NITISH HURIA

0709120058

Increasingly intelligent systemsGrowing need for alternative sources of energyproposes several potentially inexpensive and highly effective solutions Reduce dependency on battery power Complexity of wiringIncreased costs of wiringReduced costs of embedded intelligenceIncreasing popularity of wireless networksLimitations of batteriesReduce environmental impact

Ambient radiation sourcesPyroelectric energy harvestingPhoto voltaic energy harvestingEnergy harvesting using Electroactive PolymersPiezoelectric energy harvestingElectrostatic energy harvestingElectromagnetic energy harvestingThermoelectric energy harvestingMagnetostrictive energy harvesting

PIEZOELECTRIC EFFECT

The phenomenon of generation of a voltage under mechanical stress is referred to as the direct piezoelectric effect, and the mechanical strain produced in the crystal under electric stress is called the converse piezoelectric effect.

PIEZOELECTRICITY

Piezoelectricity is the ability of some materials (notably crystals and certain ceramics, including bone) to generate an electric field or electric potential in response to applied mechanical stress.

The necessary condition for the piezoelectric effect is the absence

of a center of symmetry in the crystal structure. Such an effect is not fond in crystals with a center of symmetry. Of the 32 crystals classes 21 lack a center of symmetry, and with the exceptions of one class, all of these are piezoelectric.

If lead zircon ate titan ate, a piezoceramic, is placed between two electrodes and a pressure causing a reduction of only 1/20th of one millimeter is applied, a 100,000-volt potential is produced.

The basic equations of piezoelectricity are: P = d x stress and E = strain/d Where, P = Polarization, E = electric field generated and D = piezoelectric coefficient in meters per volt

For understanding the mechanism of generation of piezoelectricity the crystal structure of unit cell of tetragonal barium titan ate (BaTiO3) as

shown on fig may be referred.

The positive ‘Ti’ ion, surrounded by an almost regular octahedron of negative oxygen ions, is not located at the centre of the octahedron, and is some what displaced along the Z- axis. This structure already has a dipole moment or spontaneous polarization, in the absence of externally applied stress. When the crystal is mechanically compressed in XY plane or is elongated along Z axis, the additional polarization associated with the deformation is the piezoelectric polarization, which generates electric field.

PVDF In 1961 polyvinylidene fluoride, a piezoelectric plastic was

invented. It is one of the most widely used piezopolymer from which substantial electricity can be generated. It is cheap and physically quite strong.

In 2001 researchers found that PVDF becomes supersensitive to pressure when impregnated with very small quantity of nanotubes, thus PVDF with its inherent superior mechanical properties when upgraded with nano-technology produces a new generation of piezopolymer, which are durable and can generate large quantity of electricity economically.

A vibrating piezoelectric element can be considered as sinusoidal current source at a particular time (t), ip (t) in parallel with its internal electrode

capacitance Cp. The magnitude of the polarization current Ip varies with

mechanical excitation level of the piezoelectric element.

ENERGY HARVESTING CIRCUIT

These waveforms can be divided into two intervals. In interval 1, denoted as u, the polarization current is chagrin the electrode capacitance of the piezoelectric element. During this time all diodes are reverse biased and no current flows to the output.

At the end of the commutation interval, interval 2 begins, and output current flows to the capacitor Crect and the load. By assuming Crect >> CP, the

majority of the current will be delivered as output current.

The magnitude of the polarization current IP

generated by the piezoelectric transducer, and hence the optimal rectifier voltage, may not be constant as it depends upon the vibration level exciting the piezoelectric element. This creates the need for flexibility in the circuit. i.e., the ability to adjust the output voltage of the rectifier to achieve maximum power transfer.

APPLICATIONS The best-known application is the electric CIGARETTE LIGHTER: pressing the button

causes a spring-loaded hammer to hit a piezoelectric crystal, producing a sufficiently high voltage electric current that flows across a small spark-gap, thus heating and igniting the gas.

Gas burners now have built-in piezo-based ignition systems PIEZOELECTRIC SENSORS have been successfully used in medical, aerospace, nuclear

instrumentation, and as a pressure sensor in the touch pads of mobile phones Several nightclubs, mostly in Europe have already begun to power their strobes and stereos

using the force of hundreds of people pounding on piezoelectric lined dance floors The armed forces toyed with the idea of putting piezoelectric materials in soldiers boots to

power radios and other portable electronic gear Several gyms, notable in Portland and a few other places are powered by a combination of

piezoelectric set ups and generators set up on stationary bikes Laying piezoelectric crystal arrays underneath sidewalks, stairwells, and pretty much any

other high traffic area to power street lights battery-less wireless doorbell push button The nanogenerator could be used to harvest electricity from shoes, car engines, tires and other

vibrations sources Piezoelectric microphones and pickups for Acoustic-electric guitars

Energy Scavenging with Shoe-Mounted Piezoelectrics

In this project the researchers lined the bottom of a shoe with piezoelectric transducers and saw what kind of power they got out of it. They eventually attached an RF-transmitter to the shoe that was powered by the piezoelectrics. The two materials they used were polyvinylidene fluoride (PVDF) and lead zirconate titanate (PZT).

Energy Harvester

This little device about the size of two AA batteries contains an electromagnetic generator inside. There are two magnets and in between them is a coil of wire. When vibrations cause the coil of wire to move around in the magnetic field, current is generated in the wire. This small energy source could be used in place of batteries or as a means to recharge batteries. The device supplies about 1 to 10 mW of power

Piezoelectric Concept Backpack

Capitalizing on the friction and heat created by walking, running and even just wearing jeans, engineers from Michigan Technological University, Arizona State University devised a way to use this type of generated energy to charge portable electronic devices, like iPods and mobile phones.

Advantages

•Power wires are minimum or absent•Requires less maintenance•Environmental friendly•Higher uptime( longer life cycle )

Disadvantages

•Strict power budget•Performance is dependent on availability of sources•Higher upfront cost•Less mature technology

From the overview, it is quite clear that piezoelectric energy harvesting has great

potential at micro level and some very important part of applications are still in the research and development stage. This paper presents an adaptive approach to harvesting electrical energy from a mechanically excited

piezoelectric element. The ability of piezoelectric equipments to convert motion

from human body into electrical power is remarkable.

It is a great hope that energy harvesting will rule the next decade in the technical field

CONCLUSION