Download Strain Sensors 14th June, 2013 Kaustubh Shinde and Obi Igwe

Wireless Power
By: Peter Woods
Supervising Professor: Dr. Chiao
July 16th 2013
Overview
• Brief history
• Basic theory
• Inductive coupling
• Important terms
• Applications
• Currently available
• Possible future applications
• Safety
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
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
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
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.”
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
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
Current Applications (Part 2)
• Transportation
• Wireless powered bus system for public transportation
• Wirelessly powered cars
• Wireless recharging purse
• Purse that can recharge cell phones
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
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
Safety (Part 2)
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
Questions