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Increasing the spatial and temporal density of data using networked sensors, known as the Internet of Things (IoT), can lead to enhanced productivity and cost savings in a host of industries. Where applications involve large outdoor expanses, such as farming, oil and gas, or defense, large regions of unelectrified land could yield significant benefits if instrumented with a high density of IoT systems. The major limitation of expanding IoT networks in such applications stems from the challenge of delivering power to each sensing device. Batteries, generators, and renewable sources have predominately been used to address the challenge, but these solutions require constant maintenance or are sensitive to environmental factors. This work presents a novel approach where conduction currents through soil are utilized for the wireless powering of sensor networks, initial investigation is within an 0.8-ha (2-acre) area. The technique is not line-of-sight, powers all devices simultaneously through near-field mechanics, and has the ability to be minimally invasive to the working environment. A theory of operation is presented and the technique is experimentally demonstrated in an agricultural setting. Scaling and transfer parameters are discussed. 

The integration of wireless power technology in large sensor networks is highly sought for in many applications, including agriculture. This is due to the accessibility and lack of wiring complexity such technologies have to offer. In an agricultural setting, the working environment can be harsh on sensing equipment due to factors that include weather, constant deconstruction and re-installation with the changing plant cycles, and vehicle traffic. Since many agriculture plots reside in difficult to access locations, the use of self-sufficient energy capturing methods have become popular. These contemporary methods generally rely on the collection of solar, wind, or ambient radio waves to charge battery banks connected to the sensing device. These methods have major limitations as sunlight can be shadowed as crops mature, wind creates obstacles for equipment to navigate, and radio frequencies do not penetrate well through soil or plants. This ultimately reduces the quantity of sensors that can be instrumented throughout a field. To address such limitations, a new wireless power transfer method will be presented that utilizes a buried transmitter to generate conduction currents through the soil to power distant sensing devices scattered throughout a field. Impedance spectra of the soil is used to determine the optimal depth of the transmitter. The power capabilities of the system are demonstrated by operating, without a battery, a moisture sensor connected to a microcontroller at a 10 m distance from the transmitter.