Witricity Or Wireless Electricity
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“Wireless Electricity”
PRESENTED BY: AMIT MAHAJAN
Witricity Basics
Short Range Coupling
Medium Range Wireless Energy Transmission: Resonant Induction
Wireless
Energy
Detailed Principle
How Safe is WiTricity?
What's the Future of WiTricity?
Advantages
Limitations
Bibliography
Transmission:
Inductive
Currently, wired electricity powers nearly everything. It travels through wires in the form of Alternating Current, and powers most of our devices in the form of Direct Current.
In our present electricity generation system we waste more than half of its resources. Especially the transmission and distribution losses are the main concern of the present power technology.
The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient. We have to think of alternate technology to transmit and distribute the electricity. The transmission of power without wires may be one noble alternative for electricity transmission.
The Transfer of Electricity from one place to another without wires is known as “WiTricity”.
On June 7 ’07, a team of researchers at MIT announced the successful operation of WiTricity concept.
They had lit up a 60W bulb with a power source at a distance of 7 feet(over 2m) with no wires.
Prof. Marin Soljacic from Massachusetts Institute of Technology (MIT), is the one who has proved that magnetic coupled resonance can be utilized in order to transfer energy without wires. What's even more interesting is how he came about this idea. Soljacic, just like any of us was fed up of his 'low battery' beeping cell phone and wondered just like any of us if there was a way to get rid of this 'charging problem'.
However, here is where the difference between Soljacic and any of us comes in. He didn't just stand there wondering, instead he tried to figure out if there existed any physical phenomenon which could be of some help. He remembered Michael Faraday's discovery of electromagnetic induction (1831) and used it to come up with WiTricity.
There are 3 major types of wireless energy transfer: – Short range; Inductive Coupling – Medium range; Resonant Induction – Long range; Electromagnetic Wave Power Transfer
What Is Inductive Coupling? Inductive Coupling is a method for short range wireless energy transfer. Its range can vary, but it’s often very short. Because of its short range it usually is used when the device containing the receiver and the device containing the transmitter are touching.
Inductive coupling works on principles of electromagnetism:
the
When a current (electricity) passes through a wire, it generates a magnetic field perpendicular to the wire. This effect can be magnified through coiling the wire. When a wire is in proximity to a magnetic field, it generates a current in that wire. Transferring energy between wires through magnetic fields is inductive coupling. Magnetic fields decay quickly , making inductive coupling effective only at very short ranges.
Pros: safe, efficient. Cons: Limited range. Inductive coupling is used for wireless charging of electronic devices. Although its range is limiting, several products use inductive coupling to charge, such as electric toothbrushes.
What Is Resonant Induction?
A group of engineers at MIT came up with the idea to use resonant induction to transmit power wirelessly. They deemed their result “WiTricity” (like Wi-Fi) . WiTricity can transmit electricity wirelessly at 40% efficiency to about 7 feet.
Resonant induction still uses the same principles as magnetic induction (magnetic fields to transfer current) , but it uses resonance to increase the range at which the transfer can efficiently take place.
“Resonance", a phenomenon that causes an object to vibrate when energy of a certain frequency is applied.
Everything resonates at a certain frequency, based on its shape and material. Energy transfers easily between resonating objects. An example of this is when an opera singer shatters wine glasses by singing at the frequency at which the glasses resonate. With resonant induction, power is transmitted between two resonating coils.
Consider two self resonating copper coils of same resonating frequency with a diameter 20 inches each. One copper wire is connected to the power source (WiTricity transmitter), while the other copper wire is connected to the device (WiTricity Receiver). The electric power from the power source causes the copper coil connected to it to start oscillating at a particular (MHz) frequency.
Subsequently, the space around the copper coil gets filled with nonmagnetic radiations. This generated magnetic field further transfers the power to the other copper coil connected to the receiver. Since this coil is also of the same frequency, it starts oscillating at the same frequency as the first coil. This is known as 'coupled resonance' and is the principle behind WiTricity.
The first copper coil (24 inches in diameter) was connected to the power source and the second was connected to the bulb, and were made to resonate at a frequency of 10 MHz. The bulb glowed even when different objects (like a wooden panel) were placed between the two coils. The system worked with 40% efficiency and the power that wasn't utilized remained in the vicinity of the transmitter itself, and did not radiate to the surrounding environment.
No, this concept of wireless electricity is not new. In fact it dates back to the 19th century, when Nikola Tesla used conduction- based systems instead of resonance magnetic fields to transfer wireless power. Further, in 2005, Dave Gerding coined the term WiTricity which is being used by the MIT researchers today.
Moreover, we all are aware of the use of electromagnetic radiation (radio waves) which is quite well known for wireless transfer of information. In addition, lasers have also been used to transmit energy without wires. However, radio waves are not feasible for power transmissions because the nature of the radiation is such that it spreads across the place, resulting into a large amount of radiations being wasted.
And in the case of lasers, apart from requirement of uninterrupted line of sight (obstacles hinders the transmission process), it is also very dangerous.
What Soljacic's team has done is that they have specifically tuned the transmitting unit to the receiving device. The transmission is also not hindered by the presence of any object in the line of sight. If the object to be charged is in the vicinity of the WiTricity source, then the energy transfer will undoubtedly take place.
In this 'coupling resonance' system, the electric energy that is not used up by the receiver does not get radiated into the surrounding environment, but remains in the vicinity of the transmitter. This ensures safety as well as minimal wastage of power. One of the five researchers, Dr. Aristeidis Karalis says that their coupling resonance system is one million times more efficient as compared to that of Nikola Tesla.
In 1891, Nikola Tesla invented a type of resonant transformer called the Tesla coil, which was used to generate very high voltage, low current, and high frequency alternating electricity. He experimented with a large variety of coils and configurations, one of which is as:
Referring to Fig. 1, the capacitor 1C forms two resonant circuits: one with the primary coil 1P, and another with the secondary coil 1S. The voltage is supplied by the Neon sign transformer 1T. The spark gap 1SG consists of two electrodes separated by a gap, filled with an inert gas. When high enough voltage is applied across it, a spark forms, ionizing the gas, and allowing conduction. As the voltage across the gap 1SG increases, the charge across the capacitor 1C also increases.
When the gap sparks, the capacitor discharges into the primary and the secondary. Thus, the voltage “bounces” back and forth at an extremely high rate. When the rate of discharge between the capacitor 1C and primary 1P, matches that of the capacitor and secondary 1S, the two circuits are said to be "in resonance". The voltage rises to such high levels that it is discharged through the discharge terminal in the form of an electric arc.
Tesla used these coils to conduct numerous innovative experiments. In 1899, he achieved a major breakthrough in his work at Colorado by transmitting 100 million volts of electric power wirelessly over a distance of 26 miles to light up a bank of 200 light bulbs and run one electric motor. He claimed to have achieved 95% efficiency. The method he used to wirelessly transmit electricity was the employment of the earth's own resonance with its specific vibrational frequency to conduct AC electricity via a large electric oscillator at about 7.8 Hz.
However, there were several safety hazards that were needed to be considered. A Tesla Coil produces high voltage electric arcs. These arcs cause permanent damage to electrical devices on contact. Many devices can also be damaged without being directly struck by the arc, due to the sheer amount of voltage being transferred. Tesla coils also destroy hearing aids and cardiac pacemakers in their vicinity. For all the above reasons, this technology has been languishing in obscurity and not much research has been carried out in the field of wireless energy transfer.
Human beings or other objects placed between the transmitter and receiver do not hinder the transmission of power. However, does magnetic coupling or resonance coupling have any harmful effects on humans? MIT's researchers are quite confident that WiTricity's coupling resonance' is safe for humans. They say that the magnetic fields tend to interact very weakly with the biological tissues of the body, and so are not prone to cause any damage to any living beings.
Safe, fairly efficient, good range: – Magnetic fields interact weakly with biological masses (humans), and energy is only transmitted between resonating objects. – Efficiency can be increased with time, most of the 60% lost is from heat radiated from the coils. Theoretically one stationary coil in a room could power multiple devices with receiving coils. No more messy wires, and with widespread enough use it could even eliminate costly batteries.
The resonance condition should be satisfied and if any error exists, there is no possibility of power transfer.
If there is any possibility of very strong ferromagnetic material presence causes low power transfer due to radiation.
MIT's WiTricity is only 40 to 45% efficient and according to Soljacic, they have to be twice as efficient to compete with the traditional chemical batteries. The team's next aim is to get a robotic vacuum or a laptop working, charging devices placed anywhere in the room and even robots on factory floors. The researchers are also currently working on the health issues related to this concept and have said that in another three to five years time, they will come up with a WiTricity system for commercial use.
WiTricity, if successful will definitely change the way we live. Imagine cellphones, laptops, digital camera's getting self charged! Wow! Let's hope the researchers will be able to come up with the commercial system soon. Till then, we wait in anticipation!
1.
2.
3. 4.
5. 6.
7.
8.
9.
An article published in the Science Magazine as “Wireless Power Transfer via Strongly Coupled Magnetic Resonances” by Andre kurs, Science 317, 83(2007); Dol:10.1126/ science.1143254. H. Haus , “Waves and Fields in Optoelectronics”, Prentice hall Publishers, Englewood http://electron9.phys.utk.edu/optics507/modules/m6/coupled_resonators.htm “Efficient Non-Radiative Midrange Energy Transfer” by Aristeidies karalis, Marlin Soljacic. Nikola Tesla, My Inventions, Ben Johnston, Ed., Austin, Hart Brothers, p. 91,1982. Thomas F. Valone, “ Tesla’ s Wireless Energy... For the 21st Century!!! One Step Beyond Direct TV!!!” Extra Ordinary Technology, 1, no. 4, Oct / Nov / Dec 2003. James O. McSpadden, “ Wireless Power Transmission Demonstration”, Texas A&M University, June, 1997. Charych Arthur (Setauket, NY), “ System and method for wireless electrical power transmission”, Patent No. 6,798,716, September 28, 2004. Joe T. Howell, et. al , “Advanced receiver / converter experiments for laser wireless power transmission”5th. Wireless transmission conference, pp 1-8, Garanda, Spain,2004.
PRESENTED BY: AMIT MAHAJAN
Witricity Basics
Short Range Coupling
Medium Range Wireless Energy Transmission: Resonant Induction
Wireless
Energy
Detailed Principle
How Safe is WiTricity?
What's the Future of WiTricity?
Advantages
Limitations
Bibliography
Transmission:
Inductive
Currently, wired electricity powers nearly everything. It travels through wires in the form of Alternating Current, and powers most of our devices in the form of Direct Current.
In our present electricity generation system we waste more than half of its resources. Especially the transmission and distribution losses are the main concern of the present power technology.
The resistance of the wire used in the electrical grid distribution system causes a loss of 26-30% of the energy generated. This loss implies that our present system of electrical distribution is only 70-74% efficient. We have to think of alternate technology to transmit and distribute the electricity. The transmission of power without wires may be one noble alternative for electricity transmission.
The Transfer of Electricity from one place to another without wires is known as “WiTricity”.
On June 7 ’07, a team of researchers at MIT announced the successful operation of WiTricity concept.
They had lit up a 60W bulb with a power source at a distance of 7 feet(over 2m) with no wires.
Prof. Marin Soljacic from Massachusetts Institute of Technology (MIT), is the one who has proved that magnetic coupled resonance can be utilized in order to transfer energy without wires. What's even more interesting is how he came about this idea. Soljacic, just like any of us was fed up of his 'low battery' beeping cell phone and wondered just like any of us if there was a way to get rid of this 'charging problem'.
However, here is where the difference between Soljacic and any of us comes in. He didn't just stand there wondering, instead he tried to figure out if there existed any physical phenomenon which could be of some help. He remembered Michael Faraday's discovery of electromagnetic induction (1831) and used it to come up with WiTricity.
There are 3 major types of wireless energy transfer: – Short range; Inductive Coupling – Medium range; Resonant Induction – Long range; Electromagnetic Wave Power Transfer
What Is Inductive Coupling? Inductive Coupling is a method for short range wireless energy transfer. Its range can vary, but it’s often very short. Because of its short range it usually is used when the device containing the receiver and the device containing the transmitter are touching.
Inductive coupling works on principles of electromagnetism:
the
When a current (electricity) passes through a wire, it generates a magnetic field perpendicular to the wire. This effect can be magnified through coiling the wire. When a wire is in proximity to a magnetic field, it generates a current in that wire. Transferring energy between wires through magnetic fields is inductive coupling. Magnetic fields decay quickly , making inductive coupling effective only at very short ranges.
Pros: safe, efficient. Cons: Limited range. Inductive coupling is used for wireless charging of electronic devices. Although its range is limiting, several products use inductive coupling to charge, such as electric toothbrushes.
What Is Resonant Induction?
A group of engineers at MIT came up with the idea to use resonant induction to transmit power wirelessly. They deemed their result “WiTricity” (like Wi-Fi) . WiTricity can transmit electricity wirelessly at 40% efficiency to about 7 feet.
Resonant induction still uses the same principles as magnetic induction (magnetic fields to transfer current) , but it uses resonance to increase the range at which the transfer can efficiently take place.
“Resonance", a phenomenon that causes an object to vibrate when energy of a certain frequency is applied.
Everything resonates at a certain frequency, based on its shape and material. Energy transfers easily between resonating objects. An example of this is when an opera singer shatters wine glasses by singing at the frequency at which the glasses resonate. With resonant induction, power is transmitted between two resonating coils.
Consider two self resonating copper coils of same resonating frequency with a diameter 20 inches each. One copper wire is connected to the power source (WiTricity transmitter), while the other copper wire is connected to the device (WiTricity Receiver). The electric power from the power source causes the copper coil connected to it to start oscillating at a particular (MHz) frequency.
Subsequently, the space around the copper coil gets filled with nonmagnetic radiations. This generated magnetic field further transfers the power to the other copper coil connected to the receiver. Since this coil is also of the same frequency, it starts oscillating at the same frequency as the first coil. This is known as 'coupled resonance' and is the principle behind WiTricity.
The first copper coil (24 inches in diameter) was connected to the power source and the second was connected to the bulb, and were made to resonate at a frequency of 10 MHz. The bulb glowed even when different objects (like a wooden panel) were placed between the two coils. The system worked with 40% efficiency and the power that wasn't utilized remained in the vicinity of the transmitter itself, and did not radiate to the surrounding environment.
No, this concept of wireless electricity is not new. In fact it dates back to the 19th century, when Nikola Tesla used conduction- based systems instead of resonance magnetic fields to transfer wireless power. Further, in 2005, Dave Gerding coined the term WiTricity which is being used by the MIT researchers today.
Moreover, we all are aware of the use of electromagnetic radiation (radio waves) which is quite well known for wireless transfer of information. In addition, lasers have also been used to transmit energy without wires. However, radio waves are not feasible for power transmissions because the nature of the radiation is such that it spreads across the place, resulting into a large amount of radiations being wasted.
And in the case of lasers, apart from requirement of uninterrupted line of sight (obstacles hinders the transmission process), it is also very dangerous.
What Soljacic's team has done is that they have specifically tuned the transmitting unit to the receiving device. The transmission is also not hindered by the presence of any object in the line of sight. If the object to be charged is in the vicinity of the WiTricity source, then the energy transfer will undoubtedly take place.
In this 'coupling resonance' system, the electric energy that is not used up by the receiver does not get radiated into the surrounding environment, but remains in the vicinity of the transmitter. This ensures safety as well as minimal wastage of power. One of the five researchers, Dr. Aristeidis Karalis says that their coupling resonance system is one million times more efficient as compared to that of Nikola Tesla.
In 1891, Nikola Tesla invented a type of resonant transformer called the Tesla coil, which was used to generate very high voltage, low current, and high frequency alternating electricity. He experimented with a large variety of coils and configurations, one of which is as:
Referring to Fig. 1, the capacitor 1C forms two resonant circuits: one with the primary coil 1P, and another with the secondary coil 1S. The voltage is supplied by the Neon sign transformer 1T. The spark gap 1SG consists of two electrodes separated by a gap, filled with an inert gas. When high enough voltage is applied across it, a spark forms, ionizing the gas, and allowing conduction. As the voltage across the gap 1SG increases, the charge across the capacitor 1C also increases.
When the gap sparks, the capacitor discharges into the primary and the secondary. Thus, the voltage “bounces” back and forth at an extremely high rate. When the rate of discharge between the capacitor 1C and primary 1P, matches that of the capacitor and secondary 1S, the two circuits are said to be "in resonance". The voltage rises to such high levels that it is discharged through the discharge terminal in the form of an electric arc.
Tesla used these coils to conduct numerous innovative experiments. In 1899, he achieved a major breakthrough in his work at Colorado by transmitting 100 million volts of electric power wirelessly over a distance of 26 miles to light up a bank of 200 light bulbs and run one electric motor. He claimed to have achieved 95% efficiency. The method he used to wirelessly transmit electricity was the employment of the earth's own resonance with its specific vibrational frequency to conduct AC electricity via a large electric oscillator at about 7.8 Hz.
However, there were several safety hazards that were needed to be considered. A Tesla Coil produces high voltage electric arcs. These arcs cause permanent damage to electrical devices on contact. Many devices can also be damaged without being directly struck by the arc, due to the sheer amount of voltage being transferred. Tesla coils also destroy hearing aids and cardiac pacemakers in their vicinity. For all the above reasons, this technology has been languishing in obscurity and not much research has been carried out in the field of wireless energy transfer.
Human beings or other objects placed between the transmitter and receiver do not hinder the transmission of power. However, does magnetic coupling or resonance coupling have any harmful effects on humans? MIT's researchers are quite confident that WiTricity's coupling resonance' is safe for humans. They say that the magnetic fields tend to interact very weakly with the biological tissues of the body, and so are not prone to cause any damage to any living beings.
Safe, fairly efficient, good range: – Magnetic fields interact weakly with biological masses (humans), and energy is only transmitted between resonating objects. – Efficiency can be increased with time, most of the 60% lost is from heat radiated from the coils. Theoretically one stationary coil in a room could power multiple devices with receiving coils. No more messy wires, and with widespread enough use it could even eliminate costly batteries.
The resonance condition should be satisfied and if any error exists, there is no possibility of power transfer.
If there is any possibility of very strong ferromagnetic material presence causes low power transfer due to radiation.
MIT's WiTricity is only 40 to 45% efficient and according to Soljacic, they have to be twice as efficient to compete with the traditional chemical batteries. The team's next aim is to get a robotic vacuum or a laptop working, charging devices placed anywhere in the room and even robots on factory floors. The researchers are also currently working on the health issues related to this concept and have said that in another three to five years time, they will come up with a WiTricity system for commercial use.
WiTricity, if successful will definitely change the way we live. Imagine cellphones, laptops, digital camera's getting self charged! Wow! Let's hope the researchers will be able to come up with the commercial system soon. Till then, we wait in anticipation!
1.
2.
3. 4.
5. 6.
7.
8.
9.
An article published in the Science Magazine as “Wireless Power Transfer via Strongly Coupled Magnetic Resonances” by Andre kurs, Science 317, 83(2007); Dol:10.1126/ science.1143254. H. Haus , “Waves and Fields in Optoelectronics”, Prentice hall Publishers, Englewood http://electron9.phys.utk.edu/optics507/modules/m6/coupled_resonators.htm “Efficient Non-Radiative Midrange Energy Transfer” by Aristeidies karalis, Marlin Soljacic. Nikola Tesla, My Inventions, Ben Johnston, Ed., Austin, Hart Brothers, p. 91,1982. Thomas F. Valone, “ Tesla’ s Wireless Energy... For the 21st Century!!! One Step Beyond Direct TV!!!” Extra Ordinary Technology, 1, no. 4, Oct / Nov / Dec 2003. James O. McSpadden, “ Wireless Power Transmission Demonstration”, Texas A&M University, June, 1997. Charych Arthur (Setauket, NY), “ System and method for wireless electrical power transmission”, Patent No. 6,798,716, September 28, 2004. Joe T. Howell, et. al , “Advanced receiver / converter experiments for laser wireless power transmission”5th. Wireless transmission conference, pp 1-8, Garanda, Spain,2004.
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