**Answers
to questions: EE789(Graduate), EE508, EE529, EE507,
EE700(Graduate)**

**EE508:
Introduction to Electromagnetic Compatibility**

*Question*:

Please Dr. i need your help in the following question :

Calculate the capacitance for
cylindrical cell membrane with resistivity of 10^7 ohm.m
, dielectric constant 3, diameter 10 micro.meter ,
thickness 7 nm , and length 50 micro. meter.

really i can not
indicate which area choose " 2*pie*r(L+r)"
OR " 2*pie*r^2". ......thanks alot
Dr

*Answer:*

Use 2*pie*r(L+r) since the charges flow through the membrane surface, i.e., between the outer and inner surfaces of the membrane. The charges flow across the membrane, not along the membrane!

*Question*:

hello please dr i have problem in chapter bioelectromagnetics .. its problem #2 and problem #3 in the notes, my question is why If I use the resistance of the cylindrical FORMULA (R=ph/2pie*r(l+r)) the answer is different because you use R=pl/A and you substitute A as A=pie (r)^2 please explain.

*Answer:*

In problems #2 and #3 in the notes, the current is flowing along the axis of the cylinder, and thus the area perpendicular to the current direction is the cross sectional area of the cylinder, i.e., A=pie (r)^2. However, for cell membrane problems, the charges inter and leave the cell through the membrane. Accordingly, the current is flowing either from outside to inside the cell or vice versa. Hence, the area perpendicular to the current direction is the surface area of the cell (or membrane).

**EE789:
Special Topics in Wireless Communications (EMC)**

*Question*:

Dear Dr. How many sheets allowed in our final_exam ? please! three or two? and thank you very much

*Answer:*

Three sheets.

*Question*:

If possible, give an numerical examples on skin effect, and relaxation time.

*Answer:*

Determine the frequency at which the skin depth is
2.032´10^{-4} m for copper with conductivity 5.8´10^{7} S/m?

The skin depth is :

δ=0.0002032=1/**√**(πfμ_{0} σ)=1/**Ö**(πf(4π×10^{-7}
)8×10^{7} )

f=105.8 KHz

Find the the
relaxation time for copper?

t=e_{0}/s=10^{-9}/(36π)/5.8×10^{7}=1.52×10^{-19}
s

**EE529:
Microwave Lab**

*Question*:

What is the definition of Gunn oscillator efficiency.

*Answer:*

Efficiency of Gunn oscillator is the output RF (radio frequency) power divided by the supply input power. In other words, the percentage of the input power that is converted to microwave power.

**EE507: Radiowave Propagation**

*Question*

Fnd the exponent of power law with distance for Hata model with fixed-site antenna height.

*Answer*:

Using the curve if available or model equations, choose two suitable distances and find the corresponding path losses. Received power difference in dB is the same as path loss difference with a negative sign. Remember that received power is inversely proportional to distance with an exponent to be determined.

*Question*

How can we get t to find the volume of rain cell illuminated by radar signal.

*Answer*:

The radar pulsed carrier duration t is the inverse of the frequency bandwidth, and vice versa. So, if the bandwidth is 2 MHz, then t is 500 ns.

*Question*:

How can we find the attenuation factor for surface wave when we are given that signal level at receiver is #db below its free space value.

*Answer*:

Attenuation= -(#db); since attenuation for surface wave is simply the difference in dB between the actual received signal level and the corresponding free-space signal level.

*Question*:

I cant find the numbers of chapters and sections
needed from Collin's book. can you help me to find
them? Thank you.

*Answer*:

In the copy that you might have, note that the books are interchanged.

**EE700:
Antennas and Propagation**

*Question*

Could you please help me to distinguish between radiated power and input power in transmitter. When i have to do gain multiplication. i referred to various editions related to antenna and each one has his own meanings.

*Answer*:

Input power is the power available at the terminals of the transmitting antenna. Radiated power is the power is available in free space. Received power is the power available at the terminals of the receiving antenna.

*Question:*

How do waves propagate in space? we know that electric field and magnetic fields are perpendicular to each other But what is the shape of a wave? such that it reaches every where. Is it like sphere?

*Answer*:

In the far field zone, the radio
wave moves through space creating variations in both the magnetic and electric
fields perpendicular to the direction of wave motion. Like ocean waves, radio
waves create disturbances perpendicular to the direction of motion. The
magnetic and electric fields also are perpendicular to each other. Radio waves
move through space the same way light waves do, since light is electromagnetic
wave. Wave fronts may be spherical, cylindrical, or plane. If the transmitting
antenna is omni-directional, then the wave will
spread in all azimuthal directions. The antenna can
be designed to concentrate the power in certain directions.