Does Atmospheric Corrosion Alter the Sound Quality of the Bronze Used for Manufacturing Bells?

Bells are made of bronze, an alloy of copper and tin. Art objects and musical instruments belong to tangible and intangible heritage. The effect of atmospheric alteration on their sound is not well documented.

Maximum directivity of flanged open-ended waveguides.

Directional beams have extensive applications in communication and sound reproduction. This paper investigates the theoretical maximum directivity of infinitely flanged open-ended waveguides and the radiation pattern synthesis. We derive a rigorous solution for the maximum directivity factor of a flanged aperture with arbitrary shape by projecting its surface velocity on the waveguide modes, enabling the creation of a directional beam in any desired direction.

Frozen sound: An ultra-low frequency and ultra-broadband non-reciprocal acoustic absorber.

The absorption of airborne sound is still a subject of active research, and even more since the emergence of acoustic metamaterials. Although being subwavelength, the screen barriers developed so far cannot absorb more than 50% of an incident wave at very low frequencies (<100 Hz). Here, we explore the design of a subwavelength and broadband absorbing screen based on thermoacoustic energy conversion.

Modulation instability in nonlinear flexible mechanical metamaterials.

In this paper, we study modulation instabilities (MI) in a one-dimensional chain configuration of a flexible mechanical metamaterial (flexMM). Using the lumped element approach, flexMMs can be modeled by a coupled system of discrete equations for the longitudinal displacements and rotations of the rigid mass units. In the long wavelength regime, and applying the multiple-scales method we derive an effective nonlinear Schrödinger equation for slowly varying envelope rotational waves.

Pedagogically treating topics as having several ways to be addressed: Harmonically varying states of free-edge circular plates.

The paper is mainly concerned with the training of students by treating exercises as having several ways to be addressed. The topic considered herein focuses on the vibrations of a free edge axisymmetric homogeneous circular thin plate excited by a time-periodic source. This topic is prepared using the three analytic methods available (but these are not fully used analytically in the literature) to show the different aspects of the problem: modal expansion, integral formulation, and exact general solution, against which the other models are tested.

Damage Localization on Composite Structures Based on the Delay-and-Sum Algorithm Using Simulation and Experimental Methods.

Damage detection and localization based on ultrasonic guided waves revealed to be promising for structural health monitoring and nondestructive testing. However, the use of a piezoelectric sensor's network to locate and image damaged areas in composite structures requires a number of precautions including the consideration of anisotropy and baseline signals. The lack of information related to these two parameters drastically deteriorates the imaging performance of numerous signal processing methods.

Distortion-product otoacoustic emissions measured using synchronized swept-sines.

Swept-sines provide a tool for fast and high-resolution measurement of evoked otoacoustic emissions. During the measurement, a response to swept-sine(s) is recorded by a probe placed in the ear canal. Otoacoustic emissions can then be extracted by various techniques, e.

Towards quantifying the effect of pump wave amplitude on cracks in the Nonlinear Coda Wave Interferometry method.

In Non-Destructive Testing and Evaluation (NDT&E), an ultrasonic method called Nonlinear Coda Wave Interferometry (NCWI) has recently been developed to detect cracks in heterogeneous materials such as concrete. The underlying principle of NCWI is that a pump wave is used to activate the crack breathing which interact with the source probe signal. The resulting signal is then measured at receiver probes.

Surface plasmon-based detection for picosecond ultrasonics in planar gold-dielectric layer geometries.

Longitudinal acoustic modes in planar thin gold films are excited and detected by a combination of ultrafast pump-probe photoacoustic spectroscopy and a surface plasmon resonance (SPR) technique. The resulting high sensitivity allows the detection of acoustic modes up to the 7th harmonic (258 GHz) with sub-pm amplitude sensing capabilities. This makes a comparison of damping times of individual modes possible.

Merging and disconnecting resonance tongues in a pulsing excitable microlaser with delayed optical feedback.

Excitability, encountered in numerous fields from biology to neurosciences and optics, is a general phenomenon characterized by an all-or-none response of a system to an external perturbation of a given strength. When subject to delayed feedback, excitable systems can sustain multistable pulsing regimes, which are either regular or irregular time sequences of pulses reappearing every delay time. Here, we investigate an excitable microlaser subject to delayed optical feedback and study the emergence of complex pulsing dynamics, including periodic, quasiperiodic, and irregular pulsing regimes.

Sound velocity mapping from GHz Brillouin oscillations in transparent materials by optical incidence from the side of the sample.

Time-domain Brillouin scattering (TDBS) is an all-optical experimental technique for investigating transparent materials based on laser picosecond ultrasonics. Its application ranges from imaging thin-films, polycrystalline materials and biological cells to physical properties such as residual stress, temperature gradients and nonlinear coherent nano-acoustic pulses. When the sample refractive index is spatially uniform and known in TDBS, analysis by windowed Fourier transforms allows one to depth-profile the sound velocity.

Comparison of three full-field optical measurement techniques applied to vibration analysis.

Digital image correlation, deflectometry and digital holography are some of the full-field optical measurement techniques that have matured in recent years. Their use in vibroacoustic applications is gaining attention and there is a need for cataloging their performance in order to provide, to a broad community of users and potential future users, quantitative and qualitative evaluations of these three approaches. This paper presents an experimental comparison of the three optical methods in the context of vibration measurements, along with classical reference measurements provided by an accelerometer and a laser Doppler vibrometer.

Emerging topics in nanophononics and elastic, acoustic, and mechanical metamaterials: an overview.

This broad review summarizes recent advances and "hot" research topics in nanophononics and elastic, acoustic, and mechanical metamaterials based on results presented by the authors at the EUROMECH 610 Colloquium held on April 25-27, 2022 in Benicássim, Spain. The key goal of the colloquium was to highlight important developments in these areas, particularly new results that emerged during the last two years. This work thus presents a "snapshot" of the state-of-the-art of different nanophononics- and metamaterial-related topics rather than a historical view on these subjects, in contrast to a conventional review article.

Pathogen-derived mechanical cues potentiate the spatio-temporal implementation of plant defense.

Background: The ongoing adaptation of plants to their environment is the basis for their survival. In this adaptation, mechanoperception of gravity and local curvature plays a role of prime importance in finely regulating growth and ensuring a dynamic balance preventing buckling. However, the abiotic environment is not the exclusive cause of mechanical stimuli.

Test-bench for the experimental characterization of porous material used in thermoacoustic refrigerators.

The design of thermoacoustic coolers involves an adequate modeling of the thermoacoustic core's performance, which requires, in particular, a precise knowledge of their thermo-physical properties. Materials such as wire mesh stacks, foams, or compressed fibrous media are hard to describe, and their thermo-physical properties are rarely well enough quantified. Moreover, the classical linear thermoacoustic theory is not sufficient to accurately describe the performance of these materials.

Empirical Mode Decomposition-Based Feature Extraction for Environmental Sound Classification.

In environment sound classification, log Mel band energies (MBEs) are considered as the most successful and commonly used features for classification. The underlying algorithm, fast Fourier transform (FFT), is valid under certain restrictions. In this study, we address these limitations of Fourier transform and propose a new method to extract log Mel band energies using amplitude modulation and frequency modulation.

Reduction of the occlusion effect induced by earplugs using quasi perfect broadband absorption.

Passive earplugs are used to prevent workers from noise-induced hearing loss. However, earplugs often induce an acoustic discomfort known as the occlusion effect. This phenomenon corresponds to an increased auditory perception of the bone-conducted part of physiological noises at low-frequency and is associated with the augmentation of the acoustic pressure in the occluded earcanal.

Using heat maps in teaching acoustics: Interaction of incident plane wave or incident beam with a solid plane structure.

Using heat maps provides frame and relevance to topics covered in physical acoustics courses as students can more easily visualize complex ideas and situations. Students can also form a much better understanding of the physical phenomena involved and build more advanced critical thinking when heat maps are used. It is the aim of the paper to provide ways for students to interact with heat maps by using two examples: first, the interaction of a plane wave (not only monochromatic) with an interface separating a fluid and a solid medium and, second, the interaction of an acoustic beam with such an interface (including a solid layer).

Ballistic dynamics of flexural thermal movements in a nanomembrane revealed with subatomic resolution.

Flexural oscillations of freestanding films, nanomembranes, and nanowires are attracting growing attention for their importance to the fundamental physical and optical properties and device applications of two-dimensional and nanostructured (meta)materials. Here, we report on the observation of short-time scale ballistic motion in the flexural mode of a nanomembrane cantilever, driven by thermal fluctuation of flexural phonons, including measurements of ballistic velocities and displacements performed with subatomic resolution, using a free electron edge-scattering technique. Within intervals <10 μs, the membrane moves ballistically at a constant velocity, typically ~300 μm/s, while Brownian-like dynamics emerge for longer observation periods.

Coherent Phononics of van der Waals Layers on Nanogratings.

Strain engineering can be used to control the physical properties of two-dimensional van der Waals (2D-vdW) crystals. Coherent phonons, which carry dynamical strain, could push strain engineering to control classical and quantum phenomena in the unexplored picosecond temporal and nanometer spatial regimes. This intriguing approach requires the use of coherent GHz and sub-THz 2D phonons.

Subwavelength Su-Schrieffer-Heeger topological modes in acoustic waveguides.

Topological systems furnish a powerful way of localizing wave energy at edges of a structured material. Usually, this relies on Bragg scattering to obtain bandgaps with nontrivial topological structures. However, this limits their applicability to low frequencies because that would require very large structures.

Deep Learning Network for Speckle De-Noising in Severe Conditions.

Digital holography is well adapted to measure any modifications related to any objects. The method refers to digital holographic interferometry where the phase change between two states of the object is of interest. However, the phase images are corrupted by the speckle decorrelation noise.

Compact resonant systems for perfect and broadband sound absorption in wide waveguides in transmission problems.

This work deals with wave absorption in reciprocal asymmetric scattering problem by addressing the acoustic problem of compact absorbers for perfect unidirectional absorption, flush mounted to the walls of wide ducts. These absorbers are composed of several side-by-side resonators that are usually of different geometry and thus detuned to yield an asymmetric acoustic response. A simple lumped-element model analysis is performed to link the dependence of the optimal resonators surface impedance, resonance frequency, and losses to the duct cross-sectional area and resonator spacing.

Acoustic Estimation of the Direction of Arrival of an Unmanned Aerial Vehicle Based on Frequency Tracking in the Time-Frequency Plane.

The development of unmanned aerial vehicles (UAVs) opens up a lot of opportunities but also brings some threats. Dealing with these threats is not easy and requires some good techniques. Knowing the location of the threat is essential to deal with an UAV that is displaying disturbing behavior.