scholarly journals Simulation of multimodal optical coherence tomography for biomedical diagnostics: comprehensive full-wave description based on ballistic scattering of arbitrary-profile beams

2021 ◽  
Author(s):  
Alexander L. Matveyev ◽  
Lev. A. Matveev ◽  
Alexander A. Moiseev ◽  
Alexander A. Sovetsky ◽  
Grigory V. Gelikonov ◽  
...  
Keyword(s):  
Fourier Transforms ◽  
Bessel Beam ◽  
Single Scattering ◽  
Computationally Efficient ◽  
Full Wave ◽  
Amplitude Profile ◽  
Arbitrary Phase ◽  
Biomedical Diagnostics ◽  
Phase Amplitude ◽  
Model Features

We present a computationally efficient full-wave spectral model of OCT-scan formation with the following capabilities/features: (i) the illuminating beam may have arbitrary phase-amplitude profile with allowance of a sharp diaphragm; (ii) paraxial approximation that limits the degree of focusing/divergence is not used; (iii) the broadly used approximation of ballistic (single) scattering by discrete scatterers is assumed without additional limitations on the density of scatterers, their distribution in space and scattering strengths with possible frequency-dependence; (iv) besides rigorous accounting for the influence of focusing/divergence of the waves, factors describing the wave decay can readily be introduced by analogy with Monte-Carlo approaches; (v) arbitrary measurement noises can easily be added to simulate required signal-to-noise ratios. The model also allows one to account for arbitrary (e.g., random or flow/deformation-induced) displacements of scatterers between subsequently generated scans. Thus, in view of the above-listed features the model can be characterized as comprehensive in the framework of ballistic scattering by discrete scatterers. The model is computationally efficient due to the use of only rapid summations and fast Fourier transforms. Main model features are illustrated, including simulations of OCT scans for a nearly non-diverging Bessel beam and a focused Gaussian beam, with the possibility to introduce at the tissue boundary arbitrary aberrations represented via Zernike polynomials often utilized for describing aberrations in ophthalmology. The unprecedented flexibility and high computational efficacy of the model open a broad range of possibilities for studying OCT-scan properties and developing new methods of their processing for biomedical diagnostics.

Offset‐domain pseudoscreen prestack depth migration

Geophysics ◽  
2002 ◽  
Vol 67 (6) ◽  
pp. 1895-1902 ◽  
Author(s):  
Shengwen Jin ◽  
Charles C. Mosher ◽  
Ru‐Shan Wu
Keyword(s):  
Heterogeneous Media ◽  
Fourier Transforms ◽  
Data Migration ◽  
Computationally Efficient ◽  
Lateral Velocity ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Narrow Angle ◽  
Domain Phase ◽  
Wavefield Extrapolation

The double square root equation for laterally varying media in midpoint‐offset coordinates provides a convenient framework for developing efficient 3‐D prestack wave‐equation depth migrations with screen propagators. Offset‐domain pseudoscreen prestack depth migration downward continues the source and receiver wavefields simultaneously in midpoint‐offset coordinates. Wavefield extrapolation is performed with a wavenumber‐domain phase shift in a constant background medium followed by a phase correction in the space domain that accommodates smooth lateral velocity variations. An extra wide‐angle compensation term is also applied to enhance steep dips in the presence of strong velocity contrasts. The algorithm is implemented using fast Fourier transforms and tri‐diagonal matrix solvers, resulting in a computationally efficient implementation. Combined with the common‐azimuth approximation, 3‐D pseudoscreen migration provides a fast wavefield extrapolation for 3‐D marine streamer data. Migration of the 2‐D Marmousi model shows that offset domain pseudoscreen migration provides a significant improvement over first‐arrival Kirchhoff migration for steeply dipping events in strong contrast heterogeneous media. For the 3‐D SEG‐EAGE C3 Narrow Angle synthetic dataset, image quality from offset‐domain pseudoscreen migration is comparable to shot‐record finite‐difference migration results, but with computation times more than 100 times faster for full aperture imaging of the same data volume.

Field Computation for Two-Dimensional Array Transducers with Limited Diffraction Array Beams

2005 ◽  
Vol 27 (4) ◽  
pp. 237-255 ◽  
Author(s):  
Jian-Yu Lu ◽  
Jiqi Cheng
Keyword(s):  
Continuous Wave ◽  
Weighting Function ◽  
Near Field ◽  
Bessel Beam ◽  
Two Dimensional ◽  
Axially Symmetric ◽  
Computationally Efficient ◽  
Annular Array ◽  
Array Transducer ◽  
Analytical Expressions

A method is developed for calculating fields produced with a two-dimensional (2D) array transducer. This method decomposes an arbitrary 2D aperture weighting function into a set of limited diffraction array beams. Using the analytical expressions of limited diffraction beams, arbitrary continuous wave (cw) or pulse wave (pw) fields of 2D arrays can be obtained with a simple superposition of these beams. In addition, this method can be simplified and applied to a 1D array transducer of a finite or infinite elevation height. For beams produced with axially symmetric aperture weighting functions, this method can be reduced to the Fourier-Bessel method studied previously where an annular array transducer can be used. The advantage of the method is that it is accurate and computationally efficient, especially in regions that are not far from the surface of the transducer (near field), where it is important for medical imaging. Both computer simulations and a synthetic array experiment are carried out to verify the method. Results (Bessel beam, focused Gaussian beam, X wave and asymmetric array beams) show that the method is accurate as compared to that using the Rayleigh-Sommerfeld diffraction formula and agrees well with the experiment.

scholarly journals Generation of Multiple Pseudo Bessel Beams with Accurately Controllable Propagation Directions and High Efficiency Using a Reflective Metasurface

2020 ◽  
Vol 10 (20) ◽  
pp. 7219
Author(s):  
Haixia Liu ◽  
Hao Xue ◽  
Yongjie Liu ◽  
Long Li
Keyword(s):  
Electromagnetic Waves ◽  
High Efficiency ◽  
Superposition Principle ◽  
Bessel Beam ◽  
Large Angle ◽  
Propagation Distance ◽  
Wireless Power ◽  
Bessel Beams ◽  
Full Wave ◽  
Measurement Results

In this paper, a generation method procedure based on a reflective metasurface is proposed to generate multiple pseudo Bessel beams with accurately controllable propagation directions and high efficiency. Firstly, by adjusting the miniaturized unit cell of the reflective metasurface to modulate the electromagnetic waves using the proposed method, some off-axis pseudo Bessel beams with different propagation directions are generated. Then, by achieving the large-angle deflection and comparing the results with previous existing methods, the superiority of the proposed method is demonstrated. Based on the generated single off-axis pseudo Bessel beam and the superposition principle of the electromagnetic wave, a reflective metasurface with 47 × 47 elements is designed and fabricated at 10 GHz to generate dual pseudo Bessel beams. Full-wave simulation and experimental measurement results validate that the dual pseudo Bessel beams were generated successfully. The propagation directions of the dual pseudo Bessel beams can be controlled accurately by the reflective metasurface, and the efficiency of the beams is 59.2% at a propagation distance of 400 mm. The energy of the beams keeps concentrating along the propagation axes, which provides a new choice for wireless power transfer and wireless communication with one source to multiple receiving targets.

scholarly journals Computationally Efficient, Fully Coupled Multiscale Modeling of Materials Phenomena Using Calibrated Localization Linkages

2012 ◽  
Vol 2012 ◽  
pp. 1-13 ◽  
Author(s):  
Surya R. Kalidindi
Keyword(s):  
Data Science ◽  
Fourier Transforms ◽  
Numerical Models ◽  
Salient Feature ◽  
Computationally Efficient ◽  
Length Scales ◽  
Multiscale Materials ◽  
Materials Modeling ◽  
Multiple Length Scales ◽  
As Stress

Most modern physics-based multiscale materials modeling and simulation tools aim to take into account the important details of the material internal structure at multiple length scales. However, they are extremely computationally expensive. In recent years, a novel data science enabled framework has been formulated for effective scale-bridging that is central to practical multiscaling. A salient feature of this new approach is its ability to capture heterogeneity of fields of interest at different length scales. In this approach, the computations at the mesoscale are handled using a novel data science approach called materials knowledge systems (MKS). The MKS approach has enjoyed tremendous success in building highly accurate and computationally efficient metamodels for localization (i.e., mesoscale spatial distribution of a macroscale imposed field such as stress or strain rate) in simulating a number of different multiscale materials phenomena. MKS derives its accuracy from the fact that it is calibrated to results from previously established numerical models for the phenomena of interest, while its computational efficiency comes from the use of fast Fourier transforms. The current capabilities and the future outlook for the MKS framework are expounded in this paper.

An accurate formulation of log‐stretch dip moveout in the frequency‐wavenumber domain

Geophysics ◽  
1996 ◽  
Vol 61 (3) ◽  
pp. 815-820 ◽  
Author(s):  
Binzhong Zhou ◽  
Iain M. Mason ◽  
Stewart A. Greenhalgh
Keyword(s):  
Fourier Transform ◽  
Impulse Response ◽  
Fourier Transforms ◽  
Computationally Efficient ◽  
Prestack Migration ◽  
Industry Standard ◽  
Computational Speed ◽  
Simple Phase ◽  
The Fourier Transform ◽  
Approximate Version

Dip moveout (DMO) processing is a partial prestack migration procedure that has been widely used in seismic data processing. The DMO process has been described in Deregowski (1986), Hale (1991) and Liner (1990). Many different DMO algorithms have been developed over the past decade. These algorithms have been designed to improve either the accuracy or the computational speed of the DMO process. Hale (1984) developed a method for performing DMO via Fourier transforms that is accurate for all reflector dips (assuming constant velocity). Hale’s method is computationally expensive because his DMO operator is temporally nonstationary, but its accuracy and simplicity have made it an industry standard. It has become a benchmark by which results from other DMO algorithms are judged. Of all the methods used to make the frequency‐domain DMO computationally efficient, the technique of logarithmic time stretching, first suggested in Bolondi et al. (1982), is widely used. After logarithmic stretching of the time axis, the DMO operator becomes temporally stationary which enables replacement of the slow temporal Fourier integration with a fast Fourier transform combined with a simple phase shift. Bale and Jakubowicz (1987) presented a log‐stretch DMO operator (hereafter referred to as Bale’s DMO) in the frequency‐wavenumber (F-K) domain without approximations, while Notfors and Godfrey (1987) suggested an approximate version of log‐stretch DMO operator (hereafter referred to as Notfors’s DMO). Surprisingly, Bale’s full log‐stretch DMO operator produces a less satisfactory impulse response than Notfors’s approximate log‐stretch DMO scheme (see Liner, 1990). Liner (1990) attributed this characteristic to the fact that Bale’s DMO derivation implicitly assumes that the Fourier transform frequency in the log‐stretch domain is not time‐dependant. He presented an exact log‐stretch DMO operator (hereafter referred to as Liner’s DMO) which was derived by transforming the time log‐stretched Hale’s (t, x) DMO impulse response into the Fourier domain. Its derivation is relatively complicated, but Liner has shown that his DMO does generate good DMO impulse responses.

Vibration Analysis of One-Dimensional Structures with Discontinuities Using the Acoustical Wave Propagator Technique

2004 ◽  
Vol 127 (6) ◽  
pp. 604-607
Author(s):  
S. Z. Peng
Keyword(s):  
Wave Propagation ◽  
Cross Section ◽  
Elastic Waves ◽  
Vibration Analysis ◽  
Fourier Transforms ◽  
Numerical Technique ◽  
Sudden Change ◽  
Computationally Efficient ◽  
Exact Analytical Solutions ◽  
One Dimensional

A numerical technique, named the acoustical wave propagator technique, is introduced to describe the dynamic characteristics of one-dimensional structures with discontinuities. A scheme combining Chebyshev polynomial expansion and fast Fourier transforms is introduced in detail. Comparison between exact analytical solutions and predicted results obtained by the acoustical wave propagator technique shows that this scheme has highly accurate and computationally efficient. Furthermore, this technique is extended to investigate the wave propagation and reflection of elastic waves in beams at the location of a sudden change in cross section.

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