This month we are featuring our latest release, Electrostatic Motors: Their History, Types and Principles of Operation by the late Professor Olef Jefimenko to whom we are indebted for permission to reprint this one-of-a-kind reference book...and what better way to describe the book but by offering a reprint from Popular Science magazine?
The second article is a valuable insight into a trend in physics, funded by DARPA, to bring quantum mechanics into mainstream macroscopic reality for the purposes of energy exchange using light. It is also intriguing since it mentions "zero-point energy, which gives an object residual motion even in its ground state." IRI predicts that the time will come when this residual energy and its corresponding negative energy states will be utilized by mankind.
The third and fourth articles emphasize how electric battery and fuel cell technology are growing by leaps and bounds. The A123 company that makes the KillaCycle batteries is one of the fastest growing battery companies because of their unique energy density product (ticker: "AONE") that powers the fastest-accelerating motorcycle (0 to 60 mph in one second!).
Nikola Tesla continues to influence the progress of energy and transportation even today in our last story with his difference engine that has been ignored until now. Toyota recognizes Tesla's ingenius design of a three magnetic phase motor that produces enough torque to obviate the need for rare-earth magnets that are becoming rare and expensive.
Thomas Valone, PhD, PE
1) Electrostatic Motors You Can Build
Ed. Note: This article and others are included in the new edition of Electrostatic Motors: Their History, Types and Principles of Operation by Oleg Jefimenko, just released by Integrity Research Institute publishers.
In "The Amazing Motor That Draws Power From the Air", last month, we told about our visit to the laboratory of Dr. Oleg Jefimenko at the University of West Virginia, who has designed and built a variety of these ingenious machines now, as promised, we bring you details on how you can build your own electrostatic motor from simple materials.
The devices that you see here are corona-discharge motors. The sharp-pointed or knife-edge electrodes create a corona, which ionizes or charges the air particles floating by. These charged particles transfer their charge to the closest part of the plastic rotor and charge it up, just as you can charge your body by walking across a wool rug on a dry winter's day.
Once a spot on the rotor assumes a charge, it is repelled from the charging electrode by electrostatic forces, and at the same time is attracted to the other electrode, which has an opposite charge. When the charged section of the rotor reaches the opposite electrode, another corona discharge reverses the polarity and starts the whole thing over again.
The Concept is Simple
And so are the motors. But that doesn't mean they're easy to build. These motors run on millionths of a watt; they've got no power to waste turning stiff bearings or slightly misaligned rotors. So they must be built with watch-making precision.
They're made of acrylic sheet, rod, and tube stock -- Plexiglas and Lucite are two of the better-known brands. Acrylic cuts and works beautifully. Cut edges can be sanded so they have a white, frosted appearance that, in contrast with clear surfaces, gives your finished motor a sparkling, jewel-like appearance. If you like clear edges, you can buff them on a wheel and the whole thing becomes transparent.
Drill and tap the acrylic and assemble parts with machine screws. This allows for fine adjustment and alignment. Later, you can make the whole thing permanent by putting a little solvent along the joints. The solvent flows into the joint and fuses it permanently.
Details of framework, support and so on aren't important; change them if you like. but work with care if you want to avoid headaches. The Poggendorff motor looked simple; we slapped it together in a couple of hours, hooked up the power source -- and nothing happened. We gave it a few helpful spins by hand, but it wouldn't keep running.
The cure took about 3 hours. First, we noticed that the outer edge of the disk wobbled from side to side about 1/16 of an inch as the wheel revolved. So the rotor-electrode distance was constantly changing. There was a little play in the 1/4" hole we had drilled for the electrodes -- so they weren't lined up absolutely square with the disk. Then we noticed that the disk always stopped with one side down. The imbalance was only a fraction of an ounce -- but it was too much.
We drilled out the old hub and cemented in a new one -- this time, carefully. We lined up the electrodes -- precisely. Then, once more spinning the disk by hand, we added bit of masking tape until it was perfectly balanced. We connected the power -- and slowly... slowly... the disk began to turn. After about a minute, we clocked some turns with a watch and found it was spinning at 200 rpm. A moment later, we lost count. It was a great feeling.
Where Tolerances Are Brutal
We had even more trouble with the octagonal-window machine. When it wouldn't run and we turned the shaft by hand, we could feel the rotor dragging. We took it apart, felt all the surfaces on the rotor and the framework's insides and found a few bits of hardened cement, which we removed. We filed down all edges on the rotor and the windows to make sure there were no beads or chips dragging.
The rotor and corner separators are made from the same sheet of 1/2" plastic, so rotor clearance is achieved by putting shims at the corners to hold the side plates slightly more than 1/2" apart. With the 1/16" shims we were using, we could see that the sides were slightly misaligned so the shaft was not being held at a true 90 degrees. We drilled slightly oversized holes in the corners of one side piece and carefully adjusted until the rotor was turning true in the slot. To give the motor more torque, we put a bead of cement along the outer edge of each aluminum-foil electrode to stop corona leakage. The motor ran.
Take a Giant Step
Once you've built these machines, why not design your own? Start with the Jefimenko 1/10 hp model as a challenge. Then plan one from scratch. You can power your motors with a laboratory high-voltage supply, a Van de Graff generator, or a Wimhurst machine or any other high-voltage source. We've been running ours on the home-built Wimhurst machine shown in the photos. (If you don't want to build one, Wimhurst machines are available from scientific supply houses such as Edmund Scientific.) (http://www.scientificsonline.com/catalogsearch/result/?q=wimhurst - Ed. Note.)
The discharge globes are traditional for high-voltage machines. They aren't necessary, but they give a quick check on machine operation and a satisfying arc when you move them within 1/2" of each other. Incidentally, that funny smell is ozone. But its concentration is too low to be harmful. The generator is safe, too. You can hold both electrodes in your hands and all you'll feel is a tingle. This particular generator, we estimate, puts out about 30,000 volts.
To make wiring simple, we used standard connectors on the Wimhurst collectors, and meter leads with regular banana plugs and alligator clips to hook up the motors.
Last month, we mentioned seeing Dr Jefimenko run his electrostatic motors on electricity tapped from the earth's field. We haven't had a chance to try this yet with ours, but it should work. If you want to try, you'll need a needle-pointed piece of music wire a few inches long to start a corona, plus several hundred feet of fine copper wire.
Connect the pointed wire to the fine conductor, get the sharp point up into the air at least 200-300 feet with a kite or balloon, and hook the wire to one side of the motor. Hook the other side of the motor to ground. The earth field antenna should at times be able to develop up to 20,000 volts from the earth's electrical field. If nothing happens, check your equipment, or try another day. The field changes constantly.
When we crank up the electrostatic motor at the end of this article, people always want to know what makes it run. It is mysterious -- there's nothing but a plastic disk and two strange electrodes. Yet there it is, spinning merrily.
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2) Moved by Light
Lasers push everyday objects into the Quantum World!
You won't drive through this far-fetched town anytime soon, but it's not as far off the map as it used to be. In laboratories across the world, bits of metal and glass are being groomed to behave in ways that defy common sense. Objects big enough to be seen and touched - some weighing kilograms - are beginning to rebel against the physical laws that govern daily experience.
For decades, scientists have used light to quell the vibrations of individdual atoms. Now teams are cooling sticks as shown above, sails, drums, and other multiatim objects to very low temperatures, where signs of quantum effects may be seen.
At the forefront of this effort is a growing discipline called optomechanics. Its practitioners use beams of light to do something utterly unfeasible a decade ago: make large objects colder than they would be in the void of outer space. Only at these temperatures do objects reach energies low enough to enter the realm of quantum mechanics and start behaving like subatomic particles.
"Our guiding principle is to see quantum effects in a macroscopic object," says physicist Ray Simmonds of the National Institute of Standards and Technology in Boulder, Colo. A number of optomechanics teams have sprung up in recent years, each cooling its own favorite bit of fairly ordinary stuff. Simmonds works with an aluminum drum (unveiled in the March 10 Nature). In Switzerland, scientists chill silica doughnuts. At Yale University, saillike membranes are the vogue.
"We're putting the mechanics back in quantum mechanics," says Yale physicist Jack Harris.
It's mainly a race of tortoises creeping steadily closer to absolute zero, the coldest of the cold. But recently an interloper hare took a shortcut to the lead. And the stakes are high: The winners will test whether quantum mechanics holds at ever-larger scales and may go on to build a new generation of mechanical devices useful in quantum computing.
Spend an afternoon watching sunbathers burn at the beach, and the idea of using light to refrigerate may seem counterintuitive. But light particles have a hidden cooling ability that comes from the tiny nudge they impart when bouncing off an object. This force, too weak for a beachgoer to feel, is so feeble that sunlight reflecting off a square-meter mirror delivers a pressure less than a thousandth of the weight of a small paper clip.
"It's an incredibly tiny effect," says physicist Steve Girvin, also of Yale. In the 1970s scientists figured out how to use this "radiation pressure" to cool individual atoms by damping their vibrations with lasers. Now a slew of new devices leverage the punch of light and other forms of electromagnetic energy to cool objects made of trillions of atoms or more. This scaled-up cooling doesn't suppress the vibrations of individual atoms. Instead, it quiets the inherent wobbling of an entire object, like a foot pressed to a flopping diving board.
Putting light's cooling power to work starts with a laser beam bouncing between two mirrors. The distance between the mirrors in this "optical cavity" determines the frequency of light that will resonate - just as the length of a guitar string determines its pitch. Keep the mirrors still and properly tuned light will bounce back and forth, as constant as a metronome.
But allow one of these mirrors to wobble, and a more intricate and subtle interplay emerges. A laser beam tuned below the resonance frequency of the cavity will push against the swaying mirror and snatch away energy. By stealing vibrational energy from the mirror, the bouncing light gets a boost up to the optical cavity's stable frequency. Robbed of energy, the mirror's swaying weakens, and it cools.
By measuring the light leaking out of this type of system, two groups of physicists showed in 2006 that they could cool mirrors to 10 kelvins (10 degrees Celsius above absolute zero). A third used a similar technique to cool a glass doughnut to 11 kelvins, colder than the object would be if it were wobbling on the dark side of the moon.
"This demonstration that you could use laser radiation to cool a mechanical object, this started the race," says Tobias Kippenberg, leader of the doughnut team at the Swiss Federal Institute of Technology in Lausanne. "Every year we improve our cooling by a factor of 10."
As papers flowed in and objects neared the bottom of the thermometer, researchers competed to suck out every last drop of energy. The goal: to reach the ground state, where an object no longer possesses any packets, or quanta, of vibrational energy. In this state, motion almost completely stops and the quantum regime begins to become a reality.
But getting those last few quanta out would be a challenging task; even the mirrors at 10 kelvins still contained tens of thousands to hundreds of thousands of quanta.
Better lasers and equipment refinements allowed three groups, publishing in Nature Physics in 2009, to reach 63, 37 and 30 quanta. Keith Schwab of Caltech bombarded a wobbling object with microwaves that drained away all but about four quanta. He and his colleagues reported in Nature in 2010 that they had put their object into its ground state 21 percent of the time - tantalizingly close to the consistency needed to test for quantum effects.
Then in April 2010, a shot rang out. An object had been spotted entering its ground state over and over again - by an outsider who wasn't even using light.
"I wanted to get to the ground state in the quickest and most efficient way possible and have there be no question that I was there," says Andrew Cleland, a physicist at the University of California, Santa Barbara, who reported his team's achievement in Nature (SN: 4/10/10, p. 10).
Cleland's secret: While other scientists built stuff that shook thousands or millions of times a second, he created a ceramic wafer 30 micro-meters long that expanded and contracted 6 billion times per second. The faster an object's natural quiver, the easier it is to remove energy, meaning less cooling needed to reach the ground state. Using a state-of-the-art liquid-helium refrigerator capable of achieving millikelvin temperatures, Cleland's team put the wafer in its ground state 93 percent of the time.
By measuring the electric fields produced by this object, Cleland and his colleagues showed that they could nudge the wafer into a state of superposition - both moving and still at the same time.
"There can be no doubt that we achieved superposition," Cleland says. This first demonstration of quantum effects in a fairly ordinary object was named the 2010 Breakthrough of the Year by Science.
But Cleland's sprint to the front of the pack has some long-term disadvantages. His technique is blind to the actual position of a fluctuating object, for one thing, and thus he can't spot one of the consequences of quantum mechanics: zero-point energy, which gives an object residual motion even in its ground state. Experimentalists using optomechanics hope to detect this motion and verify that it is proportional to how fast an object normally wobbles.
Light has been used to cool a range of mechanical objects ( some highlighted from left) in laboratories across the world. When objects get really cold, some scientists opt to measure temperature in quanta, or packets of vibrational energy, rather than in kelvins.
Girding themselves for the long haul, optomechanics teams have now begun to catch up to Cleland's hare strategy. On March 21 in Dallas at the American Physical Society meeting, members of the NIST team presented data showing that their drumlike membrane had reached the ground state about 60 percent of the time.
The aluminum skin of this drum - in technical terms, a resonator - moves up and down much more slowly than Cleland's object, vibrating less than 11 million times per second. Reaching the ground state at this slower wobble couldn't be done with Cleland's refrigerator; it required the cooling nudge of microwaves.
The payoff for going the extra mile: time. The slower an object wobbles, the longer it tends to stay in its ground state. For Cleland, the ground state lifetime was about 6 nano-seconds. "The difference with our system, our resonator, is that it has a very long lifetime, about 100 microseconds," says Simmonds. "That's the key element that sets it apart."
With the results unpublished, the team won't say whether any quantum effects have been seen. But the stability could give the researchers an advantage for using optomechanical devices to store and relay information.
A "killer app," some say, would be playing interpreter between different wavelengths of light or other electro-magnetic energy. A resonator in its ground state could theoretically be designed to absorb photons of just about any kind of light, stored as packets of vibrational energy.
Cool the resonator back to its ground state, and it could release this energy as light of a different wavelength. So gigahertz microwave energy that sets a stick to wobbling could be reemitted at optical frequencies hundreds of thousands of times higher, for instance. Such devices could bridge quantum computing systems that use different frequencies of light to transmit bits of information.
At Caltech, applied physicist Oskar Painter is taking steps toward realizing this light-to-light conversion at higher temperatures. He designs nanometer-scale optomechanical crystals that convert higher-frequency light to lower-frequency vibrations. A zipperlike object described in 2009 in Nature, for instance, could one day be useful for converting optical light into microwaves.
Optomechanical techniques, such as those used by Painter, could also shave the sensitivities of force detectors. At Yale, engineer Hong Tang develops sensors out of light-cooled resonators that promise unprecedentedly low levels of background noise.
"We want to make better accelerometers and better inertia sensors," Tang says. These devices, similar to those that sense the motion of a Wii controller, could measure tiny changes in movement and direction.
Like many other optomechanics researchers, Painter and Tang receive funding from the Defense Advanced Research Projects Agency. DARPA hopes to use laser-cooled sensors to improve the ability of vehicles to navigate underwater, says DARPA program manager Jamil Abo-Shaeer. "We want to push these things to the limits of quantum mechanics, the ultimate limit," he says.
While DARPA funds the development of devices that can't even be seen without a microscope, other scientists are putting optomechanics to work cooling some of the largest detectors in the world: the gravitational wave detectors of the LIGO project, built to search for gentle ripples in space-time thought to be produced by (among other cosmic events) colliding black holes.
Chasing ever greater sensitivities, these researchers use lasers to still the vibrations of their detectors' giant mirrors - the behemoths of the optomechanical world, weighing in at more than 10 kilograms. Despite their immense size, these mirrors have now been cooled to 234 quanta, MIT quantum physicist Nergis Mavalvala and LIGO colleagues reported in 2009 in the New Journal of Physics. "Our challenges are really the same as everyone else's, but we need to somehow cool our gram and kilogram-sized objects to nanokelvins," says Mavalvala.
Working on another gravitational wave detector called AURIGA, researchers in Italy set the record for largest object effectively cooled via optomechanics. An aluminum bar weighing more than 1 ton reached a mere 4,000 quanta, the team reported in Physical Review Letters in 2008.
Whether such large mirrors and bars could ever demonstrate quantum effects, though, is an open question. In principle, some physicists say, quantum mechanics should hold for objects of any size. "We don't know of any fundamental limit," Harris says.
Practical considerations may ultimately limit the size of quantum objects, though. Any observation, be it by a pair of eyes or a stray, colliding air molecule, can destroy a quantum state. The larger an object is, the harder it is to keep isolated. But that isn't stopping researchers with bigger objects from lining up behind Cleland and the NIST team to stretch the bounds on quantum effects.
"If we can prove that quantum mechanics holds for larger and larger objects, that would be quite spectacular," says Dirk Bouwmeester of UC Santa Barbara. "But it would also be spectacular if we can prove that it doesn't. New theories would be needed."
One of the slowest tortoises in the race, Bouwmeester's pace is deliberate. His mirrors, tens of micrometers across, vibrate a mere 10,000 or so times per second and promise an extended quantum lifetime. This durability, he says, is needed to test a controversial idea that gravity and quantum weirdness can't coexist for long at everyday scales.
More than three-quarters of a century of research has made scientists more comfortable with quantum mechanics at small scales, but supersizing it can seem as bizarre today as it did to Erwin Schr�dinger. In 1935, he poked fun at the idea in his famous thought experiment: a cat in a box that could be both alive and dead at the same time, as long as no one peeked inside the box and forced a choice, killing with curiosity.
Perhaps it is still too much to imagine Schr�dinger's cat behind the drawn curtains of Quantumville's homes, simultaneously nibbling Purina in three different rooms at once. But as researchers continue to cool knickknack after knickknack in their optomechanical grab bag, they may catch at least a faint echo of a meow.
Interest in the pressure exerted by light goes back centuries.
1619 Johannes Kepler suggests that the pressure of sunlight explains why comets' tails (above) always appear to point away from the sun.
1746 Leonhard Euler shows theoretically that the motion of a longitudinal wave might produce pressure in the direction it is propagating.
1873 James Clerk Maxwell (above) uses electromagnetic theory to show that light reflecting off a surface or absorbing into it would create pressure. Bright sunlight, he calculates, would press on the Earth with a force of about 4 pounds per square mile.
1873 That same year, Sir William Crookes invents the radiometer, or light mill (above), incorrectly suggesting that the mill spins because of the pressure of light. Scientists now understand that the heat transferred by light is responsible for the mill's spinning.
1876 Adolfo Bartoli, unaware of Maxwell's work, infers radiation pressure's existence from the second law of thermodynamics.
1900 Russian physicist Pyotr Lebedev announces at a meeting in Paris that he had measured the pressure of light on a solid body.
1903 Ernest Fox Nichols and Gordon Ferrie Hull measure the pressure to an accuracy within less than 1 percent, publishing the work in the Astrophysical Journal.
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|3) Killacycle- World Fastest Electric Motorcycle|
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Electric and Hybrid Vehicles, May, 2010,
Straddling a 619-pound motorcycle, Scotty Pollacheck tucks in his knees and lowers his head as he awaits the green light. When he revs the engine, there's no roar. The bike moves so fast that within seconds all that's visible is a faint red taillight in the distance.
Pollacheck crosses the quarter-mile marker doing 168 mph, faster than any of the gas-powered cars, trucks or motorcycles in the drag sprints on this weekend at Portland International Raceway. It's particularly impressive given that Pollacheck is riding a vehicle powered entirely by lithium-ion batteries.
Electric vehicles are making their presence felt at amateur drag races across the U.S., challenging gas-powered cars and motorcycles. The "amp heads," computer geeks and others driving the electron- powered vehicles are starting to kick some major rear end.
Pollacheck and his bike -- dubbed the KillaCycle -- are part of a growing movement that's exploiting breakthroughs in battery technology and soon could challenge the world's fastest- accelerating vehicles in the $1 billion drag-racing industry. "In professional drag racing I expect to see the electrics eventually pass up the fuel dragsters," said Dick Brown, president of AeroBatteries, which sponsors White Zombie, the world's quickest-accelerating street-legal electric car, a 1972 white Datsun 1200.
"Electric gives you instant torque whereas gasoline you have to build up," he said. Brown believes electric vehicles will challenge the top drag-racing records within five years. The KillaCycle runs on 990 lithium-ion battery cells that feed two direct current motors, generating 350 horsepower. The bike accelerates from zero to 60 mph in just under a second, faster than many professional gas- powered drag motorcycles and within striking distance of the quickest bikes that run on nitromethane.
Except for the batteries he receives from sponsor A123 Systems, Bill Dube, KillaCycle's owner and designer, pays the costs of his racing team -- about $13,000 a year -- out of his own pocket. A123 makes KillaCycle's batteries.
"We have a chance of actually taking away some nitromethane records, perhaps the overall record," said Dube.
The National Electric Drag Racing Association's vehicles are posting faster and faster times at amateur meets, but they still have a way to go before matching professional world records. The fastest quarter-mile time by an electric vehicle is the KillaCycle's 8.16 seconds; that's 2.36 seconds off the nitromethane world record for drag bikes set by Larry "Spiderman" McBride last year.
Electric vehicle racers say battery technology advances will give EVs a shot at drag records.
"This is a disruptive technology, and there is a lot of room for improvement in this area," said Ric Fulop, founder and vice president of business development for A123.
The KillaCycle uses about $0.07 worth of electricity for each run down the strip.
0-60 mph (0-96 km/h): 0.97 seconds
Acceleration: 2.89 G (almost 3 times free fall)
Best Top Speed in � mile: 174.05 MPH
Lowest � mile Elapsed Time (ET): 7.82 seconds @ 168 mph
Power: over 500 hp
Battery: 1210 lithium iron nano-phosphate™ cells from
Battery weight: 200 lbs (90 kg)
Battery voltage: 374 Volts
Battery capacity: 9.1 kWh
The KillaCycle weighs 619 lbs.
|Killacycle Battery Power Drag Bike 0-60 0.8 seconds |
|4) Solid State Batteries|
By Kevin Bullis, Technology Review, May/June 2011,
High-energy cells for cheaper electric cars
Ann Marie Sastry wants to rid electric vehicles' battery systems of most of the stuff that doesn't store energy, such as cooling devices and supporting materials within the battery cells. It all adds up to more than half the bulk of typical lithium-ion-based systems, making them cumbersome and expensive. So in 2007, she founded a startup called Sakti3 to develop solid-state batteries that don't require most of this added bulk. They save even more space by using materials that store more energy. The result could be battery systems half to a third the size of conventional ones.
Cutting the size of a battery system in half could cut its cost by as much as half, too. Since the battery system is the most expensive part of an electric car (often costing as much as $10,000), that would make electric cars far cheaper. Alternatively, manufacturers could keep the price constant and double the 100-mile range typical of electric cars.
The limitations of the lithium-ion batteries used in electric cars are well known. "Most liquid electrolytes are flammable. The cathode dissolves," says Sastry. Keeping the electrolyte from bursting into flames requires safety systems. And to extend the electrode's lifetime and prevent heat buildup, the battery must be cooled and prevented from ever fully charging or discharging, resulting in wasted capacity. All this adds bulk and cost. So Sastry wondered if she could make a battery that simply didn't need this much management.
Sastry's solid-state batteries are still based on lithium-ion technology, but they replace the liquid electrolyte with a thin layer of material that's not flammable. Solid-state batteries are also resilient: some prototypes demonstrated by other groups can survive thousands of charge-discharge cycles. And they can withstand high temperatures, which will make it possible to use materials that can double or triple a battery's energy density (the amount of energy stored in a given volume) but that are too dangerous or unreliable for use in a conventional lithium-ion battery.
To make solid-state batteries that are practical and inexpensive to produce, Sastry has written simulation software to identify combinations of materials and structures that will yield compact, reliable high-energy devices. She can simulate these materials and components precisely enough to accurately predict how they will behave when assembled together in a battery cell. She is also developing manufacturing techniques that lend themselves to mass production. "If your overall objective is to change the way people drive, your criteria can no longer only be the best energy density ever achieved or the greatest number of cycles," she says. "The ultimate criterion is affordability, in a product that has the necessary performance."
Although it may be several years before the batteries come to market, GM and other major automakers, such as Toyota, have already identified solid-state batteries as a potentially key component of future electric vehicles. There's a limit to how much better conventional batteries can get, says Jon Lauckner, president of GM Ventures, which pumped over $3 million into Sakti3 last year. If electric vehicles are ever to make up more than a small fraction of cars on the road, "something fundamental has to change," he says. He believes that Sakti3 is "working well beyond the limits of conventional electrochemical cells."
Sastry is aware that success isn't guaranteed. Her field is something of a technological battleground, with many different approaches competing to power a new generation of cars. "None of this is obvious," she says.
Cooling Down Solid-Oxide Fuel Cells
by Katherine Bourzac
A startup moves toward thin-film solid-oxide fuel cells suitable for practical devices.
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5) The Difference Engine, Nikola Tesla's revenge
ONCE again, worrywarts in Washington are wringing their hands over possible shortages of so-called "critical materials" for America's high-tech industries. In particular, the Department of Energy frets about certain metals used in manufacturing wind turbines, electric vehicles, solar cells and energy-efficient lighting. The substances in question include a bunch of rare-earth metals plus a handful of other elements which-used a pinch here, a pinch there-enhance the way many industrial materials perform.
It is not as though the rare-earth elements-scandium, yttrium and lanthanum plus the 14 so-called lanthanides-are all that rare. Some are as abundant as nickel, copper or zinc. Even the two rarest (thulium and lutetium) are more widely spread throughout the Earth's crust than gold or platinum. But because they have similar chemical properties, and tend to be lumped together in rocks along with radioactive thorium and uranium, extracting and refining them can be difficult, expensive and messy. Disposing of the toxic waste is one of the biggest headaches.
A decade ago, America was the world's leading producer of the rare-earth metals. But its huge open-cast mine at Mountain Pass, California, closed in 2002-a victim of China's much lower labour costs, America's increasingly stringent environment rules, and delays in renewing the mine's operating licence. Today, China produces 97% of the world's supply of rare-earth metals-a by-product of the country's vast iron-ore mining operations in Inner Mongolia. Over the past year, the Chinese authorities have cut back drastically on exports of rare-earths, as China's own high-tech industries absorb more of the output (see "More precious than gold", September 17th 2010).
The rare-earth the Department of Energy seems particularly paranoid about is neodymium. This is widely used for making super-strong permanent magnets. Over the past year, the price of neodymium has quadrupled, as electric motors and generators that use permanent magnets instead of electromagnetic windings in their rotors have proliferated. Cheaper, smaller and more powerful, permanent-magnet machines have been one of the main factors behind the increasing popularity of wind turbines and electric vehicles.
That said, not all makers of electric vehicles have rushed to embrace permanent-magnet motors. For one, the Tesla Roadster, an electric sportscar based on the Lotus Elise, uses no rare-earth metals whatsoever. Nor does the Mini-E, an electric version of BMW's recreation of the iconic 1960s car. Meanwhile, the company that pioneered much of today's electric-vehicle knowhow, AC Propulsion of San Dimas, California, has steered clear of permanent-magnet technology. More recently, Continental AG, a German car-components firm, has developed an electric motor for a forthcoming European electric vehicle that likewise uses no rare-earths. Clearly, a growing number of car companies think the risk of depending on a single (and not so reliable) source of rare-earth metals is too high.
The latest carmaker to seek a rare-earth alternative is Toyota. The world's largest carmaker is developing a neodymium-free electric motor for its expanding range of hybrid cars. Following in AC Propulsion's footsteps, Toyota has based its new design on industry's electromotive mainstay, the cheap and rugged alternating-current induction motor patented by Nikola Tesla, an American inventor, back in 1888.
Tesla's invention is, in essence, a rotating transformer. Its primary windings reside in a stationary steel casing (the stator) and and secondary conductors are attached to an inner shaft (the rotor). The stator surrounds-but does not touch-the rotor, which is free to rotate about its axis. An alternating current applied to the stator's windings creates a rotating magnetic field, while simultaneously inducing a current in the separate conductors attached to the rotor. With an alternating current now circulating within it, the rotor creates a rotating magnetic field of its own, which then proceeds to chase the stator's rotating field-causing the rotor to spin in the process and thereby generate torque.
Modern induction motors usually have three (or more) sets of stator windings, each using a different phase of the alternating current being applied. Having three "waves" of magnetism induced in the rotor with every revolution, instead of just one, smooths out the induction process and allows more torque to be generated.
Such machines are known as asynchronous motors, because the rotor's magnetic field never catches up with the stator's field. That distinguishes them from synchronous motors that use a permanent magnet in their rotors instead of a set of aluminium or copper conductors. In a synchronous motor, the stator's rotating magnetic field imposes an electromagnetic torque directly on the fixed magnetic field generated by the rotor's permanent magnet, causing the rotor-magnet assembly to spin on its axis in sync with the stator field. Hence the name.
In the past, the main disadvantage of asynchronous induction motors was the difficulty of varying their speed. That is no longer an issue, thanks to modern semiconductor controls. Meanwhile, the induction motor's big advantage-apart from its simplicity and ruggedness-has always been its ability to tolerate a wide range of temperatures. Providing adequate cooling for the Toyota Prius's permanent-magnet motor adds significantly to the vehicle's weight. An induction motor, by contrast, can be cooled passively-and thereby dispense with the hefty radiator, cooling fan, water pump and associated plumbing.
Better still, by being able to tolerate temperatures that cause permanent magnets to break down, an induction motor can be pushed (albeit briefly) to far higher levels of performance-for, say, accelerating hard while overtaking, or when climbing a steep hill. Hybrid vehicles like the Toyota Prius or the Chevrolet Volt have to use their petrol engines to get extra zip. Pure electric vehicles such as the Nissan Leaf depend on gearboxes to generate the extra torque for arduous tasks. By contrast, the Tesla Roadster uses just one gear-such is the flexibility of its three-phase induction motor.
So far, Toyota has remained mum about its neodymium-free electric motor-generator. The design used in the current version of the Toyota Prius (the car actually has two such units, one for propulsion and regenerative braking, and the other to run all the on-board accessories) combines both conductors and a permanent magnet in its rotor core. On light loads, the unit works more like a permanent-magnet motor. On heavier loads, the induction features predominate.
In moving to a pure induction design, Toyota could do worse than take a page out of the Tesla car company's manual. Weighing in at 52kg (115lb), the Tesla Roadster's tiny three-phase induction motor is no bigger than a watermelon. Yet it packs a hefty 288 horsepower punch. More impressively, the motor's 400 Newton-metres (295 lb-ft) of torque is available from rest to nearly 6,000 revolutions per minute. Having access to such a wide torque band eliminates the need for a second or third gear in the transmission. The result is a power unit that is light, compact and remarkably efficient.
Overall, the Tesla Roadster is said to achieve a battery-to-wheels efficiency of 88%-three times better than a conventional car. With Nikola Tesla's robust and reliable induction motor making such a successful comeback, it is puzzling to see why anyone should worry about potential shortages of neodymium and other rare-earths for alternative power and transport.
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