Rheological methods that interrogate nanolitre scale volumes of fluids and solids have advanced considerably over the past decade, yet there remains a need for methods that probe the frequency-dependent complex rheological moduli through application of homogenous strain fields. Here we describe a Micro-Electro-Mechanical System (MEMS) based approach for the measurement of dynamic rheology of soft matter where oscillatory strain is produced in a sample sandwiched between an oscillating MEMS stage and a glass plate. The resulting stress-strain relationships are revealed by measurement and analysis of the stage motion. We present preliminary data on simple viscous fluids and on viscoelastic thin films. In this proof-of-principle device, we measure moduli in the range of 50 Pa to 10 kPa over a range of 3 rad s(-1) to 3000 rad s(-1) using less than 5 nL of sample material. The device's measurement window is limited primarily by our current ability to measure the motion of the stage. This device will provide a new way to characterize dynamic microrheology of an array of novel materials and will prove useful in a number of areas including biorheology, microfluidics and polymer thin films.

This paper presents the design, fabrication methods and experimental results for a MEMS-based out-of-plane electromagnetic motion stage for scanning applications. The combination of electromagnetic actuation and a flexure-supported platform provides linear bidirectional motion with high precision. A planar microcoil and a permanent magnet are used to generate a Lorentz force, which drives the flexure-supported platform. The copper microcoil is electroplated on a silicon substrate and the platform is fabricated through silicon bulk micromachining of a silicon-on-insulator wafer. The resonant frequency of the fabricated motion stage is approximately 2.0 kHz, which results in an open-loop control bandwidth greater than 500 Hz. Experimental results verify that the stage has highly linear bidirectional motion with negligible hysteresis and nonlinearity over a ± 2.7 μm range. Additionally, excellent high-frequency tracking performance is demonstrated using open-loop control, with a tracking error below 6.5 nm RMS for scan rates up to 200 Hz.

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Broadband interference patterns measured from acoustic propagations near the axis of a deep sound channel are interpreted. Analyses using mode theory for the waveguide with bilinear sound speed profiles show that the increase in sound speed without gradient variation shifts the positions of intensity maxima to higher frequencies in a fixed range whereas the increase in the gradient shifts the maxima to lower frequencies. Analytic results imply that the frequency shift of intensity extrema appearing in the measurements could be explained by the increase in the sound speed gradient above the axis of the deep sound channel.

This paper describes the design of a very simple displacement sensor that measures the change in the position of an object by sensing the change in capacitance due to the movement of this object in the sensor fringing electric field. Two sensor geometries with small footprints were considered and several sensor variations were built and tested. At distances of approximately 0.5 μm and 30 μm, test results demonstrated that the sensors' resolution was in the order of tens of nanometers.