1. Wireless Power By: Peter Woods Supervising Professor: Dr. Chiao July 16 th 2013

2. Overview Brief history Basic theory Inductive coupling Important terms Applications Currently available Possible future applications Safety

3. History of Wireless Power Nikola Tesla 1893 Demonstrated wireless power by illuminating light bulbs at the World’s Columbian Exposition in Chicago 1917 The Wardenclyffe tower is destroyed Modern day 2007 A research group at MIT power a 60W light bulb with 40% efficiency at 2 meters

4. Theory (Part 1) Faraday’s Law Any change in the magnetic environment of a coil of wire will cause a voltage to be induced in the coil Lenz’s Law When a voltage is generated by a change in flux, there will be a current whose polarity opposes the change which it produces

5. Theory (Part 2) Efficiency Efficiency is the ratio of output to input power How much of the magnetic field is captured and is useful (not lost to resistance in coils and circuits) Coupling factor When the transmitter coil and receiver coil are separated, only a portion of the magnetic field penetrates the receiver coil and causes a voltage Determined by distance, shape, and angle of coils

6. Theory (Part 3) Quality factor of coils The ratio of inductance to the resistance of a coil multiplied by the angular frequency. The higher the quality factor of the coils, the higher the efficiency will be Resonant magnetic coupling According to WiTricity, “Magnetic coupling occurs when two objects exchange energy through their varying or oscillating magnetic fields. Resonant coupling occurs when the natural frequencies of the two objects are approximately the same.”

7. Theory (Part 4) Litz Wire Used to carry alternating current at high frequencies, consists of many strands of wire wire to reduce the skin effect

8. Current Application of Wireless Power (Part 1) Medical implants Heart pump GERD (Gastroesophageal Reflux Disease) stimulator Inductive recharging Toothbrushes Laptops Cellphones Through wall application Outside power from solar panel beamed inside to power a light bulb

9. Current Applications (Part 2) Transportation Wireless powered bus system for public transportation Wirelessly powered cars Wireless recharging purse Purse that can recharge cell phones

10. Future Applications of Wireless Power Elimination of cords and plugs for charging Creating a standard for charging stations Wireless Power Consortium VS. WiTricity ensure that mobile devices from different vendors can charge anywhere in a common wireless ecosystem. A Charging electric vehicles Parking lots Traffic lights Clothing that charges phones

12. Safety (Part 1) Tissue heating IEEE (Institute of Electrical and Electronic Engineers), and ICNIRP (International Commission on Non-Ionizing Radiation Protection) According to an article by WiTricity, “there is no established evidence showing that human exposure to radio frequency (RF) electromagnetic fields causes caner, but that there is established evidence showing that RF electromagnetic fields may increase a person’s body temperature or may heat body tissues and may stimulate nerve and muscle tissues.” SAR (specific absorption rate), is the measure of the amount of electromagnetic energy absorbed by the human body and turned into heat. For the U.S. the FCC (Federal Communications Commision) has adopted a SAR limit of 1.6 W/kg averaged over 1 g of tissue

13. Safety (Part 2)

14. Summary Wireless power is not a new technology Internal combustion engine invented in 1898 How it works Two coils, a transmitter and a receiver. An alternating current in the transmitter generates a magnetic field which induces a voltage in the receiver coil Available products Wireless chargers, medical implants, transportation Safety Difficult to measure how safe, but current experiments show that wireless power is safe

15. Questions