DESIGN GUIDE FOR COMMERCIAL MICROWAVE ABSORBERS

- May 02, 2019-

Microwave absorbers have been used in military applications for several decades. They have been traditionally used for EMI reduction, antenna pattern shaping and radar cross reduction. More recently with the rise of wireless electronics and the movement to higher frequencies microwave absorbers or “noise suppression sheets” (NSS) are used to reduce electromagnetic interference (EMI) inside of the wireless electronics assemblies. 


Two types of NSS are used for these types of applications. They are described below:


MAGNETIC ABSORBERS 

These are thin (.1 to 3 mm) polymeric materials filled with magnetic particles. These materials have both high permeability (magnetic loss properties) and high permittivity (dielectric loss properties). This combination of properties makes these materials very effective in eliminating high frequency EMI

NEWLIFE has two product types that are used for commercial applications:


• HP (high permeability) uses novel magnetic fillers to achieve extremely high permeabilities at low frequencies. This allows for relatively thin materials to provide EMI reduction at frequencies below 2 GHz. This material comes in thicknesses of .15 mm and .5 mm.

 •  HF (high frequency) is the optimum choice for cavity resonance problems from 2-18 GHz and higher. The material is available in thicknesses from .5mm to 3.2 mm and is supplied in sheets or as die cut components. Both materials are UL-VO and ROHS compliant. They can be supplied with pressure sensitive adhesive (PSA) for ease of installation.


FOAM ABSORBERS 

These absorbers are based upon open celled foam impregnated with a carbon coating. The carbon coating makes the resultant product lossy at microwave frequencies, indeed acting like a free space resistor to incoming electromagnetic energy. These foam products range from 3.2 mm to 6.4 mm for internal cavity applications and can be several centimeters thick for outdoor applications. Two main product types are offered by NEWLIFE.


• RFLS- Lossy sheets are uniformly loaded with the carbon coating and used at 3.2 mm and 6.4 mm thick. They are supplied as sheet materials and may have PSA applied and fire retardant coatings. 

• RFRET- is a reticulated foam based absorber. The materials are thicker ranging from 3/8” to 2” in thickness. They can be used for air filtration and EMI, or on the inside of cabinet doors for broadband EMI attenuation.