No abstract

In the recent, filler-polymer composites researches have been on the rise due to its implication to electromagnetic interference (EMI) applications. The composition, morphology and surface rheology of the filler-polymer composites play an immense role in determining the electrical, mechanical, and optical properties. In this paper, the preparation and characterization of micro-composites of wood (biodegradable waste material)/polycaprolactone (PCL) composites are reported. The micro-composites were prepared using melt blend technique via the solid state route. This method was selected because of its numerous advantages compared to other methods such as being easy, cheap with mass production of materials. To determine attenuation, rectangular waveguide (RWG) method was used. The magnitudes of the transmission coefficient (S 21) from the waveguide measurement were used to determine the attenuation of the wood-PCL composite substrate with respect to different percentages of wood filler. Result from the measurement showed amongst others that as the filler content increases, the attenuation increases. The highest magnitude for attenuation was calculated for the 62.5% wood-PCL composites with a value of −6.46 dB and the least attenuation was calculated for the 12.5% wood micro filler, which value gave −3.34 dB which is good for low shielding applications. Scanning electron microscope (SEM) was used to study the surface morphology of the samples.

Dielectric materials have many important functions in the microelectronics industry. The aim of this research is to characterize the dielectric constant of doped zinc-oxide composites using solid state method at microwave frequency. The methods used in this research are solid state method for sample preparation, open ended coaxial probe (OECP) for determining the dielectric constant and FTIR for bonding and IR absorption properties. The OECP results shows a sequential increase in dielectric constant as pure ZnO is doped incrementally with the filler (NiO). It also shows a sequential decrease in dielectric constant as the frequency increases. The FTIR result shows an increase in IR absorption as NiO content increases. The result from SEM was able to distinguish between the filler and matrix for each composition. Therefore NiO can be used as a filler for improving dielectric constant of ZnO as a matrix. The composite can also serve as a good agent for constructing capacitors and other dielectric materials which are hence used in manufacturing electronic and telecommunication gadgets. It was also proven that solid state method is a good method for synthesis of powdered sample like ZnO and NiO for determining their dielectric constant.

Introduction Microwave devices and communication devices produce electric fields which may be dangerous to surrounding applications. These field can be shielded using conductive shells that are closed on all sides. These close conductive shells are often designed using thin metal foils. However, for many applications these enclosures can add significant cost and weight to a product and a minute gap in the enclosure can completely damage the benefits of the enclosure. Moreso, the metal foil are not flexible to complex geometry. The solution to the gap identified is to use a material that is light, flexible and durable which can shield unwanted electromagnetic wave (EM) waves. For this work, treated and untreated corn husk powder (CHP) was produced from agricultural waste residues by grinding into powder form, while polycaprolactone (PCL) was commercially obtained. Method The composites of the materials were synthesized using melt blending technique. The dielectric property of the produced materials were investigated using open ended coaxial probe technique. The dielectric constant values was used in the computational study of the composites using finite element method. Result Results indicates that the dielectric property of the treated was greater than the untreated composites. The alkali treatment affected the value of the dielectric constant, shielding effectiveness, and transmission coefficients of the composites. The highest dielectric property obtained was 3.42 for the 30 % filler with a loss factor of 0.47. The filler played significant role in the values of shielding effectiveness (SE) obtained, where the highest filler was able to shield radiation by up to -4.21 dB at the frequency range measured. Conclusion From the electric field intensity, it was observed that the highest filler had the minimum transmitted intensity of 2185.87 v/m. Due to the high loss factor of 0.47 obtained for the 30 % filler content, waveguide terminators and other microwave components can be produced from this composite.

There is a continuous generation of electromagnetic fields through operations of electronic devices for this reason it is paramount that these fields be shielded so as to prevent interferences. The, conventional method for shielding these fields are by the use of thin metal foils or sheets. The metals foils are heavy, difficult to fabricate, costly and in many cases not suitable for use in many applications. For these reasons, this work is focused on using materials that is flexible, cost effective and durable, with considerable shielding effectiveness (SE). Hence, polycaprolactone (PCL) and nickel oxide (NiO) nanocomposite were synthesized using the conventional melt blending (CMB) technique. The synthesis method used is fast, easy and produces large mass of controlled composites within a short period. Rectangular waveguide, vector network analyzer, coaxial cable and open ended coaxial probe were used in the measurement of microwave properties. Measured scattering parameter was used to calculate the shielding effectiveness of the NiO/PCL composites. Findings indicates that the dielectric constant increased with increasing filler content, where the highest dielectric property was 5.09 for the 62.5 % filler and it was able to shield electromagnetic fields by up to -9.35 dB at the frequency range measured. The average particle size of the NiO nano particles was 40.5 nm using TEM analysis. The best hardness and tensile strength was recorded for the highest loading percentage. It is then concluded that the substrate produced can be tailored for electronic, telecommunication, medical applications and military shield applications.