tailieunhanh - CHAPTER 11: THE UNIFORM PLANE WAVEIn

Tham khảo tài liệu 'chapter 11: the uniform plane wavein', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | CHAPTER 11 THE UNIFORM PLANE WAVE In this chapter we shall apply Maxwell s equations to introduce the fundamental theory of wave motion. The uniform plane represents one of the simplest applications of Maxwell s equations and yet it is of profound importance since it is a basic entity by which energy is propagated. We shall explore the physical processes that determine the speed of propagation and the extent to which attenuation may occur. We shall derive and make use of the Poynting theorem to find the power carried by a wave. Finally we shall learn how to describe wave polarization. This chapter is the foundation for our explorations in later chapters which will include wave reflection basic transmission line and waveguiding concepts and wave generation through antennas. WAVE PROPAGATION IN FREE SPACE As we indicated in our discussion of boundary conditions in the previous chapter the solution of Maxwell s equations without the application of any boundary conditions at all represents a very special type of problem. Although we restrict our attention to a solution in rectangular coordinates it may seem even then that we are solving several different problems as we consider various special cases in this chapter. Solutions are obtained first for free-space conditions then for perfect dielectrics next for lossy dielectrics and finally for the good conductor. We do this to take advantage of the approximations that are applicable to each 348 I e-Text Main Menu Textbook Table of Contents THE UNIFORM PLANE WAVE 349 special case and to emphasize the special characteristics of wave propagation in these media but it is not necessary to use a separate treatment it is possible and not very difficult to solve the general problem once and for all. To consider wave motion in free space first Maxwell s equations may be written in terms of E and H only as 9E V X H 6q dt V r 11 V X E - 0 dt V-E 0 V-H 0 1 2 3 4 Now let us see whether wave motion can be inferred from these four