Microsensors, microelectromechanical systems (MEMS), and electronics for smart structures and systems

The technology referred to by the terms 'microelectromechanical systems' (MEMS), 'interdigital transducers' (IDTs), and 'smart systems' is a multidisciplinary one which has generated a great deal of interest in the chemical, mechanical, electrical engineering, medical, materials science, and food science communities in recent years. The term 'smart system' refers to a device or an array of devices that can sense changes in its environment and makes a useful or optimal response by changing its material properties, geometry, or mechanical or electromagnetic response. Both the sensor and actuator functions with the appropriate feedback must be integrated, and comprise the 'brain' of the material. The materials belonging to this category include a range of artificial materials, from optically active or chiral polymers to multifunctional polymers, carbon nanotubes, piezoelectrics, ferroelectrics, and other active ceramics. The miniaturization of sensors and subsequently that of the MEMS incorporating the sensors, actuators, and electronic circuitry for signal processing and control feedback have been made possible by advances in technologies originating in the semiconductor industry, and the emerging field has grown rapidly during the past ten years. Recently, microstereolithography has revolutionized the MEMS industry through multifunctional polymeric materials incorporating organic thin-film transistors with three-dimensional MEMS which is not possible with silicon processing. The integration of MEMS, IDTs, and the required microelectronics and conformal antenna in the multifunctional smart materials and composites results in a smart wireless system suitable for sensing and control of a variety of functions in automobile, aerospace, marine, and civil structures, and the food and medical industries. This unique combination of technologies also results in novel conformal sensors that can be remotely accessed by an antenna system with the advantage of no power requirements at the sensor site. After giving a brief overview of microsensors and MEMS, the paper focuses on the design and fabrication of MEMS devices and their use in engineering and medical applications. Examples include: (1) accelerometers and gyroscopes for automobiles, inertial navigation, etc; (2) drag sensing and reduction for aircraft; (3) sensing and control of ice formation and de-icing for aircraft; (4) remote measurement of tip deflection for helicopters; (5) health monitoring of structures; and (6) a 'smart tongue and electronic nose'.