Alternating current impedance spectroscopy measurement under high pressure

A microcircuit was designed and fabricated on a diamond anvil cell for alternating current impedance spectroscopy measurement under high pressure. Sputtered molybdenum film on a diamond anvil was used as an electrode, maintained the contact between the sample and the electrode stable, and reduced the electrode effect on the impedance measurement. By the empty cell and short circuit tests, the parasitic capacitive impedance from the sample chamber wall was observed to be larger than 10(5) Ω at a frequency lower than 1.0 MHz and could be ignored for samples with higher conductivity. The wire inductance was only 1.0 μH and just appeared at frequency higher than 20 kHz, which could be subtracted from measured impedance for the samples with higher impedance than several hundred ohms. Using this apparatus, the impedances of the II-VI group cadmium sulfide were measured. The pressure dependence of the grain interior conductance of CdS crystal was obtained, which reflected that the phase transitions of CdS under high pressure are the same as the single crystal measurement results.     

一种小型水下高速运动体的自主测速方法

针对水下高速运动体自主测速困难的问题,基于涡轮转速与运动载体速度在一定范围内的线性关系,提出一种适用于小型水下高速运动体的自主测速方法.建立了基于力矩平衡的涡轮转动黏性数学模型,给出了模型求解方法,计算并获得了理论曲线.设计制作了原理样机,在高速水洞中进行了模拟实验.结果表明:在实验段测速线性度误差为3.89％,初生空化数约为1.02,在水下1 m以下环境,测量30节(55.56 km/h)以内的速度不会发生明显空化.该方法经初步验证切实可行.     

薄膜谐振Lamb波传感器测量液体流速矢量的方法

针对液体流速测量领域中微型流量传感器高品质因数、高灵敏度的性能要求。本文设计一种双端增强型薄膜谐振结构实现Lamb波传感器的高品质因数,利用传感器反对称模式(A01模式)在薄膜-液体界面处的消逝波实现液体流速矢量测量。所制作的双端增强型薄膜谐振Lamb传感器A01模式的主峰品质因数为703,A01模式的频率移动量与液体流速大小存在线性关系,频率移动方向与液体流动方向存在对应关系。流速实测灵敏度约为270 Hz/mm/s,传感器稳定性噪声小于0.2Hz,流速最低检测极限值(LOD)为2.2μm/s,流量最低检测极限值(LOD)为18.3nL/min。结果表明,双端增强型薄膜谐振Lamb波传感器可以实现液体流速高灵敏度矢量测量。     

Combined ultrasonic elastic wave velocity and microtomography measurements at high pressures

Combined ultrasonic and microtomographic measurements were conducted for simultaneous determination of elastic property and density of noncrystalline materials at high pressures. A Paris-Edinburgh anvil cell was placed in a rotation apparatus, which enabled us to take a series of x-ray radiography images under pressure over a 180° angle range and construct accurately the three-dimensional sample volume using microtomography. In addition, ultrasonic elastic wave velocity measurements were carried out simultaneously using the pulse reflection method with a 10° Y-cut LiNbO(3) transducer attached to the end of the lower anvil. Combined ultrasonic and microtomographic measurements were carried out for SiO(2) glass up to 2.6 GPa and room temperature. A decrease in elastic wave velocities of the SiO(2) glass was observed with increasing pressure, in agreement with previous studies. The simultaneous measurements on elastic wave velocities and density allowed us to derive bulk (K(s)) and shear (G) moduli as a function of pressure. K(s) and G of the SiO(2) glass also decreased with increasing pressure. The negative pressure dependence of K(s) is stronger than that of G, and as a result the value of K(s) became similar to G at 2.0-2.6 GPa. There is no reason why we cannot apply this new technique to high temperatures as well. Hence the results demonstrate that the combined ultrasonic and microtomography technique is a powerful tool to derive advanced (accurate) P-V-K(s)-G-(T) equations of state for noncrystalline materials.     

A miniature cubic anvil apparatus for optical measurement under high pressure

A miniature cubic anvil apparatus was developed for optical measurement on materials in a high-pressure space of 8-10 mm(3) under high pressure, and preliminary experiments were conducted to 3.6 GPa at room temperature with optical visual observation and ruby fluorescence measurement. In the apparatus, a cubic pressure medium was squeezed with six tungsten carbide anvils, which are driven with a pair of guide blocks by tightening four loading screws. Optical access on the sample was made through holes in axial anvils and the guide blocks as well as optical windows made of Al(2)O(3) single crystals embedded in the pressure medium. The apparatus is compact and light, ~53 mm in diameter and height and ~530 g in weight, and the features of the apparatus benefit easy application of the apparatus to various types of standard optical measurement systems. The optical measurement on the sample in the high-pressure space of 8-10 mm(3) should greatly contribute to advancements of studies relevant to high-pressure behaviors of materials.     

超声多普勒流速测量中存储容量的压缩方法

介绍了多普勒频率单片机测量时的数据处理方法,即线性地址变换法。在存储容量有效压缩的基础上,进一步分析了采样数据,用软件实现可控时标,保证了测量精度。     

A novel method for digital ultrasonic time-of-flight measurement

Most ultrasonic ranging measurements are based on the determination of the ultrasonic time-of-flight (TOF). This paper develops a novel method for the TOF measurement which combines both the improved self-interference driving technique and the optional optimization signal processing algorithms. By stimulating the transmitter with the amplitude modulation and the phase modulation envelope square waveforms (APESWs), the proposed system can effectively reduce the errors caused by inertia delay and amplitude attenuation. In addition, based on different signal-to-noise ratio test conditions, the resultant received zero-crossing samples, which are deteriorated by noise, can be precisely inspected and calculated with two optimized algorithms named zero-crossing tracking (ZCT) and time-shifted superposition (TSS) method. The architecture of the designed system is divided into two parts. The novel APESW driving module, the received envelope zero-crossings phase detection module, and the ZCT method processing module are designed in a complex programmable logic device. The TSS signal processing module and the optimization algorithm discrimination program module are integrated in a digital signal processor. The TOF measurements calibrated in ultrasonic ranging experiments indicate that the relative errors of the method are limited in ±0.8%. Therefore, a feasible method is provided with the advantages of high noise immunity, accuracy, low cost, and ease of implementation.     

声速传感器测量结果中气压附加成分的发现

气体测量,如空气的测量是非常复杂的一项课题,涉及到诸如超声学、空气动力学、流体力学、电子学、材料学、制冷和计算机应用等多门学科.即使在线性声学条件下气体中声速的精确测量,也颇为复杂[1].本文在局部小环境下,使用超声波传感器测量声速的过程中,发现了气压变化与声速变化之间的变化规律.运用工程的方法,提出了声速一阶微分方程,解释了气压波动对声速的影响,对今后声速在气体中的精确计算与测量有一定的应用价值.这一计算公式还需要通过大量的物理实验来进一步验证.     

Fundamental uncertainty analysis of flowrate measurement using the ultrasonic Doppler velocity profile method

The present paper describes a fundamental uncertainty analysis for a flowrate measurement in a pipe using an ultrasonic Doppler velocity profile method and an evaluation of the estimated uncertainty by an actual flow calibration. The uncertainties are estimated for internal factors originating from the measurement equipment; UVP provided by Met-Flow sa. and external factors depending on on-site measurements, such as the inclination angle of the ultrasonic transducer. The relative expanded uncertainty due to internal factors is estimated to be 0.34% with a coverage factor of 2. The relative external uncertainty including external factors is estimated to be from 0.42% to 2.13% depends on the inclination angle of the transducer. The results of the actual flow calibration under the same condition as the uncertainty analysis are within the range of uncertainty considering the internal factors.     

High-accuracy differential measurement of ultrasonic velocity in liquids

An improved technique for measuring very accurately the difference in sound velocity between two liquids is described. The technique, which can be used over a frequency range from 1 to 100 MHz, uses a differential cell that is completely submerged in a thermostatically controlled fluid and a phase-sensitive detection scheme accurate to 2x10(-4) signal periods. Measurements of the velocity difference between water and dilute NaCl solutions (3x10(-5) to 6.6x10(-4) M), accurate to +/-0.02 cm s(-1) (relative accuracy 1 part in 10(7)), are presented.     

High-accuracy ultrasonic temperature measurement based on MLS-modulated continuous wave

Ultrasonic temperature measurement has the potential to improve measurement accuracy by increasing the length of a received signal due to its excellent performance with noise resistance. However, when the distance between the transmitter and receiver is limited, the received signal can be polluted by strong multiple echoes, which can significantly degrade temperature accuracy. This paper proposes a method for high-resolution ultrasonic temperature measurement. With the use of a maximum length sequence (MLS)-modulated continuous wave, the obstructive effect of echoes is effectively suppressed. A hybrid method is employed for accurate time-of-flight (TOF) estimation by incorporating both cross-correlation and phase shift (PS), which is the basis of highly accurate temperature measurement. The experimental results in distilled water show that the proposed method estimates TOF with a standard deviation of less than 0.3 ns, and temperature errors consistently remain within ±0.04 °C.     

A study of ultrasonic propagation for ultrasonic flow rate measurement

For the purpose of accurate flow measurement, an automatic three-dimensional (3D) sound field measurement system has been developed, and an experimental study has been conducted on ultrasonic properties. By using this system, ultrasonic sound pressure distributions and radiation angles in water have been measured. According to Snell’s law, the ultrasonic transmission properties can be obtained on the basis of incidence angle, acoustic impedance, basic frequency of ultrasound, and material and thickness of the metallic plate. However, this law cannot be applied to certain cases where an ultrasonic incident wave passes through a metallic plate and turns into a longitudinal wave, a shear wave and a Lamb wave. Consequently, the ultrasonic propagation paths have been investigated experimentally at various angles of incidence. From the experiments, it was confirmed that the ultrasonic beam paths change with incidence angles. Hence, the most suitable incidence angle has been determined from the result of measurements. Velocity measurements using an ultrasonic velocity profiler were made at various incidence angles. The accuracy of measuring flow rates changed with the incidence angles. The optimal incidence angle determined from 3D field measurements was found to yield the most accurate flow rates.     

A new method for heat measurement during high speed machining

The cutting temperature and temperature distribution along the rake face of cutting tool and work piece is an essential factor in study of machining processes due to its effect on surface quality, tool life, tolerances, metallurgical behavior and chip-removing rate. Several methods have been introduced to measure temperature during machining, such as the thermocouple technique, infrared camera and metallurgical methods. Each of these methods has some advantages and limitations. In this article, an infrared high-speed sensor with specially designed software has been used to measure the transferred heat to the work piece during high speed machining (HSM) of bronze alloys. The results revealed that this system enhances accuracy and reduces the number of tests required.     

An improved ultrasonic method for lubricant-film thickness measurement in cylindrical roller bearings under light radial load

Focusing on measuring the oil-film thickness with ultrasonic approaches in roller bearings, a new feasible method is proposed to improve the measuring accuracy. The spatial resolution, which has great influence on the measuring accuracy, is mainly determined by the focus size of the ultrasound transducer. Under the light load conditions, the width of the Hertz contact area is smaller than the focus size, which results in overlapping measurement regions by the high pulse-repetition frequency and then brings about large measurement errors. By introducing reflection coefficients of sound pressure in the non-overlapping areas, the new method improves the measuring accuracy successfully. The experimental results are achieved from the real-time lubricant-film thickness monitoring system for cylindrical roller bearings, which show good agreement with the theoretical solutions.     

冲击波测试系统的手持终端设计

由于冲击波测试中测试系统的工作状态难以监测、测试参数难以现场更改,而且传统测试系统大多以PC作为控制终端,在户外进行实验时存在着操作不便、不易携带的问题.为此,设计了基于RAM的新型冲击波测试系统的手持终端.利用Qt技术设计控制界面的应用程序,通过Wi-Fi无线控制测试系统,实现了测试系统的状态监测、数据的无线传输与波形显示的功能.此外,还设计了USB接口用于数据的有线读取,避免了数据丢失.手持终端在多次弹药试验得到了很好应用,具有良好的可靠性和稳定性.     

In situ Hall effect measurement on diamond anvil cell under high pressure

A method for in situ Hall effect measurement under high pressure was developed on a diamond anvil cell. The electrode was accurately integrated on one diamond anvil with regular shape. A uniform and strong magnetic field was introduced into the sample zone. The voltage errors brought by some negative effects during the measurement were well eliminated. The correction factor of the Hall coefficient, brought by the nonpoint contact between the electrode and the sample, was 4.51%. The measurement error of the magnetic field did not exceed 1%. The carrier character of ZnTe powders was studied up to 23 GPa. The evolution of conductivity with pressure was explained based on the variation of the carrier behavior.     

Surface wave velocity measurement using reflections from laser scribed grooves

The measurement of ultrasonic surface wave (USW) velocity is difficult using the pulse overlap method (POM) in the presence of an externally applied stress. Coupling variations between the sample and the transducer cause nonuniform distortions of the two received pulses which makes the overlap condition difficult to determine over an extended stress range. The adaptation in this paper of a single transducer configuration to generate and detect the USW eliminates coupling variations between two or more transducers. In addition, two parallel, precisely positioned and contoured grooves are laser scribed on the sample surface to provide the necessary overlap echoes. Since both echoes are reflected only once by identical grooves and are equally affected by the distortions due to coupling variations, the overlap condition is relatively unaffected by the external stress and the accuracy of the USW velocity measurement is increased significantly.     

A multiscale optimal filter method for micro-motion measurement with high accuracy

Micro-motion measurement plays an important role in technologies such as micro/nanomanufacturing and biomedicine. In this paper, micro-motion measurement is viewed as a signal processing problem, and the measured image gradients are estimated using the filter methods. A class of optimal filters for image gradient calculation is designed according to Parks-McClellan algorithm. In combination with multiscale approach, a multiscale optimal filter method for micro-motion measurement is proposed. In such a method, the larger motions are converted into multiple small motions to measure, thus the measurement accuracy can be further improved. The maximal bias magnitude of this proposed method reached 0.0064 pixels for the motions near 2 pixels. Experimental simulations show this proposed multiscale optimal filter method can measure the micro-motion with high accuracy.     

Simultaneous structure and elastic wave velocity measurement of SiO2 glass at high pressures and high temperatures in a Paris-Edinburgh cell

An integration of multi-angle energy-dispersive x-ray diffraction and ultrasonic elastic wave velocity measurements in a Paris-Edinburgh cell enabled us to simultaneously investigate the structures and elastic wave velocities of amorphous materials at high pressure and high temperature conditions. We report the first simultaneous structure and elastic wave velocity measurement for SiO(2) glass at pressures up to 6.8 GPa at around 500°C. The first sharp diffraction peak (FSDP) in the structure factor S(Q) evidently shifted to higher Q with increasing pressure, reflecting the shrinking of intermediate-range order, while the Si-O bond distance was almost unchanged up to 6.8 GPa. In correlation with the shift of FSDP position, compressional wave velocity (Vp) and Poisson's ratio increased markedly with increasing pressure. In contrast, shear wave velocity (Vs) changed only at pressures below 4 GPa, and then remained unchanged at ~4.0-6.8 GPa. These observations indicate a strong correlation between the intermediate range order variations and Vp or Poisson's ratio, but a complicated behavior for Vs. The result demonstrates a new capability of simultaneous measurement of structures and elastic wave velocities at high pressure and high temperature conditions to provide direct link between microscopic structure and macroscopic elastic properties of amorphous materials.     

Requirements for choosing the parameters of broadband transducers for testing objects with high damping of ultrasonic signals

The main concepts of the theory of optimal signal processing as applied to tasks of ultrasonic testing of articles with high integral damping of acoustic vibrations are considered. The conditions for ensuring the optimal transfer coefficient of the receiving section of an ultrasonic flaw detector’s electroacoustic channel are formulated. The requirements for the characteristics of broadband piezoelectric transducers aimed at the insurance of undistorted transmission of ultrasonic signals are formulated.