MD&M West Features World's Smallest Reed Switch

Reed switches have been around for decades. But now, Coto Technology (North Kingstown, RI), a developer of small signal-switching products, has launched what it bills as the tiniest reed switch ever. Featuring a mere 1.26-mm² footprint, the MEMS-based RedRock switch is a single-pole, single-throw component with normally open ruthenium contacts. Actuated using an electromagnet, a permanent magnet, or a combination of both, the switch is suitable for miniaturized medical device applications such as hearing aids, capsule endoscopes, and insulin-delivery devices.

In the past, reed switches consisted of stamped nickel-iron blades and a sealed glass tube. In contrast, the new component is manufactured using microlithography. A metal cantilever bridges two electrically isolated metal blocks that act as magnetic field amplifiers. A small gap between the cantilever and one of the blocks allows magnetic flux from an external magnet to build up, pulling the cantilever into electrical contact with the block.

Reed switches are advantageous for medical device applications because they are sealed, notes Stephen Day, science and engineering consultant for Coto Technology. As a result, the switch itself does not make contact with the body or body fluids. An external magnet can activate the switch through the external packaging, enabling users to either activate or program the device in question.

"While maintaining the desirable properties of conventional reed switches--including high current-carrying capability, hermetically sealed contacts, high resistance to electrostatic discharge, and zero-power operation--the new design is approximately one-tenth the size of its smallest available cousins," Day comments.

Bob Michaels is senior technical editor at UBM Canon.