Acoustic wave | EPFL Graph Search

Acoustic waves are a type of energy propagation through a medium by means of adiabatic loading and unloading. Important quantities for describing acoustic waves are acoustic pressure, particle velocity, particle displacement and acoustic intensity. Acoustic waves travel with a characteristic acoustic velocity that depends on the medium they're passing through. Some examples of acoustic waves are audible sound from a speaker (waves traveling through air at the speed of sound), seismic waves (ground vibrations traveling through the earth), or ultrasound used for medical imaging (waves traveling through the body). Wave properties Acoustic wave is a mechanical wave that transmits energy through the movements of atoms and molecules. Acoustic wave transmits through liquids in longitudinal manner (movement of particles are parallel to the direction of propagation of the wave); in contrast to electromagnetic wave that transmits in transverse manner (movement of particles at a right a

Amplitude and phase reconstruction for Low-Energy Electron Holography of individual proteins

Hannah Julia Ochner

Single-molecule imaging methods are of importance in structural biology, and specifically in the imaging of proteins, since they can elucidate conformational variability and structural changes that might be lost in imaging methods relying on averaging processes. Low-energy electron holography (LEEH) is a promising technique for imaging individual proteins with negligible radiation damage, which can be combined with a sample preparation process by native electrospray ion beam deposition (native ES-IBD) ensuring the creation of chemically pure samples suitable for holographic imaging.The central step in the analysis of data measured by LEEH is the numerical reconstruction of the object from the experimentally acquired holograms.Full information about the imaged object consists of both amplitude and phase information imprinted on the scattered wave during the interaction of the electron beam with the molecule and encoded in the hologram created by the interference of the scattered wave and the transmitted incident wave. A propagation-based algorithm with the goal of reconstructing the wave field in the plane of the object is presented and applied to holograms of individual proteins prepared by ES-IBD and measured with a low-energy electron holography microscope. The information retrieved from the reconstruction of the amplitude distribution in the object plane is discussed by analysing holograms of antibodies, demonstrating that the inherent conformational variability of these molecules can be mapped by LEEH. The influence of the sample preparation process on the surface conformations is tracked by tuning the landing energy of the proteins during deposition.To complement the amplitude data, an iterative phase retrieval algorithm is implemented to reconstruct the phase distribution in the object plane along with the amplitude distribution. The algorithm's performance and robustness is thoroughly evaluated and simulations regarding multiple scattering effects and element-dependent variations in scattering strength are carried out to provide a reference for the interpretation of phase data retrieved from experimentally acquired holograms. The iterative phase retrieval algorithm is then applied to protein data, indicating that both molecular density and charges can be related to features in the phase reconstructions, while the presence of metals does not correlate with specific phase signals at the current resolution obtainable from the experimental data.Since proteins are inherently three-dimensional, approaches towards three-dimensional reconstruction schemes are discussed, which will be the focus of future work.

EPFL2022

Study on the Performances of AlScN based SAW/BAW Hybrid Resonators A Parametric Analysis of Acoustic Wave Resonators with Large Figure of Merit

Guilain Lionel Germain Lang, Luis Guillermo Villanueva Torrijo, Soumya Yandrapalli

In this study, we analyze a 3rd type of FBAR's fundamental mode by finite element method. We show the importance of the substrate's wave velocity and conductivity on the electromechanical coupling efficiency. Then we demonstrate that etching traditional SAW sensors in between its electrodes is an effective solution to increase its performances. Finally, the finite device simulations of optimized geometries demonstrate the full potential of AlSc(0.4)N based SAW/BAW hybrid resonators: an impedance response free of spurious modes and large figure of merit (k(t)(FD, 1.35GHz)(2) = 2.48%).

IEEE2021

Contribution à l'étude des modes de rayonnement acoustique d'une structure

Olivier Schevin

Noise radiated by different industrial structures that surround us in daily life are more and more considered as environmental pollution. Standards defining a tolerable sound level for each of these noise sources are regularly called into question and respecting them becomes an additional constraint for manufacturers. The last decades have seen the increasing development of means used to fight these noise disturbances. The wide diversity of noises perceived as harmful has contributed to the progressive increase in specificity and efficiency of solutions proposed to reduce the disturbances. For some applications, passive solutions, based on the use of materials capable of absorbing or deviating acoustic or vibratory waves, have progressively been replaced by "active" solutions, based on the generation of an acoustic wave of opposite phase to the disturbing one radiated by the noise source. Power transformers are sources for which passive solutions (anti-noise walls) are usually expensive and not very efficient, particularly at low frequency. Furthermore, characteristics of noise radiated by transformers (low frequency tone noise) are such that they are particularly well suited for the implementation of an active solution. Typically, an active control system dedicated to transformers (feedforward) is composed of actuators, used to generate the anti-noise and usually located near the tank, sensors, used to measure the attenuation obtained and to provide a reference signal, and a controller used to drive the actuators as a function of the information collected by the sensors. When the sensors are microphones, they are usually moved away from the noise source, in such a way that they pick up acoustic pressure that is representative of the noise propagated far away. In the vicinity of the source, local acoustic phenomena can occur which are not propagated far away. A microphone located near the noise source would therefore pick up an acoustic pressure that did not necessarily represent the one that effectively exists far away, the area where we are in fact seeking to reduce the noise. These phenomena, frequently grouped under the term "nearfield" tend to decrease the performance of the control system, owing to the fact that the controller seeks in this case to reduce an acoustic pressure which is not representative of the noise to be reduced. In practice, the significant amount of wiring required as a result of the positioning of the microphones in the far field, has a non-negligible effect on the cost of the system. The possibility of bringing the sensors closer to the source is sufficiently advantageous to envisage to studying the feasibility and the resulting consequences. The present approach consists in representing the primary field radiated by a vibrating structure in terms of a set of "acoustic radiation modes". The use of radiation modes to characterise the behaviour of a structure has received increasing attention since the beginning of 90's, especially for active control applications. Usually, this approach consists in representing the radiated power in terms of a set of surface velocity distributions, called radiation modes, that have the property of radiating independently of each other. Radiation modes result from diagonalization of a discrete expression of the radiation operator. We propose here to study the consequences on the radiation modes of a structure from bringing the microphones closer to it. We will study how the acoustic field varies with the distance and how this can be used to obtain a model, the complexity of which is adapted to the observation distance.

EPFL2001