How to build a better magnet
Over the past two decades, renewable energy has nearly quadrupled in use worldwide. Electric cars are selling at record numbers. Household solar panels are being installed faster than ever before (PDF).
In theory, the future of green technology is looking bright – but in order to make these devices more efficient and widely adopted, engineers still have to overcome one major hurdle: building a better magnet.
“Magnets are involved in almost every step of electrical production, from power generators to transformers on utility poles, all the way down to power supplies for laptops. They’re in every electric motor. They’re really a crucial component, but it has been challenging to improve them in the past 30 or 40 years,” says Wendy Gu, an assistant professor of mechanical engineering at Stanford.
Gu wants to change that. She and Juan Rivas-Davila, associate professor of electrical engineering at Stanford, along with Mitra Taheri at Johns Hopkins University, are developing a new type of ultra-efficient material that can lead to miniaturized motors, power supplies and generators. It’s called a “soft magnetic composite,” or SMC. (The “soft” part is a bit of a misnomer – it just means that the magnetic properties can be switched on and off. This is in contrast to hard, or permanent, magnets.)
Although SMCs have been around in one form or another for at least three decades, they can be expensive to make and hard to manipulate. The reason for that is simple, Gu says: Some of the best magnetic materials are made of metal atoms that aren’t locked into defined structures like a crystal, but are instead glommed together into a glass-like substance.
The process for using these materials in SMCs is incredibly complex. First, the glassy magnetic material is made like fiberglass insulation – melted and spun at high speeds, creating thin brittle ribbons. These are then crushed, mixed with ceramics, pressed into a mold and fused together under high heat.
Gu and Rivas-Davila, however, may have found another way to achieve the same goal using nanotechnology. In the lab, they’ve produced individual grains of SMC material that are less than a micron across – using nothing but a beaker of water and some simple chemistry.
“We basically put metal ions into the water – just powder from a container – and then add another chemical that causes them to change from a positive to a neutral charge. If we do it in a controlled way, the metal ions will clump together into tiny particles,” Gu says. “It’s an incredibly cheap process, and doesn’t involve a lot of specialized equipment.”
The resulting material, Gu adds, could be used to 3D print a magnetic core in whatever shape designers call for. By laying out a thin dusting of this new SMC material, it may be possible to use a powerful laser to fuse the particles together directly. “If you add more SMC material on top of that and repeat the process, you can gradually build the part up layer upon layer into whatever shape you want,” she says.
Because of the incredibly small size of the particles Gu created, the resulting SMCs would also be far more effective than traditional ones, Rivas-Davila adds.
“Normally, when you induce an electrical signal in a magnetic metal, tiny circular eddies of current form inside it. Those eddies are trapped within crystalline regions of the metal, so they start to create a lot of heat. That wastes a lot of energy,” he says.
Nanostructured SMCs that use glassy metals, however, would create far fewer of these eddies, so they’d have a distinctive advantage over other materials doing the same job. An electric motor built with Gu and Rivas-Davila’s new material, for instance, could be half the price of ones on the market today, yet nearly 10 times more efficient.
While the pair’s work is still in its early stages, they have already attracted the attention of major players in the clean energy world. In late 2021, they were awarded a $1.9 million grant from the Advanced Research Projects Agency–Energy (ARPA-E), a governmental group that funds bold and forward-thinking energy research.
If their research pans out, the duo could eventually make key electrical devices much smaller and cheaper. One of the first parts on their priority list is a ring-shaped component called a “toroid” – a relatively large and ubiquitous part used in almost every electronic power circuit. It doesn’t look like much: just a wire wrapped around a blocky magnetic metal donut. But changing the shape and cross-section of that donut could bump up its efficiency. If that were the case, engineers could reduce its size – and the size of their entire product – without sacrificing any performance.
“The ultimate goal is to miniaturize parts so we can make smaller, more powerful devices,” Gu says. “If we can do that, it would be a major advancement in the field.”