Application of induction transducers for measuring displacements at high temperatures

Conclusions The above transducer can be used as a basis for designing an instrument for automatic checking and control of the starting and operating of powerful steam turbines. The temperature-compensated transducer can also be used for remote contactless measurements of clearances in other machines which operate at high temperatures. The above method of temperature compensation can be used for induction transducer measurements of other quantities. There exists the possibility of increasing the temperature operating range of the transducer. However, for this purpose it may be necessary to use magnetic materials with higher Curie points, for instance, cobalt.     

An inverse analysis of warpage for trilayer thin-plate under thermal cycles

Thermal–mechanical behavior of a trilayer plate with micro-scale layer thicknesses is investigated using the hybrid experimental analytical inverse method (HEAIM). This study adopts and modifies an existing analytical solution by Suhir to evaluate the warpage of trilayer structures consisting of a mid-layer comparable in thickness and mechanical properties to other layers under thermal cycles. A phase-shifted shadow moiré is employed to obtain accurate measurements of the plate thermal warpage during a thermal cycle. The measurements are then inversely analyzed following a numerical approach that finally determines those uncertain material parameters of the thermal and mechanical properties for the layered plates. If all the material parameters are known, the behavior of the trilayer structure can be further evaluated analytically with enhanced certainty. HEAIM was employed to characterize and evaluate the thermal and constitutive behavior of substrate trilayer structure and its constituent materials under a thermal cycle. The proposed method can provide pertinent guidance to the modeling and design of complex trilayer structures.     

A self-sensing nanomechanical resonator built on a single-walled carbon nanotube

We present observations of resonance behavior in a torsional nanoelectromechanical device built with an individual single-walled carbon nanotube. The effect of applied torsional strain on the transport properties of the nanotube provides an electrical signal transducer and hence a means of measuring oscillation amplitude, resonance frequency, and quality factor. The mechanical resonance is confirmed by imaging and the electromechanical signal is compared to quasi-static measurements.     

Method of determining the relative sensitivity of thermal vacuum gages to different gases

A new method is described for determining the relative sensitivity of thermal vacuum gages and their sensors (tranducers) to different gases. The method is based on compensation for the change in the transducer signal caused by the use of a gas other than nitrogen or air and by variation of the volume of the measurement chamber. This approach makes it possible to avoid some of the errors intrinsic to measurements of low pressures and small increments in the transducer signal. A vacuum system configuration that allows the given method to be realized is described. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 31–32, January, 1997.     

The acoustic evaluation of wire ropes immersed in water

This note shows that wire breaks can be detected acoustically when a wire rope is immersed in water with a transducer either attached to an end connection or remote from the rope with water acting as the carrier medium. In either case little change in transducer signal amplitude occurs. However, in propagating through water the signal duration is reduced because of the absence of shear waves. This also affects the resulting frequency spectra as frequency components below 25 kHz are greatly reduced.     

Contrast medium assisted fluid flow measurements

In this paper the development and evaluation of two new approaches for ultrasound time-domain fluid flow measurements by tracking echoes scattered by a contrast agent following injection of a bolus of the contrast agent are described. Their feasibility was investigated by measuring velocity or velocity profile of blood flowing in a mock circulatory loop in vitro. Measurements were made with a one transducer intravessel approach and a two transducer extravessel approach. A hybrid cluster or vector cross-correlation method was used to track the motion of the scatterers in the two transducer time-domain method. This cluster or vector cross correlation method was developed to reduce the ambiguity resulted from misregistration which is a common problem in target tracking by correlating signal patterns. The experimental results show a good agreement between the measured data and those estimated from timing the volume. Although the discussions given in this paper pertain only to blood flow measurements, there is no reason to indicate that these approaches can not be used for fluid flow measurements in an industrial environment if suitable contrast agents can be developed     

Ultrasonic densitometer using a multiple reflection technique

This work presents recent improvements in a density measurement cell with a double-element transducer that can eliminate diffraction effects. A new mechanical design combined with the use of more appropriate materials has resulted in better parallelism between interfaces, more robust assembly, and chemical resistance. A novel method of signal processing, named the energy method, is introduced to obtain the reflection coefficient, reducing sensitivity to noise and improving accuracy. The measurement cell operation is verified both theoretically, using an acoustic wave propagation model, and experimentally, using homogeneous liquids with different densities. The accuracy in the density measurement is 0.2% when compared with the measurements made with a pycnometer.     

In vivo scattering measurement of biological tissue by the use of a pyroelectric polymer transducer

We propose a new method, to our knowledge, for noninvasive scattering measurements of tissues by the use of a pyroelectric polymer transducer, poly(vinylidene fluoride trifluoroethylene) film. In this method, samples are irradiated with nanosecond, low-energy light pulses delivered from an optical fiber, and the pyroelectric signal induced by the diffuse reflectance is measured with a transducer. The signal is then converted into diffuse reflectance by use of a calibration factor. The validity of this method was confirmed by our measuring the scattering coefficient of a white acrylic resin within an accuracy of +/- 15%. We attempted to apply this method to the estimation of scattering coefficients of normal and burned skins in rats in vivo.     

Experimental implementation of fiber optic bundle array wide FOV free space optical communications receiver

A gimbal-free wide field-of-regard (FOR) optical receiver has been built in a laboratory setting for proof-of-concept testing. Multiple datasets are presented that examine the overall FOR of the system and the receiver's ability to track and collect a signal from a moving source. The design is not intended to compete with traditional free space optical communication systems, but rather offer an alternative design that minimizes the number and complexity of mechanical components required at the surface of a small mobile platform. The receiver is composed of a micro-lens array and hexagonal bundles of large core optical fibers that route the optical signal to remote detectors and electronics. Each fiber in the bundle collects power from a distinct solid angle of space and a piezo-electric transducer is used to translate the micro-lens array and optimize coupling into a given fiber core in the bundle. The micro-lens to fiber bundle design is scalable, modular, and can be replicated in an array to increase aperture size.     

Slider-disk clearance measurements in magnetic disk drives usingthe readback transducer

A new method is described for noninvasively measuring the mechanical clearance between a recording head slider and the magnetic medium in hard-disk drives. The method is based on the detection of the pulse width of the read transducer output. A variation in clearance produces a proportional variation in pulse width. The proportionality factor can be determined by simulating the spacing loss using a digitized isolated impulse, typical for the respective head-disk combination. Instrumentation is presented that provides an output voltage proportional to the ratio (PW_x/T) of the pulse width at x% of the peak amplitude PW_x and the period T of the readback signal. This instrumentation measures the absolute slider-disk clearance by evacuating the air from the disk drive. The bandwidth is such that clearance dynamics can also be measured. This allows clearance measurements as well as the detection of undesirable slider-disk interactions, in situ, in fully operational disk drives     

Calibration of an electronically scanned white-lightinterferometric transducer for measurements of high pressure

The paper deals with an electronically scanned white-light interferometric transducer for high-pressure measurements which consists of a sensor, a conditioning circuit, an analog-to-digital converter, and a digital signal processor of the output signal from the sensor. The calibration of such a transducer consists of identifying a function modeling the relationship between the raw result of measurement y, which is the output of the transducer, and the measured pressure p, taking into account an influence quantity-temperature T. An algorithm for calibration is proposed and studied     

Implementing the Modeling Method in Problems of Multifactor Measurements

Two implementations of multifactor measurements are considered utilizing a modeling method. They are determined by the choice of the modeled object: the filtering of single-factor signals when modeling part of the output signal of the primary transducer, and the measurement of affecting factors on the basis of modeling the whole increment of this signal.     

Designing waveforms for temporal encoding using a frequency sampling method

In this paper a method for designing waveforms for temporal encoding in medical ultrasound imaging is described. The method is based on least squares optimization and is used to design nonlinear frequency modulated signals for synthetic transmit aperture imaging. By using the proposed design method, the amplitude spectrum of the transmitted waveform can be optimized, such that most of the energy is transmitted where the transducer has large amplification. To test the design method, a waveform was designed for a BK8804 linear array transducer. The resulting nonlinear frequency modulated waveform was compared to a linear frequency modulated signal with amplitude tapering, previously used in clinical studies for synthetic transmit aperture imaging. The latter had a relatively flat spectrum which implied that the waveform tried to excite all frequencies including ones with low amplification. The proposed waveform, on the other hand, was designed so that only frequencies where the transducer had a large amplification were excited. Hereby, unnecessary heating of the transducer could be avoided and the signal-to-noise ratio could be increased. The experimental ultrasound scanner RASMUS was used to evaluate the method experimentally. Due to the careful waveform design optimized for the transducer at hand, a theoretic gain in signal-to-noise ratio of 4.9 dB compared to the reference excitation was found, even though the energy of the nonlinear frequency modulated signal was 71% of the energy of the reference signal. This was supported by a signal-to-noise ratio measurement and comparison in penetration depth, where an increase of 1 cm was found in favor for the proposed waveform. Axial and lateral resolutions at full-width half-maximum were compared in a water phantom at depths of 42, 62, 82, and 102 mm. The axial resolutions of the nonlinear frequency modulated signal were 0.62, 0.69, 0.60, and 0.60 mm, respectively. The corresponding axial resolutions for the reference waveform were 0.58, 0.65, 0.62, and 0.60 mm, respectively. The compression properties of the matched filter (mismatched filter for the linear frequency modulated signal) were tested for both waveforms in simulation with respect to the Doppler frequency shift occurring when probing moving objects. It was concluded that the Doppler effect of moving targets does not significantly degrade the filtered output. Finally, in vivo measurements are shown for both methods, wherein the common carotid artery on a 27-year-old healthy male was scanned.     

A novel approach to acoustic liquid density measurements using a buffer rod based measuring cell

A new method for measuring the pressure reflection coefficient in a buffer rod configuration is presented, together with experimental results for acoustic measurements of the liquid density, based on the measurement of the liquid's acoustic impedance. The method consists of using 2 buffers enclosing the liquid in a symmetrical arrangement with a transducer fixed to each buffer. One of the transducers is used in a pulse-echo mode while the other transducer operates as a receiver. The echo amplitudes leading to the pressure reflection coefficient as found by this method possess advantages such as reduced attenuation due to a shorter liquid transmission path and reduced interference, as compared with the ABC method. Measurements with distilled water and with special density calibration oil qualities have been performed using both the new method and the ABC method and are shown for the new method to give a density span within +/- 0.15% of the reference values. A comparison of the measured densities based on both a time-domain and a l(2)-norm frequency domain integration signal processing approach is given, along with a recommendation as to how the signal processing should be performed.     

Analysis of the performance of the capacitive displacementtransducer

An output signal from the capacitive displacement transducer has been mathematically modeled. Interest is focused on the importance of the spectral content of the signal in determining transducer performance. It has been shown that the phase-error due to the space harmonics of the capacitance between the receiving and transmitting electrodes always exhibits a ripple with the spatial frequency equal to the number of the transmitting electrodes. An analysis of the mathematical model suggests general rules of mechanical and electrical design that are necessary in order to create effective and viable devices with reduced measurement errors. In particular, a variety of the staircase functions with rapidly decreasing Fourier components can be applied as the driving supply. Another alternative is to combine a specially formed driving supply with low-pass filtering in the time domain. Experimental results for three different (four-, six-, and eight-phase) transducer systems confirm the validity of the model     

Backscattering measurement from a single microdroplet

Backscattering measurements for acoustically trapped lipid droplets were undertaken by employing a P[VDF-TrFE] broadband transducer of f-number = 1, with a bandwidth of 112%. The wide bandwidth allowed the transmission of the 45 MHz trapping signal and the 15 MHz sensing signal using the same transducer. Tone bursts at 45 MHz were first transmitted by the transducer to hold a single droplet at the focus (or the center of the trap) and separate it from its neighboring droplets by translating the transducer perpendicularly to the beam axis. Subsequently, 15 MHz probing pulses were sent to the trapped droplet and the backscattered RF echo signal received by the same transducer. The measured beam width at 15 MHz was measured to be 120 μ m. The integrated backscatter (IB) coefficient of an individual droplet was determined within the 6-dB bandwidth of the transmit pulse by normalizing the power spectrum of the RF signal to the reference spectrum obtained from a flat reflector. The mean IB coefficient for droplets with a 64 μ m average diameter (denoted as cluster A) was -107 dB, whereas it was -93 dB for 90-μm droplets (cluster B). The standard deviation was 0.9 dB for each cluster. The experimental values were then compared with those computed with the T-matrix method and a good agreement was found: the difference was as small as 1 dB for both clusters. These results suggest that this approach might be useful as a means for measuring ultrasonic backscattering from a single microparticle, and illustrate the potential of acoustic sensing for cell sorting.     

Phase-shifting interferometry using a two-dimensional regularized phase-tracking technique

Abstract

Phase-shifting interferometry is the most used method whenever the optical stability of the interferometer remain high when several phase-shifted interferograms are taken. In this work we present a two-dimensional regularized phase-tracking (RPT) technique applied to demodulate multiple phase-shifted interferograms. The main advantage of this technique with reference to classical phase-shifting interferometry is its higher signal-to-noise rejection as well as a higher signal′s harmonics rejection. In the RPT technique the unwrapping process is implicit; so it is achieved simultaneously with the phase estimation process; then, no additional unwrapping process is required.     

Choice of location of a receiving hydroacoustic transducer during measurement of standard vibroacoustic noise

Features of the choice of location of a receiving transducer in the method of compensating vibroacoustic noise hampering operation of a hydroacoustic system are considered. The method is based on the principles of adaptive signal filtration using current measurements of standard noise. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 62–64, July, 2008.     

高静水压下换能器阻抗特性的测量方法研究

针对在小腔体中阻抗分析仪发射连续波无法准确测得换能器阻抗的问题,提出一种在高静水压下使用脉冲正弦信号激励换能器测量阻抗的方法。以采样电阻法为基础,根据腔体尺寸确定发射脉冲个数以及可测频率范围来有效避免腔体边界反射对测量造成的影响。通过设置不同的发射频率,分别采集换能器两端及采样电阻两端的电压波形信号,利用已知频率的三参数正弦曲线拟合法分别得到波形信号的幅值和初始相位角,计算得到换能器的导纳值。改变静水压力,利用脉冲法测得0~10 MPa静水压下换能器导纳特性。实验结果表明,采用脉冲正弦信号激励的方法可在有限空间内准确测量换能器的阻抗特性;且随着静水压力的升高换能器的谐振频率发生偏移,导纳圆直径减小。     

A new phase retrieval algorithm with pure generalized three-step phase-shifting under matrix norm processing

Phase-shifting interferometry (PSI) is one of the most effective techniques in imaging a phase specimen, in which the phase retrieval is a basic and significant process. A new phase retrieval method based on the matrix norm algorithm in PSI is proposed in this paper. In this algorithm, the value of phase shift can be determined by three different matrix norms of the intensity difference between two phase-shifted interferograms, and then the phase can be retrieved. Neither the iterative calculation nor the extra measurements of other parameters are necessary on account of this algorithm which only requires three phase-shifted interferograms. The feasibility and accuracy of this algorithm are demonstrated by the simulated results. Experimentally, the generalized phase shift can be realized by a simple device which adjusting the angle of glass accurately. It is found that this algorithm has a good application prospect in the field of dynamic imaging.