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WALK THROUGH ENERGY GENERATION
Introduction
In the last few years, there has been an increase in demand for low-power
and portable-energy sources due to the development and mass
consumption of portable electronic devices .Furthermore, the portableenergy sources must be associated with environmental issues and
imposed regulations. These demands support research in the areas of
portable-energy generation methods .In this scope, piezoelectric materials
become a strong candidate for energy generation and storage in future
applications. Electricity can be generated with the use of piezoelectric
polymer in order to harvest energy from people walking or running on
piezoelectric polymer. In this scope, electro active β-polyvinylidene fluoride
used as energy harvesting element was introduced into a bicolor sole
prepared by injection, together with the electronics needed to increase
energy transfer and storage efficiency. An electrostatic generator was also
included in order to increase energy harvesting.
Electromagnetic, electrostatic, and piezoelectric are based
on the same principle: To convert mechanical energy into electrical energy,
one should be able to realize a movement between the mechanical parts of
the generator (e.g., the rotor and the stator of a macroscopic generator).
Vibrations consist, however, of a traveling wave in or on a solid material
and it are often not possible to find a relative movement within the reach of
a small generator. Therefore, one has to couple the vibration movement to
the generator by means of the inertia of a seismic mass.
Piezoelectric signals
There are two types of piezoelectric signals that can be used for
technological applications: The direct piezoelectric effect that describes the
ability of a given material to transform mechanical strain into electrical
signals and the converse effect, which is the ability to convert an applied
electrical solicitation into mechanical energy. The direct piezoelectric effect
is more suitable for sensor applications, whereas the converse
piezoelectric effect is most of the times required for actuator applications.
Therefore, it can be stated that a material is called piezoelectric when it
shows the ability to transform electrical into mechanical energy and,
conversely, mechanical into electrical energy.
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SYSTEM DESCRIPTION
The idea is to generate electricity by walking or running on piezoelectric
polymer in track. The polymer vibrates while someone is walking on it
because of mechanical energy applied to polymer and converts this
vibration into electrical energy which can be stored in rechargeable battery.
Polymer Preparation
The piezoelectric films used for the energy generation are constituted by
polymeric material coated in both sides by conducting material, which form
the electrodes.
The main advantages of using polymeric films instead of piezoceramics or
single crystals are that polymer films are flexible and can be fabricated in
the desired shapes and sizes through simple processing processes.
Furthermore, electro active polymers are very cheap in comparison with
their ceramic and single crystal counterparts, making them more suitable
for mass production systems and devices.
Electrode Deposition
Once the material is prepared, electrodes are deposited on both sides
either by magnetron sputtering or by thermal evaporation. Silver and
aluminum can be used as electrode materials.
Positioning of the Piezoelectric Material
As piezoelectricity is a dynamic process, the material should be positioned
in places were larger and more variable pressure is exerted during walking.
This may be at the centre of the track or one on both sides. The first one
requires less piezoelectric polymer as it is in centre of both sides and
hence generates less electricity from other because in other there are 2
polymers on tracks and hence generates more vibration. Because of more
vibration, more electricity is produced.
Electronic Circuit
In order to maximize the energy transfer to a charge or to a battery, in the
case of energy storage, a rectifying circuit is necessary in order to obtain a
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single polarity voltage. This circuit consists of a rectifier bridge based on
four Schottky barrier diodes. These diodes have a forward bias voltage
drop near 0.33 V, which is an advantage for this application, as it means
that, for potential values larger than 0.66 V(two diodes), it is possible to use
the full wave configuration. With p-n junction diodes, this value would be
approximately1.4 V. The circuit board of the full wave rectifier is then
connected to the piezoelectric element placed in the track.
Addition of an Electrostatic Generator
In order to increase the power generation, an electrostatic generator was
also coupled to the polymer. It consists basically in two metallic plates
separated by a flexible dielectric material(foam), which changes its
thickness every time a pressure is applied, i.e., when the person puts
his/her foot on the polymer. The steady-state capacitance of this
electrostatic generator is 20 pF. When the person steps with a foot on the
polymer, the capacitance increases about two times, this means that the
voltage decreases to-half. At this time, the piezoelectric voltage is higher
than the one at the electrostatic generator terminals; therefore, its
capacitance will be charged. When the person raises the foot from polymer,
the capacitance of the electrostatic generator decreases, and the voltage
increases In this case, the load is an energy storage device (battery of 3 V);
therefore, when the voltage of the electrostatic generator exceeds that of
the battery, the charge of the first is transferred to the second.
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Block diagram
Load (LED)
Piezoelectric
sensor
Up converter ckt
(Dc to dc converter)
Battery charger
circuit
Sensor
Circuit
Microcontroller
LCD
Piezoelectric sensor: The pressure applied on piezoelectric polymer or
element is converted into electrical energy by piezoelectric sensor. In other
word piezoelectric sensor converts mechanical force applied to polymers is
converted into electrical energy.
DC T0 DC converter circuit: Since the output of the piezoelectric is two
small that is around 3 v hence to boost the voltage this circuit is very much
useful for generation of high voltage. A DC-to-DC converter is an electronic
circuit which converts a source of direct current (DC) from one voltage level
to another. It is a class of power converter Switched DC to DC converters
offer a method to increase voltage from a partially lowered battery voltage
thereby saving space instead of using multiple batteries to accomplish the
same thing. Conversion methods – linear regulator, switched mode
conversion, magnetic etc.
Battery charger circuit: The output of DC to DC converter is applied to
battery charger in which battery is first charged for load and sensor circuits.
Thin film lithium batteries are always used for rechargeable batteries.
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Cross section of thin film lithium battery
Sensor circuits: It gets input from rechargeable batteries and gives it to
microcontroller.
Microcontroller: It is used for programming the lcd to display how much
voltage is generated by piezoelectric sensors or polymer?
Lcd: It is used for displaying the voltage.
Conclusion:
From the several methods available to integrate energy generating
elements harvesting human energy, piezoelectric
Materials associated with electrostatic generators seem to be
One of the most promising elements. In particular, electro active
Polymers are particularly interesting due to their low cost, flexibility,
And easy integration into elements such as clothes and
Shoes. Conventional methods were used in order to fabricate the sole, with
no modification of the industrial production process. Through the simple
configuration and electronics, energy harvesting is possible. In order to get
energy values suitable for the functioning of electronic appliances,
improvements in the material, in order to improve electromechanical
conversion, and in the read out electronics, in order to optimize the energy
transfer, and the precise determination of the geometry and number ofthe
piezoelectric generators should be performed.
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References:
1. Piezoelectric material advance in science, technology and application
by Carmen galassi, maria dimescu ,kenji uchino and Michael sayer.
2. Piezoelectric based vibration control by nader jalili.
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