Modeling of viscous damping of perforated planar microstructures. Applications in acoustics

The paper contains an analysis of the viscous damping in perforated planar microstructures that often serve as backplates or protecting surfaces in capacitive microsensors. The focus of this work is on planar surfaces containing an offset system of periodic oval holes or its limit cases: a system of circular holes or of slits. The viscous damping is calculated as the sum of squeeze film and the holes' resistances. The optimum number of holes is determined which minimizes the total viscous damping for a given percentage of open area. Graphs and formulas are provided for designing these devices. In the case the open area is higher than 15% the numerical results show that the influence of the holes' geometry (circular or oval) has a slight influence on viscous damping. As the planar structures containing oval holes assure a better protection against dust particles and water drops, they should be preferred in designing protective surfaces for microphones working in a natural environment. The obtained results also can be applied in designing other MEMS devices that use capacitive sensing such as accelerometers, micromechanical switches, resonators, and tunable microoptical interferometers.     

A real-time plane-wave decomposition algorithm for characterizing perforated liners damping at multiple mode frequencies

Perforated liners with a narrow frequency range are widely used as acoustic dampers to stabilize combustion systems. When the frequency of unstable modes present in the combustion system is within the effective frequency range, the liners can efficiently dissipate acoustic waves. The fraction of the incident waves being absorbed (known as power absorption coefficient) is generally used to characterize the liners damping. To estimate it, plane waves either side of the liners need to be decomposed and characterized. For this, a real-time algorithm is developed. Emphasis is being placed on its ability to online decompose plane waves at multiple mode frequencies. The performance of the algorithm is evaluated first in a numerical model with two unstable modes. It is then experimentally implemented in an acoustically driven pipe system with a lined section attached. The acoustic damping of perforated liners is continuously characterized in real-time. Comparison is then made between the results from the algorithm and those from the short-time fast Fourier transform (FFT)-based techniques, which are typically used in industry. It was found that the real-time algorithm allows faster tracking of the liners damping, even when the forcing frequency was suddenly changed.     

Analytical modeling for the determination of nonlocal resonance frequencies of perforated nanobeams subjected to temperature-induced loads

This paper is concerned with the investigation of thermal loads and small scale effects on free dynamics vibration of slender simply-supported nanobeams perforated with periodic square holes network and subjected to temperature-induced loads. The Euler–Bernoulli beam model (EBM) and shear beam model (SBM) developed for the determination of resonance frequency are derived by modifying the standard Timoshenko beam equations. The small scale effect is included by using the Eringen's nonlocal elasticity theory while the thermal loads effect is included by considering the additional axial thermal force in the standard differential equations. Numerical results are shown that the resonance frequency change, the thermal loads and the small scale effects are depended on size and number of holes. Thus, numerical results are discussed in detail for a properly investigation of the dynamic behavior of perforated nanobeams which are of interest in the development of resonant devices integrated in micro/nanoelectromichanical systems (M(N)EMS).     

VISHNU hybrid model for the viscous QCD matter at RHIC and LHC energies

In this proceeding, we briefly describe the viscous hydrodynamics + hadron cascade hybrid model VISHNU for relativistic heavy ion collisions and report the current status on extracting the QGP viscosity from elliptic flow data.     

A 2D spring model for the simulation of ultrasonic wave propagation in nonlinear hysteretic media

A two-dimensional (2D) approach to the simulation of ultrasonic wave propagation in nonclassical nonlinear (NCNL) media is presented. The approach represents the extension to 2D of a previously proposed one dimensional (1D) Spring Model, with the inclusion of a PM space treatment of the intersticial regions between grains. The extension to 2D is of great practical relevance for its potential applications in the field of quantitative nondestructive evaluation and material characterization, but it is also useful, from a theoretical point of view, to gain a better insight of the interaction mechanisms involved. The model is tested by means of virtual 2D experiments. The expected NCNL behaviors are qualitatively well reproduced.     

A model for the complex permittivity of water at frequencies below 1 THz

Experimental permittivity data of liquid water, compiled from the open literature, were selectively applied to support a modeling strategy. Frequencies up to 1 THz and atmospheric temperatures are covered with an expression made up by two relaxation (Debye) terms. The double-Debye model reduces to one term when the high frequency limit is set at 100 GHz, and the model can be extended to 30 THz by adding two resonance (Lorentzian) terms. The scheme was carried out by employing nonlinear least-squares fitting routines to data we considered reliable.T. Manabe was with the Institute for Telecommunication Sciences, NTIA-DoC, on leave from the Radio Research Laboratory, Ministry of Posts and Telecommunications, Koganei, Tokyo 184. He is now with ATR Optical and Radio Communications Research Laboratories, Seika-cho, Soraku-gun, Kyoto 619-02, Japan.     

A model for the complex permittivity of ice at frequencies below 1 THz

Using empirical fits to published data, formulas are suggested for the complex permittivity of ice. The radio frequency may range from 0 to 1000 GHz, and the temperature from 0° to –40°C. It then becomes apparent where additional data would be welcome.     

Elastic constants of the SrLaAlO4 and SrLrGagaO4 crystals measured at ultrasonic and hypersonic oustic frequencies

Elastic constants measured by Brillouin light-scattering experiments were compared with results estimated from the pulse-echo-overlap method for the ultrasonic frequency to find dispersion in their values. In this way Brillouin hypersonic experiments complete the ultrasonic results. The present investigation includes a careful analysis of the accuracy of the results. The measured values of elastic constants suggest a weak dispersion in acoustic wave velocities. However, given the magnitude of the experimental errors, it is difficult to conclude about the dispersion.     

Single,simultaneous and sequential applications of ultrasonic frequencies for the elimination of ibuprofen in water

The study is about the assessment of single and multi-frequency operations for the overall degradation of a widely consumed analgesic pharmaceutical-ibuprofen (IBP). The selected frequencies were in the range of 20–1130 kHz emissions coming from probes, baths and piezo-electric transducers attached to plate-type devices. Multi-frequency operations were applied either simultaneously as “duals”, or sequentially at fixed time intervals; and the total reaction time in all operations was 30-min. The work also covers evaluation of the effect of zero-valent iron (ZVI) on the efficiency of the degradation process and the performance of the reaction systems. It was found that low-frequency probe type devices especially at 20 kHz were ineffective when applied singly and without ZVI, and relatively more effective in combined-frequency operations in the presence of ZVI. The power efficiencies of the reactors and/or reaction systems showed that 20-kHz probe was considerably more energy intensive than all others, and was therefore not used in multi-frequency operations. The most efficient reactor in terms of power consumption was the bath (200 kHz), which however provided insufficient mineralization of the test chemical. The highest percentage of TOC decay (37%) was obtained in a dual-frequency operation (40/572 kHz) with ZVI, in which the energy consumption was neither low nor exceptionally too high. A sequential operation (40 + 200 kHz) in that respect was more efficient, because it required much less energy for a similar TOC decay performance (30%). In general, the degradation of IBP increased with increased power consumption, which in turn reduced the sonochemical yield. The study also showed that advanced Fenton reactions with ZVI were faster in the presence of ultrasound, and the metal was very effective in improving the performance of low-frequency operations.     

Infrared band intensities and the complete quadratic force field for planar vibrations of gaseous benzene

Infrared absolute band intensities of the planar fundamental modes were measured for benzene and its deuterium homologs in the gas phase, and were successfully interpreted in terms of effective charges and charge flux parameters. The charge flux parameters were determined from the intensities by taking the effective charge on the hydrogen atom of benzene to be 0.125 e, a value which had previously been obtained from the nonplanar modes. The parameters determined were found to be quite consistent with those of other molecules. The complete quadratic planar force field of benzene was also introduced, the 273 assigned frequencies having been reproduced with a root-mean-square difference of 2.9 cm^?1.     

Absolute measurements of the intensity of pulsed ultrasonic waves in solids and liquids with a capacitor microphone at megahertz frequencies

Measurements of absolute intensities with a capacitor microphone should be useful in monitoring the output of ultrasonic pulse generators used for medical diagnosis, where possible harm may occur with excessive intensities. The present device has the advantage over purely mechanical receivers, such as the radiometer, in that it is robust, portable and reliable and that it requires no delicate running adjustments. Further developments should provide greater increase in sensitivity and a wider frequency range of operation.     

Excitation of seismoacoustic waves by a harmonic force source acting at the boundary of a liquid layer and an elastic halfspace

A problem on the excitation of seismoacoustic waves in a system of a homogeneous isotropic elastic halfspace covered with a liquid layer is solved in the case of action of a source of point harmonic force on the surface of an elastic medium. Integral expressions are obtained for the radiation powers averaged over a wave period for longitudinal and transverse waves in a solid. Mode excitation is analyzed in detail. Expressions describing parts of the mode powers radiated into a liquid layer and an elastic medium are obtained. Numerical analysis of radiation powers is conducted for spherical longitudinal and transverse waves as well as for the radiation powers of seismoacoustic modes in a solid halfspace and a liquid layer. It is determined that in the conditions characteristic of bottom rocks in the case, where the basin depth is several times and more larger than the sound’s wavelength, about 2/3 of the total power is radiated into a liquid.     

Physical and mathematical model of the coagulation of micron and submicron aerosols with regard for evaporation and sedimentation at ultrasonic effect

A physical and mathematical model is proposed, which is based on the Smolukhovsky’s equation describing the dynamics of the variation of the distribution function of aerosol particles over their sizes with regard for ultrasonic action, evaporation (for liquid-drop aerosols), and sedimentation. The expressions are obtained for the coagulation kinetics depending on the main parameters of action, the properties of aerosol and medium: the concentration and dispersion composition of the original aerosol, viscosity and temperature of the medium, physical-chemical parameters of particles material. Computational results obtained by using the proposed model correspond to experimental data.     

Analytical solutions of the Smith model for the neutral and charged metal surface

Smith jellium model for an s-p metal surface is retreated. Exact analytical solution is obtained for the case of neutral metal. Extension of the model on the case of a charged surface is reconsidered to obtain analytical expressions for the lability coefficients, characterizing the response of the surface electronic profile to moderate charging.     

Calculations of the backscattering and radiation force functions of spherical targets for use in ultrasonic beam assessment

Knowledge of the frequency dependence of the backscattering from spherical targets, or of the associated radiation force function Y_p, is of considerable practical importance for the choice of material and size of sphere for transducer beam profiling. The former is often employed in a pulse-echo situation to define iso-echo contours, while the latter is used in absolute measurements of intensity.The present paper contains the graphical results of the calculation of the backscattering from 43 materials and the radiation force function for 48 materials, all of which were assumed to be immersed in water. The range of ka values displayed is from 0 to 20, calculations being performed in ka steps of 0.05. It is shown that the frequency behaviour of the radiation force function is an unreliable index of the frequency behaviour of the backscattering.     

Simple high-order Galerkin finite element scheme for the investigation of both guided and leaky modes in anisotropic planar waveguides

A simple high-order Galerkin finite element scheme is formulated to compute both the guided and leaky modes of anisotropic planar waveguides with a diagonal permittivity tensor. Transparent boundary conditions derived from the Sommerfield radiation conditions are used to model the fields at the computational boundaries that allow the radiation into the high index cladding/substrate and decay into the low index cladding/substrate, hence work for both guided and leaky modes. Richardson's extrapolation is employed to achieve high-order accuracy by only using simple first-order-polynomial basis functions. Schemes up to sixth-order of accuracy in the effective index are demonstrated. The resulted non-linear sparse matrix eigenvalue equation is solved using an iterative procedure. The ability of the scheme to compute leaky and guided modes of various structures with isotropic and anisotropic materials, step and graded index profiles is demonstrated; including its applications to investigate the properties of ARROW structures.     

Spin-lattice relaxation times and nuclear overhauser enhancement effect for P metabolites in model solutions at two frequencies: Implications for in vivo spectroscopy

The relaxation time T₁ values and nuclear Overhauser enhancement factor for ³¹P signal were determined in model solutions of metabolites ATP, PCr and Pi, and AMP at two frequencies and in H₂O and ²H₂O solutions. The data were analyzed to resolve the contribution of different relaxation mechanisms. A knowledge of NOE is important in the light of recent applications of double resonance methods to enhance the sensitivity of in vivo ³¹P spectroscopy. The results show that chemical shift anisotropy is the dominant mechanism for ³¹P in ATP at the high field, whereas the dipolar interaction mechanism is the main feature for the ³¹P relaxation of PCr and Pi. The dipolar mechanism responsible for NOE originates from interactions of solvent water with ³¹P moiety. Implications for in vivo spectroscopy are indicated.