Digital angiography using a matched filter

Both digital subtraction and recursive filtering schemes have been employed successfully for intravenous and intraarterial arteriography. Either processing method results in an image(s), S, which is a linear combination of discrete images Ij acquired during the flow of iodinated contrast material, i.e., S = Sum of k(j)l(j) from j = 0 to N where k(j) are the weighting coefficients for the N+1 samples. It is shown that for a given set of images {l(j)} there exists a set of weighting coefficients {k(j)} which maximizes the iodine signal to noise ratio and simultaneously removes stationary background anatomy. The k(j) are related to the contrast dilution curve measured over an artery of interest, k(j) = s[j]-Mean(s), where {s[j]} is the set of measured image variations due to the flow of contrast material, and Mean(s), is the mean value of the s[j]. This choice of k(j) defines a matched filter. Compared to subtraction angiography, matched filtering is 4-6 times more dose efficient.     

Holographic matched filter for full-field in-line signal processingof optical-fiber sensor outputs

A holographic matched filter is used to measure the changes in the output of a dual-mode fiber undergoing axial strain. The hologram is formed by interfering collimated light from a single-mode reference fiber and an unstrained dual-mode sensor fiber on a small piece of holographic material. When the hologram is illuminated by the strained sensor fiber, the cross-correlation field comparing the dual-mode output and its previous state, as recorded in the hologram, is collected, focused into a pick-up fiber, and sent to a photodiode. This arrangement allows for a compact, in-line method for full-field processing of the strain-induced changes in phase and amplitude in the sensor fiber. Other uses of such fiber-based correlators are suggested     

CORA: Correlation-based resilient aggregation in sensor networks

In this paper, we consider the problem of resilient data aggregation in sensor networks, namely, how to aggregate sensor readings collected by the base station when some of those sensor readings may be compromised. Note that an attacker can easily compromise the reading of a sensor by altering the environmental parameters measured by that sensor. We present a statistical framework that is designed to mitigate the effects of the attacker on the output of the aggregation function. The main novelty of our approach compared to most prior work on resilient data aggregation is that we take advantage of the naturally existing correlation between the readings produced by different sensors. In particular, we show how spatial correlation can be represented in the sensor network data model, and how it can be exploited to increase the resilience of data aggregation. The algorithms presented in this paper are flexible enough to be applied without any special assumption on the distribution of the sensor readings or on the strategy of the attacker. The effectiveness of the algorithms is evaluated analytically considering a typical attacker model with various parameters, and by means of simulation considering a sophisticated attacker.     

投影光刻系统中的掩模硅片相关识别对准技术

分析图像相关识别中的纯相位匹配滤波器的模式识别方法,利用该滤波器的相关识别位图计算算法,及其所具有的相干峰尖锐特性与高度旋转敏感特性,分别求取得光刻套刻过程中,掩模板和硅片基板对准标记的相对平移坐标与旋转坐标的精密量化驱动值。将此算法的实施单元建立在一套成型的大面积投影光刻系统中,使得该系统的对位精度与对位效率显著地提高。     

Novel fiber sensor arrays using erbium-doped fiber amplifiers

We examine the signal-to-noise ratio (SNR) performance of a novel type of time domain multiplexed sensor arrays in which low gain (1-10 dB) fiber amplifiers are incorporated to compensate for splitting losses between sensors. The system noise figure for passive and amplified sensor arrays is presented, along with expressions to optimize the array parameters for high SNRs. We show that practical amplified sensor arrays exhibit low system noise figures that allow much larger arrays (hundreds of sensors) than passive arrays     

Gain-flattening filter using long-period fiber gratings

We propose a novel structure for a gain-flattening filter, in which a conventional long-period fiber grating (LPFG) and a phase-shifted LPFG are written closely. The transmission characteristics are investigated in the case of a closely arranged configuration. For the fabrication of a phase-shifted LPFG, a UV-trimming method to control the amount of the phase shift is examined theoretically and experimentally. Finally, a 67-mm-long LPFG gain-flattening filter designed for an erbium-doped fiber amplifier is fabricated and the measured spectrum is shown     

Polarimetric optical fiber sensor using a frequency stabilizedsemiconductor laser

Improved performance of a polarimetric optical fiber sensor for remote temperature measurement by the use of a frequency-stabilized semiconductor laser is discussed. The temperature change is measured from the phase delay between two orthogonally polarized modes in a polarization-maintaining fiber. The sensor output signal is demodulated utilizing direct modulation of the laser frequency. The center frequency of the modulated laser is locked to a Fabry-Perot interferometer by controlling the injection current. The minimum detectable temperature is evaluated experimentally to be less than 0.005°C, which is several times smaller than that obtained with the free-running laser     

A temperature-insensitive strain sensor using a fiber Bragg grating

A novel temperature-insensitive strain sensor based on a fiber Bragg grating is demonstrated. The front section of the fiber Bragg grating is fixed to a crystal plate, and the other section is linearly etched by HF acid. The reflected power and bandwidth of the grating vary linearly with strain and is insensitive to temperature variation.     

基于可调谐FP滤波器的光纤光栅解调系统

为了进一步提高光纤光栅解调系统的性能,提出和研究了一种新颖的基于可调谐F-P(Fabry-Perot)滤波器的光纤光栅解调技术,并以此为基础构建了探测系统。系统使用一个固定波长的参考光纤光栅作为波长参考元件,通过对传感光纤光栅与参考光纤光栅的波长测量与差值运算,消除了可调谐FP滤波器腔长漂移对测量精度的影响。给出压电陶瓷电压对应的伸长量,有效地减小了压电陶瓷非线性对测量的影响,提高了光纤光栅波长的测量精度。在测量范围内,最大非线性偏差为0.5%。     

Blind matched filter receiver

Matched filter receiver (MFR) of Forney in the presence of intersymbol interference (ISI) and additive white Gaussian noise is investigated from a blind perspective, which includes blind maximum likelihood sequence detection, blind decision feedback equalization and linear blind equalization. Various realizations of the blind MFR are discussed. In a blind MFR, the channel can be easily estimated using a simple algorithm such as the constant-modulus algorithm (CMA). In this sense, the CMA can be used to estimate the channel directly without complicated matrix decomposition techniques. Zero forcing and minimum mean-square estimation based designs of the blind MFR are explored. Channel estimation using the CMA deteriorates in the presence of noise. A new method to tackle this problem is developed and shown to have satisfactory behavior in low signal-to-noise ratios. Tracking performance of the blind MFR is found to be acceptable in representative Rayleigh fading channels of mobile communication.     

基于梳状滤波器的光纤甲烷传感器的研究

采用基于Sagnac的保偏光子晶体光纤(polarization-maintaining photonic crystal fiber,PM-PCF)滤波器,将宽带光源精确匹配甲烷气体在近红外波段的几个吸收线谱.设计出一个简单合理的多反射气室,使得光源和甲烷气体之间能够充分相互作用,提高了系统的灵敏度.同时,在测量甲烷气体浓度时,加入乙炔气体作为干扰,通过实验验证了该方案能够有效减缓交叉气体的灵敏度.     

A matched filter using charge coupled device for pulse-code modulation

A matched filter using CCD for PCM is made. The experimental results of output waveform, transfer function and output signal-to-noise ratio are given and compared with the theoretical ones. The output signal-to-noise ratio for the non-return-to-zero codes is 1 dB below the theoretical value.     

Chip-delay locked matched filter for DS-CDMA systems using longsequence spreading

This paper considers an improved single-user detection technique for asynchronous direct-sequence code-division multiple-access (DS-CDMA) systems using long sequence spreading (random-CDMA) Most of the known detection schemes for DS-CDMA suffer from either poor performance under power-imbalance (near-far like) conditions, excessive complexity, or incompatibility with systems employing long sequence spreading. To address these problems, this paper considers a signal-to-noise ratio maximizing linear time-invariant filter for one-shot bit symbol detection exploiting some information about the interferers. This filter, referred to as the chip-delay locked matched filter (CLMF), exploits the cyclostationarity in multiple-access interference, and it can offer good near-far resistance while remaining suitable for systems with long sequence spreading. The CLMF requires knowledge of interferers chip delays and signal powers; however, knowledge of their pseudonoise sequences is unnecessary. This paper also demonstrates the improvement in performances offered by the CLMF over other single-user receivers such as the conventional matched filter and noise-whitening matched filter performance is evaluated in terms of probability of outage for single-rate and dual-rate DS-CDMA systems using bandwidth-efficient chip pulses, over a single-path additive white Gaussian noise channel. Errors in the interferer chip delay estimates degrade the CLMF performance. However, if the root-mean-square value of these errors is less than 5% of the chip interval, then this degradation is small     

A temperature-insensitive polarization filter and a neotype sensor based on a hybrid-circular-hole microstructured optical fiber

A temperature-insensitive polarization filter and a neotype sensor based on a hybrid-circular-hole microstructured optical fiber (MOF) are proposed. Numerical investigations demonstrate that the x polarized component of silica core mode can couple to the cladding mode in the researched wavelength, while the y polarized component would not. Furthermore, the resonant region can be controlled by changing the diameters or coordinates of the air holes, and the MOF has good performance on stability of temperature. Moreover, the hybrid-circular-hole structure is propitious to selectively integrate different functional materials. Two different materials are integrated into this proposed MOF, the application of the Sagnac interferometer in temperature sensing is studied, and two groups of dips would be observed in the transmission spectra, which have different temperature sensitivities. Therefore, the proposed MOF can be used as a flexible temperature-insensitive polarization filter or potentially applied to a two-parameter sensor.     

Sampling rate selection for a digital matched filter

The problem of selecting the sampling rate for the digital implementation of a matched filter for noncoherent digital communications is considered. The effects of bandwidth reduction and sampling are evaluated. A Nyquist rate of 8 samples per bit is found to be the critical value even with respect to the dependence on the carrier phase.     

1000 bit surface-wave matched filter

A 1010 bit, biphase-coded, surface-wave matched filter on s.t.-cut quartz is described, and waveforms are shown. The matched filter was designed to operate with a 60 MHz carrier and 10 Mbit/s code rate (0.1 ?s tap spacing). Measurements indicate that the predicted performance is achievable by application of straightforward design procedures and fabrication techniques.     

Real-time speaker tracking using particle filter sensor fusion

Sensor fusion for object tracking has become an active research direction during the past few years. But how to do it in a robust and principled way is still an open problem. In this paper, we propose a new fusion framework that combines both the bottom-up and top-down approaches to probabilistically fuse multiple sensing modalities. At the lower level, individual vision and audio trackers are designed to generate effective proposals for the fuser. At the higher level, the fuser performs reliable tracking by verifying hypotheses over multiple likelihood models from multiple cues. Unlike traditional fusion algorithms, the proposed framework is a closed-loop system where the fuser and trackers coordinate their tracking information. Furthermore, to handle nonstationary situations, the proposed framework evaluates the performance of the individual trackers and dynamically updates their object states. We present a real-time speaker tracking system based on the proposed framework by fusing object contour, color and sound source location. We report robust tracking results.     

利用波长检测的光纤温度传感器

基于应力型保偏光纤传输差对温度的敏感性及保偏光纤模式干涉理论,提出了利用波长的温度检测方法并推导出传感方程.传感方程表现出的温度与干涉频谱中对应的空间频率间呈线性关系,简化了温度解算的程序.实验中,对Fabry-Perot(F-P)可调谐滤波器的工作电压与相对应的允许通过波长的关系进行了研究,并使用F-P可调谐滤波器取代光谱仪来获取光谱,简化了实验设备.由于被测信息仅与波长信息有关,而与光在传播过程中所引起的光源光功率的浮动无关,所以,使用这种检测方法消除了光源的浮动以及光在传榆过程中的损耗等对系统的稳定性和精度的不利影响,提高了传感器的环境适应能力.     

High-resolution neural temperature sensor using fiber Bragggratings

We demonstrate a novel high-resolution neural temperature sensor using two fiber Bragg gratings (FBG's) and a modular artificial neural network which is used to learn the mapping relation among frequency, temperature, and the normalized transmission power spectrum. Because of the fast computational ability of the modular artificial neural network and the sensitivity of FBG's, the sensor can make high-resolution temperature and frequency measurements in real time. The experimental results show that the temperature resolution of this sensor can reach 0.005°C