Electromagnetic Wave Absorbers — A Solution to Wave Pollution

What is Electromagnetic Wave Absorber?

Electromagnetic wave absorbers are the materials that prevent the reflection or transmission phenomenon of electromagnetic radiations that are incident upon them. Instead, these materials absorb those electromagnetic radiations, which further depends upon many factors that determine the level of absorption they exhibit. The absorption percentage varies for different frequencies, thicknesses and type of material.

Types of Electromagnetic Wave Absorbers

Electromagnetic wave absorbers are mainly of two types:

  • Broadband absorbers: The broadband absorbers do not depend on a particular frequency, so they can work effectively across a broad spectrum. These absorbers generally rely on the materials whose properties are independent of frequency and, therefore, can absorb radiations over a large bandwidth.

Working of Electromagnetic Absorbers

Due to the speedy technological advancements in electromagnetic radiation emitting devices like radars, microwave ovens, computers, and medical equipment, etc., a lot of EM wave pollution is being produced, which is becoming a threat to mankind. This is equally hazardous to the electronic devices themselves and has harmful effects on them. Due to this reason, EMI shielding devices are in great demand these days. The phenomenon of shielding basically occurs through two mechanisms:

  • Reflection of EMR in a particular direction

Measurement of Absorption

At high frequencies, reflection and transmission are easy to measure, so scattering parameters (S-parameters) are generally measured in order to determine the absorption capacity of a material. These are measured with the help of different analysers such as vector network analyser (VNA). The VNA measures the frequency response of a component or a network of components. Rather than voltage and current, the analyser measures the power of incoming and returning high-speed signals because the power of signals can be measured more accurately at high frequencies. The processor of VNA then calculates the return loss and insertion loss of the material. The analysed results are available in different formats such as real/imaginary; magnitude/phase; smith chart etc. The range of frequency for which the electromagnetic properties are tested and number of points across that frequency band become inputs to the VNA. The VNA measures the vector response of a high-speed signal to a network by applying a continuous wave at one frequency at a time.

Different Techniques for Microwave Absorption Analysis:

  • Open circuit technique

Applications of Electromagnetic Wave Absorbers

Electromagnetic wave (EMW) absorbers have many applications varying for different frequency bands of the electromagnetic spectrum. Some of them are mentioned below:

  • Microwave Components: EMW absorbers are used in various microwave components such as filters, emitters, amplifiers, and switches, etc., for proper functionality. With the help of absorbers, these components are able to handle extremely high peak power levels.
  • Energy Harvesting: EMW absorbers are used in solar cells and help to enhance the solar energy collection due to their high absorptivity. The cells are designed in such a way that the surface impedance is matched to free space which results in perfect absorption and hence, maximum energy harvesting.
  • Sensors: EMW absorbers are used in various types of sensors such as multi-frequency sensors, healthcare sensors, thermal sensors, etc., for different application areas such as cancer detection, glucose level measurements, blood diseases diagnostics, etc.
  • Consumer and Industrial electronics: EMW absorbers are widely used in the field of Electronics for mitigation of Electromagnetic interference (EMI), enhancement of electromagnetic compatibility of the devices and development of technology related to the EMI shielding.
  • Defense and Aeronautics: EMW absorbers are largely used as radar absorbing materials in stealth technology such as hidden engines. These are used to lessen the intensity of the reflected signals from the aircraft coverings so that the enemies cannot easily detect defence aircrafts. The absorbers are formed in the form of thin layer absorbing paints and the aircrafts are coated with these paints.
  • Imaging: Absorbers are needed in the field of imaging such as phase imaging, medical imaging and thermal imaging as different types of electromagnetic waves are employed in imaging purposes.
  • For diminishing the mutual coupling of closely placed antennas.
  • For mitigating the harmful effects of cavity resonance in enclosed microwave integrated circuits (MMIC).
  • As protective shields in microwave ovens to prevent any leakage from the oven to the outer environment.

Future Scope and Conclusion

To recapitulate, according to the facts aforementioned above, one can reach to the conclusion that electromagnetic wave absorbers are being researched for a long time. However, due to the incessant increase in the use of wireless communications and various other upcoming technologies, there will be large occurrences of electromagnetic radiations so the concept of electromagnetic wave absorbers will grow significantly in the near future and their utilization will be enhanced in novel directions. There are many great options for the development of EM wave absorbers such as wide bandwidth absorbers instead of frequency selective absorbers. The concept of a unity absorber with zero reflection can be realized in the future with the use of metamaterials that derive their optimum usage from their geometry rather than their electromagnetic properties.

References

1. Tirkey, M., & Gupta, N. (2019), The quest for perfect electromagnetic wave absorber: A review, International Journal of Microwave and Wireless Technologies, 11(2), 151–167, DOI: 10.1017/S1759078718001472

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