experiencias_witricity

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2011 Cross Strait Quad-Regional Radio Science and Wireless Technology Conference

Some Experiments Related to Wireless Power

Transmission

Ak GDepartment of Information TecnologyGeneral Directorate of Land Registry and Cadastre

Kzlay/ Ankara, [email protected]

bstat- wil pow iio o v popl W ivigd ow i gw ii ipd g fo igl fd fo vl wv p W v lo pid igli d dol iv odiio

Keywords- Witrici; wireless power transfer; wirelesselectrici, strong coupng

I. NRODUCION

Since the invention of electricity, cables have beenpreferred to deliver and transmit electricity. Cases such asspreading and maintenance of cables make the delivery of electricity hard to far locations. Some studies had done byNikola Tesla [1] to transmit electricity without cables safelybt ee s no cern ndig tat thos studs were dnesuccesslly.

In 2007 aer the studies that were done at MassachusettsInstitute of Tecology, it is suggested that electricity can be

transmitted wirelessly with resonant coupling method [2]. Thismethod is based on Coupled Mode Theory [2, 3]. Severalresearches were done aer this publication. In reference [4] itis shown that how the transfer is affected if there is anotherresonator between source and device resonator. In reference[5] eciency values depending on characteristic impedance

values of resonators and distance between resonators areexplaned. In reference [6] it is explained how to createwireless sensor network with multi resonators.

To name this technology the word Witricity is used whichis a combination of English words Wireless and Electricity.

In ts researc, some experments tat are one inlaboratory environment are explained. In these experiments,resonators were aligned horizontally on the contrary of previous works where resonators were aligned vertically. As a result, it is found that when the resonators are alignedhorizontally the transfer can be done successfully; how theeciency is affected by the characteristic impedances of bothresonators; how the resonators react when there are multireceiver and transmitters. Finally some advices are given forthe transfer depending on experiment results.

978-1-4244-9793-5/11/$26.00 2011 EEE 507

A P k ADepartment of Electrical- Electronics EngineeringGazi University

Maltepe/ Ankara, [email protected]

I I. EXP E R I M EN T AL R ESUL TS

Some experiments are done to investigate how to increasethe efciency on wireless power transmission. Handmadecoils are used in the experiments. Tree coils named B, C and

D were used as shown in Fig. 1.Coil B has 54 tus, 6,4 cm height and 32 cm diameter;

coil C has 56 tus, 6,7 cm and 31,5 cm diameter, coil D has58 tus, 6,7 cm height and 32 cm diameter. Coils are formedby using copper wires which have 1 mm thickness and glazed.To calculate the inductance values of the coils, this formula

was used:

(1)

In this formula "d, "n and "I shows diameter, number oftus and length of coil respectively. With the aid of this

formula, inductances were found for B, C and D as 271 H,277 H and 297 H respectively. To calculate the capacitancevalues, the formula used given below according to resonanceequencies and inductance values:

1 = 2

(2)

Figure Coils named B, C, D that are used in the experiments

July 26-30, 2011


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Theoretical equency was picked as 1 MHz and allcalculations were done based on this equency. In theexperiment, most appropriate capacitances picked om theequipment list depending on the theoretical calculation.Capacitances that theoretically calculated and picked om the

equipment list are given in the Table I.

In the experiment, theoretically calculated and measured

resonance equencies were different. These dierences mayoccur when we consider that all the equipments are not idealand the experiment set may be affected by environment.

A Eciency Values Depending on Resistance for FixedFrequency

In this experiment, resonance equency was chosen as 923KHz where the maximum energy transfer measured and

resistance were replaced both transmitter and receiver side.Energy transfer rates were measured depending on resistance

values. The distance between two resonators was 3 mm. 100,300, 510, 750 and 1000 valued resistors were used. For

sine, square and triangle waves, different amplitude valueswere generated by signal generator. During measurements,S voltage and power values were calculated on resistors.

When the results were analyzed, it can be seen that besteciency is at sine wave and the worst eciency is at squarewave where resistors and equency are xed. At sine wave,the best eciency was observed where the resistors haveminimum value (100 ) at both transmitter and receiver side.

Also it can be seen that the eciency decreases as resistorvalues increase. Fig. 2 and 3 show the behavior of the systemdepending on wave types and resistor values. In reference [7]

it was shown that efciency increase as characteristicimpedance increase. It is predicted that this opposite situationin this experiment may be because of layout of resonators.

B Ener Transfer Rates Depending on FrequencyIn this experiment energy transfer eciency was measured

where equency values increase at resonance system.Resonators B and C were used. Capacitors which were givenin Table I were connected in series to resonators. Attransmitter and receiver side, 100 resistors were used asload. Only capacitors were replaced for each equency whereother equipments stayed xed. The distance between two

resonators was kept at 3 mm.

BLE I. CCINCE VLES H RE CLCLEDHEOREICLLY ND SED IN HE EXPERIMEN CCORDING O MHz RES ONNCE FREQENCY FOR HE RESONORS B, C NDD. LL CPCINCE VLES RE GIVEN IN PICOFR

508

S voltage is presented n Fig. 4 as a function of equency.

SO.-S +------------403130C2 -20+-+S=

100 300 SO 70 000Recever esistance Ihm)

-Se 100 m -Se300m SlneOm -Se70m SeOOO

Figure 2. Eciency graph depending on resistor values at receiver sideaccording to resistor values at trnsmitter side for xed equency and andsine wave.

5> 4-_

'u

40 +------------35

3

2

1

1

o

- -

+1 3 51 75 1

R ceiver resistance (Ohm.-- n e 1 00Om-==ure100 Oh---- r a n l 100 Ohm

Figure 3. Eciency graph for dierent wave types where resistor value at

trnsmiter side is constnt.


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300,00

300000 .

200,00

200000

10000 r100000 I

0000 000

0 5 1000

T+; I

c

"00

-

200

200Frequen

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