During the module Java Applet Animations/Simulations have been employed to conve

Question

During the module Java Applet Animations/Simulations have been employed to convey the key electromagnetic concepts, for the topics below. Referring to the Appendix 9, where there is a screenshot of the Java Applets explain how the Animations/Simulations communicate the ideas in electromagnetism. a) Attenuated Traveling Wave Simulator. b) The dependence on the geometric and material parameters for a Coaxial Cable Transmission Line. c) The dependence on the geometric and material parameters for a Lossless Microstrip Transmission Line d) Attenuated Electromagnetic Plane Wave Simulator e) Radio Wave Broadcasting and Reception Simulator

Explanation / Answer

A)

The propagation constant is separated into two components that have very different effect on signal

                           = + j

                          = attenuation constant

                           = Phase constant

The real part of the propagation constant is the attenuation constant and is denoted by (alpha). It causes signal amplitude to decrease along a transmission line. The natural units of the attenuation constant are Nepers/meter, but we often convert to dB/meter in microwave engineering. The phase constant is denoted by (beta) adds the imaginary component to the propagation constant. It determines the sinusoidal amplitude/phase of the signal along a transmission line, at a constant time. The phase constant's "natural" units are radians/meter, but we often convert to degrees/meter. To quantize the RF losses in transmission lines we need to calculate the attenuation constant . The attenuation constant can be broken down into at least four components, one representing metal loss which is proportional to metal’s resistivity, one representing dielectric loss due to loss tangent, one due to conductivity of the dielectric, and one due to stray radiation. The general solutions of the second-order, linear differential equation for voltage V and current I are:

                   V+, V-, I+, I- are constants (complex phasors).

B)A higher electric field causes two problems: first, it results in
greater line attenuation (larger ); second, it can result in
dielectric breakdown.
Dielectric breakdown results when the electric field within the
transmission line becomes so large that the dielectric material
is ionized. Suddenly, the dielectric becomes a conductor, and
the value G gets very large!

This generally results in the destruction of the coax line, and
thus must be avoided. Thus, large coaxial lines are required
when extremely low-loss is required.

C)

The characteristic impedance or surge impedance (usually written Z0) of a uniform transmission line is the ratio of the amplitudes of voltage and current of a single wave propagating along the line; that is, a wave travelling in one direction in the absence of reflections in the other direction. Characteristic impedance is determined by the geometry and materials of the transmission line and, for a uniform line, is not dependent on its length. The SI unit of characteristic impedance is the ohm.

The characteristic impedance of a lossless transmission line is purely real, with no reactive component. Energy supplied by a source at one end of such a line is transmitted through the line without being dissipated in the line itself. A transmission line of finite length (lossless or lossy) that is terminated at one end with an impedance equal to the characteristic impedance appears to the source like an infinitely long transmission line and produces no reflections.

D)With the use of measured electron–neutral cross sections, the transmission properties of an electromagnetic (EM) wave in a nitrogen (N2) plasma and a helium (He) plasma are studied by means of PIC-MCC (the particle-in-cell method with collision modeling by the Monte Carlo method) simulation. The plasmas are assumed to be uniform, collisional and non-magnetized. Each type of species presented in the plasmas is treated by the PIC method and the electron–neutral collisions are treated by direct Monte Carlo simulation of particle trajectories. And then the dependence of power attenuation of the EM wave on plasma parameters and wave parameters is obtained and discussed. It is found that power attenuation of the EM wave is strongly affected by the plasma density, species of neutral gas, density of neutral gas and the frequency of the EM wave. Moreover, it is also found that the stopband (passband) of EM wave propagation turns out to be narrower (wider) in collisional plasmas both numerically and analytically.

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