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Sommerfeld identity : ウィキペディア英語版
Sommerfeld identity
The Sommerfeld identity is a mathematical identity, due Arnold Sommerfeld, used in the theory of propagation of waves,
:
\frac
= \int\limits_0^\infty I_0(\lambda r) e^ \frac

where
:
\mu =
\sqrt

is to be taken with positive real part, to ensure the convergence of the integral and its vanishing in the limit z \rightarrow \pm \infty and
:
R^2=r^2+z^2
.
Here, R is the distance from the origin while r is the distance from the central axis of a cylinder as in the (r,\phi,z) cylindrical coordinate system. The function I_0 is a Bessel function. Here the notation for Bessel functions follows the German convention, to be consistent with the original notation used by Sommerfeld. In English literature it is more common to use
:I_n(\rho)=J_n(i \rho).
This identity is known as the Sommerfeld Identity ().
An alternative form is
:
\frac
= i\int\limits_0^\infty

Where
:
k_z=(k_0^2-k_\rho^2)^

(). The notation used here is different form that above: r is now the distance from the origin and \rho is the axial distance in a cylindrical system defined as (\rho,\phi,z).
The physical interpretation is that a spherical wave can be expanded into a summation
of cylindrical waves in \rho direction, multiplied by a plane wave in the z direction; see the Jacobi-Anger expansion. The summation has to be taken over all the wavenumbers k_\rho.
== References ==
# Sommerfeld, A.,''Partial Differential Equations in Physics'',Academic Press,New York,1964
# Chew, W.C.,''Waves and Fields in Inhomogeneous Media'',Van Nostrand Reinhold,New York,1990

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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