VOL. 11, NO. 10, MAY 2016 ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2016 Asian Research Publishing Network (ARPN). All rights reserved.
www.arpnjournals.com
6366
EXPERIMENTAL INVESTIGATION ON PIEZOELECTRIC AND
ELECTROMAGNETIC HYBRID MICRO-POWER GENERATOR
Noraini Mat Ali, KokSwee Leong and Ain Atiqa Mustapha
Faculty of Electronic and Computer Engineering Universiti Teknikal Malaysia Melaka, Durian Tunggal, Melaka, Malaysia
ABSTRACT
Piezoelectric micro-generator (MG) is popular due to its high output power density compared to other means of
energy harvesting mechanism; however the current generated is relatively low. In the other hand electromagnetic MG is
capable to generate higher output current per unit of electrical output power. By combining both of these MGs, they would
complement each other in improving the total efficiency of the energy harvesting system. It is verified from the experiment
that the hybrid system reduce the capacitor charging time compared to individual system.
Keywords: energy harvesting, micro-generator.
INTRODUCTION
Hybrid energy harvesting system is a promising
technique that extracting energy from two or more sources
which has the advantage to deal with the low power
sources. Hybrid generator is a combination of any energy
harvester such as solar panel and thermoelectric generator
[1], piezoelectric and electromagnetic MG [2], solar panel
and wind turbine [3]. Hybrid energy harvesting technique
can optimize the performance of energy conversion and
provide a solution for a low power MGsystem. The focus
on this paper is to investigate a hybrid MG based on the
combination of piezoelectric and electromagnetic energy
conversion mechanisms. The model of a hybrid vibration
energy harvester can be simplified as shown in Figure-1,
as described by Yu et al. [4], where b
M
is a mechanical
damping, b
P
is a piezoelectric damping and b
EM
is an
electromagnetic damping.
The total output power from hybrid system is
equal to the sum of the power generated from two kinds of
vibration mechanism.
Figure-1. Second-order spring mass damper system with
additional electrical damper [4].
So, the total output power of hybrid generator
consists of piezoelectric and electromagnetic MG can be
written as
P
HYBRID
=P
P
+P
EM
......................................................... (1)
where Pp is the power derived from piezoelectric
while P
EM
is the power that derived from electromagnetic.
The total output power of hybrid generator can be
simplified as [4],
P
HYBRID
=
9
64
2
ሺ
+
ሻ
2
+
ሺேሻ
2
16ሺ
+
ሻ
2
…………… (2)
where
is the modulus of unimorph
piezoelectric cantilever beam, is the length of the
piezoelectric beam, is the number of coil turns, l is the
length of coil,B is the magnetic flux density, Y is the
amplitude of a vibration source, R
coil
is the resistance of
the coil,
ெ
,
are the mechanical, piezoelectric
and damping factors respectively while is the resonant
frequency.
The basic design of hybrid harvester as described
by Sang, et al. [4] consists of one permanent magnet
mounted at the end of the cantilever beam which held by
two piezoelectric plates. The two coils are located beside
both poles of magnet. This system reported able to
produce a power of 10.7mW at a resonant frequency of
about 50Hz. The result shows that individual
electromagnetic generator generates only 5.9mW which is
lower than hybrid system.Prior to that, Wischke, et al [5]
demonstrated that different arrangement of piezoelectric
and electromagnetic give different output power, whereby
in-line structure generated about 33μW output power at
100 optimal load resistance while an across structure
generate about 54μW at 200 optimal load resistance
when excited to the same acceleration of 10mm/s
2
. The
improved version with using two magnets mounted on the
top and bottom, and at the end of the piezoelectric
cantilever beam, generates an output power of up to 60μW
at an optimal load of 200. Fauzi, et al [6] proposed of
using four poles magnets attached on the top and bottom
of the piezoelectric cantilever beam with coil was placed
underneath the bottom magnet, which is quite similar with
in-line structure proposed by Wischke et al [5], but
arranged in opposite polarity with the coil is placed
between the air gap of magnets generated greater electrical
output power compared to that of two poles magnets.
Obviously besides than increasing the magnetic field, the