封閉式超音波感測器之設計與有限元素模擬

Design and Finite Element Simulation of Closed Type Ultrasonic Sensor

胡智凱(Chih-Kai Hu)

指導教授 ： 陳俊杉

國立臺灣大學/工學院/土木工程學研究所/碩士(2007年)

https://doi.org/10.6342/NTU.2007.01032

摘要

本研究之封閉式超音波感測器，乃針對車用超音波感測器，傳統乃以試誤法設計，並以提高驅動頻率的方式避免反射自地面之超音波訊號，如此不但縮小水平方向偵測範圍，同時高頻之超音波能量於空氣中傳遞消散更快。本研究由專利文獻之分析，歸納其設計方向，提出兩種提升工作指標的設計方法，使用虛擬原型之設計流程，以有限元素建立感測器外殼，模擬預測其行為，評估共振頻率、指向性與音源強度等三個指標，再製作感測器原型進行實驗量測，驗證其設計。
第一種設計方法為改變振動面之邊界條件，設計圓形之感測器外殼，將振動面垂直方向之外殼側壁以銑刀切削孔洞驗證此設計。由模擬與實驗可知，孔洞之長度為外殼直徑之0.4倍，孔洞之位置距離振動板內側約2 mm，音源強度最佳，亦維持不錯之指向性。第二種設計方法為平移垂直之發波方向，以雪人形狀之感測器外殼驗證此設計。初步模擬可知，發波偏移方向為外殼側壁較薄處。另以上下圓之直徑與位置四個參數作最佳化分析，可知容納壓電片感測器外殼之凹槽上緣之厚度須相對較薄，但水平依然要維持較厚之側壁，可以使得發波方向偏移的同時，兼顧水平方向之指向性。
本論文有別於業界使用提高驅動頻率之方法，使用改變振動面之邊界條件與平移垂直之發波方向兩種設計方法，成功提升超音波感測器之工作指標，並歸納出超音波感測器之設計方向，並以分析模擬之方式預測其行為，以增進設計效率，減少成本。

關鍵字

超音波感測器 ； 有限元素分析 ； 虛擬原型 ； 倒車雷達 ； 共振頻率 ； 指向性 ； 半衰角 ； 音源強度

並列摘要

Closed Type Ultrasonic Sensors have been used widely in cars to detect obstacles in close range. Despite theoretical and computational advances made recently in ultrasound, these sensors have been generally designed by trial and error. The objective of this work is to develop suitable computational strategies to support virtual prototyping design of closed type ultrasonic sensors. To this end, analysis capabilities from ANSYS, a commercially available finite element analysis package, are utilized. Resonance frequency, directivity, and source level of commercially available losed type ultrasonic sensors were simulated using ANSYS. The calculated results were in a good agreement with experimental measurements.
The primary design concern for closed type ultrasonic sensors used in cars is to avoid undesired response reflected from the ground in the vertical direction while maintain its covering range in the horizontal direction. Patents related to closed type ultrasonic sensors were reviewed to guide the design direction. Salient features associated with directivity and source level from these patents were analyzed. We then used two ways to improve their performance. The first design was to alter boundary conditions of vibrating plate. To this end, we designed a sensor with a circular hollow shape to verify this design. The side wall of vertical direction of vibration plate was dug in a pair of slots by mill. We found that when the length of the slots is 0.4 times of the diameter of cases and the position of the slots is about 2 mm away from the interior of the vibration plate, an optimal performance of source level and directivity was obtained. The second design was to shift the vertical direction of the transmitting ultrasound. We designed a sensor with a snowman hollow shape to verify this design. We found that in order to shift the transmission, the thickness of the hollow circle that contains the piezoelectric element should be thicker.
In this work, a computational framework to predict resonance frequency, directivity, and source level of ultrasonic sensors has been established for virtual prototyping. We have also successfully improved the performance of closed type ultrasonic sensor by changing the boundary condition of vibration plate and shifting the vertical direction of the transmitting ultrasound.

並列關鍵字

ultrasonic sensor ； finite element analysis ； virtual prototyping ； parking sensor ； resonance frequency ； directivity ； half decay angle ； source level

參考文獻

鄒年棣(2006)，“應用有限元素法模擬壓電元件與超音波波傳”， 碩士論文，國立台灣大學土木工程研究所，台北。

Chang, S. H. and Du, B. C. (2001). “Optimization of asymmetric bimorphic disk transducers,” Acoustical Society of America, Jan Vol. 109, No. 1, pp. 194-202.

Cheng, C. C. (2007). private communication.

David, J. and Cheeke, N. (2002). Fundamentals and Applications of Ultrasonic Waves, CRC Press, Boca Raton.

Gresham, I., A. Jenkins, R. Egri, C. Eswarappa, N. Kinayman, N. Jain, R. Anderson, F. Kolak, R. Wohlert, S. P. Bawell, J. Bennett, J.-P. Lanteri (2004). “Ultra-wideband radar sensors for short-range vehicular applications,” IEEE Transactions on Microwave Theory and Techniques, Vol. 52, No. 9, pp. 2105-2122.