Honeycomb air vent panels are used to help cool electronics with air flow and while maintaining electromagnetic interference (EM) shielding. Recently, our team of experts held a webinar on EMI shielding air vent panels, now available on-demand. This blog post will highlight some topics discussed on the webinar.
Cell size
Specifies the width of the individual cells. The honeycomb is hexagonal, and the cell size is the measurement across each cell and the thickness is the measurement of the entire sheet of honeycomb material.Cell size can have an impact on air flow, but it can also have an impact on shielding effectiveness. As a general trend, the smaller the cell size, the lower the air flow or the greater the pressure drop across the air vent panel.
At the same time, the smaller the cell size, the greater the shielding effectiveness because the smaller cell size limits the amount of electromagnetic energy able to pass through the openings. The key is to find the middle ground, the largest opening to allow enough air-flow to cool the system, but also the smallest cell size to block the undesired frequencies and obtain the required shielding. Cell thickness
The thickness of the air vent panel also has an impact on both the air flow and the shielding effectiveness. If the cell size were kept the same, the lower the thickness of the vent panel, the greater the allowable air flow.
The decreased air flow is caused by the surface friction of the air flowing through the honeycomb cells. However, reducing the vent thickness will also reduce the attenuation capabilities of the honeycomb. Again, the key is to try and find the middle ground between good air-flow (less pressure drop) and shielding effectiveness.
Aluminum honeycomb is made from thin ribbons of bent aluminum that are adhered together using a non-conductive adhesive. The points at which the ribbons come together are known as nodes and can cause EMI shielding leakage. With single layer honeycomb vents, there is actual directional EMI shielding. This is known as the polarization principle.
It’s also important to note that this is only the case with aluminum honeycomb vents because with brass and steel vent construction, the nodes are welded together and therefore are inherently conductive.
OMNI-CELL™
One way to reduce the directionality of attenuation in vent panels is by using what Parker Chomerics calls an OMNI CELL construction. This means that a second layer of aluminum honeycomb is stacked on top of the first at a 90-degree angle.
The directionality is offset by the second layer and the new panel should have nearly equal attenuation in both directions. One small drawback is that the two layers will reduce air flow across the new vent panel.
OMNl-CELL can be a great option in many cases, but for applications where an OMNI-CELL construction will not work because of space or high attenuation needs, you can achieve the same effect by plating the honeycomb. The plating of aluminum honeycomb will bridge the non-conductive node, and eliminate the directional effect of the honeycomb.
It’s also a much more thorough coverage, which results in better shielding. Platings will protect the vents from corrosion and standard wear and tear. Electroless nickel is one of the most common plating option, as is a chromate conversion coating.
And lastly, EMI vents can be coated with aesthetic paints to match any enclosure design. This includes CARC paints and common military color patterns.
Want to learn more about specific applications and get more detail? Watch our on-demand webinar EMI Shielding Honeycomb Air Vent Panels: Application and Design 101 now!
This blog was contributed by Jarrod Cohen, marketing communications manager, Parker Chomerics.
Related content:
Honeycomb Air Ventilation Panels – The Polarity Principle
Can Electrical Resistance Be Used to Predict Shielding Effectiveness?
Design Decisions Relating to EMC Shielding