THz Imaging with Broadband Thermal Sources

We developed a THz imaging system based on a broadband thermal source (at 500°C) and an asymmetric semiconductor nanochannel, the self-switching nanodiode (SSD), as a room-temperature detector. The maximum resolution was better than 0.5 mm full width at half maximum. The radiation was coupled to the SSD through a microantenna, whose geometry determined the frequency bandwidth of the system. While not as accurate as coherent imaging, the compactness, low-cost, and flexibility make this system attractive for a large range of applications in medical imaging and industrial quality control

Improvement of range-free localization technology by a novel DV-hop protocol in wireless sensor networks

International audienceLocalization is a fundamental issue for many applications in wireless sensor networks. Without the need of additional ranging devices, the range-free localization technology is a cost-effective solution for low-cost indoor and outdoor wireless sensor networks. Among range-free algorithms, DV-hop (Distance Vector - hop) has the advantage to localize the mobile nodes which has less than three neighbour anchors. Based on the original DV-hop algorithm, this paper presents two improved algorithms (Checkout DV-hop and Selective 3-Anchor DV-hop). Checkout DV-hop algorithm estimates the mobile node position by using the nearest anchor, while Selective 3-Anchor DV-hop algorithm chooses the best 3 anchors to improve localization accuracy. Then, in order to implement these DV-hop based algorithms in network scenarios, a novel DV-hop localization protocol is proposed. This new protocol is presented in detail in this paper, including the format of data payloads, the improved collision reduction method E-CSMA/CA, as well as parameters used in deciding the end of each DV-hop step. Finally, using our localization protocol, we investigate the performance of typical DV-hop based algorithms in terms of localization accuracy, mobility, synchronization and overhead. Simulation results prove that Selective 3-Anchor DV-hop algorithm offers the best performance compared to Checkout DV-hop and the original DV-hop algorithm

Evaluation of Mechanical Properties of Σ5(210)/[001] Tilt Grain Boundary with Self-Interstitial Atoms by Molecular Dynamics Simulation

Grain boundary (GB) can serve as an efficient sink for radiation-induced defects, and therefore nanocrystalline materials containing a large fraction of grain boundaries have been shown to have improved radiation resistance compared with their polycrystalline counterparts. However, the mechanical properties of grain boundaries containing radiation-induced defects such as interstitials and vacancies are not well understood. In this study, we carried out molecular dynamics simulations with embedded-atom method (EAM) potential to investigate the interaction of Σ5(210)/[001] symmetric tilt GB in Cu with various amounts of self-interstitial atoms. The mechanical properties of the grain boundary were evaluated using a bicrystal model by applying shear deformation and uniaxial tension. Simulation results showed that GB migration and GB sliding were observed under shear deformation depending on the number of interstitial atoms that segregated on the boundary plane. Under uniaxial tension, the grain boundary became a weak place after absorbing self-interstitial atoms where dislocations and cracks were prone to nucleate

Low-cost plastic optical fiber sensor embedded in mattress for sleep performance monitoring

[EN] In this study, we investigated plastic optical fiber (POF) pressure sensors embedded in mattresses to measure respiration and heart rate for sleep performance monitoring. The signal is amplified in the circuit using a two stage amplification scheme to collect weak respiration and heart rate signals while an algorithm was designed to obtain respiration and heart rate. We also propose a good reliability cutting-POF technology which can be used to improve pressure sensitivity. The experimental results indicate that the mattress can distinguish four behavioral states related to sleep (on bed, lying, moving and leaving bed) and can detect respiration and heart rate values in different positions and postures. Validation experiments on 10 participants showed that absolute error was less than one breath per minute and two beats per minute, making our approach suitable for household sleeping monitoring.National Natural Science Foundation of China (62003046) ; National Defense Basic Scientific Research Program of China (JCKY2018110B011) ; The Spanish Ministerio de Ciencia, Innovacion y Universidades RTI2018-101658-B-I00 FOCAL Project; Guangdong Recruitment Program of Foreign Experts (2020A1414010393) ; Guangdong Basic and Applied Basic Research Foundation (2021A1515011997) ; C. Marques acknowledges Fundacao para a Ciencia e a Tecnologia (FCT) through the CEECIND/00034/2018 (iFish project) and this work was developed within the scope of the project i3N, UIDB/50025/2020 &UIDP/50025/2020, financed by national funds through the FCT/MEC.Han, P.; Li, L.; Zhang, H.; Guan, L.; Marques, C.; Savovic, S.; Ortega Tamarit, B.... (2021). Low-cost plastic optical fiber sensor embedded in mattress for sleep performance monitoring. Optical Fiber Technology. 64:1-8. https://doi.org/10.1016/j.yofte.2021.102541186

Dynamic structural health monitoring of a model wind turbine tower using distributed acoustic sensing (DAS)

AbstractMaintenance of wind turbine towers is currently a manual process that requires visual inspection and bolt tightening yearly. This process is costly to energy companies and its necessity is not well-defined. In this study, two Rayleigh-based distributed fiber optic sensing technologies are evaluated and compared for their ability to monitor the dynamic structural behavior of a model wind turbine tower subject to free and forced vibration. They are further tested for their ability to detect structural phenomena associated with loose bolts and material damage within the tower. The two technologies examined are optical frequency domain reflectometry (OFDR) and phase-based optical time domain reflectometry ($$\phi$$ ϕ -OTDR), which is a technology used in distributed acoustic sensing (DAS). OFDR is a tested and proven strain measurement technology commonly used for structural health monitoring but can only make strain measurements over short distances (10 s of meters). OFDR was used to validate the measurements made with $$\phi$$ ϕ -OTDR which can measure over much longer distances (several kilometers). Due to its sensing distance capability, $$\phi$$ ϕ -OTDR is a promising technology for monitoring many wind turbines networked together with a single fiber optic cable. This study presents a first-of-its-kind use of $$\phi$$ ϕ -OTDR for structural health monitoring to demonstrate its capabilities