Fine-grained water quality data can facilitate the optimized management of water resources, which have become increasingly scarce due to population growth, increased demand for safe sources of water, environmental pollutions, etc. There is a pressing need for cost-effective, reliable, re-useable, and autonomous water sensing technologies that can provide accurate real-time water quality measurements. In this paper, we present a microwave sensor array with sensing elements operating at different frequencies in the wide frequency band of 1 GHz to 10 GHz. The use of array allows for collecting more information compared to a single sensor system. The sensor array can be fabricated in a cost-effective way through standard printed circuit board (PCB) technology. Here, it is tested with water solutions of various contaminants and parameter values. Dielectric properties of the water samples with different contaminants and parameter values are measured and provided as well.

We present an inversion methodology for defect characterization using the data from magnetic flux leakage (MFL) measurements. We use a single tangential component of the leakage field as the MFL response. The inversion procedure employs the space mapping methodology. Space mapping is an efficient technique that shifts the optimization burden from a computationally expensive accurate (fine) model to a less accurate (coarse) but fast model. Here the fine model is a finite-element method (FEM) simulation, while the coarse model is based on analytical formulas. We achieve good estimation of the defect parameters using just a few FEM simulations, which leads to substantial savings in computational cost as compared to other optimization approaches. We examine the efficiency of the proposed inversion technique in estimating the shape parameters of rectangular and cylindrical defects in steel pipes. Our results show good agreement between the actual and estimated defect parameters.

Microwave holography requires knowledge of the incident field and the Green tensor of the background medium. In near-field imaging, analytical models of these are inadequate and the use of electromagnetic simulations has been previously proposed. In practice, however, the fidelity of such simulations may also be insufficient. Here, we propose a measurement method for the acquisition of this information, thus eliminating the need to estimate it analytically or numerically. We validate the approach through simulated data acquisitions as well as through experiments. It is shown that this approach characterizes the measurement system more reliably than simulations leading to significant improvement of the image quality.

We propose a procedure for full characterization of rectangular surface-breaking cracks based on measurements of only one tangential component of the magnetic field with the magnetic flux leakage (MFL) technique. The parameters of interest include orientation, length, and depth of the cracks. We assume that the length and the depth of the investigated cracks are much larger than the crack width, so that the variation of the MFL response with respect to the width is negligible. Our procedure employs fast direct methods that provide reliable estimation of the crack parameters in three separate consecutive steps. We propose denoising and correction techniques as well. We confirmed the accuracy of the methods by simulations based on the finite-element method (FEM) as well as by experimental MFL observations. A procedure is proposed for full characterization of rectangular surface breaking cracks based on measurements of only one tangential component of the magnetic field with the magnetic flux leakage (MFL) technique. The parameters of interest include orientation, length and depth of the cracks. We assume that the length and the depth of the investigated cracks are much larger than the crack width such that the variation of the MFL response with respect to the width is negligible. The proposed procedure employs fast direct methods which provide reliable estimation of the crack parameters in three separate consecutive steps. De-noising and correction techniques are proposed as well. The accuracy of the proposed estimation methods is examined via simulations based on the finite element method (FEM) as well as experimental MFL data.

Conventional nondestructive testing techniques do not suffice to efficiently inspect the defects in multiple nonmetallic pipes. Thus, in this article, we propose a novel method for inspection of these components based on near-field microwave holographic imaging augmented with beamspace transformation. This approach harnesses the ability of microwaves for 3-D imaging by measuring the backscattered fields in the near-field region. In the proposed technique, we augment the solution of near-field holographic imaging through the use of beamspace transformation which allows for focusing on each pipe during the solution process. This improves the quality of the reconstructed images, in particular, for the pipes which are further away from the measuring antennas. First, we demonstrate the performance of the proposed imaging technique using simulations. Then, we present the experimental results for imaging of concentric cylindrical polyvinyl chloride (PVC) pipes using wideband microwave data.