Search results for "ACOUSTIC"
showing 10 items of 1590 documents
An harmonic test condition for the metrological characterization and the operating principle identification of reactive static meters
2008
This paper faces the problem of the metrological characterization of the static meters for reactive energy in the presence of harmonic distortion. Starting from the only available accuracy test condition in the presence of harmonics introduced in the Standards for active static meters, an experimental approach is proposed for the verification of such meters in the presence of harmonic distortion, as well as for the individuation of their operating principle. A theoretical validation of the obtained results is presented by means of a comparison with a standard and a commercial static meter with a known operating principle.
Dynamic railroad inspection using the laser-air hybrid ultrasonic technique
2006
Laser-Air Hybrid Ultrasonic Technique (LAHUT) combines laser generation with air-coupled detection of ultrasound. The technique is non-contact and has the characteristic of operating from remote distances. Acoustic wave laser-generation apparatus can be metres away from the interrogated surface while air-coupled detection standoff can be on the order of several centimetres. The technique has the unique capability of interrogating structural materials in their true industrial environment. Dynamic tests are performed on parts with complex geometry, limited accessibility and curved surfaces. Also, dark and rough finish surfaces, which significantly reduce the efficiency of optical detection te…
Multiresolution wavelet-based approach to identification of modal parameters of a vehicle full-scale crash test
2012
In this work estimation of vehicle modal parameters was achieved by application of a wavelet-based method. The time-frequency analysis, which comprises those techniques that study a signal in both the time and frequency domains simultaneously, using Morlet wavelet properties are applied to the measured acceleration pulse of the colliding vehicle. Determination of the ridge of the wavelet coefficients matrix makes it possible to identify the frequency components of the recorded crash pulse. Subsequently, by using the estimated natural frequency of the system, the values of damping factor for a given mode shape are assessed. In this work there are concerned both: the major frequencies of the …
New method for real-time dynamic focusing through interfaces
2013
[EN] In nondestructive evaluation (NDE) a coupling medium (wedge) is frequently inserted between the array probe and the object being evaluated. In this situation, focal law computing is complicated by the refraction effects at the interface. Furthermore, there are not known techniques to perform dynamic focusing by hardware in these conditions. This work addresses these problems by following a two-step procedure. First, a virtual array that operates in a single medium with nearly equivalent time-of-flight to the foci is obtained. Then, simple hardware is proposed to perform dynamic focusing in real-time. It operates with arrays of any geometry as required by the virtual array in presence o…
A Wireless Acoustic Array System for Binaural Loudness Evaluation in Cities
2017
Networks of acoustic sensors are being deployed in smart cities to continuously monitor noise levels. In this paper, a novel acoustic sensor device is designed for binaural loudness evaluation, in a standalone platform. The audio is acquired from an array of microphones and a binaural signal is synthesized by a direction-of-arrival algorithm and a head-related transfer function. Hardware setup and software algorithms are presented and the results are discussed. Finally, the tests conducted in an early deployment show the feasibility of using the device to carry out large temporal and spatial sampling for the evaluation of binaural loudness.
Efficient CAD of Optimal Multi-Port Junctions Loaded with Partial-Height Cylindrical Posts using the 3D BI-RME Method
2005
A rigorous full-wave technique based on the 3D BI-RME (Boundary Integral-Resonant Mode Expansion) method for the analysis and design of compensated waveguide junctions is presented. This method is used to investigate the electrical performance of right-angled bends and rectangular waveguide T-junctions loaded with partial-height cylindrical posts, with the aim of extending the typical usable bandwidths of such components. It is found that the electrical performance of a two-way power divider can be significantly improved by considering a post displaced along the symmetry plane of the structure. Therefore, this contribution reveals a new crucial design parameter not considered in previous wo…
Efficient FDTD analysis of discontinuities in a square coaxial waveguide
1996
Modelling the Doppler Power Spectrum of Non-Stationary Underwater Acoustic Channels Based on Doppler Measurements
2017
This paper proposes a non-stationary time-continuous simulation model for wideband shallow underwater acoustic (UWA) channels based on measured Doppler power spectrums (DPSs). Measurement-based channel simulators are essential for the test, optimization, and performance analysis of UWA communication systems. The aim is to fit the DPS of the simulation model to that of the measured UWA channel. The performance of the designed UWA channel simulator is assessed by comparing the average Doppler shift and Doppler spread of the channel simulator with the corresponding quantities of the measured UWA channel. The results of the assessment show a good match between the statistical quantities of the …
Two Methods to Broaden the Bandwidth of a Nonlinear Piezoelectric Bimorph Power Harvester
2017
We propose two methods to broaden the operation bandwidth of a nonlinear pinned–pinned piezoelectric bimorph power harvester. The energy-scavenging structure consists of a properly poled and electroded flexible bimorph with a metallic layer in the middle, and is subjected to flexural vibration. Nonlinear effects at large deformations near resonance are considered by taking the in-plane extension of the bimorph into account. The resulting output powers are multivalued and exhibit jump phenomena. Two methods to broaden the operation bandwidth are proposed: The first method is to extend the operation frequency to the left single-valued region through optimal design. The second method is to exc…