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The RF Toolbox add-on to MATLAB [26] and several books (for example "Network scattering parameters" [27]) use this last definition, so caution is necessary. The "From S to T" and "From T to S" paragraphs in this article are based on the first definition. Adaptation to the second definition is trivial (interchanging T11 for T22, and T12 for T21 ...
In scattering theory, the S-matrix is an operator mapping free particle in-states to free particle out-states (scattering channels) in the Heisenberg picture. This is very useful because often we cannot describe the interaction (at least, not the most interesting ones) exactly.
Scattering theory is a framework for studying and understanding the scattering of waves and particles. Wave scattering corresponds to the collision and scattering of a wave with some material object, for instance (sunlight) scattered by rain drops to form a rainbow.
The standard way to calculate the T-matrix is the null-field method, which relies on the Stratton–Chu equations. [6] They basically state that the electromagnetic fields outside a given volume can be expressed as integrals over the surface enclosing the volume involving only the tangential components of the fields on the surface.
Consider the scattering of a beam of wavelength by an assembly of particles or atoms stationary at positions , =, …,.Assume that the scattering is weak, so that the amplitude of the incident beam is constant throughout the sample volume (Born approximation), and absorption, refraction and multiple scattering can be neglected (kinematic diffraction).
Radiative transfer (also called radiation transport) is the physical phenomenon of energy transfer in the form of electromagnetic radiation.The propagation of radiation through a medium is affected by absorption, emission, and scattering processes.
Multiple-scattering effects of light scattering by particles are treated by radiative transfer techniques (see, e.g. atmospheric radiative transfer codes). The relative size of a scattering particle is defined by its size parameter x, which is the ratio of its characteristic dimension to its wavelength:
Porod's law is concerned with wave numbers q that are small compared to the scale of usual Bragg diffraction; typically .In this range, the sample must not be described at an atomistic level; one rather uses a continuum description in terms of an electron density or a neutron scattering length density.