Lecture4 - Lecture 4 Notes, 95.658, Spring 2012,...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Lecture 4 Notes, 95.658, Spring 2012, Electromagnetic Theory II Dr. Christopher S. Baird, UMass Lowell 1. Introduction to Waveguides - Electrodynamics is essentially the study of the creation, propagation, and absorption of electromagnetic waves as they interact with matter. - We have looked at the propagation of waves in free space, in bulk regions of uniform material and when passing through the boundary between two materials. - We now move on to the next level of complexity: waves propagating along a waveguide. - In general, a waveguide is a structure built by appropriately placing materials such that a wave is bound inside a structure and guided along its axis. - There are two fundamental elements that must be specified before a waveguide can be designed or analyzed: the method of containing the wave within the waveguide, and the cross-sectional shape of the waveguide. - A wave is contained in the waveguide by making the walls (or areas external to the core) highly reflective so that the wave is continually reflected back into the core area. - There are four main ways to reflect the wave: (1) Use conductors for the walls. This is especially useful for low frequencies such as in radar and electronics where the surface roughness of the walls is small compared to the wavelength and the walls do not have to be fabricated at small dimensions. (2) Use plasma for the walls, such as in a highly doped semiconductor. This behaves similar to a metal, except that reflectivity can be custom-built by varying the doping. This is useful for solid state devices because the waveguide can be grown as part of the device. (3) Use dielectric cladding with a lower index of refraction and the principle of total internal reflection. Total internal reflection requires grazing angles of incidence which is accomplished by shrinking the cross-sectional areas of the waveguide. Dielectric waveguides are typically used at higher frequencies, such as visible light through optical fibers. (4) Use dielectric material where holes have been formed in the outer region. Using interference effects, a photonic crystal is formed that is reflective at the desired frequency. - The most common cross-sectional shapes for waveguides are rectangular and circular. 2. Fields at the Surface of and Within a Conductor - First consider a flat, perfect conductor bordering on a non-conducting medium. - As in the electrostatics case, the electrons react to the external fields fast enough to always cancel
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/13/2012 for the course PHYSICS 95.658 taught by Professor Staff during the Spring '11 term at UMass Lowell.

Page1 / 6

Lecture4 - Lecture 4 Notes, 95.658, Spring 2012,...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online