Analyses And Development Of Non-conventional Beams For Enhanced Vibration Energy Harvesting With Piezoelectric Patches

Nowadays,scavenging mechanical energy in form of vibration using piezoelectric(PZT)materials has become one of the potential technologies to replace battery cells.This is due to demerit of the batteries of having stringent life time and unfriendliness to environment when disposed.The PZT material bonded to a rectangular cantilever beam to form unimorph harvester has been the generic configuration used for designing vibration based piezoelectric energy harvester(PEH).Rectangular cantilever beam serving as a substrate for the PZT is used as an auxiliary structure to lower the impractical resonant frequencies of PZT materials,which is usually above the range of viable vibration sources considered for application.Despite the role played by the rectangular beam in enhancing the functionality of PZT materials(i.e.charge generation to power small-scaled electronic devices),however,the power output of the composite structure is usually below threshold needed to energize most of the targeted small-scaled electronic devices.Some of the factors associated with the low performance among others are poor strain experienced from the substrate and inability to operate at a wider frequency spectrum.Therefore,to enhance the conversion efficiency and thus the energy scavenging abilities of piezoelectric energy harvester(PEH)systems,truncating geometrical dimensions of traditional rectangular cantilever beam harvester into a defined shape and development of innovative structures have been considered as one of the premium solutions for maximum scavenging of vibration based energy.This research commenced by conducting a critical review on various geometrical configurations presented in literature for optimum energy transduction from vibrations.The structures studied were classified into classical and non-classical,where a thorough evaluation on analogies and contrast between the structures was conducted with regards to their advantages,applicability as well as their demerit in different application.The outcome of the study revealed issues that were not addressed which gave the bases for innovations,contributions and results obtained in this thesis as follows.Based on the classical structures studied,a cantilever beam tapered along its thickness which is named wedge edged cantilever beam(WEC)was considered as a research object.The thickness tapered beam is a non-prismatic beam recommended in many literatures as a replacement for uniform rectangular beam structures in harvester design.This is because of its capability to produce uniform strain distribution,which enhances charge generation of piezoelectric material when bonded to the beam.Prior to this study,the concept of utilizing the whole surface of a thickness tapered beam with layered PZT material has been established.However,when dealing with the tapered beam bonded with a single PZT patch,the best location to situate the patch for effective utilization of strain location along the beam span is vital due to non-uniformity of its geometrical dimensions.And this important concept has not been addressed in the available literature.Therefore,this work presented a theoretical framework that explains variation of optimal strain location of a thickness tapered beam for harvester design and application.Analytical models were developed to estimate deflection and hence to calculate the maximum strain position on a WEC beam for enhanced performance when bonded with a micro fiber composite(MFC)patch which is a polymer based piezoelectric material.Subsequently,finite element models were developed in numerical model software known as COMSOL Multiphysics to validate simulation results from the derived analytical models.By considering different dimensions of the WEC beam subjected to static force of 5N,results of the analytical and numerical methods showed an accurate prediction of optimal deflection and strain location on the beam with an average relative percentage error of 1.5%and 3.7%respectively.Furthermore,numerical and experimental based dynamic analyses of the WEC covered with MFC patched to form 3different configurations namely Config 1,Config 2 and Config 3 were carried out.Voltage and power output results from the numerical simulations and experimental studie s were compared and the analysis showed that Config 3 which had the optimal strain position covered with the MFC patch produces the highest voltage and output power compared to its counterparts.A relative percentage increase in power output of about 93.3%is recorded.This signifies the importance of determination of optimal deflection and strain location of the tapered beam for efficient design of cantilever beam PEH.Based on the non-classical structures studied,a non-traditional cantilever structure named gauge shaped beam(GSB)was designed and modeled in COMSOL Multiphysics 5.3a.The structure was proposed to enhance the deficit of conventional beam structure in terms of minimum stress realization,higher Eigen frequency and poor electromechanical characteristics.By considering equal mass of the conventional rectangular beam and the proposed GSB shim,static analysis results of the two configuration showed that GSB produces higher Von Mises stress location of 1.08 x10~9 N/m~2 compared to 8.68 x10~8 N/m~2 on the conventional beam,which indicated the tendency of producing higher piezoelectric charge when bonded with PZT patch.Moreover,Eigen frequency analysis of the configurations showed that first three fundamental resonant frequencies of the GSB harvester are lower(i.e.70.69 Hz,428 Hz and 704 Hz)compared to conventional beam(i.e.76.88 Hz,445.32 Hz and847.13 H)which is a desirable characteristic required in harvester design.Also,numerical and experimental analysis of electromechanical characteristics of the two configurations showed that the GSB bonded with MFC patch yielded about 20%more power output compared to the conventional beam layered with the transducer.Finally,an investigation into the influence of tipmass orientation and position on the output performance was carried out where five different configurations were studied.The best configuration was presented and discussed.In a segment of this thesis,a nonlinear piezoelectric harvester coupled with a standard rectifying circuit was developed and studied.Contrary to traditional Duffing-type magnetic harvester mechanism presented in literature,the nonlinear effect in the system was induced by a dynamic tipmass with embedded magnet.Dynamic equation of the system was derived based on Newtonian method and subsequently,its equivalent circuit model was modeled using SIMetrix/SIMPLIS software to evaluate and compare its performance with a conventional harvester system.Results reveal that the nonlinear effect due to the force coupling has a profound effect on peak output power and operational bandwidth of the harvester as compared to linear system where an overall increase of 61.4%and 100%more than the values obtained from the rectified output and bandwidth of the conventional harvester were recorded.