جستجوی مقالات مرتبط با کلیدواژه « electromagnetic wave absorption » در نشریات گروه « فنی و مهندسی »

In this study, barium strontium titanate/cobalt zinc ferrite composites that composed of two different magnetic phases were investigated. Pyroelectric phase consists of barium strontium titanate particles with particle size of about 150 nm and soft magnetic phase consists of cobalt zinc ferrite nanoparticles with particle size of about 30 nm. Two phases were prepared with sol-gel method and under appropriate stoichiometry. XRD analyses indicated formation of pure phase for each magnetic phases and FESEM analysis indicate the structural properties of Cobalt-Zinc ferrite and Barium Strontium Titanate nanoparticles. Investigation of permittivity, permeability and reflection loss of samples indicated the response of electromagnetic waves to these samples in the frequency range of 1-18 GHz. According to the reflection loss of composites, there are two mechanisms for the absorption of electromagnetic waves. In the first region of this frequency band, magnetic loss from Cobalt-Zinc ferrite nanoparticles is dominate and in the last region of this frequency band, dielectric loss from barium strontium titanate is dominate.

Electromagnetic compatibility (EMC) and electromagnetic interference (EMI) have emerged as key issues with respect to commercial and military purposes in association with electromagnetic waves. The importance of protection against electromagnetic interference in wireless communication and electronic toll collection (ETC) systems has undoubtedly increased over the years. Generally، the electromagnetic absorption properties of material depend on their intrinsic electromagnetic properties such as conductivity، magnetic permeability and dielectric constant and also factors such as thickness and frequency. The effect of each parameter on the absorption performance is yet difficult to comprehend due to the complexity of electromagnetic waves propagation in different media. Addition of pure dielectric or magnetic material to a polymer matrix is a possible way to change electromagnetic properties of the materials. In this study nanocomposites of polystyrene/multi-walled carbon nanotubes were prepared using a solution method with three different homogenizer speeds for the purpose of nanotube dispersion and evaluation of the effect of nanotube dispersion on the electromagnetic wave absorption properties. The morphology of the nanocomposits was investigated by scanning electron microscopy (SEM). The capability and properties of electromagnetic wave absorption of nanocomposites were studied in the frequency range of 5 to 8 GHz using a vector network analyzer and finally the results of their absorption were compared with each other. It was found that by improving the dispersion of nanoparticles، both the amount and bandwidth of absorption increase. Moreover، by increasing the homogenizer speed up to 10000 rpm the maximum reflection loss was reported to occur at 8 GHz.