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Abstract-This paper describes a new maximum-power-pointtracking (MPPT) method focused on low-power (< 1 W) photovoltaic (PV) panels. The static and dynamic performance is theoretically analyzed, and design criteria are provided. A prototype was implemented with a 500-mW PV panel, a commercial boost converter, and low-power components for the MPPT controller. Laboratory measurements were performed to assess the effectiveness of the proposed method. Tracking efficiency was higher than 99.6%. The overall efficiency was higher than 92% for a PV panel power higher than 100 mW. This is, in part, feasible due to the low power consumption of the MPPT controller, which was kept lower than 350 μW. The time response of the tracking circuit was tested to be around 1 s. Field measurements showed energy gains higher than 10.3% with respect to a direct-coupled solution for an ambient temperature of 26• C. Higher gains are expected for lower temperatures. Index Terms-Energy harvesting, maximum power point tracking (MPPT), solar cells, wireless sensor networks (WSNs).

This paper describes a non-invasive method for detecting leaks in buried pipes, which uses a surface linear electrode array perpendicular to the axis of the pipe. Two electrodes inject current and the remaining electrodes detect the drop in voltage on the ground surface using both the dipole-dipole array and a modified Schlumberger array. A single-step reconstruction algorithm based on the sensitivity theorem yields two-dimensional images of the cross section. A personal computer controls current injection, electrode switching and voltage detection, which allows us to easily test various arrays of electrodes and speed up the process of measurement. The system was first tested in the laboratory using a stainless steel tube immersed in water and covered by a rubber sleeve to simulate a non-conductive leak. By taking reference measurements with the immersed bare pipe, it is possible to reconstruct images showing the simulated leak using only 16 electrodes and even as few as eight electrodes, albeit with reduced resolution. Field measurements have involved simulated leaks of water from a plastic tube 1 m long and 8 cm in radius buried at a depth of about 24 cm in a farm field. The hardware system injected 1 kHz, 20 V peak-to-valley square waveforms, thus avoiding electrode polarization effects. The simulated leak was unmistakably distinguished.

Abstract-This paper proposes and analyses a microcontroller-based interface circuit for inductive sensors with a variable self-inductance. Besides the microcontroller (µC) and the sensor, the circuit just requires an external resistor and a reference inductor so that two RL circuits are formed. The µC appropriately excites such RL circuits in order to measure the discharging time of the voltage across each inductor (i.e. sensing and reference) and then it uses such discharging times to estimate the sensor inductance. Experimental tests using different commercial µCs at different clock frequencies show the limitations (especially, due to parasitic resistances and quantisation) and the performance of the proposed circuit when measuring inductances in the millihenry range. A non-linearity error lower than 0.3% FullScale Span (FSS) and a resolution of 10 bits are achieved, which are remarkable values considering the simplicity of the circuit.