Frequently Asked Questions

The proliferation of electronics into our everyday lives has driven the innovation of more efficient shield designs over a broader range of applications. Design innovations are the key to today's successful advancement since the basic technology of shielding sensitive equipment from the effects of electromagnetic interference (EMI) has not changed in the last 50 years.

In this issue of Magnetic Shield Update and continuing in the next, we will answer the most frequently asked questions regarding problems for EMI.

What is a magnetic field?

A magnetic field cannot be seen, heard, or felt. The magnetic field results from a source of magnetic flux. The source might be the Earth, a motor, transformer, electric power line or even a bar magnet. Magnetic fields also make transformers and motors function, and have many other practical applications.

What is the difference between DC and AC fields?

DC fields are non-varying, or perhaps slowly changing. A DC field might be from the Earth, a permanent magnet or a coil carrying direct current. AC magnetic fields oscillate in direction at a frequency. The most common AC magnetic fields are 60 Hertz fields emitted by electric power equipment.

How are magnetic fields measured?

We can sense magnetic fields with measuring instruments called Gaussmeters. The units for measuring magnetic fields are Gauss and Oersted. Magnetic flux density is measured in Gauss, while magnetic field intensity is measured in Oersted. The ratio of B, magnetic flux, in Gauss, to H, magnetic field, in Oersted, is defined as permeability, "µ" (pronounced "mew"). The B/H ratio, or "µ", is a measure of the material's properties. It is high for ferromagnetic materials. In air "µ is equal to one, making Gauss and Oersted identical numerically, adding to the confusion. The S/I or Metric system adds the Tesla and Ampere-turns/meter units.

Electrical Wiring Guide

Basic INTER-8 WEAVE cable is unshielded. It is also available with an outer braided shield of CO-NETIC® AA high permeability wire to provide magnetic shielding.

SPIRA-SHIELD FLEXIBLE CONDUIT

SPIRA-SHIELD flexible conduit delivers high permeability magnetic shielding for sensitive cables and conductors. Constructed of .010" thick CO-NETIC AA Alloy, SPIRA-SHIELD provides greater attenuation than braided sleeving and also furnishes physical protection.

Among typical SPIRA-SHIELD applications are ground support and communication equipment, shipboard control systems, audiolevel interconnections, sensitive instrumentation, and aerospace apparatus.

CO-NETIC BRAIDED SLEEVING

CO-NETIC braided sleeving is endowed with superior flexibility compared to foil that is spiral or channel wrapped around cable. Its tubular sleeving is braided from 36 or 34 AWG CO-NETIC AA high permeability wire. CONETIC braided sleeving's shield coverage is 85-90% at nominal I.D. diameter and can be expanded by compressing both ends toward the center of sleeving.

CO-NETIC AA WIRE

CO-NETIC AA wire in .005" diameter is widely used in magnetic shielding braid applied over cables. It is highly effective for applications requiring high permeability, low coercive force and ferromagnetic properties. CO-NETIC AA wire is corrosion resistant and has an affinity for solder.