1 research outputs found
Design analysis and fabrication of a mobile energy harvesting device to scavenge bio-kinetic energy.
The increasing prevalence of low power consumption electronics brings greater
potential to mobile energy harvesting devices as a possible power source. The main
contribution of this thesis is the study of a new piezoelectric energy harvesting device,
called the piezoelectric flex transducer (PFT), which is capable of working at non-
resonant and low frequencies to harvest bio-kinetic energy of a human walking. The
PFT consists of a piezoelectric element sandwiched between substrate layers and metal
endcaps, the endcaps are specifically designed to amplify the axial force load on the
piezoelectric element, instead of conventional designs of piezoelectric energy harvesters
that focus on utilising resonant frequency in order to increase power harvested. This
thesis presents the analyses, design, prototyping and characterisation of the PFT using a
coupled piezoelectric-circuit finite element model (CPC-FEM) to show the energy
harvesting capability of the proposed and developed novel device to harvest bio-kinetic
energy. Prior to the study of the new PFT, an initial focus was given to a traditional
Cymbal device to investigate its potential as a bio-kinetic energy harvesting device. To
gain an understanding, effects of geometrical parameters and material properties of the
device on its energy harvesting capability were studied and in doing so issues and
problems were identified with the traditional Cymbal device for use as a bio-kinetic
energy harvesting device. Its structural materials were not able to withstand higher than
a 50N applied load and it was proposed that a small adhesion area connection in a
fundamental part of the structure may have been at high risk of delamination. In order to
study these, the CPC-FEM model was developed using the commercial software of
ANSYS and validated by experimental methods. Later, based on a modelling and
experimental study, a novel PFT was proposed and implemented to overcome the issues
and problems of the traditional Cymbal device. For this initial study, the Cymbal was
analysed by studying how key dimensional parameters affect the energy harvesting
performance of the Cymbal. In addition to this, how piezoelectric material properties
affect the energy harvesting performance were studied using the developed CPC-FEM
model through comparisons of different piezoelectric materials and their electrical
performances to aid with selecting high power producing materials for the final PFT
design. It was found that (1) dββ is a more dominant material property over other
material properties for higher power output, (2) Figure of Merit (FOM) was more linear
related to the power output than either the kββ or the dββ, and (3) Ξ΅α΅ rββ had some role
when the materials have an identical dββ; a lower Ξ΅ α΅ββ was preferred. A combined FOM
with dββ parameters is recommended for selection of piezoelectric material for a higher
power outputs. The design of the new PFT is partly based on the traditional Cymbal
however, the new PFT has more potential for withstanding higher forces due to an
addition of substrate layers that reduced delamination risks. Using a similar approach to
designing the traditional Cymbal, the new PFT was designed and tested with force
frequencies of less than 5Hz and forces of up to 1kN. In the design process, the
validated CPC-FEM was used 1) to analyse then utilise correlations between geometric
parameters and power outputs, and 2) to ensure structural integrity by monitoring
mechanical stress in the PFT. The PFT was retrofitted into a shoe and the harvested
power was used to power an in-house developed wireless sensor module whilst the
subject with a body weight of 760N was wearing the shoe and ran at 3.1mph (equivalent
to 1.4Hz on the shoe), the PFT produced an average maximum power of 2.5mW over
2M⦠load and the power produced is able to power the wireless module approximately
every 10 seconds.Engineering and Physical Sciences (EPSRC)PhD in the School of Applied Science