Increasing information capacity is crucial for high-capacity and high-speed communication, especially for sub-terahertz communication. Over the last decade, spatial multiplexing based on the orbital angular momentum (OAM) by adopting a multi-mode OAM metasurface has attracted a lot of attention. However, current metasurface-based OAM multiplexing methods suffer from complex and limited multiplexing channels. In this paper, a novel method to realize multi-dimensional multiplexing combining OAM and frequency based on an angle-multiplexed metasurface over a broadband terahertz region is proposed and investigated. A frequency-independent phase profile formula of the angle-multiplexed metasurface is derived. A reflective metasurface operating from 0.25 to 0.35 terahertz (THz) is designed based on this formula. For proof of concept, nine-channel multiplexing is illustrated based on this novel method. The simulation results verify that nine-channel off-axis left-hand circularly polarized beams are converted to nine orthogonal coaxial beams. Besides, according to the conventional method for OAM multiplexing, an angle-multiplexed reflective metasurface working at 0.3 THz is designed for comparison. The simulation results show that only three-channel multiplexing can be obtained by this model with nine-channel incident waves. The proposed method has a great potential to enhance the transmission capacity of the communication system.
The torque load spectrum is an important basis for the strength design and durability test verification of tractor power take-off (PTO), and the performance and reliability of tractor PTO directly affect the quality and efficiency of agricultural operations. In this paper, taking the PTO torque load as the object, a PTO loading method based on the dynamic load spectrum acquired in the actual field work was proposed in this paper. Based on the Peak Over Threshold model, the extrapolation of the PTO load spectrum was realized, and the load spectrum throughout the whole life cycle was obtained. On the basis of this, the mobile tractor PTO loading test bench and Fuzzy-Proportional-Integral-Derivative (Fuzzy-PID) controller were developed to achieve the dynamic loading of the PTO load spectrum, and the dynamic characteristics were analyzed and verified by the simulation and laboratory test. The results showed that with the time domain extrapolation method, the load extreme value was expanded from (63.24, 469.50) to (60.88, 475.18), and the coverage was expanded by 1.98%. By comparing with the fitting results, statistical characteristics and rain flow counting results, the load spectrum extrapolation method was effective. In addition, the response time of simulation and laboratory test were 0.05s and 0.75s, respectively; the maximum error was 1.77% and 4.03%, respectively; and the goodness of fit was 16.78 N·m, which indicated that the PTO loading test bench, can accurately restore the dynamic loading of the tractor and the Fuzzy-PID controller had better accuracy and stability. It would provide a reference for the practical application of PTO load spectrum of the tractors.
Orbital angular momentum (OAM) generation based on metasurfaces has attracted tremendous interest due to its potential in capacity enhancement of high-speed wireless communication systems. Reconfigurability is one of the key desired characteristics for the design of future metasurfaces. In this paper, a metasurface taking advantage of vanadium dioxide (VO 2) is proposed. The proposed design can generate a non-diffractive OAM beam and achieve the multiple reconfigurability of the topological charge, beam radius, beam deflection angle. The operation frequency can be adjusted by controlling the state of VO 2 at terahertz (THz) region. Simulation results demonstrate that the designed metasurface can generate a non-diffractive OAM beam with tunable topological charge and beam radius, propagating along ±x or ±y directions with the controllable deflection angle between 6.74°and 44.77°, ranging from 0.69 THz to 0.79 THz.
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