Journal of the Acoustical Society of America最新文献

With the combination of two critical features from Cummer-Schurig, acoustic cloaking and the scattering cancellation technique, this study reports a hybrid design for the cloaking of elastic cylinders using alternating layered fluids (the effective density to be anisotropic), which are achieved by alternately immersing HGM (a syntactic foam, light solid material with high sound velocity) and Pb (lead, a heavy solid material) in the background fluid medium. The cloaking performance of the proposed design is investigated both by the numerical simulation and by experimental measurement. For a lead cylinder of radius 50 mm, the measured visibility reduction below -5 dB is obtained in the frequency range from 18 kHz to 23 kHz. Compared with the scattering cancellation by the thin elastic shell, the proposed cloaking can be obtained at shorter wavelengths due to the suppression of more higher-order scattering. In addition, the performance of cloaking has no dependence on the incident angles, which has an advantage over the scattering cancellation using scatters distributed unevenly. This is the first experiment using layered fluids to obtain the cloaking of an elastic cylinder, which has potential application in underwater acoustic stealth.

Directional communication plays a pivotal role in enabling odontocetes to maintain group coordination and social interactions. The fundamental frequency, number of harmonics, and their relative energy distribution in whistles exhibit temporal variation. This study investigated the whistles produced by the Indo-Pacific humpback dolphins (Sousa chinensis) in Xiamen Bay, China. Using computed tomography scanning data, we developed a numerical model of the species and used finite element modeling to examine the beam patterns at both fundamental and harmonic frequencies of whistles, ranging from 3.9 to 64.9 kHz, which corresponds to directivity indices (DIs) between 2.2 and 16.2 dB. We weighted the beams at the fundamental frequencies and harmonics based on their energy distribution to derive composite beam patterns at specific time stamps, allowing us to investigate temporal variations in the corresponding DI within individual whistles. The time-varying properties of DIs were analyzed for various whistle types, including constant, upsweep, downsweep, convex, and sine. Given that harmonics are integer multiples of the fundamental frequency, their contours exhibit similar shapes, whereas the composite DI showed more complexity. These findings indicate that the proportion of energy between the fundamental frequency and harmonics is a key determinant of whistle directivity in Indo-Pacific humpback dolphins.

Personal-sound-zones (PSZ) techniques deliver independent sounds to multiple zones within a room using a loudspeaker array. The target signal for each zone is clearly audible within that zone while inaudible or non-distracting in others, assured by applying pre-filters to the loudspeaker array. The pre-filters are traditionally designed with time-domain or frequency-domain methods, which suffer from high computational complexity and large system latency, respectively. This work proposes a subband pressure-matching method in the short-time Fourier transform domain using the convolutive transfer function approximation, termed CTF-PM. The proposed method considerably reduces computational complexity relative to time-domain methods and existing subband methods, while maintaining low system latency. Additionally, CTF-PM achieves similar performances in acoustic contrast and normalized mean square error compared to baseline methods. Moreover, by introducing a weighting vector on the reproduction error, a relaxed-reverberation framework is incorporated into CTF-PM. This framework aims for an accurate reproduction of the decaying rate instead of the random samples of the reverberations, improving the acoustic contrast of the PSZ system while preserving the perceptual experience. Our experiments demonstrated that the relaxed-reverberation framework improved broadband acoustic contrast in the 0-2 kHz range by more than 3 dB, without degrading the perceptual experience.

Parametric array loudspeakers (PALs) produce highly directional sounds due to the parametric process in air. Its application in creating personal audio zones requires simple modeling of the audible sound field near the PAL, which is crucial for subsequent designs to reduce inherent nonlinear distortion. However, current accurate methods for describing the sound field, reliant on numerical solutions to wave equations, are computationally intensive. To achieve both effectiveness and simplicity, this paper proposes a time-domain model for audible sounds generated in the Westervelt far field, called the differential Volterra filter (Diff-VF). It is obtained through two stages: first, a narrow-band (NB) approximation is introduced to decouple the virtual source energy density from interactions of ultrasonic beams when solving the Westervelt equation. This results in a NB Westervelt solution for time-domain inputs. Second, to further develop a generic response independent of inputs, a temporal-spatial discretization is used to simplify the NB Westervelt solution into the Diff-VF model with a one-dimensional kernel. Numerical simulations confirmed the effectiveness of the NB Westervelt solution when compared with an exact solution, whether on- and off-axis. Experimental results validated that the Diff-VF model achieved superior prediction performance over existing VF-based models, with insensitivity to inputs and lower complexity.

Ultrasound shear wave elastography can be useful for assessing muscle pathology. The effect of anisotropy on shear wave elasticity estimates of skeletal muscle has been reported previously. However, muscle is inherently viscoelastic, and hence, tissue viscosity is also an important material parameter to assess. The goal of this study was to systematically quantify the effect of fiber pennation angle on shear wave viscoelasticity imaging estimates. Numerical phantom simulations of skeletal muscle-mimicking phantoms were analyzed. Anisotropic polyvinyl alcohol phantoms embedded with polysulfone fibers were developed to mimic the viscoelasticity and appearance of muscle in B-mode images. Shear wave dispersion analysis, assuming a Kelvin-Voigt model, was performed to estimate the shear modulus and viscosity of the phantoms along the fibers (in-plane) and across the fibers (cross-plane) with varying pennation angles (0°-30°). A decreasing trend was observed in shear modulus estimates with increasing fiber pennation angle in the in-plane orientation for all phantoms. Notably, simulations showed that viscosity estimates decreased with increasing angle. These results provide a systematic quantification of the effect of fiber pennation angle on viscoelastic estimates under controlled conditions, which will be useful for assessing the performance of shear wave viscoelasticity imaging approaches for muscle assessment.

Rotor broadband noise is typically analyzed over time scales encompassing multiple rotor periods. However, modulation of broadband noise levels with the blade passage frequency has been shown to be significant for human perception of wind turbine and helicopter noise. In contrast, broadband noise modulation has not been extensively studied for aircraft with many rotors, such as unmanned aerial vehicles (UAVs) or advanced air mobility aircraft. In this work, significant broadband noise modulation was measured in flight tests and anechoic chamber experiments of hexacopter UAVs. The amplitude of this modulation depended on the azimuthal phase offsets between rotors, demonstrating the potential for synchrophasing control to reduce broadband noise modulation, analogous to synchrophasing control of tonal noise. If rotors are not synchronized, as in typical flight, the azimuthal phase offsets between rotors vary with time. This variation was found to follow a uniform random distribution, resulting in modulation depth also varying randomly with time. The probability distribution of modulation depth was computed using offset copies of the modulation of a single rotor. These results contribute understanding to how the broadband noise modulation of rotors sum together, and showed that this modulation is likely to be significant in flight.

This report extends the development of normative standards for estimating occupational hearing loss using data from the United States National Health and Nutrition Examination Survey (NHANES) conducted by the National Center for Health Statistics. A proposed revision of the International Organization for Standardization (ISO) 1999:2013 standard ("Acoustics-Estimation on noise-induced hearing loss") uses a linear interpolation of hearing threshold data to estimate the 25th and 75th percentiles for men and women at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz. This paper revisits the NHANES data to provide these estimates, avoiding other types of interpolations that could misrepresent the population data.

In this paper, an approach for effectively reducing nonlinear distortion in single-backplate condenser microphones is introduced, i.e., most microelectromechanical systems (MEMS) microphones, studio recording condenser microphones, and laboratory measurement microphones. This simple post-processing technique can be easily integrated on external hardware such as an analog circuit, microcontroller, audio codec, digital signal processing unit, or within the Application Specific Integrated Circuit chip in a case of MEMS microphones. It effectively reduces microphone distortion across its frequency and dynamic range, and relies on a single parameter, which can be derived from either the microphone's physical parameters or a straightforward measurement presented in this paper. An optimal estimate of this parameter achieves the best distortion reduction, whereas overestimating it never increases distortion beyond the original level. The technique was tested on a MEMS microphone. The findings indicate that for harmonic excitation, the proposed technique reduces the second harmonic by approximately 40 dB, leading to an effective reduction in the total harmonic distortion. The efficiency of the distortion reduction technique for more complex signals is demonstrated through two-tone and multitone experiments, where second-order intermodulation products are reduced by at least 20 dB.

Underwater sound propagation can be influenced by strong sound speed gradients generated by nonlinear internal gravity waves (NIWs). Additionally, the seafloor slope plays a crucial role in controlling the direction of acoustic reflections. Experimental data collected at a shelfbreak in the northeastern area of the South China Sea were analyzed to investigate the joint acoustic effects of these two environmental factors. Both two-dimensional (2D) and three-dimensional (3D) numerical sound propagation models were employed to study the observed acoustic signal variations on a hydrophone vertical line array. Comparisons between 2D and 3D sound propagation were conducted to examine changes in ray tracing paths and transmission loss associated with approaching NIWs over the sloping seafloor. 3D sound ducting between the NIW front and the bottom slope was observed to cause a significant increase in acoustic intensity, up to 9.5 dB, over a propagation distance of 4.8 km.

A parametric array loudspeaker (PAL) generates a highly directional audible sound beam. However, indoor scattering and reflecting effects diminish its advantage of high directivity, causing the scattered or reflected sound to appear in undesired regions. Deriving from the Westervelt equation, the nonlinear coupling exists between each channel, rendering linear sound field control algorithms ineffective. This paper proposes a framework of nonlinear sound field control, enabling the manipulation of nonlinear sound fields generated by the PAL in complicated acoustic environments. Besides, PAL often faces challenges in radiation efficiency due to the poor conversion efficiency of nonlinear sound. Therefore, a sound control algorithm suitable for PAL is proposed, which maximizes radiation efficiency while ensuring acoustic contrast through a two-stage non-convex optimization procedure. The simulations and experimental results verify the effectiveness of the proposed framework and algorithm of nonlinear sound field control. The undesired audible sound in the dark zone is suppressed while maintaining the desired audible sound in the bright zone. This enhances the performance of a PAL in real scenarios with existing scattering or reflecting effects.