新型Helmholtz型声子晶体的低频带隙及隔声特性

为了解决军用飞机舱室内产生的低频噪声问题,构建了一种新型的Helmholtz型二维声子晶体,该结构采用迷宫型开口通道,并在结构加入了刚性振子.研究发现,该结构在晶格常数为62 mm条件下,将第一低频带隙的下限降至15 Hz左右,且在100 Hz频率左右形成一条宽度为93 Hz的带隙宽带,表现出较好的低频隔声特性.首先,通过振型及声压场分析了其带隙成因,采用“力-声类比”的方法建立了该结构的等效模型,最后利用有限元法和传递矩阵法对第一低频的带隙范围进行了计算,两种方法所得结果基本相符;其次,通过有限元法探究了晶格常数、空气通道长度及振子材料等结构参数对低频带隙的影响.研究表明,增加开口通道长度和晶格常数都会降低第一带隙下限,增加振子材料密度能够有效降低第二带隙的上下限,进一步揭示了该结构带隙形成的实质,验证了等效模型的准确性.该研究为低频噪声控制方面提供了一定的理论支持,为低频声子晶体的设计提供了新的思路.     

双开口Helmholtz局域共振周期结构低频带隙特性研究

设计了一种双开口Helmholtz周期结构,该周期结构单元采用双开口内外腔设计,基于多腔耦合局域共振机理,可大大增加局域共振区域,增加能得到较低的低频带隙特性.通过设计调节内腔弧长,可以使带隙移动,达到特定低频频段的隔声效果.在分析低频带隙形成机理和影响因素时,采用声电类比原理建立带隙起始频率和截止频率的计算数学模型并与有限元方法进行对比分析.研究表明:该结构具有良好的低频带隙特性,其最低带隙段为86.9—138.2 Hz.外径一定的条件下,低频带隙受内腔弧长、内外腔间隔以及周期单元结构间隔影响,内腔弧长越长,低频带隙越低;内外腔间距离越大,从而内腔体积变小,带隙向高频移动,其低频效果变差;减小结构间距对低频带隙起始频率无影响,但可以大大增加低频带隙截止频率,从而增加带隙宽度.该研究结论可以为低频降噪领域提供一定的实践和理论支持.     

局域共振声子晶体复合结构的隔声特性

提出一种四振子对称局域共振声子晶体单元结构,通过改变振子的材料组份,使其在不同频率范围内存在完全带隙以及隔声峰;为拓宽结构隔声的频率范围,通过将不同结构复合的方式,使各结构在不同频率段发挥较好的隔声效果,从而实现隔声范围拓宽;采用有限元法研究了影响复合结构隔声效果的关键因素.结果表明,采用不同结构复合的方法能够有效地拓宽结构的隔声范围.该研究为声子晶体的宽频隔声提供了理论参考.     

用于汽车低频振动控制的局域共振声子晶体*

低频振动的控制是评估汽车舒适性的重要指标。针对汽车板件结构的低频振动控制问题,提出了一种基于局域共振机理的新型准二维声子晶体板。其结构由单侧复合圆柱共振单元周期排布在基板上构成。通过有限元方法得到了该结构的带隙特性,并结合其振型和传输谱分析了低频完全带隙的形成机理。研究表明,不同形式的板振动模式与圆柱共振单元的局域共振模式相互耦合形成面内带隙与面外带隙,两者叠加形成完全带隙。进一步研究发现,通过改变结构的材料和尺寸参数可以将共振带隙调节到满足实际应用要求的极低频范围,可在低于100 Hz的频段形成完全带隙,并可在更宽的频带内抑制z方向振动的弯曲波,为声子晶体在车身板件减振中的实际应用提供了依据。     

局域共振复合单元声子晶体结构的低频带隙特性研究

本文提出了一种新型局域共振复合单元声子晶体结构, 并结合有限元方法对结构的带隙机理及低频共振带隙特性进行了分析和研究. 共振带隙产生的频率位置由所对应的局域共振模态的固有频率决定, 并且带隙宽度与局域共振模态的品质因子及其与基体之间的耦合作用强度有关. 采用局域共振复合单元结构可以实现声子晶体的多重共振, 在低频范围能打开多条共振带隙, 但受到共振单元排列方式的的影响. 由于纵向和横向局域共振模态的简并, 复合单元结构能在200 Hz以下的低频范围打开超过60%宽度的共振带隙, 最低带隙频率低至18 Hz. 这为声子晶体结构获得低频、超低频带隙提供了一种有效的方法. 关键词： 局域共振 低频带隙 复合单元 声子晶体     

一种多频局域共振型声子晶体板的低频带隙与减振特性

设计了一种多频局域共振型声子晶体板结构, 该结构由一薄板上附加周期性排列的多个双悬臂梁式子结构而构成. 由于多个双悬臂梁式子结构的低频振动与薄板振动的相互耦合作用, 这种局域共振型板结构可产生多个低频弯曲波带隙(禁带); 带隙频率范围内的板弯曲波会被禁止传播, 利用带隙可以实现对薄板的多个目标频率处低频减振. 本文针对这种局域共振型板结构进行了简化, 并基于平面波展开法建立了其弯曲波带隙计算理论模型; 基于该模型, 结合具体算例进行了带隙特性理论分析. 设计、制备了一种存在两个低频弯曲波带隙的局域共振型板结构样件, 通过激光扫描测振仪测试证实该结构存在两个低频带隙, 在带隙频率范围的板弯曲振动被显著衰减.     

多振子梁弯曲振动中的局域共振带隙

从梁的弯曲振动方程出发,利用传递矩阵法,给出了无限周期结构的一维多振子声子晶体梁的弯曲振动能带结构,并利用有限元方法计算了有限周期结构梁的弯曲振动频率响应.建立了多振子声子晶体梁的简化模型,推导出带隙起始截止频率公式.结果表明:一维多振子声子晶体梁具有比单振子声子晶体梁更宽更丰富的振动带隙,可应用于呈倍频关系的减振降噪中;振动在带隙频率范围内频率响应具有明显的衰减;所建立的简化模型与理论模型结果符合较好.研究工作为梁类结构的减振提供一种新的思路.     

三角晶格磁振子晶体带结构的优化研究

用平面波展开法数值计算了椭圆柱散射体正三角排列的二维磁振子晶体带结构.结果显示,同样的填充率下,带隙的宽度和中心频率随着椭圆两半径之比s的变化出现明显的变化,椭圆柱散射体在三角晶格中可以打开低频带隙或使低频带隙加宽.     

新型负模量声学超结构的低频宽带机理研究

提出了一种具有负模量特性的新型声学超结构,并揭示了其低频带隙的形成及拓宽机理.通过理论推导给出了该新型结构的归一化有效模量表达式,由于有效模量的零值点与系统参数密切相关,可以调节合适的参数使得零值点降低或带隙下界降低,进一步实现低频带隙.理论结果表明,在一定的频率范围内,系统的弹性模量为负且负模量区域进一步拓宽,从而通过负模量区域的放大而拓宽带隙.这种新的实现低频带隙的方法克服了传统局域共振附加质量过大及惯性放大结构带隙较窄的缺点.同时,通过有限元法得到的周期结构的传输率随着结构参数的变化趋势与理论分析的变化趋势基本一致,并得到了约40—180 Hz的低频宽带.这种实现低频带隙的新思路对低频声波的控制具有很重要的理论指导意义.     

一种基于二维Helmholtz腔阵列的低频宽带隔声结构实验研究

基于圆周排列的Helmholtz共振腔单元,设计并实现了一种具有低频宽禁带的声人工结构,可以在结构中心处实现二维隔声效果.针对实际模型,搭建了二维声场测量平台,进行了相应的实验研究,实验结果与有限元仿真结果符合较好.该结构在较宽的频带内(680—1050 Hz)可以实现较好的隔声效果,最大隔声量可达41 d B.实验中还研究了单元参数及共振状态对隔声效果的影响.隔声区的大小与共振单元的分布形式有直接关系,而良好的共振状态将对提高隔声量有一定帮助.研究结果对设计新型声防护结构具有理论与应用价值.     

新型二维压电声子晶体板带隙可调性研究

设计了一种由涂有硬质材料涂层的柱状压电散射体周期性连接在四个环氧树脂薄板上构成的具有大带宽的新型二维压电声子晶体板,并利用有限元方法计算了该声子晶体板的能带结构、传输损失谱和位移矢量场.研究表明：与二组元材料构成的传统声子晶体板相比,新设计的声子晶体板的第一完全带隙频率更低,并且带宽扩大了5倍;通过在压电体表面上施加不同的电边界条件,可以实现多条完全带隙的主动调控;压电效应对能带结构有很大的影响,并且有利于完全带隙的扩大与形成.基于带隙的可调谐性,分析了可切换路径的压电声子晶体板波导,结果表明可以通过改变电边界条件来限制弹性波能量流.     

含内部连接体的二维声子晶体弹性波宽频带隙特性

声子晶体的弹性波带隙特性使得它在开发用于减振降噪的新型功能材料方面具有广阔应用前景。为获得宽频大带隙,改进了一种含连接体的正方晶格声子晶体结构.利用有限元法计算并分析了不同结构配置下其能带特性和振动模态。数值结果表明,单胞中同时引入新的质量块以及连接体将对原连接体的自由振动模态产生抑制作用,可在原分离的两带隙频率范围内获得相对带宽超过100%的单一宽频带隙。此外,通过调整几何尺寸、连接体数目、结构对称性等参数可进一步调控结构带隙特性。      

Designing a broad locally-resonant bandgap in a phononic crystals

Producing a broad locally-resonant bandgap for low frequencies in a phononic crystals is a challenging task, using conventional methods. In this paper, we describe the design of a broad, locally-resonant, bandgap in a phononic crystals using a numerical simulation. The structure consists of periodic double-sided novel composite sonators, deposited on a 2D locally-resonant phononic-crystals plate made of a rubber-filler array, which is embedded in an epoxy plate. Using the finite element method, we calculate the dispersion relations, the power-transmission spectra, and the displacement fields for the eigenmodes. Our results confirm that, the new structure facilitates a significant increase in absolute bandwidth (by a factor of 4.2) compared to conventional phononic crystals. It also broadens the range of elastic wave attenuation. The formation mechanisms that generates the broad locally-resonant bandgap is explored numerically. The simulation indicates that the formation of this bandgap is possible due to coupling between the entire vibration mode of the novel composite-resonator and the Lamb-wave mode of the 2D locally-resonant phononic-crystals plate. The bandwidth of the locally-resonant bandgap is determined by the resonator mode. This study opens new possibilities to broaden locally-resonant bandgaps of phononic crystals for low frequencies. The results can potentially be used to reduce vibration and noise in many applications.     

Anisotropic phononic crystal structure with low-frequency bandgap and heat flux manipulation

This study presents a two-dimensional phononic crystal with heat flux manipulation and wide bandgaps of out-of-plane modes within the low-frequency range. The anisotropic matrix made of spiral-multilayered materials with different thermal conductivities, and the coating layer inserted with metal are designed for heat flux manipulation. Rubber-coated metal cylinders are periodically embedded in the anisotropic matrix to obtain the low-frequency bandgaps of out-of-plane modes. Numerical simulation is carried out to validate the heat and elastic characteristics of the spiral-multilayered anisotropic structure and reveal the effects of the laying angle and temperature on the bandgaps. Subsequently, a spiral-multilayered plate with periodic structures is studied, which shows an obvious vibration attenuation in the frequency ranges of the bandgaps and a deflected heat flux from the initial propagation direction. In the experimental investigation, the multi-phase spiral-multilayered anisotropic plate is simplified to a single-phase anisotropic plate made of aluminum. The characteristics of this type of anisotropic phononic crystal structure may pave the way for the design of a new kind of thermo-acoustic metamaterial serving in combined thermal and acoustic environments.     

Complete low-frequency bandgap in a two-dimensional phononic crystal with spindle-shaped inclusions

A two-dimensional phononic crystal(PC) structure possessing a relatively low frequency range of complete bandgap is presented. The structure is composed of periodic spindle-shaped plumbum inclusions in a rubber matrix which forms a square lattice. The dispersion relation, transmission spectrum and displacement field are studied using the finite element method in conjunction with the Bloch theorem. Numerical results show that the present PC structure can achieve a large complete bandgap in a relatively low frequency range compared with two inclusions of different materials, which is useful in low-frequency noise and vibration control and can be designed as a low frequency acoustic filter and waveguides. Moreover,the transmission spectrum and effective mass are evaluated to validate the obtained band structure. It is interesting to see that within the band gap the effective mass becomes negative, resulting in an imaginary wave speed and wave exponential attenuation. Finally, sensitivity analysis of the effect of geometrical parameters of the presented PC structure on the lowest bandgap is performed to investigate the variations of the bandgap width and frequency.     

Helmholtz水声换能器弹性壁液腔谐振频率研究

针对传统Helmholtz水声换能器设计中刚性壁假设的局限性,将Helmholtz腔体的弹性计入到液腔谐振频率计算中,实现低频弹性Helmholtz水声换能器液腔谐振频率精确设计.基于细长圆柱壳腔体的低频集中参数模型,导出了腔体弹性引入的附加声阻抗表达式,得到了弹性壁条件下Helmholtz水声换能器等效电路图,给出了考虑了末端修正的弹性壁Helmholtz共振腔液腔谐振频率计算公式.利用ANSYS软件建立了算例模型,仿真分析了不同材质、半径、长度时的Helmholtz共振腔液腔谐振频率.结果对比表明弹性理论值与仿真值符合得很好,相比起传统的刚性壁理论计算结果,本文的弹性壁理论得出的液腔谐振频率值有所降低,与真实情况更加接近.本文的结论可以为精确设计低频弹性Helmholtz水声换能器提供理论支持.     

Simulations on the wide bandgap characteristics of a two-dimensional tapered scatterer phononic crystal slab at low frequency

Aiming at the problem of low-frequency vibration and noise reduction in the engineering field, a new two-dimensional tapered scatterer phononic crystals slab is designed and the bandgap characteristics and displacement vector field of the model are simulated by means of finite element method. The numerical simulations show that an extremely wide complete bandgap can be achieved at low frequency. Compared with the reference model [Acoust. Phys. 65 (2019) 322], the first complete bandgap of the designed model has a lower starting frequency and a wider bandgap which is expanded by nearly 15 times. Moreover, the mechanism of bandgap generation is analyzed, the influences of geometric parameters and structure symmetry on the band structure are also investigated.     

A chiral elastic metamaterial beam for broadband vibration suppression

One of the significant engineering applications of the elastic metamaterial (EMM) is for low-frequency vibration attenuation because of its unusual low-frequency bandgap behavior. However, the forbidden gap from many existing EMMs is usually of narrow bandwidth which limits their practical engineering applications. In this paper, a chiral-lattice-based EMM beam with multiple embedded local resonators is suggested to achieve broadband vibration suppression without sacrificing its load-bearing capacity. First, a theoretical beam modeling is suggested to investigate bandgap behavior of an EMM beam with multiple resonators. New passbands due to dynamic interaction between resonators are unpleasantly formed, which become a design barrier for completely broadband vibration suppression. Through vibration attenuation factor analysis of the resonator, an EMM beam with section-distributed resonators is proposed to enable broadband vibration attenuation function. Required unit number of the resonator in each section is quantitatively determined for complete vibration attenuation in a specific frequency range. Finally, the chiral-lattice-based EMM beam is fabricated, and experimental testing of the proposed structure is conducted to validate the design.     

二维空心散射体声子晶体板的低频带隙特性及其形成机理

利用有限元方法,对设计的涂有硅橡胶包裹层的空心铅柱体嵌入到4个环氧树脂短连接板中构成的声子晶体板的低频带隙特性进行了研究,分析了其能带结构、传输损失及位移场。与正方连接板粘连结构、嵌入结构和细连接短板粘连结构这3种传统声子晶体板的带隙特性作对比,说明具有包裹层、短连接板结构的声子晶体板更容易产生低频宽带;观察位移矢量场的振动模态,并结合弹簧质量模型,解释了带隙形成的机理;通过讨论连接板的宽度、散射体的内外半径及高度对第一完全带隙的影响,说明连接板宽度越窄,厚度越小,散射体内半径越小,外半径越大,高度越高,越有利于带隙的扩展。