<<返回上一页

Crystal surfboard

发布时间:2019-03-08 06:10:13来源:未知点击:

By Ben Crystall THE crystals that keep your TV picture in sync could be used as motors in micromachines. Japanese researchers have harnessed nanometre-high waves generated on the surface of a piezoelectric crystal to force a tiny slider to move along it. Eventually they hope to use this effect to build high-precision motors and actuators. Applying a small voltage to a piezoelectric crystal flexes and stretches its atomic lattice, creating a surface acoustic wave. In a TV set, an echo within the crystal is used to set the timing for the electron beam that scans the screen. But when these waves bounce along the surface of a crystal, small objects on top will “surf” along with them. Toshiro Higuchi and his colleagues at the Department of Precision Engineering at the University of Tokyo built their motor using a sliver of lithium niobate 60 millimetres long and 15 millimetres wide. To generate surface acoustic waves, Higuchi and his colleagues apply a 50-megahertz electric field to a piezoelectric lithium niobate crystal. The varying electric field sets a stream of waves in motion. Higuchi has used his motor to move a square silicon slider 2 millimetres along the crystal. As its atoms vibrate, they rub against the slider and push it along. To provide the friction between the crystal and the slider that is needed for the motor to work efficiently, Higuchi mounts the crystal on an iron base plate and uses a small magnet to press the slider onto its surface. A continuous stream of waves along the crystal will move the slider along at almost 1 metre per second, Higuchi has found. Single waves can move the slider in steps of 40 nanometres. This precision could be useful for controlling the position of objects such as read-write heads in disc drives. Higuchi claims his device betters motors of a similar size. It can exert a force of 3.5 newtons, has a fast response, and only requires low voltages to drive it. And, while Higuchi’s latest model is relatively large, one of the biggest advantages is that it can be miniaturised and made part of a silicon chip. “A device just three millimetres across is already possible,” says Minoru Kurosawa, who works with Higuchi. Devices 1 millimetre wide should follow. Derek Chetwynd of the Centre for Nanotechnology at the University of Warwick says the idea has promise. “It could be valuable for specialist applications—moving samples around inside an electron microscope or during chip manufacture, or moving tiny wafers between chemical treatments,