The purpose of this study is to determine the effect of heating temperature and the chemical exfoliation process on the reflection loss of r-GO synthesized from coconut shell. The heating process is carried out at temperature of 400°C and 700°C. The chemical exfoliation process is carried out by adding 1M H2SO4 solution in a ratio of 1: 1, 1: 5, and 1:10. Then, the process of washing is done using an ultrasonic cleaner. The XRD pattern indicates that coconut shell charcoal has formed the r-GO phase. In the chemical exfoliation process with the addition of 1M H2SO4 solution in a ratio of 1: 10 at a temperature of 400°C, it shows that the maximum reflection loss is -7.186 dB at 10.48 GHz with an electrical conductivity of 1.075 x 10-3 S/cm.
The purpose of this study is to optimize the thickness of the double-layered microwave absorber for obtaining the highest absorption. The graphenic-based carbon compounds and Fe3O4 magnetic particles were combined to fabricate the double-layered absorber. The thickness was optimized by employing a genetic algorithm (GA) to obtain high reflection loss R L min values. These samples at a thickness of 2 mm were measured for reflection loss (RL) with a Vector Network Analyzer (VNA). Input variables, such as relatively complex permeability and relatively complex permittivity, were obtained using a conversion program that uses Nicolson-Ross-Weir (NRW) method from VNA S-parameter values (S11 and S21) data. By entering the permeability and permittivity of the complex relative to GA, the thickness can be optimized to produce high R L min value. Optimization of the double-layer thickness of 12 absorbers produces the optimum thickness of d 1 = 5.99 mm and d 2 = 0.87 mm among the materials combination, which results in a high R L min (−44.69 dB). This optimization is very important for designing double-layer radar absorbing material (RAM) which results in high R L min values.
In this study, chemical exfoliation with the addition of hydrochloric acid (HCl) solution of old coconut shell reduced graphene oxide (rGO) was carried out. The purpose of this study was to confirm the formation of the rGO phase and to investigate the effect of heating temperature variations and chemical exfoliation processes with the addition of HCl solution on the reflection loss value of old coconut shell rGO. The heating temperature variation is at 400°C and 700°C. Three variations of 1: 1, 1: 5, and 1:10 mole ratios are used in the mixing process of HCl with rGO. Based on the results of XRD testing, the old coconut shell charcoal has formed an rGO phase. Furthermore, VNA testing shows that the biggest reflection loss value is -8.42 dB at a frequency of 10.52 GHz achieved by the sample with the lowest electrical conductivity.
Cu-doped ZnO (CZO) with Cu %mole of 0, 13, 14, and 15% have been synthesized by the co-precipitation method with controlled pH at 9. The diffraction pattern of CZO shows that a single phase of ZnO with wurtzite structure (w-ZnO) was achieved in the parent compound. In contrast, small fractions of the secondary phase of CuO monoclinic (m-CuO) were identified in the doped compounds. Rietveld-refinement on the X-Ray Diffraction (XRD) patterns reveals that the crystallite size of CZO is estimated in the range of 84 - 148 nm with instrumental correction factor and that CZO14 exhibits the most considerable fraction of m-CuO among the samples. Interestingly, lattice constants decrease by Cu doping. The effects of Cu doping on the valence state and the local structure were investigated by X-Ray Absorption Spectroscopy (XAS). Based on our analysis on both Cu K-edge and Zn K-edge XANES spectra, oxidation states of Cu and Zn ions are about +2 with no evidence of other valence states. Cu atom is likely to incorporate into wurtzite crystal lattice by occupying Zn sites in a small portion, and the doped compounds create a few oxygen vacancies.
The purpose of this study is to optimize the thickness of a layered graphenic-based carbon compound, which is a non-magnetic material derived from biomass (old coconut shell). After the sample was exfoliated using HCl solution, the morphological structure showed that the material used in this study is a reduced graphene oxide (rGO), similar to carbon but with a thickness of less than 10 nm and lateral size in submicron (100 nm). The sample with a 2 mm thickness was then characterized using a vector network analyzer (VNA) to measure its reflection loss (RL). The measurement result is evaluated by converting the S-parameter values (S11 and S21) from the VNA using the Nicolsson Ross Weir (NRW) method to obtain input variables such as relative complex permeability and relative complex permittivity. Following this, the single-layer thickness of the sample was optimized using a genetic algorithm (GA), which can predict the appropriate thickness so that the optimum RL can be obtained. The optimum thickness of the sample was found to be 3.48 mm, which resulted in a much higher RL. The RL was re-measured for verification using a sample with the corresponding optimized thickness, revealing that this optimization is feasibly operational for a radar absorbing material (RAM) design. HIGHLIGHTS Carbon compounds containing graphenic phase derived from coconut shell are functional materials having various unique properties such as superior electrical conductivity, large surface area, and excellent structural flexibility, and microwave absorbtion The single-layer microwave absorber employing carbon compounds has been prepared The layer thickness optimized using a genetic algorithm (GA) can estimate the appropriate design with the maximum reflection loss (RL)
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