High-Efficient Energy Harvester With Flexible Solar Panel for a Wearable Sensor Device

This paper proposes an optimal energy harvester (OEH) that uses a flexible photovoltaic (FPV) module to prolong battery life for a wearable body sensor node under indoor and outdoor conditions. The proposed sensor node uses a Bluetooth low-energy module, which consumes low power to wirelessly communicate with mobile devices for monitoring vital signals. A 19 cm × 4 cm FPV module that can easily conform to human body contours is used for generating a peak-power of up to 500 mW to charge the battery in outdoor environments. To optimize the power collected under various irradiances, the OEH is designed with a boost circuit for harvesting the low energy available indoors and a maximum power point tracker for collecting the high energy that is available outdoors. The booster can operate within a wide input voltage range of 0.65-3 V to generate a stable output voltage of 3.3 V, and it has a high conversion efficiency of ~95%. The MPPT uses fuzzy inference engine to find the MPP of the FPV that is required to power the system. The results of our experiment show that the proposed device can prolong the lifetime by up to 950% under an irradiance of only 2.9 mW/cm2, and the proposed node becomes an autonomous node under partial shading and sunlight conditions. Therefore, this paper can provide a useful solution for extending the lifetime of wearable sensor devices.