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Continuous monitoring of soil health is important in precision agriculture. Microbial activities can be an indicator for soil health, where the metabolism of the soil microbiota associated with plants plays a crucial role in plant development. These plant-associated microbiomes can also influence other traits such as disease resistance, growth, flowering, and abiotic stress tolerance. Activities of these microbial colonies affect all aspects of plant life because of their symbiotic relationship. Therefore, a thriving microbiota is directly related to soil health. By detecting and analyzing the variations of emitted volatile metabolites, it is possible to monitor the activities of the microbiota. These data can provide a deeper understanding of the relationship between activities of microbial communities and plant health. However, presently available low-cost, in situ sensors used in agriculture only detect a limited number of physical parameters such as moisture, pH, electrical conductivity, temperature, etc. Here we demonstrate microcantilever based photothermal spectroscopic sensors for detecting vapor phase analytes related to microbial activities such as CO2, methane, etc. Photothermal spectroscopy combines the temperature sensitivity of a bi-material cantilever with the selectivity of mid-infrared spectroscopy. Nanomechanical photothermal spectroscopy has sensitivity in the ppb range, fast response time, and requires no chemical coating for selectivity. Since the mid-infrared spectroscopy is free from overtones, it is extremely selective even in the presence of interfering compounds. Multiple IR peaks are monitored and analyzed using pattern recognition techniques for uniquely identifying the analyte molecules in vapor phase in the presence of interfering chemical compounds.

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. Keywords-Wireless power transfer, Through the Soil, Long Range, conduction I. INTRODUCTIONDecision making based on real-time/measured data is critically important to boosting revenue/productivity in many industries. Sensor installation throughout the industrial process plays a fundamental role in these tools. The number of sensors that can be installed is limited by two primary factors: (1) the cost (including installation/maintenance) of the sensor and Manuscript received Month xx, 2xxx; revised Month xx, xxxx; accepted Month x, xxxx.