This study presents the utilization of mill scale waste, which has attracted much attention due to its high content of magnetite (Fe₃O₄). This work focuses on the extraction of Fe₃O₄ from mill scale waste via magnetic separation, and ball milling was used to fabricate a microwave absorber. The extracted magnetic powder was ground-milled using two different techniques: (i) a conventional milling technique (CM) and (ii) mechanical alloying (MM) process. The Fe₃O₄/CM samples were prepared by a conventional milling process using steel pot ball milling, while the Fe₃O₄/MM samples were prepared using a high-energy ball milling (HEBM) method. The effect of milling time on the structural, phase composition, and electromagnetic properties were examined using X-ray diffraction (XRD) and a vector network analyzer (VNA). XRD confirmed the formation of magnetite after both the magnetic separation and milling processes. The results revealed that Fe₃O₄ exhibited excellent microwave absorption properties because of the synergistic characteristics of its dielectric and magnetic loss. The results showed that the Fe₃O₄/CM particle powder had a greater absorption power (reflection loss: <−10 dB) with 99.9% absorption, a minimum reflection loss of −30.83 dB, and an effective bandwidth of 2.30 GHz for 2 mm thick samples. The results revealed the Fe₃O₄/MM powders had higher absorption properties, including a higher RL of −20.59 dB and a broader bandwidth of 2.43 GHz at a matching thickness of only 1 mm. The higher microwave absorption performance was attributed to the better impedance matching property caused by the porous microstructure. Furthermore, the magnetite, Fe₃O₄ showed superior microwave absorption characteristics because of the lower value of permittivity, which resulted in better impedance matching. This study presents a low-cost approach method by reutilizing mill scale waste to fabricate a high purity crystalline Fe₃O₄ with the best potential for designing magnetic nano-sized based microwave absorbers.

Aluminum-substituted Yttrium iron garnet (Al-YIG) (Y₃Al_xFe_5−xO₁₂; x = 0.4, 0.8, 1.2, 1.6, and 2.0), samples were synthesized via an auto-combustion sol-gel technique. The obtained powder was heated at 950 °C, pressed into pellets, and sintered at 1200 °C. The sample microstructures were studied using field emission scanning electron microscopy (FESEM). The average grain size decreased from 0.46 μm at x = 0.4 to a minimum value of 0.33 μm at x = 2.0. The elemental composition of the samples was studied by energy dispersive x-ray (EDX), while the bulk density was measured by the Archimedes principle. Electrical and dielectric measurements were carried out using an Agilent impedance analyzer. Generally, the sample resistivity decreased with Al concentration. At 1 MHz frequency, the sample x = 0.4 has the highest resistivity of 2.19 × 10⁵ Ωm, which decreases down to its minimum value of 1.75 × 10⁴ Ωm at x = 2.0. The dielectric constant for all the samples decreased with frequency. For the sample x = 0.4, the ε′_r decreased from 49.03 at 40 Hz to 8.08 at 1 MHz. The dielectric loss tangent, tan δ, decreased with increasing frequency, while it increased with Al substitution. Permeability values were calculated from permittivity data. The real permeability decreased from 1263.12 at x = 0.4 to 6.96 at x = 1.2 and decreased down to 11.74 at x = 2.0. The high dielectric constant, low resistivity, and low loss values of the samples indicate their suitability for miniaturization of radio frequency devices, antenna, and filter resonators.

Soda lime silica (SLS) waste as the source of silica (SiO₂) and ark clamshell (ACS) as the foaming agent has been utilized to fabricate the low-cost and lightweight foam glass-ceramics. A series of 1 and 6 wt% foam glass-ceramics were successfully prepared by the conventional solid-state sintering method at various sintering temperatures for 60 min. The bulk density of the samples has achieved minimum density (1.014 g/cm³) with maximum expansion (62.31%) at 6 wt% of the ACS content sintered at 800 °C for 60 min. The bulk density increases while the linear shrinkage and total porosity decrease with the progression of ACS contents and sintering temperature, where the results correspond with the FESEM micrograph. The result of XRD and FTIR transmittance spectra have shown that the formation of wollastonite crystal has occurred starting at 6 wt% of the ACS content sintered at 800 °C for 30 min. The highest mechanical performance (3.90 MPa) with an average total porosity (8.04%) is observed for the sample containing 1 wt% of ACS. It can be concluded that the composition of foam glass-ceramics (1 and 6 wt%) and sintering temperatures give significant results to the structural, physical, and mechanical properties of the fabricated foam glass-ceramics.

We propose and demonstrate a passively mode-locked erbium-doped fiber laser (EDFL) based on zinc-oxide/polydimethylsiloxane (ZnO/PDMS) saturable absorber (SA) that evanescently interacts with the light on a tapered fiber. The ZnO/PDMS composite is coated on the whole surface of the tapered fiber to guarantee the maximum efficiency of the SA device, with a measured insertion loss of 0.87 dB and a modulation depth of 6.4%. The proposed laser can generate soliton mode-locking operation at a threshold power of 33.07 mW. The generated output pulse yields a repetition rate and pulse width of 9.77 MHz and 1.03 ps, respectively. These results indicate that the proposed ZnO/PDMS-clad tapered fiber could be useful as an efficient, compatible, and low-cost SA device for ultrafast laser applications.

This paper presents the generation and characterization of femtosecond pulses utilizing graphene-polymethyl-methacrylate (PMMA) thin-film saturable absorber (SA), which is subjected to different lengths of single-mode fiber (SMF) in an erbium-doped fiber laser cavity. The graphene/PMMA-SA is prepared by using a simple transfer procedure of the thin-film on a fiber ferrule. By increasing the SMF length from 0 to 4 m, the corresponding group velocity dispersion of the entire cavity is estimated to change from −0.033 to −0.121 ps². Analysis of the pulse performance shows that the pulse width behavior varies from 820 fs to 710 fs against different cavity lengths. Similarly, the pulse repetition rate and the spectral bandwidth can be adjusted from 12.5 to 10.0 MHz, and from 8.2 to 5.6 nm, respectively. A comprehensive discussion on the pulse performance is presented, which can contribute to widening the knowledge on the operation of graphene-based soliton mode-locked erbium-doped fiber lasers based on dispersion management by controlling the cavity length.