Iron-gallium alloy shows promise as a power-generation device

September 29, 2015
This picture is of the experimental setup showing the Hopkinson bar surrounded by a water-cooled electromagnet. A cylinder of Galfenol is inside of the electromagnet, sandwiched between the Hopkinson bars. The magnet was used to apply a wide range of static magnetic fields to Galfenol while it was mechanically impacted. Credit: John Domann/UCLA

An alloy first made nearly two decades ago by the U. S. Navy could provide an efficient new way to produce electricity. The material, dubbed Galfenol, consists of iron doped with the metal gallium. In new experiments, researchers from UCLA, the University of North Texas (UNT), and the Air Force Research Laboratories have shown that Galfenol can generate as much as 80 megawatts of instantaneous power per square meter under strong impacts. The team describes the findings, which could lead to the development of wireless impact detectors and other applications, in a paper in the Journal of Applied Physics.

Galfenol is a magnetoelastic material—one in which the state of magnetization can be changed by squeezing, pushing or otherwise deforming the material. Conversely, when exposed to a magnetic field, magnetoelastic materials respond by changing shape. If the materials are prevented from deforming—for example, by being held in a clamp—they instead will generate a large force.

"In general this means a magnetoelastic material can convert mechanical into , and vice versa," explained John P. Domann, a mechanical engineering graduate student at UCLA and first author of the paper. Galfenol converts energy with high efficiency; it is able to turn roughly 70 percent of an applied into magnetic energy, and vice versa. (A standard car, by contrast, converts only about 15 to 30 percent of the stored energy in gasoline into useful motion.) Significantly, 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 said.

As described in the new paper, Domann and his colleagues—including his Ph.D. advisor, Gregory P. Carman, a professor of mechanical and aerospace engineering at UCLA, and Bradley E. Martin from the Air Force Research Laboratories at Eglin Air Force Base in Florida—assessed the power-generating ability of Galfenol in experiments using a device called a Split-Hopkinson Pressure Bar to generate high amounts of compressive stress (e.g., powerful impacts). They found that when subjected to impacts, Galfenol generates as much as 80 megawatts of instantaneous power per cubic meter.

By way of comparison, a device known as an explosively driven ferromagnetic pulse generator produces 500 megawatts of power per cubic meter. However, as their name implies, such generators require an explosion—one that destroys the ferromagnet, even as it produces 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."

Among the potential applications, 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," Domann said. These devices could be embedded in vehicles—military or civilian—to detect collisions. Because electromagnetic waves travel three orders of magnitude faster than mechanical waves, information about the impact could be transmitted ahead of the waves created by the impact. "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," he added.

Although the concept requires further analysis and testing, commercial technologies based on the idea could see the market within just a few years, the researchers said.

Explore further: Researchers discover new uses for high tech alloy

More information: "High strain-rate magnetoelasticity in Galfenol," by J.P. Domann, C.M. Loeffler, B.E. Martin and G. P. Carman. Journal of Applied Physics on September 29, 2015 DOI: 10.1063/1.4930891

Related Stories

Researchers discover new uses for high tech alloy

August 22, 2012

(Phys.org) -- Materials scientists at the U.S. Department of Energy's Ames Laboratory, Etrema Products, Inc. (EPI), and the Naval Surface Warfare Center Carderock Division have developed new ways to form a high tech metal ...

Beating bird wings generate electricity for data collector

March 11, 2015

A technology that generates electricity from the beating wings of birds, bats or even moths could produce enough power to run a device that collects data – such as location, migration habits or vital physiological statistics ...

Recommended for you

Measuring tiny forces with light

August 25, 2016

Photons are bizarre: They have no mass, but they do have momentum. And that allows researchers to do counterintuitive things with photons, such as using light to push matter around.

23 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

MR166
2.8 / 5 (9) Sep 29, 2015
"Galfenol can generate as much as 80 megawatts of instantaneous power per square meter under strong impacts."

Oh great, Government sponsored hyperbole is just what we need.

80 megawatts of instantaneous power is pretty much a meaningless metric.
rgw
5 / 5 (2) Sep 29, 2015
But it is more than 70 megawatts of instantaneous power per square meter under strong impacts.
Going
1 / 5 (1) Sep 29, 2015
Repeated explosions are what we have in an internal combustion engine. Rather than a piston , crank and gearbox we could send pulses of current to Galfenol powered motors creating a highly efficient transmission.
Going
3 / 5 (1) Sep 29, 2015
Something that changes shape in response to electromagnetic energy has the potential to be both a generator and a motor.
abecedarian
1 / 5 (2) Sep 29, 2015
Watts can be converted to Joules, so how is that meaningless?
MR166
4.5 / 5 (2) Sep 29, 2015
"Watts can be converted to Joules, so how is that meaningless?"

Hummm I would be very interested to see that conversion on paper since Joules is a 2 dimensional unit of measurement and watts are a 1 dimensional unit.
lengould100
not rated yet Sep 30, 2015
As for the bit about wireless triggering of safety devices in cars in a crash, why not just run a wire from a standard impact detector mounted at the same location as the proposed galfenol sensor?
Eikka
1 / 5 (3) Sep 30, 2015
it is able to turn roughly 70 percent of an applied mechanical energy into magnetic energy, and vice versa. (A standard car, by contrast, converts only about 15 to 30 percent


Replacing the piston in an engine with a rod of galfenol would get you significantly lower efficiency.

In combustion, the rise in temperature causes a rise in pressure, which causes a force on the piston. In order to do work, the piston must move because work is force over distance. Simply squeezing a block of metal by a few microns transfers very little energy to it because the gasses are not permitted to expand, and so the energy of the combustion gets blown out when the exhaust valve opens.

The efficient operation of an engine requires that the gasses expand in volume and drop in pressure as close to atmospheric pressure as possible. For this reason, high efficiency engines cycles such as the Atkinson cycle have a longer expansion stroke than their compression stroke.
Eikka
2 / 5 (4) Sep 30, 2015
A loose spring made of galfenol could be used to satisfy the need for volume expansion, but there too you would only replace the ordinary crankshaft/flywheel mechanism with an electrical one likely consisting of a rectifier and a capacitor.

It wouldn't change the dynamics of the engine otherwise, and while a crankshaft/flywheel combination for turning pressure on top of a piston to rotary motion is close to 95% efficient as limited by friction, the galfenol converter would obviously perform worse.

So the comparison between this device, and a piston engine, is rather contrived because you have to consider how they gain their mechanical energy. Sure, if you drop a hammer on a block of galfenol, it may turn 70% of the impact energy into a magnetic field, but that's not the same thing as combusting fuel inside a cylinder.
italba
5 / 5 (1) Sep 30, 2015
But detonation is more efficient than combustion, so a "galfenol engine" could be built with a explosion chamber shaped to concentrate the shock waves to a galfenol block. The residual heat could then be used to move a turbine, maybe the total energy generated could be greater than today's one.
abecedarian
5 / 5 (1) Sep 30, 2015
"Watts can be converted to Joules, so how is that meaningless?"

Hummm I would be very interested to see that conversion on paper since Joules is a 2 dimensional unit of measurement and watts are a 1 dimensional unit.

So you're saying that since 1W = 1J/second and 1J = 1W/second, there is no conversion possible?

If I'm wrong, please correct me so I understand things better.
gkam
1 / 5 (2) Sep 30, 2015
Railguns.
Quantum Magician
not rated yet Sep 30, 2015
since 1J = 1W / second
Except that it is not.

a Watt (W) is a measure of power, while a Joule (J) is a measure of energy. Or in other words: You are mixing Apples with.. Apple Pie ;-D

Watts can be converted to Joules, so how is that meaningless?

In case you meant the conversion of electrical to mechanical energy, then we already posses the knowledge to build such devices. They usually go by the name of "electromagnetic coils", or even "electric motors" (for a more complex implementation). And what's best about them - they work both ways! :-O

I hope this helps to resolve your confusion.

And on topic:
As someone already mentioned - making springs that can be used to directly salvage some of the impact energy (f/e in car dampers) could be worth a consideration. But finding the right combination to get the desired mechanical properties while still maintaining a high enough conversion efficiency might be tricky (if at all possible). Iron-Gallium-Carbonate maybe?
abecedarian
5 / 5 (1) Oct 01, 2015
I hope this helps to resolve your confusion.

Not really, since your description doesn't agree with what the definitions of Watt and Joule are.

Watt: joule per second
Joule: work required to produce one watt of power for one second (amongst other defs)
gkam
1 / 5 (2) Oct 01, 2015
Early railguns compressed the magnetic coils with explosives to concentrate the fields. With this, it will be easier and more powerful. Expect to see them on ships.
MR166
not rated yet Oct 01, 2015
"Joule: work required to produce one watt of power for one second (amongst other defs)"

You just answered your own question. There is a big difference between a watt and a watt second. One is a measure of power and the second of work. Lets say you have a capacitor and discharge it in one second. Lets say the peak power output was one watt. Now if you were to discharge the same capacitor in one millionth of a second the peak power would jump to 1 million watts but the actual work done would remain the same.
abecedarian
not rated yet Oct 01, 2015
And one watt = 1 joule / second.
petepal55
3 / 5 (1) Oct 03, 2015
How about a series of trip-hammers, fueled by good ol' water wheels, that smack pieces of this stuff? Just trying to keep it simple. The water can already have powered turbines, right?
baudrunner
not rated yet Oct 03, 2015
The effect should be seen with a static alloy block and a dynamic magnetic field. It's kind of like, no it is exactly like, harnessing the power of inertia.
Egleton
not rated yet Oct 04, 2015
If the galfinol piston setup extracted energy from the exploding gasses then the gasses would perforce become cooler.
The gasses would enter the explosion chamber, heat up, attempt to expand transferring their energy to the galfinol and cooling.
Energy cannot be created or destroyed.
(I'm beginning to doubt those homilies that I learned as a kid.)
Nik_2213
not rated yet Oct 04, 2015
{Cough} This is kin to the piezo-electric effect, which is great for microphones, mini-speakers, ultrasonic transducers, lighting burners etc etc, but not rated for grid-power.

Snag is piezo materials are generally brittle, hard to shape, hard to interface. This related stuff seems to be 'industrial strength', so should be able to harness some 'environmental' energy. Soaking up road vibrations would be good...
Eikka
not rated yet Oct 12, 2015
But detonation is more efficient than combustion, so a "galfenol engine" could be built with a explosion chamber shaped to concentrate the shock waves to a galfenol block.


Good luck finding a material that can withstand repeated detonation millions and millions of times over.

It's a commonly held misconception that diesel engines work by detonating the fuel, but this isn't the case. No engine does, because by definition the detonation shock advances faster than the speed of sound, and so it isn't a pressure wave. It's the gas molecules themselves travelling faster than sound in a uniform front, so catching the shockwave is like catching a speeding bullet.

When it hits a relatively "stationary" object, the shockwave simply reflects back. In order to transfer momentum with maximum efficiently, the piston would have to be moving downwards at exactly half the speed of the incoming impact at roughly 1000 m/s which is practically impossible.

Eikka
not rated yet Oct 12, 2015
However, what is more likely to happen with a detonation engine is that the galfenol piston would simply shatter to bits.

http://guns.conne...tro.html

Every material (also - and especially - the hardest steel) is "atomized" to fine particles when hit by this detonation wave. When the detonation is over and no explosive is left, there are lots of reaction products (mostly H2O, CO2, CO, C, H2 and N) left. What follows is the explosion (rapid expansion) of the reaction products.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.