We present here the design and fabrication of a self-powered and autonomous fringing field capacitive sensor to measure soil water content. The sensor is manufactured using a conventional printed circuit board and includes a porous ceramic. To read the sensor, we use a circuit that includes a 10 kHz triangle wave generator, an AC amplifier, a precision rectifier and a microcontroller. In terms of performance, the sensor’s capacitance (measured in a laboratory prototype) increases up to 5% when the volumetric water content of the porous ceramic changed from 3% to 36%, resulting in a sensitivity of $S=15.5$ pF per unity change. Repeatability tests for capacitance measurement showed that the ${\theta }_v$ sensor’s root mean square error is 0.13%. The average current consumption of the system (sensor and signal conditioning circuit) is less than 1.5 $\mathsf{\mu }$ A, which demonstrates its suitability for being powered by energy harvesting systems. We developed a complete irrigation control system that integrates the sensor, an energy harvesting module composed of a microgenerator installed on the top of a micro sprinkler spinner, and a DC/DC converter circuit that charges a 1 F supercapacitor. The energy harvesting module operates only when the micro sprinkler spinner is irrigating the soil, and the supercapacitor is fully charged to 5 V in about 3 h during the first irrigation. After the first irrigation, with the supercap fully charged, the system can operate powered only by the supercapacitor for approximately 23 days, without any energy being harvested.

We present a capacitive smart sensor based on printed circuit board (PCB) technology to measure the amount of water content in a paper pulp at the wet end of a paper machine. The developed sensor incorporates in the same PCB the signal processing circuits. It is a handheld portable device, and its output is sent to the reading equipment using a Bluetooth wireless connection, providing to the sensor’s operator ease of mobility around the wet end of a paper machine. The prototype was tested in a laboratory, using a wire mesh to emulate the end of a paper machine, and we were able to measure and easily detect when it reaches the water content in the range of 90% to 92%, as required in the paper fabrication process. Standard deviation of the capacitance measurements at various moisture levels is four orders of magnitude smaller than the mean. The smart sensor was tested in the 20°C to 40°C temperature range, in a paper pulp with a gravimetric water content of 91%. Since the variation of capacitance with temperature is practically linear, we propose a simple linear compensation equation to correct the observed sensitivity with the temperature. To keep the signal processing circuits small, low cost, simple, and robust, a novel direct interface sensor to microcontroller circuit technique was used to make the capacitive measurement, allowing for measuring small capacitance deviations without high-frequency oscillators. It was shown that it is possible to integrate the signal processing circuits in the top layer of the PCB interdigitated sensor without adding noise or degrading the performance of the capacitive sensor.

This work presents a multi-parameter optical fiber monitoring solution applied to an underground power distribution network. The monitoring system demonstrated herein uses Fiber Bragg Grating (FBG) sensors to measure multiple parameters, such as the distributed temperature of the power cable, external temperature and current of the transformers, liquid level, and intrusion in the underground manholes. To monitor partial discharges of cable connections, we used sensors that detect radio frequency signals. The system was characterized in the laboratory and tested in underground distribution networks. We present here the technical details of the laboratory characterization, system installation, and the results of 6 months of network monitoring. The data obtained for temperature sensors in the field tests show a thermal behavior depending on the day/night cycle and the season. The temperature levels measured on the conductors indicated that in high-temperature periods, the maximum current specified for the conductor must be reduced, according to the applied Brazilian standards. The other sensors detected other important events in the distribution network. All the sensors demonstrated their functionality and robustness in the distribution network, and the monitored data will allow the electric power system to have a safe operation, with optimized capacity and operating within tolerated electrical and thermal limits.

We propose a fiber optic sensor system based on fiber bending loss and Optical Time Domain Reflectometry (OTDR) to application on monitoring of embankment dams. The sensing system was developed to monitor indirectly the water level penetration on the embankment dam by measuring the water pressure. The bend loss sensor performance was assessed concerning the number of fiber loops involved, the pump wavelength and temporal width of the pulse. Sensor system link is proposed to have a number of at least six sensors stages totally independent each other, in such a way that each stage can be developed to monitor a specific situation. In order to protect the sensor stage against environmental damage and to match the mechanical properties of the fiber and the water, we proposed a special packaging based on silicone rubber.

A compact high pressure FBG sensor using a single point attached fiber in a ferrule was proposed. It was compared theoretically, by simulations and experimentally to FBG fully attached to the ferrule conception. Results show that the proposed conception has 3.2 to 4.2 times higher sensitivity, suited to use in internal combustion chamber engine.

Optical fiber technologies are very appropriate for using in high voltage equipment due to their excellent characteristics, mainly, immunity to electromagnetic interferences and electrical isolation. After the Smart Grid initiative, the focus for medium voltage (13.8 to 34 kV) smart meters leveraged the development of optical sensors for distribution application. This work provides a historical overview of optical technologies used in power quality monitoring, discussing technological, economics, standards and practical installation aspects. The sensors technologies analyzed in this work are the well-known optical Pockels cells and Faraday Effect, the fiber Bragg grating (FBG) and power-over-fiber (PoF).