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Microwave absorbers are made of special materials that are used to curb and contain electromagnetic radiation from electrical appliances.  Absorbers are often elastomers or rubber-based which makes them user-friendly. Microwave absorbers provide effective absorption performance over frequencies of 500MHz to 18GHz. A microwave absorber is considered to be a dielectric medium. Since it is an electric insulator, it can be polarized in the required direction of an electric field. Due to dielectric polarization, there develops an interior electric field inside the dielectric.

What are the different classes of microwave absorbers?

There are different types of microwave absorbers that work with different frequencies and attenuation ranges. The various types of microwave absorbers are:

Broadband: These types of absorbers work on a broader range of frequencies, with low to moderate attenuation. These absorbers are based on asymmetric sectional resonator structures. In simple language, it means that the absorption of an absorber can be obtained by bringing together four or more asymmetric resonators together. The most common areas of application for broadband absorbers are energy harvesting and stealth technology. The absorption capacity and shielding capacity of broadband absorbers can significantly improve by the introduction of layered structures. Broadband absorbers are lightweight and have an increasing demand for electronic safety which is reliable and high performing.

Narrowband: These types of absorbers operate on a lower range of frequencies with high attenuation. Narrowband absorbers make use of the metamaterial properties of thick metallic grating which promotes complete absorption of transverse and magnetic polarized microwaves. The metals are believed to be complete reflectors inside the microwave. This is the reason why absorption properties of metals are accessed.

Cavity resonance absorbers: cavity resonance absorbers resemble elastomeric binders. They are intended to be applied on the metallic surface to bring the Q factor down of the cavity.  These are magnetically loaded sheet stocks that work at a high loss of microwave frequencies. These are comfortable working with frequencies that lie between 1GHz to 20GHz. These come in different levels of dielectric grades which are characterized by low levels of insertion loss at any given frequency. The absorbers can be coated with fabric that offers a protective coating. Cavity resonance absorbers find applications in amplifiers, radios, TV satellite systems, and oscillator cavities. They work with attenuate surface currents and significantly help with RF leakage areas.

Surface waves microwave absorbers: These are thin-loaded sheet stocks that work at a loss of frequencies. These are the most heavily loaded and functioning magnetic absorbers. They are meant to be applied on the surface of the metals for surface wave attenuation. Silicone is the standard elastomer for surface waves microwave absorbers. Inside a shielding can, these absorbers have a high-frequency interference. These are often mounted directly on the microstrip and look after the EMI reduction. These absorbers work with resonant cavity attenuation which promotes surface absorption.

Dielectric foam: these are carbon-loaded absorbers that provide a high level of wave loss at several incident angles. They have a broadband performance frequency between 1GHz to 40GHz. This carbon form base material can also be coated to prevent dust release.