The low temperature phase transformation in the Cu_2ZnSnS_4（CZTS） films was investigated by laser annealing and low temperature thermal annealing.The Raman measurements show that a-high-power laser annealing could c...The low temperature phase transformation in the Cu_2ZnSnS_4（CZTS） films was investigated by laser annealing and low temperature thermal annealing.The Raman measurements show that a-high-power laser annealing could cause a red shift of the Raman scattering peaks of the kesterite（KS） structure and promotes the formation of the partially disordered kesterite（PD-KS） structure in the CZTS films,and the low-temperature thermal annealing only shifts the Raman scattering peak of KS phase by several wavenumber to low frequency and the broads Raman peaks in the low frequency region.Moreover,the above two processes were reversible.The Raman analyses of the CZTS samples prepared under different process show that the PD-KS structure tends to be found at low temperatures and low sulfur vapor pressures.Our results reveal that the control of the phase structure in CZTS films is feasible by adjusting the preparation process of the films.展开更多
The transient radial shearing interferometry technique based on fast Fourier transform(FFT)provides a means for the measurement of the wavefront phase of transient light field.However,which factors affect the spatial ...The transient radial shearing interferometry technique based on fast Fourier transform(FFT)provides a means for the measurement of the wavefront phase of transient light field.However,which factors affect the spatial bandwidth of the wavefront phase measurement of this technology and how to achieve high-precision measurement of the broad-band transient wavefront phase are problems that need to be studied further.To this end,a theoretical model of phase-retrieved bandwidth of radial shearing interferometry is established in this paper.The influence of the spatial carrier frequency and the calculation window on phase-retrieved bandwidth is analyzed,and the optimal carrier frequency and calculation window are obtained.On this basis,a broad-band transient radial shearing interference phase-retrieval method based on chirp Z transform(CZT)is proposed,and the corresponding algorithm is given.Through theoretical simulation,a known phase is used to generate the interferogram and it is retrieved by the traditional method and the proposed method respectively.The residual wavefront RMS of the traditional method is 0.146λ,and it is 0.037λfor the proposed method,which manifests an improvement of accuracy by an order of magnitude.At the same time,different levels of signal-to-noise ratios(SNRs)from 50 dB to 10 dB of the interferogram are simulated,and the RMS of the residual wavefront is from 0.040λto 0.066λ.In terms of experiments,an experimental verification device based on a phase-only spatial light modulator is built,and the known phase on the modulator is retrieved from the actual interferogram.The RMS of the residual wavefront retrieved through FFT is 0.112λ,and it decreases to 0.035λthrough CZT.The experimental results verify the effectiveness of the method proposed in this paper.Furthermore,the method can be used in other types of spatial carrier frequency interference,such as lateral shearing interference,rotational shearing interference,flipping shearing interference,and four-wave shearing interference.展开更多
The computational load is prohibitive for real-time image generation in 3-D sonar systems, particularly when the steering angle approximation is required. In this paper, a novel multiple Chirp Zeta Transforms (MCZT) b...The computational load is prohibitive for real-time image generation in 3-D sonar systems, particularly when the steering angle approximation is required. In this paper, a novel multiple Chirp Zeta Transforms (MCZT) beamforming method in frequency domain is being proposed. The single long-length Chirp Zeta Transform (CZT) in the original CZT beamforming is replaced by several CZTs with smaller lengths for different partitions along each dimension. The implementing routine of the algorithm is also optimized. Furthermore, an avenue to evaluate the estimating error for the angle approximation in 3-D imaging applications is presented, and an approach to attain valid partitions for the steering angles is also illustrated. This paper demonstrates a few advantages of the proposed frequency-domain beamforming method over existing methods in terms of the computational complexity.展开更多
为获得准确的间谐波信号的频率分布估计值,文章提出了基于插值线性调频Z变换(chirp Z transform,CZT)的间谐波分析方法。该方法通过CZT变换获得精确的等价于离散傅里叶变换结果的间谐波信号的频率分布估计值,利用基于Rife-Vincent Ⅲ窗...为获得准确的间谐波信号的频率分布估计值,文章提出了基于插值线性调频Z变换(chirp Z transform,CZT)的间谐波分析方法。该方法通过CZT变换获得精确的等价于离散傅里叶变换结果的间谐波信号的频率分布估计值,利用基于Rife-Vincent Ⅲ窗的双谱线插值修正公式修正上述估计结果,得到了较精确的各次谐波和间谐波参数。仿真结果验证了该方法的正确性和有效性,与现有方法的比较结果表明,相同采样频率下该方法的检测精度更高。展开更多
为进一步研究故障电弧特征,针对三相电动机及变频器负载开展了串联故障电弧实验。首先将电流信号经过一阶差分预处理,再通过奇异值分解SVD(singular value decomposition)对信号进行两级滤波,剔除信号中的工频和噪声成分。采用柯尔莫可...为进一步研究故障电弧特征,针对三相电动机及变频器负载开展了串联故障电弧实验。首先将电流信号经过一阶差分预处理,再通过奇异值分解SVD(singular value decomposition)对信号进行两级滤波,剔除信号中的工频和噪声成分。采用柯尔莫可洛夫-斯米洛夫K-S(Kolmogorov-Smirnov)检验法分析SVD滤波信号的正态分布情况。采用线性调频Z变换CZT(chirp-Z transform)对SVD滤波信号0~500 Hz频段进行频谱细化分析。提取时域峭度和特征频段幅值平均值组成特征向量,并构建故障电弧区矩形。通过大量数据测试表明:该方法可有效识别三相电动机及变频器负载回路中发生的故障电弧。展开更多
基金Project supported by the Natural Science Foundation for Youth Fund of Hebei Province,China(Grant No.A2016201087)the Specialized Research Fund for the Doctoral Program of Higher Education of China(Grant No.20131301120003)the National Natural Science Foundation of China(Grant Nos.11504078and 61504054)
文摘The low temperature phase transformation in the Cu_2ZnSnS_4（CZTS） films was investigated by laser annealing and low temperature thermal annealing.The Raman measurements show that a-high-power laser annealing could cause a red shift of the Raman scattering peaks of the kesterite（KS） structure and promotes the formation of the partially disordered kesterite（PD-KS） structure in the CZTS films,and the low-temperature thermal annealing only shifts the Raman scattering peak of KS phase by several wavenumber to low frequency and the broads Raman peaks in the low frequency region.Moreover,the above two processes were reversible.The Raman analyses of the CZTS samples prepared under different process show that the PD-KS structure tends to be found at low temperatures and low sulfur vapor pressures.Our results reveal that the control of the phase structure in CZTS films is feasible by adjusting the preparation process of the films.
基金Project supported by the National Natural Science Foundation of China(Grant No.61705254)the Key Research and Development Program of Shaanxi Province of China(Grant No.2020GY-114).
文摘The transient radial shearing interferometry technique based on fast Fourier transform(FFT)provides a means for the measurement of the wavefront phase of transient light field.However,which factors affect the spatial bandwidth of the wavefront phase measurement of this technology and how to achieve high-precision measurement of the broad-band transient wavefront phase are problems that need to be studied further.To this end,a theoretical model of phase-retrieved bandwidth of radial shearing interferometry is established in this paper.The influence of the spatial carrier frequency and the calculation window on phase-retrieved bandwidth is analyzed,and the optimal carrier frequency and calculation window are obtained.On this basis,a broad-band transient radial shearing interference phase-retrieval method based on chirp Z transform(CZT)is proposed,and the corresponding algorithm is given.Through theoretical simulation,a known phase is used to generate the interferogram and it is retrieved by the traditional method and the proposed method respectively.The residual wavefront RMS of the traditional method is 0.146λ,and it is 0.037λfor the proposed method,which manifests an improvement of accuracy by an order of magnitude.At the same time,different levels of signal-to-noise ratios(SNRs)from 50 dB to 10 dB of the interferogram are simulated,and the RMS of the residual wavefront is from 0.040λto 0.066λ.In terms of experiments,an experimental verification device based on a phase-only spatial light modulator is built,and the known phase on the modulator is retrieved from the actual interferogram.The RMS of the residual wavefront retrieved through FFT is 0.112λ,and it decreases to 0.035λthrough CZT.The experimental results verify the effectiveness of the method proposed in this paper.Furthermore,the method can be used in other types of spatial carrier frequency interference,such as lateral shearing interference,rotational shearing interference,flipping shearing interference,and four-wave shearing interference.
基金National High Technology Research and Development Program (863 Program) of China (No. 2010AA09Z104)the Fundamental Research Funds for the Central Universities
文摘The computational load is prohibitive for real-time image generation in 3-D sonar systems, particularly when the steering angle approximation is required. In this paper, a novel multiple Chirp Zeta Transforms (MCZT) beamforming method in frequency domain is being proposed. The single long-length Chirp Zeta Transform (CZT) in the original CZT beamforming is replaced by several CZTs with smaller lengths for different partitions along each dimension. The implementing routine of the algorithm is also optimized. Furthermore, an avenue to evaluate the estimating error for the angle approximation in 3-D imaging applications is presented, and an approach to attain valid partitions for the steering angles is also illustrated. This paper demonstrates a few advantages of the proposed frequency-domain beamforming method over existing methods in terms of the computational complexity.
文摘为获得准确的间谐波信号的频率分布估计值,文章提出了基于插值线性调频Z变换(chirp Z transform,CZT)的间谐波分析方法。该方法通过CZT变换获得精确的等价于离散傅里叶变换结果的间谐波信号的频率分布估计值,利用基于Rife-Vincent Ⅲ窗的双谱线插值修正公式修正上述估计结果,得到了较精确的各次谐波和间谐波参数。仿真结果验证了该方法的正确性和有效性,与现有方法的比较结果表明,相同采样频率下该方法的检测精度更高。
文摘为进一步研究故障电弧特征,针对三相电动机及变频器负载开展了串联故障电弧实验。首先将电流信号经过一阶差分预处理,再通过奇异值分解SVD(singular value decomposition)对信号进行两级滤波,剔除信号中的工频和噪声成分。采用柯尔莫可洛夫-斯米洛夫K-S(Kolmogorov-Smirnov)检验法分析SVD滤波信号的正态分布情况。采用线性调频Z变换CZT(chirp-Z transform)对SVD滤波信号0~500 Hz频段进行频谱细化分析。提取时域峭度和特征频段幅值平均值组成特征向量,并构建故障电弧区矩形。通过大量数据测试表明:该方法可有效识别三相电动机及变频器负载回路中发生的故障电弧。
