This article presents an overview of charging technology called Shaped Magnetic Field in Resonance (SMFIR). It has been developed by a team of engineers and technologists at the Korea Advanced Institute for Science and Technology. An all-electric bus developed in Korea recharges its battery when it travels over electric coils buried at intervals along its route. The concept is called on-line electric vehicles, and the heart of OLEV technology is the transfer of enough electricity across gaps of up to 10 inches to power a fully loaded bus. Specifically, underground cables transfer power from the electrical grid to drive motors and on-board batteries via pickups beneath the OLEV bus bodies. The OLEV system wirelessly charges a bus, stopped or in motion, for continuous operation. SMFIR transfers rely on electromagnetic field resonance rather than inductive coupling. In SMFIR technology, the sending unit and the vehicle receiver resonate at 20,000 hertz.
when an electric toothbrush recharges, it sits on a little pedestal. The pedestal is plugged in, but the brush isn’t. An electromagnetic connection takes the place of a wired connection. So imagine the toothbrush is a bus, and it doesn’t sit on a pedestal, but rides 10 inches above the road. A team in Korea has proved not only that the bus can recharge without wires, but unlike the toothbrush, the bus can carry passengers.
Two new buses were put to work last August on a 15-mile route in Gumi City, an industrial center 150 miles from Seoul. The buses are all-electric, not hybrid, and they do not need to plug in for a recharge. Instead, they periodically drive over cables buried in the roadway along their route.
The charging technology is called “shaped magnetic field in resonance,” or SMFIR. It was developed by a team of engineers and technologists at the Korea Advanced Institute for Science and Technology. The work was funded by three South Korean government ministries to reduce air pollution and greenhouse gas emissions from vehicles in urban areas.
The concept is called on-line electric vehicles, and the heart of OLEV technology is the transfer of enough electricity across gaps of up to 10 inches to power a fully loaded bus. Specifically, underground cables transfer power from the electrical grid to drive motors and on-board batteries via pickups beneath the OLEV bus bodies. In Gumi City, the six sets of power cables total roughly 160 yards in length, a tiny fraction of the 15-mile bus route. The total length of the underground cables varies inversely with the size of the on-board battery; the smaller the battery, the more cable recharge sections.
The technology was installed by Dongwon OLEV, a licensee of the Korean institute. Dongwon, a South Korean industrial conglomerate, focuses on green technologies.
According to Nam Pyo Suh, an ASME Fellow and professor of mechanical engineering at the Massachusetts Institute of Technology who was part of the development team, the Gumi City buses cost the equivalent of $73,900 each. Infrastructure costs were $235,790 per kilometer of the bus route.
“Some published projections by skeptics make this technology seem too expensive,”Suh said. “Their numbers weren’t up to date.”
On-line recharging of electrically powered vehicles was pioneered in 2009 on a 1.4-mile route at a large amusement park in Seoul.Since 2010, regular OLEV buses have been running on a 2.4-mile route at the Korean technology institute campus in Daejeon, where they replaced diesel-powered buses. The Gumi City installation is the largest trial to date.
The project that developed the SMFIR system was led by Dong-Ho Cho, a vice president of the Korea Advanced Institute and a professor of communications engineering. The project teams included about 100 people from academia and industry.
Shaped magnetic field in resonance transfers power to via magnetic fields that are generated by underground power cables. In wireless power transfers, the electrical field between the magnetic poles is shaped to reach a pickup unit underneath the vehicle. This shaping accommodates any differences in the gaps between the buses’ pickups and the pavement, Suh said.
In Gumi City, power cables are needed beneath just one percent of the buses’ routes. For the rest of the distance traveled, an on-board battery supplies power. Suh said that the batteries in the Gumi City buses are typically less than one-fifth the size of those needed in battery-powered electric buses, which helps minimize the OLEV's overall cost.
Lithium-ion batteries are a major reason why battery-powered electric vehicles cost twice as much as comparable vehicles powered solely by an internal combustion engine. Regenerative braking also recharges on-board batteries. Over 180 patent applications have been filed.
SMFIR transfers rely on electromagnetic field resonance rather than inductive coupling, Suh said. In SMFIR technology, the sending unit and the vehicle receiver resonate at 20,000 hertz. According to Suh, the frequency was chosen to maximize power transfer efficiency. Some kitchen appliances use similar frequencies.
Conventional wireless power transfer has been limited to very low wattages for smartphones and similar portable electronics devices. The widely used Qi interoperability standard, developed by the Wireless Power Consortium, can transfer small amounts of electricity up to thirty feet.
Because of the potential dangers of electromagnetic radiation, engineers sought and won Korean government approvals on all aspects of OLEV operations, including power levels and system frequency.
“Months of testing at government laboratories preceded the installation of the underground power systems,” said Suh. “Approvals of the relevant government agencies verify that power transfers will not interfere with medical devices such as heart pacemakers. As one of many Gumi City safety features, only an OLEV bus can activate power transfers.”
SMFIR technology is a straightforward way of transferring large amounts of electrical power across gaps. According to Suh, the technology could replace the direct, continuous contact forms of power transfer— third rails and overhead power cables— used my mass transit systems worldwide. Third rails can cause severe shock and even electrocution, and can be disrupted by heavy snowfalls. Overhead power cables limit vehicle speed and are subject to electrical shorts during high winds.
“Many Traditional Power Engineers and Most Electronics Engineers Asserted it Would be Impossible to Wirelessly Transfer That Much Power.”
Conventional wireless transfers can power a cellphone or a toothbrush for a few days. But phones and toothbrushes need minuscule fractions of the power needed by a bus carrying 40 or 50 people. According to Suh, “Many traditional power engineers and most electronics engineers asserted it would be impossible to wirelessly transfer that much power.”
The system can transfer energy at a rate of 100 kilowatts of electricity and will charge a battery whether the bus is moving or still.
According to Suh, “The underground power system is designed considering the number of stops the bus makes at bus stations to take and discharge passengers, the number of signal lights, slope of the road, etc. For example, at a bus station where they load passengers and discharge passengers, the bus may stay there one or two minutes. At signal lights, it may stay two or three minutes to wait for the light to change. The length of the underground power system is a function of the speed. If the speed increases, the length of the underground power system must be longer.
“We considered all these factors and designed the underground power supply system,” Suh said. “We designed so that the electric charge of the battery on board of the vehicle comes back to its original state when it makes a complete round. That is, if the bus starts out with a 50 percent charge, it fluctuates about this 50 percent level over the course of its operation, but when the bus returns to the original starting station, the charge on the battery returns to the original level of 50 percent when the bus leaves the station. The bus drivers do not worry about the power supply, they simply and literally drive.
The energy transfer spans air gaps of up to seven inches between electrical contacts. “Many knowledgeable engineers said it would be impossible to transfer a significant amount of power across air gaps of more than two centimeters,” Suh said. The system works more efficiently than its developers had expected. It transfers up to 85 percent of the available power; initial efficiency targets were 60 percent.
The Gumi City buses—initially two with 10 to be added by 2015—are of carbon-fiber engineered-composite construction. And because they weigh less than the steel or aluminum of mass transit workhorses, they consume less power.
The developers have their sights on international markets. A U.S. licensee, OLEV Technologies Inc. based in North Reading , Mass., is marketing the system in the United States.
There is competition, however. A research team at Utah State University and a company called WAVE Inc. are pursuing SMFIR technology independently of the Korean institute and Dongwon; they have a prototype known as the Aggie bus.
“Trains, trams and taxis are the next obvious SMFIR candidates and, eventually, passenger cars,” Suh said. “If about ten percent of the roadways have underground power supplies, passenger cars in major cities can use SMFIR technology without fuel pumps or charging stations.”
He calculates that if all South Korean urban transportation used SMFIR, the nation would need four more 1,000-megawatt nuclear power plants to supply the electricity. South Korea's existing nuclear power plants (23 reactors total) provide for nearly half of the nation's electrical consumption; South Korea has almost no fossil-fuel resources of its own.
“Transportation of all sorts is a big contributor to the world's many environmental problems,” Suh said. “The world will be so much better with SMFIR vehicles and we will have the possibility of minimizing the global warming.”