Search results for "Acoustics"

Critical issues in the PD testing methodology for XLPE-insulated MV cables: An experimental case

2017

This paper describes some critical issues arising during the partial discharge (PD) testing of a 500m delivery length of an XLPE-insulated MV cable. At first, conventional PD measurements were performed on the whole length by using a standard acquisition system; PDs activity was detected, but the system allowed the operator to localize the PDs only on a length of 70 m. A visual inspection of this section highlighted the presence of an excoriation in the outer sheet. Aiming at a more accurate pin-pointing of the defect, more measurements were carried out in the proximity of the outer defect using a portable PD detection system. These measurements showed PDs activity, whose source was located…

The Acoustic Wave Behavior Within the PEA Cell for Space Charge Measurement

2018

In order to evaluate the acoustic wave behavior within the Pulsed Electro Acoustic (PEA) cell, a simulation model has been developed in this work. The model, implemented in Matlab environment, is based on the analogy between acoustic and electrical quantities. Therefore, it was possible to model the PEA cell as cascade connected lossy transmission lines. The model has been validated theoretically by making a comparison with a simulation result found in literature. The experimental validation has also been made by using the PEA cell of the LEPRE high voltage lab. In addition, four graphs have been realized. Two of them can be used to establish in easy and fast way to obtain the minimum groun…

A Planar Generator for a Wave Energy Converter

2019

This article presents a permanent magnet planar translational generator which is able to exploit multiple modes of sea wave energy extraction. Linear electrical generators have recently been studied for the exploitation of sea wave energy, but, to the best of our knowledge, no synchronous planar translational generator has been proposed. In this article, to maximize the energy extraction, we have considered all the potential modes of motion due to wave excitation and included them within the mathematical model of the proposed system. The principle of operation of the generator can be summarized as follows: the moving part (translator) of the generator is driven from the sea waves and induce…

Interferences in Locally Resonant Sonic Metamaterials Formed from Helmholtz Resonators

2019

[EN] The emergence of materials artificially designed to control the transmission of waves, generally called metamaterials, has been a hot topic in the field of acoustics for several years. The design of these metamaterials is usually carried out by overlapping different wave control mechanisms. An example of this trend is the so-called Locally Resonant Sonic Materials, being one of them the Phononic Crystals with a local resonant structure. These metamaterials are formed by sets of isolated resonators in such a way that the control of the waves is carried out by resonances and by the existence of Bragg bandgaps, which appear due to the ordered distribution of the resonators. Their use is b…

2019

We present a design for producing precisely adjustable and alternating single-axis magnetic fields based on nested Halbach dipole pairs consisting of permanent magnets only. Our design allows for three dimensional optical and mechanical access to a region with strong adjustable dipolar fields, is compatible with systems operating under vacuum, and does not effectively dissipate heat under normal operational conditions. We present a theoretical analysis of the properties and capabilities of our design and construct a proof-of-concept prototype. Using our prototype, we demonstrate fields of up to several kilogauss with field homogeneities of better than 5%, which are harmonically modulated at…

Enhanced acoustic pressure sensors based on coherent perfect absorber-laser effect

2021

Lasing is a well-established field in optics with several applications. Yet, having lasing or huge amplification in other wave systems remains an elusive goal. Here, we utilize the concept of coherent perfect absorber-laser to realize an acoustic analog of laser with a proven amplification of more than 10 4 in terms of the scattered acoustic signal at a frequency of a few kHz. The obtained acoustic laser (or the coherent perfect absorber-laser) is shown to possess extremely high sensitivity and figure of merit with regard to ultra-small variations of the pressure (density and compressibility) and suggests its evident potential to build future acoustic pressure devices such as precise sensor…

Thermal cloaking of complex objects with the neutral inclusion and the coordinate transformation methods

2019

We explore the cloaking of a complex shape by either the neutral inclusion or the transformation thermodynamics (TT) methods. Thin cloaks are built and the heat cloaking efficiency is investigated for both the steady-state and the transient regimes. We show that the neutral inclusion cloak is more efficient in both regimes, though it has the drawback that the thermal conductivity of the cloaked shape must be known. In practice, the neutral inclusion method is more flexible and easier to implement than the coordinate transformation method, especially for complex shapes.We explore the cloaking of a complex shape by either the neutral inclusion or the transformation thermodynamics (TT) methods…

Fundamental Noise Limits and Sensitivity of Piezoelectrically Driven Magnetoelastic Cantilevers

2020

International audience; Magnetoelastic sensors for the detection of low-frequency and low-amplitude magnetic fields are in the focus of research for more than 30 years. In order to minimize the limit of detection (LOD) of such sensor systems, it is of high importance to understand and to be able to quantify the relevant noise sources. In this contribution, cantilever-type electromechanical and magnetoelastic resonators, respectively, are comprehensively investigated and mathematically described not only with regard to their phase sensitivity but especially to the extent of the sensor-intrinsic phase noise. Both measurements and calculations reveal that the fundamental LOD is limited by addi…

Acoustic Wave Behavior in a Specimen Containing an Air Void Defect

2019

The PEA method is the most used technique for the space charge measurements. As is well known, this method uses pressure waves to detect the charges accumulated in solid dielectrics. Based on its working principle, the generated acoustic waves travel within PEA cell and the specimen under test in order to be finally detected by the piezoelectric sensor. For a multilayer specimen and, in particular, in case of different materials that make up the specimen, the acoustic wave reflection is inevitable. Considering that, in several cases, the reflected waves could be detected by the piezoelectric sensor before than the main signals, the PEA cell output profile could results distorted. Based on t…

Experimental investigation of the effect of moisture on the acoustic properties of lightweight substrates used in green envelopes

2021

International audience; Substrates are used in green walls and roofs to supply air and water to the roots of the growing plants. These substrates are porous with micropores which store water and macropores which facilitate drainage and air entry. Effect of moisture on acoustic absorption is studied for two lightweight substrates: coir dust and perlite. Measurement of dry and moistened substrates are conducted to evaluate their effective speed of sound, attenuation, characteristic impedance, compressibility and density between 100 Hz and 1000 Hz using an impedance tube and the three microphone-two load method. Effect of moisture on these quantities is found to depend strongly upon the intera…