Size-controlled synthesis of ZnO tetrapods using atmospheric pressure microwave plasma jets and application in NH3 gas detection

Design of conformal dual stop band frequency selective surface for microwave applications

Enhanced electrical and magnetic properties of Al and Sm Co-doped M-type hexaferrite for microwave applications

This study investigates the effects of lithium (Li) and potassium (K) additions on the microstructure, densification, and microwave dielectric properties of (A 1+ 0.5 Nd 3+ 0.5 )TiO 3 to CaTiO 3 resulting new ceramic complex with new microwave dielectric properties. The (1-x)CaTiO 3 -x(Li₀. 5 Nd₀. 5 )TiO 3 ceramics were synthesized with x values of 0.08, 0.1, 0.2, 0.5, and 0.9 mol.%, and (1-x)CaTiO 3 -x(K₀. 5 Nd₀. 5 )TiO 3 ceramics with x values of 0.02, 0.05, 0.08, 0.10, 0.20, 0.50, 0.90, and 1.0 mol.% via the solid-state method. The results reveal that both the type and concentration of the alkali significantly influence the dielectric properties. The 92CTLNT ceramic (x = 0.08), sintered at 1200°C, exhibited excellent dielectric properties with a dielectric constant (ε r ) of 27, Qxf value of 1.38 × 10 4 at 5 GHz, and a low dielectric loss of 0.37 × 10⁻ 3 . Meanwhile, the 98CTKNT ceramic (x = 0.02), sintered at 1300°C, showed superior performance with ε r of 40, a Qxf value of 3.33 × 10 4 at 4 GHz, and a low dielectric loss of 0.13 × 10⁻ 3 .The exceptional microwave dielectric properties of these ceramics present significant potential for advanced applications in microwave and communications technologies.

Ultra-wideband absorber design based on Sprott (2014) chaotic system for high-performance microwave applications

After compaction, wet granular pavement layers undergo a dry-back process to remove excess moisture and attain optimal strength and stiffness, and increased performance against cyclic loading. However, the current dry-back method relies on solar radiation, which is time-consuming and weather-dependent, often delaying construction timelines. In this study, the feasibility of microwave drying was investigated as an alternative method to accelerate the dry-back process of compacted unbound granular materials (UGMs). Experimental and numerical analyses were conducted to evaluate the drying behaviour under microwave exposure. The study considered two conditions: direct contact and a 1 cm gap between the microwave applicator and the UGM surface. A three-dimensional finite-element model was developed using COMSOL Multiphysics to simulate the coupled heat and mass transfer, with model validation performed using experimental data. A comparative analysis with solar drying was also conducted using HYDRUS-1D under realistic climatic conditions. The findings demonstrated that microwave drying substantially reduced drying time compared to current dry-back methods while minimising weather-related delays. Despite its efficiency, microwave drying presented challenges such as localised heating and limited energy penetration in deeper layers. The study highlights the potential of microwave technology for pavement dry-back and provides recommendations for optimising microwave drying to enhance energy efficiency in field implementation.

Flexible materials have become essential for emerging advanced wireless technologies, necessitating a thorough investigation of the material properties for suitable applications. This study explores a flexible strontium titanate (SrTiO3)-reinforced, platinum-cured liquid silicone rubber (LSR) composite for flexible microwave applications, including antennas, RF sensors, resonators, filters, and waveguides. The LSR-SrTiO3 composites were prepared with various filler contents (40, 50, and 60 phr) to tune and examine their material, dielectric, mechanical, and thermal properties. XRD and SEM analyses confirmed the distribution of the SrTiO3 nanoparticles within the LSR matrix. The measured dielectric constant increased by 33% at 20 Hz and 25% at 10 MHz, whereas the dielectric loss increased slightly, remaining in the order of 10−3 for maximum filler loading. An increment of ~43% increment was observed in the dielectric constant, accompanied by a loss of the order of 10−2 at X-band. A 37% reduction in the tensile strength was noticed, without compromising flexibility. The thermal decomposition temperature improved by 25% while the thermal expansion (CLTE) decreased to 22%, resulting in enhanced thermal stability. The results suggest that the 60 phr (maximum) reinforced LSR-SrTiO3 composite offers an optimal dielectric and thermal performance with acceptable mechanical flexibility, making it desirable for advanced flexible microwave applications.

This article presents a novel wideband (WB) tilted-beam end-fire planar antenna for microwave and millimeter-wave (mmWave) applications. The antenna comprises of a microstrip fed double semi-circular rings over a curvilinear slotted ground plane. It is impedance matched over a broad frequency range from 11.5 to 62.5GHz, covering the 5G New Radio (NR) mmWave bands n257, n258, n260, n261, and partly covering the unlicensed 60GHz band. Across this entire band, the antenna exhibits a return loss better than 12 dB and a gain exceeding 6.5 dBi, with a peak gain of 11.6 dBi at 40GHz. The overall electrical size of the antenna is 1.28 × 1 × 0.08 [Formula: see text], where [Formula: see text] corresponds to the free-space wavelength at 32GHz. Within the 24-40GHz frequency range, corresponding to a 50% fractional bandwidth and covering the four 5G NR bands, end-fire radiation is achieved with a tilted beam angle of [Formula: see text] ± [Formula: see text]. A prototype of the antenna is fabricated and experimentally characterized. The measured results show good agreement with full-wave simulations, validating the proposed design. Owing to its compact planar geometry, wide bandwidth, and high gain, the antenna is a strong candidate for future high-data-rate wireless communication systems.

Structural and magnetic tailoring of Zn2+-Doped Y-type hexaferrites for advanced spintronic and microwave applications

Diamond holds significant application potential in microwave and deep-space observation windows due to its exceptionally low dielectric loss. This study aims to systematically investigate the key factors influencing the dielectric loss tangent (tanδ) of single-crystal diamond (SCD) and to establish correlations between its dielectric properties and material characteristics. To this end, dielectric property measurements were performed on SCD samples synthesized using microwave plasma chemical vapor deposition (MPCVD) systems under different growth conditions. A comprehensive material characterization was carried out using birefringence microscopy, Raman spectroscopy, photoluminescence (PL), and X-ray diffraction (XRD) to analyze crystal quality, defect distribution, and strain. The experimental results show that the measured tanδ of the SCD samples reached a minimum value of 4.94 × 10<sup>-5</sup>. Detailed analysis reveals that the dielectric loss in SCD is attributed to a combination of factors: the density and distribution of internal defects (e.g., vacancies and impurities), the presence of internal growth sectors and boundaries, and phonon polarization losses induced by lattice vibrations under an external electric field. It is conclusively identified that defect density is the predominant factor governing dielectric loss. Furthermore, the study demonstrates that as the test frequency increases, contributions from defect polarization and interfacial polarization at sector boundaries become more pronounced, leading to higher overall loss. Interestingly, it was found that certain periodic defect structures can partially suppress the phonon-polarization related loss mechanism, thereby contributing to a lower tanδ in some samples. In conclusion, this work elucidates the multi-faceted origins of dielectric loss in SCD and provides valuable insights and a methodological framework for guiding the synthesis and processing of diamond crystals with further enhanced dielectric properties for advanced microwave and terahertz applications.

In response to the growing demand for miniaturized electronic devices, this work presents a novel triple-band band-pass filter (TBBPF) design utilizing metamaterial design. The proposed filter comprises three split-ring resonators (SRRs) featuring identical modified square shapes but different dimensions, all printed on Rogers RT/Duroid 6002 substrates with a relative electrical permittivity of 2.94 and thickness of 1.52 mm. The compact filter design, occupying just 10×10 mm², is fed by two 5.25 mm microstrip lines matched at 50 Ω. Our simulation outcomes demonstrate exceptional performance across C-, X-, and Ku-bands, with distinct resonance frequencies at 6.06 GHz, 10.71 GHz, and 13.64 GHz, respectively. The filter exhibits remarkable electrical characteristics, including minimal insertion losses (????????<1.5 dB), optimal bandwidth distribution, and notably compact dimensions. These characteristics, combined with the filter's multi-band capabilities, make it particularly suitable for diverse applications in wireless communication systems, imaging technologies, and biomedical detection devices. The innovative design approach presented here addresses the contemporary challenges in RF/microwave system miniaturization while maintaining high-performance standards, offering a versatile solution for modern electronic systems requiring multi-band functionality.

ABSTRACT This review critically examines the application of microwave‐assisted technologies in gold mining and processing, highlighting their potential to improve extraction efficiency and environmental sustainability. The study focuses on the use of microwave irradiation in ore pretreatment, leaching enhancement, treatment of waste activated carbon, and synthesis of gold nanoparticles. Evidence from recent research demonstrates that microwave‐assisted processes can significantly increase gold recovery rates, reduce processing times, and lower energy consumption compared to conventional techniques. For refractory ores, microwave pretreatment effectively improves mineral liberation and leaching kinetics, achieving extraction rates exceeding 90% in some cases. Additionally, the integration of microwave roasting with chemical additives such as NaOH and KOH has shown further enhancement in gold recovery. Despite these promising outcomes, challenges remain in terms of temperature control, process scalability, and optimization across different ore types. The review concludes by outlining key directions for future research, including the development of industrial‐scale systems, comprehensive economic assessments, and the exploration of microwave applications in combination with alternative lixiviants. Overall, microwave‐assisted technologies present a promising pathway toward more efficient and sustainable gold production.

Ku-band absorption dominated microwave application for sodium doped BZT ceramics

Abstract This study introduces a novel method for microwave soil treatment using a Substrate Integrated Waveguide (SIW) H-plane horn antenna integrated with an Electromagnetic Band Gap (EBG) unit cell array. The design enhances penetration depth(thermal), coverage area, and soil temperature regulation. Comparisons highlight the EBG antenna’s better performance, maintaining reflection coefficients below −10 dB near soil, unlike the non-EBG configuration, which suffers higher energy losses. The EBG antenna achieves temperatures of 85 °C in simulation at distances of 10 mm, compared to 80 °C at 10 mm without EBG. It also covers a larger area (29 × 29 mm 2 ) and ensures uniform heating, reaching 70 °C at a depth (thermal), of 25 mm, outperforming compared to the non-EBG antenna (27 × 27 mm 2 ). Experimental results with 28 W (RMS) input confirm soil heating to 81 °C in 75 min over a 150 mm 2 area with a penetration depth (thermal), of 50 mm. Additionally, the EBG structure minimally impacts soil nutrients, ensuring deeper penetration and uniform heating. These findings highlight the antenna’s potential to promote sustainable agriculture through optimized microwave soil sterilization

Yttrium Iron Garnet (YIG, Y3Fe5O12) has long been recognized as a foundational material in microwave engineering, owing to its exceptional combination of low magnetic losses, high resistivity, and tunable magnetic properties in the gigahertz regime. This review aims to critically assess recent progress in the synthesis, structural optimization, and integration of YIG for high-performance microwave applications. Research directions are categorized into two primary themes: frequency response engineering and materials design strategies. Particular emphasis is placed on the role of compositional modifications, ferromagnetic resonance (FMR) tuning, and their implications for device-level performance in filters, circulators, oscillators, phase shifters, and antennas. The impact of doping strategies, thin-film deposition techniques, and substrate engineering is examined in relation to key performance metrics such as FMR linewidth and insertion loss. This review further highlights current challenges, including low-temperature phase-pure synthesis and integration scalability, and outlines emerging opportunities for YIG-enabled devices in next-generation wireless communication, radar, and quantum microwave systems. The insights presented here are intended to guide future interdisciplinary research at the interface of materials science and microwave device engineering.

NiFe2O4 has gained significant attention from the scientific community due to its potential applications in microwave integrated devices, magnetoelectric coupling heterostructures, and spintronic devices such as spin filters. In this work, we explore the element specific ultrafast dynamics of NiFe2O4 films grown on ZnGa2O4 and MgAl2O4 with different lattice mismatches. To examine the dynamics, we utilize the transverse magneto optical Kerr effect at the extreme ultraviolet (XUV) regime, which provides access to the Fe and Ni M-edges. The demagnetization is almost concurrent with the pump pulse, suggesting that slower phonon based interactions are not crucial for the demagnetization. The reflectivity of the MAO sample is significantly higher than for the ZGO sample, which correlates well with the increased amount of free carriers. Furthermore, the reflectivity exhibits pronounced oscillations in both the Fe and Ni signals with a period of ∼2.8 ps (0.36 THz). Notably, the onset of the oscillations of the Fe is delayed by about 0.2–0.5 ps with respect to the Ni.

Abstract This study pioneers the cross‐disciplinary application of garnet‐type solid‐state electrolyte Li 7 La 3 Zr 2 O 12 (LLZO) in microwave dielectric ceramics. LLZO was synthesized via solid‐state reaction, achieving optimized microwave dielectric properties at 900°C: ε r = 8.13, Q × f = 31 735 GHz, τ f = −44.3 ppm/°C. Direct cofiring experiments with Ag electrodes validated its compatibility with low‐temperature cofired ceramic (LTCC). X‐ray diffractometer (XRD)/scanning electron microscope (SEM)–energy‐dispersive X‐ray spectroscopy (EDS) confirmed interfacial stability and chemical inertness, overriding standalone thermal expansion parameter considerations. A Beidou antenna prototype on LLZO substrates demonstrated 59.2 MHz bandwidth at 1.57 GHz with 4.33 dBi gain and >97% radiation efficiency. By synergizing low‐loss microwave response with inherent Li⁺ conductivity and thermal robustness, LLZO emerges as a multifunctional platform for integrated energy‐communication systems. It enables future designs of LTCC based self‐powered modules and real‐time structural health monitoring devices. This work bridges solid‐state electrolytes and microwave ceramics, offering a paradigm for material innovation in fifth‐generation (5G)/sixth‐generation (6G) networks and intelligent electronics.

Dual-band bandpass frequency selective surface with low insertion loss for microwave applications

Thin films of strontium titanate were grown on a polycrystalline aluminum oxide substrate using magnetron sputtering. These films exhibit high structural quality and nonlinear properties, which make them promising for microwave applications. Planar capacitors based on SrTiO3 films demonstrated a tunability of 1.65 with a microwave Q-factor of at least 110 in the entire range of control voltages without deterioration of losses, and a slow capacitance relaxation level no more than 4%, which is significantly better than currently published data for planar ferroelectric elements. This is the first successful attempt to create a planar SrTiO3 capacitor on an alumina, which demonstrates a commutation quality factor CQF of 3300 at microwaves.

An S-band racetrack slotted waveguide antenna (SWA) with low profile, high radiation efficiency (RE), low sidelobe levels (SLL), and high power capacity (PC) is presented. The antenna has only one feed port, eliminating the need for a complex T-type waveguide unequal-amplitude power divider network, and consists of a bent waveguide phase compensation structure (BWPCS) and a radiation array. The BWPCS is designed to ensure that each waveguide receives the residual microwave energy in phase, enabling a high gain (G) level. A new slot conductance formula is proposed to achieve high RE and low SLL. A ceramic radome was introduced to maintain the vacuum environment to enhance PC. Simulations at 2.458 GHz show a reflection coefficient below −26.6 dB, G of 28.09 dBi, RE of 99.73%, E-plane SLL of −29.4 dB, and H-plane SLL of −30 dB. The PC of the SWA reaches 1.56 GW.