Schlieren ultrasonic visualization of delaminations in composite materials

The application of Schlieren ultrasonic techniques to the visualization of delaminations in composite materials is described and discussed. It is shown that this technique can provide an efficient, practical, non-destructive testing method.     

Application of magneto-optical method for real-time visualization of eddy currents with high spatial resolution for nondestructive testing

In this paper we describe a new, laser supported, eddy current microscope for the real-time visualization of eddy current distributions. In the experimental set-up, the induction of eddy currents is conventionally performed by an alternating current excitation coil above the object surface. The magnetic field induced by the eddy currents is detected by the use of the Faraday effect. For that purpose, a laser beam is passed through a suitable thin crystal integrated in the excitation coil. The polarization direction of the laser beam is rotated in this thin crystal depending on the local magnetic field. The area distribution of the rotation angle is transformed into a grey value picture using an optical set-up, which comprises a conventional microscope, a lighting technique, an analyzator, and a CCD sensor. By choosing a suitable optic, a real-time measurement of the magnetic field with a high spatial resolution can be carried out. In this paper, the basic physics and the design of the new microscope are described. The initial results of experimental investigations concerning the resolution power of magneto-optic eddy current sensors are presented and compared with conventional eddy current sensors.     

A high resolution ultrasonic microscope

The construction and imaging capabilities of a scanning high resolution ultrasonic microscope are considered in this paper. Theoretical expressions for the resolution limits of the microscope and some of the most important properties of the ultrasonic lenses are given. Ultrasonic through-transmission and back-scattering images of different objects are presented and a quasi-three-dimensional display mode is introduced. A resolution of about 4 μm is demonstrated at 300 MHz by the present ultrasonic microscope.     

Observing ultrasonic wave propagation by stroboscopic visualization methods

The generation of various wave modes by single element devices working in the range 2 MHz to 5 MHz is illustrated and the unwanted production of spurious wave modes identified. A linear four-element phased array is described with which beam steering can be clearly demonstrated. The mode conversion of waves which can occur during reflection at component boundaries, and the interaction of compressional waves with slots and internal defects of various shapes are displayed. The diffraction of compressional waves around an obstacle has been given particular attention, both in a solid and in water by the complementary schlieren technique. The results suggest that the transparent solid effects are very much more complicated than had been anticipated. The future value of these comparisons is briefly discussed in relation to the immersion and direct contact methods of material inspection.     

Operating mode of high pressure straws with high spatial resolution

The article presents results of studying the operating mode of thin-walled drift tubes (straws) at flushing it with a high-pressure gas mixture, which allowed obtaining extremely high spatial resolution for straw detectors. The results of studying the radiation ageing of straws operating in this mode are also described.     

Schlieren成像和声场可视化

Schlieren技术是利用声场引起透明媒质光折射率的变化而实现声场可视化的光学成像技术。它具有对声场无干扰、快速、瞬态成像的特点。本文利用二维光学Fourier变换分析了Schlieren技术的成像原理,在采用连续激光和高速ICCD的Schlieren成像系统中,实验研究了平面波声场和线聚焦声场中换能器光学校准方法和声压的定量检测技术。发展声场瞬态和动态成像技术,观测了声波的聚焦过程和固-液界面的声场分布和变化。这些结果表明Schlieren技术是一种有效的声场可视化和定量检测的光学成像技术。     

The miniature light-field camera with high spatial resolution

Optical Review - A light-field camera is an optical system that provides multi-field-angle information in one shot. The microlens array (MLA) in a light-field camera system is the key to provide...     

In-duct identification of fluid-borne source with high spatial resolution

Source identification of acoustic characteristics of in-duct fluid machinery is required for coping with the fluid-borne noise. By knowing the acoustic pressure and particle velocity field at the source plane in detail, the sound generation mechanism of a fluid machine can be understood. The identified spatial distribution of the strength of major radiators would be useful for the low noise design. Conventional methods for measuring the source in a wide duct have not been very helpful in investigating the source properties in detail because their spatial resolution is improper for the design purpose. In this work, an inverse method to estimate the source parameters with a high spatial resolution is studied. The theoretical formulation including the evanescent modes and near-field measurement data is given for a wide duct. After validating the proposed method to a duct excited by an acoustic driver, an experiment on a duct system driven by an air blower is conducted in the presence of flow. A convergence test for the evanescent modes is performed to find the necessary number of modes to regenerate the measured pressure field precisely. By using the converged modal amplitudes, very-close near-field pressure to the source is regenerated and compared with the measured pressure, and the maximum error was −16.3 dB. The source parameters are restored from the converged modal amplitudes. Then, the distribution of source parameters on the driver and the blower is clearly revealed with a high spatial resolution for kR<1.84 in which range only plane waves can propagate to far field in a duct. Measurement using a flush mounted sensor array is discussed, and the removal of pure radial modes in the modeling is suggested.     

Magneto-optical visualization of three spatial components of inhomogeneous stray fields

The article deals with the physical principles of magneto-optical visualization (MO) of three spatial components of inhomogeneous stray fields with the help of FeCo metal indicator films in the longitudinal Kerr effect geometry. The inhomogeneous field is created by permanent magnets. Both p- and s-polarization light is used for obtaining MO images with their subsequent summing, subtracting and digitizing. As a result, the MO images and corresponding intensity coordinate dependences reflecting the distributions of the horizontal and vertical magnetization components in pure form have been obtained. Modeling of both the magnetization distribution in the indicator film and the corresponding MO images shows that corresponding to polar sensitivity the intensity is proportional to the normal field component, which permits normal field component mapping. Corresponding to longitudinal sensitivity, the intensity of the MO images reflects the angular distribution of the planar field component. MO images have singular points in which the planar component is zero and their movement under an externally homogeneous planar field permits obtaining of additional information on the two planar components of the field under study. The intensity distribution character in the vicinity of sources and sinks (singular points) remains the same under different orientations of the light incidence plane. The change of incident plane orientation by π/2 alters the distribution pattern in the vicinity of the saddle points.     

Broad-band NMR with a high spectral and spatial resolution

Spatially selective excitation sequence CARVE (completely arbitrary regional volume excitation) excites signal from an arbitrarily shaped profile (I. Sersa, S. Macura: Magn. Reson. Med.37, 920–931, 1997) by an interleaved sequence of precalculated small tip angle radio-frequency pulses and gradient pulses. Here we propose a spatially selective observation method based on the CARVE principles which is insensitive to the relaxation and the off-resonance effects. The method, CARVED (CARVE detection), excites spins uniformly across the sample and across the spectrum but achieves spatial selectivity by weighted coaddition of the signals after the data acquisition. CARVE-D is suitable for spatially selective high-resolution nuclear magnetic resonance spectroscopy in chemically and geometrically complex systems. The method is analyzed theoretically and demonstrated experimentally on model systems.     

MR imaging of flow with locally high spatial resolution.

Locally focused magnetic resonance imaging (LF MRI) allows imaging with variable spatial resolution within the field of view (FOV). Because LF MRI uses a priori information to provide locally high resolution in regions with rapid spatial variations in intensity (e.g., blood/tissue interface), it allows accurate reproduction of intense sharp edges in the specimen without blurring and truncation artifacts. This study employs LF MRI for 3D imaging of stationary and pulsatile flow. In the implemented version of LF MRI analytically defined basis functions are used to determine image intensity in regions depicted with low or high resolution. It is demonstrated that LF MRI of flow allows a significant (i.e. 3-4 times) reduction in scan time as compared to conventional FT MRI. It is also shown that LF images of pulsatile flow have a decreased appearance of ghosting artifacts as compared to the images reconstructed by using the conventional method.     

无序高空间分辨率影像快速拼接方法

遥感影像拼接技术作为影像成图的重要手段,一直是遥感领域研究的热点。在保证拼接精度的同时,如何提高拼接效率,成为低空遥感技术应急应用的难点。针对低空航空遥感影像成像姿态变化剧烈、数据量大等特点,提出针对无序影像改进的基于稀疏矩阵的光束平差SURF拼接算法,即对无序影像进行特征选取和匹配,自行判断相邻和相间位置信息,配准平差中引入稀疏矩阵进行加速。方法在保证精度的同时,极大提高了航空相机影像拼接算法的速度,能很好地解决无人机影像高建筑物的拼接错位问题。无人机倾斜数据集拼接和航空相机影像拼接的结果验证了利用本算法进行高空间分辨率影像拼接的精度和效率。     

Schlieren visualization of micro gas turbine exhaust plume with different shapes of nozzle

Journal of Visualization - Schlieren visualization of the plume ejected from the microgas turbine nozzle was conducted to understand infrared signal characteristics of various shapes of the exhaust...     

高分辨特性压电行波旋转马达研究

本文对一种压电行波型旋转超声马达进行了理论与实验研究。采用有限元方法对行波马达驱动定子的各阶振动模式、谐振频率进行了分析;研制的行波马达具有以下特点：低转速（0－50r.p.m）、较大力矩输出（0~1.9kgf.cm）、自锁功能、高的角分辨率和定位精度（±0.15°）。     

Guided wave arrays for high resolution inspection

The paper describes a general approach for processing data from a guided wave transducer array on a plate-like structure. The raw data set from such an array contains time-domain signals from each transmitter-receiver combination. The technique is based on linear superposition of signals in the frequency domain with some amplitude and phase factors and can be applied to any array geometry and any types of array elements. The problem of finding optimal coefficients, which allow the best resolution to be achieved with the minimum number of array elements, is investigated. It is shown that improvements in resolution are obtained at the expense of sensitivity to noise. A method of quantifying this sensitivity is presented. Results are shown that illustrate the application of the technique to a linear array and an array of circular geometry (containing a single ring of elements). Experimental data obtained from a guided wave array containing electromagnetic acoustic transducer elements for exciting and detecting the S0 Lamb wave mode in a 5-mm-thick aluminum plate are processed with different algorithms and the results are discussed. Generalization of the technique for the case of multimode media is suggested.     

A traveling wave ultrasonic motor of high torque

A traveling wave ultrasonic motor of high torque with a new configuration is proposed in this paper. In the new design, a part of the motor serves as the stator. The rotor is the vibrator consisting of a toothed metal ring with piezoelectric ceramic bonded, which generates ultrasonic vibration. The rotor is in contact with the shell of motor and is driven by the friction between the rotor and the stator. This configuration not only removes the rotor in a conventional type of traveling wave ultrasonic motor but also changes the interaction between the rotor and the stator of the motor so that it improves the output performance of the motor. Although an electric brush is added to the ultrasonic motor, it is easy to be fabricated because of the low speed of motor. The finite element method was used to compute the vibration modes of an ultrasonic motor with a diameter of 100mm to optimize the design of the motor. A 9th mode was chosen as the operation mode with a resonance frequency about 25 kHz. According to the design, a prototype was fabricated. Its performance was measured. The rotation speed-torque curves for various frequencies were obtained. The result shows that its stall torque is greater than 4 Nm within a range of 400 Hz. This ultrasonic motor was used to drive the window glass of a mobile car and the result was satisfactory. In the further the research on the friction material between the stator and the rotor is under way to improve the efficiency of the ultrasonic motor.