Search results for "Acoustics"

Using coded excitation to maintain signal to noise for FMC+TFM on attenuating materials

2019

Ultrasonic Non-Destructive Evaluation using Full Matrix Capture (FMC) and Total Focusing Method (TFM) is used for high resolution imaging as every pixel is in optimal focus. FMC excites one element in turn, so operates with lower transmitted energy compared to phased array beamforming. The energy at a reflector is further reduced by the broad directivity pattern of the single element. The large number of Tx/Rx A-scans that contribute to each pixel recover the Signal-to-Noise Ratio (SNR) in the final TFM image. Maintaining this in the presence of attenuating materials is a challenge because relevant information in each A-scan signal is buried in the thermal noise, and the TFM process assumes…

Wave propagation in 1D elastic solids in presence of long-range central interactions

2011

Abstract In this paper wave propagation in non-local elastic solids is examined in the framework of the mechanically based non-local elasticity theory established by the author in previous papers. It is shown that such a model coincides with the well-known Kroner–Eringen integral model of non-local elasticity in unbounded domains. The appeal of the proposed model is that the mechanical boundary conditions may easily be imposed because the applied pressure at the boundaries of the solid must be equilibrated by the Cauchy stress. In fact, the long-range forces between different volume elements are modelled, in the body domain, as central body forces applied to the interacting elements. It is …

Biodynamic behavior of the trunk and the abdomen during whole-body vibration

1989

Vibration strain may be defined as the sum of all reactions of the human being to vibration exposure. This also includes the biomechanical behavior of particular parts of the body. Knowledge about these reactions is necessary in the field of occupational health and ergonomics. Biomechanical models, experimental methods, and results are presented. It can be shown that under vibration exposure with different conditions (body posture, vibration direction), the body parts are in resonance at varying frequencies, mainly in a low frequency range.

SPECTRAL COMPOSITION OF EATING SOUNDS GENERATED BY CRISPY, CRUNCHY AND CRACKLY FOODS

1995

Separate air and bone conducted food sounds generated by six subjects biting into eight foods were recorded and analysed by a fast Fourier transform (FFT) signal analyser. A panel of 60 subjects classified the 8 foods according to their texture: crispy, crunchy and crackly and these textural characteristics were described by spectral characteristics of biting sounds. Crispy foods (such as extruded flat breads) were found to generate high pitched sounds that show a high level of frequencies higher than 5 kHz, especially for air conduction. Crunchy foods (such as raw carrot) generate low pitched sounds with a characteristic peak on frequency range 1.25 to 2 kHz for air conduction. And crackly…

Boundary Element Formulation for Unified Analysis of High-Speed Trains

2007

Determining cantilever stiffness from thermal noise

2013

We critically discuss the extraction of intrinsic cantilever properties, namely eigenfrequency fn, quality factor Qn and specifically the stiffness kn of the nth cantilever oscillation mode from thermal noise by an analysis of the power spectral density of displacement fluctuations of the cantilever in contact with a thermal bath. The practical applicability of this approach is demonstrated for several cantilevers with eigenfrequencies ranging from 50 kHz to 2 MHz. As such an analysis requires a sophisticated spectral analysis, we introduce a new method to determine kn from a spectral analysis of the demodulated oscillation signal of the excited cantilever that can be performed in the frequ…

Observation of topological gravity-capillary waves in a water wave crystal

2019

The discovery of topological phases of matter, initially driven by theoretical advances in quantum condensed matter physics, has been recently extended to classical wave systems, reaching out to a wealth of novel potential applications in signal manipulation and energy concentration. Despite the fact that many realistic wave media (metals at optical frequencies, polymers at ultrasonic frequencies) are inherently dispersive, topological wave transport in photonic and phononic crystals has so far been limited to ideal situations and proof-of-concept experiments involving dispersionless media. Here, we report the first experimental demonstration of topological edge states in a classical water …

Simulations of a Graphene Nanoflake as a Nanovector To Improve ZnPc Phototherapy Toxicity: From Vacuum to Cell Membrane

2017

International audience; We propose a new approach to improving photodynamic therapy (PDT) by transporting zinc phthalocyanine (ZnPc) in biological systems via a graphene nanoflake, to increase its targeting. Indeed, by means of time-dependent density functional theory simulations, we show that the ZnPc molecule in interaction with a graphene nanoflake preserves its optical properties not only in a vacuum but also in water. Moreover, molecular dynamic simulations demonstrate that the graphene nanoflake/ZnPc association, as a carrier, permits one to stabilize the ZnPc/graphene nanoflake system on the cellular membrane, which was not possible when using ZnPc alone. We finally conclude that the…

An RF-Based Positioning Method for Tracing a Cluster of Moving Scatterers in Non-Stationary Indoor Environments

2021

Author's accepted manuscript © 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. This letter presents a novel iterative positioning method for tracing the body segments of a person moving indoors using radio-frequency (RF) signals. The indoor space is equipped with a multiple-input multiple-output (MIMO) communication system. The person is modelled by a cluster of …

The Behaviour of Mistuned Piezoelectric Shunt Systems and Its Estimation

2016

This paper addresses monoharmonic vibration attenuation using piezoelectric transducers shunted with electric impedances consisting of a resistance and an inductance in series. This type of vibration attenuation has several advantages but suffers from problems related to possible mistuning. In fact, when either the mechanical system to be controlled or the shunt electric impedance undergoes a change in their dynamical features, the attenuation performance decreases significantly. This paper describes the influence of biases in the electric impedance parameters on the attenuation provided by the shunt and proposes an approximated model for a rapid prediction of the vibration damping performa…