Modeling of Multiple Dynamics in the Radiation of Bulk Acoustic Wave Antennas

An unconditionally stable finite-difference time-domain (FDTD) algorithm is proposed to predict and understand the complex response in strain-mediated multiferroic radio frequency devices, such as antennas. A system of three coupled sets of governing equations is solved simultaneously: 1) Maxwell's equations for electromagnetic (EM) wave propagation; 2) Landau-Lifshitz-Gilbert equation for magnetic spin response; and 3) Newton's law for acoustic behavior. The formulation of this algorithm is elaborated on in detail followed by a demonstration of its capability through the simulation of a 1.3-mu m-thick bulk-acoustic-wave (BAW)-based strain-mediated multiferroic antenna. Analysis of the far-field radiation efficiency of this antenna as a function of magnetic dc bias demonstrates the importance of aligning the ferromagnetic resonance (FMR) and the mechanical BAW resonance to enhance EM radiation performance. Results also show that reducing the magnetic loss, or in other words, reducing the FMR linewidth, represents the dominating feature to achieve higher radiation efficiencies in these antennas.