Micromachined Ultrasound-Based Proximity Sensors presents a packaged ultrasound microsystem for object detection and distance metering based on micromachined silicon transducer elements. It describes the characterization, optimization and the long-term stability of silicon membrane resonators as well as appropriate packaging for ultrasound microsystems. Micromachined Ultrasound-Based Proximity Sensors describes a cost-effective approach to the realization of a micro electro mechanical system (MEMS). The micromachined silicon transducer elements were fabricated using industrial IC technology combined with standard silicon micromachining techniques. Additionally, this approach allows the cointegration of the driving and read-out circuitry. To ensure the industrial applicability of the fabricated transducer elements intensive long-term stability and reliability tests were