When neodymium-based magnets first hit the scene, they offered high flux but over a very limited temperature range. Modifications to the alloys, including the addition of dysprosium, ultimately yielded powerful, thermally robust magnets that enabled the development of motors with far greater torque density and thermal range than possible with traditional materials like aluminum nickel cobalt (AlNiCo) and ferroceramics.
Suddenly, engineers had the luxury of motors that were many times smaller and lighter than their conventional counterparts. At the same time, rare earth magnets remained cost-effective courtesy of Chinese suppliers, who soon dominated the market.
Figure 1: A speculation bubble has driven up the prices of rare earth elements in the past few years, while the cost of ferrite magnets has remained steady. (Source: NovaTorque)
In part four of this five-part design series, we look at how focusing flux in three dimensions allows ferrite-magnet motors to achieve performance and form factors competitive with rare earth designs. (Read part 1 here, part 2 here, and part 3 here.)
Everything was just dandy until around 2008, when speculators began hoarding materials, causing a supply contraction that drove up prices dramatically (see figure 1). What had been a viable industrial material became exorbitantly priced. The question changed from, "What can we do with rare earth magnets?" to "What can we do without them?"
The answer, according to NovaTorque Inc., is "plenty." They developed an axial motor design that focuses flux in three dimensions, rather than the two dimensions of conventional radial designs. The result is an economical ferrite-magnet motor that delivers torque and efficiency comparable to that of rare earth versions, in a similar frame size.
Radial air-gap permanent-magnet motors consist of a radially symmetric rotor nested in a cylindrical stator, with an air gap between the two. The rotor incorporates permanent magnets, either on the surface or the interior. The stator features electromagnets consisting of copper windings energized in a specific sequence by the drive to form alternating flux patterns. Both rotor magnets and stator windings are aligned with the z-axis of the motor, which causes the flux interaction -- and, hence, force exerted on the rotor -- to take place in two dimensions. When the windings are energized, the stator flux Φs interacts with the flux ΦR of the rotor magnets to exert a force on the rotor, causing it to turn.
To me, the message here is that innovation isn't just about coming up with the next new technology idea, but also being creative enough to see there can be novel approaches to old problems. The rare earth shortages are likely to continue for some time. This is a great example of deft engineering and being able to shift gears to another way of problem solving when something stands in your way.
I know many folks are poking fun at the idea of a push to asteroid mining, but as our high-tech gadgets require more and more high-tech materials that are becoming more and more scarce, looking off-world for new supplies sounds like a logical next step. It also beats the heck out of our entire technical workforce generating new mobile apps for their entire career...
The interesting thing to me about this work is that NovaTorque initially started out working with rare-Earth magnets and only tried the technology on ferrite magnets after rare-Earth pricing got out of hand. whatthat means is that in a few years, when new sources come online and the price of rare-Earth materials drops, NovaTorque can take what they've learned and begin making rare-Earth versions of their design, which could create uber-high-performance motorseven more compact and conventional rare-Earth versions.
Kristin, That is a great point. In solving a material problem in the near term you set yourself up for even more effeciencies when that material comes down in price.
Interesting idea, William. This is the basis of the Alien movie series, that space travel will essentially be based on mining. That may be the case. Yet, given our gains in creating sophisticated robot technology, the mining missions may not involve humans.
I agree, Beth. This is a great story of innovation in the face of economic necessity -- a great example of the old saying, "It's not what you have, it's what you do with it."
I suspect that transporting tons of raw materials back to earth will be a lot more costly than transporting them from under the ocean -- unforeseen difficulties are sure to play an economic role there. Still, I agree with you that our taste for high-tech will one day make asteroid mining a reality.
Beth, there are enough rare earth metals are available in China. They are possessing about 85% of the total availability. If China is willing to open up their market for international customers/companies, most of the problem may get resolved.
As a user of rare-earth magnets I hear there are large quantities of the resources necessary here in the USA but for the cost of getting it out of the earth. I guess the "rare" part is the permits, etc.
China broke international agreements in withholding this material from the world. I think it is a brilliant maneuver to raise prices. Saudi Arabia, et al, do it with oil. I do it with my vast mental capacity and my stunning good looks. So, the solution is an engineering one. How can we get around China? We got around the buggy whip cartel with the automobile. We can find ways to extract it from our own soil effectively, safely, and cleanly (unless the government has another hidden agenda in agreements with China). Or we can find substitutes. Maybe there is a substance we can use like "I Can't Believe It's Not Neodymium!"
I don't know if I buy the "hoarding" excuse. Speculators tend to stabilize prices. I think dark-side politics are at play, Mr. Watson.
Our missing link to successful space mining is that we have no space drive like all the science fiction crafts and what has been observed in "UFO's". We need something to replace the rocket to break earth's gravity before real economic feasibility is here.
Where are we at on the carbon nanotube ribbon hooked to a geosynchronous satellite?
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