TAILIEUCHUNG - Electromagnetic Field Theory: A Problem Solving Approach Part 63

Electromagnetic Field Theory: A Problem Solving Approach Part 63. Electromagnetic field theory is often the least popular course in the electrical engineering curriculum. Heavy reliance on vector and integral calculus can obscure physical phenomena so that the student becomes bogged down in the mathematics and loses sight of the applications. This book instills problem solving confidence by teaching through the use of a large number of worked problems. To keep the subject exciting, many of these problems are based on physical processes, devices, and models. This text is an introductory treatment on the junior level for a two-semester electrical engineering. | Sinusoidal Time Variations 595 If the end at z 0 were not matched a new V would be generated. When it reached z I we would again solve the RC circuit with the capacitor now initially charged. The reflections would continue eventually becoming negligible if is nonzero. Similarly the governing differential equation for the inductive load obtained from the equivalent circuit in Figure 8-14c is LL iLZ0 2V Vo. at with solution The voltage across the inductor is at t T 47 t T 48 t T 49 Again since the end at z 0 is matched the returning V_ wave from z I is not reflected at z 0. Thus the total voltage and current for all time at z I is given by 48 and 49 and is sketched in Figure 8-14c. 8-3 SINUSOIDAL TIME VARIATIONS 8-3-1 Solutions to the Transmission Line Equations Often transmission lines are excited by sinusoidally varying sources so that the line voltage and current also vary sinusoidally with time v z t Re v z e i z t Re î z e 1 Then as we found for TEM waves in Section 7-4 the voltage and current are found from the wave equation solutions of Section 8-1-5 as linear combinations of exponential functions with arguments t z c and t z c v z t Re V V_ e t z c . 2 i z 0 VoRe V -V_c l Now the phasor amplitudes V and V_ are complex numbers and do not depend on z or t. 596 Guided Electromagnetic Waves By factoring out the sinusoidal time dependence in 2 the spatial dependences of the voltage and current are v z V e kt V_e kz 3 z r0 V e fa-V_e fa where the wavenumber is again defined as k a c 4 8-3-2 Lossless Terminations a Short Circuited Line The transmission line shown in Figure 8-15a is excited by a sinusoidal voltage source at z I imposing the boundary condition v z I t Vo cos art Re Vo e v z -I Vo V e V_ e 5 Note that to use 3 we must write all sinusoids in complex notation. Then since all time variations are of the form e we may suppress writing it each time and work only with the spatial variations of 3 . Because the transmission line is short circuited we have the .

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