Sensor systems are needed for PHM to monitor environmental, operational, and performance-related characteristics. The gathered data can be analyzed to assess product health and predict remaining life. A generic sensor system will typically have sensing elements based on a suitable transducer technology, onboard analog-to-digital converters, onboard memory, embedded computational capabilities, data transmission, and a power source or supply. Sensor systems with multiple sensing abilities, miniature size and light weight, low power consumption, long range and high rate data transmission, large onboard memory, fast onboard data processing, low cost, and high reliability are specifically advantageous to PHM applications. Recent PHM research is also focusing on the concept of “canaries” for early warning of degradation and impending failures so that risk mitigation options can be rapidly implemented. Like, canaries in a coal mine, these are sacrificial non-functional elements in the design, and are tailored to degrade in an accelerated manner in response to different stress sources. The degradation mode in the canary is typically an accelerated version of the degradation expected in the functional product, and the design is usually based on fundamental physics-of-failure concepts. Canaries can significantly reduce the uncertainties in the remaining useful life estimates because each canary is tailored to a known failure mechanism and the materials, manufacturing processes, and life-cycle stresses can be tailored to “match” the behavior of the functional elements that are being monitored. Canaries can be calibrated to provide sufficient advance warning of failure (termed ‘prognostic distance’ or ‘remaining useful life’) to enable timely maintenance and replacement actions. System level research is also needed for integrating networks of sensors and canaries; collecting, post-processing and storing their outputs, and delivering power to these networks.
