When the tiny lizard known as the sandfish moves through sand, it literally dives under the surface of the ground as if swimming. Now physicists have figured out how they do it - and want to build sandfish robots.


Georgia Tech physicist Daniel Goldman and his team observed the sandfish as they swam through sand, using X-rays and tiny sensors placed in the sand that measured how grains were displaced as the lizards moved through them. One thing they discovered right away was that the sandfish were indeed "swimming" - they tucked their legs up next to their bodies and moved in an undulatory wave like fish through water. Another interesting finding was that the lizards could go slightly faster in tightly-packed sand, as long as they varied the frequency of the wave created by the movement of their bodies. Their work is published today in Science.

Says Goldman:

When started above the surface, the animals dive into the sand within a half second. Once below the surface, they no longer use their limbs for propulsion — instead, they move forward by propagating a traveling wave down their bodies like a snake . . . The large amplitude waves over the entire body are unlike the kinematics of other undulatory swimming organisms that are the same size as the sandfish, like eels, which propagate waves that start with a small amplitude that gets larger toward the tail . . . The results demonstrate that burrowing and swimming in complex media like sand can have intricacy similar to that of movement in air or water, and that organisms can exploit the solid and fluid-like properties of these media to move effectively within them.

There are implications for this research that go beyond understanding how lizards move through sand. Goldman and his team think it could help roboticists in designing rescue bots that could worm their way through collapsed rubble. It would also be useful for creating surveillance robots that can swim invisibly under sand, tracking enemy locations or even recording conversations that take place outdoors in sandy regions.

via Science and Georgia Tech


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