nano generators by tanveer ahmed ganganalli seminar report

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CHAPTER 1: INTRODUCTION1.1 Background

The nanogenerators project has been developing and expanding since 2001 after the

idea was conceived by Dr.Zong Lin Wang.He invented a way to produce free electric

energy by harnessing the piezoelectric effect, some material have on microscale simply

by shaking,vibrating or bending the zinc oxide(zno) nano wires Wang was able to

produce an electric charge.

Wearable sensors are becoming smaller and increasingly widely used, resulting

in an increasing need for independent and compact power supplies. Electrochemical

batteries, the most common power supplies for wearable sensors, cannot meet the need

because of their limited energy storage capacity and potential environmental and health

risks, emerging as a critical bottleneck for wearable sensors. This has driven the

development of wearable energy harvesters, which harvest the mechanical energy

dissipated in human motion to provide renewable and clean energy . Several concepts of

wearable energy harvesters based on different mechanisms have been studied, such as

electromagnetic , electrostatic, thermoelectric , Nano-triboelectric and piezoelectric .

Piezoelectric energy harvesters and Nano-triboelectric generators can convert mechanical

energy into electric energy directly, thus their structures are more compact and simpler in

comparison to those of other types. The materials for Nano-triboelectric generators are

generally not accessible in the market, hence this work focuses on piezoelectric energy

harvesters. Lead zirconate titanate (PZT) and polyvinylidene difluoride (PVDF) are the

two most important piezoelectric materials for energy harvesting, owing to their high

piezoelectric performance. PZT is rigid, brittle, and heavy, bringing limitations in

wearable applications where flexibility is necessary. PVDF has considerable flexibility,

good stability, and is easy to handle and shape. Taking into account the human motion

characteristics of high amplitude and low frequency, PVDF is more appropriate for

wearable applications than PZT. PVDF has been used in wearable energy harvesters that

are implemented in shoes, bags , and clothing . Kymissis. developed an insole made of

eight-layer stacks of 28 μm PVDF sheets with a central 2 mm flexible plastic substrate. It

harnessed the parasitic energy in shoes and the average power reached 1.1 mW at 1 Hz.

Granstrom, et al. utilized PVDF straps as backpack shoulder straps to collect mechanical

energy produced by the backpack, with an average power of 45.6 mW during a walking

of 0.9–1.3 m/s. Yang and Yun fabricated a PVDF shell structure generating an output

SIET, Vijaypur Dept. of EEE

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power of 0.87 mW at a folding angle of 80° and a folding-and-unfolding frequency of 3.3

Hz, which could be worn on the elbow joint to harvest energy from human motion. The

mechanical energy dissipated in shoes can even power a computer, serving as an

attractive energy source for wearable harvesters . This paper develops a shoe-embedded

piezoelectric energy harvester, which can be integrated in a shoe readily for energy

harvesting from human locomotion with little discomfort for the wearers. The harvester is

based on a specially designed sandwich structure, resulting in a thin geometrical form, a

high performance and an excellent durability. Two harvester prototypes are made and

tested. The first one is made up of a multilayer PVDF film and a structure of engineering

plastics, which is placed under the heel. The second one is designed as an insole shape

and used as a normal insole, consisting of a structure of flexible silicone rubber and two

multilayer PVDF films. More power can be generated by the former prototype, while the

other one has an advantage of remarkable comfort. In order to store the harvested energy

and provide a constant DC output voltage, a power management circuit is designed.

In the past decade, the interest in energy harvesting technologies has grown

substantially. Traditional power supplies such as batteries have inherent limitations

including immobility, limited lifetime, maintenance difficulty, and toxic hazards. With

proliferation of wireless sensors and consumer electronics, those problems become

prominent. For example over 1.7 billion cell phones were sold worldwide in 2012 alone.

However, the need of frequent battery charging poses a major problem especially for

users who are in long-distance travel and who have heavy usage of their cellphones.

Therefore, it is highly desirable to develop a miniaturized portable power source for

charging consumer electronics whenever and wherever needed. A perpetual power source

through the addition of energy harvested from the environment would serve as a proper

solution.


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1.2 MotivationThe wastage of energy which is produced by the motion or movement of human

body parts in the form of walking, vibration, or blood pressure of body can be utilised and

can be converted to Electrical Energy and same can be utilised to power Nano devices

such as iPods, mobiles etc.

Nano generators are the future technology devices which are self-powered devices

which when implemented can utilise the energy from the day to day life activities, the

same energy can be used for devices such as mobiles, iPods without being connected to

external sources of supply.

1.3 Triboelectric NanogeneratorsIn 2012, a new type of technology called Triboelectric nanogenerator (TENG)

was invented for harvesting ambient mechanical energy. It operates in a unique principle

by coupling triboelectric effect with electrostatic induction. The TENG brings together

high performance, miniaturization,low cost, scalability and applicability. Since then, two

basic operating modes have been developed i.e. contact mode and friction mode, which

have been utilized in a variety of designs to harvest mechanical motions under different

circumstances.


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CHAPTER 2: TYPES OF NANOGENERATORS

2.1 Piezoelectric Nanogenerator:

A piezoelectric Nanogenerator is an energy harvesting device converting the

external kinetic energy into an electrical energy based on the energy conversion by Nano-

structured piezoelectric material. Although its definition may include any types of energy

harvesting devices with Nano-structure converting the various types of the ambient

energy (e.g. solar power and thermal energy), it is used in most of times to specifically

indicate the kinetic energy harvesting devices utilizing Nano-scaled piezoelectric

material.

Although still in the early stage of the development, it has been regarded as a

potential breakthrough toward the further miniaturization of the conventional energy

harvester, possibly leading the facile integration with the other types of energy harvester

converting the different types of energy and the independent operation of mobile

electronic devices with the reduced concerns for the energy source.

2.2 Triboelectric Nanogenerator:A triboelectric Nanogenerator is an energy harvesting device that converts the

external mechanical energy into electricity by a conjunction of triboelectric effect and

electrostatic induction. This new type of Nanogenerator was firstly demonstrated in Prof.

Zhong Lin Wang's group at Georgia Institute of Technology in the year of 2012. As for

this power generation unit, in the inner circuit, a potential is created by the triboelectric

effect due to the charge transfer between two thin organic/inorganic films that exhibit

opposite tribo-polarity; in the outer circuit, electrons are driven to flow between two

electrodes attached on the back sides of the films in order to balance the potential. Since

the most useful materials for TENG.

Ever since the first report of the TENG in January 2012, the output power density

of TENG has been improved for five orders of magnitude within 12 months. The area

power density reaches 313 W/m2, volume density reaches 490 kW/m3, and a conversion

efficiency of ~60% has been demonstrated. Besides the unprecedented output

performance, this new energy technology also has a number of other advantages, such as


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low cost in manufacturing and fabrication, excellent robustness and reliability,

environmental-friendly.

2.3 Pyroelectric Nanogenerator:A pyroelectric nanogenerator is an energy harvesting device converting the external

thermal energy into an electrical energy by using Nano-structured pyroelectric materials.

Usually, harvesting thermoelectric energy mainly relies on the Seebeck effect that utilizes

a temperature difference between two ends of the device for driving the diffusion of

charge carriers. However, in an environment that the temperature is spatially uniform

without a gradient, such as in outdoor in our daily life, the Seebeck effect cannot be used

to harvest thermal energy from a time-dependent temperature fluctuation. In this case,

thepyroelectric effect has to be thechoice, which is about the spontaneous polarization in

certain anisotropic solids as a result of temperature fluctuation. The first pyroelectric

nanogenerator was introduced by Prof. Zhong Lin Wang at Georgia Institute of

Technology in 2012


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CHAPTER 3: TENG-WORKING PRINCIPLE3.1 working principle (case 1)

FIG 3.1 Direct current output

The working principle for the first case is explained by a vertically grown

nanowire subjected to the laterally moving tip. When a piezoelectric structure is subjected

to the external force by the moving tip, the deformation occurs throughout the structure.

The piezoelectric effect will create the electrical field inside the nanostructure; the

stretched part with the positive strain will exhibit the positive electrical potential, whereas

the compressed part with the negative strain will show the negative electrical potential.

This is due to the relative displacement of cations with respect to anions in its crystalline

structure. As a result, the tip of the nanowire will have an electrical potential distribution

on its surface, while the bottom of the nanowire is neutralized since it is grounded. The

maximum voltage generated in the nanowire can be calculated by the following equation:

, where κ0 is the permittivity in vacuum, κ is the dielectric constant, e33, e15 and e31 are the

piezoelectric coefficients, ν is the Poisson ratio, a is the radius of the nanowire, l is the

length of the nanowire and νmax is the maximum deflection of the nanowire's tip.

The electrical contact plays an important role to pump out charges in the surface of the

tip. The schottky contact must be formed between the counter electrode and the tip of the

nanowire since the ohmic contact will neutralize the electrical field generated at the tip. In

order to form an effective schottky contact, the electron affinity (Ea) must be smaller than


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the work function(φ) of the metal composing the counter electrode. For the case of ZnO

nanowire with the electron affinity of 4.5 eV, Pt (φ=6.1eV) is a suitable metal to construct

the schottky contact. By constructing the schottky contact, the electrons will pass to the

counter electrode from the surface of the tip when the counter electrode is in contact with

the regions of the negative potential, whereas no current will be generated when it is in

contact with the regions of the positive potential, in the case of n-type semiconductive

nanostructure (p-type semiconductive structure will exhibit the reversed phenomenon

since the hole is mobile in this case). The formation of the schottky contact also

contributes to the generation of direct current output signal consequently.

CASE 3.2: working principle(case 2)

FIG 3.2 Alternating current output

A model with a vertically grown nanowire stacked between the ohmic contact at

its bottom and the schottky contact at its top is considered. When the force is applied

toward the tip of the nanowire, the uniaxial compressive is generated in the nanowire.

Due to the piezoelectric effect, the tip of the nanowire will have a negative piezoelectric

potential, increasing the Fermi level at the tip. Since the electrons will then flow from the

tip to the bottom through the external circuit as a result, the positive electrical potential

will be generated at the tip. The schottky contact will barricade the electrons being

transported through the interface, therefore maintaining the potential at the tip. As the

force is removed, the piezoelectric effect diminishes, and the electrons will be flowing

back to the top in order to neutralize the positive potential at the tip. The second case will


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generate alternating current output signal.

3.3 Basic modes and mechanisms

3.3.1 Vertical Contact-Separation Mode

FIG 3.3. Vertical Contact-Separation

The working mechanism of the triboelectric nanogenerator can be described as the

periodic change of the potential difference induced by the cycled separation and re-

contact of the opposite triboelectric charges on the inner surfaces of the two sheets. When

a mechanical agitation is applied onto the device to bend or press it, the inners surfaces of

the two sheets will get into close contact and the charge transfer will begin, leaving one

side of the surface with positive charges and the other with negative charges. This is just

the triboelectric effect. When the deformation is released, the two surfaces with opposite

charges will separate automatically, so that these opposite triboelectric charges will

generate an electric field in between and thus induce a potential difference across the top

and bottom electrodes. In order to screen this potential difference, the electrons will be

driven to flow from one electrode to the other through the external load. The electricity

generated in this process will continue until the potentials of the two electrodes get back

to even again. Subsequently, when the two sheets are pressed towards each other again,

the triboelectric-charge-induced potential difference will begin to decrease to zero, so that

the transferred charges will flow back through the external load, to generate another

current pulse in the opposite direction. When this periodic mechanical deformation lasts,

the alternating current (AC) signals will be continuously generated.


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3.3.2 Lateral Sliding Mode

FIG 3.3. Lateral Sliding

There are two basic friction processes: normal contact, and lateral sliding. We

demonstrated here a TENG that is designed based on the in-plane sliding between the two

surfaces in lateral direction. With an intensive triboelectrification facilitated by sliding

friction, a periodic change in the contact area between two surfaces leads to a lateral

separation of the charge centers, which creates a voltage drop for driving the flow of

electrons in the external load. The sliding-induced electricity generation mechanism is

schematically depicted in the figure. In the original position, the two polymeric surfaces

fully overlap and intimately contact with each other. Because of the large difference in

the ability to attract electrons, the triboelectrification will leave one surface with net

positive charges and the other with net negative charges with equal density. Since the

tribo-charges on the insulators will only distribute in the surface layer and will not be

leaked out for an extended period of time, the separation between the positively charged

surface and negatively charged surface is negligible at this overlapping position, and thus

there will be little electric potential drop across the two electrodes. Once the top plate

with the positively charged surface starts to slide outward, the in-plane charge separation

is initiated due to the decrease in contact surface area. The separated charges will

generate an electric field pointing from the right to the left almost parallel to the plates,

inducing a higher potential at the top electrode. This potential difference will drive a

current flow from the top electrode to the bottom electrode in order to generate an electric


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potential drop that cancels the tribo-charge-induced potential. Because the vertical

distance between the electrode layer and the tribo-charged polymeric surface is negligible

compared to the lateral charge separation distance, the amount of the transferred charges

on the electrodes approximately equals to the amount of the separated charges at any

sliding displacement. Thus, the current flow will continue with the continuation of the

ongoing sliding process that keeps increasing the separated charges, until the top plate

fully slides out of the bottom plate and the tribo-charged surfaces are entirely separated.

The measured current should be determined by the rate at which the two plates are being

slid apart. Subsequently, when the top plate is reverted to slide backwards, the separated

charges begins to get in contact again but no annihilation due to the insulator nature of the

polymer materials. The redundant transferred charges on the electrodes will flow back

through the external load with the increase of the contact area, in order to keep the

electrostatic equilibrium. This will contribute to a current flow from the bottom electrode

to the top electrode, along with the second half cycle of sliding. Once the two plates reach

the overlapping position, the charged surfaces get into fully contact again. There will be

no transferred charges left on the electrode, and the device returns to the first state. In this

entire cycle.

3.3.3 Single-Electrode Mode

FIG 3.3. Single-Electrode


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A single-electrode-based triboelectric nanogenerator is introduced as a more

practical and feasible design for some applications such as fingertip-driven triboelectric

nanoagenerator. The working principle of the single-electrode TENG is schematically

shown in the figure by the coupling of contact electrification and electrostatic induction.

In the original position, the surfaces of skin and PDMS fully contact with each other,

resulting in charge transfer between them. According to the triboelectric series, electrons

were injected from the skin to the PDMS since the PDMS is more triboelectrically

negative than skin, which is the contact electrification process. The produced triboelectric

charges with opposite polarities are fully balanced/screened, leading to no electron flow

in the external circuit. Once a relative separation between PDMS and skin occurs, these

triboelectric charges cannot be compensated. The negative charges on the surface of the

PDMS can induce positive charges on the ITO electrode, driving free electrons to flow

from the ITO electrode to ground. This electrostatic induction process can give an output

voltage/current signal if the distance separating between the touching skin and the bottom

PDMS is appreciably comparable to the size of the PDMS film. When negative

triboelectric charges on the PDMS are fully screened from the induced positive charges

on the ITO electrode by increasing the separation distance between the PDMS and skin,

no output signals can be observed, as illustrated. Moreover, when the skin was reverted to

approach the PDMS, the induced positive charges on the ITO electrode decrease and the

electrons will flow from ground to the ITO electrode until the skin and PDMS fully

contact with each other again, resulting in a reversed output voltage/current signal.


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CHAPTER 4: APPLICATIONS OF TENG4.1 Powering pacemakers

Flexible piezoelectric Nano generator directly simulated a living rats heart using

electrical energy converted from the small body movements of the rat. This technology

could facilitate the use of self-powered flexible energy harvesters , not only prolonging

the life time of cardiac pacemakers but also realizing real-time heart monitoring

4.2 Harvesting energy from human body motion

Since there is abundant mechanical energy generated on human bodies in people's

everyday life, we can make use of the triboelectric nanogenerator to convert this amount

of mechanical energy into electricity, for charging portable electronics and biomedical

applications. This will help to greatly improve the convenience of people's life and

expand the application of the personal electronics. A packaged power-generating insole

with built-in flexible multi layered triboelectric Nanogenerator has been demonstrated,

which enable harvesting mechanical pressure during normal walking. The TENG used

here relies on the contact separation mode and is effective in responding to the periodic

compression of the insole. Using the insole as a direct power source, we develop a fully

packaged self-lighting shoe that has broad applications for display and entertainment

purposes.

4.3 Self-powered active strain/force sensorsAn triboelectric nanogenerator automatically generates an output voltage and

current once it is mechanically triggered. The magnitude or the output signal signifies the

impact of the mechanical deformation and its time-dependent behaviour. This is the basic

principle of the TENG can be applied as a self-powered pressure sensor. The voltage-

output signal can reflect the applied pressure induced by a droplet of water. All types of

TENGs have a high sensitivity and fast response to the external force and show as a sharp

peak signal. Furthermore, the response to the impact of a piece of feather (20 mg, ~0.4 Pa

in contact pressure) can be detected. The sensor signal can delicately show these details

of the entire process. The existing results show that our sensor can be applied for

measuring the subtle pressure in real life.


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In a case that we make a matric array of the triboelectric Nanogenerator, a large-

area, and self-powered pressure map applied on a surface can be realized. The response of

the TENG array with local pressure was measured through a multi-channel measurement

system. There are two types of output signals from the TENG: open circuit voltage and

short circuit current. The Open circuit voltage is only dictated by the final configuration

of the TENG after applying a mechanical triggering, so that it is a measure of the

magnitude of the deformation, which is attributed to the static information to be provided

by TENG. The output current depends on the rate at which the induced charge would

flow, so that the current signal is more sensitive to the dynamic process of how the

mechanical triggering is applied.

The active pressure sensor and the integrated sensor array based on the triboelectric

effect have several advantages over conventional passive pressure sensors. First, the

active sensor is capable of both static pressure sensing using the open-circuit voltage and

dynamic pressure sensing using the short-circuit current, while conventional sensors are

usually incapable of dynamic sensing to provide the loading rate information. Second, the

prompt response of both static and dynamic sensing enables the revealing of details about

the loading pressure. Third, the detection limit of the TENG for dynamic sensing is as

low as 2.1 Pa, owing to the high output of the TENG. Fourth, the active sensor array

presented in this work has no power consumption and could even be combined with its

energy harvesting functionality for self-powered pressure mapping. Future works in this

field involve the miniaturization of the pixel size to achieve higher spatial resolution, and

the integration of the TEAS matrix onto fully flexible substrate for shape-adaptive

pressure imaging.


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Chapter 5: ADVANTAGES & DISADVANTAGE5.1 Advantages

Piezoelectric and triboelectric Nanogenerator have enough output suitable for self

powered system

Triboelectric Nanogenerator the output is good and don’t need poling. Both

organic and inorganic material can be used based on triboelectric behaviour

The piezoelectric Nano generators could convert [mechanical movement, blood

pressure, vibration energy] into electric energy for self powering Nano devices

Nano generators can harvest waste energy from environment and thus being a

sustainable energy source

5.2Disadvantages Amount of power generated by Nano generators is comparatively small

Shelf-life means how long these material last, in other words organic materials

decay very quickly

Nano generators are limited to small duty cycle


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CHAPTER 6: FUTURE SCOPE & CONCLUSION6.1 Future Scope

Nanogenerator for harvesting mechanical energy; self-powered Nano

systems

Solar energy

Nano-piezotronics

Bio-interfacing, bio-inspired fabrication & bioengineering

Microscopy & functional materials

6.2 Conclusion

Miniaturization is the beauty of Nanogenerator.

Generation of power needs to be updated with inventions.

Further researches in this field can save the non-renewable source of

energy

The invention of Nano generators may prove to be the start of new era

in the history of man kind


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