FFT Filter Research Articles

Ameliorating the Courant-Friedrichs-Lewy condition in spherical coordinates: A double FFT filter method for general relativistic MHD in dynamical spacetimes

Ameliorating the Courant-Friedrichs-Lewy condition in spherical coordinates: A double FFT filter method for general relativistic MHD in dynamical spacetimes

A Deep Dive into De-Doppler Algorithms for SETI

Narrowband SETI algorithms have been in use for many decades. A key processing step in the usual SETI pipeline called “De-Doppler” involves non-coherent integration of linearly-drifting lines in a spectrogram. De- Doppler (DD) is needed because a transmitted constant-frequency tone will be received as a chirp, or a tone with a near-constant frequency rate, due to relative accelerations between the transmitter and receiver. The frequency drift may be an important discriminator against certain types of radio-frequency interference. This paper examines the standard Taylor DD algorithm and finds there are significant signal losses in the integration process. Part of the loss is caused by imperfect indexing in the algorithm. Additional loss is associated with the effect of an FFT filter bank on chirp signals; DD performance is intertwined with the filter bank. Filter bank improvements involving polyphase filter banks are examined. A new DD algorithm called “fastDD” is proposed, as well as extensions to the Taylor algorithm. They both offer significant performance gains and higher resolution in frequency and drift rate in the DD detection plane. The loss mechanisms are now understood. Computational cost trade-offs for various filter bank and DD parameters are presented based on C code functions. Several “best” options are given which offer significant SNR improvements ranging from 2 to 4 dB for modest levels of additional computation. These options have the potential to dramatically improve detection rates.

棉花精量播种机铺膜质量监测系统设计与试验

To realize real-time monitoring of film laying process of cotton precision planter and improve intelligent level of cotton precision planter, based on advanced morphological filtering method and graphical programming of Labview software, a film laying quality monitoring system of cotton precision planter is designed. Using the Vision Assistant visual assistant, the system uses a color extraction function to convert colors to grayscale images. It uses LOOKup Table function and FFT filter function to perform grayscale transformation, binarization and advanced morphological filtering on it respectively. It then uses basic morphology to acquire various components in the plastic film image. It realizes the monitoring of parameters such as the width of the daylighting surface, the side length or seam length of the mechanical damaged part, and the width of the film edge covering soil. The performance test results of the film laying quality monitoring system showed that the system worked stably and reliably, the average monitoring accuracy of the width of the lighting surface and the width of the film edge covering soil reached more than 95%, and the average monitoring accuracy of the side length or the length of the seam at the mechanical damage part reached more than 88%. It solved the problems of difficulty in recognizing the similarity between the plastic film and the background interferer (soil, etc.) and could accurately detect the quality of the cotton film in real time. It effectively improved the operation quality and working efficiency of the cotton precision planter and met the practical requirements of film laying monitoring.

Robustness of ventilation systems in the control of walking-induced indoor fluctuations: Method development and case study.

Walking-induced fluctuations have a significant influence on indoor airflow and pollutant dispersion. This study developed a method to quantify the robustness of ventilation systems in the control of walking-induced fluctuation control. Experiments were conducted in a full-scale chamber with four different kinds of ventilation systems: ceiling supply and side return (CS), ceiling supply and ceiling return (CC), side supply and ceiling return (SC), and side supply and side return (SS). The measured temperature, flow and pollutant field data was (1) denoised by FFT filtering or wavelet transform; (2) fitted by a Gaussian function; (3) feature-extracted for the range and time scale disturbance; and then (4) used to calculate the range scale and time scale robustness for different ventilation systems with dimensionless equations developed in this study. The selection processes for FFT filtering and wavelet transform, FFT filter cut-off frequency, wavelet function, and decomposition layers are also discussed, as well as the threshold for wavelet denoising, which can be adjusted accordingly if the walking frequency or sampling frequency differs from that in other studies. The results show that for the flow and pollutant fields, the use of a ventilation system can increase the range scale robustness by 19.7%–39.4% and 10.0%–38.8%, respectively; and the SS system was 7.0%–25.7% more robust than the other three ventilation systems. However, all four kinds of ventilation systems had a very limited effect in controlling the time scale disturbance.

A systematic study and framework of fringe projection profilometry with improved measurement performance for in-situ LPBF process monitoring

Fringe Projection Profilometry (FPP) is a cost-effective and non-invasive technology that has been shown to measure finer features. In this work, we developed an in-situ FPP method to measure the dynamic topography of powder bed and printed layer during Laser Powder Bed Fusion (LPBF) additive manufacturing (AM) process. A systematic study towards developing a comprehensive framework of LPBF-specific FPP is demonstrated to enhance and evaluate the performance of applying FPP for in-situ LPBF monitoring, including 1) a modified sensor model with localized correction; 2) improved phase unwrapping with FFT filtering 3) quantitative uncertainty analysis; and 4) experimental validation with ex-situ characterization. The developed LPBF-specific FPP system and methods are implemented on a commercial LPBF-AM machine, achieving better accuracy, more robustness, and increased field of view while maintaining sufficient measurement range and decent resolution, in contrast to literature methods. The established FPP framework will facilitate the development of closed-loop control strategies for advancing LPBF based AM.

Modified calculation method using FFT filtering and reconstructing of an interferogram for monitoring a laser-plasma density

Modified calculation method using FFT filtering and reconstructing of an interferogram for monitoring a laser-plasma density

Speckle noise reduction of Sentinel-1 SAR data using fast fourier transform temporal filtering to monitor paddy field area

Synthetic Aperture Radar (SAR) images have the ability to work in any weather situation. It is mostly impossible to get cloud free optical image monthly in Indonesia, especially in Subang. So, the use of SAR imagery for the monthly monitoring of paddy is recommended. The disadvantage of the SAR images is noise, known as speckle noise. This noise reduces the quality of the image; reducing the speckle noise is necessary. This research proposes the FFT algorithm to remove the speckle noise. Because the frequency pattern of FFT is periodic, and the research focuses on the paddy field area, so the one year of paddy growth was used. There are many planting times in the research area, from one to three planting times a year; most of the area is twice planting time a year. Six scenarios of the FFT filter were proposed and investigated to select the optimum scenario. The scenarios use the number of FFT results to implement in filtering. The first scenario used FFT1 to FFT2, and the sixth scenario used FFT-1 to FFT-8. The performance results were measure by the correlation value of the original image and the results of FFT filtering. The results show that by increasing the number of FFT in the filtering process, the correlation increase. The minimal FFT filtering is FFT1-FFF3 filtering, with the average correlation is 87%, but some acquisition still has the correlation less than 85%. The optimum is FFT1- FFT5 filtering, with the average correlation, is 92%, and all correlations are above 85% for all data during a year. Using the optimum scenario, the backscattered trend of paddy growth could be identified better and easier, so this technique is recommended for paddy growth monitoring.

Design of iRLS Algorithm With/Without Pre-Filter for Antenna Beam Forming Technique

Beamforming is one of the most significant processes in smart antennas. To change the antenna beam pattern is the major function of beamforming for a given angle. The algorithm that is adaptive beamforming is utilized to choose the conventional weights of each array element from acquired data of array antenna to extract the desired source signal while cancelling noise and interference. A lot of algorithms are already existing for antenna beamforming technique but they all experience low convergence. So this paper deals with an iRLS algorithm for antenna beamforming technique with Particle Swarm Optimized (PSO) FFT filter. As a result, antenna beamforming based on iRLS shows fast convergence with reduced design complexity. The overall work is simulated in MATLAB. The parameters like amplitude, bit error rate, capacity, SINR and error function values are evaluated. Our work is compared with existing Applebaum, Recursive Least Squares (RLS) (with/without filter) and Least Mean Square (LMS) algorithm. Fast convergence is occurred by iRLS when compared with existing algorithms. The iRLS is converged at 90th iteration, whereas existing algorithms likewise RLS with pre-filter, RLS without pre-filter, LMS and Applebaum is converged at 200, 400, 600 and 850th iteration. So here, our proposed iRLS gives better performance when compared with others.

Dynamic Pad Surface Metrology Monitoring by Swing-Arm Chromatic Confocal System

This study aims to develop a dynamic pad monitoring system (DPMS) for measuring the surface topography of polishing pad. Chemical mechanical planarization/polishing (CMP) is a vital process in semiconductor manufacturing. The process is applied to assure the substrate wafer or thin film on wafer that has reached the required planarization after deposition for lithographic processing of the desired structures of devices. Surface properties of polishing pad have a huge influence on the material removal rate (MRR) and quality of wafer surface by CMP process. A DPMS has been developed to analyze the performance level of polishing pad for CMP. A chromatic confocal sensor is attached on a designed fixture arm to acquire pad topography data. By swing-arm motion with continuous data acquisition, the surface topography information of pad can be gathered dynamically. Measuring data are analyzed with a designed FFT filter to remove mechanical vibration and disturbance. Then the pad surface profile and groove depth can be calculated, which the pad’s index PU (pad uniformity) and PELI (pad effective lifetime index) are developed to evaluate the pad’s performance level. Finally, 50 rounds of CMP experiments have been executed to investigate the correlations of MRR and surface roughness of as-CMP wafer with pad performance. Results of this study can be used to monitor the pad dressing process and CMP parameter evaluation for production of IC devices.

Data Analysis of Hydraulic Fracturing Pressure in Unconventional Oil and Gas Fields

After the completion of fracturing construction in unconventional oil and gas fields, the phenomenon of water hammer oscillation in the process of pump stopping during fracturing construction will lead to the inaccuracy of reflecting the trend of pressure transformation and increase the difficulty of fracturing effect evaluation in the process of fracturing construction. Therefore, three filtering methods, Savitzky-Golay filter, FFT filter and wavelet transform filter, are used to calibrate the measured pressure in this paper It is found that the method of wavelet transform can achieve the most ideal effect by comparing with the measured data. The field example of well X1 in Ordos Basin proves that the method of wavelet transform can accurately reflect the trend of pressure transformation. This method is of great significance to improve the evaluation of post pressure effect in the process of fracturing construction.

Influence of mild-moderate hypocapnia on intracranial pressure slow waves activity in TBI

BackgroundIn traumatic brain injury (TBI) the patterns of intracranial pressure (ICP) waveforms may reflect pathological processes that ultimately lead to unfavorable outcome. In particular, ICP slow waves (sw) (0.005–0.05 Hz) magnitude and complexity have been shown to have positive association with favorable outcome. Mild-moderate hypocapnia is currently used for short periods to treat critical elevations in ICP. Our goals were to assess changes in the ICP sw activity occurring following sudden onset of mild-moderate hypocapnia and to examine the relationship between changes in ICP sw activity and other physiological variables during the hypocapnic challenge.MethodsICP, arterial blood pressure (ABP), and bilateral middle cerebral artery blood flow velocity (FV), were prospectively collected in 29 adult severe TBI patients requiring ICP monitoring and mechanical ventilation in whom a minute volume ventilation increase (15–20% increase in respiratory minute volume) was performed as part of a clinical CO2-reactivity test. The time series were first treated using FFT filter (pass-band set to 0.005–0.05 Hz). Power spectral density analysis was performed. We calculated the following: mean value, standard deviation, variance and coefficient of variation in the time domain; total power and frequency centroid in the frequency domain; cerebrospinal compliance (Ci) and compensatory reserve index (RAP).ResultsHypocapnia led to a decrease in power and increase in frequency centroid and entropy of slow waves in ICP and FV (not ABP). In a multiple linear regression model, RAP at the baseline was the strongest predictor for the decrease in the power of ICP slow waves (p < 0.001).ConclusionIn severe TBI patients, a sudden mild-moderate hypocapnia induces a decrease in mean ICP and FV, but also in slow waves power of both signals. At the same time, it increases their higher frequency content and their morphological complexity. The difference in power of the ICP slow waves between the baseline and the hypocapnia period depends on the baseline cerebrospinal compensatory reserve as measured by RAP.

Parallel computing using Python-based software for a high-frequency ultrasound system

Python has become a widely used programming language for scientific research. However, python’s computational speed is limited when compared with other languages. This work presents an upgraded open-source imaging software based on python, which is capable of acquiring, processing, and displaying B-mode images in real-time for a high-frequency phased array imaging system. Ultrasound systems, considered to be real-time, display images at a frame rate of &amp;gt;20 Hz. This software uses 3 central processing units (CPUs) for parallel processing. In addition, Graphics Processing Unit (GPU) parallel computing is achieved by employing OpenCL commands and executing them directly on the GPU. New features, such as frame weighted averaging, color flow overlay and image enhancement, were also implemented. Parallel computing increased the displayed frame rate in general B-mode from 20 Hz to 35 Hz. B-mode + color flow overlay was increased from 15 Hz to 29 Hz and enhanced B-mode (applying edge detection, blur, and FFT filtering) was increased from 14 Hz to 28 Hz. Finally, enhanced B-mode + color flow overlay frame rate was increased from 8 Hz to 23 Hz. Thus, even more advanced ultrasound techniques, such as shear wave elastography might be developed using the python language without compromising the frame rate.

Experimental investigation of impact forces induced by plunging breakers on a vertical cylinder

A plunging breaker propagates with different stages, each of which induces a different force on structures. In this study, physical experiments of the different stages of a plunging breaker impacting a vertical cylinder are implemented in a wave flume. The concept of decomposing the measured forces into quasi-static forces and dynamic forces is adopted. The method proposed by Irschik et al. (2004) using an FFT filter and EMD (Empirical Mode Decomposition) is applied in the decomposition process. Then a new method with a continuous wavelet-based filter is used that produces a more reasonable result. Subsequently, the results of the measured forces, the quasi-static forces, and the dynamic forces are analyzed by considering the different stages of the plunging breaker. The results show the peak forces induced by the various stages of the plunging breaker are quite different. Prior to the overturning jet impinging the free surface, the quasi-static forces due to the various stages of the plunging breaker are approximately the same, while the dynamic forces contribute to different strengths of the force oscillations and exhibit a similar response. Following the mixture of water with air, the peak value of the quasi-static force is no longer invariant but declines sharply.

The Street Air Warming Phenomenon in a High-Rise Compact City

The street thermal environment is important for thermal comfort, urban climate and pollutant dispersion. A 24-h vehicle traverse study was conducted over the Kowloon Peninsula of Hong Kong in summer, with each measurement period consisting of 2–3 full days. The data covered a total of 158 loops in 198 h along the route on sunny days. The measured data were averaged by three methods (direct average, FFT filter and interpolated by the piecewise cubic Hermite interpolation). The average street air temperatures were found to be 1–3 °C higher than those recorded at nearby fixed weather stations. The street warming phenomenon observed in the study has substantial implications as usually urban heat island (UHI) intensity is estimated from measurement at fixed weather stations, and therefore the UHI intensity in the built areas of the city may have been underestimated. This significant difference is of interest for studies on outdoor air temperature, thermal comfort, urban environment and pollutant dispersion. The differences were simulated by an improved one-dimensional temperature model (ZERO-CAT) using different urban morphology parameters. The model can correct the underestimation of street air temperature. Further sensitivity studies show that the building arrangement in the daytime and nighttime plays different roles for air temperature in the street. City designers can choose different parameters based on their purpose.

Secondary resonance of liquid sloshing in square-base tanks undergoing the circular orbit motion

The transient wave sloshing in the square-base tank horizontally shaken in a circular orbit is numerically studied. The liquid sloshing is simulated by the boundary element method (BEM) based on the fully-nonlinear potential-flow theory. The tank is firstly excited at the first odd natural sloshing frequency. Resonant swirling waves are observed travelling along the tank sides, when the even sloshing mode is aroused. Then, the tank is excited at half of the first even natural frequency. Techniques of the FFT filter and wavelet analysis are applied to distinct the wave components from the wave elevation histories, through which the occurrence of the secondary resonance is identified. During the secondary resonance, three typical wave motion patterns are observed, i.e. swirling waves, standing waves and double-peak travelling waves. Effects of the excitation amplitude and the liquid depth on the secondary resonance are investigated. Further, the secondary resonance by oscillating the tank at the difference of the first even and first odd natural frequency is studied. The first odd sloshing mode is found to contribute to the dominance of the even mode wave component during the secondary resonance.

Design of high performance filter bank multi-carrier transmitter

Filter bank multi-carrier (FBMC) is very important to achieve high spectral efficiency in the wireless communication process. Previously, orthogonal frequency division multiplexing (OFDM) technique is used to obtain a high spectral efficiency. But area, power and delay is high than the FBMC transmitter technique. The main aim of this work is to design an optimized FBMC transmitter for high speed, low power and low area applications. There is a tradeoff between power and speed. To overcome this challenge, a new compact FBMC transmitter will be introduced in the paper. Generally, the FBMC transmitter consists of serial to parallel converter, QAM modulation, inverse FFT, parallel to serial converter and filter. The existing FBMC transmitter is designed by using inverse radix 2 FFT and poly phase filter. It requires more area, power and delay. To overcome this problem, a new radix2 multipath delay commutator (R2MDC) based inverse FFT and multiple constant multiplication (MCM) based FIR filter are used in the proposed FBMC transmitter. Because MCM based FIR filter doesn’t needs multiplier structure. The multiplication process is done by shift, add and subtract operation. Hence area and power is low in MCM based FIR filters, when compared to poly base filter. Also R2MDC FFT is used for high speed application. Comparison between conventional FBMC transmitter and proposed FBMC transmitter is carried out to analyze the performance, area, complexity and power. Also the functionality of FBMC transmitter is verified by using Xilinx ISE Virtex5 device. From the comparison results, it shows that the proposed FBMC transmitter offers 17% average area, delay and power (ADP) product than the existing FBMC transmitter.

The Law of Load Variation and User’s Behavior Based on FFT Analysis

In order to study the change of load and the behavior of power users, this paper chooses the load of a large customer to analyze the power consumption. We can find the change trend and characteristics of power factor of power load by comparing the change trend between active and reactive power consumption. Using FFT filter on the active power and reactive power for low-pass filtering and high-pass filtering. And we can find the approximate range of frequency of power consumption. Finally, combing with band-pass filtering we can determine the frequency of power consumption fluctuating within a very small range. The research on the law of load variation and user's behavior can provide theoretical support for the follow-up power system research, which can improve the stability of power grid and improve the accuracy of load forecasting.

Handling of uncertainty due to interference fringe in FT-NIR transmittance spectroscopy — Performance comparison of interference elimination techniques using glucose-water system

The applicability of two elimination techniques for interferences occurring in measurements with cells of short pathlength using Fourier transform near-infrared (FT-NIR) spectroscopy was evaluated. Due to the growing interest in the field of vibrational spectroscopy in aqueous biological fluids (e.g. glucose in blood), aqueous solutions of d-(+)-glucose were prepared and split into a calibration set and an independent validation set. All samples were measured with two FT-NIR spectrometers at various spectral resolutions. Moving average smoothing (MAS) and fast Fourier transform filter (FFT filter) were applied to the interference affected FT-NIR spectra in order to eliminate the interference pattern. After data pre-treatment, partial least squares regression (PLSR) models using different NIR regions were constructed using untreated (interference affected) spectra and spectra treated with MAS and FFT filter. The prediction of the independent validation set revealed information about the performance of the utilized interference elimination techniques, as well as the different NIR regions. The results showed that the combination band of water at approx. 5200 cm−1 is of great importance since its performance was superior to the one of the so-called first overtone of water at approx. 6800 cm−1. Furthermore, this work demonstrated that MAS and FFT filter are fast and easy-to-use techniques for the elimination of interference fringes in FT-NIR transmittance spectroscopy.

Estimation of exoplanetary planet-to-star radius ratio with homomorphic processing

In this paper a homomorphic filtering scheme is proposed to improve the estimation of the planet/star radius ratio in astronomical transit signals. The idea is to reduce the effect of the short-term earth atmosphere variations. A two-step method is presented to compute the parameters of the transit curve from both the unfiltered and filtered data. A Monte Carlo analysis is performed by using correlated and uncorrelated noise to determine the parameters of the proposed FFT filter. The method is tested with observations of WASP-19b and WASP-17b obtained with the FORS2 instrument at the Very Large Telescope (VLT). The multi parametric fitting and the associated errors are obtained with the JKTEBOP software. The results with the white light of the exo-planet data mentioned above suggest that the homomorphic filtering can lead to substantial relative reductions in the error bars as high as 45.5% and 76.9%, respectively. The achieved reductions in the averaged error bars per channel were 48.4% with WASP-19b and 63.6% with WASP-17b. Open source MATLAB code to run the method proposed here can be downloaded from http://www.cmrsp.cl. This code was used to obtain the results presented in this paper.

A novel power efficient 0.64-GFlops fused 32-bit reversible floating point arithmetic unit architecture for digital signal processing applications

Floating point digital signal processing technology has become the primary method for real time signal processing in most digital systems presently. However, the challenges in the implementation of floating point arithmetic on FPGA are that, the hardware modules are larger, have longer latency and high power consumption. In this work, a novel efficient reversible floating point fused arithmetic unit architecture is proposed confirming to IEEE 754 standard. By utilizing reversible logic circuits and implementation with adiabatic logic, power efficiency is achieved. The hardware complexity is reduced by employing fused elements and latency is improved by decomposing the operands in the realization of floating point multiplier and square root. To validate the design, the proposed unit was used for realization of FFT and FIR filter which are important applications of a DSP processor. As detection is one of the core baseband processing operations in digital communication receivers and the detection speed determines the data rates that can be achieved, the proposed unit has been used to implement the detection function. Simulation results and comparative studies with existing works demonstrate that the proposed unit efficiently utilizes the number of gates, has reduced quantum cost and produced less garbage outputs with low latency, thereby making the design a computational and power efficient one.