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/Electromaanetlc fields radiated from el QC100 .U5753 N0.1314 1988 V198 C.I NBS-P

NBS

PUBLICATIONS

••'•tiiu 0* * NBS TECHNICAL NOTE 1314

U.S. DEPARTMENT OF COMMERCE / National Bureau of Standards

Electromagnetic Fields

Radiated From Electrostatic Discharges

Theory and Experiment

Perry F. Wilson

Arthur R. Ondrejka

Mark T. Ma

John M. Ladbury

-QC

100

.U5753

#1314

1988

C.2
Tm he National Bureau of Standards' was established by an act of Congress on March 3, 1901. The Bureau's overall ^j^^ goal is to strengthen and advance the nation's science and technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research to assure international competitiveness and leadership of U.S.

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'Located at Boulder, CO, with some elements at Gaithersburg, MD
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(National tiureau of Standards

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Qjlloo

Electromagnetic Fields Radiated From ^^7^3

Electrostatic Discharges—Theory mf^

and Experiment

Perry F. Wilson*

Arthur R. Ondrejka

Mark T. Ma

John M. Ladbury

Electromagnetic Fields Division

Center for Electronics and Electrical Engineering

National Engineering Laboratory

National Bureau of Standards

Boulder, Colorado 80303-3328

*Presently with BBC, Baden-Dattwil, Switzerland

U.S. DEPARTMENT OF COMMERCE, C. William Verity, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director

Issued February 1988
National Bureau of Standards Technical Note 1314

Natl. Bur. Stand. (U.S.), Tech Note 1314, 72 pages (Feb. 1988)

CODEN:NBTNAE

U.S. GOVERNMENT PRINTING OFFICE

WASHINGTON: 1988

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, DC 20402
CONTENTS

List of Figures

Abstract

1

.

INTRODUCTION

2

.

PRE-DISCHARGE EFFECTS AND DISCHARGE CURRENT

3

.

DIPOLE MODEL OF THE ESD -RADIATED FIELDS

3 .

1

Electric Field

3 .

2

Magnetic Field

4. MEASURED ESD CURRENT AND ELECTRIC -FIELD WAVEFORMS

4 .

1

Instrximentation ,

4 .

2

Experimental Results ,

5

.

CONCLUDING REMARKS AND DISCUSSIONS

6

.

ACKNOWLEDGMENTS

7 REFERENCES

APPENDIX A: Time-Dependent Fields Due to a Dipole Source

APPENDIX B: Spectrum of ESD Dipole Radiation Model

APPENDIX C: Time-Domain Antennas for Measuring Impilsive

Electromagnetic Fields

Page

V

1

2

3

5

6

8

8

8

10

14

15

15

17

24

26

iii

List of Figures

Figure Number Page

1. Diagrams showing the development of a spark channel,

based on cloud chamber observations: (a) electron

avalanche, (b) channel growth toward anode, (c) channel

growth toward both anode and cathode, and (d) conductive

bridge [7] 27

2. Conventional single RC circuit model for human

electrostatic discharge [9] 28

3. The dual RLC circuit model for human electrostatic

discharge incorporating separate, parallel paths for

body and hand discharges [11] 28

4. Computer simulation of an ESD current based on the

dual RLC circuit (fig. 3). The circuit parameters used

are C = 7.5 pF, R^ = 200 fi, L^ = 0.1 /iH, C = 100 pF,

R_ = 500 Q, L„ = 1.7 /xH, and 5-kV initial charge [11] 29

5. Computer solutions for a dual RLC-circuit model using

different single-pole simulated oscilloscope bandwidths

.

The initial applied voltage is 5 kV [15] 30

6. The raidation spectrum at 2.0 m from an ESD source

for various applied voltages [1] 31

7. A dipole above a perfect ground plane and its image 32

8

.

Measurement system schematics 33

(a) For measuring current waveform.

(b) For measuring electric field.

9. Coaxial ball target measurement configuration

(Shield material was used to prevent radiation of

the ESD simulator from interfering with the

receiving system) 34

10. Coaxial ball target current and vertical electric

field for a 1-kV discharge 35

11. Coaxial ball target current and vertical electric

field for a 2-kV discharge 36

12. Coaxial ball target current and vertical electric

field for a 4-kV discharge 37

13. Coaxial ball target current and vertical electric

field for a 6-kV discharge 38

V
14. Coaxial ball target current and vertical electric

field for a 8-kV discharge 39

15. Coaxial ball target current and vertical electric

field for a 10-kV discharge 40

16. Coaxial ball target current and vertical electric

field for a 12 -kV discharge 41

17. Predicted vertical electric field for the 4-kV

discharge of fig. 12 as a function of distance to

the observation point 42

18. Predicted magnetic field for the 4-kV discharge case: 43

(a) with the receiving antenna at 1.5 m from the

spark, and (b) as a function of the distance to the

observation point.

19. Spectral content for the coaxial ball target 4-kV

discharge of fig . 12 '. 44

20. Vertical electric field for a 1-kV spark to a ground plane 45

21. Vertical electric field for a 2-kV spark to a ground plane 46

22. Vertical electric field for a 4-kV spark to a ground plane 47

23. Vertical electric field for a 6-kV spark to a ground plane 48

24. Measurement configuration for indirect radiation

from a vertical square metal plate 49

25. Vertical electric field radiated by a vertical

square metal plate excited by a 5-kV spark 50

26. Vertical electric field radiated by a vertical

square metal plate excited by a 7-kV spark 51

27. Measurement configuration for radiation by a metal

chair above a ground plane 52

28. Vertical electric field radiated by a metal chair

above a ground plane excited by a 3-kV spark 53

29. Vertical electric field radiated by a metal chair

above a ground plane excited by a 6-kV spark 54

30. Measurement configuration for radiation by a metal

trash can on a ground plane 55

VI
31. Vertical electric field radiated by a metal trash can excited by a 4-kV spark 56

32. The UHF antenna (NBS 200-1) for measuring the

broadband electric field: dimensions in the figure

are in centimeters 57

33. Construction details of the pulse transformer in the

NBS 200-1 antenna (all dimensions in centimeters) 58

34. Comparison of the frequency response of the NBS 200-1

antenna with and without the Kydex jacket 59

35. Normalized amplitude of the transmitting pulse 60

36. Response of the NBS 200-1 antenna to the transmitting

pulse shown in fig. 35 60

37. The microwave horn antenna, NBS 50-2 61

38. The broadband balun used for the antenna in fig. 37 62

VI

1

ELECTROMAGNETIC FIELDS RADIATED FROM ELECTROSTATIC DISCHARGES

THEORY AND EXPERIMENT

Perry F. Wilson*, Arthur R. Ondrejka, Mark T. Ma, and John M. Ladbury

Electromagnetic Fields Division

National Bureau of Standards

Boulder, Colorado 80303

The fields radiated by electrostatic discharges (ESD) are studied both theoretically and experimentally. The ESD spark

is modeled theoretically as an electrically short, time

dependent, linear dipole situated above an infinite ground

plane. Experimentally, sparks of varying voltages are generated by a commerically available simulator and used to

excite a number of targets including (1) the extended inner

conductor of a coaxial cable mounted in a ground plane, (2)

direct discharges to a ground plane, (3) indirect radiation

from a large metal plate, (4) a metal chair over a ground

plane, and (5) a metal trash can. Results show that

relatively low-voltage sparks (2-4 kV) excite the strongest

radiated fields. This suggests that the spark fields can pose

a significant interference threat to electronic equipment into

the gigahertz range.

Key words: electrostatic discharge; pulsed current; radiated

electric field; radiated magnetic field; spectrum; time-domain

technique

*Presently with BBC, Baden- Dattwil , Switzerland.
1. INTRODUCTION

Electrostatic discharge, or ESD, is a common phenomenon with the

potential to seriously upset electronic equipment. Currently, electronics

manufacturers and users spend large sums for ESD prevention. As a result,

ESD testing is now a widespread practice. Considerable effort has gone into

the study of the ESD currents to develop current simulators for simplifying

and standardizing ESD testing. However, the ESD-radiated fields have

received significantly less attention, and only a few measurements have

appeared in the literature [1]. This is primarily because fast field pulses

are difficult to measure with available antennas. The recent development by

the National Bureau of Standards (NBS) of broadband, linear-phase, timedomain antennas gives us the necessary measurement capability. This report

examines theoretically and experimentally ESD- related fields and seeks to

better quantify their interference threat.

As the name implies, ESD consists of two different phases.

Electrostatic refers to the relatively slow buildup of a local voltage

differential and the associated static electric field. Discharge denotes

the rapid transfer of the resultant accumulated charge due to the breakdown

of an intervening insulator, typically air. The basic ESD phases are [2]:

(1) the corona- generated rf fields, (2) the pre-discharge effects, (3) the

discharge current, (4) the discharge electric field, and (5) the discharge

magnetic field. Each can affect sensitive electronic equipment. The

corona, pre-discharge effects, and channel development are briefly discussed

in Section 2. However, the main threat comes from the currents and fields

that result from actual discharge.

The ESD fields problem will be considered analytically in Section 3 based on a simple dipole model. The spark is modeled as an electrically

short, time - dependent , linear source (or dipole) situated above an infinite

ground plane. In practice, discharges are usually to some metal object such

as an equipment case or metal cart. If we allow the dipole to be situated

close to the ground plane, then locally this should approximately reproduce

ESD field behavior. This model allows us to examine the electric and

magnetic near- field components, either on the ground plane surface which

affects direct penetration into equipment shielding, or radiated away from

the ground plane as in the case of interference to nearby electronics. The

model is suitable for experimental confirmation and parametric studies.

Section 4 discusses the measurement system and the experimental data.

The measurement of unknown pulsed currents and fields requires that the

system be carefully calibrated with known pulses. The system response may

then be deconvolved out of the measured data to yield the true measured

pulses. The details of this procedure as well as the system limitations are presented in Section 4.1. The test results are covered in Section 4.2. The

basic procedure is to excite a metal object with a spark and measure the

radiated electric field. The objects excited are (1) the extended inner

conductor of a coaxial cable mounted in a ground plane, (2) direct

discharges to a ground plane, (3) indirect radiation from a large, vectical,

metal plate, (4) a metal chair over a ground plane, and (5) a metal trash

can. We find that it is the low-voltage (2 - 4 kV) , fast rise-time (less

than 1 ns) sparks which produce the highest radiated electric field. This

result is also expected from the theory, which predicts dependence of the
far- field radiation on the derivative of the current waveform. These fields

often exceed 100 V/m at a distance of 1.5 m from the discharge point and

clearly pose an interference threat to nearby electronics. The coaxial

target also allows us to measure the current waveform which is then used in

the theoretical model described in Section 3 to predict the radiated fields

(both electric and magnetic). The agreement between theory and experiment,

for the electric field only, is quite good considering the idealized nature

of the model. The magnetic fields are not measured due to the lack of a suitable broadband H- field antenna.

We conclude with summary of the results and suggestions for further

research.

2. PRE-DISCHARGE EFFECTS AND DISCHARGE CURRENT

Objects accumulate charge either triboelectrically or inductively.

Triboelectric charging is a mechanical process whereby relative surface

motion transfers charge. An example is a person walking on a carpet.

Charge transfer depends on the amount of contact, surface smoothness, air

humidity, contact pressure, the triboelectric properties of the rubbing

materials, and the rate of relative motion [3]. Precautionary measures to

prevent excess charging are an important step in ESD prevention. These

include anti-static carpet, anti-static mats, and control of humidity.

Despite these measures, charged persons and carts are probably unavoidable.

The voltage to which a person or cart can be charged is highly

dependent on their capacitance. Human capacitance can be modeled using

cylinders and spheres. Based on this type of calculation, a typical figure

for the lumped capacitance of an adult slightly above ground is 100 pF [4] . Common voltage figures quoted are 8-10 kV [5] for a charged person, with

some authors claiming voltages as great as 30 kV. However, corona bleed- off

likely keeps the upper bound more on the order of 25 kV. Persons typically

do not feel sparks due to voltages less than 3 kV. Thus, many potentially

upsetting ESD events go undetected.

Induction charging is the result of exposing an ungrounded object to an electrostatic field [3]. This often happens during the packaging and

transportation of electronics. Handling, conveyor belts and other friction

sources can cause a substantial charge buildup on a box or plastic package.

The resulting local electrostatic field can affect solid-state logic through

bit reversal, charge drainage, and dielectric burn through [6].

Under normal conditions, a gas such as air is a very effective

insulator. Electrons are tightly bound and current conduction is difficult.

Atoms are free to move about but are constrained by collisions. Collision

rates and speeds are determined by the gas type, pressure, and temperature.

Free electrons and positive ions may be present, but their numbers are usually very low and their motion will be random. Thus, on average, there

is no transfer of charge. Applying an electrostatic field introduces a bias

to the movement of charged particles. Electrons will now attempt to flow

toward the anode while positive ions will flow toward the cathode.

Electrons are lighter than the positive ions (at a ratio of 1:1800) and have

smaller collision cross sections. Therefore, electrons contribute the bulk

of the current. High- field levels can lead to the development of a very low
impedance channel within the gas resulting in a rapid charge transfer. The

process, referred to as the electrical breakdown of gas, is complicated and

its study has been an important research area for over a century.

ESD depends on the creation of free electrons and the formation of a conductive channel, as sequenced in figure 1, which is based on cloud

chamber observations [7]. In (a) electrons released from the cathode

collide to form additional electrons, in effect creating an avalanche in the

direction of the anode. As the electron avalanche progresses it leaves

behind positive ions, the space charge or corona cloud, which sets up a field perpendicular to the applied field. This tends to keep the avalanche

in a well-defined channel (b) . The conductive channel will continue to grow

toward the anode due to the applied field and also toward the cathode due to

the large trailing space charge (c) . When the channel reaches both

terminals (d) a conductive bridge is formed and a large current (spark) is

possible. The discharge rapidly drains the available charge and when the

current drops below some critical value, the conductive channel fails.

The pre-discharge current i may be estimated by [ 8

]

i = VCv (1)

P P

where V is the applied voltage, C is the leader capacitance (on the order of

5 pF/cm) , and v is the velocity at which the leader propagates. The

propagation velocity depends primarily on the applied voltage. For example,

a value of 0.05 cm/ns at 35 kV is quoted by Rhoades [8]. However, leader

velocities for arbitrary voltages are not well known. Using these numbers

for a 1.0 -cm gap, we see that the pre-discharge current would be 8.75 A, and

last for about 20 ns . Typical breakdown voltages are significantly less.

Thus, a level of 8.75 A for the pre-discharge current may be considered an upper bound. As will be seen in Section 4, a current building up over a 20 ns period is relatively slow compared to the actual discharge current and is

not expected to radiate significant fields. Higher voltages mean larger

spark gaps and consequently long time to form the conductive channel. The

result is a longer current rise time for higher applied voltages. Because

many ESD hazards are related to the rate of change of the discharge current,

equipment will sometimes pass high voltage tests and fail at lower discharge

voltages. This counter- intuitive effect has been noted frequently in the

literature, but is not yet universally recognized.

The pre-discharge fields and currents may pose a threat to sensitive

electronics. However, because the actual discharge currents and fields

associated with them are significantly higher, the pre-discharge effects are largely ignored when analyzing ESD hazards.

The discharge current depends on the RLC characteristics of the charge

source, the charging voltage, the rate of approach leading to the discharge,

the electrode geometry, the conductive channel characteristics, and the RLC

characteristics of the discharge victim. Given the wide ranges these

variables can cover, it is difficult to construct a simple, general model of

an ESD event. However, efforts are underway by the IEEE, the lEC, and
others to develop standard current shapes, targets, and test configurations

in order to make ESD testing more repeatable and meaningful.

For long-term ESD testing it is far too difficult and variable for

persons to repeatedly charge and discharge themselves. Thus, most ESD

testing is done with simulators. This raises the problem of how to design

an RLC circuit which realistically simulates human characteristics. Initial

proposals, such as the current version of lEC Publication 801-2 [9], suggest

a simple RC circuit as shown in figure 2. Values proposed by various

organizations range from 60 to 300 pF for C and 10 to 10000 Q for R [10].

However, this model ignores the inductance inherent to a human discharge and

is too simple to yield realistic results.

Richman [10-11] has proposed a dual RLC circuit, as shown in figure 3.

This model recognizes that the hand- forearm (Iv,,Ru,C ) and body (L , R , C ) have very different discharge characteristics and therefore should not be

lumped together. A further refinement is that proposed by Boxleitner [5].

He adds a finger capacitance which modifies the initial spike, discharge

path impedances, and lumped impedances for the discharge victim, in addition

to the arm and body impedances of the dual LRC circuit.

A computer simulation of a discharge based on the dual RLC circuit

model in figure 3 is shown in figure 4. The hand- forearm contribution

discharges quickly and contributes the fast rise -time initial spike. The

body circuit generates the longer tail as the bulk of the stored charge is

dissipated. In this particular example, the rise time is approximately 0.7 ns . If lower inductances (than 0.1 /xH) were used, still faster rise times

would result. A much faster rise time of the discharge current has also

been observed by actual measurements when a simulator is approached to a testing object with a higher speed [12-14].

The measurement of current shapes is very dependent on the bandwidth of

the oscilloscope used, as well as the characteristics of the victim [15].

Initial measurements often used fairly slow oscilloscopes (less than 100 MHz

bandwidth) and the very fast rise times possible for low voltage sparks were

not immediately recognized. Thus, the contribution due to the hand- forearm

was overlooked and the single RLC circuits resulted. At present, it is

recognized that oscilloscopes with bandwidths of at least 1 GHz are necessary to characterize current waveforms. A computer simulation by

Richman [15] illustrating how oscilloscope bandwidth affects the measured

current waveform is given in figure 5. Our measurement system has an effective bandwidth on the order of 1 GHz.

3. DIPOLE MODEL OF THE ESD-RADIATED FIELDS

The fields due to ESD currents can penetrate equipment directly or excite apertures, seams, vents, input-output cables, and the like, and

couple to susceptible internal circuitry. Thus, the designer seeks to

minimize this coupling at frequencies where problems are expected to occur. Reciprocity dictates that inefficient receivers will also be poor radiators.

Therefore, equipment which can pass stringent ESD tests are usually within

FCC- type specifications for radiated EMI limits as well.
3.1 Electric Field

Electric fields tend to excite high- impedance antennas and voltagesensitive circuitry. Unwanted coupling can therefore be reduced by keeping

the impedance of any potential receiving antenna low. This may enhance

magnetic field pickup, so there are typically trade-offs. The basic rule is

to keep lines short. Boxleitner [5] presents a detailed discussion on how

to lay out circuit boards to minimize line-antenna problems.

Honda and Ogura have performed field measurements for various idealized

ESD events [1]. They charged a pair of colinear conductive cylinders one suspended above the other and then drop the upper cylinder to bring them

together and create a spark. An example of their data is shown in figure 6.

They measure a fairly broadband spectrum which widens with increasing

applied voltage up to about 10 kV and then begins to decrease as corona increasingly dissipates the energy before the main discharge. Their data

indicate that most of the ESD energy is at frequencies below 2 GHz.

However, ESD spectral distribution will depend on the current waveform,

conductor geometry, measurement position etc., in addition to the charging

voltage. Thus, although the data in figure 6 are likely representative,

much work remains toward well characterizing ESD in the frequency domain.

We will model an ESD discharge by a dipole of length di above a perfect

ground, as shown in figure 7. We impose a cylindrical coordinate system

(p,(f),z) centered along the dipole (at z = z') and its image. At 3 GHz, 1 cm

is equal to A/10; thus, at ESD frequencies like those shown in figure 6, the

spark gap (which corresponds to the dipole current source at z = z') will be

electrically short and a dipole model is reasonable. The fields may be

analyzed using time -dependent scalar and vector potentials. The details are left to Appendix A.

Although figure 7 shows the dipole above ground, actual ESD events take

place very near the victim conductor. Thus, we will let the dipole approach

the ground, that is, z' =0. With this condition the electric field is

ound to be (see eq. A23)

-,- , - ^0 pz ,3 . 1 3i

R R

n
where R and r are defined in figure 7, and i is the current waveform as a function of time evaluated at t - R/c . If the current waveform is known,

this expression can be used to examine the resultant electric field either

at the ground plane, which represents direct penetration into susceptible

equipment, or in some spatial direction as in the case of radiation to a nearby victim. There are two basic factors controlling the magnitude of E.

2 First, geometry factors such as l/(cR) and 1/(R ), and second, the current

shape, including its derivative (i, 3i/9t). For example, if we consider

geometry as the dominant factor, then in the near field (very small R) E should behave according to

E(r,t) ~ dil -^ ia

^ + a [^ - l]} ^ i (near field). (3)

Equation (3) suggests that the near-field E is controlled by the current

waveform directly. If the victim is sensitive to electric field peaks then

the hand- forearm portion of the discharge is the most hazardous. If the

victim is upset by prolonged exposure, then the full-body discharge or current tail will be the most contributing factor.

The far-field E (large R) is dominated by

i(^,0-«^|a^£|.ij^'-l]|i^|i (far field). W

R R

Thus, here it is the derivative of the current shape that contributes most.

This suggests that for longer interference paths, such as indirect radiation

to nearby susceptible equipment, low-voltage sparks with fast rise times may

be the most damaging. However, if we again examine (2), we see that

variations in the current time dependence could be more important than the

geometry factors. In any case, exact results can be computed by including

all the terms in (2) with a known analytical waveform i(t).

In reality, it seems unreasonable to expect that current waveforms can

be written exactly in terms of simple analytical functions and substituted

into the field expressions. Thus, some approximation will be necessary. A

simple approach is to express a measured current waveform as a sequence of

linear splines, as outlined in Appendix A (eqs. A25-A30). This approach is

compatible with our measurement system since we acquire the current

waveforms using a digitizing oscilloscope, and the data points may be used

directly to generate the linear spline. This method should provide accurate

results, although there are some minor difficulties such as discontinuities

in the derivative of the current waveform. An alternative is to approximate

a measured current waveform as a summation of damped exponentials (see eq.

A-31) . Because the current is basically due to the discharge of RLC

circuits, this approach should prove reasonable. In fact, the approximated

expression may be realizable by a combination of simple circuits of lumped

parameters

In addition to the time behavior of the electric field we may take the

Fourier transform and determine its spectral behavior. This again requires
that we know the current waveform. Expressions based on our linear current

and damped exponential approximations are developed in Appendix B. These

may be used to identify the dominant frequency components excited by an ESD

signature

.

3.2 Magnetic Field

Magnetic fields can be a greater interference hazard than electric

fields because they penetrate low- impedance shields more effectively. They

also excite apertures and seams as do electric fields. They are best

received by low- impedance antennas, especially circuit loops. Thus,

avoiding loops poses a difficult design problem because loops are often

difficult to recognize. Boxleitner [5] discusses methods for minimizing

loop area by proper routing techniques

.

The magnetic field due to ESD radiation may be analyzed as was the

electric field. We find that (see eq. A23)

K

In the near-field region, H should behave according to

H(r,t) ~ a^ dl ]- ^ ~ i (near field), (6)

<i> ^TT R

pj2

while in the far field we find

"<''•" -%«R^i (far field). (7)

The near- field magnetic field depends directly on the ESD current shape as did the electric field. Thus, we would expect the highest fields to be

associated with the highest current levels. The far-field magnetic field is

dependent on the time derivative of the current, as was the case with the

electric field. Therefore, the low-voltage, fast rise-time sparks cause the

most interference to nearby equipment.

4. MEASURED ESD CUBIRENT AND ELECTRIC -FIELD WAVEFORMS

The measurement of ESD currents and the associated electric fields is a difficult task because of the very fast, broadband signals involved. The

time-domain instrumentation must respond to these signals with minimal

distortion and drift. The measurement system assembled here represents a best effort using equipment available.

4 . 1 Instrumentation

The experimental setup used to measure the ESD characteristics is shown

in figure 8. It consists of three separate parts: the source, the target,

and the measurement system.

8 1
The source was a commercially available ESD simulator indicated in fig.

8a and was made of lumped -constant circuit elements to simulate a human body

charged to a preset voltage level. The source is capable of generating

voltages from 100 V to 25 kV. It can be set to produce successive discrete

sparks at a chosen time interval.

One of the important targets we used in the experiment was provided by

the same manufacturer who supplied the ESD source. It consists of a brass

ball 8 mm in diameter (see fig. 8a), which is connected to a ground plane

through a parallel cluster of five low-value carbon resistors. It thus

provides a low-resistance path between the source and ground and a method of

determining the ESD spark current by measuring the voltage across the

resistors, since this voltage is proportional to the current through the

resistors. This voltage was measured through an extended center conductor

of a coaxial cable which was connected to the ball target through a matching

50-0 resistor. In fact, this is the only target with which we can measure

the ESD current.

The field measurement system consists of a newly designed broadband,

UHF (NBS 200-1), time-domain TEM horn antenna (see Appendix C) placed over a conductive ground plane, a digitizing oscilloscope, and a desktop computer.

The digitizing oscilloscope has two inputs enabling us to measure the

current and radiated electric field simultaneously, as indicated by two

different colors. The system was calibrated by measuring the impulse

response of the individual components (for example, pads, coaxial cable,

connectors, oscilloscope) and then deconvolving out these component

frequency responses to give the true current and field waveforms.

The antenna has a flat frequency response (± 3 dB) from 40 MHz to 1.2

GHz with minimum phase distortion, which makes it ideal for measuring the

broadband signals in the time domain. The ground plane is an indoor

facility which has a finite time window. This time window is estimated by

the indirect scattering fields interfering with the direct signal between

the source and the antenna. The shortest reflective path determines the

width of the time window. The facility used to make these measurements has

a direct path which is approximately three meters shorter than the smallest

reflection path, thus allowing roughly a 10 -ns window. It is therefore

possible to measure the spectral content of fields at 100 MHz and greater.

The oscilloscope used in this experiment has a sample rate of 40

megasamples per second, which is not sufficient to capture the high-speed

pulses generated by a single ESD spark. It was therefore necessary to

average successive ESD events to utilize the available bandwidth of 1 GHz.

The measurements were deemed repeatable enough to allow this averaging

without compromising the integrity of the signals. Measurements of ESD

current and electric field were also made with a microwave antenna (NBS 50-

2), which is flat (± 6 dB) with even broader frequency coverage (than the

UHF, NBS 200-1) from 50 MHz to 4.5 GHz and a digitizing oscilloscope with a bandwidth of 18 GHz in order to verify that there was a negligible spectral

content at frequencies beyond the range of the oscilloscope and UHF antenna

used in the original measurements. No discernable decrease in rise and fall

times was observed. Therefore, no further experiments were performed with

this system.
Basic functions of the desktop computer are for data acquisition,

digital deconvolution, and digital filtering.

The most likely cause of error in the voltage (thus current)

measurements (fig. 8a) is the assumption that the ball target consists of a pure resistance over the entire frequency range of interest up to 1 GHz. It

is possible, however, that the carbon resistors are somewhat reactive for

certain frequencies causing the target to act as a low-pass filter.

The most likely cause of error in the field measurements (fig. 8b) is

the lack of isolation of the ESD spark. As a result, the antenna receives

field compnents not only from the discharge to the ball target but also from

the ESD simulator. In fact, slight changes in the simulator positioning

caused drastic variations in the resulting measured electric field. For

this reason, every attempt was made to shield the simulator from the

measuring antenna by using absorbing material. With the absorbers in place,

the measured fields did not change significantly when the simulator was repositioned. The discharge to the ball target was then the primary

radiation source as desired.

4.2 Experimental Results

Experiments were performed for a number of different target

configurations. The targets used were (1) the low- impedance ball mounted in

a ground plane (fig. 8a), (2) direct sparking to the ground plane, (3) a vertical, square (0.91 m on a side), metal plate mounted above a ground

plane, (4) a metal chair insulated from the ground plane, and (5) a metal

waste basket. Targets (2) through (5) may simulate some practical office

environment. The low- impedance ball target allows us to capture both the

current waveform and the transient electric field simultaneously. In all

other cases only the electric field was measured. We also recorded the

relative humidity of the room, the spark gap, and the minimum voltage at

which we were able to generate a spark by the simulator. Typically, the gap was adjusted to create a preselected level for the minimum firing voltage.

Thus, we quote only the firing voltage in the data discussion. In our measurements, we use only a stationary gap because our main objective was to

vertify the theoretical model outlined in Section 3. Approaching a simulator (ESD source) toward a testing object with a variety of faster

speeds such as that which was studied recently [12-14] would have increased

the leading edge slope (rise time) of the spark current, and accordingly,

the radiated field. Thus, in this sense the experimental data presented in

this report are considered conservative.

Seven voltage levels up to 12 kV (1, 2, 4, 6, 8, 10, and 12 kV) were

set to excite the coaxial ball target. For higher voltages, the clean

window time on our indoor ground plane is not sufficient to obtain

meaningful fields data. The measurement arrangement is shown in figure 9.

The antenna was located at a distance of 1.5 m from the target at an angle

of 20 with respect to the ground plane. At this distance the antenna will

be most likely in the far-field range (distance no less than A/27r, where A is the wavelength) of the ESD source for frequencies above 30 MHz. As

mentioned before, the ESD simulator itself also radiated significantly. To

reduce this effect, absorber was placed between the simulator and the

antenna. The antenna was positioned to receive the vertical component of

10
the electric field. The horizontal component is expected to be small

because both the spark and target are vertically oriented [it can also be seen from the first term in (2)]. Measurements of the horizontal electric

field confirmed this.

The results are shown in figures 10 through 16. Each figure shows the

measured current, the measured vertical electric field, and the predicted

vertical electric field based on (2) and (A29) . For the 1-kV discharge, the

current reaches a peak amplitude of 7 A with a rise time of 700 ps. The

measured vertical electric field reaches a peak of more than 50 V/m in about

350 ps (approximately half the rise time of the current pulse) . As

expected from (4) , the electric field behaves very much as the derivative of

the current waveform. The predicted (theory) vertical electric field is

qualitatively similar to the measured data with two exceptions: first, the

peak amplitude is not as high as measured and second, the measured

undershoot is significantly greater. The first difference is not

unexpected. In order to apply the theoretical model we need to know the

length of the radiating dipole (di) . We simply took it to be the height of

the ball -target above the ground plane. However, the target consists not of

a single vertical conductor, but rather of an array of parallel resistors

which act somewhat like an array of lossy vertical dipoles. Thus, it is not

obvious how to specify an equivalent dipole length in this case. In

addition, the tip of the simulator is a small loop which may itself be

radiating and is also unaccounted for in the model. The second difference

(undershoot) is more problematic. It could be an antenna response artifact

but in that case the system deconvolution should take it out. It may also

be that the target is acting somewhat as a low-pass (capacitive) filter due

to the high-frequency response of the parallel resistors. The target

response is not accounted for in the deconvolution. The reason that this

suggests itself is the expected derivative behavior of the field response.

The negative slope of the current waveform in figure 10 is not fast enough

to cause the observed undershoot. If the target response is slowing the

leading and trailing edges, then both the peak amplitude and the undershoot

will be underestimated by our theoretical model, as we are seeing. A target

with ideal, flatter frequency response should give better agreement between

theory and experiment. Nonetheless, the theoretical model presented here

does predict well the basic electric -field behavior. The magnetic field may

also be computed by (A29) with the same approximated current based on the

measured result. In particular, under the ideal far- field condition, the

amplitude of the computed magnetic field in A/m differs approximately from

the electric field by 1207r. Because no broadband H- field sensor is

available for measuring the magnetic field to compare with the theoretical

result, only one computed magnetic field for the 4-kV case is presented in

figure 18

.

Figure 11 shows the results for a 2-kV spark. The current amplitude is on the order of 11 A while the measured peak electric field is approximately

75 V/m. Both are increased from the corresponding 1-kV values. Beyond

that, the same basic comments apply. Increasing the discharge voltage to 4

kV, as shown in figure 12, furthers this trend (26 A for current peak and

160 V/m for electric field peak). The peak field is now quite high. We

expect much higher fields nearer the spark as will be discussed later.

Raising the discharge voltage to 6 kV now reverses the growth trend. The

peak current has fallen to 21 A while the peak electric field is down

n
significantly to 60 V/m, as shovm in figure 13. For the 8-kV spark shown in

figure 14, the current amplitude remains about the same (approximately 24

A) , but the rise time of the waveform continues to slow. This reduces the

radiated electric field. Similar comments apply to figure 15 (the 10-kV

discharge) and to figure 16 (the 12-kV discharge) . For the latter case the

peak electric field is down to just 20 V/m. Thus, the field interference

threat appears to be associated primarily with lower-voltage sparks. Here,

the 4-kV case appears to radiate most strongly. The reason for this was discussed in Section 2 . As the spark gap increases and the discharge

voltage becomes higher, the channel formation slows and the channel

resistance increases. These tend to slow the discharge current. However,

the discharge now contains more energy due to the increased potential.

As the rise time of current waveforms becomes slower when the discharge

voltage is increasing, the theoretical predictions become better. In

figures 15 and 16, the deconvolution process of these slower pulses has

added some noise to the current measurements. This appears clearly in the

theoretical curves, but qualitatively, the agreement between theory and

measurement is good. This supports the supposition that it is the target

response to very fast currents that is causing the disagreement at the lower

discharge voltages

.

We were not able to place our broadband receiving antenna closer to the

ESD spark since the antenna calibration required that it be in the far- field

zone. We can, however, use the model to predict the discharge near field

according to (2) or (3). Figure 17 shows the vertical electric field for

the 4-kV (worst case) spark of figure 12. The distances chosen were 1.5m

as before, plus 1 m, 50 cm, 20 cm, and 10 cm. The near-field to far-field

transition frequencies for these distances are respectively 32, 48, 95, 239,

and 477 MHz. Thus, at 1.5m, most of the received spectra would be far

field while at 10 cm, a good portion is in the near field. The electric

field increases as the observation point is brought nearer until at 10 cm a peak amplitude of over 4 kV/m is encountered. The waveform shape also tends

toward the current profile (rather than the time derivative of the current

for the far-field case) as indicated by (3). The field levels at 10-cm, 20-

cm, and 50-cm distances in figure 17 are strictly theoretical and need to be

confirmed through measurements . But they suggest that the fields due to

low- level discharge voltages can be extremely high in the vicinity of the

spark.

The ESD electric-field spectrum for the 4-kV spark of figure 12 is

shown in figure 19. The primary spectral components are below 1 GHz which

is consistent with the findings of Honda and Ogura [1]. Above 3 GHz, the

spectrum is down to the noise of the system deconvolution. We have also

observed field pulses faster than the 4-kV case discussed here. They are difficult to capture and analyze because of limitations in our digitizing

oscilloscope. But we expect that the spectral content of some sparks may be

quite strong up to frequencies on the order of 5 GHz.

The preceding results were for discharges into a coaxial target which

allowed us to capture both the current and the field. However, as discussed, the target may be filtering the current somewhat and it certainly

represents an idealized victim. Figures 20 through 23 show measured data

for the vertical electric field created by a spark to a ground plane at

12
discharge voltages of 1, 2, 4, and 6 kV respectively. The antenna was positioned as in the ball- target measurements. The trend is similar to that

above; the peak field level grows from 80 V/m at 1 kV to 100 V/m at 2 kV and

then begins to fall to 75 V/m at 4 kV and 45 V/m at 6 kV. The maximum peak

is smaller than ball- target discharges. But in this case the radiating

dipole is significantly shorter. The largest gap was 1 . 2 mm for the 6-kV case as compared to the 39 -mm spark gap for the ball -target measurements.

Referring to (2) , we expect that reducing the dipole length di by an order

of magnitude would reduce the fields by a similar amount if the current

waveform remained the same. However, measured data suggest that the fields

are actually higher for the 1 and 2-kV cases (figs. 20 and 21 vs. figs. 10

and 11) and slightly reduced for the 4 and 6-kV cases (figs. 22 and 23 vs. figs. 12 and 13). The ground plane is a true low- impedance target with a very fast response (as opposed to the coaxial ball target necessary for

current measurements) and should not slow the current discharge. These

observations again imply that the actual current waveforms may be far faster

than we have been able to measure here with the ball target. Regardless,

the field levels for these discharges are considerable.

Perhaps more realistic than coaxial targets or ground planes are sparks

to large metal objects, such as might be encountered in a normal working

environment. As an example, we consider the indirect radiation from a large, square, vertical, metallic plate (0.915 m per side) as shown in

figure 24. The plate was excited by a discharge to the back side so that

direct radiation from both the spark and the simulator are shielded from the

antenna (again positioned 1.5 m away from the plate). A high- impedance

strap from the plate to the ground plane was also used to bleed off the

acuumulated static charge, but this should not contribute greatly to the

radiated field. The measured data for 5 and 7-kV sparks are shown in

figures 25 and 26. Rather than receiving a single pulse as in the previous

cases, the plate tends to resonate after being excited by the spark. The

fields are higher for the 5-kV spark, with the peak amplitude reaching 100

V/m. There is definitely some contamination of the data due to reflections

from walls and other scatterers after the 10-ns clean window time has been

exceeded. However, the contamination is not believed very significant due

to the highly directive property of the antenna. At least, the peak value

of 45 V/m at 14 ns is quite real. Even when the contamination is

substantial, the case may represent a more realistic laboratory environment.

The 7-kV spark plate radiation is not nearly as significant. Only the

shadow- side radiation was tested here. A thorough study by including the

antenna- side exictations , edge excitations, variations in plate size, and

other excitaion voltages would be of future interest.

Figure 27 shows the measurement configuration for radiation from a metal chair above the ground plane. The chair was insulated from the ground

plane by plastic tabs on its feet and was also provided a high- impedance

path to bleed off the static charge as for the plate. The antenna remains at

a distance of 1.5 m away from the spark point as before. The chair was excited by 3 and 6-kV sparks. The results are shown in figures 28 and 29.

Like the plate, the chair tends to resonate. For the 3-kV spark excitation

the field amplitude is quite substantial. Again, some of the data may be

contaminated after the 10-ns clean time. However, the basic indication is

that the indirect field radiation is significant and long lived. The 6-kV

spark excites a weaker field.

13
The measurement for a metal trash can in direct contact with the ground

plane is shown in figure 30. The antenna is also placed 1.5 m away from the

spark point. The received vertical electric field due to a 4-kV spark is

shown in figure 31. The initial spike within the system's clean time

exceeds 100 V/m, again demonstrating the threat of indirect radiated fields.

5. CONCLUDING REMARKS AND DISCUSSIONS

We have theoretically modeled the radiation from electrostatic

discharges by a simple elementary dipole above a ground plane. Radiated

fields were found to be dependent on two factors: the magnitude of the

transient current and its rise time. One factor may be more dominating than

the other, depending on whether the observation point is in the near- field

or far- field region of the ESD spark. When an analytical expression for the

ESD spark current is known, the electric and magnetic fields radiated from

the ESD can be computed exactly by the theoretical model. We also

implemented an experimental system with a newly designed broadband antenna

and a time-domain facility to measure both the current (for one case with a ball target) and radiated electric field waveforms produced by a stationary

ESD simulator. We approximated the measured current waveform with an analytical expression, computed the corresponding electric and magnetic

fields , and found that the theoretical electric field agreed well with the

measured result. The electric fields due to ESD events could be quite high

(although brief) , which are certainly capable of upsetting a nearby

equipment. The radiated magnetic field was not meausred because of non- existence of a broadband H- sensor.

If better experimental results are to be expected, several changes

could be made to the system. The better ball target with a constant

impedance over the entire frequency range of interest and having a low

profile and minimum radiation could be used to yield a more accurate

measured current. A better shield for the ESD simulator is also needed so that the source will not interfere with the measurements

.

It would be interesting to perform field measurements at positions

closer to the discharge to see if the transition from di/dt to i , in

addition to the change in peak amplitude, may also be observed. More

accurate measurements could be realized by using an outdoor ground screen to

obtain a much larger time window, thereby including the low- frequency

content of the radiated field.

Measurements of magnetic fields constitute another interesting research

topic, particularly in view of the fact that most shields are ineffective

against low- impedance fields. Until a broadband H- antenna becomes a reality, we can only rely on theoretical predictions and estimation derived

from the measured electric fields.

14
6. ACKNOWLEDGMENTS

We would like to thank Peter Richman, President of KeyTek Instrument

Corp., who inspired us to set up this modest study and convinced us that the

results would benefit the computer industry. Mr. Richman also critically

reviewed this manuscript. We would also like to express our appreciation to our Center Director, J. C. French, for his support and encouragement. The

enthusiastic assistance by our technician, H. W. Medley, during the course

of measurements is also acknowledged.

7. REFERENCES

[1] Honda, M. ; Ogura , Y. Electrostatic spark discharges - three critical

factors. Proc. EOS/ESD Symp . , EOS-7, 149-154, 1985; Minneapolis, MN.

[2] Richman, P. ESD simulation - configuring a full -performance

facility. IEEE Int. Symp. on EMC; 381-385, Aug. 1983; Crystal City,

VA.

[3] Bhar, T. B. Electrostatic discharge failure mechanisms of

semiconductor devices. ITEM, 276-282, 1986.

[4] Byrne, W. W. The meaning of electrostatic discharge (ESD) in

relation to the human body characteristics and electronic equipment.

IEEE Int. Symp. on EMC; 369-380, Aug. 1983; Washington, D. C.

[5] Boxleitner, W. Electrostatic discharge. Key Tronic Corp. Doc. No.

36-2464, 1986.

[6] Woods, M. H. ; Gear, G. A new electrostatic discharge failure mode.

IEEE Trans. Electron Devices, ED-26, 16-21; Jan. 1979.

[7] Penning, F. M. Electrical Discharges in Gases. New York, NY:

McMillan Co. ; 1957.

[8] Rhoades , W. T. Achieving ESD equipment protection with emission

controls. IEEE Int. Symp. on EMC; 232-237, Aug. 1985; Wakefield, MA.

[9] lEC Pub 801-2: Electrostatic Discharge for Industrial Process

Control

.

[10] Richman, P; Tasker, A. ESD Testing: the interface between simulator

and equipment under test. 6th Int. Electromagn. Compat . Symp. Rec.;

25-30, March 1985; Zurich, Switzerland.

[11] Richman, P. Classification of ESD hand/metal current waves versus

approach speed, voltage, electrode geometry, and humidity. IEEE Int.

Symp. on EMC; 451-460, Sept. 1986; San Diego, CA.

[12] Daout , B.; Ryser, H. Fast discharge mode in ESD-testing. 6th Symp.

and Tech. Exhibition on EMC; 41-46, March, 1985; Zurich, Switzerland.

15
13] Daout, B; Ryser, H.; Germond, A.; Zweiacker, P.; The correlation of

rising slope and speed of approach in ESD tests. 7th Symp . and Tech.

Exhibition on EMC; 461-466, March, 1987; Zurich, Switzerland.

14] Daout, B; Ryser, H.; The reproducibility of the rising slope in ESD

testing. IEEE Symp. on EMC; 467-474, Sept., 1986; San Diego, CA.

15] Richman, P. Computer modeling the effects of oscilloscope bandwidth

on ESD waveforms, including arc oscillations. IEEE Int. Symp. on

EMC; 238-245, Aug. 1985; Wakefield, MA.

16] Le Vine, D. M. ; Meneghini , R. Electromagnetic fields radiated from a lightning return stroke: application of an exact solution to

Maxwell's equations. J. Geophys . Res., 83, no. C5 ; 2377-2384, May

1978.

17] Lawton, R. A.; Ondrejka, A. R. Antennas and the associated time

domain range for the measurement of impulsive fields. NBS Tech Note

1008, Nov., 1978; Boulder, CO.

16
APPENDIX A: Time -Dependent Fields Due to a Dlpole Source

The fields due to a time-dependent radiation source may be found from the

potentials <I>(r,t) and A(r,t) which are given by

^r ^^ 1 f ?(•"' ,t-R/c) , , $(r,t) =

J.— / ^ 5 dv', and

(A1)

A/- .^ ^0 r J(^' ,t-R/c)^ , ^^^'"^ = H^ ^ -R ^" •

where r is the observation point, r' is the source point, R = |r - r' | is the

separation between the two, p is the charge distribution, J is the current

distribution, c is the speed of light, e^^ is the free-space permittivity, and

]x is the free-space permeability. The fields are related to the potentials

according to

E(r,t) = -V$(r,t) - |^A(r,t), and

at

H(r,t) = - VxA(r,t).

^0

The potentials satisfy the condition

V-A(r,t) + ^

It'l'^^'t) = 0,

c

which implies that

t/

(A2)

<I)(r,t) = -c^ V-A(r,t')dt' . (A3)

Thus we need only solve for A(r,t).

Consider a time-dependent dipole source above a perfect ground as shown in

figure 7. We impose a cylindrical coordinate system and note that the system

is invariant in ((). The fields for z ^ will be due to the dipole source and

its image. The current distribution J reduces to an elemental line current i oriented along the z-axis, the volume integrals simply introduce the line

length dS,, and (A1) reduces to

A(r,t) =

"l A.(r,t), where

(Ai4)

17
u i(z' ,t-R ./c)

A.(r,t) = a dl ^— . J z 4iT R

In (AM) j = 1 represents the actual dipole and j=2 its image. We may now solve

for $(r,t) . We find that

y 2 i(z',t-R /c)

V.A(r.t) = dd ^ l^[ R—^^ )• (A5)

j = 1 J

If we let u = t - R./c, and let the argument of i be implicit, then

|_ (i

) = h:2 {R. |i|H - i _J|. . (A6) 9z R. J

^ J 3u 9z dz '

Note that

3i 9i

3u 9t

1 9R.

9u 1 J

(A7)

9z c 9z

•

Thus

i(z',t-R /c) 9R R I- [ 5 ^ ] = - R:^ ^^ {i - -^ ^], (A8)

9z ^ R . ^ J 9z ^ c 9t

and

M 2 _ 9R . ^- ::> V-Mr.t) .-«^^z^r:2_J |i . J|il. (A9)

It follows that

c^y 2 9R . t R

We may now solve for the field components.

We will begin with H(r,t). Substituting (A4) into (A2) yields

V«A(r,t) . 61 "t^ Z V«(a^ i ) - ^ £ dl ^ £ |

(i ). (AH)

The p-derivative is analogous to the z-derivative found above. Thus,

1
U 2 8R. R VxA(r,t) = a dil -^ Z r/ ^-^ (i + -^ ^M . (A12)

(}) 47T ._ J dp C dt'

Thus we have

p R S(r.t) = a^dJ I^ ^Z^R-2 £^ (i .J ii). (A,3)

In order to find E(r,t) we need to evaluate V$, where

V$(r,t) = a ^ <J)(r,t) + a | $(r,t). (AU)

p dp Z dZ

Taking the proper derivatives yields

^P J ^^ ° ^^ R^ R^ cr2 A.^^

J J J J (A15)

- „9R.t R... . _,-,,2t

3z J 3z Q c 3t p3 p2 Q

J J

1 r^ _ 3(z+z')^^. _ 1 (z+z')^3i

cr2

^ r2

' e^R. r29t'

J J J J

where + designates the source (-) and its image (+). Thus we find that (note

2 that c y^ = I/Eq)

VMr.t)=-ifP z^M^I^-^i ^4-lfi "^^^0 j = l r2 r3 cr2 c^R.St

J J J J (A16)

, - dJl I \. 3(z+z' )^, ^

1 r. 3(z^2' )^. 1 (z + z')^8i,

J J J J J J where

t

I = I(z',t-R./e) = /i(t'-R./c)dt' . J Q J

Next we calculate

3A(r,t) ; ^„ — ^0 ^ 1 3i - .. 1 ^ 1 3i ,..„. r- = a dJl -J— E 5" -^ = a dil j— Z -^ x— . (A17)

dt z 4tt . , R. dt z ^Tr£_ . , 2^ dt

j = 1 J j = l c R

19
Combining results we find that

E(r t) = a ^ E |P ^"^"'^ [3 ^ , _i_. , _L ill l Oj=1j J R. cR. cR.

J J J (A18)

J J J J J

For a discharge to a conductor the spark will occur very close to the

+ conductor surface, that is z' = . If we impose this condition we find that

R. = R = (z + p ] and that

-,- ^, - di pz ,3 ^ 3 . 1 3ii E(r,t) = a -— ^ — I + —-1 + -— 3-

P 2^^0 r2 r3 cr2 c^r

9^

2 2 6i f r 3z ,

-1 /- 1 .^ 1 . ( rZ , 1 1 3i 1

(A19) -,- ^v - dil p r1 . 1 3ii

H(r,t) = a :r- ^ - 1 + — — .

(j) 2-iT R '2 cR dt

K

As a check note that in the far field the 1 /R terms should dominate. If we convert to spherical coordinates we find that

^,- ^v - dS, sine 3i

e 2lT£_ ^r^ dt

c R (A20)

dil sine 3i

2^ cR 3t'

H(r,t) - a

Thus the wave impedance tends toward n^, as expected.

Although, the above expressions have the correct radiation behavior, there

is difficulty with this model in the very near field. Consider a static

electric dipole P of length dil along the z-axis,

P = a dilQ, (A21 ) z

where Q is the total charge on either pole. Note that Q is a measure of the

net current either leaving or entering the pole,

t Q = ± / i(t' )dt' , (A22)

20
± depending on which pole is being considered. Thus, Q is related to I. The

3 appearance of a 1/R , static electric-dipole moment contribution is a result of

2 the assumption that the dipole is short (dSL/R << 1, k (dil) /R << 1). If

instead we had considered a linear antenna with appreciable length and assumed

the current to be a travelling wave, then the static I-dependent dipole moment

term does not arise [16]. Although a dipole in free space can hold a static

charge, our ESD system will not. The charge will actually decay rapidly due to

the relatively low relaxation time e/o on a good conductor. Thus, we will

neglect the I terms in our model. The field expressions therefore reduce to

^r^ ^^ ' ^0 ^0 pz r3 . 1 3ii E(r,t) = a dil :r- -^ Pr 1 + — ^Tp Z-n ^2 '2 cR 9t

n n ^a^«^l[2|'-,]i5iM^J-l]isil, and (A23)

R R R

r, r~ . \ ~ ,„1 Pfl . 1 3ii H(r,t) .^Al-l\-..--\.

R

Equation (A23) allows us to consider the fields due to a short dipole near

a ground plane. We wish to model either direct field penetration into the

victim in which case z = 0, or the effect of radiated fields on nearby objects,

for example due to a discharge to a metal cart. For the z = case (direct

victim penetration), R = p, r depends only on p,

^0 (1 . 1 9i E(p,t) = - i dSl -^ {^ i + ;^ fi}, and

z 27r 2 cp dt

P

S(r,t) = a dJi ^ |1- i . i-|i

d)Y 2tt 2 Cp dt

p

K

(A2i4)

Thus, on the ground screen in the transitional near field, not too close to the

dipole as per our assumptions, the wave impedance retains the far-field value

of 120iT Q.

In general the time behavior of an actual ESD current will be quite

erratic; thus, we do not expect to be able to model it by a simple analytic

function. One approach is to approximate the current by a series of linear

functions, each valid over a small interval. By choosing the number of

intervals to be large we should be able to generate an accurate model. In

particular, we will use a set of ramp functions

N

I n=0

i(0^,t) = i^(t), (A25)

where

i (t) = for t S t , n n

21
At

i (t) = a^ —

n n A for t < t < t , , andn n+1 (A26)

i (t) = a n n for t , S t n+1

where At see that

t - t , and A = t , - t , n n n+1 n With this linear approximation we

S + ^3

-|^i(0 ,t-R/c) = I f,i^(t-R/c)

at ^ dt n n=0

(A27)

Evaluating (A23) yields

^^i = 8t n for t-R/c S t , n

3 . ^ _

3t^n A

n

n for t S t-R/c St , , and

n n+1 (A28)

at^n = ° for t , < t-R/c.

n+1

Thus, for this approximation we have a discontinuous derivative. If we

substitute these into the field expressions (A23) we find the following

approximate forms

E(r,t) = dS, ^la

^ Z E + a E E } , and

2tt ' p ^2 ^ - pn z „ zn"

R n=0

.„ N

H(r,t) = a fjf I H

<}) 2iT R ^^Q (t)n

n=0

(A29)

where

E = pn

n 1 Ri E = -^ ^ |3At + -}

pn^ A „2 ' n c' n R

E -a 2^

pn n ?

for t - R/C < t , n

for t < t-R/c S t n

for t , < t-R/c,

n+1

n+1 '

E = zn for t-R/c < t , n (A30)

E = -H 1^ {(1| - i]At +[^-i)^} fort < t-R/c < t ,. zn A p,2 ' ^^2 ^ n *-^2 ^c' n n+1

n R R R

E = a i. [%- - 1], zn n ^2 \2 for t , < t-R/c,

n+1

H =

(j)n for t-R/c S t , n

22
a H, = T^{-^ At + —

}

for t < t-R/c < t , , and

An A ^^2 n cR

n n+1 n R

H, = a ^

for t ,<t-R/c.

4)n n ^2 n+1

K

These may be readily found via computer once a linear spline approximation to a current waveform is given.

An alternative to a direct point-matching approach such as outlined above,

is to fit a sequence of damped exponentials to the current waveform based on Prony's method. Let

N -b t i(t) = E a e " (A31

)

n=1 "

for tSO and i(t) = for t<0. Continuity thus implies that the summation of

the a be zero. The derivatives of this form are readily found and the result

n

•' will be continuous. The derivative will not be continuous at t = unless

further conditions are imposed. Inserting the exponential fit (A31 ) into the

field expressions (A23) yields

T1-. N -b t _ . i(r.t) = i dil ^£| Z a e " [\ - 1^ bj

P ^TT ^2 ^^^ n ^^2 cR n^

n=

1

n R R

^ n=1 R

23
APPENDIX B: Spectrvim of ESD Dipole Radiation Model

If the field components are determined in the time domain, the spectrum

may be found by taking the Fourier transform according to

00 F(r,u)) = / F(r,t)e'^'^^dt. (B1 )

where F represents one of the fields. Substituting in the field expressions

for E and H (eq. A23) leads to two integrals that need to be evaluated:

/ i(t) e'-^'^^dt, and

(B2)

, 9i(t) ^-ja)t

If the second integral is integrated by parts we find that

/lil^e-J^'dt = i(t)e-J'^^

d t ^° + JO) ; i(t) e -^"^^dt. (B3)

For a pulse of finite duration, i(t) = at both the endpoints and (83) reduces

to

/

^^

e'J'^'dt = jo) ; i(t)e"J'^'dt. (BM)

t

-00 —00

Thus, we need only consider this single integral in order to evaluate (B1).

We will again represent the current by a sum of linear functions (A25) as detailed in Appendix A. The pulse is zero outside the interval t e (0,t ) where we will evaluate the integral in terms of retarded time (t-R/c -> t).

Thus we have

^N+1 _ N ^N+1

/ i(t) e'J'^^dt = I ; i (t) e'-^'^^dt

n=0 "

(B5)

N a ^n+1 . ^ ^N+1 , . = I {-p. S (t-t ) e'J'^^dt -. a ; e'J'^^dt}.

n=0^ t

-^ " t n n

Evaluating the various integrals and combining results yields

24
Vl . , N a "J'^^n -ja)A "^'"^+1 N

/ i(t) e'J'^^dt = Z -^ ^-^ je '' - 1 1 + j ^ Z a . (B6)

n=0

^ 0)2 ^ n=0

"

For a pulse of finite duration, the a summation is zero. For convenience, let

S(u») denote the remaining summation in (B6); that is

N a "J'^^n -j(oA

S(a)) = Z ^ ^-j— {e ^ - l}. (B7)

n=0 n 0)

The field component spectra are found to be

R n

'h^''^ n^^- 1)-^ - (4 - 0^15(03). and (B8)

R R R

H(r-..) -i. #1 li. * i|ls(a,).

<f> 2Tr R '2 cR

n

We may also consider the damped exponential form for the current given by

(A31). In this case the equivalent expression to (B5) is

/ i(t) e •J'^^dt = Z a / e " dt

n=0 "

(B9)

N

1 = Z a^ .

' = T(w).

n=0 " t)^ ^ JO)

The spectra of the E and H fields will be again given by (B8) with T ( oj

)

substituted for SCoj).

25
APPENDIX C: Time-Domain Antennas for Measuring Impulsive Electromagnetic Fields

Since the purpose of our experiment was to study the temporal

characteristics of the electromagnetic fields emitted from ESD events, it was important to choose a broadband receiving antenna that had the greatest

possible fidelity. Some antennas produced severe distortion in the time-domain

waveform because of their poor phase response even though they did have flat

characteristics in the frequency domain. The antenna used for the major part

of the work is called UHF antenna (NBS 200-1), which is basically a truncated

TEM horn as shown in figure 32. Two elements of this antenna form a parallelplate transmission line, whose impedance depends on the ratio of the distance

between the elements to their width. Since this ratio is constant, the antenna

impedance remains 200 Q within its designed operating frequency range (from 40

MHz to 1.2 GHz). At the antenna feed point, there is a pulse transformer, which

terminates, on one side, the elements in 200 Q and produces a 50 output on

the other side. The details of this pulse transformer are given in figure 33.

It is this pulse transformer which maintains the correct impedance up to 1.2

GHz. Consequently, the standing waves of the antenna are negligibly small, and

the frequency response is flat within ± 3 dB in the designed frequency range of

40 MHz to 1.2 GHz with usable response even down to 20 MHz, as shown in figure

34. The time -domain response of this antenna to the transmitting pulse shown

in figure 35 is presented in figure 36. This antenna has a risetime response

of about 300 ps

.

Another modified version called the microwave antenna (NBS 50-2) also has

excellent fidelity and flat frequency response with a broader designed

operating frequncy range (from 50 MHz to 4.5 GHz). The antenna elements are designed to have an impedance of only 100 Q, each element of the antenna being

50 Q with respect to a ground plane located in the middle of the antenna, as shown in figure 37. Each element is brought out on a separate coaxial line.

The previously used pulse transformer is now replaced with a broadband balun

(see fig. 38). The balun accepts two input signals which are 180 degrees out

of phase with each other and combines them in a broadband resistive power

combiner (splitter in the figure) providing a single 50 Q output. Details of

this antenna are available in [17]. This antenna was used only for that part

of the experiment where we were searching potential spectra which may fall

outside of the UHF antenna frequency range, as mentioned in Section. 4.1.

26
v////////. v////////y V//////A

b

v/y/y////

d

Figure 1. Diagrams showing the development of a spark channel, based

on cloud chamber observations: (a) electron avalanche, (b)

channel growth toward anode , (c) channel growth toward

both anode and cathode, and (d) conductive bridge [7].

27
R

AAAr- /

DISCHARGE

TIP

RETURN

\

GROUND PLANE

Figure 2. Conventional single RC circuit model for human electrostatic

discharge [9].

60-300

PF

.05 -.2

777

Figure 3. The dual RLC circuit model for human electrostatic discharge

incorporating separate, parallel paths for body and hand

discharges [11].

28
Figure 4. Computer simulation of an BSD current based on the dual

RLC circuit (fig. 3). The circuit parameters used are

C^=7.5 pF, R^=200 ti, L^=0.1 uH , Cg=100 pF, Rg=500 Q, Lg=1.7

yH, and 5 -kV initial charge fll].

29
8 12 16

t (ns)

(a) 4 GHz/0. 09 ns Tp = 0.7 ns

4 8 12 16

t (ns)

(b) 1 GHz/0.35 ns Tp = 0.7 ns

8 12 16

t (ns)

(c) 400 MHz/0.9 ns Tp = 0.9 ns

18 4 8 12 16

t (ns)

(d) 100 MHz/3.5 ns Tp = 1.5 ns

t (ns)

(e) 75 MHz/4.7 ns Tp = 1.7 ns

4 8 t (ns)

(f) 60 MHz/5.8 ns Tp = 1.9 ns

Figure 5. Computer solutions for a dual RLC-circuit model using

different single-pole simulated oscilloscope bandwidths

The initial applied voltage is 5 kV [15].

30
V„ IkV Vo 3kV

-iODBI 1 0094Z

iii.t :hiK:. r1 t

200WZ/

Rinif'ipiiijifiiir^if mLiu:!,"

h —r.' •

• ^'1001/ 200B a-J..8

1• -

.

IMT fai i

Vo 6kV V„ 10 kV

Vo 15 kV

{^1 gH^B^H

-IODBI I 00li«Z

,

200W2/

Jill iii\\, !;.

* ^

. . - ... ••. ijwrm

Ml

IBjji£

Vo 20 kV

Figure 6. The radiation spectrum at 2.0 m from an ESD source for

various applied voltages [1].

31
r = (p ,(}),z)

Dipole z' I

Image Dipole

Figure 7. A dipole above a perfect ground plane and its image,

32
ESD

simulator

Ground Plane Ball O

rarget i

Digitizing

Oscilloscope

10 dB

Pad RG 55B Coax

Cable 5.5 m

10 dB

Pad

(a) For measuring current waveform.

Reals tlvely-Terralna ted Tapered-Horn

Antenna

Digitizing

Oscilloscope

10 dB Pad

RC 55B Coax

Cable ^.3 m

(b) For measuring electric field,

Figure 8. Measurement system schematics,

33
Figure 9. Coaxial ball target measurement configuration (Shield

material was used to prevent radiations of the ESD

simulator from interfering with the receiving system).

34
4-> C

S-s30

25

20

15

10

-5

-10

-I r

1 r

5

_l I L. Time (ns)

IKV SPRRK

5 1

•/< Hum.

2 Ohm TRRGET"

10 15

-a

•r—U

O

<U LU

200

150

"T r r -\ 1 r

100t50 -

-50h-

- 100

Expe r i men t

IKV SPRRK

5 1 *. hlum . 2 Ohm TRRGET

Time (ns)

Figure 10. Coaxial ball target current and vertical electric field

for a 1-kV discharge.

35
+-> c

cu

Ss- o

30

25

1 1 < 1 ' ' ' 1 2KV SPARK

5 \y. Hum.

2 Ohm TRRGET"

20 - -

15 - -

10

/^~~-\ -

5

1 \^..__________ 1

-5 -

—

10 . 1 1 . 1 1 1 1 . 1 1 1 ... 1 1 Time (ns)

10 15

200

150

T

1 1 r

-o

03O

+-> O

LU

1001-

50

-501-

-100

2KV SPHRK

5 1*^ Hum.

2 Ohm TRRGtIT

Time (ns)

Figure 11. Coaxial ball target current and vertical electric field

for a 2-kV discharge.

36
c

sSC.I

30 1 1 1 1 1 1 1 I

1

1 II T- 4KV SPRRK

5 0>: Hum.

kfb /

~\ 2 Ohm TARGET"

20 / \ -

15 / \ -

10 / \

5 - /

^-^

-5

10

J

i .1 _ .L ..

1 , . . . Time (ns)

10 15

o

•r— M-U

•I

S-

-)-> u

O)

200 1

150 -

100 -

50 -

-50 -

-100 .i , I I 1 J- Time (ns)

Figure 12. Coaxial ball target current and vertical electric field

for a 4-kV discharge.

37
4->C

O)

Ss- o

30

25

15

-5

10

'~l'

Time (ns)

T 1 r- GKV SPRRK

^SX Hum.

2 Ohm TARGET"

10 15

a

O)

u

-MO

O)

200 [ 1

1 11 II ' GKV' SPRRK

4 9:: Hum.

150 -

2 Ohm TnRGET_

100 - -

1

1 Ex pe r 1 men t 50 -

=:^^y

^V, \^ Theory ^^::;=^==~"===^3

-50 - ^^^ -

100 1 1

1 . . . . 1 . . . . 10 15

Time (ns)

Figure 13. Coaxial ball target current and vertical electric field

for a 6-kV discharge.

38
O)

s- o

30

-5 -

-10

-1 1 1 r -r r r

J 1 I Time (ns)

BKV SPRRK

^QX Hum.

2 Ohm TRRGET'

-J I I u 10 15

-a^—

^-u

•r—O

(D UJ

200

150 -

100

-100

E X p e r 1 me n t

-1 I I u _i I I L- Time (ns)

8KV SPRRK

4 8:c Hum.

2 Ohm THRGET

_L 1 L. J 1 10 15

Figure 14. Coaxial ball target current and vertical electric field

for a 8-kV discharge.

39
+->

Ss- o

30 1 1

1

25 -

20 -

15 -

10 -

5 - /^

Q

-5 -

-10 1 1

T3

o

OJ

200

150

100

50 -

-50

- 1 00

-J I u

Time (ns)

10KV SPARK

5 3 ^i Hu m . 2 Ohm THRGET"

-I 1 1 i_ 10 15

lOKV SPF^RK

5 3/. h^ u m . 2 Ohm TRRGET

Expe r I men t

I L I I L^ X I I 1 I I I i_ 5 10 15

Time (ns)

Figure 15. Coaxial ball target current and vertical electric field

for a 10-kV discharge.

40
O)

=3

C_)

30 J— . -, 1 -T- I I I I 'I ' " '' ' 12KV SPRRK

S5y, Hum.

2b 2 Ohm TRRGET"

20

^

^^-\_. "

15 /^^'^ ^^^

10 /^

5 '^^^^

-b

10 1 1 1 1 1 1 1 1 I I 1 1 1 1 Time (ns)

10 15

200

150

^ 100

-a^ 50 u

-50

-100

-1 1 1 r

L'xper 1 ment

12KV SSPRRK

5 5*. Hum.

2 Ohm TRRGET

I 1 I Time (ns)

10

Th eo r y

J I \- 15

Figure 16. Coaxial ball target current and vertical electric field

for a 12-kV discharge,

41
•r—

+-> o

OJ

5000

4000 -

3000

2000

1000

1000

-1 1 1 r

1 O cm

-I I I u Time (ns)

10 15

igu-e 17. Predicted vertical electric field for the 4-kV discharge of

fiq. 12 as a function of distance to the observation point.

42
r—

dj

•rTMO

M

CUc

en

0. 4

0.3

0. 2

0. 1

0. 1

(a)

J I L J I 1 I J 1 1 U 10 15

Time (ns)

20

15

10 -

E

-o

'r— 4-O

+^ 5

O)E

cn

-5

1 1 1 r T 1 1 r T 1 1 r

J 1 I L J I I L J 1 I L 10

Time (ns)

15

Figure 18, Predicted magnetic field for the 4-KV discharge case:

(a) with the receiving antenna at 1.5 m from the spark, and

(b) as a function of the distance to the observation point.

43
160

140

120;

1001-

> 80 -

CQ

O) G0 -

13

.^

J. ^

1. _._|_.^_j.- ^ I

CLE

40 -

20

0. I Frequency (GHz)

Figure 19. Spectral content for the coaxial ball target 4-KV discharge of

fig. 12.

44
o

O) <^u

S4-> U

O) LU

200

150

100

50 -

0-

-50

-100

I

1 . 1—

IKV SPRRK

50Ji Hum.

-I I I u -I I I L. Time (ns)

10 15

Figure 20- Vertical electric field for a 1-kV spark to a ground plane,

45
o

•I—s-o

200 1 1 1 1 1 1 1 1 1 1 1 r 1

1 2KV SPRRK

5Qy. Hum.

150 — -

100 A

-

50

-50

j\ .

- ^ ^ -

100 1. .. .. I . . 1 1 1 .1 1.1. I... —L 1 J 1 — .1 10

Time (ns)

15

Figure 21. Vertical electric field for a 2-kV spark to a ground plane,

46
a

"r— M-O•^" S-

•t-> o

O) UJ

200 1 1 1 1 . 1 1 1 1 1 1 1 1 4KV SPHRK

50>i Hum.

150 — -

100 - -

50

-50

- A

-

- \y^ -

-100 .ill 1 1 1 I 1 1 1 1 Time (ns)

10 15

Figure 22 • Vertical electric field for a 4-kV spark to a ground plane,

47
-o

O)

o

S-u

0)

200 1 . 1 1 1 1 1 1 1 1 1 1 1 6KV SPHRK

50>i Hum.

150 - -

100 - -

50 - /-X - X^_/^ ^

-50 - -

100 1 11 1 1 1 1 1 1 1 1 1 1 1 Time (ns)

10 15

Fiqure 23- Vertical electric field for a 6-kV spark to a ground plane,

48
Figure 24. Measurement configuration for indirect radiation from a vertical square metal plate.

49
150

100

-1 r —T r

• —r -J- 5KV

-T 1 T T SPRRK

irJTO 9 1 .5cm

SQUHRE PLRTE

•r— M-U

S_ 4JO

-100 -

-150 -I I I L -J 1 I U. J 1 1_. ' ' I 1- 10 20 30 40 50

Time (ns)

Figure 25. Vertical electric field radiated by a vertical square metal

plate excited by a S-kV spark.

50
150

100

^-^ 50

-a

iTu

•I

s-

+-> u

OJ |— -50

-100

-150

"T I T T 1 1 1

1 1 1 r -T 1 1 11 1 1 1 7KV SPRRK

IMTO 9 1 . 5cm

SQURRE PLRTE

.1 L I I I I I I I L 1_ -J I I L 1 I I I 1_ 10 20 30

Time (ns)

40 50

Figure 26. Vertical electric field radiated by a vertical square metal

plate excited by a 7-kV spark.

51
Figure 27. Measurement configuration for radiation by a metal chair

above a ground plane.

52
150

100

T r —I

1—11 r—I V r

-1 r—-

T- 3KV )PRRK

INTO rJBS

OFFICE CHHIR

-o%•I— M-O

•p-S- +Jo

cu

100

-150

10

._! I I 1 i__L.-.

20 30

Time (ns)

40 50

Figure 28. Vertical electric field radiated by a metal chair

above a ground plane excited by a 3-kV spark.

53
-o

'a;

s-o

(U

150 1—1

1 1 1 1

1 1 1—1 1 1

\

1 1—1

1 1 1 1 1 1

1 BKV SPRRK

IMTO NBS

100 OFFICE CHRIR_

50 -

\ —

^V^^^^^^^^

-50 -

100 -

150 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 10 20

Time (ns)

30 40 50

Figure 29. Vertical electric field radiated by a metal chair

above a ground plane excited by a 6-kV spark.

54
Figure 30. Measurement configuration for radiation by a metal trash

can on a ground plane.

55
-a

U

150

100 -

50 -

-50 -

-100

-150

T

1

1 1 1 4KV SPRRK

INTO NBS

TRHSH CRN

-I I I I- 10 20

Time (ns)

30 ^Q 50

Figure 31. Vertical electric field radiated by a metal

trash can excited by a 4-kV spark.
Note:

Two, single-sided, GIO copper-clad

glass epoxy PC boards, separated

with a wedge of styroform extruded

polystyrene insulation (copper side

down)

.

Double-sided, GIO copper clad glass

epoxy PC board, with details shown

in fig. 33.

Figure 32. The UHF antenna (NBS 200-1) for measuring the broadband

electric fields: dimensions in the figure are in

centimeters.

57
17.73

NOTE 1

Note:

1. SMA connector for 0.36 cm semirigid cable.

2. 0.36 cm semi-rigid cable wrapped

with alternating ferrite cores of

Q1,Q2, and Q3 material types with

typical dimensions of 0.97 cm outer diameter, 0.74 cm inner

diameter, and 0.33 cm thickness.

3. PC board fits into 15.24 cm slot

in foam wedge.

4. Single side copper clad antenna

piece

5.08 H H

Detail A

0.32

/

GNO

FRONT

GNO

Figure 33. Construction details of the pulse transformer in the

NBS 200-1 antenna (all dimensions in centimeters).

58
ow

rju (Um

4-1 <c 3 o O

x: j= o

CMmCO2:

(U x: • +-> -M

CD

<4- J:^U

fO cu •l-> toc X

O) Q.-a

1/1 >,

QJ 2sQJ >.-c

-M c

OJ +-> 13 =3 cr

OJ x:

S- -M M- • r-2

OJ -C "O

-(-> c

fO

<4- -C

-t-> e •1

2

00

•1

fc

s- e

fC E

Q. O) E -MC

C_) fO «

rr>

0)

s-3

en o

in o O

O

fO CM (ap) joqoBj euua^uy

59
Time (ns)

Figure 35. Normalized amplitude of the transmitting pulse,

1 —I 1 1

1

1 1

41

+ .8

o13

+->

CLE

(T3 DO)N

+.e

+ .4

^*\k

E

S-o

•

-.2

-.4

-.G

3 12.^ 2 S.'fl 37.^ 55.5 -BIT^ 75.3 -TTTt- 99.

-.8

Time (ns)

Figure 36. Response of the NBS 200-1 antenna to the

transmitting pulse shown in fig. 35.

60
01

.-

— -— \ '-^\ ^. ^w \ \ \\ V\ \\\

\. \

\\ ^

.\\, \\ \ \ \\\\\\ \ ^,N \ \ \ \\ \^\\^^VK \\\\ \ \ \x\So\\vf \^^' \\ \\ \

\^

\>1\ \\ V^ \\ N\ \^\ ^ \<\\^ \ \\ \. \ >-^\ \\ \ / / c \- o / / o / / / / / \^ / / / / / ///\ / / / / / / 1/ A / / / / / y / ^y / / / / / / / / \ / / / / / / ^ A / / / / /y/ / / \/ / / / / / / / A / / / / / / / ) • / / / / / / / / \- / 1^ / / IV / / /A / / / J / / / A' / / / / / / / \ / / / y1/ / / / / \ / / 7 / / / / A ' / / / / / / / \/ / h / / / / \ • / / / / / / / / / / / / / / / u

t-l

(LI

X D.

nj Q.o

01o. < 0* O &0

i-> c

CO •O -H

OJu

1-

H

<u o -^ ^ 1-( o o

CO (b u

OJ 01 > -u

(0 (0 oU QO u c

•H tAuo

(0 Xi<Bao

Cb

0)c

0)u

>«

4J

CO>>

iHO

OJoLn

CO

TOE

c:

»aE

S-O

x:>5o

S-o

O)

on

13

C7I

k e rj o ^

61
10.0 cm.

B.nl.inced Non-lnvertf(J l/ll ^^

10.5 cm

Ferrlte

Beads

1 ea. Ql and Q3

0.5 rm Thick \ Aluminum

3 mm Scml-rlgld

Coax

Outer Conductors

Soldered

.Space Killed Wltli Microwave Absorber

6 dn Power Splitter

R.I lanced Inverted 1/(J Precision

Type N Connector

Inverting T

Splice

.4=^

Unbalanced I/O

. Precision Type N Connector

.15.5 cm

Figure 38. The broadband balun used for the antenna in fig. 37,

62
NBS-n4A (REV. 2-BC) U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

NBS/TN-1314

2. Performing Organ. Report No. 3. Publication Date

February 1988

4. TITLE AND SUBTITLE

ELECTROMAGNETIC FIELDS RADIATED FROM ELECTROSTATIC DISCHARGESTHEORY AND EXPERIMENT

5. AUTHOR(S)

P. F. Wilson, A. R. Ondrejka, M. T. Ma, and J. M. Ladbury

6. PERFORMING ORGANIZATION (If joint or other than NBS, see instructions)

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

7. Contract/Grant No.

8. Type of Report & Period Covered

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

10. SUPPLEMENTARY NOTES

I I Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual sun-innary of most significant information. If document includes a significant

bibliography or literature survey, mention it here) The fields radiated by electrostatic discharges (ESD)

and experimentally. The ESD spark is modeled theoreti

time dependent, linear dipole situated above an infin

sparks of varying voltages are generated by a commerc

used to excite a number of targets including (1) the

coaxial cable mounted in a ground plane, (2) direct d

(3) indirect radiation from a large metal plate, (4)

plane, and (5) a metal trash can. Results show that

(2-4 kV) excite the strongest radiated fields. This

can pose a significant interference threat to electro

gigahertz range.

are studied both theoretically

cally as an electrically short,

ite ground plane. Experimen-tally,

ially available simulator and

extended inner conductor of a ischarges to a ground plane,

a metal chair over a ground

relatively low-voltage sparks

suggests that the spark fields

nic equipment into the

12. KEY WORDS (S/x to twelve entries; alphabetical order; capitalize only proper names; and separate key words by semicolons)

electrostatic discharge; pulsed current; radiated electric field; radiated

magnetic field; spectrum; time-domain technique

13. AVAILABILITY

[77] Unlimited rn For Official Distribution. Do Not Release to NTIS

r~Xl Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C

20402.

[33] Order From National Technical Information Service (NTIS), Springfield, VA. 22161

14. NO. OF

PRINTED PAGES

72

15. Price

USCOMM-DC e043-PS0

U.S. GOVERNMENT PRINTING OFFICE 1988—574-791 85.109 REGION NO 8

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