Electromagnetic waves and shielding
Electromagnetic waves consist of two components. A magnetic field (H) and an electric field (E). The ratio of E/H is called wave impedance (Zw). The relative magnitude of these two fields is important when considering shielding materials. A source which contains a large current flow such as generated by power supplies or transformers is known as a current, Magnetic (H) or low impedance source. If the source is generating a high voltage with low current such as high frequency transmitters the waves are predominantly Electric field (E) or High impedance source. The effectiveness of a shield is governed by the difference between the impedance of the electromagnetic wave and the impedance of the shielding material. The greater the difference, the better the shielding. The performance of shielding materials is measured in decibels (dB), and calculated as below:

EMC
The basic principle of the EMC gasket is to maintain good electrical contact between two surfaces, closing any gaps that may form between cabinet panels, doors and windows for example.

Galvanic Compatibility
Galvanic corrosion occurs when two incompatible metals are in contact with each other. The effect is increased in the presence of an electrolyte, such as water. Galvanic corrosion can cause serious surface and structural damage so it is essential the correct gasketing material is used for the application. The adjacent table has been designed as a guide to assist gasket selection, indicating what materials would normally be an acceptable match. Caution should be exercised as actual conditions may affect galvanic actions in different ways, so it is recommended that application tests are carried out.
As a guide, for indoor environments, where dry conditions prevail, the difference in EMF values should not exceed 0.5V (see table values).
For wet conditions, the differential voltage should not exceed 0.3V.
For harsh environments where salt water / mist may be encountered the differential value should not exceed 0.1V.

The exception to this rule is when using Silver Aluminium gasketing (SA8), it has been found that under certain circumstances, this material can still be used when voltage differential exceeds 0.5V. As an example, SA8 gaskets usually form an acceptable match with an aluminium housing, even under wet conditions.

Throughout the world it is rapidly becoming mandatory that electronic units, or systems, must not generate a level of electromagnetic emissions that could interfere with or prohibit the use of another electrical unit or system. Electromagnetic compatibility (EMC) is the ability of a unit to operate without generating, or being susceptible to, those electromagnetic waves.

Laird Technologies' shielding products have been specifically designed to solve virtually every known EMC application and are backed by an industry leading technical support team.