电磁场与电磁波第17讲时谐场.ppt

The electric field intensity in a source-free dielectric( ) region is given as (V/m),where angular frequency ，all are constants. Find: Example. (1) The phasor representation of electric field intensity (V/m) (2) The phasor representation of magnetic field intensity (A/m) Where * Field and Wave Electromagnetic 电磁场与电磁波 第17讲 1. Faraday’s Law of Electromagnetic Induction Review 2. Maxwell’s Equations 3. Electromagnetic Boundary Conditions The integral form The differential form Significance Faraday’s law(电磁感应定律) Ampere’s circuital law(全电流定律) Gauss’s law(高斯定理) No isolated magnetic charge(磁通连续性原理) 4. Potential Functions 5. Wave Equations and Their Solutions Maxwell’s equations and all the equations derived from them so far in this chapter hold for electromagnetic quantities with an arbitrary time-dependence(时间任意相关). The actual type of time functions that the field quantities assume depends on(取决于) the source(源) functions ? and J. In engineering, one of the most important cases of time-varying electromagnetic fields is the time-harmonic (sinusoidal) field(时谐场、正弦场). In this type of field ,the excitation source varies sinusoidally in time with a single frequency(单一频率). In a linear system(线性系统), a sinusoidally varying source generates fields that also vary sinusoidally in time at all points in the system(正弦变化的源产生正弦变化的场). 1) what is Time-Harmonic Fields 3. Time-Harmonic Fields 2) 讨论时谐场（正弦信号）的原因 When fields are examined in this manner,there is no loss in generality as (a) They are easy to generate (b) any time-varying periodic function can be represented by a Fourier series in terms of sinusoidal functions (c) the principle of superposition can be applied under linear conditions. In other words, we can obtain the complete response of time varying periodic fields by using linear combinations of monochromatic responses （a）正弦信号容易产生，50Hz交流