Near-Field Microwave Detection of Disbond in Carbon Fiber Reinforced Polymer Composites Used for Strengthening Cement-Based Structures and Disbond Repair Verification

Dual-Polarized Near-Field Microwave Reflectometer for Noninvasive Inspection of Carbon Fiber Reinforced Polymer-Strengthened Structures

“…Disbonds between the CFRP laminate and concrete may occur for a variety of reasons, including improper application of the CFRP laminate, presence of moisture near the concrete surface, impact damage, etc. Thus, it is of great interest to develop a fast, robust, inexpensive, one-sided, noncontact, real-time, and portable inspection system that is capable of detecting such disbonds and evaluating their properties, such as spatial extent [4], [5].…”

“…Microwave signals also partially reflect at dissimilar boundaries in a layered composite, and this information can be used to detect and evaluate the presence of a disbond [4]. Nearfield microwave noninvasive techniques, utilizing open-ended rectangular waveguide probes, have demonstrated the ability to detect defects such as disbonds and delaminations in CFRPstrengthened cement-based structures using relatively simple microwave reflectometers [5]- [9]. Unlike ultrasonic testing methods, near-field microwave methods do not require contact between the microwave probe and the material under test.…”

Dual-Polarized Microwave Near-Field Reflectometer for Non-Invasive Inspection of Carbon Fiber Reinforced Polymer (CFRP) Strengthened Structures

“…On the other hand, microwave near-field non-invasive techniques, utilizing open-ended rectangular waveguides, have demonstrated the ability to detect defects such as disbonds, delaminations in composite structures [4] and evaluate their various properties using simple microwave reflectometers and imaging techniques. To this end, measurement systems including a near-field microwave reflectometer and a computerized 2D scanner were developed and investigations were conducted for detecting defects in CFRP reinforced cement-based structures [5][6][7][8]. The investigations have clearly shown the capabilities of this technique for detecting such defects.…”

“…The former case is well-suited for detecting and evaluating disbonds and concrete damages, whereas the latter case only provides information about surface roughness, and fiber breakage in the CFRP, etc. [5][6][7][8]. Moreover, it is possible to obtain two sets of data, corresponding each polarization, and then remove the undesired effect of surface roughness and standoff distance variation using the data obtained with parallel polarization.…”

“…Such a dual-polarized inspection system with a square waveguide probe was designed and constructed at X-band (8.2-12.4 GHz). This frequency range was chosen because of successful previous investigations of CFRP reinforced cement-based structures [5][6][7][8]. output voltages which are proportional of their phase (and/or amplitude) difference.…”