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超声技术在混凝土离析检测中的应用 被引量:1
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作者 占宇飞 《江西建材》 2008年第3期80-81,98,共3页
1超声测缺和测强原理超声测缺的基本原理:超声波在不同的介质中传播时,将产生反射、折射、散射、绕射和衰减等现象,使得由接收换能器上接收的超声波信号的声时、振幅、波形或频率发生了相应的变化,测定这些变化就可以判定混凝土材料某... 1超声测缺和测强原理超声测缺的基本原理:超声波在不同的介质中传播时,将产生反射、折射、散射、绕射和衰减等现象,使得由接收换能器上接收的超声波信号的声时、振幅、波形或频率发生了相应的变化,测定这些变化就可以判定混凝土材料某些方面的性质和结构内部构造的情况。如图1所示。 展开更多
关键词 ultrasonic technology strength detection inner quality concrete strength
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Robust and Passive Motion Detection with COTS WiFi Devices 被引量:4
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作者 Hai Zhu Fu Xiao +3 位作者 Lijuan Sun Xiaohui Xie Panlong Yang Ruchuan Wang 《Tsinghua Science and Technology》 SCIE EI CAS CSCD 2017年第4期345-359,共15页
Device-free Passive(DfP) detection has received increasing attention for its ability to support various pervasive applications. Instead of relying on variable Received Signal Strength(RSS), most recent studies rel... Device-free Passive(DfP) detection has received increasing attention for its ability to support various pervasive applications. Instead of relying on variable Received Signal Strength(RSS), most recent studies rely on finer-grained Channel State Information(CSI). However, existing methods have some limitations, in that they are effective only in the Line-Of-Sight(LOS) or for more than one moving individual. In this paper, we analyze the human motion effect on CSI and propose a novel scheme for Robust Passive Motion Detection(R-PMD). Since traditional low-pass filtering has a number of limitations with respect to data denoising, we adopt a novel Principal Component Analysis(PCA)-based filtering technique to capture the representative signals of human motion and extract the variance profile as the sensitive metric for human detection. In addition, existing schemes simply aggregate CSI values over all the antennas in MIMO systems. Instead, we investigate the sensing quality of each antenna and aggregate the best combination of antennas to achieve more accurate and robust detection. The R-PMD prototype uses off-the-shelf WiFi devices and the experimental results demonstrate that R-PMD achieves an average detection rate of 96.33% with a false alarm rate of 3.67%. 展开更多
关键词 device-free passive detection Received Signal strength(RSS) channel state information MIMO
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