Microwave Dielectric Materials Research Articles

Synthesis and fabrication of proto-type microstrip patch antenna by using microwave dielectric ceramic nanocomposite material for C-band application

The microwave dielectric properties of Zn(1-x)TixAl2O4 (ZTA) ceramic nanomaterials were investigated with a focus towards their use as wireless antennas. The ZTA nanoparticles were prepared using the sol-gel technique at 700 °C for one hour. The inclusion of titanium decreased the nanomaterials' crystallite size and surface shape, which influenced their dielectric permittivity (εr). Based on the tested material and microwave antenna theory, ZTA was used to fabricate wireless patch antennas, which were then examined using a PNA series network analyzer. The measured results reveal that the return loss and impedance bandwidths of the antenna were −44.83 dB simulated and −34.88 dB measured, and 240 MHz for simulated and 220 MHz for measured, respectively. At 5.1 GHz operating frequency, the Zn0.94Ti0.06Al2O4-based patch antenna demonstrated an exceptional combination of return loss (-34.88 dB), compact size (9.3× 6.3 mm2), and broad bandwidth (220 MHz) as well as VSWR<2. Ultimately, the fabricated antenna showcases a gain of 4.24 decibels and a directivity of 5.97 decibels.

Sintering characteristics, phase structure and microwave dielectric properties of novel BaCeO3 ceramics

It is a known fact that BaCeO3 (BC) is a material widely used in catalysts and electrochemistry, but its microwave dielectric performances have not been explored. Herein, novel BC microwave dielectric ceramics are prepared by the solid-state reaction method. The single-phase BC ceramic with orthorhombic structure (Pnma space group) is confirmed via Rietveld refinements and synthesized. Raman analysis reveals that the Q × f value of ceramics is negatively correlated with the full width at half maximum of the Raman peak. High surface densification and uniform grain size are obtained at 1650 °C and exhibit decent microwave dielectric properties: εr = 14.68, Q × f = 27,037 GHz(at 9.32 GHz), and τf = -63.67 ppm/ °C. The XPS results show that the oxygen vacancy content is the lowest and the Q × f value is the largest at the sintering temperature of 1650 °C. The results indicate that the ceramic is a good candidate for microwave dielectric materials.

Phase purifying and dielectric improvement in Zn2SiO4 ceramics via simply controlling the particle size of SiO2

AbstractThe zinc orthosilicate, Zn2SiO4 ceramics, exhibit great potential as microwave dielectric materials due to their low dielectric constant and ultrahigh quality factor. The solid‐state synthesis of Zn2SiO4 ceramics often results in the presence of a secondary phase of ZnO, however, leading to significantly lower Q×f values. Cold‐isostatic‐pressing (CIP) and nonstoichiometry have been proven effective in purifying the Zn2SiO4 but need elaborate process and composition manipulation. In this work, it was found that the particle size of SiO2 plays a crucial role in purifying the Zn2SiO4 phase. Specially, nano‐sized SiO2 particles (15 and 30 nm) led to the formation of a ZnO secondary phase in synthesized Zn2SiO4 ceramics, while micro‐sized (2 and 10 µm) resulted in pure‐phase Zn2SiO4 with excellent microwave properties. Notably, when prepared with 10 µm SiO2 and sintered at 1 340°C, the resulting Zn2SiO4 exhibited outstanding microwave performances with a Q×f value of 122 570 GHz, a temperature coefficient of frequency τf of −51.9 ppm/°C, and a dielectric constant (εr) of 6.5. These findings highlight the importance of controlling particle size during synthesis to achieve desired material properties such as purity and excellent microwave performances.

Dielectric Terahertz Characterization of Microwave Substrates and Dry Resist

Microwave fabrication and design techniques are commonly employed in the terahertz (THz) domain. However, a characterization of commercially available microwave dielectric materials is usually lacking at sub-THz and THz frequencies. In this work, we characterized four substrates by Rogers and an Ordyl dry resist between 0.2 and 2 THz, in terms of relative permittivity and loss tangent. The reflectance spectra of the investigated materials were retrieved by means of THz time-domain spectroscopy in reflection mode and post-processed according to a transmission-line model in which the materials’ parameters are fit by means of the Havriliak–Negami variation of the Debye model. The relative permittivity of the investigated materials showed negligible frequency dispersion in the sub-THz and in the THz range. In terms of the loss tangent, the Rogers substrates revealed a more pronounced frequency-dispersive behavior among different materials, as dictated by the Havriliak–Negami model. The Ordyl resist was dispersive in the 0.2–1.2 THz range and presented a nearly constant loss tangent value between 1.2 and 2 THz. These results may represent a reference for the development of innovative components for THz and sub-THz emerging applications.

Sintering behavior of 0.95MgTiO3-0.05CaTiO3 ceramics with high densification, high Q and enhanced mechanical properties for 5G massive MIMO technology: Effect of particle gradation

An increase in the requirements for microwave dielectric materials was brought on by the quick growth of communication technologies. In this study, the sintering problems including the narrow sintering densification range and high sintering temperature of 0.95MgTiO3-0.05CaTiO3 (95MCT) ceramics with high densification and high Q, as one of the candidate materials for 5G filters, were discussed and overcome through the particle gradation with sub-micrometric and micrometric powders according to closest packing models. It was found that sub-micrometric (0.7–1 μm) 95MCT powder particles agreed well with the Andreasen model, while micrometric (1–3 μm) particles agreed better with the Dinger-Funk model. With increasing of sub-micrometric powders, the activation energy decreased from 926.01 ± 75.49 to 569.49 ± 31.57 kJ/mol, and the relative density of samples which contained 20–60% fine powders were increased to 98%. The average grain size and grain homogeneity decreased from 7.36 μm to 2.54 μm and 3.36 to 1.79, respectively, to improve the mechanical properties. The results show that the powder grading further improved the comprehensive performance of 95MCT, and the best performance point was J1 which exhibited excellent microwave dielectric properties with εr = 21.1, Qf = 82000 GHz, τf = −0.9 ppm/°C, RD = 98.2%, σf = 178.7 MPa and HV = 8.78 GPa after sintering at 1225 °C for 3h.

Terahertz Properties of Common Microwave Dielectric Materials

Traditional microwave design and fabrication techniques have been adopted into the terahertz domain. Understanding the properties of microwave dielectric materials at terahertz frequencies is critical for accurate component design. Nevertheless, terahertz properties for common microwave dielectric materials are largely unknown. Hence, this paper presents the relative permittivity, loss tangent, refractive index, and extinction coefficient for such materials, including microwave substrates and low-temperature co-fired ceramics (LTCCs), within the 0.1 to 3.5 THz range. Terahertz time-domain spectroscopy (THz-TDS) and a vector network analyzer produce accurate material parameter results. The material parameters presented in this paper serve as a valuable resource for component design at terahertz frequencies.

A novel NaMg(1-x)Znx(PO3)3 microwave dielectric ceramic with an ultra-low dielectric constant for LTCC application

In millimeter-wave communication, signal delay becomes increasingly pronounced as the operating frequency of the equipment rises. To accelerate signal transmission, substrates with low dielectric constants (εr < 6) are required. This study synthesized a novel microwave dielectric material, NaMg(1-x)Znx(PO3)3 (NMZPO), using the conventional solid-phase method. The microwave dielectric properties of NaMg(PO3)3 ceramics were enhanced by substituting Mg2+ with Zn2+. Specifically, Zn2+ doping increased the ceramics' densification and reduced dielectric loss. The NaMg0.9625Zn0.0375(PO3)3 ceramic exhibited optimal microwave dielectric properties at sintering temperature 880 °C for 4h: εr = 4.49, Q × f = 58237.2 GHz (at 17.792 GHz), τf = −50.6 ppm/°C. In addition, NMZPO ceramics demonstrate excellent chemical compatibility with Ag electrodes. These findings indicate that NMZPO represents a promising candidate for the next generation of ultra-low dielectric constant LTCC materials.

Characterization of TixZn(1-x)Al2O4 nanoparticles by sol-gel method for wireless patch antenna applications

Scientists have been searching for new microwave dielectric materials due to the need for miniaturization and weight reduction of wireless patch antenna. The sol–gel method was used to prepare the TiχZn(1-χ)Al2O4 (x = 0.25) microwave dielectric ceramic nanoparticles and various measurements were carried out. The distinctive peaks of titanium and zinc aluminate with the typical face-centered cubic structure was noticed in the X-ray diffraction (XRD) patterns. Fourier transform infrared spectroscopy (FTIR) was used to confirm the functional groups, field-emission scanning electron microscopy (FESEM) was used to analyze the crystalline structure and the elemental composition was confirmed using energy dispersive spectroscopy (EDS). The substitution of Zn2+ for Ti2+ in ZnAl2O4 nanoparticles increased crystallite size, affecting dielectric permittivity. The dielectric permittivity (εr) of TiχZn(1-χ)Al2O4 nanoparticles was calculated using a 100 KHz to 1 MHz LCR spectrometer. It can be demonstrated that the Ti0.25Zn0.75Al2O4 sample has εr 22.78–23.45, making it a viable material for millimeter-wave applications. Additionally, a prototype patch antenna with dimensions 2.5 cm × 1.5 cm was fabricated using these dielectric ceramic nanoparticles and tested using a network analyzer, which exhibited a return loss of −12.82 dB at an operating frequency of 2.12 GHz.

Enhanced dielectric and thermal properties of SrTiO3/polyolefin composite substrate with dopamine-modified BNNS for microwave applications

The performance of microwave devices is significantly influenced by the substrates employed. In this study, we introduce a novel microwave composite substrate material exhibiting high dielectric constant and exceptional thermal conductivity, comprising dopamine-modified boron nitride nanosheets (BNNS@PDA) and SrTiO3/polyolefin. With an 8 wt% BNNS@PDA filler content, the composite material achieves a high dielectric constant of 17.7 (@10 GHz) and remarkable thermal conductivity of 1.604 W/(m·K), representing enhancements of 34% and 104% compared to SrTiO3/polyolefin, respectively. Additionally, a low dielectric loss of 2.95 × 10−3 and minimal water absorption of 0.15% are attained. The incorporation of BNNS@PDA augments the compatibility between the ceramic particles and resin matrix, contributing to increased dielectric constant, superior density and improved mechanical properties of composite materials. As an interval within the thermal conductive pathway, the PDA coating diminishes the system's thermal conductivity. And its interplay with polymer matrix influences the resin's curing process, subtly reducing the composite's thermal stability. In summary, BNNS@PDA/SrTiO3/polyolefin represents a promising microwave dielectric substrate material, offering high dielectric constant and excellent thermal conductivity.

Phase Composition, Raman Spectrum and Microwave Dielectric Properties of glass-free low temperature co-fired ACaPr(MoO4)3 (A = Na, K) Ceramics

A novel low-temperature sintered ACaPr(MoO4)3 (A = Na, K) microwave dielectric material was prepared by the conventional solid-phase reaction method. The effects of temperatures on the crystal structure, lattice vibration characteristics, and microwave dielectric properties of the new ternary molybdate ACaPr(MoO4)3 (A = Na, K) ceramics were investigated. XRD and Rietveld refinement results show that ACaPr(MoO4)3 (A = Na, K) ceramics belong to a tetragonal scheelite structure with space group I41/a. The lattice vibration mode was analyzed by Raman spectroscopy. The ACaPr(MoO4)3 (A = Na, K) ceramics have high density(＞95%) and excellent microwave dielectric properties with εr = 10.78, Qf = 57726 GHz, τf = −44.6 ppm/°C at 775 °C and εr = 10.36, Qf = 50096 GHz, τf = −46.2 ppm/°C at 725 °C, respectively. In addition, the excellent chemical compatibility between ACaPr(MoO4)3 (A = Na, K) ceramics and Ag electrodes has developed a path for its application in LTCC technology.

Microwave dielectric properties and frequency-controlled beam scanning application of Nb5+-substituted calcium-magnesium vanadate low-temperature sintered ceramics

Beam scanning devices in the X-band allow spatial reorientation of the beam, but this poses challenges for material and device design. To meet such challenges, the development of microwave dielectric materials and the design of special structures are crucial. Here, the microwave dielectric properties of Ca5Mn4V6-xNbxO24 (x = 0.00–0.08) ceramics are systematically investigated by using first-principles calculations and microstructural analysis. The ceramic has the best microwave dielectric properties (εr = 10.92 ± 0.14, Q × f = 50032 ± 1795 GHz (@10.52 GHz), τf = −59.58 ± 3.81 ppm/°C) when x = 0.04 and T = 875 °C. As a concept demonstration for device applications, a frequency-controlled beam scanning device in the X-band is designed by using this ceramic and copper electrode. This device has a beam scanning space of 3.248° (from 27.143° to 32.371°) in the frequency range of 10–11 GHz while maintaining high reflectivity (≥0.6). This function is verified by simulation results for far-field amplitude and far-field phase. This work contributes to the application of microwave dielectric ceramics.

Effect of lattice-induced strain on microwave dielectric polarization and properties: A case study of Ga-based garnet

In microwave dielectric materials, the phenomenon that the measured permittivity (εr) is inconsistent with the calculated permittivity (εr(C-M)) often occurs. In the present work, the intrinsic factors affecting the microwave dielectric properties of Ga-based garnet Ca3B1.5Ga3.5O12 (B = Nb, Ta) are studied by bond valence and the Phillips-Van Vechten-Levine (P-V-L) methods, and the relationship between lattice-induced strain effect and dielectric polarization is elucidated. Since the ionic polarizability of Nb5+ is lower than that of Ta5+, the εr(C-M) values of Ca3Nb1.5Ga3.5O12 (CNG) and Ca3Ta1.5Ga3.5O12 (CTG) are 11.06 and 12.17, respectively. However, this is the opposite trend of the measured values (15.00 and 12.62). The global instability index (GII) is equal to 0.013 and 0.044 v.u., respectively. Both the indexes, bond strain index (BSI) and GII, are related to the entire crystal structure. A stronger lattice-induced compressive strain and a higher degree of covalency lead to a lower measured εr, a higher Q×f, a higher temperature coefficient of permittivity τε, and a larger negative τf.

Dominant role of ceramic connectivity in microwave dielectric properties of porous ceramics

The connectivity of constituting phases plays an important role in the physical properties of composites and porous materials, while it is still overlooked in many cases. In the present work, CaTiO3 is used as the model material to clarify the effect of ceramic connectivity on the microwave dielectric properties of porous ceramics. CaTiO3-A and CaTiO3-B porous ceramics are prepared by partial sintering at 700–1200 °C and sintering at the optimum temperature of 1350 °C with the aid of porogen, respectively. With increasing the sintering temperature from 700 to 1000 °C, the relative density of CaTiO3-A ceramics maintains around 58%, while their εr, Qf, and τf increase dramatically (20.4–48.2, 968–4,237 GHz, and 443.9–724.2 ppm/ °C). The three parameters are even higher in CaTiO3-B ceramic with a similar relative density of 54.1% (69.1, 5,658 GHz, and 782.9 ppm/ °C). The huge variation in microwave dielectric properties is attributed to the significantly improved ceramic connectivity with sintering temperature observed from microstructure analysis. Finite element analysis further reveals that the ceramic connectivity plays the dominant role in the microwave dielectric properties by deciding the electric field distribution in CaTiO3 phase and pores and hence their contribution to dielectric response. The exponent α in exponential dielectric mixing rule is employed to describe the ceramic connectivity, and the trinary relationship among the microwave dielectric properties, constitution, and microstructure of porous ceramics is well constructed. This relationship can be extended to ceramic-polymer and ceramic-ceramic composites, which brings new perspectives for designing such microwave dielectric materials.

Exploration of MgTiO3-CaTiO3 Ceramic-Based Dielectric Resonator Antenna for Sub-6 GHz 5G Communication Application

There has been extensive research on microwave dielectric materials considering their applications in 5G communication technologies. In this work, the microwave dielectric performances of 0.95MgTiO3−0.05CaTiO3 (MCT) ceramic for sub-6 GHz frequency 5G application have been reported. The solid-state reaction technique was used to develop the MCT ceramic. The structural as well as dielectric properties of MCT were systematically examined. X-ray diffraction (XRD) was used to examine the crystalline phase of the MCT sample. The microwave dielectric properties, including relative permittivity, temperature coefficient of resonant frequency, and quality factor of MCT were measured. Using MCT ceramic as the resonator, a dielectric resonator antenna (DRA) has been simulated using HFSS software, which realizes that the S11 curve is in good accordance and that efficiency is high at 5.22 GHz. The extraordinary performances indicate that MCT ceramic is a potential candidate for 5G application.

Microwave dielectric properties of CaCu3Ti4O12 ceramics: A clue to its intrinsic dielectric response

CaCu3Ti4[Formula: see text] (CCTO) is a potential dielectric material with giant permittivity, good stability over the wide temperature and frequency range. However, the dielectric responses of CCTO-based ceramics are mainly investigated in the frequency of 10 2–106 Hz, which is far low to clarify the intrinsic dielectric feature. So, microwave dielectric properties have been investigated for the CCTO porous ceramics sintered at low temperature ([Formula: see text]1000[Formula: see text]C). Good microwave dielectric properties of permittivity [Formula: see text] = 62.7, quality factor Qf = 3062 GHz and temperature coefficient of the resonant frequency [Formula: see text][Formula: see text] = 179 ppm/[Formula: see text]C are achieved for the CCTO ceramics sintered at 1000[Formula: see text]C, the dielectric loss significantly decreases two orders to 0.002 compared to that of CCTO ceramics sintered at critical temperature of 1020[Formula: see text]C confirmed by differential scanning calorimetry (DSC). This clue indicates that giant permittivity and high loss is not intrinsic for CCTO ceramics, but derives from composition segregation, liquid phase and defects associated with internal barrier layer capacitor (IBLC). It suggests that CCTO-based ceramics is a promising microwave dielectric materials with high permittivity.

Phase Structures and Dielectric Properties of (n + 1)SrO − nCeO2 (n = 2) Microwave Ceramic Systems with TiO2 Addition

Ti4+-ion-doped (n + 1)SrO − nCeO2 (n = 2) ceramic systems were prepared with the conventional solid-state reaction method, and the effects of the phase structures and compositions, sintering behaviors, microstructures and microwave dielectric properties of these ceramic systems were investigated in detail as a function of TiO2 content. The analytical results of the XRD patterns show that the pure (n + 1)SrO − nCeO2 (n = 2) system is a composite-phase ceramic system with coexisting SrCeO3 and Sr2CeO4 phases (represented as a SrCeO3 + Sr2CeO4 system), which belong to the orthogonal structures of the Pmcn (62) and Pbam (55) space groups, respectively. For the xTiO2-(1 − x) (SrCeO3 + Sr2CeO4) (x = 0.1–0.4) ceramic samples, the secondary phase Sr2TiO4 can also be detected within the range of the investigated components. Meanwhile, the Raman spectroscopy, SEM-EDS, and HRTEM (SAED) analysis results also verified the correctness and consistency of the phase structures and compositions for all the given specimens. In addition, complex impedance spectroscopy was used to detect the conductive behavior of these compound ceramic systems, and the calculation results show that the appropriate addition of Ti4+-ions can make the SrCeO3 + Sr2CeO4 system have better thermal stability. The composition of x = 0.2 multiphase structural ceramic sample sintered at 1330 °C for 4 h has a near zero τf value of ~−4.6 ppm/°C, a moderate εr of ~40.3 and a higher Q × f~44,020 GHz (at 6.56 GHz). The relatively superior-performing ceramics developed in this work are expected to provide a promising microwave dielectric material for communication components.

Main Trends in the Development of Microwave Dielectric Materials for Cellular Communication Devices: A Review

Main Trends in the Development of Microwave Dielectric Materials for Cellular Communication Devices: A Review

Entropy regulation in LaNbO4-based fergusonite to implement high-temperature phase transition and promising dielectric properties

High-entropy effect is a novel design strategy to optimize properties and explore novel materials. In this work, (La_1/5Nd_1/5Sm_1/5Ho_1/5Y_1/5)NbO₄ (5RNO) high-entropy microwave dielectric ceramics were successfully prepared in the sintering temperature (S.T.) range of 1210–1290 ℃ via a solid-phase reaction route, and medium-entropy (La_1/3Nd_1/3Sm_1/3)NbO₄ and (La_1/4Nd_1/4Sm_1/4Ho_1/4)NbO₄ (3RNO and 4RNO) ceramics were compared. The effects of the entropy (<i>S</i>) on crystal structure, phase transition, and dielectric performance were evaluated. The entropy increase yields a significant increase in a phase transition temperature (from monoclinic fergusonite to tetragonal scheelite structure). Optimal microwave dielectric properties were achieved in the high-entropy ceramics (5RNO) at the sintering temperature of 1270 ℃ for 4 h with a relative density of 98.2% and microwave dielectric properties of dielectric permittirity (<i>ε</i>_r) = 19.48, quality factor (<i>Q</i>×<i>f</i>) = 47,770 GHz, and resonant frequency temperature coefficient (<i>τ</i>_f) = –13.50 ppm/℃. This work opens an avenue for the exploration of novel microwave dielectric material and property optimization via entropy engineering.

Recent progress in dielectric resonator antenna: Materials, designs, fabrications, and their performance

Dielectric resonator antenna (DRA) has secured an esteemed position in the field of antenna engineering technology due to its versatile features, including compactness, light-weight, low loss, high radiation efficiency, ease of excitation, diverse feeding techniques, multiple excitation modes, ease of integration with passive and active microwave integrated circuit components, a wide variety of available materials, simple fabrication techniques, and high degree of flexibility over wide frequency range. This article presents a comprehensive up-to-date review of research carried out in the field of DRA technology which includes an overview of DRA technology, its history, present status, and prospects. The basic parameters of microwave dielectric ceramic materials and the classification of materials based on utilization and material parameters are briefly discussed. The applications of DRA in different fields of science, engineering, and technology, overview of different reported DRA shapes, and the feeding techniques used to excite different modes of DRA are mentioned. Based on the control of DRA permittivity, shape/geometry, feeding techniques, and structural modifications, performance parameters engineering of DRA and its achievable performance in terms of low profile, compactness, high gain, wide beam, circular polarization, wide bandwidth, DRA decoupling methods for multiple input multiple output arrays, dielectric patch antenna, filtering DRA, and reconfigurable DRA are discussed. Different techniques used to attain and enhance the particular performance of DRA are highlighted. This review article also dilates upon the fabrication processes and characterization methods of DRA microwave dielectric ceramics, which play a very vital role in controlling the performance and properties of DRA.

Morphology Evolution of Mg2SiO4 Particles Synthesized by Spray Pyrolysis from Precursor Solution

Forsterite (Mg2SiO4) materials have been used in the industrial applications of refractory materials, bone grafting materials, and microwave dielectric materials. In order to avoid the formation of the secondary phase of MgO or MgSiO3, spray pyrolysis with the precursors of magnesium nitrate hydrate and tetraethyl orthosilicate has been applied to synthesized Mg2SiO4 powders. In this study, three typical morphologies of smooth solid sphere, rough hollow sphere, and concaved hollow sphere were observed using scanning electron microscopy and transmission electron microscopy. The experimental results suggested that morphology and particle size distribution are strongly influenced by the calcination temperature. Finally, the corresponding powder formation mechanisms were proposed and discussed.