New phase-shifting technique for group-type unidirectional transducers used in surface-acoustic-wave filters

The letter reports a novel method of phase shifting useful in the group type of unidirectional transducers used for the design of low-loss SAW filters. This technique utilises the thin-film capacitance present between the newly described configuration of the feed-electrode layers as an essential element of the required phase shifter. The stray capacitance existing between the feed electrodes is used to advantage. The theoretical and experimental results of one of the filters fabricated are presented.     

Improved Si piezo-transistors for mechano-electrical transducers

Piezo-transistors with stresses applied to the emitter region by means of small hard styli for application as mechano-electric transducers have been improved. High signal-to-noise ratios were obtained in gold-doped n-p-n Si planar transistors. New designs for emitter electrodes have been devised which make the fabrication of the transducer units easy. Rather large stressing areas (60-µm diameter) which are surrounded by ring-type emitter electrodes with overlay bonding pads are provided in the central part of the emitter region (90-µm diameter). Signal-to-noise ratios are high and independent of the position of the stylus over the stressing area. By using these transistors mechano-electrical transducer units were fabricated with higher stabilities. It was found that noise decreases with increasing stress. Life-test results of the transducer units are also indicated. The stress dependence of transistors were explained by the combined effects of the stress dependence of the emitter efficiency and the stress dependence of the base transport factor. Gold-doping seemed to enhance the stress dependence of the base transport factor due to a very short minority carrier lifetime.     

High-performance SAW convolver using 3-phase unidirectional transducers

The development of a new SAW convolver with a bandwidth 45 MHz, interaction time 12 ?s and which employs 3-phase unidirectional transducers is discussed. The resulting device has high efficiency (?58 dBm) and displays good self-convolution suppression. Only single-stage fabrication is required.     

1.03 GHz operation of a low-loss SAW filter using 3-phase unidirectional transducers with thin dielectric layered feed electrodes

Successful working of a 3-phase unidirectional transducer (TPUDT) SAW filter at 1.03 GHz, without using any airgap crossovers, is reported in the letter. A thin-film capacitance existing between the feed electrodes of the transducers is used to advantage, as an essential element of the required phaseshifting network. The minimum insertion loss is found to be 2.0 dB. The filter is believed to have wide applications in the present and future communication systems requiring low-loss bandpass filtering.     

Optimization of unidirectional interdigital transducers via the scanning window technique

An original procedure for optimization of single-phase unidirectional interdigital transducers of surface acoustic waves (SAWs) is described. These transducers are designed for RF filters with low levels of the insertion loss and the triple-transit signal. The optimization algorithm is based on the so-called scanning window technique. Unlike most methods published in the literature, this technique optimizes not continuous (analog) weighting functions of the SAW sources and reflectors but the sequence of base electrode cells; i.e., the technique directly optimizes the transducer topology.     

Surface-acoustic-wave unidirectional transducers using anodic oxidation technology and low-loss filters

A new surface-acoustic-wave interdigital transducer (IDT) and unidirectional transducer (UDT) are described. Using a lift-off anodic oxidation method, controllable gaps between electrodes with good insulation can be obtained. Experimental results show good characteristics at 2nd-harmonic operation for a new floating electrode type unidirectional transducer (NG-FEUDT). Also, a low-loss filter of 3.46 dB with side-lobe suppression of 40 dB at 893 MHz is obtained using the above techniques.<>     

Practical feed network design for antenna arrays

Computational procedures have recently been developed which accurately determine the excitation (including mutual coupling effects) at each element of a closely spaced array enabling it to perform in some desired manner. A procedure for designing a transmission-line feed network capable of realizing these required excitations is described. The result is a narrow-band feed system composed simply of a transmission line together with a small number of stubs. A comparison between theoretical and experimental results is given.     

Wideband unidirectional patch antenna with Γ-shaped strip feed

A wideband unidirectional patch antenna composed of a shorted bowtie dipole with ?-shaped feed and an L-shaped electric dipole is designed. It achieves an impedance bandwidth of 87% for VSWR ? 2 in the range 2.2-5.6 GHz, stable peak gain of around 7 dBi, unidirectional radiation patterns and low cross-polarisation over the whole operating band. It is sufficient for accommodating recent wireless communication services such as 3G, WiFi, WiMax, Bluetooth, Zigbee, etc.     

Methodologies for characterizing ultrasonic transducers usingneural network and pattern recognition techniques

System hardware for characterizing ultrasonic transducers and the associated data acquisition software and characterizing algorithms are considered. The hardware consists mainly of a workstation computer, a receiver/pulser with gated peak detector, various monitoring devices, a microcomputer-based 3D positioning controller, and an A/D converter. The characterization algorithms are based on neural network and pattern recognition techniques. It is found that artificial neural network techniques provide far better classification results than the pattern recognition techniques. A multilayer backpropagation neural network which provides a classification accuracy of 94% is developed. Two other multilayer neural networks-sum-of-products and a newly devised neural network called hybrid sum-of-products-have a classification accuracy of 90% and 93%, respectively. The most successful pattern recognition technique for this application is found to be the perceptron, which provides a classification accuracy of 77%     

A self-matching wideband feed network for microstrip arrays

A novel technique for feeding microstrip antenna arrays is proposed. It consists of a microstrip feed network designed to operate in dual standing and traveling-wave modes and provide uniform excitation to its elements with either mode. It, therefore, produces a uniform aperture distribution, regardless of the array element input impedances. The traveling wave propagates when radiating elements are matched, but resonant standing wave prevails if loads become mismatched. Since the feed network resonance does not alter the array excitation, it can be used in combination with the radiating patch resonance to broaden the impedance bandwidth. The physical reasons for such behaviors are explained and experimental verification are provided. The generalization of the concept to large arrays is also discussed     

改进U-Net网络的接地网图像超像素分割北大核心CSCD

研究基于改进U-Net网络的接地网图像超像素分割方法,提升红外图像超像素分割效果。通过主成分分析法降维处理接地网腐蚀红外图像;利用Turbopixel超像素分割法分割降维后的红外图像,获取数个超像素区域;在全卷积U-Net网络内添加可变形卷积与重构上采样卷积,并利用反向传播算法,优化网络参数,建立改进的全卷积U-Net网络结构;在改进的全卷积U-Net网络内分割获取的数个超像素区域,输出红外图像超像素自动分割结果。实验证明:该方法可有效降维处理接地网腐蚀红外图像,实现红外图像超像素分割,分割后的红外图像边界清晰;在不同分辨率时,该方法的Dice相似性系数较高、Hausdorff距离较低,具备较高的红外图像超像素分割精度。     

Improved MOS transducer drive circuit [piezoelectric transducers]

The operation and design of a novel floating gate MOS output circuit is described. The circuit uses a unique variable positive feedback that increases the speed significantly and decreases the circuit area.     

前馈网络的信息泄漏

研究了前馈网络的局部信息泄问题，给出了收集泄漏信息的方法，并对该方法进行了成功率的计算及其有效性的理论论证。     

Improved algorithms for synchronizing computer network clocks

The Network Time Protocol (NTP) is widely deployed in the Internet to synchronize computer clocks to each other and to international standards via telephone modem, radio and satellite. The protocols and algorithms have evolved over more than a decade to produce the present NTP Version 3 specification and implementations. Most of the estimated deployment of 100000 NTP servers and clients enjoy synchronization to within a few tens of milliseconds in the Internet of today. This paper describes specific improvements developed for NTP Version 3 which have resulted in increased accuracy, stability and reliability in both local-area and wide-area networks. These include engineered refinements of several algorithms used to measure time differences between a local clock and a number of peer clocks in the network, as well as to select the best subset from among an ensemble of peer clocks and combine their differences to produce a local dock accuracy better than any in the ensemble. This paper also describes engineered refinements of the algorithms used to adjust the time and frequency of the local clock, which functions as a disciplined oscillator. The refinements provide automatic adjustment of algorithm parameters in response to prevailing network conditions, in order to minimize network traffic between clients and busy servers while maintaining the best accuracy. Finally, this paper describes certain enhancements to the Unix operating system kernel software in order to realize submillisecond accuracies with fast workstations and networks     

光总线网带宽容量分配的公平性策略研究

提出一种用于单向光总线网的新型带宽容量分配公平性策略,定义了业务类型,给出了具体算法和公平性评价方案,最后进行了公平性策略的仿真实验,并对仿真结果进行分析和讨论。仿真结果验证了公平性策略的有效性。     

太赫兹准光学馈电网络研究进展

准光学馈电网络是一种多重复合电磁波信号分集传输方法,在射电天文、大气遥感、气象探测等方面应用日趋广泛。概括了准光学馈电网络的设计方法,介绍了现阶段国内外准光学馈电网络研究进展,分析了太赫兹准光学馈电网络发展重点。对准光学器件的研究和准光系统的高精确度集成测试将是今后发展重点。     

Improved sparrow search algorithm for RFID network planning

To solve the problem that the performance of the coverage, interference rate, load balance andweak power in the radio frequency identification(RFID) network planning. This paper proposes an elite opposition-based learning and Lévy flight sparrow search algorithm(SSA), which is named elite opposition-based learning and Levy flight SSA(ELSSA). First, the algorithm initializes the population by an elite opposed-based learning strategy to enhance the diversity of the population. Second, Lévy flight ...     

Improved ID-based security framework for ad hoc network

As mobile devices with wireless communication capacity become more and more popular, the study on ad hoc networks that offer convenient infrastructure-free communication has arose the attention from both the academic and the industry. However, the previous security schemes proposed for ad hoc networks either suffer from the structure support problems or have security flaws. This paper examines the weaknesses of a Bohio–Miri’s recent work, and then proposes our new schemes to enhance the security and the performance. The security of the proposed protocols is proved in the random oracle model.     

改进的神经网络非均匀性校正方法

红外图像的非均匀性是制约红外成像系统成像质量的限制性因素,非均匀性校正是红外成像领域中的核心技术。改进了传统的神经网络非均匀性校正方法,在探测元的期望输出中加入图像均值分量,使该算法对空间相关性较强的低频非均匀性成分也具有较强的校正能力。在以TMS320C62x DSP为核心的硬件平台上,采用中波凝视红外探测器,图像帧频为50 Hz,并在实验室及室外环境分别对该算法进行了测试,非均匀性从最初的5％左右降至2‰以下,验证了改进后的算法具有校正精度高、实用性强等优点,能够满足实际应用的需要。该算法也可应用于红外成像的应用领域。