- 學位論文
具頻率校正功能之超音波換能器驅動電路設計
Design and Implementation of an Ultrasonic Transducer Driver Circuit with Frequency Calibration
摘要
壓電材料是現今應用廣泛的電、力轉換媒介，藉由壓電效應將電訊號轉換成機械振動以發射出超音波是現在發射超音波的主流方法。利用壓電式超音波換能器的應用也很多可見於生活之中，例如倒車雷達、超音波淨水、超音波物理治療等等。然而壓電材料的特性會隨環境因素及製程漂移等問題而有所改變，使得其最佳收發頻率隨之有所漂移。在本論文中，針對超音波換能器的材料及阻抗特性及進行探討，得知換能器的最佳收發頻段和介於其諧振頻附近阻抗最高及最低點之間的頻率，並且在該段頻率內，換能器晶體呈現電感性，因而以晶體振盪電路為基準，設計一具頻率校正功能的驅動電路，該電路能驅動換能器並且操作頻率能隨時位在最佳收發頻區段內。再來分析此電路的原理並進行模擬，以找出電路中各元件選值的標準。最後依據模擬得到的元件參數值進行實驗，實驗結果顯示此振盪電路確實能提供足夠電壓以驅動換能器，並同時具有頻率校正的功能。
並列摘要
Piezoelectric material is a media which is commonly adopted for conversion between electrical and mechanical energy. With the help of this material, it’s the prevalent to emitting ultrasound by transforming the electric signal into the mechanical vibration. The applications of piezoelectric ultrasonic transducers could also be widely found around us such as the vehicle backing radar, the ultrasonic water cleaning system and the therapeutic ultrasound. However, there are some problems of the piezoelectric materials. For example, temperature and the process variation have much impact on their characteristics and resulting in drifting of frequency to transmit or to receive the signal. In this thesis, the material and impedance characteristic of an ultrasonic transducer are investigated. The best operation frequency band will be located between the frequencies of the transducer’s highest impedance and the transducer’s lowest impedance. It is notable that these two frequencies are near the oscillation frequency. Besides, the transducer reactance is inductive over the frequency band. Therefore, a ultrasonic transducer driver circuit with frequency calibration has been designed on a basis of an crystal oscillator circuit. This circuit has the ability to drive the transducer and at any time, its operation frequency will be adjusted automatically to be in the best frequency band of transmission and reception. We analyze this driver circuit with simulations to find out how to decide the value of each element in the circuit. Finally, we conducted experiments to verify the previous discussion. The experimental results show that the operating voltage of this circuit is sufficiently high to drive a transducer, and the operating frequency is well calibrated at the same time.