We are implementing new concept in our project. We are going to transmit the electrical energy without wire. It is not easy concept. Here power is transmit from one place to another place using electromagnetic induction or laser concept. Wireless energy transfer or Wireless power is the transmission of electrical energy from a power source to an electrical load without interconnecting wires. Wireless transmission is useful in cases where interconnecting wires are inconvenient, hazardous, or impossible. Wireless power differs from wireless telecommunications, where the signal-to-noise ratio (SNR) or the percentage of energy received becomes critical only if it is too low for the signal to be adequately recovered. With wireless power transmission, efficiency is the more important parameter. The most common form of wireless power transmission is carried out using inductive coupling followed by resonant inductive coupling. Other methods include microwaves and lasers.
1. Electromagnetic induction
Electromagnetic induction wireless transmission techniques are near field over distances comparable to a few times the diameter of the device or devices approaching one quarter of the wavelength used. Near field energy itself is non-radiative but some radiative losses do occur. In addition there are usually resistive losses. Energy transfer by induction is usually magnetic but capacitive coupling can also be achieved.
Electrodynamic induction method
Electromagnetic induction can work on the principal of a primary coil generating a predominantly magnetic field and a secondary coil being within that field so a current is induced in the secondary. Coupling must be tight in order to achieve high efficiency. As the distance from the primary is increased, more and more of the magnetic field misses the secondary. Even over a relatively short range the induction method is grossly inefficient, wasting much of the transmitted energy. The action of an electrical transformer is the simplest instance of wireless power transmission by induction. The primary and secondary circuits of a transformer are not directly connected. Energy transfer takes place by electromagnetic coupling through a process known as mutual induction. Principle functions are stepping the primary voltage either up or down and electrical isolation. Mobile phone and electric toothbrush battery chargers, and electrical power distribution transformers are examples of how this principle is used. Induction cookers use this method. The main drawback to this basic form of wireless transmission is short range.
The receiver must be directly adjacent to the transmitter or induction unit in order to efficiently couple with it. The application of resonance improves the situation somewhat. When resonant coupling is used the transmitter and receiver inductors are tuned to a mutual frequency and the drive current is modified from a sinusoidal to a non -sinusoidal transient waveform. Pulse power transfer occurs over multiple cycles. In this way significant power may be transmitted over a distance of up to a few times the size of the transmitter. Such transmitting and receiving coils are usually single layer solenoids or flat spirals with series capacitors, which, in combination, allow the receiving element to be tuned to the transmitter frequency. Common uses of resonance-enhanced electrodynamic induction are charging the batteries of portable devices such as laptop computers and cell phones, medical implants and electric vehicles.
A localized charging technique [patent application PCT/CN2008/0728855] selects the appropriate transmitting coil in a multilayer winding array structure. Resonance is used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi wireless charging standard. It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters. [pic]
2. Laser method
With a laser beam centered on its panel of photovoltaic cells, a lightweight model plane makes the first flight of an aircraft powered by a laser beam inside a building at NASA Marshall Space Flight Center. In the case of electromagnetic radiation closer to visible region of spectrum (10s of microns (um) to 10s of nm), power can be transmitted by converting electricity into a laser beam that is then pointed at a solar cell receiver. This mechanism is generally known as “powerbeaming” because the power is beamed at a receiver that can convert it to usable electrical energy.
Advantages of laser based energy transfer compared with other wireless methods are 1. collimated monochromatic wavefront propagation allows narrow beam cross-section area for energy transmission over large ranges. 2. compact size of solid state lasers-photovoltaics semiconductor diodes fit into into small products. 3. no radio-frequency interference to existing radio communication such as Wi-fi and cell phones. 4. control of access; only receivers illuminated by the laser receive power. Its drawbacks are:
1. Conversion to light, such as with a laser, is inefficient 2. Conversion back into electricity is inefficient, with photovoltaic cells achieving 40%-50% efficiency. (Note that conversion efficiency is rather higher with monochromatic light than with insolation of solar panels). 3. Atmospheric absorption causes losses.
4. As with microwave beaming, this method requires a direct line of sight with the target. The laser “powerbeaming” technology has been mostly explored in military weapons and aerospace applications and is now being developed for commercial and consumer electronics Low-Power applications. Wireless energy transfer system using laser for consumer space has to satisfy Laser safety requirements standardized under IEC 60825. To develop an understanding of the trade-offs of Laser (“a special type of light wave”-based system) 1. Propagation of a laser beam (on how Laser beam propagation is much less affected by diffraction limits) 2. Coherence and the range limitation problem (on how spatial and spectral coherence characteristics of Lasers allows better distance-to-power capabilities)
3. Airy disk (on how wavelength fundamentally dictates the size of a disk with distance) 4. Applications of laser diodes (on how the laser sources are utilized in various industries and their sizes are reducing for better integration) Geoffrey Landis is one of the pioneers of solar power satellite and laser-based transfer of energy especially for space and lunar missions. The continuously increasing demand for safe and frequent space missions has resulted in serious thoughts on a futuristic space elevator that would be powered by lasers. NASA’s space elevator would need wireless power to be beamed to it for it to climb a tether.
NASA’s Dryden Flight Research Center has demonstrated flight of a lightweight unmanned model plane powered by a laser beam. This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system and the lack of need to return to ground. “Lasermotive” demonstrated laser powerbeaming at one kilometer during NASA’s 2009 powerbeaming contest. Also “Lighthouse DEV” (a spin off of NASA Power Beaming Team) along with “University of Maryland” is developing an eye safe laser system to power a small UAV. Since 2006, “PowerBeam” which originally invented the eye-safe technology and holds all crucial patents in this technology space, is developing commercially ready units for various consumer and industrial electronic products. [pic]