Passive microsensor for binary counting of numerous threshold events

Microsystems for autonomous limit monitoring can be used for triggering maintenance and thus help to reduce costs. We present a fully integrated passive microsystem for binary counting of off-limit conditions. The mechanical design and a mechanical characterization of the system fabricated using SOI (silicon-on-insulator) technology are shown. The binary counting mechanism is realized by utilizing mechanical coupling elements between bit elements. The mechanical energy needed for switching the first bit to the state "high" was found to be 0.1 μJ by moving the entrance 37 μm and applying a force of up to 8.2 mN. 0.36 μJ was determined for switching the bit back to the state "low" by applying a 69 μm distance and a force of up to 10.2 mN. The system needs input energy for counting only, not for storing the counter value. Expanding the design to up to ten bit elements would offer a passive microsensor able to detect 1023 off-limit conditions. A mechanical binary microcounter is presented that does not require electrical energy supply. It is suitable for counting any physical event that can be converted into an adequate force-travel-characteristic.