Acoustics Australia最新文献

The Sarasvati Veena is an Indian stringed musical instrument with a curved bridge having a parabolic equation. We study the effect of such a bridge on the timbre of the instrument. We model the interaction of the vibrating string with the bridge as frictionless impact. So we implemented an energy-conserving method where string–bridge interaction is modelled with a penalty approach. We solve the resulting Hamilton’s equations numerically. Simulations are performed with different values of bridge parameters, namely slope and curvature. The numerical model is validated by comparison with experimental analysis. We isolate the contribution of the bridge by mounting it on the sonometer in place of one of its knife-edges and a mechanism is provided on the sonometer to change the bridge slope. We mounted the sonometer on foam to minimize the effect of other structural parameters. The typical Veena timbre shows sustain of most harmonics and the revival of higher harmonics with time. These features are attributed to the shape of the metallic layer at the top of the Veena bridge, its slope and curvature. Our model also shows these features, which are further corroborated by the experiment.

Most of the continental shelf area is a weakly range-dependent shallow-water environment. Compared with range-independent Bayesian geoacoustic inversion, range-dependent inversion usually has problems with the complex forward model and low efficiency for posterior analysis. According to the adiabatic normal-mode theory, the weakly range-dependent shallow-water environment can be divided into a series of range-independent segments; thus, this paper proposes a dual-source modal dispersion inversion method for local geoacoustic parameters of a segment based on a range-independent forward model. In addition, considering that the computational cost of the forward model limits the application of sampling-based methods for posterior analysis, a novel approximate variational inference, namely variational Bayesian Monte Carlo, is applied in this study. It has superior efficiency and shows similar accuracy compared with Markov Chain Monte Carlo sampling. This work is demonstrated in the shallow-water experiment in the continental shelf area of the East China Sea, and the results indicate that the local and range-dependent geoacoustic parameters are well-estimated.

The biosonar system of bats utilizes physical baffle shapes around the sites of ultrasound reception for diffraction-based amplitude modulation. Bat antitragus has been hypothesized to affect the bat biosonar. Using numerical methods, we show that the antitragus of a Chinese horseshoe bat has an effect on increasing the acoustic near field as well as enhancing the reflection coefficient of the external ear. The simulation result provides a direct link between the biosonar signal and the morphological structure. The underlying physical mechanism suggested by the properties of the effect is that standing waves are produced between the pinna and antitragus.

This study proposes a general half-analytical method to predict the sound absorption of multiple inhomogeneous resonators inspired by Sellers’ method with small calculation cost. In this method, the sound absorption coefficient of single units is calculated by the finite element method (FEM), and superposition is used to predict the sound absorption coefficient of the overall structure. Unlike existing fully analytical methods that have difficulties with complicated or novel constructions, we combine FEM and the analytical method called the half-analytical method (HAE), which predicts sound absorption performance with excellent results. Two example structures are tested and the absorption coefficients from the analytical method, FEM, present method, and experiment show excellent agreement. The novel HAE method is promising to accurately predict the sound absorption coefficient of multiple inhomogeneous structures.

In this work, ceramsite was utilized to fabricate the sound-absorbing boards, in which two types of structure were considered, specifically, single-layer board with homogenous structure and double-layer board with gradient structure. The physical, mechanical and acoustic properties of these prepared ceramsite sound absorbing boards were studied, including the bulk density, compressive strength, flexural strength, softening coefficient, sound absorption coefficient and sound reduction index. The results show that the double-layer board with appropriatemixture designexhibited almost identical bulk density and mechanical strength to the single-layer board. All ceramsite sound absorbing boards had compressive and flexural strengths of more than 3 MPa and 1 MPa, respectively, and also demonstrated good water resistance. In terms of sound absorption and sound insulation properties, the overall performance of the double-layer board with reasonable gradient structure was better than that of the single-layer board. In addition, the physical structure models of ceramsite sound absorbing boards were established to illustrate the variation of mechanical properties and disclose the mechanism of sound absorption and insulation in the material.

Sound as a ubiquitous energy in our surroundings is clean and sustainable, and carries abundant information in a wide frequency bandwidth. However, effectively harvesting and utilizing acoustic energy is still hindered by the limitations such as low energy density of acoustic energy and lack of novel application. In this paper, we successfully present a self-powered acoustic sensor, which is composed of an adjustable spacing structure and sound-driven triboelectric nanogenerator (TENG). The acoustic sensor exhibits excellent electric output properties because of the poriferous electrode structure, ultrathin vibrating membrane as well as high-quality triboelectric materials. The sensor can deliver a maximal output voltage of 6.28 V with the sound frequency of 350 Hz and sound pressure of 110 dB. In addition, the electric output frequency is closely related to the applied acoustic wave and the corresponding directional dependence pattern as a butterfly is highly symmetrical. Our approach presents a cost-effective strategy to develop self-powered acoustic sensor and shows great potentials in home automation, self-powered microphone, sensor network and artificial intelligence.

Dolphins have a diverse acoustic communication system which includes whistles necessary for their survival. Whistle variation in dolphins could be related to the group behaviour, group size, formation and also environmental factors such as water depth, tidal phases and location. Such information is relatively unknown for the dolphin populations in Malaysia. This study aims to understand the whistle variation in Indo-Pacific humpback dolphins found in two sites in northwestern Peninsular Malaysia and possible factors that influence their whistles. A total of 4971 whistles were detected with whistle rates and parameters analysed. A GLMM analysis showed that whistle rates in both sites and in differing group sizes had significant differences. Only the mean whistle frequency significantly differed in differing group formations. Indo-Pacific humpback dolphins in a loose and uniform group had a lower mean frequency compared to other group formations. Other parameters such as the whistle duration and coefficient of frequency modulation did not show significant differences in differing behaviour, size, formation, water depth, tidal phases and location. This study is important and particularly valuable for understanding the species’ bioacoustics in the wider region of Southeast Asia.

Acoustic coatings with periodically arranged internal cavities have been widely applied to underwater vessels to reduce the underwater sound scattering. In this study, the simulation results from the finite element method (FEM) have been compared with the theoretical solutions based on the transfer matrix theory (TMT), and the reliability of the FEM has been verified. The Nelder-Mead algorithm has been employed to optimize the structure of the coatings and the material parameters with the sound absorption coefficient as the primary optimization objective. A function that characterizes the shape of a two-dimensional axisymmetric cavity has been proposed, and the peak value of the absorption coefficient can be successfully moved to the target frequency by changing the weighting strategy. The results show that the sound absorption coefficient of the optimized coating increases and the peak shape widens in the middle and low frequency band. The optimized axisymmetric cavity significantly improves the sound absorption performance of the anechoic coatings. The optimization algorithm of the cavity structure and material parameters proposed in this study provide an effective pathway for the optimal design of the anechoic coatings.

Ultrasonic probes for high-temperature applications are provided with metallic wedges, which can withstand the contact with the high temperature of the inspected structure. The ultrasonic signal travels within the wedge and gets reflected from its boundaries, causing interference signals called “ghost echoes”. The current work presents an investigation of the additional damping effect provided by porous sintered metal plates applied onto the surface of the wedge. In particular, the study evaluates the effect of damping plate thickness on the interference signal level at different transmission frequencies. Damping plates made of sintered metal SIKA-R 15 AX were attached to a wedge prototype made of steel 1.4301. The study revealed, that the most effective thickness of damping plates in the selected frequency interval of 1 to 4 MHz is equal to 4 mm. The evaluation of the interference signal has shown that the application of such damping plates to the wedge surface contributes to an additional attenuation of an interference signal of 10 to 30 dB after 500 µs of signal propagation.