What Is a Microwave Absorber?
Radar absorbent material (RAM) is a material that absorbs incident radio waves and suppresses their reflection. It is also called a radio wave-absorbing material. The energy of incident radio waves is converted into heat energy and consumed.
Several types of Microwave Absorbers have different principles of absorbing radio waves depending on the material and shape. The frequency band that can be absorbed differs depending on the type. Therefore, it is necessary to select a Microwave Absorber that matches the application and design it appropriately.
Uses of Microwave Absorbers
The main applications of Microwave Absorbers include noise suppression for electronic devices such as communication equipment and home appliances, anti-reflection for ETC and radar, and evaluation facilities such as anechoic chambers. Microwave Absorbers with characteristics suited to each application are used.
For electronic equipment, a sheet type is used that can shield against specific frequencies emitted by the electronic equipment and can be incorporated into the electronic equipment. On the other hand, for evaluation facilities such as anechoic chambers, Microwave Absorbers in a three-dimensional pyramid shape are used, which have absorption characteristics over a wide frequency band.
Principles of Microwave Absorbers
There are several types of Microwave Absorbers depending on the principle of absorbing radio waves, and the three main types are resistive, inductive, and magnetic.
The resistive type absorbs the energy of radio waves by converting the induced current generated by the incident of radio waves on the conductor into heat energy by consuming it due to the conductor’s own resistance.
The dielectric type uses the resistance component of the carbon particles themselves and the capacitance component between the carbon particles by mixing carbon particles with a dielectric such as foamed polyethylene or rubber. When the incident radio wave is low frequency, almost no electric current is generated. However, as the frequency increases, the impedance of the capacitance component decreases, and an electric current flows. The higher the frequency, the lower the impedance of the capacitive element. The higher the frequency, the more current flows, consumed by the resistor and converted into heat energy to absorb the radio wave energy.
Dielectric types are available in pyramid or sheet forms, depending on their shape. The pyramid type can be designed to absorb a wide range of frequencies because the frequency band to be absorbed is determined not only by the material mixed in but also by its shape.
The magnetic type is made of ferrite or other magnetic materials molded into tile-like shapes, which absorb radio wave energy through magnetic loss. The magnetic type can provide absorption characteristics in the low-frequency band compared to the dielectric type. For this reason, Microwave Absorbers have a wide frequency range by combining dielectric and magnetic types.
Other absorbers have a phase difference of 180 degrees concerning the incident wave to cancel out the reflected wave.