Microactuated Resettable Switch

Present battery systems allocate a large fraction of their weight to redundant capacity and protection against open circuit battery failure. If cells are redundant instead of batteries, this excess weight can be reduced. Then each cell must have a switch to short it out in case of open-circuit cell failure. Such a switch must carry significant current, but be lightweight and have low in-circuit impedance so as not to introduce power loss and heating. It is desirable that the switch be resettable to allow maximum battery management flexibility. Switches using thin-film shape-memory alloy microactuator can meet these requirements for bypass switching applications. Actuators weighing a few milligrams can provide adequate force and displacement at low voltage. Switches are made resettable by incorporating two actuators in a bistable configuration. In this research program we will design and fabricate prototype switches of two types: Type 1, weighing less than one gram, capable of conducting 20 amperes with insertion impedance less than one ohm; Type 2, weighing less than 5 grams, capable of handling 200 amperes with impedance less than 0.5 ohms. Driving circuitry will be developed for multiple-switch operation. Bistable mechanisms will be demonstrated. Benefits: This technology has very large market potential in consumer products and in automobiles. Remotely resettable circuit breakers could save significant weight in commercial and military aircraft. Arrays of micromachined switches are needed in multimedia communications networking.