lesson title: electromagnetics and antenna overview dale r. thompson computer science and computer...
TRANSCRIPT
![Page 1: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/1.jpg)
Lesson Title: Electromagnetics and Antenna
Overview
Dale R. ThompsonComputer Science and Computer Engineering Dept.
University of Arkansas
http://rfidsecurity.uark.edu 1
This material is based upon work supported by the National Science Foundation under Grant No. DUE-0736741.
Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).
Copyright © 2008 by Dale R. Thompson {[email protected]}
![Page 2: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/2.jpg)
Electromagnetic (EM) radiation
• Electromagnetic (EM) radiation is caused by charged particles that are accelerated. Charged particles have an electric field. Moving charged particles create a magnetic field, which in turn creates electromagnetic radiation sometimes called an electromagnetic wave or electromagnetic field. Therefore, changing currents are required to create electromagnetic radiation. Electromagnetic radiation has both a magnetic and electric field.
http://rfidsecurity.uark.edu 2
![Page 3: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/3.jpg)
Period, Frequency, and Wavelength• T = period, time for one cycle• f = frequency (cycles/s = Hz) = 1/T• λ = wavelength (m)• c = speed of light in vacuum = 3E8
m/s• c= λ*f• What is T, f, and λ?
– Ans: 2 s, 0.5 Hz, 6E8 m
http://rfidsecurity.uark.edu 3
![Page 4: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/4.jpg)
Phase (time delay)
• Phase: relative timing of two signals
• Could measure absolute time like seconds
• More common to use a radians or degrees
• Signal 1 = sin(θ)• Signal 2 = sin(θ-pi/4)
http://rfidsecurity.uark.edu 4
![Page 5: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/5.jpg)
Phase Lag
http://rfidsecurity.uark.edu 5
![Page 6: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/6.jpg)
Phase Lead
http://rfidsecurity.uark.edu 6
![Page 7: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/7.jpg)
Electromagnetic Radiation
• Antennas with a periodic signal create electromagnetic radiation
• Two types of electromagnetic radiation– Near field– Far field
http://rfidsecurity.uark.edu 7
![Page 8: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/8.jpg)
Near Field (Inductive Coupling)• Area from the antenna to the point where the electromagnetic field
forms. Field starts at the antenna as purely magnetic• Inductive (like a transformer) or capacitive coupling• Magnetic field decreases by a factor of 1/(r^3) in free space, where r is
distance between the tag and reader antenna• Enough power for cryptographic functions if tag close to reader
http://rfidsecurity.uark.edu 8
![Page 9: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/9.jpg)
Far Field (Radiative Coupling)• Area some distance from the transmitting antenna at which the
electromagnetic wave has fully formed and separated from the antenna. The electric and magnetic fields propagate as an electromagnetic (EM) wave.
• In the far field, inductive coupling is not possible• EM field decreases by a factor of 1/r, where r is distance between the tag
and reader antenna
http://rfidsecurity.uark.edu 9
![Page 10: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/10.jpg)
Approximating Boundary Between Near and Far Field
• Case 1: If antenna size is comparable to the wavelength (like UHF),r = 2f(d^2)/cd = maximum antenna dimensionf = frequencyc = speed of light
• Case 2: If antenna size much smaller than wavelength (like HF),r = c/(2*pi*f)
http://rfidsecurity.uark.edu 10
![Page 11: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/11.jpg)
Near-field/Far-field BoundariesBand Distance (meters) Distance (feet)
LF 382 1146
HF 3.5 11
UHF 0.16 0.5
http://rfidsecurity.uark.edu 11
![Page 12: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/12.jpg)
Periodic Signal Voltage
• v(t) = vocos(ωt)
• ω = 2*pi*f
http://rfidsecurity.uark.edu 12
![Page 13: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/13.jpg)
Power in Direct Current
• P = VI• V = IR• P = V^2/R
http://rfidsecurity.uark.edu 13
![Page 14: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/14.jpg)
Power of Periodic Signal
• Pavg = Vo2/(2R)
• Vo = peak voltage
http://rfidsecurity.uark.edu 14
![Page 15: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/15.jpg)
Power of Periodic Signal
• Root-mean-square (RMS) voltage• Vrms = Vo/sqrt(2)
• Pavg = Vrms2/R
http://rfidsecurity.uark.edu 15
![Page 16: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/16.jpg)
Decibels (dB)
• Useful to describe signals with power spectrum (Power vs frequency)
• Signal power ranges from 10-15 to 102 watts• Logarithmic notation: 10log(x) = x• GdB = 10log10(Pout/Pin)
• GdB = 20log10(Vout/Vin)
http://rfidsecurity.uark.edu 16
![Page 17: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/17.jpg)
Absolute Power
• dBm is absolute power with reference to a milliwatt
• dBm = 10log10(P/(1 mW))
• dBW = 10log10(P/(1 W))
http://rfidsecurity.uark.edu 17
![Page 18: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/18.jpg)
Isotropic Antenna
• Assume antenna radiates same power density in all directions
http://rfidsecurity.uark.edu 18
![Page 19: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/19.jpg)
Antenna Gain
• Focus energy is a particular direction• Power gain above isotropic antenna or a
dipole antenna
http://rfidsecurity.uark.edu 19
![Page 20: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/20.jpg)
Half-Wave Dipole
• 2.2 dB gain above an isotropic antenna (2.2 dBi)
http://rfidsecurity.uark.edu 20
![Page 21: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/21.jpg)
Dipole Pattern
http://rfidsecurity.uark.edu 21
![Page 22: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/22.jpg)
Effective Isotropic Radiated Power (EIRP)
• Power required if using an isotropic antenna to get the same power as the power from the main beam of a directional antenna
• Includes transmitter power and gain of antenna
• EIRP = PTX (dBm) + GTX (dBi)
http://rfidsecurity.uark.edu 22
![Page 23: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/23.jpg)
Effective Radiated Power (ERP)
• Power required if using a half-wave dipole antenna to get the same power as the power from the main beam of a directional antenna
• Includes transmitter power and gain of antenna
• ERP = PTX (dBm) + GTX (dBd)
• dBi = dBd + 2.2
http://rfidsecurity.uark.edu 23
![Page 24: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/24.jpg)
Linear Polarization
http://rfidsecurity.uark.edu 24
![Page 25: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/25.jpg)
Mismatched Polarization
http://rfidsecurity.uark.edu 25
![Page 26: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/26.jpg)
Circular Polarization• Electric field rotates as a function
of time around direction of propagation
• Orientation of electric field varies with time
• Right-hand polarization (RHP)• Left-hand polarization (LHP)• Common for reader antenna to
use circular polarization and the tag to use linear so that the system is less sensitive to tag orientation!
http://rfidsecurity.uark.edu 26
![Page 27: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/27.jpg)
Bistatic configuration
• One reader antenna is used for transmitting and a different antenna is used for receiving
http://rfidsecurity.uark.edu 27
![Page 28: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/28.jpg)
Monstatic configuration
• The same reader antenna is used for both transmitting and receiving
http://rfidsecurity.uark.edu 28
![Page 29: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/29.jpg)
Reader Antennas
http://rfidsecurity.uark.edu 29
![Page 30: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/30.jpg)
Tag Antennas
http://rfidsecurity.uark.edu 30
![Page 31: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/31.jpg)
Contact InformationDale R. Thompson, Ph.D., P.E.Associate ProfessorComputer Science and Computer Engineering Dept.JBHT – CSCE 5041 University of ArkansasFayetteville, Arkansas 72701-1201
Phone: +1 (479) 575-5090FAX: +1 (479) 575-5339E-mail: [email protected]: http://comp.uark.edu/~drt/
http://rfidsecurity.uark.edu 31
![Page 32: Lesson Title: Electromagnetics and Antenna Overview Dale R. Thompson Computer Science and Computer Engineering Dept. University of Arkansas](https://reader030.vdocument.in/reader030/viewer/2022032523/56649d825503460f94a67592/html5/thumbnails/32.jpg)
Copyright Notice, Acknowledgment, and Liability Release
• Copyright Notice– This material is Copyright © 2008 by Dale R. Thompson. It may be freely redistributed in its entirety
provided that this copyright notice is not removed. It may not be sold for profit or incorporated in commercial documents without the written permission of the copyright holder.
• Acknowledgment– These materials were developed through a grant from the National Science Foundation at the
University of Arkansas. Any opinions, findings, and recommendations or conclusions expressed in these materials are those of the author(s) and do not necessarily reflect those of the National Science Foundation or the University of Arkansas.
• Liability Release– The curriculum activities and lessons have been designed to be safe and engaging learning
experiences and have been field-tested with university students. However, due to the numerous variables that exist, the author(s) does not assume any liability for the use of this product. These curriculum activities and lessons are provided as is without any express or implied warranty. The user is responsible and liable for following all stated and generally accepted safety guidelines and practices.
http://rfidsecurity.uark.edu 32