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Periodic assessment of ageing civil structures is important for structural integrity and public safety. Numerous destructive and non-destructive techniques employing different energy sources have been proposed for structural health monitoring. Amongst the non-destructive evaluation techniques proposed for monitoring material strength and contents of concrete structures, techniques employing microwaves offer distinct advantages in that they are non-radioactive and provide good penetration, excellent contrast between steel reinforcement bar and concrete, and insensitivity to ambient temperature. In this paper, the feasibility of a far-field microwave NDE technique for concrete imaging is investigated via numerical simulations and experiments on cement based samples using far-field microwave reflection coefficients.

Onsite real-time nondestructive evaluation of aircraft using eddy current techniques has gained significance in the past few years. In this paper, emphasis is placed on developing a flexible and a fast real-time inspection system using giant magnetoresistive (GMR) field sensors. Experimental signals are compared with finite-element model (FEM) model simulations and signals acquired using traditional data acquisition methods. Several advantages of the improved design are discussed

Short‐pulsed terahertz imaging techniques have found application in recent years especially in the areas of nondestructive evaluation, homeland security and biomedical imaging. One such application involves the inspection of bonding between spray on foam insulation (SOFI) and the external tank in the NASA space shuttle. This work discusses a suite of image enhancement techniques that was developed to improve the probability of detection of voids and disbands SOFI. Physics based defect detection and profiling methods are detailed along with initial results. In addition a ray‐tracing model was developed to simulate the inspection process. Results comparing the model and experimental images will also be presented.

Terahertz imaging techniques are beginning to find many applications in areas such as nondestructive evaluation, biomedical imaging and homeland security. The NASA spray on foam insulation (SOFI) inspection is a critical application where terahertz imaging is used to detect disbonds and delamination between SOFI and the substrate metal (external tank). This paper discusses a ray-tracing model for the high frequency inspection system. Model based inversion techniques for the characterization of defects is also proposed

A new giant magnetoresistance (GMR) based eddy current field measurement system which can inspect components at rates comparable to magneto-optic imaging (MOI) sensor systems has been designed and developed. The main advantage of this system over the MOI is its ability to retain complete quantitative information about the magnetic field. Other advantages of the system include high bandwidth and sensitivity.

Terahertz imaging is a relatively new technique for sub‐surface imaging using radiations in the spectral range between 0.1 to 10 THz. The technique has been used to image artificially induced inserts simulating disbonds in metal‐foam interfaces and has shown significant promise as a possible non destructive evaluation technique for evaluating the bonding quality of foam. The data in these cases is obtained by scanning across a surface on top of the foam coated on metal structures and collecting the time signal in a window of interest at each point in the scan plane. Proper data processing and visualization techniques become critical in being able to detect the disbonds and delaminations that, additionally, become convoluted due to the wide variety of artifacts and support structures that occur on the metal substrates. In this work we discuss a wavelet based signal enhancement algorithm that provides an effective scheme for visualizing the imaging data and provides a very high contrast between disbonded areas and normal substrate. The technique also shows promise as a first step towards automatic detection and classification of the disbonds. Some preliminary results, obtained on data collected using simulated disbonds that demonstrate the usefulness of the algorithm will be presented.

Nondestructive assessment of the integrity of civil structures is of paramount importance for ensuring safety. In concrete imaging, radiography, ground penetrating radar and infrared thermography are some of the widely used techniques for health monitoring. Other emerging technologies that are gaining impetus for detecting and locating flaws in steel reinforcement bar include radioactive computed tomography, microwave holography, microwave and acoustic tomography. Of all the emerging techniques, microwave NDT is a promising imaging modality largely due to their ability to penetrate thick concrete structures, contrast between steel rebar and concrete and their non‐radioactive nature. This paper investigates the feasibility of a far field microwave NDE technique for reinforced concrete structures.

Significant advances made in the field of Terahertz Imaging have captured the attention of many applications including industrial NDE, biomedical imaging and homeland security. The NASA spray on foam insulation (SOFI) inspection is one such critical application were Terahertz imaging is used to detect disbonds and delamination between SOFI and the substrate metal (external tank). This paper discusses modeling aspects of the high frequency inspection system. The feasibility of using a simple ray‐tracing model is studied. The efficiency of the model is demonstrated by comparing the model prediction with experimental measurements and further using it in an iterative inverse problem scheme for defect reconstruction.