1. ICRTEDC-2014 6
IJEEE, Vol. 1, Spl. Issue 2 (May, 2014) e-ISSN: 1694-2310 | p-ISSN: 1694-2426
GV/ICRTEDC/01
WIRELESS ELECTRICAL POWER
GENERATION
Kevin Basenoo
University of Mauritius, Republic of Mauritius
kervin005@hotmail.com
Abstract : Wireless energy transfer or Wireless Power is
the process that takes place in any system where it is
transmitted from a power source to an electrical load
without interconnecting wires. Wireless transmission is
useful in cases where instantaneous or continuous energy
transfer is needed but interconnecting wires are
inconvenient, hazardous, or impossible. In this paper
different Wireless energy transfer methods are studied.
The objective of the paper discussed herein is to develop
an approach that maximizes the power transferred.
Keywords: Wireless, Energy Transfer.
I. INTRODUCTION
With the recent advances in wireless and micro
electromechanical systems (MEMS) technology, the
demand for portable electronics and wireless sensors is
growing rapidly. Because these devices are portable, it
becomes necessary that they carry their own power supply.
In most cases this power supply is the conventional
battery; however, problems can occur when using batteries
because of their finite lifespan. For portable electronics,
replacing the battery is problematic because the electronics
could die at any time and replacement of the battery can
become a tedious task. In the case of wireless sensors,
these devices can be placed in very remote locations such
as structural sensors on a bridge or global positioning
system (GPS) tracking devices on animals in the wild.
When the battery is extinguished of all its power, the
sensor must be retrieved and the battery replaced. Because
of the remote placement of these devices, obtaining the
sensor simply to replace the battery can become a very
expensive task or even impossible. For instance, in civil
infrastructure applications it is often desirable to embed
the sensor, making battery replacement unfeasible [1]. If
ambient energy in the surrounding medium could be
obtained, then it could be used to replace or charge the
battery. One method is to use piezoelectric materials to
obtain energy lost due to vibrations of the host structure.
This captured energy could then be used to prolong the life
of the power supply or in the ideal case provide endless
energy for the electronic devices lifespan.
Piezo- Electric Method
Piezoelectric materials[1] have a crystalline structure that
provides them with the ability to transform mechanical
strain energy into electrical charge and, vice versa, to
convert an applied electrical potential into mechanical
strain. This property provides these materials with the
ability to absorb mechanical energy from their
surroundings, usually ambient vibration, and transform it
into electrical energy that can be used to power other
devices.
The piezoelectric effect exists in two domains: the first is
the direct piezoelectric effect that describes the material’s
ability to transform mechanical strain into electrical
charge; the second form is the converse effect, which is
the ability to convert an applied electrical potential into
mechanical strain energy. The direct piezoelectric effect is
responsible for the material’s ability to function as a
sensor and the converse piezoelectric effect is accountable
for its ability to function as
an actuator.
Fig. 1. Piezoelectric Sensor [2]
Most piezoelectric electricity sources produce power in the
order of milliwatts, too small for system application, but
enough for hand-held devices such as some commercially
available self-winding wristwatches. One proposal is that
they are used for micro-scale devices, such as in a device
harvesting micro-hydraulic energy. In this device, the flow
of pressurized hydraulic fluid drives a reciprocating piston
supported by three piezoelectric elements which convert
the pressure fluctuations into an alternating current.As
piezo energy harvesting has been investigated only since
the late '90s, it remains an emerging technology.
Nevertheless some interesting improvements were made
with the self-powered electronic switch at INSA school of
engineering, implemented by the spin-off Arveni. In 2006,
the proof of concept of a battery-less wireless doorbell
push button was created, and recently, a demonstrator
showed that classical TV infra-red remote control can be
powered by a piezo harvester. Other industrial applications
appeared between 2000 and 2005, to harvest energy from
vibration and supply sensors for example, or to harvest
energy from shock.
Piezoelectric systems can convert motion from the human
body into electrical power. DARPA has funded efforts to
harness energy from leg and arm motion, shoe impacts,

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and blood pressure for low level power to implantable or
wearable sensors. The nanobrushes of Dr. Zhong Lin
Wang are another example of a piezoelectric energy
harvester [2]. They can be integrated into clothing. Careful
design is needed to minimise user discomfort. These
energy harvesting sources by association have an impact
on the body. The Vibration Energy Scavenging Project is
another project that is set up to try to scavenge electrical
energy from environmental vibrations and movements.
Pyroelectric energy harvesting
The pyroelectric effect[2] converts a temperature change
into electric current or voltage. It is analogous to the
piezoelectric effect, which is another type of ferroelectric
behavior. Like piezoelectricity, pyroelectricity requires
time-varying inputs and suffers from small power outputs
in energy harvesting applications. One key advantage of
pyroelectrics over thermoelectric is that many pyroelectric
materials are stable up to 1200 C or more, enabling energy
harvesting from high temperature sources and thus
increasing thermodynamic efficiency. There is a
pyroelectric scavenging device that was recently
introduced, which doesn't require time-varying inputs. The
energy-harvesting device uses the edge-depolarizing
electric field of a heated pyroelectric to convert heat
energy into mechanical energy instead of drawing electric
current off two plates attached to the crystal-faces.
Moreover, stages of the novel pyroelectric heat engine can
be cascaded in order to improve the Carnot efficiency[16].
II. INDUCTION METHOD
The action of an electrical transformer is the simplest
instance of wireless energy transfer. The primary and
secondary circuits of a transformer are not directly
connected. The transfer of energy takes place by
electromagnetic coupling through a process known as
mutual induction. (An added benefit is the capability to
step the primary voltage either up or down.) The battery
charger of a mobile phone or the transformers on the street
are examples of how this principle can be used. Induction
cookers and many electric toothbrushes are also powered
by this technique. A magnetic resonance[3] wireless
power supply system was discussed in one paper that’s
prototyped by the Arakawa & Komurasaki Laboratory of
the University of Tokyo together with DENSO Corp. of
Japan [3]. Professor Kimiya Komurasaki of the
Department of Advanced Energy, Graduate School of
Frontier Science at the University, stated: "The system can
supply power not only to mobile phones and notebook
PCs, but also objects moving freely in free space."
Fig. 2. Induction Principle [4]
With the prototype system researchers studied the
relationship of the resonator’s position within three-
dimensional space to transfer efficiency. Both simulated
and actual measurements are shown in figure below.
In order to achieve optimal power transfer, impedance
matching between coils is a key factor [4]. By changing
the distance between the transmitter and receiver causes a
change in the coupling constant (K) which causes a change
in the optimal impedance ratio.
Transfer Efficiency Affected by Impedance Matching.
Credit: Nikkei Electronics based on material courtesy
University of Tokyo and DENSO.
ELECTRODYNAMIC INDUCTION
The "electrodynamic inductive effect" or "resonant
inductive coupling" has key implications in solving the
main problem associated with non-resonant inductive
coupling for wireless energy transfer; specifically, the
dependence of efficiency on transmission distance.
Electromagnetic induction works on the principle of a
primary coil generating a predominantly magnetic field
and a secondary coil being within that field so a current is
induced in the secondary. Coupling must be tight in order
to achieve high efficiency. As the distance from the
primary is increased, more and more of the magnetic field
misses the secondary. Even over a relatively small range
the simple induction method is grossly inefficient, wasting
much of the transmitted energy.
ELECTROSTATIC INDUCTION
The "electrostatic induction effect" or "capacitive
coupling" is an electric field gradient or differential
capacitance between two elevated electrodes over a
conducting ground plane for wireless energy transmission
involving high frequency alternating current potential
differences transmitted between two plates or nodes. The
electrostatic forces through natural media across a
conductor situated in the changing magnetic flux can
transfer energy to a receiving device.
ELECTRICAL CONDUCTION
Electrical energy can be transmitted by means of electrical
currents made to flow through naturally existing
conductors, specifically the earth, lakes and oceans, and
through the upper atmosphere starting at approximately
35,000 feet (11,000 m) elevation— a natural medium that
can be made conducting if the breakdown voltage is
exceeded and the constituent gas becomes ionized. For
example, when a high voltage is applied across a neon
tube the gas becomes ionized and a current passes between
the two internal electrodes. In a wireless energy
transmission system using this principle, a high-power
ultraviolet beam might be used to form vertical ionized
channels in the air directly above the transmitter-receiver
stations.
III. APPLICATIONS
Future applications may include high power output
devices (or arrays of such devices) deployed at remote
locations to serve as reliable power stations for large
systems. Another application is in wearable electronics,
where energy harvesting devices can power or recharge
cellphones, mobile computers, radio communication
equipment, etc.
Such as at train stations piezo elements that would
generate electricity as commuters walk through, this sort
of human-powered electricity generation system may
provide a portion of the electricity consumed at station.

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Energy harvesters could be used extensively, for example,
to provide power for wireless monitoring and diagnostic
sensors that generate data on:
 A person’s heart rate, body temperature or blood
pressure;
 Stresses experienced by engine components,
structural elements in buildings etc;
 Brake temperatures in railway rolling stock.
IV. CONCLUSION
Existing devices can only exploit vibrations that have a
narrow range of frequencies (the frequency is the number
of vibrations occurring per second). If the vibrations don’t
occur at the right frequency, very little power can be
produced and it will be too low to be useable. This is a big
problem in applications like transport or human movement
where the frequency of vibrations change all the time.
REFERENCES
1. https://secure.wikimedia.org/wikipedia/en/wiki/Energy_harves
ting
2. Adaptive Piezoelectric Energy Harvesting Circuit for Wireless
Remote Power Supply, IEEE TRANSACTIONS ON POWER
ELECTRONICS, VOL. 17, NO. 5, SEPTEMBER 2002
3. Arakawa & Komurasaki Laboratory of the University of
Tokyo together with DENSO Corp. of Japan.
4. IEEE Electron Devices Meeting, 2007. IEDM 2007.
International Energy Harvesting - A Systems Perspective, J.
Rabaey, F. Burghardt, D. Steingart, M. Seeman, and P. Wright
Berkeley Wireless Research Center University of California,
Berkeley.