• Analysis and design of a nonlinear vibration-based energy harvester - a frequency based approach

      Uchenna, Diala; Simon, Pope; Lang, Zi-Qiang; University of Sheffield (IEEE, 2017-08-24)
      The benefits of nonlinear damping in increasing the amount of energy (power) harvested by a vibration-based energy harvester (VEH) has been reported where it was revealed that more energy can be harvested using nonlinear cubic damping when compared to a VEH with linear damping. As has been reported, this only occurs when the base excitation on the VEH, at resonance, is less than the maximum base excitation. A maximum harvester base excitation results in a maximum distance the harvester mass can move due to its size and geometric limitations. The present study is concerned with the analysis and design of a VEH using a nonlinear frequency analysis method. This method employs the concept of the output frequency response function (OFRF) to derive an explicit polynomial relationship between the harvested energy (power) and the parameter of the energy harvester of interest, i.e. the nonlinear cubic damping coefficient. Based on the OFRF, a nonlinear damping coefficient can be designed to achieve a range of desired levels of energy harvesting. It is also shown that using the OFRF the harvester throw (the displacement of the mass of the harvester), can be predicted using the designed damping coefficient.
    • Analysis and optimal design of a vibration isolation system combined with electromagnetic energy harvester

      Diala, Uchenna; Mofidian, SM Mahdi; Lang, Zi-Qiang; Bardaweel, Hamzeh; University of Sheffield (SAGE Publications, 2019-07-17)
      This work investigates a vibration isolation energy harvesting system and studies its design to achieve an optimal performance. The system uses a combination of elastic and magnetic components to facilitate its dual functionality. A prototype of the vibration isolation energy harvesting device is fabricated and examined experimentally. A mathematical model is developed using first principle and analyzed using the output frequency response function method. Results from model analysis show an excellent agreement with experiment. Since any vibration isolation energy harvesting system is required to perform two functions simultaneously, optimization of the system is carried out to maximize energy conversion efficiency without jeopardizing the system’s vibration isolation performance. To the knowledge of the authors, this work is the first effort to tackle the issue of simultaneous vibration isolation energy harvesting using an analytical approach. Explicit analytical relationships describing the vibration isolation energy harvesting system transmissibility and energy conversion efficiency are developed. Results exhibit a maximum attainable energy conversion efficiency in the order of 1%. Results suggest that for low acceleration levels, lower damping values are favorable and yield higher conversion efficiencies and improved vibration isolation characteristics. At higher acceleration, there is a trade-off where lower damping values worsen vibration isolation but yield higher conversion efficiencies.
    • Analysis, design and optimization of a nonlinear energy harvester

      Diala, Uchenna; Lang, Zi-Qiang; Pope, Simon; University of Sheffield (International Institute of Acoustics & Vibration/ Curran Associates Ltd, 2017-07)
    • Nonlinear design and optimisation of a vibration energy harvester

      Diala, Uchenna; Gunawardena, Rajintha; Zhu, Yunpeng; Lang, Zi-Qiang; University of Sheffield (IEEE, 2018-11-01)
      Nonlinear behavior has been exploited over the last decade towards improving the efficiency of most engineering systems. The effect of nonlinearities on a vibration energy harvester (VEH) has been widely studied. It has been reported in literature that a cubic damping nonlinearity extends the dynamic range (power/energy level) of a VEH system. It has also been widely shown that the operational bandwidth of a VEH system can be increased using a nonlinear hardening spring. As most energy harvesters have a maximum throw limited by the physical enclosure of the device, it is imperative to improve the operational conditions of the harvester within this limitation. This paper investigates the effects of a nonlinear hardening spring with cubic damping on a VEH system while assuming no limitation to the maximum throw (Practical VEH systems are constrained to a maximum throw and this is considered in a subsequent study). A frequency-based approach known as Output Frequency Response Function (OFRF) determined using the Associated Linear Equations (ALEs) of the nonlinear system model is employed. The OFRF polynomial is a representation of the actual system model hence used for the nonlinear VEH analysis and design. Based on the OFRF, optimal parameter values are designed to achieve any desired level of energy for the VEH.