High Loss Tangent Research Articles

Electrical properties of thin film zirconia grown by ultraviolet ozone oxidation

Zirconia films of varying thickness (ranging from 20–55 Å) have been grown by the method of UV ozone oxidation at room temperature. The electrical properties of these films have been studied in detail by capacitance–voltage (C–V) and I–V measurements. Capacitors were subjected to various anneals in differing ambient to study their effects on C–V hysteresis, dispersion and charge trapping. It was found that annealing in nitrogen followed by forming gas resulted in C–V curves with negligible hysteresis. The effects of different underlayers on the electrical properties of zirconia films have also been studied and are briefly discussed. It was found that zirconia films grown on UV-ozone grown SiO2 had lower hysteresis and lower interface trap density compared to zirconia films grown on chemical oxide. The effect of oxidation time and oxygen pressure have been investigated; in particular, detailed electrical studies have been performed on partially oxidized zirconia. Defective oxides are shown to have significant frequency dispersion in both the accumulation and depletion regions of the C–V curves along with very high loss tangent factor compared to stoichiometric oxides. A physical mechanism based on Maxwell–Wagner interfacial polarization is presented here for a model system of ZrO2–Zr to explain the experimental data qualitatively. Finally, we have attempted to correlate the C–V hysteresis to the presence of traps in the zirconia film using temperature-dependent current–voltage measurements. The leakage current was found to be nearly independent of temperature at low voltages, suggesting a tunneling mechanism, while at higher voltages the data can be modeled using the Poole–Frenkel conduction mechanism. It is suggested that C–V hysteresis in zirconia films possibly arises from electrical traps in the film and can be identified by modeling their I–V characteristics.

Vibration Reduction Ability of Polymers, Particularly Polymethylmethacrylate and Polytetrafluoroethylene

The vibration reduction ability of thermoplastics (PMMA, PTFE, PA-66 and acetal) and of a thermoset (epoxy) was compared by dynamic flexural testing at ≤ 1.0 Hz. Among these polymers, PMMA exhibited the highest loss modulus, while PTFE exhibited the highest loss tangent. A synthetic rubber had an exceptionally low loss modulus, but an exceptionally high loss tangent. Epoxy and acetal exhibited the lowest loss tangent.

Structure and Thermomechanical Properties of Polyurethane Block Copolymers with Shape Memory Effect

Shape memory polyurethane (PU) block copolymers composed of 4,4‘-methylenebis(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra showed that carbonyl peak appearing at 1700 cm-1 increased with higher hard segment content, whereas another carbonyl peak at 1730 cm-1 decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. Especially, maximum stress, tensile modulus, and elongation at break increased significantly at 30 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content. Finally, 80−95% of shape recovery was obtained at 30−45 wt % of hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties.

Superconducting multiturn flux transformers for radio frequency superconducting quantum interference devices

This article describes three planar layouts of superconducting multiturn flux transformers integrated with a coplanar resonator for radio frequency (rf) superconducting quantum interference device (SQUID) magnetometers. The best magnetic field noise values of 22 and 11.5 fT/Hz1/2 in the white noise regime were obtained for the layout with two input coils and the layout with the labyrinth resonator, respectively. Excess low-frequency noise (about 200 fT/Hz1/2 at 10 Hz) was present. Computer simulation showed that the loss in this trilayer system was dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The rf coupling coefficient krf between the resonator and the flip-chip-coupled SQUID was also estimated. The values krf2≈14×10−3 obtained for the layout with two input coils, and krf2≈45×10−3 for the layout with the labyrinth resonator were considerably higher than the typical value of krf2≈7×10−3 for the single-layer coplanar resonator. These high coupling coefficients have compensated the somewhat degraded unloaded quality factor of the resonator, thus securing the optimum operation of the rf SQUID.

Simulation of the superconducting multiturn flux transformer integrated with a coplanar resonator

The analysis of the structure of a superconducting multiturn flux transformer integrated with a coplanar resonator for radio-frequency superconducting quantum interference devices is described. Electromagnetic simulations indicate that the loss is dominated by the high loss tangent of the dielectric film used for the separation of the upper and lower superconducting films. The simulated current distribution at its resonant frequency shows that the highest current density is distributed on the multiturn input coil. This current distribution leads to a very high loss when the loss tangent of the dielectric film is high. However, for the same loss tangent of the dielectric film, it is possible to get a reasonably high unloaded quality factor by providing a normal shunt for the multiturn input coil.

Mixture Behavior and Microwave Dielectric Properties in the Low-fired TiO2–CuO System

The mixture behavior and microwave dielectric properties of TiO2 doped with CuO sintered at around 900°C for 2 h were investigated using X-ray powder diffraction and a network analyzer. Low-fired TiO2 with 2% CuO had a quality factor of 14000, relative dielectric constant (εr) of 98, and a temperature coefficient of resonant frequency (τf) of 374 ppm/°C. The microwave dielectric properties of low-fired, CuO doped TiO2 could be interpreted by observing the dielectric properties of CuO: high loss tangent (tan δ), low dielectric constant, and a negative temperature coefficient of resonant frequency. The microwave dielectric properties of low-fired, CuO doped TiO2 showed a dependence on the mixture formation of TiO2 and CuO. More importantly, the εr of low-fired TiO2 with CuO could be predicted by the logarithmic mixing model. Therefore, the variation of the microwave dielectric properties was attributed to the mixture behavior of TiO2 and CuO.

Shielding and scattering analysis of lossy cylindrical shells using an extended multifilament current approach

An investigation of the multifilament current method's (MFCM) ability to solve electromagnetic scattering and/or absorption problems involving inhomogeneous cylindrical structures is presented. Dielectric cylinders of arbitrary cross section covered by multiple layers of lossy dielectrics are considered. Both cases of wave incidence, TM and TE, are treated. Like some other moment-method solutions, the MFCM experiences numerical difficulties when dealing with a medium characterized by a high loss tangent or large electrical conductivity. To overcome this problem, a new boundary condition based on an impedance matrix equivalent circuit approach that accounts for the curvature of the surfaces has been developed. This new impedance matrix boundary condition (IMBC) extends the MFCM capability to the analysis of two-dimensional (2-D) structures involving conducting layers with ohmic losses. The usefulness of this extended method is confirmed by the study of metallic shells for which a strong energy coupling with the incident electromagnetic (EM) field is demonstrated at their structural resonance frequencies.

Improvement of damping via analysis of viscoelastic composites

High damping materials allow vibration and noise to be suppressed or at least reduced. Unfortunately, materials with high loss tangents also exhibit low modulus of elasticity. A new composite damping material is investigated, which consists of specially designed fibers embedded in a viscoelastic matrix. This new approach not only enhances damping through improvement of matrix loss tangent by the addition of elastomer, but also through selection of adequate ply orientation, ply stacking, geometry of fibers, and fraction of fibers. Theoretical analysis of the viscoelastic properties of this composite is presented in order to identify the optimum material with high stiffness and high loss tangent according to all parameters. To address validation theoretical developments are compared to experimental results.

The relationship between dynamic mechanical behavior, transverse curvature, and wear of magnetic tapes

Dynamic mechanical measurements of the viscoelastic behavior of magnetic tapes and substrates are presented. Five types of tapes were analyzed including three polyethylene terephthalate (PET) tapes with metal particulate, barium ferrite particulate, and metal-evaporated coatings. A polyethylene naphthalate (PEN) tape with a barium ferrite particulate coating was also analyzed along with an aromatic polyamide (ARAMID) tape with a metal-evaporated coating. From the dynamic mechanical analysis (DMA), the storage (or elastic) modulus, E′, was obtained as a function of temperature and frequency along with the loss tangent, tan δ, which is a measurement of viscous energy dissipation. Frequency-temperature superposition was used to predict the dynamic mechanical behavior of the tapes and substrates over a 10–12 decade frequency range. Results show that the advanced PEN and ARAMID tapes tend to have higher storage moduli than the PET tapes, and the PET tapes are more susceptible to non-recoverable deformation at higher frequencies due to their higher loss tangents. Also, storage moduli for the tapes are typically higher than those for the substrates, due to the role that the particulate or metal-evaporated coatings play in increasing the overall modulus of the tapes. Tapes with particulate coatings have somewhat higher loss tangents than their constitutive substrates, whereas ultra-thin metal-evaporated coatings contribute little to the loss tangent behavior of a tape. The DMA data is used in a model to predict the resistance of a tape to transverse curvature when tension is applied. Transverse curvature of a magnetic tape is related to higher edge wear of a head. To facilitate the prediction of edge wear and enable the design of better magnetic tapes, a technique is presented which can be used to predict transverse curvature from the elastic moduli, substrate orthotropy ratios, and thicknesses of the substrates and coatings.

Viscoelastic behavior over a wide range of time and frequency in tin alloys: SnCd and SnSb

All materials exhibit some viscoelastic response, which can manifest itself as creep, relaxation, or, if the load is sinusoidal in time, a phase angle {delta} between stress and strain. Recently, a study of pure elements with low melting points, Cd, In, Pb, and Sn disclosed that cadmium exhibited a substantial loss tangent of 0.03 to 0.04 over much of the audio range of frequencies, combined with a moderate stiffness G = 20.7 GPa. Lead, by contrast, exhibited tan {delta} of 0.005 to 0.016 in the audio range. Indium exhibited a high loss tangent exceeding 0.1 at very low frequency. A eutectic alloy of indium and tin was found to exhibit substantial damping exceeding 0.1 below 0.1 Hz, and this alloy was used to make a composite exhibiting high stiffness and high damping. It is the purpose of this communication to present viscoelastic properties of two additional low melting point alloys, SnCd and SnSb. Both InSn and SnSb are used as solders. Although the melting point of Sb is 630.74 C, T{sub H} > 0.55 at ambient temperature for the alloy of SnSb (95 wt% Sn/5 wt% Sb) which melts near 240 C. Eutectic SnCd melts at 177 C so T{submore » H} {approx} 0.65 at room temperature.« less

Experimental and theoretical study of parasitic leakage/resonance in a K/Ka-band MMIC package

In this paper, electromagnetic (EM) leakage and spurious resonances in a K/Ka-Band (18-40 GHz) MMIC hermetic package designed for a phase shifter chip are studied using the finite element method (FEM) and the numerical simulation results are compared with the measured data. Both the measured and calculated data indicate several spurious resonances in the 18-24 GHz region and the origin of this phenomenon is identified by virtue of the modeling capability of the FEM. Moreover, the effect of dc bias lines, bond wires, shielding, and the asymmetry of the package on electrical performance are closely examined. In addition, the effect of adding a resistive coating to the inside surface of the package lid and also the use of dielectric packaging materials with very high loss tangent are studied in view of the suppression of the spurious resonances. Finally, design guidelines for the improved package are presented.

Millimeter Wave Material Separation System

AbstractA new process is in development that uses high power millimeter wave energy to separate specific components from a composite material stream. The component to be separated from the material stream must have a combination of high loss tangent and low permittivity with respect to the other materials involved. In this case, when the material is subjected to a high power, high frequency RF source, the desired component can be vaporized and extracted without transferring significant heat to the remaining material. Since absorption increases significantly with frequency, it is important to use a millimeter wave source. A vacuum pump with sufficient pumping speed can transport the vaporized component for collection. The bulk material can either be collected or recycled through the system for further extraction.

Properties of shoe insert materials related to shock wave transmission during gait.

The influence of the mechanical characteristics of certain insole materials in the generation and transmission of heel strike impacts while walking was studied. Three insole materials were selected according to their mechanical characteristics under heel strike impacts. The selection of materials has made it possible to distinguish the effect of rigidity and loss tangent in the transmission of heel strike impacts. A lower rigidity and a high loss tangent have been shown to reduce the transmission of impacts to the tibia. A low rigidity was seen to significantly increase the transmission of impacts from tibia to forehead.

Measurement of Complex Volume Elastic Modulus of Liquid by Holography

This paper describes a technique for measuring the complex volume elastic modulus of a transparent liquid by time-averaged holographic interferometry. The liquid in a slender transparent container whose cross section is square, is sinusoidally vibrated by a ferrite vibrator with a step horn, and the transmitted object beam, whose optical length varies sinusoidally, is holographically recorded. This technique uses the characteristics of amplitude distribution while conventional techniques use those of the vibrational behavior at one point. The dynamic elastic modulus and the loss tangent are determined from the position of the minimum amplitude and from the ratio of the minimum amplitude to the maximum neighboring one, respectively. This technique is advantageous for measuring high loss tangent.

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

Gelation of Chicken Breast Muscle Actomyosin as Influenced by Weight Ratio of Actin to Myosin

Heat-induced gelation of reconstituted chicken breast muscle actomyosin was studied by monitoring the thermal stability and dynamic rheological properties at different weight ratios of actin (A) to myosin (M) (AM of 0:1, 1:15, and 1:1.3). Free myosin to actomyosin ratios were 0.2 and 2.4 for AM of 1:1.3 and 1:15, respectively. Addition of actin delayed the initial unfolding temperature of myosin and changed the enthalpy profile. This stabilizing effect was decreased with addition of pyrophosphate. Storage (G') and loss (G″) moduli of AM 1:1.3 sol at 30 o C were greater than those of myosin and AM 1:15 sols, but AM 1:1.3 had a higher loss tangent and lower G' at 80 o C. Pyrophosphate decreased G' of myosin and actomyosin solutions at 30 o C and increased viscous character after heating to 80 o C. Actin affected the denaturation of structural domains of myosin and possibly altered the gelation mechanism

Microwave-assisted solid-state reactions involving metal powders

The high dielectric loss tangents of metal powders at 2450 MHz have been utilised to accelerate the syntheses of a wide range of metal chalcogenides in the solid state.

Dynamic Rheological Properties and Secondary Structure of Chicken Breast Myosin As Influenced by Isothermal Heating

Gelation of chicken breast myosin in 0.6 M NaCl, pH or pD 6.5, was studied by monitoring changes in rheological properties and secondary structure using dynamic testing and Fourier transform infrared spectroscopy, respectively. Myosin heated at 75 o C had a higher loss tangent (more viscous), while myosin at 55 and 65 o C formed more elastic gels. After cooling, storage modulus (G'), loss modulus (G″), and loss tangent of myosin heated at 65 and 75 o C increased, but few changes were observed at 55 o C. Spectra of native myosin showed protein absorption bands for α-helix (1652 cm -1 ) and β-sheet (1636 cm -1 paired with 1676 cm -1 ) that decreased when heated above 45 o C

The applications of microwaves in chemical syntheses

The application of microwave dielectric heating techniques for chemical syntheses has attracted considerable interest in recent years. A fundamental understanding of the mechanisms responsible for effective coupling of microwave radiation to liquid and solid chemicals and the establishment of techniques for containing the chemicals safely within a microwave cavity have contributed to the rapid progress in this area. A wide range organic and inorganic reactions have been accelerated using microwave techniques. The rapid syntheses of these compounds can be attributed primarily to superheating effects which result from the effective coupling of microwaves to the polar organic solvent in the containment vessel. Similar methods have been used for accelerating intercalation reactions resulting in the incorporation of organic molecules between the layers of an inorganic host material. In the solid state mixed metal oxides may be synthesized at an accelerated rate if one of the components has a high loss tangent. The ceramic high temperature superconducting materials have been synthesized in this manner and have utilized the high loss tangent of copper oxide. Metal chlorides, chalcogenides and oxides have also been synthesized directly from the elements using microwave dielectric heating effects resulting from the efficient coupling of microwaves to the particles of metal powder.

Analysis of high-loss viscoelastic composites

A theoretical study of the viscoelastic properties of composites is presented with the aim of identifying structures which give rise to a combination of high stiffness and high loss tangent. Laminates with Voigt and Reuss structures, as well as composite materials attaining the Hashin-Shtrickman bounds on stiffness were evaluated by the correspondence principle. Similarly, viscoelastic properties of composites containing spherical or platelet inclusions were explored. Reuss laminates and platelet-filled materials composed of a stiff, low-loss phase and a compliant high-loss phase were found to exhibit high stiffness combined with a high loss tangent.