《电磁场基本理论》由会员分享，可在线阅读，更多相关《电磁场基本理论（25页珍藏版）》请在金锄头文库上搜索。
1、电磁问题的基本解法电磁场与天线技术专题2. 解析法：重点1. 数值法: 整体框图数值法： 全貌框图电磁场基本理论 Section1: Maxwells Equations Maxwell基本方程组、力学关系、本构关系 、边界条件、电荷与能量守恒定理、 Poyntings定理、介质电磁模型、导体电磁 模型、等离子电磁模型*问题考虑？主要知识点：1.1 Maxwells EquationsThe quantities D and B are the electric and magnetic flux densities and are in units of coulomb/m2 and web
2、er/m2, or tesla. B is also called the magnetic induction.The quantities and J are the volume charge density and electric current density (charge flux) of any external charges The charge and current densities , J may be thought of as the sources of the electromagnetic fields. The generated electric a
3、nd magnetic fields are radiated away from these sources and can propagate to large distances to the receiving antennas. Away from the sources, that is, in source-free regions of pace,Maxwells equations take the simpler form:1.1 Maxwells Equations1.2 Lorentz Force The force on a charge q moving with
4、velocity v in the presence of an electric and magnetic field E, B is called the Lorentz force and is given by: Volume charge and current distributions , J are also subjected to forces in the presence of fields. If J arises from the motion of charges within the distribution , then J = vThe quantity v
5、 f = v E = J E represents the power per unit volume of the forces acting on the moving charges, that is, the power expended by (or lost from) the fields and converted into kinetic energy of the charges, or heat. It has units of watts/m3. We will denote it by1.2 Lorentz ForceWe will find that electro
6、magnetic energy flowing into a region will partially increase the stored energy in that region and partially dissipate into heat1.3 Constitutive Relations1.3 Constitutive RelationsIn inhomogeneous materials, the permittivity depends on the location within the material:In anisotropic materials, depen
7、ds on the x, y, z direction and the constitutive relations may be written component-wise in matrix (or tensor) form:In nonlinear materials, may depend on the magnitude E of the applied electric field in the form:1.3 Constitutive RelationsMaterials with frequency-dependent dielectric constant () are
8、referred to as dispersive.1.3 Constitutive Relations1.4 Boundary ConditionsThe boundary conditions for the electromagnetic fields across material boundaries are given below:1.5 Conservation Laws1.5 Conservation Laws1.8 Harmonic Time DependenceThrough the inverse Fourier transform, general solutions
9、of Maxwells equation can be built as linear combinations of single- frequency solutions:Some interesting time averages in electromagnetic wave problems are the time averages of the energy density, the Poynting vector (energy flux), and the ohmic power losses per unit volume.1.9.1 Simple Models of Di
10、electrics：电子基本电量；E：电场强度m: 电子质量：自谐振频率；：电场频率1.9 Simple Models of Dielectrics ConductorsSince in a metal the conduction charges are unbound, we may take1.9.2 Simple Models ConductorsThe steady-state current density results in the conventional Ohms law:Power LossesTo describe a material with both dielec
11、tric and conductivity properties, the concept of effective dielectric constant is used.1.9.2 Simple Models ConductorsA convenient way to quantify the losses is by means of the loss tangent defined in terms of the real and imaginary parts of the effective dielectric constant:The ohmic loss per unit volume can be expressed in terms of the loss tangent as:1.9.2 Simple Models ConductorsProblem to be answered ?
