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21.
常规驻极体传声器阵列成像系统存在数据采集系统复杂、体积大的问题,因而阵列传感器数量一般不超过60个,成像质量较差。为此,本文以数字式MEMS声传感器基础设计了260个传感器的声阵列,数据采集系统由FPGA控制,并嵌入到前端阵列中,后端是在另一个FPGA控制下的1个DSP芯片和2个PC104模块组成的集成系统,其中高速DSP芯片完成阵列信号处理以实现声成像功能。该系统能够实现对普通车间环境下机械设备噪声、气体泄漏噪声的现场成像测试,形成动态声像图。测试表明,该系统抗干扰能力强、声像分辨率高、成像速度快,实用效果良好。 相似文献
22.
The improvement of miscibility between toughened Polyamide-6 (PA6) and Styrene-Butadiene Rubber (SBR) was carried out using grafted Glycidyl Methacrylate (SBR-g-GMA). At first, the compatibilizers were prepared using different comonomers, Styrene, and N-vinyl pyrrolidone. Central composited design (CCD) was distinctly applied to study the influence of Glycidyl Methacrylate (GMA) content and comonomer/GMA on the process of compatibilizer preparation. Four models were developed for Gel content and Degree of grafting for both comonomers using Design-expert software. The models were used to calculate the optimum operating conditions and according to the Flory-Huggins parameter and obtained results, SBR-co-NVP-g-GMA was chosen as an effective compatibilizer. Afterward, another CCD was employed to scrutinize the effect of various amounts and grafting degree of compatibilizer on morphology and mechanical properties of PA6/SBR. The Interparticle distance and polydispersity were studied using a Scanning electron microscope (SEM) and also the Izod impact test inspected in order to evaluate the mechanical properties. Finally, modulus and impact strength were optimized to minimize the former and maximize the latter. Also, the most practical terms in the fitted model are statistically specified using F-value. The root causes for the improvement of blend properties were attributed to a chemical reaction between epoxy groups in SBR-g-GMA and both the carboxylic and amine groups in PA6. Impact strength (539.8 J/m) and modulus (2017.2 N/mm2) of the optimum blend indicate an excellent agreement with the amounts predicted by the models. 相似文献
23.
This study is focused on multiscale characterization and constitutive parameters identification of selectively laser sintered PA12 specimens. The process parameters and change in crystallinity due to 3D printing were identified via differential scanning calorimetry (DSC). Tension, compression, shear, flexural and fracture tests performed on samples fabricated, both in 0° and 90° directions reveal that the tensile toughness of samples printed in 0° orientation, outperform samples printed in 90° orientation by an average of 24%. Cryogenically fractured samples were analyzed via SEM and micro-computed tomography to analyze 2D/3D defects and correlate the microstructure with macroscopic properties. The constitutive parameters for a strain-rate and temperature-dependent Three Network (TN) material model were identified using the measured mechanical properties. Furthermore, mechanical response of micro-architected Kelvin lattice structure was analyzed by Finite Element Method employing the TN constitutive model and the predictions were corroborated with measurements. 相似文献
24.
In additive manufacturing, polymer composites are used for setting tailored properties. Short glass fibers can be used as fillers for polyamide 12 for enhancing stiffness or tensile strength as well as for reducing shrinkage. In this paper, the effects of short glass fibers on polyamide 12 concerning powder properties, process behavior and part properties in laser beam melting of polymers (SLS) are investigated. It could be shown that by increasing the short glass fiber content powder properties as well as part properties are immensely affected. By adding glass fibers, powder properties, like flowability and diffuse reflection decrease. The isothermal crystallization changes resulting in a narrower processing window. Concerning mechanical properties, short glass fibers allow for a higher stiffness until a critical limit of filler concentration within this study is reached, after which the tensile strength decreases. The elongation of break decreases by rising the filler content. 相似文献
25.
β-cyclodextrin (β-CD) based materials have been studied widely as adsorbents and filter membranes for removing pollutants in air or water applications. The present study aimed to develop a sandwich structure of eletrospun nanofibrous membrane based on β-cyclodextrin and PA66 to achieve the high mechanical strength and flow-through adsorption of heavy metal ions in water. The surface and cross section morphology of PA66/β-cyclodextrin/PA66 nanofibrous membranes (PA66/β-CD/PA66 NMs) were examined using scanning electron microscopy (SEM). The physicochemical and mechanical properties of PA66/β-CD/PA66 NMs were analyzed by differential scanning calorimetry (DSC), thermogravimetric (TG) analysis and universal testing machine. The diameter of β-CD and PA66 electrospun fibers are 300–400 nm and 20–40 nm respectively. PA66/β-CD/PA66 NMs show a loosely arranged fibers and layer by layer structure. The tensile strength increases remarkably for PA66/β-CD/PA66 NMs, from 1.33 MPa of β-CD NMs to 23.17 MPa and the Young's modulus increases from 34.8 MPa to 253.3 MPa. The mechanical behavior of PA66/β-CD/PA66 NMs is a typical brittle fracture, and its microcosmic fracture diagrams are also involved. TGA/DSC results confirm the thermal crosslinking reaction is effective and complete. On the basis of SEM, DSC, TG and mechanical behavior analysis results, the molecular mechanism of in situ thermal crosslinking reaction is discussed. Fe3+、Ni2+ were used to confirm the ability to absorb heavy metal ions of PA66/β-CD/PA66 NMs. In conclusion, PA66/β-CD/PA66 NMs could be a promising solution for removal of metal ions by flow-through adsorption. 相似文献
26.
Xu Bing Cai Guanghui 《高校应用数学学报(英文版)》2007,22(3):316-324
A maximal inequality for the partial sum of NA sequence is constructed.By using this inequality the complete convergence rates in the strong laws for a class of dependent random variables for weighted sums are discussed.The results obtained extend the results of Liang(1999, 2000). 相似文献
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28.
主要介绍了传声器阵列的基本原理、结构组成及声学效果,简要叙述传声器阵列在通信与PC设备中的基本应用与市场发展前景。 相似文献
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