A 1-to-8 Fully Modular Stacked SIW Antenna Array for Millimeter-Wave Applications

This paper presents a vertically stacked SIW antenna array that enables different array configurations with the minimum number of SIW layers. This achievement lies in the modular feature offered by the proposed design. Specifically, 4 distinct array configurations can be produced with only 3 different design of SIW layers. Depending on the number of SIW layers employed in the stacked antenna, the directivity in the E-plane of radiation is modified. To obtain an equal and in-phase power distribution among the array elements, H- and E-plane corporate feeding networks are efficiently implemented in each array configuration. Array configurations of 1, 2, 4 and 8 radiating layers are offered by the proposed modular array, where each radiating layer is formed by 8 H-plane SIW horn antennas. The simulated directivity for the array configurations ranges from 15.8 dBi to 23.8 dBi and the main beam direction remains fixed along the operating frequency band. The array design has been manufactured and proper agreement between simulated and measured results are observed. The measured impedance bandwidth in all the array configurations is from 35 GHz to 41 GHz (15.79% bandwidth) with a reduction in the E-plane beamwidth as the number of radiating layers increases.

Flexible and Stretchable Memristive Arrays for in-Memory Computing

With the tremendous progress of Internet of Things (IoT) and artificial intelligence (AI) technologies, the demand for flexible and stretchable electronic systems is rapidly increasing. As the vital component of a system, existing computing units are usually rigid and brittle, which are incompatible with flexible and stretchable electronics. Emerging memristive devices with flexibility and stretchability as well as direct processing-in-memory ability are promising candidates to perform data computing in flexible and stretchable electronics. To execute the in-memory computing paradigm including digital and analogue computing, the array configuration of memristive devices is usually required. Herein, the recent progress on flexible and stretchable memristive arrays for in-memory computing is reviewed. The common materials used for flexible memristive arrays, including inorganic, organic and two-dimensional (2D) materials, will be highlighted, and effective strategies used for stretchable memristive arrays, including material innovation and structural design, will be discussed in detail. The current challenges and future perspectives of the in-memory computing utilizing flexible and stretchable memristive arrays are presented. These efforts aim to accelerate the development of flexible and stretchable memristive arrays for data computing in advanced intelligent systems, such as electronic skin, soft robotics, and wearable devices.

Nanofluid flow of Alumina-Copper/Water through isotropic porous arrays of periodic square cylinders: mixed convection and competent array shape

The flow of hybrid Alumina-Copper/Water nanofluid with mixed convection heat transfer from multiple square cylinders arranged in three different types of arrays, namely equilateral triangle (ET), rotated square (RS), and rotated rhombus (RR) in a heat exchanger has never been studied before the present study. Navier-Stokes and energy equations with a periodic condition in transverse direction for three array types having the same porosity are solved with finite volume methodology. The combined effect of aiding buoyancy (Richardson number Ri 0-2), configuration of square cylinders, and hybrid nanoparticle volume fraction (0-0.06) on flow dynamics and their impact on the overall heat transfer phenomenon through three different array configurations is thoroughly elucidated. The arrays' overall drag and friction coefficient increases with an increase in the strength of aiding buoyancy and nanoparticle volume fraction. An increment in Ri, and nanoparticle volume fraction, causes thermal boundary layer thinning and results in higher heat transfer rates across three arrays. With an increase in Ri from 0 to 2 at a nanoparticle volume fraction of 0.06, mean Nusselt number of ET, RS and RR arrays is increased by 161%, 5% and 32% respectively. While, with an increase in nanoparticle volume fraction from 0 to 0.06 at Ri=2, mean Nusselt number of ET, RS and RR arrays is augmented by 17%, 6% and 9% respectively. Finally, the efficient array configuration in terms of fluid-thermal behavior is proposed to design various heat exchange systems under differing operating conditions.

A Sub-6 GHz MIMO Antenna Array for 5G Wireless Terminals

This paper presents a novel antenna with its array and MIMO configuration for the 5G sub-6 GHz applications. The proposed antenna element operates at the central frequency of 5.57 GHz dedicated for Sub-6 GHz 5G communication applications. The antenna element holds a circular-shaped radiating portion with an inner-circular slot, plus a rectangular slot at its right edge to make the proposed design resonate at the desired frequency band. The RT5880 substrate is used with a thickness of 0.787 mm, and the low-loss tangent of 0.0009. To achieve a desired gain of 12 dB, a four-element array configuration is adopted, which improved a bore side gain to 12.4 dB from 6.66 dB. Then, the two-port configuration is adopted such that the isolation achieved between them is more than −30 dB. The total efficiency of the proposed antenna array is observed to be more than 80% within the operating bandwidth. Moreover, the Specific Absorption Rate (SAR) analysis is also presented for the proposed MIMO configuration, obeying the standard value (i.e., <2 W/kg for any 10 g of tissue). The measured results are in good agreement with the simulated results. All the simulations of the proposed design are performed in the CST MWS software.

Flow-Induced Vibrations of a Rotated Square Tube Array Subjected to Single-Phase Cross-Flow

This paper investigates the flow-induced vibration (FIV) and possibility of fluidelastic instability occurrence in a rotated square geometry tube array through a series of experimental tests. All experiments presented here were conducted in water cross-flow. The array pitch spacing ratio of approximately P/D=1.64 is somewhat larger than that commonly found in typical steam generators. The stability of a single flexible tube as well as multiple flexible tubes were investigated. The tubes were free to vibrate purely in the streamwise direction or the transverse direction relative to the upstream flow. A single flexible tube, in the otherwise rigid tube array, was found to undergo large amplitude vibrations (up to 40 % D) in the transverse direction. Tube vibration frequency analysis indicated the presence of two frequency components related to vorticity shedding in the array. This potential vorticity-induced-vibrations (VIV) and potential coupling between VIV and FEI are discussed in the paper. Test results for streamwise flow-induced vibrations are also presented. Results in water flow show a possible effect related to flow periodicity at low velocity. At significantly high flow velocities, the tubes are found to fully restabilize. This restabilization after VIV locking has not been previously reported as an unlocking result. The present results suggest that the flow-induced vibration of tubes in a rotated square array configuration is significantly more complex than in other geometries, particularly for the streamwise vibration case.

A Novel Sparse Array Configuration with Low Coarray Redundancy for DOA Estimation in Mobile Wireless Sensor Network

For tacking and localizing sources in the mobile wireless sensor network, underdetermined direction of arrival (DOA) estimation with high-accuracy is a crucial issue. In this paper, a novel sparse array configuration is developed for accurate DOA estimation from the perspective of sum-difference coarray (SDCA). As compared with most of the existing sparse array configurations, the proposed array can effectively reduce the overlap between difference coarray (DCA) and sum coarray (SCA) and can achieve more consecutive degrees of freedom (DOF), more sources can be resolved accordingly. Additionally, the proposed array has hole-free DCA and SDCA. Then, the concept of coarray redundancy ratio (CRR) is introduced for evaluating the coarray overlap quantitatively and the closed-form CRR expressions of the proposed array are derived in detail. Based on the good properties of the proposed array, vectorized conjugate augmented MUSIC (VCAM) is adopted for underdetermined DOA estimation. The theoretical propositions and numerical simulations demonstrate the superior performance of the proposed array in terms of CRR, consecutive DOF, and DOA estimation accuracy.

An Electromagnetic Time-Reversal Imaging Algorithm for Moisture Detection in Polymer Foam in an Industrial Microwave Drying System

Microwave tomography (MWT) based control is a novel idea in industrial heating systems for drying polymer foam. In this work, an X-band MWT module is designed and developed using a fixed antenna array configuration and integrated with the HEPHAISTOS industrial heating system. A decomposition of the time-reversal operator (DORT) algorithm with a proper Green’s function of multilayered media is utilized to localize the moisture location. The derived Green’s function can be applied to the media with low or high contrast layers. It is shown that the time-reversal imaging (TRI) with the proposed Green’s function can be applied to the multilayered media with a moderately rough surface. Moreover, a single frequency TRI is proposed to decrease the measurement time. Numerical results for different moisture scenarios are presented to demonstrate the efficacy of the proposed method. The developed method is then tested on the experimental data for different moisture scenarios from our developed MWT experimental prototype. Image reconstruction results show promising capabilities of the TRI algorithm in estimating the moisture location in the polymer foam.