本文设计了一种新型的二维声子晶体结构，采用有限元法和等效模型法进行了深入研究，发现该结构具有良好的低频吸声性能。通过理论推导和仿真计算发现，在21 mm的晶格常数条件下，该结构在0~800 Hz具有完整的四条带隙。第一带隙下限低至40.28 Hz，且具有约为93 Hz的带宽，计算其传声损失后，发现其在低频域内具有良好的隔声效果，最大隔声量可达87.31 dB。对该结构的多个振动模态分析，建立相应的等效模型，并基于等效模型探究了不同因素对带隙频段造成的影响，总结出该新型二维声子晶体的一般性规律。研究结果表明，增大散射体密度和减小基体密度可以增加带宽，增大填充率和对散射体适当进行开孔处理可以改善带隙特性。该研究对于解决低频噪声控制问题具有一定参考意义和工程应用价值。
声子晶体 局域共振 带隙机理 低频降噪 隔声 散射体 phonon crystal local resonance band gap mechanism low frequency noise reduction acoustic insulation scatterer
Author Affiliations
Abstract
1 State Key Laboratory for Manufacturing Systems Engineering, Xi’an Jiaotong University, Xi’an 710049, China
2 School of Information and Communications Engineering, Xi’an Jiaotong University, Xi’an 710049, China
3 Physikalisches Institut, Goethe-Universität, 60438 Frankfurt am Main, Germany
Recently, multifarious deformation approaches in nature have promoted dynamic manipulation for electromagnetic (EM) waves in metamaterials, and those representative strategies are mainly focused on the modulation of spectral parameters. Several works have also achieved tunable phase-gradient meta-devices. Here, to broaden the modulation freedom of mechanical deformation, we initially propose two reconfigurable metamaterials consisting of mirrored S-shaped meta-atoms selectively bonded on biaxially pre-stretched substrates. Planar meta-atoms with spin-insensitive transmittance are buckled into 3D morphologies to break residual symmetries by releasing the stress and to facilitate spin-dependent transmittance under circularly polarized incidence. Owing to the geometric anisotropy of S-shaped meta-atoms along the and axes, 3D chiral meta-atoms exhibit discriminate circularly cross-polarized transmittance under opposite spins. The underlying physical mechanism reveals that EM resonance originates from the excitation of electric dipoles and magnetic dipoles, and their cross coupling finally triggers the chiral effects of 3D meta-atoms. By introducing the gradient-phase design that keeps unchanged under various strains, two types of meta-atoms with specified orientations are interleaved to design a double-foci metalens, and its 2D-to-3D morphology transformation shortens the focusing length and facilitates the intensity change of two foci. Our approach in designing reconfigurable EM metamaterials with 2D-to-3D buckling transformability can be further extended toward terahertz even optical wavebands, and it may assist with deriving more applicable multi-functionalities in the aspects of imaging, sensing, and holograms.
Photonics Research
2023, 11(10): 1770
本文针对低频噪声的控制问题, 设计了一种腔体结构可调的Helmholtz型声子晶体, 该结构内腔由一活动伸缩螺杆连接的隔板分为上下两腔, 并采用弓字形开口通道设计。采用有限元法对该结构的带隙特性与隔声特性进行了分析, 并通过“声力类比”的方法构建了该结构在带隙起始频率与截止频率处的等效模型。研究表明, 该结构在500 Hz以下频段内具有6条带隙, 最低带隙频率可达31.34 Hz, 且在每条带隙频段内都表现出了良好的隔声性能, 最大隔声量可达111.95 dB。最后, 通过调整伸缩螺杆, 改变腔体结构布局, 可将多条共振带隙相连, 不仅可以构成一个较宽的带隙, 而且可以达到调节隔声频段的目的。该设计为改善Helmholtz型声子晶体的隔声性能提供了新的设计思路。
声子晶体 带隙 Helmholtz腔 隔声 低频噪声 腔体可调 phononic crystal bandgap Helmholtz resonator sound insulation low-frequency noise adjustable chamber
1 空军工程大学基础部，西安 710051
2 空军工程大学航空工程学院，西安 710038
为了解决飞机舱室中的低频噪声问题，本文设计了一种双迷宫型通道的Helmholtz周期结构。迷宫型开口通道的设计能够大大增加Helmholtz腔开口通道的长度，有效降低低频带隙下限，双通道的设计能够增加声子晶体局域共振的区域，可以增加低频带隙数目。本文采用有限元法(FEM)得到了该结构在0~500 Hz频率范围内的能带结构及隔声特性，经过深入研究发现，该Helmholtz 周期结构在0~500 Hz范围内存在多个低频带隙，且在低频范围内表现出较好的隔声特性。为了揭示其带隙产生机理，本文通过声-电类比方法建立了该结构的等效电路模型，并通过有限元法和等效电路模型，对低频带隙影响因素进行了详细分析。结果表明，增加开口通道的长度能够降低带隙起始频率，较小的晶格常数有利于拓宽带隙宽度。本文的研究进一步探索了声子晶体结构设计对带隙的影响，为解决飞机舱室的低频降噪问题提供了新方法。
声子晶体 带隙 Helmholtz腔 隔声特性 有限元法 声-电类比 低频 飞机舱室 phononic crystal band gap Helmholtz resonator sound insulation characteristic finite element method electro-acoustic analogy low-frequency aircraft cabin
Author Affiliations
Abstract
1 College of Food Science and Nutritional Engineering China Agricultural University, Beijing 100083, P. R. China
2 National Engineering Research Center for Vegetables (NERCV) Beijing 100097, P. R. China
Nondestructive evaluation of melon quality is in great need of comprehensive study. Soluble solids content (SSC) and firmness are the two indicators of melon internal quality that mostly affect consumer acceptance. To provide guidance for fruit classification, internal quality standards was preliminarily established through sensory test, as: Melon with SSC over 12° Brix, firmness 4–5.5 kgf · cm-2 were considered as satisfactory class sample; and SSC over 10° Brix, firmness 3.5–6.5 kgf · cm-2 as average class sample. The near infrared (NIR) nondestructive detection program was set as spectra collected from the stylar-end, Brix expressed by the average SSC of inner and outer mesocarp, each cultivar of melon was detected with its own optimum integration time, and the second derivative algorithm was used to equalize them. Using wavelength selected by genetic algorithms (GA), a robust SSC model of mix-cultivar melon was established, the root mean standard error of cross-validation (RMSECV) was 0.99 and the ratio performance deviation (RPD) nearly reached 3.0, which almost could meet the accuracy requirement of 1.5° Brix. Firmness model of mix-cultivar melon was acceptable but inferior.
Melon nondestructive detection near-infrared fruit quality soluble solids content firmness Journal of Innovative Optical Health Sciences
2015, 8(6): 1550032
Author Affiliations
Abstract
1 College of Food Science and Nutritional Engineering China Agricultural University 17 Qinghua East Road, Haidian District Beijing, P. R. China
2 National Engineering Research Center for Vegetables 50 Zhanghua Street, Haidian District Beijing, P. R. China
Two nondestructive methods based on visible and near-infrared (VIS-NIR) spectroscopy and X-ray image have been used for the evaluation of watermelon quality. The prediction performance based on partial least squares (PLS) by diffuse transmittance measurement (500–1010 nm) was evaluated for chemical quality attributes SSC (Rc = 0.903; RMSEC = 0.572% Brix; Rp = 0.862; RMSEP = 0.717% Brix; RPD = 1.83), lycopene (Rc = 0.845; RMSEC = 0.266 mg/ 100gFW; Rp = 0.751; RMSEP = 0.439 mg/100gFW; RPD = 1.13) and moisture (Rc = 0.917; RMSEC = 0.280%; Rp = 0.937; RMSEP = 0.276%; RPD = 2.79). The X-ray calibration linear equations developed by extracting the appropriate gray threshold were sufficiently precise for volume (R2 = 0.986) and weight (R2 = 0.993). In order to optimize prediction model of watermelon quality in growth period, multivariate multi-block technique factor analysis enabled integration of these traits: chemical information is related to physical information. Applying principle component analysis to extract common factors and varimax with Kaiser normalization to improve explanatory, the comprehensive indicator based on variances was established satisfactorily with Rc = 0.94, RMSEC = 0.244, Rp = 0.93, RMSEP = 0.344 and RPD = 2.00. A comparison of these models indicates that the comprehensive indicator determined only by portable VIS-NIR spectrometer appears as a suitable method for appraising watermelon quality nondestructively on the plant at different ripen stages. This method contributes to infer the picking date of watermelon with higher accuracy and bigger economic benefits than that by experience.
Visible and near-infrared spectroscopy X-ray imaging maturity process factor analysis comprehensive indicator Journal of Innovative Optical Health Sciences
2014, 7(4): 1350034
中国农业大学食品科学与营养工程学院, 北京 100083
近红外(NIR)光谱分级技术正越来越广泛地应用于水果的产后加工和质量评判中。介绍了水果内部品质光学特性检测原理; 分析了规则反射、透射和漫反射3种光特性测量方法在水果内部品质不同需求检测中的适用性; 化学计量学方法是近红外光谱分析技术的一个重要部分,对一些新的预处理方法和回归算法作了介绍; 探讨了水果状态对光谱影响及修正方法,如温度补偿、大小修正等; 并阐述了水果的糖度、酸度、硬度等定量检测和褐变、黑心、水心、损伤等定性判别的国内外最新研究进展; 分析了近红外技术在水果品质检测和控制方面的应用前景。
应用光学 近红外光谱 无损检测 化学计量学 光谱预处理 水果 内部品质
