Beetle-inspired Switch Uses Water For Bonding

The newbeetle-inspired switch, designed by Cornell University engineers, canwork by itself on the scale of a micron -- a millionth of a meter. Theswitches can be combined in arrays for larger applications likepowerful adhesive bonding. Like the transistor, whose varied usesbecame apparent only following its invention, the uses of the newswitch are not yet understood. But the switch's simplicity, smallnessand speed have enormous potential, according to the researchers.

"Almostall the greatest technological advances have depended on switches, andthis is a switch that is fast and can be scaled down," said Paul Steen,a professor of chemical and biomolecular engineering at Cornell andco-author of a paper published in the Proceedings of the NationalAcademy of Sciences (Vol. 102, No. 34).

Steen dreamed up the ideaof the switch after listening to Cornell entomologist Tom Eisnerlecture on palm beetles, which are native to the southeastern UnitedStates.
Like the beetle, which clings to a palm leaf at adhesivestrengths equal to a hundred times its own body weight -- the humanequivalent of carrying seven cars -- the switch in its most basic formuses surface tension created by water droplets in contact with asurface, in much the same way as two pieces of wet paper cling together.

Whenattacked, the palm beetle attaches itself to a leaf until the attackerleaves. It adheres with 120,000 droplets of secreted oil, each making abridgelike contact between the beetle's feet and the leaf. Each dropletis just a few microns wide. Whereas the beetle controls the oilcontacts mechanically, Steen's switch uses water and electricity.

Forthe switch to make or release a bond created by surface tension, awater droplet moves to the top or bottom of a flat plate surface usingelectricity from electrodes. The electricity moves positively chargedatoms, called ions, in the water through the minute capillaries of athin disk of porous glass embedded in the plate. The water moves andwells up into a micrometer-sized droplet on the plate surface. Theexposed droplet can then stick to another surface. To break the bond,electricity pulls the exposed water back through the capillary pores.

Withmillimeter-sized water droplets and micron-sized pores, 5 volts canturn the switch on in one second. At the same time, the researcherspredict that smaller droplets will require less energy to move and havefaster switching times. Steen and his colleagues believe that a switchas small as hundreds of nanometers, close to a billionth of a meter andone-tenth the size of the beetle droplets, is within reach. Researcherscould also create large effects from many tiny switches by connectingthem in various arrangements, Steen said.

"This new technologybridges the gap between scales as large as our hands and nanoscales,"said Steen. "We need devices that allow us to communicate between thetwo scales."

Co-authors include Michael Vogel, a postdoctoralresearcher in Cornell's Department of Chemical and BiomolecularEngineering, and researcher Peter Ehrhard at the Institute for Nuclearand Energy Technologies in Karlsruhe, Germany. Since much of this workwas conducted while the three scientists were at the German institute,the patent application was filed in Germany.

The study wassupported by NASA, the National Science Foundation, theForschungszentrum Karlsruhe and the Deutscher Akademischer AustauschDienst.