Current Issue : October-December Volume : 2023 Issue Number : 4 Articles : 5 Articles
In this work, a reconfigurable ultra-wideband transmissive terahertz polarization rotator based on graphene metamaterial is proposed that can switch between two states of polarization rotation within a broad terahertz band by changing the Fermi level of graphene. The proposed reconfigurable polarization rotator is based on a two-dimensional periodic array of multilayer graphene metamaterial structure, which is composed of metal grating, graphene grating, silicon dioxide thin film, and a dielectric substrate. The graphene metamaterial can achieve high co-polarized transmission of a linearly polarized incident wave at the off-state of the graphene grating without applying the bias voltage. Once the specially designed bias voltage is applied to change the Fermi level of graphene, the polarization rotation angle of linearly polarized waves is switched to 45◦ by the graphene metamaterial at the on-state. The working frequency band with 45-degree linear polarized transmission remaining above 0.7 and the polarization conversion ratio (PCR) above 90% is from 0.35 to 1.75 THz, and the relative bandwidth reaches 133.3% of the central working frequency. Furthermore, even with oblique incidence at large angles, the proposed device retains high-efficiency conversion in a broad band. The proposed graphene metamaterial offers a novel approach for the design of a terahertz tunable polarization rotator and is expected to be applied in the applications of terahertz wireless communication, imaging, and sensing....
A dynamically reconfigurable underwater robot, which can vary its configuration during a mission, would be useful for confined environment exploration and docking because of its versatility. A mission can be performed by choosing among different configurations, and the energy cost may increase, owing to the reconfigurability of the robot. Energy saving is the critical issue in long-range missions with underwater robots. Moreover, control allocation must be considered for a redundant system and input constraints. We propose an approach for an energy-efficient configuration and control allocation for a dynamically reconfigurable underwater robot that is built for karst exploration. The proposed method is based on sequential quadratic programming, which minimizes an energylike criterion with respect to robotic constraints, i.e., mechanical limitations, actuator saturations, and a dead zone. The optimization problem is solved in each sampling instant. Two popular tasks for underwater robots, i.e., path-following and station-keeping (observation) problems, are simulated, and the simulation results show the efficiency of the method. Moreover, an experiment is carried out to highlight the results....
In this article, we propose a new RIS passive beamforming scheme in two main stages. First, a fingerprint-based codebook (FP-CB) design phase occurs, where the area of interest is divided into a number of points and the optimal reflection patterns (RPs) corresponding to these points are determined and stored alongside the coordinates of these points in the codebook database (DB). Second, there is the searching and learning online stage, in which, based on the receiver (RX) and FP points’ locations, the system determines a group of candidate RPs. Then, it just searches through them instead of examining the entire CB RPs to select the best RP that can be used for configuring RIS during the data transmission period. The proposed mechanism proves that designing a positioning information-based CB can highly reduce the system overhead computational complexity and enhance performance comparable to the conventional CB-based scheme and the full channel estimation (CE)- based scheme. For example, selecting only 10 candidate RPs from the FP-CB can obtain a better effective achievable rate than a CE-based scheme in a rapidly changing channel....
A frequency counter is essential for resonance-based sensors like quartz crystal microbalance. An electronic nose or tongue using a QCM sensor array requires a multichannel frequency counter to detect the frequency shift of the sensors simultaneously. The frequency counter’s resolution, precision, and sampling speed are important factors. Board size, energy consumption, and rapid deployment are also considered in the design. This work shows the development of an independent multichannel frequency counter using a commercial Xilinx Spartan 6 series XC6SLX9 board module and a microcontroller board. Both modules are general-purpose modules; therefore, there is no need for a printed circuit board design, resulting in a quick implementation: the use of FPGA results in a compact size and low energy consumption. The developed counter is designed based on a reciprocal counter utilizing the internal logic block of the FPGA. The FPGA module has a built-in 50MHz TCXO clock and is the reference clock. The high-resolution timing of the counter is realized by multiplying the 50MHz clock by 6 to reach 300 MHz. The multiplication utilizes the PLL modules in the FPGA. The high precision and accuracy of the counter are achieved by calibrating the timing clock to a 10MHz rubidium oscillator. The data communication to the microcontroller is done via the SPI by implementing the SPI protocol in the FPGA. The resource is optimized by utilizing PLL and DSP blocks for the counter. Only 5% registers and 5% LUTs of the FPGA resource are used to build a four-channel frequency counter. The result shows that the counter can measure the frequency of incoming signals with a resolution of 0.033 Hz at 10MHz with a sampling time of 1 second. The system has been tested to monitor the frequency changes of a QCM sensor array....
In this study, a novel reconfigurable triple-band monopole antenna for LoRa IoT applications is fabricated on an FR-4 substrate. The proposed antenna is designed to function at three distinct LoRa frequency bands: 433 MHz, 868 MHz, and 915 MHz covering the LoRa bands in Europe, America, and Asia. The antenna is reconfigurable by using a PIN diode switching mechanism, which allows for the selection of the desired operating frequency band based on the state of the diodes. The antenna is designed using CST MWS® software 2019 and optimized for maximum gain, good radiation pattern and efficiency. The antenna with a total dimension of 80 mm × 50 mm × 0.6 mm (0.12λ0 × 0.07λ0 × 0.001λ0 at 433 MHz) has a gain of 2 dBi, 1.9 dBi, and 1.9 dBi at 433 MHz, 868 MHz, and 915 MHz, respectively, with an omnidirectional H-plane radiation pattern and a radiation efficiency above 90% across the three frequency bands. The fabrication and measurement of the antenna have been carried out, and the results of simulation and measurements are compared. The agreement among the simulation and measurement results confirms the design’s accuracy and the antenna’s suitability for LoRa IoT applications, particularly in providing a compact, flexible , and energy efficient communication solution for different LoRa frequency bands....
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