252Cf源驱动功率谱密度法测量系统

介绍了252Cf源驱动功率谱密度法测量原理,采用硬件和软件相结合的方式构建实现了一种实际的测量系统和研究平台,以服务于反应堆核参数测量。描述了基于3通道、1 GHz采样率和1 ns同步精度的超高速数据采集卡的中子脉冲序列检测方法,并设计了PC机端的数据处理流程和功率谱密度分析算法。实际测量结果表明,该252Cf源驱动功率谱密度法测量系统能准确高效地得到核随机过程的相关函数和功率谱密度等重要标签参数。     

Extending the response spectrum of organic photodetectors by quaternary active layer method with complementary absorption spectra

In this work, we report a new method for extending the response spectra of organic photodetectors (OPDs) by incorporating PBDT-TT-C and PBDT-TT-F in the P3HT:PC₆₁BM. The effects of PBDT-TT-C and PBDT-TT-F incorporation on the optical and electrical properties of OPDs were investigated, It was found that when the mass ratio of P3HT:PBDT-TT-F:PBDT-TT-C:PC₆₁BM was 12:2:2:8, the response spectrum of the active layer was extended to 780 nm. The responsivity (R) and external quantum efficiency (EQE) of the OPDs reached 340, 376, 315 mA/W and 67%, 88%, 85% under 630, 530, and 460 nm illumination and −1 V bias, respectively, and the detectivity (D*) reached 10¹² Jones. The results show that the inclusion of an appropriate amount of donor material with similar chemical structure and complementary absorption spectrum can reduce the influence of the doping material on the micro-morphology of the original film while improving the absorption of the spectrum. The interaction between the donor materials promotes the generation of photogenerated carriers and increases the photocurrent of the OPDs. In addition, the incorporation of the different component promotes crystallization of the film, resulting in a reduction in dark current of the OPDs.     

Acoustic power measurement using an optical heterodyne method

An optical heterodyne method is presented for measuring the Raman-Nath parameter of ultrasound. A light beam passes through a phase grating induced by ultrasound and then is recombined with another beam of light at a shifted frequency. The interference distribution of the two light beams is measured by a photodetector placed in the Fresnel region. The Raman-Nath parameter is determined from the amplitudes of frequency components in the beat signal and is independent of observation position. A theoretical analysis is given which includes pulsed ultrasound. Acoustic power determined using the technique is shown to agree fairly well with the radiation force method. Acoustic fields from a linear array transducer are also investigated. A problem involved in focused ultrasound is discussed.     

252Cf源驱动功率谱密度法测量系统

介绍了252Cf源驱动功率谱密度法测量原理,采用硬件和软件相结合的方式构建实现了一种实际的测量系统和研究平台,以服务于反应堆核参数测量。描述了基于3通道、1 GHz采样率和1 ns同步精度的超高速数据采集卡的中子脉冲序列检测方法,并设计了PC机端的数据处理流程和功率谱密度分析算法。实际测量结果表明,该252Cf源驱动功率谱密度法测量系统能准确高效地得到核随机过程的相关函数和功率谱密度等重要标签参数。     

Analysis of a loss-compensated recirculating delayed self-heterodyne interferometer for laser linewidth measurement

A loss-compensated recirculating delayed self-heterodyne interferometer (LC-RDSHI) for laser linewidth measurement is theoretically analyzed. An analytical result for the output spectrum of the LC-RDSHI is obtained. It is found that the spectrum from a LC-RDSHI is equivalent to a spectrum from a conventional delayed self-heterodyne interferometer with equivalent time delay and frequency shift, but modified by a periodical function, which could significantly influence the laser linewidth measurement. The parameters of a LC-RDSHI must be optimized to permit an accurate and direct measurement of laser linewidth from the output spectrum.     

Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors

With consideration of the modulation frequency of the input lightwave itself, we present a new model to calculate the quantum efficiency of RCE p-i-n photodetectors (PD) by superimposition of multiple reflected lightwaves. For the first time, the optical delay, another important factor limiting the electrical bandwidth of RCE p-i-n PD excluding the transit time of the carriers and RC_d response of the photodetector, is analyzed and discussed in detail. The optical delay dominates the bandwidth of RCE p-i-n PD when its active layer is thinner than several 10~nm. These three limiting factors must be considered exactly for design of ultra-high-speed RCE p-i-n PD.     

Proposal of dual-heterodyne-mixing method and application to high-speed waveform measurement using low-speed equipments

A novel method to measure a relative phase between frequency-different optical wavelengths has been proposed and named as Dual-heterodyne-mixing method. The operation principle of the method is represented, where the relative phase is simply described as dc voltage. The operation principle was experimentally confirmed with 0- and π-phase-different optical pairs generated by an intensity modulator. Also, it has been applied for a high-speed signal sensing with a high-resolution amplitude spectrum measurement method. A 12.5 Gbps signal sensing with 1/63 relatively low-speed photodetector (200 MHz) was demonstrated.     

X波段高功率微波馈源辐射总功率阵列法测量技术

分析了采用阵列法测量高功率微波(HPM)馈源辐射总功率的相关技术环节。仿真计算了某型X带HPM馈源辐射场分布,设计了积分法测量辐射总功率的参数,并对积分总功率与端口注入功率的关系以及积分方法引入的测量误差进行了计算。设计了由8路HPM辐射场功率密度测量系统组成阵列,对馈源辐射场功率密度进行测量,保证功率密度测量结果一致性和重复性。测量结果表明：多路测量系统测量波形相同,单路系统多次重复测量偏差在±0.1 dB内,多路测量系统对同一点辐射场功率密度测量偏差在±0.3 dB内,馈源热测E面方向图与冷测结果基本符合,积分总功率与等效辐射功率测量结果吻合较好。     

激光自外差相干测量中分布反馈半导体激光器电流调谐非线性的补偿方法

半导体激光器的电流调谐非线性对自外差相干测量的精度影响很大.研究了分布反馈半导体(DFB) 激光器的电流调谐特性,据此提出一种数学模型补偿方法.利用已知光程差下的差拍频率,建立了动态调频 系数的数学模型.以此模型对DFB激光器的电流调谐非线性进行补偿,可以将差拍信号频率预测值的相对误差 减小约3%,提高了系统的测量精度.数学模型补偿方法简化了测量系统的结构,适用于高精度的电流调谐 激光在线测量系统.     

Displacement power spectrum measurement by CPMG in constant gradient

The modulation of spin phase produced by Carr-Purcell-Meiboom-Gill (CPMG) sequence in combination with constant magnetic field gradient is appropriate to probe the displacement power spectrum (DPS). The spin-echo attenuation is directly proportional to the DPS value at the applied modulation frequency. Relaxation and selective excitation effects can be factored out while probing the DPS. The modulation frequency is adjusted by varying the pulse separation time while the gradient strength and the time of acquisition are kept constant. In designing the experiment gradient strength limitations, imposed by off-resonance effects, as well as limitations arising from using Gaussian phase approximation must be considered. An effective experimental strategy is presented, supported by experimental results for free and restricted diffusion.     

Fiber chromatic dispersion measurement by using a novel RF spectrum phase detection method based on DSP

In this paper, a novel chromatic dispersion (CD) measuring method based on a novel RF spectrum phase detection technique is proposed, this is performed using in-band tone monitoring RF, electrically down-converted to direct current (DC) or a low intermediate-frequency (IF) of less than 1 MHz through electronic mixing with local oscillator (LO). We theoretically and experimentally demonstrated the CD measurement for CD components (etc. fiber). The method can support any CD range measuring with good accuracy through adjusting RF frequency.     

Frequency response testing in a noisy environment or with a limited power supply

The current trend in dynamic testing is towards short duration, transient testing in the field followed by detailed computer analysis of the data at some later time. For many applications, tests must be carried out in a noisy environment, such as in frequency response studies of operating machinery and vibration tests on buildings or ships where the excitation power source is small and produces a low level response compared with ambient vibration levels. The use of time domain averaging is demonstrated and it is shown to be a suitable signal enhancement procedure for testing in poor signal to noise ratio conditions, when using a transient excitation technique. The limitations and accuracy of the technique are discussed and examples of practical application are given.     

Accuracy optimization method of ultrasonic power measurement system based on acousto-optic effect

Optical Review - Ultrasonic wave has been widely used in the medical field because of its special physical properties. However, it might cause health risk for the human body if the power is...     

Quantification of the power changes in BOLD signals using Welch spectrum method during different single-hand motor imageries

Motor imagery is an experimental paradigm implemented in cognitive neuroscience and cognitive psychology. To investigate the asymmetry of the strength of cortical functional activity due to different single-hand motor imageries, functional magnetic resonance imaging (fMRI) data from right handed normal subjects were recorded and analyzed during both left-hand and right-hand motor imagery processes. Then the average power of blood oxygenation level-dependent (BOLD) signals in temporal domain was calculated using the developed tool that combines Welch power spectrum and the integral of power spectrum approach of BOLD signal changes during motor imagery. Power change analysis results indicated that cortical activity exhibited a stronger power in the precentral gyrus and medial frontal gyrus with left-hand motor imagery tasks compared with that from right-hand motor imagery tasks. These observations suggest that right handed normal subjects mobilize more cortical nerve cells for left-hand motor imagery. Our findings also suggest that the approach based on power differences of BOLD signals is a suitable quantitative analysis tool for quantification of asymmetry of brain activity intensity during motor imagery tasks.     

浅海多径时延估计的功率谱加权自相关方法

针对浅海近距离时倒谱多径时延峰变弱难以提取的问题,提出了一种功率谱加权自相关多径时延估计方法。该方法采用FFT估计信号功率谱,对功率谱取1-α次幂(0<α<1),再进行IFFT变换,对其实部进行峰值检测获得多径时延估计。根据目标能量通过特性在正横前递增正横后递减的特点,在已检测时延前后一定区间内搜索下一个时延值,实现多径时延的自动提取.理论分析表明,多径时延估计的倒谱法与自相关法都可以看作功率谱加权自相关法的特例.海试数据处理与基于Bellhop射线模型的仿真计算表明,该方法在近距离时多径时延峰比倒谱法更清晰,输出信噪比提高了3~4 dB.采用该方法自动提取的海底反射多径时延用于单个水听器对目标距离的估计,与GPS测量距离基本相符,验证了方法的有效性.     

Controlling a time-delay system using multiple delay feedback control

In this paper multiple delay feedback control (MDFC) with different and independent delay times is shown to be an efficient method for stabilizing fixed points in finite-dimensional dynamical systems. Whether MDFC can be applied to infinite-dimensional systems has been an open question. In this paper we find that for infinite-dimensional systems modelled by delay differential equations, MDFC works well for stabilizing (unstable) steady states in long-, moderate- and short-time delay regions, in particular for the hyperchaotic case.     

一种测量功率超声振动系统振速比的简单方法

本文提出了一种测量功率超声振动系统中振动速度比的简单方法。与传统的测量方法相比,本方法将力学量转变为电学量的测量,将绝对测量变成了相对测量,降低了对实验设备的要求,有利于提高测试精度。