What physic need for SQUEEZED-FILM DAMPING MODELS FOR MEMS in COMSOL

Hi all,

I am working on SQUEEZED-FILM DAMPING MODELS FOR MEMS in COMSOL. Where one of the plate(1) is fixed and other plate(2) is movable when applying pressure. Whole structure should be inside the vacuum box or gas.

So i need to calculate damping coefficient (b) . I need to give fixed constrain on one side of plate(2) and other side is movable. For fixed constrain I need to assign SOLID MECHANICS physics but when I assigned materials for vacuum or gas ,its required Young's Modulus and Poisson ratio but as we know for gas or liquid don't have these value.

Please help me in this regard.

BR
Suzan