相移迁移法在激光超声合成孔径聚焦技术中的应用

通过分析脉冲源激光辐照于工件表面激发的多模式、宽带超声体波信号并结合合成孔径聚焦技术(SAFT),实现了对工件内部微小缺陷的检测、定位和成像。首先基于有限元仿真模拟了激光激发超声波在含缺陷样品中的传播过程,编写了基于相移迁移法(PSM)的SAFT成像算法,然后在实验中使用激光在含缺陷样品表面激发超声波,使用激光测振仪探测超声波,并基于已有算法和探测结果对样品内缺陷进行了检测和定位,以验证算法的正确性。有限元仿真以及实验结果均表明,将激光超声技术与频域SAFT-PSM结合,能够有效地对微小缺陷进行检测和定位,且其图像重构速度快于时域SAFT,可为激光超声无损检测提供更快速的实时技术方案。     

基于改进的ResNet手指静脉识别

针对指静脉提取困难和识别精度不够高等问题,提出了一种基于ResNet改进的手指静脉识别方法.首先,使用深度超参数化卷积(DO-Cony)代替网络中的传统卷积,在减少模型参数的同时提高了网络识别率.然后,将空间注意力模型(SAM)和挤压激励块(SE-Block)融合,应用于改进的残差网络(ResNet)提取图像在通道和空...     

Simultaneously Tuning Band Structure and Oxygen Reduction Pathway toward High-Efficient Photocatalytic Hydrogen Peroxide Production Using Cyano-Rich Graphitic Carbon Nitride

The demands for green production of hydrogen peroxide have triggered extensive studies in the photocatalytic synthesis, but most photocatalysts suffer from rapid charge recombination and poor 2e⁻ oxygen reduction reaction (ORR) selectivity. Here, a novel composite photocatalyst of cyano-rich graphitic carbon nitride g-C₃N₄ is fabricated in a facile manner by sodium chloride-assisted calcination on dicyandiamide. The obtained photocatalysts exhibit superior activity (7.01 mm  h⁻¹ under λ  ≥  420 nm, 16.05 mm  h⁻¹ under simulated sun conditions) for H₂O₂ production and 93% selectivity for 2e⁻ ORR, much higher than that of the state-of-the-art photocatalyst. The porous g-C₃N₄ with Na dopants and cyano groups simultaneously optimize two limiting steps of the photocatalytic 2e⁻ ORR: photoactivity, and selectivity. The cyano groups can adjust the band structure of g-C₃N₄ to achieve high activity. They also serve as oxygen adsorption sites, in which local charge polarization facilitates O₂ adsorption and protonation. With the aid of Na⁺, the O₂ is reduced to produce more superoxide radicals as the intermediate products for H₂O₂ synthesis. This work provides a facile approach to simultaneously tune photocatalytic activity and 2e⁻ ORR selectivity for boosting H₂O₂ production, and then paves the way for the practical application of g-C₃N₄ in environmental remediation and energy supply.     

用脉冲激光沉积法在Al2O3上沉积类金刚石薄膜

为了研究沉积时间和衬底温度对类金刚石薄膜的影响,在用脉冲激光沉积法在Al2O3衬底上制备类金刚石薄膜的实验中,保持其他实验参数不变,先取沉积时间分别为15 min和40 min来沉积薄膜;再取衬底温度分别30℃和300℃来沉积薄膜.用显微镜观察薄膜是否有起皱现象,用Raman光谱仪检测薄膜的微观结构,用原子力显微镜检测...     

A 9.1–10.7 GHz 10-W, 40-dB Gain Four-Stage PHEMT MMIC Power Amplifier

This letter presents a compact X-band high gain and high power four-stage AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (PHEMT) monolithic microwave integrated circuit (MMIC) high power amplifier (PA). This amplifier is designed to fully match a 50-Omega input and output impedance. Based on 0.35-mum gate-length power PHEMT technology, this PA MMIC is fabricated on a 3-mil thick wafer. While operating under 8 V and 2700-mA dc bias condition, the characteristics of 40-dB small-signal gain, a 10-W continuous-wave saturation output power, and 33% power added efficiency at 9.7GHz can be achieved     

Power Performance of AlGaN/GaN HEMTs Grown on SiC by Ammonia-MBE at 4 and 10 GHz

In this letter, we report on the microwave power and efficiency performance of AlGaN/GaN high-electron mobility transistors (HEMTs) grown by ammonia molecular beam epitaxy (ammonia-MBE) on SiC substrates. At 4 GHz, an output power density of 11.1 W/mm with an associated power-added efficiency (PAE) of 63% was measured at V _ds = 48 V on passivated devices. At 10 GHz, an output power density of 11.2 W/mm with a PAE of 58% was achieved for V _ds = 48 V. These results are the highest reported power performance for AlGaN/GaN HEMTs grown by ammonia-MBE and the first reported for ammonia-MBE on SiC substrates.     

An analytical programming model for the drain-coupling source-side injection split gate flash EEPROM

This paper presents a compact and accurate analytical model for evaluating the programming behaviors of the drain-coupling source-side injection (SSI) split-gate Flash memory. Starting with the bias-dependent and time-varying drain coupling ratio, a programming model is developed on the basis of the constant barrier height approximation and Lucky-electron model to express the full transient injection current, peak lateral electric field, and storage charge as functions of technological, physical, and electrical parameters. The extracted re-direction mean-free path of the SSI device is smaller than that of the channel hot-electron counterpart by one order of magnitude, which provides the physical intuition for the derived high injection efficiency of around 2/1000. The intrinsic coupling ratio depends only on technological parameters and is presented as the design index of the device. The usefulness of this model is its ability of constructing the complete operation plot of the time-to-program versus the programming voltage for various reliability windows and tunable technological parameters. Besides, the variance of the read current distribution of a memory array is also analytically predicted.     

A 0.25-/spl mu/m CMOS quad-band GSM RF transceiver using an efficient LO frequency plan

This paper describes a single-chip CMOS quad-band (850/900/1800/1900 MHz) RF transceiver for GSM/GPRS applications. It is the most important design issue to maximize resource sharing and reuse in designing the multiband transceivers. In particular, reducing the number of voltage-controlled oscillators (VCOs) required for local oscillator (LO) frequency generation is very important because the VCO and phase-locked loop (PLL) circuits occupy a relatively large area. We propose a quad-band GSM transceiver architecture that employs a direct conversion receiver and an offset PLL transmitter, which requires only one VCO/PLL to generate LO signals by using an efficient LO frequency plan. In the receive path, four separate LNAs are used for each band, and two down-conversion mixers are used, one for the low bands (850/900 MHz) and the other for the high bands (1800/1900 MHz). A receiver baseband circuit is shared for all four bands because all of their channel spaces are the same. In the transmit path, most of the building blocks of the offset PLL, including a TX VCO and IF filters, are integrated. The quad-band GSM transceiver that was implemented in 0.25-/spl mu/m CMOS technology has a size of 3.3/spl times/3.2 mm/sup 2/, including its pad area. From the experimental results, we found that the receiver provides a maximum noise figure of 2.9 dB and a minimum IIP3 of -13.2dBm for the EGSM 900 band. The transmitter shows an rms phase error of 1.4/spl deg/ and meets the GSM spectral mask specification. The prototype chip consumes 56 and 58 mA at 2.8 V in the RX and TX modes, respectively.     

A beam-scanning and polarization-agile antenna array using mutually coupled oscillating doublers

In this paper, a two-dimensional mutually coupled oscillator array is studied for the application of a beam-scanning and polarization-agile antenna array. In the design of antenna array, a two-dimensional oscillator array is implemented in x-y plane, the polarization agility is provided by one dimension (or y-direction) and the other dimension (or x-direction) is for beam scanning. By properly tuning the free-running frequencies of these oscillators, the array radiation direction can be scanned at the selected polarization states including linearly polarized, left-hand and right-hand circularly polarized states. The maximal phase difference of /spl plusmn/180/spl deg/ between coupled oscillating signals is acquired by utilizing their second-harmonic signals. This then gives well-defined phase differences among oscillators for beam scanning in addition to the required quadrature phase difference for circular polarization. The performances of polarization agility and beam scanning for a four-element antenna array are verified experimentally and shown to have the potential for adaptive antenna array applications.     

应用ANN的数字信号调制模式识别的特征矢量分析

数字信号调制模式的自动识别是无线通信中信号分析和处理的关键步骤之一。神经网络应用于数字信号调制模式识别的一个重要的预处理过程就是要形成完备的特征矢量空间。本文在原有分析方法的基础上，研究了信号的瞬时特征、谱特征和统计特征，特别提出了用于信号子类分析的新的高阶统计量特征，形成了数字调制模式自动识别的较为完备的特征矢量空间。通过对九种数字调制信号进行仿真表明，即使在信噪为5dB的条件下仍然能够获得较高的识别正确率。