Charge Your Cell Phone in Your Pocket

Jouya Jadidian & Dina Katabi

Wireless Charging Today: zero distance & highly sensitive to

orientation

Charger

A small increase of charging distance and a flexible orientation Big gain in user experience

Charger

A small increase of charging distance and a flexible orientation Big gain in user experience

MagMIMO

How Does It Work?

Wireless Charging Primer

Wireless Charging Primer

Tx Coil

Rx Coil

Magnetic field generates a current in Rx

Magnetic Field

Current

AC Current

Power in Rx

Wireless Charging Primer

Tx Coil

Magnetic Field

AC Current

Rx Coil

Magnetic field doesnt cross Rx No Rx current

Wireless Charging Primer

Tx Coil

Magnetic Field

AC Current

Rx Coil

Magnetic field doesnt cross Rx No Rx current

Existing chargers fail with distance or orientation

Can We Borrow from Wireless Communications?

Tx

Rx SNR too low no signal!

Can We Borrow from Wireless Communications?

MIMO Tx

Rx SNR too low no signal!

Can We Borrow from Wireless Communications?

MIMO Tx

Rx

Beamforming focuses the signal

Magnetic Field

Can We Borrow from Wireless Communications?

Can We Borrow from Wireless Communications?

Magnetic Beamforming

Steer the beam with Rx

Can We Borrow from Wireless Communications? How Do We Beam-form the Magnetic Field?

Derivation of Magnetic Beamforming

Derivation of Magnetic Beamforming

= (1 + 2)

2

1

Tx symbol

Rx symbol

Derivation of Magnetic Beamforming

= (1 + 2)

2

1

Tx symbol

Rx symbol

= . (1 +2)

2

1

Derivation of Magnetic Beamforming

= (1 + 2)

2

1

Tx symbol

Rx symbol

= . (1 +2)

2

1

Rx current

Tx current

Constant

Derivation of Magnetic Beamforming

= (1 + 2)

2

1

Tx symbol

Rx symbol

= . (1 +2)

2

1

Rx current

Tx current

Channels Magnetic Coupling Symbols Currents

Same Mathematical Framework

Beamforming

Beamforming

2

1

RF Beamforming

Beamforming

2

1 1

RF Beamforming

2

=

||2

Beamforming

2

1 1

RF Beamforming

2 2

1

Magnetic Beamforming

1

2

Shape the magnetic field in a beam

=

||2 =

||2

Are we done?

Tx needs the channels, hi, to compute i

RF Beamforming

Rx measures the channels and send them to Tx

Tx needs the magnetic coupling, Mi , to compute i

Magnetic Beamforming

Rx is out of power Cant measure and send the Mi

2

1

Magnetic Coupling can be measured locally at the transmitter

Performance

Implemented MagMIMO

6 Tx coils controlled by programmable logic, which applies the beamforming multipliers to Tx currents

Experimented with iPhone 4S

Compared Systems

System Input Power

Witricity Wit-2000M 24 [W]

Energizer Qi 22 [W]

Duracell 18 [W]

MagMIMO 20 [W]

Charging Time vs. Distance

2.16

3.24

4.32

0 0.5 1 1.5 2 2.5Char

ging

Tim

e/Pl

ugge

d Ch

argi

ng T

ime

Distance (cm)

2

1.5

1

2 1.5

1

2 1.5

1

Charging Time vs. Distance

2.16

3.24

4.32

0 0.5 1 1.5 2 2.5

Energizer

Duracell WiTricity

Char

ging

Tim

e/Pl

ugge

d Ch

argi

ng T

ime

Distance (cm)

2

1.5

1

2.16

3.24

4.32

5.4

6.48

7.56

8.64

9.72

0 5 10 15 20 25 30 35 40

MagMIMO

Char

ging

Tim

e/Pl

ugge

d Ch

argi

ng T

ime

Distance (cm)

4.5

4

3.5

3

2.5

2

1.5

1

Charging Time vs. Distance MagMIMO supports much longer distances

Dealing with Phone Orientation

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

Phone Orientation (Degree)

Rece

ived

Pow

er (W

)

Dealing with Phone Orientation

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

Phone Orientation (Degree)

Energizer (0.7cm)

WiTricity (2cm) Duracell

(0.4cm)

Rece

ived

Pow

er (W

)

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

Phone Orientation (Degree)

Energizer (0.7cm)

WiTricity (2cm) Duracell

(0.4cm)

Dealing with Phone Orientation Re

ceiv

ed P

ower

(W)

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

Phone Orientation (Degree)

MagMIMO (2cm)

Duracell (0.4cm)

Energizer (0.7cm)

WiTricity (2cm)

Dealing with Phone Orientation Re

ceiv

ed P

ower

(W)

0

1

2

3

4

5

6

0 10 20 30 40 50 60 70 80 90 100

Rece

ived

Pow

er (W

)

Phone Orientation (Degree)

MagMIMO (2cm)

MagMIMO (40cm)

Duracell (0.4cm)

Energizer (0.7cm)

WiTricity (2cm)

Dealing with Phone Orientation

Conclusion MagMIMO charges your phone in your pocket

Conclusion MagMIMO charges your phone in your pocket

Even more critical for wearables

Slide Number 1Wireless ChargingA small increase of charging distance and a flexible orientation Big gain in user experience A small increase of charging distance and a flexible orientation Big gain in user experience MagMIMOHow Does It Work?Wireless Charging PrimerWireless Charging PrimerWireless Charging PrimerWireless Charging PrimerCan We Borrow from Wireless Communications?Can We Borrow from Wireless Communications?Can We Borrow from Wireless Communications?Can We Borrow from Wireless Communications?Can We Borrow from Wireless Communications?Can We Borrow from Wireless Communications?Derivation of Magnetic BeamformingDerivation of Magnetic BeamformingDerivation of Magnetic BeamformingDerivation of Magnetic BeamformingDerivation of Magnetic BeamformingBeamformingBeamformingBeamformingBeamformingAre we done?PerformanceImplemented MagMIMOCompared SystemsCharging Time vs. DistanceCharging Time vs. DistanceCharging Time vs. DistanceDealing with Phone OrientationDealing with Phone OrientationDealing with Phone OrientationDealing with Phone OrientationDealing with Phone OrientationConclusionConclusion