醫學診療用寬頻帶超聲波壓電換能器設計與模擬

TUNG FANG Institutional Repository > 電子與資訊系(遊戲動畫系、動畫科) > 國科會計畫 > Item 987654321/163

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题名:	醫學診療用寬頻帶超聲波壓電換能器設計與模擬 The Design and Simulation of Wide-Band Ultrasonic Piezoelectric Transducer for Diagnostic Application
作者:	陳永欽 Chen, Yeong-Chin Chen, Y.C. 薛清田 Hsueh, Ching-Tien Hsueh, C. T. (行政院國家科學委員會) (東方技術學院電子與資訊系)
关键词:	超聲波診斷;壓電換能器;寬頻帶;阻抗匹配;超聲波匹配層;脈波回應時間;Ultrasonic diagnostic;Piezoelectric transducer;Wide-band;Quarter wavelength;Acoustical matching layer;Time duration;Soft-backing;Heavy-backing;Mason model;PSPICE;Design;Simulation
日期:	2005
上传时间:	2009-07-28 11:49:24 (UTC+8)
摘要:	近來醫界已廣泛且有效使用超聲波影像技術來偵測人體內部器官，以為醫師診療的重要依據，超聲波設備更可提供清析、及時之器官影像並可避免人體作X-ray 偵測時所受輻射線之影響。超聲波更被使用為超聲波影像偵測器、按摩器、藥劑導入器、碎石機、穴道按摩、血栓碎化器等醫學偵測及治療儀器。超聲波壓電換能器具有高靈敏度、好的脈波反應、高效率、低鏈波、及寬頻帶特性，為獲得良好的超聲波影像所必需。壓電陶瓷被廣泛使用為超聲波壓電換能器之材料，乃因為其具有高機電耦合係數、高阻抗及穩定的材料特性。然而壓電陶瓷之特徵聲學阻抗遠高於人體器官之特徵聲學阻抗，故超聲波壓電換能器頻寬受限於阻抗之不匹配。本計劃乃針對超聲波偵測器之壓電式超聲波探頭作為研究對象，計劃中將對低損失、寬頻帶及低的脈波回應(pulse echo)時間長度的超聲波探頭設計理論與製作技術做一深入探討，期望設計一符合人體器官及血流速度作偵測之超聲波探頭。計劃初期先對單一超聲波壓電換能器作設計，將來再將多個換能器組成線性陣列，即所謂超聲波探頭。計劃中，將使用馬森電路做為壓電換能器之等效電路。根據換能器之等效電路原理，從電子網路理論考量其匹配原理，進而設計一低損失、寬頻帶的超聲波換能器。為達到換能器具低損失及寬頻帶的特性，將設計一層或二層四分之一波長厚的阻抗匹配層於換能器頭部，以達到所需求的功能。使用傳遞聲波四分之一波長( λ / 4 )的阻抗匹配層於換能器的發射端，使換能器的阻抗與發射端介質的聲阻抗互相匹配，可達到寬頻帶的響應特性。換能器之尾部則使用λ / 4 非匹配阻抗層，其後以低聲阻抗的材料作墊背，以達到低損失，寬頻帶及提高機械特性的需求。如果以高聲阻抗的材料作墊背，可降低換能器之脈波回應時間。其中阻抗匹配層及墊背曾乃使用適當的高分子及金屬粉未組而成，如何製作達到所需的聲學阻抗匹配層亦為一複雜的材料技術。使用PSPICE 軟體，建立壓電換能器之馬森等效電路模型，可計算換能器所需之匹配層及墊背層的阻抗需求，並可模擬超聲波壓電換能器在時域及頻域的諸項特性，從而預測換能器之阻抗，插入損失，頻帶寬度及脈波回應時間長度等特性，並可與其集總電路模型作比較。具單一阻抗匹配層的空氣墊背型換能器相對頻寬預計可達35%以上，而使用雙阻抗匹配層時，相對頻寬更可達72%以上; 而尾部非匹配型換能器，當其λ / 4 非匹配阻抗層的阻抗提高時，其相對頻寬將降低，然而換能器的脈波回應時間長度將降低，以增加超聲波影像之解析度至0.5μS 以下。而換能器之相對頻寬與脈波回應時間長度必須作擇中設計，以符合實用之需求。Ultrasound imaging has become an effective and practical tool for obtaining information from within the human body as well as because it provides a clear real-time display of body tissue without exposing the patient to X-rays. Ultrasound has also been implemented to develop ultrasonic diagnostic equipment used as ultrasonic massage, transdermal drug deliverer, acupoint massage, supersonic wave stone crasher, thrombus fragmentation and so on. To obtain a good quality of ultrasound imaging, ultrasonic piezoelectric transducers with high sensitivity and good impulse response, high-efficiency, low-ripple, and wide-band performance is desired. Piezoelectric ceramics have been widely used for ultrasound transducers because of their large electromechanical coupling factors, high electrical impedance, and stable material characteristics. Since piezoelectric ceramics have a specific acoustic impedance which is far more than ten times that of body tissues, the bandwidth of the transducer is limited by the acoustical mismatch. The implementation in PSPICE provides transducer analysis in the time and frequency domain. Compared with lumped equivalent circuits of it, the Mason model may be more easily used to study a multilayered structure. The PSPICE code of the Mason model is developed to precisely predict the performance of the matched transducers such as impedance, insertion loss, bandwidth and duration of the impulse response. This PSPICE code offers a method of simplifying the transducer design and of facilitating the analysis of impedance-matching layers for broad-bandwidth applications. Through the use of the PSPICE code, the optimum impedance of the matching plate can be estimated to obtain the specific bandwidth and maximum response for special applications such as transmitting or imaging. For the ultrasound imaging application, the matching layer is evaluated using the PSPICE code and helps to achieve a compromise between the wide-bandwidth and short time duration characteristics of a two-matching-layer unmatched transducer.
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