New Metal Can Become Soft and Stiff Just Like Human Muscles

Tech created by HRL Laboratories will make comfy cars and human-like robots.

GifGrabber/HRL Laboratories

The human body is designed pretty well: Our muscles are able to switch between strength and dexterity, limbs stiffening when we do an energy-fueled task like lifting a bowling ball and softening when we do something delicate like painting with a brush. This ability is very rarely replicated in engineering systems, namely because it’s expensive, but also because it’s been damn hard to clone.

However, HRL Laboratories — the same Malibu-based researchers who brought you microlattice — has announced they’ve been able to replicate the reactions of human muscle in metal. Their goal is to use this new technology to create cars with smoother rides and, more intriguingly, more human-like robots.

In a paper published in the most recent issue of Science Advances, the researchers claim that their technology, “variable stiffness vibration isolator” can change from stiff to soft by a factor of 100 in milliseconds, independent of how much mechanical force is applied. This technology, they argue, far surpasses any previous mechanisms trying to do the same thing.

With applied force to buckle beams, the team soften stiffness up to 100 times in milliseconds.


“With HRL systems, you can switch between stiff and soft with the push of a button,” says principal investigator Christopher Churchill. “This can give us adaptive stiffness robotic joints, that are just as graceful with a paintbrush as they are lifting heavy tools.”

It all comes back to stiffness. Stiff structures, like current robotic arms and truck suspensions, are very good at supporting loads but if something shakes the base, the whole structure is going to be unsteady. With a soft system, shakes at the base won’t really affect the top, but they aren’t good at accepting a new weight load. What you need is the Goldilocks of structures: adaptive stiffness, which can isolate or transmit vibrations on demand regardless of the weight of the mass.

Adaptive metals mean more human-like robots.


Churchill and his team found that when you put strips of metal (the negative stiffness) perfectly parallel within their positive stiffness system, the stiffnesses add up to zero. Voila, metal that is both load-bearing and nimble.

Best of all, the researchers at HRL believe their technology is going to be low-cost. Robots with limbs that respond like human muscles will be cool; cars that won’t ever respond to a bump in the road are going to be outright luxurious.

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