DAMPING AND GAS VISCOSITY MEASUREMENTS USING A MICROSTRUCTURE

The equations for squeeze-film damping of a microstructure comprising two plates oscillating normal to each other are used to derive the dam ping, and hence the viscosity, of six different gases under flow condi tions ranging from molecular to almost viscous flow. For all the gases , the effective viscosity, normalized to the free gas viscosity, for f low in the gap between the plates is the same function of pressure whe n this is expressed as the inverse Knudsen number. The function is ide ntical in form to Knudsen's pipe-flow correction, but requires a scale change that effectively defines an equivalent diameter for parallel p lates. Relative viscosity measurements are made with an accuracy of 1% by the phase technique used, and with a time resolution of 1 s. The p ossibility of a gas sensor based on the method is discussed.