A compact dual-band antenna element is presented that operates in the bands 0.617-0.894 GHz [36.7% fractional bandwidth (FBW)] and 1.69-2.4 GHz (34.7% FBW). The dual-band antenna element consists of a low-band (LB) bowl-shaped antenna with a ring for the LB and a high-band (HB) dipole antenna, placed in the center of the bowl. The ring is used to reduce the size of the dual-band antenna element without compromising the bandwidth. The presence of the ring can introduce spurious resonance modes in the structure that impair the performance of the antenna. These resonances are suppressed by placing stubs on the ring. The proposed dual-band antenna element consists of robust metallic components, with some dielectric supports. As a result, the antenna provides a high radiation efficiency and power handling, making it suitable as a base station antenna (BSA). Furthermore, the presented antenna is also demonstrated to be suitable for array configurations, which is critical for the targeted application. A prototype is manufactured and tested to corroborate the simulation results, and a good agreement is found. Importantly, the measured radiation efficiency is higher than 96% and 93% in the targeted low and high bands.

The Polarization and Impedance Controlled Car (PICC) presents an innovative approach for demonstrating and teaching key principles of electromagnetic field theory, specifically polarization and impedance. Designed as an interactive learning tool, the PICC utilizes a radio-controlled car, NanoVNA, Raspberry Pi, and handheld antennas to visualize real-time effects of polarization and impedance. The system incorporates two orthogonal linearly polarized patch antennas on a shared ground plane connected to a NanoVNA. A strip grid is utilized to affect the reflection and transmission properties of the two antennas, which in turn enables controlled car movements. This paper details the design, measurements, and simulations involved in creating the PICC and introduces an open-source Python library for NanoVNA data streaming. The PICC illustrates a practical application of electromagnetic principles potentially providing a more engaging learning experience for undergraduate students.

Characteristic Mode analysis is a widely used technique in antenna design, providing insight into the fundamental electromagnetic properties of radiating structures. In this paper, we establish fundamental bounds on the slope of characteristic mode eigenvalues and angles, demonstrating that their rate of change is subject to fundamental constraints for all possible realizations within a given design region. These bounds are derived using the method of moments and reformulating the frequency derivative (slope) of the eigenvalue quantities as an optimization problem over the current distribution confined to the design region. The results reveal a direct analogy between these constraints and classical antenna Q-factors, highlighting the intrinsic limitations on modal evolution and their implications for bandwidth and miniaturization in antenna design. Moreover, by iteratively enforcing orthogonality among the modes the derived bounds can be tightened for higher-order modes, providing deeper insight into the number of simultaneous, usable modes and their associated degrees of freedom. These bounds provide a feasibility criterion for achievable modal behavior, offering insights that can guide the design process. Examples are given for various surface PEC structures.

The problem of substructure characteristic modes is developed using a scattering matrix-based formulation, generalizing subregion characteristic mode decomposition to arbitrary computational tools. It is shown that the modes of the scattering formulation are identical to the modes of the classical formulation based on the background Green's function for lossless systems under conditions where both formulations can be applied. The scattering formulation, however, opens a variety of new subregion scenarios unavailable within previous formulations, including cases with lumped or wave ports or subregions in circuits. Thanks to its scattering nature, the formulation is solver-agnostic with the possibility to utilize an arbitrary full-wave method.

This article elaborates on a technique for rapid real-time imaging of millimeter-wave (mmWave) power density over surfaces of several wavelengths in size. The approach involves using a screen-printed metasurface equipped with elements designed for absorption of mmWaves, along with an infrared (IR) camera to monitor temperature changes due to the absorption. By modulating the transmitted signal and applying the metasurface technique, which concentrates absorbed power onto specific regions, we successfully detected typical mmWave power levels. This method provides an efficient, noncontact means of rapidly evaluating and characterizing devices emitting in the mmWave spectrum. To illustrate the efficacy of the technique, we present two case studies at 28 GHz: fault detection on a 256-element square array antenna in the Ka-band, and mmWave power density imaging in the near-field of a mobile phone mockup over surfaces measuring 58 square centimeters (51 square wavelengths at 28 GHz). The results obtained can be analyzed in both the time and frequency domains, augmenting comprehension and assessment capabilities.

There is a growing interest for the possibility of using peripheral blood cells (including platelets) as markers for mitochondrial function in less accessible tissues. Only a few studies have examined the correlation between respiration in blood and muscle tissue, with small sample sizes and conflicting results.This study investigated the correlation of mitochondrial respiration within and across tissues. Additional analyses were performed to elucidate which blood cell type would be most useful for assessing systemic mitochondrial function.There was a significant but weak within tissue correlation between platelets and peripheral blood mononuclear cells (PBMCs). Neither PBMCs nor platelet respiration correlated significantly with muscle respiration.Muscle fibers from a group of athletes had higher mass-specific respiration, due to higher mitochondrial content than non-athlete controls, but this finding was not replicated in either of the blood cell types. In a group of patients with primary mitochondrial diseases, there were significant differences in blood cell respiration compared to healthy controls, particularly in platelets. Platelet respiration generally correlated better with the citrate synthase activity of each sample, in comparison to PBMCs.In conclusion, this study does not support the theory that blood cells can be used as accurate biomarkers to detect minor alterations in muscle respiration. However, in some instances, pronounced mitochondrial abnormalities might be reflected across tissues and detectable in blood cells, with more promising findings for platelets than PBMCs.

The number of degrees of freedom (NDoF) is a crucial parameter in many electromagnetic problems. In, for example, modern communication systems, spatial diversity is often employed through multiple beams to enhance capacity and reliability. However, while the degrees of freedom (DoF) can be computed, their connection to physical quantities is not as easily understood. To address this issue, this article proposes a scattering-based formulation of characteristic mode (CM) analysis that can estimate the DoF of arbitrarily shaped radiating objects. The relation between the number of dominant CMs and physical characteristics differs for electrically large and small objects. Specifically, for large objects, it is connected to the mean shadow area, while for small objects, it is linked to their average polarizability through the forward scattering sum rule. Therefore, the average shadow area and polarizability are fundamental parameters that provide insight into the NDoF for any object. These basic parameters also provide straightforward estimates of the minimum size of a device region required to support a desired number of electromagnetic DoF across a given spectral response.

Survivors of Pediatric Brain Tumors (PBTs) treated with cranial radiation therapy (CRT) often experience a decline in neurocognitive test scores. Less is known about the neurocognitive development of non-irradiated survivors of PBTs. The aim of this study was to statistically model neurocognitive development after PBT in both irradiated and non-irradiated survivors and to find clinical variables associated with the rate of decline in neurocognitive scores. A total of 151 survivors were included in the study. Inclusion criteria: Diagnosis of PBT between 2001 and 2013 or earlier diagnosis of PBT and turning 18 years of age between 2006 and 2013. Exclusion criteria: Death within a year from diagnosis, neurocutaneous syndromes, severe intellectual disability. Clinical neurocognitive data were collected retrospectively from medical records. Multilevel linear modeling was used to evaluate the rate of decline in neurocognitive measures and factors associated with the same. A decline was found in most measures for both irradiated and non-irradiated survivors. Ventriculo-peritoneal (VP) shunting and treatment with whole-brain radiation therapy (WBRT) were associated with a faster decline in neurocognitive scores. Male sex and supratentorial lateral tumor were associated with lower scores. Verbal learning measures were either stable or improving. Survivors of PBTs show a pattern of decline in neurocognitive scores irrespective of treatment received, which suggests the need for routine screening for neurocognitive rehabilitation. However, survivors treated with WBRT and/or a VP shunt declined at a faster rate and appear to be at the highest risk of negative neurocognitive outcomes and to have the greatest need for neurocognitive rehabilitation.

Properties of characteristic modes of lossless scatterers breaking time-reversal symmetry are presented utilizing the scattering formulation of characteristic decomposition. Antennas connected to nonreciprocal circuits and moving material bodies are used as numerical examples.

The scattering formulation of characteristic mode decomposition is utilized to extend modal analysis to lossless scatterers breaking time-reversal symmetry. This enables characteristic modes analysis on devices containing gyrotropic or moving media. The resulting nonreciprocity introduces features not observed in reciprocal scenarios, such as asymmetric phase progression in characteristic far fields. These new phenomena are carefully discussed using examples of varying complexity. Indicators of nonreciprocity based on modal data are also introduced.

Characteristic modes are formulated using the scattering dyadic, which maps incident plane waves to scattered far-fields generated by an object of arbitrary material composition. Numerical construction of the scattering dyadic using arbitrary full-wave electromagnetic solvers is demonstrated in examples involving a variety of dielectric and magnetic materials. Wrapper functions for computing characteristic modes in method-of-moments, finite-difference time domain, and finite-element solvers are provided as Supplementary Material.

Characteristic modes of arbitrary 2-D periodic systems are analyzed using scattering parameter data. This approach bypasses the need for periodic integral equations and allows for characteristic modes to be computed from generic simulation or measurement data. Example calculations demonstrate the efficacy of the method through comparison against a periodic method of moments (MoM) formulation for a simple, single-layer conducting unit cell. The effect of vertical structure and electrical size on the number of modes is studied, and its discrete nature is verified with example calculations. A multiband polarization-selective surface and a beamsteering metasurface are presented as additional examples.

An iterative algorithm is adopted to construct approximate representations of matrices describing the scattering properties of arbitrary objects. The method is based on the implicit evaluation of scattering responses from iteratively generated excitations. The method does not require explicit knowledge of any system matrices (e.g., stiffness or impedance matrices) and is well suited for use with matrix-free and iterative full-wave solvers, such as finite-difference time-domain method, finite-element method, and multilevel fast multipole algorithm. The proposed method allows for significant speed-up compared to the direct construction of a full transition matrix or scattering dyadic. The method is applied to the characteristic mode decomposition of arbitrarily shaped obstacles of arbitrary material distribution. Examples demonstrating the speed-up and complexity of the algorithm are studied with several commercial software packages.

Mutual coupling between antennas is a key parameter in multi-antenna systems. The present paper describes a method to map contributions to the magnitude of the mutual coupling spatially on surfaces between the ports. The method utilizes the reaction theorem for electromagnetic fields to obtain the contribution of the coupling from different regions. The derived result is valid for and applied to the strong-coupling regime, where the mutual impedance is of the same order as the self-impedance.

This abstract describes the decomposition of a matrix representing a scattering dyadic into characteristic modes. Scattering dyadic, as compared to conventionally used impedance matrices, are independent of numerical method used to compute them and the same characteristic mode formulation can be used for decomposition of composite and inhomogeneous materials. The utilization of scattering dyadic makes it possible to synthesize characteristic modes which are orthogonal over prescribed portions of the far-field sphere, or ex-post decomposition of measured data. The theory is demonstrated on a simple example and its features are discussed.

Mutual coupling, or equivalently, the isolation between antennas, is a key parameter in antenna system design. In this work, the previously defined impedance density is generalized, and it is demonstrated how it can be used to obtain spatial information about the mutual coupling. The generalized impedance density is a real-valued scalar and it can be visualized as a three-dimensional density in space. It is shown that there is a strong connection between regions with a positive (negative) generalized impedance density and a decrease (increase) of the coupling when an absorber is placed in that region. This predictive ability is a useful feature, which is tested for three numerical cases. The results are robust to the shape of the platform, and it can be compared across frequencies. By placing absorbers based on the generalized impedance density, it is possible to reduce the required amount of absorbers needed to obtain a certain reduction in mutual coupling. The visualization results and predictions of absorber positions are compared with a Poynting vector based method. Placing absorbers based on the generalized impedance density had a larger impact on the mutual coupling, compared to the predictions with the Poynting vector based method in the investigated cases.