tailieunhanh - Electromagnetic Waves and Antennas combined - Chapter 4

Propagation in Birefringent Media Thông tư thành phần E +, E-đại diện cho phân cực bên phải và bên trái (trong quy ước IEEE) nếu làn sóng di chuyển theo hướng z tích cực, nhưng bên trái và bên phải, nếu nó đang di chuyển theo hướng z tiêu cực. Bởi vì các phương tiện tuyên truyền là không đẳng hướng, chúng ta cần phải bắt đầu với các phương trình Maxwell sourcefree trước khi chúng tôi giả định bất kỳ mối quan hệ cấu thành đặc biệt:. | 4 Propagation in Birefringent Media Linear and Circular Birefringence In this chapter we discuss wave propagation in anisotropic media that are linearly or circularly birefringent. In such media uniform plane waves can be decomposed in two orthogonal polarization states linear or circular that propagate with two different speeds. The two states develop a phase difference as they propagate which alters the total polarization of the wave. Such media are used in the construction of devices for generating different polarizations. Linearly birefringent materials can be used to change one polarization into another such as changing linear into circular. Examples are the so-called uniaxial crystals such as calcite quartz ice tourmaline and sapphire. Optically active or chiral media are circularly birefringent. Examples are sugar solutions proteins lipids nucleic acids amino acids DNA vitamins hormones and virtually most other natural substances. In such media circularly polarized waves go through unchanged with left- and right-circular polarizations propagating at different speeds. This difference causes linearly polarized waves to have their polarization plane rotate as they propagate an effect known as natural optical rotation. A similar but not identical effect the Faraday rotation takes place in gyroelectric media which are ordinary isotropic materials glass water conductors plasmas subjected to constant external magnetic fields that break their isotropy. Gyromagnetic media such as ferrites subjected to magnetic fields also become circularly birefringent. We discuss all four birefringent cases linear chiral gyroelectric and gyromagnetic and the type of constitutive relationships that lead to the corresponding birefringent behavior. We begin by casting Maxwell s equations in different polarization bases. An arbitrary polarization can be expressed uniquely as a linear combination of two polarizations along two orthogonal directions t For waves propagating in the .