An Additive 3D-Printed Hemispherical Lens with Flower-shaped Stub Slot Ultra-Wideband Antenna for High-Gain Radiation

This paper presents a 3D-printed hemispherical lens integrated with a planar ultra-wideband (UWB) antenna. The flower-shaped stub slot UWB antenna is made of 0.8-mm FR-4. The operating frequency of the UWB covers 3.10 GHz - 11.6 GHz with a nominal gain at zero degrees of 1.74 dBi. To enhance the UWB antenna’s high-gain radiation, a 3D-printed additive hemispherical lens is designed and fabricated from acrylonitrile butadiene styrene (ABS). The electrical properties, i.e., relative permittivity and loss tangent, of ABS are 2.66, and 0.003, respectively. Four different lens radii (8 mm, 10 mm, 12 mm, and 14 mm) are chosen to investigate the gain of the antenna. In all four cases, the 3D-printed lens is fixed in place in front of the UWB antenna with an optimum gap of 3 mm chosen to reduce the wave reflection between the lens and source antenna. Based on the measurement results, the reflection coefficient, S11, of four conditions still covers the UWB frequency range. The nominal gain at zero-degree values for lens radii of 8 mm, 10 mm, 12 mm, and 14 mm are 3.43 dBi, 4.22 dBi, 4.73 dBi, and 5.18 dBi, respectively. The proposed additive 3D-printed dielectric lens antenna also offers many advantages, i.e., ease of design and assembly, low-cost fabrication, and size reduction for high-gain antennas. Furthermore, the high-gain antenna provides a narrow half power beamwidth, which can be implemented to increase the resolution of the imaging system

Adaptive finite-time stabilization of chaotic flow with a single unstable node using a nonlinear function-based global sliding mode

© 2018, Shiraz University. This article presents a novel adaptive finite-time stabilization technique based on global sliding mode for disturbed chaotic flow with a single unstable node. The considered chaotic flow has unusual characteristics containing attractor merging, symmetry breaking, attracting tori and different forms of multi-stability. A nonlinear function is employed in the global sliding surface to modify damping ratio and improve the transient performance. The damping ratio of the closed-loop system is improved when the states converge to the origin. Using the new chattering-free controller, the reaching mode is removed and the sliding behavior is presented right from the first instant. The adaptive finite-time tuning law eliminates the requirement of the information about the disturbances’ bounds. Illustrative simulations are provided to display the efficiency of the proposed scheme