Path-Following Control With Obstacle Avoidance of Autonomous Surface Vehicles Subject to Actuator Faults

This paper investigates the path-following control problem with obstacle avoidance of autonomous surface vehicles in the presence of actuator faults,uncertainty and external disturbances.Autonomous surface vehicles inevitably suffer from actuator faults in complex sea environments,which may cause existing obstacle avoidance strategies to fail.To reduce the influence of actuator faults,an improved artificial potential function is constructed by introducing the lower bound of actuator efficiency factors.The nonlinear state observer,which only depends on measurable position information of the autonomous surface vehicle,is used to address uncertainties and external disturbances.By using a backstepping technique and adaptive mechanism,a path-following control strategy with obstacle avoidance and fault tolerance is designed which can ensure that the tracking errors converge to a small neighborhood of zero.Compared with existing results,the proposed control strategy has the capability of obstacle avoidance and fault tolerance simultaneously.Finally,the comparison results through simulations are given to verify the effectiveness of the proposed method.

A low-cost invasive microwave ablation antenna with a directional heating pattern

Microwave ablation(MWA) is a cancer treatment method. The tumor tissue absorbs electromagnetic energy, which heats and kills it. A microwave ablation antenna plays a critical role in this process. Its radiation field must completely cover the tumor but not the healthy tissue. At present, the radiation pattern of most invasive ablation antennas is spherical.However, in the clinic, the shape of some tumors may be asymmetrical or the antenna cannot be inserted into the center of the tumor for some other reason. In order to solve these problems, a directional heating antenna for microwave ablation is proposed in this paper. The proposed antenna, operating at 2.45 GHz, consists of a monopole and a reflector. The feed is given by a substrate integrated coaxial line(SICL) and coplanar waveguide(CPW). The omnidirectional radiation field of the monopole is reflected by a reflector that is extended from the outer conductors of the SICL to form a directional radiation field. The impedance matching network is designed on SICL to match the antenna to 50 Ω. The antenna is fabricated using a mature printed circuit board(PCB). The reflection coefficient of the antenna in porcine liver tissue measured by a vector network analyzer shows good agreement with the simulations. Then, an ablation experiment in porcine liver is conducted with power of 10 W for 10 min, and the experimental results confirm the validity of the design.

A VO_(2) film-based multifunctional metasurface in the terahertz band

We proposed a multifunctional terahertz metasurface based on a double L-shaped pattern and a vanadium dioxide(VO_(2)) film separated by polyimide.When the VO_(2)film is an insulator,a dual-band electromagnetically induced transparency effect is obtained,and the physical mechanism is investigated based on the current distribution and "two-particle" model.When the VO_(2)film is a metal,a dual-band linear-to-circular polarization converter,in which the y-polarized linear wave can be effectively converted to left-handed circularly polarized(LCP) and right-handed circularly polarized simultaneously in different bands,can be achieved.By arranging the metal pattern rotating 30°,a multifunctional antenna can be obtained.When the VO_(2)is an insulator,the radiation of the LCP wave is divided into four beams,with two beams reflected and two beams transmitted.When the VO_(2)is in the metallic state,we can only get the co-polarized reflected wave with a 21° angle.Moreover,in our design,the VO_(2)film does not need lithography to obtain certain patterns,which improves the convenience of fabrication and experiment.Our design opens a new way for the development of multifunctional terahertz devices and has potential applications in the terahertz communication field.

Large-scale synthesis of fluorine-free carbonyl iron-organic silicon hydrophobic absorbers with long term corrosion protection property

Environmentally-friendly magnetic metallic absorbers with high-performing antioxidant property,thermal stability,and anticorrosion capability have attracted great attention in real-world applications.A surface modification technology of magnetic metallic absorbers with dense and inert materials has been an effective strategy to solve the aforesaid problem.Herein,fluorinefree core–shell carbonyl iron-organic silicon absorbers(CI@SiO_(2)/1,1,1,3,3,3-hexamethyl disilazane(HMDS))were fabricated via a facile one-pot synthesis using tetraethyl orthosilicate(TEOS)and HMDS as the precursor of protective layer(SiO_(2)/HMDS),and CI@SiO_(2)/HMDS hybrid reveals its long-term corrosion resistance and excellent microwave absorption performance with a minimum reflection loss value of−44.3 dB and an effective absorption bandwidth of 5.3 GHz at a thin thickness of 2.0 mm after immersion in 5.0 wt.%NaCl acidic solutions for 2,160 h.Meanwhile,CI@SiO_(2)/HMDS hybrid can still achieve the maximum radar cross-sectional(RCS)reduction values about 16.5 dB·m^(2) at the detectionθof 0°.The exceptional microwave absorption performance and structural stability are largely due to the extraordinary wave-transparent property and shielding ability against corrosive medium of SiO_(2)/HMDS hydrophobic protective layer with a contact angle of 132.5°.The research paves the way for the large-scale and batch production of high-performance magnetic metallic absorbers and increases their survivability and reliability in the harsh environments.

Strategy to boost hydrolysis resistance and stabilize low infrared emissivity of ZrB_(2) via nanoscale LaF_(3) surface modification

Owing to its excellent high-temperature resistance and high conductivity,zirconium diboride(ZrB_(2)) has been applied as an infrared suppression coating.However,ZrB_(2)is susceptible to hydrolysis under high-moisture conditions and even under mild working temperatures.The improvement in the hydrophobicity of the ZrB_(2)surface effectively reduces wetting by water and suppresses hydrolysis reaction,particularly under high-temperature and high-moisture conditions.Herein,we report a novel,easy,and highly reproducible method for producing a fully coated ZrB_(2)surface by developing a nanoscale hydrophobic layer of glassy LaF_(3)on the surface of ZrB_(2)powder particles in situ(i.e.,during the carbothermal synthesis of ZrB_(2)).Through the tests carried out at 200 ℃for 100-300 h in a hydrothermal reactor,the produced powders displayed remarkably high long-term hydrolysis resistance and pronounced chemical stability.Compared with treated ZrB_(2),ZrB_(2)@LaF_(3)remained lower infrared emissivity when continuously intensifying hydrolyzation process.The results suggest that a nanoscale surface modification strategy can be applied to stabilize the infrared emissivity of ZrB_(2)in a water-oxygen coupling environment.