A simple mass oscillator metasurface design with linear phase shift

In this paper, a simple mass oscillator metasurface is designed, which can regulate the phase shift of flexural wave covering 0-2π by adjusting the number of mass oscillators on the connecting bar. Based on the forced vibration theory, there is a simple approximately linear relationship between the number and phase shift of mass oscillators, which can more intuitively and accurately predict the phase of different number of mass oscillators, and then realize the metasurface design of mass oscillators with different requirements. Therefore, arbitrary regulation of flexural waves, such as abnormal refraction, beam focusing, and self-acceleration, can be realized by reasonably arranging the number of mass oscillators. The results show that the proposed metasurface can be greatly simplified both in the establishment of phase shift relation and in the fabrication of structure configuration, and will have broad application potential in the engineering field.

Knowledge-driven feature component interpretable network for motor imagery classification

Objective. End-to-end convolution neural network (CNN) has achieved great success in motor imagery classification without manual feature design. However, all the existing deep network solutions are purely data-driven and lack interpretability, which makes it impossible to discover insightful knowledge from the learnt features, not to mention to design specific network structure. The heavy computational cost of CNN also makes it challenging for real time application along with high classification performance. Approach. To address these problems, a novel Knowledge-driven Feature Component Interpretable Network (KFCNet) was proposed, which combines spatial and temporal convolution in analogy to ICA and power spectrum pipeline. Prior frequency band knowledge of sensory motor rhythms (SMR) has been formulated as band-pass linear-phase digit FIR filters to initialize the temporal convolution kernels to enable knowledge driven mechanism. To avoid signal distortion and achieve linear phase and unimodality of filters, a symmetry loss is proposed, which is used in combination with the cross-entropy classification loss for training. Besides the general prior knowledge, subject specific time-frequency property of ERDS (event-related desynchronization and synchronization) has been employed to construct and initialize the network with significantly fewer parameters. Main results. Comparison experiments on two public datasets have been performed. Interpretable feature components could be observed in the trained model. The physically meaningful observation could efficiently assist the network structure design. Excellent classification performance on motor imagery has been obtained. Significance. The performance of KFCNet is comparative to the state-of-the-art methods but with much fewer parameters and makes real time application possible.

A Compact Dual-Band Notched UWB Antenna for Wireless Applications

This article presents the design and analysis of a V-shaped ultrawideband (UWB) antenna and dual-band UWB notch antenna. A rectangular slot is cut into a semicircular partial ground plane of the antenna to achieve ultrawide bandwidth. A U-shape slot is etched on a V-shaped patch that radiates, and an inverted U-shape parasitic resonator is placed beside the feedline to generate dual-band notch characteristics. The overall dimension of the proposed antenna is 28×23 mm2. The proposed UWB antenna has a gain of 9.8 dB, S11 < −10 dB, impedance bandwidth in the range of 3.4 to 12.3 GHz, response with a linear phase, group delay <1 ns, and stable radiation pattern. The UWB notch antenna shows strong rejection in the WLAN band from 5.15 to 5.8 GHz with a notch at 5.6 GHz and X band from 9.1 to 10.5 GHz with a sharp notch at 9.6 GHz, having a S11 < −10 dB impedance bandwidth ranging from 3.2 to 11.7 GHz. This antenna also exhibits a stable radiation pattern, group delay <1 ns, and linear phase response throughout the bandwidth except at the rejection frequencies.

MMS Observations of Double Mid-Latitude Reconnection Ion Beams in the Early Non-Linear Phase of the Kelvin-Helmholtz Instability

The MMS satellites encountered a Kelvin-Helmholtz instability (KHI) period in the early non-linear phase at the post-noon flank magnetopause on 8 Sep 2015. The adjacent magnetosheath was characterized by a pre-dominantly northward Bz &gt; 0 magnetic field with weakly positive in-plane components in a GSM coordinate system. Ion velocity distribution functions indicate at least 17 KH vortex intervals with two typically D-shaped ion beam distributions, commonly associated with reconnection exhausts, that stream in both directions along a mostly northward magnetic field at 350–775 km/s with a median 525 km/s ion beam speed. The counter-streaming ion beams are superposed on a core population of slowly drifting magnetosheath ions with a field-aligned 50–200 km/s speed. Each interval lasted no more than 5.25 s with a median duration of 1.95 s corresponding to in-plane spatial scales 3 &lt; ΔS &lt; 22 di assuming a constant 1 di = 61 km ion inertial scale and a tailward VKH∼258 km/s KH vortex propagation speed along the MMS trajectory. The counter-streaming ions are predominantly observed in the warm KH vortex region between the cold magnetosheath proper and the hot isotropic ion temperature of a low-latitude boundary layer as the MMS constellation traverses a KH vortex. The in-plane spatial scales and the locations of the observed counter-streaming ion beams generally agree with the predictions of twice-reconnected magnetic fields at two mid-latitude reconnection (MLR) regions in a two-fluid three-dimensional numerical simulation previously reported for this KH event. MMS typically recorded a higher phase space density of the fast parallel ion beam that we associate with a tailward reconnection exhaust from the southern MLR (SMLR) and a lower phase space density of the fast anti-parallel ion beam that we associate with a tailward reconnection exhaust from the northern MLR (NMLR) of similar speed. This is either consistent with MMS being closer to the SMLR region than the NMLR region, or that the KHI conditions may have favored reconnection in the SMLR region for the observed in-plane magnetosheath magnetic field as predicted by a two-fluid three-dimensional numerical simulation.

Design of linear phase shifting transformer based on linear motor

In this paper, a linear phase shifting transformer based on linear motor is studied. The transformer is composed of four groups of three-phase full-bridge inverter system and a linear core. The DC power supply can be converted into three-phase alternating current through the inverter system and the linear phase shifting transformer. Compared with the traditional phase-shifting transformer, the linear phase-shifting transformer is easy to expand, easy to connect, and has better heat dissipation. The simulation results show that this scheme is feasible.