Hakeim Talleb

NEGATIVE REFRACTIVE INDEX BEHAVIOR THROUGH MAGNETO-ELECTRIC COUPLING IN SPLIT RING RESONATORS

An investigation on the possibility of obtaining a negative refractive index behavior in split ring resonators (SRRs) through magneto-electric coupling is presented. We have performed rigorous electromagnetic simulations using a full-wave 3D simulator, and the obtained results have been verifled by our experimental realizations and measurements. The results conflrm that the increase of magneto- electric gyrotropic activity inside a bi-anistropic medium can lead to the establishment of backward-wave propagation.

Finite-Element Modeling of Thermoelastic Attenuation in Piezoelectric Surface Acoustic Wave Devices

The assessment of thermoelastic attenuation is crucial in designing surface acoustic wave (SAW) devices. As irregular structures are more and more involved in modern applications for which efficient numerical tools are required, a multi-physics finite-element model is proposed in this paper, where thermoelastic damping in piezoelectric materials can be accounted for in both coated and uncoated conditions. The coupled equations are solved iteratively in time domain, using the Newmark method. The mechanical, electrical, and thermal degrees of freedom are calculated simultaneously at each time step. An application of the model is presented through the investigation of thermoelastic loss in a lithium niobate SAW device.

A Proper Generalized Decomposition-Based Solver for Nonlinear Magnetothermal Problems

This paper investigates solving coupled magnetothermal problems through a proper generalized decomposition-based non-incremental approach. The magnetodynamic and thermodynamic problems are strongly coupled as the electric material property changes with the temperature while the temperature field evolves due to the Joule heat generated by induced currents. A challenge to solve the coupled problem is that the electric time constant can be several orders of magnitude smaller than the thermal one. Solution through a classical time integration approach requires too many time steps, especially when a long duration needs to be simulated, hence making the problem size too large to be handled. The proposed solver overcomes this difficulty through decomposing unknown dynamic fields into the space and time modes and solving the linearized systems in space and time iteratively, using the finite element method. The material nonlinearity can be incorporated in a straightforward way. The advantages of the proposed solver are demonstrated in solving an academic problem.

Multiphysics Modeling of Thin-Layer Magnetoelectric Laminate Composites Using Shell Element

This paper proposes to use the nodal shell element in a finite-element multiphysics formulation to simulate the magnetoelectric (ME) laminate composites constituted of the thin magnetostrictive layers. The multiphysics model considers the nonlinearity of the thin-layer magnetostrictive material as well as the electrical load effects of the ME laminate composites. A trilayer ME Metglas/PZT/Metglas problem is solved in order to prove the efficiency of the proposed method. This paper provides the basis to study the ME devices composed of laminated thin layers.

Application of PGD on Parametric Modeling of a Piezoelectric Energy Harvester

In this paper, a priori model reduction methods via low-rank tensor approximation are introduced for the parametric study of a piezoelectric energy harvester (EH). The EH, composed of a cantilevered piezoelectric bimorph connected with electrical loads, is modeled using 3-D finite elements (FEs). Solving the model for various excitation frequencies and electrical load using the conventional approach results in a large size problem that is costly in terms of CPU time. We propose an approach based on the proper generalized decomposition (PGD) that can effectively reduce the problem size with a good accuracy of the solutions. With the proposed approach, field variables of the coupled problem are decomposed into space, frequency, and electrical load associated components. To introduce PGD into the FE model, a method to model the electrodes and electrical charges in the EH is presented. Appropriate choices for stopping criterions in the method and accelerating the convergence through updating after each enrichment are investigated. The proposed method is validated through a representative numerical example.