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1、电磁场基本理论本讲稿第一页，共二十五页数值法：数值法：全貌框图全貌框图本讲稿第二页，共二十五页电磁场基本理论电磁场基本理论 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、界条件、电荷与能量守恒定理、Poyntings定理、定理、介质电磁模型、导体电磁模型、等离子电磁模型介质电磁模型、导体电磁模型、等离子电磁模型*问题考虑问题考虑？主要知识点：主要知识点：本讲稿第三页，共二十五页1.1 Maxwells EquationsThe quantities D and B are t
2、he electric and magnetic flux densities and are in units ofcoulomb/m2 and weber/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本讲稿第四页，共二十五页The charge and current densities,J may be
3、 thought of as the sources of the electromagnetic fields.The generated electric and 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 for
4、m:1.1 Maxwells Equations本讲稿第五页，共二十五页1.2 Lorentz ForceThe force on a charge q moving with 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
5、arises from the motion of charges within the distribution,then J=v本讲稿第六页，共二十五页The quantity v 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
6、 units of watts/m3.We will denote it by1.2 Lorentz ForceWe will find that electromagnetic energy flowing into a region will partially increase the stored energy in that region and partially dissipate into heat本讲稿第七页，共二十五页1.3 Constitutive Relations本讲稿第八页，共二十五页1.3 Constitutive Relations本讲稿第九页，共二十五页In
7、inhomogeneous materials,the permittivity depends on the location within the material:In anisotropic materials,depends 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 elect
8、ric field in the form:1.3 Constitutive Relations本讲稿第十页，共二十五页Materials with frequency-dependent dielectric constant()are referred to as dispersive.1.3 Constitutive Relations本讲稿第十一页，共二十五页1.4 Boundary ConditionsThe boundary conditions for the electromagnetic fields across material boundaries are given
9、below:本讲稿第十二页，共二十五页1.5 Conservation Laws本讲稿第十三页，共二十五页1.5 Conservation Laws本讲稿第十四页，共二十五页本讲稿第十五页，共二十五页1.8 Harmonic Time DependenceThrough the inverse Fourier transform,general solutions of Maxwells equation can be built as linear combinations of single-frequency solutions:本讲稿第十六页，共二十五页Some interesting
10、 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.本讲稿第十七页，共二十五页1.9.1 Simple Models of Dielectrics：电子基本电量；E：电场强度m:电子质量：自谐振频率；：电场频率本讲稿第十八页，共二十五页1.9 Simple Models of Dielectrics 本讲稿第十九页
11、，共二十五页ConductorsSince in a metal the conduction charges are unbound,we may take本讲稿第二十页，共二十五页1.9.2 Simple Models Conductors本讲稿第二十一页，共二十五页The steady-state current density results in the conventional Ohms law:Power LossesTo describe a material with both dielectric and conductivity properties,the concep
12、t of effective dielectric constant is used.1.9.2 Simple Models Conductors本讲稿第二十二页，共二十五页A 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 Conductors本讲稿第二十三页，共二十五页 Problem to be answered?本讲稿第二十四页，共二十五页本讲稿第二十五页，共二十五页