Membrane sandwich squeeze film pressure sensors

Squeeze film pressure sensors, exploiting the dynamical modification of the mechanical properties of oscillating elements due to the compression of a fluid in a small gap region, allow for direct and absolute pressure measurements. This tutorial article discusses the working principles of membrane sandwich squeeze film pressure sensors, i.e. sensors consisting in a parallel arrangement of two large area, ultrathin suspended films forming a few-micron gap and immersed in a fluid, and focuses on their operation in the free molecular flow regime. The effects of gas pressure on the vibrations of the membrane resonators and their coupled dynamics are discussed in general terms before recent experimental implementations using high tensile stress silicon nitride membranes are presented.