Relative Tangent Research Articles

EM Performance Analysis of Radomes With Material Properties Errors

Modern radomes are commonly made of composites, whose material properties inevitably have errors due to the complicated manufacturing process, thus degrading the electromagnetic (EM) performance of radomes. In this letter, both systematic and random material properties errors are introduced in the EM analysis of radomes. A statistical method is proposed, which relates the random material properties errors to the EM performance of radomes. The tolerance of material properties, including relative permittivity and loss tangent, are determined from experiment. Several significative characteristics about the effect of material properties errors on EM performance are provided. Then, the compensation method through modifying the geometrical thickness is applied to improve the EM performance of radomes with material properties errors, which is proved to be effective.

Dielectric and microwave absorption properties of polymer derived SiCN ceramics annealed in N2 atmosphere

Abstract Porous SiCN ceramics were successfully fabricated by pyrolysis of a kind of polysilazane. The effects of annealing temperature on the microstructure evolution, direct-current electrical conductivity, dielectric properties, and microwave absorption properties of SiCN in the frequency range 8.2–12.4 GHz (X-band) were investigated. With the increase of annealing temperature, SiC, Si3N4 and free carbon nanodomains are gradually formed in the SiCN. Both the SiC and free carbon nanodomains lead to the increases of the complex relative permittivity and loss tangent of SiCN. With the increase of the annealing temperature, the average real permittivity, imaginary permittivity and loss tangent increase from 4.4, 0.2 and 0.05 to 13.8, 6.3 and 0.46, respectively. The minimum reflection coefficient and the frequency bandwidth below −10 dB for SiCN annealed at 1500 °C are −53 dB and 3.02 GHz, indicating good microwave absorption properties.

Dielectric properties of composite magnetic dielectrics made using wave technology

The results of studying dielectric properties of the composite magnetic dielectric by theoretical calculations and experiments are given. The calculated values of the relative permittivity and loss tangent agree well with the experimental data obtained using the capacitance method.

ZrTi2O6 filled PTFE composites for microwave substrate applications

A new kind of ZrTi2O6 filled polytetrafluoroethylene (PTFE) microwave composite substrates was fabricated through the hot-pressing process. The microwave dielectric properties of ZrTi2O6/PTFE composites were measured using stripline resonator method. The relative dielectric constant (er) and loss tangent (tanδ) of the composites increase with an increase of the volume fraction of ZrTi2O6 ceramic (0–46 vol%). The experimental dielectric constants of the composites match well with theoretically predicted values by Lichtenecker mixing rule. As the volume fraction of ZrTi2O6 ceramic increases, the thermal expansion coefficient and the temperature coefficient of dielectric constant decrease. The ZrTi2O6 filled PTFE composite exhibits a dielectric constant of 7.42 with a loss tangent of 0.0022 (10 GHz) at an optimum filler loading of 46 vol%.

Method to characterize dielectric properties of powdery substances

An open ended coaxial cavity method for dielectric characterization of powdery substance operating at 4.5 GHz in TEM mode is presented. Classical mixing rules and electromagnetic modeling were utilized with measured effective permittivities and Q factors to determine the relative permittivity and dielectric loss tangent of different powders with εr up to 30. The modeling enabled determination of the correction factor for the simplified equation for the relative permittivity of an open ended coaxial resonator and mixing rules having the best correlation with experiments. SiO2, Al2O3, LTCC CT 2000, ZrO2, and La2O3 powders were used in the experiments. Based on the measured properties and Bruggeman symmetric and Looyenga mixing rules, the determined dielectric characteristics of the powders exhibited good correlation with values in the literature. The presented characterization method enabled the determination of dielectric properties of powdery substances within the presented range, and therefore could be applied to various research fields and applications where dielectric properties of powders need to be known and controlled.

Polypropylene-Based Dual-Band CPW-Fed Monopole Antenna [Antenna Applications Corner

A flexible, wearable CPW-fed monopole antenna, based on aluminum-metallized polypropylene (PP), is presented. Its low cost, light weight, and moisture robustness make it proper for 2.45 GHz and 5.8 GHz dual-band RFID applications. A polypropylene sample was electromagnetically characterized in terms of relative dielectric permittivity and loss tangent in order to design the antenna. The performance of the polypropylene-based antenna in both simulation and measurement was compared to the performance of a commercial rigid-dielectric substrate-based antenna with the same geometry. The robustness to moisture of the manufactured polypropylene-based antenna was also tested.

Electrical, dielectric and microwave-absorption properties of polymer derived SiC ceramics in X band

Porous silicon carbide ceramics were successfully fabricated by pyrolysis of a polycarbosilane precursor. The direct-current electrical conductivity, dielectric and microwave absorption properties over the frequency range of 8.2–12.4GHz (X band) were investigated. Polymer derived silicon carbide is composed of SiC nano-crystals and free carbon nanodomains. The high-temperature direct-current conductivities of samples indicate the transformation of amorphous semiconductor into polycrystalline semiconductor with the increase of the annealing temperature. After annealed at 1500°C, the real permittivity, imaginary permittivity and the loss tangent increase from 3.6, 0.17 and 0.05 to 8.49, 10.01 and 1.18, respectively. The increases of the relative complex permittivity and loss tangent are ascribed to the appearance of SiC nano-crystals and free carbon nanodomains. The average reflectivity of the polymer derived SiC ceramics annealed at 1400°C is −9.9dB, which exhibits a promising prospect as microwave absorbing materials.

Comparative Evaluation on Product Properties and Energy Consumption of Single Microwave Dryer and Combination of Microwave and Hot Air Dryer for Durian Peel Particleboards

In this study, the idea is to use alternative “green” based on renewable resources as a raw material so as to be the adhesive into space in order to decrease formaldehyde emission in Thailand's particleboard manufacturing industries. It was found that dried durian peel could be used to replace formaldehyde-based resin for particleboard manufacture. In addition, drying the durian peel particleboard reduces biochemical and microbiological degradation.This paper presents the comparative evaluation on product properties and specific energy consumption of single microwave dryer and combination of microwave and hot air dryer for durian peel particleboards. Microwave in a continuous belt system, consists of twelve 800 watts 2.45GHz coupled into the cavity wall inside the system. A rectangular microwave cavity of dimensions 45cm x 90cm x 270cm combined with hot-air generator having the maximum operating temperature at 240°C was chosen. Particleboards from Monthong peel with dimension of 20cm x 20cm were manufactured. The physical (Density, Moisture Content and Thickness Swelling), mechanical property (Internal Bond, dielectric (Relative dielectric constant, Dielectric Constant and Loss Tangent) properties of end products were determined. In addition, Electron Structure using Scanning Electron Microscopy and thermal photograph of end products were also investigated.

Electrical, optical, and rheological properties of ozone-treated multiwalled carbon nanotubes–polystyrene nanocomposites

The functionalization of multiwalled carbon nanotubes was performed through the treatment of multiwalled carbon nanotubes with ozone using UV-ozone irradiation to improve their dispersion in polystyrene matrix. Multiwalled carbon nanotubes–polystyrene nanocomposites were prepared at different multiwalled carbon nanotubes weight ratios to investigate the effect of multiwalled carbon nanotubes loadings on the electrical, optical, and rheological properties of polystyrene matrix. The obtained results revealed that incorporation of functionalized multiwalled carbon nanotubes into polystyrene improved the electrical, optical, and rheological properties of neat polystyrene which indicated that multiwalled carbon nanotubes were well dispersed in the polymer matrix. Results obtained from DC and AC electrical measurements revealed that the percolation threshold was around 0.8 wt% multiwalled carbon nanotubes and incorporation of 3% multiwalled carbon nanotubes into polystyrene increased polystyrene electrical conductivity up to six orders of magnitude. Besides, increasing of multiwalled carbon nanotubes loadings increased the relative dielectric permittivity, dielectric loss, and loss tangent while decreased the total impedance of polystyrene matrix. Rheological results indicated that incorporation of multiwalled carbon nanotubes into polystyrene elevated the magnitudes of storage modulus and loss modulus up to two orders of magnitude with increasing of multiwalled carbon nanotubes loadings up to 3 wt%. Finally, the addition of multiwalled carbon nanotubes to polystyrene matrix enhanced the UV/visible absorption of polystyrene and decreased the optical energy gap with a total reduction ratio of 5.8% compared to neat polystyrene with increasing multiwalled carbon nanotubes loadings up to 2 wt%.

Dielectric and electric properties of plasticized PEO‐AgCF3SO3‐SiO2 nanocomposite polymer electrolyte system

AbstractThe effect of plasticizer poly(ethylene glycol) (PEG) on dielectric and electrical properties of an ionically conducting polymer nanocomposite electrolyte PEO: AgCF3SO3: SiO2: PEG has been investigated. The variation of relative dielectric constant and tangent loss peak with frequency have been discussed. The ionic and polymer segmental motions have been analyzed by electrical modulus and dielectric permittivity. The electrical modulus formalism is used to study the ionic relaxation process in these composites in terms of conductivity relaxation time. On addition of plasticizer, the modulus peak shifts toward higher frequency side suggesting the speeding up of the relaxation time. The frequency dependence of AC conductivity follows the universal power law. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

Butyl rubber–Ba0.7Sr0.3TiO3 composites for flexible microwave electronic applications

Butyl rubber–Ba0.7Sr0.3TiO3 composites (BR–BST) were prepared by sigma mixing followed by hot pressing. The stress–strain studies show the good flexibility of the composite. The dielectric properties of the composites were investigated at both radio and microwave frequencies. The relative permittivity (εr) and loss tangent (tanδ) improved with filler loading at both the frequencies. The relative permittivity and loss tangent of the BR–BST composites at a maximum filler loading of 0.39 volume fraction (vf) are 13.1 and 0.009 respectively at 5GHz measured by Split Post Dielectric Resonator (SPDR). The effective relative permittivity of the BR–BST composites is compared with theoretical models. The variation of εr with temperature was also investigated in the range 22–80°C at 1MHz. The microwave dielectric properties of the composites are also studied after repeated bending. The coefficient of thermal expansion (CTE) of the butyl rubber–BST composites decreased with the addition of the BST ceramic.

Dielectric properties of nanopowder dispersions in paraffin oil

This work contributes to the study of nanofluids, by investigating polarization phenomena induced by nanoparticle inclusions in paraffin oil, an insulating organic liquid. Fine metal oxide powders and nanopowders of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CuO, Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O and Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> were dispersed at concentrations up to 5% w/v in the liquid matrix, using ultrasonic treatment. The relative dielectric constant and loss tangent (tanδ) of both pure oil and the prepared nanofluids were recorded in the 20 Hz-1 MHz frequency range. Results depend both on grain size and on the specific compound. In the case of alumina nanoparticles, dielectric behavior is dominated by grain surface polarization phenomena induced by adsorbed water. This effect can be partially cancelled out by the addition of titania nanoparticles. Titanium and (to a lesser extent) ferric oxide increased the dielectric constant at middle and high frequencies. Cupric and cuprous oxides exhibit a distinct relaxation mechanism at the high end of the examined frequency range.

Dielectric and Piezoelectric Characteristics in Lead-Free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 Piezoelectric Ceramics Prepared by Two-Step Calcination Method

Lead-free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 piezoelectric ceramics samples prepared by the conventional solid-state reaction and two-step calcination method were achieved and compared. The effects of the amount of Li2O3 on the phase structure, microstructure, dielectric, and piezoelectric properties of Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples were systematically discussed and investigated. It was found that the Li2O3 content in Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples strongly affects the structure and electrical properties. For the two-step calcination method, the lead-free ceramics samples exhibited excellent dielectric and piezoelectric properties. The relative dielectric constant (εr) and loss tangent (tan δ) of the lead-free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 piezoelectric ceramics samples for x = 0.03 compositions prepared by the two-step calcination method were 1223 and 0.021, respectively. In addition, the electromechanical coupling factor (kp) and Curie temperature (TC) were 48.5% and 315 °C, respectively. These results show that Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples are promising candidates for lead-free piezoelectric materials.

Dielectric and Piezoelectric Characteristics in Lead-Free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3Piezoelectric Ceramics Prepared by Two-Step Calcination Method

Lead-free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 piezoelectric ceramics samples prepared by the conventional solid-state reaction and two-step calcination method were achieved and compared. The effects of the amount of Li2O3 on the phase structure, microstructure, dielectric, and piezoelectric properties of Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples were systematically discussed and investigated. It was found that the Li2O3 content in Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples strongly affects the structure and electrical properties. For the two-step calcination method, the lead-free ceramics samples exhibited excellent dielectric and piezoelectric properties. The relative dielectric constant (εr) and loss tangent (tan δ) of the lead-free Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 piezoelectric ceramics samples for x = 0.03 compositions prepared by the two-step calcination method were 1223 and 0.021, respectively. In addition, the electromechanical coupling factor (kp) and Curie temperature (TC) were 48.5% and 315 °C, respectively. These results show that Lix(K0.5Na0.5)1-x(Nb0.8Ta0.2)O3 ceramics samples are promising candidates for lead-free piezoelectric materials.

Nanomechanical mapping of the osteochondral interface with contact resonance force microscopy and nanoindentation

The bone–cartilage, or osteochondral, interface resists remarkably high shear stresses and rarely fails, yet its mechanical characteristics are largely unknown. A complete understanding of this hierarchical system requires mechanical-property information at the length scales of both the interface and the connecting tissues. Here, we combined nanoindentation and atomic force microscopy (AFM) methods to investigate the multiscale mechanical properties across the osteochondral region. The nanoindentation modulus M ranged from that of the subchondral bone (M=22.8±1.8GPa) to that of hyaline articular cartilage embedded in PMMA (M=5.7±1.0GPa) across a narrow transition region <5μm wide. Contact resonance force microscopy (CR-FM), which measures the frequency and quality factor of the AFM cantilever’s vibrational resonance in contact mode, was used to determine the relative storage modulus and loss tangent of the osteochondral interface. With better spatial resolution than nanoindentation, CR-FM measurements indicated an even narrower interface width of 2.3±1.2μm. Furthermore, CR-FM revealed a 24% increase in the viscoelastic loss tangent from the articular calcified cartilage into the PMMA-embedded hyaline articular cartilage. Quantitative backscattered electron imaging provided complementary measurement of mineral content. Our results provide insight into the multiscale functionality of the osteochondral interface that will advance understanding of disease states such as osteoarthritis and aid in the development of biomimetic interfaces.

Growth and dielectric properties of Ta2O5 single crystal by the floating zone method

AbstractLarge Ta2O5 single crystal with high‐dielectric permittivity was successfully grown by floating zone (FZ) method under air atmosphere. The grown crystal that has been obtained was typically about 8 mm in diameter and 90 mm in length. The crystal growth parameters were optimized. The crystal symmetry, characterized by means of X‐ray diffraction (XRD), was found to be tetragonal. The relative permittivity and loss tangent along growth and [001] direction were measured in the temperature range between ‐200 °C and 200 °C, which showed a strong dielectric anisotropy. At a frequency of 1 MHz and 20 °C, the dielectric permittivity along the growth direction and [001] direction are 81.17 and 25.04 respectively. The stabilization of high‐temperature phase can explain the dielectric enhancement.

Preparation of graphene nanoflakes/polymer composites and their performances for actuation and energy harvesting applications

Composites based on polyurethane (PU) or P(VDF-TrFE-CFE) terpolymer (T30) filled with various amounts of 60-nm thick graphene nanoflakes were prepared. The dielectric properties, including relative permittivity, loss tangent, and conductivity over a broad range of frequencies were presented and discussed according to the percolation theory. The percolation threshold was found to differ for the two systems, respectively, 7.2 and 3.0 vol. % for the PU and the T30 composites. Differential scanning calorimetry demonstrated that there was practically no interaction between the polymeric matrix and the fillers. The increase in permittivity could not be related to this very slight modification of the polymer but rather to the space charges induced by the graphene flakes. Moreover, measurements of the thickness strain under an applied electric field demonstrated a twofold increase of the actuation capability. The optimal value of the M33 electrostriction coefficient was for both systems obtained for a filler content somewhat lower than the percolation threshold. The PU-graphene composite exhibited better performances compared to its T30-graphene counterpart and this was attributed to the good ratio of relative permittivity to the Young modulus in addition to the specific morphology of the used polyurethane. The energy harvesting properties were investigated by monitoring the evolution of the current under a DC electric field and under AC mechanical strain. The T30-graphene composite was found to be the best material for energy harvesting as previously predicted based on its high permittivity.

Influence of Lithium and Potassium Doping on Structure and Electrical Characteristics of Lix(KyNa1-y)1-x(Nb0.9Ta0.06Sb0.04)O3 Lead-Free Piezoelectric Ceramics

The influence of lithium and potassium doping on the structural and electrical characteristics of Lix(KyNa1-y)1-x(Nb0.9Ta0.06Sb0.04)O3 lead-free piezoelectric ceramic prepared by the conventional solid-state reaction method was investigated and discussed. X-ray diffraction (XRD) and the scanning electron microscopy (SEM) were carried out to analyze the phases and microstructures of the ceramic specimens, respectively. An impedance analyzer (HP4294A) was used to measure the relative dielectric constant and loss tangent. The electromechanical coupling factor (kP) and the relative dielectric constant (εr) of Lix(KyNa1-y)1-x(Nb0.9Ta0.06Sb0.04)O3 piezoelectric ceramic for x = 0.06 and y = 0.485 were 1280 and 42.8%, respectively. Finally, the Curie temperature (Tc) of the piezoelectric ceramic was about 340 °C and the orthogonal-to-tetragonal phase transition temperature (To–t) was about 110 °C.

Dielectric response of fibrous polyethyleneterephtalate

The effect of the electric periodic field on the dielectric parameters (relative dielectric permeability and dielectric tangent of losses) of fibrous polyethyleneterephtalate (PET) different structures was studied. The analysis of dielectric relaxation spectra has been performed in the frequency range from 90kHz to 3MHz, while the sample was heating from 120 to 355K. In this range of measurements, β relaxation is observed and the activation energy of molecular motion is established. Through a comparison of obtained results, a relationship is noted between dielectric parameters and structural properties of a sample. It is observed that samples whose yarn is obtained from short fibre have lower value of dielectric parameters than samples with monofilament and multifilament yarn. Samples with higher values of volume fraction of fibres show higher values of dielectric parameters. In room conditions a comparison between dielectric parameters of the samples and a sample with incorporated electrically conductive threads has been performed. The dielectric response of the tested fibrous PET is comparable with the dielectric response of other PET – based structures.

Dielectric and Magnetic Properties of Sintered Cobalt Ferrite Derived from Nanocrystalline Powders

A kind of Cobalt ferrite ceramics were successfully prepared by using nanocrystalline powders synthesized by citrate gel method. The relative dielectric constant and loss tangent of the ceramic as a function of frequency (100 Hz - 1 MHz) was investigated at room temperature. Both of them decrease with increase in frequency showing dispersion. Hysteresis loop magnetization was measured and the ceramic show good magnetic characteristics at room temperature.