Alloy made twenty years ago by US Navy could provide more efficient way of producing electricity today

Galfenol, an iron doped with the metal gallium, was first made by the US Navy nearly twenty years ago. It’s a relatively unknown material and so hasn’t seen much use over the last two decades, but a recent study into it might change all that. 

Researchers from UCLA, the University of North Texas, and the Air Force Research Laboratories, have published a report that details Galfenol is capable of generating as much as 80 megawatts of instantaneous power per square meter under strong impacts. 

Should this reaction prove scalable, it could lead to the eventual development of wireless impact detectors and other applications.

Taking a closer look, Galfenol is a magnetoelastic material; that is, its state of magnetization can be changed by squeezing, pushing, or otherwise deforming the material. On the flipside, when it’s exposed to a magnetic field, it changes shape. And if it’s prevented from deformation like, say, if one were to place it in a clamp, it will react by generating a large force.

“In general this means a magnetoelastic material can convert mechanical energy into magnetic energy, and vice versa,” explained John P. Domann, a mechanical engineering graduate student at UCLA and first author of the paper. He goes on to explain that galfenol converts energy with high efficiency — it can turn roughly 70% of an applied mechanical energy into magnetic energy, and vice versa (for comparison purposes, a standard car converts about 15 to 30% of the stored energy in gasoline into useful motion.) Beyond its efficiency, and perhaps a bit more importantly, the magnetoelastic effect can be used to generate electricity. “If we wrap some wires around the material, we can generate an electrical current in the wire due to a change in magnetization,” Domann explained.

In the actual paper, the team assessed the power-generating ability of Galfenol in experiments using a Split-Hopkinson Pressure Bar to generate large amounts of compressive stress. When subjected to this pressure, Galfenol generated nearly 80 megawatts of instantaneous power per cubic meter. 

Putting this into comparison, the already available explosively-driven ferromagnetic pulse generator can produce 500 megawatts of power per cubic meter. But, as the name suggests, this generator requires an explosion, one at a level that destroys the ferromagnet, even as it’s producing power. 

“Destroying a material requires a lot of wasted energy, creating only one-shot devices,” Domann said. “This wasteful energy and destruction is not a concern in our method using Galfenol, meaning our devices can be used repeatedly and cyclically.”

Domman believes that, immediately speaking, Galfenol-powered devices could be used as wireless impact detectors. “Essentially, we could fabricate small devices that send out a detectable electromagnetic wave when a mechanical pulse moves through it,” he said. Specifically, they could be embedded in vehicles to detect collisions. You see, because electromagnetic waves travel three orders of magnitude faster than mechanical waves, data about the impact could be transmitted ahead of the waves created by the impact itself. 

“In this manner, we could wirelessly determine that an impact has occurred, before the majority of the vehicle (or any passengers) even have time to feel it. This would allow a fast computer to take actions mitigating damage or injury,” Domman added.

Further analysis and testing of the concept is needed in the immediate future, but commercial technologies based on the idea could reach the market in a few years, the team concluded.

Read the full report, entitled: High strain-rate magnetoelasticity in Galfenol. It was published in the Journal of Applied Physics.

Via the American Institute of Physics