Spectrum distribution of electroinagnetic field radiated by electrostatic discharge on the ground screen.

In-ho Kang, Osamu Fujiwara”, Chang-bok Lee**

Dept. of Radio Science & Engineering Korea MaritimeUniversity $1 Dongsam-Dong Yeongdo-Ku Pusan, Korea. 606-791 8 Dept. of Electrical and Computer Engineering Nagoya Institute of Technology Go&o-Cho, Showa-Ku, Nagoya 466, Japan ** Korea Research Institute of Standard and Science

summary 2. Analysis Series troubles may occur in electromagnetic equipments When ESD event occurs, it can be modeled as a current due to electrostatic discharge(ESD). The number of the dipole with the length of 1 through which an impulse damping incidents has been significantly increasing with increased use of integrated elements with current flows, as shown Figure 1. In this case, the lower operation power. In this paper, the dipole moment electromagnetic fields radiated by ESD current can be as is used to analyze the transient electromagnetic fields follows[3l: caused by ESD. When ESD occurs at the parallel to the perfect ground, the spectrum distribution of the radiated impulsive will be analyzed. P(r,

1. Introduction An advanced electronic system or digital control equipment is easily affected by a radiated electrostatic .Y discharge (ESDI which takes place in its neighborhood, and in some cases fatal faults which the designer has v never imagined may happen. For impulsive +4 electromagnetic interference of this kind, there are strange happeningsl-11, l-21 which are well known as a peculiar phenomenon of unknown origin. Indirect ESD Figure. 1 and dipole model occurred at the location distant from an equipment causes the stronger electromagnetic interference than direct ESD does. The interference level is not always proportional to the spark . In this paper, it was verified that the electromagnetic interference level was not always to the inverse of the distance on the perfect ground. The frequency spectra of electromagnetic fields caused by spark on the ground screen will be analyzed.

0:7803-5015-4/98/$10.00 0 1998 IEEE 994 (9) =-*:*S(jwl

Xs a result, the Fourier transform of the equations (l),(2),(3) are respectively expressed as follows: where c is the speed of light and Z,=m, is the - 1 . E,oI,cos*. (1;jC w7)- ($1’.S(j,) (10) intrinsic impedance of free space. For spark resistance, r Et * Rompe-Weizel’s resistance formula expresses the developing process of the spark discharge very well. Rompe-Weizel resistance is given by (11)

dt)=y-Tz&G (4) H&w) -.1 =sinB- (l+jT) - (5)’ - S(jw) (12) t HI

The discharge circuit and v(t) = i(t)l(t) are used to drive the following equations[41. 2 0‘’?---1.86 . 1 (5)

30 F(x) = - exp (3Ci(x- 24) (6) - [21+exP~3G~x--u)J1P5 L DIM-&SIOIuZESS&ME The Fourier transform of Rx- U) is expressed as t/r-r/(cT) follows:

J-LF(x- 24)e- ‘“‘df (7) -jrnrr . =r’ e s IF(x) em’““& Z-XL Y I z 1 We assume 10-I 10-l 1 2.5 10 10' DMEN~IONUSS Ai’GULii? FREQLiEVCY I .e S(jw) = e -hr . s :-F(x) eet’dx (8) Figure. 2 (a) The waveform of F(t/d and its derivative (/ I) (b) Frequency spectra of the waveforms Therefore, the waveform of F&-U) has Fourier aF taii; r cr transform r - S(jw). The Fourier transform of the 2F( t/ r- 7j cd of F(t/r)and its a(f/r) derivative of F(x- 4, w is given by

(jwr)r* S(jw). Figure 2 (a) shows the waveforms of F(t/d and its

a5-ttlr-7Id 1 - I,‘F(x’ - UMX’ is the integral of IQ- U) derivative am * Figure 2 ib) presents the

frequency spectra of F( t/r) and aFc!&rt~r~‘cr’ which

995 are obtained by FFT(Fast Founer Transform). higher than at near distance. Figure 5 shows a dipole 0 bservation 3. Experiment and result Point Figure 3 shows the configuration of experiment setup Dipole P[O.R,,Z’j and ESD detection, indicating the top view. The ESD detector was placed at a distance r from sphere eieccrodes as shown in Figure 3[5].

Sohere Carbon electrode string d-w/r: 2a :

Figure. 5 Dipole model of ESD on the perfect ground

model of ESD on the perfect ground plane. At a point P, the radiation components of the electric fields are expressed as follows:

Figure. 3 The configuration of experimental setup and L&f ESD detection E,= -z.--&- (13) 1 amir- R,lcd .rR,’ a( ttr- R,lcr) The height of generation of ESD is l(m) and that of the observation point is also l(mm). ESD detector sound a 44 p Km= a,.-$- (14) buzzer when the peak level of exceeds a 1 aF( t/r- Rijcr) threshold level. The spark was generated at a two ‘rlii’ act/r- RJcr) seconds interval and then simultaneous measurements of

where R, is the distance between the observation point

0 0 P and the dipole on the plane, R, is one from the

0 image dipole, z is l(m), and z’ is also l(m). Figure 6 0 shows the peak radiated electric field calculated with 0 respect to the distance from ESD point. Figure 7, 8 0 express the electric fields in the time domain concerning each distance. The normalized phase difference of two 6 7 6 9 10

Distance r [ml electric fields is given by Figure. 4 The detection rate at observation distance r. -J-(R,-R~)= -J-(4 p2+ (L--z’)?--d p2+ (~+2’)~}(151 the ESD detection frequency and the spark voltage were made for fifty sparks. Figure 4 shows the detection rate From the above equation, the longer the distance from ?i was measured at an observation distance r. It can be ESD point is, the smaller the phase difference is. Due to estimated from occurance probability where the radiated electric field exceeds a threshold level. From Figure 4, there is a case that detection rate q at far distance is

996 Figure 6 can not precisely explain the reason that the intensity of electric field at far distance is stronger than at near distance. It is necessary to examine the characteristic of the spectrum distribution of electric field in order to interpret the strange phenomenon in the Figure 4. Figure 9, 10, 11 show the frequency spectra of

Distance r [ml Figure 6. The peak radiated electric field calculated with respected to the distance r

such phase property of electric field the peak value decrease very slowly in the region r= 7%9( z-z). The waveforms of electric field with respect to the distance are expressed each other by the Figure 7, 8. But the

-4 -2 -! 0 I normalized time Figure. 7 The waveforms of the summed electric Figure. 10 The power of radiated wave at the distance fields(r=3,5,7(ml) r=8(m)

Figure. 11 The power of radiated wave at the distance Figure. 8 The waveforms of the summed electric r=9(m) fields(r=7,8,9(m))

997 powers at r=‘i, 8, 9(m) respectively which are obtained by FFT from the data of Figure T. 8. The frequent!, band of the wave at far distance have a cendancy to be wide. The broadband frequency characteristic of electric field is thought to have an effect on the reaction of the ESD locator.

4. Conclusion For analyzing the transient electromagnetic fields caused by electrostatic discharge(ESD1, the dipole model was presented here. The frequency spectrum of the electromagnetic field was analyzed. It is verified that the radiated field on the ground plane is not always proportional to the inverse of observation distance. The cause is based upon the fact that the phase difference between the directly porpagating wave and the reflected wave at the ground plane changes the field waveforms according to the variation of the observation distance. But it is yet insufficient to explain the strange distance characteristic of electric field. The spectrum distribution of impulsive wave was derived with respective to the distance from the ESD point. The frequency band width at the far distance has tendency to spread widely. The above frequency property is thought to influence the reaction of ESD locator.

References [ll. Honda, M., and Kawamura, T.: ‘ESD characteristics and their effects on a computer(part2)‘, EMCJ-Japan, 83-86, pp.13-17 [21. GREASON, W.D.: ‘Indirect effect of ESD: modeling and measurerxnt’, Proc. 11th Int. Zurich Symp. Tech. 8r Exh. on EMC, 116R1, March 1995, pp.613618 [3]. FUJIWARA, O., and Andoh, 0.: ‘Analysis of transient electromagnetic fields radiated by electrostatic discharges’, IEICE. Trans. Commun, 1993, E76-B, (11) pp.1478-1480 [41. FUJTWARA, O., and ALXEMIYA, Y.: ‘Calculation of ignition noise level caused by plug gap breakdown’, IEEE Trans. Electromagn Compt, 1982, 24, (11, pp.26-32 El. FUJTWARA, 0: ‘An Analytical Approach to Model Indirect Effect Caused by Electrostatic Discharge’, IEICE. Trans. Commun. 1996, E79-B, No.4 pp.483-489

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