###### Abstract  
Wireless sensor networks (WSN) have emerged as a robust and cost-effective solution for buried pipeline monitoring due to the low cost (a maximum of a few tens of UK pounds (GBP)), low power supply capacity (in the order of \(1\) watt/hour) and small size (centimette scale) requirements of the wireless sensor nodes. One of the main challenges for WSN deployment, however, is the limited range of underground data communication between the wireless sensor nodes of less than \(3\) m, which subsequently increases deployment costs for a utility owner for buried pipeline monitoring. A promising alternative to overcome this limitation is using low-frequency (\(<\)1 kHz) acoustic signal propagation along the pipe. This paper examines the feasibility of using low-frequency acoustic signal propagation along exposed and buried medium-density polyethylene (MDPE) pipes and makes predictions of the potential distances at which reliable data communication can be achieved. Quantification of the acoustic attenuation was performed using both analytical and numerical models in addition to laboratory and field experiments. The predicted acoustic data communication distance ranged between approximately \(18\) m for an exposed and approximately \(11\) m for a buried MDPE pipe. These results demonstrate the feasibility of using low-frequency acoustic signal propagation for achieving reliable wireless underground communication. buried pipeline monitoring: wireless sensor network; acoustic signal propagation; finite element analysis; acoustic data communication +
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the above-ground wireless network [13; 14; 15]. Reliable wireless underground communication in this case is however either still through the air (within an underground chamber) (e.g., [9; 13]) or limited to less than 1 m [15] when the radio transceiver is buried in soil. For UG/UG communication, the communication channel exists entirely below the ground. An underground communication link must therefore be established between individual sensors located along the buried pipeline. Since wireless communication (especially through air) is typically enabled by electromagnetic (EM) wave propagation, existing research for wireless underground communication through soil has naturally focused on investigating EM signal performance in soil. One of the earliest recorded field trials on EM signal propagation in soil using commercially available WSN nodes (MICA2 nodes from Crossbow Technology) was by [16], followed by [17] who used an ultra-low-power (1.31-5.25 \(\upmu\)W) WSN node for radio signal transmission within the soil. Both [16; 17] demonstrated radio signal transmission at 433 MHz with a maximum power of 0.01 W. In both cases, the radio signal propagation range, beyond which the radio signal was indistinguishable from background noise, was limited to well below 3 m. [PERSON] (2014) [18] further observed an even lower radio signal propagation range (less than 0.5 m) in soils with high clay content due to the higher signal attenuation experienced by the radio wave in such soils. A non-radio-based approach for enabling wireless underground communication through soil uses the buried water pipe as an acoustic waveguide. Unlike radio signal transmission, acoustic signal transmission requires the presence of a medium for wave propagation between a communication transmitter and receiver. [PERSON] (2006) [19], using numerical simulations, was the first to examine a water pipe waveguide as an acoustic propagation medium for wireless sensor communication. The simulations were, however, focused on acoustic propagation between an internally located acoustic transmitter and receiver within the water pipe.