A Filter Structure Based Broadband Electrical Impedance Matching Method for Piezoelectric Transducer of Acoustic Well-Logging

Piezoelectric transducer is a key component of acoustic well-logging tool. Transducers used in acoustic well-logging tools usually have limited bandwidth, and their dominant frequencies severely drift with drastic change of borehole temperature when tools are working downhole. An appropriate impedance matching is necessary to broaden the operating bandwidth of the transducer and improve the power output stability of the acoustic emission. In this study, an electrical impedance matching (EIM) method for piezoelectric transducer is proposed based on Butterworth response and network theory. The method can broaden the bandwidth of narrowband transducers while ensuring stable transducer power gain (TPG). A band-pass filtering circuit and its low-pass prototype are constructed on the basis of the equivalent circuit of the piezoelectric transducer and the external impedance matching circuit. According to the filtering characteristics of the filter circuit and a target TPG function, we derive the analytical formulas for calculating power transmission characteristics and electronic component values of arbitrary order matching network. Using different electronic design automation (EDA) software, we simulated the matching network of a specific transducer obtained by the theoretical calculations. Then, we built an experimental system to verify the performance of the matching network. Theoretical calculation, simulation and experimental results demonstrate that the impedance matching network obtained by the proposed method can effectively broaden the operating bandwidth of narrowband transducers and provide stable output power.