Record-Breaking Frequency of 44 GHz Based on the Higher Order Mode of Surface Acoustic Waves with LiNbO_(3)/SiO_(2)/SiC Heterostructures

Surface acoustic wave (SAW) technology has been extensively explored for wireless communication, sensors, microfluidics, photonics, and quantum information processing. However, due to fabrication issues, the frequencies of SAW devices are typically limited to within a few gigahertz, which severely restricts their applications in 5G communication, precision sensing, photonics, and quantum control. To solve this critical problem, we propose a hybrid strategy that integrates a nanomanufacturing process (i.e., nanolithography) with a LiNbO_(3)/SiO_(2)/SiC heterostructure and successfully achieve a record-breaking frequency of about 44 GHz for SAW devices, in addition to large electromechanical coupling coefficients of up to 15.7%. We perform a theoretical analysis and identify the guided higher order wave modes generated on these slow-on-fast SAW platforms. To demonstrate the superior sensing performance of the proposed ultra-high-frequency SAW platforms, we perform micro-mass sensing and obtain an extremely high sensitivity of approximately 33151.9 MHz·mm2·μg−1, which is about 1011 times higher than that of a conventional quartz crystal microbalance (QCM) and about 4000 times higher than that of a conventional SAW device with a frequency of 978 MHz.

Control system design for a pressure-tube-type supercritical water-cooled nuclear reactor via a higher order sliding mode method

Nuclear power plants exhibit non-linear and time-variable dynamics.Therefore,designing a control system that sets the reactor power and forces it to follow the desired load is complicated.A supercritical water reactor(SCWR)is a fourth-generation conceptual reactor.In an SCWR,the non-linear dynamics of the reactor require a controller capable of control-ling the nonlinearities.In this study,a pressure-tube-type SCWR was controlled during reactor power maneuvering with a higher order sliding mode,and the reactor outgoing steam temperature and pressure were controlled simultaneously.In an SCWR,the temperature,pressure,and power must be maintained at a setpoint(desired value)during power maneuvering.Reactor point kinetics equations with three groups of delayed neutrons were used in the simulation.Higher-order and classic sliding mode controllers were separately manufactured to control the plant and were compared with the PI controllers speci-fied in previous studies.The controlled parameters were reactor power,steam temperature,and pressure.Notably,for these parameters,the PI controller had certain instabilities in the presence of disturbances.The classic sliding mode controller had a higher accuracy and stability;however its main drawback was the chattering phenomenon.HOSMC was highly accurate and stable and had a small computational cost.In reality,it followed the desired values without oscillations and chattering.

Dispersion Management with Higher Order Mode Fibers

Dispersion compensation with few-mode fibers is emerging as a promising technique that can provide full dispersion and dispersion-slope compensation. The inherent modal path diversity of these fibers allows implementation of static as well as tunable dispersion management schemes. In addition, the low non-linearity of this technology can improve system OSNR, leading to enhancements in transmission distances.

Robust Adaptive Gain Higher Order Sliding Mode Observer Based Control-constrained Nonlinear Model Predictive Control for Spacecraft Formation Flying

This work deals with the development of a decentralized optimal control algorithm, along with a robust observer,for the relative motion control of spacecraft in leader-follower based formation. An adaptive gain higher order sliding mode observer has been proposed to estimate the velocity as well as unmeasured disturbances from the noisy position measurements.A differentiator structure containing the Lipschitz constant and Lebesgue measurable control input, is utilized for obtaining the estimates. Adaptive tuning algorithms are derived based on Lyapunov stability theory, for updating the observer gains,which will give enough flexibility in the choice of initial estimates.Moreover, it may help to cope with unexpected state jerks. The trajectory tracking problem is formulated as a finite horizon optimal control problem, which is solved online. The control constraints are incorporated by using a nonquadratic performance functional. An adaptive update law has been derived for tuning the step size in the optimization algorithm, which may help to improve the convergence speed. Moreover, it is an attractive alternative to the heuristic choice of step size for diverse operating conditions. The disturbance as well as state estimates from the higher order sliding mode observer are utilized by the plant output prediction model, which will improve the overall performance of the controller. The nonlinear dynamics defined in leader fixed Euler-Hill frame has been considered for the present work and the reference trajectories are generated using Hill-Clohessy-Wiltshire equations of unperturbed motion. The simulation results based on rigorous perturbation analysis are presented to confirm the robustness of the proposed approach.

Speech-stream detection in short-wave channel based on empirical mode decomposition and higher-order statistics

To capture the presence of speech embedded in nonspeech events and background noise in short-wave non-cooperative communication,an algorithm for speech-stream detection in noisy environments is presented based on Empirical Mode Decomposition (EMD) and statistical properties of higher-order cumulants of speech signals.With the EMD,the noise signals can be decomposed into different numbers of IMFs.Then,the fourth-order cumulant (FOC) can be used to extract the desired feature of statistical properties for IMF components.Since the higher-order cumulants are blind for Gaussian signals,the proposed method is especially effective regarding the problem of speech-stream detection,where the speech signal is distorted by Gaussian noise.With the self-adaptive decomposition by EMD,the proposed method can also work well for non-Gaussian noise.The experiments show that the proposed algorithm can suppress different noise types with different SNRs,and the algorithm is robust in real signal tests.

On the accuracy of higher order displacement discontinuity method(HODDM) in the solution of linear elastic fracture mechanics problems

The higher order displacement discontinuity method(HODDM) utilizing special crack tip elements has been used in the solution of linear elastic fracture mechanics(LEFM) problems. The paper has selected several example problems from the fracture mechanics literature(with available analytical solutions) including center slant crack in an infinite and finite body, single and double edge cracks, cracks emanating from a circular hole. The numerical values of Mode Ⅰ and Mode Ⅱ SIFs for these problems using HODDM are in excellent agreement with analytical results(reaching up to 0.001% deviation from their analytical results). The HODDM is also compared with the XFEM and a modified XFEM results. The results show that the HODDM needs a considerably lower computational effort(with less than 400 nodes) than the XFEM and the modified XFEM(which needs more than 10000 nodes) to reach a much higher accuracy. The proposed HODDM offers higher accuracy and lower computation effort for a wide range of problems in LEFM.

Nth Order Voltage Mode Active-C Filter Employing Current Controlled Current Conveyor

This paper proposes an nth order (where n = 2,3, ,n) voltage mode active-C filter using n number of current controlled current conveyors (CCCIIs) and n number of equal valued grounded capacitors. The proposed topology can implement both band pass and low pass responses without alteration of any components. The filters offer the following important features: use of minimum number of current controlled current conveyors (CCCIIs) and passive components, no matching constraint, use of all grounded capacitors and absence of external resistor suitable for integration, cut off frequency can easily be electronically adjusted using AMS 0.35 μm CMOS technology. PSPICE simulation results of third order band pass and low pass responses are provided. The results are found to agree well with the theory.

Sliding Mode Control Design via Reduced Order Model Approach

This paper presents a design of continuous-time sliding mode control for the higher order systems via reduced order model. It is shown that a continuous-time sliding mode control designed for the reduced order model gives similar performance for thc higher order system. The method is illustrated by numerical examples. The paper also introduces a technique for design of a sliding surface such that the system satisfies a cost-optimality condition when on the sliding surface.

近远场地震下RC大跨轻柔拱桥减隔震支座方案优化

为探明不同地震动输入对某大跨轻柔拱桥减隔震的影响,通过非线性有限元模型分析近远场地震下桥梁结构的响应规律,得到大桥支座的优化布置方案.首先,基于模态分析,对比该桥与传统钢筋混凝土(RC)拱桥动力特性差异;其次,选取不同脉冲周期的近场地震动、近场无脉冲及远场长周期地震动记录;最后,研究近远场地震下拱桥的响应行为和损伤演化路径,得到优化桥梁的减隔震支座设计方案.研究结果表明:近场脉冲及远场长周期地震下的桥梁结构响应大于无脉冲地震响应;纵竖向地震下高墩柱剪力及弯矩包络曲线呈“S”形,墩身中部易形成塑性铰,高阶振型影响显著;桥梁纵桥向先于横向震损,损伤路径依次为矮柱、高墩柱及拱肋实心-空心截面段;摩擦摆支座减震效果最佳但位移较大,高阻尼支座方案在近场中长脉冲周期及远场长周期地震下仍会发生损伤,板式橡胶支座方案因无法保证支座同步滑移而不能形成准隔震体系;“高阻尼+摩擦摆”混合方案的支座位移小,拱肋及墩柱均处于弹性,是近断层大跨轻柔RC拱桥的优选减隔震方案.

基于自适应干扰观测器的巡航导弹掠海飞行轨迹跟踪控制

构建了巡航导弹动力学模型,将不确定性项与风浪干扰项合并,同时引入一种自适应干扰观测器予以补偿,提高导弹控制系统的鲁棒性,并利用高阶滑模控制器和任意阶微分器实现控制系统反馈环节的有限时间镇定.仿真实验表明,该方案可实现在1∼7级海况下巡航导弹掠海飞行的高精度轨迹跟踪,同时具备较高的收敛速度和良好的适应性.

基于高阶滑模的PMSM无传感器控制

针对传统永磁同步电机(PMSM)无传感器控制存在的超调量大、抖振明显,易受负载扰动影响的现象。提出一种基于高阶滑模的控制策略,结合超螺旋算法(STA)和任意阶算法设计出新型高阶滑模控制器,将新型的控制器分别应用于速度控制器、状态观测器和扭矩观测器,用饱和函数代替符号函数,同时采用积分滑模面和模糊控制对控制系统进行优化。系统使用状态观测器和锁相环(PLL)获取转子位置信息,并通过扭矩观测器将观测值前馈补偿至速度控制器。经过模拟仿真表明该高阶滑模控制系统可以有效地抑制超调和抖振,提升转子位置的估算精度,同时大大提升了系统的抗干扰性和鲁棒性。

某型离心叶轮共振疲劳危险点预测及试验验证

高阶模态对高周疲劳失效有很大影响,但对高阶模态下的离心叶轮振动特性研究较少。本研究建立某型离心叶轮有限元模型,并通过测频试验验证了模型的准确性;开展离心叶轮高阶振动特性分析,获得了危险点位置;开展了试车试验,分析叶轮裂纹特性,验证危险点位置预测方法的合理性。结果如下:离心叶轮主1阶固有频率仿真计算结果与试验结果的误差仅为1.2%;叶轮相对应力最大值位于排气边主叶片叶根处,此处即为共振疲劳危险点;叶轮裂纹性质为高周疲劳裂纹,裂纹起源于排气边叶根处,与有限元分析结果一致,证明了使用共振频下的振动应力预测其共振疲劳危险点的合理性。本研究的结论可以为离心叶轮的设计和改进提供理论基础和技术支持。

一种宽阻带腔体滤波器的设计

本文设计了一种覆盖整个Ku频段(10.7 GHz-14.5 GHz)的紧凑型宽阻带腔体滤波器,该滤波器为“块模式”滤波器。通过将皱折波导滤波器的皱折波导上开一些纵向槽,以有效地抑制高次模。通过优化“块模式”滤波器的各个金属矩形块的尺寸,使其满足滤波器3倍频的阻带内有很好的带外抑制效果。该滤波器相比于传统的金属虹膜腔体滤波器,具有良好的宽通带及高衰减的宽阻带,并且可以有效的抑制很多高次模。仿真结果表明,在所需要的10.7 GHz-14.5 GHz频段内|S11|均优于-25 dB,并且对整个Ka频段的均抑制低于-75dB。本文所设计的滤波器结构紧凑,易于加工,在多馈源系统的工程应用中具有良好的应用前景。

面向高阶思维训练的实验教学模式设计与实践

通过深度学习在课堂教学中来发展学生高阶思维能力是近年来教育改革中的一个重点。我们在面向本科一年级新生的物理实验课程中,对传统的教学模式进行了改革,增加了激发高阶思维产生的最大动力来源——“真实情境问题”为导向的课程内容。以此为核心抓手和发力点,通过引入探索型实验课题,依托传统实验和探索型实验课题这两类不同层次实验教学具有的互补性特性,对大学物理实验的教学内容和形式进行了合理的重构,将大一新生高阶思维能力的培养有机地融入实验教学过程之中,形成了促进学生快速进入大学探究性深度学习的教学模式。问卷、访谈和成绩对比等数据表明该模式在一年级本科生的高阶思维能力和研究素养养成上起到积极的作用。这一变革在新形势下对物理实验教学具有积极的指导意义,也对于实践类课程教学具有一定借鉴作用。

MODE THEORY OF MULTILAYER WAVEGUIDE STRUCTURE WITH DISCONTINUITIES

TEn mode (whose electric field is zero in the normal direction of theboundafiesbetween layers) and TMn mode (whose magnetic field is zero in the normal direction of the bound-aries between layers) are defined. Then conditions under which pure TEn (TMn) modes may existin multilayer waveguide structure with discontinuities are presented. E (H) step wavguides, ridgedwavguides, microstrip lines and fin lines all satisfy the conditions, and hold for TEn (TMn) mode.The conventional conclusion that ridged waveguides with inhomogeneous dielectric-slab loading,microstrip lines and fin lines only hold for hybrid modes is revised. Compared with hybrid modes,the number of unknown variations and matching equations is reduced by half for pure TEn (TMn)modes, and the computation cost is decreased dramatically.

An Extended Model for Interaction Between Left-hand Superluminous Waves and Magnetospheric Electrons

The left-hand superluminous electromagnetic waves, L-O mode and L-X mode, can be excited and observed in the auroral cavity of the Earth during the magnetic storms. The two modes can propagate into outer radiation zone and encounter enhanced resonant interactions with the trapped energetic electrons over a wide range of magnetosphere. A current first-order resonant model is extended to evaluate the stochastic acceleration of electrons by the L-O mode and L-X mode at the higher-order resonance. Similar to the first-order resonance, L-O mode can produce significant acceleration of electrons at the higher harmonic resonances over a wide range of wave normal angles and spatial regions. However, the higher harmonic resonance＇s contribution for significant electron acceleration by L-X mode is less than that of the first order resonance, with the requirement of higher minimum energies, e.g., -1 MeV in the outer radiation belt. This indicates that L-O mode may be one of the efficient mechanisms for the stochastic acceleration of electrons within the outer radiation zone.

面向高阶思维培育的DREAM教学模式及应用

高阶思维是高阶能力的核心,集中体现了智能时代对人才素质的新要求.针对雷达系统课程中学员高阶思维培育难的问题,围绕“相关”或者“关联”这一高阶思维核心特征,提出了问题驱动的DREAM教学模式,给出了DREAM模式的实施过程.课堂实践表明,该模式能够有效提升学员的高阶思维能力.

基于高阶Lamb波模态频谱差异系数的腐蚀检测

针对工业设备中大型薄壁结构件的腐蚀检测问题,提出一种基于频谱相干性分析的高阶Lamb波腐蚀损伤检测方法.首先,利用略高于截止频率的A1模态Lamb波对含腐蚀薄壁结构的不同位置进行激励,并采集各传播路径上的响应信号;随后,采用频散补偿技术消除信号中的频散效果,通过合适的窗函数对信号中的A1模态直达波包进行分离提取,建立其与激励信号的频谱差异系数(frequency spectrum difference coefficient,FSDC),通过有限元仿真研究该指标对不同宽度、深度腐蚀损伤的敏感性;最后,在含腐蚀铝板上进行实验验证,结合各路径FSDC指标与概率成像算法,对检测区域的腐蚀损伤进行定位与成像.结果表明:FSDC值在健康状态下为0,而在不同宽度、深度的腐蚀影响下FSDC在0~1;相较于传统层析成像方法,所提出方法具有更好的检测灵敏度和抗干扰能力.

高职教育“订单式”培养有效评价机制的研究

“订单式”人才培养模式作为高职教育的最佳办学方式之一,其评价机制对人才培养有着重要意义。“订单式”人才培养模式下的质量评价机制可以更好地优化高职院校的教学资源,为技能型人才的培养提供标准,能有效激活高职教育的人才培养体系,使用人单位、职业院校、学员得到各自的利益,实现共赢。

基于共面波导的全角度频率波束扫描天线

为满足平面集成系统、雷达等领域对宽角度频率波束扫描天线的需求,提出了一种低剖面、小型化、全角度频扫天线的设计方案.天线通过在共面波导上刻蚀周期性孔阵列,形成人工表面等离子体激元结构,利用其高次模辐射的特性产生频率扫描波束.通过在共面波导一侧金属地上刻蚀周期性的梳状结构,并由共面波导为其馈电,产生低频反向端射波.仿真结果表明,天线在9.1~53 GHz频带内平均增益为12.75 dBi,频率波束扫描范围为180°.由于矢量网络分析仪频率量程限制,实测结果在9.1~40 GHz与仿真结果具有较好的一致性.该天线具有加工易、剖面低、成本低、全角度扫描的特点,为平面集成系统、雷达等领域宽角度频扫天线提供了一种新的设计思路.