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Technology is a double-edged sword – on the one hand, it’s brought comfort and convenience to our lives; on the other, it has made us overly reliant on our gadgets. People nowadays have a hard time extricating themselves from the siren call of their smartphones, televisions, laptops, and computers. The constant demand for consumer electronics has prompted device manufacturers to try and outdo one another with the next it system. However, this level of technological progress and development comes at a cost. And that cost is electromagnetic interference (EMI). Not only can EMI disrupt the performance of electronic products and cause equipment failure, but it also affects user health. As a result, modern electronic items are required to follow the stringent electromagnetic compatibility (EMC) requirements all over the world. Placing the smart technology in regular plastic cases flouts the recommendation. So, every electronic product must undergo an adequately planned EMI control program for effective shielding. These programs include leveraging suitable shielding materials, grounding, and filtering. Unfortunately, not all substances provide suitable shielding. Of late, the use of fabric over foam shielding gaskets has increased tremendously. The question is, given the wide spectrum of metals, fabrics, foams, and other substances available at their disposal, why is this particular variety gaining more recognition from the gasket manufacturing industry? And which type should you consider for your application? Find out below:
Fabric Over Foam Shielding Gasket Components
Depending on the usability, fabric over foam shielding gaskets have two major components – the foam core and the conductive fabric. These two parts dictate the choice and practical usage of fabric over foam shielding gaskets. Conductive fabric over foam materials are great for applications that don’t have high mechanical durability requirements, need an environmental seal, or complex profile. The covering consists of nylon thread with conductive metal coatings woven into the fabric and wrapped over a soft urethane foam, making it the lowest-cost EMI shielding option available to engineers and designers. You can even use a woven fabric metalized with nickel-copper or other metal coating wrapped around the foam core as a substitute.
Application of Fabric Over Foam EMI Shielding Gaskets
The fabric over foam setup offers a comfortable degree of flexibility and conformity between the surfaces along with the lowest compression for applications needing low closure force. What’s more, the contact between the irregular surfaces is snug around bends and corners. This is ideal for electronic enclosures, including access panels and doors. Fabric shielding gaskets are also commonly used in less demanding EMI applications, especially the ones that involve grounding contact pads in laptops and cell phones. The input/output backplane of desktop computers and laptops is also shielded with fabric over foam shielding gaskets.
As such, fabric over foam shielding gaskets are widely used in wireless telecommunications in cellular phones and base stations. In mobile handsets, the circuit boards are isolated by erecting thin ledges and covering them with EMI shielding material. To ensure the ultrathin gasket’s firm placement, a form-in-place conductive elastomer is laid down on top of the ledges.
The only time fabric over foam shielding fails to provide the desired shielding performance is when the designer or engineer needs more complex profiles. That’s because the manufacturing process limits these gaskets’ production to simple cross-sectional profiles, like rectangles, D-shapes, and squares. For example, in wireless base stations, aluminum casing poses environmental and EMI shielding challenge as the electronics need to be isolated with thin walls forming separate compartments. But these walls are far too thin to support fabric over foam gaskets. So, a conductive elastomer is molded with a rigid insert in the pattern to fits over the compartments.
Impact of the Rate of Conductivity
EMI shielding depends more on the reflective nature rather than the absorptive nature. This is because the thickness of the metal around the fiber determines the absorption of heat, thereby impacting the shielding process as a whole. So, two main equations come into play – absorption loss and the rate of reflection.
The more magnetic capability a particular metal has, the greater will be its rate of permeability. Thus, such metals work well for absorption loss. EMI shield thickness is inversely proportionate to the absorption loss rate. However, manufacturers must bear in mind that the more EMI a metal absorbs, the thinner it becomes. So, a calculative analysis should reveal that reflection loss is common when conductive metals are used.
No wonder copper is the preferred metal when it comes to the production of fabric over foam EMI shielding gaskets. Upon exposure to free air, copper reacts with the oxygen and other reacting particulates to produce copper oxide aside from other non-conductive copper compounds. This causes the resistance of the fabric over foam shielding gaskets to rise automatically. Besides copper, another prevalent metal used in the manufacturing of commercial fabric over foam shielding gaskets is silver. Of course, there is always the possibility of galvanic corrosion when silver is used, but that can easily be avoided through the application of a conductive base coating.
Advantages
Fabric over foam shielding gaskets provide lots of different benefits other than EMI attenuation. The presence of copper and nickel in the fiber material helps these gaskets impart shielding performance between 65 dB – 80 dB, low resistance, and improved durability for greater conductivity. Manufacturers can mold them easily into a variety of shapes as per their requirements and produce gaskets with different host materials. The result is optimized performance together with low compression and easy installation. Of course, the best feature of fabric over foam gaskets is its ability to deliver a consistent shielding performance over a long time, even when the temperature hits a freezing minus 40 degrees Fahrenheit or a high 158 degrees Fahrenheit. Also notable is the fact that the components hardly cause any damage to the environment.
When it comes to protecting sensitive electronic components from harmful EMI radiation, fabric over foam gaskets come with their share of benefits. However, not all products offer the same level of protection. Therefore, manufacturers of sensitive electronic equipment would do well to choose the right type of fabric over foam shielding gasket, so their products get the maximum protection.
