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Unformatted text preview: PRELIM 2 ECE 303 26 October 2004 NAME 50hr 7L' V“ 5 SECTION 1. (30 points). Fresh water has a conductivity of about 10‘3 S/m (much less than the
conductivity of sea water), a dielectric constant (8780) of 81, and a permeability u = no.
A plane wave propagates in this water in the positive 2 direction, and at z = 0 the average
power density in the wave is 1 watt/m2. What is the approximate (to within 2%, say)
power density in the wave at z = 200 m if the wave frequency is (a) 104 Hz, or (b) 5 x 106 Hz? Firéf“ oﬂécréeﬂ 710 (45+ /055 5/} /W 3/1me . [é’ﬂ—V/cd >>e’ m <<c~’3) IO g’= 8/60: 81(9291/0‘” ) = 717 we p/w.
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M Wye/12:17M ls /€$5 , AH} MW a: 4+ WW Mew/26754; 51’) ZN»: , PRELIM 2 ECE 303 26 October 2004 NAME 50/“7L’” 5 SECTION 2. (30 points). A linearly polarized wave, with E parallel to the x axis, propagates in the
negative y direction. The frequency of the wave is 500 MHZ and the measured phase
velocity is 2 x 108 m/s. The instantaneous value of E at y = t = 0 is 1 V/m in the positive
x direction, and the wave attenuates by 5 dB in 200 meters. (a) Write a complete expression for the electric ﬁeld E in complex notation, giving the
values of all the parameters in the expression. (b) If u = no in the medium, what is the value of the (complex) permittivity constant a? 4001‘ +ﬁgl 1" 0(5) (a) if = ED ex e a? ,
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3. (40 points). The electric ﬁeld of a plane wave propagating in free space is described
by
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1" 04c {70} (a) Give an expression for an orthogonally polarized electric ﬁeld E2 with the same
average power.
( 5) (b) Sketch the instantaneous values of E1 and E2 as a ﬁmction of time for z = 0 (show the vectors at (Dt = 0 and cot = n/Z).
00) (0) Give an expression for H1 that corresponds to E1 and sketch this ﬁeld also as a
ﬁJnction of time at z = 0. p p r
1;) ((1) Write an expression for a right circularly polarized wave, with the same time and
space variation, and then resolve this wave into a sum of the two orthogonal waves E1
and E2, i.e., ﬁnd the values of E01 and E02 in terms of ERC. K tiff:
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 Fall '06
 RANA
 Polarization, Electromagnet, Frequency, Permittivity, Dielectric

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