Microwave imaging of defects in graphite reinforced composite materials

ND T Abstracts 51866 Wynn, C.C.; Fletcher, W.M.; Jones, W.D. Nondestructive evaluation of hollow d a y tile walls Oak Ridge Y- 12 Plant, Tennessee (United States), DE92013937/GAR, 12pp. (Mar. 1992) Experiments have been conducted using sonics, ultrasonics, infrared thermography, and microwave NDE techniques on hollow clay file masonry construction at the Department of Energy Oak Ridge Y-12 Plant in Oak Ridge, Tennessee. The experiments are part of a major test program to evaluate the seismic and wind load capacity of existing hollow clay tile infilled steel frame buildings at the Y-12 Plant and to recommend the extent of retrofit required to ensure these structures will meet the current requirements for natural I~,~ds survival.

d'Ambrosio, G.; Massa, R.; Migliore, M.D.; Ciliberto,A.; Sabatino, C. 51862

Microwave defect detection on low-loss composites Materials Evaluation, Vol. 51, No. 2, pp. 285-289 (Feb. 1993) The reflectioncoefficientof fiberglass/Kevlarslabs,includinga layerof a different material, was calculated as a function of permittivities, thicknesses, defect depth, and microwave frequency. Expefimenlni tests were done both with a single-frequency amplitude-and phase-sensitive circuit and with a swept-frequency amplitude-only- sensitive setup. In this latter case, a suitable processing of data allowed effective and fast defect detection. 51827 Forde, M.C.; McCavitt, N.; Batchelor, A.l. Evaluating structures using impulse r a d a r and sonic techniques Decommissioning and Demolition 1992, Manchester (United Kingdom), 25-26 Mar. 1992. pp. 118-122. Edited by I.L. Whyte, Thomas Telford Ltd. (1992) This paper outlines new and sophisticated impulse digital nondestructive testing techniques.The techniques used include impulse digital time domain testing, impulse digital frequency domain testing and digital impulse radar testing. The techniques are described in relation to applications to concrete bridges. It is shown that the techniques of impulse sonic and radar testing are complementary in nature and can be used cost effectively to identify the geome~es of structures in addition prior to decommissioning.

Sekine. L; Yuasa. M.; Hotta, A.; Noro, M.; Yoshida, T.; Uematsu, K.

51595

Nondestructive microwave exploratory corrosion tests of e m b e d d e d steels Corrosion Engineering, Vol. 41, No. 5, pp. 353-365 (1992) Nondestructive exploratory corrosion tests on steel embedded in water, rubber, cement, or soil were carried out using microwave radar measurement, while the possibility of such tests was investigated by simulation (theoretical analysis). The time to the first reflection wave peak (t) of corroded steel was delayed with reference to that of an-corroded steel. Experimental t data and delay times (At) corresponded to those obtained by simulation. It is thought that from the embedding conditions of steels such as 1) ~ 2) tan 5; 3) thickness of the embedding medium; 4) e; 5) tan 8 of corrosion layers,, and the relationship between At and corrosion:layer thickness, the degree of corrosion of embedded steels can be predicted by At

measurements. 51591 Wang, J.$.;Ida, N. Simulation of nondestructive testing of materials in microwave cavities Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States),28 Jul.-2 Aug. 1991), Vol. IIB, pp. 1869-1875. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) A materialmay be characterizedby itsintrinsicresonantfrequenciesand Q-factorsin an elecuomagneticcavity.A numericalmodel was shown to be quitepromisingfor the characterizutionof materialsin a microwave cavity. But the model re~inireda relativelylarge mesh size if cavity walls and material interfaces are curved, since the model used quasi-lineur tetrabedral elements. In this work, the model is improved by using curvilinear bexahedral elements, allowing accurate prediction of lower modes with a relatively small mesh size. The new model is used for simulation of more realistic testing situations. These situations include incorporating cavity wall losses, characterizing anisou'opic materials (such as composites), and comparing solutions with available results. 51587 Ida, N. M i c r o w a v e NDT Kluwer, 394pp. (1992) This volume describes a unified approach to microwave nondestructive

testing by presenting the three essential components of testing: theory, practice, and modelling. The text is divided into four parts. The first part presents the field theory background necessary for understanding the microwave domain. The second part treats microwave measurements as well as devices and sources. The third part discusses practical tests applicable to a variety of materials and geometries. The fourth part discusses modelling of microwave testing. Each chapter contains a bibliography. 51357 Kratochvil, G.; Fenner, T.; Benson, R. SIR technology helps ensure safe landings for NASA Materials Evaluation, Vol. 50, No. 12, pp. 1412-1414 (Dec. 1992) When a U.S. space shuttle lands, most often it touches down on an unpaved runway at Edwards Air Force Base in California's Mojave Desert. Its 190,000 pounds (86,184 kg) hit the natural lake-bed runway at 185 knots, placing tremendous stresses on the soil of the desert floor. Three times-once during a landing and twice as the shuttle was being towed from the lakebed landing strip to the edge of the lakebed-the wheels broke through the crust of the desert floor. To prevent danger to shuttle crews and damage to the spacecraft, NASA's shuttle program office instituted re~mlar, programmed inspections of the landing strips in 1988. These investigations, managed by the Geologic Science Advisor, began as visual checks but now use a subsurface interlace radar (SIR) system designed and manufactured by Geophysical Survey Systems, Inc., to ensure that the lake-bed runways will be free of unseen fissures and voids. 51352 Adams, MJ ~. Synthetic a p e r t u r e techniques for diffraction tomographic imaging with microwaves and ultrasonics Ph.D. Thesis, University of Sheffield (UK), Department of Electronic and Electrical Engineering, 316pp. (Aug. 1982) Tomography, a technique which allows the determination of the internal structure of an object and its display as cross sectional slices, is well established for the cases where the wavelength of the interrogating radiation is so small that geometric optics applies. Whea the wavelength of the radiation is relatively long and comparable to the object structure the effects of diffraction must be considered. These effects are examined in terms of plane-wave expansions of the measured field distributions and the concept of inverse diffraction or focusing is introduced. The effects of experimental limitations (finite recording aperture and sampling interval) are considered. The effects of the characteristics of the object on the radiation (both acoustic and elec~mngnetic) are considered and it is shown that, with the Born approximation for weakly scattering objects, the object may be reduced to a region of point scatterers re-radiating in a homogeneous medium. Experimental results in the microwave regime with both scattering and dielectric targets, and in the ulwasonic regime with 'tissue-like' phantoms are presented to illustrate aspects of the theory. 51350 Bakhtiari, S.; Ganchev, S.; Zoughi, R. A novel technique for microwave thickness measurement of dielectric slabs using an open-ended rectangular waveguide Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2 Aug. 1991. Vol. 11A, pp. 529-535. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) Information exlracted in terms of reflection coefficient and phase is commonly used in microwave nondestructive testing of materials. Here, a thickness measurement technique using an open-ended rectangular waveguide place on top of the dielectric slab backed by a conducting plate is presented. Although the theoretical derivation deals with admittance of the guide, results can be uasfly transformed to the desired reflection coefficient information. The admittance expression is then used in two root finding codes in an iterative manner to extract information about the thickness and permittivity of the material. Some preliminary measurement results are provided to verify the validity of the theoretical analysis. 51349 Flam, R.P~;Deats, B.W. Microwave imaging of defects in graphite reinforced composite materials Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2 Aug. 1991. Vol. 11A, pp. 537-544. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) In an effort to develop and evaluate new non-destructive evaluation (NDE) techniques for resin-matrix composites, we have investigated the feasibility of utilizing electromagnetic imaging for materials evaluation and have demonstrated the ability of existing electromagnetic imaging techniques to detect and locate flaws within carbon-epoxy samples. This paper presents the technical issues associated with using electromagnetic imaging for NDE measurements. These include the selection of test

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ND T Abstracts frequencies, sample orientation, signal processing techniques, and the impact of material properties on the measurement results. Measured results are presented for carbon- epoxy material samples.

Brandass, M.; Langenberg, K.I. Polarimetric microwave inverse scattering as applied to nondestructive testing 51345

Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2 Aug. 1991. Vol. I IA, pp. 741-748. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) In this paper we want to develop a unified theory for the electromagnetic inverse scattering problem relying on the weak scattering (Born) approximation with full use of polarization information. This theory based on the scalar formulation of the multidimensional linearizad scattering problem and essentially treats the electromaguetie inverse scattering problem within the physical optics (Kirehhoff) approximation. 50878

Konev, V.A.; Lubetsky, N.V.; Mikhnev, V.A.; Tikhanovich,

S.A. N o n d e s t r u c t i v e testing of dielectric materials in industry using m i l l i m e t e r radiowaves Non-Destructive Testing 92. Proceedings of the 13th World Conference on Non-Destructive Testing, Sao Paulo (Brazil), 18-23 Oct. 1992, Vol. 1, pp. 567-571. Edited by C. Hallal and P. Kulcsar. Elsevier (1992) In this investigation, some new possibilities of using the dielectric waveguide and beam guide sensors to measure dielectric permirdvity and/or thickness of the slabs and coatings have been demonstrated. Both parameters are obtained independently by using the frequency responses of the dielectric waveguide and of the horn antenna. Another approach based on measuring the broad-hand dielectric waveguide output for orthogonally polarized guided modes is shown to be useful to evaluate both the tangential and the normal components of the slab permittivity. In the field of millimeter wave ellipsometry, a minimal azimuth of transmitted wave in the frequency band of operation is shown to be determined by the slab permittivityand does not depend on itsthickness.The agreement between theory and experiment is shown to be quite good.

package, compatible with existing software, that will cancel the internal antenna reflections and the surface reflections from the total reflected signal; be capable of testing the correlation technique of matched filtering for impulse detection: identify variations in the amplitude and location of waveform peaks (employing cluster analysis or statistical variation of waveforms) and use this information to further improve the detection of deterioration, evaluate end result specifications, detect deterioration under pavements and assess the precision and accuracy of the system

Temple, J.A.G. Modelling radar inspections of concrete

49360

AEA industrial Technology, Harweil, AEA-lntec-0900, 15pp. (Mar. 1992) Previous experience with ultrasonic inspections has shown that simple models for predicting the signals observed from, possibly complex, defects can he of use in interpreting inspection data. It is our belief that a similar approach will be as useful in developing our radar inspection capability for civil engineering uses. This report gives the details of the basic simple model which is seen as a building block towards a model capable of modelling more complex cases. The model is of propagation through and reflection from plane, parallel, layers of materials with different electromagnetic properties. The plane wave solution is valid for any angle of incidence and for the incident electric field polarised either perpendicular or parallel to the plane of incidence. From this solution, results for more complicated cases can he constructed by the principle of superposition. Comparison with textbook formulae for the reflection at single planar interfaces demonstrates that the model behaves as expected. An example of how the simple model can be used in more realistic cases is given for a single cycle of 1GHz sine-wave incident form air onto concrete backed with a copper sheet. Future developments are hinted at.

Bakhtiari, S.; Zoughi, R. Microwave thickness m e a s u r e m e n t of Iossy layered dielectric slabs using incoherent reflectivity 49118

50114 Akhmetshin, A.M.; Matveev, V.I. S u p e r h i g h f r e q u e n c y introscopy of the parameters of layered s t r u c t u r e s on the basis of the frequency dependence of the

Research in Nondestructive Evaluation, Vol. 2, No. 3, pp. 157-168 (1990). Radiative transfer theory is used to calculate the incoherent effective reflectivity for a mulfilayer Iossy dielectric medium backed by a conducting plate. The theoretical results of this formulation are compared with that of the coherent approach. Several test cases are presented to show the characteristics of incoherent effective reflectivity as a function of thickness, and dielectric constant of the dielectric layers, and frequency. The results can ultimately be used in nondestructive dielectric thickness measurement.

modulus of the reflection coefficient in the presence of a priori information on the distribution of layers

49117

Soviet Journal of Nondestructive Testing, Vol. 27, No. 11, pp. 834-841 (Jul. 1992) Investigations were carried out into the possibilities of determining the dielectric permittivity and geometrical thickness of layered- materials with tan sigma < 0.01 in wide-band superhigh frequency inspection under the conditions with undermined thickness of layers of the structure followed by synthesis of its pulsed characteristics on the basis of utilization of a priori information on the distribution of the layers. Possible sources of errors are analyzed. The results are presented of numerical modeling and experimental verification in an example of a two-layer dielectric structure. 49377 Cribbs, R.W. M i c r o w a v e imaging for NDE of non-conductive composites NDE - The Vehicle to the Future, Orlando, Florida (United States), 30 Mar. - 3 Apr. 1992. pp. 145-147. ASNT (1992) Microwaves have been used for some time for the inspection of nonconductive materials and composites. Most of the installed systems systems operate at a single frequency. This paper deals with swept frequency systems. From the standpoint of the user, these systems behave like pulse-echo ultrasound; that is, the primary display is an A-h-ace. B-scans and synthetic aperture image reconstructionsare also available. The displays in this report were produced with a system operating in Ka-band (26-40 GHz) with a bandwidth of 14 GHz. This provides a wave length in typical dielectrics of 4 nun. Systems at triple this frequency and bandwidth can now be made that yield resolution comparable to 2.25 MHz ultrasound in metals. 49372 Chung, T.: Carter, C.R. R a d a r signal e n h a n c e m e n t for DART Ontario Ministry of Transportation, Toronto (Canada), Mic-9006108/GAR, 268 pp. (1989) Previous studies have shown that the Deck Assessment by Radar and Thermography (DART) system is capable of distinguishing between areas of good bridge deck and areas which suffer from one of several forms or deterioration. This project was undertaken to develop new software

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Zoughi, r.; Bakhtiari, S. Microwave nondestructive detection a n d e v a l u a t i o n of voids in layered dielectric slabs Research in Nondestructive Evaluation, Vol. 2, No. 4, pp. 195-205 (1990). A microwave nondestructive testing technique is discussed for detection and evaluation of voids in layered dielectric media backed by a conducting plate. This technique utilizes the phase properties of the effective reflection coefficient of the medium as a microwave signal penetrates inside the dielectric layers and is reflected by the conducting plate. Properties of the difference between this phase in the absence and presence of an air gap is investigated as a function of the void thickness, frequency, and dielectric properties of the layers. Utilizing a simple experimental apparatus measurements were also conducted, the results of which were compared with the theoretical predictions. 48857 Bramanti, M. A slot line microwave dielectric permittivity s e n s o r for m e a s u r e and control of laminated materials Journal of Microwave Power & Electromagnetic Energy, Vol. 26, No. 2, pp. 67-71 (1991) A dielectric permittivity sensor for microwave frequency range is proposed, based on a slot line resonator loaded by the material under test which appears particularly suited for characterization of laminated type dielectric materials. The experimentally measured sensitivity resulted about 160 MHz/unit ofe. Some results on the use of the sensor to detect air gaps inside dielectric materials are also reported.

Koh, G. Experimental study of electromagnetic wave propagation in dense random media

48854

Waves in Radon Media, Vol. 2, No. 1, pp. 3%48 (1992) Controlled experiments have been conducted to measure the propagation of synthetically generated pulses in dense random media. The dense media were prepared by embedding spherical dielectric scatterers in a