How to find an electric potential in anisotropic, inhomogeneous mediumby Agent007 Tags: anisotropic, electric, inhomogeneous, potential 

#1
Nov2512, 11:52 PM

P: 1

Hello!
(I am sorry for probable mistakes. English is not my native language. I have never written anything about mathematics and physics in English.) I have an electrostatic problem. I need to find an electric potential [itex]\psi[/itex] ([itex]\vec{E}=\nabla\psi[/itex]) in anisotropic, inhomogeneous medium. Let's introduce a cylindrical coordinate system ([itex]\rho[/itex], [itex]\varphi[/itex], z). The only source of the field is the linear charge on the endless thread: [itex]\rho=\lambda\delta(\rho).[/itex] Here [itex]\rho[/itex] is the volume charge density, [itex]\lambda[/itex] is a constant that describes the linear charge density. 1. If [itex]\rho<a[/itex], medium is homogeneus and anisotropic. Permittivity [itex]\widehat{\varepsilon}[/itex] is the given Hermitian matrix (3 x 3). All its entries are nonnil, some of them depend on the polar angle [itex]\varphi[/itex] so [itex]\widehat{\varepsilon}=\widehat{\varepsilon}( \varphi )[/itex]. From Gauss's flux theorem we obtain ([itex]\rho<a[/itex]): div([itex]\widehat{\varepsilon}(\varphi)\nabla\psi[/itex])=4[itex]\pi\rho[/itex]. This is the hyperbolic partial differential equation due to properties of [itex]\widehat{\varepsilon}[/itex]. 2. If [itex]\rho\geq a[/itex], medium is homogeneus and isotropic. Permittivity [itex]\varepsilon=1[/itex], its a scalar. From Gauss's flux theorem we obtain ([itex]\rho\geq a[/itex]): div([itex]\nabla\psi[/itex])=4[itex]\pi\rho[/itex]=0. This is the elliptic partial differential equation. ________ So I have to solve these equations. Unfortunately, it's impossible to separate variables in the area [itex]\rho<a[/itex]. The only thing that may help is that nothing depends on z. I have the boundary conditions: [itex]\psi(a0)=\psi(a+0)[/itex], [itex]\widehat{\varepsilon}\frac{\partial\psi}{\partial \rho}(a0)=\frac{\partial\psi}{\partial\rho}(a+0)[/itex], [itex]\psi(\rho\rightarrow\infty)\rightarrow 0[/itex]. If somebody has any ideas, it will be great! 


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