Rotational piezoelectric energy harvester for wearable devices

Electronic devices are mostly powered externally via batteries. The dependency on the recharging process limits the usage of these devices to work in a specified period of time. This research work highlights the capability of a piezoelectric energy harvester to generate sufficient electricity to power up electronic devices by using low frequency vibrations alone, without relying on external power supplies. In general human motions consists of low frequency vibrations, therefore the capability to power up electronic devices using low frequency vibrations will also eventually become useful to power up wearable devices. Simulations were conducted using COMSOL Multiphysics® to identify the dimensions of a piezoelectric beam which will produce the optimum level of voltage output. A specially fabricated rotational piezoelectric energy harvester prototype that consists of a 40 mm piezoelectric bimorph beam that rotates with the aid of a rotor and aluminum proof-mass was developed together with a corresponding Arduino Uno based data logger. With a given input frequency of 18 Hz, the maximum voltage output that could be generated was recorded at 0.024 V. This research highlights the optimistic possibility that clean energy could be generated and utilized in powering various applications without depending on external power supplies

Impact-Driven Energy Harvesting: Effect of Stress on Piezoelectric Bender

This research is experimentally characterized and evaluates the effect of stress on a piezoelectric transducer by employing different bending mechanism. Three forms of bender: flat, unstressed, and pre-stressed are being investigated for their maximum electrical charge generation subjected to the applied stress. These mechanisms were fabricated using 3D printer where the piezoelectric beam can be inserted in to maximize the applied stress onto it. Variable impact forces are being exerted to bend the piezoelectric transducer for generating an electrical power across its terminals when connecting to an external load. In this respect, a rectangular shaped piezoelectric transducer with the size of (70X32X0.55) mm manufactured by Piezo System utilized to empirically study the relation between the impact force and the electrical output from the proposed piezoelectric bender. From the experimental results, the instantaneous AC volt output at open-circuit improved gradually and reached saturation of 10VAC, 50 VAC, and 70 VAC for flat, unstressed, and pre-stressed piezoelectric bender respectively. It is also found that the output power increases from 4mW of that recovered by using a flat mechanism to a double when using that an unstressed bending mechanism, while under the condition of pre-stressed, the electrical power further increases to 53mW at the same impact force

An efficient genetic algorithm for large-scale transmit power control of dense and robust wireless networks in harsh industrial environments

The industrial wireless local area network (IWLAN) is increasingly dense, due to not only the penetration of wireless applications to shop floors and warehouses, but also the rising need of redundancy for robust wireless coverage. Instead of simply powering on all access points (APs), there is an unavoidable need to dynamically control the transmit power of APs on a large scale, in order to minimize interference and adapt the coverage to the latest shadowing effects of dominant obstacles in an industrial indoor environment. To fulfill this need, this paper formulates a transmit power control (TPC) model that enables both powering on/off APs and transmit power calibration of each AP that is powered on. This TPC model uses an empirical one-slope path loss model considering three-dimensional obstacle shadowing effects, to enable accurate yet simple coverage prediction. An efficient genetic algorithm (GA), named GATPC, is designed to solve this TPC model even on a large scale. To this end, it leverages repair mechanism-based population initialization, crossover and mutation, parallelism as well as dedicated speedup measures. The GATPC was experimentally validated in a small-scale IWLAN that is deployed a real industrial indoor environment. It was further numerically demonstrated and benchmarked on both small- and large-scales, regarding the effectiveness and the scalability of TPC. Moreover, sensitivity analysis was performed to reveal the produced interference and the qualification rate of GATPC in function of varying target coverage percentage as well as number and placement direction of dominant obstacles. (C) 2018 Elsevier B.V. All rights reserved