Special Issue "Acoustic Metamaterials, Applications in Engineering"

A special issue of Applied Sciences (ISSN 2076-3417). This special issue belongs to the section "Acoustics and Vibrations".

Deadline for manuscript submissions: 1 September 2019.

Special Issue Editor

Guest Editor
Dr. Daniele Ragni

Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands
Website | E-Mail
Interests: metamaterials; acoustic absorption; refractive index; noise control; aircraft noise; absorption noise control.

Special Issue Information

Dear Colleagues,

Acoustic metamaterials are commonly used in engineering in a wide range of applications. From room insulation to reduction of noise from commercial aircraft, they typically play an important role in our life. The modifications of the original properties of conventionally targeted materials, aim at increasing their acoustic performance with respect to the overall dimension of the installation. This has led, for example, to the creation of ultrathin acoustic barriers and to materials for the elimination of the scattering from acoustic sources or for the increase of the signal‑to‑noise ratio in microphones and pressure sensors. In the last decade, one of the main achievements of research in this field has been the determination of materials with equivalent negative properties, such as negative refraction. By crossover with parallel developments in electromagnetics, negative refraction and cloaking have been applied to acoustic materials for the creation of acoustic lens designs that can overcome the diffraction limit. The creation of such new acoustic materials has paved the way for the investigation of pentamode materials, exotic products that only resist one mode of deformation to address future acoustic challenges. Research in this field has been significantly aided by steady improvements in technology, primarily computer simulation and additive manufacturing. In this Special Issue, we invite all those contributions at the forefront of this stimulating research, with a specific focus on the application for noise reduction in the aerospace sector.

Dr. Daniele Ragni
Guest Editor

Manuscript Submission Information

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Keywords

  • metamaterials
  • acoustic absorption
  • refractive index
  • noise control
  • aircraft noise
  • absorption noise control

Published Papers (3 papers)

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Research

Open AccessArticle
Temperature-Activated Change of Permeable Material Properties for Low-Noise Trailing Edge Applications
Appl. Sci. 2019, 9(15), 3119; https://doi.org/10.3390/app9153119
Received: 27 June 2019 / Revised: 20 July 2019 / Accepted: 24 July 2019 / Published: 1 August 2019
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Abstract
The present work analyses broadband noise scattering from permeable trailing edges with identical micro-structure but under a change of temperature. Experiments are performed in an anechoic wind tunnel using a NACA0018 airfoil at chord-based Reynolds numbers between 1.88 × 105 and 3.14 [...] Read more.
The present work analyses broadband noise scattering from permeable trailing edges with identical micro-structure but under a change of temperature. Experiments are performed in an anechoic wind tunnel using a NACA0018 airfoil at chord-based Reynolds numbers between 1.88 × 105 and 3.14 × 105 and no incidence. A microphone array is used to determine far-field sound pressure level changes upon trailing edge heating. It is found that broadband noise emission can be actively controlled by varying the temperature of the porous trailing edge inserts. Specifically, the electrically heated inserts yield a noise level variation of up to 2.5 dB with the heated one being noisier compared to a baseline, unheated material with similar micro-structure. Resistivity measurements of permeable samples with varying temperature show that flow resistivity increases with the fluid temperature which is in agreement with the reported trailing edge noise increase. Full article
(This article belongs to the Special Issue Acoustic Metamaterials, Applications in Engineering)
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Open AccessArticle
A New Method of Simultaneous Localization and Mapping for Mobile Robots Using Acoustic Landmarks
Appl. Sci. 2019, 9(7), 1352; https://doi.org/10.3390/app9071352
Received: 21 February 2019 / Revised: 21 March 2019 / Accepted: 26 March 2019 / Published: 30 March 2019
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Abstract
The simultaneous localization and mapping (SLAM) problem for mobile robots has always been a hotspot in the field of robotics. Simultaneous localization and mapping for robots using visual sensors and laser radar is easily affected by the field of view and ground conditions. [...] Read more.
The simultaneous localization and mapping (SLAM) problem for mobile robots has always been a hotspot in the field of robotics. Simultaneous localization and mapping for robots using visual sensors and laser radar is easily affected by the field of view and ground conditions. According to the problems of traditional sensors applied in SLAM, this paper presents a novel method to perform SLAM using acoustic signals. This method enables robots equipped with sound sources, moving within a working environment and interacting with microphones of interest, to locate itself and map the objects simultaneously. In our case, a method of microphone localization based on a sound source array is proposed, and it was applied as a pre-processing step to the SLAM procedure. A microphone capable of receiving sound signals can be directly used as a feature landmark of a robot observation model without feature extraction. Meanwhile, to eliminate the random error caused by hardware equipment, a sound settled in the middle of two microphones was applied as a calibration sound source to determine the value of the random error. Simulations and realistic experimental results demonstrate the feasibility and effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Acoustic Metamaterials, Applications in Engineering)
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Open AccessArticle
Attenuation Zones of Two-Dimensional Periodic Foundations Including the Effect of Vertical Loads
Appl. Sci. 2019, 9(5), 993; https://doi.org/10.3390/app9050993
Received: 24 January 2019 / Revised: 22 February 2019 / Accepted: 1 March 2019 / Published: 10 March 2019
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Abstract
Periodic foundations for seismic isolation are getting increasing attention in the field of civil engineering. Initial stresses due to the vertical loads from the upper structures exist in periodic foundations. In the present paper, attenuation zones of two-dimensional periodic foundations including the effect [...] Read more.
Periodic foundations for seismic isolation are getting increasing attention in the field of civil engineering. Initial stresses due to the vertical loads from the upper structures exist in periodic foundations. In the present paper, attenuation zones of two-dimensional periodic foundations including the effect of vertical loads are studied by the weak form quadrature element method. Comparisons with existing results in special cases without the effect of vertical loads are conducted to validate the proposed method, and good agreement is found. A comprehensive parametric study is conducted to investigate the effects of vertical loads on the attenuation zones. Moreover, frequency-domain and time-domain response analyses of a two-dimensional periodic foundation with finite unit cells are conducted to verify the theoretical results. The results show that bound frequencies of the attenuation zones, corresponding to the vibration mode of the core, are affected by vertical loads. It is also found that vertical loads shift the complete attenuation zones to lower frequencies and reduce the attenuation coefficients in the attenuation zones. Full article
(This article belongs to the Special Issue Acoustic Metamaterials, Applications in Engineering)
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