Farohaji Kurniawan

This work evaluates the impact of manufacturing method and fiber orientation on the mechanical properties of carbon fiber-reinforced polymer (CFRP) for automotive applications. CFRP composites were fabricated using vacuum bagging (VB), vacuum-assisted resin infusion (VARI), and hand lay-up (HLU) processes. Composites in each method were manufactured with 0° and 90° fiber orientations for compressive and tensile tests, and ±45° for in-plane shear response by tensile test. Short beam and V-notched beam tests were performed to determine the interlaminar shear and shear properties. Microstructural characterization was performed on the manufactured composites and the fracture specimens after testing. Unlike previous studies that mainly focused on selected mechanical properties or a single manufacturing route, this study provides a comprehensive comparative assessment of HLU, VB, and VARI unidirectional CFRP laminates by integrating mechanical characterization, CT-scan defect analysis, SEM observations, and finite element validation. The findings reveal that superior laminate compactness and tensile-related properties achieved by VARI do not necessarily translate into higher interlaminar shear strength, providing new insight into the role of manufacturing-induced laminate architecture on composite performance. The study results showed that composites manufactured with vacuum infusion using 0° and ±45° fiber direction had higher tensile strength and stiffness than those fabricated with vacuum bagging and hand lay-up. The ultimate tensile strengths of the 0° CFRP composites for HLU, VB, and VARI specimens are 507.72 ± 52.14 MPa, 685.69 ± 62.65 MPa, and 774.31 ± 58.18 MPa, respectively. Meanwhile, for the 45° CFRP composite specimens, the tensile strength values were measured as 20.85 ± 0.82 MPa for HLU, 21.20 ± 0.45 MPa for VB, and 22.18 ± 0.81 MPa for VARI. However, at 90° fiber direction, the manufacturing method did not significantly affect the tensile strength, although the tensile modulus was still affected by the method used. The compressive strength results of the 0° composites showed that hand lay-up specimens (124.8 ± 13.1 MPa) had the highest values, while vacuum infusion specimens had the highest compressive strength at 90° fiber direction (44.60 ± 0.82 MPa). The vacuum infusion composites had lower shear (15.31 ± 1.01 MPa) and interlaminar shear strength (13.68 ± 0.85 MPa), indicating that the high fiber volume fraction did not significantly affect this behavior. However, it has a significant effect on composite stiffness, where the tensile (39.31 ± 4.58 GPa) and shear (1.50 ± 0.15 GPa) modulus values of these composites are the highest. Microstructural evaluation showed that the improvement of resin distribution and fiber/matrix bonding in vacuum infusion composites contributed to the improvement in mechanical properties.

The mixer is an essential component in RF transceiver subsystems. It has a role in shifting the signal frequency for more convenient processing of up-conversion as well as down-conversion. Despite generating the desired signal, the mixer also generates spurious noise that wastes power and reduces the performance of the overall system. This research proposes the design of a microstrip mixer that can enhance the suppression of spurious signals by utilizing the characteristics of the load resistor termination. The simulation results show that by adding the load resistor, the parasitic electrical field on the diode and the reflection signal inside the mixer can be reduced. The measurement result also validates that the suppression of the spurious signal is enhanced, where the signal-to-noise ratio can reach above 50 dB on the single-balanced mixer and above 60 dB on the double-balanced mixer.

Light weight dual polarized horn antenna for polarimetry C-band synthetic aperture radar sensor onboard UAV

The effect of printing parameters (nozzle diameter, layer height, nozzle temperature, and printing speed), dimensions (wall thickness), and filament material on the crashworthiness performance of 3D-printed thin-walled multi-cell structures (TWMCS) undergoing quasi-static compression is presented. The ideal combination of parameters was determined by employing the Signal-to-Noise ratio (S/N), while Analysis of Variance (ANOVA) was utilized to identify the significant parameters and assess their impact on crashworthiness performance. The findings indicated that the ideal parameters for the specific energy absorption (SEA) consisted of a nozzle diameter of 0.6 mm, layer height of 0.3 mm, nozzle temperature of 220 °C, printing speed of 90 mm/s, wall thickness of 1.6 mm, and PLA(+) filament material. Afterward, the optimal parameters for crushing force efficiency (CFE) included a nozzle diameter of 0.8 mm, layer height of 0.3 mm, nozzle temperature of 230 °C, print speed of 90 mm/s, wall thickness of 1.6 mm, and PLA(ST) filament material. The optimum parameter to minimize manufacturing time is 0.3 mm for layer height and 90 mm/s for printing speed. This research presents novel opportunities for optimizing lightweight structures with enhanced energy absorption capacities. These advancements hold the potential to elevate passenger safety and fortify transportation systems. By elucidating the fundamental factors governing the crashworthiness of thin-walled multi-cell PLA 3D-printed tubes, this study contributes to a deeper understanding of the field.

A custom lithium-Ion battery was built for the payload system on a single-engine two-seaters glider. The stages of software development in forming the Battery Management System as a way to provide security in the charging and discharging processes need some parameters to indicate the conditions of the battery. Therefore, in this study, the process of the State of Charge estimation which used in the Electrical Equivalent Circuit Methods and Adaptive Extended Kalman Filter was carried out in a 42 Ah Li-ion battery. As the results, a Mean Absolute Error, and a Root Mean Square Error in which the value of less than 1%. In the actual process, the real error value has never been discovered. The noise is given to determine the adaptive ability between the extended Kalman Filter and the Adaptive Extended Kalman Filter (AEKF) algorithms. In addition, the primary SoC is set at a certain value to see the estimation accuracy. The investigation shows that this method is possible to be applied in the development of the BMS software for payload systems.

Synthetic Aperture Radar (SAR) is a very powerful tool in microwave remote sensing due to its capability of all-weather and day-to-night time operation [1]. Carl Wiley invented SAR in 1951 to overcome the poor azimuth resolution in conventional Side-Looking Airborne Radar (SLAR), followed by a patent filed in 1954 [2]. Unlike SLAR, using the forward motion of the platform and the principle of Doppler beam sharpening, the azimuth resolution of a SAR is equal to half the antenna length and is independent of the range distance [3]. Since the invention of SAR, steered by the breakthrough in science and technology, many advanced SAR techniques have been proposed and realized. These techniques include, but are not limited to, spotlight SAR for a finer image resolution [4], scan SAR for a wider swath coverage [5], and the remarkable polarimetric [6] and interferometric [7] SAR techniques using multichannel SAR system [8], [9], [10] for advanced remote sensing applications. Over the years, SAR has been widely used in different types of application, particularly in Earth observation such as disaster damage assessment [11], land deformation observation [12], oceanography [13], terrain classification [14], target detection [15], and so on. The diversified applications of SAR have encouraged the rapid development of airborne and spaceborne SAR sensors.

Radio beacons enable measurements of ionospheric radio scintillations and total electron content (TEC). These beacons transmit unmodulated, phase-coherent waves in S-band frequencies. Many satellite applications require circularly polarized (CP) wideband antennas. Their compact size, lightweight, and simple fabrication method make CP antennas suitable for small satellite systems. The slot antenna has wideband impedance, but the 3 dB axial ratio bandwidth (ARBW) is narrower compared to the impedance bandwidth (IBW). In this paper, a circularly polarized circular-slotted antenna (CSA) is proposed to enhance the ARBW and the antenna gain. A pair of asymmetrical rectangular slots, a simple 50 Ω feedline and a parasitic patch were introduced to a CSA to enhance the 3 dB ARBW and the antenna gain. Rectangular slots were inserted on the diagonal axis of the CSA, the feedline was shifted to the left side of the x-axis, and a parasitic patch was attached to the circular slot. The lengths of the rectangular slots correspond to the resonant frequency, and the parasitic patch width corresponds to the higher frequency of the 3 dB ARBW. The asymmetrical rectangular slots, the shifted feedline, and the parasitic patch successfully improved the measured 3 dB ARBW of the antenna by 787.5 MHz or 35.79%. The measured gain of a CSA with left-hand circular polarization (LHCP) was also improved by shifting the feedline and the rectangular slot, achieving a peak gain of 5 dBic.