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Beamforming and massive multiple-input-multiple-output (mMIMO) technologies are key features of base stations (BSs) in the fifth-generation (5G) of mobile networks. This technology is used to focus more radio frequency (RF) energy towards actively connected users to improve their connection/performance, resulting in high variations in the radio frequency electromagnetic fields (RF-EMFs). This paper proposes a new methodology for modelling the RF-EMF exposure for 5G new radio (NR) mMIMO BS by means of a physics-informed machine learning (ML) approach using empirical measurement data. More precisely, the main focus of our work is to develop a suitable traceable RF-EMF exposure prediction tool in the context of 5G mMIMO BSs that can serve multiple mobile users (i.e. multiple-user MIMO (MU-MIMO)) within realistic real-world environments and scenarios. Our RF-EMF prediction tool relies on empirical measurement data acquired via a user-controllable mMIMO beamforming testbed and traceable RF-EMF measurement capability, where both indoor and outdoor RF-EMF measurement campaigns have been carried out. During the measurement campaigns various factors such as number of users, position of users and data duty cycles were considered. Using an ensemble of gradient boosted decision trees, we show that a physics-informed approach can improve predictive performance of RF-EMF compared with a purely data-driven approach, with the ability to extrapolate values of RF-EMF exposure to larger distances. Results show a coefficient of determination value of 0.86 on a 10-fold cross-validated experimental dataset. We also compare the sensitivity of RF-EMF exposure to various factors in the model, and show that model predictions become isotropic for large numbers of beam configurations, simplifying the exposure measurement methodology of 5G systems.

Providing reliable connectivity to cellular-connected Unmanned Aerial Vehicles (UAVs) can be very challenging; their performance highly depends on the nature of the surrounding environment, such as density and heights of the ground Base Stations (BSs). On the other hand, tall buildings might block undesired interference signals from ground BSs, thereby improving the connectivity between the UAVs and their serving BSs. To address the connectivity of UAVs in such environments, this paper proposes a Reinforcement Learning (RL) algorithm to dynamically optimise the height of a UAV as it moves through the environment, with the goal of increasing the throughput or spectrum efficiency that it experiences. The proposed solution is evaluated in two settings: using a series of generated environments where we vary the number of BS and building densities, and in a scenario using real-world data obtained from an experiment in Dublin, Ireland. Results show that our proposed RL-based solution improves UAV Quality of Service (QoS) by 6% to 41%, depending on the scenario. We also conclude that, when flying at heights higher than the buildings, building density variation has no impact on UAV QoS. On the other hand, BS density can negatively impact UAV QoS, with higher numbers of BSs generating more interference and deteriorating UAV performance.

In the realm of radio frequency identification (RFID) technology, the integration of reconfigurable intelligent surfaces (RISs) has opened up new possibilities for real-time remote data capturing and seamless connectivity. By manipulating the electromagnetic properties of the environment, RIS enables the control of electromagnetic wave propagation and allows for virtual line-of-sight (LOS) in cases where physical LOS is blocked. This has tremendous implications for the future of RFID applications, particularly with the emergence of chipless RFID technology. In this regard, this paper develops free-space path loss models for RIS-assisted RFID wireless communications. The proposed models in this study have taken into account several crucial physical factors, including tag radar cross-section (RCS), the physical properties of the RIS, and the radiative near-field/far-field effects of the RIS. To further validate the theoretical findings, we have conducted experimental measurements using a fabricated RIS. Numerical simulations were also utilized to validate the models and verify our findings. The channel measurements have demonstrated good agreement with the proposed path loss models, further bolstering the potential of RIS-assisted RFID wireless communications.

Recently, large offshore wind power plants have been installed far from the shore, using long HVAC three-core armored cables to export power. Its high capacitance may contribute to the appearance of unwanted phenomena, such as overvoltages or resonances at low frequencies. To adequately assess these problems, detailed and reliable cable models are required to develop time-domain/frequency-domain analyses on this type of cables. This paper presents, for the first time in the literature, an assessment on the performance of 3D finite element method-based (3D-FEM) models for developing frequency-domain analyses on three-core armored cables, confronting simulation results with experimental measurements found in the literature for three real cables. To this aim, a simplified ultra-shortened 3D-FEM model is proposed to reduce the simulation time during frequency sweeps, through which relevant aspects never analyzed before with frequency-domain 3D-FEM simulations are addressed, such as total losses, induced sheath current, magnetic field around the power cable, positive and zero sequence harmonic impedances, as well as resonant frequencies. Also, a time-domain example derived from the frequency-domain analysis is provided. Remarkable results are obtained when comparing computed values and measurements, presenting the simplified ultra-shortened 3D-FEM model as a valuable tool for the frequency-domain analysis of these cables. [ABSTRACT FROM AUTHOR]

A line-start synchronous reluctance motor (LS-SynRM) that meets the IE4 efficiency and has satisfactory starting and synchronizing capabilities while operating with acceptable power factor will find application in constant speed drives. This paper introduces a line-start synchronous reluctance motor with V-shape rotor laminations (LS-SynRM-VSRL). The motor, which has been designed from an IE2-132S4 conventional foot mounted three-phase induction motor NEMA frame, was modeled using the three-dimensional (3D) Finite Element Method (FEM), then prototyped and tested for transient, dynamic, and steady-state performance under different load conditions. The Finite Element Analysis (FEA) and measured results of the LS-SynRM-VSRL are compared with those of a conventional line-start synchronous reluctance motor (CLS-SynRM). The results evidenced that both LS-SynRMs achieved successful synchronization on no-load, with the proposed LS-SynRM-VSRL reaching the steady state condition much quicker than the CLS-SynRM. Under steady-state operations, both LS-SynRMs achieved IE4 efficiency, with the proposed LS-SynRM-VSRL reaching an efficiency of 93.6% on full-load, in contrast to the 84.9% that the IE2-132S4 induction motor has achieved under the same loading condition.

Base stations (BSs) rely on the massive multiple-input multiple-output (mMIMO) technology in the fifth generation of mobile networks (5G). A technology having a major impact on the nature of the electromagnetic field (EMF) exposure in such systems. This work has used a fully reconfigurable mMIMO testbed (operating at 2.63 GHz), capable of mimicking realistic 5G new radio (NR) BS beamforming performance, to first gather experimental-based evidence of 5G BS EMF exposure within a real-world outdoor environment, to then analyze its stochastic behaviour, and to finally understand its impact on the definition of exclusion boundaries for 5G BSs. The exposure data of our testbed have been complemented by exposure data collected from a typical commercial 5G BS (operating at 3.65 GHz) to confirm the result trends and findings of our analysis. A robust metrology has been followed to obtain all the EMF exposure data. Our data and analysis indicate that significant exposure variations can be noticed according to the beam directions, i.e. the relative position of the exposure measurement location to the beam directions as well as the environment, confirming the stochastic nature of 5G BS exposure. The variance of the exposure tends to decrease as the number of users increase for a constant traffic load. Whereas the exposure grows sub-linearly with the traffic load, regardless of the number of users. As far as the exclusion boundary of 5G BS is concerned, its revised definition based on 95-th percentile seems still not flexible enough to accommodate the deployment of 5G BS in countries/places with stringent EMF exposure limits, as for instance in Belgium.

We present a study of the natural (resonance) frequencies of a tunable in-plane Microelectromechanical portal frame (U-shape) under DC electrostatic loads. The structure is designed and fabricated to excite the in-plane anti-symmetric (sway, first) and the symmetric (second) modes. Experimental results show high tunability of the resonance frequencies of both modes due to the electrostatic forces. Finite element simulations show good agreement with the experimental measurements. Further simulations are presented for the tunability of the natural frequencies of other higher-order modes using various electrode configurations. Frequency-response curves are presented for pure AC actuation of the first two modes showing strong nonlinear softening behavior due to the geometric nonlinearities of the portal frame. [2020-0269] [ABSTRACT FROM AUTHOR]

Signal identification systems recognize the type of the received signal usually without a priori information of some of the signal parameters and without the requirement of preprocessing tasks, such as frequency and timing recovery. These instruments have been employed in different military and commercial applications, such as spectrum surveillance, electronic warfare, and software-defined and cognitive radios. The focus of this paper is automatic instruments that can identify cellular network signals. Novel identification features are presented, which are based on the statistical properties and characteristic features of the candidate signals. In particular, the signal cumulative distribution function is employed as an identification feature for the global system for mobile communication and long term evolution (LTE) downlink signals. The presence of the cyclic prefix is exploited to identify the LTE uplink signal, while the estimated signal bandwidth is used to differentiate between the universal mobile telecommunication system and code division multiple access 2000 signals. Experimental tests are performed to verify the validity of the proposed identification method. The experimental results show that the identification method achieves very good performance with short observation intervals leading to improved response time under different channel conditions. Moreover, the presented method is robust to timing and frequency offsets. [ABSTRACT FROM AUTHOR]

This paper presents an electrodynamic/magnetorheological fluid (MRF)-based clutch activated using permanent magnets (PMs) attached to one shaft. During the electro-mechanical transient phase, when the two clutch shafts rotate at different speed, the PMs induce eddy currents on some conductive materials strategically placed in the system. The interaction between these currents and the magnetic induction produces an electromagnetic torque, which is added to that of the MRF, helping the clutch engagement in the start-up phase when an extra torque is necessary to overcome possible static frictions. Once the two shafts have reached the same speed, the eddy currents (and, consequently, the electromagnetic torque) vanish and the torque transmission is assured by the MRF only. The conductive material is arranged as a copper sheet and the performance of the device is investigated. The proposed clutch is analyzed using a 3-D finite-element code, which considers the $B$ – $H$ curve of the nonlinear materials (e.g., MRF, PMs, and ferromagnetic materials) and the movement of the different parts. Finally, in order to verify the finite element method model, some experimental measurements are performed on a prototype. [ABSTRACT FROM AUTHOR]

Previous work has shown that the emissivity of crude oil is lower than that of the seawater in the thermal-infrared (TIR) spectrum. Thus, oil slicks cause an emissivity decrease relative to the seawater in that region. The aim of this paper was to carry out experimental measurements to characterize the spectral and angular variations of crude oil and seawater emissivities. The results showed that the crude oil emissivity is lower than the seawater emissivity and that it is essentially flat in the atmospheric window of 8-13 μm. The crude oil emissivity has a marked emissivity decrease with the angle (from 0.956 ± 0.005 at 15 ° to 0.873 ± 0.007 at 65 °), which is even higher than that of the seawater, and thus, the seawater-crude emissivity difference increases with the angle (from +0.030 ±0.007 at close-to-nadir angles up to +0.068 ±0.010 in average at 65 °). In addition, the experimental results were checked by using the dual-angle viewing capability of the Environmental Satellite Advanced Along-Track Scanning Radiometer (ENVISAT-AATSR) images (i.e., 0 °-22 ° and 53 °-55 ° for the nadir and forward views, respectively), with the data acquired during the BP Deepwater Horizon oil slick in 2010. The objective was to explore its applicability to satellite observations. Nadir-forward emissivity differences of +0.028 and +0.017 were obtained for the oil slick and the surrounding clean seawater, respectively. The emissivity differences between the seawater and the oil slick were +0.035 and +0.046 for the nadir and forward views, respectively, which was in agreement with the experimental data. The increase in the seawater-crude emissivity difference with the angle gives significant differences for off-nadir observation angles, showing a new chance of crude oil slick identification from satellite TIR data. [ABSTRACT FROM PUBLISHER]

This paper proposes the design of a novel dc excitation control for a wound-rotor induction generator (WRIG) under autonomous-generation mode using a microcontroller based on a reduced instruction set chip (RISC). The source of the dc excitation control for the studied WRIG is obtained from its generated ac voltage through a step-down transformer, a bridge rectifier, and a dc-to-dc buck converter. In order to effectively modulate the desired dc voltage for controlling the generated voltage of the WRIG, a fuzzy controller embedded in the RISC-based microcontroller is properly designed and implemented using the PIC 8-bit microcontroller under voltage variations. The calculation results are sent to the pulsewidth-modulation ports to drive the power MOSFET switch of the dc-to-dc buck converter. The proposed WRIG system with its dc excitation control is practically implemented in a laboratory wound-rotor induction machine driven by a dc motor. From both experimental measurements and computer simulations, it can be concluded that the proposed isolated WRIG with its dc excitation controlled by the microcontroller can provide better voltage profile than a self-excited induction generator containing only excitation capacitors under various loading and switching conditions. [ABSTRACT FROM AUTHOR]

Free-space optical (FSO) communication links provide high data rates; however, their reliability is heavily dependent on weather conditions. This paper presents our experimental urban 1.87 km FSO link based on a customized commercial system and develops a library of channel measurements in clear and light rain weather conditions. A channel model for the link is proposed and experimentally quantified. Channel measurements are obtained by modulating a 60 mW laser source. At the receiver, a 2 GSa/s data converter is used and 16 fast-Fourier transform cores are implemented in the hardware to improve noise immunity. The resulting signal-to-noise ratio of the channel samples is around 40 dB under clear weather conditions. Fittings with log-normal, gamma-gamma, and Erlang distributions are presented, and the scintillation index and coherence time are measured. A computationally efficient finite-state Markov chain is derived for the channel to model both the distribution and the autocorrelation of the fading and is verified by the measurements. The Markov models and channel measurements in a variety of atmospheric conditions are available for download to permit easy verification of communication algorithms on this urban FSO channel. [ABSTRACT FROM PUBLISHER]

Models describing the polarimetric response of a multipath channel are considered. Conventional cross-polarization coupling (XPC) models are found to provide an ambiguous polarization representation and are sensitive to the receive antenna polarization configuration. These limitations are contrasted with polarization mode dispersion (PMD) models, which provide unambiguous frequency-dependent polarization characterizations. The XPC model is augmented using received signal power ratios associated with three orthogonally polarized antenna pairs. The revised model is shown to provide higher fidelity polarization characterizations. A comparison of the polarization behavioral models is illustrated using measured data from channel sounding experiments conducted in the 2.4-GHz industrial, scientific, and medical band in an urban propagation environment. [ABSTRACT FROM PUBLISHER]

We present the results of an experimental study of dimensional ratios dependencies on the performance of a ballistic deflection transistor (BDT) operating in a quasi-ballistic regime. Experimental transconductance change based on geometry variations is studied for smaller and larger devices with channel width of 300 and 500 nm, respectively. Transconductance variation for a series of drain biases is also observed for a specific geometry and dimension. By means of Monte Carlo modeling we report the effect of different geometry parameters on the transfer characteristics of BDTs. The strength of the gate control in the InGaAs channel is analyzed. [ABSTRACT FROM PUBLISHER]

A new approach in analysing an all-fiber phase modulator using a commercially available finite-element software package is presented. A single-mode fiber coated with a radially poled piezoelectric unoriented vinylidene fluoride (73 mol%)/trifluoroethylene (27 mol%) copolymer was successfully modeled using a two-dimensional axi-symmetric approach. The response of the phase modulator was determined over a wide frequency range, from 10 Hz to 50 MHz. Results showed a phase shift of 0.155 rad/V/m in the low-frequency (axially unconstrained) region, and 0.045 rad/V/m in the high-frequency (axially constrained) region. An excellent agreement exists between the simulation results and experimental measurements [ABSTRACT FROM PUBLISHER]