21 research outputs found
Intelligent Omni-Surfaces Aided Wireless Communications: Does the Reciprocity Hold?
Intelligent omni-surfaces (IOS) have attracted great attention recently due
to its potential to achieve full-dimensional communications by simultaneously
reflecting and refracting signals toward both sides of the surface. However, it
still remains an open question whether the reciprocity holds between the uplink
and downlink channels in the IOS-aided wireless communications. In this work,
we first present a physics-compliant IOS related channel model, based on which
the channel reciprocity is investigated. We then demonstrate the
angle-dependent electromagnetic response of the IOS element in terms of both
incident and departure angles. This serves as the key feature of IOS that
drives our analytical results on beam non-reciprocity. Finally, simulation and
experimental results are provided to verify our theoretical analyses.Comment: 5 pages, 6 figure
Intelligent Omni-Surfaces: Reflection-Refraction Circuit Model, Full-Dimensional Beamforming, and System Implementation
The intelligent omni-surface (IOS) is a dynamic metasurface that has recently
been proposed to achieve full-dimensional communications by realizing the dual
function of anomalous reflection and anomalous refraction. Existing research
works provide only simplified models for the reflection and refraction
responses of the IOS, which do not explicitly depend on the physical structure
of the IOS and the angle of incidence of the electromagnetic (EM) wave.
Therefore, the available reflection-refraction models are insufficient to
characterize the performance of full-dimensional communications. In this paper,
we propose a complete and detailed circuit-based reflection-refraction model
for the IOS, which is formulated in terms of the physical structure and
equivalent circuits of the IOS elements, as well as we validate it against
full-wave EM simulations. Based on the proposed circuit-based model for the
IOS, we analyze the asymmetry between the reflection and transmission
coefficients. Moreover, the proposed circuit-based model is utilized for
optimizing the hybrid beamforming of IOS-assisted networks and hence improving
the system performance. To verify the circuit-based model, the theoretical
findings, and to evaluate the performance of full-dimensional beamforming, we
implement a prototype of IOS and deploy an IOS-assisted wireless communication
testbed to experimentally measure the beam patterns and to quantify the
achievable rate. The obtained experimental results validate the theoretical
findings and the accuracy of the proposed circuit-based reflection-refraction
model for IOSs.Comment: 33 pages, 20 figure
Intelligent Omni-Surfaces for Full-Dimensional Wireless Communications: Principle, Technology, and Implementation
The recent development of metasurfaces has motivated their potential use for
improving the performance of wireless communication networks by manipulating
the propagation environment through nearly-passive sub-wavelength scattering
elements arranged on a surface. However, most studies of this technology focus
on reflective metasurfaces, i.e., the surface reflects the incident signals
towards receivers located on the same side of the transmitter, which restricts
the coverage to one side of the surface. In this article, we introduce the
concept of intelligent omni-surface (IOS), which is able to serve mobile users
on both sides of the surface to achieve full-dimensional communications by
jointly engineering its reflective and refractive properties. The working
principle of the IOS is introduced and a novel hybrid beamforming scheme is
proposed for IOS-based wireless communications. Moreover, we present a
prototype of IOS-based wireless communications and report experimental results.
Furthermore, potential applications of the IOS to wireless communications
together with relevant research challenges are discussed
RIS-based IMT-2030 Testbed for MmWave Multi-stream Ultra-massive MIMO Communications
As one enabling technique of the future sixth generation (6G) network,
ultra-massive multiple-input-multiple-output (MIMO) can support high-speed data
transmissions and cell coverage extension. However, it is hard to realize the
ultra-massive MIMO via traditional phased arrays due to unacceptable power
consumption. To address this issue, reconfigurable intelligent surface-based
(RIS-based) antennas are an energy-efficient enabler of the ultra-massive MIMO,
since they are free of energy-hungry phase shifters. In this article, we report
the performances of the RIS-enabled ultra-massive MIMO via a project called
Verification of MmWave Multi-stream Transmissions Enabled by RIS-based
Ultra-massive MIMO for 6G (V4M), which was proposed to promote the evolution
towards IMT-2030. In the V4M project, we manufacture RIS-based antennas with
1024 one-bit elements working at 26 GHz, based on which an mmWave dual-stream
ultra-massive MIMO prototype is implemented for the first time. To approach
practical settings, the Tx and Rx of the prototype are implemented by one
commercial new radio base station and one off-the-shelf user equipment,
respectively. The measured data rate of the dual-stream prototype approaches
the theoretical peak rate. Our contributions to the V4M project are also
discussed by presenting technological challenges and corresponding solutions.Comment: 8 pages, 5 figures, to be published in IEEE Wireless Communication
Removal of fluoride from aqueous solution by TiO2 and TiO2–SiO2 nanocomposite
Adsorption plays an important role in the removal of pollutants such as fluoride from aqueous solutions. With the rapid development of environmental technology, TiO2 particle has become promising material to adsorb fluoride ion because of its low cost, non-toxic, good chemical stability, and good sorption ability. This work used sol-gel and hydrothermal synthesis methods to prepare TiO2 particles and load them onto SiO2 particles. The physicochemical properties such as heat stability, particle size, and surface area of the resulting TiO2 adsorbents were characterized with various analytical methods. In addition, their adsorption abilities to fluoride were determined under various conditions including different initial fluoride concentration, pH and coexisting ions. The maximum adsorption capacity of the TiO2 adsorbents can reach up to 94.3 mg/g. The adsorption isotherms of fluoride onto the TiO2 adsorbents can be closely described by the Langmuir model, suggesting the monolayer adsorption process
Evaluation of geological disaster susceptibility of transmission lines under different grid resolutions
Objective The safe operation of transmission lines is of great significance for national economic construction and development, but there were few studies on the evaluation of geological hazards susceptibility to transmission lines. Methods This study focuses on the Beijing-Tianjin-Hebei region as an example, where eight index factors, including elevation, slope, aspect, terrain relief, stratigraphic lithology, distance from fault, distance from water system, and land use type were selected. The frequency ratio method was used to classify each index factor to construct a susceptibility evaluation system.Then used different machine learning models and grid of different spatial resolutions as evaluation units to evaluate the susceptibility of the study area.Finally, the machine learning model with the highest accuracy and the traditional Analytic Hierarchy Process (AHP) were selected to complete the susceptibility zoning map of the study area. Results The research results show that the Bayesian Network model (Bayesian Network, BN) had the best application effect and the strongest model performance in the susceptibility evaluation of regional transmission lines, and the maximum AUC value was 0.876. The BN model outperformed the traditional AHP model, displaying superior precision in susceptibility mapping in the study area. Conclusion In addition, emplpying 50 m grid as the evaluation unit had achieved the best application effect in the evaluation of transmission line geological disaster susceptibility, which provided ideas and references for transmission line geological disaster evaluation and grid resolution selection
Influence of a Scanning Radial Magnetic Field on Macroparticle Reduction of Arc Ion-Plated Films
Cathode spot motion influences the physical characteristics of arc plasma and the related macroparticles (MPs) in resultant films; these MPs limit the application of arc ion plating (AIP). In this paper, a scanning radial magnetic field (SRMF) was applied to the cathode surface to control the cathode spot motion and reduce the MP contamination in the deposited films. It was shown that film surface morphologies prepared using SRMF were better than those using a static radial magnetic field (RMF). The improvement was greater with increased scanning range and frequency. Using SRMF, cathode spot motion was confined to a spiral trajectory on the cathode surface and the spots moved over a large area and at a fast-moving velocity. Both the large moving area and the fast velocity decreased the temperature on the cathode surface and thus reduced the emission of the MPs