ELEC 425 Interference Control in Electronics Lecture 0 Introduction to the Course & Syllabus

Transcription

1 Dr. Gregory J. Mazzaro Fall 2017 ELEC 425 Interference Control in Electronics Lecture 0 Introduction to the Course & Syllabus THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA 171 Moultrie Street, Charleston, SC 29409

2 ELEC 425 Interference Control 2

3 ELEC 425 Interference Control 3

4 ELEC 425 Interference Control 4

5 Dr. Gregory J. Mazzaro Fall 2017 ELEC 425 Interference Control in Electronics Lecture 1(a) Introduction to Electromagnetic Interference & Compatibility THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA 171 Moultrie Street, Charleston, SC 29409

6 Electromagnetic Interference Where does electromagnetic energy (in the form of waves) come from? time-varying current / potential H E E, H t t e.g. spark gaps, lightning, relays, motors, fluorescent lights, radio transmitters, radar, power lines, digital devices (computers) intentional vs. unintentional receivers designed to receive electromagnetic waves vs. not e.g. AM/FM radio vs. digital computer interference: unintentional reception of electromagnetic energy which causes undesired behavior in the receiver generation reception transmission 6

7 Compatibility & Interference Reduction compatible: (a) does not interfere with other electronic systems, (b) can withstand interference from other electronic systems, and (c) does not interfere with itself to eliminate interference (a) suppress the emission at its source (b) make the coupling path inefficient (c) make the receiver less susceptible Generally, high-frequency signals (e.g. digital pulses with fast rise times) make for efficient coupling paths. generation reception transmission 7

8 Emissions & Susceptibility radiated emissions: currents on wires/enclosures generate waves radiated susceptibility: waves generate currents on wires/enclosures conducted emissions: currents on wires/enclosures stray to other devices conducted susceptibility: currents from other devices stray to our device 8

9 Emissions & Susceptibility wires/enclosures act as unintended antennas (60-Hz) power cords often carry higher-frequency signals conduction paths are more efficient than radiation paths conducted emissions can become radiated emissions and vice versa 9

10 Dr. Gregory J. Mazzaro Fall 2017 ELEC 425 Interference Control in Electronics Lecture 1(b) Waves & Electrical Dimensions THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA 171 Moultrie Street, Charleston, SC 29409

11 Electrical vs. Physical Length electrical length: distance measured in wavelengths ; equal to physical length L divided by wavelength/l electrical signals travel at propagation speed u, not instantaneously: u 1 1 c r 0 r 0 r r therefore (a) voltages along the same node may not have the same value, and (b) currents along the same wire may not be the same, instantaneously 11

12 Electrical vs. Physical Length for electrical lengths << l ( electrically small, usually l/10 or smaller) electrical signals arrive approximately instantaneously Kirchhoff s Laws operate as presented in Electric Circuit Analysis and Electronics (a) voltages along the same node have the same value, and (b) currents along the same wire are the same 12

13 Wave Propagation: Time Domain z electrical signals travel at propagation speed u, not instantaneously: 1 1 c u r 0 r 0 r r the time delay T D required for a wave to travel a physical distance L is TD L u 13

14 Wave Propagation: Sinusoidal i(t, z 1 ) our mathematical model for wave propagation as a function of time t and distance z is, cos i z t I t z T/2 T t where is the phase constant in radians/meter: 2 l i(t, z 2 ) T t thus i(z,t) may be rewritten: z iz, t I cos t 2 l negligible until z > l/10 14

15 Wave Propagation: Sinusoidal the speed of this wave is determined by tracking any one point on the wave in time & distance: t z 0 dz 2 f u dt 2 l fl thus i(z,t) may be written yet another way: 15 z iz, t I cos t u phase shift is equivalent to time delay

16 Frequency vs. Wavelength u fl 1 1 r c r r r c F m H m m s 16

17 Frequency Bands u fl 1 1 r c r r r c F m H m m s 17

18 Permittivity () and Permeability () r s r r = r 0 s = s r s copper = r 0 18

19 Examples: Wave-, Electrical Length Determine the wavelength corresponding to the following frequency & medium: (a) 600 MHz in epoxy glass Determine the electrical length corresponding to the following physical length: (b) one-mile length of 60-Hz transmission line, in air 19