Dielectric or Magnetic Resonant Frequency Absorbers: Which One to Choose?


Microwave absorbers are used to solve a number of problems like high-frequency interference, antenna pattern shaping or cavity resonances. These materials are used in sectors such as aerospace, military as well as consumer electronics to improve appliance performance. The magnetic or electrical properties present in the microwave absorbing materials are modified to help in the absorption of microwave energy and radiofrequency interference.

The common dielectric materials include plastics, elastomers and foams with zero magnetic properties. Their permeability value is one. The high dielectric materials like fibers, carbon and graphite are generally used to tweak the dielectric properties of the fundamental material. When you use magnetically loaded substances, the fillers like iron, unique alloys or ferrites help to improve the permeability of the basic material. So, which of the two are you going to choose? Read on to get your answers.


Dielectric Microwave Absorbers

Dielectric microwave absorbers have good absorption capabilities. This is possible via a measured narrowing of impedance from a free space to that of a lossy condition. You’ll find less initial reflection in materials with sufficient transformation from a free space to a lossy state. This leads to maximum levels of attenuation. As far as the absorption agency or medium is concerned, it is made of a conductive carbon coating. This is layered upon a polyurethane-based foam surface or substrate. Materials with less than one-third of wavelength thickness can achieve maximum levels of reflection loss. In most of the cases, it is more than 20dB.

As far as the reticulated foam absorbing materials are concerned, they are open-celled, and help you use a tapered carbon layering throughout the foam’s thickness, thus reducing preliminary reflections. You can attain graded impedance by narrowing the coatings manually as done with convoluted foam absorbers. You’ll find graded dielectric microwave absorbers having thickness of 0.125 inches to 5 inches.

Magnetic Resonant Frequency Absorbers

Opt for magnetic resonant frequency absorbers to absorb energy at a distinct frequency or at numerous frequencies. These magnetic absorbing materials function through phase cancellation. The wave incident on the absorbing substance is partly reflected and partly radiated. The radiated parts are subjected to several internal reflections. This gives rise to a number of potential waves. Theoretically, no reflection occurs at the design frequency, however, practically, an absorption rate of more than 30dB could be achieved.

The commonly resonant frequency absorbers include the distributed magnetic filters suspended in a supple elastomeric matrix. If you increase the permittivity and permeability of the elastomer, the refractive index will also increase. This lets you use a finer material. You will get magnetic resonant absorbers in a thickness from 0.020 to 0.175 inches. The amount of thickness depends on the frequency of the materials for which they are optimized. Depending on phase cancellation, the lesser the attenuated frequency, the thicker should be the absorbing material.

Making the Right Choice

Choose the right material by consulting with the designers of microwave absorbers and RF absorbing products. They will be help you select the right product based on physical, electrical and application properties. The engineers will be able to help you choose the right absorber by accounting for frequency band, desired impact, coverage area, surface wave attenuation and environment.

Opt for dielectric absorbing materials if you are to use them in a protected environment. It’s true that polyurethane foams are good at checking interference, but when exposed to harsh surroundings, they may fail in due course of time. Magnetic absorbing materials, on the contrary, provide more environmental resistance compared to dielectric materials. They are used in microwave and radiofrequency absorbers even in the most disagreeable environments.

Choose the right microwave absorber based on your requirements and the material’s absorbing efficiency. Talk to a reliable shielding supplier to make an informed decision.

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