Measurement of diagnostic electronic linear arrays by miniature hydrophone scanning

Ultrasonic pressures, intensities and power were computed using a calibrated miniature hydrophone scanning system. To accomplish these measurements, the electronically scanned beam was stopped, and raster scans were made with the hydrophone over a number of planes perpendicular to the beam axis. Ultrasonic power also was measured using a radiation force balance, and the results compared well with those obtained using the hydrophone. Spatial average-temporal average intensities for the stopped beam ranged from 0.13 to 3.71 mW/cm(2 ) (for a -40-dB beam area), and spatial peak-temporal peak intensities varied from 8.31 to 45.2 W/cm(2). Such measurements are important in setting equipment safety standards, in encouraging minimum use of ultrasonic exposures, and in quantifying exposure levels that may result in harmful biological effects.     

Primary calibration of ultrasonic hydrophone using optical interferometry

A primary calibration method for ultrasonic hydrophones which uses a Michelson interferometer to determine the particle displacement in an ultrasonic field is discussed. The acoustic pressure is derived from this measurement and used to determine the free-field sensitivity of a hydrophone in the frequency range 0.5-15 MHz. The random uncertainty of the method is typically 1%, whereas the systematic uncertainty varies from 2.3 to 6.6% over the frequency range. To obtain this accuracy, the performance of the system has been carefully examined and appropriate correction factors derived. The greatest difficulty in the method lies in determining the frequency response of the optical detection system, and two different approaches have been used to measure this response. Several acoustical effects have also been studied and the calibration procedure modified to take account of them. The calibration results are in agreement with those of other methods and with the theoretically predicted frequency response of a hydrophone. The method has been used to determine the temporal stability of a hydrophone over a period of two years.     

Comparison of hydrophone calibration methods in the infra-to ultrasonic frequency range

An evaluation of the measurement reliability is made by a comparison of hydrophone calibration methods in the frequency range from 0.1 Hz to 63 kHz.Translated from Izmeritel'naya Tekhnika, No. 12, pp. 39–43, December, 1995.     

The metrology of a miniature FT spectrometer MOEMS device using white light scanning interference microscopy

Micro-optical electro-mechanical systems (MOEMS) technology, making use of existing silicon based fabrication techniques shows great potential for making complete miniaturized hybrid devices. Such technology has been used to make a Fourier transform spectrometer based on a time-scanning Michelson interferometer. An electrostatic comb drive actuator moves the scanning mirror over a distance of 40 μm. The measured resolution of the spectrometer is 6 nm at a wavelength of 633 nm. The dimensions of the device are 5×5×0.5 mm, and the depth of feature is 75 μm. During quality control of such devices it is necessary to check the dimensions of micron wide structures that are tens of microns deep, over areas of tens of square millimeters. In this work we have investigated the use of white light scanning interference (WLSI) microscopy for making rapid, non-destructive precision three-dimensional measurements. While a high axial precision can be achieved, an artifact has been observed with classical configurations that tend to extend the location of deep step discontinuities by up to 3 μm and so broaden narrow structures. With certain modifications in the optical configuration, this error can be considerably reduced. The results of this work demonstrate that WLSI shows great potential for the rapid and precise quality control of MOEMS devices.     

真空比对法校准装置的研究

真空比对法校准装置采用了动态直接比对法、静态直接比对法和静态膨胀法,在一台装置上复合了三种方法,满足了拓宽量程的需求.该装置可以1×105-5×10-4 Pa范围内的各类真空规进行校准,是一种结构简单、操作方便、检定效率高、实用性强的真空标准装置.整套装置由涡轮分子泵、校准容器、副标准真空计和金属膨胀阀等部件组成,主要技术指标符合国际标准化组织和国内有关真空标准的规定.     

示波器探头校准方法探讨

示波器探头不仅是将测试信号送到示波器输入端的一个分压线路 ,而且是测量系统的一个重要组成部分 ,探头的正确使用直接关系到测量结果的准确性。在实际工作中 ,常常忽略了探头的校准 ,本文介绍了一种示波器探头的校准方法     

The influence of misalignment on the uncertainty of vertical torque calibration machine

Misalignment of torque calibration machines can cause parasitic bending loads inside the torque transducers in use. These parasitic loads may affect the machine uncertainty, specially for secondary torque calibration machines. Therefore, this study discusses the contribution of misalignment to the measurement uncertainty for a newly designed 3 kNm secondary vertical torque calibration machine. Radial axes shift up to 4 mm was applied which introduce small increased uncertainty.     

Two approaches to the continuous-radiation field calibration of a hydrophone in a nonanechoic water tank

A comparative analysis is carried out of a time-delay spectrometry method and a proposed method for the sliding complex weighted averaging of the frequency dependence of the transfer impedance of a radiator and receiver, which provide different approaches to the free-field continuous-radiation calibration of hydrophones in a nonanechoic water tank. The advantages of the second method are demonstrated.     

Alignment of glycolipid nanotubes on a planar glass substrate using a two-step microextrusion technique

We have developed a two-step microextrusion technique to align lipid nanotubes of 200 nm in diameter in parallel on planar glass substrates. This technique is useful to align self-assembled molecular nanofibers or nanotubes with diameters ranging from 100 to 300 nm. In the first step, we applied relatively large air pressure (approximately 40 hPa) onto a microcapillary filled with aqueous dispersion of lipid nanotubes to push them out. An aqueous droplet with 60 microm diameter was then extruded from the tip of the microcapillary. After one end of the lipid nanotube moved out, we changed the air pressure to be smaller, approximately 20 hPa to reduce the flow rate of the dispersion. The decrease in size of the droplet allowed us to fix the exposed end of the lipid nanotube onto the planar substrate. By dragging the microcapillary along the planar surface, we were able to align the whole nanotube onto the substrate. Using this technique, we have achieved the parallel alignment of the lipid nanotubes on the glass substrate.     

机器人激光扫描式焊缝跟踪测量系统研究

提出了机器人激光扫描式焊缝跟踪系统参数的标定方法和基于数字图像处理的焊缝特征点识别方法.采用中值滤波、自适应阈值分割和孤点滤波法等对激光图像进行预处理,以数字形态学方法获得焊缝特征点坐标;然后以一组平行线为靶标,获得激光平面上无穷远处一点在摄像机中的投影,实现结构光参数的标定;最后以多个机器人位姿对固定目标点进行检测,求解出机器人的手眼矩阵.整个系统标定过程简单,精度可靠,可用于空间曲面的U型焊缝检测.     

Spatial mismatch calibration using circular carrier technique in the simultaneous phase shifting interferometry

In most simultaneous phase shifting interferometry (SPSI) systems, a group of phase shifting interferograms are captured simultaneously at the different physical locations to retrieve the phase. The data of different interferograms should be spatially matched correctly, which is hard to realize by existing methods or this spatial mismatch will lead to phase retrieving error. In this paper, a spatial mismatch calibration method is proposed, where the circular carrier is introduced in the interferograms of the SPSI system, and the modulating phases of any two interferograms can be retrieved by the demodulation technique of circular carrier interferogram. The slope of the difference between these two phases is proportional to the mismatch value, so this error can be extracted and the experiment setup calibrated. The main error sources of the proposed method are analyzed with the conclusion that its match precision can be achieved up to 0.5 pixel. In addition, the simulated interferograms and actual interferograms captured in a SPSI system are processed to validate our proposed method.     

Thermomechanical nonlinear in-plane analysis of fix-ended FGM shallow arches on nonlinear elastic foundation using two-step perturbation technique

International Journal of Mechanics and Materials in Design - An attempt is made in this research to analyse the nonlinear response of functionally graded material shallow arches with both edges...     

The influence of electrostatic fields on films of liquid helium

Prompted by the recent striking experimental results reported by Babkin and Hakonen that appeared to show that liquid helium-II does not wet magnesium fluoride, we have examined the effects that an inhomogeneous electrostatic field has on thin films of liquid helium at temperatures below 0.5K. Our model includes the influence of gravity, surface tension, the electric field and the van der Waals interaction between the helium and its supporting substrate. We show that, an inhomogeneous charge on the substrate can produce effects that mimic the surface profiles between wetted and non-wetted areas. The calculations also indicate that some special precautions may be necessary when studying films of liquid or solid helium on insulators.     

The influence of high temperatures on calibration of non-destructive testing of concrete

The intention of this experimental work is to investigate the influence of elevated temperatures of short duration (usually during fires in buildings) on the properties of concrete that affect the measurements by non-destructive methods (rebound hammer and pulse velocity). Relationships between strength of concrete as well as rebound and pulse velocity versus heating temperatures are established. Finally, the above results are evaluated to find the direct relation between non-destructive measurements and strength of concrete exposed to fire.     

全自动生化分析仪校准方法初探

全自动生化分析仪由于灵敏度高,自动化程度好,速度快等优点,已成为生化分析中广泛使用的仪器之一。但该仪器在国内尚无任何通行的校准方法。该文提出了全自动生化分析仪的校准方法,供大家探讨。     

The influence of electrodes on the strength of planar zirconia solid oxide fuel cells

The strength of symmetric anode/electrolyte/anode and cathode/electrolyte/cathode planar multiple electrode assemblies (MEAs), fabricated by screen printing electrodes onto pre-fired tape-cast electrolyte plates was measured in biaxial flexure. The electrolyte was Zr_0.84Y_0.16O_1.92 (YSZ), the anode NiO/YSZ and the cathode La_0.75Sr_0.2MnO_3–. The residual stress in the electrodes was estimated by curvature measurement after removal of one electrode. The residual stress in the anodes was very low (11 MPa) due to stress relief by extensive channel cracking. The residual stress in the cathodes was much higher (39 MPa) and was in reasonable agreement with the expected thermoelastic stress. The applied load at failure, and the stress in the electrolyte at failure (343 MPa), for anode MEAs were almost equal to those of electrolyte plates (374 MPa). This is consistent with the low residual stress and observed crack deflection by delamination at the anode/electrolyte interface. The applied load at failure, and the stress in the electrolyte at failure (182 MPa), for cathode MEAs were much lower. This is partially explained by the residual stress in the cathode acting to increase the applied stress intensity at defects in the electrolyte, but this effect is not large enough to explain fully the reduced strength.     

颅脑CT扫描技术方法的改进

本文阐述了在颅脑计算机断层射线摄影的扫描过程中,改变扫描层平面距离的情况,即把该距离由10mm增加为11mm,从而形成一个宽1mm的未扫描空间。作者认为,由于一般的CT设备空间解像力低,形成的像素尺寸为1.0×1.0mm,因此,这些未扫描区不会影响诊断。