Honeycomb Air Ventilation Panels – The Polarity Principle

For more than 100 years, the car has simply been used as a device for transporting a driver and passengers from point A to point B at speed with minimum effort.  

With the introduction of Advanced Driver Assistance Systems (ADAS) and other semi-autonomous driving technologies, a different concept of the vehicle is emerging. In the future, the car will be a media playback center, telephone, office and extension of the home’s living room which also happens to be able to convey passengers from A to B.

This is having a profound effect on the characteristics and on the sheer number of electronics systems in new vehicles and this in turn will dramatically extend the demands on the EMI shielding devices used to attenuate the radiated emissions that could affect circuits in the car. EMI shielding materials will need to perform over a wide range of frequencies, in more applications as electronic systems take over more and more aspects of the car’s driving operations, while adding as little as possible to the weight of the vehicle.   

The time for OEMs to consider the options for achieving EMC in new car designs is at the start of a new design project, before the electrical and mechanical features of the vehicle’s systems have been decided. This gives design engineers the opportunity to bring considerations of EMI and shielding devices into the design process and enable optimization of the size, cost and performance of EMI shielding in the final system. 

Top challenges of next generation 5G networks

• The first challenge for automotive design engineers is the range of frequencies that need to be attenuated will be far greater in new cars than it was in the past. Until recently, the main frequencies of interest were the AM and FM bands used by radio and frequencies below 3GHz used by Bluetooth radio and mobile phone networks.

  With the future introduction of 5G mobile phone network coverage, frequency coverage of EMI shielding materials will need to be extended. A higher frequency range is not the only issue. Cars are also going to support a much greater number of wireless communications systems within the vehicle.

New strict measures to attenuate RF emissions in compliance with safety standards

• The second challenge is that the effectiveness of EMI shielding is likely to be more tightly specified in the future as automotive manufacturers move towards a strict view of the functional safety of the electronics systems in cars, codified in the ISO 26262 functional safety standard.

  So, what does this mean for the specification of EMI shielding materials?

Continuous development of new elastomer fillers

Parker Chomerics maintains an intensive research and development program aimed at producing new filler materials for electrically conductive elastomer products. An important goal for this research program is to produce EMI gaskets that can cover the broader frequency range of interest in autonomous vehicles, while maintaining the desirable mechanical characteristics. Parker Chomerics CHO-SEAL conductive elastomers are widely used in automotive systems and offer useful properties, including resistance to high temperatures and contaminants, and the ability to provide environmental sealing to protect circuits from the ingress of liquids.

These elastomer gaskets resist compression set, accommodate low closure force, and help control air flow. They are available in standard sheet form, extruded or custom shapes. 

In addition, Parker Chomerics CHOFORM Form-In-Place automated EMI gasket material can be dispensed directly onto castings, machined metal and conductive plastic and is widely used in tightly packed electronic housings. This advanced technology allows dispensing of precise positioned gaskets in very small cross sections and can free up valuable packing space of up to 60%. CHOFORM offers excellent shielding effectiveness which exceeds 100dB between 200 MHz and 12GHz.

New opportunities for weight saving

The development of autonomous and semi-autonomous vehicles is leading to a huge increase in the number of electronics modules per vehicle. This increases the scope for car makers to reduce weight by replacing conventional metal housings with lighter conductive plastic housings. While the weight saving on each module might appear small, when multiplied across the 100 or more electronics modules, the total weight saving becomes invaluable.

Parker Chomerics PREMIER™ PBT-225 is a single-pellet conductive plastic for use in automotive housings. PREMIER PBT-225 offers excellent resistance to hydrolysis when exposed to extreme temperatures and provides for easy processing and uniform filler dispersion. As a result, EMI housings made from PBT-225 offer tightly controlled electrical and mechanical performance throughout complex geometries. A weight saving of 30% is also possible when replacing an equivalent metal or aluminium housing with PBT-225.

By collaborating early in development projects with Parker Chomerics, automotive system designers can ensure that their electronic and mechanical design is optimized for shielding purposes.

Learn more about Parker Chomerics EMI shielding and thermal solutions for the automotive Industry.

 

 

 

 

 

 

 

 

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

 

 

 

 

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Design Decisions Relating to EMC Shielding

Improved EMI Shielding Consistency of Single Pellet Conductive Plastics

 

Honeycomb 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.

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

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. 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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. 

   

 

 

 

 

 

 

 

 

 

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

 

 

 

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

 

As the defense industry continues to push the boundaries on advanced electronic systems and state-of-the-art communication devices, the requirements governing these programs must follow suit. Among the many technical requirements is Electromagnetic Compatibility, defined as the ability of a device to withstand both anticipated and unanticipated electronic interference (EMI) as well as minimize the interference being radiated.

It’s important to note that electromagnetic compatibility is a requirement across a variety of platforms in military technology including, but not limited to: missile and missile defense, ground vehicles, man-portable communication, electronic warfare/radar, stationary shelters, and avionics. Additionally, commercial technology such as aircraft and satellites often adopt military standards for electromagnetic shielding.

Missiles and missile defense

Innovation and improvements in war-fighting over the past several decades have led to the improvement of key weapons systems, most notably the missile defense arsenal. As weapons improve range, minimize collateral damage, and attempt to outpace anti-missile efforts, a greater focus has been placed on electronic controls and built in fail-safe measures. These measures are developed to the highest EMI standards for the safety of military personnel, with elastomer gaskets and conductive paints serving to ensure weather sealing and minimization of interference.

Ground vehicles

Humvees and tanks are built for durability in all environments, with safety of the crew a top priority. To ensure proper function of the engine components, weapons systems, and data transmission, these vehicles must meet EMI standards. Expanded aluminum gaskets for turret and antenna mounts are just one example of shielding efforts on both the interior and exterior of the vehicle

 

Man-portable communication

Defense research and development continues to optimize the gear used by servicemen and women, both in combat and support roles. The first line of communication is the direct unit carried by those who serve, whether built into helmets/headsets or carried in the form of hand-held devices. Each device is tested and retested, verifying that interference will not present hazards at the most inopportune times. EMI shielded displays on these devices ensure minimal interference with maximum information transmission.

Electronic warfare/radar

Radar and electronic warfare modules come in all sizes, from under-wing units on fighter jets to stationary units the size of a small island. Each unit, whether stationary or mobile, must pass stringent electronic emissions and susceptibility standards to ensure that billions of dollars of development and manufacturing yield the most advanced technology.

Stationary shelters

Ground control shelters have become mobile mission control hubs, storing a great deal of technology inside. EMI shielding caulks and compounds at the seams ensure that only the proper information is relayed as expected.

Avionics

On-board electronics equipment such as flight recorders, navigation units, flight-control systems, and radios are perfect examples of components that must comply with EMI shielding specifications. These devices are mission-critical, with the slightest interference potentially causing communication delays or misinformation presented to the crew or ground control staffs. Commercial aircraft observe similar safety requirements, while including additional electronics such as in-flight entertainment units that utilize custom shielded display units.

EMI shielding is a crucial consideration in the safe and effective operation of defense electronic systems. Nearly every device developed for military and aerospace applications must utilize gaskets, coatings, adhesives, or a variety of other sub components in meeting rigorous military electronics standards. Additional technical information and specific metrics on defense requirements for electromagnetic compatibility can be found in MIL-STD 461G.

 

 

 

 

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

 

 

 

 

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