricated. LiNbO3 is used as the piezoelectric material with a thickness of 184μm after lapping. The pitch is 75μm, within which 65μm is the electrode width and 10μm is the spacing between electrodes. The elevational focus is 9mm. We use flexible printed circuit board for circuit connection.　Experimental data shows that 20 MHz ultrasonic signal can be generated successfully. The pulse echo signal has a peak-to-peak voltage of 0.7 V with a 20 dB pre-amp. We also use a hydrophone to measure the cross-talk level of adjacent elements. The average cross-talk level within 3 consecutive elements is about -3 dB.致謝 中文摘要 英文摘要 目錄 圖目錄 表目錄 弟一章 緒論..............................................................................................1 1.1 超音波探頭.................................................................................1 1.2 高頻超音波探頭.........................................................................5 1.3 無切割陣列探頭.........................................................................7 1.4研究動機與目標..........................................................................9 1.5論文架構.....................................................................................10 第二章 陣列單元間的Cross-talk現象...................................................11 2.1 Cross-talk的產生.......................................................................11 2.2 Cross-talk對影像之影響...........................................................13 2.3 無切割陣列探頭cross-talk之模擬..........................................15 2.4 如何降低cross-talk...................................................................21 第三章 無切割陣列探頭製作................................................................30 3.1 探頭規格制定...........................................................................30 3.1.1 壓電材料..........................................................................30 3.1.2 其他元件..........................................................................32 3.2 探頭製作流程...........................................................................34 3.3 探頭組裝以及後端電路連接...................................................45 第四章 探頭分析及討論........................................................................46 4.1 探頭訊號量測...........................................................................46 4.2 Cross-talk量測...........................................................................50 第五章 討論、結論與未來工作............................................................53 5.1 討論...........................................................................................53 5.2 結論...........................................................................................57 5.3 未來工作...................................................................................58 參考文獻..................................................................................................591119953 bytesapplication/pdfen-US單一探頭陣列探頭高頻陣列探頭壓電材料無切割cross-talk鈮酸鋰single crystalarray transducerhigh frequency arraypiezoelectric materialkerflessLiNbO3thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/53588/1/ntu-96-R94921054-1.pdf