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Field-induced phase behavior of a confined monodisperse ferrofluid emulsion was studied using optical microscopy, light transmission, and static light scattering techniques. Upon application of magnetic field, randomly-dispersed magnetic emulsion droplets form solid structures at λ = 1.5, where λ is defined as the ratio of the dipole–dipole interaction energy to the thermal energy at room temperature. The new solid phase consists of either single droplet chains, columns, or worm-like clusters, depending on the volume fraction, cell thickness and rate of field application. For the column phase, an equilibrium structure of equally-sized and spaced columns was observed. Our measurements taken for cell thickness 5µ m ≤ L ≤ 500µ m and volume fraction 0.04 show the column spacing to be reasonably described by d = 1.49L0.34.

Laser Doppler Vibrometry (LDV) is a widely accepted tool for dynamic characterization of MEMS. Using automated scan capability, the Polytec system can measure structural resonance and display out-of-plane deflection shapes with amplitudes down to the picometer level and frequencies to 30 MHz. By adding stroboscopic video microscopy for in-plane motion analysis, our combined Micro Motion Analysis (MMA) system is capable of threedimensional dynamic characterization. The MMA system opens up new possibilities to measure in-plane actuators previously difficult or impossible for LDV measurements. To exemplify the use of this technology, we present characterization measurements on MEMS devices fabricated by Sandia National Labs SUMMiT V process. Multiaxis measurements reveal the complex motions exhibited by an electrostatic comb drive driven at resonance. Also, ultra-high resolution velocity measurements are made on passive cantilever structures oscillating under thermal excitation. Picometer resolution makes possible detection of these purely mechanical resonances. Both comb drive and cantilever data are used to determine mechanical properties important to evaluate the reliability of fabrication processes. This study demonstrates the unique performance of our hybrid LDV / strobe video measurement system for quick, accurate, high-resolution dynamic response measurements.

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