基于脉冲位相的红外热波无损检测法测量缺陷深度

提出了基于脉冲位相分析的数据处理方法以实现红外热波无损检测法对缺陷深度的测量。对脉冲红外热波无损检测的时间信号进行傅里叶变换(FFT),提取位相频率信息,根据热波频率与传导深度的关系完成缺陷深度的检测。以热传导较快的铝材料为例,对自行设计的深度不同的平底洞缺陷进行实验,并通过应用Matlab的FFT分析得到不同深度平底洞缺陷在不同频率下的位相曲线,同时,应用VC++得到位相序列热图。实验结果表明了脉冲位相对缺陷深度检测的可行性,缺陷实际深度与实验深度存在d≈1.98μ的关系,同时位相图有效抑制了噪声的干扰,为材料和结构内部缺陷检测提供了一种有效处理方法。

红外热波脉冲位相法无损检测缺陷深度方法研究

针对目前缺陷深度定量无损检测的需求,利用脉冲式红外热波无损检测脉冲激励的特点,对平底洞试件进行脉冲式红外检测实验,在VC++中通过傅里叶变换处理得到位相热图序列,分析不同深度缺陷的盲频,进而得到缺陷深度.两种材料的深度校正曲线和误差表明,脉冲位相法为缺陷深度检测提供了有效手段.

γ射线脉冲星脉冲位相关系的研究

本文分析γ射线脉冲星最近的观测数据，研究各波段辐射位相的一些关联，它们对于揭示γ射线脉冲星的辐射机制可能有重要的意义，

应用于多程脉冲激光放大器的宽带放大算法研究

依据激光在均匀加宽增益介质中的宽带放大理论模型,在亚纳秒量级,分别使用短时傅里叶变换、极化强度时域解析法和龙格-库塔法等三种数值模拟方法详细研究了时间域位相调制脉冲激光在多程放大器中的宽带放大效应,得到了激光通过多程放大器之后的脉冲时空波形演化。结果表明,在脉冲激光持续时间远大于增益介质退相时间的条件下,极化强度时域解析法在三种数值模拟方法中耗时最少、精度最高;而且该方法可以在几十皮秒至纳秒量级使用。

Frequency synthesizer for DRM/DAB/AM/FM RF front-end

This paper describes a wideband low phase noise frequency synthesizer.It operates in the multi-band including digital radio mondiale DRM digital audio broadcasting DAB amplitude modulation AM and frequency modulation FM .In order to cover the signals of the overall frequencies a novel frequency planning and a new structure are proposed. A wide-band low-phase-noise low-power voltage-control oscillator VCO and a high speed wide band high frequency division ratio pulse swallow frequency divider with a low power consumption are presented.The monolithic DRM/DAB/AM/FM frequency synthesizer chip is also fabricated in a SMIC＇s 0.18-μm CMOS process.The die area is 1 425 μm ×795 μm including the test buffer and pads. The measured results show that the VCO operating frequency range is from 2.22 to 3.57 GHz the measured phase noise of the VCO is 120.22 dBc/Hz at 1 MHz offset the pulse swallow frequency divider operation frequency is from 0.9 to 3.4 GHz.The phase noise in the phase-locked loop PLL is-59.52 dBc/Hz at 10 kHz offset and fits for the demand of the DRM/DAB/AM/FM RF front-end. The proposed frequency synthesizer consumes 47 mW including test buffer under a 1.8 V supply.

Asymmetry in the Strong-field Photodetachment of H- by Linearly Polarized Few-cycle Pulses

Photodetachment of H- irradiated by linearly polarized few-cycle laser field is investigated by time-dependent SchrSdinger equation numerically. The photo-electron left-right asymmetry parameter as a function of carrier-envelop （CE） phase of few-cycle pulses is attained. We confirm the asymmetry of photoelectron distribution in H- photodetachment and find that the maximal asymmetry parameter of H- is equal to that of H atom under the same conditions but the corresponding CE phases are quite different. Thus a CE phase shift appears. Compared to that of H atom and field free electron, the zero asymmetry CE phase shift is sensitively affected by Coulomb field. The Coulomb effect on the asymmetry of H- photodetachment mainly behaves in the CE phase shift of H- instead of the amplitude of asymmetry parameter curve.

Low-Density Parity-Check Codes for Noncoherent UWB Communication Systems

In order to guarantee reliable data transmission, powerful channel coding techniques are usually required in noncoherent ultra-wideband(UWB) communication systems. Accordingly, several forward error correction(FEC) codes, such as Reed-Solomon and convolutional codes have been used in noncoherent UWB systems to improve the bit error rate(BER) performance. In this paper, low-density parity-check(LDPC) codes are further studied as more powerful FEC candidates for noncoherent UWB systems. Two LDPC codes and the corresponding decoding procedures are presented for noncoherent UWB systems. Moreover, performance comparison between the LDPC codes and other FEC codes are provided for three major noncoherent UWB communication systems, namely, noncoherent pulse position modulation(NC-PPM), transmitted reference(TR) and transmitted reference pulse cluster(TRPC). Both theoretical analysis and simulation results show that the two investigated LDPC codes outperform other existing FEC codes with limited penalty in terms of complexity and therefore they are promising FEC candidates for noncoherent UWB systems with low-cost and low-power consumption.

Contrast enhancement of medical ultrasound imaging with reversal phase-inversion pulse technology

A new ultrasound contrast imaging technique was proposed for eliminating the harmonic components from the emission signal transmitted by the broadband ultrasonic system.Reversal phase-inversion pulse was used for the first time to separate the contrast harmonics from the harmonics in the emission signal to improve the detection of contrast micro-bubbles.Based on the nonlinear acoustic theory of finite-amplitude effects and the associated distortion of the propagating wave,the Bessel-Fubini series model was applied to describe the nonlinear propagation effects of the reversal phase-inversion pulse,and the Church's equation for zero-thickness encapsulation model was used to produce the scattering-pulse of the bubble.For harmonic imaging,the experiment was performed using a 64-element linear array,which was simulated by Field II.The results show that the harmonic components from the emission signal can be completely cancelled,and the harmonics generated by the nonlinear propagation of the wave through the tissue,can be reduced by 15-30 dB.Compared with the short pulse,the reversal phase-inversion pulse can improve the contrast and definition of the harmonic image significantly.

Modified nonlinear chirp scaling algorithm for curvilinear trajectory synthetic aperture radar

The original nonlinear chirp scaling(NCS) algorithm was extended for high precision processing of the highly squinted curvilinear trajectory synthetic aperture radar(CTSAR).Based on the analysis of slant range model and the frequency spectrum characteristics of the echo signal,a novel nonlinear chirp scaling function and more complex phase compensation factors with both velocity and acceleration parameters were proposed in the new algorithm for accommodation to curvilinear trajectory.The processing flow and computational complexity of modified NCS algorithm were fundamentally the same as the original NCS algorithm.However,the higher order phase compensation,range cell migration correction(RCMC) and range-variant secondary range compression(SRC) caused by the non-linear aperture and the severe range-azimuth coupling were accomplished accurately and efficiently without interpolation.Simulation results show that data acquired with a curvilinear aperture and a squint angle up to about 50° for X-band can be processed with no evident degradation of impulse response function.

Fault Diagnosis and Phase Disposition Reconfiguration of a 5-Level Double-Boost Power Factor Corrector with Fault-Tolerant Capability

A 5-level PFC （power factor correction） topology with fault-diagnostic and fault-tolerant capability is proposed and compared to known structures. It is derived from a 3-level non differential double-boost PFC including fly-cap cells. The series-connection of the two low-voltage switching-cells is decoupled by a single flying capacitor that provides a direct fault-tolerant capability and a post-failure operation increasing the availability of converter. The monitoring of the voltages across flying capacitors allows a rapid detection and localization either for open circuit failure or short-circuits failure. A PWM （pulse width modulation） phase-disposition type reconfiguration is also used and presented in order to optimize both normal operation and post-fault continuation. The design and the most important features are highlighted thanks to a digital control frame and a mock-up rated to： AC voltage network 115 V-load 400 V-nominal power 4 kW-switching frequency 62 kHz.

Effect of Carried-Envelope Phase on Transient Process in a Cascade-Type System

This paper investigates the effect of carried-envelope phase on transient process in a cascade-type atomic system, which is driven by two ultrashort laser pulses （probe and signal laser）. It is found that the one- and two-photon processes corresponding to pathway ｜0〉→｜1〉and ｜0〉→｜1〉→｜2〉 can be enhanced or ,suppressed by modulating the carried-envelope phases of probe laser pulse. Our numerical results also show that the transient populations of two excited states can be periodically affected by the carried-envelope phase of probe laser pulse. With certain time, the partial population transfer between two exited states can be realized just by adjusting the carried-envelope phase of probe laser pulse.

Suppression of Pulse Interference in Partial Discharge Measurement Based on Phase Correlation and Waveform Characteristics

Partial discharge measurement is one of the most effective methods to find insulation defects and early failure of high voltage power equipments. The accuracy is significantly reduced by the interference in the partial discharge on-site detection or on-line monitoring, especially by the pulse interference. This paper studies the phase correlation of some types of typical partial discharge pulses and their characteristics in time domain and frequency domain. By collecting enough partial discharge pulse data, the correlation coefficient can be calculated based on both phase correlation and waveform similarity. The type of pulse will be determined by the scope of the calculated correlation coefficient. The pulses with very strong correlation will be identified as periodic pulse interference. The pulses with very weak correlation will be identified as random pulse interference. Only the pulses whose correlation coefficients fall into a specific range will be identified as partial discharge signals. In laboratory, simulated pulse interference is injected into measurement circuit, and typical partial discharge pulses are sampled by a high-speed acquisition system. The pulse interference can be effectively separated from partial discharge signals by correlation coefficient.

Pulse phase and doppler frequency estimation of X-ray pulsars under conditions of spacecraft and binary motion and its application in navigation

The pulse phase and doppler frequency estimation of X-ray pulsars in dynamic situations and its application in navigation is a problem that has not been fully investigated. In this paper, solutions are proposed to solve this problem under conditions of spacecraft and binary motion. A high-precision doppler frequency (velocity) measurement model as well as a phase (range) measurement model is established. The averaged maximum-likelihood estimator is developed for the dynamic pulse phase estimation. The pulse phase tracking technique is used in the doppler frequency determination. The tracking filter is redesigned and compared with the existing algorithms. The comparison verifies the advantage of the filter algorithm presented in this pa- per. Unlike traditional views, it is found that in dynamic situations, shorter observation interval lengths will result in higher-accuracy phase and frequency estimates as the tracking filter outputs. A photon-level integrated numerical simulation is performed. Simulation results testify to the validity of the proposed phase and doppler frequency estimation scheme, and show that incorporation of velocity measurements as well as the range ones into the navigation estimator will improve the navigation steady-state performance.

X-ray pulsar-based navigation using pulse phase and Doppler frequency measurements

In order to eliminate the impact of the Doppler effects caused by the motion of the spacecraft on the X-ray pulsar-based navigation, an innovative navigation method using the pulse phase and Doppler frequency measurements of the X-ray pulsars is proposed. Given the initial estimate of the spacecraft's state,the real-time photon arrival model is established at the spacecraft with respect to the spacecraft's position and velocity predicted by the orbit dynamic model and their estimation errors. On this basis, a maximum likelihood estimation algorithm directly using the observed photon event timestamps is developed to extract a single pair of pulse phase and Doppler frequency measurements caused by the spacecraft's state estimation error. Since the phase estimation error increases as the observation time increases, we propose a new measurement updating scheme of referring the measurements to the middle time of an observation interval. By using the ground-based simulation system of X-ray pulsar signals, a series of photon-level simulations are performed. The results testify to the feasibility and real-timeliness of the proposed navigation method, and show that the incorporation of the Doppler measurement as well as the pulse phase into the navigation filter can improve the navigation accuracy.

Supercontinuum generation at 1.55 μm in an all-normal dispersion photonic crystal fiber with high-repetition-rate picosecond pulses

We demonstrate the generation of supercontinuum(SC) spectrum covering S+C+L band of optical communication by injecting 1.4 ps optical pulses with center wavelength of 1552 nm and repetition rate of 10 GHz into an all-normal dispersion photonic crystal fiber(PCF) with length of 80 m. The experimental results are in good agreement with the numerical simulations, which are used to illustrate the SC generation dynamics by self-phase modulation and optical wave breaking(WB).

Mechanisms of self-similar pulses generation in a normal dispersion-decreasing fiber

Based on the principle of virtual equivalent gain,the evolution of self-similar pulses in a normal dispersion-decreasing fiber is investigated.The occurrence of wave breaking during the process under highly nonlinear conditions and the effect of its revealed four-wave mixing on the process are also analyzed.The results indicate that the pulse spectrum broadeningin the initial stage is dominated by self-phase modulation while by four-wave mixing in the later stage.The more intense nonlinearity is,the faster the pulse evolution converges to the self-similarity synchronously in both the time domain and the spectrum domain.

Photonic envelope detection and fiber transmission of 24 GHz IR-UWB signal based on phase modulation

A novel scheme for photonic envelope detection and fiber transmission of 24 GHz impulse radio ultra-wideband(IRUWB) signal is proposed based on phase modulator(PM). In the system, an optics assisted envelope detection unit(OAEDU) is used for filtering one of the first sidebands at the output of PM, then this narrow band optical signal transfers over single-mode fiber(SMF), and the envelope of 24 GHz IR-UWB signal is obtained after photodetection(PD) and low pass filter(LPF). The numerical simulation results show that the combination of PM and OAEDU can alleviate the fiber chromatic dispersion(CD) effectively. The proposed system may provide a simple and cost-effective solution for IR-UWB receiver.

Numerical study on pulse trapping in birefringent photonic crystal fibers

Using an adaptive split-step Fourier method,the coupled nonlinear Schrdinger equations have been numerically solved in this paper.The nonlinear propagation of an ultrashort optical pulse in the birefringent photonic crystal fibers is investigated numerically.It is found that the phenomenon of pulse trapping occurs when the incident pulse is deviating from the principal axis of the fiber with some angle.Owing to the birefringence effect,the incident pulse can be regarded as two orthogonal polarized pulses.The phenomenon of pulse trapping occurs because of the cross phase modulation(XPM) between the two components.As a result,the bandwidth of the supercontinuum(SC) decreases compared with the case that the incident pulse is input along the principal axis.When the polarization direction of the incident pulse is parallel to the fast axis,the bandwidth of the supercontinuum is maximal.