以電流積分方法實現頻率校正功能之超音波換能器驅動電路設計與實作

本論文提出一種校正頻率的方法，此方法能夠追蹤超音波換能器的最佳運作頻率。超音波換能器利用壓電效應使能量在電能與聲能之間轉換，然而由於超音波換能器的最佳運作頻率會因為環境變化、製造飄移或損耗而偏離原有設計的頻率，偏離最佳運作頻率將導致超音波強度減弱。　　本論文利用所提出的校正方法，設計一個能自動校正超音波換能器頻率的驅動電路。使用掃頻的方式觀察驅動電壓與電流的相位差，藉此推測換能器的最佳運作頻率。使用方波電壓驅動的方式，減小換能器中並聯電容造成的電流相位偏移。然後用積分器收集相位與電流振幅資訊，以擴大頻率追蹤的範圍。在實驗中使用三種不同特性的超音波換能器進行校正，實驗結果顯示經過校正後的驅動頻率誤差在0.86 %以內。

關鍵字

壓電效應；超音波換能器；頻率校正；驅動電路；電流積分方法

並列摘要

In this thesis, a calibration method which traces the proper operating frequency of an ultrasonic transducer is proposed. The ultrasonic transducer converts electrical energy into acoustical energy and vice versa. However, the characteristics of piezoelectric materials will change with the environment, the process deviation, the damage of the material and so on. Thus, the proper operating frequency of the ultrasonic transducer will not be the same in different circumstances. The drift of the proper operating frequency may decrease the strength of the ultrasonic wave. In this thesis, a driving circuit for the ultrasonic transducer with automatic frequency calibration has been designed. A control circuit detects the phase difference between the driving voltage and the input current to obtain the proper operating frequency. The transducer is driven by square wave in order to reduce the effect of the parallel capacitance, which gives the input current an unwanted phase shift. An integrator collects the information from the phase difference and the input current amplitude to extend the frequency tracing range. Finally, we conducted experiments with three ultrasonic transducers which have different characteristics. The experimental results show that the operating frequencies are calibrated with errors less than 0.86 %.

並列關鍵字

piezoelectric effect ； ultrasonic transducer ； frequency calibration ； driving circuit ； current integrating method

參考文獻

[1] A. Manbachi and R. S. C. Cobbold, “Development and application of piezoelectric materials for ultrasound generation and detection,” Ultrasound, vol. 19, no. 4, pp. 187-196, Nov. 2011.

[3] J. Souquet, P. Defranould, and J. Desbois, “Design of low-loss wide-band ultrasonic transducers for noninvasive medical application,” IEEE Transactions on Sonics and Ultrasonics, vol. SU-26, no. 2, pp. 75-81, Mar. 1979.

[4] D. Damjanovic, “Stress and frequency dependence of the direct piezoelectric effect in ferroelectric ceramics,” Journal of Applied Physics, vol. 82, no. 4, pp. 1788-1797, May 1997.

[6] M. Birkholz., “Crystal-field induced dipoles in heteropolar crystals II: Physical significance,” Z. Phys. B., vol. 96, no. 3, pp. 333-340, 1995.

[7] B. Jaffe, W. R. Cook Jr., and H. Jaffe, “The Piezoelectric Effect in Ceramics,” in Piezoelectric Ceramics, New York: Academic Press, 1971.

國際替代計量

以電流積分方法實現頻率校正功能之超音波換能器驅動電路設計與實作

全文下載

主題瀏覽