High Loss Tangent Research Articles

High temperature dielectric constant and loss tangent measurements [advertisement

High temperature dielectric constant and loss tangent measurements [advertisement

Investigation of low loss Z-type hexaferrites for antenna applications

Z-type hexaferrites in series (Ba0.5Sr0.5)3Co2Fe24O41 + xWO3 (where x = 0.0, 0.1, 0.2, 0.3, and 0.4 wt. %) were prepared by a conventional ceramic technique. The addition of WO3 has been used to enhance sintering density and magneto-dielectric properties of low loss Co2Z ferrites. A second phase of BaWO4 can be found in the XRD patterns. The replacements of hexagonal phase by high valence W6+ ions improved sintering and accelerated density of the ferrites, which resulted in the increase of real permeability. Due to the formation of Fe2+, excessive WO3 resulted in undesired high permittivity and dielectric loss tangent. Comparatively, a ferrite sample with 0.2 wt. % WO3 gave the best performances in terms of density, microstructure, magneto-dielectric property, and loss tangent. Since loss tangent was kept low with the frequency ranging from 10 to 300 MHz, such magneto-dielectric material could be used in this frequency range for antenna applications.

High temperature dielectric constant and loss tangent measurements [advertisement

High temperature dielectric constant and loss tangent measurements [advertisement

Powder preparation in aerosol deposition for Al2O3-polyimide composite thick films

The influence of the pre-treatment of starting powders for Al2O3-polyimide composite thick films fabricated by an aerosol deposition (AD) process was investigated. The microstructures and the dielectric properties of the Al2O3-polyimide composite thick films in relation to their particle size of polyimide in the starting powder were characterized. As a result, polyimide starting powders larger than 1 μm in size were remained in the films after the deposition. Also, the Al2O3-polyimide composite thick films showed high loss tangents with large frequency dependences when the polyimide starting powders larger than 1 μm in size were used, due to the porous microstructure with cracks and rough surfaces. In comparison, the Al2O3-polyimide composite thick films had dense nanostructures, and the number of pores and cracks in the films were also noticeably decreased by using polyimide powders of less than 1 μm. Moreover, the frequency dependence of loss tangent was remarkably decreased, and the loss tangent was totally decreased below 0.01.

High loading of nanostructured ceramics in polymer composite thick films by aerosol deposition

Low temperature fabrication of Al2O3-polyimide composite substrates was carried out by an aerosol deposition process using a mixture of Al2O3 and polyimide starting powders. The microstructures and dielectric properties of the composite thick films in relation to their Al2O3 contents were characterized by X-ray diffraction analysis. As a result, the crystallite size of α-Al2O3 calculated from Scherrer's formula was increased from 26 to 52 nm as the polyimide ratio in the starting powders increased from 4 to 12 vol.% due to the crushing of the Al2O3 powder being reduced by the shock-absorbing effect of the polyimide powder. The Al2O3-polyimide composite thick films showed a high loss tangent with a large frequency dependence when a mixed powder of 12 vol.% polyimide was used due to the nonuniform microstructure with a rough surface. The Al2O3-polyimide composite thick films showed uniform composite structures with a low loss tangent of less than 0.01 at 1 MHz and a high Al2O3 content of more than 75 vol.% when a mixed powder of 8 vol.% polyimide was used. Moreover, the Al2O3-polyimide composite thick films had extremely high Al2O3 contents of 95 vol.% and showed a dense microstructure close to that of the Al2O3 thick films when a mixed powder of 4 vol.% polyimide was used.

Development of Three Phase Composites Using Polyetherimide-Carbon Nanotubes-(Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 Ceramic Powder

Organic acids were covalently bonded onto the π-conjugated skeleton of surface-modified multi-wall carbon nanotubes (MWNTs) by treating them with carboxylic acid. Analysis of the Raman spectra of these MWNTs demonstrated that the acid treatment process increased the number of defects in the graphitic layers. Polyetherimide (PEI) was mixed with various amounts of well-dispersed MWNTs to form MWNTs/PEI composites. The dielectric properties of these composites were developed under different frequencies and the Lichtenecker logarithmic mixing rule was used to find the effective dielectric constant of the MWNTs. Because the MWNTs/PEI composites had high loss tangents, (Ba0.8Sr0.2)(Ti0.9Zr0.1)O3 (BSTZ) ceramic powder was mixed with PEI and MWNTs to form BSTZ/MWNTs/PEI composites. The Lichtenecker logarithmic mixing rule was also used to predict the dielectric constants of these composites. The addition of BSTZ ceramic powder greatly improved the characteristics of the MWNTs/PEI composites, as the glass transition temperatures and dielectric constants increased.

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.

Ferroelectric and Dielectric Properties of BaTiO3/Ba0.30Sr0.70TiO3 Superlattices

BaTiO3/Ba0.30Sr0.70TiO3 (BT/BST3070) artificial superlattice (SL) was fabricated by pulsed laser deposition on La0.67Sr0.33MnO3 (LSMO) coated (001) MgO substrates. Satellite reflections in X-ray diffraction are used to calculate the periodicity of SL structure indicates a period ∼14 nm. Cross polarized Raman spectra show upward shift of the E(1TO) soft mode, this is markedly changed with respect to its parent BT layer thin film. The BT/BST3070 SL illustrates high dielectric constant (1100-1300) and low loss tangent (<0.1) below to 104 Hz. Polarization and dielectric constant show strong switching behavior under applied external electric field with well saturated hysteresis loop and high dielectric tunability.

Dielectric properties and electrical response of grain boundary of Na 1/2La 1/2Cu 3Ti 4O 12 ceramics

The dielectric properties and electrical response of grain boundaries of Na 1/2La 1/2Cu 3Ti 4O 12 ceramics were investigated as a function of temperature. High dielectric permittivity (6.1–8.7 × 10 3) and low loss tangent (0.032–0.038 at 10 kHz) were observed in Na 1/2La 1/2Cu 3Ti 4O 12 ceramics. Through analyses using complex impedance and electric modulus, it was found that the dielectric properties of Na 1/2La 1/2Cu 3Ti 4O 12 ceramics are closely related to the electrical response of grain boundaries. The investigation of non-Ohmic characteristics at various temperatures suggests that the potential barrier at the grain boundaries of Na 1/2La 1/2Cu 3Ti 4O 12 ceramics is due to the Schottky effect. The giant low frequency dielectric response in Na 1/2La 1/2Cu 3Ti 4O 12 ceramics is attributed to Maxwell–Wagner polarization at the grain boundaries.

Microwave and infrared dielectric response in BaTiO3 based relaxor ferroelectrics

AbstractMicrowave (MW), infrared (IR) dielectric response, and Raman spectra of BaZryTi1‐yO3 (BZT) (y = 0.25–0.40) and BaTi1‐zSnzO3 (BTS) (z = 0.15–0.30) ceramics were studied systematically. As the substitution levels increased, the evolution from normal ferroelectric to canonical relaxor was observed. BaTiO3 based relaxor ferroelectrics have high tunability, MW permittivity, and loss tangent. IR analysis confirmed that the relaxor behavior in BZT and BTS was caused by the cationic disorder with BO6 octahedron and the origin of larger diffuseness in BTS dielectric peak was attributed to a distinct split of BO6 bending. Compared with BST, the soft mode in BaTiO3 based relaxor ferroelectrics hardened slightly and became harmonic with increasing substitution levels, resulting in high tunability for BaTiO3 based relaxors. The variation in tunability of BZT with composition is larger than that of BTS, due to the larger variation in softest mode with composition for BZT. Raman scattering showed that, in comparison with cubic‐BST, the bands at ∼730 cm−1 were observed in cubic‐BZT and ‐BTS, owing to the positional disorder at B‐site cation. However, an extra band at ∼770 cm−1 in BZT appeared and red‐shifted, whose intensity increased with the substitution levels increasing. It is of particular interest that the upward shift of A1(TO2) mode of the samples with higher substitution levels indicated a tighter bonding between the cations and the anions, which led to a smaller permittivity of the samples with higher substitution levels.

Influence of the Precursor Solution Molarity on the Dielectric Response of Chemical Solution Deposited Strontium Titanate Thin Films on Si

SrTiO3 films were deposited using metallo-organic solution deposition with different precursor solution molarities. The films were characterized via X-Ray diffraction and field emission scanning electron microscopy. The dielectric constant, loss tangent, tunability, and leakage current were measured as a function of electric field, frequency, and temperature. The film deposited with a lower precursor solution molarity solution had a larger permittivity and tunability, but it also had higher loss tangent and leakage current density. The internal stresses in the films are almost completely relaxed, and this is the main reason for the large, bulk-like dielectric constant in these films.

Polymer-Carbon Nanotube Sheets for Conformal Load Bearing Antennas

We propose a conductive carbon nanotube (CNT) sheet to realize conformal antennas on polymer substrates. Polymer-ceramic composites (rubber-like structures) have good RF (high dielectric constant and low loss tangent) and desirable mechanical properties (conformal, flexible and lightweight). However, there is a challenge in printing metallization circuits on polymer substrates due to their hydrophobic nature. Also, they are associated with low metal-polymer adhesion, causing peeling under stain or tensile stresses. To address these issues, in this paper, we consider the approach of embedding high density vertically-aligned carbon nanotubes within the polymer composite to achieve a CNT sheet having high structural compatibility. We present the fabrication process to achieve high conductivity CNT sheets and construct a sample polymer-CNT patch antenna, yielding a 5.6 dB gain. This is only 0.8 dB lower than that of an ideal patch made of perfect electric conductor (PEC). Strain and tensile tests are also carried out to evaluate electrical performance of the polymer-CNT sheet as it is bent and stretched. Our measurements show that the proposed conductive polymer-CNT sheet is highly flexible and preserves good conductivity under small bending and stretching. The CNT sheet retains acceptable performances even after 100° bending and 13% stretching. The proposed polymer-CNT sheets are well suited for load bearing antenna applications.

Magneto-thermal and dielectric properties of biferroic YCrO 3 prepared by combustion synthesis

Microstructural, magnetothermal and dielectric properties of YCrO 3 powders prepared by combustion and solid state methods have been studied by a combination of XRD, specific heat, magnetization and permittivity measurements. The TEM and XRD characterization confirm that the combustion powders are amorphous plate-like agglomerates of nano-sized crystalline particles. A more uniform grain size along with an increase of the relative density is observed by SEM in the sintered samples prepared by combustion route with respect to those produced by solid state reaction. Similar to the material obtained through solid state synthesis, the material prepared by the combustion method also shows spin canted antiferromagnetic ordering of Cr +3 ( S=3/2) at ∼140 K, which is shown by magnetization as well as λ-type anomaly in the total specific heat. Furthermore, the magnetic contribution to the total specific heat reveals spin fluctuations above T N and a spin reorientation transition at about 60 K. Both YCrO 3 compounds show a diffuse phase transition at about 450 K, typical of a relaxor ferroelectric, which is characterized by a broad peak in the real part of the dielectric permittivity as a function of temperature, with the peak decreasing in magnitude and shifting to higher temperature as the frequency increases. The relaxor dipoles are due to the local non-centrosymmetric structure. Furthermore, the high loss tangent in a broad range of temperature as well as conductivity analysis indicates a hopping mechanism for the electronic conductivity as we believe it is a consequence of the outer d 3-shell, which have detrimental effects on the polarization and the pooling process in the YCrO 3 bulk material. The more uniform particle size and higher density material synthesized through the combustion process leads to an improvement in the dielectric Properties.

Electrical and magnetic properties of NiCuZn–CaCu 3Ti 4O 12 composites doped with Bi 2O 3

Bi 2O 3 was used to promote grain growth and to improve magnetic and dielectric properties of NiCuZn ferrite–CaCu 3Ti 4O 12 composites during sintering. For a sintering temperature lower than 950 °C, the static permeability of the composites increases with the Bi 2O 3 content. Comparing with the composites without Bi 2O 3, the composite with Bi 2O 3 has a higher real permittivity and a lower loss tangent. With further increasing sintering temperature, it was found that the sample with 1 wt% Bi 2O 3 sintered at 1050 °C has the maximum static permeability, however, this was accompanied by an extremely high dielectric loss tangent. These results were analyzed in terms of the microstructures of the composites by scanning electron microscopy.

Intelligent Viscoelastic Polyurethane Intrinsic Nanocomposites

Polyurethanes are multiphase systems comprising intrinsically variant nanodomains. The material properties can be tailored by adjusting the relative proportions and organizing the structure of the hard and soft segments akin to the spring-dashpot system in an automobile. This article describes how an intelligent polyurethane (PU) system is created to offer smart response to mechanical and vibration stimuli. In this work, unidirectional, dynamic mechanical thermal analysis (DMTA), acoustic, and impact testing results are qualified with the unique viscoelastic character that determines the rate-temperature response of the nanocomposite. Attenuated total reflection– infrared spectroscopy (ATR-IR) and DMTA offer a logical explanation of the observed viscoelastic behavior in terms of the nanodomains. Enhanced nanophase segregation between the polymer building blocks (hard and soft segments) is the primary mechanism that leads to a higher loss tangent peak in DMTA at a lower glass transition temperature (Tg) for greater energy dissipation in the polymer matrix. Acoustic and impact attenuation are correlated with the mechanical modulus and loss tangent of the polymer. Finally, autodyne simulation reveals the unique shock absorbent behavior of the material layer when retrofitted to concrete structure. Typically, shock overpressure spikes of the order of 9.97 × 104 MPa experienced by the unprotected surface are entirely evened out at a lower overpressure threshold.

Next Generation High Dk, Low Df Organic Laminate for RF Modules and High Frequency Applications

In this paper, we present a novel high density high performance ultra-thin organic laminate, X-R-1, with low cost standard PCB fabrication processes for RF and high frequency applications. The X-R-1 substrate, developed at Zeon Corporation is a new generation halogen-free high dielectric constant (Dk) and low loss tangent (Df) dielectric laminate material. Its dielectric constant is 6.5–6.7 in the range of 1–20GHz, similar to typical LTCC substrates but larger than most organic materials such as LCP, PTFE and Epoxy based materials. Its dielectric loss tangent is 0.003, similar to that of LTCC, LCP and PTFE but much lower than epoxy based materials. The thicknesses of the core used in this study are 50um. The clad copper on both sides is a 12um thick profile-free copper foil which provides extremely smooth surface. Microminiaturization of RF devices can be achieved by the combination of high Dk and ultra-thin substrate. The combination of low Df and smooth surface leads to RF and high frequency signals having minimum propagation loss. The material is suitable for mechanical and laser through hole drilling and fully compatible with the low cost standard PCB facilities and processes. Because of the smooth surface, 25um very fine copper lines and spaces were achieved by wet etching process. Copper filled through holes with 40um diameter drilled by CO2 laser have been demonstrated. Panel size of 6″×6″ test vehicles with RF filters and transmission lines was fabricated and measured. Test data on the filters at 2.4GHz and 5GHz has been presented in this paper. This high Dk and low Df laminate with standard PCB processes provides a low cost organic platform for RF and high frequency circuit applications.

Unprecedented vibration damping with high values of loss modulus and loss tangent, exhibited by cement–matrix graphite network composite

This paper reports a material with unprecedented vibration damping ability, as shown by high values of both the loss tangent (vibration amplitude decay rate) and the loss modulus (energy dissipation ability, equal to the product of the storage modulus and the loss tangent) under flexure at 0.2Hz at room temperature. The loss modulus (7.5GPa) exceeds that of any previously reported material, including the best metal-based material, which suffers from a low loss tangent. The loss tangent (0.81) is comparable to or exceeds that of any previously reported material, including rubber, which suffers from a low loss modulus. This material is a cement–matrix graphite network composite containing 8vol.% graphite and made by compressing a mixture of cement particles and exfoliated graphite, which binds by mechanical interlocking, followed by curing in water. The graphite network structure is supported by microscopy and the low electrical resistivity of the composite (0.04Ωcm perpendicular to the compression direction and 0.5Ωcm in the compression direction). The composite is much more conductive than the most conductive cement–matrix composite containing a conductive admixture. The high loss tangent is attributed to the graphite network, while the high storage modulus is attributed to the cement matrix.

Dielectric and leakage current properties of Li doped (Ba,Sr)TiO 3 thick film interdigital capacitors on the alumina substrates

Li doped (Ba,Sr)TiO 3 thick films were fabricated by employing the screen printing method on the alumina (Al 2O 3) substrates. Interdigital capacitor patterns with seven fingers of 200 μm gap, 250 μm length were designed and screen printed on the alumina substrates. Ba 0.5Sr 0.5TiO 3 materials, paraelectric state at the room temperature, have been chosen for the microwave devices due to high dielectric permittivity and low loss tangent, however, the sintering temperature of (Ba,Sr)TiO 3 is over 1350 °C. In order to lower the sintering temperature, Li (3 wt%) was added to the (Ba,Sr)TiO 3 materials. Li doped (Ba,Sr)TiO 3 thick films screen printed on the alumina (Al 2O 3) substrates were sintered at 900 °C for 1.5 h. The structural feature was analyzed with X-ray diffraction method. Temperature dependent dielectric properties were characterized from 303 to 403 K at 1 MHz. Within the ±100 V of bias voltage, current–voltage characteristics of Li doped (Ba,Sr)TiO 3 films were investigated from 303 to 403 K. Through the current–voltage characteristics, the resistivity of Li doped (Ba,Sr)TiO 3 films were calculated. In this paper, the significant negative temperature coefficient of resistance (NTCR) of Li doped (Ba,Sr)TiO 3 films will be presented through the activation energy fitting. Measured activation energy is approximately 0.366 eV.

Effect of bottom electrodes on dielectric properties of high frequency Ba 0.5Sr 0.5TiO 3 parallel plate varactor

Three types of Ba 0.5Sr 0.5TiO 3 (BST) thin film parallel plate varactor with different bottom electrodes were fabricated. The bottom electrodes of three types of varactor were perovskite conducting oxide La 0.7Sr 0.3MnO 3 (LSMO), Pt and Au, respectively. Dielectric properties of the BST thin films were characterized in the frequency range from 10 MHz to 15 GHz. The microstructure of the BST thin films was investigated by X-ray diffraction and scanning electron microscope. The microstructural analysis shows that the BST thin films grown on LSMO and Pt bottom electrodes are polycrystalline textured with columnar grains. Dielectric measurement indicates that the BST thin film grown on LSMO bottom electrode has a maximum dielectric constant and a little higher loss tangent.

Electromechanical Properties of BaTiO3 Ceramics Prepared by Spark Plasma Sintering and Other Methods

BaTiO3 (BT) ceramics with various grain sizes are prepared by spark plasma sintering (SPS), two-step sintering, and conventional sintering. The field-induced displacement and piezoelectric constant measured by a resonant–antiresonant frequency method are evaluated. The BT ceramics prepared by SPS are characterized by high permittivity, high loss tangent, linear-field-induced strain, and low Qm, and exhibit a relatively higher field-induced strain and a higher d31 value than the fine-grained BT ceramics fabricated by other methods. These characteristics of the SPS-BT ceramics are probably due to the high internal stress of the samples.