- 标题
- 摘要
- 关键词
- 实验方案
- 产品
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Waveguide-input resonant tunnelling diode mixer for THz communications
摘要： This paper considers a group of drogues whose objective is to estimate the physical parameters that determine the dynamics of ocean nonlinear internal waves. Internal waves are important in oceanography because, as they travel, they are capable of displacing small animals, such as plankton, larva, and ?sh. These waves are described by models that employ trigonometric functions parameterized by a set of constants such as amplitude, wavenumber, and temporal frequency. While underwater, individual drogues do not have access to absolute position information and only rely on inter-drogue measurements. Building on this data and the study of the drogue dynamics under the ?ow induced by the internal wave, we design two strategies, referred to as the Vanishing Derivative Method and the Passing Wave Method, that are able to determine the wavenumber and the speed ratio. Either of these strategies can be employed in the Parameter Determination Strategy to determine all the remaining wave parameters. We analyze the correctness of the proposed strategies and discuss their robustness against different sources of error. Simulations illustrate the algorithm performance under noisy measurements as well as the effect of different initial drogue con?gurations.
关键词： underwater robotic drifters,Ocean internal waves,Lagrangian dynamics,robustness to error,cooperative parameter estimation
更新于2025-09-19 17:13:59
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[IEEE 2019 21st International Middle East Power Systems Conference (MEPCON) - Cairo, Egypt (2019.12.17-2019.12.19)] 2019 21st International Middle East Power Systems Conference (MEPCON) - Optimization of Voltage Source Invertera??s Controllers Using Salp Swarm Algorithm in Grid Connected Photovoltaic System
摘要： The dynamic characteristic of an autonomous underwater vehicle (AUV) is affected when it is reconfigured with different payloads. It is desirable to have an updated model, such that the control and guidance law can be redesigned to obtain better performance. Hence, we develop a method to enable online identification of AUV dynamics via in-field experiments, where the AUV is commanded to execute a compact set of maneuvers under doublet excitation. The identification process has two stages. In the training stage, state variable filter and recursive least square (SVF-RLS) estimator is used to estimate the unknown parameters. In the validation stage, the prediction capability of the model is checked using a fresh data set. The parameters converged within 12 s in the experiments using five different thrusts. Validation results show that the identified models are able to explain 78% to 92% of the output variation. Next, we compare the SVF-RLS estimator with the conventional offline identification method. The comparison shows that the SVF-RLS estimator is better in terms of prediction accuracy, computational cost and training time. The usefulness of the identified models is highlighted in two applications. We use it to estimate the turning radius of the AUV at different speeds, and to design a gain-scheduled controller.
关键词： Autonomous underwater vehicles (AUV),system identification
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 4th Advanced Information Technology, Electronic and Automation Control Conference (IAEAC) - Chengdu, China (2019.12.20-2019.12.22)] 2019 IEEE 4th Advanced Information Technology, Electronic and Automation Control Conference (IAEAC) - Research on Sparse Code Shrinkage denoise in Underwater 3D Laser Scanning Images
摘要： Noise removal is the pre-stage and essential step for many image processing tasks. Sometimes it is hard to have correct exposure for camera in underwater environment. In general, we need to have long exposure time to collect the weak light signal which increase the background electrical noise and higher than the signal. Underwater laser scanning is such special case with white laser stripe and dark background images. Hence, noise including which dots, lumps have heavy impact to our laser image. This paper discuss underwater laser scanning image denoise and presents the method based on Sparse code shrinkage algorithm to reduce such noise effect in ?nal reconstructed 3D model. The comparative study using natural and real 3D underwater scanning images is presented on the experimental section.
关键词： SCS,3D laser scanning,Image denoise,Underwater Images
更新于2025-09-19 17:13:59
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Toward Long-Distance Underwater Wireless Optical Communication Based on A High-Sensitivity Single Photon Avalanche Diode
摘要： In this study, we built a single photon avalanche diode (SPAD) receiver based underwater wireless optical communication (UWOC) system. The bit error rate (BER) and signal-to-noise ratio (SNR) performance of UWOC with different distances and data transmission rates were obtained. Based on the water attenuation coefficient of 0.12 m-1, a series of neutral density (ND) filters were exploited to attenuate the light output power from the blue laser diode (LD) to simulate the long distance UWOC. The maximum estimated distances of 144 m and 117 m with corresponding BERs of 1.89 × 10-3 and 5.31 × 10-4 at data transmission rates of 500 bps and 2 Mbps were acquired in UWOC system using on-off keying (OOK) modulation scheme, respectively. Furthermore, we compared the differences between free-space and underwater channels, and a divergence angle of ~1.02 mrad was measured experimentally at a distance of 50 m in the free space. The long UWOC distances obtained in this study partly benefit from high sensitivity SPAD, the small laser divergence angle and low light attenuation. This study provides an approach to achieve long distance UWOC using SPAD.
关键词： laser,on-off keying,single photon avalanche diode (SPAD),Underwater wireless optical communication (UWOC)
更新于2025-09-19 17:13:59
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[IEEE 2019 Device Research Conference (DRC) - Ann Arbor, MI, USA (2019.6.23-2019.6.26)] 2019 Device Research Conference (DRC) - WSe <sub/>2</sub> based Valley-Coupled-Spintronic Devices for Low Power Non-Volatile Memories
摘要： Underwater acoustic (UWA) channels are characterized by a severe spread in time and frequency, and are usually labeled as “doubly spread channels.” In this paper, we propose Doppler-resilient orthogonal signal-division multiplexing (D–OSDM), to provide a highly reliable communication environment in doubly spread channels for UWA communication. D–OSDM multiplexes several data vectors in addition to a pilot vector, and preserves orthogonality among them even after propagation through doubly spread channels, under the assumption that the channel can be modeled by a basis expansion model (BEM). We describe the signal processing steps at the transmitter and the receiver for D–OSDM, and evaluate its performance by both simulations and experiments. To generate a doubly spread channel, a test tank with a wave generator is employed. The obtained results suggest that D–OSDM can provide low-power and high-quality UWA communications in channels with large delay and Doppler spreads; for example, D–OSDM succeeds to achieve a block error rate (BLER) of 10 while BEM-based orthogonal frequency-division multiplexing (OFDM) has a BLER ?oor of in the experiments. Equivalently, D–OSDM can reduce the 10 signal power required for communications to achieve the same BER signi?cantly. Overall, it was found that D–OSDM can become a powerful communication tool for underwater operations.
关键词： underwater acoustic (UWA) communication,multipath channels,Doppler
更新于2025-09-19 17:13:59
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Active Plasmonic Sensors for High-sensitivity Microwave Measurements
摘要： A nominally circular 2-D broadband acoustic array of 1.3-m diameter, comprising 508 sensors and associated electronics, was designed, built, and tested for ambient noise imaging (ANI) potential in Singapore waters. The system, named Remotely Operated Mobile Ambient Noise Imaging System (ROMANIS), operates over 25–85 kHz, streaming real-time data at 1.6 Gb/s over a fiber optic link. By using sensors that are much larger than half-wavelength at the highest frequency of interest, so with some directionality, good beamforming performance is obtained with a small number of sensors compared to a conventional half-wavelength-spaced array. A data acquisition system consisting of eight single-board computers enables synchronous data collection from all 508 sensors. A dry-coupled neoprene cover is used to encapsulate the ceramic elements as an alternative to potting or oil filling, for easier maintenance. Beamforming is performed in real-time using parallel computing on a graphics processing unit (GPU). Experiments conducted in Singapore waters yielded images of underwater objects at much larger ranges and with better resolution than any previous ANI system. Although ROMANIS was designed for ANI, the array may be valuable in many other applications requiring a broadband underwater acoustic receiving array.
关键词： data acquisition,Ambient noise imaging (ANI),underwater acoustics,broadband array design
更新于2025-09-19 17:13:59
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CaOH Molecular Emissions in Underwater Laser-Induced Breakdown Spectroscopy: Spatial–Temporal Characteristics and Analytical Performances
摘要： Recently, molecular emissions from the laser-induced plasma in ambient gas have gained increasing interest; however, very little is known about the case in water solutions. In this work, we investigated the spatiotemporal characteristics of molecular emissions, CaOH for instance, in underwater laser-induced breakdown spectroscopy (LIBS) by using time-resolved spectroscopy, spectral-resolved imaging, and shadowgraph techniques. It was shown that clear CaOH molecular bands can be observed in the spectrum at very early times after the laser pulse and presented a much longer lifetime and more homogeneous emission distribution compared with the Ca I and Ca II lines. Such unique characteristics of CaOH molecular emission inspired us to improve the performances of underwater LIBS by using the CaOH molecular bands instead of Ca I and Ca II lines. We demonstrated the excellent quanti?cation results of CaOH with higher stability, less self-absorption, and reduced matrix e?ect. Meanwhile, the limit of detection (LOD) of Ca with the CaOH molecular band (2.46 ppm) is comparable to that with the atomic line of Ca I (2.07 ppm), and much lower than that with the ionic line of Ca II (13.81 ppm), indicating a good sensitivity of CaOH. This work gives not only some insights into the molecule formation mechanisms in underwater plasmas, but also provides new ideas to improve the analytical performances of underwater LIBS.
关键词： analytical performances,CaOH molecular emissions,underwater laser-induced breakdown spectroscopy,spatiotemporal characteristics
更新于2025-09-19 17:13:59
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[IEEE 2019 13th International Conference on Software, Knowledge, Information Management and Applications (SKIMA) - Island of Ulkulhas, Maldives (2019.8.26-2019.8.28)] 2019 13th International Conference on Software, Knowledge, Information Management and Applications (SKIMA) - Real-Time Video Dehazing for Industrial Image Processing
摘要： The dynamic characteristic of an autonomous underwater vehicle (AUV) is affected when it is reconfigured with different payloads. It is desirable to have an updated model, such that the control and guidance law can be redesigned to obtain better performance. Hence, we develop a method to enable online identification of AUV dynamics via in-field experiments, where the AUV is commanded to execute a compact set of maneuvers under doublet excitation. The identification process has two stages. In the training stage, state variable filter and recursive least square (SVF-RLS) estimator is used to estimate the unknown parameters. In the validation stage, the prediction capability of the model is checked using a fresh data set. The parameters converged within 12 s in the experiments using five different thrusts. Validation results show that the identified models are able to explain 78% to 92% of the output variation. Next, we compare the SVF-RLS estimator with the conventional offline identification method. The comparison shows that the SVF-RLS estimator is better in terms of prediction accuracy, computational cost and training time. The usefulness of the identified models is highlighted in two applications. We use it to estimate the turning radius of the AUV at different speeds, and to design a gain-scheduled controller.
关键词： system identification,Autonomous underwater vehicles (AUV)
更新于2025-09-19 17:13:59
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Underwater wire-feed laser deposition of the Ti–6Al–4V titanium alloy
摘要： Underwater wire-feed laser deposition (UWLD) of the Ti-6Al-4V alloy was firstly carried out utilizing a laser deposition nozzle, and the deposition appearance, geometry characteristics, microstructure and microhardness of deposited tracks were studied. At a lower gas flow rate, the absorption of residual water and scattering of aerosol particles on laser beam caused UWLD instability and decreased molten metal wettability. Upon increasing the gas flow rate, the aerosol particle density decreased, increasing the laser density and decreasing the cooling rate of molten metal; thus, the height and deposition angle of UWLD track decreased as the corresponding width and fusion depth increased. The microstructures of the deposited metal at a gas flow rate of 10 L/min were composed of the coarse lath α phase in upper region and the acicular martensite α′ with different size scales in middle and bottom regions. With increasing the gas flow rate to 20 L/min, the microstructure was primarily acicular martensite along with a small amount of α phase, and the martensite exhibited a larger grain size and stronger texture. At a gas flow rate of 20 L/min, the deposited process was stable and uniform deposition track without oxidation layer was obtained for UWLD Ti-6Al-4V alloy.
关键词： Ti-6Al-4V alloy,Laser propagation mechanism,Microstructure,Microhardness,Underwater wire-based laser deposition,Geometrical characteristics
更新于2025-09-19 17:13:59
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Caustic and Weakly Diverging Beams in Horizontally Inhomogeneous Oceanic Waveguides
摘要： Using approximate analytical calculations based on the WKB and adiabatic approximations for the mode representation of the field, as well as numerical simulation based on the theory of adiabatic modes, geometric acoustic approximation, and the parabolic equation method, the patterns of the formation and propagation of caustic and weakly diverging acoustic beams in a horizontally inhomogeneous refractive oceanic waveguide are studied. The horizontal distance regions are determined at which the dependences of the acoustic field intensity on the horizontal distance typical of caustic and weakly diverging beams are retained. The study considers the processes involved in reformation of caustic and weakly diverging beams in an oceanic waveguide with increasing water layer depth and constant sound speed profile, which near the source characterized an underwater sound channel open toward the bottom. The conditions are formulated for an effectively matched transition of shallow-water waveguide modes refracted in the thermocline and interacting with the bottom to purely refracted modes of the underwater sound channel in a relatively deep water part of the oceanic waveguide.
关键词： caustic beams,vertical arrays,oceanic waveguides,tone sources,weakly diverging beams,point sources,underwater sound channels
更新于2025-09-19 17:13:59