NEDC manufactures RF/Microwave absorbers into custom shapes through die-cutting, and waterjet cutting. Microwave absorbers have been used in military applications since their inception. However, more and more microwave absorbers are used in commercial applications. Applications such as computers, consumer electronics, network servers, and wireless antenna systems are common with microwave absorbers.
What are Microwave Absorbers?
Oftentimes electronics can cause cavity resonances inside of electronic enclosures. Different types of microwave absorbers can be employed to attenuate the signal. The problem with normal EMI gaskets is they can actually exacerbate the problem by creating an additional conductive surface. This contains the issue within the cavity. Microwave Absorbers function by eliminating cavity resonances through lossy magnetic materials. Magnetically loaded elastomers are most seen by NEDC. Oftentimes electrical engineers will pick and place the microwave absorbers along the enclosure and then test the device. This is usually preferable to the time-consuming and complex nature of selecting a material by modeling.
What type of Microwave Absorbers are available?
There are a few different considerations when reviewing the different types of absorbers available. There is frequency ranges, elastomers, and differently loaded materials.
Dielectrically Loaded Materials
Dielectrically Loaded materials are typically foam materials coated with carbon. These foams are open-cell elastomers that can be made up of multiple layers. Obviously these foams are much thicker than their magnetically loaded elastomer counterparts. They range from .125”(3.2mm) to 2.00”(5.08mm) in thickness. This is a drawback with these foams. At .125”(3.2mm) being the thinnest available size can become a concern. With smaller and smaller packages coming to market size matters.
Magnetically Loaded Materials
NEDC commonly deals with elastomeric like absorbing materials. These materials are typically magnetically loaded with iron-based fillers. Different loading levels of the ferrous fillers affect the level of attenuation. Manufacturers design different absorber materials to withstand different environments. Oftentimes silicone rubber is the binder material, but other materials such as nitrile, neoprene, and urethane can be used. However for NEDC, silicone-based elastomers are still the most commonly seen. This is because silicone offers a great balance of temperature range, availability, Different manufacturers offer different options for different applications including high-temperature, different frequency requirements, and assembly options. NEDC cuts magnetically loaded absorbers as thin as .010’’ to as thick as .250’’.
Broadband is the largest category of microwave absorbers. These products operate over a bigger frequency spectrum. Broadband absorbers are much more available. For that reason, NEDC deals with mostly broadband microwave absorbers. They offer a great price point that ultimately offers great value for most applications.
It is good to keep in mind that while broadband absorbers are more available, narrowband absorbers exist. These narrowband absorbers absorb at a specific frequency. Custom thicknesses, and formulations can help address more narrow frequencies that may need to be attenuated. Many different manufacturers offer microwave absorbers. Finding the right one for your application may take time, but there are many options available.
Manufacturers of Microwave Absorbers
- 3M Company
- Mast Technologies
- 3G Shielding
- Cuming Microwave
Cutting Methods/Application Notes on Microwave Absorbers
NEDC die-cuts and waterjet cuts these materials into unique shapes. Typically, absorbers are placed in enclosures two ways. The first is through the use of RTV(room-temperature vulcanizing) adhesives. These RTVs usually take time to cure, and are a bit more labor intensive. The second is through the use of tape. Most absorbers are available with tape backing to enable easy placement of the absorbers onto different surfaces. However, it is good to keep in mind the surface the absorber is being placed on when choosing either method. When using either method of application, a properly cleaned surface, and following the manufacturers datasheet is critical.
For more information on RF/microwave absorbers, please contact firstname.lastname@example.org.
RF Absorbers Blog
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All of the information presented above is believed to be factual and accurate; however, NEDC is not liable for any design or application utilizing this information.
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