Electronics has revolutionized our society by providing many devices e.g. laptops, palm pilots, digital cameras, household robots, etc. However most of these devices are powered by batteries, which need to be recharged through cables. Wireless powering of these and similar devices is now set to complete our transition to cable free wireless life.
A new method developed by Disney Research for wirelessly transmitting power throughout a room enables users to charge electronic devices as seamlessly as they now connect to WiFi hotspots, eliminating the need for electrical cords or charging cradles. The researchers demonstrated their method, called quasistatic cavity resonance (QSCR), inside a specially built 16-by-16-foot room at their lab. They safely generated near-field standing magnetic waves that filled the interior of the room, making it possible to power several cellphones, fans and lights simultaneously.
“This new innovative method will make it possible for electrical power to become as ubiquitous as WiFi,” said Alanson Sample, associate lab director & principal research scientist at Disney Research. “This in turn could enable new applications for robots and other small mobile devices by eliminating the need to replace batteries and wires for charging.”
The QSCR method involves inducing electrical currents in the metalized walls, floor and ceiling of a room, which in turn generate uniform magnetic fields that permeate the room’s interior. This enables power to be transmitted efficiently to receiving coils that operate at the same resonant frequency as the magnetic fields. The induced currents in the structure are channeled through discrete capacitors, which isolate potentially harmful electrical fields. “Our simulations show we can transmit 1.9 kilowatts of power while meeting federal safety guidelines,” Chabalko said. “This is equivalent to simultaneously charging 320 smart phones.”
In the demonstration, the researchers constructed a 16-by-16-foot room with aluminum walls, ceiling and floor bolted to an aluminum frame. A copper pole was placed in the center of the room; a small gap was created in the pole, into which discrete capacitors were inserted.
“It is those capacitors that set the electromagnetic frequency of the structure and confine the electric fields,” Chabalko explained. Devices operating at that low megahertz frequency can receive power almost anywhere in the room. At the same time, the magnetic waves at that frequency don’t interact with everyday materials, so other objects in the room are unaffected.
Rezence technology has improved the wireless charging capabilities to 1-50W range (operating at frequencies of 6.78 MHz) that has expanded the range of products beyond smart phones to include laptops, tablets, and other consumer electronics while also supporting multi-device charging.
Intel is developing charging system with 20 watts of power enough to power a laptop, and is expected to hit the market in 2016. At the IFA trade show in Berlin, the company demonstrated a wireless charging unit that can be attached to the underside of a desk and send power to devices sitting on the desk. It was shown to power two smart phones simultaneously or, a convertible PC.
Currently, wireless power transmission is mostly used in the Consumer Electronics segment, which includes electric toothbrushes, smart phones, laptops, tablets, and wireless powering of radiofrequency identification (RFID) tags. Notably, wireless power transmission technology is being increasingly implemented in the Healthcare, Defense, and Industrial Applications segments. It is also being used to develop electric vehicles and to enable wireless charging.
The Global Wireless Power Transmission Market is expected to grow at a CAGR of 51.3 percent during the period 2015-2019, reaching $17.04 billion by 2020.
Wireless power transfer (WPT)
Wireless power transfer (WPT) or wireless energy transmission is the transmission of electrical energy from a power source to a consuming device, without the use of discrete man-made conductors. WPT use wireless transmitter that uses any of time-varying electric, magnetic, or electromagnetic fields to convey energy to one or wore receivers, where it is converted back to an electrical current and then used.
Wireless power techniques fall into two categories, non-radiative and radiative. In non-radiative techniques, power is typically transferred by magnetic fields using inductive coupling between coils of wire. A current focus is to develop wireless systems to charge mobile and handheld computing devices such as cellphones, digital music players and portable computers without being tethered to a wall plug. Power may also be transferred by electric fields using capacitive coupling between metal electrodes. In radiative far-field techniques, also called power beaming, power is transferred by beams of electromagnetic radiation, like microwaves or laser beams.
Researchers make breakthrough in wireless charging technology
Scientists at the Australian National University (ANU) have made a wireless charging breakthrough that allow wireless sensors to be charged with energy harvested from “solar or ambient radio frequency sources,” such as communication towers or other mobile phone base stations.
In a first, we have accurately modelled how much energy it takes to sense and transfer information by wireless sensors and are working on further ways to analyse the problem,” says lead researcher for the study Dr Salman Durrani.
“A major problem hindering the widespread deployment of wireless sensor networks is the need to periodically replace batteries. If we can use energy harvesting to solve the battery replacement problem for wireless sensors, we can implement long-lasting monitoring devices for health, agriculture, mining, wildlife and critical national infrastructure, which will improve the quality of life,” says lead researcher for the study Dr Salman Durrani.
Power over Wi-Fi or PoWi-Fi
Vamsi Talla and pals at the University of Washington in Seattle, have developed a way to broadcast power to remote devices using an existing Wi-Fi technology, they call their new approach power over Wi-Fi or PoWi-Fi. In their experiment camera could use Wi-Fi signals to create and store power, though slowly to take no more than one photograph every half an hour using their Wi-Fi charging system. PoWiFi can power devices up to 17-28 feet away from a normal Wi-Fi router.
The UW researchers have already launched the PoWiFi system in six homes in a metropolitan area and measured the impact on the residents’ browsing experiences. Browsing speeds were hardly slowed down at all with PoWiFi in place, and users typically didn’t notice a difference. With that test, the researchers demonstrated that the system can work in real-world networking situations, and won’t create a nuisance.
Because of limitations on the router power to 1 watt in the US (100 milliwatts in the Europe), the team has been able to charge up only low-power devices such as simple rechargeable batteries, simple temperature sensor, a grayscale camera with low resolution, and the charger for a Jawbone Up24 wearable fitness tracker. Another downside is that the farther the object is away from the router, it takes longer to charge.
In future, PoWiFi could be used to charge “Internet of Things”, area that embeds computing sensors in everyday objects.
Wireless charging for electric cars
Wireless charging for cars is more difficult than phones, due to the higher wattage necessary. “Wireless charging will win,” said Brusa’s CEO Josef Brusa in a press statement about the agreement. “It will give e-mobility a big boost; it will set new, sustainable technology apart from old gasoline-based technology. We are determined to make wireless charging a reality.” Although wireless charging isn’t any faster than using cables, companies hope that the convenience of park-to-charge will win customers.
ORNL surges forward with 20-kilowatt wireless charging for vehicles
The Department of Energy’s Oak Ridge National Laboratory has made a recent breakthrough with a proof-of-concept 20kW charger working at 90 percent efficiency. That’s enough to put 60 miles of charge into a Tesla every hour, right on par with Tesla’s own home chargers.
“The high-frequency magnetic fields employed in power transfer across a large air gap are focused and shielded,” Chinthavali said. “This means that magnetic fringe fields decrease rapidly to levels well below limits set by international standards, including inside the vehicle, to ensure personal safety.”
The researchers are already looking ahead to their next target of 50-kilowatt wireless charging, which would match the power levels of commercially available plug-in quick chargers. Providing the same speed with the convenience of wireless charging could increase consumer acceptance of electric vehicles and is considered a key enabler for hands-free, autonomous vehicles. Higher power levels are also essential for powering larger vehicles such as trucks and buses.
Qualcomm Shows Off Wireless Charging Technology for Electric Cars
Qualcomm has already fitted its Halo system of inductive chargers to Formula E course cars and other test vehicles, now it has licensed Swiss electric car parts maker Brusa, to develop, manufacture, and supply its Halo charging plates to other companies.
Japanese automaker, Toyota, has signed an agreement to licence the intellectual property of WiTricity Corp. that will allow charging of the electric vehicles by parking over small fifty centimeter square charging pad. One of the major limitations of this technology is the limited operating distance.
This wireless charging solution works by fitting vehicles with a compatible receiver. Cars can then simply be driven into position over a charging pad measuring around one meter across and just a few centimeters thick. Charging pads can be portable or fixed permanently in place, depending on requirements. Once parked over the charging pad, the driver launches the charge cycle via an accompanying mobile application. As well as monitoring the process, the app helps guide drivers into position when aligning the vehicle over the charging pad, ensuring optimal results.
Qualcomm imagines a future in which wireless charging plates are as ubiquitous as Wi-Fi hotspots, even suggesting highway charging lanes, where electric can top up their batteries as they drive.
UK to trial in-road wireless charging tech for electric vehicles
Highways England has announced plans to test concept of “Electric Charging Roads” that will charge electric vehicle as we drive on it. It will initially carry out test track trials initially, followed by subsequent on-road trials of the technology, which is designed to increase the range of EVs. Highways England says it is also committed to installing plug-in charging points every 20 miles (32 km) on the motorway network.
Cables buried underneath the roadway would generate electromagnetic fields that could be picked up by a receiver in the vehicle and transformed into electric power. The system would require a communication system, so that the roads can detect if a vehicle is coming and initiate the process.
UK Transport Minister Andrew Jones says the trials will help to keep Britain at the forefront of the development of this technology.
Wireless power transfer achieved at 5-meter distance
Chun T. Rim, a professor of Nuclear & Quantum Engineering at KAIST, and his team developed the “Dipole Coil Resonant System (DCRS)” for an extended range of inductive power transfer, up to 5 meters between transmitter and receiver coils. “With DCRS,” Professor Rim said, “a large LED TV as well as three 40 W-fans can be powered from a 5-meter distance.”
The researchers improved upon MIT’s (Massachusetts Institute of Technology) Coupled Magnetic Resonance System (CMRS) proposed in 2007 by replacing its complicated coil structure with only two compact ferrite core rods with windings at their centers, compacted the bulky structure, reduced the coil’s resonant frequency from 10 MHz to 100 KHz, reduced the high Q factor of 2,000 to 100, making the resonant coils less sensitive to surroundings such as temperature, humidity, and human proximity.
The team conducted several experiments and achieved promising results: for instance, under the operation of 20 kHz, the maximum output power was 1,403 W at a 3-meter distance, 471 W at 4-meter, and 209 W at 5-meter. For 100 W of electric power transfer, the overall system power efficiency was 36.9% at 3 meters, 18.7% at 4 meters, and 9.2% at 5 meters.
Professor Rim’s team completed a research project with the Korea Hydro & Nuclear Power Co., Ltd in March this year to remotely supply electric power to essential instrumentation and control equipment at a nuclear power plant in order to properly respond to an emergency like the one happened at the Fukushima Daiichi nuclear plant. They succeeded to transfer 10 W of electricity to the plant that was located 7 meters away from the power base.
To further improve the power transfer efficiency over distance, previous works have proposed the addition of an intermediate material between the source and receiver of a WPT system. These intermediate material are placed between the sources and receive coil assemblies and are independent of the source/receiver realization.
Wireless Power transfer for Military
WPT has the unique potential to transform war fighting of the future and alleviate the battlefield battery burden for both soldiers and manned and unmanned vehicles on land, air, and undersea. QinetiQ’s Talon robots that were deployed in Afghanistan automatically recharged their batteries when they were docked to an armored vehicle.
Other recent examples are charging of Soldier’s central battery from vehicle seat back as they sit in vehicles, charging of handheld devices through vests, powering helmet-mounted devices through Soldier vest-to-helmet WPT, Soldier helmet-to-goggle WPT to power devices such as night vision, radio devices and defog optics.
In the future advancements in wireless energy transfer will enable distribution of power amongst power sources, multimodal energy harvesters, and loads to occur wirelessly on the Soldier as a platform, so that all carried equipment will be powered and ready for operation at all times without thought to replacing individual equipment power sources.
As a long term goal, the Army is looking to supply troops remotely using wireless systems that could transfer power from a drone to solar panels or other devices that soldiers could plug into on the battlefield, officials said.
US Navy developing undersea wireless technology to recharge UUVs
The US Navy is developing methods to recharge underwater unmanned vehicles (UUVs) with the support of undersea wireless technology, in a bid to reduce time between missions and enhance overall utility. The underwater energy transfer programme was performed using data that is transferred wirelessly underwater using underwater optical communications system.
“Underwater data and energy transfer are expected to multiply the effectiveness of Navy-operated UUVs and other unmanned platforms by providing a vehicle-agnostic method for autonomous underwater energy charging,” said Alex Askari, Naval Surface Warfare Center, Carderock Division (NSWCCD) technical lead.
Carderock Division’s developed technology enables power transmission between underwater systems, such as UUVs. During the main demonstration, the team was successful in transferring power wirelessly from an underwater docking station to a MARV UUV section, and ultimately to the UUV’s battery, which was charged at 2 kilowatts while submerged. The Mid-sized Autonomous Research Vehicle (MARV) UUV is 16.5 feet long and just slightly more than one foot in diameter.
WiTricity engineers have also demonstrated the ability to wirelessly transfer several hundred watts of power through seawater. WiTricity envisions UUVs being recharged simply by floating alongside a dock, larger vessel, or other power source, eliminating the need for tight mechanical coupling and allowing power to be transferred underwater safely, reliably, and efficiently.
The main issue facing wireless energy transfer is its efficiency, which deteriorates rapidly as the distance between the transmitter and receiver increases, however it is predicted to improve over time. To reach its maximum potential and meet the demands of tomorrow’s wireless war fighter, next-generation components, systems, and devices must also be designed and developed with WPT in mind to optimize form, fit, and function and also to ensure that the systems are efficient, safe, and accurate.
Wireless power transfer enhanced by magnetic resonant field enhancers (MR-FE)
Researchers from North Carolina State University and Carnegie Mellon University, by placing a magnetic resonance field enhancer (MRFE)—a loop of copper wire resonating at the same frequency as the AC current feeding the transmitter coil—between the transmitter and receiver coil, they could boost the transmission efficiency by at least 100 percent. “Our experimental results show double the efficiency using the MRFE in comparison to air alone,” David Ricketts of NC State, said in a press release.
The researchers conducted an experiment that transmitted power through air alone, through a metamaterial, and through an MRFE made of the same quality material as the metamaterial. The MRFE significantly outperformed both of the others. In addition, the MRFE is less than one-tenth the volume of metamaterial enhancers.
“We performed a comprehensive analysis using computer models of wireless power systems and found that MRFE could ultimately be five times as efficient as using metamaterials and offer 50 times the efficiency of transmitting through air alone,” Ricketts says.
A fully integrated wireless power receiver has been demonstrated in CMOS (Complementary Metal-Oxide-Semiconductor) process. The GaN chips are also predicted to be key enablers of wireless charging, the devices help systems stay tuned to the resonance needed for wireless charging.
Wireless power transfer enhanced by Metamaterials
Metamaterial (MM) due to their unique electromagnetic properties like negative permeability can act as a near field super-lens to focus or concentrate the magnetoquasistatic field generated by the source at the receiver coil. By enhancing the evanescent waves of the near-field, inductive link can be strengthened with potential mutual coupling improvement of up to 50 times has been reported.
In a new study published in EPL, scientists at Tongji University in Shanghai, China, have experimentally demonstrated a way to improve the efficiency of wireless power transfer by using magnetic metamaterials. The new method improves the efficiency of the design from a few percent to nearly 20% at a distance of 4 cm, which could pave the way toward new applications, including wireless charging of implanted pacemakers and electric vehicles.
The performance of MM for WPT system has been proved effective in various environments. However, early reported MMs may be too thick and large in size to increase the PTE and efficient transfer distance, which may limit their practical applications. Therefore, a thin and compact MM for WPT working in ISM band is needed.
Junfeng Chen and others have proposed a MM structure is very compact and ultra-thin in size. They designed an ultra-thin and assembled planar MM structure for 13.56 MHz WPT system numerically and experimentally, which consists of a singlesided periodic array of the capacitive loaded spiral resonators (CLSRs) by FR-4 substrate.
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