The rapid advancement toward smart cities has accelerated the adoption of various Internet of Things (IoT) devices for underground applications, including agriculture, which aims to enhance sustainability by reducing the use of vital resources such as water and maximizing production. On-farm IoT devices with above-ground wireless nodes are vulnerable to damage and data loss due to heavy machinery movement, animal grazing, and pests. To mitigate these risks, wireless Underground Sensor Networks (WUSNs) are proposed, where devices are buried underground. However, implementing WUSNs faces challenges due to soil heterogeneity and the need for low-power, small-size, and long-range communication technology. While existing radio frequency (RF)-based solutions are impeded by substantial signal attenuation and low coverage, acoustic wave-based WUSNs have the potential to overcome these impediments. This paper is the first attempt to review acoustic propagation models to discern a suitable model for the advancement of acoustic WUSNs tailored to the agricultural context. Our findings indicate the Kelvin-Voigt model as a suitable framework for estimating signal attenuation, which has been verified through alignment with documented outcomes from experimental studies conducted in agricultural settings. By leveraging data from various soil types, this research underscores the feasibility of acoustic signal-based WUSNs.

In recent years, there has been an increasing necessity for monitoring facilities like gas or water pipelines to ensure high security and adequate infrastructure maintenance. The pipeline network is very large, and the main problem is its continuous monitoring. In particular, there is the necessity to monitor the cathodic protection (CP) voltage, which ensures maintaining the pipeline under a state of protection from corrosion and avoids considerable damage to the infrastructure. A communication channel is necessary to monitor the pipeline network continuously. Most of the pipeline monitoring systems make use of wireless communication, like global system for mobile communications (GSM) or general packet radio service (GPRS) technology and even Wi-Fi, to transmit the measurements. By their nature, the implementation of these systems is often expensive and furthermore, not all the pipeline is covered by the signals of the mobile operators. In this article, the communication approach is presented, and, in particular, the pipeline is used as a communication channel. Due to the challenges of pipelined transmission, an identification of the characteristic impedance of the medium must be conducted to obtain the best possible performance. This value is used to design a circuit that can match the function generator output to the impedance of the communication channel. The circuit to be made must allow bidirectional communication of the half-duplex type. Given the low frequencies that can be used for communication on the pipe, a low-frequency circulator must be created. Given the frequencies involved, the bidirectional circuit will be composed of operational amplifiers. The presented circulator allows matching the signal generator output impedance with the pipeline input impedance, to obtain an improvement in the transmission distance achievable using the pipeline as a communication channel.