Microwave Properties Research Articles

The microwave properties of tin sulfide thin films prepared by RF magnetron sputtering techniques

In this paper we present the microwave properties of tin sulfide (SnS) thin films with the thickness of just 10 nm, grown by RF magnetron sputtering techniques on a 4 inch silicon dioxide/high-resistivity silicon wafer. In this respect, interdigitated capacitors in coplanar waveguide technology were fabricated directly on the SnS film to be used as both phase shifters and detectors, depending on the ferroelectric or semiconductor behaviour of the SnS material. The ferroelectricity of the semiconducting thin layer manifests itself in a strong dependence of the electrical permittivity on the applied DC bias voltage, which induces a phase shift of 30 degrees mm−1 at 1 GHz and of 8 degrees mm−1 at 10 GHz, whereas the transmission losses are less than 2 dB in the frequency range 2–20 GHz. We have also investigated the microwave detection properties of SnS, obtaining at 1 GHz a voltage responsivity of about 30 mV mW−1 in the unbiased case and with an input power level of only 16 μW.

Composition effect on transport and microwave properties of YBCO thin films prepared by metalorganic chemical vapor deposition

YBa2Cu3O7−δ (YBCO) thin films deposited on LaAlO3 single-crystal substrates have great potential for application in microwave field due to their low microwave surface resistance (Rs). In order to prepare high-performance films and facilitate adjustment of experimental parameters, we designed novel metalorganic chemical vapor deposition system. This system adopts single liquid-source pulse feed that provides facile control over film composition through the adjustment of Y, Ba, and Cu ratios in precursors. Here, we thoroughly study influence of film composition on performance. By conducting energy-dispersive spectroscopy measurements, Y, Ba, and Cu composition ranges of 21–24%, 28–31%, and 46–54%, respectively, are found to optimize YBCO film transport and microwave properties. Composition affects purity of film phase which in turns determines film performance. To confirm this observation, we adjust ratio through input–output relationship to obtain film with composition ratio within abovementioned optimal range. Obtained YBCO film has critical current density of 2.8 MA/cm2 at 77 K and 0 T and Rs of 0.285 mΩ at 77 K and 10 GHz. The full width at half maximum of YBCO (005) peak and (103) plane, measured via X-ray diffraction, are 0.235° and 0.762°, respectively.

Sintering behavior, structure, and microwave properties of novel Li2xCu1-xMoO4 ceramics

In this study, we prepared a novel series of Li2xCu1-xMoO4 (x = 0.02, 0.04, 0.06, 0.08, and 0.10) microwave ceramics. The dynamic sintering behavior, crystal phases, micro-morphologies, and dielectric properties of the samples were studied. The substitution of Li+ contributed to refining the crystal grain size, promoting the densification of microstructure, and enhancing the quality factor. Due to different valence substitutions, Cu+ ions were created, which were verified by X-ray photoelectron spectroscopy (XPS) and Raman experiments. In addition, the Raman shift, full width at half maximum (FWHM) value of the A1g peak, and crystal microstrains were analyzed to gain a mechanistic understanding of the influence of structure on the dielectric properties. When x = 0.08, the Li2xCu1-xMoO4 ceramic sintered at 675 °C exhibited optimal comprehensive properties with εr = 8.17, Qf = 68 476 GHz, and τf = −25 ppm/°C, and good chemical stability between the ceramic and Al electrode was also achieved. These promising properties make Li2xCu1-xMoO4 (x = 0.08) more suitable for ultra-low temperature co-fired ceramic (ULTCC) applications.

Structure and Electrical Properties of Microwave Sintered BTS-BCT-xBF Lead-Free Piezoelectric Ceramics.

Barium titanate (BT)-based ceramics are one of the promising piezoelectric materials for environment-friendly electro-mechanical transformation. However, high performance materials are often sintered at high temperatures, resulting in volatile components and increased energy consumption. Here, 0.82Ba(Ti0.89Sn0.11)O3-(0.18-x)(Ba0.7Ca0.3)TiO3-xBiFeO3 (BTS-BCT-xBF) piezoelectric ceramics were prepared by microwave sintering (MWS) method, and the structure and properties were emphatically studied, aiming to reveal the regulatory mechanism of MWS on the structure and properties. Compared with conventional solid sintering (CS), the phase structure presents a similar evolution in MWS ceramics as a function of BF, while the more refined grain size and the denser structure are observed in MWS ceramics. The electrical properties (e.g., d33, εr, tan δ, etc.) of MWS ceramics are superior to the CS ceramics owing to the refined grain size and denser microstructure. It is worth noting that the energy storage performance (e.g., energy storage density, energy storage efficiency) significantly outperformed expectations due to the slender hysteresis loop resulting from the smaller grain and high cubic phase. Therefore, the MWS sintering mechanism can further drive practical application of BT-based ceramics.

A study on the conductivity, dielectric, and microwave properties of SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) nanohexaferrites

In this paper, conductivity, dielectric, and microwave properties of SrNbxYxFe12-2xO19 (0.00 ≤ x ≤ 0.05) hexaferrites (SrNbY HFs) synthesized by the citrate sol–gel method were investigated. Some key parameters compatible with the electrical and dielectric functions of SrNbY HFs have been extensively evaluated as functions of bias frequency, measurement temperature, and co-substitution ratios in logarithmic 3D graphs by complex impedance spectroscopy. It has been observed that although the co-substitution ratio is highly functional on dielectric parameters such as both the dielectric constant and dielectric loss, as well as the dissipation factor, it has a very low influence on the conductivity mechanism. Depending on the substitution ratios of Nb and Y ions and the transition temperature region, the activation energy was calculated to vary between 58 and 476 meV. Microwave properties were measured as S-parameters using a coaxial line in the range of 2–12 GHz. It was analysed the frequency dependences of the real/imaginary parts of the permittivity and permeability for all samples. Reflection losses vs. frequency were calculated as a function of the substitution level. Coefficients of the RL (−12.5 … −16.8 dB) confirm practical importance for electromagnetic compatibility at high frequencies.

Investigation of exchange coupling and microwave properties of hard/soft (SrNi0.02Zr0.01Fe11.96O19)/(CoFe2O4)x nanocomposites

This article deals with the synthesis and the investigation of the structural features, magnetic and microwave properties of hard/soft (H/S) SrNi0.02Zr0.01Fe11.96O19 (SrNiZr)/CoFe2O4 (CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) nanocomposites (NCs). Products were manufactured via one-pot sol-gel auto-combustion approach. The formation of hard/soft phases was verified via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HR-TEM) techniques. XRD analyses proved the presence of both hexagonal and cubic crystal structure in each H/S NCs. Vibrating sample magnetometer was employed to examine the magnetic features of the prepared NCs at room (RT; T = 300 K) and low temperatures (LT; T = 10 K). The magnetization (M) vs. applied field (H) curves displayed complete and good exchange coupling among the hard and soft phases for the different samples at 300 K. In contrast, an incomplete and weak exchange-coupled interaction was observed for all NCs at 10 K, excepting the SrNiZr/(CFO)1.0 NCs. The different magnetic parameters (Hc,Ms,Mr, and nB) were extracted for the H/S SrNiZr/(CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) NCs at both temperatures. All products exhibited a single magnetic domain since the value of squareness ratio is Mr/Ms> 0.5. The correlation of the electromagnetic properties (frequency dependences of the permittivity/permeability and reflection losses) as function of the magnetic phase ratio in H/S SrNiZr/(CFO)x (x = 1.0, 1.5, 2.0, 2.5, 3.0) functional NCs were analyzed from S11–S21 parameters (2–18 GHz). It was observed strong correlation between the CFO content (x) and electrodynamic parameters (permittivity, permeability, and reflection losses). It is established that these materials can be applied for electromagnetic compatibility and radar-technologies.

Microwave and Terahertz Properties of Spark-Plasma-Sintered Zr0.8Sn0.2TiO4 Ceramics.

Zr0.8Sn0.2TiO3 (ZST) powders synthesized by solid-state reaction were subject to processing by spark plasma sintering (SPS). A single-phase ceramic with a high relative density of 95.7% and 99.6% was obtained for sintering temperatures of 1150 °C and 1200 °C, respectively, and for a dwell time of 3 min. In order to reduce the oxygen vacancies, as-sintered discs were annealed in air at 1000 °C. The dielectric loss of the annealed samples, expressed by the Q × f product, measured in the microwave (MW) domain, varied between 35 THz and 50 THz. The intrinsic losses (Q × f ~ 60 THz) were derived by using terahertz time-domain spectroscopy (THz-TDS).

Skyrmion Dynamics in Concentric and Eccentric Nano-Ring Structures

Skyrmions are found to be promising for next-generation energy-efficient spintronic applications. Moreover, ultrafast skyrmion dynamics in gigahertz-band offer an excellent opportunity to exploit such topologically protected nanostructures in high-frequency applications. Here, we present a systematic investigation of the microwave properties of the skyrmions in concentric and eccentric ring structures using micromagnetic simulations. Two gyrotropic modes with clockwise and counterclockwise gyration are observed in skyrmion when excited by an in-plane microwave field. The high-frequency response is found to be enhanced by 3.5 GHz by using a small bias field of 40 mT. The skyrmion dynamics are found to be extremely sensitive to the edge repulsions and a remarkably large frequency shift of 2 GHz of the skyrmion resonance modes is observed by simply varying the position of a skyrmion in an eccentric ring structure. The results are substantiated by directly correlating the observations with inertial mass associated with a skyrmion calculated analytically. The results provide an additional functionality of the skyrmions based on their tunable microwave properties which may have potential implications in the field of miniaturized reconfigurable microwave devices.

Improved microwave absorption and EMI shielding properties of Ba-doped Co–Zn ferrite

Herein, we report the synthesis of Ba-doped Co–Zn ferrite nanoparticles using the sol-gel auto combustion technique. The single-phase formation of the samples with F d 3m space group was confirmed by X-ray diffraction (XRD). The crystallite size, lattice parameter, and x-ray density, decreases with increasing dopant concentration. Scanning Electron Microscopy (SEM) shows the formation of irregular grains for all the samples. The oxidation states of Ba, Co, Zn, Fe, and O were estimated using X-ray photoelectron spectroscopy (XPS), which confirmed the chemical purity of the samples. Cationic distributions at tetrahedral and octahedral sites were proposed based on XPS studies. Fourier transformation infrared (FTIR) spectra shows the presence of two strong peaks around 430 cm −1 and 580 cm −1 that confirmed the formation of ferrite structure. The M − H curves were acquired to analyze the magnetic ordering in the specimens where the highest saturation magnetization (Ms) value of 43.479 emu/g was witnessed for x = 0.05. The microwave properties shows a decrease in magnetic loss and dielectric loss from 0.486 to 0.319 and 0.178 to 0.168 when Ba concentration was increased. EMI shielding analysis shows an increase in effective shielding ( S E T ) from 11.43 dB to 12.82 dB.

Enhanced magnetic properties of strontium ferrites through constructing magnetoelastic stress

Strontium ferrites, which exhibit large remanence, high coercivity (Hc), are fascinating for applications in motors and high-frequency microwave devices. Here we demonstrate the strontium ferrites (Sr0.34Ca0.25La0.41Fe11.4Co0.19O19-δ) sintered at 1150 °C with enhanced magnetic properties through constructing magnetoelastic stress. The effects of applied pressure (Pc-axis) of 0–16 kPa during the sintering process on phase compositions, morphologies, magnetic and microwave properties are investigated in detail. We note that the Pc-axis could contribute to enhanced c-axis preferred orientation. This mechanism of enhancement has been also discussed according to the magnetoelastic theory. By applying an external pressure of 8 kPa, intrinsic coercivity (Hcj) of 4657 Oe and magnetic coercivity (Hcb) of 3781 Oe are obtained. The increments are 8.1% and 18.0% for Hcj and Hcb, respectively, compared to the sample with Pc-axis of 0 kPa. However, the enhancement of Hc by the Pc-axis is seen to be limited above 8 kPa, which can be attributed to the enlarged grain size and porosity observed. In addition, the ferromagnetic resonance frequency (fr) is also increased by the increased Pc-axis.

Physical properties of microwave and solid state synthesized La0.7Na0.3MnO3

We report the structural, magnetic, electrical and broadband microwave absorption in La0.7Na0.3MnO3 sample synthesized by microwave (MW) irradiation (Na0.3LMO_MW) and compare them to the sample synthesized by solid-state (SS) reaction method (Na0.3LMO_SS). Single phase Na0.3LMO_MW was synthesized at 800 °C in 30 min, whereas, Na0.3LMO_SS sample was obtained by sintering at 1200 °C for 48 h. Although both these samples show ferromagnetic transition at TC ∼324.8 K, the MW-synthesized sample shows distinct physical properties: broad ferromagnetic transition, smaller saturation magnetization, a large difference between the magnetic ordering and metal-insulator transition temperatures, a large high-field magnetoresistance, a table top-like magnetocaloric effect, and a large low-field microwave absorption compared to the solid state synthesized sample. These differences are suggested to arise from magnetic heterogeneity induced by smaller grain size and surface spin disorder in the MW synthesized La0.7Na0.3MnO3.

Low Intensity Microwave Fields and Radiation and Their Interaction with the Human Body

Sources of low-intensity microwave signals formation, which affect the metabolism processes when they interact with human body, are considered in the article. It’s noticed that increasing intensity level of the technogenic signals in environment significantly exceeds natural electromagnetic fields and radiation (EMR). The peculiarities of the registration and measurement of low-intensity signals parameters of the microwave range are considered. The processes of the interaction of the microwave signals and human organism are analyzed. Formation mechanisms of the positive and negative microwave flows of the electromagnetic radiation are revealed. Particularly, possible formation mechanism of the microwave EMR fluxes of implants in the human body. The results of the experimental study of the EMR signals levels of the objects contacting with human body, partly materials for bone defects replacement and soft tissues regeneration so as materials for physiotherapy, are given. The use of the term “electromagnetic compatibility” for materials which contacting the human body, is proposed. The expediency of its use is proven. Microwave properties of materials for clothes, minerals and building materials, which can affect the human body and environment, have been also studied.

Synthesis of low temperature firing scheelite-type BaWO4 microwave dielectric ceramics with high performances

The synthesis of scheelite-structured BaWO 4 ceramics at low temperatures using a Li 2 O–B 2 O 3 –BaCO 3 –CuO (LBBC) glass frit is reported in this study. Composite ceramics with the chemical formula BaWO 4 - x LBBC ( x = 0.25, 0.5, 1, and 2 wt%) were synthesized via the standard solid-phase method. A compact BaWO 4 matrix containing glass crystallized when sintered at 850 °C for only 30 min. The BaWO 4 ceramic with 1 wt% LBBC glass exhibits optimum microwave dielectric performance with Q × f = 58,855 GHz, ε r = 8.33, and τ f = −61.43 ppm/°C. A results of XRD and SEM analyses, microwave properties and the liquid-phase sintering mechanism for the ceramics are presented. • The Q × f value remained excellent for 58855 GHz while the temperature decreased from 1100 °C to 850 °C. • The compound was still the pure BaWO 4 phase. • The shorter soaking time (30min) can effectively reduce the energy consumption.

Coupling-induced microwave transmission transparency with quarter-wavelength superconducting resonators

<sec>The electromagnetic induced transparency (EIT) to atomic systems and its various applications have been extensively investigated, both theoretically and experimentally. In this paper, we study how to similarly verify these phenomena in the waveguide coupled to the transmission line resonators. By making use of real space quantum scattering theory, we calculate the transmission spectrum of the waveguide photons scattered by a single quarter-wavelength transmission line resonator. Our experimental results show that the resonant microwave transporting along the feedline is completely reflected by the resonator. This is similar to the situation of the light absorbed by the resonant atomic medium, and thus its transmission is significantly suppressed.</sec><sec>Like the EIT phenomena in atomic gas, wherein the resonant absorption can be significantly suppressed by applying a strong pumping light to control the optical properties of medium, the transport properties of the resonant microwave can be investigated by coupling it into an auxiliary quarter-wavelength resonator in this paper. If the frequency of the auxiliary quarter-wavelength resonator is different from the resonant frequency, the calculated transmission spectrum shows that the coupling with auxiliary quarter-wavelength resonator induces the complete transmission of the resonant microwave. This is one of the features of the EIT-like effect, and can be simply explained as the frequency renormalization of the coupling resonators. Also, by adjusting the coupling strength between the resonators, the width of the microwave transmission spectrum window can be manipulated. Our experimental observations verify such an argument, but the phase shift mutation (another typical signs of the EIT effect) of the resonant microwave cannot be observed. In physics, this is because the interference between the transmitted microwave and the reflected micowave with different frequencies does not take place in the coupling region between the two resonators.</sec><sec>It is expected that the effects with the complete EIT-like phenomena can be observed, in future, by fabricating the sample of two quarter-wavelength transmission line resonators with the same frequency, and thus the coupling between the two resonators can be controlled.</sec>

Correction: Effect of a chelating agent at different pH on the spectroscopic and structural properties of microwave derived hydroxyapatite nanoparticles: a bone mimetic material

Correction for ‘Effect of a chelating agent at different pH on the spectroscopic and structural properties of microwave derived hydroxyapatite nanoparticles: a bone mimetic material’ by Vijay Kumar Mishra et al., New J. Chem., 2016, 40, 5432–5441, DOI: 10.1039/C5NJ03322E.

Microwave Properties of GNP-Polymer Composites with a Segregated Conductive Network

Microwave Properties of GNP-Polymer Composites with a Segregated Conductive Network

Электромагнитные свойства полимерных композитов Li-=SUB=-0.33-=/SUB=-Fe-=SUB=-2.29-=/SUB=-Zn-=SUB=-0.21-=/SUB=-Mn-=SUB=-0.17-=/SUB=-O-=SUB=-4-=/SUB=-/П(ВДФ-ТФЭ) в области частот 100-7000 МГц

The article describes electromagnetic and microwave properties of the polymer composite with the lithium spinel ferrite inclusion of composition Li0.33Fe2.29Zn0.21Mn0.17O4 in the frequency range 100 MHz - 7000 MHz. It is shown that samples with a mass fraction of ferrite 60, 80% have pronounced radio-absorbing properties, measured using the reflection coefficient on a metal plate (return losses). For a composite with 80% ferrite, the minimum return loss was -37.5 dB at 2.71 GHz with an absorption width at -10 dB of 3 GHz. High absorption characteristics are directly related to the use of ferroelectric polymer P(VDF-TFE) as a binder, which is expressed in the combined action of the absorption mechanisms of the magnetic and ferroelectric phases.

Electromagnetic properties of polymer composites Li-=SUB=-0.33-=/SUB=-Fe-=SUB=-2.29-=/SUB=-Zn-=SUB=-0.21-=/SUB=-Mn-=SUB=-0.17-=/SUB=-O-=SUB=-4-=/SUB=-/P(VDF-TFE) in the frequency range 100-7000 MHz

The article describes electromagnetic and microwave properties of the polymer composite with the lithium spinel ferrite inclusion of composition Li0.33Fe2.29Zn0.21Mn0.17O4 in the frequency range 100-7000 MHz. It is shown that samples with a mass fraction of ferrite 60, 80% have pronounced radio-absorbing properties, measured using the reflection coefficient on a metal plate (return losses). For a composite with 80% ferrite, the minimum return loss was -37.5 dB at 2.71 GHz with an absorption width at -10 dB of 3 GHz. High absorption characteristics are directly related to the use of ferroelectric polymer P(VDF-TFE) as a binder, which is expressed in the combined action of the absorption mechanisms of the magnetic and ferroelectric phases. Keywords: lithium ferrite, polymer composite, polyvinylidene fluoride, radio-absorbing material.

Влияние контактного сопротивления интерфейса YBCO|Au на транспортные и СВЧ-свойства массивов джозефсоновских контактов из высокотемпературных сверхпроводников

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.

Sintering temperature optimization for terbium doped strontium hexaferrite with improved microwave properties

Optimizing reaction parameters while undergoing synthesis process can help in customization of materials to be used in high frequency devices. However, optimization in terms of reaction parameters remains a challenge and not much success has been achieved so far even after years of sustained research efforts in this direction. We in this paper report our results on synthesization of M−type hexaferrite nanoparticles with composition Sr1-xTbx Fe12O19 (where × varies from 0 to 0.10 in steps of 0.02) using chemical co-precipitation method. Thorough investigations have been carried out to find out the variation in crystallite size of nanoparticles with change in terbium ion concentration from 2 % −10 %, using XRD results and TEM micrographs. Detailed analysis has also been carried out to study the impact of increase in sintering temperature on the dielectric properties for a frequency range of 1–6 GHz using Vector network Analyzer. While dielectric constant values were found to be in the range of 4–21, absorbance showed a variation of 5 % with change in sintering temperature. The average value of dielectric loss for pure strontium hexaferrite sample has been found to be 6.0 × 10−2 and vary between 5.1 × 10−2 and 1.38 × 10−1 for other compositions. According to the results, the sintering temperature of 1200 °C has been established as optimum for the sintering of the material. The material thus synthesized is suitable for millimeter wave antenna applications.