Abstract:
The ultrasonic transducer is recognized as the most critical component in the in-seam wave 3D seismic physical modeling data acquisition system, with its performance determining the success of physical simulations. Conventional seismic physical modeling currently employs cylindrical transducers with diameters around 1 cm, which are deemed unsuitable for solid data acquisition in in-seam wave physical modeling due to their excessive dimensions, thereby limiting applications across varying coal seam thicknesses. A novel design approach is introduced, incorporating the axial expansion-contraction vibration mode of a piezoelectric ceramic square column and a stepped piezoelectric crystal structure combined with a backing layer. Finite element simulations are conducted using COMSOL Multiphysics to analyze the modal characteristics of the stepped square-column piezoelectric crystal, with structural optimization implemented to enhance radiated energy and reception sensitivity. This design enables point contact between the transducer and the model, eliminating the need for coupling agents. Backing layer material formulations are experimentally developed, utilizing a mixture of solid powder and ethylene-vinyl acetate co-polymer to absorb residual vibrations. Consequently, narrow pulses are achieved with minimal sensitivity loss, and the transducer’s bandwidth is effectively broadened. The developed high-power, low-frequency, point-contact, narrow-pulse, dry-coupled ultrasonic transducer exhibits a dominant frequency of 32 kHz, a bandwidth of approximately 20 kHz (−3 dB from 23 kHz to 43 kHz), and a front-end dimension of 2 mm. Comparative evaluations are performed using both the developed point-contact transducer and conventional cylindrical transducers as seismic sources in physical model reflection/transmission observations. Results indicate that the point-contact transducer demonstrates superior energy characteristics, evidenced by reduced signal attenuation and improved signal-to-noise ratios. However, its high-frequency cutoff frequency of 43 kHz precludes the reception of high-frequency signals. Conversely, the cylindrical transducer, while exhibiting lower energy output, provides broader frequency coverage capable of capturing high-frequency in-seam wave components. Transducer selection for in-seam wave three-dimensional seismic physical modeling is recommended based on factors such as model dimensions and coal seam thickness.