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With the development of the wireless network techniques, the number of cyber-attack increases significantly, which has seriously threat the security of Wireless Local Area Network (WLAN). The traditional intrusion detection technology is a prevalent area of study for numerous years, but it may not have a good detection performance in a real-time way. Therefore, it is urgent to design a detection mechanism to detect the attacks timely. In this paper, we exploit a CDBN (Conditional Deep Belief Network)-based intrusion detection mechanism to recognize the attack features and perform the wireless network intrusion detection in real time. To avoid the impact of the imbalanced dataset and the data redundancy on the detection accuracy, a window-based instance selection algorithm “SamSelect” is adopted to undersample the majority class data samples, and a Stacked Contractive Auto-Encoder (SCAE) algorithm is proposed to reduce the dimension of the data samples. By doing so, our proposed mechanism can effectively detect the potential attack and achieve high accuracy. The experiment results show that CDBN can be effectively combined with “SamSelect” and SCAE, and the proposed mechanism has a high detection speed and accuracy, with the average detection time 1.14 ms and the detection accuracy 0.974.

Considering Chinese listed companies’ repurchases in manufacturing industry from 2005 to 2018 as a sample, this paper uses the mediation effect model to empirically study the relationship between share buybacks and sustainable financial growth. The conclusions of the study are as follows. (1) Regarding the Chinese capital market, share repurchase can in general promote corporate sustainable development. (2) Capital structures plays a partial mediating role between share repurchases and sustainable financial growth. This study expands the research scope of the economic consequences of share repurchases and has certain implications for the implementation of repurchase decisions by firms.

In this paper, we propose a new shared control method based on Petri net for the cooperative control of human intelligence and machine intelligence. Our method divides the brain-computer interface (BCI) system into different functional modules, adds control places to ordinary Petri nets to describe the results of each function, and simplifies the modeling process of Petri nets through the composition of nets. We first establish a Petri net model that contains EEG information, robot state information, and surrounding environment information. This model can be used to visually analyze the state and rules of the entire system. Then the Petri net-based brain-computer interface system is designed, and the simulation is carried out on the mobile robot simulation platform of MobileSim. The results show that the shared control method based on Petri net is reasonable and feasible. Modeling the BCI system through the Petri net method can better describe the state of the system, facilitate the analysis and improvement of the control rules of the system to improve the applicability of the BCI system.

Highly stretchable, bio-compatible interconnects are of particular interest for medical and military applications as Wearable Performance Monitors (WPMs) and sensors. Screen printed trace interconnects on highly compliant Thermoplastic Polyurethanes (TPU) provides a low cost, viable option. But these stretchability has high ramification on the reliability aspects of WPM construction. In this paper, we perform the reliability testing of two screen printed inks under repeated mechanical loads 'as-printed' and after exposure to temperature and humidity.

Nowadays, with the birth of 5G and the Internet of Things, more and more business signals have emerged. The identification of signal service types has become a hot research topic. Whether it is suitable for daily life in the military field, there is a wide application prospect. Using the power spectrum data of the wireless signal, the characteristics of the power spectrum waveform are captured to identify the type of traffic of the wireless signal. This paper proposes the use of convolutional neural networks to extract and classify the wireless signal power spectrum data. After hundreds of iterative training, it can achieve an ideal recognition effect.

We report a chirped pulse amplification laser designed to produce Joule-level pulses of picosecond duration at 1 kHz repetition rate. This laser is based on cryogenically-cooled Yb:YAG active mirror amplifiers. A technique for mapping the temperature distribution within the active mirrors in 3D is discussed.

The use of commercial electronics components with Tin-Silver-Copper solder bumps normally calls for relatively high cost substrates, posing a challenge for disposable (inexpensive) products. The present effort addresses the feasibility of reducing reflow temperatures through the use of a eutectic Tin-Bismuth solder paste for products that do not have to survive significant thermal cycling. A set of experiments was conducted to assess the effects of paste volume and reflow profiles on solder joint strength and low cycle fatigue resistance. Both strength and fatigue resistance tended to decrease with decreasing peak temperature and paste volume, but indications are that performances comparable to those of conventionally reflowed Tin-Silver-Copper solder joints can be achieved even with laser reflow and a peak temperature as low as 160C. This offers promise for the use of low cost substrates such as PET.

In an effort to replace Pb-based solders commonly used in high-temperature electronics (operating at 200°C or higher) with a new high-temperature capable material, we have developed a transient liquid phase (TLP) bonding between bismuth (Bi) and nickel (Ni) in our previous study. To address the reliability concerns and also to warrant the manufacturing efficiency of the TLP bonds, the current study was focused on the optimization of the interlayer structure and alloying via: i) thin bond-line-thickness (BLT) ( 60 um). These TLP bonded coupons were then tested for bonding reaction, microstructure development, and mechanical reliability. A thin BLT was made via sputter deposition of Bi on Ni-metallized die, which enabled a Ni layer (? 1 um) remaining during reflow without being completely consumed. The intermediate BLT sample was made using a Bi preform as in our previous study. For the thick BLT case, a powder/paste of Bi-xNi (from x=0 to 21.9 wt.%) was used. In particular, as pure Bi will not react with the Cu metallized surface (or Cu substrate), an interlayer consisting of Bi-Ni mixed powder/paste will enable Cu surface to be bondable with this TLP system. In this paper, the reflow conditions and the interlayer microstructures for the Bi-Ni TLP bonding with the three different approaches are discussed.

The development of reliable Flexible Hybrid Electronics (FHE) that are light, wearable and conforming to the human body while still preserving full operational integrity requires among other an understanding of the fatigue behavior of interconnects such as traces on flexible substrates (Polyimide, Polyethylene Terephthalate, etc.). There are different loading modes of potential concern, such as tension, bending and peeling. The present study addresses effects of tension on aerosol printed AgNP (silver nano-particles) traces. These traces are nano-porous and as such inherently brittle, but the presence of a flexible substrate has major effects on their behavior. Electroplated Cu traces are included for reference. Major increases in electrical resistance were observed for even minor deformation but inspection by SEM did not reveal any damage, and the presence of the substrate prevents the detection of changes in trace properties through direct measurement of deformation vs. the applied loads. Studies of the evolution of damage were therefore limited to characterization of the resistance vs. variations in strain. Interpretations of results were further complicated by the time-dependent viscoelastic deformation of the substrate. Nevertheless, systematic trends are appearing.

This paper introduces a low noise readout circuit for a novel rotational gyroscope. By phase sensitive detection technique, the proposed circuit is virtually immune of low frequency noise due to 1/f noise and specific interferences due to driving circuits. An amplititude stabilization technique is introduced to the excitation signal source. With this technique the noise contribution from the signal source is greatly reduced. The influence from matching of feedback capacitance is calculated and recommended matching level is given. The prototype circuit is fabricated and tested together with the rotational gyroscope. Rate table test results show that the minimum detectable input angular rate change is 0.05° /s, with a sensitivity up to 95mV/° /s and linearity better than 0.1%.

To take full advantage of silicon carbide (SiC) devices' superior electrical and thermal performance, advanced power module packaging designs and suitable materials are required. In this paper, the development of a new high power density module using the Power Overlay (POL) packaging platform is presented. The wirebond-less packaging platform has shown significantly reduced electrical parasitics, while providing a thin profile to allow double-side cooling and the integration of gate drive circuits. Various characterization tests were conducted on specimens fabricated and assembled by production equipment, including highly accelerated temperature and humidity stressing (HAST) and high temperature/current exposure. The results presented here were used to establish design guidelines for reliable operation of POL-based power modules.

Predominant high melting point solders for high temperature electronics contain lead (Pb), which will soon be banned by environmental regulations as in most of consumer electronics. In an effort to replace the Pb-based solders with a new high-temperature capable material, we developed a transient liquid phase (TLP) bonding of bismuth (Bi) and nickel (Ni). A molten Bi (m.p. of 271°C) strongly reacts with Ni to form a Bi3Ni or BiNi intermetallic layer, both of which can withstand over 400°C. To study microstructural developments and their influences on reliability performance, the die attached coupons were assembled using Bi-Ni TLP bonds. It was shown that Bi3Ni is the first phase to form, after which the diffusion of Bi controls the growth kinetics of this intermetallic phase with the activation energy of 65.5 kJ/mol for the temperature range from 160 to 240°C. The solid-state transformation of Bi3Ni to BiNi follows, which is a slower process and only occurs at a long-term aging (activation energy of 17.8 kJ/mol, for the temperature range from 260 to 300°C). When tested at high temperatures (up to 350°C) or exposed under long-term storage at 200°C over 1000 hours, such bonds showed no degradation in die shear strength. It indicates the potential of the Bi-Ni TLB bonds as a Pb-free alternative to replace high-Pb solders for high temperature electronics that operate at 200°C or higher.

Wide band gap (WBG) semiconductor devices have demonstrated superior electrical and thermal performance, compared to their silicon-based counterparts. However, innovative power module packaging design and materials suitable to WBG devices are required. In this paper, the development of a new high power density module using the Power Overlay (POL) packaging platform is presented. The wirebond-less packaging platform has shown significantly reduced electrical parasitics, while providing a thin profile to allow double-side cooling and the integration of gate drive circuits. Thermal cycling and high temperature storage tests were conducted on specimens fabricated and assembled by production equipment. The results presented here were used to establish design guidelines for reliable operation of POL-based power modules.

According to the variable conductivity of the graphene and the principle of surface acoustic wave, a new type of 30THz three billing graphene frequency selective switch is proposed in this paper. The selection switch has 3 selection paths. By controlling the conductivity of graphene, we can change the refractive index of the intermediate graphene lens, then change the direction of the plane wave and choose signal pathway flexibly. There is a good isolation between the output ports, the minimum value can reach -30dB. And the attenuation of signal input and output is about -10dB. On the whole, the selection switch has the characteristics of scalable, tunable, and high isolation, has a greater inspiration for graphene device design in the future.

A novel circular polarization rectenna with multi-orders harmonic suppression is proposed in this paper. The circular polarization is realized by corner perturbation on a rectangular radiation patch, and enhanced by a diagonal slim slot etched at the center of the patch. An open stub connects to the transmission line is used to suppress harmonics. The realized results show that the antenna obtained -18dB return loss at 2.4GHz, and -7dB, -20dB and -20dB suppression on second to fourth harmonic frequency bands respectively. With a voltage doubling rectifier circuit connecting to the output of the antenna, 75% of RF-to-DC conversion efficiency is achieved.

Our recent progress in the development of high energy, picosecond lasers with high average power will be presented, including the demonstration of a cryogenic Yb:YAG laser that produces 1 Joule, 5 picosecond pulses at 0.5 kHz repetition rate.

Present technologies and applications for multiple surfaces inspection of chips are based on a complicated architecture with multiple opto-mechanical devices to acquire the surface images of a chip separately. In practical, system reconfiguration and calibration of position and orientation for all opto-mechanical devices become more complicated and uneasy to be completed when the size or optical features of the inspected chips changed. Moreover, the system throughput will be substantially decreased because all inspected chips have to be moved in and out the image acquisition regions among all opto-mechanical devices of the inspection system. Here we proposed a new architecture with multiple pick and place (PP) heads to suck the inspected chips and move the chips for acquiring surface images of different chips at corresponding acquisition stations. The computation loading of defect inspection for each chip also can be distributed because of sequential image acquisition. Considering the computing loading of chip surface are different, image acquisition for the front and back sides of chips is arranged to be the first and second stations, and then 4 other edge sides of chips. The reconfiguration and calibration of position and orientation for each opto-mechanical devices become simpler and easier when the characteristics of inspected chips changed. Thus the system can accomplish the inspection for 6 surfaces of a chip and determine its quality in real-time before the inspected chip is put on the target wafer. Providing real-time inspection in high throughput during chip sorting process, enables the opto-mechanical devices of the system can be simply and easily adjusted and calibrated for different type chips are the major advantages and system progress, that makes the developed inspection system can meet the inspection requirements of different types of inspected chips. The inspection system is developed by two phases. Tasks of the first phase have been completed to build up the inspection system for 5 surfaces of the chip, i.e. back side, and 4 edge sides. The results of preliminary system integration and tests are presented in this work.

Predominant high melting point solders for high temperature electronics (operating temperatures over 200°C) are high Pb containing alloys. The new regulation will have banned the use of Pb in all electronics by 2019. We designed a "new" class of solder alloys with high bismuth (Bi) content (≥ 70 wt.%) to evaluate their potential as a high temperature Pb-free solder. Although having high melting point (271°C), pure Bi exhibits poor thermal conductivity, limited plasticity and wetting issues on common metallized surface such as Ni and Cu. In this work, alloying elements such as Sb and Cu were added to Bi in an attempt to negate such shortcomings by creating innovative alloy microstructures and optimum alloy compositions. As an extension to this work, a transient liquid phase (TLP) bonding between Bi and Ni was also investigated as Bi in a molten state reacts strongly with Ni to be converted into a Bi3Ni or BiNi intermetallic layer. Once formed, these phases can be stable until reaching ~ 470°C (with Bi3Ni), or ~ 617°C (with BiNi). We tested the reliability of the die attached coupons using Bi-Sb-Cu solders and Bi-Ni TLP bonds under high temperatures (up to 200°C for Bi solders and up to 350°C for TLP bonds), thermal shock (from -55 to 200°C), and high temperature storage (at 200°C). The resultant data indicate the potential of these two Bi systems as Pb-free alternatives for high temperature electronics.

BiAgX is one of the potential lead-free substitutes for lead-rich solders for high temperature interconnections, with a melting temperature above 533K after reflow. This study focuses on the mechanical properties of a particular BiAgX solder alloy. These properties are compared to a selected lead-rich solder for reference. The paste for this solder is in the form of mixed solder powder alloys and the reflow process is done in a vacuum oven to prevent oxidation and to minimize voids. The mechanical constitutive tests conducted in this study include: (i) monotonic elastic-plastic stress-strain response at constant strain rates and constant temperatures; and (ii) isothermal, viscoplastic creep strain response at several constant stress levels and different temperatures. The sensitivities of the material viscoplastic constitutive response to temperature and stress level were systematically studied, so that the mechanical performance of this lead-free BiAgX solder can be compared with those of other solders, at similar test conditions. At temperatures above 373K, BiAgX solder paste is found to strain harden more than the selected lead-rich reference solder in monotonic displacement-controlled tests. In isothermal constant-force creep tests, BiAgX is found to be 1-2 orders of magnitude more creep resistant than the selected lead-rich reference solder. The Ramberg-Osgood model is used to represent the elastic-plastic behavior of this BiAgX solder paste and the corresponding model constants are presented in this paper.

The IEEE 802.11 is a set of Media Access Control (MAC) and Physical Layer (PHY) specifications which concern the Wireless Local Area Network (WLAN) service. However, most IEEE 802.11 WLAN services are easily affected by external elements, such as the homogeneous interference caused by the high-density deployment of IEEE 802.11 devices, the attenuation effect caused by complicated indoor obstacles, and the heterogeneous interference caused by other devices which operate out of unlicensed 2.4GHz ISM bands. In this paper, we first present a method to capture IEEE 802.11n Bit Error Patterns (BEP) under the network effect such as the homogeneous interference and the signal attenuation caused by obstacles. We separate the two issues by showing the specific BEP distributions under different channel conditions. In addition to the IEEE 802.11n BEP analysis, we further simulated the impact of the LTE-Unlicensed (LTE-U) signal to the IEEE 802.11ac at the 5GHz, and analyzed similar BEPs through a purely experiment based method.

This article relates to the configuration design method of the product based on the extension case-based reasoning for transferring the demanding information into expected matter element so as to implement the mapping relationship between the customer needs and the configuration structures, to implement the mapping relationship between the configuration structures and configuration modules by relationship matter element reasoning, to get a group of module case that can satisfy the requirements of the customers from the configuration module library, and to realize the initial conceptual design. Take a complex system as an example to verify the feasibility of the configuration design method of the product.

A coordinated multi-point visible light communication (CoMP-VLC) downlink is investigated, where the time-frequency (TF) resources are shared by a group of users relying on space division multiple access (SDMA). Linear zero-forcing (ZF) transmit precoding (TPC) is tailored to the CoMP-VLC system in order to eliminate the inter-user interference while accommodating the linear operating region of the light emitting diodes (LEDs). A SDMA user-group sharing the same TF has to host users having sufficiently different user-signatures, i.e. channel gains in a non-dispersive VLC channel. Hence we develop efficient resource allocation (RA) and SDMA user-grouping algorithms in the context of VLC systems that use intensity modulation and direct detection (IM/DD). Finding the optimal SDMA user-group requires an exhaustive search (ES), which has exponentially increasing complexity as the number of users increases. Therefore, a low-complexity user-grouping method is conceived and compared to three existing algorithms in terms of the attainable area spectral efficiency (ASE) and throughput fairness. Our simulation results demonstrate that the proposed algorithm gives a better performance-fairness trade-off than existing benchmarks.

A new concept for indoor positioning using visible light communication (VLC) is presented in this paper. The feasibility of uplink localization is verified so that the proposed system can work in conjunction with downlink positioning systems to improve overall localization accuracy. We propose to use an angle diversity transmitter (ADT) associated with accelerometers for uplink three-dimensional localization. Unlike other techniques using VLC for positioning, the proposed system can achieve indoor localization without making assumptions about the height or orientation angle of a mobile user. The received signal strength (RSS) method is used to minimize implementation costs while achieving satisfactory positioning accuracy. Simulation results show that an average localization error of less than $0.15$ $\rm m$ can be achieved even when the receiver is tilted by $45^{\circ}$. Also, compared with a single light emitting diode (LED), the ADT is found to be more robust to accelerometer measurement errors.

Module division is the basis for product modularization. The rationality of the product module division directly affects the function, performance, development time, cost, general degree of module, convenience of maintenance and so on. A module partition method has been proposed based on the interface relationship of Pros and Cons. It parted the module using fuzzy theory, based on the qualitative hierarchy decomposition of the function, considering the interface depending factors of the parts at the same time in this method. And it introduced "information entropy" concept to evaluate the different module partition schemes, then choose the best module partition scheme. Finally, an example validated the method.

In this paper, the performance of non-orthogonal multiple access (NOMA) is characterized in a downlink visible light communication (VLC) system. Analytical expressions of the system performance are derived for two separate scenarios. In the scenario of achieving guaranteed quality of service (QoS), the outage probability of each user is studied and the effect of power allocation coefficients on the system coverage probability is investigated. In the scenario of providing opportunistic best-effort service, system ergodic sum rate is formulated based on a fixed power allocation (FPA) strategy. Both simulation and analytical results demonstrate that, in the first scenario, the maximum coverage probability can be achieved through the exhaustive search (ES) method to find the optimum set of power allocation coefficients. In the second scenario, it is shown that unlike orthogonal multiple access (OMA) techniques, NOMA can achieve a higher system capacity for a larger number of users. Also, the performance of NOMA can be further enhanced by choosing LEDs with a suitable semi-angle. When compared with OMA, NOMA can increase the system capacity by 125% if LEDs with 30° semi-angle are used.

We study a coordinated multi-point visible light communication (CoMP-VLC) system where space division multiple access (SDMA) is enabled. A novel SDMA grouping algorithm is proposed for achieving a better performance-fairness trade-off.

High temperature electronics (>200˚C) is an emerging technical area in electronics that requires new materials and processes or existing materials and processes in new ways. Results of reliability testing of packaging materials for >200˚C are presented so that the selection of appropriate packaging may be made to target an applications temperature and lifetime requirements. Polymer and ceramic substrates are compared using experimental testing. Lifetime comparisons at 200C for polymer substrates and limitations due to composition are made. Thick film alumina, Low Temperature Co-fired Ceramic, and thin film AlN substrate qualification test results and limitations in material selection are presented.