Quantization error of CCD cameras and their influence on phase calculation in fringe pattern analysis

We present an investigation into the phase errors that occur in fringe pattern analysis that are caused by quantization effects. When acquisition devices with a limited value of camera bit depth are used, there are a limited number of quantization levels available to record the signal. This may adversely affect the recorded signal and adds a potential source of instrumental error to the measurement system. Quantization effects also determine the accuracy that may be achieved by acquisition devices in a measurement system. We used the Fourier fringe analysis measurement technique. However, the principles can be applied equally well for other phase measuring techniques to yield a phase error distribution that is caused by the camera bit depth.     

Characterization and calibration of a CCD detector for light engineering

This paper describes the methodology developed for characterizing a commercial charge-coupled device (CCD) camera as a luminance meter for analyzing lighting systems and especially for measurements in road light plants. Today, several luminance meters based on commercial CCD cameras are on the market. They are very attractive for the lighting engineer: The availability of a high number of closely spaced small detectors (pixels) on a single chip permits analyses almost impossible with a traditional luminance meter. These commercial-industrial CCD cameras are sold at prices lower than scientific grade ones. They are factory equipped with a dedicated filter to reach the correct photopic sensitivity V(/spl lambda/), and they are factory calibrated in luminance SI units. The main counterparts in using these cameras are in the difficulties to define the measurement accuracy and the influence of the environment luminance on the measured values of the framed scene, in the low resolution of their A/D converter (usually 8 or 12 bit), and the higher noise level (usually the CCD chip is not cooled). To reach the measurement accuracy required by lighting norms, it is necessary to characterize metrologically a camera and quantify all the possible external influences which could degrade its performances, in real measurement situations, and which could affect the measurement results. A carefully controlled measurement set up and operating procedure could limit the causes of errors and improve the accuracy of measurements obtained in operating conditions. In this way, the measurement uncertainties might be evaluated completely, and considerations on the results could suggest particular operating practices to limit the causes of error due to measurement setup and environmental conditions.     

Limitations of self-phase-modulation-based tunable delay system for all-optical buffer design

The distortion, noise, and bit-delay performance of a self-phase-modulation-based tunable delay system are analyzed. The pulse amplification required for achieving large spectral broadening results in large amplifier noise. We quantify the resulting delay versus signal-to-noise ratio trade-off. We demonstrate that for high bit rates it is difficult to achieve both large bit delay and good data fidelity. We find that for a given bit rate, reducing the duty cycle improves the fractional bit delay. For a duty cycle of 16%, a maximum bit delay of 15 bits is achieved.     

随机采样系统的误差分析和校正技术研究

在随机采集系统中,采用模拟内插技术可提高系统的等效采样率,但是模拟内插中的时间间隔测量电路会受到温度、器件特性、随机噪声等因素的影响,导致测时准确度降低,重建波形质量下降。分析了其中的主要误差的影响及来源,并提出通过相干平均、低通滤波等方法来降低误差,提高测时的准确度,实验结果表明波形的有效位数提高了约3 bit,信噪比提高了约2倍。     

水泵、制冷机组及管道的隔振降噪设计及效果

文章通过对高层建筑物内部水泵机组以及管道的噪声与振动现状调查测试,通过对现场的调研,分析了噪声与振动产生的原因以及传递途径,根据现场噪声和设备振动测试结果以及相关的声学标准,结合具体的治理项目,对存在的问题进行整改。设计了可行的隔振降噪措施,通过水泵、热泵和管道隔振改造后,内总体降噪幅度为6.7dBA￣12.7dBA。最终取得了规范要求的效果。     

Biomimetic Mechanosensor Array Processing for 2-D Airflow Direction and Amplitude Sensing

This paper presents a computational study and preliminary experimental results of mechanosensor arrays for 2-D airflow sensing. In particular, the analysis presented here applies to a recently developed biomimetic microelectromechanical system (MEMS) inspired by the array of airflow-sensitive hairs found on the crickets' cercus. Based on the maximum-likelihood principle, an estimator that allows reconstruction of both the airflow direction and the airflow velocity amplitude is derived. Given this algorithm, different topologies of hair arrays are investigated in terms of sensitivity for measurement errors. In addition, it is analyzed how redundancy, i.e., the presence of many more than the minimum number of hairs, in the array can be used for lessening the effect of measurement noise. Multiple types of hardware failure common in biological and artificial array systems, as well as the occurrence of saturation, are analyzed, and it is shown how redundancy again increases the robustness of the sensor. Experimental results are shown to validate the theoretical model and its assumptions.      

异步触发CCD摄像机电子快门的预测方法和实现

用激光回波脉冲控制电子快门来操纵摄像机的曝光时间，是抑制背景噪声的一种有效方法。提出了异步触发摄像机电子快门的预测方法，并将它应用在激光光斑的捕捉和测量中，提高了光斑图像的信噪比。该方法适宜 和于测量经过编码后的远距离激光脉冲光斑，为应用电视摄像机捕捉有规律的瞬态存在的目标提供了一个途径。     

A new method for estimating the aperture uncertainty of A/Dconverters

Aperture uncertainty measurements are strongly influenced by quantization, converter nonlinearity and test setup noise. The proposed method solves the difficulties arising from quantization, and nonlinearity. The method estimates the noise distribution function by fine adjustment of the input signal offset. The contribution of jitter-induced voltage noise is separated from additive noise in two different ways. Finally, the aperture uncertainty, assumed independent of the frequency, is estimated by varying the signal frequency. Experimental results obtained on 8 and 10 bit converters are discussed     

Analysis of track-edge noise in thin-film recording media

Track-edge noise has been analyzed to clarify track-edge noise mechanisms. Edge noise arises from two different regions: the bit edge where the magnetization direction is opposite to the previously dc-erased direction and the magnetic transition edge. The edge noise at low density is mainly due to the magnetic distribution at the bit edge. The transition edge noise increases with increasing recording density, and it becomes dominant at high-recording density for an oriented medium. On the other hand, the transition edge noise is almost constant with increasing recording density for an isotropic medium     

Color-coded projection grating method for shape measurement with a single exposure

A fast and efficient technique for profilometric measurement with a color-coded grating is proposed. Eight colors are used to code the grating, and each color represents only one logical state. There are 64 stripes in one period of the color grating, which is large enough for normal measurement. Compared with the previous techniques, it has the advantages of simple hardware without moving mechanical parts, single exposure for obtaining three-dimensional information, little influence from noise and from nonlinearity of the CCD camera on the measurement accuracy, and higher anti-color-blurring capability. The suggested technique is suitable for on-line inspection and dynamic measurement of moving objects.     

A min-norm approach for estimating phase distribution in an interferogram

Phase distribution in an interferogram is usually computed from several phase shifted intensity images acquired temporally by means of a CCD camera. These phase shifts are commonly accomplished by translation of a mirror with a piezoelectric transducer (PZT). In reality the PZT motion is not exact. Thus the aim of this paper is to present a novel approach for estimating the phase steps that are imparted to the PZT in the presence of nonsinusoidal waveforms and random noise. The method functions by designing an autocovariance matrix from the intensity registered on the CCD for N data frames. The eigendecomposition of an autocovariance matrix yields the signal and noise subspaces. The phase step values are estimated pixelwise from the noise subspace. This approach provides the flexibility of using arbitrary phase steps, a feature most commonly attributed to generalized phase shifting algorithms. Once the phase steps are estimated the Vandermonde system of equations is applied to estimate the phase distribution.     

The cross algorithm for phase-aberration correction in medical ultrasound images formed with two-dimensional arrays

Common-midpoint signals in the near-field signal-redundancy (NFSR) algorithm for one-dimensional arrays are acquired using three consecutive transducer elements. An all-row-plus-two-column algorithm has been proposed to implement the one-dimensional NFSR algorithm on two dimensional arrays. The disadvantage of this method is that its ambiguity profile is not linear and a timeconsuming iterative method has to be used to linearize the ambiguity profile. An all-row-plus-two-column-and-a-diagonal algorithm has also been proposed. Its ambiguity profile is linear, but it is very sensitive to noise and cannot be used. In this paper, a novel cross algorithm is proposed to implement the NFSR algorithm on two-dimensional arrays. In this algorithm, common-midpoint signals are acquired using four adjacent transducer elements, which is not available in one-dimensional arrays. Its advantage includes a linear ambiguity profile and a higher measurement signal-to-noise ratio. The performance of the cross algorithm is evaluated theoretically. The region of redundancy is analyzed. The procedure for deriving the phaseaberration profile from peak positions of cross-correlation functions between common-midpoint signals is discussed. This algorithm is tested with a simulated data set acquired with a two-dimensional array, and the result shows that the cross algorithm performs better than the all-row plus-twocolumn NFSR algorithm.     

D／A转换器的模型化测试策略

本文提出了模型化测量D/A转换器非线性误差的方法,讨论了建模技术和选择优化试验点的方法。利用这些工具,可以从一组充分、必要的测量数据,准确估计出在所有码态时转换器的非线性误差、位误差和重叠误差。     

Design of high-performance photodiode receivers for optical tomography

The design of instrumentation hardware for tomographic systems must take careful account of measurement noise. This is especially true in near-infrared absorption tomography, where the signal of interest is typically only a few percent of the total signal at the detector, and the available optical power may have to be shared among many measurement channels. In this paper, the monitoring of photodiodes in near-IR absorption tomography is examined in detail, but much of the material is applicable at wavelengths ranging from the UV to beyond 2.5 /spl mu/m. The authors' application involves the frequency region 50 kHz to 2 MHz, which lies above that utilized in the majority of radiometric sensing systems, yet substantially below telecoms bit rates. The problem is further distinguished by the use of phase-sensitive detection schemes, which make local noise density more relevant than wideband noise performance and relax the requirement for dc precision. Alternative transimpedance circuit configurations, including both single-ended and differential topologies, are analyzed with a view to optimization of the signal-to-noise ratio. Typical values of photodiode capacitance and shunt resistance are shown to result in significant noise gain, greatly increasing the importance of amplifier voltage noise relative to other intrinsic noise sources. It is shown that for applications of this type, viable alternatives to the traditionally dominant FET amplifier do exist. The relative susceptibility to coupled interference is also considered. The results of practical tests, involving class-leading operational amplifiers, are presented to support the analyses. These results also underline the need for careful circuit layout and shielding if the capabilities of these devices are to be fully exploited.     

Standoff determination of the particle size and concentration of small optical depth clouds based on double-scattering measurements: validation with calibrated target plates and limitations for daytime and nighttime measurements

Diffractive target plates are used to emulate aerosols of known size and concentration. These target plates are used to validate and determine the sensitivity of a multiple-field-of-view lidar signal inversion technique based on double-scattering measurement to retrieve the particle size and the concentration of small optical depth clouds. We estimate that nighttime and daytime quantification (size and concentration) is possible for optical depths as low as 0.005 and 0.016, respectively. The recovery technique limiting factors are the shot noise, the laser features, the optical lens quality, the background illumination level, the background aerosol fluctuations, and the noise introduced by the lidar detector, a gated intensified camera (camera G-ICCD).     

System performances of optical space code-division multiple-access-based fiber-optic two-dimensional parallel data link

Optical space code-division multiple access is a scheme to multiplex and link data between two-dimensional processors such as smart pixels and spatial light modulators or arrays of optical sources like vertical-cavity surface-emitting lasers. We examine the multiplexing characteristics of optical space code-division multiple access by using optical orthogonal signature patterns. The probability density function of interference noise in interfering optical orthogonal signature patterns is calculated. The bit-error rate is derived from the result and plotted as a function of receiver threshold, code length, code weight, and number of users. Furthermore, we propose a prethresholding method to suppress the interference noise, and we experimentally verify that the method works effectively in improving system performance.     

Measurement and system impact of multipath interference from dispersion compensating fiber modules

Dispersion compensating modules (DCM) are key components in long distance and high-speed fiber-optic transmission systems. However, many types of DCMs exhibit multipath interference (MPI) that acts as noise in transmission and degrades the bit error rate of the system. Further, MPI generated in DCMs is mostly due to forward scattering and mostly of the coherent type. This type of MPI cannot be correctly measured using conventional measurement techniques that use electrical spectrum analysis to measure post-detection noise. We demonstrate an accurate and simple method of MPI measurement using a swept wavelength system apparatus. We discuss the strengths and limitations of this measurement method and show system results of Q penalty due to MPI from concatenated DCMs.     

Front-end receiver electronics for high-frequency monolithic CMUT-on-CMOS imaging arrays

This paper describes the design of CMOS receiver electronics for monolithic integration with capacitive micromachined ultrasonic transducer (CMUT) arrays for highfrequency intravascular ultrasound imaging. A custom 8-inch (20-cm) wafer is fabricated in a 0.35-μm two-poly, four-metal CMOS process and then CMUT arrays are built on top of the application specific integrated circuits (ASICs) on the wafer. We discuss advantages of the single-chip CMUT-on-CMOS approach in terms of receive sensitivity and SNR. Low-noise and high-gain design of a transimpedance amplifier (TIA) optimized for a forward-looking volumetric-imaging CMUT array element is discussed as a challenging design example. Amplifier gain, bandwidth, dynamic range, and power consumption trade-offs are discussed in detail. With minimized parasitics provided by the CMUT-on-CMOS approach, the optimized TIA design achieves a 90 fA/√Hz input-referred current noise, which is less than the thermal-mechanical noise of the CMUT element. We show successful system operation with a pulseecho measurement. Transducer-noise-dominated detection in immersion is also demonstrated through output noise spectrum measurement of the integrated system at different CMUT bias voltages. A noise figure of 1.8 dB is obtained in the designed CMUT bandwidth of 10 to 20 MHz.     

Noise in high performance thin-film longitudinal magnetic recording media

The problem of noise in thin-film longitudinal media is analyzed experimentally and theoretically. The physical mechanism for the noise is shown to be fluctuations in the geometry of the zig-zag transitions separating bit cells. The shifted-transition noise model is introduced as a means of quantifying the noise processes. Spatial, spectral, and autocorrelation properties are introduced. A calculation of the RMS noise voltage yields the characteristic noise versus density curves found experimentally, and clarifies their interpretation with respect to the signal-to-noise ratio. The corresponding experimental data for several plated and sputtered media are presented and analyzed in the light of the model predictions.     

Performance Analysis and Evaluation of Geometric Parameters in Stereo Deflectometry

This paper presents a novel geometric parameters analysis to improve the measurement accuracy of stereo deflectometry. Stereo deflectometry can be used to obtain form information for freeform specular surfaces. A measurement system based on stereo deflectometry typically consists of a fringe-displaying screen, a main camera, and a reference camera. The arrangement of the components of a stereo deflectometry system is important for achieving high-accuracy measurements. In this paper, four geometric parameters of a stereo deflectometry system are analyzed and evaluated: the distance between the main camera and the measured object surface, the angle between the main camera ray and the surface normal, the distance between the fringe-displaying screen and the object, and the angle between the main camera and the reference camera. The influence of the geometric parameters on the measurement accuracy is evaluated. Experiments are performed using simulated and experimental data. The experimental results confirm the impact of these parameters on the measurement accuracy. A measurement system based on the proposed analysis has been set up to measure a stock concave mirror. Through a comparison of the given surface parameters of the concave mirror, a global measurement accuracy of 154.2 nm was achieved.