  Realistic models of the components and processes are required for molecular
communication (MC) systems. In this paper, a spheroidal receiver structure is
proposed for MC that is inspired by the 3D cell cultures known as spheroids
being widely used in organ-on-chip systems. A simple diffusive MC system is
considered where the spheroidal receiver and a point source transmitter are in
an unbounded fluid environment. The spheroidal receiver is modeled as a porous
medium for diffusive signaling molecules, then its boundary conditions and
effective diffusion coefficient are characterized. It is revealed that the
spheroid amplifies the diffusion signal, but also disperses the signal which
reduces the information communication rate. Furthermore, we analytically
formulate and derive the concentration Green's function inside and outside the
spheroid in terms of infinite series-forms that are confirmed by a
particle-based simulator (PBS).
