Porous materials with functionally graded porosity are achieved by tailoring the size and density of the internal pores in one or more directions that leads the desired mechanical properties. Thus, due to the promotion of porous materials in engineering applications such as the foam core in sandwich plates, the compact heat exchangers, lightweight structures, biomedical systems and separation processes, in this paper, the free vibration of sandwich circular and annular plates with a core made of materials with functionally graded porosity are investigated. Different porosity distributions through the radial direction are introduced for the core of the plate. The governing equations of motion for the free vibration of a plate are obtained based on the first order shear deformation plate theory (FSDT). Clamped and simply supported edges are assumed for the plates. The collocation version of spectral method called the pseudo-spectral (PS) method using Chebyshev polynomials as the basis function is adopted to solve the equations of motion. Validation studies are also done to demonstrate the accuracy of the results. The natural frequencies of the clamped and simply-supported sandwich circular and annular plates with a porous core are calculated. The effects of different porosity distributions, porosity parameter, core thickness and geometric parameters on the results are investigated.
