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Chapter 7.Nanodevices > 7.9Fluidic Devices - Pg. 153

7.9 Fluidic Devices 153 railway systems to prevent a signalman from selecting operationally incompatible combinations; and as sensors. The advent of ultrastiff carbon-based materials (Chapter 9) has generated renewed interest in mechanical devices that can now be made at the nanoscale (nanoelec- tromechanical systems, NEMS). Ultrasmall cantilevers (taking the cantilever as the prototypical mechanical device) have extremely high resonant frequencies, effective stiffnesses and figures of merit Q and, evidently, very fast response times Q=! 0 . It therefore becomes conceivable that a new generation of relays, constructed at the nanoscale, could again contend with their solid-state (transistor-based) rivals that have completely displaced them at the microscale and above. Relays have, of course, excellent isolation between input and output, which makes them very attractive as components of logic gates. Sensing applications can operate in either static or dynamic mode. For cantilevers (Figure 7.21) used as sensors, as the beam becomes very thin, its surface character- istics begin to dominate its properties (cf. Section 2.2). Classically the adsorption of particles onto such a beam would increase its mass, hence lower its resonant fre- quency. This effect would be countered if the adsorbed adlayer had a higher stiffness than the beam material, thereby increasing its resonant frequency. In static sensing