Errors in Broadband Permittivity Determination Due to Liquid Surface Distortions in Semi-Open Test Cell

We study how surface distortions of liquid samples due to a meniscus and a tilt of a semi-open coaxial test cell affect errors in a broadband permittivity determination. The study is based on the scattering parameters, obtained using the electromagnetic simulations of samples with flat and distorted surfaces in a broad frequency range up to 18 GHz. The parameters are processed with the classic Nicolson–Ross–Weir (NRW) method and our new meniscus removal technique. We analyze the errors for several samples of different properties, such as distilled water and propan-2-ol. The results show that the meniscus removal technique is more robust and provides smaller errors in the permittivity determination compared to the classic NRW method. The effect of the cell tilt, to our best knowledge, has not been considered in the literature yet.

Study on the optimal Zernike order in the phase parameterization for global phase retrieval algorithm

Phase retrieval algorithm is an effective method to reconstruct the surface distortions for reflector antennas. As the traditional Fourier iterative algorithms usually stagnate at local minima, we previously proposed a global phase retrieval algorithm, named CMAES-HIO, based on the hybridization of hybrid-input-output algorithm and covariance matrix adaptation evolution strategy. We address the problem of selection of the Zernike order used in the phase parameterization for CMAES-HIO algorithm in this paper. By introducing a hybrid evaluation parameter, which combines the algorithm accuracy and time consumption, we utilize the Monte-Carlo method to simulate the algorithm performance under different random surface distortions. Simulation results show that for an unknown surface distortion, a Zernike order of 5 or 6 is probably the optimum for the comprehensive algorithm performance with respect to time and accuracy.

Surface Roughness Effects on the Broadband Reflection for Refractory Metals and Polar Dielectrics

Random surface roughness and surface distortions occur inevitably because of various material processing and fabrication techniques. Tailoring and smoothing the surface roughness can be especially challenging for thermomechanically stable materials, including refractory metals, such as tungsten (W), and polar dielectrics, such as silicon carbide (SiC). The spectral reflectivity and emissivity of surfaces are significantly impacted by surface roughness effects. In this paper, we numerically investigated the surface roughness effects on the spectral reflectivity and emissivity of thermomechanically stable materials. Based on our results, we determined that surface roughness effects are strongly impacted by the correlation length of the Gaussian surface. In addition, our results indicate that surface roughness effects are stronger for the materials at the epsilon-near-zero region. Surface roughness effects are stronger between the visible and infrared spectral region for W and around the wavelength of 12 μ m for SiC, where plasma frequency and polar resonance frequency are located.

Effect of Surface Error Distribution and Aberration on Electromagnetic Performance of a Reflector Antenna

In this paper, a method based on the Zernike distribution and the optical aberration is proposed to investigate the effects of the distribution characteristics of surface distortions of a reflector antenna on its electromagnetic performance (EMP). For large-scale errors, an analytical model is introduced to describe the arbitrary distortions, based on the orthogonal Zernike polynomials. The effects of error distribution described by the Zernike series on typical EMP are analyzed. The numerical results indicate that the distortions in the distribution feature of defocus or spherical aberration have a greater impact on gain, and the distribution feature of tilt or coma mainly influences boresight offset; the distribution feature of defocus, astigmatism, and spherical aberration has a greater impact on sidelobe levels. The results indicate that the beam contour patterns are related to the distribution forms of distortions and are similar with the same aberration feature. On the basis of the Seidel aberration, the relationships between typical EMP and the aberration coefficient are presented. Based on these, the error profile of the primary influence and the approximate feature of EMP can be determined, and the antenna performance can be predicted in a simple manner.

Volumetric and Shape Analysis of the Subcortical Regions in Schizophrenia Patients: A Pilot Study

Objective: Investigation of brain structure in disease has been enhanced by developments in shape analysis methods that can identify subtle regional surface distortions. High-resolution magnetic resonance (MR) imaging was used to compare volumetric and shape analysis in schizophrenia (SCZ) patients and healthy controls (CON). Methods: T1-weighted, 1-mm thick MR images were acquired for 15 patients with SCZ and 15 age-matched healthy controls using subcortical volume and shape analysis, which we believe to be complimentary to volumetric measures. Results: SCZ patients showed significant shape differences compared to healthy controls in the right hippocampus (P < 0.005), left and right putamen (P < 0.044 and P < 0.031), left caudate (P < 0.029), right pallidum (P < 0.019), and left thalamus (P < 0.033). Conclusion: Our results provide evidence for subcortical neuroanatomical changes in patients with SCZ. Hence, shape analysis may aid in the identification of structural biomarkers for identifying individuals of SCZ.