Wireless Power Supply

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Wireless Power Supply

• Final Presentation
• Speakers Ralph Leijenaar
• René van Bussel

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Outline

• Introduction
• Choice of applications
• BikeLights
• PowerSaver
• Conclusion
• Questions

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Choice of applications
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All applications
PowerWifi
CET desktop
BikeLights
Powercast
Backpack
Speakers
StandbySaver
Laptop screen
Vacuum cleaner
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Criteria

• Criteria for applications
• User-friendly, easily standardized
• Technically possible to make now
• Economically feasible, compete with current
  technology
• Sustainable
• Health and environment safe, FCC compliant

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Criteria
BikeLights
StandbySaver
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Bike lights
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Design

• Hub dynamo powers 5.8 GHz transmitter
• Hub dynamo delivers 3 W of power
• LED lights
• Consisting of 3 to 4 LEDs
• Complete back surface is 5.8 GHz rectenna

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Power

• Received power Pr calculated with Friis equation
  (front)
• Average LED light power consumption
• 60-80mA
• 3V circuit 180-240mW
• Wireless powering without batteries not feasible
  ? use for recharging batteries

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Health hazards

• Most problematic effect of RF radiation on the
  body heating effect
• Measured by Specific Absorption Rate
  (SAR) (power absorbed by the body per unit mass)
• Applications have to comply with SAR limits

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Health hazards SAR calculation

• Male human
• ? 1070 kg/m3
• Speed of light c 3108 m/s
• permittivity of free space is e0 8.85 10-12
  F/m.
• s and er tissue and frequency dependant,
  calculation
• s 3.87 S/m
• er 36.9
• BikeLights
• average distance to the body r 0.5 m
• distance to nearest body part (foot/leg) r 0.3
  m
• Input power P 3 W

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Health hazards BikeLight SAR values

• Whole-body SAR (averaged distance) 0.035 W/kg
• Local SAR (foot/leg) 0.098 W/kg

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Environment

• Assuming the batteries are only recharged while
  the LED light itself is in use an estimation of
  the ratio of the time the LED lights can be used
  with and without recharging can be made (Tr)
• Assuming a power usage of 60mA and recharging
  with 1,72mA (5.17 mW / 3V)
• Increase of 3
• Charge batteries when lights are off ? better
  increase
• No real environmental benefits

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Economic aspects

• With respect to wired lighting using a normal
  dynamo
• Hub dynamo more expensive
• Normal dynamo starting at 10,- to 25,-
• Hub dynamo starting at 30,- to 40,-
• Transmitter and rectenna costs
• Rechargeable batteries used
• With respect to normal LED lighting ? no extra
  costs
• With respect to wired lighting ? only costs of 1
  set of batteries

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Bike lights conclusion
Criteria Points before Points after
User friendliness 9 6
Technical feasibility 8 5
Economical feasibility 9 6
Sustainability 9 6
Health 8 8
Total 43 31
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Future improvements

• Main goals
• Increase power received by LED lights
• Reduce power needed by LED lights

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Recommendations

• Increase power received by LED lights
• Improve transmitting antenna gain
• Second dynamotransmitter in rear hub for rear
  light
• No interference cyclist
• Back light virtually same amount of received
  power as front light ? easier to standardize the
  LED lights
• Reduce power needed by LED lights
• Use high efficiency LEDs ? preferably low powered
• Note
• Increasing power output dynamo transmitter ?
  health issues ? no solution/improvement

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Standby saver
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Design

• Antenna in the remote control
• Radio waves of 5.8 GHz
• Rectenna in TV switches relay

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Power

• Transmitted power again calculated with the Friis
  equation
• A lot of power required, but for a short time,
  3ms
• Possible to use longer, lower power pulse
• At 500 ms only 12 W is needed

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Health hazards SAR

• Again, heating and SAR important
• s, ?, c, e0, and er are the same as the bike
  lights, r and P are different
• Differences
• average distance to the body r 0.4 m
• distance to nearest body part (thumb/hand) r
  0.02 m
• Input power P 12 W

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Health hazards, calculation

• The SAR is calculated averaged over time
• Whole-body SAR (averaged distance) 0.00031 W/kg
• Local SAR (hand) 0.12 W/kg
• Used just one time in six minutes
• Directivity, probably lower SAR

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Environment

• Standby functions 5 of power used in developed
  countries
• Suitable for TV, not convenient for VCR
• TVs average 21 kWh/year per household
• Remote uses batteries, but surprisingly little
• Very difficult to implement in existing devices

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Economic aspects

• Saves electricity, thus money
• 4,20 per year per household
• More batteries used, not significant
• TV more expensive remote, antennas, more
  materials
• Could be sold as environment saving idea

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Conclusions
Criteria Points before Points after
User friendliness 8 8
Technical feasibility 8 7
Economical feasibility 9 8
Sustainability 9 8
Health 8 8
Total 43 39
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Future improvements Recommendations

• Reduce power needed to switch the relay
• Less power less batteries
• For existing devices a seperate standby saver
  could be used between the plug and socket
• The converting of a half-second-long radio beam
  to a millisecond pulse is idealised

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Conclusion
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Conclusion bike lights

• Impossible to use wireless power for bike lights
• Charging is an option
• SAR calculations show no health hazards
• Little environmental impact
• Batteries still needed
• Material costs higher than existing lights
• Recommendations
• Increase the antenna gain use a second dynamo
  for the back light
• Improve LED efficiency

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Conclusion standby saver

• Possible using a frequency of 5.8 GHz
• SAR within limits
• Assuming it is not used often in six minutes
• Environment 5 of power used in developed
  countries is standby power
• Not suited for all applications
• For the same reason not a lot of money saved per
  household
• 4,20
• Recommendations
• Reduce power to switch relay, use a separate
  device for existing devices, look into the
  conversion

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Questions?

• ?

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