Tan Δe Research Articles

Effect of polyacrylamide on morphology and electromagnetic properties of chrysanthemum-like ZnO particles

Through hydrothermal process, the chrysanthemum-like ZnO particles are prepared with zinc acetate dihydrate (Zn(CH3COO)2·2H2O) and sodium hydroxide (NaOH) used as main resources under the different concentrations of surfactant polyacrylamide (PAM). The microstructure, morphology and the electromagnetic properties of the as-prepared products are characterized by high-resolution transmissïon electron microscopy (HRTEM), field emission environment scanning electron microscope (FEESEM) and microwave vector network analyzer, respectively. The experimental results indicate that the as-prepared products are ZnO single crystalline with hexagona wurtzite structure, that the values of slenderness ratio Ld are different in different PAM concentrations, and that the good magnetic loss property is found in the ZnO products, and the average magnetic loss tangent tan δu increases with PAM concentration increasing, while the dielectric loss tangent tan δe decreases.

Hydrothermal synthesis and dielectric properties of chrysanthemum-like ZnO particles

By orthogonal design theory, technological parameters of chrysanthemum-like ZnO particles prepared in a hydrothermal process are optimized. This paper reports a set of technological parameters for growing chrysanthemum-like ZnO particles on a large scale. It investigates the morphologies and crystalline structures of the as-synthesized three-dimensional ZnO particles with a scanning electron microscope, x-ray diffractometer and transmission electron microscope, and the possible growth mechanism on the three-dimensional ZnO particles. The experimental results indicate that the values of ∊′, ∊″ and tan δe gradually increase in the X band with the improvement of the developmental level of chrysanthemum-like ZnO particles, implying that the electromagnetic wave absorbing property depends on the morphologies of three-dimensional ZnO particles.

The microwave absorption properties of La0.8Sr0.2Mn1−yFeyO3 nanocrystalline powders in the frequency range 2–18GHz

Abstract La1−xSrxMn1−yFeyO3 nanocrystalline powders were prepared by the sol–gel method as a microwave absorption material. The reflectance, the dielectric loss tan δe and the magnetic loss tan δm of the samples were calculated according to the data of electromagnetism parameters measured by a microwave vector network analyzer in the frequency range 2–18 GHz. The dielectric loss tan δe and the magnetic loss tan δm had a step-change at a certain frequency so that the superiority of dielectric loss change into the superiority of magnetic loss, which indicated that anti-ferromagnetic clusters in the material change into ferromagnetic clusters by absorbing quantum of microwave electromagnetic field when the frequency of incident microwave reaches a certain value. The effective absorption bandwidth higher than 10 dB reached 6.2 GHz. As a result, the La0.8Sr0.2Mn1−yFeyO3 has shown useful applications as a microwave absorption material.

Mechanism of Enhanced Dielectric Properties of SiC/Ni Nanocomposites

Dielectric properties of SiC/Ni nanocomposites prepared by a simple and facile electroless plating approach at X band are investigated. Compared to the original SiC nanoparticles (SiCP), the real part of the permittivity, ∊′, and the dielectric loss tangent tan δe of SiC/Ni nanocomposites are clearly enhanced by about 31% and 33%, respectively. The effective equations for complex permittivity of SiC/Ni nanocomposites are proposed. We also calculate ∊′ and tan δe of SiC/Ni nanocomposites and the calculated results are well consistent with the measured data.

Absorption of microwaves in La1−xSrxMnO3 manganese powders over a wide bandwidth

We present the frequency dependence of microwave-absorbing properties of La1−xSrxMnO3 (x=0.4, 0.5, 0.6, and 0.7) powders at room temperature. The absorbing properties change gradually with x in the frequency range of 8–12 GHz. The optimal absorption can be achieved for a x=0.4 sample and its microwave loss peak value is about 25 dB. Further experimental results show that the absorption can be attributed to magnetic and dielectric losses and the microwave loss peak corresponds to the maximum dielectric loss tangent tan δe near 10.5 GHz. Furthermore, the absorbing properties of the oxides mixed with carbonic fiber and Y-type planar hexagonal ferrite have been rudimentarily studied. Results show that these additives greatly enhance the microwave-absorbing properties of the oxides.

Complex polarizability as used to analyze dielectric relaxation measurements

The effect of representing dielectric properties in terms of the complex polarizability αc = α′ − iα″ is examined. Loss curves (e″ and tan δe) are shifted towards higher frequencies, revealing the existence of new relaxations and allowing the clarifications of ones already known. We have calculated the shift ratios ω (at maximum α″ or tan δα)/ω (at maximum e″ or tan δα) from the more conventional empirical equations representing the dielectric behavior. Some examples are given.

Interaction of Tire Material and Design

Abstract An analytical study based on the Halpin-Tsai equations in their complex form has been conducted over a reasonably practical range of variables typical of a composite construction involving steel-cord reinforcement in a rubber matrix. Curves are presented which show the influence of several material properties on the composite characteristics of bias-angle constructions. From these curves, it is possible to deduce the influence of these constituent material properties on the overall composite response. The most significant deductions from these results are: (1). The elastic extension modulus of the composite, E′, is highly dependent on the bias angle and moderately dependent on the volume fraction of cord. On the other hand, E′ is essentially independent of the loss modulus of the matrix E″r. (2). The elastic shear modulus of the composite, G′, is also dependent on the bias angle and volume fraction of cord, but independent of the loss modulus of rubber. Also G′ is symmetric about a 45 degree bias angle. (3). The loss modulus in tension of the composite, E″, is highly dependent on the bias angle and moderately dependent on the volume fraction of cord and loss modulus of the matrix. (4). The loss modulus in shear of the composite, G″, is dependent on the bias angle and volume fraction of cord and nearly independent of the loss modulus of the matrix except at bias angles near zero and 90 degrees. (5). The loss tangent in tension of the composite, tan ΔE′ is highly dependent on the bias angle from 0 to 20 degrees and is approximately a constant for all other bias angles. The magnitude of the constant value is the same as tan δr of the matrix. (6). The loss tangent in shear of the composite, tan ΔG′ is nearly a constant except for very small or very large bias angles. The magnitude of this constant is approximately the small value of the loss modulus of the cord. Also tan ΔG is symmetric about 45 degrees. (7). For most bias angles, the loss tangent of the composite in shear is much less than the loss tangent of the composite in tension.

Dynamic mechanical and rheo-optical studies of collagen and gelatin.

AbstractThe frequency dependence of dynamic mechanical properties of rat tail tendon (RTT), enzyme‐solubilized collagen membranes (ESC), AKM‐23 dialysis membranes, and gelatin film have been measured at 110, 11, and 3.5 Hz from ‐ 160 to 220°C. RTT and AKM‐23 are devoid of a rubbery region; there are as many as six mechanical loss transitions. Gelatin and ESC membranes behave as rubbery materials above room temperature; only three tan δE peaks can be resolved for these materials. Strain birefringence was used to measure the crystalline and amorphous contribution of orientation induced by strain. Both the birefringence and the strain optical coefficient are sensitive to the amount of water in a sample. The effect of chemical swelling agents and of annealing on birefringence are described. Stress relaxation data on gelatin film were analyzed with the rubber elasticity theory to give the average number of chains per unit volume, the specific polarizability, the stress‐birefringence ratio and the average molecular weight between hydrogen bonds were calculated. The intrinsic amorphous birefringence for “wet” gelatin film is 1.25 × 10−2; it is estimated to be about 6 × 10−2 for “dry” gelatin film.

Piezoelectric Properties in Polarized Poly(vinyl Fluoride)

Poly(vinyl fluoride) films were elongated twice the original length by rolling, subjected to a d.c. field of 350 kV/cm at 80°C for 90 minutes, and cooled down to room temperature for 2 hours. The piezoelectric strain-constant d of the electret films was about 1×10-8 cgs esu at room temperature. The complex piezoelectric, elastic, and dielectric constants showed two dispersions at the low and high temperatures, respectively. The maximum value of piezoelectric loss factor tan δd is roughly the same as the sum of the maximum values of elastic and dielectric loss factor tan δE and tan δε. This fact may be explained by assuming that the piezoelectric constant h is a real quantity.

Coaxial variable-length resonator for determining the electromagnetic parameters of materials at normal and higher temperatures

It is possible by means of the above resonator, according to our analysis and in the absence of air gaps between the sample and the line, to evaluate the real components μ′ and e′ of permeability and permittivity respectively in the range of 2 to 100 with an error between ±3% and ±10% in the temperature range from room temperature to +400°C, and the imaginary components μ″ and e″(for tan δμ and tan δe in the range of 0.001 to 2) with an error of 7 to 20% over the same temperature range.