RF/Microwave Absorbers – Broadband/Narrowband

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. NEDC is a Laird converter, and can provide many different types of RF absorber solutions through supply chain.

 

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. This approach offers superior electromagnetic interference solutions compared to traditional EMI gaskets. The materials are available in various formulations for RF absorber manufacturing, including silicone-based elastomers that balance temperature resistance with effective RF absorption across 1-40GHz frequency ranges. 

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 Absorbers

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.