The Casimir force between two inhomogeneous metal-dielectric composite slabs with spatial dispersion is investigated theoretically. The equivalent permittivity and permeability of the nonlocal metallic nanosphere is originally derived based on full-wave nonlocal Mie theory. We then adopt two nonlocal effective medium models to study the effective permittivity and permeability of the composite slabs and calculate the Casimir force with Casimir-Lifshitz theory. Due to the excitation of the longitudinal modes, the attractive Casimir force between nonlocal composite materials is much weaker than that of the local composites, and numerical results show that the relative errors between local and nonlocal calculations of Casimir force can be on the order of $25\%$. Moreover, the nonlocal effects on the Casimir force are strongly dependent on the microstructures, and they become significant near the percolation threshold of the composite media. The study may be of great interest for making a precise comparison between theoretical and experimental results on the Casimir force between inhomogeneous composite materials.

• Received 24 August 2013

DOI:https://doi.org/10.1103/PhysRevA.89.012508