Mechanical and electromagnetic shielding properties of carbon fiber reinforced silicon carbide matrix composites

Reflection of microwave radiations from single layer and two-layer materials is calculated. Microwave absorbing materials are formulated by mixing a commercially available paint or rubber with the conducting polypyrrole (PPy) powder. The reflection loss strongly depends on thickness and complex permittivity of the material. For a single layer material, optimum values of the real part, ɛ′, and imaginary part, ɛ′′, of the complex permittivity are found by calculations which lead to a minimum reflectivity at a given sample thickness. The ability to readily tailor the conductivity of the PPy powder enables the design of microwave absorbers according to theoretical desired values of ɛ′ and ɛ′′. A paint panel containing 2 wt% of PPy powder with a thickness of 2.5 mm exhibits a reflectivity < − 10 dB (i.e. at least 90% absorption of the incident radiation) over 12 to 18 GHz. Blending and milling during the manufacturing process can destroy the original fibrous shape of PPy aggregates leading to low radiation absorption. In an attempt to achieve a broadband absorber, a two-layer system consisting of a first layer containing PPy powder and a second layer containing carbonyl iron has been fabricated.

Polypyrrole Based Microwave Absorbers

Electromagnetic properties and mechanisms of multiwalled carbon nanotubes modified cementitious composites

With the advent of more sophisticated network analyzers and spectrum analyzers, the ability to fully characterize the constitutive parameters of material over very broad frequency ranges has become feasible with relatively simple fixtures. The paper reviews various methods of measurement and the advantages and limitations of each technique. Newer methods, such as the permeameter and force gradient magnetometer, are examined as well as older approaches such as the VSM and transmission line methods. A brief discussion of shielding measurements and simple models is included. A comprehensive reference list is provided. >

Measurement techniques for permeability, permittivity and EMI shielding: a review

Static bifurcation of electromagnetic wave transmission differential equation for multilayered structural composite materials has been studied to explain the transformation effect of absorption and reflection. Experimental result is given to illustrate the absorption and reflection transformation caused by variation of inherent impedance of the composite.

Bifurcation analysis of absorption and reflection effects in electromagnetic wave absorbing composites with multi-layered structure

Permeability and permittivity measurement and reflectivity calculation for a microwave-absorbing composite material containing a resonator and an electromagnetic loss substance

Y.X. Gan

Papers

Permeability and permittivity measurement and reflectivity calculation for a microwave-absorbing composite material containing a resonator and an electromagnetic loss substance