R. Zoughi

Missouri University of Science and Technology, Missouri, United States

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Publications (222)133.31 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Millimeter wave near-field nondestructive testing (NDT) and imaging techniques are well-suited for the inspection of exposed (bare) and coated metallic surfaces for detecting surface-breaking discontinuities such as cracks and corrosion under coatings. However, one drawback of near-field imaging is the long scan time due to the dense grid requirements at these high frequencies. This paper presents a novel imaging technique for NDT of metallic surface for detecting surface-breaking cracks. This technique incorporates wideband measurements, synthetic aperture radar (SAR) based imaging algorithms, and surface wave propagation. The proposed technique vastly reduces the required scan time to produce an image. This paper introduces the imaging technique and studies its efficacy using full-wave numerical electromagnetic simulations. Results of measurements at K-band (26.5-40 GHz) and V-band (50-75 GHz) are provided illustrating the feasibility of the proposed technique for rapid detection of metal surface discontinuities.
    2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC); 05/2014
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    ABSTRACT: Microwave materials characterization techniques based upon dielectric property measurements are well-suited for detection and evaluation of physical and chemical changes in cement-based materials. In this investigation, microwave dielectric properties of several mortar samples were measured at S-band (2.6-3.95 GHz) and X-band (8.2-12.4 GHz) at two different times nearly one year apart. It was found that during this period, while the samples remained in ambient environment conditions, their masses remained essentially constant over time. However their dielectric properties underwent a relatively substantial change. To investigate the reason(s) behind this phenomenon, both pH indicator test and thermogravimetric analysis were conducted and the results confirmed carbonation in the samples. In this paper, the results of these investigations are presented. Additionally, a first-order dielectric mixing model capable of carbonation depth estimation is described.
    2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC); 05/2014
  • M. Fallahpour, R. Zoughi
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    ABSTRACT: Previously, a Wiener filter-based synthetic aperture radar (SAR) technique was developed to successfully image embedded objects in a general layered structure. The results of the imaging technique were then verified through performing extensive measurements. Here, the sensitivity of this technique to different critical parameters is investigated using a full-wave electromagnetic simulation software. These parameters include those related to the sample being imaged (e.g., electrical properties of layers), those related to measurements (e.g., electromagnetic wave polarization), and those associated with the modeling process (e.g., electrical properties of layers used in the image reconstruction procedure).
    2014 IEEE International Instrumentation and Measurement Technology Conference (I2MTC); 05/2014
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    ABSTRACT: The presence of reactive aggregates combined with sufficient moisture and concentration of alkalis are the three basic requirements for damage due alkali-silica reaction (ASR) gel formation and expansion in concrete. For health-monitoring of concrete structures, and in order to investigate the potential for detecting ASR gel formation in existing structures, one potential technique involves studying changes in the temporal complex dielectric constant of concrete structures. In this paper, a microwave nondestructive testing approach is proposed which involves soaking two hardened mortar samples and measuring the change in their temporal complex dielectric constant in order to distinguish between the sample containing ASR gel and the one devoid of it. Part of the free water becomes bound in the sample containing ASR gel and since a portion of the microcracks in this sample contain ASR gel, the rate of evaporation of water of the two samples is expected to be different. The complex dielectric constant of the samples is significantly dependent upon the volumetric level and movement (in and out of the samples) of free water. Therefore, studying the relative different temporal rate of change in this parameter is expected to yield information about the presence or absence of ASR gel.
    01/2014; 1581(1).
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    ABSTRACT: Robust detection of vertical cracks in high-density polyethylene (HDPE) pipes is a challenging task for the majority of nondestructive testing (NDT) techniques. Vertical cracks are specifically referred to those whose largest planar view is parallel to the signal direction of propagation, leaving very little signal to be scattered for detection. In such pipes this commonly occurs between two pipes sections when thermally or adhesively joined. This work presents the utility and efficacy of three-dimensional (3D) millimeter wave holographical imaging based on synthetic aperture radar (SAR) algorithm for imaging such cracks. Such a 3D millimeter wave image can readily represent the type, size, and location of various flaws within a structure. Two-dimensional (2D) slices of the 3D image, at different orientations, can also be readily produced showing the cross-sectional views of the structure and flaws, further aiding in identifying, and sizing a flaw or vertical crack. Imaging results for planner and curved (pipe section) specimen with machined flaws are presented. These images are produced using a novel field-portable, small, and low-cost wideband millimeter-wave reflectometer capable of rapid 3D image production.
    01/2014; 1581(1).
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    ABSTRACT: In this paper we evaluate the utility of microwave and mechanical wave nondestructive testing techniques to detect delamination in reinforced concrete bridge deck mock-up samples. The mechanical wave tests comprise air-coupled impact-echo measurements, while the microwave measurements comprise three-dimensional synthetic aperture radar imaging using wideband reflectometery in the frequency range of 1-4 GHz. The results of these investigations are presented in terms of images that are generated from these data. Based on a comparison of the results, we show that the two methods are complementary, in that provide distinct capabilities for defect detection. More specifically, the former approach is unable to detect depth of a delaminated region, while the latter may provide this information. Therefore, the two methods may be used in a complementary fashion (i.e., data fusion) to give more comprehensive information about the 3D location of delamination.
    01/2014; 1581(1).
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    ABSTRACT: In this paper, two new techniques for microwave imaging of layered structures are introduced. These techniques were developed to address the limiting issues associated with classical synthetic aperture radar (SAR) imaging techniques in generating focused and properly-positioned images of embedded objects in generally layered dielectric structures. The first method, referred to as piecewise SAR (PW-SAR), is a natural extension of the classical SAR technique, and considers physical and electrical properties of each individual layer and the discontinuity among them. Although this method works well with low loss dielectric media, its applicability to lossy media is limited. This is due to the fact that this method does not consider signal attenuation. Moreover, multiple reflections within each layer are not incorporated. To improve imaging performance in which these important phenomena are included, a second method was developed that utilizes the Green's function of the layered structure and casts the imaging approach into a deconvolution procedure. Subsequently, a Wiener filter-based deconvolution technique is used to solve the problem. The technique is referred to as Wiener filter-based layered SAR (WL-SAR). The performance and efficacy of these SAR based imaging techniques are demonstrated using simulations and corresponding measurements of several different layered media.
    IEEE Transactions on Antennas and Propagation 01/2014; 62(1):282-294. · 2.33 Impact Factor
  • J.T. Case, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Recent technological advancements have made it possible to produce synthetic aperture radar (SAR) based microwave images in real time by using a variety of microwave imaging (array) systems. However, depending on the imaging array construction and the data collection scheme, the pertinent data of interest may be corrupted by undesired signals resulting from array element mutual coupling and overall poor isolation. Poor isolation associated with array elements may result from imperfect RF switching, internal coupling mechanisms inherent in a measurement system, or imperfect signal tagging schemes (i.e., multiple elements modulating when using the modulated scatterer technique). Images produced from such corrupted data are blurred or have artifacts that tend to mask the desired indications. This paper demonstrates the extension of a well-known correlation canceling technique for the purpose of preprocessing the data to remove such undesired coupling effects. To demonstrate its effectiveness, it is applied to a recently developed 2-D high-resolution and real-time microwave imaging system (camera). This camera is composed of 576 array elements, which are susceptible to the type of signal degradation mentioned above. Three correction estimates of the preprocessor are performed and compared. Two of the correction estimates directly address coupling, and the third, which does not consider coupling, is used for comparison purposes. Simulation results show the efficacy of this method, which is then corroborated by experiments.
    IEEE Transactions on Instrumentation and Measurement 01/2014; 63(5):1310-1319. · 1.71 Impact Factor
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    ABSTRACT: Nondestructive evaluation of stratified (layered) composite structures at microwave and millimeter-wave frequencies is of great interest in many applications where simultaneous determination of the complex dielectric properties and thicknesses of multiple layers is desired. Open-ended rectangular waveguide probes, radiating into such structures, are effective tools for this purpose. The technique utilizes a full-wave electromagnetic model that accurately models the complex reflection coefficient as a function of frequency and material properties. While the electromagnetic model assumes an infinite waveguide flange (or ground plane), the measurements are conducted using a finite-sized flange. Consequently, the results of the electromagnetic model and those from measurements may not be sufficiently alike for accurate dielectric property and thickness evaluation. This paper investigates the effect of using an open-ended waveguide with a standard finite-sized flange on the error in evaluating the complex dielectric properties of a composite structure. Additionally, we present the design of a novel flange that markedly reduces this undesired effect by producing very similar electric field properties, at the flange aperture, to those created by an infinite flange. Finally, the efficacy of the design for evaluating the dielectric properties of a layered composite structure is demonstrated as well.
    IEEE Transactions on Instrumentation and Measurement 01/2014; 63(6):1524-1534. · 1.71 Impact Factor
  • A. Kothari, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Wideband waveguide-based couplers have many utilities in microwave and particularly millimeter wave frequency ranges. This paper presents the design for a versatile full waveguide band nondirectional coupler used in conjunction with noncoherent single-port reflectometers, and for other pertinent applications. The design offers several parameters that once simultaneously optimized can provide a constant coupling level throughout the desired frequency band. The design procedure and simulation results for a Ka-band (26.5–40 GHz) coupler are presented. Such a coupler was then designed and constructed to operate in X-band (8.2–12.4 GHz) and the measured and simulated coupling levels show good agreement.
    IEEE Transactions on Instrumentation and Measurement 01/2014; 63(4):984-986. · 1.71 Impact Factor
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    ABSTRACT: Detection of surface-breaking cracks in metals is an important issue in many industries (e.g., transportation, aerospace, nuclear). Commonly, eddy current and ultrasonic techniques are used for this purpose. In recent years, a significant amount of work has also been conducted using microwave methods. Consequently, to better understand the interaction between a microwave probe (i.e., open-ended rectangular waveguide or coax) and a crack, a number of electromagnetic models have been developed. For an open-ended coaxial probe, when a crack coincides with the center conductor region of the probe, all previously developed models significantly underestimate the results obtained from measurements. This paper examines the primary reason for this discrepancy, which turns out to be due to a geometrical perturbation in the probe center conductor geometry and its subsequent interaction with a crack.
    IEEE Transactions on Instrumentation and Measurement 01/2014; 63(7):1877-1879. · 1.71 Impact Factor
  • J.T. Case, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Recently, a real-time and portable 2-D microwave imaging system operating at 24 GHz, incorporating modulation schemes similar to modulated scatterer technique and synthetic aperture radar (SAR) imaging technique, was designed using a heterodyne receiver with superior performance compared with a homodyne receiver. Multifrequency SAR images have the added advantage of providing for: 1) coherent averaging of image data over frequency and hence increasing system signal-to-noise ratio (SNR) and 2) enable volumetric (3-D) image production. This letter describes modifications to this receiver for enabling multifrequency operation through phase uncertainty (PU) analysis. These modifications show significant reduction in PU, thereby allowing the coherent addition of data necessary for SAR image formation with higher overall SNR.
    IEEE Transactions on Instrumentation and Measurement 01/2014; 63(1):243-245. · 1.71 Impact Factor
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    ABSTRACT: In this communication, a new approach for feeding a PIN diode-loaded resonant elliptical slot used in microwave imaging arrays for nondestructive testing applications is considered. The proposed feed is based on coupling the transmitted and received signals into the slot using an out-of-plane (perpendicular) microstrip line. An imaging array prototype with this slot, a 90 °-bent microstrip-line feed and a coplanar waveguide (CPW) to microstrip line transition was designed and experimentally validated. The design readily accommodates placement of the switching and PIN diode biasing networks on the feeding plane using CPWs, enabling one-sided imaging measurements. The relevant design steps and imaging results obtained with this prototype, in mono-static and bi-static modes, are presented.
    IEEE Transactions on Antennas and Propagation 01/2013; 61(10):5311-5314. · 2.33 Impact Factor
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    ABSTRACT: High-resolution millimeter-wave imaging for nondestructive testing applications offers certain unique and practical advantages. Traditionally, imaging for this purpose is performed by raster scanning a single probe/antenna across a two-dimensional (2D) grid. Raster scanning requires bulky, slow and expensive scanning platforms, in addition to being a slow process. Utilizing an array of probes significantly reduces these limitations. This paper presents the design of a linear one-dimensional millimeter wave imaging array operating at 30 GHz and capable of rapid image production. The imaging array is 150 mm long, operates in quasi-mono-static reflection mode, and provides coherent vector reflection coefficient data for generating high spatial resolution synthetic aperture radar images. This imaging array performs fast electronic scan along one dimension and may be readily moved along the other direction to produce 2D images, greatly reducing the required scan time compared to raster scanning. The design and utility of this imaging array along with several imaging examples are presented in this paper.
    IEEE Transactions on Antennas and Propagation 01/2013; 61(9):4733-4740. · 2.33 Impact Factor
  • A. Kothari, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Sensitivity analysis is presented for wideband single-port vector reflectometers designed based on a noncoherent detection scheme. Simulations are performed to obtain the sensitivity of the systems to noise associated with the measured standing-wave voltage. The effect of insertion loss in phase-shifter, total phase shift and error in detector characterization on the accuracy of measuring the reflection coefficient of a device under test (DUT) is investigated. Results of this analysis are validated using measurements performed by custom-designed single-port reflectometer systems at X-band (8.2 - 12.4 GHz) and Ka-band (26.5 - 40 GHz).
    Instrumentation and Measurement Technology Conference (I2MTC), 2013 IEEE International; 01/2013
  • J.T. Case, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Wideband synthetic aperture radar (SAR) technique is a robust imaging tool for microwave and millimeter-wave imaging such as nondestructive evaluation applications. In this paper, we present an alternative method to conventional raster scanning involving manually selected and nonuniformly distributed measurement positions, enabling the production of complete SAR images-potentially using only a fraction of the conventionally required measured data. The user is kept informed throughout the scanning process by a stream of real-time SAR images. Finally, data reconstruction algorithms are used offline to produce high-quality images with considerably lower background noise and image artifacts as compared to the real-time images. We also introduce a novel reconstruction method that uses the components of the SAR algorithm to advantageously exploit the inherent spatial information contained in the data, resulting in a superior data reconstruction and final SAR image. This paper presents the measurement methodology along with the images obtained from three different specimens of increasing geometrical complexity.
    IEEE Transactions on Instrumentation and Measurement 01/2013; 62(5):1250-1258. · 1.71 Impact Factor
  • M.T. Ghasr, P. Puleo, R. Zoughi
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    ABSTRACT: Small, portable, and low-cost millimeter wave imaging systems are desired in many nondestructive testing and imaging applications, as these system are capable of producing high-resolution images of interior of composite structures. Typically, systems capable of producing holographic three-dimensional images incorporate expensive and bulky wideband heterodyne coherent reflectometers or vector network analyzers. This paper presents a novel wideband, small, and low-cost reflectometer capable of producing holographic three-dimensional millimeter wave images.
    Instrumentation and Measurement Technology Conference (I2MTC), 2013 IEEE International; 01/2013
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    ABSTRACT: Multi-modal data fusion techniques are commonly used to enhance decision-making processes. In previous research, a comprehensive structural analysis process was developed for quantizing and evaluating characteristics of defects in aircraft lap-joint mimics using eddy current (EC) nondestructive evaluation (NDE) data collected for structural health monitoring. In this research, a comprehensive multi-modal structural analysis process is presented that includes intra- and inter-modal NDE data fusion based on EC, millimeter wave (MW), and ultrasonic (UT) data obtained from five lap-joint mimic test panels. The process includes defect detection, defect characterization, and finite-element modeling-based simulated fatigue loading for structural analysis. The multi-modal structural analysis process is evaluated using four test panels with corroded patches at different layers of the lap joints and one painted pristine panel used as a reference. The test panels are subjected to two rounds of mechanical loading, preceded by multi-modal NDE data obtained before each round. Different NDE modality combinations are examined for test panel modeling, including: 1) EC, 2) UT, 3) MW, 4) EC and UT, 5) EC and MW, and 6) EC, UT, and MW. Experiments are performed to compare the simulated fatigue loading, based on models determined from the different modality combinations, and the mechanical loading results to find susceptible-to-failure areas in the test panels. Experimental results showed that the EC and UT modality combination yielded a correct vulnerable (crack) location recognition rate of 98.8%, an improvement of 14.7% over any individual modality, demonstrating the potential for multi-modal data fusion for characterizing corrosion and defects.
    IEEE Transactions on Instrumentation and Measurement 01/2013; 62(4):814-827. · 1.71 Impact Factor
  • J.T. Case, M.T. Ghasr, R. Zoughi
    [Show abstract] [Hide abstract]
    ABSTRACT: Recently, new technologies have made it possible to produce synthetic aperture radar (SAR) based microwave images in real-time by using different microwave imaging arrays. However, depending on the imaging array construction the data of interest may be corrupted by mutual coupling and poor isolation. SAR images created from this data have an increased level of artifacts. This paper presents a method for correcting or pre-processing the data by using correlation canceling technique and provides an analysis of three different estimates of the correction. Simulation results show the efficacy of this method, which is corroborated by experiment.
    Instrumentation and Measurement Technology Conference (I2MTC), 2013 IEEE International; 01/2013
  • M. Kempin, M.T. Ghasr, R. Zoughi
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    ABSTRACT: Open-ended waveguide material characterization is an effective nondestructive testing (NDT) technique for evaluating the dielectric constant and thickness of individual layers in a multilayered composite structure. A limitation of this technique is that the finite flange contributes to the estimation error, depending on the thickness and dielectric loss factor of the layers. Its effects are non-negligible in particular when measuring the dielectric constant of low-loss and thin materials. This paper studies the effect of using a common finite-flanged open-ended waveguide on the error in estimating the permittivity and loss-tangent of a dielectric sheet. This paper also presents a proposed modification to the flange geometry in order to markedly reduce this undesired effect.
    Instrumentation and Measurement Technology Conference (I2MTC), 2013 IEEE International; 01/2013

Publication Stats

1k Citations
133.31 Total Impact Points

Institutions

  • 2008–2014
    • Missouri University of Science and Technology
      • Department of Electrical Engineering
      Missouri, United States
  • 2010–2011
    • The University of Western Ontario
      London, Ontario, Canada
  • 2001–2008
    • University of Missouri
      • Department of Electrical and Computer Engineering
      Columbia, MO, United States
  • 2007
    • Università degli Studi di Genova
      Genova, Liguria, Italy
  • 2000–2001
    • Hewlett-Packard
      Palo Alto, California, United States
  • 1991–2001
    • Colorado State University
      • Electrical & Computer Engineering
      Fort Collins, CO, United States
  • 1997
    • American Society for Nondestructive Testing Inc.
      Syracuse, New York, United States