172 research outputs found
Iron mineral type controls organic matter stability and priming in paddy soil under anaerobic conditions
No full texthttp://dx.doi.org/10.13039/501100001809 National Natural Science Foundation of Chinahttp://dx.doi.org/10.13039/501100004731 Natural Science Foundation of Zhejiang Provincehttp://dx.doi.org/10.13039/501100019974 Nanning Science and Technology Burea
A Novel Multiband Low Mutual Coupling Quad-Element MIMO Antenna for Advanced Communication Systems
Get PDFThis study presents a compact multi-band fork-shaped multiple input multiple output (MIMO) antenna design that integrates Carrel’s log-periodic concept with the planar log-periodic array (PLPA) mechanism to improve C, Ku, K, Ka, and Q band performance. The suggested MIMO antenna full size is mm . The study empirically shows improved isolation and high gain of wideband MIMO antenna, addressing the requirements for modern wireless communication. The suggested self-multi-band coupling counteraction, characterized by a straightforward antenna design and extensive self-decoupling capabilities, is expected to offer considerable application value for compact and wideband MIMO systems. The observed data supports the assertion that the proposed MIMO antenna is designed to operate across a variety of frequency bands, including the C-band (4.4-5.21 GHz), Ku-band (14.30-17.64 GHz), K-band (20.10-28.10 GHz), Ka-band (28.95-30.76 GHz) and (32.38-36.42 GHz), and a segment of the Q-band (38.34-39.55 GHz). The proposed MIMO antenna’s wideband performance is achieved by applying the Carrel log-periodic theory, which prescribes the geometric scaling of radiating elements. Moreover, it was found that a microstrip feed line with a diameter of was noteworthy in conjunction with the carrel concept. The microstrip feed line is connected to two orthogonal branches. Decoupling structures eliminate the necessity for the MIMO antenna to achieve its maximum gain of 7.21 to 9.53 dBi and exceptional element isolation of 21.54 dB. MIMO performance measurements, encompassing envelope correlation coefficient (ECC), diversity gain (DG), and channel capacity loss (CCL), demonstrate favorable characteristics and field correlation performance over the operational spectrum band. The design suggested suits Ku/K-band and multi-band MIMO applications across diverse wireless systems in communication
Microwave to mmWave Wireless Power Transfer: An Overview of the Design Challenges with a Focus on UK-Based R&D
Get PDFMicrowave and mmWave wireless power transfer (WPT) continues to attract significant interest. This paper presents an overview of selected UK-based activities in WPT and energy harvesting, and highlights the emerging research trends and future directions, with focus on mmWave power transfer. The justification for mmWave power transfer, fueled by beyond-5G hardware, is first introduced. Rectenna and WPT-specific innovations such as beam-forming, bandwidth enhancement, and frequency scanning are then highlighted. The developments are then reviewed from an application perspective, highlighting the novel material and implementations of rectennas, along with the outstanding research challenges. Quantitative performance comparisons are presented summarizing state-of-the-art rectifiers, rectennas, and antennas
Machine learning solutions for intelligent reflecting surface-assisted communications
Get PDFIntelligent reflecting surface (IRS) has been recognised as a promising technology for future wireless systems. Consequently, several conventional optimisation
schemes have been proposed for solving IRS-assisted communication problems.
However, these conventional optimisation methods come with high computational
complexity, especially for the multiple-input-multiple-output (MIMO) communication systems. Fortunately, it has been shown in the literature that machine
learning (ML)-based schemes have been successful in tackling diverse problems in
the wireless communications domain with reduced complexity. Motivated by this,
in this Thesis, ML-based solutions are proposed for IRS-assisted MIMO communication systems aiming to maximise the spectral efficiency and/or secrecy rate
of the proposed systems. First, a deep learning (DL) based model is proposed to
jointly optimise the hybrid beamformers and the IRS reflection matrix for an IRS-aided MIMO communication system wherein a two-stage neural network is trained
sequentially to estimate the IRS matrix (from a formulated effective channel), as
well as the hybrid beamformers while aiming to maximise the spectral efficiency of
the system. In the second and final contributions, a deep reinforcement learning
(DRL) algorithm is proposed to optimise the phase shift of the reflecting elements
of an IRS for IRS-assisted MIMO communication systems aiming to maximise the
system’s spectral efficiency and secrecy rate respectively. Specifically, the deep
deterministic policy gradient (DDPG) framework is proposed to tackle the formulated non-convex problems following its success in handling high-dimensional
continuous action spaces and tackling non-convex optimisation problems. Numerical simulations are provided to validate the competitive performance of the
proposed ML-based solutions
mmWave Wireless Power Transmission to Flexible Rectennas in Absorptive and Reflective Media
Get PDFMillimeter-Wave (mmWave) wireless power transmission (WPT) can provide theoretical improvements to the end-to-end link efficiency compared sub-6 GHz bands. However, mmWave propagation in the WPT is yet to be explored. Herein, we present the first evaluation of a broadband mmWave rectenna on a lossy phantom based on radiation absorbing material (RAM). The ground reflection is observed over distance from a 20 dBi horn antenna with a 1 W input around 23 and 28 GHz, where the effect of multi-paths reflections is demonstrated and compared to a varying input from the generator. A DC power output over 10 µis measured at 15 cm from a 51 dBm source, showing the potential for meters-range mmWave wearable WPT with the licensed 5G 75 dBm EIRP levels. It is concluded that the electromagnetic (EM) environment and propagation media can have significant influences on mmWave WPT requiring novel signal and EM co-design
圖書資訊學的時代定位 Positioning Librarianship
No full text無This article is aimed at exploring the issue of positioning librarianship in the contemporary era. The author first analyzes the impact of Information Age on human society, and brings out the consequences of this impact on the field of library & information sciences. Reflected on the nature and tradition of the field, the author then proposes a strategic thinking of positioning librarianship. Finally, the potential career expansion is illuminated based on this thinking
A New Smart Sensing System Using LoRaWAN for Environmental Monitoring
Get PDFAn increasing interest is drawn to environmental monitoring applications such as weather monitoring, smart city, and smart agriculture. This paper proposes a new Internet of Things (IoT) sensing system for environmental monitoring. The system consists of wireless sensor nodes, communication network, and data visualization and storage cloud. The wireless sensor node is powered by a solar panel and Radio Frequency (RF) energy harvester (in case solar energy is not available) to avoid changing batteries frequently and save the maintenance cost. It has a compact size and can sense many environmental parameters, such as temperature, air pressure, humidity, loudness, and air quality. A low power communication technology named LoRaWAN is used to connect different sensor nodes for a wide coverage area. Finally, a cloud server named Cayenne myDevice is employed to receive, present and store measured data. This smart sensing system with energy harvester can be used for many other IoT applications
A new circularly polarized antenna for GNSS applications
No full textA new and circularly polarized (CP) antenna is proposed for global navigation satellite systems (GNSS) applications. The antenna employs a single feed and two orthogonally elliptical printed dipoles. The dipoles are crossed through a 90° phase delay line of a vacant-quarter printed ring to achieve CP radiation. In order to achieve broad beamwidth, four metallic cylinders are introduced. The proposed antenna has achieved a bandwidth of about 43% from 1.08 to 1.69 GHz for S11 < -10 dB. Meanwhile, the CP bandwidth is from 1.55 to 1.63 GHz (L1) and 1.12 to 1.26 GHz (L2, L5) for axial ratio < 3 dB. Additionally, the antenna yields right-hand circular polarization (RHCP) and high antenna efficiency over a wide frequency band. The simulated results have shown that the proposed antenna is a good candidate for GNSS applications.</p
Comparison of stochastic reduced order model and stochastic collocation methods for the sensitivity analysis of crosstalk
Get PDFSensitivity analysis is a crucial tool to reduce the randomness dimension of stochastic problems, thus to reduce computation cost. However, the efficacy of different stochastic methods for sensitivity analysis was totally missing. Therefore, two popular stochastic methods, i.e., the stochastic reduced order model (SROM) and stochastic collocation (SC) methods, are performed to analyse crosstalk sensitivity to different cable variables. The Monte-Carlo (MC) method is used as the reference. Both the SROM and SC methods are shown to be much more efficient by orders of magnitude compared with the MC method. The result also shows that the SROM performance is not as remarkable as that of the SC method in terms of efficiency. As a result, the SC method could be recommended as a promising efficient approach for sensitivity analysis in stochastic electromagnetic compatibility (EMC) problems
Investigation of Graphene Film-based Circular Monopole Antenna for UWB Applications
No full textGraphene film based circular shaped monopole antennas with ultra- wideband (UWB) performance is presented. Proposed antennas consist of a circular patch radiator made by graphene films and a ground plane made by copper and graphene film, respectively. This proposed nonmetal antenna can achieve a bandwidth of 120% and covers the frequency range from 2.5 to 10.5 GHz for a return loss greater than 10 dB. In addition, the antenna is implemented and experimental results are in good agreement with the simulated ones
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