Microwave Applications Research Articles

Coplanar Waveguide (CPW) Loaded with Symmetric Circular and Polygonal Split-Ring Resonator (SRR) Shapes

This paper investigates the performance of coplanar waveguide (CPW) structures loaded with symmetric circular and polygonal split-ring resonators (SRRs) for microwave and RF applications, leveraging their unique electromagnetic properties. These properties make them suitable for metamaterials, sensors, filters, resonators, antennas, and communication systems. The objectives of this study are to analyze the impact of different SRR shapes on the transmission characteristics of CPWs and to explore their potential for realizing compact and efficient microwave components. The CPW-SRR structures are fabricated on a dielectric substrate, and their transmission properties and spectrogram are experimentally characterized in the frequency range of 4 GHz to 10 GHz with the rotation angles of the SRR gap. The simulation results demonstrate that the resonant frequencies and magnitude of the transmission coefficient of the CPW-SRR structures are influenced by the geometry of the SRR shapes and the rotation angles of the SRR gap, with certain shapes exhibiting enhanced performance characteristics compared to others. Moreover, the symmetric circular and polygonal SRRs offer design flexibility and enable the realization of miniaturized microwave components with improved performance metrics. Overall, this study provides valuable insights into the design and optimization of CPW-based microwave circuits utilizing symmetric SRR shapes, paving the way for advancements in the miniaturization and integration of RF systems.

Single phase metamaterial behavior in [formula omitted] and [formula omitted] doped cobalt ferrites

This paper reports the characteristic properties of CoFe2O4(CFO), Co0.98Ag0.02Fe2O4(CAFO), and Co0.98Ti0.02Fe2O4(CTFO) spinel ferrites of Fd3‾m space group and grain size in the range of 160 – 170 nm. Fourier transform infrared spectra of these samples have revealed the metal-oxygen bands in the range of 448– 542 cm−1. Raman spectra have shown six distinct peaks corresponding to the mixed spinel structure, which have been used to calculate the cation distribution of the samples. The magnetic measurement at room temperature shows that after the doping of Ti4+ ions, the saturation magnetization increases from 47.70 to 66.68 emu/g, and coercivity decreases from 1.84 to 1.61 kOe, making the sample magnetically softer. The law of approach to saturation magnetization has been used to estimate the value of magneto crystalline anisotropy constant. The dielectric behavior of the samples has been thoroughly studied in this paper. The dielectric constant is positive below 300 °C; its value is comparable for CFO and CAFO samples but higher for CTFO. Above this temperature, the samples show an uncommon behavior of negative dielectric constant corresponding to the single phase metamaterial state and its value increases as temperature rises. This behavior can be interpreted with the help of Drude model of plasmonic resonance. The Nyquist plots change their properties from RC to RL type in this region. Such single phase metamaterials with negative dielectric constant could be useful for high temperature microwave applications.

Bulk glass-ceramic composites and ULTCC substrates for microwave and millimetre-wave applications

In this study, a new ultra-low-temperature co-fired ceramic (ULTCC) glass-ZnO-SiO2-B2O3CeO2−MgO-Al2O3 composite was developed and its applicability as a dielectric substrate in emerging high-performance communication technologies in the microwave and millimetre-wave frequency ranges was investigated. The novel material composition enables achieving good sinterability at a low fabrication temperature of 470 °C. Extensive studies have been conducted on the microstructure, porosity, water absorption, surface roughness, and thermal expansion coefficient. Following this analysis, the dielectric properties of the bulk glass-ceramic composites and the final ULTCC substrates were characterised. These measurements were conducted within a broad frequency range of 5 GHz–1.1 THz using split-post dielectric resonators, a Fabry-Perot open resonator, and a time-domain spectrometer, resulting in quasi-continuous frequency characteristics of the complex permittivity. Furthermore, the fabricated ULTCC substrates were subjected to surface-wise measurements, which provided 2D maps of the dielectric properties as qualitative and quantitative measures of the uniformity and quality of the material.

Sustainable microwave-supported biodiesel production using sandbox oil and its waste shell as a nanoparticle green alkali heterogeneous catalyst

This present work explored the possible use of sandbox seed (Hura crepitans) shell (SSS) waste as a feedstock for synthesizing green solid alkali biocatalyst in the microwave-aided sandbox oil (SBO) transesterification to obtain SBO biodiesel (SBOB). The solid catalyst was produced using a calcination method by burning raw SSS in the open air to obtain ash heated for 3 h in a furnace at 500 °C. The calcined sandbox shell ash (CSSA) produced was characterized using standard techniques to establish its catalytic potency. Also, a model was developed to simulate the process and examine the interactive effect of process input variables on SBOB yield using the Taguchi approach. The CSSA characterization showed it composed of K (44.99 %), Ca (1.54 %), and Mg (1.87 %) with crystalline compounds of K and Mg. The physisorption results gave a mean pore size of 18.142 nm and a surface area of 6.1125 m2/g. The best combination of the input variables determined for the process is a heating power of 450 W, methanol:SBO of 8:1, time of 1.5 min, and CSSA loading of 2 wt% with an optimum SBOB yield of 98.27 wt%. The SBOB produced met standard specifications for biodiesel. Microwave application to the SBO transesterification aided in rapidly completing the reaction. The study concluded that sandbox seeds and their shells are promising feedstock for cheap and sustainable biodiesel production.

Influence of Pr-cations on structural, spectral, elemental, and electrical features of Zr2–R type ferrites

Hexagonal ferrites have gained much attraction due to extensive applications in telecommunication and stealth fields. R-type hexagonal ferrites are rare hexagonal ferrites used in various technological applications. In the current work, the sol-gel auto-combustion method was used to prepare samples of R-type hexagonal ferrites with the chemical formula BaZr2Fe4-xPrxO11 (x = 0.00, 0.03, 0.06, and 0.09) respectively. The impact of substituting Praseodymium (Pr) on its structural, electrical, dielectric, and magnetic properties was investigated. X-ray diffraction (XRD) patterns suggest all samples exhibit a single phase. The lattice parameters and unit cell volume experienced alterations with varying Praseodymium (Pr3+) substitution levels. The atomic dynamics study of the Pr-doped R-type hexagonal ferrites was evaluated using FTIR analysis. Two absorption bands in the infrared spectroscopy were utilized to designate the tetrahedral and octahedral sites. X-ray photoelectron spectroscopy (XPS) findings verified the presence of all metal ions alongside their respective electronic states. Jonscher's power law elucidates the conduction mechanism of charge carriers in the synthesized ferrite samples. Impedance analysis was employed to investigate the influence of relaxation time and grain boundaries on the electrical characteristics of the fabricated nanomaterials. Impedance Cole-Cole plots provide evidence that all samples demonstrate multiple relaxation processes of a non-Debye nature. The minimum reflection loss (RL) of −32.46 dB at 3.27 GHz was achieved for x = 0.09. Pr-doped R-type hexagonal ferrite has potential applications in microwave high-frequency applications.

Determination of calcium, iron, and selenium in human serum by isotope dilution analysis using nitrogen microwave inductively coupled atmospheric pressure plasma mass spectrometry (MICAP-MS).

In this study, we demonstrate the applicability of nitrogen microwave inductively coupled atmospheric pressure mass spectrometry (MICAP-MS) for Ca, Fe, and Se quantification in human serum using isotope dilution (ID) analysis. The matrix tolerance of MICAP-MS in Na matrix was investigated, revealing that high Na levels can suppress the signal intensity. This suppression is likely due to the plasma loading and the space charge effect. Moreover, 40Ca and 44Ca isotopic fractionation was noted at elevated Na concentration. Nine certified serum samples were analyzed using both external calibration and ID analysis. Overestimation of Cr, Zn, As, and Se was found in the results of external calibration, which might result from C-induced polyatomic interference and signal enhancement, respectively. Further investigations performed with methanol showed a similar enhancement effect for Zn, As, and Se, potentially supporting this assumption. The mass concentrations determined with ID analysis show metrological compatibility with the reference values, indicating that MICAP-MS combined with ID analysis can be a promising method for precise Ca, Fe, and Se determination. Moreover, this combination reduces the influence of matrix effects, broadening the applicability of MICAP-MS for samples with complex matrixes.

Electron mobility enhancement by electric field engineering of AlN/GaN/AlN quantum-well HEMTs on single-crystal AlN substrates

To enhance the electron mobility in quantum-well high-electron-mobility transistors (QW HEMTs), we investigate the transport properties in AlN/GaN/AlN heterostructures on Al-polar single-crystal AlN substrates. Theoretical modeling combined with experiment shows that interface roughness scattering due to high electric field in the quantum well limits mobility. Increasing the width of the quantum well to its relaxed form reduces the internal electric field and scattering, resulting in a binary QW HEMT with a high two-dimensional electron gas (2DEG) density of 3.68×1013 cm–2, a mobility of 823 cm2/Vs, and a record-low room temperature (RT) sheet resistance of 206 Ω/□. Further reduction of the quantum well electric field yields a 2DEG density of 2.53×1013 cm–2 and RT mobility > 1000 cm2/V s. These findings will enable future developments in high-voltage and high-power microwave applications on the ultrawide bandgap AlN substrate platform.

Snow water equivalent retrieved from X- and dual Ku-band scatterometer measurements at Sodankylä using the Markov Chain Monte Carlo method

Abstract. Radar at high frequency is a promising technique for fine-resolution snow water equivalent (SWE) mapping. In this paper, we extend the Bayesian-based Algorithm for SWE Estimation (BASE) from passive to active microwave (AM) application and test it using ground-based backscattering measurements at three frequencies (X and dual Ku bands; 10.2, 13.3, and 16.7 GHz), with VV polarization obtained at a 50° incidence angle from the Nordic Snow Radar Experiment (NoSREx) in Sodankylä, Finland. We assumed only an uninformative prior for snow microstructure, in contrast with an accurate prior required in previous studies. Starting from a biased monthly SWE prior from land surface model simulation, two-layer snow state variables and single-layer soil variables were iterated until their posterior distribution could stably reproduce the observed microwave signals. The observation model is the Microwave Emission Model of Layered Snowpacks 3 and Active (MEMLS3&a) based on the improved Born approximation. Results show that BASE-AM achieved an RMSE of ∼ 10 cm for snow depth and less than 30 mm for SWE, compared with the RMSE of ∼ 20 cm snow depth and ∼ 50 mm SWE from priors. Retrieval errors are significantly larger when BASE-AM is run using a single snow layer. The results support the potential of X- and Ku-band radar for SWE retrieval and show that the role of a precise snow microstructure prior in SWE retrieval may be substituted by an SWE prior from exterior sources.

A novel bifunctional metasurface based on independent control of transmission and reflection amplitudes and phases

ABSTRACT A novel bifunctional metasurface (MS) operating at two frequencies is proposed to manipulate reflected and transmitted waves independently. The element is composed of a slot sandwiched by two C-shape spilt rings (CSRRs). The middle layer is the metal sheet etched the slots, and it is used to select polarization mode of reflection and transmission. Also, it isolates the reflection and transmission elements and eliminates the coupling between them. Therefore, the reflection or transmission amplitude and phase of the proposed MS can be regulated by the corresponding single metal layer compared with the current bifunctional elements. This is helpful to shorten design time. Also, a higher transmission amplitude is achieved with fewer substrate layers and lower profile. The reflection and transmission mode operate at 17.6 GHz and 12.6 GHz, respectively. As a proof of concept, a full-space multibeam generator is validated both numerically and experimentally and a full-space bifocal metalens is demonstrated numerically. The proposed MS provides a new kind of low cost, lightweight, and easily modularized planar devices for microwave applications.

A sustainable and energy efficient approach for development of electrically conductive materials and their characterizations

In this study, composite castings of electrically conductive materials were prepared using electromagnetic energy of frequency 2.45 GHz. Three separate sets of castings were produced inside the domestic microwave applicator cavity, with reinforced compositions of up to 15% in steps of 5% for each composite cast (copper (Cu) + 5% molybdenum (Mo), Cu + 10% Mo, and Cu + 15% Mo). A microwave radiation exposure time of 12 min was required for the complete melting of pure copper powder. However, the addition of Mo reinforcement caused a reduction in exposure time to 11.33 min (min) for the Cu-15% Mo composite cast. The formation of different phases was revealed by the X-ray diffraction analysis of the cast samples. Only a 0.92% copper oxide phase was detected in the pure copper cast samples. The composite cast samples exhibited peaks corresponding to Cu64O, Cu6Mo5O18, and MoO2. Microstructure analysis demonstrated that the grains grew in an equiaxed manner with a uniform dispersion of the reinforcements. The maximum microhardness achieved is 99.2 ± 4.99 Hv for Cu + 15% Mo which is 1.66 times better than microwave-cast copper sample.

Investigating the ultralow dielectric loss of spinel-like and modified orthorhombic perovskite ceramic structures for microwave applications

ABSTRACT This study prepared ultralow electron-loss perovskites with spinel-like structures via a solid-state reaction. The (Mg0.95Co0.05)2(Ti0.95Sn0.05)O4 (MCTS) ceramic exhibited approximate values for ultrahigh quality factor, permittivity, and negative temperature coefficient (τf) of 310,000 GHz, 14.25, and −48.1 ppm/oC, respectively. To bring the τf closer to zero, a trace amount of (Ca0.95Sr0.05)(Ti0.97Sn0.03)O3 (CSTS) perovskite was added to MCTS during ceramic manufacturing. CSTS exhibited a permittivity of 92 and a large positive τf value of 810 ppm/°C. A 0.92MCTS–0.08CSTS hybrid ceramic sintered at 1325°C achieved remarkable microwave dielectric properties of εr ~18.42, Q×f ~ 237,000 GHz and τf ~3.72 ppm/°C. This mixed ceramic has significant potential for applications in manufacturing microwave devices.

Strain-rate sensitivity analysis of microwave processed polypropylene-carbon nanotube composites

The study investigates the strain rate sensitivity of microwave-processed polypropylene nanocomposites containing a 10% volume fraction of multi-walled carbon nanotubes (MWCNTs), synthesized using a domestic microwave applicator (DMA). Through experimental analysis under various loading conditions including tensile, flexural, and multistep relaxation loads, the mechanical strength of these nanocomposites is assessed alongside destructive testing and scanning electron microscopy (SEM) results. Mathematical models are proposed to elucidate the mechanical response under different strain rate loadings. The nanocomposite exhibits elastoplastic behavior, with maximum elongation observed at a strain rate of 3 mm/min. During uniaxial tension tests, the ultimate strength increases significantly from 5.74 MPa at 1.52 mm/min to 13.8 MPa and 15.7 MPa at 1 mm/min and 2 mm/min respectively during multistep relaxation tests. The true stress-true strain curve follows a power law of strain hardening under high strain rate tensile tests. Flexural tests reveal maximum flexural strength and modulus at a strain rate of 1.25 mm/min, with elongation peaking at 1.50 mm/min. Mechanical properties, including modulus and ultimate strength, show an increasing trend with strain rate until a limiting value is reached, beyond which thermal softening occurs. SEM fractography illustrates the random and spatial distribution of CNTs at low strain rates, whereas agglomeration and CNT pull-out are observed at higher strain rates. This comprehensive analysis sheds light on the intricate mechanical behavior of microwave-processed polypropylene nanocomposites, offering insights into their potential applications and optimization strategies.

A Low-Reflection Tuning Strategy for Three-Stub Waveguides

In high-power microwave applications, the reflection of energy can be effectively reduced by adjusting the three-stub waveguide. However, most of the existing tuning algorithms do not make an arrangement for the adjustment sequence of stubs, and accurately calculating the depth of the stubs requires a great deal of time via electromagnetic (EM) simulations, which may cause large reflection in the matching process. To solve these problems, we first propose an improved calculation method that can accurately calculate the input impedance of a three-stub waveguide. Then, an impedance matching algorithm is designed based on the equivalent circuit model that can quickly and accurately calculate the optimal depth of the stubs. Finally, we present a low-reflection tuning strategy to suppress the large reflection during the adjustment of the stub process. An experimental system is built to verify the calculation method and the tuning strategy. The results show that the strategy can avoid large reflection in the case of load mutation and can maintain low reflection when the load changes continuously. The algorithm meets the needs of the industry and can be used for automatic and real-time adjustment of three-stub waveguides of different specifications.

Cascades of Parametric Instabilities in the Tokamak Plasma Edge during Electron Cyclotron Resonance Heating.

We report observations of nonlinear two-plasmon decay instabilities (TPDIs) of a high-power microwave beam, a process similar to half-harmonic generation in optics, during electron cyclotron resonance heating in a tokamak. TPDIs are found to occur regularly in the plasma edge due to wave trapping in density fluctuations for various confinement modes, and the frequencies of both observed daughter waves agree with modeling. Emissions from a cascade of subsequent decays, which indicate a generation of ion Bernstein waves, are correlated with fast-ion generation. This emphasizes the limitations of standard linear microwave propagation models and possibly paves the way for novel microwave applications in plasmas.

Theoretical Study of Electric, Dielectric, and Optical Properties in Ion Doped Multiferroic SrFe12O19 Nanoparticles.

Electric, dielectric, and optical (band gap) properties of pure multiferroic as well as La- and Ni-doped SrFe12O19 (SFO) (at different sites) are investigated using a microscopic model and Green's function technique. The concentration dependence of the polarization P is considered for substitution of rare earths ions on the Sr sites. For a small La ion doping concentration, x = 0.1, La-doped SFO is ferroelectric, whereas for a larger doping concentration, for example x = 0.5, it is antiferroelectric. The real part of the dielectric constant ϵ increases with an increasing magnetic field h. ϵ decreases with an increasing frequency and La dopants. Therefore, La-doped SFO is suitable for microwave application with a low dielectric constant. The magnetic properties of pure SFO NPs are also studied. Ni doping at the Fe site of SFO leads to enhanced ferroelectric polarization and dielectric constant. The band gap decreases or increases by substitution of Ni or In ions on the Fe site, respectively. The results reveal that the tuned band gap of Ni-doped SFO makes it a crucial candidate for optoelectronic and solid oxide fuel cell applications.

Miniaturized power detection module operating in millimeter wave band

The miniaturized broadband detection module can be embedded into the microwave application system such as the front end of the transmitter to detect the power or other parameters in real time. It is highly prospective in military and scientific research. In this paper, a broadband power detection module operating at 26.5 ​GHz–40.0 ​GHz is designed by using low-barrier Schottky diode as the detector and a comparator for threshold output. This module can dynamically detect the power range between −10 ​dBm and 10 ​dBm with the detection accuracy of 0.1 ​dB. Further, the temperature compensation circuit is also applied to improve the measurement error. As a result, the resulted error low to ±1 ​dB in the temperature range of −55 ​°C to +85 ​°C is achieved. The designed module is encapsulated by a Kovar alloy with a small volume of 9 ​mm ​× ​6 ​mm ​× ​3 ​mm. This endows the designed module the advantages of small size, easy integration, and low cost, and even it is applicable to high-reliability environments such as satellites.

Structural engineering of vertically aligned nanocomposite films fabricated via magnetron and pulsed laser co-deposition for microwave application

Microwaves are often used in communication engineering, including in microwave relays as well as multichannel, mobile, and satellite communications. To meet the demand for a “small, light, thin, and precise” modern electronic machine, developing highly tunable microwave materials to manufacture miniaturized microwave devices has become a top priority. Ferroelectric materials are excellent microwave materials, showing outstanding dielectric properties and tunability. Introducing low dielectric loss oxides in the construction of vertical self-assembly nanocomposites (VSNs) effectively improves their tunability and reduces dielectric loss. However, the optimal doping content of simple VSN films limits further improvement of tunability. Herein, we propose a strategy-gradient VSN to achieve combined improvement in tunability and dielectric constant by designing a sputtering and pulsed laser co-deposition. The resulting VSN composite film has a dielectric constant of 428.08, a dielectric loss of 0.0212, and a tunability of 78.69 %. Our results contribute to the development of filters and have broad application prospects in the microwave industry.

Abstract 5747: Microwave responsive thermosensitive lipid nanoparticles for spatiotemporal delivery of chemotherapeutics

Abstract Pancreatic cancer is a highly lethal malignancy with an urge for the exploration of novel treatments. One promising approach is microwaved-induced hyperthermia, which has shown great antitumor and synergistic effects when combined with other therapies. The application of microwaves produces heat by dielectric hysteresis which depends on the dielectric properties of molecules. Ionic liquids (ILs) are compounds composed of ions with <100 °C melting point and have strong dielectric properties. In short, we propose the creation of microwave-sensitive nanoparticles using IL, enabling precise hyperthermia induction with low-powered microwaves in localized areas. To achieve this, we stabilize a core composed of 1-butyl-methylimidazolium bromide or 1-butyl-3-methylimidazolium hexafluorophosphate using Span 80, Tween 20, and Triton-X as surfactants, along with phosphatidylcholine lipids as “cosurfactants”. Employing a double emulsion procedure for fabrication, nanoparticles are characterized using dynamic light scattering, Fourier-transform infrared spectroscopy, and transmission electron microscopy. Furthermore, we assess microwave sensitivity by comparing thermal changes between liposomes loaded with 120 mM and 250 mM NaCl solutions. Subsequently, we evaluate biocompatibility and heat effects by incubating IL nanoparticles with BXPC3 and KPC cells, monitoring cell viability through MTT assays. We aim to confine the ILs within the nanoparticle core rather than incorporating them into the membrane. We anticipate increased microwave sensitivity, translating to reduced off-target effects and enhanced precision in hyperthermia treatment. This research holds promise for improving the therapeutic outcomes of pancreatic cancer treatment. Citation Format: Cesar B. Aparicio-Lopez. Microwave responsive thermosensitive lipid nanoparticles for spatiotemporal delivery of chemotherapeutics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5747.

Predicting dielectric properties of fruit juices at 915 and 2450 MHz using machine learning and physicochemical measurements

Microwave-assisted thermal processing can provide superior quality for fruit-based products when compared to conventional thermal processing. Understanding the temperature-dependent dielectric properties of liquid foods is needed for the analysis and optimization of the microwave applicator chamber since they govern the heating rate and temperature distribution. While literature offers correlations for specific products, there is a scarcity of methods capable of accommodating variability in composition or predicting behavior for broader product groups. In this study, we measured the dielectric properties (dielectric constant and loss factor) of eight fruit juices (passion fruit, melon, pineapple, cashew, orange, lemon, acerola, and guava) using an open-ended coaxial-line technique for temperatures ranging from 5 to 90 °C at commercial frequencies of 915 and 2450 MHz, alongside electrical conductivity. These properties were successfully correlated with the temperature for each individual juice; then, machine learning techniques (random forest, gradient boosting machine, and multilayer perceptron) were used to predict the properties of this diverse group of eight juices based on various physicochemical measurements. These techniques revealed temperature and electrical conductivity as the most critical predictors, while total solids, pH, acidity, ashes, and select color parameters also emerged as significant variables. These findings demonstrate that the integration of physicochemical analyses with machine learning tools offers an objective approach to correlate and predict dielectric properties for a group of food products, facilitating adjustments in product composition without additional measurements, thus enhancing the efficiency and accuracy of microwave-assisted thermal processing simulations and optimizations.

Microwave absorbing performance of reduced graphene oxide @ alumina fabricated by atomic layer deposition method

In this work, a series of alumina coating reduced graphene oxide (RGO@Al2O3) composites with core-shell structure was synthesized by the atomic layer deposition (ALD) method. The alumina (Al2O3) thickness of the RGO@Al2O3 could be controlled by changing the number of ALD cycles. The microstructure, high-temperature resistance, and microwave absorbing properties of the composites were investigated in detail. The composite could provide excellent high-temperature resistance and microwave absorbing properties. The composite started decomposition at 620 °C. The maximum reflection loss value of the composite obtained by applying 200 Al2O3 deposition cycles is −14.2 dB at 15.7 GHz, and its effective absorption bandwidth reaches 5.0 GHz (13.0–18.0 GHz). The results show that the RGO@Al2O3 composite has the potential application in high-temperature microwave absorbing fields, due to excellent high-temperature resistance, reflection loss, and effective absorption bandwidth.