Energy Harvesting——Technical Analysis of Evolution,Control Strategies,and Future Aspects

This paper provides a technical analysis of energy harvesting (EH) in the field of power and energy sector, including different aspects of harvesting energy, individual case history, control strategies of harvesting in the field of power and energy sector together with the current trend and future aspects of it. EH is comparatively a new concept which is growing very fast since the 20th century and catching new generation research approaches. This paper not only describes the past and current scenarios of harvesting energy with radio frequency (RF) and renewables but also gives author’s own anticipation of the upcoming future trends of it by comparing the case histories.

Field test of multi-hop image sensing network prototype on a city-wide scale

Wireless multimedia sensor networks drastically stretch the horizon of traditional monitoring and surveillance systems. Most existing research has utilized Zigbee or WiFi as the communication technology. Both technologies use ultra-high frequencies (primarily 2.4 GHz) and suffer from a relatively short transmission range (i.e., 100 m line-of-sight). The objective of this study is to assess the feasibility and potential of transmitting image information using RF modules with lower frequencies (e.g., 433 MHz) to achieve a larger-scale deployment as in a city scenario. The Arduino platform is used because of its low cost and simplicity. Details of hardware properties are provided in this article, and we investigate optimum configurations for the system. After achieving an initial range test transmission distance of more than 2000 m line-of-sight, the prototype network is installed in a real life city plot for further examination of performance. A range of suitable applications is proposed and suggestions for future research are provided.

Self-Powered Absorptive Reconfigurable Intelligent Surfaces for Securing Satellite-Terrestrial Integrated Networks

Satellite communications have attracted significant interests due to its advantages of large footprint and massive access.However,the commonly used onboard beamforming is hard to achieve reliable security because of the highly correlated legitimate and wiretap downlink channels.We exploit the benefits of satellite-terrestrial integrated network(STIN)and a novel absorptive reconfigurable intelligent surface(RIS)for improving the security of satellite downlink communications(SDC)in the presence of eavesdroppers(Eves).This paper aims to maximize the achievable secrecy rate of the earth station(ES)while satisfying the signal reception constraints,harvested power threshold at the RIS,and total transmit power budget.To solve this nonconvex problem,we propose a penalty-function based dual decomposition scheme,which firstly transforms the original problem into a two-layer optimization problem.Then,the outer layer and inner problems are solved by utilizing the successive convex approximation,Lagrange-dual and Rayleigh quotient methods to obtain the beamforming weight vectors and the reflective coefficient matrix.Finally,simulation results verify the effectiveness of the proposed scheme for enhancing the SDC security.

Enhanced thermal conductivity of epoxy composites with core-shell SiC@SiO_(2) nanowires

Electronic packaging materials and thermal interface materials(TIMs)are widely used in thermal management.In this study,the epoxy composites with core-shell structure SiC@SiO_(2) nanowires(SiC@SiO_(2) NWs)as fillers could effectively enhance the thermal conductivity of epoxy composites.The unique structure of fillers results in a high thermal conductivity of epoxy composites,which is attributed to good interfacial compatibility epoxy matrix and bridging connections of SiC@SiO_(2) NWs.From neat epoxy to 2.5 wt%loading of SiC@SiO_(2) NWs,the thermal conductivity is significantly increased from 0.218 to 0.391 W m^(−1) K^(−1),increased by 79.4%.In addition,the composite with 2.5 wt%filler possess lower coefficient of thermal expansion and better thermal stability than that of neat epoxy.All these outstanding properties imply that epoxy/SiC@SiO_(2) NWs composites could be the ideal candidate for TIM.

Generic functional modelling of multi-pulse auto-transformer rectifier units for more-electric aircraft applications

The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.

Fault Detection for PMSM Motor Drive Systems by Monitoring Inverter Input Currents

This paper has proposed a fault detecting method for DC supplied permanent magnet synchronize motor(PMSM)drive systems by monitoring the drive DC input current.This method is based on the fault signal propagation from the torque disturbance on the motor shaft to the inverter input currents.The accuracy of this fault signal propagation is verified by the Matlab simulation and experiment tests with the emulated faulty conditions.The feasible of this approach is shown by the experimental test conducted by the Spectra test rig with the real gearbox fault.This detection scheme is also suitable for monitoring other drive components such as the power converter or the motor itself using only one set of current transducers mounted at the DC input side.

PI controller relay auto-tuning using delay and phase margin in PMSM drives

This paper presents an auto-tuning method for a proportion plus integral（PI） controller for permanent magnet synchronous motor（PMSM） drives, which is supposed to be embedded in electro-mechanical actuator（EMA） control module in aircraft. The method, based on a relay feedback with variable delay time, explores different critical points of the system frequency response.The Nyquist points of the plant can then be derived from the delay time and filter time constant.The coefficients of the PI controller can then be obtained by calculation while shifting the Nyquist point to a specific position to obtain the required phase margin. The major advantage of the autotuning method is that it can provide a series of tuning results for different system bandwidths and damping ratios, corresponding to the specification for delay time and phase margin. Simulation and experimental results for the PMSM controller verify the performance of both the current loop and the speed loop auto-tuning.

Comparison between Pt/TiO_2/Pt and Pt/TaO_X/TaO_Y/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices.In this article,the performances of T1O_2 and TaO_2nonvolatile memristive devices were compared and the factors that make TaO_2 memristive devices better than T1O_2 memristive devices were studied.TaO_2 memristive devices have shown better endurance performances（10~8times more switching cycles） and faster switching speed（5 times） than TiO_2 memristive devices.Electroforming of TaO_2 memristive devices requires ~ 4.5 times less energy than TiO_2 memristive devices of a similar size.The retention period of TaO_2 memristive devices is expected to exceed 10 years with sufficient experimental evidence.In addition to comparing device performances,this article also explains the differences in physical device structure,switching mechanism,and resistance switching performances of TiO_2 and TaO_2 memristive devices.This article summarizes the reasons that give TaO_2 memristive devices the advantage over TiO_2 memristive devices,in terms of electroformation,switching speed,and endurance.

A gate driver for parallel connected MOSFETs with crosstalk suppression

New semiconductor materials offer several advantages for modern power systems,including low switching and conduction losses,excellent thermal conduction of a die,and high operation temperature.Avionics is one of the main beneficiaries of the progress in power devices,as it enables more compact and lighter converters for future More Electrical Aircraft.However,these advancements also come with new challenges that must be addressed to avoid potentially dangerous situations and fully utilize the capabilities of fast SiC MOSFETs.One such challenge is the high drain voltage rate during the switching process,which leads to a significant injection of current into the gate circuit(crosstalk effect).This increased current injection increases the risk of shoot-through conduction and thermal runaway.Although preventive measures are well-known,they offer limited protection in the case of parallel MOSFET connections.Therefore,this paper considers crosstalk features for parallel MOSFET connections,such as parasitic inductance of gate driver trace and gate voltage distribution.A special model is proposed to predict the magnitude of induced gate voltage under different conditions considering the nonlinear behavior of the MOSFET reverse capacitance.A new clamp circuit with an individual low-inductance path for each parallel switch is also proposed to suppress the consequences of crosstalk.The modified circuit operates independently from the main gate driver circuit;therefore,it does not change the switching time and electromagnetic interference pattern of the inverter.The efficiency of the new gate driver is confirmed through simulation and experimental results.

Flexible ultra-thin super-resolution endoscopy

In recent years, multimode fiber(MMF) has become an important tool for high-resolution endoscopic imaging in narrow channels(e.g., in the brain via needles or inside blood vessels) due to its high mode density and fine diameter, typically <0.125 mm [1-6]. However, a major obstacle to widespread deployment in applications is that realistic perturbations, including bending, twisting and changes in temperature, cause unacceptable image degradation.