Near-Field Millimeter-Wave Imaging of Exposed and Covered Fatigue Cracks

In this paper, the efficacy of near-field millimeter-wave nondestructive techniques, using open-ended flange-mounted rectangular waveguide probes, for extracting information of 3-D crack area deformation (i.e., in-plane and out-of-plane deformation) is demonstrated. It is shown that this information can be obtained from indications of unique interference patterns that are generated between the probe and the metal surface during the raster scan of a surface-breaking exposed and covered fatigue crack using a phase-sensitive reflectometer

Detection of Surface Cracks in Metals using Microwave and Millimeter-Wave Nondestructive Testing Techniques-A Review

Integrity Assessment of Metallic Structures Requires Inspection Tools Capable of Detecting and Evaluating Cracks Reliably. to This End, Many Microwave and Millimeter-Wave Nondestructive Testing and Evaluation (NDT&E) Methods Have Been Developed and Applied Successfully in the Past. Detection of Fatigue Cracks with Widths Less Than 5 Μ M using Noncontact Microwave-Based Inspection Methods Was Demonstrated in the 1970s. Since their Introduction, These Methods Have Evolved Considerably Toward Enhancing the Detection Sensitivity and Resolution. Undertaking Key Application Challenges Has Attracted Considerable Attention in the Past Three Decades and Led to the Development of the Near-Field Techniques for Crack Detection. to Address a Need that Cannot Be Fulfilled by Other NDT&E Modalities, Innovative Noncontact Microwave and Millimeter-Wave NDT&E Methods Were Devised Recently to Detect Cracks of Arbitrary Orientations under Thick Dielectric Structures. While the Reported Methods Share the Same Underlying Physical Principles, They Vary Considerably in Terms of the Devised Probes/sensors and the Application Procedure. Consequently, their Sensitivity and Resolution as Well as their Limitations Vary. This Article Reviews the Various Crack Detection Methods Developed To-Date and Compares Them in Terms of Common Performance Metrics. This Comprehensive Review is Augmented with Experimental Comparisons and Benchmarking Aimed to Benefit NDT&E Practitioners and Researchers Alike

Microwave detection of surface breaking cracks in metallic structures under heavy corrosion and paint

We live in the world of aging infrastructures . In this environment, critical and heavily utilized infrastructure, i.e. ships, planes, bridges, etc., are operating at or beyond their designed age. Replacement is no longer an option and retirement for cause is the current approach to maintenance and replacement. Consequently, there is an ever-increasing demand for efficient and robust nondestructive evaluation (NDE) methods that can determine the physical health of these structures. Large structures, which are primarily made of metals, either steel or aluminum, are susceptible to high-stress cracking and corrosion. Stress-induced cracks in heavily corroded steel, used in bridges, railroads, storage tanks, etc., are extremely difficult to detect. Current methods have limitations that render inspection to take longer either than it should or risk not detecting an existing crack. Microwave signals readily penetrate through dielectric materials such as paint and corrosion byproducts (i.e., rust), while conducting materials (i.e., metals) strongly reflect microwave signals. Therefore, interrogating a metal surface for surface-breaking cracks is readily possible even in the presence of a relatively thick layer of corrosion or paint. Normally, surface-breaking cracks are very small and the perturbations they cause to an irradiating microwave signal are small in amplitude unless the detection is performed very close to the surface. In this thesis, the implementation of a microwave imaging system that utilizes a synthetic aperture radar (SAR) approach to detect surface-breaking cracks in metallic structures under heavy corrosion and corrosion preventive paints is investigated. The resulting SAR images were analyzed and compared to numerical simulations to identify real-world capabilities and theoretical limitations --Abstract, page iii

Application of Millimeter Wave, Eddy Current and Thermographic Methods for Detection of Corrosion in Aluminum Substrate

Aluminum structures exposed to the elements are susceptible to corrosion. Corrosion may cause various mechanical and structural deficiencies such as material thinning. It is desirable to rapidly detect and evaluate the properties of an aluminum substrate early in the corrosion process to avoid costly maintenance actions later. There are several nondestructive testing methods for this purpose. To investigate capabilities of millimeter wave, conventional eddy current, and flash thermography techniques for detection of large corrosion areas in aluminum substrates, two corroded samples were inspected with and without dielectric coating (appliqué). This paper presents the results of the c-scan imaging of these samples using the methods mentioned above. The attributes of these methods for detection and evaluation of large, severe and non-uniform corrosion areas with and without a dielectric coating are discussed

Development of a High-Sensitivity Millimeter-Wave Radar Imaging System for Non-Destructive Testing

Murakami Hironaru, Fukuda Taiga, Otera Hiroshi, et al. Development of a High-Sensitivity Millimeter-Wave Radar Imaging System for Non-Destructive Testing. Sensors 24, 4781 (2024); https://doi.org/https://doi.org/10.3390/s24154781.There is an urgent need to develop non-destructive testing (NDT) methods for infrastructure facilities and residences, etc., where human lives are at stake, to prevent collapse due to aging or natural disasters such as earthquakes before they occur. In such inspections, it is desirable to develop a remote, non-contact, non-destructive inspection method that can inspect cracks as small as 0.1 mm on the surface of a structure and damage inside and on the surface of the structure that cannot be seen by the human eye with high sensitivity, while ensuring the safety of the engineers inspecting the structure. Based on this perspective, we developed a radar module (absolute gain of the transmitting antenna: 13.5 dB; absolute gain of the receiving antenna: 14.5 dB) with very high directivity and minimal loss in the signal transmission path between the radar chip and the array antenna, using our previously developed technology. A single-input, multiple-output (SIMO) synthetic aperture radar (SAR) imaging system was developed using this module. As a result of various performance evaluations using this system, we were able to demonstrate that this system has a performance that fully satisfies the abovementioned indices. First, the SNR in millimeter-wave (MM-wave) imaging was improved by 5.4 dB compared to the previously constructed imaging system using the IWR1443BOOST EVM, even though the measured distance was 2.66 times longer. As a specific example of the results of measurements on infrastructure facilities, the system successfully observed cracks as small as 0.1 mm in concrete materials hidden under glass fiber-reinforced tape and black acrylic paint. In this case, measurements were also made from a distance of about 3 m to meet the remote observation requirements, but the radar module with its high-directivity and high-gain antenna proved to be more sensitive in detecting crack structures than measurements made from a distance of 780 mm. In order to estimate the penetration length of MM waves into concrete, an experiment was conducted to measure the penetration of MM waves through a thin concrete slab with a thickness of 3.7 mm. As a result, Λexp = 6.0 mm was obtained as the attenuation distance of MM waves in the concrete slab used. In addition, transmission measurement experiments using a composite material consisting of ceramic tiles and fireproof board, which is a component of a house, and experiments using composite plywood, which is used as a general housing construction material in Japan, succeeded in making perspective observations of defects in the internal structure, etc., which are invisible to the human eye

Detection of Sub-Millimeter Surface Cracks using Complementary Split-Ring Resonator

Many interesting ideas have emerged from research on electromagnetic eld interactions with di erent materials. Analyzing such interactions has extracted some essential proper- ties of the materials. For example, extracting constitutive parameters such as permittivity, permeability, and conductivity, clari es a material's behavior. In general, the electromag- netic eld interacts with materials either in the far- eld or near- eld of a source. This study focuses on the principle of near- eld microwave microscopy for detection purposes. Many studies have focused on the use of an electrically small resonator, such as a split-ring resonator (SRR) and a complementary split-ring resonator (CSRR), to act as a near- eld sensor for material characterization and detection. At the resonance frequency, the electric and magnetic energy densities are enhanced dramatically at certain locations in the resonator. Any disturbance of the eld around such a resonator with a material under test causes the resonance frequencies to exhibit a shift that is used as an indicator of the sensor sensitivity. In this thesis, a single CSRR is used as a sensing element for detecting cracks in metal surfaces. Many microwave techniques have been developed for crack detection. However, these techniques have at least one of the following drawbacks: working at high frequencies, measurement setup complexity and cost, and low sensitivity. The rst part of this thesis presents a new sensor based on the complementary split-ring resonator (CSRR) that is used to detect sub-millimeter surface cracks. The sensing mechanism is based on perturbing the electromagnetic eld around an electrically small resonator, thus initiating a shift in the resonance frequency. Investigation of the current distribution on a CSRR at the resonance frequency shows the critical location at which the enhanced energy is concentrated. In addition, the current distribution demonstrates the sensing element in the CSRR. The sensor is simple to fabricate and inexpensive, as it is etched-out in the ground plane of a microstrip-line using printed circuit board technology. The microstrip-line excites the CSRR by producing an electric eld perpendicular to the surface of the CSRR. The sensor exhibits a frequency shift of more than 240 MHz for a 200 m crack. In the second part of this thesis, the sensitivity of the sensor is increased by lling the same crack with a dielectric material such as silicon oil. While using CSRR to scan a block with 200 m wide and 2 mm depth dielectric lled crack, the resonance frequency of the sensor shifts 435 MHz more than a case scanning a solid aluminum. Finally, the total Inductance of a CSRR for miniaturizing purposes is increased using either lumped or distributed elements. In this thesis, the designs and the results are validated experimentally and numerically

Algorithm development for the non-destructive testing of structural damage

Monitoring of structures to identify types of damages that occur under loading is essential in practical applications of civil infrastructure. In this paper, we detect and visualize damage based on several non-destructive testing (NDT) methods. A machine learning (ML) approach based on the Support Vector Machine (SVM) method is developed to prevent misdirection of the event interpretation of what is happening in the material. The objective is to identify cracks in the early stages, to reduce the risk of failure in structures. Theoretical and experimental analyses are derived by computing the performance indicators on the smart aggregate (SA)-based sensor data for concrete and reinforced-concrete (RC) beams. Validity assessment of the proposed indices was addressed through a comparative analysis with traditional SVM. The developed ML algorithms are shown to recognize cracks with a higher accuracy than the traditional SVM. Additionally, we propose different algorithms for microwave- or millimeter-wave imaging of steel plates, composite materials, and metal plates, to identify and visualize cracks. The proposed algorithm for steel plates is based on the gradient magnitude in four directions of an image, and is followed by the edge detection technique. Three algorithms were proposed for each of composite materials and metal plates, and are based on 2D fast Fourier transform (FFT) and hybrid fuzzy c-mean techniques, respectively. The proposed algorithms were able to recognize and visualize the cracking incurred in the structure more efficiently than the traditional techniques. The reported results are expected to be beneficial for NDT-based applications, particularly in civil engineering