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Successful STSM

Dr Logan Schwan, LAUM – UMR CNRS 6613, Le Mans (FR)


HOST: Olga Umnova, Acoustics Research Centre, University of Salford, SALFORD (UK)
STSM Period: 2016-08-01 – 2016-08-19 (19 days)

Unconventional mode conversion of acoustic waves by resonant metasurface
This STSM aimed at investigating sound interaction with resonant metasurfaces through experiments performed in anechoic environment on full-scale prototypes with more than 500 resonators arranged at a rigid backing, and under realistic working conditions (finite size array and point-source excitation). Uniform and graded resonant metasurfaces have been tested, to observe the conversion of bulk waves into surface waves and the apparent violation of Descartes’ Laws upon reflection.

Mr Luis J. Salmerón-Contreras, Universitat Politècnica de València, València (ES)

HOST: Jean-Philippe Groby, LAUM – UMR CNRS 6613, Le Mans (FR)
STSM Period: 2016-10-01 – 2016-10-31 (31 days)

Vibroacoustic measurements in periodic elastic beam
The aim of this STSM was to acquire skills in vibroacoustic measurements and its corresponding processing. For this purpose the LAUM has provided the equipment required to perform an experimental set-up which basically consists in a 1D phononic crystal (from now called PC). It is made by cylindrical layers of aluminum and poly(methyl methacrylate) (PMMA), also known as by the trade name, Plexiglas or Lucite. The excitation of PC is performed by an ultrasonic transducer and the motion acquirement by a laser vibrometer and an accelerometer (Detailed report).

Dr Timo Lähivaara, University of Eastern Finland, Kuopio (FI)


HOST: Jean-Philippe Groby, LAUM – UMR CNRS 6613, Le Mans (FR)
STSM Period: 2016-10-24 – 2016-11-06 (14 days)

Full-wave inversion techniques for porous material characterization
There is a clear need for accurate methods for modelling wave fields in poroelastic media. Applications for modelling such wave fields are, for example, groundwater exploration, medical ultrasonics, and noise absorbing materials. In many cases, the material properties of the poroelastic media are the primary unknowns. Typically, we have only indirect measurements of the material properties that makes the actual estimation problem often very challenging. During the STSM grant, we took major steps in the code development of estimating poroelastic plates.

Dr Noé Jiménez González, LAUM – UMR CNRS 6613, Le Mans (FR)

HOST: Trevor Cox, The University of Salford, Salford, Greater Manchester (UK)
STSM Period: 2016-10-15 – 2016-12-01 (48 days)

Deep-subwavelength acoustic diffusers based in slow-sound metamaterials
Sound diffusers composed of acoustic metamaterials are presented. These sound diffusers are rigid backed panels composed of periodic array of slits, each one loaded by an array of Helmholtz resonators (HRs). Strong dispersion is produced in each slit generating slow sound conditions. Thus, the length of the slits can be shortened to the sub-wavelength regime to achieve the quarter wavelength resonance. By tuning the geometry of the system, the complex reflection coefficient of each slit can be tailored to obtain either a desired phase or strong absorption. Based of this concept, we present thin diffusers where the geometries of the metamaterials have been tuned to get surfaces with a spatially dependent reflection coefficient having uniform magnitude Fourier transforms. Various designs are shown, where quadratic residue diffusers, primitive root diffusers, and index and ternary sequence diffusers are mimicked by using metadiffusers from 20 to 40 times thinner than the wavelength. Finally, a broadband metadiffuser panel of 3 cm thick was designed using optimization methods presenting a high diffusion coefficient for frequencies ranging from 500Hz to 2 kHz.
Jiménez, N., Cox, T.J., Romero-García, V., Groby, J.-P., 2017. Metadiffusers: Deep-subwavelength sound diffusers. Scientific Reports 7. doi:10.1038/s41598-017-05710-5

Dr Vicent Romero Garcia, LAUM – UMR CNRS 6613, Le Mans (FR)

HOST: Luis Miquel Garcia Raffi, Departamento de Matématica Aplicada, Valencia (ES)
STSM Period: 2017-01-09 – 2017-02-09 (32 days)

Nonlinear propagation in periodic acoustic media
In this STSM we have developed theoretical and numerical models to study the nonlinear wave propagation in periodic and locally resonant acoustic media. In particular in the framework of this STSM we have develop analytical models for the study of large amplitude waves propagating in 1D multilayered structures. The theoretical tools have been borrowed from optics by using the couple mode theory (CMT), in which the host institution has a deep understanding in the linear regime. Here, we have collaborated to extend this method to the nonlinear regime.

Mr Alexandre Lardeau, ISAT, NEVERS CEDEX (FR)Photo_A_Lardeau.JPG

HOST: Olga Umnova, Acoustics Research Centre, University of Salford, SALFORD (UK)
STSM Period: 2017-02-06 – 2017-02-17 (12 days)

Propagation of high amplitude sound waves in structured materials with periodic inner cavities
Metamaterials are an ever growing topic in the acoustic community, and used for sound absorption purposes amongst other applications. Though their behaviour in the linear regime are well known, their nonlinear behaviour is much less studied. This STSM aims at studying experimentally the propagation of high amplitude sound waves in structured materials with periodic inner circular cavities. The results are meant to help us derive a model for these materials.

Prof Kirill Horoshenkov, University of Sheffield, Sheffield (UK)horoshenkov.jpg

HOST: Patrizio Fausti, University of Ferrara, Ferrara (IT)
STSM Period: 2017-03-06 – 2017-03-10 (5 days)

A new laboratory method for acoustic characterisation of nanoporous media
This STSM grant was used to develop further research links with Ferrara University in Italy. The work was focused on acoustic properties of materials with pores which diameter can be as small as a few nano-meters. The properties of these materials are unique and poorly understood. The purpose of this STSM was to focus on new methods to measure the acoustical properties of these materials and predict them with a mathematical model. One outcome of this STSM is a new PhD student at the University of Sheffield who will start her work from September 2017. She will focus on studying of nano-porous membranes for water purification. She will use acoustic methods to measure the size of nano-pores and effects of various catalysts and chemical reactions on the pore size.

Prof Livia Cveticanin, University of Novi Sad, Novi Sad (RS)Cveticanin.jpg

HOST: Dan Sporea, National Institute for Laser, Plasma and Radiation Physics, Magurele (RO)
STSM Period: 2017-03-19 – 2017-03-25 (7 days)

Advances in Theoretical and experimental investigation in metamaterials and structures
This STSM Grant was used to establish links between two research entities: one, where the theory of acustic metamaterial is developed and the other, where the experiments are done. Namely, the theoretically obtained result for nonlinear acoustic metamaterial has to be proved experimentally. We discuss about the preliminary setup for some tests on metamaterials which would be used in sound insulation. We plan future cooperation which will include the work of our PhD students at Laboratories in Romania.

Mr Jean-Philippe Groby, LAUM – UMR CNRS 6613, Le Mans (FR)


HOST: Víctor J. Sánchez Morcillo, Polytechnical University of Valencia, Department of Applied Physics, Gandia (ES)
STSM Period: 2017-03-06 – 2017-03-31 (26 days)

Design of perfect subwavelength natural sound absorbing materials with poseidonia balls
The aim of this STSM was to investigate the potential of posidonia based material for sound absorption. Several samples were characterized and a toy model was developed to describe the evolution of the Johnson Lafarge model parameters depending on the porosity of the sample. This material was found to have huge potential of applications.

Dr Alan Geslain, Université de Bourgogne Franche-Comté, Nevers (FR)

HOST: José Sánchez-Dehesa, Universitat Politècnica of València, Valencia (ES)
STSM Period: 2017-03-06 – 2017-03-31 (26 days)

Acoustic characterization of superlattice metamaterials made of aerogel disks for the elastic energy damping
Silica aerogel has been widely studied in the past as bulk material for its extremely low density and low thermal conductivity. Plates or membranes made of this extremely soft materials, exhibits sub wavelength resonances. With a suitable structure made of combination of aerogel plates, possibly exhibits interesting properties as a negative density, as a near zero density and as a perfect absorption (acoustic absorption near 1). The aim of this STSM project is to exploited the aerogel plates in a tunable configurations (1D or 2D) to obtain interesting metamaterials properties. The first step of this project is covered by the STSM and is consist to acoustically characterize the aerogel in order to determine the material parameters. The second step of this project is the perspective of a future collaboration, is to design 1D metamaterials or 2D superlatticemetasurfaces.

Dr Timo Lähivaara, University of Eastern Finland, Kuopio (FI)timo

HOST: Peter Göransson, KTH Royal Institute of Technology, Stockholm (SE)
STSM Period: 2017-04-02 – 2017-04-08 (7 days)

Bayesian framework for optimal alignment of a multilayered anisotropic poroelastic acoustic absorber
Simulations of wave propagation in poroelastic media are necessary for solving many problems of physics and engineering. Applications for poroelastic models are wide, including groundwater exploration and noise absorbing materials. The latter one was the main research topic during the STSM. We used a Bayesian inversion framework together with a model based on a Transfer Matrix Method approach to optimizing multilayered anisotropic poroelastic systems in terms of acoustic absorption.

Mr Iván Herrero-Durá, Universitat Politècnica de València, Grao de Gandia (ES)ivan_herrero.jpg

HOST: Vicente Romero García, LAUM – UMR CNRS 6613, Le Mans (FR)
STSM Period: 2017-03-15 – 2017-04-15 (32 days)

Experimental analysis of sonic crystals made of clamped elastic beams
The purpose of the STSM is the experimental and numerical characterization of a periodic distribution of clamped scatterers embedded in air. The attention has been focused in 1D periodic structures made of clamped cylindrical membranes and beams and, thus, four different systems have been analysed: a complete membrane, a membrane with slits at both sides, a cantilever beam and two cantilever beams. Two main effects are expected, the resonances of the structures and the Bragg reflections due to periodicity.

Dr Paolo Bonfiglio, Engineering Department University of Ferrara, Ferrara (IT)Bonfiglio

HOST: Christ Glorieux, KU Leuven, Leuven (BE)
STSM Period: 2017-04-24 – 2017-04-28 (5 days)

Micro-macro characterization and modelling of porous media
The main purpose of this short-term scientific mission was the comparison between two different techniques for the determination of the complex modulus of porous media using a laser Doppler vibrometer approach. The sample was excited at a fixed position (at the outer end of the sample) by mean of a shaker. The response of the sample wes measured by means of a laser Doppler vibrometer, along the full length of the sample. As a preliminary step the team worked extensively to improve the S/N ratio of measured signals introducing an impulse response with exponential sine sweep calculation in order to avoid non-linear (harmonic) distortions from the force transducer. The result was successful and the quality of the data was improved in a larger frequency range of investigation. Results from both measurement methods can be considered reliable although additional tests have been already planned to investigate the wave front of propagating waves.

Dr Tomasz G. Zielinski, Institute of Fundamental Technological Research of the Polish Academy of Sciences, Warsaw (PL)Zielinski.jpg

HOST: Elke Deckers, KU Leuven, Department of Mechanical Engineering, Leuven (BE)
STSM Period: 2017-04-09 – 2017-04-29 (21 days)

Application of homogenization techniques to micro-slit materials
Two research topics were investigated during the STSM: (1) micro-slit materials, (2) poroelastic layers with small mass/elastic inclusions. In the first case, the techniques common in microstructure-based modelling of porous media (IPPT PAN) were applied to micros-slit metamaterials (proposed by KU Leuven). In the second case, the effects related to the presence of local mass inclusions inside poroelastic layers were investigated and found to be very promising with respect to the development of novel poroelastic composites for overall or selective attenuation of waves.

Dr Nicolaas Bernardus (Bert) Roozen, NOVIC Noise and Vibration control, Heeze (NL) & KU Leuven, Leuven (BE)Roozen.jpg

STSM Period: 2017-07-02 – 2017-07-21 (20 days)
HOST: Francesco Pompoli , Engineering Department University of Ferrara, Ferrara (IT)

Characterization of elastic parameters of acoustical porous materials using Lamb-waves
The scientific work during the STSM was mainly focused on the estimation of the Young’s modulus and loss factor from measurement data, which are relevant for the structure-borne transmission of waves through porous materials. New methods were developed that take into account the thickness of the test samples (Mindlin theory, Lamb wave theory),using both propagating and evanescent waves. The complex wavenumber of the propagating wave was thus estimated. Moreover, the type of excitation (a knife) and its reflections from the boundaries were taken into account using the Green’s function of the Mindlin theory and an image source type of model. Numerical experiments were carried out first to test the fitting algorithms and these algorithms were finally applied to experimental data.

Dr Logan Schwan, LAUM – UMR CNRS 6613, Le Mans (FR)


HOST: Andrew Norris, Rutgers University, Piscataway (USA)
STSM Period: 2017-08-10 – 2017-08-30 (21 days)

Asymptotic homogenisation of elastic metaporous materials with embedded resonant inclusions
This STSM has been concerned with the development of a homogenised model for the propagation of long-waves in elastic metaporous materials, that is poro-elastic media with periodically-embedded resonant inclusions. In particular, the case of periodically-embedded Helmholtz resonators with an extended neck and with elastic walls has been studied. To tackle the problem, the theory of two-scale asymptotic homogenisation has been applied. It  gives access to a generalised poroelastic Biot model which encapsulates in a closed-form the complex multiple interactions between the inclusions themselves and between the inclusion array and the wavefield.