Array Of Line Sources Research Articles

Investigation into NSAW excitation and modulation utilizing the grating mask technique

Narrowband surface acoustic wave (NSAW) method is a promising ultrasonic detection technique, with its laser-induced excitation technology offering the advantages of non-contact and flexible regulation. This paper proposes an NSAW excitation and modulation system based on the grating mask method to detect the nonlinear characteristics of the spectra caused by the variation in material surface properties. According to Doyer’s sharp line excitation theory, a strip line source array excitation model formed by superposition principle is established, and the effects of duty ratios of the masks on NSAW spectra amplitude characteristics are interpreted. An NSAW excitation and B-scan experimental system that can realize line source spacing changes is developed, and the effects of cylindrical lens height and masks with different duty ratios on NSAW spectra modulation are studied. The experimental results show that the amplitude ratios (the ratio of the double frequency amplitude to the second harmonic amplitude) are consistent with the results of the Doyer superimposed strip line source array excitation model in which the excitation light source energy is evenly distributed. The second-order nonlinear coefficients extracted from the experimental spectra can effectively characterize the surface properties of 6061 aluminum alloy at different annealing temperatures.

Sound Field Reconstruction Using Prolate Spheroidal Wave Functions and Sparse Regularization.

Near-field acoustic holography (NAH) based on compressing sensing (CS) theory enables accurate reconstruction of sound fields using a limited number of sampling points. However, the successful implementation of this technique depends on two crucial factors: (1) the appropriate selection or construction of the spatial basis and (2) an effective sparse regularization process. To enhance reconstruction performance for elongated sound sources, this paper proposes a novel sound field reconstruction method that combines prolate spheroidal wave functions (PSWFs) with the orthogonal matching pursuit (OMP) algorithm. In this method, PSWFs serve as a sparse spatial basis for representing the radiated sound field. The sparse coefficients are determined by the OMP algorithm in a linear subspace composed of basic functions that best match the residual error. The OMP algorithm effectively identifies significant components before potentially selecting incorrect ones by setting an appropriate stopping rule. Numerical simulations are conducted using a line-array source model. The results show that the proposed method can accurately reconstruct the sound pressures of the elongated source model using a relatively small number of samplings. In addition, the proposed method exhibits robustness across a wide frequency range, diverse array configurations and various sampling numbers. The experimental results further validate the feasibility and reliability of the proposed method.

Laser array line source with adjustable period used for LGUS chemical corrosion detection

A novel optical arrangement to generate a laser array line source of laser-generated ultrasound based on two-beam interference is proposed. The arrangement simplifies the adjustment of the laser array source period by changing the intersection angle of two interference beams. The performance of the arrangement is illustrated through measurements of the surface acoustic wave generated by the nanosecond laser array line source in aluminum metal. The surface acoustic wave generated by the laser line array source has stronger directivity parallel to the direction of the line source. The intensity of the measured surface acoustic wave is higher than that generated by a laser spot source with the same incident energy. The optical arrangement generating the laser array line source will be particularly advantageous in laser-generated ultrasound systems used for chemical corrosion detection.

Array of line sources that produces preselected plane waves

A generalized Poisson summation formula produces an explicit expression for the surface current on a plane that radiates a set of preselected plane waves. Specifically, the surface current is expressed as an integral in the complex plane of a function whose poles determine the plane-wave directions of propagation and whose residues determine the corresponding plane-wave amplitudes. When only a finite number of plane waves are specified, the surface current is a continuous function. If an infinite number of plane waves are specified, the surface current can degenerate into a discrete set of line sources. In such situations, the expression for the surface current determines both the location and strength of the line sources that radiate the infinite set of plane waves. One can specify both propagating and evanescent plane waves. Explicit formulas are derived for line sources that radiate plane-wave sets determined by both periodic and almost-periodic functions. The closed-form expressions can be applied directly to the problem of scattering by gratings.

Millimeter-Wave Integrated Side-Fire Leaky-Wave Antenna and Its Application as a Spectrum Analyzer

An analog, low-profile and shielded spectrum analyzer is proposed for operation at mm-wave frequencies around the 60 GHz band based on a novel side-fire leaky-wave antenna (LWA) configuration. The proposed side-fire periodic LWA is systematically developed from a conventional three-port waveguide T-junction which is modified to a LWA unit cell with an internal matching mechanism to suppress the stopband and enable broadside radiation based on unit cell symmetry considerations. The resulting periodic side-fire antenna radiates in the plane of the antenna, whereby the leakage power can either be allowed to radiate in free-space or kept confined inside a parallel-plate waveguide (PPW) structure. The proposed side-fire structure can therefore be completely shielded, making it useful as a broadband spectrum analyzer that is compatible with substrate-integrated waveguide (SIW) technology. Furthermore, a convex side-fire antenna is demonstrated to focus the radiated beams in the near-field of the structure to make the entire system compact. The integrated spectrum analyzer is experimentally demonstrated between 59 and 66 GHz providing 1 GHz frequency resolution. Furthermore, a simple mathematical model consisting of an array of line sources is used to efficiently model the beam-scanning characteristics of the curved side-fire LWA in the near-field of the structure.

Pseudospin-Polarized Topological Line Defects in Dielectric Photonic Crystals

Electromagnetic topological insulators have been explored extensively due to the robust edge states they support. In this work, we propose a topological electromagnetic system based on a line defect in topologically nontrivial photonic crystals (PCs). With a finite-difference supercell approach, modal analysis of the PCs structure is investigated in detail. The topological line-defect states are pseudospin polarized and their energy flow directions are determined by the corresponding pseudospin helicities. These states can be excited by using two spatially-symmetric line-source arrays carrying orbital angular momenta. The feature of the unidirectional propagation is demonstrated and it is stable when disorders are introduced to the PCs structure.

Experimental and numerical investigation of evaporation from line sources of water in low porosity surfaces

We report evaporation characteristics due to higher heating from above from surfaces having an array of line sources. The line sources are created by vertically stacked rectangular plates in a box with water. Two different types of plates were used. In one case line source or film thickness was 66 µm and open area ratio was 4%, and in the second case film thickness was 28 µm and 20% was the open area ratio. Even at the 4% open area ratio the evaporation rate was ∼85% compared to a bare water surface, at the same heat flux. Lateral conduction of heat from the impervious hotter regions to the line sources and the 2-D nature of diffusion near these tiny line sources enhances the evaporative flux, owing to increase in the concentration gradient of water vapour, explains the high evaporation rate, observed in the present work. This system bridges the gap between the understanding of evaporation from bare water surfaces (1-D vapour diffusion) and leaf surfaces (3-D vapour diffusion). Evaporation rates for the fully saturated conditions are in good agreement with the theoretical predictions of Suzuki and Maeda (1968) and Schlünder (1988). The computed surface temperatures and its width-wise variation match well with the experimental values. We also propose a simple film model for the unsaturated condition of the porous medium and show that the temperature distribution obtained using this model is in reasonably good agreement with the measured values.

Mixed Analytical-Numerical Filter Design for Optimized Electronic Control of Line Source Arrays

Mixed Analytical-Numerical Filter Design for Optimized Electronic Control of Line Source Arrays

Mixed Analytical-Numerical Filter Design for Optimized Electronic Control of Line Source Arrays

Mixed Analytical-Numerical Filter Design for Optimized Electronic Control of Line Source Arrays

An Analytical Approach for Optimizing the Curving of Line Source Arrays

An Analytical Approach for Optimizing the Curving of Line Source Arrays

スリットを通過する音波の偏向に関する実験及び解析的検討

It is well known that the diffraction and the interference are characteristic properties of waves as commonly observed in various physical phenomena. Additionally, the recent optical engineering has made advances in the application of acousto-optical effect, which is characterized by the diffraction and the deflection of light waves through the interaction with acoustic waves. Being inspired by the effect, the present investigation deals with an acoustic-acoustic wave interaction where the diffraction and deflection of a sound wave occur when it passes transversely across the strong acoustic standing wave, namely the ‘virtual slit’, generated by coaxially placed loudspeakers. First, an approximate numerical model is developed based on phased line array source theory which simulates the interaction of outgoing sound wave through apertures into free space. Based on the numerical prediction, the wave deflection by both the physically existing slit and the virtual slits is then explored experimentally by measuring sound field over the slits. Both numerical and experimental investigations show that the incoming sound waves into the tilted slits can be deflected in the direction approximately as intended. Leaving some issues to be solved for the practical use, the suggested wave deflection control method can be used as one of the noise abatement technologies.

Quantitative simulation of ultrasonic time of flight diffraction technique in 2D geometries using Huygens–Fresnel diffraction model: Theory and experimental comparison

This article presents an analytical approach for simulation of ultrasonic diffracted wave signals from cracks in two-dimensional geometries based on a novel Huygens–Fresnel Diffraction Model (HFDM). The model employs the frequency domain far-field displacement expressions derived by Miller and Pursey in 2D for a line source located on the free surface boundary of a semi-infinite elastic medium. At each frequency in the bandwidth of a pulsed excitation, the complex diffracted field is obtained by summation of displacements due to the unblocked virtual sources located in the section containing a vertical crack. The time-domain diffracted wave signal amplitudes in a general isotropic solid are obtained by standard Fast Fourier Transform (FFT) procedures. The wedge based finite aperture transducer refracted beam profiles were modelled by treating the finite dimension transducer as an array of line sources. The proposed model is able to evaluate back-wall signal amplitude and lateral wave signal amplitude, quantitatively. The model predicted range-dependent diffracted amplitudes from the edge of a bottom surface-breaking crack in the isotropic steel specimen were compared with Geometrical Theory of Diffraction (GTD) results. The good agreement confirms the validity of the HFDM method. The simulated ultrasonic time-of-flight diffraction (TOFD) A-scan signals for surface-breaking crack lengths 2mm and 4mm in a 10mm thick aluminium specimen were compared quantitatively with the experimental results. Finally, important applications of HFDM method to the ultrasonic quantitative non-destructive evaluation are discussed.

Efficient computation of the 2-D Green's function for 1-D periodic line sources in planar multilayered media

Periodic Green's function (PGF) of an infinite 1-D periodic array of line sources in planar multilayered media is calculated by the use of the of the 3-level discrete complex image method (DCIM) together with the surface wave pole (SWP) extraction. The Ewald's method is then applied to accelerate the evaluation of the PGF. The recipe to choose the Ewald's splitting parameter is also given. It is shown that the Ewald's transformation needs a few terms to approximate the PGF with high accuracy. The SWP contributions, which are extracted before the DCIM application, are added to this approximation. The spatial domain surface wave pole contributions are observed to be highly oscillatory and converge to zero. The numerical results are provided to demonstrate the efficiency and the accuracy of the procedure followed.

Simulation of Line Array Sound Source

This paper is focused on the simulation of line array source that consists of eight separate loudspeaker enclosures of the same type having some directional characteristics influenced by the position within the line array. The influence on these characteristics caused by the different positions of enclosures in the array was tested. The characteristics of the line array source were measured in the anechoic chamber. The comparison between the results of the simulation of ideal and real sources is shown.

Focusing light in a bianisotropic slab with negatively refracting materials

We investigate the electromagnetic response of a pair of complementary bianisotropic media, which consist of a medium with positive refractive index (+ε, +μ, +ξ) and a medium with negative refractive index(−ε, −μ, −ξ). We show that this idealized system has peculiar imaging properties in that it reproduces images of a source, in principle, with unlimited resolution. We then consider an infinite array of line sources regularly spaced in a 1D photonic crystal (PC) consisting of 2n layers of bianisotropic complementary media. Using coordinate transformations, we map this system into 2D corner chiral lenses of 2n heterogeneous anisotropic complementary media sharing a vertex, within which light circles around closed trajectories. Alternatively, one can consider corner lenses with homogeneous isotropic media and map them into 1D PCs with heterogeneous bianisotropic layers. Interestingly, such complementary media are described by scalar, or matrix valued, sign-shifting parameters, which satisfy a new version of the generalized lens theorem of Pendry and Ramakrishna. This theorem can be derived using Fourier series solutions of the Maxwell–Tellegen equations, or from space–time symmetry arguments. Also of interest are 2D periodic checkerboards consisting of alternating rectangular cells of complementary media which are such that one point source in one cell gives rise to an infinite set of images with an image in every other cell. Such checkerboards can themselves be mapped into a class of 3D corner lenses of complementary bianisotropic media. These theoretical results are illustrated by finite element computations.

Investigation of the sound distribution in street canyons with non-parallel building Façades

Sound propagation in street canyons have been a topic of interest for decades. In a congested city such as Hong Kong, street canyons with large height to width ratios are a common sight. Many prediction models have been developed over the years, but the problem is still of interest because of the complexity due to the multiple reflections and varying surface conditions in real life cases. In this paper, a 1:4 scale model experiment of a street canyon, 4 m long and 2 m high, is presented where one of the facades is inclined. The reference case is with two parallel facades, which is compared with cases when one facade is tilted 80°, 70°, and 60°. The measurements were conducted in an anechoic chamber and a line source array generating white noise was used for simulating traffic noise. The sound distribution patterns were studied on the reference wall and the inclined wall. It was observed that the sound strength and the reverberation decrease rapidly when inclining the opposite wall. For low and mid frequencies, the sound reduction was more significant closer to the top of the inclined facade, while the opposite could be seen for the vertical facade.

Effects of Geometrical-Size of Cylindrical-Shell Transducer on Acoustic-Beam Steering Efficiency for a Slim-Hole Acoustic-Logging Tool~!2009-05-05~!2010-03-01~!2010-05-04~!

The slim-hole acoustic-logging tool is often used for measurement while drilling and horizontal well logging. The source and receiver are generally thin cylindrical-shell piezoelectric transducers. The radius of the drilling-collar limits the size of the cylindrical-shell transducer in the logging tool. The smaller the radiation area of the transducer, the smaller the radiated acoustic energy, and the smaller its radius, the higher the frequency of the radiated acoustic signals. Besides, the attenuation for higher frequency wave propagating in the medium is higher. Due to these reasons the amplitude of the measured acoustic signal by using the slim-hole logging tool is usually much smaller than that by using the conventional logging tool. Therefore, the acoustic-beam steering technology is important for enlarging the amplitude of the received acoustic signal during logging with a slim-hole logging tool. The geometrical-size of the cylindrical-shell transducer influences the acoustic-beam steering efficiency of the logging tool with a line-array source and a receiver. In this paper, in the frame work of the acoustic-logging transmission network model with the concept of directivity-weighted coefficient, we have carried out the calculation and analysis of the effects of geometrical-size of the transducer on the acoustic-beam steering efficiency of the slim-hole acoustic-logging tool with a line-array source and a receiver. The calculated results are useful for optimizing the design of the slim-hole acoustic-logging tool with a line-array source and a receiver.

Midfrequency backscatter imaging of fish schools in a shallow water waveguide.

In this experimental effort, field data and modeling are used to investigate backscatter imaging of schools of pelagic fish in a shallow water oceanic waveguide. Two-dimensional (2-D) circular images of an oceanic waveguide are created using a monostatic circular receiving array and vertical line array source (12 kHz) deployed from a stationary ship. Horizontal multibeam images of a radial (depth integrated) cross section of the ocean are formed with targets and reverberation structure observed at ranges up to several Km. Examples of waveguide images are presented for data taken in the Puget Sound of Washington state. In some instances, the backscatter from aggregations of fish was observed to be higher than the reverberation; in other cases, fish schools could not be resolved. Fish school locations were independently observed by vertical echo sounding. Preliminary experimental results are shown to illustrate the potential of resolving the 2-D horizontal structure of aggregations of fish using such methods. Modeling is used to interpret the effects of waveguide propagation on imaging. Operational issues related to using waveguide imaging for fisheries’ research and signal processing issues related to waveguide imaging will be discussed. [Work funded by NOPP with support from ONR and NOAA-OE.]

Efficient Calculation of the Green's Function for 2-D Periodic Line Sources Using Ewald Method

An accelerated calculation scheme is presented for the Green's function of the two-dimensional (2-D) periodic array of line sources based on the Ewald sum technique. The contour integral representation of the Hankel function and the Poisson sum formula are employed to accelerate the slowly convergent Green's function series. The resulting Green's function is expressed as the sum of an exponential series in the spatial domain and a spectral series consisting of the exponential integral functions, both with Gaussian convergence.

Choosing splitting parameters and summation limits in the numerical evaluation of 1‐D and 2‐D periodic Green's functions using the Ewald method

Accurate and efficient computation of periodic free‐space Green's functions using the Ewald method is considered for three cases: a 1‐D array of line sources, a 1‐D array of point sources, and a 2‐D array of point sources. A limitation on the numerical accuracy when using the “optimum” E parameter (which gives optimum asymptotic convergence) at high frequency is discussed. A “best” E parameter is then derived to overcome these limitations. This choice allows for the fastest convergence while maintaining a specific level of accuracy (loss of significant figures) in the final result. Formulas for the number of terms needed for convergence are also derived for both the spectral and the spatial series that appear in the Ewald method, and these are found to be accurate in almost all cases.