Holographic interferometric methods typically require the use of three sensitivity vectors in order to obtain three-dimensional (3-D) information. Methods based on multiple directions of illumination have limited applications when studying biological tissues that have temporally varying responses such as the tympanic membrane (TM). Therefore, to measure 3-D displacements in such applications, the measurements along all the sensitivity vectors have to be done simultaneously. We propose a multiple-illumination directions approach to measure 3-D displacements from a single-shot hologram that contains displacement information from three sensitivity vectors. The hologram of an object of interest is simultaneously recorded with three incoherently superimposed pairs of reference and object beams. The incident off-axis angles of the reference beams are adjusted such that the frequency components of the multiplexed hologram are completely separate. Because of the differences in the directions and wavelengths of the reference beams, the positions of each reconstructed image corresponding to each sensitivity vector are different. We implemented a registration algorithm to accurately translate individual components of the hologram into a single global coordinate system to calculate 3-D displacements. The results include magnitudes and phases of 3-D sound-induced motions of a human cadaveric TM at several excitation frequencies showing modal and traveling wave motions on its surface.
The eardrum or tympanic membrane (TM) transforms acoustic energy at the ear canal into mechanical motions of the ossicles. The acousto-mechanical transformer behavior of the TM is determined by its shape, three-dimensional (3-D) motion, and mechanical properties. We have developed an optoelectronic holographic system to measure the shape and 3-D sound-induced displacements of the TM. The shape of the TM is measured with dual-wavelength holographic contouring using a tunable near IR laser source with a central wavelength of 780 nm. 3-D components of sound-induced displacements of the TM are measured with the method of multiple sensitivity vectors using stroboscopic holographic interferometry. To accurately obtain sensitivity vectors, a new technique is developed and used in which the sensitivity vectors are obtained from the images of a specular sphere that is being illuminated from different directions. Shape and 3-D acoustically induced displacement components of cadaveric human TMs at several excitation frequencies are measured at more than one million points on its surface. A numerical rotation matrix is used to rotate the original Euclidean coordinate of the measuring system in order to obtain in-plane and out-of-plane motion components. Results show that in-plane components of motion are much smaller (<20%) than the out-of-plane motions’ components.
The eardrum or Tympanic Membrane (TM) transfers acoustic energy from the ear canal (at the external ear) into
mechanical motions of the ossicles (at the middle ear). The acousto-mechanical-transformer behavior of the TM is
determined by its shape and mechanical properties. For a better understanding of hearing mysteries, full-field-of-view
techniques are required to quantify shape, nanometer-scale sound-induced displacement, and mechanical properties of
the TM in 3D. In this paper, full-field-of-view, three-dimensional shape and sound-induced displacement of the surface
of the TM are obtained by the methods of multiple wavelengths and multiple sensitivity vectors with lensless digital
holography. Using our developed digital holographic systems, unique 3D information such as, shape (with micrometer
resolution), 3D acoustically-induced displacement (with nanometer resolution), full strain tensor (with nano-strain
resolution), 3D phase of motion, and 3D directional cosines of the displacement vectors can be obtained in full-field-ofview
with a spatial resolution of about 3 million points on the surface of the TM and a temporal resolution of 15 Hz.
Acoustically induced vibrations of the tympanic membrane (TM) play a primary role in the hearing process, in that these motions are the initial mechanical response of the ear to airborne sound. Characterization of the shape and three-dimensional (3-D) displacement patterns of the TM is a crucial step to a better understanding of the complicated mechanics of sound reception by the ear. Sound-induced 3-D displacements of the TM are estimated from shape and one-dimensional displacements measured in cadaveric chinchillas using a lensless dual-wavelength digital holography system (DWDHS). The DWDHS consists of laser delivery, optical head, and computing platform subsystems. Shape measurements are performed in double-exposure mode with the use of two wavelengths of a tunable laser, while nanometer-scale displacements are measured along a single sensitivity direction with a constant wavelength. Taking into consideration the geometrical and dimensional constrains imposed by the anatomy of the TM, we combine principles of thin-shell theory together with displacement measurements along a single sensitivity vector and TM surface shape to extract the three principal components of displacement in the full-field-of-view. We test, validate, and identify limitations of this approach via the application of finite element method to artificial geometries.
Quantitative techniques to characterize thermomechanical effects of light on canvas paintings are necessary in order to
better understand the deleterious effects that light has on precious art collections in museum exhibitions. In this paper,
we present advances in the development of a customized laser shearography system for temporal characterization of inplane
displacements of canvas paintings when subjected to specific lighting conditions. The shearography system is
synchronized with a thermal IR camera and concomitant measurements of derivatives of displacements along two
orthogonal shearing directions as well as thermal fields are performed. Due to the nature of the measurements, we have
developed real-time temporal phase unwrapping algorithms and high-resolution Fast Fourier Transform (FFT) methods
to calibrate applied shearing levels. In addition, we are developing methods to isolate thermally-induced components
from randomly-induced mechanical vibrations that occur in museum environments by application of IR imaging data.
Representative examples are shown, which illustrate capabilities to measure, detect, and map crack propagation as a
function of lighting conditions and time.
Recent technological advances of miniaturization engineering are enabling the realization of components and systems
with unprecedented capabilities. Such capabilities, which are significantly beneficial to scientific and engineering
applications, are impacting the development and the application of optical metrology systems for investigations under
complex boundary, loading, and operating conditions.
In this paper, and overview of metrology systems that we are developing is presented. Systems are being developed and
applied to high-speed and high-resolution measurements of shape and deformations under actual operating conditions for
such applications as sustainability, health, medical diagnosis, security, and urban infrastructure. Systems take advantage
of recent developments in light sources and modulators, detectors, microelectromechanical (MEMS) sensors and
actuators, kinematic positioners, rapid prototyping fabrication technologies, as well as software engineering.
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