Microwave Properties Research Articles

Influence of the contact resistance of the YBCO/Au interface on the transport and microwave properties of arrays of high-temperature Josephson junctions

The influence of the contact resistance of the interface of the YBCO/Au structure on the transport and microwave properties of arrays of high-temperature bicrystal Josephson junctions embedded in a coplanar transmission line has been studied. The current-voltage characteristics of Josephson structures fabricated using various technologies are studied: in situ and ex situ with annealing in an oxygen atmosphere. The results obtained can be used to create a quantum ac voltage generator based on high-temperature Josephson junctions. Keywords: high-temperature superconductors, Josephson junctions, microwave, contact resistance.

Effect of Ba Substitution on Structure, Magnetic Properties and Microwave Properties of Ndfeo3

Effect of Ba Substitution on Structure, Magnetic Properties and Microwave Properties of Ndfeo3

Effect of Fe substituted on the monovalent La0.85Ag0.15Mn1-xFexO3 doped manganites : Their electromagnetic and microwave properties

New microwave absorber material, La0.85Ag0.15Mn1-xFexO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) monovalent-based manganites with epoxy resin as a binder were prepared to investigate the effect of Iron (Fe) substitution on microwave absorption properties. The La0.85Ag0.15Mn1-xFexO3 (x = 0, 0.05, 0.10, 0.15 and 0.20) manganites were prepared using solid state method. The phase identification investigated by using X-ray diffraction (XRD) pattern, showed that all samples were single phase rhombohedral crystal structure. Fe substitution caused increase in room temperature resistivity and decrease in ferromagnetic–paramagnetic transition temperature, TC, indicating changes in carrier concentration and weakening of double exchange mechanism. Microwave reflection loss, RL measurements in the frequency range of 8 GHz to 18 GHz showed the highest reflection loss for x = 0 sample where value of reflection loss of − 57.2 dB at 16.41 GHz with a bandwidth of 2.67 GHz corresponding to reflection loss below − 10 dB was observed. However, Fe substitution produced lower reflection loss values with lowering of matching frequency with an upturn at x = 0.20. Permeability measurements showed real part of magnetic permeability increased but magnetic loss tangent decreased above 13 GHz with increasing Fe. Further analysis showed contribution of eddy current loss for most samples at high frequency region. On the other hand, permittivity measurements showed both real part of permittivity and dielectric loss tangent increased with Fe content at high frequencies indicates Fe substitution enhancing the dielectric loss component thus may dominantly contributes to the microwave absorption in the Fe substituted samples.

Breast tissue mimicking phantoms for combined ultrasound and microwave imaging

We present a new formulation for a breast tissue-mimicking phantom for combined microwave and ultrasound imaging to assist breast cancer detection. Formulations based on coconut oil, canola oil, agar and glass beads were used to mimic skin and fat tissues. First, 36 recipes were fabricated, and properties were measured to determine the relationship and possible interaction between ingredients with the ultrasound and microwave properties. Based on these results, the formulae were developed to mimic different tissues found in breast, including skin, fat, fibroglandular, and tumour tissues. All phantoms contained a base of agar and glass beads at different proportions depending on the tissue mimicked. Tumour and fibroglandular tissues were best mimicked by adding polyvinylpyrrolidone (PVP), while using coconut oil for skin and canola oil for fat produced the best results. Five final phantoms with different internal structures were fabricated and imaged using B-mode ultrasound and a microwave transmission system. Microwave permittivity maps were obtained from the microwave system and compared to ultrasound images. The structure and composition of the phantoms were all confirmed through this microwave and ultrasound imaging.

Microwave excitations and hysteretic magnetization dynamics of stripe domain films

FeNi films with the stripe domain (SD) pattern are prepared by electrodeposition and sputtering methods. The magnetic domain, static magnetic parameters, and quality factor, as well as dynamic properties of the two films, are respectively performed. The results show the magnetizations of the film were dependent on the direction of SD, and the rotation of the SD is lagging behind the magnetization reversal. The microwave properties of the SD emerge dynamic hysteresis before the saturation magnetic field. These microwave properties are selectively excited with acoustic mode, optical mode, and spin-wave mode. The frequency and intensity of different resonance modes of stripe domain are determined by the local magnetization. The magnetization variations and the rotation of SD of different modes are further illuminated by the micromagnetic simulation. The magnetic anisotropy and the resonance intensity of permeability of different modes were finally described by the modified resonance equations.

Improved microwave absorption performance with negative permittivity of polyaniline in the Ku-band region

Polyaniline (PANI) plays major role in the field of wide range of applications because of its versatile and flexible properties. In present work, PANI powder is synthesized by tuning its synthesis parameters such as constant oxidant-monomer ratio (1.25), lower bath temperature (0 -5°C), variation in HCL acid concentration and changing washing treatment. It is crucial to control the synthesis parameters to obtain the desired value of conductivity and dielectric properties in order to improve the microwave absorption performance. The negative permittivity is appeared in the prepared PANI samples. The structural and surface topography characterizations were carried through different techniques including FTIR, Micro Raman and Bio-AFM analysis. Microwave absorption characteristics of PANI samples were studied using a vector network analyzer in the Ku band (12-18 GHz) region. Surface topography studies show the granular topography for PANI samples. Sample P2 with 0.5M HCL concentration has a maximum conductivity of 11.37 S.cm−1 and showed minimum reflection loss of -50.73 dB (99.99% microwave absorption) at 13.79 GHz frequency with 5mm thickness. These findings reveal that microwave properties of PANI material can be improved by tuning its synthesis parameters.

Effect of activated carbon/in situ synthesized magnetite hybrid fillers on the microwave properties of natural rubber composites

The purpose of the study is to synthesize nanosized magnetite in situ the nanosized porous texture of activated carbons and to examine the impact of the resulting hybrid filler upon the microwave properties and electromagnetic interference shielding effectiveness of composites based on natural rubber. The fillers have been characterized by X-ray diffraction and photoelectron spectroscopy establishing the influence of the magnetite layer on the texture characteristics. Studies have been carried out on the effect that the fillers synthesized have on the microwave properties, the real and imaginary part of the permittivity and permeability as well as on the dielectric and magnetic loss angle tangent of the composites. It has been found that filler comprising externally about 5% of magnetite phase is the most effective. The introduction of the magnetic phase contributes to the improvement in the microwave characteristics and expanding the frequency range in which the composites are of good microwave properties due to the combination of high dielectric and the high magnetic losses. Copyright © 2017 VBRI Press.

An Optimization-Based Approach to Radar Image Reconstruction in Breast Microwave Sensing.

Breast microwave sensing (BMS) has been studied as a potential technique for cancer detection due to the observed microwave properties of malignant and healthy breast tissues. This work presents a novel radar-based image reconstruction algorithm for use in BMS that reframes the radar image reconstruction process as an optimization problem. A gradient descent optimizer was used to create an optimization-based radar reconstruction (ORR) algorithm. Two hundred scans of MRI-derived breast phantoms were performed with a preclinical BMS system. These scans were reconstructed using the ORR, delay-and-sum (DAS), and delay-multiply-and-sum (DMAS) beamformers. The ORR was observed to improve both sensitivity and specificity compared to DAS and DMAS. The estimated sensitivity and specificity of the DAS beamformer were 19% and 44%, respectively, while for ORR, they were 27% and 56%, representing a relative increase of 42% and 27%. The DAS reconstructions also exhibited a hot-spot image artifact, where a localized region of high intensity that did not correspond to any physical phantom feature would be present in an image. This artifact appeared like a tumour response within the image and contributed to the lower specificity of the DAS beamformer. This artifact was not observed in the ORR reconstructions. This work demonstrates the potential of an optimization-based conceptualization of the radar image reconstruction problem in BMS. The ORR algorithm implemented in this work showed improved diagnostic performance and fewer image artifacts compared to the widely employed DAS algorithm.

Electronic, magnetic, and microwave properties of hard/soft nanocomposites based on hexaferrite SrNi0.02Zr0.02Fe11.96O19 with variable spinel phase MFe2O4 (M = Mn, Co, Cu, and Zn)

Hard/soft nanocomposites (NCs) of SrNi 0.02 Zr 0.02 Fe 11.96 O 19 (SrNiZr)/MFe 2 O 4 (M = Mn, Co, Cu, and Zn) were prepared using a one-pot sol-gel auto-combustion technique. All produced samples showed smooth M − H curves and single peaks on the dM/dH against H curves. This indicates that complete exchange-coupled effects between phases were achieved. Furthermore, the squareness ratio SQR=(M r /M s ) was obtained and found to be higher than 0.5 at 300 K. This refers to the occurrence of excellent exchange coupling behavior among the soft and hard ferrites, and their structures consist of a single magnetic domain. The electrodynamic parameters were investigated in the 2–18 GHz frequency band using a coaxial line. The dependences of the real and imaginary parts of μ and ε as a function of frequency were determined from the measured S-parameters. A strong correlation between the chemical composition of the soft magnetic phase and the electrodynamic parameters of the composite was observed. This was analyzed in terms of the atomic weight and configuration of the electronic shells of the A-cation in the soft phase. The electromagnetic absorption (EMA) of the investigated composites was estimated from the reflection losses calculated from μ and ε. The maximal EMA value was observed.

Structural, Electromagnetic and Microwave Properties of Magnetite Extracted from Mill Scale Waste via Conventional Ball Milling and Mechanical Alloying Techniques.

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.

Functionalized-CNT Polymer Composite for Microwave and Electromagnetic Shielding.

In this research work, we studied the microwave properties of multi-wall carbon nanotube (MWCNT) surface functionalized with metallic oxides composites. Three different concentrations (5%, 10%, and 20%) of metallic oxides were used, namely cobalt, iron, and cobalt ferrite. The surface-decorated CNTS were impregnated into polyurethane (PU) matrix. The surface-decorated MWCNTs and the MWCNTs-PU composites were characterized using electron microscopy. The dielectric properties of the samples are studied using an open-ended coaxial probe technique in a wide frequency range of (5–50 GHz). The metallic oxide-decorated surface MWCNTs-PU composites demonstrated different microwave-frequency absorption characteristics depending on the concentration of the metallic oxides.

Microwave absorption and magnetic properties of thin-film Fe3O4 @polypyrrole nanocomposites: The synthesis method effect

In this study, a thin film of magnetic polymer nanocomposite for microwave absorption was prepared using a core-shell structure in an epoxy resin medium. The co-precipitation technique was used to synthesize the Fe3O4 NPs; and core-shell Fe3O4 @polypyrrole nanocomposites were made by two different synthesis methods through chemical oxidative polymerization with and without hydrochloric acid (HCl) and then, they were filmed by mixing the resulting powder with epoxy resin to explore their microwave absorption properties. The Fe3O4, Fe3O4 @PPy-A, and Fe3O4 @PPy-B nanostructures were characterised using Fourier transform infrared (FTIR), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), and thermogravimetric analysis (TGA) techniques, and the results confirmed synthesis of nanomaterial's pure structure. The transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM) techniques were used to determine morphology, magnetic properties of the nanocomposites were investigated by vibrating-sample magnetometer (VSM) at room temperature and electrical conductivity were calculated by four-point probe method. Finally, the microwave absorption properties of Fe3O4, Fe3O4 @PPy-A, and Fe3O4 @PPy-B nanocomposites were determined by epoxy resin serving as a host using a vector network analyser. According to the results of assessing microwave absorption, it was found that addition of HCl played a significant role. However, the maximum reflection loss of the Fe3O4 @PPy-A and Fe3O4 @PPy-B nanocomposites was equal to − 33.8 dB (˃99.9%) at 11.5 GHz and − 26.2 dB at 7.2 GHz, but demonstrating an effective bandwidth of 6.5 and 1 GHz, respectively. Compared to other previously reported studies, microwave properties of the core-shell Fe3O4 @PPy-A nanocomposite not only had better reflection loss performance but also it possessed wider effective absorption bandwidth < −20 dB for thinner thickness of 1.5 mm.

Millikelvin temperature cryo-CMOS multiplexer for scalable quantum device characterisation

Quantum computers based on solid state qubits have been a subject of rapid development in recent years. In current noisy intermediate-scale quantum technology, each quantum device is controlled and characterised through a dedicated signal line between room temperature and base temperature of a dilution refrigerator. This approach is not scalable and is currently limiting the development of large-scale quantum system integration and quantum device characterisation. Here we demonstrate a custom designed cryo-CMOS multiplexer operating at 32 mK. The multiplexer exhibits excellent microwave properties up to 10 GHz at room and millikelvin temperatures. We have increased the characterisation throughput with the multiplexer by measuring four high-quality factor superconducting resonators using a single input and output line in a dilution refrigerator. Our work lays the foundation for large-scale microwave quantum device characterisation and has the perspective to address the wiring problem of future large-scale quantum computers.

Electromagnetic Properties of Carbon Nanotube/BaFe12-xGaxO19/Epoxy Composites with Random and Oriented Filler Distributions.

The microwave properties of epoxy composites filled with 30 wt.% of BaFe12–xGaxO19 (0.1 ≤ x ≤ 1.2) and with 1 wt.% of multi-walled carbon nanotubes (CNTs) were investigated in the frequency range 36–55 GHz. A sufficient increase in the microwave shielding efficiency was found for ternary 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites compared with binary 1% CNT/epoxy and 30 wt.% BaFe12–xGaxO19/epoxy due to the complementary contributions of dielectric and magnetic losses. Thus, the addition of only 1 wt.% of CNTs along with 30 wt.% of barium hexaferrite into epoxy resin increased the frequency range where electromagnetic radiation is intensely attenuated. A correlation between the cation Ga3+ concentration in the BaFe12–xGaxO19 filler and amplitude–frequency characteristics of the natural ferromagnetic resonance (NFMR) in 1 wt.%CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was determined. Higher values of the resonance frequency (51.8–52.4 GHz) and weaker dependence of on the Ga3+ concentration were observed compared with pressed polycrystalline BaFe12–xGaxO19 ( = 49.6–50.4 GHz). An increase in the NFMR amplitude on the applied magnetic field for both random and aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composites was found. The frequency of NFMR was approximately constant in the range of the applied magnetic field, H = 0–5 kOe, for the random 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite, and it slightly increased for the aligned 1 wt.% CNT/30 wt.% BaFe12–xGaxO19/epoxy composite.

Dielectric and microwave absorption properties of Na0.5Bi0.5TiO3–SrTiO3 system

In this work, we have investigated the structural, dielectric and microwave properties of Sr x (Na0.5Bi0.5)1– x TiO3 (0.25 ≤ x ≤ 0.75) prepared using the solid state reaction technique. The Rietveld refinement of the X-ray diffraction pattern at room temperature of the samples is performed to confirm the phase formation as well as the crystal structure of the materials. All the materials are synthesized in cubic Pm3m phase. The low-frequency dielectric properties of the materials are investigated using alternate current impedance spectroscopy in the frequency range from 50 to 1 MHz. The temperature dependence of the dielectric constant at different frequencies gives diffuse peaks which have been attributed to the occurrence of relaxor behavior in these materials. The magnitudes of ε′m, the maximum value of dielectric constant and T m, the temperature corresponding to ε′m are decreased with an increase of Sr2+ ion in the materials. The Vogel-Fulcher relation has been considered to explain the relaxor behavior of the materials. The microwave dielectric properties as well as reflection loss of the materials have also been studied in the frequency range from 1 GHz to 15 GHz.

Prospects toward flexible magnonic systems

This paper presents the prospects for periodic magnetic nanostructures in the form of magnonic crystals on polymer substrates. Indeed, arrays of magnetic nanostructures on flexible substrates are promising for microwave applications in the GHz frequency range. In particular, the mastery of the potentially coupled physical properties (magnetic and mechanical) allows one to consider devices for microelectronics in general, combining the microwave properties of spin waves with the lightness and conformability of polymer substrates. However, there are still scientific hurdles to be overcome, particularly with regard to the reliability of these systems, which is the focus of this review. Subsequently, we propose a general state of the art, a summary of the precursor works, and a general strategy for the optimization of these systems and their future possibilities.

Cylindrical nanowire arrays: From advanced fabrication to static and microwave magnetic properties

This article reviews information on arrays of cylindrical magnetic nanowires grown electrochemically inside ordered nanoporous alumina membranes, summarizing some of the most relevant aspects about the advanced synthesis of nanowires and their overall static and microwave magnetic properties. The electrochemical details for the preparation of templates with well-defined hexagonal ordering are addressed focusing on the different anodization methods including mild, hard, pulsed or anodization of aluminum rods. A section follows on the growth of metallic nanowires, either as single element (i.e., Fe, Ni, Co), alloys (i.e., CoFe, CoNi, FeNi) or modulated in composition (i.e., Ferromagnetic/Metal). The static magnetic properties as anisotropy, coercivity and magnetostatic interactions are overviewed with particular emphasis on the influence of magnetocrystalline anisotropy and on the temperature dependence of those properties. The last section is devoted to the ferromagnetic resonance of nanowire arrays of different composition. The dependence of microwave absorption on the orientation of applied field is also a useful tool to determine the magnetic anisotropy parameters and the significance of magnetostatic interactions. The magnetization easy axis can be switched from the nanowire direction to the plane of the membrane as the nanowire filling factor increases or at a compensation temperature, in both cases it derives from the energetic balance of anisotropy and magnetostatic interactions among nanowires. A final subsection is devoted to the spin waves resonance spectra, and the perspectives of applications making use of microwave properties. We expect the article can be useful for researchers interested on the topic and provide a wide overview on the matter to those starting a new research line.

Features of structure, magnetic state and electrodynamic performance of SrFe12\u2212xInxO19

Indium-substituted strontium hexaferrites were prepared by the conventional solid-phase reaction method. Neutron diffraction patterns were obtained at room temperature and analyzed using the Rietveld methods. A linear dependence of the unit cell parameters is found. In3+ cations are located mainly in octahedral positions of 4fVI and 12 k. The average crystallite size varies within 0.84–0.65 μm. With increasing substitution, the TC Curie temperature decreases monotonically down to ~ 520 K. ZFC and FC measurements showed a frustrated state. Upon substitution, the average and maximum sizes of ferrimagnetic clusters change in the opposite direction. The Mr remanent magnetization decreases down to ~ 20.2 emu/g at room temperature. The Ms spontaneous magnetization and the keff effective magnetocrystalline anisotropy constant are determined. With increasing substitution, the maximum of the ε/ real part of permittivity decreases in magnitude from ~ 3.3 to ~ 1.9 and shifts towards low frequencies from ~ 45.5 GHz to ~ 37.4 GHz. The maximum of the tg(α) dielectric loss tangent decreases from ~ 1.0 to ~ 0.7 and shifts towards low frequencies from ~ 40.6 GHz to ~ 37.3 GHz. The low-frequency maximum of the μ/ real part of permeability decreases from ~ 1.8 to ~ 0.9 and slightly shifts towards high frequencies up to ~ 34.7 GHz. The maximum of the tg(δ) magnetic loss tangent decreases from ~ 0.7 to ~ 0.5 and shifts slightly towards low frequencies from ~ 40.5 GHz to ~ 37.7 GHz. The discussion of microwave properties is based on the saturation magnetization, natural ferromagnetic resonance and dielectric polarization types.

Comparative Evaluation of Microstructural and Mechanical Properties of Microwave and Spark Plasma Sintered ZrB2-SiC-TiC Composites

Comparative Evaluation of Microstructural and Mechanical Properties of Microwave and Spark Plasma Sintered ZrB2-SiC-TiC Composites

Studies of photocatalytic and optoelectronic properties of microwave synthesized and polyethyleneimine stabilized carbon quantum dots

The paucity of fresh drinking water is one of the chief issues of the twenty-first century. This has driven the advancement of various procedures for water refinement, for example, wastewater treatment. Organic coloring agents like Rhodamine-B (RhB) are quite possibly the foremost troublesome substances to manage. RhB is among the most significantly used coloring agents, which is hard to manage using conventional methodologies. Here, we report the photocatalytic degradation of RhB using microwave synthesized carbon quantum dots (CQDs). UV–vis absorption study and fluorescence study were used to confirm the formation of CQDs. The transmission electron microscope studies confirmed the small size of about 2 nm of spherical shaped CQDs. Degradation of RhB was studied under dark, under visible, and UV light irradiation. The highest degradation of 99.7% was obtained under UV- light irradiation in 150 min.