A multimode metamaterial for a compact and robust dualband wireless power transfer system

To release more flexibility for users to charge their portable devices, researchers have increasingly developed compact wireless power transfer (WPT) systems in recent years. Also, a dual-band WPT system is proposed to transfer power and signal simultaneously, enriching the system’s functionality. Moreover, a stacked metasurface has recently been proposed for a single band near-field WPT system. In this study, a novel multimode self-resonance-enhanced wideband metasurface is proposed for a robust dual-band WPT system, which significantly improves the performance of both bands. The size of the transmitter (Tx) and the receiver (Rx) are both 15 mm × 15 mm only. The proposed metasurface can improve efficiency from 0.04 up to 39% in the best case. The measured figure of merit (FoM) is 2.09 at 390 MHz and 2.16 at 770 MHz, respectively, in the balanced mode. Especially, the FoM can reach up to 4.34 in the lower mode. Compared to the previous state-of-the-art for similar applications, the WPT performance has significantly been improved.

The circulation near the Reykjanes Ridge in summers 2015, 2016 and 2017

<p>Located south of Iceland, the Reykjanes Ridge is a major topographic structure of the North Atlantic Ocean that strongly influences the spatial distribution and circulation of the North Atlantic Subpolar Gyre water masses. Around the ridge, the circulation is composed of two main along-ridge currents, the southwestward East Reykjanes Ridge Current (ERRC) in the Iceland Basin and the northeastward Irminger Current (IC) in the Irminger Sea. To study the along Reykjanes Ridge flow variability and the inter-basin connection through the ridge and connections with the interior of each basin, volume and water mass transports over the Reykjanes Ridge during summer 2015, 2016 and 2017 are analyzed. Data used are velocity and hydrographic measurements carried out along and perpendicular to the crest of the Reykjanes Ridge during the RREX (Reykjanes Ridge Experiment Project) cruises in June–July 2015 and June–July 2017 and BOCATS cruise in July 2016. The new circulation scheme in the area described in 2015  by Petit et al. (J. Geophys. Res., 2018) with flows connecting the ERRC and IC branches at specific locations set by the bathymetry of the ridge is again observed  in 2016 and  2017, with variations concerning the connections with the interiors of the basins. The data set reveals remarkable changes in the hydrological properties and transports of the ERRC, IC and cross ridge flows. The westward transport across the ridge, which represents the subpolar gyre intensity, was estimated at -19.6±3.4 Sv in 2015 and -35.2±3 Sv in 2017. A freshening and a decline in density mainly affecting the Subpolar Mode Water was observed in 2017. It was associated with a lower mode water  transport partly compensated by a higher transport of intermediate and Arctic waters. We further document each water mass contribution to the westward flow of the gyre and the structure of the ERRC and IC.</p>

Multilayer cloud conditions in trade wind shallow cumulus – confronting two ICON model derivatives with airborne observations

Airborne remote sensing observations over the tropical Atlantic Ocean upstream of Barbados are used to characterize trade wind shallow cumulus clouds and to benchmark two cloud-resolving ICON (ICOsahedral Nonhydrostatic) model simulations at kilometer and hectometer scales. The clouds were observed by an airborne nadir-pointing backscatter lidar, a cloud radar, and a microwave radiometer in the tropical dry winter season during daytime. For the model benchmark, forward operators convert the model output into the observational space for considering instrument-specific cloud detection thresholds. The forward simulations reveal the different detection limits of the lidar and radar observations, i.e., most clouds with cloud liquid water content greater than 10−7 kg kg−1 are detectable by the lidar, whereas the radar is primarily sensitive to the “rain” category hydrometeors in the models and can detect even low amounts of rain. The observations reveal two prominent modes of cumulus cloud top heights separating the clouds into two layers. The lower mode relates to boundary layer convection with tops closely above the lifting condensation level, which is at about 700 m above sea level. The upper mode is driven by shallow moist convection, also contains shallow stratiform outflow anvils, and is closely related to the trade inversion at about 2.3 km above sea level. The two cumulus modes are sensed differently by the lidar and the radar observations and under different liquid water path (LWP) conditions. The storm-resolving model (SRM) at a kilometer scale barely reproduces the cloud modes and shows most cloud tops being slightly above the observed lower mode. The large-eddy model (LEM) at hectometer scale reproduces better the observed cloudiness distribution with a clear bimodal separation. We hypothesize that slight differences in the autoconversion parameterizations could have caused the different cloud development in the models. Neither model seems to account for in-cloud drizzle particles that do not precipitate down to the surface but generate a stronger radar signal even in scenes with low LWP. Our findings suggest that even if the SRM is a step forward for better cloud representation in climate research, the LEM can better reproduce the observed shallow cumulus convection and should therefore in principle better represent cloud radiative effects and water cycle.

Nonlinear Vibration of a Pre-Stressed Water-Filled Single-Walled Carbon Nanotube Using Shell Model

This paper is an attempt to study the nonlinear vibration of a pre-stressed single-walled carbon nanotube (SWCNT) with water-filled and simply supported ends. A new analytical formula is obtained for the nonlinear model based on the simplified Donnell’s shell theory. The effects of internal fluid on the coupling vibration of the SWCNT–water system are discussed in detail. Furthermore, the influence of the different nanotube thicknesses and radiuses on the nonlinear vibration frequencies is investigated according to the shell theory. Numerical calculations are done to show the effectiveness of the proposed schemes. The results show that the nonlinear frequency grew with the increasing nonlinear parameters (radius and thickness of nanotube). In addition, it is shown that the influence of the nonlinear parameters is greater at the lower mode in comparison with the higher mode for the same nanotube thickness and radius.

Frequency characteristics of a viscoelastic graphene nanoplatelet–reinforced composite circular microplate

This is the first research on the frequency analysis of a graphene nanoplatelet composite circular microplate in the framework of a numerical-based generalized differential quadrature method. Stresses and strains are obtained using the higher order shear deformation theory. The microstructure is surrounded by a viscoelastic foundation. Rule of the mixture is used to obtain varying mass density and Poisson’s ratio, whereas the module of elasticity is computed by a modified Halpin–Tsai model. Governing equations and boundary conditions of the graphene nanoplatelet composite circular microplate are obtained by implementing Hamilton’s principle. The results show that outer to inner radius ratio [Formula: see text], ratios of length scale and nonlocal to thickness ( l/ h and [Formula: see text]), and graphene nanoplatelet weight fraction [Formula: see text] have significant influence on the frequency characteristics of the graphene nanoplatelet composite circular microplate. Another necessary consequence is that by increasing the value of [Formula: see text], the distribution of the displacement field extends from radial to tangent direction, especially in the lower mode numbers; this phenomenon appears much more remarkable. A useful suggestion of this research is that for designing the graphene nanoplatelet composite circular microplate at a low value of [Formula: see text], [Formula: see text] and [Formula: see text] should be given more attention, simultaneously. An interesting result which has come down from the article is that the effect of [Formula: see text] on the dimensionless frequency of the structure is really dependent on the value of C d.

Multi-layer Cloud Conditions in Trade Wind Shallow Cumulus – Confronting Models with Airborne Observations

Airborne remote sensing observations over the tropical Atlantic Ocean upstream of Barbados are used to characterize trade wind shallow cumulus clouds and to benchmark two cloud-resolving ICON (ICOsahedral Nonhydrostatic) model simulations at kilo- and hectometer scales. The clouds were observed by an airborne nadir pointing backscatter lidar, a cloud radar, and a microwave radiometer in the tropical dry winter season during daytime. For the model benchmark, forward operators convert the model data into the observational space for considering instrument specific cloud detection thresholds. The forward simulations reveal the different detection limits of the lidar and radar observations, i.e., most clouds with cloud liquid water content greater than 10−7 kg/kg are detectable by the lidar, whereas the radar is primarily sensitive to the rain-category hydrometeors in the models and can detect even low amounts of rain. The observations reveal two prominent modes of cumulus cloud top heights separating the clouds into two layers. The lower mode relates to boundary layer convection with tops closely above the lifted condensation level, which is at about 700 m above sea level. The upper mode is driven by shallow moist convection, also contains shallow outflow anvils, and is closely related to the trade inversion at about 2.3 km above sea level. The two cumulus modes are reflected differently by the lidar and the radar observations and under different liquid water path (LWP) conditions. The storm-resolving model (SRM) at kilometer scale reproduces the cloud modes barely and shows the most cloud tops slightly above the observed lower mode. The large-eddy model (LEM) at hectometer scale reproduces better the observed cloudiness distribution with a clear bimodal separation. We hypothesize that slight differences in the autoconversion parametrizations could have caused the different cloud development in the models. Neither model seems to account for in-cloud drizzle particles that do not precipitate down to the surface but generate a stronger radar signal even in scenes with low LWP. Our findings suggest that even if the SRM is a step forward for better cloud representation in climate research, the LEM can better reproduce the observed shallow cumulus convection and should therefore in principle represent cloud radiative effects and water cycle better.

Buckling and Frequency Responses of a Graphene Nanoplatelet Reinforced Composite Microdisk

This is the first research on the vibration and buckling analysis of a graphene nanoplatelet composite (GPLRC) microdisk in the framework of a numerical based generalized differential quadrature method (GDQM). The stresses and strains are obtained using the higher-order shear deformable theory (HOSDT). Rule of the mixture is employed to obtain varying mass density, thermal expansion, and Poisson’s ratio, while the module of elasticity is computed by modified Halpin–Tsai model. Governing equations and boundary conditions of the GPLRC microdisk are obtained by implementing Extended Hamilton’s principle. The results show that outer to inner ratios of the radius ([Formula: see text], ratios of length scale and nonlocal to thickness [Formula: see text] and [Formula: see text], and GPL weight fraction [Formula: see text] have a significant influence on the frequency and buckling characteristics of the GPLRC microdisk. Another necessary consequence is that by increasing the value of the [Formula: see text], the distribution of the displacement field extends from radial to tangent direction, especially in the lower mode numbers, this phenomenon appears much more remarkable. A useful suggestion of this research is that, for designing the GPLRC microdisk at the low value of the [Formula: see text], more attention should be paid to the [Formula: see text] and [Formula: see text], simultaneously.

Возбуждение низкочастотной моды межкраевого магнитоплазмона протекающим постоянным током / Петров А.С., Свинцов Д.А.

Первое наблюдение краевых плазменных мод в двумерных электронных системах (ДЭС) относится к 1985 году [1]. Их теоретическое описание опирается на самосогласованное решение уравнений электростатики и гидродинамики электронной жидкости. Точное решение этой задачи было получено Волковым и Михайловым с помощью весьма громоздкого метода Винера-Хопфа [2,3], который ещё более усложняется в случае систем с координатно-зависимой недиагональной проводимостью (систем с дрейфом или вязкостью) [4]. Вследствие этого, исследования влияния дрейфа на спектр (меж)краевых мод производились ранее лишь в моделях с упрощённой электростатикой [5,6]. Эти модели предсказывали, что краевые моды существуют только при ненулевой скорости электронного дрейфа, а их спектр носит характер белого шума. Поэтому считалось, что краевые моды подавляют резонансное возбуждение ‘нормальных’ (некраевых) мод в плазмонных источниках терагерцового (ТГц) излучения и уширяют спектр излучения [7]. В настоящей работе мы определяем влияние дрейфа на спектр межкраевых плазменных мод, исходя из точных моделей [2,3]. Для решения задачи мы используем разработанный нами пертурбативный подход [8,9], основанный на применении методов квантово-механической теории возмущений к уравнениям электронной гидродинамики, записанным в операторной форме. Этот подход впервые позволяет в рамках единого подхода описать влияние электронного дрейфа, магнитного поля, вязкости, затухания, кривизны Берри и возмущений граничных условий на спектр колебаний плазмонов (в т.ч. краевых) в ДЭС с произвольным окружением контактов. В качестве наглядного объекта для исследований мы выбрали низкочастотную моду межкраевого магнитоплазмона [3] (LIEMP, Lower mode of Inter-Edge MagnetoPlasmon). В пределе слабых магнитных полей её спектр пропорционален циклотронной частоте, а амплитуда экспоненциально спадает внутрь каждой из соприкасающихся ДЭС, что делает расчёт матричных элементов оператора дрейфа по теории возмущений предельно простым. Мы обнаружили, что линейная по дрейфу поправка к спектру LIEMP является чисто мнимой (что соответствует нарастанию/затуханию волн) и пропорциональной волновому вектору и разности концентраций носителей в соседних ДЭС. Таким образом, мы показываем, что дрейф носителей может приводить к самовозбуждению (меж)краевых плазменных мод в ДЭС с чётко определённым спектром. Это делает возможным создание резонансных источников ТГц излучения на краевых модах, причём в случае LIEMP спектр излучения может плавно регулироваться внешним магнитным полем, не превышающим 1 Т.

Vibration of the rotating rectangular orthotropic Mindlin plates with an arbitrary stagger angle

In this article, the vibration analysis of rotating moderately thick cantilever orthotropic plate is analytically investigated. Based on the first order shear deformation plate theory, the partial differential equations of motion are derived using Hamilton’s principle. The centrifugal inertia forces and Coriolis effects due to the rotation are all considered. The analytical approaches, both extended Kantorovich method and extended Galerkin method, are employed to obtain the solution of the problem. Results obtained by these two methods are compared with those available in the open literature and good agreements are observed. The effects of various parameters, individually or in combination, on the vibrational behaviors are analyzed in detail. From the studies, it is found that in the rotating plates, when the stiffness ratio increases, the crossing/veering phenomenon occurs in the lower mode orders and/or rotation speeds. The results show that for each stiffness ratio, the effect of hub radius ratio is more significant on the out-of-plane mode frequencies than on the in-plane ones.