Conversion of Vibration in Shoes Wearing into Electricity Using Piezoelectric Materials

By Siti Nurrohmah

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 energy 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 vibration 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

Job Diagram Electrical Energy Generation Process

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.

Referensi:

Dongna Shen, 2009, “Piezoelectric Energy Harvesting Devices For Low Frequency Vibration Aplications”, Dissertation,Auburn University, Alabama U.S

F.Cottone, 2011, “Introduction to Vibration Energy Harvesting”, NiPS Energy Harvesting Summer School, August 1-5, 2011

H.A. Sodano, D.J. Inman, and G. Park, 2004  "A review of power harvesting from vibration using piezoelectric materials," The Shock and Vibration Digest, vol. 36, n. 3, pp. 197-205, 2004.

Karthik Kalyanaraman, Jaykrishna Babu, 2010, “Power Harvesting System in Mobile Phones and Laptops using Piezoelectric Charge Generation” Proceedings of the World Congress on Engineering and Computer Science 2010 Vol II WCECS 2010, October 20-22, 2010, San Francisco, USA

N.Muensit, 2012, “Small-Scale Energy Harvesting With Low Dimensional Piezoelectric”, Proceeding of International Conferences on Physics and Application, October 03, 2012, Solo Indonesia

Schwartz, Robert W, 1997 “Chemical Solution Deposition of Perovskite Thin Film”, Chem. Mater, 2325-2340

U.K. Singh, R Hmiddleton, 2007, “Piezoelectric Power Scavenging of Mechanical Vibration Energy”, Australian Minning Technology Conference