30-06-2012, 03:45 PM
RECENT TRENDS IN POWER DISTRIBUTIONS: WIRELESS POWER TRANSMISSION
[attachment=26328]
1. INTRODUCTION
Wireless power transmission is the process that takes place in any system where electromagnetic energy is transmitted from a power source (such as a Tesla coil) to an electrical load, without interconnecting wires. Wireless transmission is employed in cases where interconnecting wires are inconvenient, hazardous, or impossible. Though the physics can be similar (pending on the type of wave used), there is a distinction from electromagnetic transmission for the purpose of transferring information (radio), and where the amount of power transmitted is only important when it affects the integrity of the signal.
Wireless energy transfer, the transmission of electrical energy without wires, has been around since about 1856 in the form of mutual induction. Using induction it is possible to transmit and receive signals over a considerable distance. However, to draw significant power in that way, the two inductors must be placed fairly close together. If resonant coupling is used, where inductors are tuned to a mutual frequency, power may be transmitted over a range of many meters. Another form of wireless energy transfer is electromagnetic radiation, such as in radio waves. For example, a fluorescent tube held near an active radio transmitter radiating more than a few watts (such as an amateur radio transmitter) will glow. The reason behind this phenomenon is similar to the physics involved in the aurora borealis.
As wireless telecommunications technologies were being developed during the early 1900s, researchers were investigating different wireless energy transfer methods to power more significant loads than the high-resistance sensitive devices that were being used to detect the received energy. At the St. Louis World's Fair (1904), a prize was offered for a successful attempt to drive a 0.1 Horsepower air-ship motor by energy transmitted through space at a distance of least 100 feet.
2. METHODS OF WIRELESS POWER TRANSMISSION
2.1. SHORT DISTANCE METHOD:
These methods can reach at most a few centimeters. The principle beyond in this method is Electromagnetic induction. The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are electrically isolated from each other. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The electric toothbrush charger is an example of how this principle can be used. The main drawback to induction, however, is the short range. The receiver must be in very close proximity to the transmitter or induction unit in order to inductively couple with it.
2.1.1. Applications:
• The electric toothbrush battery charger.
• The induction cooker stovetop.
2.2. MODERATE DISTANCE METHOD:
These methods achieve distances of a few meters. The principle beyond in this principle is Evanescent wave coupling. In a short theoretical analysis they demonstrate that by sending electromagnetic waves around in a highly angular waveguide, evanescent waves are produced which carry no energy. If a proper resonant waveguide is brought near the transmitter, the evanescent waves can allow the energy to tunnel (specifically evanescent wave coupling, the electromagnetic equivalent of tunneling) to the power drawing waveguide, where they can be rectified into DC power. Since the electromagnetic waves would tunnel, they would not propagate through the air to be absorbed or dissipated, and would not disrupt electronic devices or cause physical injury like microwave or radio wave transmission might. Researchers anticipate up to 5 meters of range for the initial device, and are currently working on a functional prototype. On June 7, 2007, it was reported that a prototype system had been implemented. The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb from a power source that was seven feet (2 meters) away at roughly 40% efficiency. (Ability to power a 60 watt light bulb from a power source that was 2 meters away.
2.2.1 Basic principle:
Witricity is nothing but the short name of Wireless Electricity. The basic Concept behind this is Magnetic Resonance. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while dissipating relatively little energy inextraneous off-resonant objects. In systems of coupled resonances, there is often a general “Strongly Coupled” regime of operation. If one can operate in that regime in a given system, the energy transfer is expected to be very efficient. Midrange power transfer implemented in this way can be nearly omni directional and efficient, irrespective of the geometry of the surrounding space, with low interference and losses into environmental objects. The above considerations apply irrespective of the physical nature of the resonances. Magnetic resonances are particularly suitable for everyday applications because most of the Common materials do not interact with Magnetic Fields, so interactions with Environmental objects are suppressed even further. We were able to identify the strongly coupled regime in the system of two coupled magnetic resonances by exploring Non-radioactive (near-field) magnetic resonant induction at Megahertz frequencies.
2.2.2. Experimental Design:
Our experimental scheme consists of two Self-resonant coils. One coil (source coil) is coupled inductively to an oscillating circuit; the other (device coil) is coupled inductively to a resistive load. Self-resonant coils rely on the interplay between distributed inductance and distributed capacitance to achieve resonance.
The coils are made of anelectrically conducting wire of total length ‘l’ and cross-sectional radius ‘a’, wound into a helix of ‘n’ turns, radius ‘r, and height ‘h’. There is no exact solution for a finite helix in the literature, and even in the case of infinitely long coils, the solutions rely on assumptions that is inadequate for this system. So here the method implemented is simple Quasi-static model to find the parameters. Those are in Electro Magnetic equations.
The efficiency of the system is the ratio of output power to input power.
The output power is the device power rating and input power is sum of the power dissipated by source, power loss due to decay. The experiment done in 7th June, 2007 by the Massachusetts Institute of Technology, Cambridge gives the result that in order to get 60W approximate power is the output useful power with 40% efficiency. They resonated the circuit at ≈9.9 MHz so that they developed the power is transmitted up to8 times greater than radius of the coil used.
2.2.3. Advantages:
There are so many advantages with this Witricity concept, some of those are:
• Unaffected by the day night cycle, weather or seasons.
• It is a boon for the devices which use midrange power.
2.2.4. Limitations:
There are a few of limitations with this system. Those are:
1. The resonance condition should be satisfied and if any error exists, there is no possibility of power transfer.
2. If there is any possibility of Very Strong ferromagnetic material presence, then there may be a possibility of low power transfer due to radiations.
[attachment=26328]
1. INTRODUCTION
Wireless power transmission is the process that takes place in any system where electromagnetic energy is transmitted from a power source (such as a Tesla coil) to an electrical load, without interconnecting wires. Wireless transmission is employed in cases where interconnecting wires are inconvenient, hazardous, or impossible. Though the physics can be similar (pending on the type of wave used), there is a distinction from electromagnetic transmission for the purpose of transferring information (radio), and where the amount of power transmitted is only important when it affects the integrity of the signal.
Wireless energy transfer, the transmission of electrical energy without wires, has been around since about 1856 in the form of mutual induction. Using induction it is possible to transmit and receive signals over a considerable distance. However, to draw significant power in that way, the two inductors must be placed fairly close together. If resonant coupling is used, where inductors are tuned to a mutual frequency, power may be transmitted over a range of many meters. Another form of wireless energy transfer is electromagnetic radiation, such as in radio waves. For example, a fluorescent tube held near an active radio transmitter radiating more than a few watts (such as an amateur radio transmitter) will glow. The reason behind this phenomenon is similar to the physics involved in the aurora borealis.
As wireless telecommunications technologies were being developed during the early 1900s, researchers were investigating different wireless energy transfer methods to power more significant loads than the high-resistance sensitive devices that were being used to detect the received energy. At the St. Louis World's Fair (1904), a prize was offered for a successful attempt to drive a 0.1 Horsepower air-ship motor by energy transmitted through space at a distance of least 100 feet.
2. METHODS OF WIRELESS POWER TRANSMISSION
2.1. SHORT DISTANCE METHOD:
These methods can reach at most a few centimeters. The principle beyond in this method is Electromagnetic induction. The action of an electrical transformer is the simplest instance of wireless energy transfer. The primary and secondary circuits of a transformer are electrically isolated from each other. The transfer of energy takes place by electromagnetic coupling through a process known as mutual induction. (An added benefit is the capability to step the primary voltage either up or down.) The electric toothbrush charger is an example of how this principle can be used. The main drawback to induction, however, is the short range. The receiver must be in very close proximity to the transmitter or induction unit in order to inductively couple with it.
2.1.1. Applications:
• The electric toothbrush battery charger.
• The induction cooker stovetop.
2.2. MODERATE DISTANCE METHOD:
These methods achieve distances of a few meters. The principle beyond in this principle is Evanescent wave coupling. In a short theoretical analysis they demonstrate that by sending electromagnetic waves around in a highly angular waveguide, evanescent waves are produced which carry no energy. If a proper resonant waveguide is brought near the transmitter, the evanescent waves can allow the energy to tunnel (specifically evanescent wave coupling, the electromagnetic equivalent of tunneling) to the power drawing waveguide, where they can be rectified into DC power. Since the electromagnetic waves would tunnel, they would not propagate through the air to be absorbed or dissipated, and would not disrupt electronic devices or cause physical injury like microwave or radio wave transmission might. Researchers anticipate up to 5 meters of range for the initial device, and are currently working on a functional prototype. On June 7, 2007, it was reported that a prototype system had been implemented. The MIT researchers successfully demonstrated the ability to power a 60 watt light bulb from a power source that was seven feet (2 meters) away at roughly 40% efficiency. (Ability to power a 60 watt light bulb from a power source that was 2 meters away.
2.2.1 Basic principle:
Witricity is nothing but the short name of Wireless Electricity. The basic Concept behind this is Magnetic Resonance. Two resonant objects of the same resonant frequency tend to exchange energy efficiently, while dissipating relatively little energy inextraneous off-resonant objects. In systems of coupled resonances, there is often a general “Strongly Coupled” regime of operation. If one can operate in that regime in a given system, the energy transfer is expected to be very efficient. Midrange power transfer implemented in this way can be nearly omni directional and efficient, irrespective of the geometry of the surrounding space, with low interference and losses into environmental objects. The above considerations apply irrespective of the physical nature of the resonances. Magnetic resonances are particularly suitable for everyday applications because most of the Common materials do not interact with Magnetic Fields, so interactions with Environmental objects are suppressed even further. We were able to identify the strongly coupled regime in the system of two coupled magnetic resonances by exploring Non-radioactive (near-field) magnetic resonant induction at Megahertz frequencies.
2.2.2. Experimental Design:
Our experimental scheme consists of two Self-resonant coils. One coil (source coil) is coupled inductively to an oscillating circuit; the other (device coil) is coupled inductively to a resistive load. Self-resonant coils rely on the interplay between distributed inductance and distributed capacitance to achieve resonance.
The coils are made of anelectrically conducting wire of total length ‘l’ and cross-sectional radius ‘a’, wound into a helix of ‘n’ turns, radius ‘r, and height ‘h’. There is no exact solution for a finite helix in the literature, and even in the case of infinitely long coils, the solutions rely on assumptions that is inadequate for this system. So here the method implemented is simple Quasi-static model to find the parameters. Those are in Electro Magnetic equations.
The efficiency of the system is the ratio of output power to input power.
The output power is the device power rating and input power is sum of the power dissipated by source, power loss due to decay. The experiment done in 7th June, 2007 by the Massachusetts Institute of Technology, Cambridge gives the result that in order to get 60W approximate power is the output useful power with 40% efficiency. They resonated the circuit at ≈9.9 MHz so that they developed the power is transmitted up to8 times greater than radius of the coil used.
2.2.3. Advantages:
There are so many advantages with this Witricity concept, some of those are:
• Unaffected by the day night cycle, weather or seasons.
• It is a boon for the devices which use midrange power.
2.2.4. Limitations:
There are a few of limitations with this system. Those are:
1. The resonance condition should be satisfied and if any error exists, there is no possibility of power transfer.
2. If there is any possibility of Very Strong ferromagnetic material presence, then there may be a possibility of low power transfer due to radiations.