Harvesting.ppt

5/20/2018 Harvesting.ppt

1/15

NITISH HURIA

0709120058


2/15

Increasingly intelligent systems

Growing need for alternative sources of energy

proposes several potentially inexpensive and highly effective

solutions

Reduce dependency on battery power

Complexity of wiring

Increased costs of wiring

Reduced costs of embedded intelligence

Increasing popularity of wireless networks

Limitations of batteries

Reduce environmental impact


3/15

Ambient radiation sources

Pyroelectric energy harvesting

Photo voltaic energy harvesting

Energy harvesting using Electroactive Polymers

Piezoelectric energy harvesting

Electrostatic energy harvesting

Electromagnetic energy harvesting Thermoelectric energy harvesting

Magnetostrictive energy harvesting


4/15

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 andcertain ceramics, including bone) to generate an electric field or

electric potential in response to applied mechanical stress.


5/15

The necessary condition for the piezoelectric effect is the absenceof a center of symmetry in the crystal structure. Such an effect isnot fond in crystals with a center of symmetry. Of the 32 crystals

classes 21 lack a center of symmetry, and with the exceptions ofone class, all of these are piezoelectric.

If lead zircon ate titan ate, a piezoceramic, is placed between twoelectrodes and a pressure causing a reduction of only 1/20th ofone 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


6/15

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.


7/15

PVDF

In 1961 polyvinylidene fluoride, a piezoelectric plastic wasinvented. It is one of the most widely used piezopolymer fromwhich substantial electricity can be generated. It is cheap andphysically quite strong.

In 2001 researchers found that PVDF becomes supersensitive topressure when impregnated with very small quantity of nanotubes,thus PVDF with its inherent superior mechanical properties whenupgraded with nano-technology produces a new generation ofpiezopolymer, which are durable and can generate large quantity of

electricity economically.


8/15


9/15

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


10/15

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 nocurrent 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 outputcurrent.

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.


11/15

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 highvoltage electric current that flows across a small spark-gap, thus heating and igniting thegas.

Gas burners now have built-in piezo-based ignition systems

PIEZOELECTRIC SENSORS have been successfully used in medical, aerospace, nuclearinstrumentation, and as a pressure sensor in the touch pads of mobile phones

Several nightclubs, mostly in Europe have already begun to power their strobes andstereos 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 bootsto power radios and other portable electronic gear

Several gyms, notable in Portland and a few other places are powered by a combinationof piezoelectric set ups and generators set up on stationary bikes

Laying piezoelectric crystal arrays underneath sidewalks, stairwells, and pretty muchany 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 andother vibrations sources

Piezoelectric microphones and pickups for Acoustic-electric guitars


12/15

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 werepolyvinylidene 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


13/15

Piezoelectric Concept Backpack

Capitalizing on the friction and heat created by walking, running and even justwearing jeans, engineers from Michigan Technological University, Arizona

State University devised a way to use this type of generated energy to chargeportable electronic devices, like iPods and mobile phones.


14/15

Advantages

Power wires are minimum or absentRequires less maintenance

Environmental friendly

Higher uptime( longer life cycle )

Disadvantages

Strict power budgetPerformance is dependent on availability of sources

Higher upfront cost

Less mature technology


15/15

From the overview, it is quite clear thatpiezoelectric 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 isremarkable.

It is a great hope that energy harvesting will

rule the next decade in the technical field

CONCLUSION

Harvesting.ppt

Documents

Transcript of Harvesting.ppt