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Miscellaneous

Electrical Shielding

9-87Catalog 1654025 Dimensions are in millimeters Dimensions are shown for USA: 1-800-522-6752 South America: 55-11-3611-1514Revised 12-04 and inches unless otherwise reference purposes only. Canada: 1-905-470-4425 J apan: 81-44-900-5102

specified. Values in brackets Specifications subject Mexico: 01-800-733-8926 Singapore: 65-4866-151www.tycoelectronics.com are U.S. equivalents. to change. C. America: 52-55-5-729-0425 UK:44-1793-528171

Interference Designingfor the Threat

Available Shields

Shield type Construction Typical Application

Aluminized Mylar Electrostatic shielding

Single Braid Low level EMILow sensitivity

Single Optimized Braid Sensitive linesHigh EMI

Double Optimized Braid Highly sensitive linesSevere EMI

Supershielded EMP/Tempest

Double Supershielded Severest of applications

Applications

In many applications,

shielding of cables is

important, whether it be

to minimize cross-talk

within the cable, to prevent

interference from external

sources, or to eliminate

radiation from the cable

itself.

The design of cables to

provide effective shielding

over a broad frequency

spectrum is complex, and

cables must be tailored to

specific electromagnetic

environments. From simple

aluminized M ylar film that

provides electrostaticshielding, progressively

more complex shielding can

be designed incorporating

plated copper braids and

M u metal wraps.

Optimization

Performance of conven-

tional braiding can be

significantly improved by

computer optimization.

This tightly controlled

process can give many

times the shielding per-

formance of a basic

braided shield with minimalweight penalty or increase

in optical coverage.

Supershielded cables

combine M u metal wraps

with optimized braids to

provide even further

enhanced performance,

especially at low

frequencies.

Available in:

Americas I

Europe I

Asia Pacific I

MYLAR is a trademark ofDupont Teijin Films U.S.

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Miscellaneous

Electrical Shielding (Continued)

9-88Catalog 1654025 Dimensions are in millimeters Dimensions are shown for USA: 1-800-522-6752 South America: 55-11-3611-1514Revised 12-04 and inches unless otherwise reference purposes only. Canada: 1-905-470-4425 J apan: 81-44-900-5102

specified. Values in brackets Specifications subject Mexico: 01-800-733-8926 Singapore: 65-4866-151www.tycoelectronics.com are U.S. equivalents. to change. C. America: 52-55-5-729-0425 UK:44-1793-528171

M easuring ShieldingEfficiency

Surface Transfer Impedance (Zt)

To assess the effectiveness

of a shield, Tyco Electronicshas adopted the line injec-

tion method as described in

IEC 1196-1 to measure the

surface transfer impedance

(Zt) of a cable shield. This

relates the open circuit volt-

age generated on a compo-

nent wire inside the cable to

the current injected on the

overall shield. The unit of Zt

is O hms per meter, thus the

voltage coupling is length

dependent and long cables

exhibit more leakage than

similar but shorter length

ones. To determine the sur-face transfer impedance

across a range of frequen-

cies, a drive signal is gener-

ated by the internal tracking

generator of a spectrum

analyzer, and amplified. T he

voltage is induced on the

center conductor of the

sample which is amplified

and returned to the signal

generator for measurement.

The understanding of leak-

age mechanisms has

enabled Tyco Electronics to

design R aychem cableswith guaranteed minimum

Zt values for the desired

operating environment.

Supershielding

EMP Hardened Cables

The requirements for

nuclear hardened cables

present the engineer with

a range of problems. The

waveform of the EM P is such

that the majority of power is

dissipated in a frequency

band between 1 KHz

and 5 M Hz, where little

protection is given by con-

ventionally shielded cables.

Tyco Electronics has solved

this problem with a range of

Design and Manufacturing

Expertise

The problems of shielding

cables are complex.

However, with the introduc-

tion of optimized braids andsupershielded cables, Tyco

Electronics has the capabil-

ity to solve the most difficult

shielding problems.

Shielding of cables without

degrading cable flexibility

can be provided for coaxial

and multiconductor cables

for all EM C and EM P

conditions. To complement

this range of cables,

Tyco Electronics manufac-

tures Raychem cable

terminations and connector

back fittings to give totalinterconnection system

shielding performance.

supershielded cables which

give shielding performance

at these frequencies by

incorporating materials

which change the induc-

tance of the shield andlower the transfer imped-

ance. R aychem super-

shielded cables have a

sandwich construction of

M u metal tapes between

optimized braids. M u metal

is a ferro-magnetic material

which has a high perme-

ability over a wide range of

field strengths. It is applied

to the cable in a way which

maintains cable flexibility

and minimizes work harden-

ing and any consequent

reduction in permeabi lity.

Supershielded cables not

only give protection against

EM P but also other major

interference modes.

Shielded Cables

Controlling the Threat

Testing

Tyco Electronics EM C test

facilities have the capability

for bulk current injection

and radiation field testing in

addition to surface transfer

impedance measurements.The installation is a proven

facility in characterizing

new design parameters.

100

10

1

0.1

0.01

0.001

0.0001

103 104 105 106 107 108

Screening performanceof various types of screen constructions

55

65

75

85

95

105

115

125

135

145

155

165

175

EM

Shieldingeffectiveness(dB/meter)

Frequency (Hz)

Surfacetransf

erimpedance

(m.o

hms/meter)

AluminizedMylar

SingleStranded Braid

SingleOptimized

DoubleOptimized

SingleSuperscreen

SolidCopper screen

DoubleSuperscreen