ABSTRACTIn this article, Frequency Modulated Thermal Wave Imaging (FMTWI) [1–6] is introduced for the first time for determining power distribution of electromagnetic waves on plane surfaces. The advantage with this technique is that we can extract multiple amplitude and phase images from a single run of experiment. The applied excitation signal in this technique is a frequency modulated chirp signal instead of a single frequency signal used in conventional lock-in infrared (IR) thermography [7–11].The thermal images obtained using FMTWI can be used qualitatively, e.g., to detect field leakage near electromagnetic junctions and microstrip feed lines. As a practical demonstration of this technique, an example of 2 × 2 patch antenna array at 8 GHz is considered. First, amplitude images at various modulation frequencies are obtained. Next, signal to noise ratio (SNR) values at each frequency are calculated. It is seen that SNR is lower at higher frequencies. It is observed that at higher modulation frequencies, micro-strip lines feeding the individual patch antennas of the array, are not visible in amplitude images, while at lower frequencies they are clearly visibleMathematical modeling of the microwave absorption screen has also been carried out to show variations of incident, reflected, and transmitted powers as a function of screen surface impedance. It is also observed that the screen minimally perturbs the electromagnetic fields.

ABSTRACT In this research, gamma radiation has been used to graft styrene and acrylic acid monomers onto marble (M) and granite (G) powder, with irradiation doses 30, 10 kGy, respectively. The grafted marble and granite powders were used as filler of epoxy composites. They added to an epoxy resin at 20, 60, and 100 wt% and then cured at room temperature. Ultrasonic velocities and attenuation measurements in epoxy composites at 4 MHz in the 25–300°C temperature range in addition to Fourier Transform Infrared (FTIR) analysis had been investigated. The ultrasonic compression wave velocity and the shear wave velocity measurements were performed using the pulse-echo technique, and then wecalculated elastic modulus, Young’s modulus, longitudinal and shear moduli, and Poisson’s ratio. In addition to attenuation at different temperatures of epoxy/granite composites, ultrasonic results indicated that the ultrasonic wave’s velocities VL and Vs increased with the increase of (M, G) content and a linear relation was observed. Also, the attenuation of epoxy was stable and appeared to increase at temperature 385°C, while the addition M or G to epoxy composites increased the attenuation.

ABSTRACTIn order to analyze the aging of the active Ethylene-Propylene Rubber (EPR) cable, the dielectric dissipation factor (tan δ) was proposed as a nondestructive method of cable insulation condition assessment. Firstly, the EPR marine cable was investigated in this article, and the data of elongation at break retention rate (EAB%) after accelerated aging under different temperatures were used to fit by means of the optimized time-temperature shift factor. The endpoint judgment index of dielectric dissipation factor was deduced when EAB% reached to 50%. Secondly, the cable’s lifetime calculated by tan δ was compared with the EAB% in order to confirm the accuracy of the method. The results show that the lifetime of tan δ is consistent with EAB% and provides a new method for the rapid evaluation of the EPR cable’s remaining life.

ABSTRACTNondestructive evaluation (NDE) techniques of phased array ultrasonic testing (PAUT) and digital X-ray radiography were employed on friction stir (FS)-welded Aluminum Alloy (AA)-2219-T87 specimens. PAUT intricacies required for scanning of FS-welded specimens with a 10-MHz 32-element transducer are discussed. The time corrected gain (TCG) calibration is required for scanning with an increase in index offset to compensate for decrease in A-Scan signal peak amplitude. Calibration techniques to find small defects with appropriate size tolerances are also established. The NDE technique of digital X-ray radiography is compared to PAUT, where it was found that a calibrated PAUT system is able to discover defects less than 0.2 mm where X-ray radiography could not. Incomplete penetration (IP), wormhole (WH), surface cavity (SC), and internal void (IV) defects are analyzed. Furthermore, an online PAUT system for FSW has been developed and successfully tested. The work provided herein will provide a gateway for an ultimate goal of an automated PAUT online sensing system.

ABSTRACTIntergranular corrosion (IGC) is one of the major localized corrosion problems faced by austenitic stainless steel components in ultra-supercritical power plants, which occurs along the grain boundaries of material and results in loss of engineering properties. Ultrasonic technique was applied to the early detection of IGC in austenitic stainless steel super304H. Acoustic attenuation and nonlinear parameter were measured at multiple excitation frequencies, and an equivalent attenuation factor and an equivalent nonlinear factor were defined to evaluate the IGC damage. Results indicated that both factors increased monotonously as the degree of IGC developed, and the equivalent nonlinear factor is more sensitive to IGC at early stage. Thus they can be utilized for early detection of IGC in austenitic stainless steel.

We present an experimental study where guided ultrasonic waves were used for the noncontact nondestructive evaluation of an aluminum plate immersed in water. Broadband leaky Lamb waves were generated using a pulsed laser and were detected with an array of immersion transducers arranged in a semicircle. The signals were processed to extract some features from the time, frequency, and joint time-frequency domains. These features were then fed to an unsupervised learning algorithm based on the outlier analysis to detect the presence of damage, and to a supervised learning algorithm based on artificial neural networks to classify the types of defect. We found that the hybrid laser-immersion transducers system and both learning algorithms enable the detection of the defects and their classification with good success rate.

A microwave imaging technique based on particle swarm optimization (PSO) and asynchronous particle swarm optimization (APSO) are proposed for the electromagnetic inverse scattering. In this article, the finite-difference time-domain (FDTD) method is employed for the analysis of the forward scattering part, while PSO and/or APSO schemes (combining with FDTD) are applied to tackle the inverse scattering part. These two schemes aim for the simultaneous reconstruction of the location, shape, and permittivity of the dielectric scatterer in a slab medium. The reconstruction is based on the minimization of a cost functional, which evaluates the difference between measured and estimated values of the electric field. These two schemes are tested by several numerical examples, and the numerical results indicate that APSO outperforms PSO in terms of reconstruction accuracy and convergence speed. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise.

To determine the position of a metallic target in a cylindrical background made of soil, the electromagnetic tomography, as a nondestructive method, is employed. It is a difficult goal to produce precise electromagnetic tomography images using analytical methods. To cope with this issue, an artificial neural network is trained to mimic the electromagnetic tomography system. A hybrid optimization algorithm, which is a combination of intelligent global harmony search and Levenberg–Marquardt algorithms, is proposed to optimize the artificial neural network weights and biases. Simulation results show that the proposed method can estimate the position of target with an acceptable accurately.

The probability of detection (POD) of a well-controlled, automated eddy current (EC) procedure is evaluated in a numerical model and compared with experiments. The procedure is applied in laboratory environment with a single absolute probe which is positioned for raster scan over flat surfaces containing fatigue cracks. The variability of the signal amplitude, due to small fatigue cracks in the Titanium alloy Ti-6Al-4 V, is expected to mainly originate from crack characteristics and the index distance of the raster scan. The POD model is based on the signal versus crack size ( versus a) result. The presented procedure provides a well-defined basis for a comparison between a simulated and an experimentally based POD assessment. Finite element analysis is used to model the EC method. A simplified fatigue crack model is first introduced and evaluated experimentally. Numerical computations are then used to build the corresponding model-based POD curve which shows good agreement with the experimental result. The model-based POD curve is generated both by means of a parametric and a nonparametric approach. Differences between model-based and experimental POD are discussed as well as the delta POD approach using transfer functions.

In eddy current (EC) testing, presence of lift–off and material property variation makes the defect detection as a challenging task. In view of this, a signal processing approach comprising of independent component analysis (ICA) and wavelet packet analysis (WPA) is attempted. In this paper, performance of hybrid signal processing approach and the resultant improvement in signal-to-ratio (SNR) is discussed.