A Design Method for Sound Absorbing Structure at Low Frequency

2020 ◽  
Vol 982 ◽  
pp. 39-50
Author(s):  
Ying Jie Fu ◽  
Xiao Ming Wang ◽  
Yu Lin Mei
Keyword(s):  
Design Method ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Channel Structure ◽  
Response Analysis ◽  
Acoustic Metamaterials ◽  
Element Analysis ◽  
Low Frequencies ◽  
Mass Unit ◽  
The Masses

Traditional acoustic absorbing materials are not effective for low-frequency engineering applications, but on the basis of the locally resonant principle, acoustic metamaterials can utilize the resonance of vibrators to dissipate acoustic energy and realize the subwavelength design of acoustic absorbers, therefore the acoustic metamaterials have great potential applications for noise reduction at low frequencies. This paper firstly employs the Bloch theory to investigate the effects of the parameters of the unit cell of the embedded membrane-and-mass metamaterials on the dispersion characteristics of the metamaterials, and the band gap is verified by the full wave finite element analysis. And then, a model of acoustic metamaterials is constructed by embeding an array of membrane-and-masses into a channel structure filled with acoustic materials. Next the transient frequency response analysis is performed to simulate the wave propagation in the model, the results show that the acoustic metamaterials can absorb the sound through the local resonance of the membrane-and-mass vibrators. Finally, an acoustic metamaterial maze structure is designed and analyzed, in the structure the membrane-and-mass array is embedded and the masses varies periodically. The research illustrates that the acoustic metamaterials with membrane-and-mass unit cells have excellent performances on the sound absorption at low frequency.

scholarly journals Finite Element Analysis on Acoustic and Mechanical Performance of Flexible Perforated Honeycomb-Corrugation Hybrid Sandwich Panel

2021 ◽  
Vol 2021 ◽  
pp. 1-14
Author(s):  
Jiaming Hu ◽  
Junyi Wang ◽  
Yu Xie ◽  
Chenzhi Shi ◽  
Yun Chen
Keyword(s):  
Finite Element ◽  
Sandwich Panel ◽  
Mechanical Performance ◽  
Mechanical Energy ◽  
Low Frequency ◽  
Rigid Wall ◽  
Acoustic Metamaterials ◽  
Mechanical Stiffness ◽  
Element Analysis ◽  
Low Frequencies

Since proposed, the perforated honeycomb-corrugation sandwich panel has attracted a lot of attention due to its superior broadband sound absorption at low frequencies and excellent mechanical stiffness/strength. However, most existing studies have assumed a structure made of high-strength materials and studied its performance based on the ideal rigid-wall model with little consideration for acoustic-structure interaction, thereby neglecting the structural vibrations caused by the material’s elasticity. In this paper, we developed a more realistic model considering the solid structural dynamics using the finite element method (FEM) and by applying aluminum and rubber as the structural material. The enhancement of the low-frequency performance and inhibition of broadband absorption coexisted in low-strength rubbers, implying a compromise in the selection of Young's modulus to balance these two influences. Further analysis on thermal-viscous dissipation, mechanical energy, and average structural stress indicated that the structure should work right below the resonant frequency for optimization. Based on these findings, we designed a novel aluminum-rubber composite structure possessing enhanced low-frequency absorption, high resistance to shear load, normal compression, and thermal expansion. Our research is expected to shed some light on noise control and the design of multifunctional acoustic metamaterials.

An Analytical Model for the Interaction of Mass Inclusions in Heterogeneous (HG) Blankets

2011 ◽  
Vol 133 (6) ◽  
Author(s):  
A. Wagner ◽  
M. E. Johnson ◽  
K. Idrisi ◽  
D. P. Bartylla
Keyword(s):  
Elastic Layer ◽  
Analytical Approach ◽  
Low Frequency ◽  
Control Device ◽  
Effective Stiffness ◽  
Special Focus ◽  
Dynamic Vibration Absorber ◽  
Low Frequencies ◽  
Dynamic Vibration ◽  
The Masses

The heterogeneous (HG) blanket is a passive treatment used to reduce the low frequency transmission of sound through partitions. HG blankets, glued onto a structure, consist of an elastic medium with embedded mass inhomogeneities that mechanically replicate a mass-spring-damper system to reduce efficient radiating structural modes at low frequencies. The elastic layer typically used has sound absorption properties to create a noise control device with a wide bandwidth of performance. The natural frequency of an embedded dynamic vibration absorber is determined by the mass of the inhomogeneity as well as by its effective stiffness due to the interaction of the mass inclusion with the elastic layer. A novel analytical approach has been developed to describe in detail the interaction of the mass inclusions with the elastic layer and the interaction between the masses by evaluating special elastomechanical concepts. The effective stiffness is predicted by the analytical approach based on the shape of the mass inclusions as well as on the thickness and material properties of the layer. The experimental validation is included and a simplified direct equation to calculate the effective stiffness of a HG blanket is proposed. Furthermore, the stress field inside the elastic material will be evaluated with focus on the stresses at the base to assess the modeling of one or more masses placed on top of the elastic layer as dynamic vibration absorbers. Finally, the interaction between two (or more) masses placed onto the same layer is studied with special focus on the coupling of the masses at low distances between them.

scholarly journals Demultiplexing Infrasound Phonons With Tunable Magnetic Lattices

2020 ◽  
Vol 7 ◽  
Author(s):  
Audrey A. Watkins ◽  
Osama R. Bilal
Keyword(s):  
Self Assembly ◽  
Small Volume ◽  
Low Frequency ◽  
Acoustic Metamaterials ◽  
Propagation Characteristics ◽  
Low Frequencies ◽  
Experimental Realization ◽  
Nonlinear Properties ◽  
Potential Applications ◽  
Low Frequency Waves

Controlling infrasound signals is crucial to many processes ranging from predicting atmospheric events and seismic activities to sensing nuclear detonations. These waves can be manipulated through phononic crystals and acoustic metamaterials. However, at such ultra-low frequencies, the size (usually on the order of meters) and the mass (usually on the order of many kilograms) of these materials can hinder its potential applications in the infrasonic domain. Here, we utilize tunable lattices of repelling magnets to guide and sort infrasound waves into different channels based on their frequencies. We construct our lattices by confining meta-atoms (free-floating macroscopic disks with embedded magnets) within a magnetic boundary. By changing the confining boundary, we control the meta-atoms’ spacing and therefore the intensity of their coupling potentials and wave propagation characteristics. As a demonstration of principle, we present the first experimental realization of an infrasound phonon demultiplexer (i.e., guiding ultra-low frequency waves into different channels based on their frequencies). The realized platform can be utilized to manipulate ultra-low frequency waves, within a relatively small volume, while utilizing negligible mass. In addition, the self-assembly nature of the meta-atoms can be key in creating re-programmable materials with exceptional nonlinear properties.

A compact and low-frequency acoustic energy harvester using layered acoustic metamaterials

2019 ◽  
Vol 28 (2) ◽  
pp. 025035 ◽  
Author(s):  
Xiaole Wang ◽  
Jiajie Xu ◽  
Jingjing Ding ◽  
Chunyu Zhao ◽  
Zhenyu Huang
Keyword(s):  
Energy Harvester ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Acoustic Metamaterials

Active Control of Sound Radiation Into Enclosures Using Structural Error Sensors

2002 ◽  
Author(s):  
D. S. Li ◽  
L. Cheng ◽  
C. M. Gosselin
Keyword(s):  
Genetic Algorithms ◽  
Active Control ◽  
Polyvinylidene Fluoride ◽  
Design Method ◽  
Low Frequency ◽  
Acoustic Energy ◽  
Sensor Design ◽  
Optimal Theory ◽  
Structural Surface ◽  
Control Forces

Active control of vibration and sound inside a structure-surrounded enclosure leads to many applications such as noise control inside vehicle cabins. Despite the extensive research carried out in the last two decades, ANVC technology is still in its infancy and has not yet been introduced massively in practical engineering applications. One of the problems to be resolved is that most of presently used techniques require the use of microphones inside the cavity, which is not practical in many situations. In addition, due to the coupling between the vibrating structure and the confined enclosure, demand for more robust control strategy is apparent. This paper tackles the aforementioned problem using a benchmark system in which only PVDF (Polymer polyvinylidene fluoride) sensors are used on the structural surface. A new method based on genetic algorithms is developed for sensor design. This design process ensures a proper consideration of the acoustic energy in the enclosure without the direct use of acoustic sensors inside the cavity. Roughly speaking, the sensor is designed to capture the most radiating motion of the structure via an automatic optimization process. In the proposed method, Genetic Algorithms and the least quadratic square optimal theory are organically combined together. For each configuration of error sensors, the amplitude of control forces, which can either be point forces or excitation generated by piezoceramic actuators, is first determined by minimizing the sum of the squared outputs of error sensors using the least quadratic square optimal theory. Then with the optimal amplitude of control forces, the acoustic potential energy of the sound cavity is computed and used as the evaluation criteria in the evolution process. Using Genetic Algorithms, the optimal configuration of the error sensors can be determined. A cylindrical shell with an internal floor partition is used as an example to illustrate the effectiveness of the proposed approach. To increase the computational efficiency, the structural surface is assumed to be covered with strip-typed PVDF sensors along both the circumferential and longitudinal directions. Both numerical and experimental results show the great effectiveness of the proposed GA-based design method. The sound reduction is achieved not only at the design frequency but also at most frequencies in the low frequency range. The proposed method demonstrates great merits in sensor design for complex structures.

Design and Experimental Verification of Torsion-Bending Low-Frequency Piezoelectric Energy Harvesters

2016 ◽  
Author(s):  
Hichem Abdelmoula ◽  
Nathan Sharpes ◽  
Hyeon Lee ◽  
Abdessattar Abdelkefi ◽  
Shashank Priya
Keyword(s):  
System Analysis ◽  
Energy Harvester ◽  
Excitation Frequency ◽  
Low Frequency ◽  
Load Resistance ◽  
Mode Shapes ◽  
Low Frequencies ◽  
Piezoelectric Energy ◽  
The Masses ◽  
Tip Mass

We design and experimentally validate a zigzag piezoelectric energy harvester that can generate energy at low frequencies and which can be used to operate low-power consumption electronic devices. The harvester is composed of metal and piezoelectric layers and is used to harvest energy through direct excitations. A computational model is developed using Abaqus to determine the exact mode shapes and coupled frequencies of the considered energy harvester in order to design a broadband torsion-bending mechanical system. Analysis is then performed to determine the optimal load resistance. The computational results are compared and validated with the experimental measurements. More detailed analysis is then carried out to investigate the effects of the masses on the bending and torsion natural frequencies of the harvester and generated power levels. The results show that due to the coupling between the bending and torsion modes of the zigzag structure, highest levels of the harvested power are obtained when the excitation frequency matches the coupled frequency of torsion type for three different values of the tip mass.

scholarly journals Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction

2020 ◽  
Vol 10 (24) ◽  
pp. 8902
Author(s):  
Ki-Hong Park ◽  
Zhi-Xiong Jiang ◽  
Sang-Moon Hwang
Keyword(s):  
Sound Pressure ◽  
Low Frequency ◽  
Experimental Results ◽  
Multimedia Content ◽  
The Novel ◽  
Element Analysis ◽  
Low Frequencies ◽  
Acoustic Performance ◽  
Technological Developments ◽  
New Type

In the era of multimedia devices, smartphones have become the primary device for consuming multimedia content. As technological developments have facilitated a more immersive multimedia experience, enlarged displays and the use of several sensors have limited the allowable size of microspeakers. Although sound plays an important role when consuming multimedia content, the limited space for microspeakers in modern devices leads to poor acoustic performance, especially at low frequencies. To address this issue, this paper proposes a novel microspeaker structure that enhances the low-frequency sound pressure level (SPL), while also featuring reduced exterior dimensions. The structure was designed and analyzed using 3D finite element analysis. Through coupling analysis, the simulation results were verified on the basis of the experimental results. The novel microspeaker has one outer magnet surrounding the entire coil, unlike in prototype microspeakers, which have two outer magnets. The gap between the top plates and coil is reduced, and a new type of coil is introduced for the purpose of increasing electromagnetic force. The samples were manufactured, and their SPLs were tested in an anechoic chamber. The experimental results prove that the proposed microspeaker offers an improved SPL at low frequencies compared with prototype microspeakers.

Novel Low-Frequency Rectangular-Loop Piezoelectric Energy Harvester

2014 ◽  
Vol 635-637 ◽  
pp. 928-931
Author(s):  
Shuai Yuan ◽  
Bing Jiang ◽  
Li Juan Chen ◽  
Yu Guo Hao ◽  
Jian Bo Xin ◽  
...  
Keyword(s):  
Resonant Frequency ◽  
Output Voltage ◽  
Energy Harvester ◽  
Low Frequency ◽  
Effective Bandwidth ◽  
Response Analysis ◽  
Element Analysis ◽  
Piezoelectric Energy ◽  
The Finite Element Analysis ◽  
Harmonic Response Analysis

The ambient energy harvesting based on piezoelectric has become an important subject in recent research publications. A new rectangular-loop piezoelectric energy harvester(RLPEH) is proposed. The characteristic is analyzed by the finite element analysis (FEA) which includes the static analysis, modal analysis and harmonic response analysis. The analysis results show that the RLPEH could reduce the resonant frequency and improve the output voltage. The three order resonant frequency is 18.6Hz, 40.8Hz and 85.4Hz. The output voltage is 42V under 3m/s2 of acceleration and the effective bandwidth is 18.7Hz with output voltage above 10V.

Facile and Effective Phononic Structures for Ultrasound Focusing Application

2014 ◽  
Author(s):  
Qiuquan Guo ◽  
Xiaobing Cai ◽  
Jun Yang
Keyword(s):  
Penetration Depth ◽  
Acoustic Energy ◽  
Ultrasound Therapy ◽  
Acoustic Metamaterials ◽  
High Frequency Ultrasound ◽  
Low Frequencies ◽  
Non Invasive ◽  
Wavelength Resolution ◽  
Invasive Method ◽  
Sub Wavelength

Ultrasound therapy is a highly popular non-invasive method to treat diseases. It is desired to increase the resolution of ultrasound therapy, providing more efficient therapeutic effect. In this study, a simple but effective phononic structure was designed to achieve higher resolution close to wavelength resolution of ultrasound focusing. The objective of this study is to design a unique phononic structure to focus acoustic wave into human body more deeply and precisely. It is known that overheating by high frequency ultrasound will cause a series of side effects including bone burns, soft tissue burns, swelling and bleeding problems. In addition, due to the limited propagation of recovered evanescent wave, the penetration depth of acoustic energy being focused by the acoustic metamaterials is often hindered. In this study, we will design a multilayer acoustic metamaterial which shows sub-wavelength focusing ability at relatively low frequencies. More importantly, our design will also extend the ability of penetration depth by manipulating the focusing length through optimization of the phononic structure.

scholarly journals Numerical Study on the Phase Sensitivity Variation in Low Frequency Primary Microphone Calibrations

2020 ◽  
Vol 10 (11) ◽  
pp. 3799
Author(s):  
Fan Zhang ◽  
Di Liu ◽  
Aibing Liu ◽  
Xianyue Gang ◽  
Lijun Li
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Low Frequency ◽  
Phase Variation ◽  
Time Domain Analysis ◽  
Phase Sensitivity ◽  
Element Analysis ◽  
Low Frequencies ◽  
The Time Domain ◽  
Frequency Phase

The low frequency phase characteristics of microphones in a monitoring system are crucial for characterizing large-scale natural and artificial activities—e.g., earthquakes, nuclear explosions, or rocket launchings. At present, microphones are simultaneously calibrated using in-situ or calibrator methods to get their phase consistency. However, the essential primary calibration, which traces their phase sensitivity to basic physical quantities, is grossly overlooked. Recently, we speculated that the microphone phase sensitivity is acoustically controlled by the pressure leakage and heat conduction effects in its back chamber, which will vary at low frequencies. Therefore, by means of the FEA (Finite Element Analysis) technique, simulations of laser pistonphone-based primary microphone calibrations are conducted both in the frequency and time domains. The frequency domain simulation quantifies the phase variation, while the time domain analysis helps us to understand the variation mechanism. It is found that the low frequency phase sensitivity is greatly influenced by its geometries and the venting state and should be pre-calibrated before serving.

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