Ali Foudazi

Application of Active Microwave Thermography to delamination detection

Health monitoring of infrastructure is very important in the transportation and infrastructure industries. Many nondestructive testing (NDT) techniques have been applied for structural health monitoring including microwave NDT, ultrasound, thermography, etc. Due to the complex materials (composites, concrete, etc.) commonly used, it may be difficult to thoroughly inspect a structure using one method alone. Thus, hybrid NDT methods have also been developed. Recently, the integration of microwave NDT and thermography, herein referred to as Active Microwave Thermography (AMT), has also been considered as a potential structural health monitoring tool. This hybrid method uses microwave energy to heat a structure of interest, and then the thermal surface profile is measured using a thermal camera. This paper investigates the potential of AMT to inspect rehabilitated cement-based structures. Preliminary simulations and measurements provided herein indicate that AMT has the potential to detect delaminations under carbon fiber patches bonded to concrete.

Characterization of Corroded Reinforced Steel Bars by Active Microwave Thermography

Detection and characterization of corrosion on steel is important in the transportation and infrastructure industries. Many nondestructive testing (NDT) methods have been applied to this inspection need. To overcome the existing limitations of traditional NDT methods, integrated NDT techniques have also been developed. To this end, the integration of microwave and thermography, referred to as active microwave thermography (AMT), is proposed as a potential NDT tool for detection and characterization of corrosion on steel bars. This method utilizes microwave energy to provide heat excitation. Subsequently, a thermal camera is used to monitor the thermal surface profile. This paper presents preliminary simulations and measurements of AMT as a potential method for corrosion detection and characterization.

Application of active microwave thermography to inspection of carbon fiber reinforced composites

Inspection of carbon fiber reinforced polymer (CFRP) composites is very important in the aeronautical and transportation industries. Many nondestructive testing (NDT) techniques have been applied for health monitoring including ultrasound, thermography, etc. Although thermography has been widely used for this purpose, it often requires powerful heat lamps which may increase the risk of (thermal) damage to the structure under test. Thus, hybrid NDT methods have also been developed. Recently, the integration of microwave heating and thermography, herein referred to as Active Microwave Thermography (AMT), has also been considered as a potential health monitoring tool for infrastructure. This hybrid method uses microwave energy to heat a structure of interest, and subsequently the thermal surface profile is measured using a thermal camera. This paper investigates the potential of AMT for inspection of CFRP-rehabilitated airframes. Preliminary simulations and measurements indicate that AMT has the potential to detect disbonds under carbon fiber patches bonded to aluminum.

Active Microwave Thermography for Defect Detection of CFRP-Strengthened Cement-Based Materials

Nondestructive testing (NDT) of rehabilitated cement-based materials (RCMs) with carbon-fiber-reinforced polymer (CFRP) composites is quite important in the transportation and infrastructure industries. Among various NDT methods, active microwave thermography (AMT) has shown good potential. This method uses microwave energy to heat a structure of interest, and subsequently the surface thermal profile is measured using a thermal camera. In this paper, the application of AMT for defect detection (unbond, delamination, and crack) in CFRP composites used in RCMs is presented. More specifically, the effect of defect size and depth and polarization on the resultant surface thermal profile with defects is first studied through simulation. The effect of polarization on detection of defects with regard to the orientation of CFRP fibers is also experimentally investigated. Finally, a quantitative analysis of the measured results based on the thermal contrast and signal-to-noise ratio (SNR) for all the three aforementioned defect types is presented. The results show that the SNR is improved when utilizing perpendicular (compared with parallel) polarization, and that the maximum effective heating time is ~60 s, even for small defects.

Effect of Sample Preparation on Microwave Material Characterization by Loaded Waveguide Technique

Microwave material characterization is an important nondestructive evaluation tool, as many physical and chemical properties can be related to a materials dielectric properties. These properties can be measured using a number of methods including the loaded waveguide technique. This method requires that a sample be placed in a waveguide sample holder and subsequently utilizes measured complex reflection (S11) and transmission (S21) properties to calculate the samples dielectric properties. As such, it is important that the sample be prepared carefully, as the dielectric property calculation assumes a perfect (ideal) sample geometry. However, in practice, samples are oftentimes prepared by hand, resulting in a distorted sample geometry. This paper presents a simulation and measurement study on a number of potential sample preparation errors and the effect of these errors on calculated dielectric properties. Finally, a statistical analysis (including mean, standard deviation, coefficient of variation, and confidence interval) was applied to provide a method by which calculated dielectric properties (even when imperfect samples are used) can be checked to ensure that proper accuracy of the results has been achieved.

Mutual coupling in aperture-coupled patch antennas fed by orthogonal SIW line

In this paper, the mutual coupling of a rectangular microstrip patch antenna with an aperture-coupled feed by an orthogonal substrate integrated waveguide (SIW) feed line is presented. This feed design is beneficial for 2D array configurations in millimeter wave imaging systems due to the limited availability of space for such arrays. From the results, the proposed (compact size) antenna provides 7% bandwidth (|S11| <; -10 dB), 65% total efficiency and 5 dB gain at 30 GHz. The mutual coupling of two antenna configurations (two antennas located collinearly with respect to their length and width) with center-to-center spacing of 0.4λ-1.5λ are studied. The results show that there is less mutual coupling when the antennas are located collinear with respect to their width (due to the polarization from feed network). In addition, -17 dB mutual coupling for antennas with spacing of 0.5λ is shown for both cases.

Design of a microstrip patch antenna for microwave sensing of petroleum production lines

In this paper, the design of a microstrip patch antenna for microwave sensing of sand production in petroleum pipelines is presented. Two antennas are designed in order to cover the entire sensing regime (gas to liquid including large percentages of brine) common to petroleum production lines. The antennas are designed to operate at ∼5GHz. The antenna intended for sensing with low-loss fluids (gas or oil) is capable of ∼4% bandwidth (|S11|<−10 dB), and the antenna intended for sensing with high loss fluids (brine) is capable of ∼7% bandwidth.

Polarization-insensitive Ku-band Frequency Selective Surface (FSS)

A wideband, low profile frequency selective surface (FSS) is presented for Ku-band (12.4 – 18 GHz). The proposed design is fabricated on two substrates with a total thickness of <λ/10. The complimentary unit cell shape results in a miniaturized FSS design as well as wideband performance. The designed FSS is polarization-independent due to the unit cell symmetry. The simulated results of the proposed unit cell show the flexibility for selecting the desired bandwidth by changing the relevant parameters easily.

Mutual coupling reduction in orthogonally fed aperture-coupled patch antennas via an integrated metasurface

An aperture-coupled rectangular microstrip patch antenna fed by an orthogonal substrate integrated waveguide (SIW) feed line is of high interest for one-sided imaging systems. This type of feeding technique is beneficial for 2D imaging array configurations in millimeter wave imaging systems due to the limited availability of space for compact array design. In order to reduce the coupling between two adjacent patches (which deteriorates the quality of the imaging results), an artificial impedance metasurface can be used. When properly designed for this purpose, the imaging frequency corresponds to the bandgap frequency of the metasurface. In this paper, a metasurface integrated with this new type of feeding technique is presented. The improved structure shows a 20 dB reduction in coupling (|S21|) between two adjacent antennas separated by a spacing of one wavelength at an imaging frequency of 30 GHz.

Microwave characterization of fly ash geopolymerization

Alkali-activated fly ash geopolymers are structural materials that can be used as a sustainable alternative to ordinary portland cement concrete in infrastructure applications. However, the widespread use of geopolymers by the construction industry has been limited in part by a lack of understanding about the fundamental reaction mechanisms that occur during their formation. Since microwave signals are very sensitive to the presence and binding state of water, microwave materials characterization is used to investigate the role of water in two fly ash geopolymers during reaction at early ages. The results indicate that this measurement technique has a promising potential for assessment of changes in geopolymer material properties during their formation. This will allow for better prediction and control of the setting behavior and mechanical and durability properties of geopolymers.