High Frequency Sound Propagation Research Articles

Investigation of the effect of neglecting reflections in Power-based sound in ducts

In high frequency sound propagation inside ducts, the modal density is very high that the sound starts to propagate in rays. The acoustic performance of a duct network can be simulated using power-based models. The application of such situations is for HVAC systems and large silencers for power generation. Several standards are available for the analysis of HVAC systems using the same technique, such as ASHRAE and VDI. For each element, the flow-generated sound power inside the element is added to the input sound power and the output sound power is calculated by subtracting the Insertion Loss of the element. The attenuated sound energy can be either dissipated inside the element or reflected back to the system. Standards always assume that no energy is reflected and all the attenuation happens inside the element. This assumption is investigated in this paper. Several standard HVAC elements are considered, calculating the amount of energy dissipated inside the element and that reflected back. It was found that if all the reflected energy is considered, this will affect the output power from the system, especially in the highly reflective elements. The investigation was done using the Finite Element Method with the ray tracing technique.

High frequency sound propagation in a network of interconnecting streets

We propose a new model for the propagation of acoustic energy from a time-harmonic point source through a network of interconnecting streets in the high frequency regime, in which the wavelength is small compared to typical macro-lengthscales such as street widths/lengths and building heights. Our model, which is based on geometrical acoustics (ray theory), represents the acoustic power flow from the source along any pathway through the network as the integral of a power density over the launch angle of a ray emanating from the source, and takes into account the key phenomena involved in the propagation, namely energy loss by wall absorption, energy redistribution at junctions, and, in 3D, energy loss to the atmosphere. The model predicts strongly anisotropic decay away from the source, with the power flow decaying exponentially in the number of junctions from the source, except along the axial directions of the network, where the decay is algebraic.

Research on experiments for high frequency sound propagation with rough surface in shallow water

A experiment was carried out to research high frequency underwater sound propagation with rough surface in shallow water. A wave-maker was used to simulate the sine wave surface with different wavelength, amplitude and cycle in a pool (108m×7m×3.5m). The multiple propagation tracks and the multiple reflections at surface and bottom as well as focusing and defocusing due to reflection from surface waves were measured and analyzed. The accuracy and efficient of experiment are verified by the agreement between the numerical simulation and the analysis results of the measured experimental data.

Ultrasound attenuation measurements in the A-like phase of superfluid 3He in aerogel

Liquid 3He impregnated in high porosity aerogel shows many interesting features: significant suppression of superfluid transition and substantial modification of the the A-like to B-like transition. Ultrasound has been found to be a sensitive tool to measure these changes. Recently, the ultrasound attenuation measurements done in the B-like phase provided strong evidence for gapless superfluidity in liquid 3He in aerogel. We conducted high frequency sound propagation measurements at 6.22 MHz in the A-like phase of superfluid 3He induced by magnetic fields up to 4.44 kG. The magnetic field is applied perpendicular to the direction of sound propagation to see the noticeable change in attenuation between the A-like and the B-like phases. We measured the sound attenuation in the A-like phase to be larger than in the B-like phase, and this observation enabled us to identify the A-like to B-like phase transition as a function of magnetic field and pressure.

Critical sound propagation in MnF 2

We analyse the critical sound attenuation in the antiferromagnet MnF2 above its Neel temperature. A general formula for the acoustic self-energy, derived in the model in which a sound mode is coupled to both the order-parameter fluctuations as well as to the energy mode, is applied to interpret the experimental data in MnF2. It has been shown that a very interesting competition between three asymptotic singularities is responsible for the complex behaviour of the sound attenuation coefficient in the high-temperature phase. The relative strength of these terms depends also on the ultrasonic frequency. For high frequency sound propagation also a background attenuation starts playing an important role. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

High-frequency acoustic wave propagation modeling in shallow water

High-frequency sound propagation in a shallow water environment is modeled using a recent version of OASES [H. Schmidt and F. B. Jensen, J. Acoust. Soc. Am. 77, 813–825 (1985)] that has been modified to include poroelastic layers. In shallow water, sound propagation may be strongly influenced by the properties of the bottom. The conditions under which bottom properties become important are identified. Through selected examples, the effects of sediment properties on propagation loss are examined, particularly the differences between elastic and poroelastic approximations of the sediment. Examples of forward reflected and bottom penetrating acoustic pulses are examined. [Work supported by ONR, Code 321 OA.]

High-frequency sound propagation in duct on impedance boundary

High-frequency sound propagation in duct on impedance boundary

High-frequency sound propagation in deep ocean symmetrical duct.

High-frequency sound propagation in deep ocean symmetrical duct.

High-frequency sound propagation in a spatially varying mean flow

An equation for acoustic ray paths in a spatially varying mean flow has been examined to determine some of the characteristics of the flow gradient effects on sound propagation. In a potential flow the acoustic rays are deflected in the direction of increasing mean flow, and the gradient of the mean flow speed is the dominant factor causing the ray deflection. In contrast, in a sheared mean flow, the vorticity is the dominant factor in deflection of the acoustic rays.

Hypersonic sound velocities in aqueous salt solutions

High frequency sound propagation has been studied for aqueous solutions of NaCl, KCl, and KBr at various concentrations and temperatures. We believe the data taken at high temperature are reported for the first time. Our results are consistent with ultrasonic and most of light scattering data whenever available but disagree with findings of Gross et al. By analyzing the various physical processes which may give rise to a sound velocity dispersion, we show that Gross et al. findings are probably due to artifacts.

Brillouin scattering studies of normal and supercooled water

High frequency sound propagation in water has been studied by Brillouin scattering in the entire temperature range of −9°C⩽t⩽100°C. Sound speeds deduced from the data show a peak at t≃70°C in agreement with previous ultrasonic results. Damping constants measured in a temperature range −9°C⩽t⩽20°C are also consistent with the ultrasonic values whenever available. A small negative dispersion of sound velocity is found however in the range 0°C⩽t⩽15°C. We explain this by a simple relaxation model similar to that used by Boon and Fleury in the case of rare gas liquids. We also use a theory of Brillouin scattering which takes into account the temperature fluctuation, and find a small correction term to the expression of the Landau–Placzek ratio. The correction term is calculated and is shown to be nonnegligible for water near 4°C. We believe the data taken in the supercooled regime are reported for the first time and their steep temperature dependence is as yet to be understood theoretically.

Scaling of High-Frequency Sound Propagation near the Ferromagnetic Transition of MnP

Scaling of High-Frequency Sound Propagation near the Ferromagnetic Transition of MnP

High-Frequency Sound Propagation near Magnetic Phase Transitions

The results of ultrasonic attenuation and velocity experiments near the magnetic phase transitions in RbMn${\mathrm{F}}_{3}$ and Mn${\mathrm{F}}_{2}$ are presented. For $Tg{T}_{N}$, the data give additional evidence that the sound couples to the spin-energy-density fluctuations which decay via spin-lattice relaxation. The attenuation results for RbMn${\mathrm{F}}_{3}$ could be fitted with a single relaxation formula for the frequency range 90-930 MHz and for the temperature range of $\ensuremath{\epsilon}[=\frac{(T\ensuremath{-}{T}_{N})}{{T}_{N}}]$ from ${10}^{\ensuremath{-}4}$ to ${10}^{\ensuremath{-}2}$. The spin-lattice relaxation time ${\ensuremath{\tau}}_{L}$ was found to vary from 4\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ to 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}10}$ sec in the same $\ensuremath{\epsilon}$ range. Furthermore, both the critical attenuation and velocity changes are independent of sound-wave propagation direction. In Mn${\mathrm{F}}_{2}$, we found from the critical velocity dispersion a constant relaxation time ${\ensuremath{\tau}}_{L}=(2.7\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}$ sec for $\ensuremath{\epsilon}\ensuremath{\ge}{10}^{\ensuremath{-}3}$, in good agreement with Kawasaki and Ikushima's quoted value. A small divergence was found for smaller $\ensuremath{\epsilon}$. For $Tl{T}_{N}$, it was found that the maxima of the attenuation and the minima of the velocity shifted to lower temperatures with increasing frequency in RbMn${\mathrm{F}}_{3}$. In addition, in RbMn${\mathrm{F}}_{3}$, a second attenuation peak was found below ${T}_{N}$ which shifted to lower temperatures with increasing frequency. This subsidiary attenuation peak was found to be strongly sample dependent. In Mn${\mathrm{F}}_{2}$, broad attenuation maxima and velocity minima are observed in the ordered region. Possible mechanisms for these effects are discussed.