Optimal rate for continuous phase modulation in standing surface acoustic waves

Journal of Mechanical Science and Technology - Acoustofluidics, which combines microfluidics and acoustics, has been actively studied in order to manipulate micro-sized particles, cells and...     

A pulse ultrasonic gauge for measuring velocities of surface acoustic waves

A pulse broadband gauge designed for measurements of the velocities of surface acoustic waves is described. The gauge’s output signal is formed during mechanical translation of focused ultrasonic transducers relative to a specimen under study placed in an immersion liquid. A design of the device with line-focused lensless ultrasonic transducers for the frequency range 2–25 MHz is considered. The results of measurements of test samples are presented, and the algorithms for processing the output spatial-temporal signals for determining the frequency dependences of phase velocities of acoustic waves are described. Using a carbon steel sample as an example, it is shown that the random error component in acoustic-wave velocity measurements can be estimated as ±(2–8) and ±(1–3) m/s for longitudinal and lateral scanning modes, respectively.     

Prospects of using a sensor operating on surface acoustic waves for leak hunting

A brief review of leak hunting methods is presented as well as some estimates of sensitivity thresholds and other properties for different methods. It is shown that gas-analysis methods are of particular interest due to their high sensitivity and universality. The main problematic properties of these methods such as, mainly, their bulkiness and instantaneous nature of testing are formulated. Taking the above into account, the use of solid-state sensors is justified in designing gas-analysis leak-hunting systems, including systems that operate alongside technological equipment and use fumes of working substances inside the equipment as tracer leak-hunting gases. A sensor operating on surface acoustic waves (SAW-sensor) is considered as one of the most promising sensors.     

Love-type surface acoustic waves in a material with a heterogeneous layer

Results of theoretical studies of Love-type horizontally polarized surface acoustic waves in a material with near-surface heterogeneities are reviewed. It is shown that the possibilities of applying most results are limited because of the preset type of the functional dependence of mechanical parameters on the depth of the heterogeneous layer or on the high-frequency range. A technique and results of spectrum calculation on the basis of the proposed approach without specification of a particular kind of heterogeneities are presented, and the conditions for existence and the frequencies of Love-type waves in the long- and short-wavelength regions are determined.     

Beam distortion detection and deflectometry measurements of gigahertz surface acoustic waves

Gigahertz acoustic waves propagating on the surface of a metal halfspace are detected using different all-optical detection schemes, namely, deflectometry and beam distortion detection techniques. Both techniques are implemented by slightly modifying a conventional reflectometric setup. They are then based on the measurement of the reflectivity change but unlike reflectometric measurements, they give access to the sample surface displacement. A semi-analytical model, taking into account optical, thermal, and mechanical processes responsible for acoustic waves generation, allows analyzing the physical content of the detected waveforms.     

Measuring permeability of porous materials at low frequency range via acoustic transmitted waves

An acoustical transmission method is proposed for measuring permeability of porous materials having rigid frame. Permeability is one of the several parameters required by acoustical theory to characterize porous materials such as plastic foams and fibrous or granular materials. The proposed method is based on a temporal model of the direct and inverse scattering problem for the diffusion of transient low frequency waves in a homogeneous isotropic slab of porous material having a rigid frame. This time domain model of wave propagation was initially introduced by the authors [Z.E.A Fellah and C. Depollier, J. Acoust. Soc. Am. 107, 683 (2000)]. The viscous losses of the medium are described by the model devised by Johnson et al. [J. Fluid. Mech. 176, 379 (1987)]. Reflection and transmission scattering operators for a slab of porous material are derived from the responses of the medium to an incident acoustic pulse. The permeability is determined from the expressions of these operators. Experimental and numerical validation results of this method are presented. This method has the advantage of being simple, rapid, and efficient.     

Interaction of travelling shock waves with orifices inside ducts

When a shock wave moves down in a duct and reaches an orifice plate located inside it, reflected and transmitted shocks appear. A theoretical model to estimate such effects has been outlined, and experiments have been carried out measuring pressures upstream and downstream of the orifice. The experimental results obtained agree fairly well with the theoretical ones. Some anomalous phenomena have been observed, probably due to unsteady boundary layer growth or time lag in the establishment of steady-flow conditions through the orifice.     

一种基于基波分离算法的变频介质损耗测量仪

基于市场上对全自动、数字式及有较强抗干扰能力为特征的介质损耗测量仪的迫切需要,在基波相位分离算法基础上,采用45 Hz和55 Hz两种频率的变频电源避开工频干扰,用这两种频率各测量5次,将所有测量值的平均值作为被测试品的介质损耗角正切值,并给出了以dsPIC30F4013为核心的该测量仪器的实现方案。试验结果表明,这种介质损耗测量仪具有运算速度快、测量精度高、抗干扰能力强等特点,具有广阔的应用前景。     

桥式起重机的新型运行机构

大型桥式起重机的分别驱动运行机构常布置在箱形主染内部，为此要求它外形尺寸小，重量轻，并昼减少因主染变形引起的传动部件变位，延长零部件的使用寿命，本文介绍的新型运行机构可以基本满足这些要求，特别是由于采用了涡流制动器调速系统，更加改善了运行机构的运行特性。     

Interaction of acoustic surface waves induced by inter-digital transducer with wall thinning defect in pipe structure

Most structural health monitoring (SHM) systems require transducers permanently attached to or integrated with the monitored structure to form a type of smart structure. It is difficult to permanently attach traditional ultrasonic transducers for non-destructive testing of structures for health monitoring. However, inter-digital transducers (IDTs) can be considered for on-site SHM because of the small size and economic efficiency of the IDT sensor. In this paper, an alternative sensor approach is proposed using IDT rather than conventional transducers to identify the interaction of surface acoustic waves (SAWs) with a wall-thinning defect. The SAWs generated by IDT sensors are modeled using the finite element analysis method. Acoustic wave propagation behavior in plate and pipe structures was reviewed, and the effect of the curvature of curved plate was investigated. From the interaction behavior observed between SAWs and a wallthinning defect in the pipe, which was determined using numerical simulation and tests, a novel concept is proposed for characterizing wall-thinning defects in pipelines.     

The effect of temperature and applied stresses on electromagnetic-acoustic transformation of surface acoustic waves in ferromagnetic materials

It has been experimentally found that, if an electromagnetic-acoustic transformation (EMAT) is applied to surface acoustic waves (SAWs) in ferromagnetic materials, a combination of temperature and applied stresses can cause either an increase or a decrease in the amplitude of a detected signal. This depends on the SAW type. Applied stresses can be tested by the EMAT SAW method by the amplitude of the detected signal at a fixed magnetic shift field (in this case, it is necessary to take the temperature into account) or by the bias of the maximum of the field characteristic of the EMAT disregarding the temperature.     

Device for microparticle array preparation

A simple device is described for preparing arrays of microballoons to be characterized by radiography for use as laser fusion fuel containers.     

High frequency pressure oscillator for microcryocoolers

Microminiature pulse tube cryocoolers should operate at a frequency of an order higher than the conventional macro ones because the pulse tube cryocooler operating frequency scales inversely with the square of the pulse tube diameter. In this paper, the design and experiments of a high frequency pressure oscillator is presented with the aim to power a micropulse tube cryocooler operating between 300 and 80 K, delivering a cooling power of 10 mW. Piezoelectric actuators operate efficiently at high frequencies and have high power density making them good candidates as drivers for high frequency pressure oscillator. The pressure oscillator described in this work consists of a membrane driven by a piezoelectric actuator. A pressure ratio of about 1.11 was achieved with a filling pressure of 2.5 MPa and compression volume of about 22.6 mm(3) when operating the actuator with a peak-to-peak sinusoidal voltage of 100 V at a frequency of 1 kHz. The electrical power input was 2.73 W. The high pressure ratio and low electrical input power at high frequencies would herald development of microminiature cryocoolers.     

表面弹性波OPCM传感器的标定

标定了一种被称为正交异性压电复合材料(OPCM)的声发射(AE)传感器.利用断铅信号作为声源,SR-15型AE传感器作为标准传感器,以比较法研究了OPCM的脉冲响应.在玻璃纤维板上重点研究了OPCM的正交异性特性--陶瓷项数量的影响及响应规律的描述.实验结果表明,该传感器适于探测表面弹性波,陶瓷项数达到30,正交异性显著,能够很好地减小噪声、边界回弹波等信号对诊断信号的干扰,有助于板类结构健康监测.     

The frequency range chosen for tightness testing via the acoustic technique

In accordance with the structural and design features of ships and vessels being built, their hulls include solid (welded) and detachable (rubber seal) field joints. The data on welded joints [1] have confirmed that the amount of through microflaws in the form of pores is 88%, while the remainder of the flaws are cracks and fault fusions.     

Measurement of the plasma potential with ion acoustic waves

Plasma potentials are determined from the bias of a Langmuir probe at which the ac probe current due to an externally excited ion wave vanishes.     

A cohesive surface separation potential

This paper presents a form of the cohesive surface separation potential, which can produce potential curves by varying a single dimensionless parameter. Results show that a partial modification of Xu and Needleman’s (1994) cohesive surface separation potential makes it possible to present the other potential curves as a special case as long as the normal separation is concerned. The proposed potential may describe interfacial debonding-crack initiation and growth-character of materials and, through numerical simulation, provide an insight for the effect of different cohesive surface separation potentials on the interfacial debonding.     

A simple approach for bioactive surface calibration using evanescent waves

When investigating the interaction of cells with surfaces, it is becoming increasingly important to perform quantitative measurements of surface protein density to understand reaction kinetics. Previously, to calibrate a surface for an experiment one would have to use a radiometric assay or strip the surface with acid and perform a mass quantification. Although both of these methodologies have been proven to be effective measurement techniques for surface quantification, they can be time consuming and require substantial amounts of material. The latter is particularly problematic when working with specialized molecules or constructs that may be expensive to produce and/or only available in small quantities. Here we present a simple method to measure the intensity and penetration depth of an evanescent wave, and use this information to quantify the density of surface molecules in a microscopic region of a transparent surface.     

A method for measuring small-amplitude waves on a water surface

A device for measuring the water level using a resistive sensor is described. The measurement accuracy is ±0.01 mm. The characteristics of the device and the example of its use for measuring waves on a water surface are presented.     

轮轨滚动接触高频振动的研究

利用有限元原理,研究由轨道不平滑而引起的铁路轮轨接触的高频振动。应用ANSYS软件对结构进行有限元分析,确定轮对模态和固有频率,计算轮对在随机谱激励下的响应。