This article presents an in-depth study of material measurement, at G-band (140-220 GHz), using a commercially available material characterization kit (MCK). The permittivity of homogeneous ...dielectric materials, obtained from MCK measurements, rises slightly with frequency, and this does not agree with the expected physical behavior. Based on electromagnetic simulations and measurements, it has been identified that this small error is due to the dispersion associated with the corrugated horn antennas of the MCK. To address this problem, a simple phase compensation scheme has been proposed and applied to the measurement results of five common kinds of dielectric materials. The processed results eliminate the rising slope error observed in the raw data and are in good agreement with permittivity values reported in the literature, which validates the proposed approach.
A waveguide-based measurement configuration is proposed, as a modification to the traditional completely filled waveguide technique, for microwave characterization of relatively thin and high-loss ...materials. This method is aimed to overcome the large measurement errors caused by gaps and cross-sectional distortions, which are of great concern when measuring high-loss samples, such as unidirectional (UD) carbon-fiber reinforced polymer (CFRP) composite sheets. In this article, the influences of critical parameters, namely, dielectric constant, loss factor, material thickness, and waveguide misalignment, on measured complex permittivity of several diverse samples, are fully investigated through numerical electromagnetic simulations and measurements at <inline-formula> <tex-math notation="LaTeX">X </tex-math></inline-formula>-band (8.2-12.4 GHz). By the virtue of the electromagnetic properties associated with high-loss dielectric materials, it is found that this technique coupled with the Nicolson-Ross-Weir (NRW)/Backer-Jarvis conversion procedure is a capable method for measuring high-loss dielectric materials.
The THz band has attracted considerable attention for next-generation wireless communications due to the large amount of available bandwidth that may be key to meet the rapidly increasing data rate ...requirements. Before deploying a system in this band, a detailed wireless channel analysis is required as the basis for proper design and testing of system implementations. One of the most important deployment scenarios of this band is the outdoor microcellular environment, where the Transmitter (Tx) and the Receiver (Rx) have a significant height difference (typically <inline-formula> <tex-math notation="LaTeX"> \ge 10 </tex-math></inline-formula> m). In this paper, we present double-directional (i.e., directionally resolved at both link ends) channel measurements in such a microcellular scenario encompassing street canyons and an open square. Measurements are done for a 1 GHz bandwidth between 145-146 GHz and an antenna beamwidth of 13 degree; distances between Tx and Rx are up to 85 m and the Tx is at a height of 11.5 m from the ground. The measurements are analyzed to estimate path loss, shadowing, delay spread, angular spread, and multipath component (MPC) power distribution. These results allow the development of more realistic and detailed THz system performance assessment.
We present a new approach for estimating the parameters of three-phase untransposed electrically short transmission lines using voltage/current synchrophasor measurements obtained from phasor ...measurement units (PMUs). The parameters to be estimated are the entries of the longitudinal impedance matrix and the shunt admittance matrix at the rated system frequency. Conventional approaches relying on the admittance matrix of the line cannot accurately estimate these parameters for short lines, due to their high sensitivity to measurement noise. Our approach differs from conventional ones in the following ways. First, we model the line by the three-phase transmittance matrix that is observed to be less sensitive to measurement noise than the admittance matrix. Second, we compute an accurate noise covariance matrix using the realistic specifications of noise introduced by instrument transformers and PMUs. This noise covariance matrix is then used in least-squares-based estimation methods. Third, we derive different least-squares-based estimation methods based on a statistical model of estimation and show that the weighted least-squares and the maximum likelihood methods, which make use of the noise covariance matrix, produce the best estimates of the line parameters. Finally, we apply the proposed methods to a real data set and show that our approach significantly outperforms existing ones.
Antenna pattern measurement generally requires an anechoic chamber with a single line-of-sight (LOS) propagation. However, it may not be satisfied due to cost and size limitations, leading to a ...nonanechoic environment (with echoes) and a distorted measured antenna pattern. To address this challenge, this article proposed an echo suppression method using phaseless data at a single frequency. With the proposed method, one can discriminate the multipath characteristic convoluted with the actual antenna pattern by measuring the antenna gain pattern at multiple spatial locations. Different from the state-of-the-art methods requiring phase information, the proposed method is an amplitude-only technique, thus enabling cost-effective and true over-the-air (OTA) measurement for the wireless device. Furthermore, we derived a systematic guideline for the proposed method to improve measurement efficiency based on numerical simulations. The proposed method is experimentally validated by placing a metal plate in the chamber to emulate a nonanechoic environment, and a good agreement between the true antenna pattern and the reconstructed antenna gain pattern is found. Both numerical and experimental validations demonstrated the feasibility and robustness of the proposed technique.
Achieving the optimal design of power converters requires a deep understanding of the system's dissipation elements to meet the desired performance and safety standards. Once the power converter is ...designed, it is of key importance to estimate the actual power losses in the real setup, in order to redesign the power converter or monitor and control the semiconductor power losses. With that purpose, calorimetric techniques have outperformed electrical methods. However, they come with mechanical limitations and depend on analytical electrothermal equivalent circuits. These models are highly topology and technology dependent, often resulting in simplistic representations that underestimate thermal effects or complex sets of differential equations. To overcome these challenges, we present a novel post-design automatic method for characterizing semiconductor power losses through its converter thermal dynamics. Our method is rooted in an optimization program that identifies the optimal discrete-time linear model according to a set of power vs. temperature profiles. The proposed approach ensures accurate identification and integration of desired modeling requirements. The methodology is applicable to any power converter topology, and the derived linear model enables the use of standard control theory techniques for monitorization and control. Experiments with a real power converter validate the proposal's versatility and accuracy.
The importance of fairness, validity, and accessibility in assessment is greater than ever as testing expands to include more diverse populations, more complex purposes, and more sophisticated ...technologies. This book offers a detailed account of fairness in assessment, and illustrates the interplay between assessment and broader changes in education. In 16 chapters written by leading experts, this volume explores the philosophical, technical, and practical questions surrounding fair measurement. Fairness in Educational Assessment and Measurement addresses issues pertaining to the construction, administration, and scoring of tests, the comparison of performance across test takers, grade levels and tests, and the uses of educational test scores. Perfect for researchers and professionals in test development, design, and administration, Fairness in Educational Assessment and Measurement presents a diverse array of perspectives on this topic of enduring interest.
Terahertz (THz) communications are envisioned as a promising technology for sixth-generation (6G) and beyond systems, owing to its unprecedented multi-gigahertz (GHz) bandwidth. In this paper, ...channel measurement campaigns in indoor scenarios at low-THz frequencies, i.e., 201-209 GHz, are reported. Four different communication scenarios including 90 transmitter-receiver pairs are measured in two channel measurement campaigns of a meeting room and an office room, respectively. The two measurement campaigns contains four scenarios, namely, a meeting room, cubicle area, hallway and non-line-of-sight (NLoS) case. The propagation of multi-path components (MPCs) in the four scenarios is characterized by the power-delay-angular profiles. Based on them, the temporal and spatial consistency for varying receiver locations in the complex hallway and NLoS scenarios are verified. To characterize, the large-scale best-direction and omni-directional path losses in indoor scenarios are separately analyzed and modeled by the close-in (CI) model. Furthermore, the small-scale channel parameters, e.g., the number of clusters, delay spread, angular spread, and cluster time-of-arrival are analyzed and modeled by proper distributions. As a general framework, a ray-tracing-statistical hybrid model is proposed for wireless propagation at 201-209 GHz, although, admittedly, the measurement results and analysis reveal that the channel characteristics in various indoor scenarios exhibit noticeable differences that need tailored parameter settings.
This paper presents the metrological characterization of a four-electrode compact system able to measure the dielectric properties of biological tissues at extremely low and ultra-low frequencies, ...where data available from the literature are very limited. The cell constant k of the system, together with its expanded uncertainty, is found measuring different saline solutions of known conductivity. Since the cell constant plays a key role in the determination of tissue dielectric properties, it has been further verified through tests on other saline solutions, containing a different type of solute, confirming the accuracy of the system. In particular, results on a saline solution with a given molar concentration of KCl and on a physiological solution (Eurospital 0.9% NaCl) show that the system maximum relative error is lower than 3.3%. Therefore, it can be concluded that the system correctly measures the conductivity in saline solutions and the parameter k can be properly used for the measurement of dielectric properties of biological tissues. As an application example, the system is used to perform measurements on bovine liver. Liver conductivity measurements show a constant behavior as a function of frequency in the examined range. Furthermore, the comparison of our results with the few data found in the literature at low frequencies shows good agreement. These observations point out the feasibility and convenience of the proposed method for the measurement of the conductivity at very low frequency.
This article presents a thorough study of spherical probe-corrected phaseless near-field measurements with the two-scans technique. Such technique is based on retrieving the antenna under test ...radiation pattern from the measurement of the near-field amplitude signals on two spheres of different radii. The postprocessing of this type of measurements results in a highly nonlinear algorithm, prone to get trapped in local minima and provide incorrect solutions when the measurement conditions are not properly selected. Through a series of numerical simulations, the influence of different measurement parameters on the phaseless technique is analyzed. It will be shown how both the relative and absolute values of the measurement spheres highly affect the convergence of the phase retrieval algorithm. The type of AUT and its radiation pattern characteristic also play a fundamental role in the feasibility of phaseless measurements. Other parameters such as sampling rate, noise, probe correction, polar truncation, and measurement offsets are also investigated. The conducted study allows to extract a set of guidelines to improve the accuracy of phaseless spherical near-field algorithms. In addition, purely phaseless antenna measurement examples are given to demonstrate the algorithm capabilities and limitations, and to validate the developed numerical investigations.
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