1. Wireless Power Transmission
EE563-Graduate Seminar
Fall 2004 Group 5
Alan Chun-yip Yeung
Leanne Cheung
Jeff Samandari
Wehibe Belachew
Tesfa Mael
Jose A. Becerra

2. Presentation Outline
1. Introduction //Background
1. Introduction Background
2. Theory of Wireless Power Trans.
2. Theory of Wireless Power Trans.
3. Major Research Projects
3. Major Research Projects
4. Comparison of Efficiency …
4. Comparison of Efficiency …
5. Proposed Project/Experiment
5. Proposed Project/Experiment
6. Conclusion
6. Conclusion

3. 1. Introduction // Background
1. Introduction Background

4. Outline
• History/Background
• Solar Power Satellite
• Microwave Power Transmission
• Conclusion
Reference:
http://www.kentlaw.edu/classes/fbosselm/Spring2004/Power
Points/Wireless%20Power%20Transmission%20-
%20Soubel.ppt

5. Background, Nikola Tesla
• 1856-1943
• Innovations:
– Alternating current
– Wireless power
transmission
experiments at
Wardenclyffe

6. Wardenclyffe
• 1899
– Able to light lamps
over 25 miles away
without using wires
– High frequency
current, of a Tesla
coil, could light
lamps filled with
gas (like neon)

7. 1940’s to Present
• World War II developed ability to convert
energy to microwaves using a magnetron,
no method for converting microwaves
back to electricity
• 1964 William C. Brown demonstrated a
rectenna which could convert microwave
power to electricity

8. Solar Power from Satellites
• 1968’s idea for Solar Power Satellites
proposed by Peter Glaser
– Would use microwaves to transmit power to
Earth from Solar Powered Satellites
• Idea gained momentum during the Oil
Crises of 1970’s, but after prices stabilized
idea was dropped
– US Department of Energy research program
1978-1981

10. Problems
• Issues identified during the DOE study
– Complexity—30 years to complete
– Size—6.5 miles long by 3.3 miles wide
• Transmitting antenna ½ mile in
diameter(1 km)
– Cost—$74 billion
– Interference

11. From the Satellite
• Solar power from the satellite is sent
to Earth using a microwave
transmitter
• Received at a “rectenna” located on
Earth
• Recent developments suggest that
power could be sent to Earth using a
laser

12. Microwaves
• Frequency 2.45 GHz microwave
beam
• Retro directive beam control
capability
• Power level is well below international
safety standard

13. Microwave vs. Laser Transmission
• Microwave • Laser
– More developed – Recently developed
– High efficiency up to solid state lasers allow
85% efficient transfer of
– Beams is far below the power
lethal levels of – Range of 10% to 20%
concentration even for efficiency within a few
a prolonged exposure years
– Cause interference – Conform to limits on
with satellite eye and skin damage
communication
industry

14. Rectenna
“An antenna comprising a mesh of
dipoles and diodes for absorbing
microwave energy from a transmitter
and converting it into electric power.”
• Microwaves are received with about
85% efficiency
• Around 5km across (3.1 miles)
• 95% of the beam will fall on the
rectenna

15. 5,000 MW Receiving Station
(Rectenna). This station is about a
mile and a half long.

16. 2. Theory of Wireless Power Trans.
2. Theory of Wireless Power Trans.

17. Theory of Operation
• Electromagnetic Radiation
• Antenna basics
• Phased-array antenna
• Diffraction analogy
• Energy distribution
• Rectenna
• Physical limitations & relationships

18. Physics of Wireless Power
Transmission
• Forms of
Electromagnetic
radiation
• Travel at same speed
• F = frequency
• C = velocity of light
•http://imnh.isu.edu/digitalatlas/clima/atmosph/images/waves.jpg • L =wavelength

19. Dipole Antenna
• Transmission of power
is simpler than TV &
Radio
• Transmitter: wire half a
wavelength
• Pushes electrons back
and forth
• Receiver: wire half a
wavelength
http://www.zorg.org/radio/dipole_antenna.shtml

20. Antenna Radiation Pattern
http://www.astromag.co.uk/portable/dipole.gif

21. Phased-array antenna
• The λs for microwaves
are small  dipoles small
• Beam focusing: phased-
array antenna
• Electronically steered by
varying the timing or
phase
• Waves will merge
together
http://www.mcs.harris.com/oceannet/features/antenna.html

22. Phased-Array Antenna
http://www.cea.com.au/products/phasedarray/i2_ceafar.html

23. Diffraction analogy
• Light same properties
• Laser beam shinning
trough a narrow
opening & spreads
out or diffracts
• Bright spot in the
center w/fainter spots
on the side
http://planetquest.jpl.nasa.gov/technology/diffraction.html

24. Diffraction & Microwaves
• Waves reinforce at
some points and they
cancel out at other
points (bright and
fainter points)
• In microwaves: is a
scaled up version of
diffraction

25. Intensity

26. Main lobe energy
• Circular central max
 Main lobe
• 84% of energy
• Sidelobes surround
• No energy  minima

27. Intensity 84% in main lobe

28. Rectenna
• Array of dipole
antennas known as
rectifying antenna or
Rectenna
• Diameter = Dr

29. Rectenna

30. Physical Limitations
• The receiving diameter Dr increases with
transmitter receiver separation distance S.
• Dr increases if transmitter diameter Dt
decreases

31. Physical Limitations

32. 2. Sample Calculations
2. Sample Calculations

33. Calculations/Analysis
• Frequency, f (Hz)
• Intensity, I (watts per square meter)
• Wave-Length, L (meters)
• Received Main Beam Lope (“spot”) Diameter, Dr
(meters or kilometers)
• Transmitting Phased Array Diameter, Dt (meters
or kilometers)
• Example: how to estimate Intensity, I ?

34. Frequency Formula
Dt * Dr
• Frequency, f (Hz) = -------------- (2)
(L * S)
Dt: transmitting phased array diameter
Dr: received main beam lobe (“spot”)
diameter
L: wavelength
S: separation

35. Frequency Analysis
Dt * Dr
If (Frequency, f (Hz) = ----------- ) ≥ 2.44 GHz (2)
(L * S)
Then at least, 84% of the energy of the beam will be captured
Note:
• This energy is not linear; 42% of the energy is not
equivalent to 1.22 GHz.
• Equation (2) represent a best case scenario.
• Practical antenna sizes may have to be larger if most of
the beam is to be captured.
• The rectenna will have to be at least as large as Dt,
even if (2) says Dr is smaller.

36. Frequency Analysis
• Such a wide beam can be focused, but only to a minimum size Dr.
• For low Earth-orbit power-beaming demonstrations, it is easier to
put the smaller antenna in space and the larger antenna on
Earth.
• Early demonstrations may capture only a small percentage of the
total power, in order to keep antenna sizes small.
– to light up a 60 watt bulb, thousands of watts may have to be
transmitted.
– Since costly to launch such a power generating apparatus, the
most feasible demonstration project may be Earth-to-space
transmission from a large transmitting antenna (such as the
Arecibo dish) to a smaller rectenna in space.

37. Intensity, I Formula
• Intensity, I (watts per square meter)
P Dt
= ½ ( Pi * -----) * ( --------- ) (3)
4 L*S
Pi: 3.14…
P: total power transmitted
Dt: transmitted phased array diameter
L: wave length
S: transmitter to receiver distance (separation)

38. Wave-Length, L Calculations
• Wave-Length, L (meters)
c 300,000,000 meter/sec
= ----- = ( -------------------------------- ) = 0.1224 (1)
f 2,450,000,000/sec meter
c: speed of light
f: frequency

39. Received Main Beam Lope Diameter, Dr Calculations
• Received Main Beam Lope (“spot”) Diameter, Dr
(meters or kilometers)
f*L*S 2.44 * 0.12224m * 35,800,000m
= -------------- = --------------------------------------------
Dt 1000m
= 10,700 meter = 10.7 kilometers
L: wave length
S: separation
Dt: transmitting phased array diameter

40. Transmitting Phased Array Diameter, Dt Calculations
• Transmitting Phased Array Diameter, Dt (meters or
kilometers)
f*L*S 2.44 * 0.12224m * 35,800,000m
= -------------- = ----------------------------------------------
Dr 10,700 meter
= 1000m = 1 kilometers
L: wave length
S: separation
Dr: received main beam lope (“spot”) diameter

41. Example
What is the Intensity, I = ?
Given: f, Dr, and a typical solar power satellite transmitting 5
billion watts from geostationary orbit 35800 kilometers
high.
Solution: Use the following (1), (2), & (3)
C
f = -----  L (1)
L
Dt * Dr
Frequency, f (Hz) = --------------  Dt (2)
(L * S)
P Dt
Intensity, I (watts/m^²) = ½ ( Pi * -----) * ( --------- ) (3)
4 L*S

42. Example Calculations
• Intensity, I (watts per square meter)
P Dt
= ½ ( Pi * -----) * ( --------- ) (3)
4 L*S
2287485.869w 1000m
= ½ ( Pi * ---------------------------) * ( ----------------------------------- )
4m 0.1224m* 35800,000m
= 205 watts/m^² or 20.5 milliwatts/cm^²

43. Example Analysis
• peak beam intensity, Ip = 20.5 milliwatts/cm^²
 This is about twice US industrial standard for human exposure
 This is converted (by rectenna) to electricity by 90% efficiency
• Average intensity, Ia ≈ 1/3 * 20.5 milliwatts/cm^²

44. Rectangular Transmitting antenna array Calculations
• Mathematics slightly different, but the same general principles
apply.
• Central maximum of the beam contain 82% of the transmitted
energy.
• Rectangular in shape, but will spread out more along TX array’s
short direction than its long direction.
• Example: Canada’s Radar sat
rectangular transmitting antenna: 1.5m × 15m
“footprint” on the ground: 7,000m × 50,000m
frequency: 5.3 GHz
altitude: 800,000m
output power: 5000 watts
 The power is too spread out at the ground to use in a practical
demonstration project.

45. Two more points
1. Use certain transmitting methods
– to reduce the level of the sidelobes
– to put some of the sidelobe energy into the main
lobe
–  Price to pay: Larger Rectenna (because main
lobe spreads out)
2. Principal of diffraction also limits the resolution of
optical systems:
– Lenses
– Telescopes

46. 3. Major Research Projects
3. Major Research Projects

47. 1979 SPS Reference System concept
(GEO)

49. Accomplishments of Solar Power
Satellites
• 1980, 30 kW of microwave power was
transmitted to a receiving antenna over
one mile
• 1993, Japan successfully transmitted a
800W microwave beam from a rocket to a
free-flying satellite in space.
• 1998, Microwave to DC conversion
efficiency of 82% or higher by the
rectenna.

50. NASA’s 1995-1997 Fresh Look Study
• MEO (Mid-Earth Orbit)
Sun Tower:
- 6 SPS yields near 24-hr
power to sites
- ± 30 degrees Latitude
Coverage
- Power services of 200-
400 MW

51. Continued
• Solar Disc
- 1 SPS provides nearly 24-
hr
power to markets
- Spin-stabilized solar array,
de-spun phased array with
electronic beam-steering
- Geostationary Earth Orbit
- ± 60 degrees Latitude
Coverage
- Power services of about 5
GW

52. 1999-2000 Space Solar Power (SSP)
Exploratory Research and Technology
(SERT) program
• Exploration and Commercial Development

54. Integral Symmetrical Concentrator

55. NASA’s SSP Strategic Research &
Technology Roadmaps

56. SPS 2000

57. Details of SPS 2000
• Japan is to build a low cost
demonstration of SPS by
2025.
• Eight countries along the
equator agreed to be the
rectenna sites.
• 10 MW satellite delivering
microwave power in the low
orbit 1100 km(683 miles)
– Will not be in
geosynchronous orbit,
instead low orbit 1100 km
(683 miles)
– Much cheaper to put a
satellite in low orbit

58. Japan’s Recent Research Efforts
• Japan
- 2001, Japanese’s Ministry of Economy,
Trade and Industry (METI) launched a
research program for a solar-powered-
generated satellite.
- By 2040, beginning of a SPS operation. The
planned satellite will be able to generate
1GW/Sec. (equivalent to the output of a
nuclear plant) in a geostationary orbit. The
receiving antenna (rectenna) on the ground will
be either positioned at desert or sea.

59. Japan’s Roadmaps for SPS
Development

60. References
• www.on-orbit-servicing.com/pdf/OOS2004_
presentations_pdf/OOSIssuesOverview_Oda.pdf
• www.kentlaw.edu/classes/fbosselm/Spring2004/ PowerPoints/Wireless
%20Power%20Transmission%20-%20Soubel.ppt
• www.spacefuture.com/.../a_fresh_look_at_space_
solar_power_new_architectures_concepts_and_technologies.shtml
• Lin, James C., “Space solar power stations, wireless power transmissions,
and biological implications”, IEEE microwave magazine, March, 2002

61. 4. Comparisons Among Other Power
4. Comparisons Among Other Power
Sources
Sources

62. Efficiency and Costs
•Space Solar Power (Wireless Power
Transmission)
•Ground Based Solar Power
•Nuclear Energy
•Fossil Fuel

63. Advantages over Earth-based solar power
• More intense sunlight
• In geosynchronous orbit, 36,000 km (22,369
miles) an SPS would be illuminated over 99%
of the time
• No need for costly storage devices for when
the sun is not in view

64. Cont.
• Waste heat is radiated back into space
• Power can be beamed to the location where it
is needed, don’t have to invest in as large a
grid
• No air or water pollution is created during
generation
• Ground based solar only works during clear
days, and must have storage for night. Thus
it is More reliable than ground based solar
power

65. Advantages over Nuclear Power
There are advantages…
• Possible power generation of 5 to 10
gig watts
• If the largest conceivable space
power station were built and
operated 24 hours a day all year
round, it could produce the
equivalent output of ten 1 million
kilowatt-class nuclear power
stations.

66. Cont…
• Nuclear power doesn't pollute the
atmosphere like fossil fuels. But it does
produce waste. This stays radioactive for
thousands of years and is very dangerous. At
the moment most stations bury their waste
deep underground, at sea or send it to other
countries. (Britain, for example, accepts and
buries nuclear waste from several countries.)

67. Cont…
• One of the disadvantage of Nuclear
• On April 26, 1986 the worst catastrophe in nuclear
history occurred in the station at Chernobyl, Ukraine.
• Due to the failure of one of reactor, two people died
immediately from the explosion and 29 from radiation.
About 200 others became seriously ill from the radiation;
some of them later died. It was estimated that eight
years after the accident 8,000 people had died from
diseases due to radiation (about 7,000 of them from the
Chernobyl cleanup crew). Doctors think that about
10,000 others will die from cancer. The most frightening
fact is that children who were not born when the
catastrophe occurred inherited diseases from their
parents.
• Source http://oii.org/html/story.html by Vessela
Daskalova

68. Advantages over Fossil Fuel
• Fossil fuels won't last forever (next 50yrs)
• It is not renewable
• The ability to match supply to demand
may already have run out, especially for
oil
• Fossil Fuel fired electric power plants in
the US emits about 2 billion tons of
greenhouse gas CO2 in to air every year.
This courses climate change in the future
via greenhouse effect.

69. Cost
• Cost—prototype would have cost $74 billion
• “According to Kyle Datta the Oil Factor,”
which predicts that oil could hit $100 a barrel
by 2010.

70. Disadvantages
• If microwave beams carrying power could be
beamed uniformly over the earth. They could
power Mobile Devices Eg. cell phones
• Microwave transmission
– Interference with other electronic devices
– Health and environmental effects

71. Cont…
• Possible health hazards
– Effects of long term exposure
– Exposure is equal to the amount that
people receive from cell phones and
Microwaves
• Location
– The size of construction for the rectennas
is massive and also Implementation
Complexity

72. Initial conceptual looks at a mega-engineering project as shown in this Boeing design.
New technologies point to more efficient, less expensive space solar power systems.
Credit: Boeing/Space Studies Institute

73. Early and simple schematic of how a space solar power satellite would beam
energy to electrical power grid on Earth. Credit: Space Studies Institute

74. Sustainable energy
• To meet the final goal of providing sustainable energy for
future growth and protection of the environment, the
design and technology for space solar power should be
evaluated by the criteria of availability of resources,
energy economy (payback time) and waste production
such as carbon-dioxide through all the processes
required for production of SPS . Power from space
should be competitive with other energy sources in this
respect. We also need a space solar future if our
children are to live in an intact environment. They will be
grateful to us

75. 5. Proposed Project/Experiment
5. Proposed Project/Experiment

76. Goal of the Proposal
• Obtain $10,000 grant from EPA to fund
our research

77. Proposed Project
• Transmit power from AC outlet to
a remote circuit wirelessly
– to demonstrate the capability of the
technology,
– to explore the problems we'll face in a small-
scale experiment, and
– to use this experiment as a “probe” to explore
the potential problems of transmitting power
from space to earth

78. Benefits
1) For graduate and undergraduate
students to research and study about
wireless power transmission
2) Demonstration tool for a potential
laboratory course
3) Potential commercialization of the
proposed project

79. Block Diagram of Proposed Experiment
—1
Transmitting
Side:
AC Power Power Microwave
Outlet Conversion Transmitter
This
This converts transmits
This is the
the AC power the
AC power to a microwave microwave
supply power signal
power
signal

80. Block Diagram of Proposed Experiment
—2
Receiving
Side:
Rectenna Power Power Remote
Conversion Regulator Device
Remote
This Device uses
This converts the
regulates this DC
microwave power signal to power the
DC voltage
DC power signal same way it
level
uses a battery

81. Vision on Future Development
Local
Local Regional
Regional Orbital
Orbital
Ability to transmit
Ability to transmit
Ability to transmit
Ability to transmit power
power
Ability to transmit power
Ability to transmit power power from a
power from a from a
from a
within a laboratory
within a laboratory local power
local power geostationary
geostationary
plant to local households satellite to a specific
plant to local households satellite to a specific
reception site
reception site

82. 6. Conclusion
6. Conclusion

83. Conclusion
• This idea worth to invest in since this
technology brings in virtually unlimited
power from the sun.
• This also benefits the intercontinental
power providers.
• Absolutely environmentally friendly since it
is emission-free.

84. Reference
1) “A Few Things you occasionally wanted to know about wireless power
transmission.” Potter, Seth.
http://www.spacefuture.com/archive/a_few_things_you_occasionally_wanted_to_know_ab
2) “Solar Power Satellites and Microwave Power Transmission”
http://www.kentlaw.edu/classes/fbosselm/Spring2004/PowerPoints/Wireless%20Power%2
3) www.on-orbit-
servicing.com/pdf/OOS2004_presentations_pdf/OOSIssuesOverview_Oda.pdf
4) www.kentlaw.edu/classes/fbosselm/Spring2004/ PowerPoints/Wireless%20Power
%20Transmission%20-%20Soubel.ppt
5) www.spacefuture.com/.../a_fresh_look_at_space_
solar_power_new_architectures_concepts_and_technologies.shtml
6) Lin, James C., “Space solar power stations, wireless power transmissions, and
biological implications”, IEEE microwave magazine, March, 2002