A Simulation Study on Figure Error Correction Using Near-Gaussian Removal Function in Numerical Controlled Local Wet Etching

2012 ◽  
Vol 523-524 ◽  
pp. 276-280 ◽  
Author(s):  
Xin Min Shen ◽  
Mikinori Nagano ◽  
Wen Qiang Peng ◽  
Yi Fan Dai ◽  
Kazuya Yamamura
Keyword(s):  
Fourier Transform ◽  
High Frequency ◽  
High Spatial Resolution ◽  
Gaussian Function ◽  
Wet Etching ◽  
Eccentric Rotation ◽  
Ultra Precision ◽  
Inner Diameter ◽  
Nozzle Head ◽  
Optics Fabrication

Local wet etching (LWE) is a non-conventional deterministic surface figuring and finishing technique in ultra-precision optics fabrication fields. The general removal function in LWE is cylinder, so fringe of the removal function is sharp and scale of the removal function is determined by inner diameter of the nozzle head. When fabricating some specimen with high frequency figure error, ideal designed shape can’t be achieved easily. Compared with general LWE removal function, Gaussian removal function is more suitable for figuring owing to its smoother fringe and the centralization of its energy. At the same time Gaussian removal function can improve the efficiency in calculation of the dwelling time, because it’s very suitable for Fourier transform. What’s more, theoretical residual figure error can also be reduced for Gaussian removal function’s high spatial resolution. Ideal Gaussian function is difficult to obtain in LWE, so we have proposed near-Gaussian removal function by eccentric rotation of the nozzle head. Through controlling offset of the eccentric rotation, we achieve the optimal near-Gaussian removal function in LWE. Aims of the introduction of near-Gaussian removal function in LWE are to improve the fabrication efficiency and to remove the surface’s high frequency residual figure error.

The Improvement of Removal Function in Local Wet Etching by Using Eccentric Rotation System

2012 ◽  
Vol 516 ◽  
pp. 504-509 ◽  
Author(s):  
Xin Min Shen ◽  
Yi Fan Dai ◽  
Wen Qiang Peng ◽  
Mikinori Nagano ◽  
Kazuya Yamamura
Keyword(s):  
Experimental Validation ◽  
Gaussian Function ◽  
Wet Etching ◽  
Precision Machining ◽  
Functional Material ◽  
Eccentric Rotation ◽  
Cross Sectional ◽  
Rotation System ◽  
Ultra Precision ◽  
Sectional Shape

Numerical controlled local wet etching is a novel non-contact deterministic figuring method in ultra precision optics fabricating and functional material manufacturing fields, and the cross-sectional shape of the traditional removal spot is a simple cylinder, so the removal function has no adjustability. In order to create more practical and regular removal function, an eccentric rotation system is introduced to improve the LWE system. By controlling the eccentricity, it can achieve varied shapes removal function. When the rotary axis is controlled to a proper eccentricity, the removal function can be close to the Gaussian function. Moreover, the theoretical calculation and experimental validation are coincident and can give the research a steady foundation. The improvement not only can increase the adjustability of the removal function in LWE, but also can expand its applied field and provide reference for other ultra precision machining methods whose removal function does not have circular symmetry.

ИССЛЕДОВАНИЯ АКУСТИЧЕСКИХ ХАРАКТЕРИСТИК ВЕРХНЕГО СЛОЯ МОРЯ МЕТОДОМ МНОГОЧАСТОТНОГО АКУСТИЧЕСКОГО ЗОНДИРОВАНИЯ

2020 ◽  
Author(s):  
V.A. Bulanov ◽  
I.V. Korskov ◽  
A.V. Storozhenko ◽  
S.N. Sosedko
Keyword(s):  
High Frequency ◽  
Wave Motion ◽  
High Spatial Resolution ◽  
Wind Waves ◽  
Acoustic Parameter ◽  
Sea Surface ◽  
Near Surface ◽  
Acoustical Properties ◽  
Acoustic Spectroscopy ◽  
Sea Bottom

Описано применение акустического зондирования для исследования акустических характеристик верхнего слоя моря с использованием широкополосных остронаправленных инвертированных излучателей,устанавливаемых на дно. В основу метода положен принцип регистрации обратного рассеяния и отраженияот поверхности моря акустических импульсов с различной частотой, позволяющий одновременно измерятьрассеяние и поглощение звука и нелинейный акустический параметр морской воды. Многочастотное зондирование позволяет реализовать акустическую спектроскопию пузырьков в приповерхностных слоях моря,проводить оценку газосодержания и получать данные о спектре поверхностного волнения при различных состояниях моря вплоть до штормовых. Применение остронаправленных высокочастотных пучков ультразвукапозволяет разделить информацию о планктоне и пузырьках и определить с высоким пространственным разрешением структуру пузырьковых облаков, образующихся при обрушении ветровых волн, и структуру планктонных сообществ. Участие планктона в волновом движении в толще морской воды позволяет определитьпараметры внутренних волн спектр и распределение по амплитудам в различное время.This paper represents the application of acoustic probingfor the investigation of acoustical properties of the upperlayer of the sea using broadband narrow-beam invertedtransducers that are mounted on the sea bottom. Thismethod is based on the principle of the recording of thebackscattering and reflections of acoustic pulses of differentfrequencies from the sea surface. That simultaneouslyallows measuring scattering and absorption of the soundand non-linear acoustic parameter of seawater. Multifrequencyprobing allows performing acoustic spectroscopy ofbubbles in the near-surface layer of the sea, estimating gascontent, and obtaining data on the spectrum of the surfacewaves in various states of the sea up to a storm. Utilizationof the high-frequency narrow ultrasound beams allows us toseparate the information about plankton and bubbles and todetermine the structure of bubble clouds, created during thebreaking of wind waves, along with the structure of planktoncommunities with high spatial resolution. The participationof plankton in the wave motion in the seawater columnallows determining parameters of internal waves, such asspectrum and distribution of amplitudes at different times.

Gravity anomaly reconstruction based on nonequispaced Fourier transform

Geophysics ◽  
2019 ◽  
Vol 84 (6) ◽  
pp. G83-G92
Author(s):  
Ya Xu ◽  
Fangzhou Nan ◽  
Weiping Cao ◽  
Song Huang ◽  
Tianyao Hao
Keyword(s):  
Fourier Transform ◽  
Compressed Sensing ◽  
Gravity Data ◽  
Signal Reconstruction ◽  
Gaussian Function ◽  
Reconstruction Algorithm ◽  
Data Reconstruction ◽  
Reconstruction Method ◽  
Grid Data ◽  
2D Data

Irregular sampled gravity data are often interpolated into regular grid data for convenience of data processing and interpretation. The compressed sensing theory provides a signal reconstruction method that can recover a sparse signal from far fewer samples. We have introduced a gravity data reconstruction method based on the nonequispaced Fourier transform (NFT) in the framework of compressed sensing theory. We have developed a sparsity analysis and a reconstruction algorithm with an iterative cooling thresholding method and applied to the gravity data of the Bishop model. For 2D data reconstruction, we use two methods to build the weighting factors: the Gaussian function and the Voronoi method. Both have good reconstruction results from the 2D data tests. The 2D reconstruction tests from different sampling rates and comparison with the minimum curvature and the kriging methods indicate that the reconstruction method based on the NFT has a good reconstruction result even with few sampling data.

scholarly journals VLA Polarization Observation of the Radio Arc at 15 Ghz

1989 ◽  
Vol 136 ◽  
pp. 269-274 ◽  
Author(s):  
M. Inoue ◽  
E. Fomalont ◽  
M. Tsuboi ◽  
F. Yusef-Zadeh ◽  
M. Morris ◽  
...  
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
High Spatial Resolution ◽  
Intrinsic Polarization ◽  
Linear Feature ◽  
Field System ◽  
Polarization Observation ◽  
Field Systems ◽  
Relativistic Particles ◽  
Accelerated Particles

Polarization measurements of the radio Arc were made with the VLA at 15 GHz. High frequency polarimetry made with high spatial resolution minimizes Faraday depolarization and reveals polarized filaments which correspond to the predominant filaments of the radio Arc. We notice a peculiar linear feature in the polarization map (“thorns”) which suggests the presence of a second magnetic field system. The total intensity maps show no evidence for an interaction between the two field systems, so the thorns may be foreground magnetized structures. However, if the two magnetic field systems do interact, it would allow a model in which the acceleration of relativistic particles takes place at their intersection. The accelerated particles would flow toward both ends of the radio Arc, and account for the intrinsic polarization observed along the entire length of the system. Thermal electrons responsible for the Faraday depolarization occuring at longer wavelengths may be supplied by the interaction of the streams of relativistic particles with relatively dense, ambient thermal clouds.

Coherence based on spectral variance analysis

Geophysics ◽  
2018 ◽  
Vol 83 (3) ◽  
pp. O55-O66 ◽  
Author(s):  
Yanting Duan ◽  
Chaodong Wu ◽  
Xiaodong Zheng ◽  
Yucheng Huang ◽  
Jian Ma
Keyword(s):  
Fourier Transform ◽  
Seismic Data ◽  
High Frequency ◽  
Seismic Interpretation ◽  
Variance Analysis ◽  
Frequency Spectra ◽  
Amplitude Spectra ◽  
Frequency Components ◽  
Spectral Variance ◽  
Coherence Estimation

The eigenstructure-based coherence attribute is a type of efficient and mature tool for mapping geologic edges such as faults and/or channels in the 3D seismic interpretation. However, the eigenstructure-based coherence algorithm is sensitive to low signal-to-noise ratio seismic data, and the coherence results are affected by the dipping structures. Due to the large energy gap between the low- and high-frequency components, the low-frequency components play the principal role in coherence estimation. In contrast, the spectral variance balances the difference between the low- and high-frequency components at a fixed depth. The coherence estimation based on amplitude spectra avoids the effect of the time delays resulting from the dipping structures. Combining the spectral variance with the amplitude spectra avoids the effect of dipping structures and enhances the antinoise performance of the high-frequency components. First, we apply the short-time Fourier transform to obtain the time-frequency spectra of seismic data. Next, we compute the variance values of amplitude spectra. Then, we apply the fast Fourier transform to obtain the amplitude spectra of spectral variance. Finally, we calculate the eigenstructure coherence by using the amplitude spectra of spectral variance as the input. We apply the method to the theoretical models and practical seismic data. In the Marmousi velocity model, the coherence estimation using the amplitude spectra of the spectral variance as input shows more subtle discontinuities, especially in deeper layers. The results from field-data examples demonstrate that the proposed method is helpful for mapping faults and for improving the narrow channel edges’ resolution of interest. Therefore, the coherence algorithm based on the spectral variance analysis may be conducive to the seismic interpretation.

Gaussian Window of Optimal Time-Frequency Resolution in Numerical Implementation of Short-Time Fourier Transform

2011 ◽  
Vol 48-49 ◽  
pp. 555-560 ◽  
Author(s):  
Yang Jin ◽  
Zhi Yong Hao
Keyword(s):  
Fourier Transform ◽  
Continuous Time ◽  
Gaussian Function ◽  
Frequency Resolution ◽  
Optimal Time ◽  
Numerical Implementation ◽  
Short Time Fourier Transform ◽  
Time Frequency ◽  
Gaussian Window ◽  
Short Time

In this paper, we report the condition to keep the optimal time-frequency resolution of the Gaussian window in the numerical implementation of the short-time Fourier transform. Because of truncation and discretization, the time-frequency resolution of the discrete Gaussian window is different from that of the proper Gaussian function. We compared the time-frequency resolution performance of the discrete Gaussian window and Hanning window based on that they have the same continuous-time domain standard deviation, and generalized the condition under which the time-frequency resolution of the Gaussian window will prevail over that of the Hanning window.

Automated Finishing of Diamond Turned Dies for Hard X-Ray and EUV Optics Replication

2013 ◽  
Vol 552 ◽  
pp. 115-123
Author(s):  
Anthony T.H. Beaucamp ◽  
Yoshiharu Namba ◽  
Richard R. Freeman
Keyword(s):  
Electroless Nickel ◽  
Diamond Turning ◽  
Work Piece ◽  
Space Telescopes ◽  
Bonnet Polishing ◽  
X Ray ◽  
Manufacturing Method ◽  
Ultra Precision ◽  
Delivery Unit ◽  
Optics Fabrication

Ultra-precision diamond turning can deliver very accurate form, often less than 100nm P-V. A possible manufacturing method for thin Wolter type-1 mirrors in hard X-ray space telescopes thus involves generating electroless nickel plated mandrels by diamond turning, before coating them with a reflective film and substrate. However, the surface texture after turning falls far short from the requirements of X-ray and EUV applications. The machining marks need to be removed, with hand polishing still widely employed. There is thus a compelling need for automated finishing of turned dies. A two step finishing method is presented that combines fluid jet and precessed bonnet polishing on a common 7-axis CNC platform. This method is capable of finishing diamond turned electroless nickel plated dies down to 0.28nm rms roughness, while deterministically improving form error down to 30nm P-V. The fluid jet polishing process, which consists of pressurizing water and abrasive particles for delivery through a nozzle, has been specially optimized with a newly designed slurry delivery unit and computer simulations, to remove diamond turning marks without introducing another waviness signature. The precessed bonnet polishing method, which consists of an inflated membrane rotated at an angle from the local normal to the surface and controlled by geometrical position relative to the work-piece, is subsequently employed with a novel control algorithm to deliver scratch-free surface roughness down to 0.28 nm rms. The combination of these two deterministic processes to finish aspheric and freeform dies promises to unlock new frontiers in X-ray and EUV optics fabrication.

Theory of High Frequency Differential Interferometry: Application to the Measurement of Infrared Circular and Linear Dichroism via Fourier Transform Spectroscopy

1979 ◽  
Vol 33 (2) ◽  
pp. 130-135 ◽  
Author(s):  
Laurence A. Nafie ◽  
Max Diem
Keyword(s):  
Fourier Transform ◽  
High Frequency ◽  
Linear Dichroism ◽  
Periodic Variation ◽  
Polarization Modulation ◽  
Differential Absorption ◽  
Differential Interferometry ◽  
Infrared Spectrometer ◽  
Alternate States ◽  
General Method

A general method for the direct measurement of differential absorption intensities using a Fourier transform infrared spectrometer is described. The differential intensities must be higher in frequency than the interferogram frequencies and may arise from a periodic variation of the absorption strength of the sample, or by dichroic response of the sample to alternate states of polarization of the infrared beam. Specific expressions are presented for the measurement of circular and linear dichroism. These expressions represent an extension of the Grosjean-Legrand polarization modulation technique to Fourier transform interferometry.

Diagnosis of Ganglions in the Hand and Wrist by Sonography

1994 ◽  
Vol 35 (1) ◽  
pp. 35-39 ◽  
Author(s):  
M. Höglund ◽  
P. Tordai ◽  
C. Muren
Keyword(s):  
Soft Tissue ◽  
Diagnostic Accuracy ◽  
High Frequency ◽  
Preoperative Planning ◽  
High Spatial Resolution ◽  
Clinical Symptoms ◽  
Hand Surgery ◽  
Joint Space ◽  
Clinical Value ◽  
Joint Project

In the practice of hand surgery, imaging of soft tissue structures can provide useful information for diagnosis and preoperative planning. Sonography with high frequency technique giving high spatial resolution is especially rewarding. In a joint project of the Departments of Radiology and Hand Surgery we evaluated the diagnostic accuracy and clinical value of sonographic assessment of ganglions of the hand and wrist. The material comprises 68 soft tissue lesions clinically suspected to be ganglions. Sonography revealed a ganglion in 53 cases, 34 of which went to surgery. The diagnosis was confirmed in every case. One collapsed ganglion was missed. Nonpalpable ganglions causing clinical symptoms could be demonstrated, and a suspected ganglion could sometimes be ruled out in favor of other diagnoses. Sonography could delineate the entire ganglion and often its connection with the joint space.

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