Microwave Properties Research Articles

Complex permittivity of epoxy composites with carbon nanotubes and TiO2 in microwave range

Titanium oxide (TiO2) particles, used with conductive particles as fillers for composite materials (CMs) have recently been shown to produce high dielectric constant with low dielectric loss at frequencies up to 10 MHz. This work describes the microwave properties of L285 epoxy, filled with 1–5 wt. % of carbon nanotubes (CNTs) and 35 wt. % of TiO2 powder. A correlating dependence of the real and imaginary parts of permittivity versus CNT content has been observed, suggesting there are multiple factors taking part in formation of the permittivity with interfacial and dipole polarizations of filler clusters taking the main part. These factors can be exploited by varying the filler contents and particle size to obtain CMs with high permittivity and low dielectric loss as well as superior microwave absorbers.

Impact of the Zr-substitution on phase composition, structure, magnetic, and microwave properties of the BaM hexaferrite

Rapid developments in information technologies and a large rise in electrical and electronic equipment have generated different forms of electronic environmental contamination. Microwave absorption materials are important to avoid the damage that can be caused by electromagnetic radiation. A necessary condition for the absorption of the most incoming radiation is balanced wave impedance at the air/shield interface, which depends on the studied materials' magnetic and electrical properties. The paper introduces the preparation of BaFe12-xZrxO19 (x = 0.1, 0.3, 0.6, 0.9, and 1.2) using a solid-state reaction technique. The studied samples were examined by X-ray diffraction, scanning electron microscopy, vibrating sample magnetometer, and a vector network analyzer. The studied samples showed that controlling the grain size and the prepared samples' magnetic properties play an important role in enhancing the microwave radiation absorption. The examined samples can be a promising absorption material in electromagnetic shielding applications.

Impact of Al3+ ions on magnetic and microwave properties of BaM:Ti hexaferrites

BaFe(11.5-x)Ti0.5AlxO19 (0.1 ≤ x ≤ 3.0) samples were produced using solid state reaction method. Systematic studies of the crystal structure parameters, magnetic and microwave properties were carried out. All samples were single phase and described by the P63/mmc space group. It was established that an increase in the content of Al3+ ions in BaFe(11.5-x)Ti0.5AlxO19 (or BaM:Ti, where BaM – M-type barium hexaferrite) leads to a decrease in the lattice parameters and density of the samples. This correlates well with the ionic radii and atomic weight of Fe3+ and Al3+ ions. The weakening of Fe3+-O-Fe3+ exchange interactions induced a decrease in the temperature of the magnetic phase transition and saturation magnetization. The microwave properties as well as the frequency dependences of the permittivity and permeability in the range from 0.1 to 18 GHz were discussed in terms of the resonance of domain boundaries. A strong correlation between Al3+ concentration, crystal structure, magnetic and microwave properties was shown for BaFe(11.5-x)Ti0.5AlxO19 (0.1 ≤ x ≤ 3.0) samples.

Enhancement of structural and microwave properties of Zn2+ ion-substituted Li2MgSiO4 ceramics for LTCC applications

In this study, Zn2+-substituted Li2MgSiO4 ceramics (Li2(Mg1-xZnx)SiO4, x = 0.00, 0.05, 0.10, 0.15, and 0.20) were synthesized using a traditional solid-state method. A fixed amount of LiF sintering aid (1.5 wt%) was added to the ceramics for decreasing the sintering temperature and adjusting their microwave dielectric properties. X-ray diffraction (XRD) results revealed no secondary phases, and scanning electron microscopy (SEM) data suggest that the Zn2+ ion substitution increased the size and uniformity of the grains, thereby affecting the densification of the prepared ceramics. The maximum bulk density (2.94 g/cm3) was found in a Zn2+ ion-substituted ceramic with x = 0.10 at a relative density of 94.2% (compared with the XRD theoretical density). Excellent microwave dielectric properties (εr = 6.28, Q × f = 50400 GHz, and τf = −145 ppm/°C) can also be obtained at this zirconium content. We believe that the developed ceramics are promising for use as antenna substrates or transmit/receive modules in low-temperature co-firing ceramic applications.

Crystal structure, Raman spectra and microwave dielectric properties of novel low-temperature cofired ceramic Li4GeO4

A low-permittivity and low-loss ceramic, Li4GeO4, was fabricated via solid state reaction route. XRD showed that a single orthorhombic Li4GeO4 phase with olivine structure was prepared over the sintering temperature range of 660–740 °C. Dense ceramic sintered at 720 °C revealed excellent microwave properties, with εr ~6.99, Q × f ~47,813 GHz (at 15.5 GHz), and τf ~ − 159.2 ppm/°C. The microwave dielectric performances were analyzed with the intrinsic characteristics of crystal structure by ionic polarizability and Raman spectra. Additionally, the Li4GeO4 ceramic showed good chemical compatibility with Ag sintered at 720 °C. In the low-temperature cofired ceramic (LTCC) application, aforesaid results manifested that Li4GeO4 ceramic was considered as a potential candidate.

Studies on Exchange-Coupled Magnetodielectric Ceramics for Microwave Absorption in Ku-Band

Series of exchange-coupled BaFe12O19 (BaM)/CoFe2O4 (CFO) and BaM/Co0.5Zn0.5Fe2O4 (CZFO) composites were synthesized using the autocombustion method. Effect of soft (CFO/CZFO) phase weight fraction on structural, magnetic, and microwave properties of composites has been investigated and compared. X-ray diffraction patterns and scanning electron microscope (SEM) micrographs confirmed the presence of BaM and CFO/CZFO phases with well-distinguished grains in the composites. Existence of interfacial coupling was verified by smooth demagnetization behavior and single peak in corresponding $\text{d}M/\text{d}H$ curves. Saturation magnetization ( $M_{s}$ ) and coercivity showed strong dependence on exchange interactions between hard and soft magnetic spins. Compared to BaM, $M_{s}$ of composites were 22% and 36% higher with CFO and CZFO, respectively. Frequency-dependent complex permittivity ( $\varepsilon$ ) and permeability ( $\mu $ ) in ${\text{K}}_{u}$ -band were found to be dependent upon the relative composition and nature of soft phase. Maximum $\varepsilon $ of 45 and $\mu $ of 1.6 were achieved for BaM/CFO (50/50) composite. Exchange-coupled magnetodielectric with high $\varepsilon $ and $\mu $ were developed for various microwave applications.

Microwave Characterisation of PANI treated Jute Using Suitable Solvent Methanol and DMSO

This work discusses the study on the dielectric properties of PANI(Polyaniline) treated jute fabric. The method involvesusage of liquid dielectric measurement probe.Suitable solvents such as Methonal and DMSO(Dimethyl Sulfoxide) are used. The microwave properties such as dielectric constant, dielectric loss, absorption coefficient, and conductivity are studied in x-band(8-12 GHz)frequency band. In both the solvents, the PANI reacts in a similar manner. This exhibits similar nature of results with negligible deviations.

Application of microwave waveguide techniques for investigating the effect of concrete dielectric and reflection properties during curing

This study deals with the measurement of dielectric constant, the magnitude of reflection coefficient, and compressive strength for G30, G40, G50, and G60 concrete mix after 0, 3, 7, 14, 21, and 28 days curing. The open-ended coaxial probe of 4.8 cm, WR510, and WR340 waveguide models operating over a frequency range of 85 MHz to 1.8 GHz, 1.45–2.2 GHz, and 2.17–3.3 GHz, respectively, are applied. Fifteen concrete cube samples 150 × 150 × 150 mm size were casted for each mix. The experimental result shows that the dielectric constant and magnitude of the reflection coefficient decrease gradually until 21 days, then increase at 28 days age of concrete. Correlated the concrete dielectric constant with design compressive strength. The results corroborate that microwave techniques correlate well for evaluating the strength of concrete. The strength characterization is suitable with related material composition, necessary experimental setup, and environmental conditions applied in this study. Furthermore, curing conditions, effects must be accounted; it is valuable in establishing a correlation between conventional properties and microwave properties of concrete.

Fabrication of exchange coupled hard/soft magnetic nanocomposites: Correlation between composition, magnetic, optical and microwave properties

This paper studied the exchange coupling performance beside structural and microwave properties of SrFe12O19 (SFO) and x(CoTm0.01Tb0.01Fe1.98O4) (CoTmTb) (x ≤ 3.0) hard/soft ferrites nanocomposites (NCs). The structure and morphology of NCs were investigated by XRD, SEM, TEM and HR-TEM. Diffuse reflectance spectroscopic (DRS) measurements were applied on hexagonal ferrite, on spinel ferrite nanoparticles and on hard/soft NCs to specify the optical properties. Estimated Eg data are in a range between 1.32 and 1.79 eV. The magnetic properties were also inspected via measurements of magnetization (M) against magnetic field (H) at 300 K (RT) and 10 K (LT). The measurements performed at RT along with the plots of dM/dH versus H indicated that the NCs display good magnetic properties (exchange coupling behavior). The magnetic parameters such as (Ms, Mr, and Hc) show an enhancement in their values with an increasing the soft content at RT. Similarly, the maximum energy product (BH)max rises and reaches its max value for SFO/3(CoTmTb) NCs. Microwave properties of the SFO/x(CoTmTb) NCs were measured in the frequency range 33–50 GHz. From measured S11 and S21 parameters the main electrodynamic characteristics – permittivity and permeability (real and imaginary parts) were computed.

Microwave absorption performance of hexagonal nano boron nitride doped basalt fabric-reinforced epoxy composites

PurposeThe purpose of this paper is to investigate the effect of doping element on the microwave absorption performance of hexagonal nano boron nitride (h-nBN)-reinforced basalt fabric (BF)/epoxy composites. A new type of hybrid composite that will be produced by the use of boron nitride as an additive that leads to increased radar absorption capability will be developed and a new material that can be used in aeronautical radar applications.Design/methodology/approachThis study is focused on the microwave absorption properties of h-nBN doped basalt fabric-reinforced epoxy composites. Basalt fabric (BF)/epoxy composites (pure composites) and the BF/h-nBN (1 Wt.% h-nBN doped composites) hybrid composites were fabricated by vacuum infusion method. Phase identification of the composites were performed using X-ray diffraction (XRD), the 2θ scan range was from 10 to 60 with the scanning speed of 3°/min and surface morphologies of the composites were investigated using scanning electron microscopy (SEM). Microwave properties of samples were investigated through transmission/reflection measurements in Agilent brand 2-Port PNA-L Network Analyzer in the frequency range of 3–18 GHz. The prepared sample is positioned between two horn antennas with and without metal plate.FindingsExperimental results show that h-nBN doped composite was synthesized successfully and the produced hexagonal nano boron nitride-added fiber laminated composite material has good absorption behavior when they are used with metallic sheets and good for isolation applications at many points in the 3–18 GHz band.Originality/valueThis paper will contribute to the literature on the use of basalt fabric, which are new types of fibers, and hexagonal nano boron nitride and the effects of boron nitride on radar absorption properties of composite material. It presents detail characterization of each composite by using XRD and scanning electron microscopy.

Effects of washing method of nickel slag to the structural properties of composite nickel slag/laterite soil for high electromagnetic wave absorption performance

Laterite soil (LS) doped with nickel slag (NS) for different solvent was successfully use to enhance the microwave absorption properties. First, NS/LS-01 is laterite soil doped with nickel slag for washed by using hydrogen chloride and second, NS/LS-02 for nickel slag washed by using sodium chloride. All samples are prepared by milling method at low frequency (10 Hz). X-ray diffraction (XRD) result revealed that the as polycrystalline of a cubic phase and diffraction spectra were dominated by magnetite (Fe3O4). X-ray peak broadening was analyzed to evaluate the structural properties. The quantitative analysis of structural properties in this studies are Scherrer, Williamson-Hall and Size strain plot method. Crystallite size (D), micro strain (ε), stress (σ) and energy density (u) were extracted from the peak line broadening. NS/LS-02 shows the smallest volume lattice, the energy density and the best reflection loss (RL) from the vector network analyzer (VNA). It is reveals the unit cell with high energy density strong relationship with microwave properties. In this study easy method to find the best correlation between structural and microwave properties.

Synthesis of a hollow-structured flower-like Fe3O4@MoS2 composite and its microwave-absorption properties.

In order to realize the characteristics of new types of wave-absorbing materials, such as strong absorption, broad bandwidth, low weight and small thickness, a hollow-structured flower-like Fe3O4@MoS2 composite was successfully prepared by simple solvothermal and hydrothermal methods in this paper. The structural properties were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Besides, the microwave properties and magnetic properties were measured using a vector network analyzer and via a hysteresis loop. SEM and TEM images revealed that MoS2 nanosheets grew on the surface of hollow nanospheres. The results showed that the composite exhibited excellent absorbing property. When the molar ratio of Fe3O4 and MoS2 was 1 : 18, the minimum reflection loss value reached −49.6 dB at 13.2 GHz with a thickness of 2.0 mm and the effective absorption bandwidth was 4.24 GHz (11.68–15.92 GHz). Meanwhile, the effective absorption in the entire X-band (8–12 GHz) and part of the C-band (4–8 GHz) and Ku-band (12–18 GHz) could be achieved by designing the sample thickness. In addition, the hollow structure effectively reduced the density of the material, which was in line with the current development trend of absorption materials. It could be predicted that the hollow core–shell structure composite has a potential application prospect in the field of microwave absorption.

Preparation and microwave properties of ZnTiNb2O8/SmTiNbO6composite dielectric ceramics

In order to get a microwave dielectric ceramics having near zeroτƒ, different ratio of ZnTiNb2O8and SmTiNbO6powders are sintered together at different temperature. XRD and SEM of these composite ceramics are tested to analyze the composition. The microwave properties and density of the composite ceramics are measured in order to find the best ratio of ZnTiNb2O8and SmTiNbO6. For (1-x)ZnTiNb2O8-xSmTiNbO6ceramics, the ceramics have very good microwave properties(εr= 24.63, Q*ƒ=11846GHz,τƒ= 0.16ppm/℃) when x is 0.35.

Microwaves in Chemistry

The unique properties of microwaves make them useful in many diverse applications across a wide range of fields, spanning much of engineering and science. In the chemical sciences, microwaves provide a toolkit of electric and magnetic effects with which, at high power, unconventional heating modes can be used to produce new materials not obtainable by conventional heating. At low power, unique microwave properties can be used to make revealing spectroscopic measurements. In this review, we consider the current outlook for microwaves in chemistry beginning with the theoretical framework for our understanding of microwaves interactions and the causes of results observed. We then survey major application areas including in synthesis and emerging areas in catalysis, energy, and environmental applications. Finally, we review new concepts in dielectric and magnetic spectroscopy at microwave frequencies with a focus upon dielectric property measurement and electron paramagnetic resonance. This nonexhaustive review seeks to highlight important and emerging areas in the chemical sciences and put into context recent developments and advances in our understanding of microwave applications in this diverse area of science and engineering.

Physicochemical properties of microwave heated sago (Metroxylon sagu) starch

Sago starch is an underutilized starch due to its low functionality in food formulation. Modification is effective in improving starch functional properties. In this study, the starch were modified to enhance its functional properties. The starch was microwave-heated with different treatment durations of 5, 10, 15, or 20 min, separately, yielding microwave-heated starches (MHT1, MHT2, MHT3, and MHT4). The modified starches have irregular shaped granules and fissures while maintaining their mean diameters. The degree of double helix had increased, indicating more double helix structure of amylose formed. The modified starches’ moisture content, solubility, and paste clarity were significantly decreased. The MHT4 had its swelling power and syneresis increase. In conclusion, the treatment duration influenced the physicochemical properties of the sago starch, which is related to the formation of amylose double helix structure. Further study should focus on the formation of double helix structure in starch and its impact towards food structure.

Microstructure and electrical properties of microwave sintered Nb-doped NBT ceramics

Nb5+-doped sodium bismuth titanate (NBT) ceramics ((Na0.5Bi0.5)1-x/2Ti1-xNbxO3 where x = 0, 0.005, 0.01 and 0.015) were obtained by microwave assisted solid state reaction route and microwave sintered at 1000 ?C. Microwave processing technique was chosen for the sintering as it is a powerfulmethod which enables sintering in a short time with fast heating rate avoiding grain growth. The influence of Nb5+-doping on microstructure and electrical properties of the NBT ceramics was studied. X-ray diffraction analyses revealed that solubility limit of niobium in NBT lattice is up to 1mol%, as with further increase in niobium concentration pyrochlore appeared. Microstructure of all the ceramics was investigated by field emission scanning electron microscopy and it was observed that the average grain size decreased with doping. Temperature dependent dielectric study was carried out for all the ceramics at different frequency. All ceramics show diffusive dielectric behaviour around Tm and introduction of Nb even increases compositional fluctuation compared to the parent NBT. Nb-doping shifts the Tm toward lower temperature. Leakage current study showed that for whole range of electric field ohmic type conduction mechanism is dominant for all the ceramics. Room temperature polarization-electric field (P-E) hysteresis loop confirms the ferroelectric behaviour of all the ceramics.

Использование метода самовозгорания для получения замещённого алюминием гексаферрита бария

Oxide materials have traditionally attracted the attention of researchers around the world. This is due to their wide range of applications: electrical engineering, electronics, special coatings, chemical technologies, etc. Doping of oxide materials with various elements such as Al, Bi, Zn, Co, Sn, Ti, B, Sb and others is widespread in order to fine-tune their physicochemical properties. In particular, doping of barium hexaferrite with aluminum is of particular interest, since this allows one to change such important parameters as saturation magnetization (σS), coercive force (HC), squareness coefficient of the hysteresis loop (K), as well as to influence the anisotropy field and microwave properties of the material. Since the preparation of BaAlxFe12-xO19 by the classical ceramic method requires thorough grinding of the starting materials, preliminary sintering, high temperature (above 1300 °C) and duration of the synthesis, it was decided to test an alternative method for obtaining aluminum-substituted barium hexaferrite. As such, we have chosen the self-combustion method. During the synthesis a solution of nitrates of the corresponding metals with citric acid was prepared. After neutralization and evaporation of the solution, the resulting mass was heated in a muffle furnace to carry out the spontaneous combustion process and remove residual carbon. The final sintering of samples with the composition BaAlxFe12-xO19 (for x = 0, 1, 2, and 3) was carried out in a muffle furnace with a precision temperature controller at 1100 °C for 4 hours. The obtained samples were studied by the powder diffractometry method, scanning electron microscopy, and X-ray spectral microanalysis. It has been established that the self-ignition method makes it possible to obtain homogeneous samples of barium hexaferrite substituted with aluminum at a lower temperature compared to the classical ceramic method. The parameters of the structure of the obtained samples were also determined. The tested method not only makes it possible to obtain aluminum-substituted barium hexaferrite at lower temperatures, but also makes it possible to dope ferrites with highly volatile elements.

Synthesis of BaTi5O11 by an aqueous co-precipitation method via a stable organic titanate precursor

BaTi5O11 has been widely researched due to its unique microwave properties. Conventionally, it is challenging to obtain this compound as a single phase. The BaTi5O11 was synthesized via a co-precipitation technique using an aqueous solution of titanium(IV)(triethanolaminato) isopropoxide, barium nitrate and ammonia as precursors, which are stable in aqueous media. The phase evolution, purity, and structure were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopy analysis. The desired BaTi5O11 structure was obtained by calcination at 900?C. Furthermore, the structure was characterized by TGA, FT-IR and Raman studies. The study showed that the particles were between 80 and 120 nm in size and the average crystallite size was determined from the Scherrer formula as 68.1 nm at 900?C.

Experiment of measuring targets' full-parameters microwave properties

Experiment of measuring targets' full-parameters microwave properties

Structure and Microwave Properties of Nanocomposites With Embedded Spinel Particles Subjected to High-Temperature Annealing

The nanocomposite materials with particles of ferrites-spinel with ceramic structure are obtained. The nanocomposite materials are prepared on the basis of an opal matrix SiO2. Structure and phase composition of the obtained materials with particles Ni0.5Zn0.5Fe2O4 and Co0.5Zn0.5Fe2O4 are investigated. Permittivity in the frequency range from 26 to 38 GHz is measured. It is found that the samples of the same composition with a higher annealing temperature have a greater real part of the permittivity. The samples, in which palladium particles are added, in addition to the particles of nickel-zinc ferrite-spinel, have a lower permittivity than similar nanocomposites without palladium. The dependences of the transmission and reflection coefficients on the magnetic field are measured. It is shown that the phenomena of ferromagnetic resonance and antiresonance are observed in these materials.