Interferometric measurement of femtosecond optical pulses emitted from a fibre probe

An interferometric technique is applied to a temporal analysis of the far-field radiation from a near-field optical fibre probe. A balanced homodyne scheme combined with lock-in detection at dual harmonics allows one to evaluate the temporal form of weak signal pulses, even in the presence of some environmental vibrations that disturb the optical interference. The transmission properties of a small aperture are formulated theoretically. It is shown that the sub-wavelength aperture should not distort the femtosecond optical pulses temporally, which is consistent with the experimental observation.     

Interferometric measurement of femtosecond optical pulses emitted from a fibre probe

An interferometric technique is applied to a temporal analysis of the far-field radiation from a near-field optical fibre probe. A balanced homodyne scheme combined with lock-in detection at dual harmonics allows one to evaluate the temporal form of weak signal pulses, even in the presence of some environmental vibrations that disturb the optical interference. The transmission properties of a small aperture are formulated theoretically. It is shown that the sub-wavelength aperture should not distort the femtosecond optical pulses temporally, which is consistent with the experimental observation.     

Modeling of acoustic-emission processes in a solid

On the basis of a model for describing the processes of acoustic emission (AE) and the relationships following from it and relating the AE parameters to the structural and physical characteristics of a solid subjected to damage, AE processes are mathematically simulated. It is shown that the morphology of the AE amplitude-frequency spectrum is determined by both the crack-size distribution function and the dependences of the displacement amplitude of interphase surfaces and the difference of elastic stresses on the surfaces of radiating cracks on their effective radius.     

An electromagnetic model of a piezoelectric transducer

A one-dimensional electromechanical model of a piezoelectric transducer, which reproduces excitation of ultrasonic pulses in a product, reception of echo signals, and calculation of waves in all its elements (damper, protector, piezoelectric element, contact-liquid layer, etc.), is considered. The results of calculations of electric and wave processes in a normal ultrasonic transducer, when it operates jointly with a generator of probing pulses, are presented. Good agreement between the calculation and experimental results is demonstrated.     

The influence of temperature on the characteristics of piezoelectric transducers and errors of localization of acoustic-emission signals

The experimental dependences of changes in the output signals of standard and high-temperature acoustic-emission transducers (AETs) during heating and cooling are considered. It is shown that high-temperature AETs have a hysteresis that must be taken into account in high-temperature tests of various materials. The errors in localizing acoustic-emission signals from a simulator during heating and cooling of high-temperature and standard AETs are analyzed using the two-interval method.     

Comparison of acoustic-emission tomography images to an etalon

Criteria for comparing images of acoustic-emission tomography to an etalon via numerical simulation are tested. The results of approbation of metric and correlation criteria for comparing images and the signal-to-noise ratio for 3D inhomogeneities of sinusoidal and gaussoid types are presented. The pixel-by-pixel absolute and relative differences between images are efficient for obtaining the spatial distribution of differences between images and are quite sensitive to the inhomogeneity parameters and the data-collection and tomographic-reconstruction schemes. The comparison of the reconstructed images to a gaussoid-type etalon has shown that the image-correlation coefficient and the signal-to-noise ratio are quite sensitive to the inhomogeneity parameters and the data-collection and tomographic-reconstruction schemes. The integral metric criteria (the mean absolute and rms deviations) are almost insensitive to these parameters. The comparison of the reconstructed images to a sinusoidal etalon characterized by a large constant component has shown that the metric criteria and the centered-data correlation coefficient are sensitive to changes in the inhomogeneity parameters and the data-collection and tomographic-reconstruction schemes.     

The influence of the coordinate errors of setting sensors of a piezoelectric antenna on the accuracy of localizing sources of acoustic-emission signals

The main factors that affect the error of determining the coordinates of an acoustic-emission (AE) signal source are considered. The influence of errors of determining coordinates ±Δx _i and ±Δy _i of piezoelectric-antenna transducers on the AE-signal localization accuracy are analyzed. It is theoretically and experimentally proven that the errors in the coordinates of the transducers substantially influence the AE-signal localization accuracy, especially at a low sampling frequency of the analog-to-digital converter of the AE system’s measuring channel and when low-frequency AE transducers are used.     

Dependence of the number of acoustic-emission pulses on the mechanical testing load of bearing races in an axle unit

Acoustic-emission tests of flawless bearing races in axle units are performed on a special loading stand. Dependences of the number of AE pulses on the loading force are established for objects with and without flaws. The spatial distribution of AE sources in the flawless bearing races and a change in activity during reloading of the races are studied. Numerical parameters of the local-dynamic rejection criterion are determined on the basis of the analysis of the experimental data on races containing fatigue cracks.     

Pressure response and droplet ejection of a piezoelectric inkjet printhead

The present study aims to investigate the pressure rise in the ink flow channel and the ink droplet formation process of a piezoelectric printhead after an electrical pulse is applied to the printhead. The ink flow channel is modeled as a straight circular pipe followed by a convergent nozzle. Both numerical analysis and experimental observations are performed in this study. In the numerical analysis, a characteristic method is used to solve the one-dimensional wave equation to obtain the transient pressure and velocity variations in the flow channel of the printhead. In this analysis, the channel is assumed to have a non-uniform cross section. In addition, a flow visualization system was set up to observe the ink droplet injection process. After the piezoelectric material is driven by the input electric pulse, the ink droplet images are immediately captured by a charge-couple device (CCD) camera converted to a digital image via a frame grabber, and stored in a computer. The results obtained from the experimental observations are also compared with the numerical prediction. The effects of electric pulse shape and voltage on the ink injection length and the ejected droplet weight are also presented.     

Ultrasonic response of a piezoelectric aluminum nitride film deposited on silicon

An aluminum nitride (AlN) thick film for ultrasonic transduction was deposited on a silicon wafer by magnetron sputtering. A columnar structure with uniform elemental depth profiles with 40 at.% to 60 at.% (Al-N) concentrations and with a c-axis preferential orientation was observed by X-ray diffraction. The ultrasonic response of the Al/AlN/Si overmoded resonator was characterized from 1.24 MHz to 2 GHz using a vector network analyzer. The time domain transform and the gate features of the vector network analyzer were used to characterize the AlN thick film capabilities in the time and frequency domains. The results show that the obtained resonator operates over a broad frequency range with a central frequency at approximately 930 MHz and a 738 MHz bandwidth at -6 dB. The results were compared with those obtained from a one-dimensional simulation to highlight and predict the AlN response features. A comparison was performed to validate the experimental measurements and to validate the circuit modeling. Overall agreement between the experiment values and the simulation was observed.     

Ultra-precise tracking control of piezoelectric actuators via a fuzzy hysteresis model

In this paper, a novel Takagi-Sugeno (T-S) fuzzy system based model is proposed for hysteresis in piezoelectric actuators. The antecedent and consequent structures of the fuzzy hysteresis model (FHM) can be, respectively, identified on-line through uniform partition approach and recursive least squares (RLS) algorithm. With respect to controller design, the inverse of FHM is used to develop a feedforward controller to cancel out the hysteresis effect. Then a hybrid controller is designed for high-performance tracking. It combines the feedforward controller with a proportional integral differential (PID) controller favourable for stabilization and disturbance compensation. To achieve nanometer-scale tracking precision, the enhanced adaptive hybrid controller is further developed. It uses real-time input and output data to update FHM, thus changing the feedforward controller to suit the on-site hysteresis character of the piezoelectric actuator. Finally, as to 3 cases of 50 Hz sinusoidal, multiple frequency sinusoidal and 50 Hz triangular trajectories tracking, experimental results demonstrate the efficiency of the proposed controllers. Especially, being only 0.35% of the maximum desired displacement, the maximum error of 50 Hz sinusoidal tracking is greatly reduced to 5.8 nm, which clearly shows the ultra-precise nanometer-scale tracking performance of the developed adaptive hybrid controller.     

Estimating the strength of welded hull elements of a submersible based on the micromechanical model of temporal dependences of acoustic-emission parameters

A nondestructive technique for evaluating the strength of hull elements of submersibles is described. The technique is based on the micromechanical model of temporal dependences of the parameters of acoustic emission that is registered under an original novel technique of loading of a cylindrical hull section. The technique is also suitable for assessing the information value of resource-related acoustic-emission diagnostic indicators.     

Influence of the size of a normal probe’s piezoelectric plate on the amplitude of a detected echo signal

A computer model for operation of ΠPиз-д11 Π111-2.5-K12-002, Π111-2.5-K20-002) normal probes combined with a Yд2-12 flaw detector was used to consider the effect of the size (radius) of a piezoelectric plate on the amplitude of a detected echo signal. It is shown that the amplitude variation is mainly related to the acoustic part of the electroacoustic channel (a function of signal damping during wave propagation to and from a flaw).     

Dynamic response of an anti-plane shear crack in a functionally graded piezoelectric strip

The dynamic response of a cracked functionally graded piezoelectric material (FGPM) under transient anti-plane shear mechanical and in-plane electrical loads is investigated in the present paper. It is assumed that the electroelastic material properties of the FGPM vary smoothly in the form of an exponential function along the thickness of the strip. The analysis is conducted on the basis of the unified (or natural) crack boundary condition which is related to the ellipsoidal crack parameters. By using the Laplace and Fourier transforms, the problem is reduced to the solutions of Fredholm integral equations of the second kind. Numerical results for the stress intensity factor and crack sliding displacement are presented to show the influences of the elliptic crack parameters, the electric field, FGPM gradation, crack length, and electromechanical coupling coefficient.     

Real-time inverse hysteresis compensation of piezoelectric actuators with a modified Prandtl-Ishlinskii model

This paper presents a novel real-time inverse hysteresis compensation method for piezoelectric actuators exhibiting asymmetric hysteresis effect. The proposed method directly utilizes a modified Prandtl-Ishlinskii hysteresis model to characterize the inverse hysteresis effect of piezoelectric actuators. The hysteresis model is then cascaded in the feedforward path for hysteresis cancellation. It avoids the complex and difficult mathematical procedure for constructing an inversion of the hysteresis model. For the purpose of validation, an experimental platform is established. To identify the model parameters, an adaptive particle swarm optimization algorithm is adopted. Based on the identified model parameters, a real-time feedforward controller is implemented for fast hysteresis compensation. Finally, tests are conducted with various kinds of trajectories. The experimental results show that the tracking errors caused by the hysteresis effect are reduced by about 90%, which clearly demonstrates the effectiveness of the proposed inverse compensation method with the modified Prandtl-Ishlinskii model.     

QUASAR-370G hybrid vacuum photodetector response to Cherenkov radiation pulses in air

The response of a QUASAR-370G hybrid vacuum photodetector to a Cherenkov radiation pulse in air has been investigated. It is shown that, when the photocathode is wholly illuminated by a Cherenkov radiation pulse with a single-photoelectron intensity and a subnanosecond duration, the time resolution of the photodetector is ??1 ns. In this case, its detection efficiency for Cherenkov radiation is ??7%.     

A holographic technique for recording acoustic-emission signals due to deformation of solids

A promising technique for recording elastic stress waves due to deformation in solids based on the analysis of optical wave fronts using reference reflection Fourier holograms is discussed.     

悬臂梁式压电发电结构理论模型及其仿真研究

为提高压电悬臂梁发电能力以及将压电发电技术应用到日常生活中,开展了压电振动理论分析,建立了压电装置的发电能力与压电材料的厚度比、长度以及悬臂梁的材料、长度等之间的关系,提出了数学建模的分析方法,在理论上对压电悬臂梁的发电能力进行了评价,并进行了Matlab仿真实验.其结果表明:悬臂梁压电发电模型中,压电材料存在最佳厚度...