Papers by Keyword: Microwave Absorber

Abstract: The proliferation of X-band microwaves across wireless networks, satellite communications, and radar systems has raised global concerns regarding their potential impact on human health and communication security. Additionally, advancements in radar detection technology have diminished the effectiveness of military equipment in modern warfare, driving a heightened demand for materials capable of absorbing microwaves across the X-band spectrum in both civilian and military sectors. Effective microwave absorbing materials (MAM) ideally exhibit lightweight construction, robust absorption capabilities, and a broad effective absorption band. Among the array of reported MAM, rubber-based microwave absorbers emerge as particularly promising for practical application. Their exceptional flexibility, environmental resilience, favorable mechanical properties, versatility, and ease of processing distinguish them in this domain. Cobalt Titanate (CoTiO₃), a common perovskite with the ABO₃ structure, showcases remarkable magnetic and semiconducting characteristics, including outstanding photochemical stability, efficient light absorption, and high carrier mobility. These attributes render it versatile for various applications, spanning catalysis, adsorption, dielectric ceramics, magnetic recording, gas sensors, and pigments. A composite material comprising Cobalt Titanate and Natural Rubber holds significant promise as a microwave absorbing material in the X-band spectrum. Its potential lies in leveraging the synergistic properties of both constituents to achieve enhanced microwave absorption performance, offering substantial implications for various civilian and military applications.

Abstract: The present research focuses on the development of highly efficient and lightweight electromagnetic wave (EMW) absorbers to address the growing issue of electromagnetic pollution. We investigate the use of carbon derived from biomass, specifically durian husks, to create carbon-based microwave absorbers with enhanced performance. A two-step process involving carbonization followed by potassium hydroxide (KOH) activation was employed to synthesize porous carbon materials. The microwave absorption properties were then analyzed using a vector network analyzer across a frequency range from 2 to 18 GHz, with a focus on key parameters such as reflection loss and complex permittivity. The sample, which was 2.0 mm thick and had 15% carbon nanomaterials mixed in with paraffin wax, had an optimal reflection loss of -30.8 dB at 12.8 GHz with an effective absorption bandwidth of 9.0 GHz, highlighting its strong electromagnetic wave absorption performance. The porous structure and large specific surface area significantly contributed to the material’s ability to absorb electromagnetic radiation. These findings highlight the potential of durian husk-derived carbon material as a highly effective and lightweight EMW absorber for practical applications.

Abstract: Microwave absorber is commonly used in defense, electromagnetic compatibility (EMC)/electromagnetic interference (EMI) reduction and anechoic chamber application. Conventional electromagnetic (EM) absorbers have some constraints in practical handling due to its heavy weight. In this paper, the research focuses on the development of high performance and lightweight microwave absorber. A lightweight and simple design configuration of different rectangular slot size array implemented on hollow pyramidal microwave absorber are carried out. There are two different designs of different slot size array calculated based on 3GHz, 6GHz and 9GHz frequency slot size. The two designs have an opposite slots size array arrangement namely different slot size 3GHz, 6GHz, 9GHz order design array and different slot size 9GHz, 6GHz, 3GHz order design array. The absorption is measured using the Naval Research Laboratory (NRL) arch free space method in the frequency range of 1GHz to 12GHz covering L, S, C and X band. In the measurement result, the maximum absorption performance is obtained by the different slot size 9GHz, 6GHz, 3GHz order design array which is up to -44.23dB at X-band. The measurement results for both designs array show good absorption performance which exhibit below than -20dB especially at high frequency band. The proposed designs have been identified as the new approach to increase absorption improvement over a broad frequency range application.

Abstract: In recent year, the development of the electronic devices is rapidly growing and that was used in entire world but electronic devices generate the electromagnetic wave (EM) radiation. That radiation can affect the people’s health and interference normal operation of other electronic devices. Hence the researchers have conducted studies in the field of microwave absorption to reduce the risk of electromagnetic (EM) radiation. Microwave absorber comes with many form and material to enhance the absorption performance. This study aims to improve absorption performance of pyramidal geopolymer microwave absorber by using slotted design. The slotted design used on pyramidal geopolymer microwave absorber is triangular shape and that shape was isosceles triangle type. The hollow pyramidal was coated with a geopolymer absorbing material to form hollow pyramidal microwave absorber. Geopolymers are formed by a process called geopolymerization, which involves the chemical bonding of the ingredients together. This study used sodium silicate (Na₂SiO₃), sodium hydroxide (NaOH), and Powder Activated Carbon (PAC) to make geopolymer absorbing material. Measurement had been done successfully via far field measurement using arch method at 1 GHz to 12 GHz. The absorptivity of hollow pyramidal triangular slotted geopolymer microwave absorber is observed at each frequency band covering the L, S, C and X bands. The result is compared with their maximum absorption in each frequency band and also shows geopolymer material produces good absorption performance. The result shows triangular slotted design is capable of achieving very high absorption performance which is -26.32 dB.

Abstract: The present work investigate the microwave absorption properties of reduced graphene oxide (RGO)-Silicon carbide (SiC)-Linear low-density polyethylene (LLDPE) composites prepared in different concentration of fillers(10, 20, 30, 40 wt. %) with LLDPE matrix. Synthesis of RGO is confirmed from XRD analysis and SiC is used as received from supplier. Complex permittivity of the composites is measured using Nicolson Ross method showing an increasing trend with increasing filler concentrations with maximum and for 40 wt. % composite sample. Based on transmission line theory and using measured value of complex permittivity, conductor backed single and double layer absorber is designed by thickness optimization. The calculated reflection loss (RLc) value of ~-71 dB at 11.23 GHz is observed for 40 wt. % composite sample of 7 mm thickness with -10 dB absorption bandwidth of 1.48 GHz and -20 dB bandwidth of 0.64 GHz.

Abstract: The synthesize of Nd³⁺-strontium hexaferrite magnetic material by the solid-state reaction method has been successfully carried out. This study aims to determine the effect of Nd³⁺ on the structure, magnetic properties, and microwave absorption capability of the material. Preparation of (1-x)SrO:xNd₂O₃:6Fe₂O₃ where x = 0, 10, 20, and 30 mol% using basic material in the form of SrCO₃ powder, Nd₂O₃ powder and Fe₃O₄ from natural iron sand. The characterization includes the X-Ray Diffraction (XRD) examination to determine the crystal structure, the Scanning Electron Microscope (SEM) for exploring the surface morphology, Vibrating Sample Magnetometer (VSM) for the magnetic properties investigation of material, and Vector Network Analyzer (VNA) for microwave absorption capability analysis. The XRD results show that the addition of Nd³⁺ doping increases the number of SrNdFeO₄ phases. The phase has a tetragonal crystal system that has cell parameters a = b = 3.846 Å, and c = 12.594 Å. The magnetic properties of the material showed that the addition of Nd³⁺ decreased the saturation and remanence magnetization values, whereas the value of the coercivity field increased. Meanwhile, the best microwave absorption occurs in samples with the addition of Nd³⁺ as much as 0.3 mol, which results in a reflection loss value of -18.9 dB with a frequency bandwidth of 3.9 GHz.

Abstract: The synthesis and characterization of the Ba_0.6Sr_0.4Fe_12-3xZn_2xTi_xO₁₉ microwave material with x = 0, 0.2, 0.4, and 0.6 has been successfully carried out. Samples were processed with the solid reaction method through milling at seven hundred revolutions per minute for five hours. X-ray diffraction was used to characterize the phase formation and crystal structure. Scanning electron microscopy was used to see the shape and size of particles, while the vibrating sample magnetometer was used to measure magnetic quantities, which are: the coercivity field and magnetic saturation. All samples have a hexagonal structure, for samples x = 0 and 0.2 have a single phase, while for samples x = 0.4 and 0.6 other phases are detected. The shape of the particles are heterogeneous, with size ranging from 10-25 μm. All samples were not saturated even until the external magnetic field reaches 1 T. As the value of x increases, the magnetization will decrease. Samples substituted by Zn and Ti (x ≠ 0) have higher coercivity field values when compared to sample without substitution (x = 0).

Abstract: Microwave absorption characteristics of double layer of barium hexaferrite attached on the silica to from a composite on the basis of wave propagation theory have been investigated. Barium hexaferrite, BaFe₁₂O₁₉, was synthesized through ceramic method from stoichiometric mixtures of BaCO₃ and Fe₂O₃ as precursors. The mixture was pelletized under the pressure of 10 MPa and sintered at 1100 °C for 5 hours. Silica in the forms of powder was purified by using HCl. The crystal structure of the samples was characterized using X-ray diffraction (XRD), microstructure was examined using scanning electron microscope (SEM), hysteresis curves recorded by PERMAGRAPH techniques, whereas the microwave absorbing properties for X-band was recorded using a vector network analyzer (VNA). Relative complex permeability and permittivity, and reflection loss values were calculated at given thickness according to transmittance line theory within the range 8.2–12.4 GHz. Based on this study, the layer dimension and frequency that results in low reflection loss can be estimated from the material properties of the barium hexaferrite/silica composite material.

Abstract: This paper will introduce the new technique to design new type of microwave absorber. Microwave absorbers are used in anechoic chamber to diminish the unwanted RF signal, so that the measurement obtain have perfect and good results. The basic theories of slot antenna combining with the theory of microwave absorber are used in this paper. As a result of studies, the new design called as the slot radial array design on hollow pyramidal microwave absorber. The design of pyramidal microwave absorber and the slot was introducing in this paper. The simulation process was done by using CST software. The new design of the absorber was measured to make sure it can be compared in terms of the performance. Lastly, the performance of new slot radial array design pyramidal microwave absorber will be analysed by identifying the characteristics performance. The Slot Radial Array proved to be as one of the way to improve the performance.

Abstract: Radiation Absorbing Material (RAM) is used to absorb radiations of electromagnetic wave surrounding us. Thus, the multiple layers’ microwave absorber using biomass composite materials could be one of the solutions to address the problem. In order to effectively absorb the radiation of electromagnetic wave, the multiple layers’ absorber is characterized to optimize the performance of the absorber. The characterization is made by varying biomass composite material contents, thickness and other possible considerations. CST Microwave Studio software is first used to design and simulate the multiple layers’ absorber to estimate its performance. Development of multiple layers’ prototype is carried out to test its performance at free space environment. Free space dielectric measurement method is used to determine the value of multiple layers’ absorber dielectric. The dielectric value is then used in CST software in order to make the simulation more precise. Free space arch which is connected to Agilent Analyzer is used to measure absorption of multiple layers’ microwave absorber.