电液谐振式高频疲劳试验台动态特性研究

针对由单出杆液压缸与二位三通2D阀组成的电液谐振式高频疲劳试验台,因单出杆液压缸无杆腔与2D阀相连,有杆腔恒通油源。而2D阀突破常规电液伺服阀频宽极限,具有宽频带、高频响等特点,通过改变阀芯旋转速度及阀口轴向开度,可对系统分别进行变频、变幅控制。对采用2D阀控制技术的电液谐振式高频疲劳试验台建立数学、仿真模型,并对该试验台谐振工况进行仿真与实验研究,结果表明该系统谐振工况输出位移（载荷力）与激振力大,消耗外界功率低。     

共振式水泥混凝土路面破碎车共振频率和振幅的控制研究

基于共振式水泥混凝土路面破碎车共振机构的载荷分析,给出了其共振频率和振幅的模型。针对共振机构电液比例控制系统的非线性和不确定性问题,建立了基于比例泵控马达的频率控制数学模型,设计了自适应反推滑模的频率控制算法,针对系统模型中的不确定项,给出了各参数项的自适应律,基于Lyapunov函数,证明了频率输出跟踪的渐近收敛。仿真和车载实验结果表明,该方法具有较好地频率跟踪性能,能满足共振式水泥混凝土路面破碎车的施工作业要求。     

Self-temperature-testing of the quartz resonant force sensor

Temperature characteristics of a quartz resonant force sensor are important features, which should be seriously considered in the sensor's practical application. This paper analyzes the temperature characteristics of a quartz resonant force sensor and presents a self-temperature-testing method for the sensor by analyzing the different temperature characteristics when the quartz resonator vibrates in its fundamental mode and in its third overtone mode. A beat frequency results from the resonator's fundamental and third overtone frequencies. Experimental result show that the sensor's operating temperature can be measured by making use of this beat frequency rather than applying a temperature sensor     

Influence of split ring resonators on the properties of propagating structures

The study of a 50 Omega microstrip line and microstrip resonators loaded with resonant elements called split-ring resonators (SRRs) is presented. The two different filtering phenomena observed lead to make an analogy with those observed when waveguides are loaded with these elements. So, in order to make this analogy, the different results obtained with the SRRs loaded in a propagating and an under cut-off waveguide are shown. Then, another technique to achieve and even improve these results is presented. The technique consists of using, respectively, a 50 Omega microstrip line and capacitive-gap-coupled microstrip resonators instead of the propagating and under cut-off waveguides. The numerical and experimental results obtained with the two structures (waveguides and microstrip lines) are compared and discussed. This study shows that the combination of SRRs with guiding structures helps in the design of compact structures, but an enhancement of the performances needs a better fabrication accuracy     

Dynamic in-plane resonant characteristics of piezoceramic and piezolaminated composite plates.

Piezolaminated composite plates have received considerable attention in various industrial applications due to their intelligent characteristics. In this investigation, two experimental measurement techniques are used to determine the in-plane resonant vibration of angle-ply laminated composites embedded with a piezoceramic layer (piezolaminated plates) for different stacking angles. The first method is a full-field optical technique, which is called the AF-ESPI (amplitude-fluctuation electronic speckle pattern interferometry). This is the major experimental method. The AF-ESPI method is used to determine the in-plane resonant frequency and corresponding mode shape of a single-layer piezoceramic plate and piezolaminated plates with five different stacking angles. The second experimental technique, the impedance analyzer, is employed to determine the in-plane resonant frequency. Finally, numerical computations based on the finite element analysis are presented for comparison of the two experimental results. Excellent agreement between the experimentally measured data and the numerically calculated results are found for in-plane resonant frequencies and mode shapes. This study indicates that the dynamic characteristics of inplane resonant vibrations for piezolaminated plates with different stacking angles are quite different.     

一种采用激振器激励的扬声器振动部件共振频率测量方法及系统

提出了一种采用激振器激励方式的扬声器振动部件共振频率测量方法及系统。采用激振器作为激励被测部件振动的激励源,并通过加速度传感器实时检测夹具的振动加速度（包括幅度和相位）,以确保被夹具夹持住的被测部件在测量频率范围内上下平稳振动;通过激光位移传感器测量被测部件在不同频率点振动时的振动位移,可得到被测部件振动的频率响应（被测部件振动加速度和夹具振动加速度的比值的频率响应）;根据该频率响应进行计算最后可得到被测部件的共振频率。实验结果表明,实测频率响应的曲线与理论分析相一致,测量结果的可重复性和准确性良好,可测量的振动部件的种类和范围更广。     

基于Helmholtz共振腔阵列的声学超材料研究

为有效控制特定频段的噪声,基于Helmholtz共振腔阵列,通过Helmholtz共振腔短管位置的控制,设计了一种新型的局域共振型声学超材料。利用COMSOL Multiphysics软件求得新型声学超材料的能带图和传递损失曲线,并与具有单一方向开口的Helmholtz共振腔阵列的传递损失曲线进行对比;同时,为分析新型声学超材料的带隙形成机理,求得了其在带隙频率范围内的声压分布云图。通过试验测试了新型声学超材料的吸声性能。结果表明：新型声学超材料的能带图中产生了2段较窄带隙和1段较宽带隙,在带隙频率范围内,声学超材料传递损失出现峰值;第1带隙和第2带隙较窄,原因是单个Helmholtz共振腔局域共振,声波能量消耗少;第3带隙较宽,原因是Helmholtz共振腔与其周期排列形成的外部波导联合共振吸声,消耗大量声波能量。试验测试结果与仿真计算结果较为吻合,新型声学超材料可有效控制1 300~1 500 Hz和1 500~2 000 Hz频率范围内的噪声。研究结果表明,所设计的新型局域共振型声学超材料可有效实现中低频减振降噪,为声学超材料在中低频的降噪控制研究提供了新的思路。     

Design and implementation of FPGA-based phase modulation control for series resonant inverters

Owing to the tremendous advances in the digital technology, and improved reliability and performance of the digital control mechanisms, this paper focuses on design and implementation of digital controller using FPGA-based circuit design approach. The digital controller proposed is designed for series resonant inverter used in DC-DC converter applications. Phase modulation technique is proposed for the realization of digital controller on FPGA. The Series Resonant Converter (SRC) is considered in this paper as a preferred converter topology for high power, high voltage power supplies. This paper studies the implementation of phase shift modulation technique using FPGA. The inverter designed, is IGBT based, and Zero Voltage Switching (ZVS) technique is implemented due to reduced stresses on devices and increased efficiency. The phase modulated series resonant inverters (PM-SRC) promotes ZVS operation when its switching frequency is greater than resonant frequency. The designed PM controller is realized using FPGA on which control algorithm and other features of a controller are developed. The series resonant inverter is built and tested for full load under open loop and closed loop conditions at a switching frequency of 20 kHz. The results are presented under varying load conditions. The simulation and the experimental results were found to match closely.     

On the hysteresis phenomenon in the directly excited nonlinear resonant sloshing waves in a tank

Summary Steady nonlinear resonant standing waves obtained in a rectangular tank by a direct excitation are studied in detail both experimentally and numerically. The experimental study demonstrates the existence of a well defined hysteresis between two quite different wave distributions in the tank. The dissipation coefficient at the wavemaker is estimated from the present experimental results. Numerical simulations based on the solution of the nonlinear Schrödinger equation, with the dissipation coefficient at the wavemaker obtained experimentally, show that this hysteresis may be reproduced in calculations when a nonlinear boundary condition at the wavemaker is adopted. Such a boundary condition is indeed supported by experimental evidence.     

哑铃形热声谐振器的谐振频率

热声自激振荡模态取决于声学谐振器结构形式和特征尺度。级联型热声热机依靠哑铃形谐振器来调制所需要的局部高阻抗行波声场,谐振管通常由几段不同横截面的管段组成。哑铃形热声谐振器的谐振频率由共鸣腔容积、谐振管截面和长度共同决定。根据哑铃形谐振器不同截面管段内的声传播规律、共鸣腔声学边界条件以及管段间的声压和体积流率连续条件,利用行波叠加的方法,建立均匀管模型、变截面模型和热声网络模型,得到了系统谐振频率随共鸣腔容积变化和谐振管特征尺寸变化的规律。系统谐振频率的变化将引起最佳听音点的位置的移动,进一步起到调节回热器声阻抗的作用。实际热声热机实验研究中,通过改变谐振器特征尺度或结构形式调节系统的谐振频率,也是热声热机调试过程中实现自激振荡的主要手段。     

锁相环跟踪超声振动系统谐振频率的改进

锁相式频率跟踪超声发生器的频率跟踪范围较小且易出现死锁现象,通常要人为重新启动,系统才能恢复跟踪状态,在应用时会带来麻烦。根据超声振动系统的等效电路研究其阻抗特性,并通过实验绘制换能器特性曲线,分析应用CD4046跟踪串联谐振频率容易造成死锁的具体原因,提出带解锁的频率跟踪系统的方案。实验结果表明此方案有较大的跟踪调节范围与较强的适应负载变化的能力,对超声发生器的具体应用有一定的参考意义。     

Effect of metal coating and residual stress on the resonant frequency of MEMS resonators

MEMS resonators are designed for a fixed resonant frequency. Therefore, any shift in the resonant frequency of the final fabricated structure can be a denting factor for its suitability towards a desired application. There are numerous factors which alter the designed resonant frequency of the fabricated resonator such as the metal layer deposited on top of the beam and the residual stresses present in the fabricated structure. While the metal coating, which acts as electrode, increases the stiffness and the effective mass of the composite structure, the residual stress increases or decreases the net stiffness if it is a tensile or compressive type respectively. In this paper, we investigate both these cases by taking two different structures, namely, the micro cantilever beam with gold layer deposited on its top surface and the MEMS gyroscope with residual stresses. First, we carry out experiments to characterize both these structures to find their resonant frequencies. Later, we analytically model those effects and compare them with the experimentally obtained values. Finally, it is found that the analytical models give an error of less than 10% with respect to the experimental results in both the cases.     

Theoretical and numerical analysis of the resonant behaviour of the Minkowski fractal dipole antenna

The resonant behaviour and the size reduction capabilities of the Minkowski fractal dipole antenna are investigated. The antenna is analysed at each resonant frequency by considering the radiation efficiency and the fractional bandwidth. Besides, a method for deriving the approximate positions of the resonant frequencies of the Minkowski dipole at each fractal iteration is proposed. The presented analysis is based on the inductive circuit model and is validated by simulations. Moreover, in order to quantify the advantages provided by the Minkowski geometry, the proposed study performs a comparison with the generalised Koch dipole in terms of fractal dimension and lacunarity.     

Performance comparison of thermoacoustic engines with constant-diameter resonant tube and tapered resonant tube

Two standing-wave thermoacoustic engines with a constant-diameter resonant tube and a tapered one, respectively, are simulated with linear thermoacoustics to explore the reasons for performance improvement of the thermoacoustic engine with the tapered resonant tube substituting for the constant-diameter one. Computed results indicate that the viscous loss in the tapered resonant tube is much lower than that in the constant-diameter one, and the smooth joint between the tapered resonant tube and its resonant cavity may avoid the acoustic power loss derived from sharp variation of flow area. The comparison between the computed results and the experimental data indicates that the simulation can roughly predict the performance of thermoacoustic engines with these two types of resonant tubes.     

High-frequency resonant characteristics of triple-layered piezoceramic bimorphs determined using experimental measurements and theoretical analysis

This is an experimental, theoretical, and numerical investigation of vibration characteristics in high-frequency resonance, which are studied for parallel- and series-type piezoelectric bimorphs. In the experimental measurements, the full-field optical technique known as electronic speckle pattern interferometry (ESPI) is used to measure the transverse (out-of-plane) and planar (in-plane) resonant frequencies and corresponding mode shapes for piezoelectric bimorphs. In addition, in-plane resonant frequencies are obtained from impedance analysis and the response curves of the frequency spectra show different vibration characteristics of the piezoelectric bimorphs with different electrical connections. Piezoelectric bimorphs with normal connections have three-dimensional coupled vibration characteristics and the out-of-plane vibration dominates the motion. However, only in-plane vibration motions can be excited in the high-frequency range for abnormal connections, and the resonant characteristics are similar to the single-layered piezoelectric plate. The triple-layered piezoelectric bimorphs with abnormal connection are also analyzed using theoretical analysis. The resonant frequencies, mode shapes, and normalized displacements are calculated based on the analytical solution. The experimental results and the theoretical analysis are in good agreement with the numerical calculations using the finite element method. From the discussion of the results for the parallel- and series-type piezoelectric bimorphs with normal and abnormal connections, the vibration characteristics at high frequencies are completely analyzed in this study.     

Experimental measurement and numerical analysis on resonant characteristics of cantilever plates for piezoceramic bimorphs

Three experimental techniques are used in this study to access the resonant characteristics of piezoceramic bimorphs in parallel and series connections. These experimental methods, including the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI), laser Doppler vibrometer-dynamic signal analyzer (LDV-DSA), and impedance analysis, are based on the measurement of full-field displacement, point-wise displacement, and electric impedance, respectively. Because the clear fringe patterns will be shown only at resonant frequencies, both the resonant frequencies and the corresponding vibration mode shapes are successfully obtained at the same time by the AF-ESPI method. LDV-DSA is used to determine the resonant frequencies of the vibration mode for out-of-plane motion. The impedance analysis is used to measure the resonant and antiresonant frequencies for in-plane motion. Although the out-of-plane mode is the dominant motion of piezoceramic bimorphs, it is found in this study that the amount of displacement for the in-plane motion in parallel connection is large enough to be measured by AF-ESPI and impedance. It is interesting to note that resonant frequencies of the specimen in parallel connection for the out-of-plane motion determined by LDV-DSA are the same as that for the in-plane motion obtained by impedance. Furthermore, both in-plane and out-of-plane mode shapes for the specimen in parallel connection are obtained in the same resonant frequency from the AF-ESPI method. It is concluded in this study that the particle motions of piezoceramic bimorphs for parallel connection in resonance are essentially three-dimensional. However, it is found that only out-of-plane vibration modes can be excited for the specimen in series connection. Numerical computations based on the finite-element method are presented, and the theoretical predicted results are compared with the experimental measurements. Good agreements between the experimental measured data and numerical calculated results are found for resonant frequencies and mode shapes of the piezoceramic bimorph.     

Adjusting the resonant frequency of a PVDF bimorph power harvester through a corrugation-shaped harvesting structure

We propose a corrugated polyvinylidene fluoride (PVDF) bimorph power harvester with the harvesting structure fixed at the two edges in the corrugation direction and free at the other edges. The resonant frequency of a corrugated PVDF bimorph is readily adjusted through changing either its geometrical configuration or the span length, which can keep the harvester operating at the optimal state in environments with different ambient vibrations. The governing equations of a PVDF bimorph with a corrugation shape are derived from the transfer-matrix technique. Statistical results show that the adaptability of a harvester to the operating environment can be improved greatly by designing the harvesting structure with adjustable resonant frequency.     

Sources and implications of resonant mode splitting in silicon nanowire devices

This work investigates the effects of asymmetric cross-sectional geometry on the resonant response of silicon nanowires. The work demonstrates that dimensional variances of less than 2% qualitatively alter a nanosystem's near-resonant response, yielding a non-Lorentzian frequency response structure, which is a direct consequence of resonant mode splitting. Experimental results show that this effect is independent of device boundary conditions, and can be easily modeled using continuous beam theory. Proper understanding of this phenomenon is believed to be essential in the characterization of the dynamic response of resonant nanowire systems, and thus the predictive design of such devices.     

Performance improvement of rectangular-plate linear ultrasonic motors using dual-frequency drive

To improve the performances of a rectangular-plate linear ultrasonic motor for specific applications, a dual-frequency drive has been proposed and investigated. Through careful design of the rectangular piezoelectric ceramic plate, its first longitudinal resonant frequency coincides with its second lateral bending resonant frequency and is one-third of its higher lateral bending resonant frequency. When a square-wave voltage is used to drive the motor, its first longitudinal and second bending and the higher bending vibration modes are excited. Experimental results show that the maximum thrust force and maximum velocity of the motor are over 170% of those obtained from the single-frequency sine-wave drive when the voltage performance of the motor becomes saturated.     

The piezoelectric properties and the stability of the resonant frequency in Mn–Cr Co-doped PSZT ceramics

Changes of microstructure and piezoelectric properties by Mn-doping, Cr-doping, and Mn–Cr co-doping were investigated in (Pb_0.9Sr_1.0)(Zr_0.5Ti_0.5)O₃ (PSZT) ceramics. Temperature stability and ageing characteristics of a resonant frequency were also studied in Mn-doped, Cr-doped, and Mn–Cr co-doped PSZT ceramics. Both Mn-doping and Mn–Cr co-doping decreased average grain size and both Cr-doping and Mn–Cr co-doping made the piezoelectric properties hard. Mn–Cr co-doped PSZT ceramics had a similar microstructure and temperature dependence of the resonant frequency to Mn-doped ones, but similar piezoelectric properties and ageing characteristics of the resonant frequency to Cr-doped ones. The changes of the resonant frequency with temperature and with ageing time in PSZT ceramics resulted from different origins. The ageing characteristic of the resonant frequency is closely related to an acceptor doping effect.