Search

We develop a method to model the microwave transmissivity of row crops that explicitly accounts for their periodic nature as well as multiple scattering. We hypothesize that this method could eventually be used to improve satellite retrieval of soil moisture and vegetation optical depth in agricultural regions. The method is characterized by unit cells terminated by periodic boundary conditions and Floquet port excitations solved using commercial software. Individual plants are represented by vertically oriented dielectric cylinders. We calculate canopy transmissivity, reflectivity, and loss in terms of S-parameters. We validate the model with analytical solutions and illustrate the effect of canopy scattering. Our simulation results are consistent with both simulated and measured data published in the literature.

The boundary element method (BEM) is an efficient way to compute solutions of eddy current nondestructive evaluation (NDE) problems. However, in boundary element analysis of eddy currents, the computational accuracy and efficiency depend on the element discretization employed and are very sensitive to the liftoff distance and the relative geometry size between the detecting coil and object under evaluation or test. In this paper, the skin depth parameter is applied to study the element discretization effects on boundary element analysis for 3D eddy current NDE problems. The element discretization rules are concluded by conducting numerical experiments for different liftoff distances and relative probe sizes so that they can be adjusted to account for variations in these parameters, and validated against the analytical method, semi-analytical method, and experiments of some benchmark problems. With the help of the rules, the overall computational accuracy is improved while the cost is reduced for the BEM modeling of eddy current NDE problems.

Model-assisted probability of detection (MAPOD) and sensitivity analysis (SA) are important for quantifying the inspection capability of nondestructive testing (NDT) systems. To improve the computational efficiency, this work proposes the use of polynomial chaos expansions (PCEs), integrated with least-angle regression (LARS), a basis-adaptive technique, and a hyperbolic truncation scheme, in lieu of the direct use of the physics-based measurement model in the MAPOD and SA calculations. The proposed method is demonstrated on three ultrasonic testing cases and compared with Monte Carlo sampling (MCS) of the physics model, MCS-based kriging, and the ordinary least-squares (OLS)-based PCE method. The results show that the probability of detection (POD) metrics of interests can be controlled within 1% accuracy relative to using the physics model directly. Comparison with metamodels shows that the LARS-based PCE method can provide up to an order of magnitude improvement in the computational efficiency.

Electromagnetic compatibility (EMC) compliance to transient conducted immunity (CI) tests is required for automotive electronic/electrical systems. An example is the CI 220 test that employs the transient pulses which are generated by relay contact arcing during switching of an inductive load. To realize compliance with minimum efforts, apposite but simple modeling that enables evaluation at early product design phase is therefore desiable for the EMC engineers to avoid failures in advance. In this paper, as an extension of our previous work, an improved circuit modeling method is developed to fully encompass all the operating modes specified in the CI 220 test by combining of the simulation of both contact arcing phenomenon and stochastic contacts opening and closing process. Experimental validation of the developed model using a non-linear load is also demonstrated. The proposed method is featured by its easy-to-implement without requiring numbers of information on arc dynamic physics.

This letter reports on a fully conformal square-patch frequency-selective surface (FSS) consisting of liquid metal alloy embedded within a flexible silicone elastomer. The flexible and elastic nature of the FSS provides high conformity to doubly curved surfaces. The transmission properties of the FSS on both singly and doubly curved surfaces are studied. This FSS can facilitate electromagnetic interference reduction in the X-band frequency range when wrapped on cylindrical or spherical radomes over dipole-like antennas, thus surpassing many existing flexible FSS technologies that usually allow conformable contact only with singly curved surfaces.

Automotive electronic/electrical systems are required to operate as designed while exposed to transient electromagnetic compatibility (EMC) tests. An example of such an EMC test is the CI 220 test, in which pulse voltages produced by switch contact arcing and contact bounce during switching of an inductive load are employed. Apposite but simple modeling is thereby desirable for the EMC engineer to evaluate at the early design phase and avoid failures in advance. In this work, an easy-to-implement circuit model simulating both contacts arcing and contact bounce phenomenon is derived and implemented in L Tspice., in which arc behavior parameters, as well as bounce time, are extracted from the experimental measurement results using a home-made pulse generator. Experimental validation of this developed circuit model under three different loads is also demonstrated.

In this paper, we simulate some of the benchmark problems proposed by the World Federation of Nondestructive Evaluation Centers (WFNDEC) using a full wave simulation model based on accurate solutions to the boundary integral equations for ultrasonic scattering. Much of the previous work on modeling these problems relied on the Kirch-hoff approximation to find the scattered fields from defects. Here we instead use a numerical method, called the Nystrom method, for finding the scattered fields more accurately by solving the boundary integral equations of scattering. We compare our model’s predictions with both measurements and Kirchhoff approximation based models. We expect the presented results to serve as a validation of our model as well as a comparison between the Kirchhoff approximation and the Nystrom method.

Elastic waves in solids find important applications in ultrasonic non-destructive evaluation. The scattering of elastic waves has been treated using many approaches like the finite element method, boundary element method and Kirchhoff approximation. In this work, we propose a novel accurate and efficient high order Nystrom method to solve the boundary integral equations for elastodynamic scattering problems. This approach employs high order geometry description for the element, and high order interpolation for fields inside each element. Compared with the boundary element method, this approach makes the choice of the nodes for interpolation based on the Gaussian quadrature, which renders matrix elements for far field interaction free from integration, and also greatly simplifies the process for singularity and near singularity treatment. The proposed approach employs a novel efficient near singularity treatment that makes the solver able to handle extreme geometries like very thin penny-shaped crack. Nume...