Miniature embedded prognostic probe

Sensing systems for reliability prognostics are used extensively in lifeand missioncritical electronics systems. They allow monitoring of reliability stresses in real time and scheduling of preventative maintenance before system failure. However, reliability prognostics systems are, in general, large and expensive and cannot be used in lower cost, small sized or portable products. This paper presents a sensing module for reliability prognostics which is only 1.2cm³ in volume and uses only commercial off-the-shelf components. In its 1.2cm³ package, the module combines all the necessary elements to act as an embedded prognostic sensor system for multi axial strain and temperature monitoring. The system consists of microcontroller, sensors, data storage, signal conditioning and communications interface in a single package. The module takes a cube form factor and can measure 3D strain, 3D temperature, and humidity at the point it is located. The use of commercial-off-the-shelf components throughout the module and its modular design mean that the system can be readily customised in terms of both size and functionality, a major advantage over approaches which use custom-designed test chips. The module was subjected to a range of stress tests for both calibration and characterisation. Mechanical testing of "dog-bone" encapsulated test specimens verified that the direction and magnitude of all components of 3D strain could be resolved with a correlation on average of better than 10% with finite element analysis results when subjected to tensile loads. Climatic test results verify the systems functionality over the range of 0-85 degrees Celsius as well as providing data for calibration of the device. The module is small and modular enough that it can be used in applications such as structural health monitoring and reliability prognostics and for calibration of mechanical/ thermomechanical simulations.