Dual-Band Impedance Matching Method for LWD Acoustic Transducers Considering Drill Collar Mechanical Coupling

The LWD acoustic transmitting system acts as a capacitive load with a narrow effective operating bandwidth and significant reactive power. In this paper, a KLM equivalent circuit model of the transmitting system, incorporating the mechanical coupling of the drill collar, is established based on its structural characteristics. This model is coupled with a dual-frequency impedance matching network to formulate an impedance function, whose parameters are solved using an adaptive Gauss-Newton algorithm. Subsequently, systematic electrical and acoustic tests were conducted on an anechoic water tank platform. Experimental results demonstrate that the active power at the transducer terminals is significantly enhanced within the target frequency bands after impedance matching. Taking 14 kHz and 4.5 kHz as examples, the peak-to-peak transmitting voltage at the transducer increases to approximately 1.75 times the pre-matching level at both frequencies. Meanwhile, the peak-to-peak receiving voltage of the hydrophone increases to about 1.7 and 3.5 times the pre-matching values at 14 kHz and 4.5 kHz, respectively. Furthermore, the transmitting voltage responses (TVR) of the quadrupole and monopole modes within their target bands improve by approximately 5-17 dB and 10-18 dB, respectively. Directivity measurements reveal that the horizontal main lobe of the quadrupole mode is highly pronounced, while the monopole mode maintains a near-circular radiation pattern with an overall increase in the sound pressure level.