This paper investigates the RF electrophoretic response of ellipsoidal gold nanoparticles (AuNPs). Since the existing works generally consider the electrophoretic heating of spherical AuNPs, this work provides an important step towards understanding the behavior of ellipsoidal AuNPs. We first develop an analytical framework for modeling of electrophoretic response of ellipsoidal AuNPs. Thereafter, due to the lack of experimental studies of non-spherical electrophoretic RF heating of AuNPs, we validate our theory by comparison to the existing experimental results of spherical AuNPs as a special case, and estimate a few additional parameters not considered before. Then, parameter studies are performed on surface charge, friction constant, frequency, and ionic background, with respect to AuNP size and shape. Finally, we present new results for the electromagnetic absorption and heat rates of ellipsoidal AuNPs in human tissue. Our results from the tissue testing indicate a strong difference between aqueous media and realistic human tissues due to the major difference in the host medium viscosity. We demonstrate the electrophoresis' strong dependency on the host medium's viscosity, where we note that cancer tissue viscosity is more than a thousand times higher than that of water. We thereby confirm negative results for RF AuNP heating, indicated by our own previous study and two other previous studies. Our results provide important insights into the feasibility of RF AuNP heating in a medical context.

Ultra-wideband (UWB) technology is known to have a high data rate in wireless communications due to its broad frequency range and low power consumption. Its flexibility enables a wide range of applications, including multiple-input multiple-output (MIMO) systems, suited for advanced wireless communication systems. In this manuscript a novel meandered MIMO antenna, designed explicitly for UWB applications, is proposed and studied. The antenna features meandered strips arranged in a circular pattern, resembling a sunflower. The antenna structure is built on an FR4 with 24 x 24 x 1.6 mm3 size for a single element and 48 x 48 x 1.6 mm3 for the MIMO configuration. The antenna operates over a wide frequency range between 2.9 and 20 GHz, achieving a fractional bandwidth of 151%. In the MIMO configuration, it maintains good isolation, exceeding 15 dB across the entire operating band. The measured efficiency of the antenna surpasses 75%, with a peak gain of 5.9 dBi. Additionally, key parameters for MIMO performance include an envelope correlation coefficient (ECC) below 0.002, mean effective gain (MEG) less than -3 dB, channel capacity loss (CCL) under 0.25 bps/Hz, and a total active reflection coefficient (TARC) below -20 dB.

This article presents the design of a high-gain, highly isolated four-element multiple-input multiple-output (MIMO) antenna system operating at the millimeter-wave (mm-wave) 28 GHz frequency band. The radiating element of the MIMO antenna comprises a 1 × 2 array of crescent-shaped patch elements backed by a full ground plane, having overall dimensions of 33 × 33 mm² (3.08λ × 3.08λ), where λ is the wavelength at 28 GHz. A 0.787-mm-thick low-loss dielectric substrate having a relative permittivity (ε<inf>r</inf>) of 2.2 and a loss tangent (tanδ) of 0.009 is used for the antenna design. It is observed that the designed radiating element provides resonance at 28.18 GHz and has a 6.21% fractional bandwidth (FBW) and a peak realized gain of 10.5 dBi. The radiation and total efficiency of the radiator are noted to be >85% and ≥75%, respectively, in the operating bandwidth. For polarization diversity and high isolation characteristics, the MIMO elements are arranged in an orthogonal manner, which helps achieve an isolation of >22.5 dB for adjacent elements and >32.5 dB for diagonally placed elements in the entire band of interest. Furthermore, MIMO system parameters such as envelope correlation coefficient (ECC) <0.003, diversity gain (DG) >10 dB, total active reflection coefficient (TARC) < −10 dB, and channel capacity loss (CCL) <0.5 bps/Hz are observed, which fall within the operational limits. Based on the achieved outcomes, the proposed design is well suited for mm-wave 28 GHz communication devices.

In this study, we introduce a cost-effective antenna designed for ultrawideband (UWB) spectrum. The antenna employs a single-layer coplanar waveguide (CPW) feed on a 1.6 mm FR4 board. Notably, the antenna demonstrates a bandwidth from 3.7 to 15.7 GHz (12 GHz) for a single element. Expanding its utility, a four-element Multiple Input Multiple Output (MIMO) assembly is arranged orthogonally, aiming to achieve diversity characteristics. The MIMO elements are connected through a common ground plane. In the MIMO configuration, the bandwidth response is increased to 2.9–16.2 GHz. To mitigate mutual coupling between the antenna elements, a simple geometric parasitic element is inserted between them, resulting in a significant improvement of 15 dB in isolation. In addition, a maximum gain of 5.5 dBi is noted at 14 GHz with total efficiency exceeding 80% throughout the resonance bandwidth. The individual antenna element boasts a compact footprint of 20 × 26 mm2, while the MIMO configuration occupies an area of 46 × 48 mm2. Furthermore, we conduct a thorough analysis of various MIMO performance metrics, including the envelope correlation coefficient (ECC), mean effective gain (MEG), and diversity gain (DG), all of which fall within acceptable thresholds. These analyses validate the potential of our proposed UWB–MIMO antenna for diverse UWB applications.

Metamaterials are mostly studied using the time-harmonic approach, where the wave propagation is spatially described. Recently, studies of media having electromagnetic properties that change in time have been given the attention of the scientific community, aiming to describe wave-matter interaction in both space and time. In the present paper, we use the space-harmonic method for the general description of wave propagation in time. Such a method can be used to effectively describe a "temporal multilayered" (or temporal multi-stepped) metamaterial by alternating the effective material parameters of the medium in time between two values. We obtain the exact analytical solution for the fields in two examples of temporally periodic metamaterials. Numerical simulations for the impedance-matched scenario are also carried out, showing an excellent agreement when compared to the exact analytical field. Our results also demonstrate the duality between the descriptions of the temporally periodic metamaterial and its spatial counterpart, spatially periodic metamaterials.

Over the last decades, metamaterials have mostly been studied using the time-harmonic approach, with wave propagation described in terms of the spatial coordinates. The metamaterials community has only recently initiated studies of temporal metamaterials, with electromagnetic properties that change in time. In this work, we propose the space-harmonic method to study a "temporal multistepped"metamaterial. By alternating the material parameters in time, the medium can be described using periodic mathematical functions. The exact analytical solutions for the fields in temporally periodic metamaterials are then obtained. The space-harmonic analysis of temporally periodic metamaterials is dual to the time-harmonic analysis of spatially periodic metamaterials, previously studied by one of the present authors.

In this paper, we study transverse electric (TE) wave propagation inside a hollow circular waveguide filled with a lossy graded multilayered dielectric composite. The dielectric composite grading and the wave propagation are directed along the z-direction. The z-dependent permittivity of the dielectric composite is modeled using a periodic sinusoidal function. The exact analytical solutions to Maxwell's equations are obtained, and the field solutions and wave behavior confirm the expected properties of a lossy graded multilayered dielectric medium inside a hollow circular waveguide. Thereafter, through a numerical study performed using the commercial software COMSOL Multiphysics, we show that the analytical and numerical results are in perfect agreement. The analytical model applies to any combination of the material parameters relevant to the graded multilayered dielectric medium. The significance of the proposed method is that it can be utilized for analytically studying wave propagation and wave phenomena in a variety of media with characteristics including, but not limited to, periodicity, grading, negative refraction, and spatial- and frequency dependence. The validity is not restricted to any given frequency regime, therefore, allowing the proposed method to be useful for different types of applications, such as super-resolution imaging, electromagnetic cloaking, sub-wavelength focusing, and microwave absorbers.

This paper presents a novel wideband circularly polarized (CP) cavity-backed slot antenna based on Substrate Integrated Waveguide (SIW) technology, designed for compact and high-efficiency performance. The proposed antenna utilizes a hexagonal SIW cavity to simultaneously excite two closely spaced resonant modes (TM110 and TM210 ), resulting in enhanced bandwidth for linear polarization (LP). To achieve circular polarization, a passive, single-layer linear-to-circular polarization converter is integrated above the cavity, offering a structurally simple and PCB-compatible solution. Unlike conventional CP designs that rely on complex feeding networks or multilayered structures, this configuration maintains a planar profile and efficient performance. A fabricated prototype demonstrates strong agreement between simulation and measurement, achieving a peak gain of 9.2 dBic and a 14% axial ratio (AR) bandwidth. These results highlight the antenna's suitability for modern wireless systems requiring wideband CP functionality, including satellite communications, 5G modules, and compact embedded devices.

This study presents a novel, compact, diamond-shaped Multiple Input Multiple Output (MIMO) antenna system for 5G wireless communication. The proposed MIMO antenna system encompasses an array configuration, with each array unit comprising two antenna elements. The array elements are then orthogonally oriented making it a dual-port MIMO antenna system. The system is printed on a commercially available Rogers 5880, characterized by a permittivity ( epsilon(r) ) of 2.2 and a loss tangent (tan( delta) ) of 0.0009. The overall dimensions of the MIMO antenna system are 26 x 16 x 0.254 mm(3), operating in an mm-wave band with a frequency spectrum spanning from 26.2 to 34.2 GHz. The single antenna element exhibited a gain of 3.8 dBi and is then improved up to 7.6 dBi with two elements array arrangement. The system exhibited satisfactory MIMO characteristics with a maximum diversity gain of 10 dB, an envelope correlation coefficient of less than 0.0005, and an impressive 25 dB isolation between the antenna elements. Moreover, the proposed MIMO antenna array consistently maintained a radiation efficiency exceeding 90% across the entire desired frequency spectrum. Measurements were conducted with fabricated prototypes to validate the simulation results and were found in good agreement. The remarkable features of the proposed MIMO antenna system, such as compact size, wide bandwidth, good efficiency, and satisfactory gain values make it a promising candidate for 5G millimeter-wave wireless communication networks.

This paper investigates the RF electrophoretic response of ellipsoidal gold nanoparticles (AuNPs). Since the existing works generally consider the electrophoretic heating of spherical AuNPs, this work provides an important step towards understanding the behavior of ellipsoidal AuNPs. We first develop an analytical framework for modeling of electrophoretic response of ellipsoidal AuNPs. Thereafter, due to the lack of experimental studies of non-spherical electrophoretic RF heating of AuNPs, we validate our theory by comparison to the existing experimental results of spherical AuNPs as a special case, and estimate a few additional parameters not considered before. Then, parameter studies are performed on surface charge, friction constant, frequency, and ionic background, with respect to AuNP size and shape. Finally, we present new results for the electromagnetic absorption and heatrates of ellipsoidal AuNPs in human tissue. Our results from the tissue testing indicate a strong difference between aqueous media and realistic human tissues due to the major difference in the host medium viscosity. We demonstrate the electrophoresis’ strong dependency on the host medium’s viscosity, where we note that cancer tissue viscosity is more than a thousand times higher than that of water. We thereby confirm negative results for RF AuNP heating, indicated by our own previous study and two other previous studies. Our results provide important insights into the feasibility of RF AuNP heating in a medical context.