Electromagnetic Compatibility Measurements in Reverberation Chambers

Electromagnetic Compatibility Measurements
in Reverberation Chambers
Mathias Magdowski
Chair for Electromagnetic Compatibility
Institute for Medical Engineering
Otto von Guericke University Magdeburg
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Mathias Magdowski (Chair for EMC) EMC Measurements in Reverb Chambers 1 / 70

Some words about myself
Personal background:
born in 1984
live in Magdeburg, Germany
married, two children

Some words about myself
Personal background:
born in 1984
live in Magdeburg, Germany
married, two children
Educational background:
2003 – 2008: studied “Electrical Engineering” at the Otto-von-Guericke-University in
Magdeburg
since 2008: Scientific co-worker at the Chair for EMC
2012: Ph. D. (Dr.-Ing.) with the dissertation “Comparison of the Coupling of
Deterministic and Stochastic Electromagnetic Field to Transmission Lines”
since 2015: teaching as flying faculty

Faculty for Electrical Engineering and Information Technology

Cathedral of Magdeburg seen from the river “Elbe”

Location of Magdeburg inside Germany
Magdeburg
Hannover Berlin
Dresden

Organizational matters
Slides:
yes

Slides:
yes
Recording:
maybe

Slides:
yes
Recording:
maybe
Questions:
with pleasure

What is EMC?
Intermediate overview
1 What is EMC?
2 Examples
3 Calculation in dB
Figures
Levels
4 Radiated EMC Measurements
5 Reverberation Chambers

What is EMC?
What is electromagnetic compatibility?

What is EMC?
Survey: Have you heard of
EMC before?
https://www.menti.com/123456

What is EMC?
EMC before?
Electromagnetic compatibility . . .
. . . is the ability of electrical equipment and
systems to function acceptably in their
electromagnetic environment, by limiting the
unintentional generation, propagation and
reception of electromagnetic energy which
may cause unwanted effects such as
electromagnetic interference (EMI) or even
physical damage in operational equipment.

What is EMC?
EMC before?
Electromagnetic compatibility . . .
. . . is the ability of electrical equipment and
systems to function acceptably in their
electromagnetic environment, by limiting the
unintentional generation, propagation and
reception of electromagnetic energy which
may cause unwanted effects such as
electromagnetic interference (EMI) or even
physical damage in operational equipment.
Aspects:
Immunity
Emission

What is EMC?
Coupling model:
Source Coupling path Victim

What is EMC?
Coupling model:
Source Coupling path Victim
Example:

What is EMC?
Coupling paths
(a) conducted (b) electric fields
(c) magnetic fields (d) wave fields

Examples
1 What is EMC?
2 Examples
3 Calculation in dB
Figures
Levels

Examples
Experiment

Examples
Survey on other EMC examples

Examples
Lightning discharges
Figure: 3 lightning discharges near an overhead line.

Examples
Lightning discharges
Countermeasures:
persons: take cover, feet close together
buildings: lightning arrester
vehicles: Faraday cage
electrical equipment: overvoltage protection
(a) overvoltage protection (b) aircraft as Faraday cage

Examples
Electrostatic discharge
Figure: Electrostatic discharge between a person and a doorknob.

Examples
Electrostatic discharge
Countermeasures:
protective elements in electronic devices
testing of devices with standard pulses from ESD guns
caution while handling unprotected modules
ESD-safe packaging
(a) Conducting wrist straps for dissipation of
the triboelectricity
(b) ESD-safe packing material of a network
card made of conductive plastic

Examples
Examples of real-life EMC problems
USS Forrestal fire in 1967:
aircraft carrier USS Forrestal (CVA-59)
before North Vietnam
electrical anomaly discharged a Zuni rocket
on the flight deck
deck contained fueled aircraft, loaded with
1000-pound bombs, as well as air-to-air and
air-to-ground missiles
devastating fire and series of chain-reaction
explosions
134 sailors killed and 161 injured

Examples
USS Forrestal fire in 1967
Problem:
RF voltage across the contacts of a shielded connector by the ship’s high-power
search radar
power surge when the pilot transferred his systems from external to internal power

Examples
Examples of real-life EMC problems
Military aircraft crash near a large radio transmitter station:
medium wave transmitter station Radio Free Europe
power of 150 kW with an antenna gain of 8
Tornado IDS aircraft passing the mean beam of the antenna
problem in the control system, ejection seats fail, two pilots dead

Examples
Mobile phone radiation
Figure: Mobile phone and active speaker

Examples
Active principle:
Amplitude-
modulated signal
Antenna Active speaker
with diodes
Envelope after
demodulation

Examples
Figure: Ferrite on a USB cable

Calculation in dB
1 What is EMC?
2 Examples
3 Calculation in dB
Figures
Levels

Calculation in dB
Decibel experience
How large is your experience with
using decibels?
excellent
good
okay
very small
no experience at all

Calculation in dB
Motivation
Measurement result of a spectrum analyzer:
A
TRG
RBW 10 MHz
VBW 10 MHz
SWT 50 µs
Att 20 dB
Ref −10 dBm
Center 800 MHz 5 µs/
*
1 PK
VIEW
*
2 PK
AVG
PRN
−70
−65
−60
−55
−50
−45
−40
−35
−30
−25
−20
−15
−10
SWP 4144 of 10000
1
Marker 1 [T1 ]
−24.68 dBm
51.025000 µs
2
Delta 2 [T1 ]
−23.29 dB
5.600000 µs
3
Marker 3 [T1 ]
−56.17 dBm
80.525000 µs
RBW 10 MHz
VBW 10 MHz
SWT 50 µs
Att 20 dB
Ref −10 dBm
Delta 2 [T1 ]
−23.29 dB
5.600000 µs

Calculation in dB
Reminder of the logarithmic identities
Preconditions: x, y, b, r > 0 and b ̸= 1

Calculation in dB
Product:
logb(x · y) = logb x + logb y (1)

Calculation in dB
Product:
Quotient:
logb

x
y

= logb x − logb y (2)

Calculation in dB
Preconditions: x, y, b, r 0 and b ̸= 1
Product:
Quotient:
logb

x
y


Calculation in dB
Preconditions: x, y, b, r 0 and b ̸= 1
Product:
Quotient:
logb

x
y

Power:
logb (xr
) = r logb x (3)

Calculation in dB Figures
Definition of gain figures
Definition for power quantities:
P1: input power
P2: output power
GP = 10 · lg

P2
P1

dB (4)

Definition of gain figures
P1: input power
P2: output power
GP = 10 · lg

P2
P1

dB (4)
Definition for root power quantities (like a voltage):
U1: input voltage
U2: output voltage
GU = 10 · lg

P2
P1

dB = 10 · lg

U2
2/R
U2
1/R

dB = 20 · lg

U2
U1

dB (5)

Not to be confused with:
Figure: “Figure” of Otto von Guericke in Magdeburg
source: http://commons.wikimedia.org/wiki/File:Magdeburg_Guericke.jpg#/media/File:Magdeburg_Guericke.jpg

Origin of the unit name bel
Alexander Graham Bell
(1847–1922)
speech therapist, engineer
and inventor
made the telephone
commercially successful
after his death all telephones
in the US were silenced for
one minute Figure: Alexander Graham Bell
(ca. between 1914–1919)
source: https:
//commons.wikimedia.org/w/index.php?curid=1559

Some numbers to bear in mind
Table: Conversion dB – linear values
Figure Power ratio Voltage ratio
in dB approx. exact approx. exact
0 1 1 1 1
3 2 1.995 1.4 1.412
6 4 3.98 2 1.995
10 10 10 3 3.162
20 100 100 10 10
40 10 000 10 000 100 100
60 1 000 000 1 000 000 1000 1000

Some numbers to bear in mind
Table: Conversion dB – linear values
Figure Power ratio Voltage ratio
in dB approx. exact approx. exact
0 1 1 1 1
−3 0.5 0.501 0.7 0.708
−6 0.25 0.25 0.5 0.501
−10 0.1 0.1 0.3 0.316
−20 0.01 0.01 0.1 0.1
−40 0.0001 0.0001 0.01 0.01
−60 0.000 001 0.000 001 0.001 0.001

Calculation in dB Levels
Definition of levels
P: power
P0: reference value
LP (re P0) = LP/P0
= 10 · lg

P
P0

dB (6)

Definition of levels
P: power
P0: reference value
LP (re P0) = LP/P0
= 10 · lg

P
P0

dB (6)
Definition for root power quantities:
U: voltage
U0: reference value
LU (re U0) = LU/U0
= 20 · lg

U
U0

dB (7)

Not to be confused with:
Figure: “Level” of the river Elbe in Magdeburg
source: https://commons.wikimedia.org/wiki/File:Pegelhaus_Magdeburg.jpg

Summary of calculation rules
Sum or difference of two figures is again a figure:
20 dB + 30 dB =

20 dB + 30 dB = 50 dB (8)

20 dB + 30 dB = 50 dB (8)
Sum of figure and level gives a level:
0 dB (mW) + 50 dB =

20 dB + 30 dB = 50 dB (8)
0 dB (mW) + 50 dB = 50 dB (mW) (9)

20 dB + 30 dB = 50 dB (8)
0 dB (mW) + 50 dB = 50 dB (mW) (9)
Difference of two levels gives a figure:
50 dB (mW) − 0 dB (mW) =

20 dB + 30 dB = 50 dB (8)
0 dB (mW) + 50 dB = 50 dB (mW) (9)
50 dB (mW) − 0 dB (mW) = 50 dB (10)

20 dB + 30 dB = 50 dB (8)
0 dB (mW) + 50 dB = 50 dB (mW) (9)
50 dB (mW) − 0 dB (mW) = 50 dB (10)
Sum of two levels does not make sense:
20 dB (mW) + 30 dB (mW)

20 dB + 30 dB = 50 dB (8)
0 dB (mW) + 50 dB = 50 dB (mW) (9)
50 dB (mW) − 0 dB (mW) = 50 dB (10)
Sum of two levels does not make sense:
20 dB (mW) + 30 dB (mW) wrong! (11)

Radiated EMC Measurements
1 What is EMC?
2 Examples
3 Calculation in dB
Figures
Levels

How to verify the electromagnetic compatibility?
Verification of devices by:
Calculations
Simulations
Measurements

How to verify the electromagnetic compatibility?
Verification of devices by:
Calculations
Simulations
Measurements
Certification by the CE mark:
Conformité Européenne China Export

Open area test site
Figure: Open area test site at the Technical University in Dresden

Experiment

Scattering parameters
Complex scattering parameters of a two-port:


b1
b2

=

s11 s12
s21 s22

·

a1
a2

(12)


b1
b2

=

s11 s12
s21 s22

·

a1
a2

(12)
s21 =
b2
a1
(13)

Shielded room
Figure: By M.junghans at nl.wikipedia, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=4696426

Semi-anechoic chamber
Figure: Semi-anechoic chamber with 10 m measurement distance in Magdeburg

Reverberation Chambers
1 What is EMC?
2 Examples
3 Calculation in dB
Figures
Levels

Mode-stirred chamber
Figure: Large mode-stirred chamber at the chair for EMC in Magdeburg

Carl Baum: The Microwave-Oven Theorem
Question:
What is the difference
between a microwave oven
and a mode-stirred
chamber?
Answer:
The former cooks chicken
and the latter cooks
electronics.

Microwave oven

First commercial oven from Raytheon

Percy Spencer

“Eggsperiment”

“White chicken egg square” by Ren West

“Eggsplosion”

Photo: Wolfgang Gerlach

Pot in the microwave oven?

Spoon in the microwave oven?

12 cm

c = λ · f

c = λ · f = 12 cm · 2450 MHz

c = λ · f = 12 cm · 2450 MHz = 294 000 km
s

Kahoot! Quiz
https:
//create.kahoot.it/share/quiz-for-the-course-electromagnetic-compatibility-measurements-in-reverberation-chambers/
80804c8c-d5f6-480d-a658-a4d90befce67

Vibrating intrinsic reverberation chamber
(a) Demonstration with neon tubes (b) In-situ testing on a ship
Source: Prof. Frank Leferink, University of Twente and THALES, Netherlands

Pros and cons of EMC measurements in reverberation chambers
Advantages:
high field strength with small input power
relatively small costs
robust tests
Disadvantages:
no information about directivity or polarization
statistical electrodynamics
coupling between generator and EUT
comparability with established test environments

PInput = PWalls + PStirrer + PChicken

PWalls = 0

PWalls = 0
PStirrer = 0

PWalls = 0
PStirrer = 0
PInput = PChicken

PWalls = 0
PStirrer = 0
PInput = PChicken
All Power to the Chicken

https://twitter.com/MarkusRidderbu8/status/
1523708966039351297
Thank you very much for
your attention!
Are there any questions?

Electromagnetic Compatibility Measurements in Reverberation Chambers

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