presentasi elektromagnetika ground & shield

7/31/2019 Presentasi Elektromagnetika Ground & Shield

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Grounds


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Electrical Ground actually a path forcurrent to return from some load back

to the source.


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A Ground to earth is REQUIRED of mostelectrical equipment to protect against

shock hazard!


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Proper Grounding is EXTREMELYIMPORTANT for minimizing EMI

problems.


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Grounds Symbol :

1. Signal/Earth Ground2. Chassis Ground3. Special Ground

(1) (2) (3)


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Bond Wires

Circuit connected to Ground using bondwires.

Keep leads short and keep impedancelow.

Lower inductance is attained using flat,wide-cross-section conductive straps.


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Signal Grounds

1. Single-Point

Tying the grounds together at a singlepoint,so all signal ground will be at the

same potential. The facility ground may not be

equipotential.

Avoid significant difference in the groundpotential in some case (ex: lightning strike).


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Ground Loop

Circuit

FacilityGround


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1. Single-Point

a) Series-Connected Single-Point

Circuit 1 Circuit 3Circuit 2

Source


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Very commonly used.

Can see a potential difference at

the ground level that can affectoperation and cause EMIproblems. For this reason, the

bond leads must be kept as shortas possible.

a) Series-Connected Single-

Point


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1. Single-Point

b) Parallel-Connected Single-Point


Source


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b) Parallel-Connected Single-

Point Offers much better EMI control.

The circuit operates best at lowfrequency where the wireinductance is low.

Can require an excessive amountof wire for a large system.


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Signal Grounds

2. Multipoint Arrangement


Source


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2. Multi-Point Arrangement

A better approach for highfrequency.

Work best for frequencies above10 MHz.

It is CRITICAL that the groundleads from circuit to the commonground plane be as short as

possible (preferably less than


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Loop Area

IC

+5V

IC IC

IC

+5V

SmallerLoop AreaLarger

Loop Area


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Loop Area

A circuit containing : a source,connecting wire, load, and groundcreates a current loop that resemblesa loop antenna. It can serve an

unintentional source of radiatedemissions and also susceptible toreception of incident fields (ex: fromradio transmitters)

Because of radiated power from a loopantenna is proportional to the looparea squared, the area enclosed by

these current loops should beminimized to reduce EMI.


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Shields


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Shields is metal or metal screen boxplaced around circuit to block radiation.

Metal/ metal box/ metal braid Shield attenuate electromagnetic

wave and reflect waves


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Fundamentals of Electromagnetics With Engineering Applicationsby Stuart M. Wentworth

Copyright 2005 by John Wiley & Sons. All rights reserved.

Figure 9-23 (p. 479)Some of a field Ei incident on a shield will be reflected at the air -shield boundary,

some will be transmitted and attenuated within the shield, some will be reflected at

the shield-air boundary, and finally some will be transmitted as Et.


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Shielding effectiveness = SE

SE adalah tingkat performa Shield,didefinisikan sebagai desibel

SE = 10log (Pns/Ps) = 20log (|Ens|/|Es|)= 20log (|Hns|/|Hs|)


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Atenuasi (attenuation) atau absorsimengkonfersi energi electromagneticmenjadi panas dalam materi Shield

Material dengan permebealitas tinggimembuat proses absorsi yang bagus,karena

=


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SE tergantung dari : komposisi dan ketebalan Shield itu

sendiri

Frekuensi radiasi gelombangelektromagnetik

Bentuk dari Shield itu sendiri

Diskontinuitas yang mungkin beradadalam Shield


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Dalam Shield terkadang terpadatbeberapa lubang yaitu: Opening untuk mnejalankan sinyal,

power dan koneksi grounding

Ventilasi Shield

Lubang yg tidak tertutup sempurna pada

penggabungan dua Shields

Lubang-lubang ini terkadangmengurangi integritas SE

presentasi elektromagnetika ground & shield

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