Microwave Properties Research Articles

Crystal structure, dielectric properties, and far-infrared reflectivity spectrum of a novel phosphate KBaPO4 ceramic at microwave frequency

A novel orthophosphate ceramic KBaPO4 was successfully synthesized via a solid-state reaction route and surveyed systematically in microwave properties. X-ray diffraction patterns confirmed that single phases were obtained of all ceramics sintered at 900–1100 °C. The dense ceramics with homogeneous microstructure was obtained when sintered at 1050 °C and revealed by density and microstructural studies. According to the chemical bond theory, P–O made a more significant contribution to the microwave properties of KBaPO4 ceramics. Infrared reflection spectrum results showed that the permittivity was related to the absorption of phonon oscillation. The optimum properties (εr = 7.58, Q×f = 31,577 GHz, τf = −13.3 ppm/°C) of KBaPO4 ceramics were obtained when sintered at 1050 °C.

Positive stretching dependence of resonance frequency in CoFeB films modulated by lateral growth pre-strain

We demonstrated a method via applying a lateral pre-strain to achieve a positive stretching dependence of resonance frequency in CoFeB films. An artificial wrinkling surface structure by adhering CoFeB films to biaxially pre-strained elastomeric polydimethylsiloxane (PDMS) supports was employed to fabricate stretchable magnetic films. The lateral growth pre-strain was used to adjust the longitudinal stretching dependence of resonance frequency of CoFeB films. For the sample fabricated on an elastomeric support that can freely contract in the lateral direction, the resonance frequency fr monotonously decreases with applying a tensile strain εapp. For the sample fabricated on an elastomeric support that can partially contract in the lateral direction, the fr first decreases and then increases as the εapp increases. The sample fabricated on an elastomeric support in which the lateral contraction is strictly limited display a positive stretching dependence of fr in the whole range of εapp. Thousands of fatigue tests show that the stretching dependence of microwave properties have a good repeatability.

A novel BaMg1.98Zn0.02V2O8 ceramic with low dielectric loss and good temperature stability for low temperature co-fired ceramic technology

In this paper, a series of BaMg2-xZnxV2O8 (0.02 ≤ x ≤ 0.08) ceramic has been obtained by ionic substitution at the Mg-site of BaMg2V2O8 ceramics through the conventional solid-state reaction method. The relationship between the surface morphology and the microwave properties of ceramic samples was analyzed intensively. The results showed that the substitution of Mg2+ by an appropriate amount of Zn2+ can promote their densification, lower their sintering temperature, and reduce the dielectric loss of BaMg2V2O8 ceramics significantly. The BaMg1.98Zn0.02V2O8 ceramic exhibits microwave dielectric properties as εr ∼13.4, Q × f ∼ 178,760 GHz, τf ∼ -14.9 ppm/°C at the optimum sintering temperature (940 °C). This indicates that the ceramic prepared in this work, which combines low dielectric loss, good temperature stability, and low-temperature sintering ability, can be an ideal microwave dielectric material for low-temperature co-firing technology.

Low loss Ba3Ti4Nb4O21 microwave dielectric ceramics through (Mn1/3Nb2/3)4+ ion control engineering for LTCC applications

In this work, a new low loss Ba3Ti4-x(Mn1/3Nb2/3)xNb4O21 (MN-BTN, 0 ≤ x ≤ 12 mol%) ceramics configuration was presented through preparing by the solid-state route. The XRD patterns, Rietveld refinement, microstructure, and microwave properties were systematically analyzed. All the fabricated MN-BTN ceramics belonged to the hexagonal structure with a P63/mcm space group. More specifically, the 6MN-BTN ceramic exhibited a high relative density of ~92.3 %, homogeneous grains distribution with an average size of ~71.95 µm, and several excellent microwave dielectric properties: εr = 59.67, Q×f= 16,226 GHz, τf= +103.9 ppm/℃ sintered at 1220 ℃. The incorporation of 1.5 wt% BaCu(B2O5) (BCB) compound within the 6MN-BTN ceramic not only effectively reduced the sintering temperature from 1220 ℃ to 950 ℃, but also the excellent microwave dielectric properties were maintained: εr = 42.33, Q×f= 11,300 GHz, τf= +24.7 ppm/℃. Interestingly, the 6MN-BTN + 1.5 wt% BCB ceramic showed better chemical compatibility with Ag. The proposed 6MN-BTN + 1.5 wt% BCB ceramic configuration could be regarded as a promising material for LTCC applications.

Barium hexaferrites with narrow ferrimagnetic resonance linewidth tailored by site‐controlled Cu doping

AbstractBarium hexagonal ferrites exhibiting unique self‐biasing characteristics have great potential for application in planar microwave devices, such as self‐biased circulators. Cu doping is an effective method to tailor their anisotropy field and ferrimagnetic resonance (FMR) linewidth to meet the requirements for low‐frequency low‐loss microwave devices. However, the regulation mechanism of Cu doping is still obscure, and its regulation effect is not optimized. Here, the magnetic and microwave properties of two groups of barium hexaferrites with site‐controlled Cu doping are reported. The diffusion dynamics of Cu2+ ions are comprehensively investigated, revealing significant differences in the concentration distribution and polycrystalline morphology, when comparing CuO as a reactant and sintering additive. The accumulation of Cu2+ ions at grain boundaries contributes to the increase in coercivity, whereas the dispersion of Cu2+ ions in crystallites leads to the decrease in the anisotropy field. Moreover, by introducing Cu2+ ions into the interstitial positions of the lattice, barium hexaferrites with a narrow FMR linewidth of 303 Oe and a high remanence ratio of 0.82 are achieved. These results represent the lowest FMR linewidth reported in polycrystalline hexagonal ferrites and prove the great technological value and commercial potential of Cu‐doped barium hexaferrites for next‐generation planar microwave devices.

Synthesis, sintering and microwave dielectric properties of Zn-doped Li3Mg4NbO8 ceramics

In this work, the effect of ionic substitution at the Mg-site in pure Li3Mg4NbO8 ceramics, including sintering characteristics and microwave properties, has been investigated for the first time. A novel Li3(Mg1−xZnx)4NbO8 ceramic has been successfully synthesized via the solid-phase reaction method by replacing Mg2+ with appropriate amounts of Zn2+. The relationship between crystal structure and properties has been established based on complex chemical bonding theory. There is a strong correlation between dielectric constant and ionicity, while the quality factor is related to the density and the lattice energy. The temperature coefficient of the resonance frequency and the dielectric constant after correction for porosity are closely related. Doping with appropriate amounts of Zn2+ can significantly improve the properties of pure Li3Mg4NbO8 ceramics. The Li3(Mg0.96Zn0.04)4NbO8 ceramic obtained at x = 0.04 has the following sintering properties at 1075 °C: εr = 15.0 ± 0.08, Q×f = 121,157 ± 1300 GHz, τf = −8.23 ± 0.11 ppm/°C, which combines characteristics of low dielectric constant, high quality factor, and temperature coefficient close to zero. Therefore, the resulting ceramic can be an ideal microwave dielectric material for the miniaturization and integration of microwave devices in 5 G.

A Novel Method to Synthesize Co/Fe3O4 Nanocomposites with Optimal Magnetic and Microwave Performance.

The magnetic interactions between neighboring magnetic nanoparticles make the synthesis of nanocomposites made of two kinds of magnetic nanoparticles extremely difficult. In this paper, to achieve an effective nanocomposite of Co and Fe3O4 nanoparticles, a special urchin-like Co nanomatrix was used to prepare the Co/Fe3O4 nanocomposites. The Fe3O4 nanoparticles are evenly embedded into the branches of the CO clusters, bringing the two types of particles into close contact and ensuring the optimal magnetic and microwave properties. The electromagnetic (EM) parameters at 1–18 GHz and the magnetic loss tangents can be effectively modulated, and the absorption frequency bands of the EM waves are shifted to the X-Ku bands (8–18 GHz) from the S-C bands (2–8 GHz) after the Fe3O4 nanoparticles are compounded.

Structural, magnetic, and microwave absorbing properties of NiTiO3/CoFe2O4 composites

In this study, different volume ratios (NiTiO 3 : CoFe 2 O 4 = 1:3, 2:3, 1:1) of NiTiO 3 /CoFe 2 O 4 composites were synthesized using the sol-gel method. The effects of different NiTiO 3 volume ratios on the structural, morphological, magnetic, and microwave properties were systematically investigated by X-ray diffraction spectroscopy (XRD), field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy (RAMAN), vibrating-sample magnetometery (VSM), and vector network analysis. Electromagnetic wave absorption analysis indicated that 1:3 composite sample showed the greatest reflection loss (−21.7 dB at 17.1 GHz frequency) at a thickness of 10.0 mm. The microwave absorbing properties decrease with the increasing NiTiO 3 volume ratio. The observed improvement can be attributed to the low degree crystallization of NiTiO 3 that increases magnetic losses through increased exchange resonance. • Different volume ratios of NiTiO 3 /CoFe 2 O 4 were synthesized by sol-gel method. • Microwave absorbing properties of NiTiO 3 are very poor, nearly no broad peak with lower than − 10 dB. • 1:3 composite sample showed greatest reflection loss (−21.7 dB at 17.1 GHz) at 10.0 mm thickness. • The improvement attributed to low degree crystallization of NiTiO 3 that increases exchange resonance.

Investigation of microstructure and mechanical properties of microwave consolidated TiMgSr alloy prepared by high energy ball milling

The nanostructured TiMgSr (at.% 70:10:20) was synthesized by ball milling process followed by cold compaction and microwave sintering. XRD results after 30 h milling showed crystallite size of ⁓41 nm with a lattice strain of 2.5% and evolution of solid solutions like Mg 5 . 2 Sr, MgTiO 3 . The phases formed from 30 h mechanically alloyed powder are in good agreement with TEM SADP results. Consolidation using microwave sintering resulted in the retention of nanostructure with crystallite size of 78 nm and lattice strain of 1.2%. Densification study results in porosity of 19.8% with almost 20% density reduction compared to CP-Ti. The obtained porosity has promoted density reduction along with low elastic modulus that could be biocompatible with human bone tissue. Nanoindentation test results showed a low modulus of 36 ± 7 GPa with a hardness of 1.8 ± 0.8 GPa. These results are comparable with those Ti alloys produced by various techniques and found to be relatively superior for biomedical applications. • Powder metallurgy routes developed novel nanostructured Ti-Mg-Sr alloy. • Nanoindentation test shows Young's moduli of 36 ± 7 GPa with hardness 1.8 ± 0.8 GPa. • Successfully retained the nanostructure in Ti-Mg-Sr sample even after sintering. • Developed Ti-Mg-Sr alloy could be promising for orthopedic and dental applications.

Magnetic and Microwave Properties of Nanocomposites Containing Iron Particles Encapsulated in Carbon.

The magnetic and microwave properties of nanocomposites containing iron particles encapsulated in a carbon shell (Fe@C), as well as carbon nanotubes (CNT), have been experimentally studied. The examination of magnetic properties of composites shows that the materials under study contain a ferromagnetic component. The availability of ferromagnetic ordering for the dielectric matrix-based nanocomposite sample with Fe@C particles has been confirmed by the measurement results of the transmission and the reflection coefficients of the microwaves, since the ferromagnetic resonance has been observed. Furthermore, in the fields less than the field of ferromagnetic resonance, there are the signs of the presence of ferromagnetic antiresonance. The ferromagnetic resonance leads to minima in the transmission and reflection coefficients, whereas the antiresonance, conversely, leads to maxima in the reflection coefficient. The measurement results have been compared with the theoretical calculations of the field dependence of microwave transmission and reflection coefficients.

Dielectric/thermal characteristics of recycled borosilicate glass-filled polytetrafluoroethylene

Polytetrafluoroethylene (PTFE) composites filled with recycled borosilicate (rBRS) glass were fabricated for printed circuit board (PCB) substrate application. The rBRS powder prepared via a ball milling technique was dispersed in the PTFE matrix in different volume fractions (5%–25%) to produce the composites through a dry powder mixing technique. The effects of filler content on the composites' structural, dielectric, and thermal properties were examined. Scanning electron microscopy showed that rBRS filler was more dispersed in the composites at lower filler contents. The composites showed excellent microwave properties with relative permittivity of 2.31 and a loss tangent of 0.0018 at the highest filler content of 25%. The composites also revealed a good thermal property with a mean CTE of 60.54 ppm/°C at 25% filler content. Experimental data were compared with theoretical predictions. The results showed that experimental values of relative permittivity agreed with calculated values from regression analysis. It was also found that the logarithmic general mixing model gave an excellent estimate of the loss tangent of the composites.

Structural, morphological, optical, magnetic, and microwave properties of La3+- Mn2+ substituted Zn2-Y-type barium-strontium hexaferrite

This experimental study examines the effects of the La3+-Mn2+ substitution on structural, morphological, optical, magnetic, and microwave properties of Ba1.7-xSr0.3LaxZn2Fe12-xMnxO22 (x = 0.0, 0.1, 0.2) using sol-gel auto combustion. We characterize the as-prepared nanoparticles structurally using XRD and FTIR, and the morphology is determined using FESEM micrographs. Elemental analysis (EDX) verifies the presence of the entire experimental elements. The optical band gap was determined using UV Visible spectroscopy with the help of Tauc theory. VSM and VNA analyses determine the magnetic and microwave properties, respectively. The small coercivity and small area under the hysteresis loop show that the materials are soft magnetic. The microwave properties of the prepared material were affected by the grain size and saturation magnetization. A single absorption peak from the reflection loss graph and high shielding effectiveness of the synthesized nanoparticles indicates that the material may have the potential as an effective EMI shielding material in Ku-band.

Determination of Transmission Coefficient and Electric Field Distribution of Rice Husk/ Pcl Composites Using Finite Element Method for Microwave Devices

Material thickness is one factor that is considered in the selection of materials for usage in microwave applications. The demand for microwaves technology is widely needed in modern applications such as cellular telephone, satellite communication, radar system, global positioning system, and microwave remote sensing systems. Experiments and results abound for microwave properties determination for inorganic materials. Focus has recently been shifted to agricultural waste composite for microwave application. It is on this basis that this work primarily focuses on investigates microwave transmission coefficients and electric field visualization of different rice husk/PCL sizes placed inside a rectangular waveguide using the finite element method (FEM). Determination of the transmission coefficient for different thickness of rice husk/PCL composites were performed at X-band frequency using FEM. The thicknesses for the rice husk/PCL composites simulated were 10, 15, 20, 30, and 50 mm. The results of the simulation for the transmission coefficient revealed that the 50 mm composites had the lowest value of 0.148468 for the transmission coefficient at 12 GHz while the electric field visualization showed that the 50 mm composites have the least value of electric field intensity. The results confirms that the 50 mm thick sample absorbs the highest radiation. Based on the results obtained, all sample thickness can be used for microwave dummies.

Coupled electromagnetic heat transfer model for cemented tailings backfill cured by microwave energy

Cemented tailings backfill (CTB) is a composite material containing binder, tailings and water, and it is commonly made available for filling mine-out areas and managing waste tailings. When backfilled, the CTB strength and its gain rate should be guaranteed for safe and efficient mining. It is acknowledged that increasing the CTB temperature is beneficial to its strength development. For this reason, microwave heating is introduced and applied to raise the CTB temperature quickly and thus accelerate its strength gain. To date, no numerical research has been conducted to investigate the electromagnetic and thermal properties of microwave cured CTB. Therefore, the present study proposes a coupled electromagnetic heat transfer model for the CTB heated by microwave energy. This proposed model considers the conversion of energy (electrical to electromagnetic and then to thermal), courses of heat conduction and convection, and relevant temperature variation. Two groups of experimental data are used to verify the prediction ability of the model simulation, and this model can accurately describe the thermal properties of the microwave heated CTB. Based on the validated model, the effects of input power, frequency and sample dimension on the distribution of heat and electromagnetic field are discussed. This study can be a contribution to the optimization of microwave parameters and sample dimension, for higher temperature development, less energy consumption and more uniform heating, in future laboratory experiments and field applications.

Epoxy composites filled with graphite nanoplatelets modified by FeNi nanoparticles: Structure and microwave properties

This paper is concerned with investigation of the structure and microwave properties of epoxy resin composites with graphite nanoplatelets (GNPs) decorated by FeNi nanoparticles prepared by the salt impregnation. It was confirmed by SEM and XRD that the method gives nanopowder where the metal componentFe20Ni80 is in the form of nanoparticles (20–40 nm in diameter) which are distributed over the surface and edges of the GNPs. The graphite phase in the investigated nanopowder is predominant, and Fe20Ni80 component mainly contains fcc FeNi3. Measurements of magnetic properties confirmed that Fe20Ni80 are small, randomly oriented assembly of spherical (or close to spherical) particles on the GNPs surface. The saturation magnetization of GNP-Fe20Ni80 particles is 25 emu/g and it weakly depends on temperature. Electrical resistivity measurements have shown that decoration of GNPs leads to essential increase of conductivities well as improvements EMR absorption properties in high frequency range (26–60 GHz) in (GNP-Fe20Ni80)/with in compression GNP/epoxy under the same volume content of 1.45 vol.%(GNP-Fe20Ni80)/L285 composites demonstrated superior broadband absorption properties with microwave absorption efficiency higher than 97% in the whole investigated frequency region.The effective absorption bandwidths are as high as 12.2 GHz were observed at the frequency range 41.9 and 53.2 GHz and 13.3 GHz at the frequency range 51.1 GHz–64.4 for this composite. It is assumed that decoration of GNPs surface by nanoscale Fe20Ni80 particles leads to a formation of the multiple dielectric and magnetic loss mechanisms, such as interfacial polarization, dipole polarization, space-charge polarization, eddy current loss, Debye dipolar relaxation, natural resonance and exchange resonance, which improve the microwave absorption properties of the investigated composites.

Dielectric properties of conventional and microwave sintered Lanthanum doped CaCu3Ti4O12 ceramics for high-frequency applications

The colossal dielectric response of La-doped CaCu3Ti4O12 ceramics has been probed at room temperature for a frequency of 1Hz–20 MHz. In this work, the La-doped (CaCu3Ti4O12)x samples for x = 0.1, 0.2, and 0.3 have been sintered at 1100 °C using two different heating modes. SEM and EDS analysis investigated the microstructural chrysalis, grain size distribution, and the inhibitions of Cu-rich phase segregation into grain boundaries by the effect of La3+. The presence of main cubic single-phase of CCTO and the diminutive Bragg peak shift due to ion size effect of La3+ and Ca2+ have been identified by XRD for both conventional (CS) and microwave sintered (MWS) samples. XPS study revealed the effect of La3+ on the binding energies of Cu and Ti in CCTO. The dielectric properties namely dielectric constant (ϵ), tan δ, and dielectric relaxation peaks were measured using BDS in which CS and MWS La-doped samples demonstrated (ϵ) ∼ >104 and ∼ >103 along with low tan δ for x ≥ 0.1 at medium and high frequency (104–107Hz) than pure CCTO.

Low temperature fired CaF2-based microwave dielectric ceramics with enhanced microwave properties

Low-temperature-fired microwave ceramics are key to realizing the integration and miniaturization of microwave devices. In this study, a facile wet chemical method was applied to synthesize homogenous nano-sized CaF2 powders for simultaneously achieving low-temperature sintering and superior microwave dielectric properties. Pure CaF2 ceramics sintered at 950 °C for 6 h with good microwave dielectric properties (εr = 6.22, Q×f = 36,655 GHz, and τf = −102 ppm/°C) was achieved. The microwave dielectric properties of the CaF2 ceramics were further improved by introducing LiF as a sintering aid. The sintering temperature of CaF2-based ceramics was effectively lowered from 950 °C to 750 °C with 10 wt% LiF doping, and excellent microwave dielectric properties (εr = 6.37, Q×f = 65,455 GHz, and τf = −71 ppm/°C) were obtained.

Electric Tunable Structures Based on BaZr<sub>x</sub>Ti<sub>1–x </sub>O<sub>3</sub> and BaSn<sub>x</sub>Ti<sub>1–x</sub>O<sub>3</sub> Solid Solutions for Microwave Applications

Introduction. An experimental study of the structural and electrophysical properties of multicomponent films of solid solutions of barium titanate-zirconate and barium titanate-stannate on sapphire substrates has been carried out. These materials are an alternative to the more studied barium-strontium titanate for use in microwave technology, due to the relatively high controllability. In this paper, it is shown that when using post-post high-temperature annealing, films with a component composition close to the composition of the sprayed targets are formed on the substrate. Optimal deposition temperatures of thin films of barium titanate-zirconate and barium titanate-stannate have been determined to obtain the best electrophysical parameters.Aim. Investigation of structural and microwave properties of BaZrxTi1-xO3 (BZT) and BaSnxTi1–xO3 (BSnT) films on dielectric substrates. These ferroelectric materials are promising in terms of losses and nonlinearity, and the formation of planar structures based on these materials on a dielectric substrate allows for a significantly higher level of operating power of the microwave device.Materials and methods. The crystal structure and phase composition of the obtained films were studied by X-ray diffraction using a DRON-6 diffractometer on the emission spectral line CuKa1 (λ = 1.5406 Å). Capacitance C and Q-factor (Q = 1/tg δ) of capacitors were measured at frequencies of 1 and 3 GHz using a resonator and an HP 8719C vector analyzer.Results. It is established that high-temperature annealing after film deposition has a significant effect on the crystal structure, phase composition of films and their electrical characteristics. For the first time, a low level of dielectric losses of planar capacitive elements based on titanate-stannate and barium titanate-zirconate films in the frequency range of 1…60 GHz with acceptable controllability has been demonstrated.Conclusion. The results obtained indicate the prospects of using thin ferroelectric films of BaSn0.5Ti0.5O3 and BaZr0.5Ti0.5O3 solid solutions in microwave devices.

Emerging magnetodielectric materials for 5G communications: 18H hexaferrites

With the rapid development of 5G technologies, it is crucial to seek magnetodielectric materials with high permeability and permittivity, low magnetic and dielectric losses, and high cutoff frequency over the sub-6 GHz frequency bands. Due to limited resonant frequency and large natural resonance linewidth, conventional microwave ferrites and their composites do not meet these requirements. Here, the microwave properties and their temperature dependence of a unique type of hexaferrites, Mg-Zn 18H hexaferrite (Ba5Mg2−xZnxTi3Fe12O31), are reported. Polycrystalline Mg-Zn 18H hexaferrite exhibited an extremely low damping coefficients (α = 0.1-0.2), remarkably low magnetic loss (tan δm = 0.06), excellent thermal stability of the damping coefficient (Δα/ΔT = 0.0004 K−1), and a narrow ferromagnetic resonance (FMR) linewidth (ΔH = 486–660 Oe). Moreover, Mg-Zn 18H hexaferrite possessed significant enhancement in the figure of merit (FOM = μ'Qf) compared to conventional microwave ferrites and their composites. When employed as the substrate of a 3.6-GHz patch antenna, Mg-Zn 18H hexaferrite demonstrated significant advantages for miniaturization (∼5 ×) and bandwidth improvement (∼50–110%) over conventional dielectric substrates. These results represent the best magnetic performance among the microwave ferrites reported at the S band and reveal the great technological value and commercial potential for 5G communications.

Sintering characteristic, structure, microwave dielectric properties, and compatibility with Ag of novel 3MgO-B2O3-xwt% BaCu(B2O5)-ywt% H3BO3 ceramics

ABSTRACT In this study, 3MgO-B2O3-xwt%BaCu(B2O5) (BCB)-ywt%H3BO3 (2 ≤ x ≤ 8, 0 ≤ y ≤ 20) ceramics were sintered at the optimum temperature to form Mg3B2O6 and MgO phases. The effects of H3BO3 and BCB on the product characteristics, phase transition, microstructure, and microwave dielectric properties of 3MgO-B2O3 ceramics were investigated. The intensities of diffraction peaks of two phases varied with changing the x and y values. After sintering at 950°C, the ceramics with x = 6 and y = 15 achieved the excellent microwave properties with a εr of 6.72, Q × f of 83,205 GHz and τf of – 65.05 ppm/°C. Besides, the ceramics with x = 8 and y = 5 sintered at 925°C also achieved good microwave dielectric properties with a εr of 6.64, Q × f of 78,173 GHz and τf of – 57.27 ppm/°C. The sintering temperatures of above both ceramics are well lower than the melting point of Ag, showing promising applications in low temperature cofired ceramic devices. In particular, these two ceramics can be used as the potential candidate materials for microwave ceramics for 5 G technology, provided that τf can be further optimized.