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More and more underwater robots are deployed to investigate marine biodiversity autonomously, and tools are needed by underwater robots to discover and acknowledge marine life. This paper has proposed a convolutional neural network-based method for intelligent fish detection and recognition with a dataset used for training and testing generated and augmented from an open-source Fish Database regarding 6 different types. Firstly, to improve image quality, a hybrid image enhancement algorithm is used to preprocess underwater images with a weighted fusion strategy of multiple traditional methodologies and comparisons have been made to prove the effectiveness according to various indexes. Secondly, to increase detection and recognition accuracy, different attention modules are integrated into the YOLOv5m network structure and the convolutional block attention module(CBAM) has outperformed other modules in recall rate and mAP while maintaining the capability of real-time processing. Lastly, to meet real-time requirements, lightweight adjustments have been made to CBAM-YOLOv5m with the GSConv module and C3Ghost module and a nearly 25% reduction in network parameters and a 20% reduction in computational consumption are obtained. Besides, the lightweight network has realized better accuracy than YOLOv5m. In conclusion, the method proposed in this paper is effective in real-time fish detection and recognition with practical application prospects. [ABSTRACT FROM AUTHOR]

This paper investigates the terrain-following problem for an autonomous underwater vehicle (AUV) from control perspectives with full consideration of terrain characteristics. By equipping the AUV with three simple single-beam echo sounders, a set of precise along-track bottom slopes are obtained in a real-time manner, and the occurrence of the lost bottom lock phenomenon caused by a single sonar altimeter is eliminated. A slope-based data processing method is developed, which enables an AUV to characterize seafloor features with complementary sensing modalities to generate proper adaptive height-modified values. In order to keep a fixed height when maneuvering over rugged terrains, a back-stepping depth control is implemented by adjusting horizontal rudder angle, and Lyapunov theory is adopted to analyze the asymptotic stability of the resulting terrain-following control system. At last, simulation results indicate the feasibility and effectiveness of the proposed methodology with a discussion of various sensor configurations. [ABSTRACT FROM AUTHOR]

A new wideband cross-dipole antenna (CDA) with a circularly polarized (CP) characteristic is proposed in this article. The antenna consists of four L-shaped patches, two modified trapezoid-microstrip lines as an impedance tuner, a pair of vacant-quarter feeding loops as a continuous-phase feeding network, and four grounded inverted L-shaped strips as parasitic elements. It is noticed that the grounded inverted L-shaped strips are inserted directly below the L-shaped patches to increase the CP bandwidth and enhance the gains of the antenna, which is different from the conventional parasitic elements. First, a pair of vacant-quarter feeding loops is used as a feeding structure to provide a sequential phase characteristic. Second, four L-shaped patches as driven elements are connected to the feeding structure to excite two CP resonant modes. Third, two modified trapezoid-microstrip lines are inserted into the feeding structure to adjust the impedance match. Moreover, four grounded inverted L-shaped strips are introduced into the square reflector to achieve wider CP operation by utilizing a gap capacitive coupling feeding way. Finally, the proposed antenna is simulated, manufactured, and measured to verify the design rationality. The measured results indicate the proposed antenna has a broad 3-dB ARBW of 82.5% (1.38–3.32 GHz, 2.35 GHz) and a wide −10-dB IBW of 81.2% (1.18–3.04 GHz, 2.29 GHz). Furthermore, the measured and simulated CP bandwidths are 75.1% (1.38–3.04 GHz, 2.21 GHz) and 74.7% (1.36–2.98 GHz, 2.17 GHz), which is suitable for CP applications in WiBro (2.3–2.39 GHz) and GPS (L1 1.575 GHz) bands. [ABSTRACT FROM AUTHOR]

The global fixed-time sliding mode control strategy is designed for the manipulator to achieve global fixed-time trajectory tracking in response to the uncertainty of the system model, the external disturbances, and the saturation of the manipulator actuator. First, aiming at the lumped disturbance caused by system model uncertainty and external disturbance, the adaptive fixed-time sliding mode disturbance observer (AFSMDO) was introduced to eliminate the negative effects of disturbance. The observer parameters can adaptively change with disturbances by designing the adaptive law, improving the accuracy of disturbance estimation. Secondly, the fixed-time sliding surface was introduced to avoid singularity, and the nonsingular fixed-time sliding mode control (NFSMC) design was put in place to ensure the global convergence of the manipulator system. Finally, the fixed time saturation compensator (FTSC) was created for NFSMC to prevent the negative impact of actuator saturation on the manipulator system, effectively reducing system chatter and improving the response speed of the closed-loop system. The fixed-time stability theory and Lyapunov method were exploited to offer a thorough and rigorous theoretical analysis and stability demonstration for the overall control system. Simulation experiments verify that the designed control scheme has excellent control effects and strong practicability. [ABSTRACT FROM AUTHOR]

A novel broadband circularly polarized square-slot antenna with parasitic elements is presented in this article. The proposed antenna with dimensions of 77.6 × 77.6 × 1.6 mm3 is composed of a L-shaped strip, a pair of rectangular slots, a L-shaped branch, and an inverted L-shaped feeding line. First, a pair of rectangular slots are used to excite an impedance resonance point that appears near 4.8 GHz and improve the axial ratio bandwidth (ARBW). Second, a L-shaped strip etched into the square-slot ground plane is used to enhance the ARBW. Third, a L-shaped branch is inserted into the inverted L-shaped feeding line to improve the impedance matching at high frequencies. At a result, the multiple circularly polarized (CP) resonant points could be excited by using these slot and strips as perturbation elements to alter the surface current distribution of the antenna. To demonstrate the design rationality, a designed antenna model is simulated, manufactured, and measured. The tested results show the proposed antenna has a wider −10-dB impedance bandwidth from 2.6 to 6.6 GHz (86.9%) and a broad 3-dB ARBW from 2.35 to 5.80 GHz (84.7%). In addition, the measured peak gain of the antenna is 4.8 dBi. The presented antenna has a potential application value in C band wireless communication. [ABSTRACT FROM AUTHOR]

For the large equipment, system model is usually difficult to obtain, or changes slowly with the running time. Therefore, some methods based on accurate model are difficult to apply, such as wind turbine. Therefore, the data‐based robust value iteration method based on data is studied for variable pitch control of wind turbine for the first time, which can deal with uncertainty and do not require an accurate model. First, a new data‐driven Bellman equation is derived base on the system operation data. Next, the robust VI structure based on data is designed, which is a model free iteration algorithm. Then, a data‐driven value iteration pitch controller is proposed, the simulation results show the effectiveness of the control method. [ABSTRACT FROM AUTHOR]

In this article, a novel wideband circularly polarized (CP) square‐slot antenna with perturbation elements is proposed. The antenna comprises of an inverted L‐shaped feeding line, pairs of corner cuts, a rectangular slot, and a semi‐elliptical patch. The numerous CP resonant modes were excited simultaneously using these slots and patches as perturbation elements. To verify this concept, an antenna prototype was built and tested. The measured results indicate the −10‐dB impedance bandwidth (IBW) is 69.2% (2.42–4.98, 3.7 GHz) and 3‐dB axial ratio bandwidth (ARBW) is 59% (2.58–4.74, 3.66 GHz). Furthermore, the measured peak gain is 4.3 dBi, and the gain variation within the certain bandwidth is less than 1 dB. Therefore, the presented antenna features wide CPBW and stable gain characteristics. [ABSTRACT FROM AUTHOR]

In this paper, a novel 2 × 2 square slot wideband circularly polarized antenna array (CPAA) is proposed. The antenna consists of a sequential rotation feeding structure, four asymmetric U‐shaped feeding strips and a slotted ground plane formed by four square slots with cut corners, four rectangular slots, and four L‐shaped strips. In contrast to the traditional L‐shaped feeding strips used in CPAAs, an asymmetric U‐shaped feeding strip is, for the first time, presented to improve the antenna performance. By using these strips and slots as perturbation elements, the slotted CPAA is able to stimulate multiple circular polarized (CP) radiation modes, resulting in wideband CP radiation. The measured results revealed that the 3‐dB axial‐ratio (AR) bandwidth for AR < 3 reached 81.3% (1.75–4.15 GHz), whereas the −10‐dB impedance bandwidth (|S11| < −10 dB) reached 88.6% (1.96–5.08 GHz). [ABSTRACT FROM AUTHOR]

In this article, we propose a wide square-slot CPA loaded with a semi ellipse patch. The proposed antenna consists of a sequential rotation feeding structure, a square-slot ground-plane with corner cuts, and an asymmetric U-shaped feeding strip. In contrast to the traditional strips and slots etched into the square-slot ground-plane, semi ellipse patch is first inserted into the ground-plane to increase the antenna bandwidth. In addition, four rectangular slots are used to adjust the impedance matching. The slot CPAA could excite multipole CP resonant modes using these slots and patches, which result in the wideband radiation. The proposed slot CPAA has outstanding characteristics of 85.7% (2.0–5.0 GHz) −10-dB IBW and 68.3% (2.20–4.48 GHz) 3-dB ARBW, which would be a potential candidate in the wideband communication. [ABSTRACT FROM AUTHOR]

This paper proposes a novel wideband circularly polarized (CP) dielectric resonator antenna (DRA) loaded with strips. The CP DRA comprises a circular DR, two pairs of driven L-like DR strips with different lengths, and a square ground-plane. To couple the electromagnetic energy to circular DR, an orthogonal cross-slot is used, and a stepped microstrip-line is also used to adjust the impedance matching. Influenced by the concept of deformed DR, two pairs of L-like DR strips of different lengths are inserted into the circular DR as part of the driven element to excite a new axial ratio (AR) resonant point. An antenna prototype is simulated, manufactured, and measured to validate the unique design. The measured results show that the designed antenna has broadband characteristic with a −10 dB IBW of 54% (1.91–3.32 GHz) and 3 dB ARBW of 42.1% (2.10–3.22 GHz). [ABSTRACT FROM AUTHOR]

Cooperative tracking control problem of multiple water–land amphibious robots is discussed in this article with consideration of unknown nonlinear dynamics. Firstly, the amphibious robot dynamic model is formulated as an uncoupled nonlinear one in horizontal plane through eliminating relatively small sway velocity of the platform. Then cooperative tracking control algorithm is proposed with a two-stage strategy including dynamic control stage and kinematic control stage. In dynamic control stage, adaptive consensus control algorithm is obtained with estimating nonlinear properties of amphibious robots and velocities of the leader by neural network with unreliable communication links which is always the case in underwater applications. After that, kinematic cooperative controller is presented to guarantee formation stability of multiple water–land amphibious robots system in kinematic control stage. As a result, with the implementation of graph theory and Lyapunov theory, the stability of the formation tracking of multiple water–land amphibious robots system is proved with consideration of jointly connected communication graph. At last, simulations are carried out to prove the effectiveness of the proposed approaches. [ABSTRACT FROM AUTHOR]