This work presents a combined numerical and experimental investigation into the laser machining of aluminum alloy Al 1050 H14 using a high-power Continuous Wave (CW) fiber laser. Advanced three-dimensional, coupled thermal-structural Finite Element Method (FEM) simulations are developed to model key laser-material interaction processes, including laser-induced plastic deformation, laser etching, and engraving. Cases for both static single-shot and dynamic linear scanning laser beams are investigated. The developed numerical models incorporate a Gaussian heat source and the Johnson-Cook constitutive model to capture elastoplastic, damage, and thermal effects. The simulation results, which provide detailed insights into temperature gradients, displacement fields, and stress-strain evolution, are rigorously validated against experimental data. The experiments are conducted on an integrated setup comprising a 2 kW TRUMPF CW fiber laser hosted on a 3-axis CNC milling machine, with diagnostics including thermal imaging, thermocouples, white-light interferometry, and strain gauges. The strong agreement between simulations and measurements confirms the predictive capability of the developed FEM framework. Overall, this research establishes a reliable computational approach for optimizing laser parameters, such as power, dwell time, and scanning speed, to achieve precise control in metal surface treatment and modification applications.

This work presents a complete methodology for the precise characterization of the acoustic field inside crystal-based devices driven by high-frequency ultrasounds toward the generation of tunable narrowband and directional γ-radiation via undulation of ultra-relativistic charged particles. Such γ-ray sources have long been anticipated by the scientific community, as they promise new powerful tools for the study of high-energy physical phenomena and the development of novel nuclear technologies. In such devices, a piezoelectric transducer induces tens of MHz harmonic waves inside a silicon monocrystal. Ultra-relativistic charged particles traversing the crystal get trapped within the channels formed by the extremely strong electric fields of the acoustically modulated lattice planes, undergoing undulation and emitting γ-radiation. Precise characterization of the acoustic field in the crystal is crucial for the determination of the expected characteristics of the secondarily generated γ-rays. For this purpose, fast laser refraction imaging is used here to image the acoustic waves by exploiting the spatial redistribution of a laser beam's optical intensity, caused by the acoustic field. A dedicated computational model is developed for the estimation of spatial distribution of the pressure and lattice deformation inside the crystal. This methodology provides a framework for future novel γ-ray sources in high-energy facilities.

Acoustic metamaterials and phononic crystals are progressively consolidating as an important technology that is expected to significantly impact the science and industry of acoustics in the coming years. In this work, the impact of unit cell multiplicity on the spectral features of the acoustic response of phononic crystals is systematically studied using the recently demonstrated laser-plasma sound source characterization method. Specifically, by exploiting the advantages of this method, the impact of the number of repeated unit cells on the depth of the phononic band gaps and the passband spectral features across the entire audible range is demonstrated. These experimental findings are supported by specially developed computational simulations accounting for the precise structural characteristics of the studied phononic crystals and are analysed to provide a phenomenological understanding of the underlying physical mechanism. It is shown that by increasing the unit cell multiplicity, the bandgaps deepen and the number of resonant peaks in the crystal transmission zones increases. The resonant mode shapes are computationally investigated and interpreted in terms of spherical harmonics. This study highlights the tunability and design flexibility of acoustic components using phononic crystals, opening new paths towards applications in the fields of sound control and noise insulation.

In this paper, we present a novel scheme for the controlled generation of tunable narrowband γ-ray radiation by ultrarelativistic positron beams inside acoustically driven periodically bent crystals. A novel acoustic crystalline undulator is presented, in which the excitation of a silicon single crystal along the (100) planar direction by a piezoelectric transducer periodically modulates the crystal lattice in the [100] axial direction. An ultrarelativistic positron beam is directed diagonally into the crystal and propagates along the (110) planes. The lattice modulation forces the positrons to follow periodic trajectories, resulting in the emission of undulator radiation in the MeV range. A computational methodology for the design and development of such acoustically based light sources is presented together with the results of simulations demonstrating the favorable properties of the proposed technology. The longitudinal acoustic strains induced in the crystal by high-frequency piezoelectric elements are calculated by finite element simulations. The resulting bending profiles of the deformed crystal planes are used as geometrical conditions for the relativistic molecular dynamics simulations that calculate the positron trajectories and the spectral distribution of the emitted radiation. The results show a strong enhancement of the emitted radiation within a narrow spectral band defined by the bending period, demonstrating the feasibility and potential of the proposed technology.

The complex frequency domain assurance criterion is here applied for the comparison of a pristine to an altered state of a vibrating system. The criterion was originally proposed for the detection of defects in vibrating structures, while in later research studies it has been successfully used in musical acoustics. In this paper, we evaluate the differences in the vibrational behavior of finished and non-finished cymbals by adopting the proposed correlation criterion. Since idiophones are playable and produce sounds after any manufacturing process, the methodology presented correlates the vibrational state of a cymbal, at any stage of manufacturing, to a reference pristine cymbal. The evaluation of the cymbals is performed by the comparison of finished cymbals with semi-finished and blank 8-inch cymbals of the same material. The correlation criterion is applied to the vibrational measurements of blank, semi-finished, and finished B8 and B20 cymbals. Additionally, commercially available finished cymbals of the same material and geometrical characteristics are introduced in this correlation study. The measuring methodology and the vibration symmetry are discussed, and valuable results and conclusions are presented. The proposed methodology highlights the influence of the manufacturing processes of forming, hammering, and finishing on the vibrational behavior of cymbals, offering manufacturers and drummers a quantifiable criterion for evaluating cymbals’ vibroacoustic performance. Representative evaluations of blanks, semi-finished, and finished cymbals demonstrate the capability of the correlation criterion to monitor, identify, and visualize the vibrational state of any cymbal compared to a pristine reference. This enables the development of a novel methodology for both manufacturers and musicians.

The evolution of musical instrument manufacturing has prompted a quest for innovative materials beyond traditional wood. This review explores the utilization of composite materials, 3D-printed materials, and metamaterials as favorable alternatives. The investigation is driven by challenges such as the scarcity of high-quality tonewoods, variations in wood properties, and environmental concerns. Carbon fiber, graphite fiber, ceramic polymers, and nanocomposites present promising alternatives, offering advantages in durability, weight reduction, and customizable acoustics. The integration of 3D printing technology introduces a cutting-edge dimension, enabling intricate, precisely engineered components, optimizing instrument structure, and allowing unprecedented customization. Additionally, this article explores metamaterials, leveraging unique mechanical properties from structural design rather than constituent materials. Metamaterials offer unprecedented capabilities for tailoring instrument vibrational characteristics by providing unparalleled control over sound production. The review provides a thorough analysis, including manufacturing methods for composite materials, metamaterials, and 3D printing in musical instruments. Comprehensive examinations of vibrational and acoustical analyses related to composite materials, 3D-printed materials, and metamaterials, for the evaluation of musical instruments, are presented. This overview, supported by experimental and numerical simulation methods, offers valuable insights for the future development of musical instruments.

The Department of Music Technology and Acoustics of the Hellenic Mediterranean University offers a unique higher education program in Greece, addressing the growing demand for specialists in music technology, sound technology, and acoustics. It aims to educate specialized professionals in the rapidly advancing scientific fields of music technology and acoustics, mainly driven by the swift progress in electronic technology. The Department aims to address a gap in the professional market by producing highly skilled graduates, capable not only of keeping up with the latest scientific and technological developments but also of leading the way by introducing innovative approaches and methods. The Department combines art, science, and technology, focusing on sound recording, analysis, synthesis, and music production. Music technology encompasses various cutting-edge fields such as network music performance, artificial intelligence in music, and music embodiment. Acoustics refers to fundamental aspects of sound as well as its generation, transmission, and related phenomena. It includes research fields such as physical acoustics, optoacoustics, and vibroacoustics. This overview presents the research activities, methodologies, and results. A discussion of future research works and pointers to future technological evolution towards real-world music and acoustics applications is also provided.

Laser-plasma sound sources are increasingly utilized in technological and scientific applications as attractive alternatives to conventional electromechanical or piezoelectric transducers. This work presents a systematic experimental study of laser-plasma sound sources generated in atmospheric air by strong, short and ultrashort laser pulses. Emphasis is given on the dependence of their acoustic emission on the characteristics of the optical radiation. In the experiments, nanosecond and femtosecond laser pulses with different energies and optical wavelengths are focused in atmospheric air using lenses of different focusing power. The produced acoustic pulses are captured via a system with high dynamic range and broad frequency response in the far field of the plasma source. The acoustic signals are analysed both in the time and frequency domains to extract their primary characteristics, particularly the total acoustic energy, peak pressure, spectral magnitude and spectral peak frequency. The results are systematically examined and compared with respect to the characteristics of the exciting laser pulses. The experimental observations are supported by theoretical calculations of the generated plasma density via rate equations that account for the main ionization and electron loss mechanisms. The presented analysis provides a frame for controlling the acoustic characteristics of laser-plasma sound sources, which is particularly important for applications in the fields of acoustic measurements, sound reproduction and biomedicine.

Phononic crystals and acoustic metamaterials are expected to become an important enabling technology for science and industry. Currently, various experimental methods are used for evaluation of acoustic meta-structures, such as impedance tubes and anechoic chambers. Here we present a method for the precise characterization of acoustic meta-structures that utilizes rapid broadband acoustic pulses generated by point-like and effectively massless laser plasma sound sources. The method allows for broadband frequency response and directivity evaluations of meta-structures with arbitrary geometries in multiple sound propagation axes while also enabling acoustic excitation inside the structure. Experimental results are presented from acoustic evaluations of various phononic crystals with band gaps in the audible range, notably also in the very low frequencies, validating the predictions of numerical models with high accuracy. The proposed method is expected to boost research and commercial adoption of acoustic metamaterials in the near future. Phononic crystals and acoustic metamaterials hold great promise in advancing technology and scientific understanding of materials. Here, the authors demonstrate a characterization method for acoustic meta-structures based on broadband acoustic pulses generated by laser-plasma sound sources.

We introduce a novel, gaseous target optical shaping laser set-up, capable to generate short scale length, near-critical target profiles via generated colliding blast waves. These profiles are capable to maintain their compressed density for several nanoseconds, being therefore ideal for laser-plasma particle acceleration experiments in the near critical density plasma regime. Our proposed method overcomes the laser-target synchronization limitations and delivers energetic protons, during the temporal evolution of the optically shaped profile, in a time window of approximately 2.5 ns. The optical shaping of the gas-jet profiles is optimised by MagnetoHydroDynamic simulations. 3D Particle-In-Cell models, adopting the spatiotemporal profile, simulate the 45 TW femtosecond laser plasma interaction to demonstrate the feasibility of the proposed proton acceleration set-up. The optical shaping of gas-jets is performed by multiple, nanosecond laser pulse generated blastwaves. This process results in steep gradient, short scale length plasma profiles, in the near critical density regime allowing operation at high repetition rates. Notably, the Magnetic Vortex Acceleration mechanism exhibits high efficiency in coupling the laser energy into the plasma in the optically shaped targets, resulting to collimated proton beams of energies up to 14 MeV.

The present study encompasses a thorough analysis of the vibrations in a splash musical cymbal. The analysis is performed using a hybrid methodology that combines experimental measurements with parametric computer-aided design and finite element method simulations. Experimental measurements, including electronic speckle pattern interferometry, and impulse response measurements are conducted. The interferometric measurements are used as a reference for the evaluation of finite element method modal analysis results. The modal damping ratio is calculated via the impulse response measurements and is adopted by the corresponding simulations. Two different approximations are employed for the computer-aided design and finite element method models: one using three-point arcs and the other using lines to describe the non-smooth curvature introduced during manufacturing finishing procedures. The numerical models employing the latter approximation exhibit better agreement with experimental results. The numerical results demonstrate that the cymbal geometrical characteristics, such as the non-smooth curvature and thickness, greatly affect the vibrational behavior of the percussion instrument. These results are of valuable importance for the development of vibroacoustic numerical models that will accurately simulate the sound synthesis of cymbals.

The scope of the study is the design and prototyping of a musical instrument made from carbon, specifically the bouzouki, which is traditionally manufactured by wood.The use of carbon fiber is expected to facilitate the manufacturing of such a musical instrument, independent of factors that affect wood in an often unpredictable or uncontrollable way, such as inhomogeneities and environmental conditions like humidity and temperature.This approach will also allow for a significant reduction of the production costs, benefiting the broader musical instrument community.We focus on the development of a prototype carbon fiber bouzouki, able to acoustically perform comparably to the traditional wooden bouzouki.It is expected that the results of the presented research will eventually lead to the manufacturing of a carbon fiber bouzouki ready for commercial exploitation, thus setting the basis for the design and manufacturing of other traditional musical instruments from carbon fiber.

A novel 3D auto-drum machine system for the generation and recording of percussion sounds is developed and presented. The capabilities of the machine, along with a calibration, sound production, and collection protocol are demonstrated. The sounds are generated by a drumstick at pre-defined positions and by known impact forces from the programmable 3D auto-drum machine. The generated percussion sounds are accompanied by the spatial excitation coordinates and the correspondent impact forces, allowing for large databases to be built, which are required by machine learning models. The recordings of the radiated sound by a microphone are analyzed using a pre-trained deep learning model, evaluating the consistency of the physical sample generation method. The results demonstrate the ability to perform regression and classification tasks when fine tuning the deep learning model with the gathered data. The produced databases can properly train machine learning models, aiding in the investigation of alternative and cost-effective materials and geometries with relevant sound characteristics and in the development of accurate vibroacoustic numerical models for studying percussion instruments sound synthesis.

An integrated method of determining the vibration characteristics of musical instruments is here presented. The method includes modal measurements and holographic imaging, FEM modelling and simulations. Parts of musical instruments made of composite materials have been simulated, printed and measured. The vibrational response of 3D printed cymbals and Tzouras top plates, a Greek traditional stringed musical instrument, is experimentally measured and computationally simulated. The PLA printed parts vary in geometry and thickness. The frequency response functions, and the vibrational modes are presented and further studied in relation to the aforementioned geometry variations. The experimental findings provide inputs to FEM modeling and simulation parameters.

Ion acceleration in the near-critical density regime is a captivating research area in high-energy physics and plasma physics. High-pressure gas jets have gained popularity as targets for ion acceleration experiments, due to their potential to offer debris-free ion sources that support high repetition rates. The purpose of this research is the design and fabrication of such gas targets for future ion acceleration experiments in the near-critical density regime. The optimization of two nozzle geometries has been studied using the ANSYS Student simulation program. The Computational Fluid Dynamics (CFD) problem is efficiently solved, and the determination of their cubic particle density maps is achieved. In addition, these nozzle geometries were fabricated using 3D printing and characterized in a vacuum environment, using Mach-Zehnder interferometry. These results make a significant contribution to the production of high-pressure gas targets for ion acceleration experiments and offer valuable insights for the design of future experiments.

An integrated method, which combines Electronic Speckle Pattern Interferometry, impulse response measurements, finite element method simulations, and psychoacoustic tests, is proposed to evaluate the vibroacoustic behavior of a carbon fiber bouzouki. Three of the carbon fiber instruments are manufactured, and one is qualified via interferometric experimental measurements with reference to a traditional wooden bouzouki, which was evaluated for its sound and playability by the proposed method. Psychoacoustic tests were used to evaluate the sound and playability of the newly qualified carbon fiber bouzouki, which was further modeled by the finite element method and simulated. The simulation results agreed well with the experimental measurements. Furthermore, finite element simulation results of the qualified carbon fiber bouzouki were demonstrated with reference to the traditional wooden bouzouki experimental results, providing new findings crucial for the optimization of the manufacturing and the vibroacoustic behavior of the carbon fiber instrument. The proposed integrated method can be applied to a variety of carbon fiber stringed musical instruments.

Nano-acoustic strain generation in thin metallic films via ultrafast laser excitation is widely used in material science, imaging and medical applications. Recently, it was shown that transition metals, such as titanium, exhibit enhanced photoacoustic transduction properties compared to noble metals, such as silver. This work presents experimental results and simulations that demonstrate that among transition metals tantalum exhibits superior photoacoustic properties. Experiments of nano-acoustic strain generation by femtosecond laser pulses focused on thin tantalum films deposited on Silicon substrates are presented. The nano-acoustic strains are measured via pump-probe transient reflectivity that captures the Brillouin oscillations produced by photon–phonon interactions. The observed Brillouin oscillations are correlated to the photoacoustic transduction efficiency of the tantalum thin film and compared to the performance of titanium thin films, clearly demonstrating the superior photoacoustic transduction efficiency of tantalum. The findings are supported by computational results on the laser-induced strains and their propagation in these thin metal film/substrate systems using a two-temperature model in combination with thermo-mechanical finite element analysis. Finally, the role of the metal transducer-substrate acoustic impedance matching is discussed and the possibility to generate appropriately modulated acoustic pulse trains inside the crystalline substrate structures for the development of crystalline undulators used for γ-ray generation is presented.

The dynamic behavior of solid Si targets irradiated by nanosecond laser pulses is computationally studied with transient, thermοmechanical three-dimensional finite element method simulations. The dynamic phase changes of the target and the generation and propagation of surface acoustic waves around the laser focal spot are provided by a finite element model of a very fine uniformly structured mesh, able to provide high-resolution results in short and long spatiotemporal scales. The dynamic changes in the Si material properties until the melting regime are considered, and the simulation results provide a detailed description of the irradiated area response, accompanied by the dynamics of the generation and propagation of ultrasonic waves. The new findings indicate that, due to the low thermal expansion coefficient and the high penetration depth of Si, the amplitude of the generated SAW is small, and the time and distance needed for the ultrasound to be generated is higher compared to dense metals. Additionally, in the melting regime, the development of high nonlinear thermal stresses leads to the generation and formation of an irregular ultrasound. Understanding the interaction between nanosecond lasers and Si is pivotal for advancing a wide range of technologies related to material processing and characterization.

This research work emphasizes the capability of delivering optically shaped targets through the interaction of nanosecond laser pulses with high-density gas-jet profiles, and explores proton acceleration in the near-critical density regime via magnetic vortex acceleration（MVA）. Multiple blast waves（BWs） are generated by laser pulses that compress the gas-jet into near-critical steep gradient slabs of a few micrometres thickness. Geometrical alternatives for delivering the laser pulses into the gas target are explored to efficiently control the characteristics of the density profile. The shock front collisions of the generated BWs are computationally studied by 3D magnetohydrodynamic simulations. The efficiency of the proposed target shaping method for MVA is demonstrated for TW-class lasers by a particle-in-cell simulation.

It was recently demonstrated that a newly explored instability, which was named electro-thermo-mechanical (ETM) instability, was developed in the solid elastic phase in the case of an electrically exploded conductor in the skin effect mode. Here, we present new advances in the exploration of the role of the ETM instability as seed of the magneto-hydro-dynamic instabilities that are later observed in the plasma phase. Our study, through analytical calculations, simulations and experiments, demonstrates the whole evolution dynamics of the instability amplitude, from the solid to the plasma phase, including the phase transitions. It is validated that the sustained axial wavelength modes in the plasma phase lie in the range of values of those of the ETM instability developed in the solid phase. The results are of significant importance for understanding the role of the ETM instability as seeding for the later observed instabilities in the plasma phase.