As wireless networks continue to advance and the need for low-latency communication links increases, calibrating antennas installed in the field is essential. In this context, Unmanned Aerial Vehicles (UAVs) are very useful for applications such as UAV-based measurements. Given its light weight, wide bandwidth makes Printed Log-Periodic antenna (PLPDA) an ideal solution as UAV probe. Our study examines the performance of a PLPDA mounted on a UAV. Extensive simulations are performed to determine the optimal position for the PLPDA on a UAV. Simulations are carried out in CST Studio Suite 2022 using the time domain Finite Integration Technique (FIT) with appropriate mesh settings. At the optimized location PLPDA achieves a -10 dB bandwidth of 6.2 GHz.

The continuous emergence of new wireless communication systems increases the need for intelligent planning prior to their deployment. This planning phase includes determining the position and transmit power of wireless access points, to meet quality of service objectives along with electromagnetic compatibility standards. How to effectively place a set of transmitters in an environment is a long-standing problem that has been widely studied over the years. This process has mainly relied on expensive measurement campaigns, low-fidelity empirical models, or high-fidelity but time-consuming simulations. Recent advances in scientific machine learning create new possibilities for overcoming the standard dichotomy between speed and accuracy. In this paper, we train a deep neural network (U-Net) to predict received signal strength levels for a variety of different geometries and for positions of multiple transmitters. Then, we leverage the computational efficiency of the trained model to determine the position of access point transmitters in new geometries. This approach dramatically accelerates the process of selecting the position of access points, meeting multiple optimization objectivesin an efficient manner.Â

This letter introduces a novel physics-informed approach for neural network-based three-dimensional electromagnetic modeling. The proposed method combines standard leap-frog time-stepping with neural network-driven automatic differentiation for spatial derivative calculations in the wave equation. This methodology effectively addresses the challenge of accurately modeling high-frequency electromagnetic fields with physics-informed neural networks, often characterized as “spectral bias”, in the time domain. We demonstrate that the resultant numerical scheme enables unconstrained time-stepping with respect to stability, in contrast to the Finite-Difference Time-Domain method, which is subject to the Courant stability limit. Furthermore, the use of neural networks allows for seamless GPU acceleration. We rigorously evaluate the accuracy and efficiency of this finite-difference automatic differentiation approach, by comprehensive numerical experiments.

This paper presents the derivation of the Lorentz factor and time dilation used in the Einstein’s theory of special relativity.

Reflector antenna systems used in applications such as radio astronomy and radiometry are required to have a stable and predictable receiving sensitivity response as a function of frequency, among other characteristics. It is well known that a chromatic aberration, or ripple, occurs in the frequency response of the these systems due to the multiple reflections between the feed antenna and reflector surface. In clear aperture optics, such as an offset Gregorian system, this effect is drastically reduced by removing the feed out of the optical path. However, this paper shows how diffraction mechanisms may cause further ripples in the response, whose structure is a strong function of reflector pointing angle. For the analysis herein the reflector/feed interaction is completely removed from the simulation to highlight the diffraction interference effects, which are illuminated by a graphical illustration of the mechanisms at play.

The interference and diffraction are two fundamental phenomena in optics. The patterns evolution phenomena have been shown for the interference and diffraction experiments respectively. In this article, we show for the first time the novel patterns, the Interference + Diffraction Hybrid Patterns of the novel double slit experiment, namely the interference pattern embedded in diffraction patterns. We also show how the patterns evolve, i.e., how the Interference + Diffraction Hybrid Patterns are formed. blob:https://www.techrxiv.org/c7b6a724-f88b-43cd-9693-b4c579429ded It is a challenge to theoretically interpret/describe.

In this paper, a method to solve magnetostatic problems for non-conforming meshes using penalty method is presented, where the interface conditions are imposed at the integration points. In the case of non-conforming meshes, there are two interfaces at the contact of the two bodies, so in order to impose the interface conditions, which connect the two bodies involved, the interface conditions must be expressed with respect to one interface, in this case I call slave, the body containing this interface and the other the master one. The best choice of the slave body, in order to obtain the most accurate solution, is investigated in this paper. Furthermore, this paper introduces a novel formulation known as the bi-pass or symmetric formulation, where each body is taken simultaneously as slave and as master, so there is no need to make the best choice of the slave body which in some situations is difficult to do. Additionally, this formulation leads to more accurate solutions

A novel metasurface reflector unit cell based on two coupled resonators is proposed and demonstrated for real-time reconfigurable beamforming in the X-band (8-12 GHz). The unit cell is composed of a split-ring resonator (SRR) with tunable capacitance and a dipole-ring resonator (DRR) with tunable resistance, whose collective variations allow for control over the complex reflectance at a desired frequency. To gain physical insight into its working mechanism, the proposed unit cell is modeled as a coupled Lorentz oscillator using the surface susceptibility description of the unit cell. Thereafter, a metasurface reflector based on the proposed unit cell is demonstrated in full-wave simulations to achieve various beamforming examples, such as beam-steering, side-lobe level control, beam-steering with amplitude control, and multi-beam patterns, from a single normally incident plane wave excitation. Three metasurface reflectors are fabricated to experimentally demonstrate the proposed concept; the first is based on a SRR with a varactor diode, the second is based on a DRR with a PIN diode, and the third is based on the proposed coupled SRR-DRR configuration with both varactor and PIN diodes, for simultaneous magnitude and phase control. The metasurface reflector based on the coupled resonator unit cell is experimentally demonstrated to achieve versatile beam transformations including beam-steering with amplitude control and multi-beam patterns.

This letter proposes a method for accurately calculating RF power at a standing wave (SW) transmission line system. It uses two directional couplers and a low-level radio frequency(LLRF) control system. The RF power is calculated from the proposed equations using amplitude and phase measurements of the coupling signals from the two directional couplers. The method is demonstrated adopting two directional couplers with directivity 26 dB and 28 dB respectively at 162.5 MHz over a whole wavelength range. The average power errors observed when using a single directional coupler are about 6.6% and 5.8% respectively, and the calculated power error can be reduced to about 1.0% through the proposed method.

Contribution: The study discusses the relationship between interpersonal trust and team performance in an exploratory way. The empirical data is collected from students in Electrical Engineering Practice Training Course classes to evaluate their team performance. Background: Interpersonal trust within a team plays a critical role in solving problems and enhancing group performance effectiveness. Research Question: Does interpersonal trust within a team have an impact on team performance? Can interpersonal trust between teammates be improved? Design/Approach: This research presents a case study of 132 electrical engineering university students in China. The students worked in teams completing six simulation experiments in a semester. Findings: The teams always with permanent teammates had the highest level of interpersonal trust and performed the best and the teams always with tentative teammates had the lowest level of trust interpersonal trust and performed worse and worse while the teams whose members were fixed by the instructor increased their interpersonal trust quickly and performed better and better over time. Conclusions: The higher the interpersonal trust within a team, the better the team performance; low initial interpersonal trust within a team can be promoted through intervention.

A lightweight cylindrical Frequency Selective Surface (FSS) using high-pass inductive mesh grid is proposed as a radiofrequency (RF) shield for solenoid coils at 2.84 MHz working in a portable MRI system with a transversal B0-field averaged at 67 mT. Using a solenoid coil of 60 mm diameter as an example, the proposed FSS shield shows good shielding effectiveness at different wall-to-wall distances between the coil and the shield (5-25 mm). It also shows less compromise in B1-sensitivity when compared to the coil with a copper shield. The effects of the FSS shield were examined numerically and validated experimentally. When the wall-to-wall distance is 5 mm, the solenoid coil with the proposed FSS shield is compact, lightweight, and shows B1-sensitivity of more than 50% higher than the copper counterparts with comparable shieding effectiveness. Compared to an unshielded coil, it shows a wider bandwidth which benefits the excitation of an MRI system that has less homogeneous fields and a smaller inductance which indicates less trapping of energy and thus can enable different pulse sequence programming by taking this approach. This study shows that an FSS shield with inductive mesh grids around a solenoid coil is a promising approach for compact shielding without a big shielding box. It will contribute to the compactness of a portable MRI system.

The design of metasurfaces and metasurface-based devices (e.g. reflective intelligent surfaces - RIS) is inherently affected by unpredictable variations of the unit-cell response, due, for instance, to fabrication tolerances, physical discontinuities, presence of bumps, etc. Such effects may dramatically affect the accuracy of the conventional design models, such as the one based on the local surface impedance (LSI). In this work, we present a statistical model resulting in a probability density function that allows defining a random local surface impedance (rLSI), that takes properly into account potential random variations derived from the von Mises distribution. To compensate for these variations, we propose a transformation kernel that matches the expected rLSI value to the design target. By using an analytical formulation and a proper set of full-wave simulations, we demonstrate the effectiveness and robustness of the method against unpredictable variations caused by the mutual coupling among the unit-cells and fabrication tolerances/errors. The proposed method paves the way to foster advancements in realistic metasurface engineering.

The Null result of the Michelson & Marley Experiment is explained by the invariant wavelength of light while propagating or transiting from one inertial reference frame to another. It is shown that under classical kinematics wavelength remains constant as observed by two reference frames. Thus the explanation for the Null result of the M&M experiment is the simpleset under classical kinematics.

The sub-6 GHz spectrum and the millimeter wave frequency band, with its huge spectrum, have been exploited in the past years to meet the traffic demands of wireless communication networks. However, the limited and licensed spectrum of these bands cannot support the massive connectivity requirements, the exponential growth of data traffic, and the strict quality-of-service requirements for 6G and beyond wireless systems. Extremely high frequencies, such as optical and terahertz, which offer much wider transmission bandwidths with extreme data rate capabilities, are expected to play key roles in the 6G and beyond era. As a result, future-generation wireless networks will transition from single-band and heterogeneous networks to multi-band networks (MBNs), where various frequency bands coexist. Despite the great potential of MBNs, they face novel challenges from channel modeling, transceiver and antenna design, programmable simulation platforms, standardization activities, and resource allocation. This paper provides a tutorial overview from the communication design perspective of the various frequency bands, elaborating on the above issues. Then, we introduce and examine typical MBN architectures for future networks and provide a detailed overview of state-of-the-art resource allocation problems for existing MBNs that typically operate on two frequency bands. The considered resource allocation optimization problems and solution techniques are discussed comprehensively. We then identify key performance metrics and constraint sets that should be considered for resource allocation optimization in future MBNs and provide numerical results to depict how various system parameters and user behaviors can influence their performance. Finally, we present several potential research issues as future work for the design and performance optimization of MBNs.

It is universally accepted that Maxwell equations do not remain invariant under the Galilean transformation. This conflicts the principle of relativity which states that the physical law must remain invariant in the mathematical form in all inertial frames of reference. For this reason, the Lorentz transformation is invented, and the Galilean transformation is nowadays superseded by the Lorentz transformation. However, this paper challenges this widely held belief that the Maxwell equations are not invariant under the Galilean transformation. By applying the Galilean transformation to Lienard-Wiechert electromagnetic fields it is mathematically proven that the Maxwell equations indeed remain invariant under the Galilean transformation. In addition, the critical error in Lorentz’s proof of Galilean non-invariance of Maxwell equations is pointed out, and  it turns out that Lorentz’s conclusion that Maxwell equations are not invariant under the Galilean transformation is the result of a mathematical error.

Currently, interest in the prospects for practical implementation of methods that allow retrieving the true radiation pattern when irradiating the navigation antenna under test from an insufficiently large distance is noticeably growing. The use of directed radiation in this case, on the one hand, reduces the level of reflections from the walls of the chamber, but on the other hand, increases the heterogeneity of the irradiating field. The paper aims to elucidate the influence of the directed properties of the auxiliary antenna, which forms the irradiating field, on the measurement process and the accuracy of the radiation pattern retrieval, under the condition that both of them are by the methodology of a converging cluster of plane waves. Simulating measurement and data processing were carried out when the size of the auxiliary antenna varied. The simulation results confirm that the reconstruction accuracy is practically independent of the nature of the irradiating field.

Rydberg atom receivers have the potential to supplement or replace traditional sensing technologies due to the high sensitivity, electrically small packaging, and unconventional field detection mechanisms they can provide. Given the importance of angle of arrival (AoA) estimation for geolocation and the potential impact of these technologies, more work is needed to understand the Rydberg sensor’s impact on AoA estimation. While there have been many experimental and theoretical efforts to improve the sensitivity and bandwidth of these quantum sensors, few papers have explored the impact these technologies will have on AoA estimation. This paper presents a numerical study of AoA estimation using a simulated linear array of Rydberg atom receivers consisting of vapor cells with laser-defined sense volumes. By utilizing atomic physics and electromagnetics simulations, it is shown that uncompensated atomic transient effects and RF dispersion in glass vapor cell arrays can substantially degrade AoA estimation when compared with a traditional dipole array.

In the above paper, Ahn et al. proposed a small-size four-port in-phase and out-of-phase hybrid coupler. However, the design equations proposed in [1, eq.(9)] are incorrect. In this letter, the incorrectness of the design equations has been demonstrated through a numerical example. Also, corrected design equations are provided in this letter for small-size couplers with unequal port impedances.