High-speed Characteristics Research Articles

Avalanche Photodiodes With Composite Charge-Layers for Low Dark Current, High-Speed, and High-Power Performance

In this work, a novel In_0.52Al_0.48As based top-illuminated avalanche photodiode (APD) is demonstrated. By combining the composite charge-layer design with a special p-side up etched mesa structure to zero the electric (E)-field at the periphery of this APD's multiplication (M-) layer, the edge breakdown phenomenon can be eliminated. This in turn leads to the simultaneous high-speed, high-saturation-power, high responsivity, and low-dark current performance characteristics of our APDs, which are essential for high-performance coherent receiver applications. The demonstrated device, with its simple top-illuminated structure exhibits a wide optical-to-electrical (O-E) bandwidth (21 GHz), high responsivity (5.5 A/W at 0.9 V_br), and saturation current as high as 8 mA with a large active diameter of 24 μm for easy optical alignment. Furthermore, the nonlinear driving of a wavelength sweeping laser in the self-heterodyne beating setup can generate an optical pulse train like waveform, providing an effective optical modulation depth of up to 158%, which leads to a maximum photo-generated RF power (at 10 GHz) from our APD as high as +5.5 dBm. The excellent performance of our demonstrated APDs opens up new possibilities for the next generation of coherent receivers.

Towards traffic supervision in 6G: a graph neural network-based encrypted malicious traffic detection method

As an important direction for the evolution of next-generation wireless communication technology, 6G will comprehensively promote the wave of economic and social digitization. Services carried by 6G network will rely heavily on the sharing and processing of massive amounts of data between entities, data security is therefore of great importance. Currently, most network applications utilize SSL/TLS protocols to ensure the confidentiality and security of network communications, while encryption mechanism also brings huge challenges to network security supervision. Though encrypted malicious traffic detection in traditional networks has become a research hotspot, existing technologies cannot be directly applied in 6G networks. In a 6G network with massive, instant and unlimited communications between heterogeneous terminals, network communication behavior patterns are much more diversified, which makes the boundary between normal traffic and malicious traffic more blurred in 6G networks than in traditional networks. Existing studies either analyze encrypted traffic in isolation or aggregation, while they all ignore the rich correlations among encrypted traffic. To this end, we propose an encrypted malicious traffic detection framework based on the graph neural network towards the network security problem of future 6G networks, ET-RSGAT. First, considering the characteristics of super high speed and super large connection of 6G network, we design a simple feature extraction method of encrypted traffic: extracting the TLS handshake raw bytes and TLS record length sequence for one single encrypted session. Second, in view of the correlations of large numbers of heterogeneous terminals and the coexistence of multi-source heterogeneous data communication in 6G networks, we analyze the correlations between encrypted sessions from 2 aspects, which are service correlations and communication behavior correlations. Then we construct an encrypted traffic graph, named ETG. On the basis of ETG, we introduce a graph attention network to utilize the correlations between encrypted sessions to enrich the feature representation of nodes. With rich representation, we build the detection model based on a multi-layer perceptron to identify threats. Considering that the simulation environment of 6G networks is immature, we deploy a variety of heterogeneous terminal nodes and run various network services to simulate the 6G communication scenario, and design related experiments for the interconnection of many heterogeneous terminals in 6G networks. The evaluation and experimental results show that our method can obtain satisfactory detection results in both traditional network and simulated environment datasets.

Modelling and Analysis of High-Speed Angular Contact Ball Bearing

Angular contact bearings are of primal importance in accommodating rotational mechanisms with high-speed characteristics. Their applications are centric to heavy axial and radial loads sustaining thrust loads to a single direction. In high-speed applications, factors such as centrifugal force, gyroscopic moments and relative displacements in various geometric features of the bearings are to be taken into consideration. This study focuses on establishing the contact angles, contact forces and spin speed for angular contact bearing to withstand varied rotational angular velocities. The forces experience a non-linear variation with respect to the body stiffness thus necessitating the involvement of numerical methods to converge at precise solutions through each juncture. The outer raceway of the bearing is accepted to be static with respect to the inner raceway as the input shaft for any application is predominantly affixed to the inner raceway of the angular contact bearing. Geometrical variations are determined under combined load conditions to simulate the natural working of the bearing at accelerated speeds. The analyses involve results for spatial parameters which are iteratively solved for each of the rolling elements in the bearing taken into concern. The spin speeds of the rolling elements are shown to dampen and exponentially increase with respect to their angular positions. The outputs manifested through this work can be utilized to accurately predict shift of salient design attributes of an angular contact bearings through low and high-speed applications.

Integration of Big Data with International Graduate Ideological and Political Education

Nowadays, colleges and universities have a large amount of information about political thought and education in addition to complex student data. Like big data, it has the characteristics of large capacity, high speed, and diversity. The ideological and political education in colleges and universities urgently needs scientific decision-making and the ability to predict possible problems ahead of time. It also perfectly matches the technical advantages of big data technology that can efficiently process data, analyze and extract information, as well as propose solutions. The traditional higher education model can no longer meet the needs of current international higher education. Under the new background, universities must explore a new model of postgraduate international education, which is practical, multi-channel, and comprehensive, on a deeper level. According to data on graduate students’ interest, psychology, and behavior, higher education teachers can purposefully innovate the methods and approaches to higher education. The integration of international graduate education with big data has been examined in this research, and a series of cultural exchanges has been carried out for foreign students at Central South University. This kind of introduction seems to have effectively boosted the attractiveness of ideological and political education, improved the research level of international graduate students, and deepened the role of campus cultural activities in educating people on a deeper level.

Impact of Thermal Boundary Resistance on Thermoelectric Effects of the Blade-Type Phase-Change Random Access Memory Device

Phase-change random access memory (PCRAM) is widely regarded as one of the most promising candidates to replace Flash memory as the next generation of non-volatile memories due to its high-speed and low-power consumption characteristics. Recent advent of the blade-type PCRAM with low programming current merit further confirms its prospects. The thermoelectric effects existing inside the PCRAM devices have always been an important factor that determines the phase-transformation kinetics due to a fact that it allows PCRAM to have electric polarity dependent characteristics. However, the potential physics governing the thermoelectric effects for blade-type PCRAM device still remains vague. We establish a three-dimensional (3D) electro-thermal and phase-transformation model to study the influences of thermal boundary resistance (TBR) and device scaling on the thermoelectric effects of the blade-type PCRAM during its “RESET” operation. Our research shows that the presence of TBR significantly improves the electric polarity-dependent characteristics of the blade-type PCRAM, and such polarity-dependent characteristic is found immune to the scaling of the device. It is therefore possible to optimize the thermoelectric effects of the blade-type PCRAM through appropriately tailoring the TBR parameters, thus further lowering resulting power consumption.

Multiphase Parallel Demodulation for Remote Sensing Satellite Data Transmission—Filter Bank Based on WOLA Structure

With the rapid increase of data generated by remote sensing satellites, the demand of real-time demodulation of ultra-high-speed remote sensing data by digital receivers has become a research hotspot and difficulty. Aiming at the international research gap of parallel demodulation of remote sensing satellite data using multi-channel channelization technology, a parallel matched filtering architecture of filter banks based on Weighted OverLap-Add (WOLA) structure is designed. This structure has the following advantages: (a) The decimation factor is flexible and adjustable when the signal is channelized, which is not restricted by the number of channels. (b) The signal is divided into several sub-bands according to the frequency spectrum, which is beneficial to the parallel analysis and processing of the signal. This paper completes the parallel matched filtering processing and provides ideas for the subsequent processing operation. (c) The structural channelization decomposition has strong expandability and can be flexibly applied to signal transmission of different systems. Aiming at the characteristics of high speed and wide bandwidth of remote sensing data transmission, this paper designs the channelization method of filter bank based on WOLA structure, and deduces and realizes the sub-band matching filtering operation. Taking QPSK modulation as an example, the simulation results show that parallel matched filtering has almost no loss in bit error performance. The research results of this paper have great reference value for designing multiphase parallel receivers of high-speed remote sensing data in the future.

Motion State Recognition and Trajectory Prediction of Hypersonic Glide Vehicle Based on Deep Learning

Hypersonic glide vehicle (HGV) has brought severe challenges to the existing defense system due to its characteristics of high maneuverability, high speed and high precision. Simultaneously, these characteristics also bring great difficulties to trajectory prediction. In this paper, a method for HGV motion state recognition and trajectory prediction based on deep learning is proposed. The proposed method consists of two modules, namely the motion state recognition module and the trajectory prediction module. The motion state recognition module can identify the HGV’s motion state according to state information, and divide it into eight categories. The softmax function is added to the state recognition module to calculate the probability of each motion state. The trajectory prediction module comprises a nonlinear prediction part and a linear prediction part. According to the result of motion state recognition, the appropriate prediction scheme is adopted to better extract the linear and nonlinear characteristics of HGV trajectory, which improves the robustness and prediction accuracy of the proposed method. The experimental results of HGV trajectory prediction show that the proposed method can maintain good stability when the HGV maneuver state changes, and has higher accuracy than the four benchmark methods.

High-speed, large-area and high-precision fabrication of aspheric micro-lens array based on 12-bit direct laser writing lithography

Aspheric micro-lens array (AMLA), featured with low dispersion and diffraction-limited imaging quality, plays an important role in advanced optical imaging. Ideally, the fabrication of commercially applicable AMLAs should feature low cost, high precision, large area and high speed. However, these criteria have been achieved only partially with conventional fabrication process. Herein, we demonstrate the fabrication and characterization of AMLAs based on 12-bit direct laser writing lithography, which exhibits a high fabrication speed, large area, perfect lens shape control via a three-dimensional optical proximity correction and average surface roughness lower than 6 nm. In particular, the AMLAs can be flexibly designed with customized filling factor and arbitrary off-axis operation for each single micro-lens, and the proposed pattern transfer approach with polydimethylsiloxane (PDMS) suggests a low-cost way for mass manufacturing. An auto-stereoscopic-display flexible thin film with excellent display effect has been prepared by using above technology, which exhibits a new way to provide flexible auto-stereoscopic-display at low cost. In brief, the demonstrated fabrication of AMLAs based on direct laser writing lithography reduce the complexity of AMLA fabrication while significantly increasing their performance, suggesting a new route for high-quality three-dimentional optical manufacturing towards simplified fabrication process, high precision and large scale.

JBNN: A Hardware Design for Binarized Neural Networks using Single-Flux-Quantum Circuits

As a high-performance application of low-temperature superconductivity, superconducting single-flux-quantum (SFQ) circuits have high speed and low-power consumption characteristics, which have recently received extensive attention, especially in the field of neural network inference accelerations. Despite these promising advantages, they are still limited by storage capacity and manufacture reliability, making them unfriendly for feedback loops and very large-scale circuits. The Binarized Neural Network (BNN), with minimal memory requirements and no reliance on multiplication, is undoubtedly an attractive candidate for implementing inference hardware using SFQ circuits. This work presents the first SFQ-based Binarized Neural Network inference accelerator, namely JBNN, with a new representation to binarize weights and activation variables. Every SFQ gate is essentially a pipeline stage, making conventional design methods of the accumulator unsuitable for SFQ circuits. So an SFQ-based accumulative parallel counter using SFQ logic cells including T1, OR, and AND is designed to realize the accumulation, where the data size is reduced to a quarter after passing the XNOR column and the AU layer, largely declining the hardware cost. Our evaluation shows that the proposed design outperforms a cryogenic CMOS-based BNN accelerator design running at 77K by 70.92 times while maintaining 97.89% accuracy on the MNIST benchmark dataset. Without the cooling cost, the power efficiency increases up to 929.18 times.

Forward Flight Performance Analysis of Supercritical Airfoil in Helicopter Main Rotor

In this research, the aerodynamic performance and flow characteristics of NASA SC (2)-0714 airfoil and HH02 airfoil in the helicopter main rotor are evidently analyzed. The supercritical airfoil is used in the aircraft for attaining better transonic and high-speed flow characteristics. Moreover, a specialized helicopter airfoil called HH02 is used in the Apache helicopter rotor for increasing the operational speed. As most of the high-speed helicopters are using four-bladed main rotor configuration, it is analyzed with prior attention. The lift and thrust act in different directions for the forward phase of the flight whereas the lift and thrust act in the same direction for the other phases of flight, which is analyzed in this work. The computational analysis is done by using ANSYS Fluent whereas the rotational analysis is done by using the Multiple Reference Frame (MRF) method. An analysis is carried out for different RPM of 400,600 and 800 with the combination of 0.3, 0.4 and 0.5 Mach numbers with the assistance of grid independence test. The result shows that the NASA SC (2)-0714 rotor increases the thrust of the rotor around 5% to 10% under various rotor and forward speeds. Thus, the results proves that the supercritical airfoil is highly capable of producing higher thrust and good aerodynamic characteristics.

Study on thermal contact resistance of low melting alloy used as thermal interface material

The development of reliable electronic equipment is a big challenge due to miniaturization and performance characteristics of high speed and high power electronic devices. Thermal control is one of the key roles to meet the above challenge. Thermal Interface Material (TIM) plays a significant role in thermal control. TIM has been extensively used in diverse electronic devices for next generation electronics. To improve or enhance heat transfer performance at the interface region between copper substrates, Low Melting Alloy (LMA) Bi-Sn-Pb is usually used as TIM. In the present work, Thermal contact resistance (TCR) and Temperature variation by TIM is experimentally investigated. In the study, Bi39.4Sn30.8Pb29.8 is used as TIM material. The variation of TCR subjected to heat flow, variation of temperature between the interface and specimen thickness is reported and discussed.

Research on high-speed synchronous motor direct torque control

High-speed motor is increasingly used in ultra-high precision machining and high-performance machinery. It is necessary to achieve closed-loop control of high-speed motor in order to realize high-performance motor control. The high-frequency and high-speed characteristics of high-speed motor have brought great difficulties for its realization of closed-loop control. The performance of the hexagonal flux direct torque control (DTC) method that can reduce the switching frequency of power devices is researched for high-speed synchronous motor in this paper. After adopting this control method, the harmonics in the motor current and torque can be suppressed by adopting an appropriate filtering method. The same effect as the conventional DTC can still be achieved. It provides a basis for the application realization of the high-speed synchronous motor control system.

Experimental research on influence of wave environment on high-speed water entry load and trajectory characteristics

Wave environment is a common fact happened when objects enter water under real conditions, which changes the morphology of the free interface when entering water. However, the influence of wave environment on the flow when entering water and on the evolution of object motion parameters after entering water is not clear. In this research, a rocking plate wave maker is used to generate a wave environment in the test pool, and a truncated cone rotating body equipped with an internal test system is used as the test model. The compressed air cannon is used to provide launch power, and the launch control system uniformly controls the start timing process of the wave maker and the launcher. The wave maker and the launcher will control the relative position of the object's entry point and the wave surface in collaboration. Various condition tests were carried out, including enter in static water, different wave surface positions and different wave heights. Quantitative trajectory parameters including the acceleration, and attitude angle of the model in the water-entry process were obtained, and the evolution of the flow field was photographed. The experimental results show that under high-speed conditions, the influence of waves on the water-entry process is mainly reflected in the change of the water entry angle relative to the water surface at the water-entry moment. The wave surface encountering negative inclination can effectively reduce the impact load of water entry, but it is more likely to induce the extreme situation such as "jumping".

Investigation of the characteristics of a marine diesel engine when running on fuel with a water additive

Currently, environmental specifications of marine diesel engines become more stringent. There are two well-known and popular ways to improve engine environmental performance: the internal method is based on operation process improvement, as well as on the use of various fuel additives or air supply to the diesel cylinder. Another method is external (gas purification using catalysts and filters). The article considers one of these possible ways of reducing nitrogen oxides in marine diesel engines by using a water agent in fuel with various water phase dispersion degrees. The high-speed characteristics of the ship engine operation under various modes using “L” brand diesel fuel and emulsions are given. Studies have shown that when converting diesel from pure fuel to a microheterogenous emulsion (water inclusions’ diameter 5-10 microns), the concentration of NOx decreased by 1.4 times, fuel consumption increased by (4-5) g/(kWh), with an increase in the maximum combustion pressure by 0.7 MPa. The tests have confirmed the effectiveness of using a microheterogenous emulsion to reduce nitrogen oxide emissions.

Injection-production optimization of fault-karst reservoir\u2014considering high-speed non-Darcy effect

Fault-karst reservoirs are featured by complex geological characteristics, and accurate and fast simulation of such kind of reservoirs using traditional simulator and simulation methods is pretty hard. Herein, we tried to discrete the complex fault-karst structures into one-dimensional connected units connecting the well, fracture and cave based on reservoir static physical parameters and injection-production dynamics. Two characteristic parameters, conductivity and connected volume, are proposed to characterize the inter-well connectivity and material basis. Meanwhile, the high-speed non-Darcy seepage term is introduced into the material balance equations for well-fracture-cave connected units to describe the actual seepage characteristics within the fault-karst reservoirs, and to better simulate the oil/water production dynamics. Based on this method, a fracture reservoir model of 1 injection-3 production was established. The change of oil–water action law in different injection and extraction systems under two production regimes of fixed production rate and fixed pressure is analyzed. A case study was conducted on S fault zone, where the flow of oil and gas did not follow the Darcy seepage rule and with a β value of 103–104, the single well flow pressure and oil production were perfectly matched with the real data. In addition, connected units with more prominent high-speed non-Darcy features were found to have better connectivity, which might shed light on the more accurate prediction of inter-well connectivity. Moreover, an improved injection-production well pattern and was proposed based on connectivity prediction model and reservoir engineering method to solve the problems of insufficient natural energy supply and overhigh oil production rate in Block S. Furthermore, the injection/production rate as well as the timing and cycle of water injection was predicted and optimized so as to better guide to site operations.

An Ultra-High-Speed Maglev Test Rig Designed for HTS Pinning Levitation and Electrodynamic Levitation

The interaction between the superconductor and the permanent magnet guideway (PMG) is very important in the system of high temperature superconducting (HTS) maglev. At present, HTS maglev has entered the key stage of engineering application. In order to study its dynamic characteristics and stability under higher speed conditions, an ultra-high-speed maglev test rig is developed to undertake this research task. The test rig is mainly composed of an inverter fed AC motor, the transmission mechanism, a brake, a guideway rotor, the control system, the HTS maglev measurement system and the permanent magnet electrodynamics levitation (EDL) measurement system. In the test rig, the circular guideways are rotated vertically, and the Halbach-array PMG and aluminum guideway are fixed inside the stainless-steel rotor to solve the centrifugal effect of high-speed rotation. In order to ensure that the test rig can run stably at the speed of 600 km/h, the design is strictly in accordance with the standard of 700 km/h during the development process. This paper verified the reliability of the important component through modeling and simulation of the guideway rotor. The ultra-high-speed maglev test rig has abundant functions, which can be used to study the high-speed dynamic characteristics and stability of HTS maglev and permanent magnet EDL, which has great practical significance to promote the research and development of maglev technology.

Flight Dynamics Modeling, Trim, Stability, and Controllability of Coaxial Compound Helicopters

Coaxial compound helicopters feature high-speed characteristics that are not possessed by conventional helicopters. The aim of this paper is to develop a flight dynamics model of coaxial compound helicopters and investigate the trim, stability, and controllability. A flight dynamics model including a coaxial rotor model and a propeller model is introduced. Based on the flight dynamics model, the trim of hover and level flights of a coaxial compound helicopter is performed. Considering the influence of flapping motions, stability and control derivatives are assessed under the small disturbance hypothesis by using a numerical differentiation method. Then, stability and response of the coaxial compound helicopter are presented. The results of trim show good agreement with those of the reference, which verifies the flight dynamics model. The speed static stability derivative is stable in whole trim range, while the angle of attack static stability derivative is unstable. The yawing control with collective differential of the coaxial compound helicopter will induce serious roll effect in high-speed flights.

Variable Coefficient Terminal-Phase Guidance Design for Deep Space High-Speed Impact

Asteroid impact poses a major threat to human survival. High-speed direct impact is a feasible and effective means to change the orbit of an asteroid. This paper takes Bennu, a potentially hazardous asteroid , as object to design the terminal guidance law of deep space high-speed impact. In view of the characteristics of high relative speed and high impact accuracy, the acceleration command is derived based on the Augmented Proportional Navigation Guidance law (APNG), considering the acceleration of the target. Moreover, the proportional coefficient is designed as a function of the relative distance to meet both the requirements of reducing fuel consumption and improving impact accuracy. An ignition strategy is designed to convert the continuous command into impulse command, without the need to give maneuvering time in advance. The simulation results show the effectiveness of the proposed algorithm. The miss distance constraint is satisfied, and the ignition times and fuel consumption are less than those of the constant proportional coefficient algorithm.

Heterogeneously integrated, superconducting silicon-photonic platform for measurement-device-independent quantum key distribution

Integrated photonics provides a route to both miniaturization of quantum key distribution (QKD) devices and enhancing their performance. A key element for achieving discrete-variable QKD is a single-photon detector. It is highly desirable to integrate detectors onto a photonic chip to enable the realization of practical and scalable quantum networks. We realize a heterogeneously integrated, superconducting silicon-photonic chip. Harnessing the unique high-speed feature of our optical waveguide-integrated superconducting detector, we perform the first optimal Bell-state measurement (BSM) of time-bin encoded qubits generated from two independent lasers. The optimal BSM enables an increased key rate of measurement-device-independent QKD (MDI-QKD), which is immune to all attacks against the detection system and hence provides the basis for a QKD network with untrusted relays. Together with the time-multiplexed technique, we have enhanced the sifted key rate by almost one order of magnitude. With a 125-MHz clock rate, we obtain a secure key rate of 6.166 kbps over 24.0 dB loss, which is comparable to the state-of-the-art MDI-QKD experimental results with a GHz clock rate. Combined with integrated QKD transmitters, a scalable, chip-based, and cost-effective QKD network should become realizable in the near future.

Attacks and Solutions for a Two-Factor Authentication Protocol for Wireless Body Area Networks

As an extension of the 4G system, 5G is a new generation of broadband mobile communication with high speed, low latency, and large connection characteristics. It solves the problem of human-to-thing and thing-to-thing communication to meet the needs of intelligent medical devices, automotive networking, smart homes, industrial control, environmental monitoring, and other IoT application needs. This has resulted in new research topics related to wireless body area networks. However, such networks are still subject to significant security and privacy threats. Recently, Fotouhi et al. proposed a lightweight and secure two-factor authentication protocol for wireless body area networks in medical IoT. However, in this study, we demonstrate that their proposed protocol is still vulnerable to sensor-capture attacks and the lack of authentication between users and mobile devices. In addition, we propose a new protocol to overcome the limitations mentioned above. A detailed comparison shows that our proposed protocol is better than the previous protocols in terms of security and performance.