Holographic otoscope for nanodisplacement measurements of surfaces under dynamic excitation

Abstract

Summary We describe a novel holographic otoscope system for measuring nano-displacements of objects subjected to dynamic excitation. Such measurements are necessary to quantify the mechanical deformation of surfaces in mechanics, acoustics, electronics, biology and many other fields. In particular, we are interested in measuring the sound-induced motion of biological samples, such as an eardrum. Our holographic otoscope system consists of laser illumination delivery (IS), optical head (OH), and image processing computer (IP) systems. The IS delivers the object beam (OB) and the reference beam (RB) to the OH. The backscattered light coming from the object illuminated by the OB interferes with the RB at the camera sensor plane to be digitally recorded as a hologram. The hologram is processed by the IP using Fresnel numerical reconstruction algorithm, where the focal plane can be selected freely. Our holographic otoscope system is currently deployed in a clinic, and is packaged in a custom design. It is mounted in a mechatronic positioning system to increase its maneuverability degrees to be conveniently positioned in front of the object to be measured. We present representative results highlighting the versatility of our system to measure deformations of complex elastic surfaces in the wavelength scale including a copper foil membrane and postmortem tympanic membrane (TM).

Wave motion on the surface of the human tympanic membrane: Holographic measurement and modeling analysis

“…Our group has been studying the sound-induced motion of the TM using fiber-optic-based opto-electronic holographic (OEH) interferometery (Furlong and Pryputniewicz, 1998;Furlong et al, 2009;Hern andez-Montes et al, 2009;Flores-Moreno et al, 2011). Our previous studies have shown that sound-induced motions of the mammalian TM follow different patterns (simple, complex, ordered) within different stimulus frequency ranges .…”

In-plane and out-of-plane motions of the human tympanic membrane

“…The temporal bones were then mounted on a 3D positioner placed on a vibration-isolated table, which also supported multiple lasers and optical devices needed for the holographic measurements (Hern andez-Montes et al, 2009;Flores-Moreno et al, 2011). The bones were positioned such that the planes of their tympanic rings were parallel to the holographic recording CCD camera, and the TM image was centered in the camera plane.…”

Three-dimensional vibrometry of the human eardrum with stroboscopic lensless digital holography

“…Typically, each laser pulse has a duration of 2% to 5% of the period of the tonal stimulus. 11,18 This generates the same effect as a strobe light by only capturing the motion of the TM at desired phases of the stimulus wave.…”

“…[4][5][6] Therefore, full-field-of-view techniques are required to quantify shape, sound-induced displacements, and mechanical properties of the TM. [7][8][9] In our previous works, [10][11][12] we have reported holographic interferometric measurements of sound-induced displacements over a majority of the surface of mammalian TMs. A potential criticism of these measurements is that the displacements were measured only along one direction that was along the normal vector to the tympanic ring.…”