Experimental study of acoustic channel characteristics of rigid and elastic pipelines

Abstract

In this work we describe an experimental investigation into wideband channel models for acoustic wave propagation in rigid and elastic pipelines operating over the 1∼50 kHz frequency band. We provide frequency domain transfer function measurements for both rigid and elastic pipes, from which time domain responses of the pipeline channel can be calculated. Narrowband impulse responses are studied to illustrate the frequency selectivity of the channel. We extend the narrowband impulse responses to a spectrogram representation to further highlight the channel characteristics. Signal attenuation is investigated experimentally. Preliminary results of channel noise characterization are also provided in the water pipe channel consisting of noise power spectrum density (PSD) in a laboratory environment. It is shown that the pipeline channels exhibit three major characteristics: (a) wave travels in modes and the cutoff frequency of two modes are found to be zero in the elastic pipe, in comparison with only one plane wave mode existing in the rigid pipe; (b) the signal dispersion is obvious in the pipeline channel, but the delay spread is only insufferable when the wave speed changes dramatically within the signal bandwidth; (c) it is also observed that acoustic waves up to 50 kHz can propagate through both water pipes but exhibit distinctive average power loss per meter (1 dB/m for acrylic-air channel, and 3 dB/m for HDPE-water channel). In addition to the effect of pipe material, signal attenuation is also found to be mode and frequency dependent in experiments. We hope the channel characterization can be utilized to develop communication and imaging systems for pipeline channels.