Phones require an absorber.
In this era of technology and wireless communication, the need for absorbers increases. As Vladimir B. Bregar et al wrote in their paper "Development and Characterization of an Electromagnetic Absorber," because the use of radar and wireless communications increases, there is a significant increase in electromagnet radiation that requires a corresponding increase in the need to "protect both electronic devices and humans from the adverse effects of this [electromagnetic] radiation." As might be expected, thanks to the multitude of wireless and radar devices, there is a need for many types of absorbers.
Resonant Absorber
A resonant absorber works well for a limited frequency band. These resonant absorbers are generally thin and are often made from a sheet made of polyurethane or silicone. These absorbers are an excellent choice for use in radio equipment that has a narrow band. It works well for frequencies between 1.5 to 18 GHz.
Ferrite Absorber
A ferrite absorber can be either soft or hard and made of ceramic. These absorbers work well in broadband applications. Ferrite absorbers are usually made of Manganese-Zinc ferrite and Nickel-Zinc ferrite. Absorbers made of Nickel-Zinc ferrite are commonly used in EMC chambers or chambers that are used to conduct tests as well as measurements of radiation.
Multi-layer Absorber
A multi-layer absorber consists of layers of foam with varying levels of carbon loading. The foam used in these absorbers is usually polymer foam. The different layers of this absorber have different roles: The first layer absorbs the impedance of air, the second electromagnetic energy. Depending on the number of layers, the electromagnetic energy can be reduced still further, depending on the requirements of the device or machine in which this absorber is used. The presence of carbon in the absorber means that it will be used in conjunction with an electric load, though these absorbers work well with a magnetic load as well.
Geometric Transition Absorbers
These absorbers can be divided into four forms within this category: pyramidal absorber, which resembles the back of a porcupine; a truncated pyramidal absorber, which resembles a porcupine with dulled spines; a wedge absorber, which resembles stiff waves; and the convoluted microwave absorber, which resembles the interior of a flattened egg carton. These absorbers are all made of foam; of them all, the pyramidal absorber is the most common. The pyramidal absorber works well for high frequencies, for the spikes help channel any reflections down into the depths of the absorber. The truncated pyramidal absorber is also used in EMC chambers (see Section 3), though it can be used effectively for frequencies that are more than 1 GHz. The wedge absorber works especially well where the intention is to direct the energy in a chamber into a terminating wall. The convoluted microwave absorber works well for broad-band microwaves.
Combination Absorbers
As might be imagined, it's possible to have a combination absorber that makes use of the varying kinds of absorbers to create a hybrid absorber as well as a mixed absorber. For example, you can have a ferrite absorber and a pyramidal absorber used in combination, which works well for bandwidths ranging from 30 MHz to 100 GHz. This combination is often referred to as a hybrid absorber. However, if you mix a geometric absorber with a multi-layer absorber, the range of bandwidth increases: 30 MHz up to 100 GHz. This cimbination of absorbers is termed a mixed absorber.
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