Not to indulge in hyperbole, but people who missed the eighth annual Electric Aircraft Symposium will, like the laggards mentioned in Henry V’s speech, “think themselves accurs’d they were not here” (Shakespeare, Henry V, act 4, scene III).
After the Friday morning introductions by Dr. Brien Seeley, founder and president of the CAFE Foundation, things immediately went into high gear with the presentation by Dr. Ajay Misra, NASA Glenn Research Center. A member of the Senior Executive Service, he is Chief of the Structures and Materials Division in the Research & Technology Directorate. In this position, Dr. Misra has the responsibility for planning, advocating, coordinating, organizing, directing and supervising all phases of Division research and business activities.
His degrees in metallurgy, an MBA degree and a doctorate in materials science and engineering demonstrate the high intellectual skills necessary to manage the 120 employees and 100 contractors in Dr. Misra’s Division.
His discussion on “Nano-Magnets and Additive Manufacturing for Electric Motors” implied NASA’s great interest in researching and testing nanomaterials in flight structures and Dr. Misra’s strong interest in electric aircraft, decreasing the weight and volume of electric components, and improving the materials involved. He discussed the basics of motor construction, including magnets, conductors and insulation; and the necessity for keeping things cool by managing the thermal buildup in motors through proper selection of materials and cooling technologies.
Along with an advanced topology for the motor’s configuration; better, lighter, more powerful units require advances in permanent magnets. Dr. Misra traced the evolution of materials used in magnets, starting with ferrite magnets almost from their beginning, advancing to alnico (aluminum-nickel-cobalt), on to samarium-cobalt (SM-CO) the first of the rare-earth materials used in motors and instrumental in the Boucher Brothers’ successful early solar-powered models), and neodymium-iron-boron ( Nd-Fe-B – the most widely used of the rare earth magnets).
Dr. Misra took it one step further, explaining that nano-composite magnets allow even stronger magnetism and better coercivity, the magnet’s ability to retain its magnetism while withstanding an external magnetic or electric field.
The IEEE expands on that. “To find out how magnetically hard something is, physicists measure the strength of the coercive field, the reverse-directed magnetic field that’s required to erase the material’s magnetization completely. The greater the coercive field, the better, because magnets always work in a hostile magnetic environment, one that tends to demagnetize them. The rub here is that materials with strong coercive fields don’t usually have much magnetic oomph—which is to say that at best, they exhibit modest saturation magnetizations.”
To enable best use of nanostructured permanent magnets, Dr. Misra relies on advanced topology design for the motor, combining soft phase, high magnetic saturation materials and Hard phase, Nd-Fe-B high coercivity materials in alternating hard and soft magnet layers.
His team faced several fabrication challenges in making a uniform mixture of hard and soft magnetic materials at the nano-scale. Aligning anistropy axes for instance, required making thin film magnets that could reach a theoretical maximum energy product of 54 MGOe’s (Mega Gauss Oersteds; unit of measure typically used in stating the maximum energy product for a given material).
Advanced processing techniques included high-energy ball milling to produce nanoparticles of uniform sizes, and using additive manufacturing to manufacture a motor stator. Note the video below is not as shown by Dr. Misra, but is typical of the direct writing process used on permanent magnet motors crafted by the NASA technicians – but at a much larger scale. Dr. Misra’s team made 50 micron lines that crossed over a 500 micron trench, for instance.
The 3D printing of the motor’s electromechanical system, the potential to increase the maximum energy product in magnets, new electromagnet design, and the reduced volume, weight and cost of the resulting motor all show a promising direction for future electric aircraft.
More reports to come. The Symposium was an educational and inspirational event which CAFE wants to share with everyone.