Microwave Applications Research Articles

A metal-only transmission metasurface with dual-layer configuration for generation of orbital angular momentum wave

In this paper, we present a metal-only transmission metasurface adopting dual-layer elements with I-shaped grooves etched on each layer, which is designed for orbital angular momentum (OAM) generation. The special arrangement of the grooves on the elements results in a wider phase compensation range, and by varying the length of the grooves, a full 360° phase coverage with a transmission amplitude of more than −2 dB can be achieved at 10 GHz. As a proof of concept, a metal-only transmission metasurface composed of 400 elements is designed, fabricated, and measured. The simulated and measured results suggest that the OAM transmitted waves with the mode l = −1 can be efficiently generated by a double-layer metal-only metasurface at around 10 GHz. Compared with conventional configurations of OAM transmitted beam generation, this configuration has great potential for high power microwave and space environment applications.

Design and Fabrication of a Patch Antenna for 5G Wireless Communications from a Low-Permittivity LiAlSi2O6-Based Ceramic.

A microwave dielectric ceramic based on lithium aluminum silicate (LiAlSi2O6) with ultralow permittivity was synthesized using the traditional solid-state reaction technique, and its dielectric characteristics at microwave frequencies are presented. The nominal LiAlSi2O6 ceramic exhibited a relative permittivity of 3.95. To enhance the material properties, LiAlSi2O6-x wt % B2O3 microwave dielectric ceramics were fabricated by incorporating a low-melting-point sintering aid (B2O3), achieving a relative density exceeding 94%. The resultant ceramics exhibited a relative permittivity (εr) ranging from 3.95 to 4.42, a microwave quality factor (Q × f) between 24,720 and 28,990 GHz, and a resonant frequency temperature coefficient (τf) varying from -45.9 to -20.6 ppm/°C. Additionally, the introduction of B2O3 broadened the sintering temperature window and effectively lowered the optimal sintering temperature from 1400 to 1200 °C. Furthermore, LiAlSi2O6 ceramics demonstrated a near-zero coefficient of thermal expansion (CTE) of 1.44 ppm/°C, which is advantageous for applications requiring high thermal stability. Based on LiAlSi2O6-2.0 wt % B2O3 ceramics with εr = 4.42, Q × f = 28,990 GHz, and τf = -20.6 ppm/°C, a microstrip patch antenna was designed and fabricated. Testing of the antenna revealed exceptional performance, including a center frequency of 4.98 GHz, a bandwidth of 280 MHz (-10 dB), and a total efficiency reaching up to 93.7%. These findings underscore the promising potential of this material in advanced microwave and wireless communication applications.

Advanced mechanisms and applications of microwave-assisted synthesis of carbon-based materials: a brief review.

The interaction of microwave radiation with carbon-based materials induces rapid, instantaneous heating. When combined with the plasma excitation capabilities of microwaves, this property presents novel avenues for synthesizing carbon-based materials that require high temperatures and catalytic activity. This review investigates the response of carbon-based materials to microwave radiation, analyzes the dielectric loss mechanism responsible for heat generation, and details the microwave plasma excitation mechanisms employed in the synthesis and processing of carbon-based materials. Furthermore, the structure of microwave reactors is discussed, followed by a discussion of their diverse applications in both laboratory and industrial settings. Lastly, the review addresses the challenges associated with the practical implementation of microwave technology and explores future development prospects, with a particular focus on the application of microwaves in carbon-based material synthesis.

Electromagnetic shielding enhancement in cement composites: a comparative study of mechanically and thermally recycled carbon fibers

Abstract The recycling of carbon fibers that have reached the end of their service life and their reintegration into new applications hold significant importance from an environmental and sustainable perspective. In this study, the aim is to enhance the electromagnetic wave shielding properties of cement-based composites by incorporating mechanically and thermally recycled and ball-milled carbon fibers at volumetric ratios of 1%, 2%, and 3%. Electromagnetic tests are conducted in the X-band frequency range (8-12.5 GHz), commonly preferred for microwave applications. The obtained results demonstrate an improvement in the SEA (absorption loss )and SET (total power loss) values of the composite with the use of recycled fibers. This improvement is particularly more pronounced in composites containing thermally recycled fibers. The enhanced performance is attributed to the electrical conductivity imparted by carbon fibers. At a frequency of 11.9 GHz, the SET value increased from 8.5 dB for the control sample to 9.2 dB for composites with 3% mechanically recycled fibers and up to 19 dB for composites with 3% thermally recycled fibers. These findings indicate that using recycled carbon fibers enhances the electromagnetic wave shielding properties, with thermal recycling contributing more significantly to this enhancement.

Application of Microwave for Core Plug Cleaning

Rock extraction is a particularly major step for the preparation of rock samples for core analysis, it can be performed by many traditional techniques like Soxhlet, centrifuge, and flooding system. In this study, a new technique was suggested for core cleaning by microwave. New experiments were conducted as part of this research project, focusing on the cleaning of several types of core plugs under different conditions such as temperature and solvent volume. Additionally, the goal was to extract hydrocarbons from naturally saturated reservoir rocks that had been prepared for standard testing. These findings were then compared with the conventional method of cleaning samples using an organic solvent, specifically toluene. The experiments successfully employed microwave technology for the cleaning process, effectively optimizing key variables including time, temperature, energy, and solvent quantity. The operational duration was set at 3 hours per day, using 20 ml of solvent, following numerous trials and iterations. This method allowed for the extraction of crude oil from 36 plug samples while achieving complete cleanliness of the rocks. Conducting porosity tests before and after the cleaning procedures showed the absence of any damage to the rock samples. Notably, there was an observed alteration in granular size within an acceptable range of 0.02 to 0.6. Further analyses were conducted, including gas chromatography and infrared analysis, both of which indicated that microwaves had no adverse effect on the crude oil extracted. Conclusively, the use of microwaves in the cleaning of rocks appears as a harmless, economically viable, environmentally friendly technique. The feasibility of this method was proved at the laboratory level, showcasing its potential for wider application.

Investigation low-temperature densification and dielectric properties of glass/Al2O3/nano-TiO2 ceramics for microwave applications

Investigation low-temperature densification and dielectric properties of glass/Al2O3/nano-TiO2 ceramics for microwave applications

Rational optimizations of high K microwave dielectric ceramic Bi2(Li0.5Ta1.5)O7 toward LTCC applications

AbstractMicrowave dielectric ceramics have drawn intensive interests in recent years due to the advanced development in communication area. High‐permittivity dielectric ceramics have thus become the highlight owing to dielectric ceramics with high permittivity could meet the demand of electronic components in both stabilization and miniaturization features. Bi2(Li0.5Ta1.5)O7 shows its great potential among various high‐permittivity dielectric ceramics with a suitable permittivity and a considerable quality factor. Based on previous studies, a series of rational optimizations were conducted on Bi2(Li0.5Ta1.5)O7 to manipulate the temperature coefficient of resonant frequency (TCF) and the sintering temperature for potential Low Temperature Co‐fired Ceramic (LTCC) applications. Two distinguished ceramics were obtained, Bi2(Li0.5Ta1.5)O7–0.03Bi2O3 (sintering temperature of 850°C, εr ∼ 64.1, Qf ∼ 8510 GHz, TCF—25.3 ppm/°C) and Bi2[(Li0.5Ta1.5)0.975Ti0.05]O7–0.015Bi2O3 (sintering temperature of 980°C, εr ∼ 66.2, Qf ∼ 10 950 GHz, TCF—8.5 ppm/°C). Dielectric resonator antenna (DRA) simulation was subsequently conducted and proved the ceramics holding excellent potential for microwave applications.

Characterization of the Microstructure of Sr0.75Ba0.25Nb2O6 Thin Films by Brillouin Light Scattering.

Strontium-barium niobate (SrxBa(1-x)Nb2O6) films can be considered as a promising material for microwave applications due to high dielectric nonlinearity and relatively low losses. Since strontium-barium niobate has a disordered structure that determines its unique electrical properties, the identification of structural features of the SrxBa(1-x)Nb2O6 films is the key to their successful use. The SrxBa(1-x)Nb2O6 films were synthesized on a sapphire substrate by magnetron sputtering. The structure of the films was studied by both traditional methods of electron microscopy, X-ray diffraction, and the rarely used for thin films investigation Brillouin light scattering method, which was the focus of our study. We show that Brillouin light scattering is an excellent nondestructive method for studying the structural features of thin ferroelectric strontium-barium niobate films. An analysis of the features of the Brillouin light scattering spectra in thin-film structures and their comparison with the spectra of bulk crystals allowed us to determine with high accuracy the thickness of the films under study and their structural features determined by the resonant scattering of acoustic waves.

The Effect of Microwave Application on the Drying of Banana (Musa paradisiaca formatypica) Flour Inoculated by Cronobacter sakazakii Bacteria

Background: Instant baby porridge contains ingredients that allow it to be served instantly, eliminating the need for lengthy cooking process as the case with traditional porridges. Thanks to the 88.00% carbohydrates that it contains, banana flour can be utilized for instant baby porridge. As in the process of producing any flour, drying is a critical phase in the production of banana flour. According to previous studies Cronobacter sakazakii bacteria are resistant to drying. The purpose of this research is to determine the effect of Power level and length of drying in the microwave on the total reduction of Cronobacter sakazakii bacteria and to determine the combination of microwave power and duration, which results in the most elevated total reduction of Cronobacter sakazakii bacteria. Methods: A completely randomized design (CRD) was employed in this investigation and microwave power was the first component. (100, 200, 300 watts) and the second factor being drying duration (10s, 20s, 30s). Result: The research findings indicated that the microwave power and drying time and their interactions affected the total reduction of Cronobacter sakazakii bacteria. The greatest decrease in total Cronobacter sakazakii bacteria was found in the treatment of 300 watts for 30 seconds at a total microbe of 4.75 log CFU/g, color for lightness (L*) 75.76; for redness (a*) +2.98; for yellowness (b*) +16.42; ash content of 3.45%; amount of protein of 3.04%; content of fat 0.67% and carbohydrates content of 84%.

Nonlinear Magnetic Sensing with Hybrid Nitrogen-Vacancy/Magnon Systems.

Magnetic sensing beyond the linear regime could broaden the frequency range of detectable magnetic fields, which is crucial to various microwave and quantum applications. Recently, nonlinear interactions in diamond nitrogen-vacancy (NV) centers are proposed to realize magnetic sensing across arbitrary frequencies. In this work, we enhanced these capabilities by exploiting the nonlinear spin dynamics in hybrid systems of NV centers and ferri- or ferromagnetic (FM) thin films. We studied the frequency mixing effect in the hybrid systems and demonstrated that the introduction of FM films not only amplifies the intensity of nonlinear resonance signals that are intrinsic to NV spins but also enables novel frequency mixing through parametric pumping and nonlinear magnon scattering effects. The discovery and understanding of the magnetic nonlinearities in hybrid NV/magnon systems position them as a prime candidate for magnetic sensing with a broad frequency range and high tunability, particularly meaningful for nanoscale, dynamical, and noninvasive materials characterization.

Unit Cell Optimization of Groove Gap Waveguide for High Bandwidth Microwave Applications

Recently, groove gap waveguides (GGWs) have shown significant potential in power handling and bandwidth enhancement compared to conventional waveguides. In this research work, we designed and developed an innovative mushroom-unit-cell-based groove gap waveguide (MGGW) that has shown improved bandwidth compared to conventional GGW structures. The dispersion characteristics of the MGGW were analyzed through the eigenmode solver feature of Microwave Studio CST, which showed that the bandwidth was improved by 8% compared to conventional unit cells in the microwave spectrum. To validate our proposed method for the physical dimensions of unit cell structures, we developed an MGGW structure for the S band, which shows similar trends aligning with the simulation results. The measurement results are promising as a reflection coefficient of less than −20 dB was achieved over the entire band for the WR284 Electronic Industries Alliance (EIA) standard waveguide adapter. The proposed MGGW structure with improved bandwidth will open new doors for researchers to develop ultra-wide bandwidth microwave applications, i.e., filters, transmission lines, resonators, attenuators, etc.

Effect of Fe Doping on the Crystal Structure and Dielectric Properties of LiGaCr4O8 Breathing Pyrochlore

In this study, LiGaCr4−xFexO8 (x = 0, 0.2, 0.4, 0.6) ceramics are synthesized using the solid‐phase reaction method. The effects of Fe doping on the lattice structure and dielectric properties are systematically examined using X‐ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and dielectric measurements. It is found from XRD analysis that the evolution of lattice constant decreases from 8.2552 Å at x = 0 to 8.2449 Å at x = 0.6, demonstrating a lattice contraction with doping. SEM shows a grain size reduction and irregular structures with higher Fe doping levels developed. The grain size decreases from 1.716 μm at x = 0 to 1.155 μm at x = 0.6. Due to Fe doping, the Raman spectroscopy obviously changes in high‐frequency phonon modes. The F2g1 and A1g modes shift to higher frequencies due to the reduction in lattice constant, while the F2g2, F2g3, and Eg modes shift to lower frequencies due to the increased ionic mass caused by the heavier Fe ions. Notably, Fe doping increases the dielectric constant and reduces the dielectric loss, especially at higher doping level. In these results, it is suggested that moderate Fe doping improves dielectric properties, offering potential applications in microwave and high‐frequency devices.

Modeling of 2-D Periodic Array of Dielectric Bars with a Low Reflection Angle for a Wind Tunnel High-Power Microwave Experiment

Two-dimensional periodic dielectric bars have potential applications in high-power microwave (HPM) radiation effect experiments performed in wind tunnels. Such a bar is designed to consist of two types of dielectric materials, and two lined-up blocks can be considered as a period along the bar. Under plane excitation, the theoretical period length of the beat wave pattern fits well with the simulation result, which requires modifying the previously presented field-matching method. The phase distribution on the cross-section can be non-uniform when two different guiding modes are excited independently and propagate along different materials. Directional reflection with a low reflection angle can be obtained by reasonably choosing the parameters of the dielectric array. The designed array can decrease the returned-back microwave power toward the microwave source by 6 dB according to the numerical simulation, which included the wind tunnel, the input antenna, the test target, and the reflect array in one model.

Experimental and Simulated Investigation of S-parameters and Power Loss Characteristics of PTFE/Glass Composites at X-band Frequency

Polytetrafluoroethylene (PTFE)-based substrates are in high demand for high-frequency (microwave) applications because of their low relative permittivity, enabling efficient signal transfer. In this work, PTFE composites have been prepared with different content (5 wt.% - 25 wt.%) of soda lime silica glass (SLSG) for substrate application. The composites were characterized by their complex permittivity and S-parameters through the rectangular waveguide (RWG) measurement method over x-band frequency (8.2 GHz – 12.4 GHz). The RWG set-up was connected to a vector network analyser for the characterization. Power loss of the composites due to material absorption was calculated using the measured S-parameters. As the content of the SLSG increased from 5 - 25 wt.%, complex permittivity rose from 2.18-j0.0035 to 2.56-j0.0047 in the frequency range considered. In addition, |S11| reduced from 0.623 and 0.700 to 0.418 and 0.441, whereas |S21| varied from 0.780 and 0.713 to 0.906 and 0.895 for 5 wt.% and 25 wt.% SLSG contents at 8.2 GHz and 12.4 GHz, respectively. The calculated power loss increased from 2.94 dB to 3.29 dB and 4.01 dB to 4.88 dB for the same filler contents and frequency. Furthermore, the S-parameters were simulated using the finite element method (FEM) via COMSOL software and compared with the measured values. The comparison revealed a mean relative error of < 0.1, denoting the accuracy of the RWG method. Also, the electric field distribution across the waveguide length was visualized. Thus, the optimal performance of the composite was found at 5 wt.% SLSG filler content for microwave substrate application.

Tunable magnetic properties and microwave absorbing properties of (Nd1-xYx)2Fe17N3-δ

Magnetic microwave absorbing materials of rare earth-transition metal (R-T) intermetallic compounds have the advantage of high absorbing performance, low matching thickness, and rich tunability. In this work, we report the magnetic and microwave absorbing properties of R-T intermetallic compounds (Nd1-xYx)2Fe17N3-δ (x = 0 ∼ 1). The crystalline structure of these compounds transitions from Th2Zn17-type rhombohedral (for x < 0.6) to Th2Ni17-type hexagonal (for x > 0.8) as the composition varies, attributed to the reduction in lattice volume. The saturation magnetization (Ms) of the (Nd1-xYx)2Fe17N3-δ remains almost unchanged as x changes. However, the out-of-plane anisotropy field decreases significantly from 111kOe to 25kOe while x increases. The high-frequency magnetic permeability of the material is also significantly elevated and thus leads to a significant enhancement in microwave absorbing performance. A 5.8 GHz maximum effective absorption bandwidth (EAB, RL < -10 dB) could be achieved within a thickness of only 1.1 mm for Y2Fe17N3-δ(x = 1)/paraffin composite primarily due to its heavy magnetic loss. Furthermore, the minimum reflection loss (RL) reaches −49 dB at 6.6 GHz with a thickness of 2.2 mm. The tunable magnetic properties and excellent microwave absorbing performances of (Nd1-xYx)2Fe17N3-δ make it a strong contender for applications in high-performance microwave absorbing materials.

Performance and Characterization of Additively Manufactured BST Varactor Enhanced by Photonic Thermal Processing

The demand for reconfigurable devices for emerging RF and microwave applications has been growing in recent years, with additive manufacturing and photonic thermal treatment presenting new possibilities to supplement conventional fabrication processes to meet this demand. In this paper, we present the realization and analysis of barium–strontium–titanate-(Ba0.5Sr0.5TiO3)-based ferroelectric variable capacitors (varactors), which are additively deposited on top of conventionally fabricated interdigitated capacitors and enhanced by photonic thermal processing. The ferroelectric solution with suspended BST nanoparticles is deposited on the device using an ambient spray pyrolysis method and is sintered at low temperatures using photonic thermal processing by leveraging the high surface-to-volume ratio of the BST nanoparticles. The deposited film is qualitatively characterized using SEM imaging and XRD measurements, while the varactor devices are quantitatively characterized by using high-frequency RF measurements from 300 MHz to 10 GHz under an applied DC bias voltage ranging from 0 V to 50 V. We observe a maximum tunability of 60.6% at 1 GHz under an applied electric field of 25 kV/mm (25 V/μm). These results show promise for the implementation of photonic thermal processing and additive manufacturing as a means to integrate reconfigurable ferroelectric varactors in flexible electronics or tightly packaged on-chip applications, where a limited thermal budget hinders the conventional thermal processing.

Improved structural and dielectric traits of Cd-Zn spinel ferrites by co-substitution of La3+ and Er3+ cations

In the present work, the effect of co-doping of rare earth (Re3+), La and Er cations on the physical and dielectric performance of Cd-Zn spinel ferrites fabricated by sol-gel auto combustion method is reported. The prepared ferrites were doubly calcinated at 550 ℃ and 750 ℃ for 2 hours and 8 hours, respectively. The obtained samples were investigated using XRD, FTIR and dielectric measurements. XRD powder patterns verified the single-phase growth of spinel structure of all the as-synthesized ferrites with Fd-3m space group. The obtained results revealed that the Lattice constant reduces with increasing Er3+ concentrations, while crystallite size showed increasing behavior with increasing Er3+ concentration. FTIR results revealed the existence of two major absorptionbands i.e. low frequency bands in range 405-428 cm-1 and high frequency bands in range 523- 550 cm-1 which are evidence of spinel structure formation. LCR measurements are used to investigate the impact of co-doping of La3+ and Er3+ on the various dielectric parameters of prepared samples in response to frequency. Dielectric constant and loss decreased with the incorporation of Er3+, while an increase in ac conductivity was observed. The observed properties reveal that the prepared materials are suitable candidates for application in the high-speed microwave and radio frequency devices.

Conformally printed additively manufactured RF demonstrator for circuit compaction

Abstract Recently, there has been interest in applying Additive Manufacturing (AM) to RF and Microwave applications, especially in packaging of microelectronic devices. Additive packaging offers advantages of expanded functionality in restricted volume, through miniature, low-SWaP-C sensors, allowing for non-traditional form factors. In this work, design, fabrication, and characterization of a non-planar multi-material MMIC structure is presented to demonstrate significant footprint reduction and circuit compaction. Performance of a non-planar passive RF device and details of planar to non-planar AM connections for characterization of the transitions will be demonstrated. The work will present details of the design and fabrication of the non-planar structure, optimization of the process parameters for the Optomec 5-axis Aerosol Jet Printer for multi-material printing, and the results of the characterization and testing. RF measurements were conducted to demonstrate the functionality of the developed non-planar circuit and compared with simulations which showed good agreement. The results of this work show that fully additive approach is feasible for non-planar circuits, which will allow for footprint reduction, weight reduction, and achievement of novel form factors that are critical for microwave applications.

Polarization insensitive eye-shape enclosed split ring resonator-based multi-band metamaterial absorber/sensor for S, C, X, Ku, and K-band microwave applications

Polarization insensitive eye-shape enclosed split ring resonator-based multi-band metamaterial absorber/sensor for S, C, X, Ku, and K-band microwave applications

Enhancing microwave absorption of bio-inspired structure through 3D printed concentric infill pattern

Despite numerous reports on microwave absorbing materials and structures with excellent performance, research on the impact of the carrier of microwave absorbers and their preparation processes on microwave absorption performance still faces challenges. To address this issue, this study combines theoretical analysis, simulation, and experimental validation to compare the differences in microwave absorption performance between 3D printed ABS/CF/MWCNTs materials and traditionally cast paraffin/CF/MWCNTs materials. Furthermore, the study explores the impact of linear and concentric filling patterns in 3D printing processes on the performance of tree-shaped microwave absorbing meta-structures. From a material level perspective, the 3D printed ABS/CF/MWCNTs composite plate with a thickness of 3 mm has an effective absorption bandwidth of 5.16 GHz. Additionally, the bio-inspired tree-shaped structure optimized by the ant colony algorithm achieves an effective absorption bandwidth of up to 11.5 GHz at a thickness of 10.8 mm, with a minimum reflection loss of less than −9 dB across the entire frequency range (2–18 GHz). Moreover, the microwave absorbing meta-structure reinforced with carbon fiber-reinforced plastic laminates exhibits outstanding tensile and bending strength, with an average tensile strength and bending strength reaching 197.7 MPa and 188.6 MPa, respectively. In summary, this study provides valuable insights into the optimization of preparation processes for microwave absorbing materials or structures and offers a scientific basis for the design and application of high-performance microwave absorbing materials.