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Lecture

Distance to First Voltage Minimum

In course

EE-200: Electromagnetics I : Transmission lines and waves

Le signal électrique est un vecteur essentiel pour la transmission d'information et d'énergie. En haute fréquence elle se manifeste comme un signal électromagnétique dont l'étude demande le développement de modèles physiques et mathématiques spécifiques ba ...

Description

This lecture continues the study of voltage and current distributions in a line terminated by an impedance ZL, focusing on the concept of distance to the first voltage minimum. By analyzing the phase angle of the voltage phasor V2Z, the lecture explores the conditions for minimum and maximum voltage amplitudes along the line. The behavior of the reflection coefficient gamma2Z in the complex plane is examined to determine the positions where voltage amplitudes are minimized. The lecture also discusses the relationship between gamma2Z and the voltage phasor V2Z, highlighting the conditions for maximum and minimum voltage amplitudes. Additionally, it explains how measuring the distance between consecutive voltage minima on the line allows for the determination of lambda/2, aiding in the calculation of the propagation velocity.

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Instructor

Romain Christophe Rémy Fleury

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Related concepts (21)

Phase velocity

The phase velocity of a wave is the rate at which the wave propagates in any medium. This is the velocity at which the phase of any one frequency component of the wave travels. For such a component, any given phase of the wave (for example, the crest) will appear to travel at the phase velocity. The phase velocity is given in terms of the wavelength λ (lambda) and time period T as Equivalently, in terms of the wave's angular frequency ω, which specifies angular change per unit of time, and wavenumber (or angular wave number) k, which represent the angular change per unit of space, To gain some basic intuition for this equation, we consider a propagating (cosine) wave A cos(kx − ωt).

Group velocity

The group velocity of a wave is the velocity with which the overall envelope shape of the wave's amplitudes—known as the modulation or envelope of the wave—propagates through space. For example, if a stone is thrown into the middle of a very still pond, a circular pattern of waves with a quiescent center appears in the water, also known as a capillary wave. The expanding ring of waves is the wave group or wave packet, within which one can discern individual waves that travel faster than the group as a whole.

Propagation constant

The propagation constant of a sinusoidal electromagnetic wave is a measure of the change undergone by the amplitude and phase of the wave as it propagates in a given direction. The quantity being measured can be the voltage, the current in a circuit, or a field vector such as electric field strength or flux density. The propagation constant itself measures the change per unit length, but it is otherwise dimensionless. In the context of two-port networks and their cascades, propagation constant measures the change undergone by the source quantity as it propagates from one port to the next.

Velocity factor

The velocity factor (VF), also called wave propagation speed or velocity of propagation (VoP or of a transmission medium is the ratio of the speed at which a wavefront (of an electromagnetic signal, a radio signal, a light pulse in an optical fibre or a change of the electrical voltage on a copper wire) passes through the medium, to the speed of light in vacuum. For optical signals, the velocity factor is the reciprocal of the refractive index.

Wave

In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (resting) value at some frequency. When the entire waveform moves in one direction, it is said to be a traveling wave; by contrast, a pair of superimposed periodic waves traveling in opposite directions makes a standing wave.

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