Semi-analytical time-domain low-frequency scattering formulation for biological applications

In this paper, an efficient time domain formulation is proposed for a low-frequency scattering by a complicated inhomogeneous dielectric scatterer. The formulation is based on the Born approximation and a sampling theorem. To extend the valid region of the proposed solution, the Rayleigh scattering formulation for a small dielectric object is used to modify the Born current inside the scatterer. In order to verify the obtained formulation, scatterings by several canonical objects such as a cubic box and a sphere are compared, which are calculated by the proposed formulation and the known exact or approximate solutions of a Mie series and the Rayleigh scattering. In addition, scattering by a human head is investigated at a very low-frequency band (< 100 Hz). For the simulation, two excitations are considered: plane wave incidence from outside the head and an artificial point source located inside the head. The head model is discretized by a 3 × 3 × 3 mm ³ cubic box, which is comprised of eight types of tissue. These are blood, bone, fat, grey matter, white matter, muscle, skin and vitreous humor.