Showing papers on "Guided wave testing published in 1997"
Patent•
12 Feb 1997
TL;DR: In this paper, a variety of optical components or nodes are provided which components are formed utilizing holographically polymerized polymer/liquid crystal composites, and which components include free space/unguided wave switches, guided wave switches and out/in couplers, reflection nodes/reflection filters and guided wave interconnect nodes.
Abstract: A variety of optical components or nodes are provided which components are formed utilizing holographically polymerized polymer/liquid crystal composites, and which components include free space/unguided wave switches, guided wave switches, out/in couplers, reflection nodes/reflection filters and guided wave interconnect nodes. Selected ones of these nodes may be designed to operate either in a single wavelength mode or in a multiwavelength WDM mode. All of the components are switchable so as to able to modify the component output to which an optical signal received on a component input is applied as a function of an electric field applied across the component, and to vary the channel outputted on a given output for WDM operation. Nodes of the same type or node of two or more different types may be interconnected into two dimensional and/or three dimensional structures, particularly switching structures for a telecommunications or other purposes, including such structures adapted for multiwavelength operation. For preferred embodiments, guided wave optical paths, and in particular waveguides, are utilized for node interconnects, with various techniques being presented for forming nodes and/or structures as integrated optical structures.
138 citations
TL;DR: The studies presented indicate that defect characterization is possible if a proper mode selection criteria can be established and the suitable features related to transmission and reflection coefficient data can also be used for algorithm development and implementation purposes of defect characterization.
Abstract: The potential use of guided waves for defect characterization is studied. The influence of defect shape and size on transmitted and reflected fields is considered. Using the hybrid boundary element technique, the reflection and transmission coefficients for selected guided wave modes are numerically calculated and compared to experimental data. Selecting the aspect ratio as a shape parameter for various defects, the transmission and reflection coefficients are measured for certain guided wave modes input to the defect. The influence of defect size is then studied by monitoring the transmission and reflection coefficients for defects of various shapes and depths. The studies presented indicate that defect characterization is possible if a proper mode selection criteria can be established. The suitable features related to transmission and reflection coefficient data can also be used for algorithm development and implementation purposes of defect characterization.
112 citations
TL;DR: Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California as mentioned in this paper, and they were observed on linear, three-component seismic arrays deployed across the fault trace.
Abstract: Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California. The guided waves were observed on linear, three-component seismic arrays deployed across the fault trace. These waves were not excited by explosions located outside the fault zone. The amplitude spectra of guided waves show a maximum peak at 2 Hz at Parkfield and 3 Hz at Cienega Valley. The guided wave amplitude decays sharply with observation distance from the fault trace. The explosion-excited fault-zone guided waves are similar to those generated by earthquakes at Parkfield but have lower frequencies and travel more slowly. These observations suggest that the fault-zone wave guide has lower seismic velocities as it approaches the surface at Parkfield. We have modeled the waveforms as S waves trapped in a low-velocity wave guide sandwiched between high-velocity wall rocks, resulting in Love-type fault-zone guided waves. While the results are nonunique, the Parkfield data are adequately fit by a shallow wave guide 170 m wide with an S velocity 0.85 km/sec and an apparent Q ∼ 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an S velocity 0.7 km/sec and a Q ∼ 30.
97 citations
TL;DR: In this article, a modal analysis is presented to describe the excitation of Lamb waves in an elastic plate using a liquid wedge transducer, where the contribution of reflected wave is included in the input exciting forces using a perturbation theory, and the conversion efficiency is related to a single parameter which depends on the rate of attenuation due to leakage from the guided wave into the liquid wedge.
Abstract: A modal analysis is presented to describe the excitation of Lamb waves in an elastic plate using a liquid wedge transducer. Analytical expression for the displacement of a given mode is derived for the excitation by a uniform bounded beam. In contrast to previous studies, the contribution of the reflected wave is included in the input exciting forces using a perturbation theory. The conversion efficiency, defined as the ratio of the guided mode power to the incident power, is related to a single parameter which depends on the rate of attenuation due to leakage from the guided wave into the liquid wedge. Numerical results relevant to the fundamental Lamb modes are obtained as a function of frequency for various incident beam widths and plate thickness. Using optical interferometric detection, direct measurements of the Lamb modes displacements have been carried out in aluminium plates to verify the theoretical analysis.
68 citations
TL;DR: In this article, the authors investigated the spontaneous emission of erbium atoms implanted in various planar multidielectric stacks and performed computational and experimental analyses to assess the amount of light leaking into the radiative and the guided modes of the structures.
Abstract: Spontaneous emission of erbium atoms implanted in various planar multidielectric stacks is investigated. Computational and experimental analyses are performed so as to assess the amount of light leaking into the radiative and the guided modes of the structures. The key point is the demonstration of the dominant emission into the guided modes, even though the atoms are implanted in the spacer of a resonant microcavity structure. The result is of practical interest since it challenges the conventional idea about the electromagnetic confinement, which is likely to be reached within planar microcavities.
45 citations
TL;DR: In this paper, the cross-section of a longitudinally homogeneous dielectric waveguide is decomposed into rectangles with constant permittivity, and the wave equation for modal fields is solved analytically by expanding into functions with harmonic or exponential dependence on the transverse coordinates.
Abstract: Frequently the cross-section of a longitudinally homogeneous dielectric waveguide may be decomposed into rectangles with constant permittivity. For points inside these rectangles the wave equation for modal fields is solved analytically by expanding into functions with harmonic or exponential dependence on the transverse coordinates. Minimization of a least-squares expression for the remaining misfit on the boundary lines allows us to determine propagation constants and fields for guided modes. Semivectorial calculations for two sets of rib waveguides and the centre sections of a directional coupler and an MMI device show very good agreement with results found in the literature.
40 citations
TL;DR: In this paper, the effect of axisymmetric guided waves by cracks and weldments of anisotropic bonding material in welded steel pipes is investigated by a hybrid method employing finite element and modal representation techniques.
Abstract: Scattering of axisymmetric guided waves by cracks and weldments of anisotropic bonding material in welded steel pipes is investigated in this paper by a hybrid method employing finite element and modal representation techniques. The study is motivated by the need to develop a quantitative ultrasonic technique to distinguish flaws and bonding materials in welded cylindrical structures. Numerical results for reflection coefficients are presented for a steel pipe with cracks and V-shaped weldments with and without cracks at the interface between the weldment and the steel pipe. It is shown that as the frequency increases, the coefficients of reflection exhibit resonant peaks at the cutoff frequencies of higher guided modes. These peaks become increasingly pronounced as the slope and the length of the crack increase. Numerical results presented have important applications in quantitative nondestructive evaluation.
39 citations
TL;DR: In this paper, a combination of finite element formulation and wave function expansion is used to investigate the scattering of axisymmetric guided waves by an interphase region with bonding material between two laminated cylinders.
Abstract: A combination of finite element formulation and wave function expansion is used to investigate the scattering of axisymmetric guided waves by an interphase region with bonding material between two laminated cylinders. The motivation of this study is to develop an effective numerical technique to characterize the material properties and the thickness of the bond region between two cylinders that are laminated and anisotropic. Numerical results of wave scattering are presented for a welded steel pipe with different weldment shapes and for two cross-ply symmetrically laminated composite cylinders that are bonded end to end. It is shown that as the frequency increases the reflection coefficients have resonance peaks while the transmission coefficients have sharp drops at the cutoff frequencies of higher guided modes in the cylinders. The resonance peaks of reflection coefficients become increasingly pronounced as the thickness of the joint increases. Another interesting feature is that the reflection coefficients have minimums at frequencies that depend on the thickness and the material properties of the joint. These features may be useful in quantitative nondestructive evaluation of joint properties.
38 citations
TL;DR: In this article, the transient electric fields of a horizontal electric dipole excited by a short pulse current and located on a layered dielectric medium were analyzed using the Cagniard-de-Hoop method.
Abstract: The transient electric fields of a horizontal electric dipole excited by a short pulse current and located on a layered dielectric medium were analyzed using the Cagniard-de-Hoop method. The fields are expressed as the convolution of the exciting current with the layered medium response. The layered medium response is obtained directly from the integral representation for the electric fields in the frequency domain and is expressed as a finite integral. In contrast to the conventional frequency synthesis approach, the Cagniard-de-Hoop (1960) method proves to be computationally more efficient and numerically more stable. Compared with the asymptotic approach, the solution involves no approximation. The nature of the various waves, reflected waves (guided wave and leaky wave), and lateral waves can be easily recognized on the Cagniard integral path. Numerical results are obtained to provide a rigorous forward modeling for the geo-radar operating on layered media.
37 citations
TL;DR: In this article, the effect of surface roughness on ultrasonic guided waves in plates is investigated and an approximate dispersion relation is derived for the traction-free rough waveguide that is formally identical to the conventional Lamb wave equation, but incorporating the roughness parameter as a complex plate thickness.
Abstract: This paper reports analytical research on the effect of surface roughness on ultrasonic guided waves in plates. The theoretical model is constructed by exploiting the phase-screen assumption that takes advantage of the Kirchhoff approximation, where, on a local scale, the roughness degrades only the signal phase. The effect of the rough surface on the guided wave is treated by decomposing the wave modes into their constituent partial waves and considering individually the effect of the roughness on the partial wave components as they reflect from the plate surfaces. An approximate dispersion relation is derived for the traction-free rough waveguide that is formally identical to the conventional Lamb wave equation, but incorporating the roughness parameter as a complex plate thickness. A more accurate version of the model calculation is generalized to fluid-immersed plates having only a single rough surface either on the same, or opposite, side of the plate as the incident ultrasonic field. Calculations of the reflection coefficients in the presence of roughness serve to illustrate the phenomena for the case of the guided waves.
34 citations
TL;DR: In this article, a quasi-static model for ultrasonic guided waves interaction with imperfect interfaces is proposed, and the effect of this condition on the velocity is comprehensively discussed, with the objective of discriminating imperfect bonds.
TL;DR: In this article, fundamental experimental measurements on guided waves in plates with surface roughness are compared to theoretical calculations presented in Part I. All experiments, in either immersion or contact coupling mode, are modeled by the theory developed in I that exploits the phase-screen approximation.
Abstract: In this artice are reported fundamental experimental measurements on guided waves in plates with surface roughness; the experimental data are critically compared to theoretical calculations presented in Part I. All experiments, in either immersion or contact coupling mode, are modeled by the theory developed in I that exploits the phase-screen approximation. In this theory the effect of the rough surface on the received signal, on a local scale, is assumed to be restricted to the signal phase. The comparisons between experiment and predictions show good agreement in most regimes, despite the rather simplifying approximations contained in the calculation. The model is shown to fail only when the guided wave vector is close to a branch point, that is when the guided wave phase velocity approaches the compressional or shear wavespeeds of the plate. Near these values the internal partial waves comprising the guided wave strike the surfaces at grazing incidence or are evanescent, and a simple phase-screen mode...
TL;DR: In this paper, the propagation-mode spectra of integrated open-boundary waveguides are identified and classified through a singularity expansion of their currents/fields in the axial Fourier transform plane.
Abstract: The propagation-mode spectra of integrated open-boundary waveguides are identified and classified through a singularity expansion of their currents/fields in the axial Fourier transform plane. Complex analysis in the latter plane is based upon a transform-domain integral equation formulation for the unknown currents/fields of the guiding structure. Pole and branch-point singularities of those unknown guided wave quantities are identified in the complex transform plane, and appropriate branch cuts are chosen. It is demonstrated that both poles and branch points associated with the layered background environment lead to branch points in that plane. The complete proper propagation-mode spectrum is contributed by singularities on the top Riemann sheet; discrete modes arise from the poles there, while the continuous spectrum is associated with forced solutions to the transform domain integral equations at points along the branch cuts. Leaky-wave modes arise from poles on the lower Riemann sheets and a...
05 Oct 1997
TL;DR: In this paper, a numerical model, providing a time domain wave propagation solution for the field generated by a transducer on an elastic plate, is presented, which is of practical significance in NDE.
Abstract: Investigations of the characteristics of an ultrasonic comb transducer have been performed for a range of transducer parameters. A numerical model, providing a time domain wave propagation solution for the field generated by a transducer on an elastic plate, is presented. The ability of mode selection and isolation is demonstrated, which is of practical significance in NDE.
TL;DR: In this paper, a technique for large enhancement of the diffraction efficiency of a guided-wave magnetooptic (MO) Bragg cell modulator using a non-uniform bias magnetic field in bismuth-doped yttrium iron garnet-gadolinium gallium garnet waveguide is reported.
Abstract: A technique for large enhancement of the diffraction efficiency of a guided-wave magnetooptic (MO) Bragg cell modulator using a nonuniform bias magnetic field in bismuth-doped yttrium iron garnet-gadolinium gallium garnet waveguide is reported. Since the velocity of propagation of the magnetostatic forward volume wave (MSFVW) varies with the bias magnetic field, a bias magnetic field of proper spatial distribution will modify its wave front and, thus, create a lensing effect upon the MSFVW. This lensing effect in turn reduces the angular beam spread of the MSFVW, and results in a higher MO Bragg diffraction efficiency. The experimental data obtained for the cases with uniform and nonuniform bias magnetic fields at the carrier center frequency range of 2.0–3.5 GHz have demonstrated a diffraction efficiency enhancement by two to six times. A diffraction efficiency as high as 70% has also been accomplished. Furthermore, the measured frequency responses indicate that the nonuniform bias magnetic field has had...
TL;DR: In this paper, a new method is developed to reconstruct the permittivity profile of a dielectric slab in a guided wave formulation, where the propagation constants of the slab eigenmodes are used as input data for inversion of the boundary value problem for the nonlinear differential equation representing the condition of existence of the modes.
Abstract: A new method is developed to reconstruct the permittivity profile of a dielectric slab in a guided wave formulation. The propagation constants of the slab eigenmodes are used as input data for inversion of the boundary-value problem for the nonlinear differential equation representing the condition of existence of the modes. The permittivity profile is expanded into a set of special functions so that the propagation constant of a particular mode depends mainly on only one term of the set. This ensures fast convergence of an iterative procedure to find the coefficients of expansion. The method is shown to be valid for the discontinuous profiles of high contrast as well as for both symmetrical and asymmetrical profiles provided that in the last case additional measurements of the slab placed on a metal plate are performed. Several simulated and experimental examples are presented.
TL;DR: In this paper, the authors present theoretical considerations for the determination of the diffraction of ultrasonic guided waves propagating in a non-uniform elastic adhesive layer, where the nonuniformity results from changes in the adhesion bond characteristics between the adhesive and the adherent layer.
TL;DR: In this article, it is demonstrated experimentally that the range of incident angles over which any given mode can be generated is dependent upon the size of the transducer used to excite the mode, its frequency content and the pressure distribution across its surface.
TL;DR: In this paper, Fan-out energy distribution for substrate-guided wave optical interconnects with a surface-normal configuration is addressed, where up to nine optimized waveguide holograms are independently fabricated on the same substrate.
Abstract: Optimization of fan-out energy distribution for substrate guided wave optical interconnects with a surface-normal configuration is addressed in this paper. Up to nine optimized waveguide holograms are independently fabricated on the same substrate. Energy fluctuation affected by the deviation of the designed diffraction efficiency is theoretically analysed. Using DuPont photopolymer film HRF-600X001-20, we demonstrate 1-to-5 and 1-to-9 surface-normal fan-out devices operating at 850 nm. The output non-uniformities of ±4% and ±10% are experimentally confirmed for the two devices, respectively.
TL;DR: In this paper, the surface and guided wave polaritons for a magnetic layered structure on a substrate were studied and analytic equations for implicit dispersion relations were solved numerically for a variety of layering patterns, and profiles showing the localization of both guided waves and surface waves were obtained.
Abstract: We study the surface and guided wave polaritons for a magnetic layered structure on a substrate. Using the effective-medium approximation we obtain analytic equations for implicit dispersion relations. These dispersion relations are solved numerically for a variety of layering patterns, and profiles showing the localization of both guided waves and surface waves are obtained. Explicit results are presented for an - superlattice on a substrate.
TL;DR: A new method for calculating coupling efficiency is derived by introducing a compensation for the mismatch in the operating process of the system, allowing the new optical interconnect architecture to provide a higher design accuracy and an optimized coupling efficiency, even though it is under the case of momentum mismatch.
Abstract: We report on a new optical interconnect architecture for three-dimensional, multiple electro-optic gratings with LiNbO(3) used in conjunction with substrate guided waves. First the operating mechanism of the system is studied in detail, and the momentum mismatch in the operating process of the system is also demonstrated. We then derive a new method for calculating coupling efficiency by introducing a compensation for the mismatch. This theoretical research allows the new optical interconnect architecture to provide a higher design accuracy and an optimized coupling efficiency, even though it is under the case of momentum mismatch. We achieve this result by introducing a substrate guided wave with 45 degrees bouncing angle and 100-V applied voltage. The successful design and its theoretical analysis will be helpful for research on the grating coupler.
01 Jan 1997
TL;DR: In this paper, a pitch-catch technique was used to detect material loss and thickness reduction in a plate-like structure, which can be used for non-destructive inspection of aircraft.
Abstract: Many airplanes, both military and commercial, have exceeded their original design service lives. For such aging structures, the presence of hidden damage can severely limit their performance. It is important to monitor the progress of damage to ensure the safety and integrality of these structures. Typical damage can be several types of corrosion and fatigue cracking. Lap-joints trap moisture and air and are initiation sites for corrosion. These sites are potential locations for wide spread fatigue damage. Generally, corrosion can cause material loss and thickness reduction, which can be detected by non-destructive ultrasonic methods. Conventional methods require point-by-point inspection, which is a time-consuming process. Guided waves, which direct wave energy in the plate, carry information about the material in their path and offer a possible more efficient tool for non-destructive inspection of material loss or thickness reduction. Using a pitch-catch technique, in which one transducer sends a guided wave in a plate structure and a second transducer picks up the signal at a different position, guided waves can be launched and detected to inspect plate-like structures, line by line, thus increasing the inspection efficiency by an order of magnitude. Also, when guided waves pass through a region with material loss, some energy would be reflected back. By studying the characteristics of the reflected waves, information about material loss can be obtained.
TL;DR: In this paper, it was shown that laser-generated, ultrasonic-guided waves can be successfully generated in steam generator tubes. But the authors did not show that defects are detectable with this technique.
Abstract: Results are shown that prove laser-generated, ultrasonic-guided waves can be successfully generated in steam generator tubes. Specific guided wave modes are identified by determination of the frequency and velocity of each. In addition, the authors show results that confirm defects are detectable with this technique.
TL;DR: In this paper, a measurement technique to obtain dispersion curves for guided acoustic modes in porcelain-coated steel is described using two angled ultrasonic longitudinal transducers in a pitch catch configuration by employing an immersion technique.
Abstract: In this paper a measurement technique to obtain dispersion curves for guided acoustic modes in porcelain-coated steel is described. The measurement is performed with two angled ultrasonic longitudinal transducers in a pitch catch configuration by employing an immersion technique. Phase velocities for the guided modes are selected through the variation of the angle formed by the transmitter beam with the surface normal vector. The excitation signal of the transmitting transducer is a narrow band pulse. For each phase velocity, the guided mode frequencies are recovered by evaluating the frequency minima of the reflection coefficient.
TL;DR: In this paper, a waveguide diffractive doublet consisting of a uniform grating coupler and a diffractive optical element was used for two-dimensional optical fan-out.
TL;DR: In this article, a new kind of neutron De Broglie wave leaky coupler-guide structure is proposed, which allows only one neutron polarization to be coupled into a magnetic neutron thin film waveguide.
Abstract: In the present paper a new kind of neutron De Broglie wave leaky coupler-guide structure is proposed. This new magnetic coupler allows only one neutron polarization to be coupled into a magnetic neutron thin film waveguide. It is shown theoretically that this new thin film coupler decrease considerably the losses due to the roughness of the interfaces of the multilayer structure. Moreover a transmitted resonance peak is observed in a wavelength region accessible only for guided neutron waves. Thus a magnetic neutron coupler is proposed and a transmitted polarized neutron guided wave is observed experimentally.
25 Apr 1997
TL;DR: In this article, a theoretical study aimed at the optimum design of thermo- optic guided-wave switches realized in silicon-on-oxide technology is reported, where the heat transfer processes occurring inside such devices are analyzed by means of a 3D finite element thermal simulator.
Abstract: A theoretical study aimed at the optimum design of thermo- optic guided-wave switches realized in silicon-on-oxide technology is reported. The heat transfer processes occurring inside such devices are analyzed by means of a 3D finite element thermal simulator. In particular, in rib waveguiding structures, we demonstrate that the optimum values of the oxide layer thickness and of the outer rib height are a function of the heating pulse power used to drive the device. The theoretical results carried out are consistent with the experiments reported in literature.
23 Jan 1997
TL;DR: In this paper, a review of phase mask fabrication technology and commercially available products is presented, in particular, wavelength demultiplexing devices, gain flattening filters for EDFA and dispersion compensators, all of which are critical elements in high data rate lightwave systems.
Abstract: The advent of phase mask technique has made it possible to fabricate Bragg gratings to tight tolerances in a repeatable, reliable and cost effective manner. These gratings are in turn making it possible to manufacture a wide variety of high performance guided wave devices for lightwave communication and sensor applications. This paper will review the phase mask fabrication technology and the commercially available products. the paper will then discuss a few successful applications of grating based devices currently entering the market, in particular, wavelength demultiplexing devices, gain flattening filters for EDFA and dispersion compensators, all of which are critical elements in high data rate lightwave systems.