Below are the questions asked during the live event, along with their respective answers.
Q: If testing only goes up to 6 GHz, why should we make our chambers work up to 40 GHz?
A: New technologies are emerging that might interact with signals that leak into our out of the chamber. You lso want to future proof and in some cases prepared for MIL-STD 461 type testing as well.
For example:
Automotive radars are operating in the 77 GHz region.
or
5G is operating above 20 GHz and there are plenty of 5G enabled devices that might be working within a few feet of the chamber either contaminating the test environment inside, or being exposed to undesireable energy leaking out of the chamber (ie; Harmonics from a Radiated Immunity test).
Q: When we show our chambers to customers, the absorber in our chamber is beat up and embarrassing and our managers want to know if it is still working. Is it possible to make it look better and get better performance?
A: Old ugly absorbers can easily be replaced by re-lining the chamber with our absorber. We do this on a regular basis. Our Project Managers and Installation Teams are quite capable of making this happen. We would recommend performing a Shielding Effectiveness test after the old absorber comes out, but before the new absorber goes up. This way fixing a leaky area can be accomplished much easier.
One of the benefits of our polystyrene absorbers is that they are lighter than polyurethane foam so there’s no concern about needing to enhance the structural integrity of the room.
Q: Does the dimension of the absorber depend on the frequency?
A: The dimensions of the absorber get bigger as the frequency goes down. Typically, Hybrid absorbers (ferrite and pyramidal combination) work from about 25 MHz to beyond 40 GHz. Our automotive EMC absorbers can be a short as 10in. or 25cm. To get reflection loss as low as 30 MHz without the use of ferrite, the absorber will need to be approximately 2.5m in length.
Q: What are those white caps? Are they Ferrite tiles?
A: No, they are made of polystyrene. They are transparent to RF energy at EMC test frequencies and are used to brighten the room by enhancing the lighting. And they provide a protective layer for the pyramidal section. The ferrite tiles are located below the pyamidal section.
Q: What is average lifespan of absorbers?
A: Good absorbers should last at least 25 years. Our polystyrene foam will not lose carbon due to carbon dust falling out. Ferrite tiles do not degrade unless they are exposed to significant heat, such as being placed close to Halogen Lights. Our absorbers are warranted for 25 Years for electrical characteristics as long as the environmental criteria are adhered to according to the warranty.
Q: What length is for 20MHz?
A: This depends on how much absorption (reflection loss) you are in need of. Using Hybrid technology the ferrite tiles can provide ~12dB reflection loss at 20 MHz using 6.05mm ferrite tile. At this frequency, the pyramidal (foam) portion of hybrid absorber is mostly innefective, all of the reflection loss is due to the ferrite. In order to get a reasonable amount of reflectivity loss with ONLY a pramidal type absorber, it would need to be >12ft or >3.75m in length.
Q: How do you mount ferrites on this type of wall structure? Maybe this was touched on in slide 9 – not sure…
A: Good question…
One of the layers in slide 9 (3rd from the right) is a wooden sub-structure attached to vertical furring strips (2nd from the right).
Ferrite tiles are made using a few form factors, however we will talk about only 2 of them. Both are 10cm x 10cm square and they are produced as one solid plane or with a 9mm hole in the center of the square. The hole is there to accept a small screw that would hold the ferrite to the wooden sub-structure. The solid tiles would require adhesive (glue), however, either type can be glued to the sub-structure which is a common method of attachment.
This is typically accomplished using epoxy.
We also use small, pre-assembled panels with 9 ferrite tiles already mounted to an 11-7/8 in. x 11-7/8 in. (29.5 cm x 29.5 cm) wooden sub-structure panel to speed up the process of installation. In this case, the wooden sub-structure layer in the slide is eliminated and the ferrite tiles are guaranteed to be touching.
Gaps between the ferrite tiles are called “shiners” when you use a flashlight to examine the installation. Shiners are a sign of poor workmanship.