Smart Mater. Struct.
(2000) 953–972. Printed in the UK
(MEMS), and electronics for smart
structures and systems
V K Varadan andVVVaradan
Center for the Engineering of Electronic and Acoustic Materials and Devices,
Pennsylvania State University, University Park, PA 16802, USA
Received 24 February 1999
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 arti±cial 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 ±eld has grown rapidly during
the past ten years. Recently, microstereolithography has revolutionized the MEMS industry
through multifunctional polymeric materials incorporating organic thin-±lm 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 de²ection for helicopters;
(5) health monitoring of structures; and (6) a ‘smart tongue and electronic nose’.