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Universidad Nacional Abierta y a Distancia Vicerrectoría Académica y de Investigación Managing unit: Escuela de Ciencias Básicas, Tecnología e Ingeniería ECBTI Program: Ingeniería Electrónica Course: Teoría Electromagnética y Ondas Code: 203058 Annex 2 – Task 2 The activity consists of: To explore web resources on the propagation of electromagnetic waves in open media to understand concepts, develop exercises, calculate parameters, and interpret results. Activity
1. Explore the bibliographic references in the "Learning Guide - Task 2 - Electromagnetic waves in open media" or consult the UNAD library and answer the following questions: Questions: (write with your own words)
Is the speed of light equal to 300.000 km / s through all media or materials?
In material properties, what is electrical permittivity? In material properties, what is magnetic permeability?
2. Explore the bibliographic references, participate in the web conferences and CIPAS for the course, and complete the following exercises: Application exercise: The following 4-step exercise describes the method to characterize an electromagnetic wave when propagating in an open medium, for which, each student must choose 1 propagation media of the proposed in Table 1 and announce it within the “Task 1” forum to avoid repetition.
Table 1: Conductivity σ and electrical permittivity^ ε^ r of some media.
Media σ [ S / m ] ε r [ ]
1. Copper 5.80 x 107 1
- Sea water (^4 )
3. Air 5.5 x 10 −^15 1.
4. Vegetable soil 1 x 10 −^2
5. Dry soil 1 x 10 −^4
6. Sweet water 1 x 10 −^3
- Vacuum (^0 )
ε = ε r ε o ; ε o =8.8542 x 10
− 12
C
2
/ N m
2
a. Calculate the tangent of losses Tan (δ) and the angle of losses δ of the medium chosen in Table 1 , if through it travel an electromagnetic wave E of frequency
f =( CCC + 20 ) MHz. Note that CCC are the last 3 digits of your identification number:
tan ( δ )=
2 πf ε r ε o
δ =tan
− 1
2 πf ε r ε o )
Attention, for the calculations:
- Replace your values (with units) in the equation editor.
- Write the answer with your units.
- Perform the operation in MATLAB or on a virtual scientific calculator. *
- Paste the calculator image into the report. **If the image is not included, the exercise rating is 0 points. *** You can use https://la.mathworks.com/products/matlab-online.html or https://www.geogebra.org/scientific b. According to the result obtained in point 1, classify the behavior of the chosen medium according to one of the five options in Table 2 :
Table 2: Classification of propagation media.
c. According to the classification obtained in point 2 and using Table 3 shown below, calculate the following propagation parameters of the wave in the chosen medium: Propagation constant (gamma). Attenuation constant (Alpha). Phase constant (Beta). Paramete r Not dissipative Lost low dielectric Dielectrics with losses Good conductors
jω √ με jω √ με √ jωμ ( σ + jωε ) √ jω σμ o
0 ση / 2 ℜ() √ πf σμ o
ω √ με ω √ με ℑ() √ πf σμ o
√ μ / ε √ μ / ε √ jωμ /( σ + jωε ) √ jω μ o / σ
Interpretation of the signal power: –30dBm to –50dBm → Excellent (very strong) –51dBm to –65dBm → Good –66dBm to –75dBm → Acceptable (may fail) –76dBm to –90dBm → Weak (with interruptions) < –90dBm → Very weak or no connection Note: In Wi-Fi signals, decibels (dBm) are a way of measuring the signal power received by the mobile phone. Signal values are measured in dBm (decibels-milliwatts), which is a logarithmic unit. Values are always negative (for example: – 30 dBm, – 60 dBm, – 90 dBm). The closer to 0, the better the signal. Why is dBm used? Because the range of signal power is very wide, and decibels make it possible to represent these changes in a more understandable way. For example: –30 dBm ≈ 1 mW (milliwatt) –60 dBm ≈ 0.001 mW –90 dBm ≈ 0.000000001 mW
Dintance [ m ] Signal power [ dBm ]
