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- 摘要
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- 实验方案
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FFT analysis of surface structures fabricated by laser interference lithography
摘要： This paper presents an FFT (fast Fourier transform) analytical method for the study of surface structures fabricated by laser interference lithography (LIL). In the work, the FFT analytical method combined with Gaussian fitting is used to determine the periods and pattern distributions of surface structures from frequency spectra. For LIL, the processing parameters of incident and azimuth angles can be obtained corresponding to the period and pattern distribution. This work facilitates the detection of micro- and nano-structures, the analysis of pattern distribution in engineering, and the processing error analysis of LIL.
关键词： surface structures,micro- and nano-structures,pattern distribution,laser interference lithography,FFT analysis
更新于2025-11-25 10:30:42
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Real-time signal processing of photoplethysmographic signals to estimate the on-demand and continuous heart rate by spectral analysis
摘要： In healthcare applications, heart rate is one of the vital signs which give the health informatics of a person. Nowadays, the evolution of PPG sensors help to develop low cost heart rate monitoring devices with minimal hardware resources compared to ECG. In this paper, an efficient algorithm is proposed to find the heart rate using frequency spectrum analysis on PPG signals. Using the proposed algorithm, the heart rate is calculated with a pass percentage of 99.2, mean absolute percentage error (MAPE) of 1.59%, mean absolute error (MAE) of 1.20 BPM and reference closeness factor (RCF) of 0.989. The first reliable heart rate output comes in 6.5th second, which is the minimum possible time. The algorithm operates with a speed of 2 MIPS and with a memory of 18 KB. So the proposed method can be integrated to any low cost real-time embedded platforms to accurately measure the heart rate.
关键词： PPG,fast Fourier transform,heart rate,smoothing,frequency domain,FFT,photoplethysmography,decimation
更新于2025-09-23 15:23:52
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Powerful topographic analyzing technique using Fast Fourier Transform for c-Si solar cells and emerging technologies
摘要： Light management of a solar cell can be enhanced by improving Jsc with proper texturing. Topographic images obtained by confocal laser microscopy or AFM are used to study the roughness of textured surfaces. Fast Fourier Transform is employed to separate and select spatial frequencies, which will be analyzed through MountainsMap?. Various kind of samples can be studied such as textured c-Si solar cells or even tandem devices made of perovskite grains evaporated on Si pyramids. The structural, morphological and geometrical results can be extracted in a fast, automatic and repeatable way with a good throughput to enable statistical analysis.
关键词： spatial frequencies,FFT,roughness,silicon
更新于2025-09-23 15:21:01
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Extension of an FFT-Based Beam Propagation Method to Plasmonic and Dielectric Waveguide Discontinuities and Junctions
摘要： We adapted a fast Fourier transform-based Beam Propagation Method (FFT-BPM) to investigate waveguide discontinuities in plasmonic waveguides. The adaptation of the FFT-BPM to treat transverse magnetic (TM) fields requires the circumvention of two major difficulties: the mixed derivatives of the magnetic field and waveguide refractive index profile in the TM wave equation and the step-like index change at the transverse metal-dielectric boundary of the plasmonic guide and the transverse boundaries of the dielectric waveguide as well. An equivalent-index method is adopted to transform TM fields to transverse electric (TE) ones, thus enabling the benefit of the full power and simplicity of the FFT-BPM. Moreover, an appropriate smoothing function is used to approximate the step-like refractive index profile in the transverse direction. At the junction plane, we used an accurate combined spatial-spectral reflection operator to calculate the reflected field. To validate our proposed scheme, we investigated the modal propagation in a silicon waveguide terminated by air (like a laser facet in two cases: with and without a coating layer). Then we considered a subwavelength plasmonic waveguide (metal-insulator-metal MIM) butt-coupled with a dielectric waveguide, where the power transmission efficiency has been calculated and compared with other numerical methods. The comparison reveals good agreement.
关键词： butt-coupler,plasmonics,FFT-BPM,sensors,plasmonic waveguide,bi-directional BPM,photonics,reflection formalism,TM fields,optical propagation
更新于2025-09-23 15:19:57
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The Inspection of CFRP Laminate with Subsurface Defects by Laser Arrays Scanning Thermography (LAsST)
摘要： Laser array scanning thermography (LAsST) was used to detect the subsurface defects of carbon fiber reinforced composite (CFRP). A series of bottom flat hole (BFHs) of CFRP were prepared for LAsST. Truncation pseudo-static matrix reconstruction (TC-PSMR) method was used to reconstruct the thermal response signal. Fast Fourier transform (FFT), principal component analysis (PCA) and partial least squares regression (PLSR) were used to process the thermal response signals, forming FFT image, PCA image, and PLSR image. The signal noise ratios (SNRs) of defects is calculated, and it is used to evaluate the defect detection ability of different post-processing algorithms. The experimental results show that the image based on FFT phase has a higher signal-to-noise ratio with PLSR image, and the FFT amplitude image and PLSR image can accurately represent the defect size.
关键词： FFT,Laser arrays scan thermography,Partial least squares regression,CFRP
更新于2025-09-23 15:19:57
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Two numerical methods for the Zakharov-Rubenchik equations
摘要： Two numerical methods are presented for the approximation of the Zakharov-Rubenchik equations (ZRE). The first one is the finite difference integrator Fourier pseudospectral method (FFP), which is implicit and of the optimal convergent rate at the order of O(N ?r + τ 2) in the discrete L2 norm without any restrictions on the grid ratio. The second one is to use the Fourier pseudospectral approach for spatial discretization and exponential wave integrator for temporal integration. Fast Fourier transform is applied to the discrete nonlinear system to speed up the numerical computation. Numerical examples are given to show the efficiency and accuracy of the new methods.
关键词： Unconditional convergence,Fourier pseudospectral method,Exponential wave integrator,FFT,Zakharov-Rubenchik equations
更新于2025-09-23 15:19:57
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[Institution of Engineering and Technology 12th European Conference on Antennas and Propagation (EuCAP 2018) - London, UK (9-13 April 2018)] 12th European Conference on Antennas and Propagation (EuCAP 2018) - Antenna Range Measurements for Airborne Remote Sensing Antennas
摘要： The DLR Compact Test Range (CTR) is a dual reflector compact range in an electromagnetically shielded chamber for antenna and Radar Cross Section (RCS) measurements under far-field conditions [1]. The quiet zone dimensions allow an evaluation of a volume under test, containing the antenna under test (AUT) in position on the original support structure and surface. Precise in-situ parameters offer extra information about the installed AUT characteristics. These properties are particularly substantial for the radiometric and the polarimetric correction of the propagating signals in imaging microwave sensors, such as Synthetic Aperture Radar (SAR) instruments. F-SAR [2] is a high-resolution multi-frequency fully polarimetric airborne SAR with interferometric capabilities that is developed and operated by the DLR Microwaves and Radar Institute. Spherical swept frequency antenna measurements with continuous moving axis and forward/reverse scanning on offset position AUTs impose specific demands on the analysis. Higher order modes that are present due to test setup and physical constraints are considered in the post-processing. Still, stray signals from the antenna carrying aircraft structure in the proximity contribute to the antenna pattern and remain unfiltered. The particular requirements and status of the applied measurement and processing techniques are described.
关键词： MARS,airborne SAR,Compact Range,SWE,spherical antenna measurement,FFT-Filter
更新于2025-09-23 15:19:57
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Fast algorithms for integral formulations of steady-state radiative transfer equation
摘要： We investigate integral formulations and fast algorithms for the steady-state radiative transfer equation with isotropic and anisotropic scattering. When the scattering term is a smooth convolution on the unit sphere, a model reduction step in the angular domain using the Fourier transformation in 2D and the spherical harmonic transformation in 3D significantly reduces the number of degrees of freedoms. The resulting Fourier coefficients or spherical harmonic coefficients satisfy a Fredholm integral equation of the second kind. We study the uniqueness of the equation and proved an a priori estimate. For a homogeneous medium, the integral equation can be solved efficiently using the FFT and iterative methods. For an inhomogeneous medium, the recursive skeletonization factorization method is applied instead. Numerical simulations demonstrate the efficiency of the proposed algorithms in both homogeneous and inhomogeneous cases and for both transport and diffusion regimes.
关键词： FFT,radiative transfer,Fredholm integral equation,anisotropic scattering,Fast algorithm,recursive skeletonization
更新于2025-09-19 17:15:36
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[IEEE 2019 IEEE Sustainable Power and Energy Conference (iSPEC) - Beijing, China (2019.11.21-2019.11.23)] 2019 IEEE Sustainable Power and Energy Conference (iSPEC) - Analysis on Load Characteristics of Distributed Photovoltaic Access to EVs industry
摘要： In this communication, the computation of the perturbation-based electric field integral equation of the form Rn?1, n = 0, 1, 2, . . . , is accelerated by using fast Fourier transform (FFT) technique. As an effective solution of the low-frequency problem, the perturbation method employs the Taylor expansion of the scalar Green’s function in free space. However, multiple impedance matrices have to be solved frequency orders, and the computational cost becomes at different extremely high, especially for large-scale problems. Since the perturbed kernels still satisfy Toeplitz property on the uniform Cartesian grid, incorporated the FFT based on Lagrange interpolation can be well to accelerate the multiple matrix vector products. Because of the nonsingularity property of high-order kernels when n ≥ 1, we do not need to do any near field amendment. Finally, the efficiency of the proposed method is validated in an iterative solver with numerical examples.
关键词： perturbation method,integral equation (IE),Fast Fourier transform (FFT),low frequency
更新于2025-09-19 17:13:59
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[IEEE 2019 IEEE 3rd Advanced Information Management, Communicates, Electronic and Automation Control Conference (IMCEC) - Chongqing, China (2019.10.11-2019.10.13)] 2019 IEEE 3rd Advanced Information Management, Communicates, Electronic and Automation Control Conference (IMCEC) - Research on Control algorithm of Photovoltaic Grid-connected Inverter Based on Fuzzy Logic
摘要： In this communication, the computation of the perturbation-based electric field integral equation of the form Rn?1, n = 0, 1, 2, . . . , is accelerated by using fast Fourier transform (FFT) technique. As an effective solution of the low-frequency problem, the perturbation method employs the Taylor expansion of the scalar Green’s function in free space. However, multiple impedance matrices have to be solved frequency orders, and the computational cost becomes at different extremely high, especially for large-scale problems. Since the perturbed kernels still satisfy Toeplitz property on the uniform Cartesian grid, incorporated the FFT based on Lagrange interpolation can be well to accelerate the multiple matrix vector products. Because of the nonsingularity property of high-order kernels when n ≥ 1, we do not need to do any near field amendment. Finally, the efficiency of the proposed method is validated in an iterative solver with numerical examples.
关键词： integral equation (IE),perturbation method,Fast Fourier transform (FFT),low frequency
更新于2025-09-19 17:13:59