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THE TECTORIAL MEMBRANE COCHLEAR MECHANICS
COMPUTER MICROVISION
 MEMS METROLOGY
COHERENT IMAGING MICROFLUIDICS

THE TECTORIAL MEMBRANE

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TM Traveling Waves: Suspending the TM between two parallel supports allows us to measure the properties of traveling waves that propagate along the TM.
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Shear Stiffness Probes: These microfabricated probes are customized with a variety of stiffnesses to allow measurements of the shear stiffness of biological tissues.
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Shear Probe on a Human Hair: The shearing plate of a probe is placed on a human hair. Forces applied to the base of the plate are transmitted to the hair through the cantilever arms, which act like springs.
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Shear Probe on a Tectorial Membrane: The shearing probe exerts force on an isolated tectorial membrane (TM). Forces in either of two directions allow direct measurements of the shear impedance of the TM. In this image, forces are being exerted in the radial direction.
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Exerting Force With Magnetizable Beads: Another way to exert force is to place magnetizable beads in an oscillating magnetic field. This image shows such a bead placed on a TM.
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Measuring Transverse Stiffness of the TM: To measure TM stiffness in the transverse direction, an AFM cantilever is brought into contact with the surface of the TM as shown here. Vertical motions of the chamber holding the TM deflect the cantilever, and these deflections are measured using laser-Doppler vibrometry.
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Measuring TM Electrical Properties: Like many extracellular gels, the TM contains significant fixed charge. Microfabrictaed chambers like the one shown here allow us to apply and measure voltages to detemrine the amount of fixed charge in the TM and its contribution to TM mechanics.

COCHLEAR MECHANICS

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Doppler Optical Coherence Microscopy: DOCM enables measurements of the motion of structures internal to the organ of Corti. This image shows a fixed organ of Corti along with motions of some of its internal structures when the cochlea was vibrated.
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Mechanical Tuning of Hair Bundles: Individual hair bundles in the alligator lizard cochlea are mechanically tuned. This image shows the motion of several such hair bundles in response to a 4 kHz tone.
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Quantifying Hair Bundle Motion: This image shows a colorized view of the motion of individual hair bundles. The phase of motion is encoded as color, and changes systematically from one end of the basilar papilla to the other.
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Motion of the Basilar Papilla: In response to sound, the basilar papilla simultaneously undergoes translation and rotation, resulting in elliptical patterns of motion.

COMPUTER MICROVISION

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Stroboscopic Illumination: We measure driven motions of microscopic structures at frequencies ranging from milliHertz to megaHertz by strobing a light source at the drive frequency.
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Linnik Interferometry: Linnik interferometry makes brightness a strong function of height, allowing more sensitive measurements of motion in the direction of the microscope axis.
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Mirau Interferometry: Commercially-available Mirau interferometers greatly simplify the use of interferometric image-based motion measurement.
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Stroboscopic Mirau Interferometry: As a target moves in the direction of the microscope axis, the interferometric pattern changes. Measuring changes in this pattern allows sensitive measurement of the motion.
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Measuring Motion Interferometrically: The interference pattern at any point is a sinusoidal function of distance from the target to the light source. Measuring changes in brightness in response to motions of both the target and the microscope objective allow motion to be quantified.
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Line-Scan Motion Measurement: High-speed line-scan cameras allow measurements of transient and spontaneous motions in one dimension. This image shows the response of a piezoelectric bimorph to a step change in voltage.

MEMS METROLOGY

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MEMS Devices: MEMS, or MicroElectroMechanical Systems, are microfabricated devices with mechanical components. This image shows measurements of the motion of a reliability test structure, designed by Exponent Inc.
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Verifying Motion Measurements: One advantage of computer microvision is the ability to visually verify motion measurements. This figure shows the result of shifting a set of images to compensate for the measured motion of the test structure.
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Multi-Dimensional Motion Measurements: Unlike many motion measurement systems, computer microvision is inherently multi-dimensional. This image shows measurements of the motion of a MEMS structure in two translational and one rotational directions.
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Profilimetry: Interferometric methods allow measurements of the absolute position of MEMS devices, a technique called profilimetry. This image shows the dynamic profile of a MEMS diffraction grating.

COHERENT IMAGING

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Making a Synthetic Aperture: Several mutually coherent laser beams (in this image, fifteen) are made to converge on a single point. This convergence creates a well-defined structured illumination pattern at the target.
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Interpreting The Images: Each image taken with structured illumination preferentially highlights particular features of the target. By combining information from multiple images with different illumination patterns, an image of the target can be rendered with unprecedented detail.

MICROFLUIDICS

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Microfluidics Teaching Lab Equipment: The microfluidics teaching lab is a low-cost system for demonstrating diffusion, osmosis, chemotaxis, and other topics in biological transport. The main component of the system is a student-grade microscope custom-fit with a digital camera.
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Camscope Software: The lab runs custom software that allows quantitative measurement of brightness, distance, and velocity from camera images. This image shows a screenshot of the software.
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Microscopic Diffusion: At small length scales, fluids mix primarily through diffusion. This image shows two fluids that meet in a microfluidic channel. At the junction, the fluids flow side-by-side, and mix by diffusion.