Frequency Dependence Of Loss Tangent Research Articles

Understanding the dielectric and electrical transport behaviors of plasma polymerized diethanolamine thin films under alternating electric field

A capacitively coupled parallel plate glow discharge reactor has been utilized to develop plasma polymerized diethanolamine (PPDEOA) thin films to look into the alternating current (AC) features of PPDEOA thin films. It is observed that the dielectric constant, ɛ′ in PPDEOA thin films enhances by declining the frequency and that increases with increasing temperature. The AC electrical conductivity, σac is frequency dependent. The frequency exponent, s values are found to be 0.32 to 1.0 and 1.0 to 1.8 in the lower (102–103 Hz) and higher (>103 Hz) frequencies, respectively. These suggest the presence of hopping conduction in the lower frequency region and other mechanisms in the higher frequency region. The activation energies are derived to be 0.03 to 0.28 eV illustrating the less effect of temperature on them. The real part, M´ and imaginary part, M ̋ of electric modulus vary with frequency. The frequency dependent loss tangent, tanδ is obtained. The ɛ′, σac , and tanδ deviate by the virtue of film thicknesses.

Grain Growth Dominance on Complex Permittivity of MgTiO3

Uncovering the relationship between microstructural and dielectric properties is beneficial for designing new dielectric materials for technological purpose. Thus, this work attempts to understand the evolving relationship between complex permittivity and microstructural in magnesium titanate (MgTiO3) at 40 Hz to 1 MHz. Magnesium oxide and titanium dioxide were mechanically crushed using a high energy ball mill for 12 hours via the mechanical alloying method. Pellets were formed followed by a sintering process from 500 oC up to 1400 oC. The phase formations of the sintered samples showed a development in their crystalline structure and their phase was confirmed by X-ray diffraction patterns, yielding a completed phase of MgTiO3 formed at 800 oC. Observation by scanning electron microscopy revealed an improvement in grain growth as the sintering temperatures are elevated. The density proportionally increased with the sintering temperature. From the complex permittivity studies, the dielectric constant, ԑr’ showed a decreasing trend with increasing frequency and attained constant limitation value of ԑr’ at higher frequency at room temperature. Below 104 Hz, the relaxation belonged to the interfacial polarization while beyond 104 Hz, it is dominant by dipolar polarization. The frequency dependence of loss tangent, tan δ decreased with value almost zero at higher frequency for all sintering temperatures. A significant increasing trend was observed which correlated the polarization-crystallinity behaviors at 1 MHz from 500 oC up to 1400 oC. The improvement in microstructure properties with respect to the sintering temperature was observed which give rise to the dielectric permittivity at infinite frequency, ε∞’. It revealed the dependency of dipolar polarization on the grain sizes and the crystallinity of the sample.

Dynamic mechanical analysis of cement mortar prepared with recycled cathode ray tube (CRT) glass as fine aggregate

Using recycled cathode ray tube (CRT) funnel glass as a substitute for sand contributes to both reducing natural aggregate consumption and the disposal of CRT funnel glass. Currently, most studies have focused on the mechanical and durability properties of mortar or concrete containing CRT glass as fine aggregate. However, the study of the dynamic loadings (e.g., earthquake load, wind load and impact load) of major concrete structures containing CRT glass is still limited. In this paper, a dynamic thermo-mechanical analysis test with various frequencies (0.1 Hz–2.0 Hz) and temperatures (−30 °C−30 °C) is undertaken on mortars with different CRT replacement ratios (0, 20%, 40%, 60%, 80%, and 100%). The test results show that the storage modulus (stiffness) of mortar with incorporated CRT glass is lower than that of control mortar in most cases, but the decreasing trend is not proportional to the CRT replacement ratio. However, the presence of CRT glass in the mix has a negligible impact on the frequency dependence of the storage modulus of mortar. The storage modulus of each replacement ratio is nearly constant for all excitation frequencies. The frequency dependence of loss tangent (damping behavior) is significantly improved with CRT glass under 0 °C. This indicates that a frequency dependent damping model is needed when dynamic analysis is conducted on concrete structures with incorporated CRT glass in cold weather.

Dielectric properties, impedance analysis and modulus behavior of CaTiO3 ceramic prepared by solid state reaction

Calcium titanate (CaTiO3) with the general formula for perovskites, ABO3, is of technological importance, particularly with regard to dielectric properties. In this work, CaTiO3 ceramic material was prepared by the conventional solid state reaction method. The dielectric properties, impedance characteristics and modulus behavior of the CaTiO3 ceramic material sintered at 1240°C were investigated in the frequency range of 10−2–106Hz and temperature range of 100–250°C. The XRD analysis of the sintered CaTiO3 shows that it is an orthorhombic structure with lattice parameters a=5.4398Å, b=7.6417Å, and c=5.3830Å. The FESEM micrograph shows a significant difference in grain size distribution ranging from 0.26 to 2.32μm. The AC conductivity, σAC, is found to increase with increasing temperature within the frequency range of 10−2–106Hz confirming the hopping of electrons to be the conduction mechanism. Due to the decreasing values of the frequency exponent s with increasing temperature, the results of the σAC are discussed using the correlated barrier height (CBH) model. For dielectric studies, the dielectric constant, ε′ is found to decrease with increasing frequency. In the whole temperature range of 100–250°C, high and low frequency plateau are observed. Each converges at high frequency (>105Hz) for all the temperatures. The frequency dependence of loss tangent, tanδ, decreases with rise in temperature, with the loss tangent peak shifting to higher frequency. Due to its dielectric characteristics, it is a suitable candidate for developing a variety of capacitors. For the master modulus plot, the shapes remain unchanged in the temperature range considered. The Cole–Cole plots reveal that two primary relaxation processes exist in the sample for each temperature. The Nyquist plots reveal that at temperatures below 150°C, a linear response in the imaginary part of the impedance, Z′′, is noticed. At and above 175°C, the linear response gradually changes to a semicircle arc. The modulus behavior indicates the presence of correlation between the motions of mobile charge carriers. The plots of Arrhenius diagram of relaxation times of loss tangent, τtanδ, and imaginary part of dielectric modulus, τM′′, obey the Arrhenius law, where the activation energies calculated from the slopes are 2.09 and 2.38eV respectively.

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.

DYNAMIC RHEOLOGICAL ANALYSIS AS A SENSITIVE METHOD FOR ANALYZING STRUCTURAL CHANGES DURING THERMO-OXIDATION OF POLYOLEFIN ELASTOMERS

Dynamic rheological analysis and Fourier transform infrared spectroscopy (FTIR) were used to study the effects of thermo-oxidation on the viscoelasticity and microstructure of polyolefin elastomers (POE). It was found that dynamic storage modulus (G') and dynamic loss modulus (G") at low frequency region can sensitively reflect the change of microstructure of POE, which can be seen through the "second plateau" appeared in G' versus ω plots at low frequencies. The frequency dependence of loss tangent (tanδ) measured under different frequency sweeps showed that the thermo-oxidative behaviors of POE relied on the holding time. The dynamic rheology test was found to be a sensitive technique for analyzing the structural changes during thermo-oxidation of polymers.

High-Frequency Modeling of Frequency-Dependent Dielectric and Conductor Losses in Transmission Lines

This paper details the implementation of three theoretical techniques to calculate dielectric and conductive losses in transmission lines at high frequencies. Those techniques are the Kramers-Kronig relationship to account for the frequency-dependent loss tangent, inclusion of surface roughness in estimating conductor losses, and a method for calculating moisture effects. When these mechanisms are incorporated into a contemporary stripline model, the high-frequency results are in much closer agreement with measured data than when they are not included

Frequency dependence of loss tangent of thermally annealed undoped lead iodide crystals in the dark

The effect of isothermal annealing ( T an ⩽ 120 ° C ) on the frequency dependence of the loss tangent, tan δ, of undoped lead iodide (PbI 2) crystals in the dark has been investigated in the range 0.1–15 kHz at different ambient temperatures ( T = 15 – 120 ° C ) without and with DC biasing ( V DC ⩽ 2 V ). Thermal annealing of as-grown PbI 2 crystals modified both the magnitude and frequency dependence of their tan δ. The tan δ–ƒ data ( T = 17 ° C ) of unbiased as-grown crystals were found to fit a tan δ∝ƒ − m dependence, with m∼0.94 in the range 100 Hz <ƒ<10 kHz. After annealing these crystals at T an = 70 ° C for 1 h, the tan δ∝ƒ − m relation was obeyed for unbiased samples at any T over most of the frequency range studied, with the exponent m being reduced to around 0.55; a behavior that was also found for isothermally annealed PbI 2 crystals when were DC biased, but at high ambient temperatures. The tan δ− T data (ƒ=1 kHz) of the unbiased prolonged annealed ( T an = 120 ° C ) PbI 2 crystals exhibited two different thermally activated regimes, with activation energies E a∼0.23 and 0.087 eV in the ranges 75–120 °C and 15–75 °C, respectively, which were related to trapping cationic Pb +2-vacancies/hole-impurity levels in the crystal band gap. An interpolytypic phase transformation of the 2H-PbI 2 upon isothermal annealing may not, however, be entirely excluded.

Dc field and temperature dependent acoustic resonances in parallel-plate capacitors based on SrTiO3 and Ba0.25Sr0.75TiO3 films: Experiment and modeling

Experimentally observed resonant absorption peaks in frequency dependent loss tangent in thin film parallel-plate SrTiO3 and Ba0.25Sr0.75TiO3 capacitors are explained by electrostriction and piezoelectric effects. A simple theory (linear approximation) is proposed to model the electric field and temperature dependences of the acoustic resonant frequencies, and the intensities of the microwave into acoustic transformations. The electric field dependence of the acoustic resonant frequencies may be used to develop tunable thin film bulk acoustic wave resonators (TFBARs) operating at frequencies up to 10GHz and above. The expected tuneability of the TFBARs is more than 5%.

Investigation of the field dependence of magnetic fluids exhibiting aggregation

Measurement of the frequency dependent, complex susceptibility, χ( ω)= χ′( ω)− iχ″( ω), over the frequency range 100 Hz to 1 MHz, of a colloidal suspension of cobalt ferrite particles, by means of the toroidal technique, indicates the presence of aggregation in the samples: the aggregation being identified by the appearance of a low-frequency loss-peak in the χ″( ω) component of the susceptibility. By means of the application of a polarising field, H (A/m), the field dependence of the complex susceptibility of the aggregates, χ( ω, H), the frequency dependent loss tangent, tan δ and mean power loss, T (J/m 3), are investigated for polarising fields over the approximate range 0–13.6 kA/m. It is shown that the plots of both χ( ω), H and tan δ may be fitted in terms of the Cole–Cole parameter, α, and it is demonstrated how the fits can be used to determine data outside the measurement frequency range. A novel method for determining the tan δ data is also presented. It is also shown how, with increase in polarising field, the magnetic losses of the fluid are reduced.

Effects of end boundary conditions and specimen geometry on the viscoelastic properties of cancellous bone measured by dynamic mechanical analysis.

The viscoelastic properties of cancellous bone can be measured nondestructively in compression testing using a dynamic mechanical analyzer. In this study, we examined the effects of end boundary conditions and specimen geometry on the viscoelastic properties of cancellous bone measured by dynamic mechanical analysis. During dynamic compression testing, the cancellous bone specimens may be mechanically fixed (e.g., glued) to the loading platens or they may be free to expand across the platen surface. When specimens of cancellous bone were tested between platens with gluing, the dependence of loss tangent on frequency was not consistent with previously observed strain-rate-dependent mechanical behavior of cancellous bone. When long specimens of cancellous bone (length = 10 mm, diameter = 8 mm) were tested without gluing, the relationship between loss tangent and frequency depended on the level of load applied. For short specimens (length = 5 mm, diameter = 8 mm) tested without gluing, however, the frequency dependence of loss tangent agreed with existing data reported for the strain-rate-dependent behavior of cancellous bone and also with the frequency dependence of cortical bone viscoelasticity. Therefore, we recommend that short cancellous bone cylinders with a length of 5 mm and a diameter of 8 mm should be used without gluing in the dynamic mechanical analysis of cancellous bone. This is consistent with the American Society for Testing and Materials testing recommendations for plastics, but different from current practice for unimodal mechanical testing of cancellous bone.

Electrical properties of single-wall carbon nanotube and epoxy composites

The homogeneous composites of single-wall carbon nanotube (SWNT) and Stycast 1266 epoxy were made with the nanotube concentrations of 0.01–0.21 wt % by using a high frequency sonication method. Direct current conductivities of various mass fractions show typical percolation behavior and the percolation threshold pc is found to be 0.074 wt % and the conductivity exponent t is estimated as 1.3±0.2. The anomalously small pc is attributed to the large aspect ratio of the nanotubes. Dielectric measurement was performed at temperatures 220–300 K with the frequency range of 20 Hz–1 MHz. There appeared different dielectric aspects according to the mass fractions p≪pc, p∼pc, or p&amp;gt;pc. The dielectric relaxation of epoxy dominates at low concentrations (p≪pc), while at high concentrations (p&amp;gt;pc) we found a scaling property in the frequency dependence of loss tangent. The scaled loss tangent spectra show a Debye type relaxation. Near the percolation threshold (p∼pc), the composites show peaks in the frequency dependence of the imaginary part of their electric moduli. Log–log plots of ac conductivity versus frequency for the midrange (p∼pc) composites exhibit the scaling and universal behavior regardless of temperature and mass fraction of SWNT.

Damping at high homologous temperature in pure Cd, In, Pb, and Sn

Typically, if a material possesses the stiffness necessary to be considered a structural material, its damping is low. Conversely, materials with high damping usually do not possess the stiffness necessary to be considered a structural material. Candidate materials for the high stiffness-low damping phase exist in abundance, whereas candidate materials for the moderate stiffness-high damping phase remain to be identified. One possible class of candidate materials for the moderate stiffness-high damping phase is metals at high homologous temperatures. Shear moduli of the specimens at 100 Hz are as follows: 4.1 GPa for indium, 5.7 GPa for lead, 15.7 GPa for tin, and 20.7 GPa for cadmium. Considering the behavior typical of metals, one may think of In and Pb as relatively compliant, while Sn and Cd could be called moderately stiff. The results are of some technological interest in view of the utility of materials with moderately high stiffness and damping. The combination of moderate stiffness and reasonably high loss tangent makes Cd the most promising metal tested with respect to technological applications. The shear modulus of Cd was highest of the metals tested (and very near that of aluminum (G = 27 GPa), which exhibits a loss tangent ofmore » about 0.001 at room temperature). The loss tangent of Cd at audio-frequencies was as high or higher than that of the other metals. In addition, frequency dependence of loss tangent was not as large as that observed in the other metals. No clear pattern relating damping to melting point emerged. An understanding in terms of viscoelastic mechanisms is not forthcoming at this time. Among the metal studied, cadmium exhibited a substantial loss tangent of 0.03 to 0.04 over much of the audio range, combined with a moderate stiffness, G = 20.7 GPa.« less