Lorentz force electrical impedance tomography using pulse compression technique

Lorentz force electrical impedance tomography(LFEIT) combines ultrasound stimulation and electromagnetic field detection with the goal of creating a high contrast and high resolution hybrid imaging modality. In this study, pulse compression working together with a linearly frequency modulated ultrasound pulse was investigated in LFEIT. Experiments were done on agar phantoms having the same level of electrical conductivity as soft biological tissues. The results showed that:(i) LFEIT using pulse compression could detect the location of the electrical conductivity variations precisely;(ii)LFEIT using pulse compression could get the same performance of detecting electrical conductivity variations as the traditional LFEIT using high voltage narrow pulse but reduce the peak stimulating power to the transducer by 25.5 dB;(iii)axial resolution of 1 mm could be obtained using modulation frequency bandwidth 2 MHz.     

频域近红外光谱方法定量测量组织氧饱和度

通过精确测量光子密度波的相位延迟和幅度衰减,借助于一个光学参数已知的校准模型,可以定量检测组织的光学吸收参数和约化散射系数.通过测量多个波长下组织的吸收系数,就可以进一步求解出人体局部组织的血氧饱和度.血液－酵母溶液仿真模型和前臂动脉阻断实验的结果都表明该三波长的频域近红外光谱系统可以实时定量地检测组织氧饱和度的动态变化情况.     

New demodulation filter in digital phase rotation beamforming

In this paper, we present a new quadrature demodulation filter to reduce hardware complexity in digital phase rotation beamforming. Due to its low sensitivity to phase delay errors, digital quadrature demodulation is commonly used in ultrasound machines. However, since it requires two lowpass filters for each channel to remove harmonics, the direct use of conventional finite impulse response (FIR) filters in ultrasound machines is computationally expensive and burdensome. In our new method, an efficient multi-stage uniform coefficient (MSUC) filter is utilized to remove harmonic components in phase rotation beamforming. In comparison with the directly implemented FIR (DI-FIR) and the previously-proposed signed-power-of-two FIR (SPOT-FIR) lowpass filters, the proposed MSUC filter reduces the necessary hardware resources by 93.9% and 83.9%, respectively. In simulation, the MSUC filter shows a negligible degradation in image quality. The proposed method resulted in comparable spatial and contrast resolution to the DI-FIR approach in the phantom study. These preliminary results indicate that the proposed quadrature demodulation filtering method could significantly reduce the hardware complexity in phase rotation beamforming while maintaining comparable image quality.     

Full-field optical coherence tomography by two-dimensional heterodyne detection with a pair of CCD cameras

A two-dimensional heterodyne detection technique based on the frequency-synchronous detection method [Jpn. J. Appl. Phys. 39, 1194 (2000)] is demonstrated for full-field optical coherence tomography. This technique, which employs a pair of CCD cameras to detect the in-phase and quadrature components of the heterodyne signal simultaneously, offers the advantage of phase-drift suppression in interferometric measurement. Horizontal cross-sectional images are acquired at the rate of 100 frames/s in a single longitudinal scan, with a depth interval of 6 microm, making the rapid reconstruction of three-dimensional images possible.     

最小均方误差解调算法在彩色超声血流成像中的研究

研究了最小均方误差正交解调算法在超声血流成像中的应用。首先由设计的期望信号与接收信号在最小均方误差原则下得到其迭代解调形式,获得回波信号同相分量和正交分量,然后由得到的正交解调信号通过自相关的方法对血流流速进行估计。解调算法的仿真结果表明,对高斯噪声信噪比为0.5—10dB的正弦波调制信号,解调输出平均信噪比与Hilbert变换法和I/Q解调法相比分别提高了15dB和4dB;血流成像的仿真结果表明,在流速估计性能相当的情况下,解调的乘法运算量仅分别为上述对比方法的18%和9%。因此在超声血流成像中应用最小均方误差正交解调算法,对于提高估计性能和降低运算量都有一定意义。      

Generation of pure electrical quadrature amplitude modulation with photonic vector modulator

A photonic vector modulator architecture for generating pure quadrature amplitude modulation (QAM) signals is presented. An electrical quadrature-modulated signal at microwave-millimeter-wave frequencies is generated from its corresponding baseband in-phase (I) and quadrature (Q) components. In the proposed scheme, no electrical devices apart from the electrical tone oscillator are needed in the generation process. In addition, the purity of the generated signal is increased, and the hardware requirements are reduced when compared with previously proposed architectures so a highly compact low-cost architecture can be implemented. A pure 1.25 Gbit/s 4-QAM signal has been experimentally generated at a 42 GHz carrier frequency.     

简易脑功能近红外光谱系统设计

功能近红外光谱(functional near-infrared spectroscopy, fNIRS)是一种无损的脑成像技术,经过20年的发展,已广泛应用于认知神经科学研究领域。基于神经血管耦合机制,与功能相关的大脑神经活动增强会引起局部脑血流量的升高,进而引发血液中氧合血红蛋白与脱氧血红蛋白浓度相应的变化,间接反映了大脑中神经激活程度。研制了一套基于多功能采集卡的单通道连续波fNIRS系统。在该系统中,选择激光二极管作为光源具有较好的单色性和较低的发散角,690和830 nm波长的组合有助于降低发色团之间的串扰。频分复用技术用于区分来自不同光源的信号,同时也消除了环境光、工频干扰等特定频率的噪声源。利用LabVIEW软件平台实现了光源的时序控制、自动增益调节、数字正交相干解调,以及数据可视化与存储等功能。屏气和心算实验结果表明,该系统可用于监测大脑局部血红蛋白浓度的实时变化,并可以检测与高级脑功能相关的激活。     

Time division vector optical sampling for ultrafast amplitude/phase modulation device characterization

A technique is proposed and demonstrated for measuring the waveforms of optical signals by making use of homodyne in-phase and quadrature detection combined with nonlinear optical sampling. The technique is based on time division sampling of electric field components with a discretely phase-modulated local oscillator light and is applied for the evaluation of the ultrafast response in a semiconductor optical amplifier.     

Digital detection and processing of multiple quadrature harmonics for EPR spectroscopy

A quadrature digital receiver and associated signal estimation procedure are reported for L-band electron paramagnetic resonance (EPR) spectroscopy. The approach provides simultaneous acquisition and joint processing of multiple harmonics in both in-phase and out-of-phase channels. The digital receiver, based on a high-speed dual-channel analog-to-digital converter, allows direct digital down-conversion with heterodyne processing using digital capture of the microwave reference signal. Thus, the receiver avoids noise and nonlinearity associated with analog mixers. Also, the architecture allows for low-Q anti-alias filtering and does not require the sampling frequency to be time-locked to the microwave reference. A noise model applicable for arbitrary contributions of oscillator phase noise is presented, and a corresponding maximum-likelihood estimator of unknown parameters is also reported. The signal processing is applicable for Lorentzian lineshape under nonsaturating conditions. The estimation is carried out using a convergent iterative algorithm capable of jointly processing the in-phase and out-of-phase data in the presence of phase noise and unknown microwave phase. Cramér-Rao bound analysis and simulation results demonstrate a significant reduction in linewidth estimation error using quadrature detection, for both low and high values of phase noise. EPR spectroscopic data are also reported for illustration.     

High-speed fringe analysis by using stair-shaped virtual grating demodulation

This article describes a novel fringe analysis technique using stair-shaped virtual grating demodulation algorithm for extracting the phase information from a single fringe pattern. In contrast to the Fourier transform technique and quadrature multiplicative moire method, the new method processes a fringe pattern in the integer signal domain instead of the frequency domain and real-signal domain. The spatial carrier of fringe image is not limited to any particular frequency as long as it fulfills the sampling theorem. The errors analysis of this technique is conducted by computer simulation and experiments.     

基于信号自相关原理的光纤光栅数字解调方法

为满足工程测试领域对光纤光栅波长漂移高分辨探测技术的需要,提出一种基于信号自相关原理的新型光纤光栅数字解调技术.该技术在可调谐滤波法的基础上,通过对信号序列采用自相关分析以实现对波长漂移的测量以及对传感光栅反射谱形状的识别,能够有效克服噪音对信号的影响.仿真结果表明：光纤光栅自相关数字解调方法可以准确测量光纤光栅波长的漂移,适用于传感光栅具有相同波长的变化范围.     

Performance Comparison of Long-Haul Direct Detection Optical Transmission Systems Adopting Dispersion Management with Pre-Compensation

Abstract

This article reports a numerical investigation on the performance of return-to-zero intensity-modulated direct detection, return-to-zero differential phase shifting key, and return-to-zero differential quadrature phase shifting key systems operating in G.652 links adopting dispersion management. Also illustrated are the role and benefits of pre-compensation. For such an aim, the influence of the non-linear Kerr impairments on the in-phase and quadrature components of the signal are studied, along with the consequent degradations in terms of the Q-factor for the different modulation formats. Such an investigation is applied to evaluate the maximum propagation distances for 40- and 80-Gb/s capacities.     

Quadrature demodulation technique for self-mixing interferometry displacement sensor

A new, to the best of our knowledge, signal processing method based on quadrature demodulation technique is presented for laser diode self-mixing interferometry(LDSMI) displacement sensor. Phase modulation of the laser beam is obtained by an electro-optic modulator (EOM) in the external cavity. Detection of the target's displacement can be easily achieved by sampling the interference signal at those times which satisfied certain conditions. The major advantage of the technique is that it does not involve any complicated calculation and insensitive to the sampling error. Experimental results show that the proposed method can effectively improve the displacement measurement resolution of the laser diode self-mixing displacement sensor to a few nanometers.     

Identification of the dynamic characteristics of a structure with coulomb friction

The effect of coulomb friction on the Kennedy and Pancu vector plot of a single degree-of-freedom system is analyzed by using the method of harmonic balance. It is shown that the resulting diagram no longer conforms to a locus of a circle in the resonant region, which restricts the usual methods of analysis. A technique, based upon the in-phase and quadrature power dissipated when exciting a normal mode, is presented which allows the magnitude of the non-linear friction force and the hysteretic damping constant to be evaluated. The technique is also applied to systems having several degrees-of-freedom and it shows that it is possible to identify the characteristics of a single non-linear coulomb device situated within a structure, but in the case of more than one device, the technique has some restrictions. The theoretical results are compared with experimental data from a structure containing a non-linear coulomb device.     

An improved arctangent algorithm based on phase-locked loop for heterodyne detection system

We present an ameliorated arctangent algorithm based on phase-locked loop for digital Doppler signal processing,utilized within the heterodyne detection system. We define the error gain factor given by the approximation of Taylor expansion by means of a comparison of the measured values and true values. Exact expressions are derived for the amplitude error of two in-phase quadrature signals and the frequency error of the acousto-optic modulator. Numerical simulation results and experimental results make it clear that the dynamic instability of the intermediate frequency signals leads to cumulative errors, which will spiral upward. An improved arctangent algorithm for the heterodyne detection is proposed to eliminate the cumulative errors and harmonic components. Depending on the narrow-band filter, our experiments were performed to realize the detectable displacement of 20 nm at a detection distance of 20 m. The aim of this paper is the demonstration of the optimized arctangent algorithm as a powerful approach to the demodulation algorithm, which will advance the signal-to-noise ratio and measurement accuracy of the heterodyne detection system.     

激光多普勒微振动信号的直接强度解调

在传统的激光多普勒测振方法中,频移信号的检测通常需要具有比较复杂的频率或相位解调系统。从激光多普勒频移和干涉理论出发,提出了一种测量振幅小于纳米量级的方法———直接强度解调法。分析了直接强度解调法的适用范围。实验中利用了迈克尔逊干涉仪结构,采用了直接强度解调的方法。对振幅约为1nm的振动信号来说,其信噪比为23dB。     

量子干涉效应对原子共振荧光非经典特性的影响

研究了两个自发辐射路径之间的量子干涉效应对V型三能级原子压缩谱和光子反聚束效应的影响 .结果表明 ,量子干涉可以加强压缩效应和展宽出现压缩的相位角分量的范围 ,但却会减弱反聚束效应.Phase-dependent squeezing spectrum and photon antibunching of resonance fluorescence from a three-level V-type atom driven by a coherent field are investigated. We show that for weak excitation intensities quantum interference can greatly enhance squeezing and change the phase quadrature at which the maximum squeezing occurs. We also notice that the maximum squeezing can appear not only in either the in-phase or the out-of-phase quadrature but also in any phase quadrature, and at which phase quadrature...     

Error analysis of dual wavelength quadrature phase demodulation for low-finesse Fabry-Pérot cavity based fibre optic sensor

An analysis of the errors in the dual wavelength quadrature phase demodulation technique for low-finesse Fabry-Pérot cavity based fibre optic sensor is presented. A simple numeric model for calculating the error is established. For sensors that experience only small cavity length changes during measurement, a simplified analytical expression of relative error is also derived. Errors for various sets of interrogation wavelengths are calculated and analyzed. The results show that two wavelengths with very slight difference should be chosen to avoid significant errors.     

利用全光纤干涉解调技术的光纤光栅复用传感系统

提出了一种用于光纤光栅传感波长检测的新方法。系统采用全光纤Mach Zehnder干涉仪,运用动态的自参考相位检测方式,结合微机实时处理技术,实现了对三点复用传感器的高分辨率(0.99pm)解调,单点测量范围达3.32nm。系统结构简单、成本低,可以同时检测静态和低频动态信号。     

A quadrature demodulation method based on tracking the ultrasound echo frequency

The ultrasound echo attenuation depends on frequency, propagating depth and tissue characteristics. Thus, the attenuation dependent on frequency results in a larger attenuation of high frequencies than lower when the wave propagates through the tissue. As a result, the central frequency of the echo generates the increasing downshift with the increasing of depth. In the traditional I/Q demodulation method, it is assumed that the central frequency of the echo is the same as the transmitting frequency and unchanged all time. The assumption directly causes that the acquired I/Q signals are not perfect baseband ones but biased due to the echo attenuation. In addition, the unreasonable assumption will keep the echo from getting better signal-to-noise ratio. A quadrature demodulation method based on tracking the ultrasound echo frequency is proposed in this paper. The method consists of the traditional I/Q demodulator, the frequency tracking module, the phase compensation module and the dynamic filtering module. The outputs of I/Q demodulator are biased. Autocorrelation technique is utilized in the frequency tracking unit to estimate the frequency bias according to the outputs of I/Q demodulator. The estimated bias feeds to the phase compensation unit which can eliminate the frequency bias by simple trigonometric function transform. The compensated signals feed to the dynamic filter and are further processed. The bandwidth of the dynamic filter decreases with the increasing of the depth, which makes the echo acquire better SNR in different depth. The efficiency of the proposed method is testified by both simulations and experiments.