1. Wireless Power Transmission (WPT)
How It Works
Wireless Power Transmission (WPT)
Janaya Walter

2. Overview Background Categories of WPT Near-field Techniques
Far-field Techniques
Advantages/Disadvantages and Applications
Summary

3. Background
WPT: transmission of electrical energy without the use of wires
Requires transmitter (connected to a power source) and receiver
Advantages:
Useful for devices when wires are inconvenient, hazardous, impossible
Protection to possible failures in the power source that can damage the device

4. Categories of WPT Non-Radiative (Near Field) Radiative (Far Field)
Nonresonant Short Range (up to 1 antenna diameter)
Resonant Mid Range (up to 10 times antenna diameter)
Radiative (Far Field)
Long Range (can reach up to several meters)

5. WPT Techniques Near-Field Techniques Far-Field Techniques
Inductive Coupling
Capacitive Coupling
Magneto Dynamic Coupling
Far-Field Techniques
Microwaves
RF Energy
Lasers
Ultrasonic Waves

6. Non-Resonant Inductive Coupling
Current generated in a coil by magnetic field induces current in nearby coil
Separation, alignment, size of coils determine efficiency of power transfer
Involves base station (transmitter) with device placed on top
coil diameter, D
ReceiverCoil
coil distance, z
Transmitter Coil
[1]

7. Non-Resonant Inductive Coupling
Advantages
High Efficiency (30-60% of power)
Low heat generation
Quick charging cycles
Disadvantages
Power transfer only up to a few centimeters
Cannot pass through solid objects
Cannot use device while charging
More expensive than traditional charging

8. Qi Wireless Standard (2008)
Inductive Coupling up to distances of 4 cm
Generated Power:
5W delivered by low Qi Standard (i.e. mobile devices)
120W delivered by medium Qi Standard (i.e. laptops)
Use of placement marks, grooves, or magnets for alignment
Alignment between transmitter and receiver is key
[2]

9. Qi Wireless Standard (2008)
Mobile Devices (Nokia, LG, Samsung, iPhone)
Qi “Hotspots” (Cafés, airports, etc.)
Vehicles (personal or public)
IKEA (i.e. lamps, tables)
[2.5]

10. Resonant Inductive Coupling
Induced current in primary coil still induces current in secondary coil
Coils operate at identical resonant frequencies
Primary coil induces high current amplification in secondary coil
Provides greater allowable distance between coils
[3]

11. Resonant Inductive Coupling
Advantages
Power transfer up to 10 times distance of Inductive Coupling
Does not require exact precision between coils (as Inductive Coupling does)
Low heat generation
Disadvantages
Low Efficiency (compared to non-resonant inductive coupling)
Slower charging cycles (compared to non-resonant inductive coupling)
Cannot pass through solid objects

12. Resonant Inductive Coupling
Rezence (2012) WiPower (2004) PMA (2012) Open Dots (2015)

13. Radio Frequency Far Field Technique Advantages
Transmitter emits electromagnetic waves (10MHz to 6GHz)
Receiver “harvests” energy and converts into DC power
Advantages
Long-range transfer, No ‘line-of-sight’ system, High efficiency
No risk to prolonged exposure (cannot cause radiation sickness)
[6]
Visible Spectrum

14. Powercast (2003) Far Field Radio Frequency Charging
1 W of power delivered up to 1.5 meter distance
Transmits power to multiple devices at a time
No charging mats or direct line-of-sight needed
Obstruction does not affect power transfer
Acts as ‘Wi-Fi system’
Efficiency up to 80 percent

15. Ultrasonic Waves Radiative (Far Field) Technique
Transducer converts power source into sound energy (45-75 kHz)
High frequency waves above hearing range (~20 kHz)
Inaudible to people and animals
“Light of Sight” system
No power emitted if no receiver detected or beam is obstructed
[4]

16. Ultrasonic Waves Advantages Disadvantages
No risk to prolonged exposure (cannot penetrate skin or cause radiation sickness or genetic damage)
No interference with communication systems (ideal for aircraft)
Can charge multiple devices and when devices are in motion
Disadvantages
Currently only a prototype (uBeam - expected 2018)
[5]

17. uBeam (2012) Far Field Ultrasonic Charging
1.5 W of power up to distances of 4 meters
Line-of-sight technology allows “device in motion” charging
Similar charging speed to traditional wired charging
Less expensive than Inductive Coupling
Slim and lightweight mobile device charging cases

18. Summary Technology Type Range Directivity Antenna Device
Applications (Current or Future)
Non-Resonant Inductive Coupling
Near Field
Short
Low
Wire Coils
Mobile devices, electric tooth brushes, induction stove tops
Resonant Inductive Coupling
Mid
Mobile Devices, Biomedical Implants, Electric Vehicles
Capacitive Coupling
Metal Plate Electrodes
Mobile Devices, Smartcards
Magnetodynamic Coupling
N/A
Rotating Magnets
Electric Vehicles, Biomedical Implants
Radio Frequency Waves
Far Field
Long
High
RF Antennas
Solar Power Satellites, GPS Systems, RFID Tags, Biomedical Implants, Sensors
Light Waves
Lasers, photocells, lenses
Drone Aircraft, Space Elevator Climbers
Ultrasonic Waves
Transducer
Mobile Devices, Communication, drone aircraft

19. Summary Future? Increasing efficiency and maximum power transmission
Lowering costs
Exploring new techniques
Proposed space-based wireless electricity system (JAXA; via Microwaves)

20. Questions?

21. References https://en.wikipedia.org/wiki/Wireless_power_transfer

22. Image References
[1] [2] [2.5] [3] electronics_in_action_ php [4] [5] [6]