As the Earth’s population continues to grow, the demand for electricity will outpace our ability to produce it and transmit it around the world. Eventually, wireless power will become a necessity.
There are two different means of wirelessly transferring power, far field and near-field. Far-field methods permit long-range energy transfers and typically involve lasers or microwave transmissions. Near-field transmissions typically involve the use of inductive techniques and magnetic fields to move energy across much shorter distances.
Wireless information transfer and wireless energy transfer are similar, as they are both based on electromagnetic field. When transferring wireless information, signal-to-noise ratio is the most important consideration. When transferring wireless energy, receive-to-transmit ratio is the important factor. The methods of wireless transfer are divided into two categories: far-field and near-field.
When moving wireless energy across great distances (far-field), microwaves will be used to transmit electricity to earth from solar power stations on the moon. Tens of thousands of receivers on Earth would capture this energy, and a rectenna would convert it to electricity. A rectenna is a rectifying antenna that is used to convert microwave energy into direct current electricity.
Rectennas are used in wireless power transmission systems that transmit power by radio waves (microwaves). A simple rectenna element consists of a dipole antenna with a diode connected across the dipole elements. The diode rectifies the AC current induced in the antenna by the microwaves, to produce DC power, which powers a load connected across the diode.
Schottky diodes are usually used because they have the lowest voltage drop and highest speed and therefore have the lowest power losses due to conduction and switching. Large rectennas consist of an array of many such dipole elements.
Microwave power is beamed from a space solar satellite to a receiving antenna or “rectenna” on Earth.
(Image courtesy of Space Studies Institute)
Because microwaves pass through the atmosphere easily, and rectennas rectify microwaves into electricity efficiently, an earth-based rectenna could be constructed with a mesh-like framework, allowing the sun’s rays and rain to pass through to the ground, diminishing environmental effect.
The other method of far-field wireless transmission is the laser beam, which is a coherent light beam capable to transport very high energy, which makes it an efficient means to transfer energy point to point using a line of sight.
Power can be transmitted by converting electricity into a laser beam that is then pointed at a solar cell receiver. This procedure is generally known as “power-beaming,” because the power is beamed at a receiver that can convert it to usable electrical energy.
Photo Image: NASA
By collecting solar energy in space instead of on earth, dependency on cloud-free days is eliminated. In traditional solar collecting, energy is lost on its way through the atmosphere through reflection and absorption, but space-based solar power systems convert energy outside the atmosphere to avoid this loss.
Near-field transmissions typically involve the use of inductive techniques and magnetic fields to move energy across much shorter distances. Both far-field and near-field transmissions utilize the principles of electromagnetism and the intrinsic relationship of electric and magnetic fields. Near-field transmissions are safer and more efficient; therefore most consumer-based development is being built around this method.
Most of near-field transmissions use resonant inductive coupling, where a primary coil generates a magnetic field, which induces an alternating electric current in a secondary coil that resides within this field. This magnetic field is then coupled with another magnetic field, which has its own secondary alternating electric current that is resonating at a similar frequency. The wireless transfer of power is naturally produced between these two fields, and the higher the resonance, the lower the loss of power during transmission.
WiTricity is building a near-field wireless charging apparatus for consumer devices. With the help of the Haier Group, a Chinese electronics manufacturer, WiTricity demonstrated this technology by wirelessly powering a 32-inch television at a distance of six feet.
The company’s prototype consists of a transmitter that converts AC power (using a wall socket) into a magnetic field, and then uses the field to transmit this magnetic energy to a capture device. This device then converts the magnetic energy into electricity. The two devices are highly resonant, which means the wireless energy transfer is highly efficient.
Delphi Automotive is working with WiTricty to develop a wireless charging system for electric cars. The groundbreaking technology will enable automotive manufacturers to integrate wireless charging into the design of hybrid and electric vehicles. This wireless charging system would not use plugs or charging cords. Drivers would park their electric vehicle over a wireless energy source that sits on, or is embedded in the garage floor, and the system will automatically transfer power to the battery charger on the vehicle, transferring enough watts to fully charge an electric car at the same rate as most residential plug-in chargers.
To make wireless transmission of energy work, a single global standard needs to be developed through a cooperative organization of international developers, manufacturers and distributors. This standard will be the blueprint for utilizing wireless energy transmission worldwide. The safety and range of energy needs can be addressed collectively, bringing wireless energy into the world of a practical real world solution.
Samsung and Qualcomm, joined with a group of other technology companies to announce a new project that aims to promote the “global standardization of a wireless power transfer technology,” which is named “Alliance for Wireless Power (A4WP)” The organization’s approach includes a transmitter and receiver antenna design that is easily implemented, a simple wireless power control system, and the ability to transfer power through non-metallic surfaces.
There is another standard protocol for charging mobile phones initiated by the Wireless Power Consortium (WPC), which is backed by more than 100 companies. A4WP and WPC use the same fundamental magnetic induction to transfer energy wirelessly at a close distance, using a highly resonant magnetic circuit. There does not appear to be a fundamental difference in technology, so why have two standards? Marketing. Let’s get the marketing people out of technology advancements. Remember what happened with VHS and Betamax?
Wireless power is an exciting new frontier, opening up new possibilities for manufacturers and consumers around the world. This new frontier will have a major impact on many significant market segments and create new ways to interact with the design of appliances and corresponding products. As this technology is adopted by consumers, it is imperative that engineering and design teams, wireless power providers, manufacturers and governing bodies join forces to insure that a universal solution that meets present and future consumer needs is always the main concern. Only by working together will universal wireless energy delivery reach its potential and make wireless truly wireless.
For additional information:
http://www.powerbeaminc.com/media/cmp_eetimes_altenergy_20100621.pdf
http://www.witricity.com/pdfs/patents/EP2345100.pdf
http://arxiv.org/ftp/physics/papers/0611/0611063.pdf
http://iccd.et.tudelft.nl/2009/proceedings/517Mazlouman.pdf
http://www.esa.int/gsp/ACT/doc/POW/ACT-RPR-NRG-2009-SPS-ICSOS-concepts-for-laser-WPT.pdf
http://authors.library.caltech.edu/5349/1/KARaipcp06.pdf
http://www.ipcbee.com/vol6/no2/51-f20017.pdf