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Feb 08

Conversion of Vibration in Shoes Wearing into Electricity Using Piezoelectric Materials

Energy consumption increases with the increase in population, resulted in the State
Electricity Company (PLN) which had to work harder to fulfill the demand of electrical
energy. During the time, many sources of electrical energy obtained from the conversion of
fossil energy such as petroleum, coal, and gas. Global situation indicates that fossil energy
(especially petroleum) increasingly depleted because it is non-renewable. It is affected on
its price that is also rising.

 

The newest concept for the fulfillment of electrical energy in a circuit is the enegy
harvesting of scavenging energy. Energy scavenging has several advantages such as cheap,
safe, maintenance free, flexible, and can be used in various occasions. There are several
sources of energy in our environment that can be used and they are renewable, for example
energy from temperature changes, solar energy, energy of vibration, etc.

 

Vibration energy produces greater electrical energy density than other energies. The
vibration is also easily found around us. Some techniques that can be used for the
conversion of vibrational energy into electrical energy are electrostatic, electromagnetic
and piezoelectric. Piezoelectric materials have a high priority because of its stable energy
density and it does not require outside powers (N. Muensit, 2012). Piezoelectric materials
can be used as a source of energy harvester, which can be applied as a supplier of power to
the sensor (UK Singh, 2007). In addition, the piezoelectric material has the ability to
convert mechanical stress into electrical energy. (H, A Sodano, 2004). Piezoelectric
materials are made of materials such as Lead Zirconate titanate (PZT), Zinc Oxide (ZnO),
Barium titanate, and Barium Strontium Titanate (BST).


Vibration in Shoes Wearing

 

Shoes are a kind of footwear, which usually consist sections soles, heel, tongue, and
toe cap. Shoes are grouped by function or type, such as formal shoes (party), casual shoes,
dance shoes, sports shoes, work shoes, orthopedic and minimalist. The pressure caused by
foot stepping into the shoes is one of the sources of vibration which can be used as a
trigger to produce energy using piezoelectric materials.

 

A system of micro-scale electrical energy can be generated using piezoelectric
materials by employing mechanical vibration energy (energy scavenging system) on the
shoes / footwear. The process of designing micro-scale electrical energy generation
consists of installation of piezoelectric materials in shoes and its integration with electronic
circuits (rectifier, DC-DC converters, Buck Booster).

 

Conversion of Vibration in Shoes Wearing into Electricity
Piezoelectric materials are materials (usually in the form of rock crystal, ceramics,
including bone and polymers) that have the ability to generate an electric potential in
response to mechanical stress given into material. The mechanism process of energy
generation in the piezoelectric material is when there is pressure / mechanical energy of the
piezoelectric material, it causes deformation / mechanical shift, then it causes a shift in the
charge / dipoles. When the pressure / mechanical energy is removed, the charge will return
to normal. The process of pressure granting and removing on the piezoelectric material are
repeated / periodic charge will cause a shift causing alternating electric current. Electrical
energy generation scheme on the piezoelectric material can be seen in figure above.

Mechanical electrical energy generation piezoelectric materials (Peter Woas, 2012)
Generating electricity by using piezoelectric materials has three main stages:
1. Piezoelectric sensors as electrical energy generation module, which performs the
conversion of vibrational energy into electrical energy
2. Rectifier Module as part of the conversion to electrical energy into DC power supply
3. Functioning amplifier module comprising a voltage amplifier and voltage regulator.
Output voltage generated can be used as a source of electrical energy or can be stored in
the battery

This part of the principal on the prototype consists of :
• Piezoelectric sensor as converter the pressure into electrical energy
• The pressure generated by the foot of the shoes put pressure on piezoelectric materials
• AC-DC voltage rectifier circuit
• DC-DC voltage booster using the Joule Thief circuit schematic or Buck Boost

Simply put, piezoelectric sensor applied on the shoes between the insole and
outsole. The pressure caused by foot stepping into the shoes is one of the sources of
vibration that will be used as a trigger to produce energy using piezoelectric materials.
Piezoelectric material produces AC voltage. AC voltage is converted into DC voltage
using AC-DC voltage rectifier circuit. DC voltage is increased using Joule Thief method
and voltage regulator circuit. Finally, the generated electrical energy will then be used as a
source to produce voltage of the battery cell phone charger, mini power bank, etc. This
method can be used to produce the renewable energy in our daily life and reduce the using
of unrenewable energy.

karya: Siti Nurrohmah, Universitas Negeri Sebelas Maret Surakarta, Juara 3 ESSAY COMPETITION 2012, IEEE SB UGM.

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