DCS Tx filters using AlN resonators with iridium electrodes.

In this paper we present the design, fabrication technology, and characterization of BAW filters for the Digital Cellular System (DCS) Tx-band at 1.75 GHz. The filters are fabricated with AlN-based solidly mounted resonators (SMR) using iridium electrodes, in an attempt to increase the effective electromechanical coupling factor of the BAW devices and achieve the bandwidth requirements of DCS filters. The design and optimization of the filters is performed with a simulation tool that uses a circuit model to compute the filter frequency response. Tx filters with balanced inputs and outputs and different topologies are designed and fabricated. The experimental filter response is compared with the simulations to determine the suitability of each design. DCS bandwidth requirements are fulfilled by using Ir/AlN/Ir stacks.

Equality of the energy and group velocities of bulk acoustic waves in piezoelectric media.

The equality of the energy and group velocities of bulk acoustic waves in a lossless piezoelectric medium is demonstrated, with the energy velocity defined from the generalized energy density and the generalized Poynting vector.

Three-dimensional modelling of micromachined-ultrasonic-transducer arrays operating in water.

We report on the 3-D modelling of periodic arrays of capacitive micromachined ultrasonic transducers (cMUTs) operating in fluid. Specific developments have been performed to model biperiodic transducer arrays and to take into account radiation into any stratified media at the front-side as well as the back-side of the device. The model is based on a periodic finite-element-analysis/boundary-element-method (FEA/BEM). It is applied to micromachined ultrasonic transducers (MUTs), based on silicon-nitride-circular-membrane arrays on a silicon substrate, and operating in water. The spectrum characteristics of MUTs excited in phase are investigated, showing that very-large-band emission is achievable as previously demonstrated by many authors. However, other contributions are also found, depending on the excitation conditions, that do not radiate in the fluid. These contributions are identified as guided modes that could generate significant cross-talk effects. The origin and the nature of these modes is analyzed to gain insight in the actual operation of MUTs.

Dyadic Green's functions of a laminar plate.

We introduce the concept of dyadic Green's functions of a laminar plate. These functions generalize classical Green's functions. In addition to relating displacements and stresses at the surface of a medium, they relate these quantities at both the top and the bottom surfaces of a medium of finite thickness and infinite extent in the transverse directions. We describe here the calculation of these functions in the spectral domain and provide some academic examples demonstrating their interest.

Fast FEM/BEM simulation of SAW devices via asymptotic waveform evaluation.

The finite element method/boundary element method (FEM/BEM) computation model applied to surface acoustic wave devices requires the solution of a large linear system for each frequency point. An asymptotic waveform evaluation technique is used to obtain an approximate solution of the linear system that is valid over a large frequency bandwidth. The approximate solution was shown to be very accurate and vastly reduces the computation time.