J. Goedbloed received the M.Sc. degree in experimental physics
from Amsterdam University in 1967 and the Ph.D. degree from the
Technical University of Eindhoven in 1973. From 1954 to 1978 he
worked at Philips Research, Eindhoven, in various fields, such
as electro-mechanical coupling systems, noise in IMPATT-diode
microwave oscillators and low-noise avalanche photo-diodes. In
the period 1963-1967 he investigated effects of gamma irradiation
of silicon at the Physics Laboratories of Amsterdam University.
From 1978 until 1997 when he retired, he was
with the EMC Department of Philips Research as Supervisor and
Senior Scientist. Until 2002 he was an active member of CISPR/A,
concentrating on uncertainties in standardized compliance testing.
EMC education is his great interest. He is the
author of a textbook on EMC, has presented many EMC courses and
founded the Post-Graduate Course on EMC in the Netherlands in
1984. He has also participated several times in the Experiment
Demonstration Sessions of the IEEE EMC Symposia.
Dr. Goedbloed is a Member of the Dutch Physical
Society (NNV) and the Dutch Society for Radio and Electronics
(NERG). He is a Senior Member of the IEEE EMC Society and an Honorary
Life Member of the Dutch EMC/ESD Society. EMC
of the Threat of Intentional Electromagnetic Interference (IEMI)
Abstract: The new threat of intentional
electromagnetic interference (IEMI) has become more important
today given the reliance of society on sophisticated electronics
and the threat of global terrorism. This paper defines important
terms, describes the different types of electromagnetic threats,
summarizes the current understanding of equipment susceptibility,
provides several approaches for protection of buildings, and summarizes
the new work in international standardisation.
Keywords: High Power Electromagnetics,
Intentional EMI, Transients, Standardisation
What is Intentional EMI?
The term Intentional Electromagnetic Interference or IEMI has
been used in recent years to describe all categories of interference
caused to electronic equipment whether it is by terrorists, criminals
or hackers. While the motives of the attacker may be different,
the results can be the same on society. The scientific community
has been working to understand and define this threat in a more
In February 1999 at a workshop held at the Zurich EMC Symposium
a widely accepted definition was suggested: "Intentional
malicious generation of electromagnetic energy introducing noise
or signals into electric and electronic systems, thus disrupting,
confusing or damaging these systems for terrorist or criminal
purposes." Note that hackers are not mentioned explicitly
in this definition, although in most countries of the world, an
attack on commercial interests for "entertainment" is
against the law.
The first question one might ask is whether
there really is any reason for society to be concerned about this
problem. In fact there are many as indicated below:
Types of IEMI Threat Environments
In order to understand the threats to electronic equipment, it
is necessary to understand the different types of electromagnetic
environments that can be produced and that can create operational
problems for exposed equipment. There are two major categories
of EM environments of concern: narrowband and wideband. There
are also two major ways for this energy to be delivered to a system:
radiated and conducted.
A narrowband waveform is nearly a single frequency
(typically a bandwidth of less than 1% of the center frequency)
of power delivered over a fixed time frame (often on the order
of microseconds). For experiments performed on equipment where
vulnerabilities have been noted due to radiated fields, frequencies
between 0.3 and 3 GHz seem to be of most concern. Of course higher
and lower frequencies may also cause problems with system performance,
especially if a system resonance is found. Also some environments
in this category include modulation of the sine waves, shifting
frequencies and repetitive applications. This category of radiated
threat is often referred to as high power microwaves (HPM), although
this term is used loosely to include frequencies outside of the
A wideband waveform is usually one in which
a time domain pulse is delivered, often in a repetitive fashion.
The term "wideband" indicates that the energy in the
waveform is produced over a substantial frequency range relative
to the "center frequency". Of course many pulse waveforms
do not have an explicit center frequency; and more precise definitions
are being considered at this time to divide the wideband category
into several subcategories. One of the common terms used for radiated
fields includes the ultrawideband pulse or UWB, and it typically
rises in 0.1 nanoseconds and decays in approximately 1 nanosecond.
In terms of creating system vulnerabilities,
the narrowband threat is usually one of very high power, since
the electrical energy is delivered in a narrow frequency band.
It is fairly easy to deliver fields on the order of thousands
of volts/meter at a single frequency. Of course each system under
test may have a vulnerable frequency that is different from the
next. Often the malfunctions observed in testing equipment with
narrowband waveforms are those of permanent damage.
The wideband threat is somewhat different in
this respect. Since a time domain pulse produces energy over many
frequencies at the same time, the energy density at single frequencies
are much less. This means that damage is not as likely as in the
narrowband case; however, it is easier to find a system's vulnerability
since many frequencies are exposed at the same time. Sources that
have been built in the past typically produce repetitive pulses
that can continue for many seconds or minutes thereby increasing
the probability of producing a system upset.
While the waveform characteristics are defined
above, there are two primary ways that they may be delivered to
a system. One is through the application of radiated fields, and
the other is through conduction along cables and wires. These
two methods of delivery are consistent with the general treatment
of electromagnetic disturbances in the field of electromagnetic
compatibility (EMC) where nearly all environments and tests are
defined in terms of radiated and conducted environments (e.g.,
The above discussion clearly indicates that there are four general
cases to be considered for IEMI: radiated narrowband, radiated
wideband, conducted narrowband, and conducted wideband.
For the two radiated cases, it seems clear that
frequencies above 100 MHz are of primary concern in that they
are able to penetrate unshielded or poorly protected buildings
very well and yet couple efficiently to the equipment inside of
the building. In addition, they have the advantage that antennas
designed to radiate efficiently at these frequencies are small.
Tests performed in the IEC using standard 61000-4-3 indicate that
most equipment sold commercially in Europe should be immune to
radiated narrowband fields of 3 to 10 V/m (between 80 MHz and
2.5 GHz), depending on the equipment type. For wideband radiated
threats, the IEC equivalent is the electrostatic discharge test
(61000-4-2), which produces a peak electric field on the order
of 1 kV/m near the ESD arc; this pulse has a rise time of 0.7
ns and a decay time of approximately 30 ns. Although this field
is produced by a discharge on or near an equipment enclosure,
the EM fields propagating away from the arc couple well to and
propagate through small apertures in the enclosure walls. This
is very similar to the exposure from a radiated field.
For the two conducted cases, there are some
differences in terms of the frequency range of interest. It is
well known that if conducted signals are injected into the power
supply or telecom cables outside of a building, that frequencies
below 10 MHz (and pulse widths wider than 50 ns) propagate more
efficiently than higher frequencies. In fact it is known that
power line disturbances caused by lightning pulses (see IEC 61000-4-5)
and electric fast transients (IEC 61000-4-4) propagate well enough
from the outside to the inside of a building to provide peak pulse
voltages as high as 2 kV at the wall plugs. These pulses have
rise times between 5 ns and 10 microseconds with pulse widths
typically a factor of 10 longer than the rise. While these lower
frequency waveforms are not ultrawideband, they satisfy the general
wideband definition. Of course narrowband conducted signals also
can be injected into a building's wiring, including its grounding
system at frequencies even lower than 50 Hz. Experiments by Parfenov
et. al. have shown that even these low frequency narrowband waveforms
can disrupt the operation of equipment inside a building .
In completing the discussion about the threat
environments, it must be realized that there are two aspects of
interest in terms of deciding which types of waveforms are the
most important. For buildings with wooden construction or with
dielectric windows, the radiated waveforms (narrowband and wideband)
will be most dangerous at frequencies above 100 MHz. These fields
will easily penetrate the outer walls of a building and expose
the equipment and its wiring in offices near the outer walls.
For energy to penetrate further without attenuation into the building
there will be a need to have a straight clear path into inner
portions of the building. This is because reflections and diffraction
will reduce the strength of the fields as they penetrate deeper
inside a building. For the conducted threat that is injected on
the outside of cables entering a building, frequencies below 10
MHz (narrowband or wideband) tend to be more important if the
threat is to propagate beyond the interface. These insights will
be useful when it comes to designing mitigation methods to deal
with this threat.
of Commercial Equipment
Over the past five years there have been significant experiments
that have tested the response of commercial equipment to narrowband
and wideband threats. In general this experience can be summarized
in the following way:
Modern computers and other types of equipment
using microprocessors appear to be vulnerable to malfunction from
radiated narrowband fields above 100 V/m . Of course there
are large variations in the responses of equipment due to the
specific experiment setups and the quality of the equipment enclosures
that are used. In addition, tests performed in the range of 1
- 10 GHz seem to indicate that malfunctions occur at lower field
levels at the lower frequencies . Unfortunately there have
not been many experimental results published that have covered
frequencies below 1 GHz, so it is not clear if this trend continues
to lower frequencies. There is less experience with the use of
wideband radiated field testing, however, there are some indications
that peak pulse field levels of 1 kV/m will produce malfunctions
for a 0.1/1 nanosecond pulse, that is repetitively pulsed.
One should note that these experiments are usually
performed by directly exposing the equipment under test within
line of sight of a radiating antenna. Of course if the equipment
is within a building or in a room without a window, there will
be a reduction of the incident field from outside to inside. Also
most experiments have not really examined the polarization and
angle of incidence aspect thoroughly, and therefore most of the
effects noted during testing will likely occur at lower field
levels when an optimum coupling geometry is applied. Of course
what is really needed is to understand the average vulnerability
of equipment since the orientations of equipment and the polarization
of the threats are likely to be extremely variable.
For the conducted threats, it seems clear that
if access to external telecom or power cables is not prevented,
it is fairly easy to inject harmful signals into a building. Experiments
have shown that narrowband voltages injected into the grounding
system of a building can cause significant equipment malfunctions
inside. Frequencies below 100 Hz and levels below 100 volts have
been known to cause problems . For wideband waveforms, it appears
that pulse widths on the order of 100 microseconds can create
damage to equipment power supplies and with interface circuit
boards at levels of 2 - 4 kV .
While these values may seem to be low, they
should not really be a surprise. When one examines the EMC test
requirements for immunity in Europe, it is unusual to see a narrowband
radiated field level requirement above 10 V/m (for frequencies
above 80 MHz). This is the required level for medical devices
that are needed to support life (IEC 60601-1-2). Higher levels
are not recommended because of the expense of providing the increased
protection. For narrowband voltages induced on cables connected
to equipment, 10 V is the upper level required in most cases (IEC
61000-4-6). The frequencies of application are below 80 MHz. Clearly
the immunity levels required for commercial equipment are well
below the levels that can be produced by commercially available
IEMI sources today.
In the area of wideband conducted transients,
most of the lightning and electric fast transient tests are performed
for levels up to 2 kV. Only in special cases, such as for equipment
in a power generating facility or a substation will the levels
be higher. The typical EMC wideband test waveforms have rise times
as fast as 5 ns and pulse widths as slow as 700 microseconds.
There is one area in which a wideband threat
has higher levels to consider - the high altitude electromagnetic
pulse. HEMP is generated from a high altitude nuclear detonation.
HEMP standards developed by the IEC required radiated field testing
for fully exposed equipment to a standard level of 50 kV/m with
a 2.5/25 ns wideband pulse. There are corresponding wideband conducted
waveforms that are created during the coupling process. These
induced voltages may reach levels of hundred of kilovolts on an
external power line. Of course we cannot expect that commercial
equipment connected to these lines are immune to HEMP threats,
and therefore it is clear that the intentional EMI threats clearly
exceed the levels that equipment are protected to using standard
When it comes to protecting a building and its internal equipment
from the threat of IEMI, there are several aspects of protection
to keep in mind:
After the HPEM environment document receives
clear support from the National Committees of the IEC, then work
will begin on the protection methods to deal with these threats.
In this overview of the problem of Intentional EMI, we have defined
the problem and the terminology involved in simple terms. We have
further described the basic types of threat environments involved
and have summarized our current understanding of the importance
of the different types of threats. In addition, some of the basic
concepts have been laid out for protection from this new threat,
although it is clear that more work remains to be done. Finally
the work of the IEC is briefly mentioned in order to assure the
reader that there are strong international efforts underway to
understand and to standardize ways to protect our society from
 V. Fortov, V. Loborev, Yu. Parfenov, V. Sizranov, B. Yankovskii,
W. Radasky, "Estimation of Pulse Electromagnetic Disturbances
Penetrating into Computers Through Building Power and Earthing
Circuits," Metatech Corporation, Meta-R-176, December 2000.
 J. LoVetri, A. Wilbers, A. Zwamborn, "Microwave interaction
with a personal computer: Experiment and modeling," 13th
International Zurich Symposium and Technical Exhibition on EMC,
February 1999, pp. 203-206.
 M. Bäckström, "HPM testing of a Car: A Representative
Example of the Susceptibility of Civil Systems," 13th International
Zurich Symposium Supplement, February 1999, pp. 189-190.
 V. Fortov, Yu. Parfenov, L. Zdoukhov, R. Borisov, S. Petrov,
L. Siniy, "A computer code for estimating pulsed electromagnetic
disturbances penetrating into building power and earthing connections,"
14th International Zurich Symposium and Technical Exhibition on
EMC, February 2001.
William A. Radasky's current interests include studies to
understand the threat of Intentional EMI and to develop mitigation
and monitoring methods to protect equipment from this new threat.
He is Chairman of IEC Subcommittee 77C, which is developing high-power
electromagnetic environment and test standards for civil systems.
He is also the Chairman of TC-5 (High Power EM) for the IEEE EMC
Society. In addition, he is the Chairman of the IEC Advisory Committee
on EMC (ACEC), which is tasked to coordinate all EMC standardization
work for the IEC. During his 35-year career, he has published
over 250 technical papers and reports dealing with electromagnetic
interference (EMI) and protection.
Manuel W. Wik has been a Senior
Member of IEEE until his retirement by the end of year 2001 and
a valued IEEE member for 25 years. He was born in Stockholm, Sweden,
in 1936 and became Master of Science in Electrical Engineering
from The Royal Institute of Technology in Stockholm in 1962.
He became Chief Engineer and the first
person to receive the title Strategic Specialist at the Defence
Materiel Administration (FMV) in Stockholm in 1990. He is still
active at FMV after his retirement. He was previously head of
procurement at the Swedish Armed Forces Telecommunication Transmission
Network Section at FMV. Earlier on he worked as research engineer
at The Research Institute of National Defence (FOA) responsible
for protection against electromagnetic effects from low and high
altitude nuclear explosions. He contributed to the International
Council of Scientific Union, Scientific Committee on Problems
of the Environment project on Environmental Consequences of Nuclear
War (ICSU SCOPE ENUWAR) resulting in a series of books. He has
written numerous articles, contributed to books, government reports
and conference proceedings, and given presentations in the fields
of Nuclear Electromagnetic Pulse effects (EMP), Electromagnetic
compatibility, Intentional electromagnetic interference, Electronic
warfare, Threats to telecommunications, and National strategy
for enhanced IT-security and protection against information operations.
His present interest as Strategic Specialist includes emerging
technologies such as High Power Electromagnetics (HPEM), and systems
and methods for Network Centric Warfare (NCW, in Sweden named
Network Based Defence).
Mr. Wik is Fellow of the Royal Swedish
Academy of War Sciences and Secretary of its Division of military
technology, Member of the Swedish National Committee of the International
Union of Radio Science (URSI), Secretary of the International
Electrotechnical Committee (IEC) standardisation Sub-Committee
77C and recognised as an EMP Fellow by the US Summa Foundation.
He has been awarded the Carolus XIV medal Ingenio et Fortitudine
from the King of Sweden. EMC
The Polarization Ellipsoid
Many problems of EMC and EMI require a detailed
knowledge of the polarization status of emitted radiation by devices
or interfering radiation on devices. The topic of wave polarization
is a classic one. Despite that, erroneous ideas still can be found
in the literature. Moreover, the way the topic is traditionally
treated leaves some loose ends -the question being not what is
told but what is omitted. In this tutorial article a concise but
complete discussion of the topic of field polarization is provided.
Let us consider the description of a sinusoidal time-varying electric
field vector E(t) in a fixed point in space, using a Cartesian
reference frame. If the field vector is described by one single
component, for instance along x, we write
where w is the angular frequency, Ex is the
field magnitude, ax is the phase angle, and ux is the unit vector
along the x-direction. Both Ex and ax are time-invariant scalar
quantities. In this case, the field is said to be linearly polarized
in the x-direction, [1-4].
Consider now a two-dimensional representation for E, using for
instance its x and y components,
In this case, for an arbitrary combination of
values of Ex, Ey, ax and ay the field is said to be elliptically
polarized [1-4] in the x-y plane. If, in addition, Ex=Ey and ax-ay=±p/2
then a circularly polarized field is obtained [1-4].
All the above considerations can be found in most modern textbooks
on Electromagnetics [2-4]. However very seldom  can one find
the topic of polarization discussed for the case of a three-dimensional
representation of E(t).
In a recent article  appearing in the EMC Society Newsletter,
the theme of the polarization status of a field vector characterized
by three simultaneous components has been addressed. There, it
is claimed that in the general case of E fields given by
the tip of the vector moves on the surface of
a three-axial ellipsoid, which would then be the generalization
of the polarization ellipse found for E fields described by only
two Cartesian components.
Well, this idea seems to make sense and sounds appealing, but,
unfortunately, it is a mistake. In fact, as we are going to show,
even for the 3D representation in (3), the most general polarization
status one may find is the elliptical polarization on a plane.
For analysis purposes we employ the phasor representation of sinusoidal
time-varying scalar and vector quantities. Let us begin with the
scalar components of the E field. For k = x, y, z we have
where the phasors Ex, Ey, and Ez are complex
time-invariant scalar quantities.
Substitution of (4) into (3) yields
The complex quantity in parenthesis is the so-called
phasor vector representation of E(t), which can be broken down
into its real and imaginary parts
Both vectors E1 and E2 are time-invariant vectors defined in the
three-dimensional real space, with fixed magnitudes and fixed
directions, E1=E2u1, E2=E2u2 , .
Substitution of (6) into (5) then yields
According to (7) we finally see that, in general,
the vector field E(t) is the result of the superposition of just
two linear polarization states (not necessarily orthogonal) oscillating
with a phase lag of p/2; the result of which is not an ellipsoid
but instead an ordinary ellipse belonging to the plane defined
by the directions u1 and u2, which make an angle q,
The sense of rotation of the tip of vector E(t)
is from E2 to E1.
The major and minor axes of the polarization ellipse are not,
in general, coincident with the directions u1 and u2. To determine
the sizes and directions of the ellipse principal axes we should
use (7) to find E2(t)=E.E. With the help of basic trigonometry
results we obtain
Now, using (9) and (7), we conclude that the
following orthogonal vectors define the major and minor axes of
the polarization ellipse
The effective or rms value of the time-varying
electric field E(t) can be directly obtained from its general
Then, using (9), we find
For arbitrary combinations of values of Ex, Ey,
Ez, ax, ay
and az the ellipse axial ratio AR = Emax/Emin
can take any value from 1 to ∞ . AR = 1 means the field
is circularly polarized, and AR = ∞ it is linearly polarized.
In this article we addressed the issue of the polarization of
harmonic electric field vectors E in the general case (ordinarily
not discussed) when the fields are given by 3D expressions with
all its spatial components explicit. It was shown that for arbitrary
field components, the tip of vector E(t) does not describe, as
it may be believed, a three-axial ellipsoid, but, instead, a simple
ordinary ellipse, whose characterization has been made.
 J. Perini, "What is a Phasor Anyway?" IEEE EMC Society
Newsletter, no. 195, pp. 23-25, 2002.
 C. A. Balanis, Advanced Engineering Electromagnetics, New
York: Wiley, 1989.
 J. A. Kong, Electromagnetic Wave Theory, New York: Wiley,
 S. Ramo, J. Whinnery, T. Duzer, Fields and Waves in Communication
Electronics, 2nd Ed. New York: Wiley, 1984.
 M. Born, E. Wolf, Principles of Optics, Cambridge UK: Pergamon
Brandão Faria was born in Portugal in 1952. He received
his degrees in Electrical Engineering from the Instituto Superior
Técnico (IST) of the Technical University of Lisbon/Portugal,
including the Ph.D in 1986 and the Aggregate title in 1992. He
has been teaching since 1975 at the Department of Electrical Engineering
of the IST, where he is currently a Full Professor. From 1994
to 2000 he served as President of the Centro de Electrotecnia
Teórica e Medidas Eléctricas -a University Center
for Research & Development in Lisbon. His areas of interest
include wave propagation phenomena in multiconductor transmission-line
structures, optical fibers, and electrooptic devices. Professor
Faria has authored two textbooks and contributed over 80 papers
to refereed journals and conferences. He is a Member of the Optical
Society of America and a Senior Member of the EMC Society, MTT
Society, PE Society, and Education Society of the Institute of
Electrical and Electronics Engineers. EMC