Loss Factor Measurements Research Articles

On the level of mechanical loss in metallic glasses

Metallic glass samples with compositions Zr65Al7.5Cu27.5 and Pd77Cu6Si17, for which loss factors of up to 10-2 have been reported, are reinvestigated with an electrostatic vibrating cantilever technique that detects dissipation factors tan δ as low as 10-4. It is found that tan δ ≈ 4×10-4 is a typical value for these alloys well below T g , suggesting that previous results were limited by instrumental resolution. While aging the glasses increases their elastic moduli considerably, the measured loss factor is affected only marginally by thermal history.

Terahertz electromagnetic crystal waveguide fabricated by polymer jetting rapid prototyping

An all-dielectric THz waveguide has been designed, fabricated and characterized. The design is based on a hollow-core electromagnetic crystal waveguide, and the fabrication is implemented via polymer-jetting rapid prototyping. Measurements of the waveguide power loss factor show good agreement with simulation. As an initial example, a waveguide with propagation loss of 0.03 dB/mm at 105 GHz is demonstrated.

Measurements of dynamic properties of concrete structures using flexural wave propagation characteristics

Flexural wave propagation characteristics influence the impact noise generation of concrete structures that are found in building floors, railroads, bridges, and many other engineering structures. The flexural vibration of the structure is affected by concrete dynamic properties. The purpose of this study is to measure the concrete dynamic characteristics using a wave propagation approach. The flexural wave speeds, bending stiffness and their loss factors were measured. The measured characteristics are essential for understanding sound radiation and vibration dissipation capabilities of the concrete structures. Various concrete beam structures were made and tested. The dynamic stiffness and loss factor were influenced by its components and showed frequency-dependent variation, especially for the measured loss factor.

Dynamic stiffness and loss factor measurement of engine rubber mount by impact test

Dynamic stiffness and loss factor for engine rubber mount are important dynamic behaviours to represent the performance of an engine mount system. The investigation of the dynamic behaviour of engine mount system using impact technique, particularly in the simultaneous measurement of the dynamic transfer stiffness and driving point stiffness where the impact hammer replaces the shaker as the source of excitation is presented in this paper. The results showed that the dynamic driving point stiffness can only be used to represent the dynamic transfer stiffness for the lower range of frequency. The curve fitted functions of the loss factor obtained from the dynamic driving point stiffness measurement showed linear dependency on the frequency and the loss factor obtained from the transfer stiffness measurement showed non-linear dependency on the frequency. Both of the stiffnesses are accurately reproduced by using these functions. The values of both dynamic stiffnesses obtained from impact technique are validated with the values obtained from shaker.

Dielectric polarization in Sb2Te3 thin films

Dielectric properties of Sb2Te3 films prepared by thermal evaporation technique onto clean glass substrates using ohmic aluminum electrodes have been investigated in the frequency range of 0.01– 100 kHz and within the temperature range of 293K– 373 K. Both the dielectric constant ε1 and dielectric loss factor were found to depend on frequency and temperature. The activation values were evaluated and good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements were obtained.

Re-evaluation of the mechanical loss factor of hydroxide-catalysis bonds and its significance for the next generation of gravitational wave detectors

New measurements of the mechanical loss factors of hydroxide-catalysis bonds have been made and these have been found to be significantly lower than previously reported. We provide the first estimate for the resulting thermal noise limitation for a practical test mass geometry for next generation gravitational wave detectors.

Studies on initial permeability and loss factor in Ni–Zn ferrites synthesized by oxalate precursors

Abstract Ni X Zn 1− X Fe 2 O 4 ferrites with ( X = 0.28–0.40 in step of 0.2) have been synthesized by oxalate precursor method and investigated for their, initial permeability and loss factor measurements. Initial permeability has been observed to increase with the increase in Ni 2+ up to X = 0.32, beyond which it decreases. The variation of initial permeability has been explained by considering the factors such as grain size, saturation magnetization and anisotropy constant. Thermal variation of initial permeability reveals a peak height in μ i – T curves which tends to increase with increase in Ni 2+ content. μ i – T curves also exhibit thermal hysteresis, which reveals the inverse relationship between the difference in heating and cooling curves at which hysteresis falls between Hopkinson peak and T c with value of initial permeability. Loss factor values are small which is attributed to high density of the samples and processing techniques.

Measurement of resonance frequency and loss factor of a microphone diaphragm using a laser vibrometer

The pressure sensitivity of a laboratory standard microphone is determined using a reciprocity technique that measures the electrical transfer impedance of two microphones connected acoustically by a coupler. The electrical transfer impedance is a function of the coupler volume and the equivalent volumes of the microphones. The equivalent volume given as a function of the frequency can be determined in experiments or can be calculated if the equivalent volume at a low frequency as well as the resonance frequency and loss factor of the microphone diaphragm are known. Therefore, it is necessary to determine the resonance frequency and the loss factor accurately to obtain an accurate reading of the pressure sensitivity. In this paper, a new method to determine the resonance frequency and loss factor of a microphone diaphragm is proposed. The frequency response of the diaphragm displacement is measured by a laser vibrometer and the part of the response near the resonance frequency is used to determine the microphone parameters via least square fitting with the equation of a vibration model with one degree-of-freedom. Since the values measured by this method are close to the nominal values and the repeatability is highly feasible, the proposed method will be useful to determine the resonance frequency and loss factor of a microphone diaphragm.

Methods for Measurement of Loss Factor on Damping Materials

Methods for Measurement of Loss Factor on Damping Materials

Relaxation spectrum of the TlSbSe2 thin films

The dielectric constant and the dielectric loss of TlSbSe2 thin films, obtained via thermal evaporation of TlSbSe2 crystals grown by Stockber-Bridgman technique, have been measured using ohmic Al electrodes in the frequency range 0.2–100 KHz and within the temperature interval 293–353 K. The capacitance are found to decrease with increasing frequency and increase with increasing temperature. The activation energy values were evaluated too. A good agreement between the activation energy values obtained from capacitance and dielectric loss factor measurements has been observed.

Determination of Structural Damping and Optimal Vibration Control of an Adhesively-Bonded Double Containment Cantilever Joint

In this study, the loss factors of an adhesively-bonded double containment cantilever joint were determined for different plate and support lengths. The response of the adhesive joint subjected to a transverse excitation force was measured with a contactless eddy-current sensor and the first bending natural frequency was determined using the Fast Fourier Transform method. The loss factor was calculated using the half-power bandwidth method based on the power spectrum of the joint vibration. After an excitation force was applied to the joint, the damped free vibration analysis was carried out using the finite element method and its measured loss factor. The transverse vibration attenuation was actively controlled with different numbers of actuators located on the top surface of the plate. The optimal control of the vibration attenuation was achieved based on a performance index by considering the strain energy, the kinetic energy, the work done on the adhesive joint by the actuators as well as the vibration attenuation time. Genetic Algorithm was implemented to this optimization problem in which the optimal control force histories, the optimal locations and the optimal numbers of the actuators were searched. Eight actuators exhibited the best control force history minimizing the performance index to 3.34 × 10–2. Thus, the attenuation time was reduced from 16 s to 0.15 s and the absolute displacement was decreased from 13.1 mm to 17.15 × 10–3 mm for 0.15 s. In addition, the modal strain energy and kinetic energy were found to be at lowest levels. As the actuator number was increased only a minor decrease in the performance index was observed after four actuators.

Measurements of loss factors of honeycomb sandwich structures

Loss factor measurements were performed on different sandwich panels to determine the effects of different skin and core materials on the acoustical properties of sandwich structures. The study included the following panel/beam designs: glass-epoxy skin with a meta-aramid (m-aramid) core, glass-epoxy skin with a para-aramid core, carbon skin with a m-aramid core, and a carbon skin with a m-aramid core of subsonic wave speed. The loss factors were calculated for all the above configurations. Analysis of the results revealed that panels constructed with carbon fiber skins exhibited larger loss factors than glass fiber skins. Panels designed to achieve a subsonic wave speed did not show a significant increase in loss factor above the coincidence frequency. The para-aramid core had a larger loss factor value than the meta-aramid core. The data indicated that judicious choice of sandwich materials can lead to reductions in noise transmission.

Theoretical prediction of hysteretic rubber friction in ball on plate configuration by finite element method

This paper has investigated theoretically the influence of sliding speed and temperature on the hysteretic friction in case of a smooth, reciprocating steel ball sliding on smooth rubber plate by finite element method (FEM). Generalized Maxwell-models combined with Mooney-Rivlin model have been used to describe the material behaviour of the ethylene- propylene-diene-monomer (EPDM) rubber studied. Additionally, the effect of the technique applied at the parameter iden- tification of the material model and the number of Maxwell elements on the coefficient of friction (COF) was also investigated. Finally, the open parameter of the Greenwood-Tabor analytical model has been determined from a fit to the FE results. By fitting, as usual, the Maxwell-model to the storage modulus master curve the predicted COF, in a broad fre- quency range, will be underestimated even in case of 40-term Maxwell-model. To obtain more accurate numerical predic- tion or to provide an upper limit for the hysteretic friction, in the interesting frequency range, the Maxwell parameters should be determined, as proposed, from a fit to the measured loss factor master curve. This conclusion can be generalized for all the FE simulations where the hysteresis plays an important role.

Determination of mechanical properties of non-linear coatings from measurements with coated beams

Coatings are applied to structural components for several various reasons, such to protect against erosion or corrosion, as thermal barrier coatings, or to increase the energy dissipation. As determining the material properties of such coatings from homogeneous specimens is often difficult, it is sometimes necessary to conduct testing on coated specimens, with the properties of the coating then to be extracted from the results of testing. A methodology for doing this is given here. While applicable to other materials, the properties of such coatings as ceramics, metallics, or compounds to be applied to rotating and static components of gas turbines are of special interest. Such materials present a special challenge as the mechanical properties have generally been found to display a strong dependence on the amplitude of cyclic strain. Application of the methodology requires careful measurement of specimen dimensions, weights, natural frequencies, and system loss factors before and after coating. From these, the storage (Young’s) modulus, the loss modulus, and the loss factor can be extracted. The methodology is demonstrated through the use of data taken on flat specimens of titanium with plasma-sprayed coatings of NiCrAlY and a titania–alumina blend ceramic, vibrating in a cantilever mode.

Thermal, mechanical and dielectric properties of nanostructured epoxy-polyhedral oligomeric silsesquioxane composites

This paper presents the results of the thermal, mechanical and dielectric measurements conducted on polymer nanocomposites consisting of epoxy and polyhedral oligomeric silsesquioxane (POSS). The material composites were analyzed with a scanning electron microscope (SEM), an atomic force microscope (AFM) and a transmission electron microscope (TEM). Glass transition temperatures of the composites were measured with differential scanning calorimeter (DSC). Stress, strain, modulus and impact strength of epoxy nanocomposites were tested. Ac and lightning impulse (LI) breakdown strength of the composites were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, glycidyl and octaglycidyldimethylsilyl, were used in different quantities. Statistical analysis was applied to the measurement results to determine the effects of the additive type and amount on the properties of epoxy. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.

Acoustical Effectiveness of Damping Coating

Damping coatings have again become popular in the shipbuilding industry to reduce onboard and underwater noise. Understanding of the actual effectiveness of damping tiles applied to ship structures is important for noise prediction during the design stage and for optimizing noise control. The commonly held opinion that energy loss is proportional to loss factor values is not confirmed by tests conducted on actual structures. This paper discusses differences between loss factors measured on the Oberst beam and on two-dimensional real structures. The paper shows how loss factor change may influence transmission loss, radiation efficiency and acceptance. The results of loss factor measurements in different conditions including water-loaded media are demonstrated. influences of resonant and non- resonant modes on damping tile effectiveness is discussed. Corrections for SEA noise prediction algorithms, taking into account results of this research, are proposed.

Measurement of SEA damping loss factor for complex structures

Statistical Energy Analysis has become extremely popular in the transportation industry. As a prediction tool, it offers appealing advantages such as its wide frequency range and short computational time, which conventional methods do not offer. Critical parameter in every SEA model, the damping characteristics of the subsystems must be determined by way of experimentations. A variety of different techniques of measuring the damping loss factor were developed. These techniques can be divided into three main groups: (i) method based on the identification of modal damping by curve-fitting frequency response function, (ii) decay techniques based on-determination of the reverberation time and, (iii) steady-state techniques involving measurements of power input method much closely related to the definition of SEA since its starting point is the power balance. This work presents an experimental study of these techniques for various structures such as flat metallic panels, aircraft side walls (ribbed curved panels) and sandwich-composite panels in both low and high damping configurations (additions of damping materials, sound packages in both single wall and double wall configurations, mounting effects, ...). In particular, a critical discussion is made on the implementation, advantages and drawbacks of each method regarding its use in SEA modeling of complex structures.

Digital algorithm based on orthogonal decomposition for measurement of dielectric loss factor

As one of the most important technical indexes for the evaluation of insulation condition, the dielectric loss factor is necessary in preventive experiments and online monitoring of insulation of high-voltage apparatuses in an electric power system. First, the definition of the dielectric loss factor and the impact of the harmonic voltage on that was discussed. Secondly, the voltage and the leakage current were defined as vectors in normed linear space. By using the characteristic of an orthogonal vector in the inner product space, the leakage current signal was decomposed to active and reactive components that were orthogonal. Subsequently, a novel digital algorithm of the dielectric loss factor measurement, which was defined as the ratio of norms of the active current to the reactive current, was proposed. At last, the proposed algorithm was simulated under several conditions such as harmonic voltage and voltage frequency fluctuation. In addition, the proposed algorithm was tested on two electric power capacitors. Both simulation and experiment results were provided and show that the proposed algorithm is simpler and less sensitive to influence factors than the Fourier analysis method.

Dielectric properties of nanostructured polypropylene-polyhedral oligomeric silsesquioxane compounds

This paper presents the results of the dielectric measurements conducted on polymer nanocompounds consisting of polypropylene (PP) and polyhedral oligomeric silsesquioxane (POSS). The material compounds were analyzed with a scanning electron microscope (SEM) and Raman-atomic force microscope (Raman-AFM). Ac and lightning impulse (LI) breakdown strength of the material compounds were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, octamethyl and isooctyl, were used in different quantities. The thickness of the samples was approximately 600 mum. Statistical analysis was applied to the results to determine the effects of the additive type and amount on the breakdown strength of polypropylene. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes.

MEASUREMENT OF RF PCB DIELECTRIC PROPERTIES AND LOSSES

This paper presents the calculations of transmission line loss factor by extracting from the Q-factor measurement of the quarterwavelength open stub resonators over the designed frequency and other resonant frequencies. A comparison of the loss factor of the design frequency with other resonant frequencies of each of the stub’s quarter-wave resonances is provided in this paper. The radiation and discontinuity losses are undesirably included in the unloaded Q-factor measurement and it shows that the unloaded Q-factor is not repeatable at different designed frequency. The implementation of the loss factor measurement by quarter-wavelength open stub resonators is becoming more and more important to be considered with the increase of using the electronic circuits operating at high frequencies. † This author is also with Department of Electronic Engineering, Tam Kang University, 151 Ying-chuan Road, Tamsui, Taipei County, Taiwan 25137, R.O.C.