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Wireless power for mobile phones -

System overview

Nov 25, 2012V1.1

System overview

Rx

Tx

• Embedded in mobile device• After market case/dongle

connected through the power connector

• Add-on connected through dedicated WLC pins

• Embedded in furniture/car/infrastructure

• After market mat

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Resonance circuit & power driver

Power Source

TXCoil

RXCoil

ControlUnit

Demodulator

Matching circuit & Rectifier

ControlUnit

Modulator

DC/DCCommunication

Power

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Block diagram

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Tx-Rx coils

Electric current flowing in a wire gives rise to a magnetic field around it.Alternating the current will alternate the magnetic field

Shaping the wire as a loop will band that field in a “lung” shape.

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Tx-Rx coils – Magnetic induction basics

Figures: http://ipodphysics.com/magnets-loop-or-coil.phpt

Figure 1: http://www.electrical4u.com/what-is-transformer-definition-working-principle-of-transformer/ Figure 2: http://makezine.com/2013/11/04/component-of-the-month-transformer/ Figure 3: http://www.britannica.com/EBchecked/media/1355/Magnetic-field-B-of-two-current-loops-with-currents-in

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Tx-Rx coils – Magnetic induction basics

Wireless power system is an air core transformer between planar coils one on top of the other.

Energy coupling means that an energy source has a mean of transferring its energy to a second object. Transformers may use iron core to deliver the magnetic flux

Single coil– Most common designPros – chip and easy solution / Cons – difficult alignment

Fig1:http://www.qitah.com/blog.htmlFig2:http://phys.org/news203691107.htmlFig3:http://patentimages.storage.googleapis.com/US20130119773A1/US20130119773A1-20130516-D00015.png

Large Tx coil – Common in loosely coupled systemsPros – easy alignment / Cons – difficult design and tune

Array of small Tx coil – One or more coils provide power simultaneouslyPros – easy alignment / Cons – Cost of coils and drivers

3 coil array – Only one coil provides power at a timePros – easy alignment / Cons – Cost of coils and drivers

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Tx-Rx coils – Coil designs

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Resonance circuit and power driver

Power driver Resonance circuit

Figure 1: HIGH EFFICIENCY LOOSELY COUPLED WIRELESS POWER TRANSFER SYSTEM VIA MAGNETIC INDUCTION By ZHEN NING LOW

Resonant circuit - Determines the self resonance frequency of the Tx,Mainly influenced by the coil and the resonance capacitors.

Power driver - pushes the current to the resonance circuit in different frequencies around the self resonance

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Resonance circuit and power driver

Figure 1: http://perlgeek.de/blog-en/perl-6/rakudo-memory-leaks.html10

Resonance circuit

• The overall impedance the driver “sees” when modeled as a series RLC circuit

• At the resonance frequency the capacitive and inductive impedance equals

The driver then sees resistive only minimum overall impedance and the power delivery to the Rx is maximal

• The resonance curve changes with each different : Rx design (EE & ME) Phone material Misalignment from the center Variation during manufacturing Load drawn

Frequency

Ampl

itude

Frequency control – the driver changes the frequency along the resonance curve Control becomes difficult when Q is high & at resonance control is unstable Frequency range shall be dynamic due to curve changes Passing to the second side of the peak may reverse the control rules

Frequency

Ampl

itude

Other methods of control:Voltage control – increasing the input voltage will increase the current through the coil and the transmitted powerPulse width control – increasing the on time of the signal will increase the transmitted power

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Driving the power

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Data modulation

Power driver

Modulator

Demodulator

Matching circuit & Rectifier

load modulation - •Rx modulates the operational frequency by short circuiting the coil to a secondary load•The secondary load changes both the load of the Tx and the resonance curve•The demodulator sense the change in voltage, current or phase between them on the operational frequency

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Data modulation

Example of voltage change at the Tx

Example of phase change at the Tx

Signals in reality may vary a lot from the simulation presented….14

Data modulation

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Questions? Comments? Remarks?

Thanks,Rotem Shraga

(shraga.rotem@gmail.com ; 052-6443944)Figure: http://www.fodrizzle.com/wp-content/uploads/2012/02/funny-birds-wire-drawing.jpg

It’s called wireless power, it’s the future