电磁场基本理论PPT讲稿.ppt

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1、电磁场基本理论第1页，共25页，编辑于2022年，星期日数值法：数值法：全貌框图全貌框图第2页，共25页，编辑于2022年，星期日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定定理、介质电磁模型、导体电磁模型、等离子电理、介质电磁模型、导体电磁模型、等离子电磁模型磁模型*问题考虑问题考虑？主要知识点：主要知识点：第3页，共25页，编辑于2022年，星期日1.1 Maxwells EquationsT

2、he quantities D and B are the 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第4页，共25页，编辑于2022年，星期日The c

3、harge and current densities,J may be 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,Max

4、wells equations take the simpler form:1.1 Maxwells Equations第5页，共25页，编辑于2022年，星期日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 subjec

5、ted to forces in the presence of fields.If J arises from the motion of charges within the distribution,then J=v第6页，共25页，编辑于2022年，星期日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 conve

6、rted 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 electromagnetic energy flowing into a region will partially increase the stored energy in that region and partially dissipate into heat第7页，共25页，编辑于2022年，星期日1.3 Constitutive

7、 Relations第8页，共25页，编辑于2022年，星期日1.3 Constitutive Relations第9页，共25页，编辑于2022年，星期日In 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 tens

8、or)form:In nonlinear materials,may depend on the magnitude E of the applied electric field in the form:1.3 Constitutive Relations第10页，共25页，编辑于2022年，星期日Materials with frequency-dependent dielectric constant()are referred to as dispersive.1.3 Constitutive Relations第11页，共25页，编辑于2022年，星期日1.4 Boundary Co

9、nditionsThe boundary conditions for the electromagnetic fields across material boundaries are given below:第12页，共25页，编辑于2022年，星期日1.5 Conservation Laws第13页，共25页，编辑于2022年，星期日1.5 Conservation Laws第14页，共25页，编辑于2022年，星期日第15页，共25页，编辑于2022年，星期日1.8 Harmonic Time DependenceThrough the inverse Fourier transfor

10、m,general solutions of Maxwells equation can be built as linear combinations of single-frequency solutions:第16页，共25页，编辑于2022年，星期日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

11、 unit volume.第17页，共25页，编辑于2022年，星期日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；：电场频率第18页，共25页，编辑于2022年，星期日1.9 Simple Models of Dielectrics 第19页，共25页，编辑于2022年，星期日ConductorsSince in a metal the conduction charges are unbound,we may take第20页，共25页，编辑于2022年，星期日1.9.2 Simple Models Conduct

12、ors第21页，共25页，编辑于2022年，星期日The steady-state current density results in the conventional Ohms law:Power LossesTo describe a material with both dielectric and conductivity properties,the concept of effective dielectric constant is used.1.9.2 Simple Models Conductors第22页，共25页，编辑于2022年，星期日A convenient way

13、 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第23页，共25页，编辑于2022年，星期日 Problem to be answered?第24页，共25页，编辑于2022年，星期日第25页，共25页，编辑于2022年，星期日