Certain characteristics of electrically excitable mechanical resonant modes of a virgin PZT65/35 disc

In this paper we present experimental measurements of the in-phase and quadrature components of the axial mechanical displacements of particular flexural resonant modes exhibited by a virgin PZT65/35 disc specimen which is driven by alternating voltages. In particular, it is shown that the in-phase components of those resonances with nodal diameters exhibit the vibrational patterns due to a new electric-to-mechanical coupling phenomenon and the vibrational patterns which mimic the resonant mode shapes given by the quadrature components. We also present results concerning the frequency dependences of the in-phase and quadrature components in the neighborhoods of the resonances.     

Feedback compensated synchronous and multiplier type phasesensitive detectors

A feedback technique for phase sensitive detection (PSD) is developed, which is suitable for both synchronous and multiplier modes of implementation. The feedback-compensated PSD straightaway provides a DC output proportional to the amplitude of the measurand. The technique is very useful in a noisy environment where post-processing of the in-phase and quadrature components would otherwise deteriorate the stability, accuracy, and sensitivity. Quantitative comparison of the extent of compensation obtained experimentally with that estimated by PC-simulation indicates good agreement     

基于复包络提取的波束形成方法

结合带通信号的特性,提出了一种基于复包络提取的波束形成方法。首先,提取各阵元接收的信号的同相分量和正交分量;其次,分别对上述同相分量和正交分量进行相移;最后再对移相之后的同相分量和正交分量进行延时相加,从而形成入射方向的波束。该方法有效降低了波束形成器的输入和输出采样率以及数字处理的复杂度。     

Characterization of four-terminal-pair resistance standards: acomparison of measurements and theory

Coaxial straight-wire resistance standards with calculable frequency dependence, link AC measurements to DC measurements of resistance. Several coaxial standards of values 100 Ω and 1000 Ω are compared with each other and with other resistance standards at frequencies of 1592 Hz (ω≅10⁴) and 15920 Hz (ω≅10⁵) using AC bridges. The data are compared with calculations based on the geometry of this resistor design. Our results provide good assurance that the calculations are accurate for the quadrature component of admittance (phase angle), which is directly proportional to frequency. Frequency-dependent contributions to the in-phase component of admittance, which increase as the square of the frequency, are larger than predicted by the calculations     

Resolving quadrature fringes in real time

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 x 10(-13) m Hz(-1/2) at 2 Hz.     

Full-field imaging of Gigahertz film bulk acoustic resonator motion

A full-field view laser ultrasonic imaging method has been developed that measures acoustic motion at a surface without scanning. Images are recorded at normal video frame rates by using dynamic holography with photorefractive interferometric detection. By extending the approach to ultra high frequencies, an acoustic microscope has been developed that is capable of operation at gigahertz frequency and micron length scales. Both acoustic amplitude and phase are recorded, allowing full calibration and determination of phases to within a single arbitrary constant. Results are presented of measurements at frequencies of 800-900 MHz, illustrating a multitude of normal mode behavior in electrically driven thin film acoustic resonators. Coupled with microwave electrical impedance measurements, this imaging mode provides an exceptionally fast method for evaluation of electric-to-acoustic coupling of these devices and their performance. Images of 256 /spl times/ 240 pixels are recorded at 18 fps rates synchronized to obtain both in-phase and quadrature detection of the acoustic motion. Simple averaging provides sensitivity to the subnanometer level at each pixel calibrated over the image using interferometry. Identification of specific acoustic modes and their relationship to electrical impedance characteristics show the advantages and overall high speed of the technique.     

Reactive power measurement using the wavelet transform

This paper provides the theoretical basis for the measurement of reactive and distortion powers from the wavelet transforms. The measurement of reactive power relies on the use of broad-band phase-shift networks to create concurrent in-phase currents and quadrature voltages. The wavelet real power computation resulting from these 90° phase-shift networks yields the reactive power associated with each wavelet frequency level or subband. The distortion power at each wavelet subband is then derived from the real, reactive and apparent powers of the subband, where the apparent power is the product of the v, i element pair's subband rms voltage and current. The advantage of viewing the real and reactive powers. In the wavelet domain is that the domain preserves both the frequency and time relationship of these powers. In addition, the reactive power associated with each wavelet subband is a signed quantity and thus has a direction associated with it. This permits tracking the reactive power flow in each subband through the power system     

Performance analysis of rectangular quadrature amplitude modulation with combined arbitrary transmit antenna selection and receive maximal ratio combining in nakagami-m fading

The average symbol error probability (SEP) performance of arbitrary rectangular quadrature amplitude modulation in the context of arbitrarily ordered transmit antenna selection and receive maximal ratio combining diversity system is analysed. The channel gains are assumed to follow Nakagami-m fading distribution with in general arbitrary fading parameters. Exact expressions for the average SEP performance are derived for the general case of unequal in-phase and quadrature decision distances as well as distinct in-phase and quadrature modulation orders. The results generalise many previous case studies, and can be used to investigate the impact of various diversity-combining schemes and different modulation and channel parameters on the system average SEP performance.     

Closed-form integration of singular terms for constant,linear and quadratic boundary elements. Part 1. SH wave propagation

One of the most important aspects in the application of boundary element techniques to wave propagation problems is the accurate representation of the singular terms at the points of application of the virtual loads. It is current practice to carry out this task by means of numerical quadrature. This paper presents an analytical evaluation of the singular integrals for constant, linear and quadratic boundary elements involving SH waves, the results of which are then used to model inclusions in a two-dimensional acoustic medium illuminated by dynamic anti-plane line sources. Finally, the BEM results are compared with the known analytical solutions for cylindrical inclusions.     

数字微差补偿器及其在电流比较仪电桥中的应用

设计一种能够在四象限内对输出信号进行调节的数字微差补偿器,核心器件为16 位串行输入乘法型数模转换器,以正弦电压信号作为参考,可根据接收的数字编码分别调节输出补偿信号的同相分量和正交分量。提出一款计算机控制的电流比较仪电桥线路,应用数字微差补偿器和牛顿迭代算法实现电流比较仪磁势的自动平衡。利用研制的电桥对双螺线型计算电阻进行测量,结果表明,该电桥在1592 Hz频率范围内的标准测量不确定度为2×10^-7,能够满足交流电阻量值传递要求。     

Application of X-Y separable 2-D array beamforming for increased frame rate and energy efficiency in handheld devices

Two-dimensional arrays present significant beamforming computational challenges because of their high channel count and data rate. These challenges are even more stringent when incorporating a 2-D transducer array into a battery-powered hand-held device, placing significant demands on power efficiency. Previous work in sonar and ultrasound indicates that 2-D array beamforming can be decomposed into two separable line-array beamforming operations. This has been used in conjunction with frequency-domain phase-based focusing to achieve fast volume imaging. In this paper, we analyze the imaging and computational performance of approximate near-field separable beamforming for high-quality delay-and-sum (DAS) beamforming and for a low-cost, phase-rotation-only beamforming method known as direct-sampled in-phase quadrature (DSIQ) beamforming. We show that when high-quality time-delay interpolation is used, separable DAS focusing introduces no noticeable imaging degradation under practical conditions. Similar results for DSIQ focusing are observed. In addition, a slight modification to the DSIQ focusing method greatly increases imaging contrast, making it comparable to that of DAS, despite having a wider main lobe and higher side lobes resulting from the limitations of phase-only time-delay interpolation. Compared with non-separable 2-D imaging, up to a 20-fold increase in frame rate is possible with the separable method. When implemented on a smart-phone-oriented processor to focus data from a 60 x 60 channel array using a 40 x 40 aperture, the frame rate per C-mode volume slice increases from 16 to 255 Hz for DAS, and from 11 to 193 Hz for DSIQ. Energy usage per frame is similarly reduced from 75 to 4.8 mJ/ frame for DAS, and from 107 to 6.3 mJ/frame for DSIQ. We also show that the separable method outperforms 2-D FFT-based focusing by a factor of 1.64 at these data sizes. This data indicates that with the optimal design choices, separable 2-D beamforming can significantly improve frame rate and battery life for hand-held devices with 2-D arrays.     

Energy transfer and photodegradation of a Perylene Orange:LDS821 system in poly(methyl methacrylate)

The luminescence of Perylene Orange and LDS821 in poly(methyl methacrylate) (PMMA) following a 532 nm irradiation yielded information on photodegradation and energy transfer. The irradiation of the Perylene Orange/LDS821/PMMA films resulted in (i) a maximum in the Perylene Orange fluorescence photodegradation profile and (ii) an enhancement of the LDS821 fluorescence relative to the LDS821/PMMA films. These results are attributed to an energy transfer from the Perylene Orange to the LDS821 with an energy transfer rate constant of 5.1+/- 0.75 (2sigma) x 10(11) M(-1) s(-1) and a F?rster critical radius of 65.7 A. Fluorescence half-quenching and time-resolved fluorescence measurements attributed energy transfer to the F?rster energy transfer with minor contributions of radiative energy transfer.     

Collection of fluorescence from single molecules in microspheres: effects of illumination geometry

The collection of fluorescence from a molecule inside a sphere illuminated with single or counterpropagating plane waves is modeled. The results are applicable to microdroplet-based single molecule detection techniques and to some microparticle characterization techniques using inelastic emission. The large position-dependent variations in the fluorescence collection rate are primarily attributable to variations in the excitation intensity. With plane-wave illumination the collection from shadow regions is low because the incident energy is refracted by the droplet surface away from these regions. The average collection rate from molecules in shadow regions can be increased by illuminating with counterpropagating beams.     

Electrical behaviour of chemically activated fly ash

The temporal change in electrical properties is used to study the hydration kinetics of chemically activated fly-ash systems at room temperature. Four low-lime ashes and one high-lime ash were used in the experimental programme and the electrical response was measured in terms of the in-phase (i.e. conductance) and quadrature (i.e. capacitance) components of the sample admittance. The low-lime ash and high-lime ash exhibited markedly different electrical response. The work highlights the applicability of the testing methodology as a non-invasive, non-destructive technique in the assessment of the efficacy of a particular activator or combination of activators.     

Fluorescence detection in capillary zone electrophoresis using a charge-coupled device with time-delayed integration

A fluorescence detection system for capillary zone electrophoresis is described in which a charged-coupled device (CCD) views a 2-cm section of an axially illuminated capillary column. The CCD is operated in two readout modes: a snapshot mode that acquires a series of images in wavelength and capillary position, and a time-delayed integration mode that allows long exposure times of the moving analyte zones. By use of the latter mode, the ability to differentiate a species based on both its fluorescence emission and migration rate is demonstrated for fluorescein and sulforhodamine 101. The detection limit for fluorescein isothiocyanate (FITC) is 1.2 X 10(-20) mol; detection limits for FITC-amino acids are in the (2-8) X 10(-20) mol range.     

An Electronic Ratio Error Set for Current Transformer Calibrations

A direct-reading electronic ratio error set for current transformer calibrations is described. It is capable of generating direct and quadrature error currents from 1 ppm to 5 percent of transformer secondary currents up to 10 A. The uncertainty is less than one percent of the generated current. The set features electronic display of the direct and quadrature components with three digits each and is direct reading at 50, 60, and 400 Hz.     

Intensity-modulated, stepped frequency cw lidar for distributed aerosol and hard target measurements

A compact frequency-modulated, continuous wave (FM-cw) lidar system for measurement of distributed aerosol plumes and hard targets is presented. The system is based on intensity modulation of a laser diode and quadrature detection of the return signals. The advantages of using laser diode amplitude modulation and quadrature detection is a large reduction in the hardware required for processing and storing return signals as well as the availability of off-the-shelf integrated electronic components from the wireless and telecommunication communities. Equations to invert the quadrature signal components and determine spatial distributions of multiple targets are derived. Spatial scattering intensities are used to extract aerosol backscatter coefficients, which can then be directly compared to microphysics aerosol models for environmental measurements. Finally, results from laboratory measurements with a monostatic FM-cw lidar system with both hard targets and aerosols are discussed.     

Miniature Accelerometer and Multichannel Signal Processor for Fiberoptic Fabry–Pérot Sensing

A miniature accelerometer based on silicon microelectromechanical systems (MEMS) fabrication technology has been developed. Using a beam-suspended proof mass and a Fabry-Peacuterot sensing gap, this accelerometer is fiber coupled to a miniature, multichannel, optical readout system which was developed for application in compact optical sensor systems. The approximately 4 mmtimes7 mmtimes2 mm accelerometer can be tailored to cover milli-g to kilo-g acceleration ranges. The miniature readout system is enclosed in approximately a 2 cmtimes8 cmtimes1 cm package, one of the smallest ever reported, and implements the complete optical path for a three-channel embodiment of a multichannel, highly sensitive and accurate, in-phase and quadrature (IQ) optical measurement system for Fabry-Peacuterot sensors. A variety of fiber-based sensors (temperature, strain, pressure, etc.) are commercially available using this Fabry-Peacuterot technique. The complete measurement system with the accelerometer was tested using a shaker table. Sample results are presented for 100 Hz, 10-g peak-peak acceleration     

On modeling biomedical ultrasound RF echoes using a power-law shot-noise model

We propose a new model for the RF ultrasound echo, namely the power-law shot-noise process. Based on this model, the in-phase and quadrature components of the echo are shown to exhibit 1/f^β -type spectral behavior, in a sense that is defined in the paper. The envelope also exhibits this type of spectral behavior, but with a different exponent. This result explains the experimental observations by other researchers of the power-law trend of the RF echo spectrum. Although the shot-noise model has been used in the past for modeling the RF echo, this is the first time that a power-law impulse response filter is used and that the resulting 1/f^β-type spectral behavior of the RF echo has been investigated. The model parameters are linked to tissue characteristics, such as scatterer density and attenuation; thus, they have the potential to be used as tissue characterization features. The validity of the proposed model is tested based on a database of 100 clinical ultrasound images of the breast