Microwave Dielectric Constant Research Articles

On the Characteristics of Coaxial-Type Microwave Excited Linear Plasma: a Simple Numerical Analysis**supported by National Natural Science Foundation of China (Nos. 11205201 and 61205139), and the Scientific Foundation of Ministry of Education of China (No. N130405008)

To unveil the characteristics and available propagation mechanism of coaxial-type microwave excited line-shape plasma, the effects of parameters including microwave power, working pressure, dielectric constant, and external magnetic field on the plasma distribution were numerically investigated by solving a coupled system of Maxwell's equations and continuity equations. Numerical results indicate that high microwave power, relatively high working pressure, low dielectric constant, and shaped magnetic field profiles will help produce a high-density and uniform plasma source. Exciting both ends by microwave contributed to the high-density and uniform plasma source as well. Possible mechanisms were analyzed by using the polarization model of low temperature plasma. The generation and propagation processes of the line-shape plasma mainly depend on the interaction of three aspects, i.e. the transmitted part, penetration part and absorptive part of the electromagnetic field. The numerical results were qualitatively consistent with available experimental results from literature. More elaborate descriptions of the three aspects and corresponding interactions among them need to be investigated further to improve the properties of the line-shape plasma.

Dielectric Behavior of Low Microwave Loss Unit Cell for All Dielectric Metamaterial

With a deep study of the metamaterial, its unit cells have been widely extended from metals to dielectrics. The dielectric based unit cells attract much attention because of the advantage of easy preparation, tunability, and higher frequency response, and so forth. Using the conventional solid state method, we prepared a kind of incipient ferroelectrics (calcium titanate, CaTiO3) with higher microwave permittivity and lower loss, which can be successfully used to construct metamaterials. The temperature and frequency dependence of dielectric constant are also measured under different sintering temperatures. The dielectric spectra showed a slight permittivity decrease with the increase of temperature and exhibited a loss of 0.0005, combined with a higher microwave dielectric constant of ~167 and quality factorQof 2049. Therefore, CaTiO3is a kind of versatile and potential metamaterial unit cell. The permittivity of CaTiO3at higher microwave frequency was also examined in the rectangular waveguide and we got the permittivity of 165, creating a new method to test permittivity at higher microwave frequency.

Influence of TiO<sub>2</sub> Crystalline Structure on Dielectric Resonator Properties from ZnO-Nb<sub>2</sub>O<sub>5</sub>-TiO<sub>2</sub> Ceramic System for Use in Telecommunications

This paper presents an investigation of the correlation between dielectric properties and microstructure and TiO2 crystalline-phase characteristics (rutile and anatase) in ZnO-TiO2-Nb2O5 system ceramics. Such ceramics were produced from powder mixtures of zinc oxide, niobium oxide and titanium oxide. Powder mixtures were compressed by pressing (100 MPa uniaxial and 300 MPa isostatic) and sintered at 1100, 1200 and 1250 °C. The sintered ceramics were characterized on the crystalline phases, density and microstructure and microwave frequencies. As for the microwave dielectric properties, dielectric constant, quality factor and thermal coefficient in the temperature range from-20 to 50 °C were measured. The results showed that the type of titanium oxide structure (rutile or anatase) causes influence on the type and quantity of crystalline phases in relative density of sintered ceramics and, consequently in their dielectric properties measurements.

Structural and microwave characterization of Ni0.2CoxZn0.8−xFe2O4 for antenna applications

Abstract Nickel–cobalt–zinc ferrites, Ni 0.2 Co x Zn 0.8− x Fe 2 O 4 (with x =0, 0.2, 0.4, 0.6, 0.8,) have been prepared using the auto-combustion method. X-ray diffraction, Fourier transform infrared (FT-IR) and Raman spectroscopy confirmed the cubic spinel structure of the ferrites. Microwave dielectric constant ( e r ) and quality factor ( Q × f ) were measured by using the Hakki–Coleman technique. Dielectric constant calculated using the Clausius–Mossoitti relation showed good agreement with the experimental value. Relative permeability of the ferrites was calculated by using the Nicholson–Ross–Weir conversion technique. Dielectric constant ( e r ) decreased from 7.474 to 5.548 and temperature coefficient of resonant frequency ( τ f ) increased from −75.85 ppm/°C to −19.32 ppm/°C, respectively, and relative permeability increased from 2.1085 to 3.2179 with increase in Cobalt content. The composition Ni 0.2 Co 0.2 Zn 0.6 Fe 2 O 4 was used to develop ferrite resonator antennas (FRA) and was studied in cylindrical, triangular and cuboid shapes with co-axial probe feeding mechanisms. The antenna characteristics were simulated using high frequency structure simulation (HFSS) software and a good agreement has been achieved between the measured and simulated results. The cuboid shaped FRA show maximum bandwidth of 990 MHz, while the cylindrical shaped FRA show a maximum gain of 3.48 dB, respectively.

Dielectric-Resonant Antenna Studies of Dysprosium Doped Barium Zirconate Ceramic

The structural properties of the Ba(1−x)Dy(2x/3)ZrO3 system were investigated by means of XRD, FT-Raman, and FTIR spectroscopy. XRD analysis exhibited that lattice parameter gradually decreased with increase of Dy content. FT-Raman and FTIR analyses showed that with increase of Dy content more ordered structure was formed in the composition. The surface morphology of sintered pellets was studied by the SEM. The microwave dielectric constant and quality factor were investigated by the method as proposed by Hakki–Coleman. The microwave dielectric constants of sintered pellets were found to be decreased from 38.40 to 21.13, and the value of τf changed from 384.71 to 62.71 ppm/°C. The Q × f values changed from 5731 to 5173 in the composition between x = 0.0 and 0.1. The dielectric resonator antenna (DRA) was investigated experimentally and numerically, using a monopole antenna through an infiniteground plane and Ansoft’s high-frequency structure simulator software, respectively. The required resonance frequency and bandwidth of DRA were investigated in the composition between 0 ≤ x ≤ 0.1.

Quasi-rapid thermal annealing studies on barium strontium titanate thin films deposited on fused silica substrates

Thin films of (Ba0.5,Sr0.5)TiO3 (BST5) were deposited at ambient temperature on fused silica substrates by RF magnetron sputtering technique. Nano-crystalline films were obtained upon quasi-rapid thermal annealing (Q-RTA) at temperatures ⩾800°C for 60s. The influence of Q-RTA temperature on the structural, morphological, optical and microwave dielectric properties of BST5 thin films have been investigated. The as-deposited and Q-RTA films annealed up to 700°C were amorphous in nature. On increasing the Q-RTA temperature to 800°C and above resulted in an amorphous–crystalline phase transition in the films. All the crystalline films show similar full width at half maxima (FWHM) and hence, similar crystallite size of about 12±1nm. The amorphous–crystalline transition was accompanied by a decrease in the optical band gap from 4.5 to 3.6 and increase in the refractive index from 1.9 to 2.2 as well as in the microwave dielectric constant from 40 to 262. The Root Mean Square roughness (RMSroughness) as measured from AFM show an increase from 0.6nm to 5.6nm with an increase in Q-RTA temperature from 400°C to 1000°C.

Electron–electron attraction caused by dispersion forces in metal–ammonia solutions

Using the theory of polarizable fluids, we investigated the dispersion attraction of electrons solvated in metal–ammonia solutions. We have found that the dispersion attraction results in a negative osmotic coefficient and a negative mean force potential between excess electrons and provides a phase separation at intermediate metal concentrations. Our analysis indicates that the dispersion attraction determines dielectric properties of solution. It is responsible for the experimentally observed shift of the maximum in the conductivity spectrum. Another effect of the dispersion attraction is a sharp enhancement of the microwave dielectric constant, leading to a nonmetal–metal phase transition.

Structural and microwave dielectric properties of ferroelectric poly(vinylidene difluoride)–polyaniline composite thin films

Nano composites of poly(vinylidene difluoride) (PVDF)–polyaniline (PANI) were prepared by spin coating method. Also, the influence of PANI doping (20, 30 and 40% by weight) on the microwave dielectric parameters was investigated. The structural aspects of samples were studied by atomic force microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. Dielectric properties of PVDF:PANI composites were characterized as a function of composition and frequency. The microwave dielectric constant increased smoothly with an increase in the concentration of PANI. Moreover, when the PANI content reaches 40wt.%, there is a transition from an insulator to semiconductor.

Microwave dielectric properties of bismuth zinc niobate thin films deposited on alumina by pulsed laser deposition

Abstract Bi2Zn2/3Nb4/3O7 thin films were prepared on Al2O3 substrates by pulsed laser deposition. The phase compositions and microstructures were characterized by X-ray diffraction and atomic force microscopy. The as-deposited films were all amorphous in nature. All films were crystallized after the post annealing at the temperature range of 700–900 °C for 30 min in air. The texture characteristics change with annealing temperature. A split post dielectric resonator method was used to measure the microwave dielectric performance at the resonant frequencies of 10, 15 and 19 GHz. For the films annealed at 900 °C, the preferential orientation is similar to the monoclinic BZN bulk. The microwave dielectric constants at 10, 15 and 19 GHz are 69.4, 58.9 and 47.9, respectively, which are closer to these of the monoclinic BZN bulk.

Solubility limits and microwave dielectric properties of Ca(ZrxTi1−x)O3 solid solution

The Ca(ZrxTi1−x)O3 ceramic was prepared by solid state reaction method. Structural characterizations were performed by means of XRD, FT-Raman and FTIR. The formation of monophasic compounds obtained in the composition x=0.0–0.2 and 0.9–1.0 were confirmed from XRD, FT-Rama and FTIR spectroscopy. However the compositions between x=0.3 and 0.8 showed presence of mixed phase or secondary phase. The microwave dielectric constant, Q×f and τf changed from 158 to 141, 4321 to 5945 and from 843.9 to 732.33ppm/°C respectively in the composition between x=0.0 and 0.2. The anomalous results of dielectric constant, Q×f and τf values in the composition between x=0.3 and 0.8 were observed. The microwave dielectric constant and τf were found to be decreased from 42 to 27 and 81.75 to −19.98ppm/°C in the composition between x=0.9 and 1.0 respectively. The Q×f values increased from 10728 to 16543 with the increase of x value from 0.9 to 1.0. The dielectric resonator antenna (DRA) was investigated experimentally and numerically using a monopole antenna through an infinite ground plane and Ansoft’s high frequency structure simulator software, respectively. The required resonance frequency and bandwidth of DRA were investigated in the composition between 0≤x≤1.0.

RELAXOR FERROELECTRIC MATERIALS FOR MICROWAVE TUNABLE APPLICATIONS

With strong dependences of dielectric constant on external applied electric fields, relaxor barium zirconium titanate ( BaZr x Ti 1-x O 3 or BZT) and barium stannate titanate ( BaSn x Ti 1-x O 3 or BTS), in both bulk ceramic and thin film forms, are increasingly being recognized as potential candidates of microwave tunable materials for device applications. This paper is aimed to review the recent progress in understanding the dielectric properties (such as tunability, dielectric loss and dielectric constant) of these relaxor materials. However, due to their relatively high dielectric constant and loss tangent, pure Ba(Zr,Ti)O3 and Ba(Sn,Ti)O3 do not fully satisfy the requirements of practical device applications. Therefore, various strategies have been developed to improve the dielectric properties of these two groups of relaxor materials. In this paper, we first discussed the dielectric tunability characteristics of pure Ba(Zr,Ti)O3 and Ba(Sn,Ti)O3 and then summarized the strategies that have been used, including (i) small amount acceptor or donor doping (such as rare-earth ions and transition metal ions) and (ii) forming composites with low loss and low dielectric constant microwave dielectric materials (such as MgO , MgTiO3 and so on). At the same time, the relationship between relaxor behavior and dielectric tunability was also discussed.

Studies of dielectric constant measurements at microwave frequency using mixing equations-The analyses on five rules

The microwave dielectric constants of ceramic dispersions in the polyethylene matrix are studied by five well-known mixture equations in this article. Three ceramic powders of fillers with various dielectric constants at 10 GHz are investigated. The experimental dielectric constant values of the mixtures are compared to the theoretical curves of the five mixing rules. The dielectric constants of pure ceramics are then estimated by these mixing laws from the dielectric constants of composites of various filler concentrations. The theoretical errors of estimations of rules are derived and analyzed. The most adequate mixture law(s) for measuring the dielectric constants of ceramic fillers will be recommended. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:2481–2485, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26357

Phase evolution and microwave dielectric properties of Bi 3SbO 7 ceramic

The Bi 3SbO 7 ceramic was prepared by the solid state reaction method and its phase evolution at different temperatures was studied. Low temperature phase α-Bi 3SbO 7 was formed at about 890 °C and it started to transform to high temperature phase β-Bi 3SbO 7 at about 960 °C. Microwave dielectric constants of α-Bi 3SbO 7 ceramic and β-Bi 3SbO 7 ceramic were 43.2 and 37.6, Qf value were 2080 and 5080 GHz, respectively. TCF of α-Bi 3SbO 7 ceramic was near zero and TCF of β-Bi 3SbO 7 ceramic was about −120 ppm/°C. The Bi 3SbO 7 ceramic is a promising candidate for low temperature co-fired ceramic (LTCC) technology due to its large dielectric constant, low dielectric loss at microwave region, low sintering temperature and simple composition.

Measurements of Microwave Dielectric Properties of (1-x)TiO2-xCaTiO3 and (1-x)TiO2-xSrTiO3 thin Films By The Cavity Perturbation Method

This research studies the measurements of dielectric properties of thin films at microwave frequencies by the cavity perturbation method. The measured frequency is in X-band (8.2–12.4 GHz). The titanium dioxide based (1-x)TiO2-xCaTiO3 and (1-x)TiO2-xSrTiO3 thin films deposited by the RF reactive magnetron sputtering method are adopted for the measurements. It was found that the dielectric constants of the films are increased as the compositions of CaTiO3 or SrTiO3 are increased. The microwave dielectric constants and loss tangents of films are measured. The accuracy of measurements is discussed.

Barium Strontium Zirconate Titanate (Ba,Sr)(Zr,Ti)O3 Thin Films for Tunable Microwave Applications

(Ba0.55Sr0.45)(Zr0.1Ti0.9)O3 (BSZT) thin films were deposited by pulsed laser deposition on LSAT(001) substrates. X-ray diffraction characterization reveals a good quality of crystallization and epitaxial nature of the films. The in-plane dielectric properties of the films were characterized over a wide frequency range from 50 MHz to 20 GHz by using ring resonator-structured samples. Based on the S-parameter measurements and electromagnetic simulation it was found that microwave dielectric constant of the BSZT thin film is ∼350. Large dielectric tunability was also observed in this material.

Modification of nanostructured mixed hexaferrite using a polyethylene glycol template

The present Letter deals with the investigation on the synthesis and properties of nanostructured mixed barium hexaferrites of M-type (BaFe12O19) and Y-type (Ba2Co2Fe12O22). The nanoparticles of mixed hexaferrite (Ba–M–Y) were obtained using co-precipitation technique with and without addition of polyethylene Glycol (PEG) during synthesis. The precipitate was calcined at 600°C for 6 h and characterised for structural, morphological, electrical and microwave properties. PEG acts as a template for the formation of hexaferrite nanoparticles. Significant reduction in crystallite size and grain size was obtained for Ba–M–Y synthesised in the presence of PEG template. Owing to PEG template the temperature-dependent resistivity showed negative temperature coefficient properties whereas without PEG the Ba–M–Y showed positive temperature coefficient properties. The microwave dielectric constant of Ba–M–Y–PEG (5.5 at 10.4 GHz) was higher than that of Ba–M–Y (4.1 at 10.4 GHz). Owing to PEG the microwave absorption increases to almost 50% from less than 1% in the10–10.7 GHz range.

Develop CPW‐FED monopole broadband implantable antennas on the high dielectric constant ceramic substrates

AbstractA compact broadband planar monopole antenna fed by coplanar waveguide is developed and screen‐printed on the high dielectric constant microwave dielectric ceramic substrate for the applications of implanted biotelemetry. Biocompatible ceramic materials are selected for substrate (MgTa1.5Nb0.5O6, εr = 28) and superstrate (Al2O3, εr = 9.8). Additionally, for protecting from the tissue erosion, the metal parts (the body of the implanted antenna) are screen printed on a MgTa1.5Nb0.5O6 ceramic substrate and covered by a Al2O3 ceramic superstrate. Because the inductive loading effect generated by the rectangular type meander and the use of high dielectric constant ceramics, both size miniaturization and bandwidth enhancement can be achieved. The measured S11 of the proposed antenna in lossy emulated tissue is −43 dB, and the bandwidth of this proposed antenna can be improved to 100 MHz (351–461 MHz), which it is wide enough for the applications of modern MICS band (402–405 MHz) and ISM band (433–435 MHz). © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 2136–2139, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25376

Microwave permittivity of leaf using an Ag thick-film microstrip resonator

The X-band microwave dielectric constant, dielectric loss and the conductivity of the leaves of four different plants were measured from even and odd mode resonance characteristics of an Ag thick-film microstrip straight resonator, due to the perturbation caused by leafy vegetation as an overlay. Using the changes in the frequency response, the moisture-dependent X-band microwave properties of the leaves of Ficus Bengalensis, Ficus Religiosa, Acalypha Wilkensiana, and Acalypha Hispidia have been calculated. The permittivity obtained depends on the position of the overlay and moisture content. A partial overlay method might be a low-cost alternative for dielectric characterisation of biomaterials since a very small size of leaf is needed.

Effect of lanthanide ion substitution on RF and microwave dielectric properties of BiNbO4 ceramics

Abstract Ceramic samples of BiNbO4 and (Bi0.95Ln0.05)NbO4 (Ln = Dy3+, Gd3+, Nd3+ or La3+) with 0.5 wt% V2O5 addition sintered at 960 °C were investigated. The dense (>92%) polycrystalline niobate samples revealed clean orthorhombic (Pnna) phase by powder XRD (except La3+ substitution, showing co-existing ∼31% triclinic phase (Pī)). The values of (C-band) microwave dielectric constant ( e ′ r ) and quality factor (Qu.f) of the niobates were found to increase with increasing ionic radius of the substituted Ln ion. The Qu.f values showed a strong dependence on the bond valance parameter, whereas, the e ′ r values replicated changes in dielectric polarizability. The e ′ r values (at ∼4–5 GHz) were 46.5 (pure BiNbO4), 40.8 (Ln = Dy3+), 41.7 (Ln = Gd3+), 43.4 (Ln = Nd3+) and 47.5 (Ln = La3+). Dielectric measurements made on the sintered samples at RF frequencies (1 kHz–1 MHz) showed 44.7 ≤ e ′ r ≤ 53.4 , and also revealed almost a monotonic rise of antiferroelectric–ferroelectric transition temperature from ∼360 to ∼370 °C with Ln (Dy3+ to La3+) substitution. The Arrhenius plot of d.c. conductivity for the Ln ion substitutions corroborated with the variations seen in Qu.f values.

Raman spectra and extended X-ray absorption fine structure characterization of La (2− x)/3 Na xTiO 3 and Nd (2− x)/3 Li xTiO 3 microwave ceramics

A-site deficient perovskite compounds, La (2− x)/3 Na x TiO 3 (0.02 ≤ x ≤ 0.5) and Nd (2− x)/3 Li x TiO 3 (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd (2− x)/3 Li x TiO 3 (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm −1) and A 1 (322 cm −1) modes of La (2− x)/3 Na x TiO 3 were found to decrease with x. However, the E (254 cm −1) and A 1 (338 cm −1) of Nd (2− x)/3 Li x TiO 3 were found to blueshift with x, which was caused by Li substitution. The redshift of the A 1 (471 cm −1) phonon of Nd (2− x)/3 Li x TiO 3 (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd (2− x)/3 Li x TiO 3.