Abstract: We used an optomechanical microphone to measure the acoustic signals emitted by compressed-air jets emanating from apertures as small as ~ 5 um. In keeping with the predictions of aeroacoustic theory, spectra extending into the high-frequency (MHz) ultrasound region were observed. Most of this acoustic energy lies well above the range of a conventional ultrasonic microphone. Conversely, the broadband response of the optomechanical sensor offers the potential to localize and quantify leaks based on a more complete knowledge of the acoustic spectrum. We show that the minimum detectable flow rate, set by the onset of turbulence, scales with the hole size and was as low as ~ 10^-3 Pa·m^3·s^-1 for the smallest holes studied here. The results demonstrate that a sufficiently broadband and sensitive microphone might enhance the utility of ‘acoustic sniffer’ tools for quantitative gas leak detection.

Abstract: Addressing the limitations of restricted coding capacity and material dependency in acoustic identity tags for autonomous underwater vehicles (AUVs), this study intro-duces a novel passive acoustic identification tag (AID) design based on multilayered elastic cylindrical shells. By developing a Normal Mode Series (NMS) analytical model and validating it through finite element method (FEM) simulations, the work elucidates how material layering strategies regulate far-field target strength (TS) and establishes a time-domain multi-peak echo-based encoding framework. Results demonstrate that optimizing material impedance contrasts achieves 99% detection success at a 3dB sig-nal-to-noise ratio. Jaccard similarity analysis of 3,570 material combinations reveals a system-wide average recognition error rate of 0.41%, confirming robust encoding reli-ability. The solution enables combinatorial expansion of coding capacity with structural layers, yielding 210, 840, and 2,520 unique codes for 3-, 4-, and 5-layer configurations, respectively. These findings validate a scalable, hull-integrated acoustic identification system that overcomes material constraints while providing high-capacity encoding for compact AUVs, significantly advancing underwater acoustic tagging technologies through physics-driven design and systematic performance validation.

Abstract: The aim of the Italian Integrated Environmental Research Infrastructures System (ITINERIS) project is to establish the Italian Hub of Research Infrastructures within the environmental scientific domain. ITINERIS seeks to facilitate the observation and investigation of environmental processes across the atmosphere, marine domain, terrestrial biosphere, and geosphere. The project also endeavors to promote sustainable, cross-disciplinary research by leveraging existing data and services, emphasizing accessibility for users. The cornerstone of this initiative is the creation of the ITINERIS HUB, designed to provide users with seamless access to data and services. Notably, ITINERIS opts for the optimization and harmonization of existing data centers rather than creating new ones. The project will fortify these centers through various activities, with a particular focus on enhancing the Findable, Accessible, Interoperable, and Reusable paradigm across all participating entities. This contribution highlights the role of Laboratori Nazionali del Sud of Istituto Nazionale di Fisica Nucleare in the project. LNS is leading the Italian Ocean Sound sub-system in the contest of the marine domain of ITINERIS. An overview on the acoustic data acquisition chain and storage will be reported, with a particular insight into the use of high-sensitivity and large band-width hydrophones installed on the mooring station of LNS for real-time and long-term data capture. Hydrophones’ data are continuously transmitted to shore and analyzed. A selection of raw data and sound pressure levels in third-octave bands are calculated and stored to study the soundscape at the site.

Abstract:

In this paper, we developed our own software that can analyze piano performance by utilizing short-time Fourier transform, non-negative matrix decomposition, and root mean square. In addition, for the reliability of the developed software, we provided results reflecting the characteristics of various performers and signal analysis. In conclusion, it shows the possibility that musical flow and waveform analysis can be visually interpreted in various ways. Based on this, we were also able to derive an additional approach suitable for designing the system to seamlessly connect hearing and vision.

Abstract:

Introducing vegetation is an effective strategy for improving air quality and mitigating the heat island effect. Green façades, which consist of modules that support substrates and various plant species, integrate these elements. This study analyzes the acoustic absorption properties of a specific green wall module using an impedance gun and the Scan and Paint method for laboratory and on-site measurements. The impedance gun method is effective for in-situ analysis, offering advantages over standardized techniques for inhomogeneous samples. We measured the sound absorption coefficient of the substrate and the effects of different plant species. Key findings reveal that the substrate primarily influences sound absorption, with its coefficient increasing with frequency, similar to porous materials Vegetation enhances acoustic absorption of the substrate, depending on coverage and thickness, with 80-90% of absorption attributed to the substrate and 4-20% to vegetation. However, not all dense plant species improve absorption; some configurations may decrease it. Improvement correlates with substrate coverage and vegetation layer thickness, while the impact of plant morphology remains unclear. These findings confirm vegetation's potential as an acoustic absorption tool in urban settings. Additionally, green walls can enhance acoustic comfort in indoor environments such as offices and schools by reducing reverberation. They also improve air quality and provide aesthetic appeal, making them a multifunctional solution for modern architecture.

Abstract: We do not know how the earliest musical instruments -such as idiophones and aerophones- were played, but their acoustic properties can provide valuable clues. As a first step, we present here dissonance curves for a sound of a given spectrum. These curves show the relative dissonance that results for all intervals of a given instrument. This then leads to the association of spectra and scales, which are related because the dissonance curve has minima in the intervals that define the scale. A computational method for calculating dissonance curves is presented and several examples of its use in practical cases, both for Western and Eastern musical instruments, are given and interpreted. These results allow us to explain from a physical point of view the existence of well-known modern twelve note scales, as well as some uncommon but documented scales for various instruments in early musical history.

Abstract: This study presents a novel approach to remote speech recognition using a millimeter- 7wave micro-Doppler radar system operating at 94 GHz. The proposed method uses high-frequency 8radar to detect subtle speech-related vibrations, enabling speech recognition that is both non-contact 9and privacy-preserving. Tests with actual human speech followed initial experiments in which a 10piezoelectric crystal was used to simulate vocal cord vibrations. Radar returns were processed using 11state-of-the-art signal processing techniques, including short-time Fourier transform (STFT), to 12generate spectrograms and reconstruct speech signals. The system demonstrated high accuracy in 13speech reconstruction, with a strong correlation between the radar-reconstructed audio and the 14original speech signals. Cross-correlation analysis quantitatively confirmed the similarity between 15the reconstructed and original audio. These results validate the system's effectiveness in detecting 16and characterizing speech-related vibrations without direct audio recording. The findings support 17this innovative approach, with significant implications for applications in security, surveillance, and 18assistive technologies where privacy-preserving solutions are essential. Future research will focus 19on diverse real-world scenarios and further integration of advanced signal processing and machine 20learning techniques to enhance accuracy and robustness.

Abstract: A simple pore microstructure of parallel, identical, inclined smooth walled slits in a rigid solid, for which prediction of its geometrical and acoustic properties is straightforward, can yield useful sound absorption. This microstructure should be relatively amenable to 3D printing. Discrepancies between measurements and predictions of normal incidence sound absorption spectra of 3D printed vertical and slanted slit pore samples have been attributed to the rough surfaces of the slit walls and uneven slit cross sections perpendicular to the printing direction. Theories for the influence of (a) sinusoidal walls and (b) periodically varying uniform slit widths on the normal incidence absorption spectra of a slit pore medium are outlined. Although the slit wall surface and geometrical imperfections due to 3D printing differ from these idealizations, predictions assuming the ideal forms of roughness confirm that pore wall roughness could account for differences between predictions and data. Pore wall roughness is predicted to increase both flow resistivity and tortuosity thereby increasing the low frequency sound absorption of thin hard-backed layers. The extent to which sinusoidal slit walls or periodically varying uniform slit widths could improve sound absorption is explored.

Abstract: In this paper we demonstrate that torsional surface elastic waves can propagate along the curved surface of a metamaterial elastic rod (cylinder) embedded in a conventional elastic medium. The crucial parameter of the metamaterial rod is its elastic compliance which varies as a function of frequency analogously to the dielectric function in Drude's model of metals. In fact, the proposed torsional elastic surface waves can be considered as an elastic analogue of Surface Plasmon Polariton (SPP) electromagnetic (optical) waves propagating along a metallic rod (cylinder) embedded in a dielectric medium. Consequently, we developed the corresponding analytical equations, for the dispersion relation and group velocity of the new torsional elastic surface wave. The newly discovered torsional elastic surface waves exhibit virtually all extraordinary properties of their electromagnetic SPP counterparts, such as: strong subwavelength concentration of the wave energy in the vicinity of the cylindrical surface ) of the guiding rod, very low phase and group velocities, etc. Therefore, the new torsional elastic surface waves can be used in: a) near-field subwavelength acoustic imaging (superresolution), b) amplification of the evanescent waves c) acoustic wave trapping (zero group and phase velocity). Importantly, the newly discovered torsional elastic surface waves can form a basis for the development of a new generation of ultrasonic sensors (e.g., viscosity sensors), biosensors and chemosensors with a very high mass sensitivity.

Abstract: The capabilities of Physics-Informed Neural Networks (PINNs) to solve the Helmholtz equation in a simplified three-dimensional room are investigated. From a simulation point of view, it is interesting since room acoustic simulations often lack information from the applied absorbing material in the low-frequency range. This study extends previous findings toward modeling the 3D sound field with PINNs in an excitation case using DeepXDE with the backend PyTorch. The neural network is memory-efficiently optimized by mini-batch stochastic gradient descent with periodic resampling after 100 iterations. A detailed hyperparameter study is conducted regarding the network shape, activation functions, and deep learning backends (PyTorch, TensorFlow 1, TensorFlow 2). We address the computational challenges of realistic sound excitation in a confined area. The accuracy of the PINN results is assessed by a Finite Element Method (FEM) solution computed with openCFS. For distributed sources, it was shown that the PINNs converge to the solution, with deviations occurring in the range of a relative error of 0.28%. With feature engineering and including the dispersion relation of the wave into the neural network input via transformation, the trainable parameters were reduced to a fraction (around 5%) compared to the standard PINN formulation while yielding a higher accuracy of 1.54% compared to 1.99%.

Abstract: Forensic speaker recognition plays a key role in criminal investigations, providing important conclusions for the justice system. The mandatory use of protection masks during the COVID-19 pandemic has posed a challenge for forensic speaker recognition, as they act as voice barriers or filters. Although the pandemic has been declared over, analyzing their impact in forensic speaker recognition contributes to a better understanding of the use of coverings as a voice disguise technique. This study aims to evaluate the impact of two types of face masks on an automatic forensic speech recognition system. For this purpose, the Multilingual Forensic Voice Database (FMVD), developed under the CERTAIN-FORS project, funded by the European Union, was used. Comparisons were made between dialog speech samples and reading samples collected without a mask, with a surgical mask, and with an FFP2 mask for both sexes in eight different languages. The performance metrics equal error rate (EER) and cost of likelihood ratio (Cllr) were calculated and analyzed. The results show that the presence of face masks has an impact on the performance metrics. The effect observed varies according to the language spoken, the gender of the speaker, and the type of mask.

Abstract: Diabetes mellitus is a prevalent disease with a rapidly increasing incidence projected worldwide, affecting both industrialized and developing regions. Effective diabetes management requires precise therapeutic strategies, primarily through self-monitoring of blood glucose levels to achieve tight glycemic control, thereby mitigating the risk of severe complications. In recent years, there have been significant advancements in non-invasive techniques for measuring blood glucose using photoacoustic spectroscopy (PAS) as it shows great promise for the detection of glucose using the Infrared region (e.g. MIR & NIR) of light. A critical aspect of this method is the detection of the photoacoustic signal generated from blood glucose, which needs to be amplified through a photoacoustic resonator (PAR). In this work, an overview of various types of PARs used for noninvasive glucose sensing is reviewed, highlighting their operating principle, design requirements, limitations, and potential improvements needed to enhance the analysis of photoacoustic signals. This analysis will be helpful for the basic understanding and achieving the highly sensitive PAR required for noninvasive glucose monitoring.

Abstract: Cellulose-based materials are now commonly used, including in the field of acoustic comfort. Often presented as a less environmentally impactful alternative to traditional acoustic absorbents (such as melamine, glass wool, etc.), these cellulose-based materials are more frequently derived from recycling, thus undergoing in most cases the technical process allowing these cellulose fibers to be obtained, thus inheriting the acoustic properties of the latter, with limited or even non-existent control. This paper proposes a manufacturing process that allows for the production of cellulose foam with precise control over its porosity, pore size, and interconnections. In addition to exhibiting remarkable sound absorption properties, this process also enables the fabrication of gradient porous structures and other hybrid materials that can result in remarkable sound absorption properties.

Abstract: Recent publications on acoustic MEMS transducers present a new three-dimensional folded diaphragm that utilizes buried in-plane vibrating structures to increase the active area from a small chip volume. Characterization of the mechanical properties plays a key role in the development of new MEMS transducers, whereby established measurement methods are usually tailored to structures close to the sample surface. In order to access the lateral vibrations, extensive and destructive sample preparation is required. This work presents a new passive measurement technique that combines acoustic transmission measurements and Lumped-element modelling. For diaphragms of different lengths, compliances between 0.08 ∙ 10-15 and 1.04 ∙ 10-15 m³/Pa are determined without using destructive or complex preparations. In particular, for lengths above 1000 µm, the results differ from numerical simulations only by 4% or less.

Abstract: Piezoelectric c-axis oriented zinc oxide (ZnO) thin films, from 1.8 up to 6.6 µm thick, have been grown by radio frequency magnetron sputtering technique onto fused silica substrates. A delay line consisting in two interdigital transducers (IDTs) with wavelength λ = 80 µm was photolith-ographically implemented onto the surface of the ZnO layers. Due to the IDTs split finger con-figuration and metallization ratio (0.5), the propagation of both the fundamental, third and nineth harmonic Rayleigh waves is excited; also, three leaky surface acoustic waves (SAWs) were detected travelling at velocity close to that of the longitudinal bulk wave in SiO2. The acoustic waves propagation in ZnO/fused silica was simulated by using 2D finite-element method (FEM) tech-nique to identify the nature of the experimentally detected waves. It turned out that, in addition to the fundamental and harmonic Rayleigh waves, also high-frequency leaky surface waves are ex-cited by the harmonic wavelengths; such modes are identified as leaky-Sezawa (LS) waves under cut-off. The velocity of all the modes was found in good agreement with the theoretically calcu-lated values. The existence of a low-loss region for the Sezawa wave below the cut off was theo-retically predicted and experimentally assessed.

Abstract: The use of tuning forks to measure fluid density and viscosity is widely employed in fields such as food, medicine, textiles, automobiles, petrochemicals, and deep drilling. The explicit analytical model based on Euler-Bernoulli cantilever beam theory for the relationship between tuning fork resonance characteristics and the density and viscosity of fluid is only applicable to the situation where the fluid viscous effect is very small. In this paper, the finite element method is used to simulate the influence of large variations in fluid density and viscosity on the resonance characteristic parameters (resonant frequency and quality factor) of the tuning fork. The numerical simulation results are compared with the analytical analysis results and experimental measurement results. Then, the sensitivity of tuning fork resonance characteristic parameters to fluid density and viscosity is studied. The results show that compared with the analytical results, the numerical simulation results have a higher degree of agreement with the experimental measurement results. The relative difference in resonant frequency is less than 2%, and the relative difference in quality factor is less than 4%. This indicates that the finite element method includes the influence of fluid viscosity on tuning fork resonance parameters, which is more in line with the actual conditions than the analytical model. Simulating and analyzing the sensitivity of the tuning fork to fluid density and viscosity by the finite element method, it is possible to consider the situation where fluid density and viscosity vary over a large range. Compared with experimental measurements, this method has higher efficiency and can significantly save time and economic costs. This study can overcome the limitation of existing explicit analytical models, which are only applicable when the viscous effects of the fluid are very small. It enables a more accurate simulation of the coupling vibration between tuning forks and fluids, thereby providing theoretical references for further optimizing tuning fork structural parameters to enhance the accuracy of measuring fluid characteristic parameters.

Abstract: The penetrability and directivity of ultrasound in different media is of interest in engineering and medical applications (imaging, nondestructive testing, sonochemistry, among others). The nonlinearity of a liquid can be used in the parametric antenna framework to generate low-frequency components with particular features from several ultrasonic signals at the source. Bubbly liquids are dispersive liquids in which a small amount of tiny gas bubbles leads to the increase of the nonlinear parameter of the media over certain frequency ranges. Parametric antenna applied to this huge nonlinear media gives rise to low-frequency components with relatively small intensity at the source. The evolution of a low-frequency component (difference-frequency component obtained from two primary signals) during its propagation in a bubbly liquid is somehow unknown. It is thus interesting to analyse its characteristics to establish whether this component can benefit from the quality of its own frequency and from the primary frequencies in terms of directivity and penetrability into the medium. It must be noted that no such study in bubbly liquids exists in the litterature, but only for homogeneous media. To this end, several numerical models developed previously are used here to analyse the difference-frequency component obtained from a parametric antenna emitting from two ultrasonic signals at the source in one and two-dimensional domains. These models allow us to observe the behavior of this frequency component. An angle that measures the directivity of a beam is also defined. Our results show a point hardly found in the literature: the high directivity and the huge penetrability of the secondary beam associated to the difference-frequency component into the bubbly liquid, compared to the same frequency signal excited directly from the source in the bubbly liquid and to the parametric acoustic array in homogeneous fluids.

Abstract: A labyrinth metamaterial wall with glass coverage is measured in a reverberating chamber and after its installation in a restaurant. Glass is used to meet two aims, namely acoustic absorption and visual design demands. The wall consists of five multiple labyrinth elements of 1.83 m$^2$ each. Glass was taken to make the wall act as a room lightning device where a translucent cover material is needed. Absorption measurements show about four times improved absorption compared to typical glass. Due to the metamaterial behavior, absorption is high in the low-frequency range below 300 Hz where damping is problematic with traditional materials. Especially in this range, the glass metamaterial wall is an excellent compromise between room acoustic and visual design demands, as loud low-frequencies make visitors speak louder and experience less intimacy with additionally reduced speech intelligibility. For mid-frequencies, absorption is shown less effective and improvements are discussed.

Abstract: Different types of resonators are used to create acoustic metameterials and metasurfaces. Recent studies focused on the use of multiple resonators of dipole, quadrupole, octupole and even hexadecapole types. This paper considers the theory of an acoustic metasurface, which is a flat surface with a periodic arrangement of multiple resonators. The sound field reflected by the metasurface is determined. If the distance between the resonators is less than a half the wavelength of the incident plane wave, the far field can be described by a reflection coefficient that depends on the angle of incidence. This allows to characterize the acoustic properties of the metasurface by a homogenized boundary condition, which is a high order tangential impedance boundary condition. The tangential impedance depending on the multiple order of the resonators is introduced. In addition, we analyze sound absorption properties of these metasurfaces, which are a critical factor in determining their performance. The paper presents a theoretical model that accounts for the multiple orders of resonators and their impact on sound absorption. The maximum absorption coefficient for a diffuse sound field, as well as the optimal value for the homogenized impedance, are calculated for arbitrary multipole orders.

Abstract: Traversal time in tunneling effect for ultrasonic waves in tapered waveguides is derived considering its analogy with quantum and electromagnetic waves tunneling. If, as traversal time, the so called phase time is considered, the ultrasonic wavepacket shows the equivalent in acoustics of superluminality i.e. the derived velocity , crosses the limit of bulk transverse ultrasonic waves in the medium of the waveguide that is the equivalent of c in the quantum and electromagnetic cases. Graphs clearly illustrating this so called Hartman effect are obtained confirming the experimental results in the three different fields.