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Unformatted text preview: ECE 329 Homework 8 Due: Tues., Nov. 2, 2010, 5PM 1. ( wave propagation inside conductors ) In the measurement of power or intensity with respect to a given reference level, the logarithmic unit of decibel (dB) is commonly used. For example, the ratio of a power value P A to another power value P B , which is used as the reference value, is expressed in dB through the calculation 10 log 10 ( P A P B ) A linearly-polarized, time-harmonic, uniform plane wave is propagating inside a lossy medium with electromagnetic properties µ = µ o , ϵ = ϵ o , and σ = 4 × 10 7 S/m. a) Classify the lossy medium (good conductor, imperfect dielectric, or none of the above) for fre- qencies in the range 10 MHz ≤ f ≤ 5 GHz . b) Show that the attenuation of the time-average power of the wave in dB/m is given by − 8 . 686 α , where α is the attenuation constant of the wave in the lossy medium. (the negative sign is often dropped in practice since it is implied by the term “attenuation”). c) Calculate the attenuation in dB per skin depth inside this lossy medium at the two end frequen- cies of the frequency range indicated in question (a). d) A layer of this lossy material is used to cover the walls of a room that houses a set of sensitive experiments that need to be screened from electromagnetic interference (EMI) in the frequency range indicated in question (a) above. It is known that time-average electric field intensity of electromagnetic fields outside the room does not exceed . 1 V/m. Given that the maximum al- lowable electric field intensity of external EMI inside the room is 1 µ V/m, calculate the minimum thickness of the lossy material cover....
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- Spring '08
- Wave propagation, electric field intensity, Current sheet, lossy medium