电磁场基本理论复习进程.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,电磁场基本理论,1.1 Maxwells Equations,The quantities,D,and,B,are the electric and magnetic flux densities and are in units of,coulomb/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,The charge 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,Maxwells equations take the simpler form:,1.1 Maxwells Equations,1.2 Lorentz Force,The 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 arises from the motion of charges within the distribution,then J=v,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 units of watts/m3.We will denote it by,1.2 Lorentz Force,We will find that electromagnetic energy flowing into a region will partially increase the stored energy in that region and partially dissipate into heat,1.3 Constitutive Relations,1.3 Constitutive Relations,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 tensor)form:,In nonlinear materials,may depend on the magnitude E of the applied electric field in the form:,1.3 Constitutive Relations,Materials with frequency-dependent dielectric constant()are referred to as dispersive.,1.3 Constitutive Relations,1.4 Boundary Conditions,The boundary conditions for the electromagnetic fields across material boundaries are given below:,1.5 Conservation Laws,1.5 Conservation Laws,1.8 Harmonic Time Dependence,Through the inverse Fourier transform,general solutions 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 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,1.9 Simple Models of Dielectrics,Conductors,Since in a metal the conduction charges are unbound,we may take,1.9.2 Simple Models Conductors,The steady-state current density results in the conventional Ohms law:,Power Losses,To describe a material with both dielectric and conductivity properties,the concept of effective dielectric constant is used.,1.9.2 Simple Models Conductors,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,Problem to be answered?,此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢,