Presented by
Siddharth Patel

---

[attachment=10418]
Wireless Power Transmission
What is WPT?
 The transmission of energy from one place to another without using wires
 Conventional energy transfer is using wires
 But, the wireless transmission is made possible by using various technologies
Why not wires?
 As per studies, most electrical energy transfer is through wires.
 Most of the energy loss is during transmission
◦ On an average, more than 30%
◦ In India, it exceeds 40%
◦ Why WPT?
 Reliable
 Efficient
 Fast
 Low maintenance cost
 Can be used for short-range or long-range.
History
 Nikola Tesla in late 1890s
 Pioneer of induction techniques
 His vision for “World Wireless System”
 The 187 feet tall tower to broadcast energy
 All people can have access to free energy
 Due to shortage of funds, tower did not operate
 Tesla was able to transfer energy from one coil to another coil
 He managed to light 200 lamps from a distance of 40km
 The idea of Tesla is taken in to research after 100 years by a team led by Marin Soljačić from MIT. The project is named as ‘WiTricity’.
Energy Coupling
 The transfer of energy
◦ Magnetic coupling
◦ Inductive coupling
 Simplest Wireless Energy coupling is a transformer
Types and Technologies of WPT
 Near-field techniques
◦ Inductive Coupling
◦ Resonant Inductive Coupling
◦ Air Ionization
 Far-field techniques
◦ Microwave Power Transmission (MPT)
◦ LASER power transmission
 Inductive coupling
 Primary and secondary coils are not connected with wires.
 Energy transfer is due to Mutual Induction
 Resonance Inductive Coupling(RIC)
 Combination of inductive coupling and resonance
 Resonance makes two objects interact very strongly
 Inductance induces current
 How resonance in RIC?
 Coil provides the inductance
 Capacitor is connected parallel to the coil
 Energy will be shifting back and forth between magnetic field surrounding the coil and electric field around the capacitor
 Radiation loss will be negligible
 An example
 WiTricity
 Based on RIC
 Led by MIT’s Marin Soljačić
 Energy transfer wirelessly for a distance just more than 2m.
 Coils were in helical shape
 No capacitor was used
 Efficiency achieved was around 40%
 WiTricity (contd…)
 WiTricity… Some statistics
 Used frequencies are 1MHz and 10MHz
 At 1Mhz, field strengths were safe for human
 At 10MHz, Field strengths were more than ICNIRP standards
 WiTricity now…
 No more helical coils
 Companies like Intel are also working on devices that make use of RIC
 Researches for decreasing the field strength
 Researches to increase the range
 RIC vs. inductive coupling
 RIC is highly efficient
 RIC has much greater range than inductive coupling
 RIC is directional when compared to inductive coupling
 RIC can be one-to-many. But usually inductive coupling is one-to-one
 Devices using RIC technique are highly portable
Air Ionization
 Toughest technique under near-field energy transfer techniques
 Air ionizes only when there is a high field
 Needed field is 2.11MV/m
 Natural example: Lightening
 Not feasible for practical implementation
Advantages of near-field techniques
 No wires
 No e-waste
 Need for battery is eliminated
 Efficient energy transfer using RIC
 Harmless, if field strengths under safety levels
 Maintenance cost is less
Disadvantages
 Distance constraint
 Field strengths have to be under safety levels
 Initial cost is high
 In RIC, tuning is difficult
 High frequency signals must be the supply
 Air ionization technique is not feasible
 Far-field energy transfer
 Radiative
 Needs line-of-sight
LASER or microwave
 Aims at high power transfer
 Tesla’s tower was built for this
Microwave Power Transfer(MPT)
 Transfers high power from one place to another. Two places being in line of sight usually
 Steps:
◦ Electrical energy to microwave energy
◦ Capturing microwaves using rectenna
◦ Microwave energy to electrical energy
 AC can not be directly converted to microwave energy
 AC is converted to DC first
 DC is converted to microwaves using magnetron
 Transmitted waves are received at rectenna which rectifies, gives DC as the output
DC is converted back to AC
LASER transmission
 LASER is highly directional, coherent
 Not dispersed for very long
 But, gets attenuated when it propagates through atmosphere
 Simple receiver
◦ Photovoltaic cell
 Cost-efficient
Solar Power Satellites (SPS)
 To provide energy to earth’s increasing energy need
 To efficiently make use of renewable energy i.e., solar energy
 SPS are placed in geostationary orbits
 Solar energy is captured using photocells
 Each SPS may have 400 million photocells
 Transmitted to earth in the form of microwaves/LASER
 Using rectenna/photovoltaic cell, the energy is converted to electrical energy
 Efficiency exceeds 95% if microwave is used.
Rectenna
 Stands for rectifying antenna
 Consists of mesh of dipoles and diodes
 Converts microwave to its DC equivalent
 Usually multi-element phased array
Rectenna in US
 Rectenna in US receives 5000MW of power from SPS
 It is about one and a half mile long
Other projects
 Alaska’21
 Grand Bassin
 Hawaii
Advantages of far-field energy transfer
 Efficient
 Easy
 Need for grids, substations etc are eliminated
 Low maintenance cost
 More effective when the transmitting and receiving points are along a line-of-sight
 Can reach the places which are remote
Disadvantages of far-field energy transfer
 Radiative
 Needs line-of-sight
 Initial cost is high
 When LASERs are used,
◦ conversion is inefficient
◦ Absorption loss is high
 When microwaves are used,
◦ interference may arise
◦ FRIED BIRD effect
Applications
 Near-field energy transfer
◦ Electric automobile charging
 Static and moving
◦ Consumer electronics
◦ Industrial purposes
 Harsh environment
 Far-field energy transfer
◦ Solar Power Satellites
◦ Energy to remote areas
◦ Can broadcast energy globally (in future)
Conclusion
 Transmission without wires- a reality
 Efficient
 Low maintenance cost. But, high initial cost
 Better than conventional wired transfer
 Energy crisis can be decreased
 Low loss
 In near future, world will be completely wireless