Dustin D. Gerrard

Rheology of attractive emulsions.

We show how attractive interactions dramatically influence emulsion rheology. Unlike the repulsive case, attractive emulsions below random close packing, φ(RCP), can form soft gel-like elastic solids. However, above φ(RCP), attractive and repulsive emulsions have similar elasticities. Such compressed attractive emulsions undergo an additional shear-driven relaxation process during yielding. Our results suggest that attractive emulsions begin to yield at weak points through the breakage of bonds, and, above φ(RCP), also undergo droplet configurational rearrangements.

Q-factor optimization in disk resonator gyroscopes via geometric parameterization

We present an assortment of geometrically parameterized disk resonator gyroscopes (DRGs) individually designed for resonant frequency (f) and quality factor (Q). This work demonstrates accurate FEM-based predictions of Q for fabricated devices, and geometric optimizations that significantly improve this key performance metric for the DRG. Measurements on suites of fabricated devices confirm that losses are dominated by thermoelastic dissipation (TED). Qted is shown to account for 64-80% of the total energy dissipation. The temperature dependence of Q is also used to confirm and quantify the presence of pressure damping in the fabricated devices. At frequencies near 300 kHz, we show that Q can be increased by a factor of 2.6 and demonstrate feasibility of geometric/topological optimization of the fabricated devices with the aid of finite element software.

Modeling the effect of anchor geometry on the quality factor of bulk mode resonators

High quality factor (Q) resonators are desired for numerous applications such as clocks and gyroscopes. For bulk acoustic wave resonators, energy dissipation through the anchors (i.e. anchor loss or anchor damping) can often limit Q. This work explores several designs of anchor geometries for a width extensional resonator with experimental results confirming that the geometry of the anchor can have a large effect on the mode shape as well as the quality factor. We present a Perfectly Matched Layer (PML) COMSOL model which is able to predict Q for several anchor loss limited anchor designs. Temperature dependencies of f and Q are also reported and favorable designs are set forth.

Wide-range temperature dependence studies for devices limited by thermoelastic dissipation and anchor damping

The aim of this study is to measure the quality factor (Q) for double-ended tuning fork (DETF) devices dominated by Thermoelastic Dissipation (TED) and width-extensional (WE) devices dominated by Anchor Damping over a wide temperature range. Testing of these two device families over this wide range led to two related findings. First, our results indicate that it is possible to completely account for the dissipation in these devices through the use of quantitative models and measurements over a wide temperature range. A second finding, presented for the first time, is that anchor damping can be clearly seen in WE mode devices, and this damping term shows a clear temperature dependence.

Wafer-scale encapsulation of fully differential electrodes for mutli-axis inertial sensing

This work demonstrates, for the first time, a wafer-scale encapsulation process incorporating fully circumferential electrodes (in-plane and out-of-plane) for applications towards multi-axis inertial sensing. Bottom and top electrodes were incorporated in the device package utilizing epitaxial silicon deposition. By this method, we present fully differential, vacuum-encapsulated, oxide-coated polysilicon resonators.

Topology optimization for reduction of thermo-elastic dissipation in MEMS resonators

This paper presents a topology optimization approach for reducing thermo-elastic dissipation (TED) in MEMS resonators. This algorithm is applied to a clamped-clamped resonant beam to maximize the quality factor (Q). Optimal designs have a Q ten times higher than a solid beam and are 75% higher than previously optimized devices. Furthermore, new designs have intuitive topologies. Beams are fabricated in <111> silicon wafers and experimental measurements of Q agree well with simulation.