October 29, 2011

SHOCK EFFECT:

What Woody Woodpecker Can Teach Us About Football (Jennifer Ouellette, October 17, 2011, Scientific American)

One of my more distinct childhood memories is of visiting my grandmother's house in Lewiston, Maine, a small-ish (back then) town in the southern part of the state. It was a big clapboard house on a quiet street, on the edge of a large wooded area.

I wandered aimlessly in those woods one afternoon, pretending to be an explorer of some sort (as children do), until I stumbled onto a clearing and snapped out of my fantasy world, suddenly aware that (1) I had no idea where I was, and (2) it was eerily quiet. Quiet, except for an occasional rapid-fire tap-tap-tap echoing through the clearing from a nearby tree. I found myself wondering: Doesn't all that pounding away at tree trunks give the woodpecker a headache? Because it looked like it should hurt. A lot.

Kids always ask the best, most basic questions; they haven't learned yet to pretend to be smart, to be ashamed of their ignorance; they're just curious about how the world works. And the best scientists ask those kinds of questions too, which is why we might roll our eyes and chuckle a bit when we read about two California scientists who decided to delve into the underlying science of why it is that woodpeckers don't get headaches.

There's more to it than an easy punchline. Ivan R. Schwab of UC-Davis and his late colleague, Philip May of UCLA, won the 2006 Ig Nobel Prize in Ornithology for their work, published in the Journal of Ornithology -- and the Ig Nobels, as founder Marc Abraham would be the first to tell you, are designed to honor research that first makes you laugh, and then makes you think.

See, it's not such a stupid question, especially since, during courtship, the male woodpecker can drum a good 12,000 times a day (normal rate is still an impressive 500-600 times a day, usually to forage for food). And those aren't just light taps, either.

A woodpecker typically drums away at a rate of 18-22 times per second, with a "deceleration" force of 1200 g. (Recall from high school physics class that the more slowly you decelerate, the less the impact, because the energy is dissipated over a longer period of time. Sudden stops or sharp blows, therefore, can pack quite a wallop.) Humans, on the other hand, will lose consciousness under 4 to 6 g's. and a sudden deceleration of 100 g will cause a concussion.

In February 2011 a new paper appeared in Bioinspiration and Biomimetics entitled, "A Mechanical Analysis of Woodpecker Drumming and Its Application to Shock-Absorbing Systems," building on Schwab and May's earlier research. Schwab and May's study found that the key to protecting the pileated woodpecker from chronic headaches or more serious concussion had to do with the structure of their heads -- "thick muscles, sponge-like bones, and a third inner eyelid," all of which work together to absorb impact -- and the fact that woodpeckers make straight, clean linear strikes. Per Live Science:

    One millisecond before a strike comes across the bill, dense muscles in the neck contract and the bird closes its thick inner eyelid. Some of the force radiates down the neck muscles and protects the skull from a full blow. A compressible bone in the skull offers cushion, too. Meanwhile the bird's closed eyelid shields the eye from any pieces of wood bouncing off the tree and holds the eyeball in place. "The eyelid acts like a seat belt and keeps the eye from literally popping out of the head," Schwab [said]. "Otherwise acceleration would tear the retina."

Okay, that's interesting, you might be thinking, but what good is that insight? That's where UC-Berkeley's Sang-Hee Yoon and Sungmin Park come in. They're the authors of the most recent paper, and they studied videos of woodpeckers in action, and also took CT scans of the bird's head and neck (see image, above) to more clearly determine how it absorbs mechanical shock so well.

Specifically, the beak is both hard and elastic, there is an area of spongy shock-absorbing bone in the skull, and woodpeckers have another springy structure in back of the skull called a hyloid. The skull structure works in concert with cerebrospinal fluid to further suppress vibrations.

Yoon and Park then set about finding ways to artificially mimic these attributes in a manmade mechanical shock absorbing system, specifically to protect microelectronics components. Per New Scientist:

    To mimic the beak's deformation resistance, they use a cylindrical metal enclosure. The hyoid's ability to distribute the mechanical loads is mimicked by a layer of rubber within that cylinder, and the skull/cerebrospinal fluid by an aluminum layer. The spongy bone's vibration resistance is mimicked by closely packed 10-millimeter-diameter glass spheres, in which the fragile circuit sits. To test their system, Yoon and Park placed it inside a bullet and used an airgun to fire it at an aluminum wall.

Science! Personally, I can get behind any research that involves playing with airguns in the lab. And this is about more than being able to drop your iPhone without the electronics going all wonky.

It will also help protect, say, the electronics in airplane flight recorders, making it less likely that critical information will be damaged in the event of a crash. The scientists found that their mechanical shock-absorbing system reduced the failure rate of the microelectronics from 26.4% (using the conventional hard resin method) to 0.7%, despite the fact that the microelectronics suffered shock levels as high as 60,000 g.

Other applications being bandied about include using the shock absorber system in "bunker-busting bombs", and to protect spacecraft from space debris (a growing problem, especially given our current reliance on orbiting satellites for communications).

It might even be useful in Formula One racing, protecting drivers from serious brain injury and internal damage suffered during the inevitable accidents.

Here's another suggestion for a possible application: protecting football players from concussion.

Posted by at October 29, 2011 8:38 AM
  

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