Analysis of acoustic transmission method in the periodic cascade channel with its application to drill pipes

A finite-differential model for the one-dimensional propagation of longitudinal waves along the drill string was established. The influences of acoustic transducer positions and carrier wave signals on acoustic transmission signals in the periodic pipe structure transmission channel were analyzed by use of the time and frequency domain simulation. An on-off keyed (OOK) modulation of time-delayed pulses was designed. Then, the narrow pulse modulated signal transmission experiments were performed by applying the longitudinal excitation to the length-limited simulated drill string in the axial direction of pipes. The results show that under the conditions of excitation power of 1W, transmission rate of 77 bit/s and 6.44-meter simulated drill string, the proposed transmission method can implement the data transmission and signal detection of test signals via low-frequency extensional waves in the laboratory. Moreover, the simulation and experimental research on acoustic wave propagation along the drill string provides the theoretical and trial foundation for the design of downhole acoustic telemetry system.