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Abstract:The dielectric and magnetic behaviour and thermal properties of composites based on nickel-zinc ferrite (NZF) filler can be improved by the addition of various types of materials. Amongst others, ferrite-polymer composites have been subjected to a wide range of research, due to their extensive applications: electromagnetic interference shielding, microwave absorption, electrodes and sensors. Currently, the interest in scientific and technical searches for the potential outcomes of ferrite-polymer materials due to their different uses in applications such as telecommunication applications, microwave devices and electromagnetic interference shielding has been growing stronger. The dielectric and magnetic behaviour and thermal properties for such composite materials depend on size, shape and the amount of filler addition. Nickel-zinc ferrite material was prepared using the conventional solid-state reaction technique. This study highlights the development of microwave-absorbing material from NZF by adding natural fibres, Oil Palm Empty Fruit Bunch (OPEFB) and polycaprolactone (PCL). OPEFB is considered in this study because it is a solid waste product of the oil palm milling process which is widely and cheaply available. The use of OPEFB in this product may save the environment from oil palm solid waste. A Thermal Hake blending machine was used in blending the powder structure of NZF + OPEFB + PCL, which made it homogeneous. These composites were characterized by the use of Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM). The thermal degradation behaviour of the composites was analyzed using thermogravimetric analysis (TGA) and differential thermogravimetric (DTG) thermograms. The effective permittivity and effective permeability was obtained over a broad frequency range from 8 to 12 GHz at room temperature. It was observed that the values of effective permittivity and permeability increased as the content of NZF content increased. A rectangular waveguide connected to a microwave vector network analyser (PNA) (HP/Agilent model PNA E8364B) was employed in measuring the reflection coefficient S 11 and transmission coefficient S 21 parameters of composites for different percentages of NZF filler. This parameter was then used in calculating the microwave absorbing properties (dB).

The development of microwave absorbing materials based on recycled hematite (α-Fe 2 O 3 ) nanoparticles and polycaprolactone (PCL) was the main focus of this study. α-Fe 2 O 3 was recycled from mill scale and reduced to nanoparticles through high energy ball milling in order to improve its complex permittivity properties. Different compositions (5% wt., 10% wt., 15% wt. and 20% wt.) of the recycled α-Fe 2 O 3 nanoparticles were melt-blended with PCL using a twin screw extruder to fabricate recycled α-Fe 2 O 3 /PCL nanocomposites. The samples were characterized for their microstructural properties through X - ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The complex permittivity and microwave absorption properties were respectively measured using the open ended coaxial (OEC) probe and a microstrip in connection with a vector network analyzer in the 1–4 GHz frequency range. An average α-Fe 2 O 3 nanoparticle size of 16.2 nm was obtained with a maximum imaginary (ε " ) part of permittivity value of 0.54 at 4 GHz. The complex permittivity and power loss values of the nanocomposites increased with recycled α-Fe 2 O 3 nanofiller content. At 2.4 GHz, the power loss (dB) values obtained for all the nanocomposites were between 13.3 dB and 14.4 dB and at 3.4 GHz, a maximum value of 16.37 dB was achieved for the 20 % wt. nanocomposite. The recycled α-Fe 2 O 3 /PCL nanocomposites have the potential for use in noise reduction applications in the 1–4 GHz range.

Epoxy resin (ER) composites reinforced with micro‐sized oil palm empty fruit bunch (OPEFB) were fabricated to improve the biodegradability of electromagnetic interference connector gasket. The dielectric properties, transmission coefficient |S21|, reflection coefficient |S11|, reflection loss, power loss and shielding effectiveness were studied at a frequency range of 8–12 GHz. OPEFB–ER composites were prepared by varying the percentages of OPEFB (0, 5, 10, 15, 20, 25, 30 and 40%) at room temperature (25°C ±2). Dielectric constant (ɛ′), loss factor (ɛ″), reflection and transmission coefficients of the composites were measured using rectangular waveguide connected to vector network analyser. In addition, ɛ′ and ɛ″ were used in finite element method technique to obtain |S11| and |S21|. The results showed that the dielectric properties increased but |S11| and |S21| decreased with increasing OPEFB percentage in the composites. The shielding effectiveness, power loss and reflection loss increased with increasing OPEFB percentage in the composites. The simulated and measured results of |S11| and |S21| were in good agreement.

A material description was established for oil palm empty fruit bunch (OPEFB) fibre waste for microwave absorber applications by determining its dielectric properties with respect to fibre size and frequency. The proposed OPEFB material was studied at frequencies from 1 to 4 GHz. The study was conducted using the open-ended coaxial probe (OECP) HP85071C technique. The effect of microwave frequency on complex permittivity properties for powdered OPEFB and compressed OPEFB with different particle sizes (100, 200, 300, 400, and 500 μm) were investigated. Results showed that the microwave frequency and particle size significantly influenced the complex permittivity (real and imaginary) properties of the samples. Moreover, the complex permittivity decreased as the powder fibre size increased. The complex permittivity of the smallest and largest powder fibre sizes (100 and 500 μm) were (2.050 − j 0.197) and (1.934 − j 0.137), respectively; and the complex permittivity of the smallest and largest compressed OPEFB fibre sizes (100 and 500 μm) were (3.799 − j0.603) and (3.326 − j0.486), respectively. The compressed OPEFB complex permittivity was higher than that of the OPEFB powder.