Showing papers on "Guided wave testing published in 2004"

Geometries and materials for subwavelength surface plasmon modes.

Abstract: Plasmonic waveguides can guide light along metal-dielectric interfaces with propagating wave vectors of greater magnitude than are available in free space and hence with propagating wavelengths shorter than those in vacuum. This is a necessary, rather than sufficient, condition for subwavelength confinement of the optical mode. By use of the reflection pole method, the two-dimensional modal solutions for single planar waveguides as well as adjacent waveguide systems are solved. We demonstrate that, to achieve subwavelength pitches, a metal-insulator-metal geometry is required with higher confinement factors and smaller spatial extent than conventional insulator-metal-insulator structures. The resulting trade-off between propagation and confinement for surface plasmons is discussed, and optimization by materials selection is described.

The reflection of guided waves from notches in pipes: a guide for interpreting corrosion measurements

Abstract: Ultrasonic guided waves are used for the rapid screening of pipelines in service and simple, standard testing procedures are already defined. The implementation of the method enables the localization of the defects along the length of the pipe and offers a rough estimate of defect size. In this article we present a systematic analysis of the effect of pipe size, defect size, guided wave mode and frequency on the reflection from notches. The maximum and minimum value of the reflection coefficient at varying axial extent are identified and used for the purpose of defect sizing. Maps of reflection coefficient as a function of the circumferential extent and depth of the defect are presented for a 3 in. schedule 40 steel pipe. An approximate formula, which allows these results to be extrapolated to other pipe sizes, is proposed and evaluated.

Optical off-chip interconnects in multichannel planar waveguide devices

Abstract: The multichannel waveguide device includes an array of waveguides located in a plane. Each waveguide channel has a redirecting element for redirecting a guided wave out of said plane, or vice versa. The redirecting elements are staggered in the direction of the waveguides so as to transform a one-dimensional array of in-plane waves into a two-dimensional array of out-of-plane waves, or vice versa.

Guided wave inspection potential of defects in rail

Abstract: The authors provide the results of experiments they have conducted on rail at test tracks and on an operating railroad. Results are presented that suggest that the frequency range [40,80] kHz readily supports guided waves. Theoretical results including roots of the dispersion relations for rail and a sample of wave displacement within a railhead are presented. Non-contact air-coupled and electromagnetic acoustic transducers (EMATs) are discussed as receivers of sound energy emanating from rail. The results of an experiment that used air-coupled transducers to profile the radiation pattern of a rail are presented. A rail cutting experiment with EMATs that simulated a transverse rail defect is discussed. Conclusions that the authors have drawn from their work are summarized at the end of the paper.

Comparison among various Si/sub 3/N/sub 4/ waveguide geometries grown within a CMOS fabrication pilot line

Abstract: Low-pressure chemical-vapor deposition (LPCVD) thin-film Si/sub 3/N/sub 4/ waveguides have been fabricated on Si substrate within a complementary metal-oxide-semiconductor (CMOS) fabrication pilot line. Three kinds of geometries (channel, rib, and strip-loaded) have been simulated, fabricated, and optically characterized in order to optimize waveguide performances. The number and optical confinement factors of guided optical modes have been simulated, taking into account sidewall effects caused by the etching processes, which have been studied by scanning electron microscopy. Optical guided modes have been observed with a mode analyzer and compared with simulation expectations to confirm the process parameters. Propagation loss measurements at 780 and 632.8 nm have been performed by both using the cutback technique and measuring the drop of intensity of the top scattered light along the length of the waveguide. Loss coefficients of approximately 0.1 dB/cm have been obtained for channel waveguides. These data are very promising in view of the development of Si-integrated photonics.

Guided wave propagation in an elastic hollow cylinder coated with a viscoelastic material

Abstract: The propagation of ultrasonic guided waves in an elastic hollow cylinder with a viscoelastic coating is studied. The principle motivation is to provide tools for performing a guided wave, nondestructive inspection of piping and tubing with viscoelastic coatings. The theoretical boundary value problem is solved that describes the guided wave propagation in these structures for the purpose of finding the guided wave modes that propagate with little or no attenuation. The model uses the global matrix technique to generate the dispersion equation for the longitudinal modes of a system of an arbitrary number of perfectly bonded hollow cylinders with traction-free outer surfaces. A numerical solution of the dispersion equation produces the phase velocity and attenuation dispersion curves that describe the nature of the guided wave propagation. The attenuation dispersion curves show some guided wave modes that propagate with little or no attenuation in the coated structures of interest. The wave structure is examined for two of the modes to verify that the boundary conditions are satisfied and to explain their attenuation behavior. Experimental results are produced using an array of transducers positioned circumferentially around the pipe to evaluate the accuracy of the numerical solution.

Guided wave propagation in three-layer pavement structures

Abstract: A study on guided waves in a layered half-space with large velocity contrasts and a decreasing velocity with depth is presented. Multiple mode dispersion curves are calculated in the complex wave number domain, taking into consideration the attenuation caused by leakage into the underlying half-space. The excitability of the modes by a vertical point force on the surface is also calculated. Results show that the measurable wave field at the surface of a pavement structure is dominated by leaky quasi-Lamb waves in the top and second layers. The fundamental antisymmetric mode of vibration is the dominating mode generated in the stiff top layer. This mode drives the complete system and continuity across the boundaries generates higher order modes in the embedded second layer. The interaction of leaky Lamb waves in the first two layers results in large variations in the excitability and the attenuation, so that only the waves corresponding to certain portions of the dispersion curves are measurable remote from the source at the pavement surface. It is concluded that these portions of dispersion curves can be individually resolved in practice, by using multichannel processing techniques. This holds the potential for a refined nondestructive testing technique for pavements.

Magneto-inductive waves supported by metamaterial elements: Components for a one-dimensional waveguide

Abstract: The propagation and manipulation of magneto-inductive waves is studied under conditions when there is reflection due to lack of matching, when power is coupled from one waveguide to another, when coupling causes directional properties and when tunnelling occurs between two waveguides. The relationships obtained are compared and contrasted with those occurring in traditional transmission lines.

Lamb wave propagation in elastic plates coated with viscoelastic materials

Abstract: This paper addresses the effects of attenuative coatings on the dispersion characteristics of Lamb wave propagation in elastic plates. The topology of phase velocity and guided wave attenuation spectra is analyzed as a function of the coating internal damping (longitudinal and shear bulk attenuations) and it is proved that in contrast to elastic plates, all modes are propagating albeit with large attenuation in some cases. An energy-based correspondence between the dispersion of the attenuative bilayer and that of a related elastic bilayer is derived in order to investigate separately the effects of the longitudinal and shear bulk attenuations on the attenuation of the guided modes. It is shown that at low frequency the guided wave attenuation is only slightly affected by the longitudinal bulk attenuation, while the contribution of the shear bulk attenuation is substantial. The attenuation characteristics of shear horizontal modes are compared with those of Lamb modes in order to identify the mode and the frequencies which result in minimum guided wave attenuation.

Spectral methods for modelling guided waves in elastic media

Abstract: An efficient, accurate, and flexible numerical scheme based on spectral methods is developed here to determine dispersion curves and displacement/stress profiles for modes in elastic guiding structures, possibly curved, layered, damped, inhomogeneous, or anisotropic. Numerical examples and comparisons with existing techniques are given to demonstrate the efficiency and flexibility of the scheme.

Parallel-plate THz transmitter

Abstract: Direct THz excitation of a parallel plate waveguide is demonstrated. The transmitter yields a THz signal with and without an applied bias, and is the next step toward a guided wave TEM-mode THz bandwidth device.

Modeling the Excitation of Lamb and SH Waves by Point and Line Sources

Abstract: The guided wave field excited in a plate‐like structure from any weakly coupled transducer can be calculated from the superposition of the guided wave fields due to a number of suitable point or line excitation sources. In this paper, the fields from various point and line excitation sources are reviewed and relationships between them are demonstrated. The performance of pancake coil EMATs is modeled using the superposition of the fields from point sources and the results compared with experiment.

Guided Lamb waves and L-SAFT processing technique for enhanced detection and imaging of corrosion defects in plates with small depth-to wavelength ratio

Abstract: The Lamb synthetic aperture focusing technique (L-SAFT) imaging algorithm in the Fourier domain is used to produce Lamb wave imaging in plates while considering the wave dispersive properties. This artificial focusing technique produces easy-to-interpret, modified B-scan type images of Lamb wave inspection results. The high level of sensitivity of Lamb waves combined with the L-SAFT algorithm allows one to detect and to produce images of corrosion defects with small depth-to-wavelength ratio. This paper briefly presents the formulated L-SAFT algorithm used for Lamb waves and, in more details, some experimental results obtained on simulated and real corrosion pits, demonstrating the benefit of combining L-SAFT with pulse-echo Lamb wave inspection. The obtained images of the real corrosion defects showed detection of pits with a depth-to-wavelength ratio of approximately 2/11.

Nondestructive inspection apparatus and nondestructive inspection method using guided wave

Abstract: A nondestructive inspection apparatus includes a pair of guided wave sensors disposed on an outer surface of a piping and a guided wave inspection device connected to the pair of guided wave sensors which, outputs a transmitting signal for propagating a guided wave to the guided wave sensors, and obtains a receiving signal by receiving a propagated signal by the guided wave sensors. An inspection-result storage device stores the guided wave as a digitized signal of the received wave and an inspection-result diagnostic device performs arithmetic processing of judging whether or not a signal associated with a defect exists.

Load measurement and health monitoring in cable stays via guided wave magnetostrictive ultrasonics

Abstract: Loaded cables made of wires, strands or bars are employed in civil structures as load carrying members in cable stayed and suspension bridges. Steel strands are also employed in prestressed structures for the pretensioning or posttensioning of concrete. Accurate and real time knowledge of the force acting on these stressing systems can contribute immensely to ensuring the safety of a bridge structure. Monitoring cable loads in service can also allow for detection of excessive wind and traffic overloads or, in the worst scenario, problems such as accidental broken wires and corrosion. The overall objective of this paper is to further the understanding of an ultrasonic method that is able to monitor live loads in multiwire steel strands as well as detect possible discontinuities such as indentations and broken wires. The characterization of wave propagation in steel strands is achieved through a broadband, laser ultrasonic setup and time frequency wavelet transform processing. Those vibrating frequencies propagating with minimal losses are identified as they are suitable for long range testing of the strands. In addition, the wave transmission spectra are found to be sensitive to the load level. Sensors based on the magnetostrictive effect are used for the wave generation and detection. The acoustoelastic effect is also considered for live load monitoring. Signal processing based on the discrete wavelet transform is used to enhance the discontinuity detection sensitivity and acquisition speed.

Physics of propagation in left-handed guided wave structures at microwave and millimeter-wave frequencies.

Abstract: A microstrip configuration is loaded with a left-handed medium substrate and studied regarding its dispersion diagrams over the microwave and millimeter-wave frequency bands for a number of different modal solutions. Ab initio calculations are accomplished self-consistently with a computer code using a full-wave integral equation numerical method based upon a Green's function employing appropriate boundary conditions. Bands of both propagating and evanescent behavior are discovered in some of the modes. Electromagnetic field plots in the cross-sectional dimension are made. New electric field line and magnetic circulation patterns are discovered.

Directional scholte wave generation and detection using interdigital capacitive micromachined ultrasonic transducers

Abstract: Directional generation and detection of Scholte waves and other guided modes in liquids and microfluidic channels by capacitive micromachined ultrasonic transducers (cMUTs) is reported An interdigital transducer structure along with a phased-excitation scheme is used to enhance the directionality of Scholte interface waves in microfluidic environments Finite element models are developed to predict the performance of the devices in both fluid half-spaces and microchannels Experiments on the interdigital cMUTs show that a five-finger-pair device in a water half-space has 12 dB of directionality in generating Scholte waves at the design frequency of 10 MHz A 10-finger device operating at 10 MHz in a water-filled microchannel has 134 dB of directionality These directionality figures agree well with the modeling results Using the results of the finite element model of a cMUT in a fluid half-space, it was determined that 41% of the acoustic power radiated into the fluid is contained in the Scholte wave propagating in the desired lateral direction Transducers are demonstrated to perform bidirectional pumping in fluid channels with input power levels in the milliwatt range Interdigital cMUTs fabricated using low temperature processes can be used as compact ultrasonic transducers with integrated electronics for sensing and actuation in fluidic environments

Guided modes in a plane elastic layer with gradually continuous acoustic properties

Abstract: A theoretical study of wave propagation through an inhomogeneous plane infinite elastic layer of constant density whose velocities vary continuously with the depth is presented. If the shear speed gradient effects are to be modelled, then the simple Helmholtz representation of the displacement field cannot be used; however, for high frequencies, the longitudinal and transversal wave equations are decoupled. The study is conducted for two symmetrical velocity profiles for which the wave equations have exact solutions. The effect of the relative amplitude of gradients on the position of cutoff-frequencies of guided modes existing in the structure is examined. The numerical results show a shift of cutoff-frequencies compared to those of the homogeneous layer.

Inspection of rail track head surfaces using electromagnetic acoustic transducers (EMATs)

Abstract: A 'pitch-catch' low-frequency wideband Rayleigh wave EMAT system has been developed that has been used for gauge corner cracking defect detection on the head of samples of rail track. Strictly speaking, the generated waves are a type of guided wave mode as the propagation surface is not a flat halfspace, and these waves propagate along the surface of the rail penetrating down to a depth of several millimetres. Crack depth can be estimated by measuring the relative amount of the Rayleigh wave at a particular frequency that passes underneath the crack. The EMAT system also has the potential to assess the condition of the combined microstructure and stress state around the rail head by measuring accurately the velocity of the surface waves.

Multiple-source arrays fed by guided-wave structures and resonant guided-wave structure cavities

Abstract: A multiple source array including a guided-wave structure having a dielectric core and a cladding covering the dielectric core; and an array of dielectric-filled, guided-wave cavities in the cladding extending transversely from the dielectric core and forming an array of apertures through which optical energy that is introduced into the core exits from the core.

Properties of Guided Waves in Composite Plates, and Implications for NDE

Abstract: Guided waves are potentially very useful for the rapid NDE of plate structures. In the aerospace industry in particular, they have been proposed for the structural health monitoring of carbon fibre skin panels, in either an active or a passive configuration. In an active configuration a guided wave is deliberately generated and then later received after it has travelled through the structure; in a passive configuration an acoustic emission sensor is used to listen to sound created by the structure itself. The successful development of these ideas depends on a good knowledge of the properties of the guided waves, yet it has been found that the properties of guided waves in such materials are very much more complicated than those in a simple metal skin. The complications include steering of the direction of the group velocity by the anisotropy of the plate, and attenuation because of damping of the matrix material and scattering by the fibres. The authors have studied these phenomena both analytically and experimentally. This paper presents an overview of the findings and identifies the key implications for practical developments of structural health monitoring techniques.

Calculation for guided waves in pipes and rails

Abstract: This paper describes a calculation technique with a semi-analytical finite element method for guided waves and its application to simulation and modal analysis of wave propagation in a pipe and a bar with an arbitrary cross-section as rail. Dispersion curves and wave structures for any kinds of bar like structures can be calculated by the SAFEM. This study examines dispersion curves for a square bar and a rail. Also, visualization results of guided wave propagation are shown for a straight pipe, a pipe with an elbow, and a pipe with a spherical defect. Introduction Ultrasonic guided waves are a type of wave propagation in which the wave is guided in plates, rods, pipe or elongated structures such as rails and I beams. Recently, long-range inspection of pipes by the use of guided waves has attracted considerable attention because this technique largely reduces inspection time and costs compared to the ordinary point-by-point testing in large pipeworks [1]-[3]. Especially in Japan, since a large number of pipeworks constructed 30 years ago in highly economic era are aging and require maintenance work or replacements, the inspection technique for large structures has become a very urgent subject. Commercial equipments with guided waves are installed at one location of a pipe and reflection echoes analyzed indicating the presence of corrosion or other defects. In guided wave inspection of a pipe with elbows and defects or a bar with an arbitrary cross-section, however, guided waves propagate with very complicated wave structures due to a mixture of multi-modes and mode conversions, which prevents guided waves from being widely used. Modal analysis and simulation of guided wave propagation with computations are very useful for solving lots of problems due to the complexity of guided wave. The authors have carried out guided wave calculations with a semi-analytical finite element method (SAFEM)[4]-[6]. Since the SAFEM does not require divisions in the longitudinal direction, long-range calculations can be done with no problems of calculation time and memory. Modal analysis is also possible, because guided wave propagation is calculated as a summation of resonance modes in the SAFEM. This paper describes several applications of the SAFEM applied to guided wave simulation and analysis. After brief description about the SAFEM, calculation results on guided waves in a pipe and a bar with an arbitrary cross-section are presented. Dispersion curves and wave structures for a square bar and a rail are discussed, and simulation results of wave propagation in a pipe with an elbow and a defect are visualized. The semi-analytical finite element method for guided wave propagation Guided waves have a potential of long-range inspection in the meter or hundred-meter order, which is significantly larger than an ultrasonic wavelength. Using ordinary finite element or boundary element methods, therefore, extremely large calculation times and memory are required for calculations of guided wave propagation in a pipe and a rail. Since a semi-analytical finite element method (SAFEM) Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 410-415 doi:10.4028/www.scientific.net/KEM.270-273.410 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-13/03/20,17:37:45) Title of Publication (to be inserted by the publisher) does not require discretization in the propagation direction of the guided waves, it is very useful for long-range guided wave calculations. The cross-sections of a pipe and a bar are discretized into small sections as shown in Fig.1. Instead of dividing the region in the longitudinal direction as in ordinary FEM, the orthogonal function exp(iξz) is used for expressing the distribution of the displacement field in the longitudinal direction. Similarly to ordinary FEM, the virtual work principle or minimization of potential energy in the entire volume of an object rewrites the governing equations into an integration form. Discretizing the integration form then gives an eigensystem with respect to the wave number ξ for a certain frequency. Eigenvalues and eigenvectors obtained from the eigensystem correspond to wave numbers and wave structures for resonance guided wave modes in the bar-like object. For given boundary conditions, displacement fields can be obtained as a summation of guided wave modes. Wave propagation can be simulated by collecting these displacement data for all frequency steps in the frequency bandwidth. 12x12 elements exp(iξz) e le m e n t r z

Estimating the diameter/thickness of a pipe using the primary wave velocity of a hollow cylindrical guided wave

Abstract: A method for measuring the diameter/thickness (d∕t) of a pipe using a characteristic of a hollow cylindrical guided wave (HCGW) is presented. The HCGW is an ultrasonic guided wave propagating along a pipe. In the first part of this letter, we briefly show that the primary wave (first-arriving wave packet from an impulse source) of the HCGW achieves a faster group velocity for a larger d∕t. Experimental verifications were carried out for aluminum pipes (several different d∕t’s) using a laser ultrasonic method to generate the HCGW. The experimental results are in fairly good agreement with the theoretical prediction described.

Sensitivity to termination morphology of light coupling in photonic-crystal waveguides

Abstract: We use a transfer-matrix method to investigate light coupling problem in single-end photonic-crystal (PC) waveguides. We find that the coupling efficiency is sensitive to the surface termination morphology of the waveguide. A slightly tapering geometry can lead to an order of magnitude difference in the coupling efficiency of an external extended wave into the waveguide. However, this tapering geometry does not necessarily lead to enhanced coupling of a guided wave out of the PC waveguide. We have attributed this strong asymmetric coupling characteristic to the significant difference in the scattering behavior of an extended wave and a localized wave by the complex surface microstructure of a PC waveguide.