nfc project report on wirless power transmission.doc

8/17/2019 NFC Project report on Wirless Power Transmission.doc

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LIST OF FIGURES

FIGURE 1: Animated View of Resonant Coupling .......................................................5FIGURE 2: Deliverable-Oriented Research plan............................................................1FIGURE 3: Comparison between !"#" and !$% s&stem.............................................1'

FIGURE 4: !ireless electricit& could ma(e this phenomenon a realit&........................15FIGURE 5: %he 1)*-ft !ardencl&ffe %ower +%esla %ower, in 1.............................1*FIGURE 6: /icrowave 0ower %ransmission.................................................................1*FIGURE 7: %he %ran receiving circuit for wireless power transmission...1FIGURE 8: 2&stem and method for wireless electrical power %ransmission................'FIGURE 9: $lectric 0ower %ransmission using 3A2$R...............................................'1FIGURE 10: shows a unidirectional pattern..................................................................'4FIGURE 11: shows a bidirectional antenna pattern.......................................................'*FIGURE 12: 0attern of omni-direcrional antenna.........................................................'FIGURE 13: $lectric toothbrush batter& charger..........................................................FIGURE 14: "nduction Coo(er 2tovetop......................................................................

FIGURE 15: Resonance Coupling between Coils........................................................'FIGURE 16: 3C switching circuit................................................................................4FIGURE 17: eginning of oscillations.........................................................................*FIGURE 18: time 167t...................................................................................................*FIGURE 19: time 16't...................................................................................................)FIGURE 20: time 67t...................................................................................................)FIGURE 21: Resonating circuit....................................................................................FIGURE 22: "mpedance curves of R83 9 C.................................................................7FIGURE 23: :ualit& #actor at different values of R....................................................7'FIGURE 24: Capacitor charged; voltage at < pea(8 inductor discharged.....7FIGURE 25: Capacitor discharging voltage decreasing inductor charging......7

FIGURE 26: Capacitor full& discharged and "nductor full& charged.......77FIGURE 27: Capacitor charging with opposite polarit& and inductor discharging......77FIGURE 28: Capacitor full& charged +-, and inductor full& discharged......77FIGURE 29: Capacitor discharging and inductor is charging......75FIGURE 30: Capacitor is full& discharged and inductor is full& charged +-,...75FIGURE 31: Capacitor charging and inductor is discharging..........74FIGURE 32: Capacitor full& charged +


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LIST OF TABLES

TABLE 1: 0ro@ect 0lan; 2chedule6phasingTABLE 2: "mpedances of R8 3 9 C......................7TABLE 3: A comparison of different t&pes of 0!/ "Cs.....................4'

TABLE 4: %ransmitter Circuit Components 3ist.......................*TABLE 5: Receiver Circuit Components 3ist...*1TABLE 6: %ransmitter and Receiver 0arameters..*

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ABSTRACT

%his thesis report e=plains the implementation of !ireless $lectric 0ower %ransmission

2&stem using Resonant Coupling. !e have designed two circuit first circuit is called

power sending circuit and second circuit is called receiving circuit. oth the circuits are

wor(ing on resonant coupling s&stem. "n this wa& power is wirelessl& transfer between

two resonant coils. %he device would plug into the wall and ad@ust the fre?uenc& of the

wall voltage to the resonant fre?uenc& of the 3C circuit +47 B, b& rectif&ing and

inverting the wall signal. After power is transmitted to the receiving 3C circuit8 this

voltage will be transformed8 rectified and filtered to produce around ''V to power up

''!att energ& saver bulbs at a contact less distance of 4 cm. %he power is wirelessl&

transmitted even if an& thic( obstacle is placed between transmitter and receiver. All the

bloc( diagrams8 e?uipment8 circuit elements have been completel& e=plained in the

report.


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CHAPTER 1

PROJECT OVERVIEW

Ob!"#$%!&"n this chapter8 the main focus is on describing the general structure. %his chapter is

mainl& concentrated on;

1., >oals and Ob@ectives

'., 2cope of the 0ro@ect

., 3iterature Review 2ummar&

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P'(!"# O%!'%$!)

1*1: P'(+(&!, Ob!"#$%!

Our main ob@ective is to develop a s&stem for !ireless $lectric 0ower %ransfer. %oda&8

portable technolog& is a part of ever& da& life. Baving &our stereo8 telephone or computer

tied to a wall is a thing of the past. ut from portabilit&8 emerges another challenge;

energ&. Almost all portable devices are batter& powered8 meaning that eventuall&8 the& all

must be rechargedt&ing the user bac( to the wall he was tr&ing to avoid.

Eow imagine that instead of plugging in &our cell phone8 laptop or mp pla&er to

recharge it8 it could receive its power wirelessl&?uite literall&8 Fout of thin airG. 2ound

li(e science fictionH "tIs much closer to realit& than &ou might thin(.

!ireless $lectric 0ower %ransmission is the process where electrical energ& is

transmitted from a power source to an electrical load8 without interconnecting wires.

#1g. 1 Animated View of Resonant Coupling J1K

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%he techni?ue being used for !ireless $lectric 0ower %ransfer is FR!&(-.-# C(/+$-*

%his techni?ue introduces a concept called FResonanceG to the wireless energ& e?uation.

2imilar to mutual induction8 wherein electricit& traveling along an electromagnetic wave

moves between coils on the same fre?uenc&8 Resonant Coupling functions on the concept

that if &ou ma(e both coils resonate at the same fre?uenc&8 electricit& can be passed

between them at farther distances and without health dangers. Lsing this techni?ue8 one

can even send electricit& to multiple devices at once8 as long as the& all share the same

resonance fre?uenc&.

%wo ob@ects of the same resonant fre?uenc& tend to e=change energ& efficientl&8 while

interacting wea(l& with ob@ects that have a different resonant fre?uenc&. "n ph&sics8

resonance is the tendenc& of an ob@ect to oscillate at ma=imum amplitude at a certain

fre?uenc&. "f the ob@ect is e=cited with a different fre?uenc&8 its oscillation will die down.

Coupling is particularl& suitable for ever&da& applications because most common

materials interact onl& ver& wea(l& with electromagnetic fields8 so interactions with

e=traneous environmental ob@ects are suppressed even further. %his ma(es it a safe design

for people and other living creatures.

%he crucial advantage of using the non-radiative field lies in the fact that most of the

power not pic(ed up b& the receiving coil remains bound to the vicinit& of the sending

unit8 instead of being radiated into the environment and lost. Although the two coils are

currentl& of identical dimensions8 it is possible to ma(e the device coil small enough to fit

into portable devices without decreasing the efficienc&. Lsing a non-radiative field means

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that most of the power not pic(ed up b& the receiving coil remains bound to the vicinit&

of the sending unit8 instead of being radiated into the environment and lost.

1*2: S"(+! .-, I-#'(,/"#$(- ( #! P'(!"# Ab'."# !e are tr&ing to investigate whether8 and to what e=tent8 the ph&sical phenomenon of

long-life time resonant electromagnetic states with localied slowl&-evanescent field

patterns can be used to transfer energ& efficientl& over non-negligible distances8 even in

the presence of e=traneous environmental ob@ects. Via detailed theoretical and numerical

anal&ses of t&pical real-world model-situations and realistic material parameters8 we can

establish that such a non-radiative scheme can lead to Fstrong couplingG between two

medium-ranges distant such states and thus could indeed be practical for efficient

medium-range wireless energ& transfer.

!e investigate the feasibilit& of using long-lived oscillator& resonant electromagnetic

modes8 with localied slowl&-evanescent field patterns8 for efficient wireless non-

radiative mid-range energ& transfer J)K. %he proposed method is based on the well

(nown principle of resonant coupling +the fact that two same-fre?uenc& resonant ob@ects

tend to couple8 while interacting wea(l& with other off-resonant environmental ob@ects,

and8 in particular8 resonant evanescent coupling +where the coupling mechanism is

mediated through the overlap of the non-radiative near-fields of the two ob@ects,. %his

well (nown ph&sics leads triviall& to the result that energ& can be efficientl& coupled

between ob@ects in the e=tremel& near field +e.g. in optical waveguide or cavit& couplers

and in resonant inductive electric transformers,. Bowever8 it is far from obvious how this

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same ph&sics performs at mid-range distances and8 to our (nowledge8 there is no wor( in

the literature that demonstrates efficient energ& transfer for distances a few times larger

that the largest dimension of both ob@ects involved in the transfer. "n the present paper8

our detailed theoretical and numerical anal&sis shows that such an efficient mid-range

wireless energ&-e=change can actuall& be achieved8 while suffering onl& modest transfer

and dissipation of energ& into other off-resonant ob@ects8 provided the e=change s&stem is

carefull& designed to operate in a regime of Fstrong couplingG compared to all intrinsic

loss rates. %he ph&sics of Fstrong couplingG is also (nown but in ver& different areas8

such as those of light-matter interactions. "n this favorable operating regime8 we

?uantitativel& address the following ?uestions; up to which distances can such a scheme

be efficient and how sensitive is it to e=ternal perturbationsH %he omni directional but

stationar& +lossless, nature of the near field ma(es this mechanism suitable for mobile

wireless receivers. "t could therefore have a variet& of possible applications including for

e=ample8 placing a source +connected to the wired electricit& networ(, on the ceiling of a

factor& room8 while devices +robots8 vehicles8 computers8 or similar, are roaming freel&

within the room..

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1*3: P'(!"# P.-: SCHEULE PHASIG

No.

Elapsed

timefrom start

(inmonths) of the project

Milestone Deliverables

1. 1 /onths "nitial 3iterature Review

A comprehensive report on stud&and anal&sis of different methods of$lectric 0ower %ransmission

'. /onths

2tud& of FCoupling /ode

%heor&G

A Comprehensive Report on stud&of Coupling /ode %heor& 9 "ts

Applications in Real 3ife 9 Bow itCan be Belpful in Our 0ro@ect

. 5 /onths2tud& of ResonantCoupling

Report on F Resonant Coupling F9 its iological $ffects 9 effectson other Eon-Resonating Ob@ects

7. 4 /onths

Bardware DesigningDesigning of F%ransmitter-ReceiverG s&stem for !ireless

%ransmission of $lectric 0ower in4cm range

5. 1 /onths Bardware "mplementations"mplementation of a F%ransmitter-ReceiverG s&stem for !ireless%ransmission of $lectric 0ower in4cm range

4. 11 /onths

Compilation anddocumentationof the e=perimental results

and publication of research paper

#inal 0ro@ect Report and proposal#or future wor(.

Table 1 Project Plan: Schedule / Phasing


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#ig. ' J1K

1*4: L$#!'.#/'! R!%$!) S/.'; "n our present electricit& generation s&stem we waste more than half of its resources.

$speciall& the transmission and distribution losses are the main concern of the present

power technolog&. /uch of this power is wasted during transmission from power plant

generators to the consumer. %he resistance of the wire used in the electrical grid

distribution s&stem causes a loss of '4-M of the energ& generated. %his loss implies

that our present s&stem of electrical distribution is onl& *-*7M efficient. !e have to

thin( of alternate state - of - art technolog& to transmit and distribute the electricit&. Eow-

a- da&s global scenario has been changed a lot and there are tremendous development in

ever& field. "f we donIt (eep pace with the development of new power technolog& we

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have to face a decreasing trend in the development of power sector. %he transmission of

power without wires ma& be one noble alternative for electricit& transmission.

"n the earl& da&s of electromagnetism8 before the electrical-wire grid was deplo&ed8

serious interest and effort was devoted +most notabl& b& Ei(ola %esla J1K, towards the

development of schemes to transport energ& over long distances without an& carrier

medium +e.g. wirelessl&,. %hese efforts appear to have met with little success. Radiative

modes of omni-directional antennas +which wor( ver& well for information transfer, are

not suitable for such energ& transfer8 because a vast ma@orit& of energ& is wasted into free

space. Directed radiation modes8 using lasers or highl&-directional antennas8 can be

efficientl& used for energ& transfer8 even for long distances +transfer distance LTRANS »L DEV 8

where L DEV is the characteristic sie of the device,8 but re?uire e=istence of an

uninterruptible line-of-sight and a complicated trac(ing s&stem in the case of mobile

ob@ects. Rapid development of autonomous electronics of recent &ears +e.g. laptops8 cell-

phones8 house-hold robots8 that all t&picall& rel& on chemical energ& storage, @ustifies

revisiting investigation of this issue. %oda&8 we face a different challenge than %esla;

since the e=isting electrical-wire grid carries energ& almost ever&where8 even a medium-

range + LTRANS N few∗ L DEV , wireless energ& transfer would be ?uite useful for man&

applications. %here are several currentl& used schemes8 which rel& on non-radiative

modes +magnetic induction,8 but the& are restricted to ver& close-range + LTRANS «L DEV , or

ver& low-power +m!, energ& transfers J'8 8 78 58 4K.

>etting around these issues is tric(&. %here have been a number of moderatel& successful

efforts to ma(e wor(ing s&stems8 mostl& based on near-contact +i.e.8 centimeter-range,

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power transfer. %hese use the sort of magnetic field induction found in a transformer or

an induction motor8 both of which rel& on a non radiating FevanescentG field that reduces

the power lost to radiation. ut the power transfer falls off ver& steepl& and the range is

ver& short. %he result is a powered pad on which a suitabl& enabled device can be placed

to chargePwireless indeed8 but not ver& mobile. %hese issues can be handled b& ma(ing

both the FsenderG and the FreceiverG of electrical power operate at the same fre?uenc&.

#1g. Comparison between !"#" and !$% s&stem J'K

!ith carefull& chosen parameters8 the two coils form a single coupled resonant structure

and behave as though a FtunnelG was opened between them that can carr& substantial

power over ranges of several meters. %he deca& in the coupling between the source and

receiver with increasing source receiver separation is still ?uite steep relative to sunlight-

st&le radiative transfer. Bowever8 this no longer translates directl& into a deca& of power

transfer efficienc&8 because un-transferred power remains trapped around the source and

all the power could still be transferred with ideal components. %his techni?ue cannot in

realit& e=tend the range indefinitel&P for e=ample8 the power trapped around the source

will tend to rise unacceptabl&8 and imperfect real components will cause lossesPbut it

does help a lot.

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And there is another li(el& benefit from the use of these resonances8 which addresses the

possible health concern. Lnli(e a freel& propagating electromagnetic wave +such as

sunlight,8 where the electric and magnetic components are alwa&s of similar intensit& on

average8 these resonances are overwhelmingl& magnetic in character. %his could be

e=tremel& helpful in reducing the haard to health8 because most ordinar& materials

+including people, interact far more strongl& with the electric than with the magnetic

component of an electromagnetic wave J'4K8 so the absorbed power can be much less for

a given amount of power transferred. %his helps efficienc& but8 far more important8 it

reduces the microwave ovenst&le heating within brain tissue that defines the (nown

haard limits for all radiofre?uenc& devices such as mobile phones. %his effect has not

&et been proven b& standard safet& tests8 but it loo(s ver& promising.

CHAPTER 2

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HISTOR<

Ob!"#$%!&

"n this chapter8 the need for a !ireless 2&stem of $nerg& %ransmission and the various

earlier technologies available so far for wireless transmission of electricit& and is being

discussed to find its possibilit& in actual practices8 their advantages8 disadvantages and

economical consideration. %his chapter is mainl& concentrated on;

1., %he most popular concept (nown as %esla %heor&.

'., %he microwave power transmission +/0%, called solar power satellite.

., %he highl& efficient fiber lasers for wireless power transmission.

HISTOR<

2*1: ITROUCTIO

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%oda&8 portable technolog& is a part of ever& da& life. Baving &our stereo8 telephone or computer

tied to a wall is a thing of the past. ut from portabilit& emerges another challenge; energ&.

Almost all portable devices are batter& powered8 meaning that eventuall&8 the& all must be

recharged8 t&ing the user bac( to the wall he was tr&ing to avoid.

Eow imagine that instead of plugging in &our cell phone8 laptop or mp pla&er to recharge it8 it

could receive its power wirelessl&?uite literall&8 Fout of thin airG. %he power is wirelessl&

transmitted even if an& thic( obstacle is placed between transmitter and receiver.

#ig; 7 !ireless electricit& could ma(e this phenomenon a realit& JK

"n our present electricit& generation s&stem we waste more than half of its resources. $speciall&

the transmission and distribution losses are the main concern of the present power technolog&.

/uch of this power is wasted during transmission from power plant generators to the consumer.

%he resistance of the wire used in the electrical grid distribution s&stem causes a loss of '4-M

of the energ& generated. %his loss implies that our present s&stem of electrical distribution is onl&

*-*7M efficient. !e have to thin( of alternate state - of - art technolog& to transmit and

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distribute the electricit&. Eow- a- da&s global scenario has been changed a lot and there are

tremendous development in ever& field. "f we donIt (eep pace with the development of new

power technolog& we have to face a decreasing trend in the development of power sector. %he

transmission of power without wires ma& be one noble alternative for electricit& transmission.

2*2: THE E=ISTIG TECHOLOGIES AVAILABLE

In this remar(able discover& of the Q%rue !irelessQ and the principles upon which transmission

and reception8 even in the present da& s&stems8 are based8 Dr. Ei(ola %esla shows us that he is

indeed the Q#ather of the !ireless.Q %he most well (nown and famous !ardencl&ffe %ower +%esla

%ower, was designed and constructed mainl& for wireless transmission of electrical power8 rather

than telegraph&. %he most popular concept (nown is %esla %heor& in which it was firml& believed

that !ardencl&ffe +#ig.1, would permit wireless transmission and reception across large distances

with negligible losses. "n spite of this he had made numerous e=periments of high ?ualit& to

validate his claim of possibilit& of wireless transmission of electricit&. ut this was an unfortunate

incidence that people of that centur& was not in a position to recognie his splendid wor(

otherwise toda& we ma& transmit electricit& wirelessl& and will convert our mother earth a

wonderful adobe full of electricit&.

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#ig.5; %he 1)*-ft !ardencl&ffe %ower +%esla %ower, in 1. J7K

%he modern ideas are dominated b& microwave power transmission +/0%8 #igure , called 2olar

power satellite to be built in high earth orbit to collect sunlight and convert that energ& into

microwaves8 then beamed to a ver& large antenna on earth8 the microwaves would be converted

into conventional electrical power.

!illiam C. rown J'1K8 the leading authorit& on wireless power transmission technolog&8 has

loaned this demonstration unit to the %e=as 2pace >rant Consortium to show how power can be

transferred through free space b& microwaves. A bloc( diagram of the demonstration components

is shown below.

%he primar& components include a microwave source8 a transmitting antenna8 and a receiving

antenna.

#ig.4; /icrowave power transmission. J5K

%he microwave source consists of a microwave oven magnetron with electronics to control the

output power. %he output microwave power ranges from 5 ! to ' ! at '.75 >B. A coa=ial

cable connects the output of the microwave source to a coa=-to-waveguide adapter. %his adapter

is connected to a waveguide ferrite circulator which protects the microwave source from reflected

power. %he circulator is connected to a tuning waveguide section to match the waveguide

impedance to the antenna input impedance. %he slotted waveguide antenna consists of )

waveguide sections with ) slots on each section. %hese 47 slots radiate the power uniforml&

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through free space to the antenna. %he slotted waveguide rectenna is ideal for power transmission

because of its high aperture efficienc& + 5M, and high power handling capabilit&. A rectif&ing

antenna called a rectenna receives the transmitted power and converts the microwave power to

direct current +DC, power. %his demonstration rectenna consists of 4 rows of dipoles antennas

where ) dipoles belong to each row. $ach row is connected to a rectif&ing circuit which consists

of low pass filters and a rectifier. %he rectifier is a >a As 2chott(& barrier diode that is impedance

matched to the dipoles b& a low pass filter. %he 4 rectif&ing diodes are connected to light bulbs

for indicating that the power is received. %he light bulbs also dissipated the received power. %his

rectenna has a '5M collection and conversion efficienc&8 but rectennas have been tested with

greater than M efficienc& at '.75 >BJ''K. %he transmission of power without wires is not a

theor& or a mere possibilit&8 it is now a realit&. %he electrical energ& can be economicall&

transmitted without wires to an& terrestrial distance8 man& researchers have established in

numerous observations8 e=periments and measurements8 ?ualitative and ?uantitative. %hese have

demonstrated that it is practicable to distribute power from a central plant in unlimited amounts8

with a loss not e=ceeding a small fraction of one per cent8 in the transmission8 even to the greatest

distance8 twelve thousand miles - to the opposite end of the globe. %his seemingl& impossible feat

can now be readil& performed b& electrical researchers familiar with the design and construction

of m& Qhigh-potential magnif&ing transmitter8Q %here were three popular theories present in the

literature of the late 1)Ss and earl& 1Ss. %he& were;

1. %ransmission through or along the $arth8

'. 0ropagation as a result of terrestrial resonances8

. Coupling to the ionosphere using propagation through electrified gases +#ig.795,.

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#ig.*; %he %rans receiving circuit for wireless power transmission J4K

"t has been proven that electrical energ& can be propagated around the world between the surface

of the $arth and the ionosphere at e=treme low fre?uencies in what is (nown as the 2chumann

Cavit&. nowing that a resonant cavit& can be e=cited and that power can be delivered to that

cavit& similar to the methods used in microwave ovens for home use8 it should be possible to

resonate and deliver power via the 2chumann Cavit& to an& point on $arth. %his will result in

practical wireless transmission of electrical power. %he intent of the e=periments and the

laborator& %esla had constructed was to prove that wireless transmission of electrical power was

possible. Although %esla was not able to commerciall& mar(et a s&stem to transmit power around

the globe8 modern scientific theor& J'K and mathematical calculations support his contention that

the wireless propagation of electrical power is possible and a feasible alternative to the e=tensive

and costl& grid of electrical transmission lines used toda& for electrical power distribution.

0ower transmission s&stem using directional ultrasound for power transmission includes a

transmitting device and a receiving device. %he transmitting device has a set of ultrasound

transducers forming an ultrasound transducer arra&8 where in the arra& is a set of spaced

individual transducers placed in the T-U plane disposed to generate anJ'*K ultrasound beam in

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the direction +#ig.4,. Another possibilit& is to use highl& efficient fiber lasers for wireless

power transmission where the possibilities are similar to microwaves concept but lasers emit

energ& at fre?uencies much higher that microwaves. #or several &ears EA2A8 $E%$CB8 and

LAB have been wor(ing on various aspects of collection of the laser radiation and conversion to

electrical power for laser wireless power transmission.

#ig.); 2&stem and method for wireless electrical power %ransmission +directional ultrasound for power %ransmission,. J5K

3aser technolog& can also be used to transmit electric power wirelessl& over a long distance. %his

technolog& is used b& EA2A to transmit high electric power to their remote satellite or to their

robots present on moon for the research wor(. J'7K %he onl& disadvantage of the 3aser is that it

wor(s onl& in direct line of sight so it can be interrupted b& obstacle.

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#ig. $lectric 0ower %ransmission using 3A2$R J*K

2*3: >ERITS? E>ERITS @ ECOO>ICS OF EARLIERWIRELESS TECHOLOGIES

>!'$#&

An electrical distribution s&stem8 based on this method would eliminate the need for an

inefficient8 costl&8 and capital intensive grid of cables8 towers8 and substations. %he s&stem would

reduce the cost of electrical energ& used b& the consumer and rid the landscape of wires8 cables8

and transmission towers J'5K. %here are areas of the world where the need for electrical power

e=ists8 &et there is no method for delivering power. Africa is in need of power to run pumps to tap

into the vast resources of water under the 2ahara Desert. Rural areas8 such as those in China8

re?uire the electrical power necessar& to bring them into the 'th centur& and to e?ual standing

with western nations. %he wireless transmission will solve man& of these problems the electrical

energ& can be economicall& transmitted without wires to an& terrestrial distance8 so there will be

no transmission and distribution loss. /ore efficient energ& distribution s&stems and sources are

needed b& both developed and under developed nations. "n regards to the new s&stems8 the

mar(et for wireless power transmission is enormous. "t has the potential to become a multi-billion

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dollar per &ear mar(et. %he increasing demand for electrical energ& in industrial nations is well

documented. "f we include the demand of third J')K world nations8 pushed b& their increasing rate

of growth8 we could e=pect an even faster rise in the demand for electrical power in the near

future. %hese s&stems can onl& meet these re?uirements with 7 Mefficient transmission.

Bigh %ransmission "ntegrit& and 3ow 3oss; %o transmit wireless power to an& distance without

limit. "t ma(es no difference what the distance is. %he efficienc& of the transmission can be as

high as 4 or * per cent8 and there are practicall& no losses.

!!'$#&

B$(($". I+."#

One common criticism of the %esla wireless power s&stem is regarding its possible biological

effects. Calculating the circulating reactive power8 it was found that the fre?uenc& is ver& small

and such a fre?uenc& is ver& biologicall& compatible.

2*4: E"(-($" I+."#

%he concept loo(s to be costl& initiall&. %he investment cost of %esla %ower was W158 +15,.

"n terms of economic theor&8 man& countries will benefit from this service. Onl& private8

dispersed receiving stations will be needed. Xust li(e television and radio8 a single resonant energ&

receiver is re?uired8 which ma& eventuall& be built into appliances8 so no power cord will be

necessar&Y /onthl& electric utilit& bills from old-fashioned8 fossil-fuelled8 loss prone electrified

wire-grid deliver& services will be optional8 much li(e Fcable %VG of toda&. "n the '1st centur&8

FDirect %VG is the rage8 which is an e=act parallel of %eslaIs FDirect $lectricit&.G

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CHAPTER 3

WIRELESS TECHOLOGIES

Ob!"#$%!&"n this chapter the reader ma& find a discussion of the issues involved so that one can

ma(e an informed decision on the antenna t&pe as per need. And the various wireless

technologies available so far for wireless transmission are being discussed. %he chapter

includes;

1., R.,$.#$%! >!#(,

• Lni- Directional

• Omni Directional

'., (- R.,$.#$%! >!#(,

• Resonant Coupling

• /agnetic "nduction

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WIRELESS TECHOLOGIES

3*1: I-#'(,/"#$(-

Concurrent with steadil& increasing signal fre?uencies B# and microwave antennas get more and

more important for applications such as broadband transmission lin(s8 radar remote sensing 6

navigation8 and wireless transfer of high data rates. /ost actual developments li(e satellite and

mobile communications are strongl& e=panding all over the world. /iniaturied antenna sensor

arra&s support novel techni?ues of detection of earth resources8 control of soil 6 water

contamination8 robotics8 etc.

3*2: A-#!--. C.'."#!'$$"&

%he stud& of antennas involves the following terms with which we must become familiar;

3*2*1: A-#!--. R!"$+'("$#;

%he abilit& of an antenna to both transmit and receive electromagnetic energ& is (nown as its

reciprocit&. Antenna reciprocit& is possible because antenna characteristics are essentiall& the

same for sending and receiving electromagnetic energ&.

$ven though an antenna can be used to transmit or receive8 it cannot be used for both functions at

the same time. %he antenna must be connected to either a transmitter or a receiver.

3*2*2: A-#!--. F!!, P($-#

#eed point $& the point on an antenna where the R# cable is attached. "f the R# transmission line

is attached to the base of an antenna8 the antenna is end-fed* "f the R# transmission line is

connected at the center of an antenna8 the antenna is mid-fed or center-fed*

'7


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3*2*3: $'!"#$%$#;

%he directivit& of an antenna refers to the width of the radiation beam pattern. A directional

antenna concentrates its radiation in a relativel& narrow beam. "f the beam is narrow in either the

horiontal or vertical plane8 the antenna will have a high degree of directivit& in that plane. An

antenna can be highl& directive in one plane onl& or in both planes8 depending upon its use.

3*3 R.,$.#$%! >!#(,

"n general8 we use three terms to describe the t&pe of Radiative ?ualities associated with an

antenna;

• Omni- directional

• i- directional

• Lni- directional

Omni directional antennas radiate and receive e?uall& well in all directions8 e=cept off the

ends. idirectional antennas radiate or receive efficientl& in onl& two directions. Lnidirectional

antennas radiate or receive efficientl& in onl& one direction. /ost antennas used in naval

communications are either omni directional or unidirectional. idirectional antennas are rarel&

used.

3*3*1: U-$ $'!"#$(-. @ B$ $'!"#$(-. >!#(,

>ain and directivit& are intimatel& related in antennas. %he directivit& of an antenna is a

statement of how the R# energ& is focused in one or two directions. ecause the amount

of R# energ& remains the same8 but is distributed over less area8 the apparent signal

strength is higher. %his apparent increase in signal strength is the antenna gain. %he gain

is measured in decibels over either a dipole +dd, or a theoretical construct called an

'5


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isotropic radiator +di,. %he isotropic radiator is a spherical signal source that radiates

e?uall& well in all directions. One wa& to view the omni- directional pattern is that it is a

slice ta(en horiontall& through the three dimensional sphere.

#igure 1 J)K shows a unidirectional pattern such as found on Uagi and ?uad beams and

certain other antennas. %he main lobe is the direction of ma=imum radiation or reception.

"n addition to the main lobe8 there are also sidelobes and bac(lobes. %hese lobes represent

lost energ& so good antenna designs attempt to minimie them. "n the unidirectional

antenna pattern8 signals QAQ8 QCQ and QDQ are suppressed8 while signal QQ is ma=imied.

%he beam widt of the antenna is a measure of its directivit&. "n the case of the pattern of

3ocal installation factors can affect the radiation pattern. "n Qfree space8Q i.e. the antenna

is installed at great distance from the surface of the $arth8 trees8 houses8 wiring and so

forth8 the pattern will be nearl& perfect. ut in practical situations8 the two lobes might

not be e?ual8 or the minima might be less distinct.

'4


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#ig. 11 J)K shows a bidirectional antenna pattern. %his pattern is associated with half

wavelength dipoles8 ?uad loops8 and a number of other antennas. %here are two preferred

directions +ma=ima, and two null directions +minima,. "n the half wavelength dipole the

minima and ma=ima are positioned as shown. #or receivers8 signals arriving from the

direction of the minima +2ignal QAQ and 2ignal QCQ, are suppressed because the antenna

is not sensitive in that direction. %he suppression is not complete8 but it can be

tremendous. %he signals arriving from the direction of the ma=ima +2ignal QQ and

2ignal QDQ, are received the loudest. #or transmitters8 the radiated signal is the lowest in

the direction of the minima and greatest in the direction of the ma=ima. Again8 the signal

level radiated off the ends of the antenna8 i.e. in the direction of the minima8 is not ero8

but is ver& low.

'*


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"t is common practice to mount unidirectional antennas in a manner that allows the main

lobe to be positioned in an& direction. %his approach is easil& achievable on the higher

fre?uencies of the B# shortwave bands and throughout the VB#6LB# spectrum. At lower

fre?uencies8 however8 the sie of the antenna is usuall& too large. #or e=ample8 the Uagi

beam uses elements about half wavelength long8 so at 15-/B the elements are about

.5- meters +1.'-feet, long. At 7 /B8 on the other hand8 the& are 4-meters +11)-feet,

long. #or an& given installation a decision has to be made on the mechanical aspects

because the larger beams are also ver& e=pensive to install.

3*3*2: O-$ $'!"#$(-. >!#(,

%he omni- directional antenna radiates or receives e?uall& well in all directions. "t is also

called the Qnon-directionalQ antenna because it does not favor an& particular direction.

#igure 1 shows the pattern for an omni- directional antenna8 with the four cardinal

signals. %his t&pe of pattern is commonl& associated with verticals8 ground planes and

other antenna t&pes in which the radiator element is vertical with respect to the $arthSs

surface.

')


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#ig. 1' 0attern of omni-direcrional antenna J)K

%he (e& factor to note is that for receivers all four signals +or signals from an! direction8

for that matter, are received e?uall& well. #or transmitters8 the radiated signal has the

same strength in all directions. %his pattern is useful for broadcasting a signal to all points

of the compass +as when calling QC:Q,8 or when listening for signals from all points.

3*4: (- R.,$.#$%! >!#(,

"n general8 we use two terms to describe the t&pe of Eon- Radiative ?ualities associated with an

antenna;

• /agnetic "nduction

• Resonant Coupling

'


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3*4*1: >.-!#$" I-,/"#$(-

%he action of an electrical #'.-&('!' is the simplest instance of wireless energ& transfer. %he

primar& and secondar& circuits of a transformer are electricall& isolated from each other. %he

transfer of energ& ta(es place b& electroCoupling through a process (nown as /#/. $-,/"#$(-.

+An added benefit is the capabilit& to step the primar& voltage either up or down., %he electric

toothbrush charger is an e=ample of how this principle can be used. %he main drawbac( to

induction8 however8 is the short range. %he receiver must be in ver& close pro=imit& to the

transmitter or induction unit in order to inductivel& couple with it.

A++$".#$(-&

• %he electric toothbrush batter& charger.

#ig. 1 $lectric toothbrush batter& charger JK

• %he induction coo(er stovetop.

#ig.17 "nduction Coo(er 2tovetop J1K


31/88

"t can be argued the coo(ware part of an induction coo(er is not a secondar& in the strictest sense

of the term. "t is more accuratel& described as the non-laminated core of an alternating-current

electromagnet8 in which edd& currents are induced resulting in the heating effect.

• A'#$$"$. !.'#& and other surgicall& implanted devices.

• Devices using induction to charge portable consumer electronics such as cell phones.

3*4*2: R!&(-.-"! C(/+$-

"n '48 the researchers at the /assachusetts "nstitute of %echnolog& applied the near field

behavior well (nown in electromagnetic theor& to a wireless power transfer concept based on

coupled resonators. "n a short theoretical anal&sis the& demonstrate that b& sending

electromagnetic waves around in a highl& angular waveguide8 evanescent waves are produced

which carr& no energ&. "f a proper resonant t waveguide is brought near the transmitter8 the

evanescent waves can allow the energ& to tunnel +specificall& evanescent wave coupling8 the

electromagnetic e?uivalent of tunneling, to the power drawing waveguide8 where the& can be

rectified into DC power. 2ince the electromagnetic waves would tunnel8 the& would not propagate

through the air to be absorbed or dissipated8 and would not disrupt electronic devices or cause

ph&sical in@ur& li(e microwave or radio wave transmission might. Researchers anticipate up to 5

meters of range for the initial device8 and are currentl& wor(ing on a functional protot&pe.

QResonant inductive couplingQ has (e& implications in solving the two main problems associated

with non-resonant inductive coupling and electromagnetic radiation8 one of which is caused b&

the otherZ distance and efficienc&. $lectromagnetic induction wor(s on the principle of a primar&

coil generating a predominantl& magnetic field and a secondar& coil being within that field so a

current is induced within its coils. %his causes the relativel& short range due to the amount of

power re?uired to produce an electromagnetic field. Over greater distances the non-resonant

induction method is inefficient and wastes much of the transmitted energ& @ust to increase range.

1

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%his is where the resonance comes in and helps efficienc& dramaticall& b& QtunnelingQ the

magnetic field to a receiver coil that resonates at the same fre?uenc&. Lnli(e the multiple-la&er

secondar& of a non-resonant transformer8 such receiving coils are single la&er solenoids with

closel& spaced capacitor plates on each end8 which in combination allow the coil to be tuned to

the transmitter fre?uenc& thereb& eliminating the wide energ& wasting Qwave problemQ and

allowing the energ& used to focus in on a specific fre?uenc& increasing the range.

#ig. 15 Resonance Coupling between Coils J11K

'

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CHAPTER 4

RESOAT COUPLIG

Ob!"#$%!&"n this chapter8 we are focusing on FResonant CouplingG8 the %echni?ue being used in our

0ro@ect. %his chapter is mainl& concentrated on;

1., %he idea of Resonance 9 its role in !$% 2&stem.

'., ehavior of a Resonant Circuit.

., Advantages of Resonant Coupling.


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R!&(-.-# C(/+$-

4*1: I-#'(,/"#$(-

!ireless $lectric 0ower %ransmission 2&stem is based on using coupled resonant ob@ects.

%wo ob@ects of the same resonant fre?uenc& tend to e=change energ& efficientl&8 while

interacting wea(l& with ob@ects that have a different resonant fre?uenc&. "n ph&sics8

resonance is the tendenc& of an ob@ect to oscillate at ma=imum amplitude at a certain

fre?uenc&. "f the ob@ect is e=cited with a different fre?uenc&8 its oscillation will die down.

%hin( of a swing for e=ample - a (id needs to pump his legs with the right rh&thm in

order to gain more momentum from it. %wo ob@ects with the same resonant fre?uenc&8

allowing them to e=change energ& efficientl&8 while not interacting strongl& with

e=traneous off-resonant ob@ects. 2uch strongl& coupled s&stems have the abilit& of

allowing relativel& efficient energ& transfer.

Another e=ample; weIve all heard the m&th about the opera singer brea(ing the glass with

a high note8 but has an&one ever seen it happening in real lifeH "tIs not actuall& a m&th8

though - if the singer sings a sufficientl& loud single note of the same fre?uenc& as the

natural fre?uenc& of the glass8 the latter will accumulate energ& until it finall& e=plodes.

%he e=ample of a room with 1 identical water glasses each filled with water up to a

different level8 so the& all have different resonant fre?uencies. "f an opera singer sings a

sufficientl& loud single note inside the room8 a glass of the corresponding fre?uenc&

might accumulate sufficient energ& to even e=plode8 while not influencing the other

glasses.

7


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!hile there are few different (inds of resonant s&stems8 our team focused on one

particular t&pe; magneticall& coupled resonators. !e have e=plored a s&stem of two

electromagnetic resonators8 each consist of a helical copper coil placed about '.5-feets

apart8 coupled mostl& through their electromagnetic fields. Lsing the mathematical

theor&8 we calculated the optimal sies of the coils in order to match their fre?uencies and

ma=imie the energ& transfer efficienc&.

4*2: R!&(-.-"!

"tSs hard to grasp the idea that electric circuits can resonate because we canSt see it

happening. 2till8 itSs one of the most useful and common forms of resonance.

Resonance can occur in something called an R3C circuit. %he letters stand for the

different parts of the circuit. R is for resistor. %hese are devices which convert electrical

energ& into thermal energ&. "n other words8 the& remove energ& from the circuit and

convert it to heat. 3 stands for inductor. +Bow the& came up with 3 for inductor is hard to

understand., "nductance in electric circuits is li(e mass or inertia in mechanical s&stems.

"t doesnSt do much until &ou tr& to ma(e a change. "n mechanics the change is a change in

velocit&. "n an electric circuit it is a change in current. !hen this happens inductance

resists the change. C is for capacitors which are devices that store electrical energ& in

much the same wa& that springs store mechanical energ&. An inductor concentrates and

stores magnetic energ&8 while a capacitor concentrates charge and thereb& stores electric

energ&.

5


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4*2*1: E-!'; F() $- .- E!"#'$" C$'"/$#

Of course8 the first step in understanding resonance in an& s&stem is to find the s&stemSs

natural fre?uenc&. Bere the inductor +3, and the capacitor +C, are the (e& components.

%he resistor tends to damp oscillations because it removes energ& from the circuit. #or

convenience8 weSll temporaril& ignore it8 but remember8 li(e friction in mechanical

s&stems8 resistance in circuits is impossible to eliminate.

(A) (B)

Fig. 16 LC switching circuit [12]

!e can ma(e a circuit oscillate at its natural fre?uenc& b& first storing electrical energ&

or8 in other words8 charging its capacitor as shown in #igure 14 +A,. !hen this is

accomplished the switch is thrown to the position shown in #igure 14 +,.

At time [ all of the electrical energ& is stored in the capacitor and the current is ero

+see #igure 1*,. Eotice that the top plate of the capacitor is charged positivel& and the

bottom negativel&. !e canSt see the electronsS oscillation in the circuit but we can measure

4


37/88

it using an ammeter and plot the current versus time to picture what the oscillation is li(e.

Eote that % on our graph is the time it ta(es to complete one oscillation.

Fig.17 [12]

Current flows in a cloc(wise direction +see #igure 1),. %he energ& flows from the

capacitor into the inductor. At first it ma& seem strange that the inductor contains energ&

but this is similar to the (inetic energ& contained in a moving mass.

Fig. 18 [12]

$ventuall& the energ& flows bac( into the capacitor8 but note8 the polarit& of the capacitor

is now reversed. "n other words8 the bottom plate now has the positive charge and the top

plate the negative charge +see #igure 1,.

*


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Fig. 19 [12]

%he current now reverses itself and the energ& flows out of the capacitor bac( into the

inductor +see #igure ',. #inall& the energ& full& returns to its starting point read& to

begin the c&cle all over again as shown in #igure 1*.

Fig. 20 [12]

The freuenc! "f the "sci##$ti"n c$n %e $&&r"'i$te $s f"##"ws*

"n real-world 3C circuits thereSs alwa&s some resistance which causes the amplitude of

the current to grow smaller with each c&cle. After a few c&cles the current diminishes to

)


39/88

ero. %his is called a Qdamped sinusoidalQ waveform. Bow fast the current damps to

ero depends on the resistance in the circuit. Bowever8 the resistance does not alter the

fre?uenc& of the sinusoidal wave. "f the resistance is high enough8 the current will not

oscillate at all.

Obviousl&8 where thereSs a natural fre?uenc& thereSs a wa& to e=cite a resonance. !e do

this b& hoo(ing an alternating current +AC, power suppl& up to the circuit as shown in

#igure '1. %he term alternating means that the output of the power suppl& oscillates at a

particular fre?uenc&. "f the fre?uenc& of the AC power suppl& and the circuit itSs

connected to are the same8 then resonance occurs. "n this case we measure the amplitude

or sie of the oscillation b& measuring current.

Fig. 21 [1+]

Eote in figure '1 that we have put a resistor bac( in the circuit. "f there is no resistor in

the circuit the currentSs amplitude will increase until the circuit burns up. "ncreasing

resistance tends to decrease the ma=imum sie of the currentSs amplitude but it does not

change the resonant fre?uenc&.

As a rule of thumb8 a circuit will not oscillate unless the resistance +R, is low enough to

meet the following condition;


40/88

4*2*1*1: I+!,.-"! ( "(+(-!-#&

3etSs recap what we now (now about voltage and current in linear components. %he

$+!,.-"! is the general term for the ratio of voltage to current. Resistance is the special

case of impedance when \ [ 8 reactance the special case when \ [ ] ^. %he table

below summaries the impedance of the different components. "t is eas& to remember that

the voltage on the capacitor is beind the current8 because the charge doesnSt build up

until after the current has been flowing for a while.

T$%#e 2 ,&e$nces "f - L / C [1]

%he same information is given graphicall& below. "t is eas& to remember the fre?uenc&

dependence b& thin(ing of the DC +ero fre?uenc&, behavior; at DC8 an inductance is a

short circuit +a piece of wire, so its impedance is ero. At DC8 a capacitor is an open

circuit8 as its circuit diagram shows8 so its impedance goes to infinit&.

Fig. 22 ,&e$nce cures "f -L / C [1]

7


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4*2*1*2: S!!"#$%$#; .-, /.$#; F."#(' ( . C$'"/$#

Resonant circuits are used to respond selectivel& to signals of a given fre?uenc& while

discriminating against signals of different fre?uencies. "f the response of the circuit is

more narrowl& pea(ed around the chosen fre?uenc&8 we sa& that the circuit has higher

Qselectivit&Q. A Q?ualit& factorQ :8 as described below8 is a measure of that selectivit&8 and

we spea( of a circuit having a Qhigh :Q if it is more narrowl& selective.

An e=ample of the application of resonant circuits is the selection of A/ radio stations

b& the radio receiver. %he selectivit& of the tuning must be high enough to discriminate

strongl& against stations above and below in carrier fre?uenc&8 but not so high as to

discriminate against the sidebands created b& the imposition of the signal b& amplitude

modulation.

%he selectivit& of a circuit is dependent upon the amount of resistance in the circuit. %he

smaller the resistance8 the higher the Q:Q for given values of 3 and C. %he parallel

resonant circuit is more commonl& used in electronics8 but the algebra necessar& to

characterie the resonance is much more involved. Lsing the same circuit parameters8 the

illustration at left shows the power dissipated in the circuit as a function of fre?uenc&.

2ince this power depends upon the s?uare of the current8 these resonant curves appear

steeper and narrower than the resonance pea(s for current above.

%he ?ualit& factor : is defined b&

where _` is the width of the resonant power curve at half ma=imum.

2ince that width turns out to be _` [R638 the value of : can also be e=pressed as

71

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%he : is a commonl& used parameter in electronics8 with values usuall& in the range of

:[1 to 1 for circuit applications.

#ig. ' :ualit& #actor at different values of R J15K

4*2*2: A- E!"#'$" P!-,//

Capacitors store energ& in the form of an electric field8 and electricall& manifest that

stored energ& as a potential; static voltage. "nductors store energ& in the form of a

magnetic field8 and electricall& manifest that stored energ& as a (inetic motion of

electrons; c"rrent . Capacitors and inductors are flip-sides of the same reactive coin8

storing and releasing energ& in complementar& modes. !hen these two t&pes of reactive

components are directl& connected together8 their complementar& tendencies to store

energ& will produce an unusual result.

"f either the capacitor or inductor starts out in a charged state8 the two components will

e=change energ& between them8 bac( and forth8 creating their own AC voltage and

7'


43/88

current c&cles. "f we assume that both components are sub@ected to a sudden application

of voltage +sa&8 from a momentaril& connected batter&,8 the capacitor will ver& ?uic(l&

charge and the inductor will oppose change in current8 leaving the capacitor in the

charged state and the inductor in the discharged state; +#igure '7,

#ig . '7 Capacitor charged; voltage at +


44/88

#ig. '4 Capacitor full& discharged and "nductor full& charged J14K

%he inductor will maintain current flow even with no voltage applied. "n fact8 it will

generate a voltage +li(e a batter&, in order to (eep current in the same direction. %he

capacitor8 being the recipient of this current8 will begin to accumulate a charge in the

opposite polarit& as before; +#igure '*,

#ig. '* Capacitor charging; voltage with opposite polarit& +-, and inductor dischargingJ14K

!hen the inductor is finall& depleted of its energ& reserve and the electrons come to a

halt8 the capacitor will have reached full +voltage, charge in the opposite polarit& as when

it started; +#igure '),

#ig. ') Capacitor full& charged +-, and inductor full& discharged J14K

77


45/88

Eow weSre at a condition ver& similar to where we started; the capacitor at full charge and

ero current in the circuit. %he capacitor8 as before8 will begin to discharge through the

inductor8 causing an increase in current +in the opposite direction as before, and a

decrease in voltage as it depletes its own energ& reserve; +#igure ',

#ig. ' Capacitor discharging and inductor charging J14K

$ventuall& the capacitor will discharge to ero volts8 leaving the inductor full& charged

with full current through it; +#igure ,

#ig. Capacitor full& discharged and inductor full& charged +-, J14K

%he inductor8 desiring to maintain current in the same direction8 will act li(e a source

again8 generating a voltage li(e a batter& to continue the flow. "n doing so8 the capacitor

will begin to charge up and the current will decrease in magnitude; +#igure 1,

75


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#ig#1 Capacitor charging and inductor discharging J14K

$ventuall& the capacitor will become full& charged again as the inductor e=pends all of

its energ& reserves tr&ing to maintain current. %he voltage will once again be at its

positive pea( and the current at ero. %his completes one full c&cle of the energ&

e=change between the capacitor and inductor; +#igure ',

#ig. ' Capacitor full& charged +


47/88

At the pea( height of each swing of a pendulum8 the mass briefl& stops and switches

directions. "t is at this point that potential energ& +height, is at a ma=imum and (inetic

energ& +motion, is at ero. As the mass swings bac( the other wa&8 it passes ?uic(l&

through a point where the string is pointed straight down. At this point8 potential energ&

+height, is at ero and (inetic energ& +motion, is at ma=imum. 3i(e the circuit8 a

pendulumSs bac(-and-forth oscillation will continue with steadil& dampened amplitude8

the result of air friction +resistance, dissipating energ&. Also li(e the circuit8 the

pendulumSs position and velocit& measurements trace two sine waves + degrees out of

phase, over time; +#igure ,

#ig. 0endulum energ& transfer J14K

"n ph&sics8 this (ind of natural sine-wave oscillation for a mechanical s&stem is called

2imple Barmonic /otion +often abbreviated as F2B/G,. %he same underl&ing principles

govern both the oscillation of a capacitor6inductor circuit and the action of a pendulum8

hence the similarit& in effect. "t is an interesting propert& of an& pendulum that its

periodic time is governed b& the length of the string holding the mass8 and not the weight

of the mass itself. %hat is wh& a pendulum will (eep swinging at the same fre?uenc& as

7*


48/88

the oscillations decrease in amplitude. %he oscillation rate is independent of the amount

of energ& stored in it.

%he same is true for the capacitor6inductor circuit. %he rate of oscillation is strictl&

dependent on the sies of the capacitor and inductor8 not on the amount of voltage +or

current, at each respective pea( in the waves. %he abilit& for such a circuit to store energ&

in the form of oscillating voltage and current has earned it the name tan( circuit. "ts

propert& of maintaining a single8 natural fre?uenc& regardless of how much or little

energ& is actuall& being stored in it gives it special significance in electric circuit design.

Bowever8 this tendenc& to oscillate8 or resonate8 at a particular fre?uenc& is not limited to

circuits e=clusivel& designed for that purpose. "n fact8 nearl& an& AC circuit with a

combination of capacitance and inductance +commonl& called an F3C circuitG, will tend

to manifest unusual effects when the AC power source fre?uenc& approaches that natural

fre?uenc&. %his is true regardless of the circuitSs intended purpose.

"f the power suppl& fre?uenc& for a circuit e=actl& matches the natural fre?uenc& of the

circuitSs 3C combination8 the circuit is said to be in a state of resonance. %he unusual

effects will reach ma=imum in this condition of resonance. #or this reason8 we need to be

able to predict what the resonant fre?uenc& will be for various combinations of 3 and C8

and be aware of what the effects of resonance are.

REVIEW:

• A capacitor and inductor directl& connected together form something called a

tan$ circ"it 8 which oscillates +or resonates, at one particular fre?uenc&. At that

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fre?uenc&8 energ& is alternatel& shuffled between the capacitor and the inductor in

the form of alternating voltage and current degrees out of phase with each

other.

• !hen the power suppl& fre?uenc& for an AC circuit e=actl& matches that circuitSs

natural oscillation fre?uenc& as set b& the 3 and C components8 a condition of

resonance will have been reached.

4*2*3: A++$".#$(-& ( R!&(-.-"!

E.+! 1: >.-!#$" L((+ A-#!--.

/agnetic loop antennas +also (nown as 2mall %ransmitting6Receiving 3oops, have a

small antenna sie compared to other antennas for the same wavelength. %he antenna is

t&picall& smaller than 167 wavelength of the intended fre?uenc& of operation. Antennas

for shortwave communication are t&picall& ver& large8 sometimes several hundred

meters. %he advantage of the magnetic loop is high efficienc& despite its small sie.

%he technical mechanism uses a capacitor to QenlargeQ the antenna and bring it to

resonance. %he disadvantage of this method is the low bandwidth of the antenna8 also

(nown as high :8 which limits efficient operation to a narrow fre?uenc& range. A high-:

can be advantageous8 however. 2ince well-tuned magnetic loops function best within a

narrow fre?uenc& range when tuned8 the& tend to re@ect harmonic noise from other R#

sources. %his (eeps the level of unwanted noise down as compared with wider-bandwidth

antennas.

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#ig. 7 /agnetic 3oop Antenna J1*K

As a result of the narrow operating bandwidth of the antenna8 if the fre?uenc& of

operation is changed8 the antenna needs to be retuned b& changing the capacitive value of

the antenna. andwidth is the usable fre?uenc& range of an antenna in relation to the area

of desired operation. !hen the antenna is operated outside of its bandwidth8 the energ&

from the transmitter is reflected bac( from the antenna8 down through the feed line bac(

to the transmitter. %he term bandwidth relates to the concept of 2tanding !ave Ratio or

2!R. !hen the reflected power e=ceeds a '.5;1 power reflection ratio +too much energ&

being reflected from the antenna bac( into the feed line, the antenna will not maintain its

performance characteristics. %his t&pe of condition relates specificall& to the antennaSs

abilit& to transmit radio energ& from the transmitter to the antenna.

%he magnetic loop antenna is an old antennaZ however8 man& militar&8 commercial8 and

amateur radio operators still use them toda&. %he /agnetic 3oop was widel& used in the

Vietnam !ar due to its high portabilit&.

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E.+! 2: A++$".#$(- $- O/' S;!

Our WET &;! relies on two coils. $lectricit&8 traveling along an electromagnetic

wave8 can #/--! from one coil to the other as long as the& both have the same resonant

fre?uenc&. %he effect is similar to the wa& one vibrating trumpet can cause another to

vibrate.

#ig. 5 /agnetic loop coil J1)K

As long as both coils are out of range of one another8 nothing will happen8 since the fields

around the coils arenSt strong enough to affect much around them. 2imilarl&8 if the two

coils resonate at different fre?uencies8 nothing will happen. ut if two resonating coils

with the same fre?uenc& get within a few meters of each other8 streams of energ& move

from the transmitting coil to the receiving coil. According to the theor&8 one coil can even

send electricit& to several receiving coils8 as long as the& all resonate at the same

fre?uenc&. %he researchers have named this -(-'.,$.#$%! !-!'; #'.-&!' since it

involves stationar& fields around the coils rather than fields that spread in all directions.

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4*3: A,%.-#.!& ( R!&(-.-# C(/+$-

C(/+$- is particularl& suitable for ever&da& applications because most common

materials interact onl& ver& wea(l& with electromagnetic fields8 so interactions with

e=traneous environmental ob@ects are suppressed even further. %his ma(es it a safe design

for people and other living creatures8 and in order to prove it8 the team released couple of

photos with themselves standing between the coils while the s&stem was operating. Bere

&ou can see that the s&stem still wor(s even when thereIs an obstruction in the middle;

%he crucial advantage of using the -(-'.,$.#$%! field lies in the fact that most of the

power not pic(ed up b& the receiving coil remains bound to the vicinit& of the sending

unit8 instead of being radiated into the environment and lost. Although the two coils are

currentl& of identical dimensions8 it is possible to ma(e the device coil small enough to fit

into portable devices without decreasing the !$"$!-";.

Bowever8 as the distance between the source and the device coils increases8 the efficienc&

of transfer decreases. 2till8 for laptop-sied coils8 power levels more than sufficient to run

a laptop can be transferred across a roomZ as long as the laptop is in a room e?uipped

with a source of such wireless power8 it would charge automaticall&8 without having to be

plugged in.

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CHAPTER 5

S ESIG

Ob!"#$%!&"n this chapter8 Bardware Design of !$% 2&stem is being discussed. Different 2&stem

Components and 0arameters are described in detail. %his chapter is mainl& concentrated

on;

1., 2&stem Components

'., /athematical !or(

., Cost of Design

7., Circuit Diagrams

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S ESIG

5*1: !%!(+!-# R!&!.'" >!#(,((;

$fficient mid-range power transfer occurs in particular regions of the parameter space

describing resonant ob@ects strongl& coupled to one another. Lsing coupled-mode theor&

to describe this ph&sical s&stem8 we obtain the following set of linear e?uations;

!here the indices denote the different resonant ob@ects

%he variables am+t , are defined so that the energ& contained in ob@ect m is am+t ,'8 m is the

resonant angular fre?uenc& of that isolated ob@ect8 and m is its intrinsic deca& rate +e.g.8

due to absorption and radiated losses,. "n this framewor(8 an uncoupled and undriven

oscillator with parameters and would evolve in time as e=p+i t t ,. %he mn [ nm

are coupling coefficients between the resonant

ob@ects indicated b& the subscripts8 and

% m+t , are driving terms.

!e limit the treatment to the case of two ob@ects8 denoted b& source and device8 such that

the source +identified b& the subscript 2, is driven e=ternall& at a constant fre?uenc&8 and

the two ob@ects have a coupling coefficient . !or( is e=tracted from the device +subscript

D, b& means of a load +subscript !, that

acts as a circuit resistance connected to the

device8 and has the effect of contributing an additional term ! to the unloaded device

ob@ectSs deca& rate D. %he overall deca& rate at the device is therefore SD [ D < !. %he

wor( e=tracted is determined b& the power dissipated in the load8 that is8 ' !aD+t ,'.

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/a=imiing the efficienc& of the transfer with respect to the loading !8 given $?.8 is

e?uivalent to solving an impedance-matching problem. One finds that the scheme wor(s

best when the source and the device are resonant8 in which case the efficienc& is

%he efficienc& is ma=imied when !6 D [J1< +

'

6 2 D,K

16'

.

"t is eas& to show that the (e&

to efficient energ& transfer is to have '6 2 D 1. %his is commonl& referred to as the

strong coupling regime. Resonance pla&s an essential role in this power transfer

mechanism8 as the efficienc& is improved b& appro=imatel& '6 D' + 14 for t&pical

parameters, relative to the case of inductivel& coupled non resonant ob@ects.

5*2 T!('!#$". (,! (' &!'!&(-.-# "($&

Our e=perimental realiation of the scheme consists of two self-resonant coils. One coil

+the source coil, is coupled inductivel& to an oscillating circuitZ the other +the device coil,

is coupled inductivel& to a resistive load +#ig. 1,. 2elf-resonant coils rel& on the interpla&

between distributed inductance and distributed capacitance to achieve resonance. %he

coils are made of an electricall& conducting wire of total length l and cross-sectional

radius a wound into a heli= of n turns8 radius r 8 and height . %o the best of our

(nowledge8 there is no e=act solution for a finite heli= in the literature8 and even in the

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case of infinitel& long coils8 the solutions rel& on assumptions that are inade?uate for our

s&stem.

F$* 36 J11K2chematic of the e=perimental setup. A is a single copper loop of radius '5

cm that is part of the driving circuit8 which outputs a sine wave with fre?uenc& 5 B.

2 and D are respectivel& the source and device coils referred to in the te=t. is a loop of

wire attached to the load +light bulb,. %he various s represent direct couplings between

the ob@ects indicated b& the arrows. %he angle between coil D and the loop A is ad@usted

to ensure that their direct coupling is ero. Coils 2 and D are aligned coa=iall&. %he direct

couplings between and A and between and 2 are negligible

!e start b& observing that the current must be ero at the ends

of the coil8 and we ma(e

the educated guess that the resonant modes of the coil are well appro=imated b&

sinusoidal current profiles along the length of the conducting wire. !e are interested in

the lowest mode8 so if we denote b& s the parameteriation coordinate along the length of

the conductor8 such that it runs from l 6' to


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As the coil is resonant8 the current and charge densit& profiles are 6' out of phase from

each other8 meaning that the real part of one is ma=imum when the real part of the other is

ero. $?uivalentl&8 the energ& contained in the coil is at certain points in time completel&

due to the current8 and at other points it is completel& due to the charge. Lsing

electromagnetic theor&8 we can define an effective inductance L and an effective

capacitance ( for each coil as follows;

where the spatial current J+', and charge densit& +', are obtained respectivel& from the

current and charge densities along the isolated coil8 in con@unction with the geometr& of

the ob@ect. As defined8 L and ( have the propert& that the energ& ) contained in the coil is

given b&

>iven this relation and the e?uation of continuit&8 the resulting resonant fre?uenc& is f [

16J' + L( ,16'K. !e can now treat this coil as a standard oscillator in coupled-mode theor&

b& defining a+t ,[J+ L6',16'K & +t ,.

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!e can estimate the power dissipated b& noting that the sinusoidal profile of the current

distribution implies that the spatial average of the pea( current s?uared is & '6'. #or a coil

with n turns and made of a material with conductivit& 8 we modif& the standard formulas

for ohmic + Ro, and radiation + Rr , resistance accordingl&;

%he first term in $? is a magnetic dipole radiation term +assuming r ' c6 8 where c is

the speed of light,Z the second term is due to the electric dipole of the coil and is smaller

than the first term for our e=perimental parameters. %he coupled-mode theor& deca&

constant for the coil is therefore [+ Ro


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!here + is the effective mutual inductance8 is the scalar potential8 A is the vector

potential8 and the subscript 2 indicates that the electric field is due to the source. !e then

conclude from standard coupled-mode theor& arguments that D2 [ 2D [ [ + 6

J'+ LS L D16',K. !hen the distance D between the centers of the coils is much larger than their

characteristic sie8 scales with the D dependence characteristic of dipole-dipole

coupling. oth and are functions of the fre?uenc&8 and 6 and the efficienc& are

ma=imied for a particular value of f 8 which is in the range 1 to 5 /B for t&pical

parameters of interest. %hus8 pic(ing an appropriate fre?uenc& for a given coil sie8 as we

do in this e=perimental demonstration8 pla&s

a ma@or role in optimiing the power

transfer.

5*3 F() $.'. ( #! S;!

#ig. * #low Diagram of 2&stem J1K

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5*3*1 AC #( C C(-%!'#!'

Q$lectronic power converterQ is the term that is used to refer to a power electronic circuit

that converts voltage and current from one form to anotherG.

%hese converters can be classified as;

• Rectifier converting an ac voltage to a dc voltage8

• "nverter converting a dc voltage to an ac voltage8

• Chopper or a switch-mode power suppl& that converts a dc voltage to another

dc voltage8 and

• C&clo-converter and c&clo-inverter converting an ac voltage to another ac

voltage.

"n our design8 we can use an AC to DC converter that converts ''V AC suppl& into

different DC values of 1'V8 1)V8 '7V8 4V.

"n this pro@ect we are using 17V 6 'A because of the 0ower limitations of the Oscillator

Circuit.

%he Circuit Diagram of this AC to DC converter is given as follows;

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#ig. ) AC to DC converter +0roteus *.4 sp7,

5*3*2 O&"$.#(' C$'"/$#

%he Output of AC to DC converter is than applied to an Oscillator Circuit. %he main

component being used in Oscillator circuit is PW> IC*

%he 0!/ "C is used for;

• /odulating the !idth of the 0ulse

• 0ulse-width modulation control wor(s b& switching the power supplied to the

coil on and off ver& rapidl&.

• %he DC voltage is converted to a s?uare-wave signal8 alternating between full& on

and ero8 giving the %ransmitter8 a series of power Q(ic(sF.

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A comparison of different t&pes of 0!/ "Cs is given in following table;

>.-/."#/'!' IC D ('. /&! C(!-#

STSG1524

S>PS >.; (+!'.#! .# /+ #( 100 ,/#; ";"!SG3525A

>.$ >A=038 S$-. !-!'.#$(-PW> (/#+/# (-; b!#)!!- 15 .-,

85* G!-!'.#!& #'$.-! @ &$-! ).%!&#((*

A#! U2352BPW> G!-!'.#('(' &+!!, "(-#'(( +('#.b! #((&

I-"/,!& $-#!'.#!, "/''!-# $$#$-"$'"/$#'; (' (/#+/# >OSFET&*

TI TL494 S>PS >. 90 ,/#; ";"!

TI UC2638PW> !-!'.#('(' (#(' "(-#'(

P'(%$,!& .-; (#!' !.#/'!& (' C(#(' &+!!, "(-#'(*

%able. A comparison of different t&pes of 0!/ "Cs

%he 0!/ "C named as 2>5'5A is the "C of our choice due to its different

characteristics as;

• ) %O 5 V O0$RA%"OE2

• 5.1 V R$#$R$EC$ %R"//$D %O ] 1 M

• 1 B %O 5 B O2C"33A%OR RAE>$

• 2$0ARA%$ O2C"33A%OR 2UEC %$R/"EA3

• ADXL2%A3$ D$AD%"/$ COE%RO3

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• "E%$REA3 2O#%-2%AR%

• 0L32$-U-0L32$ 2BL%DO!E

• "E0L% LED$RVO3%A>$ 3OCOL% !"%B BU2%$R$2"2

• 3A%CB"E> 0!/ %O 0R$V$E% /L3%"03$ 0L32$2

• DLA3 2OLRC$62"E OL%0L% DR"V$R2

5*3*2*1: I-&$,! SG3525A IC

%he bloc( diagram of 2>5'5A JA00$ED"T AK is as follows;

#ig. "nside 2>5'5A J'K

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#ollowing are the details of Operation for 0!/ "C;

• %he speed demand signal is input at pin '8 the op-amp non-inverting input.

• %he demand signal is then applied to the 0!/ comparator.

• %his compares the demand level with the oscillator output.

• %he fre?uenc& of the oscillator8 and therefore the 0!/ signal produced8 is

governed b& the value of the resistor to ground on the R% pin.

• %he s&nc and osc out pins are not re?uired for our purpose.

• %he soft start feature prevents the output from saturating at 1M ratio when the

chip is powering up.

• %he 2hutdown input is an active-high input that immediatel& shuts down the

outputs8 and resets the soft-start feature.

%he Circuit Diagram for the Oscillator Circuit is given as follows;

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#ig. 7 %ransmitter Circuit +0roteus *.4 sp7,5*3*3: T! T'.-&$##!' C$'"/$# C.+."$#('& .-, C($

%he ver& basic e?uation governing our pro@ect wor( is;

( 1 2 L C

"nductance +3, of the coil ; 3 [ .14 uB

Capacitance ; C [ n#

Resonant fre?uenc& +f,; # [ 47 B

Capacitive Reactance; TC [ .47''

"nductive Reactance; T3 [ .47

%he "nductance +3, is measured & using e?.

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L ( RK-8R.2

On the transmission side 3C circuit we connected capacitor with value of n#. A coil

with following parameters is used;

O/#!' "($:

Eo. of %urns E [ 1

Radius of Coil R [ 17.*5mm

Diameter of the coil D [ ')*.5mm

!ire radius a [ 1)um

Bence8

Value 3 [ 11.1) mB

>$,,! "($:

Eo. of %urns E [ 7'

Radius of Coil R [ )1.'5mm

Diameter of the coil D [ 14'.5mm

!ire radius a [ 1.)um

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Bence8

Value 3 [ 1.17 mB

I--!' "($:

Eo. of %urns E [ '

Radius of Coil R [ 54.'5mm

Diameter of the coil D [ 11'.5mm

!ire radius a [ 1'*.'um

Bence8

Value 3 [ .'uB

R!&/#.-# I-,/"#(' V./!:

3[.14uB

5*3*4 T! R!"!$%!' C$'"/$#

Eow calculate inductance of each coil and then Lsing resonance fre?uenc& e?uation we

calculate value of capacitors at resonance fre?uenc& of 47(h. %hree capacitors with

values of +apro=, u# on each receiving coil are connected.

4*

8/17/2019 NFC Project report on

nfc project report on wirless power transmission.doc

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