• Home
  • Investors
  • Contact Parker
  • Sign In / Register
Parker Community
  • Site
  • User
  • Site
  • Search
  • User
  • Products
  • Support
  • Divisions
  • Where to Buy
  • Careers
  • About Parker
Home Parker Community Technologies Sealing and Shielding Sealing and Shielding Blog Honeycomb Air Ventilation Panels – The Polarity Principle
Sign In / Register

Sign In

Register

Subscribe
    RSS Subscribe by email

    Manage Email Subscriptions

Categories
  • Aerospace Blog
  • Climate Control Blog
  • Electromechanical Blog
  • Filtration Blog
  • Fluid and Gas Handling Blog
  • Hydraulics Blog
  • Parker Global Blog
  • ParkerStore Blog
  • Pneumatics Blog
  • Process Control Blog
  • Sealing and Shielding Blog
  • Technologies
    • Aerospace
    • Climate Control
    • Electromechanical Group
      • Parker IPS Design Center Community
    • Filtration
    • Fluid and Gas Handling
    • Hydraulics
    • Pneumatics
    • Process Control
    • Sealing and Shielding
  • Blogs
  • Forums
  • Knowledge Base
  • Home
  • All Blogs
  • Home
  • Sealing and Shielding Blog
  • Sealing and Shielding Forum
  • Sealing and Shielding Knowledge Base
  • Sealing and Shielding Members
  • Mentions
  • Tags
Related
Follow Us
  • Follow Parker Hannifin on social media

Follow Parker Hannifin on social media:

Honeycomb Air Ventilation Panels – The Polarity Principle

Posted by Sealing & Shielding Team on 14 Mar 2019

    RSS Subscribe by email
Print Friendly and PDF

Honeycomb EMI Vent PanelsHoneycomb air ventilation panels are used in applications where superior electromagnetic interference (EMI) shielding must be incorporated with heat dissipation in the form of airflow. Every vent panel has a variety of design features, each providing benefits to end customers based on specific application needs. These design features can include framing, plating/painting, gasketing, and vent size control.

An often overlooked but highly important phenomenon to consider when designing EMI vent panels is that of polarity.

Polarity is the difference in EMI shielding of honeycomb in different X/Y directions.

What this means is that honeycomb vents can have differences in shielding effectiveness, sometimes as great at 50 dB, depending on the direction of the electromagnetic waves. 

For example, a basic aluminum honeycomb vent may provide shielding of 70 dB in the horizontal direction while only providing shielding of 25 dB in the vertical direction. This characteristic is due to the manufacturing process of standard aluminum honeycomb vent panels.

Basic aluminum honeycomb is created using thin ribbons of aluminum that are bonded using a non-conductive adhesive. Polarity is associated with seam leakage caused by the non-conductive bonds from cell to cell created during the manufacturing process of adhering aluminum ribbons together to make the honeycomb. While thin, this non-conductive gap is the cause of difference in shielding effectiveness (SE). It is important to note that polarity is only an issue for aluminum vents, not for steel, stainless steel, and brass honeycomb due to a different manufacturing process (steel and brass honeycomb use a welding process, eliminating the non-conductive gap). The below graph demonstrates the significant difference in shielding effectiveness in the horizontal and vertical directions.

Straight Cell Vent - No Plating

 

 

 

 

 

 

 

 

 

 

 

 

 

Fortunately, there are several solutions to combat this polarity issue:

Layered vents

With the addition of a second layer of honeycomb, offset at a 90-degree angle, the polarization effect can be dramatically reduced. The Chomerics term for these layered vents is Omni Cell. By rotating the second layer of honeycomb 90 degrees, RF wave interaction in both the X and Y axes are combated by the seam orientation of each layer of honeycomb. This means that while the electromagnetic waves may pass through one layer of the honeycomb, the offsetting layer will not allow them to pass through the entire vent assembly. Of note, airflow through the vent is not significantly impacted, allowing for enough heat dissipation. 

Omni Cell Vent Shielding Effectiveness

 

 

 

 

 

 

 

 

 

 

 

 

 

While the maximum shielding effectiveness of the Omni Cell vents is nearly identical compared to that of a single layer vent, the directional consistency is instantly noticeable. There is no longer a difference in the horizontal and vertical shielding effectiveness, with the offsetting layers eliminating the polarity effect.

Plating

Electroless nickel plating is an ideal plating option to combat polarity on aluminum vents. The nickel plating covers the non-conductive bonds and eliminates seam leakage between aluminum ribbons. The nickel plating electrically connects the aluminum ribbons which overcome the non-conductive adhesive.  Not only does nickel plating effectively eliminate the polarity effect, it increases the durability of the vents and improves their lifespan in harsh environments.

Straight Cell Vent Shielding Effectiveness

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As with Omni Cell vents, the polarization effect is eliminated with the vent exhibiting nearly no difference in shielding between horizontal and vertical testing. A properly plated vent will also increase the SE of the entire honeycomb array, creating conductive contact between every individual aluminum ribbon in the assembly. The nickel plating also improves the electrical connection of the honeycomb to the frame if the plating process is done after assembly.

Based on the above graphs, a conclusion can be made about the techniques used in eliminating the polarity effect. Since the plating process can eliminate the polarization effect AND increase the SE, this approach is most common. Omni Cell construction is effective if it meets the desired shielding effectiveness level. It is rare to see a nickel plated Omni Cell vent.

Individual project specifications such as airflow requirements, shielding performance, environmental exposure, budget and a myriad of others will drive the design process of EMI shielding honeycomb ventilation panels, but it is important to know about principles such as polarity in making final considerations. 

   

Application and Design Guide to EMI Shielding Honeycomb Vents

 

 

 

 

 

 

 

Ben Nudelman Parker Chomerics

 

 

Article contributed by Ben Nudelman, market development engineer, Parker Chomerics Division.

 

 

 

  Related content:

Top Three Design Tips for Corrosion Resistant EMI Protection

Solving EMI Issues in Mobile Electronic Devices

What Are Electromagnetic Interference and Electromagnetic Compatibility Measurements, and Why Do We Care?

 

Categories

  • Thermal Management
  • Sealing & Shielding
  • EMI Shielding
Latest Blog Posts
  • Tags
  • Contact author
  • Subscribe by email
  • More
  • Cancel
  • Managing EMI and Lightning Strike Protection in Today's Aircraft - Aircraft - Parker ChomericsComposite materials have been replacing metal structures throughout the aircraft industry primarily to save weight, improve fuel economy and reduce costs.  But the lack of electrical conductivity in these materials is a disadvantage when compared to the conventional metal airframes of the past. The conventional, metal airframe allowed designers to take advantage of the natural Faraday cage it formed to protect equipment against interference. There were many opportunities to ground items of equipment reliably by connecting directly to a convenient surface ground.

    Today, a typical airframe consists of around 50% composites. Major structures include the fuselage and wing fairing, as well as large sections of the wings, fin and horizontal stabilizers. 

      Causes of electrical interference

    Inside the aircraft there are numerous electrical systems capable of generating EMI which can potentially disturb the operation of critical systems. These include fluorescent lights, light switches, dimming circuits, AC-powered window heaters, motors and generators, data and power cables, and transmitters such as radio and radar. 

    External storms are also a major source of potentially disruptive electrical interference and can cause physical damage to the aircraft through lightning strike impact.  

      Recovering lost properties

    Replacing metal structures with composites means compromising the EMI shielding and lightning strike protection of the aircraft, as the composites themselves are not electrically conductive. To overcome this issue, woven or non-woven copper-aluminium mesh, or an expanded foil, can be embedded in composite structures to restore lost shielding and grounding properties. The embedded metal provides an optimal combination of electrical conductivity, weight, and corrosion resistance. Solid metal strips can be used in the radome area to handle very high concentrations of lightning energy. 

    Embedded conductors, however, do not solve all the technical challenges that come with the increasing use of composites. It is very difficult to ensure reliable electrical continuity between individual composite panels after the airframe is assembled and still promote conduction of lightning energy. 

    Electrical components are typically bonded or grounded directly to the airframe. These connections to the mesh can often fail to meet the very low impedance requirements because of environmental stresses such as vibration and temperature variation. The exposed mesh in the locations where grounded or bonded modules are made (fig 1, at left), can be vulnerable to environmental exposure (temperature, humidity, oxidation) that increases electrical impedance.

      Applied performance enhancement

    To overcome this challenge, a lightweight coating such as Parker Chomerics CHO-SHIELD technology can be applied to optimize conductivity in this area. CHO-SHIELD® 4994 is a highly conductive, silver-filled polyurethane coating designed for aerospace applications and has superior EMI shielding properties. The coating provides excellent adhesion and wear resistance and is resilient to most operation and environmental fluids. The coating is compatible with many primers and top coat systems.

    In areas where high corrosion protection is needed, a copper-based urethane coasting such as Parker Chomerics CHO-SHIELD® 2002 can be used. When used on a composite, CHO-SHIELD 2002 provides the conductivity necessary to achieve excellent shielding effectiveness while maintaining its electrical and mechanical stability in hostile environments. CHO-SHIELD 2002 is designed to be used with Chomerics CHO-SHIELD® 1091 primer to ensure correct adhesion. 

     

    The aircraft antennas will also need to be shielded and grounded against lightning strike. This can be achieved by using an expanded woven MetalasticTM EXP-URE gasket material. Electrically conductive grease can be applied at ground connections, to support reliable electrical connectivity under temperature and vibration. Attention must be paid to viscosity and surface-wetting properties when formulating greases for aerospace applications. Parker Chomerics CHO-LUBE® 4220 has a resistivity better than 100mΩ-cm and is an example of an aerospace-grade grease. It is formulated to support electrical interconnections, improve metal to metal contact and provide long-term oxidation protection for exposed mesh or electrical terminals.

    Conductive sealants such as Parker Chomerics CHO-BOND® 2165 or CHO-BOND® 1019 can be applied at locations requiring electrical continuity and environmental protection. Typical airframe areas treated are screw holes, fasteners, antenna connection points and exposed conductors on external areas. Where conductive gaskets are used to promote electrical continuity between composite components, a conductive sealant can be applied to provide improvement in continuity. These areas are generally around the wheel wells, engine mounts, wings and the tail section, where high vibration occurs (figure 2, above). 

    In addition to these methods which will improve EMI performance throughout the airframe, a lightweight conductive heat shrinkable tube such as Parker Chomerics CHO-SHRINK® 1061 can be used to shield the aircraft’s cabling against the effects of EMI and can provide a weight saving of up to 60% compared to traditional methods.

     

     

    This blog post contributed by Mel French, marketing communications manager, Chomerics Division Europe

     

     

     

    Related content:

    How to Reduce Galvanic Corrosion Using Conductive Filler Systems

    Interesting New Developments in Commercial Aerospace Gaskets

    Top Three Design Tips for Corrosion Resistant EMI Protection

     

    Sealing & Shielding Team
    Sealing & Shielding Team
    • 11 Dec 2019
    Managing EMI and Lightning Strike Protection in Today’s Aircraft
    Composite materials have been replacing metal structures throughout the aircraft industry primarily to save weight, improve...
  • Form-In-Place Gaskets: What They Are and What They Are Not - FIP Gaskets - Parker ChomericsForm-in-place EMI gaskets, also known as FIP EMI gaskets, is a robotically dispensed electromagnetic interference (EMI) shielding solution that is ideal for modern densely populated electronics packaging.

    The most important distinction of form-in-place EMI gaskets is that they were developed for applications where inter-compartmental isolation is required to separate signal processing and/or signal generating functions.

    Simply put, form-in-place gaskets are meant to reduce “noise” between cavities on a printed circuit board (PCB) or in an electronics enclosure. 

    In addition, form-in-place gaskets provide excellent electrical contact to mating conductive surfaces, including printed circuit board traces for cavity-to-cavity isolation. Parker Chomerics form-in-place gasket materials are known as CHOFORM. 

      7 reasons why form-in-place EMI gaskets can be an ideal choice
    1. Small form factor - form-in-place gaskets can be dispensed in smaller bead sizes than most traditional EMI shielding gasket solutions, 0.018” tall by 0.022” wide. 
       
    2. Excellent adhesion - 4-12 N/cm adhesion on prepared surfaces such as machined metals, cast housings, and electrically conductive plastics.
       
    3. High shielding effectiveness - Parker Chomerics CHOFORM materials can provide more than 100 dB shielding effectiveness in the 200 MHz to 12 GHz frequency range.
       
    4. Quick programming - Because form-in-place EMI gaskets are robotically dispensed, a standard CAD file can be used to program the dispensing system and quickly map out the dispensing pattern.
       
    5. Complex geometries - The positional tolerance of the gasket can be held to within 0.001” and is able to follow very complex geometries including sharp turns, corners, and serpentine patterns. Other gaskets such as die cut sheets or o-rings manufacture and/or fabricate into such shapes and patterns. 
       
    6. “T” joints - Traditional extruded gaskets are difficult to mate at intersections or “T” joints. The robot dispensing systems produce reliable junctions between bead paths to provide continuous EMI/EMC shielding and environmental sealing.
       
    7. Integrated solutions - CHOFORM technology combined with a Parker Chomerics supplied metal or conductive plastic housing provides an integrated solution ready for the customers’ highest level of assembly. This approach requires no additional assembly or process steps for the installation of gaskets and/or board-level auxiliary components. 
      Form-in-place EMI gasket limitations 
    1. Large form factor enclosure sealing that can accommodate a groove. For larger areas such as machined covers that can accommodate a gasket groove, other EMI shielding solutions are better suited. In most applications, conductive elastomers such as the CHO-SEAL product line by Parker Chomerics will provide better shielding and sealing. Form in place gaskets can be dispensed in bead sizes only as large as about 0.062” tall x 0.075” wide.
       
    2. Enclosures requiring submersion or durable weather sealing. Because of the small form factor, FIP gaskets will not meet stringent environmental sealing requirements such as IP 67 or higher. While silicone-based, the material is better at preventing dust and environmental moisture from entering an enclosure. FIP gaskets can be paired with additional sealing gaskets for enhanced weatherproofing. 
       

    Form-In-Place Gaskets: What They Are and What They Are Not - FIP Gasket Properties - Parker Chomerics


     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

     

    Form-In-Place Gaskets: What They Are and What They Are Not - Ben Nudelman - Parker ChomericsThis blog post was contributed by Ben Nudelman, market development engineer, Chomerics Division.

     

     

     

     

    Related content:

    6 Benefits of Overmolded Covers for Aerospace and Defense Applications

    7 Most Common EMI Shielding Elastomer Gasket Mounting Choices

    New Essential Handbook for EMI Shielding Applications

    Sealing & Shielding Team
    Sealing & Shielding Team
    • 27 Nov 2019
    Form-In-Place Gaskets: What They Are and What They Are Not
    Form-in-place EMI gaskets, also known as FIP EMI gaskets, is a robotically dispensed electromagnetic interference (EMI)...
  • EMI and Environmental Sealing for Munitions_Missile_Parker CHomericsMaterial selection for military applications requires careful consideration, as there are strict requirements to ensure maximum durability, security and of course performance. In munitions, or missiles and missile launch systems, materials that provide electromagnetic interference (EMI) shielding and environmental sealing are critical for the functionality and field life of the application.

    Let's look at three areas of a munitions application -- specifically nose cones, cable shielding, and connectors, as each of these areas exemplify why EMI and environmental shielding are a necessity.

      Nose cones

    EMI and Environmental Sealing for Munitions Applications - Nose Cone - Parker ChomericsNose cones are what goes over the top of missiles, planes and other airborne technologies to assist with aerodynamics and to protect the electronic components inside. In missiles, all the electronics are stored within the nose cone and the fuel is held inside the canister. If these two parts are not properly shielded from each other, contamination can become a catastrophic event.

    Therefore, shielding the nose cone from EMI and other outside environmental dangers and shielding the components of the missile from each other is of utmost importance.

    Another threat to missile electronic malfunction is external tampering from malicious forces. Unintended or intentional EMI can result in misfires, false trajectory, and other problems. Often, anti-jammers are installed to help prevent this problem in combination with EMI shielding materials.

      Cable shielding

    Cable shielding is a woven fabric that goes over cables to prevent electromagnetic cross-talk between the cables and the components. Typically, a metal mesh is wrapped around the cables that will prevent any EMI from interacting with the cables or emitting from the cables.

    EMI and Environmental Sealing for Munitions Applications - Connector Gaskets - Parker Chomerics

    Different amounts of layers can be added to increase EMI shielding effectiveness, however adding more layers will also add more weight. Cable shielding that is lighter, typically non-metal based, is ideal for applications where weight is of concern like in munitions.

      Connectors

    Connectors are where wires are plugged into to keep electric circuits intact. In munitions, connectors can be a failure point because environmental agents can more easily enter which is why they require more attention to be shielded properly.

    The complexity of military electronics has increased significantly on air, sea and land-based applications. The environments in which systems are required to operate are often extreme. Design engineers need to consider wide variations in ambient temperature, shock and vibration, and electromagnetic interference (EMI).

    With a wide choice of shielding materials and a range of advanced shielded optical windows, Parker Chomerics helps ensure the protection of complex electronics from damage and compromised reliability caused by EMI.

    Sensitive electronic components can be kept within their operating temperature range limits by using heat management materials that include highly conformable, thermally efficient gap fillers and gels.

    Parker Chomerics offers the products, technical know-how, close customer support and supply chain capabilities to meet these challenges and deliver superior, reliable and cost-effective solutions.

     

     

    EMI and Environmental Sealing for Munitions Applications - Learn More - Parker Chomerics

     

     

     

     

    EMI and Environmental Sealing for Munitions ApplicationsThis blog post was contributed by Paige Ludl, marketing co-op, Chomerics Division.


     

     

     

     

     

    Related content:

    EMI Shielding Caulk Delivers Superior Performance in Military Radar Systems

    EMI Shielding Technology Applications in Defense Systems

    Conductive Heat Shrinkable Tubing for Cable Shielding

    Sealing & Shielding Team
    Sealing & Shielding Team
    • 26 Nov 2019
    EMI and Environmental Sealing for Munitions Applications
    Material selection for military applications requires careful consideration, as there are strict requirements to ensure...
  • Technologies
    • Aerospace
    • Climate Control
    • Electromechanical Group
      • Parker IPS Design Center Community
    • Filtration
    • Fluid and Gas Handling
    • Hydraulics
    • Pneumatics
    • Process Control
    • Sealing and Shielding
  • Home
  • All Blogs
  • Home
  • Sealing and Shielding Blog
  • Sealing and Shielding Forum
  • Sealing and Shielding Knowledge Base
  • Sealing and Shielding Members
  • Mentions
  • Tags
Follow Us
  • Follow Parker Hannifin on social media

Follow Parker Hannifin on social media:

Parker Hannifin Parker Hannifin

  • Products
  • About Parker
  • Investors
  • Community
  • Careers

Global Operations Global Operations

  • Divisions
  • Sales Companies
  • Worldwide Locations
  • Distribution Network
  • ParkerStore™ Network

Company Information Company Information

  • Newsroom
  • Event Calendar
  • Working with Parker
  • Product Brands
  • History

Global Support Center Global Support Center

  • Support
  • CAD
  • Where to Buy
  • Contact Parker
  • Manage Online Orders
Parker - Engineering Your Success
  • Site Map
  • Safety
  • Privacy Policies
  • Terms and Conditions
© Parker Hannifin Corp 2019