F. Mendoza Santoyo

3D displacement measurements of the tympanic membrane with digital holographic interferometry

A digital holographic interferometry (DHI) system with three object-illumination beams is used for the first time to measure micro-deformations along the x, y and z axes (3D) on the tympanic membrane (TM) surface of a post-mortem cat. In order to completely and accurately measure the TM surface displacements its shape is required to map on it the x, y and z micro-deformations. The surface contour is obtained by applying small shifts to the object illumination source position. A cw laser in stroboscopic mode and a CCD camera were used and synchronized to the acoustic excitation wave that produces a resonant vibration mode on the tympanic membrane surface. This research work reports on the 3D full field of view response of the TM to sound pressure, and has as its main goal the presentation of DHI as an alternative technique to study the TM real displacement behavior when subjected to sound waves, so it can be used as a diagnostic tool to prevent and treat TM diseases.

3D displacement measurements of vibrating objects with multi-pulse digital holography

An optoelectronic system based on multi-pulse digital holography is used to measure three different displacement-vector components of a vibrating cylindrical object. Four pulses from a Q-switched ruby laser are used to record image plane holograms which are later digitally reconstructed on three CCD cameras. Three different illumination directions are used to obtain the resultant three-dimensional (3D) object deformation from the vectorial addition of three sensitivity displacement vectors. In order to complete the 3D integral study of the object deformation its cylindrical shape is calculated. The shape and 3D vectorial are combined and graphically presented. Thus, this paper describes the integration of a novel methodology for 3D deformation evaluation of vibrating objects.

Digital holographic interferometer using simultaneously three lasers and a single monochrome sensor for 3D displacement measurements.

The use of digital holographic interferometry for 3D measurements using simultaneously three illumination directions was demonstrated by Saucedo et al. (Optics Express 14(4) 2006). The technique records two consecutive images where each one contains three holograms in it, e.g., one before the deformation and one after the deformation. A short coherence length laser must be used to obtain the simultaneous 3D information from the same laser source. In this manuscript we present an extension of this technique now illuminating simultaneously with three different lasers at 458, 532 and 633 nm, and using only one high resolution monochrome CMOS sensor. This new configuration gives the opportunity to use long coherence length lasers allowing the measurement of large object areas. A series of digital holographic interferograms are recorded and the information corresponding to each laser is isolated in the Fourier spectral domain where the corresponding phase difference is calculated. Experimental results render the orthogonal displacement components u, v and w during a simple load deformation.

Modal vibration analysis of a metal plate by using a laser vibrometer and the POD method

The proper orthogonal decomposition (POD), also known as Karhunen–Loeve expansion, is applied to the modal vibration analysis of a metal plate. The metal plate was subject to vibrations with an electrodynamical shaker in a range of frequencies from 100 to 5000 Hz. The data were obtained from the measurements with a laser vibrometer. The plate vibration measurements were used to calculate the eigenfunctions and the eigenvalues. It was found that a large fraction of the total energy of the vibrations is contained within the first four POD modes. The essential features of the vibrations are thus described by only the first four eigenfunctions.

Particle positioning from CCD images: experiments and comparison with the generalized Lorenz-Mie theory

This paper describes the experimental imaging of a spherical particle diffraction pattern obtained in back, forward and side scattering configurations, using illumination from three different beam shapes. The experimental problems encountered for each of the viewing configurations and the theoretical analysis of the diffraction pattern of the particle on its image plane using the generalized Lorenz-Mie theory are discussed. The images obtained are quantitatively compared with calculated results and implications for particle position estimation are discussed.

Piezoelectric-modulated optical fibre Bragg grating high-voltage sensor

A high-voltage sensor was developed by driving optical fibre Bragg gratings, mechanically fixed along the radial direction, with a conventional piezoelectric disc. A wavelength shift modulation is obtained as a result of the converse piezoelectric effect. The measured output signal is linear. The voltage upper limit depends on the type and thickness of the piezoceramic. A sensor built with a disc of piezoelectric PZT-4 type, 6.33 mm thick, has a dynamic range of 6.33 kVrms, a sensitivity of ~0.108 mVp-p kV-1rms, and a resolution of ~0.15 kVrms, at 60 Hz. Changing the piezoelectric dimensions may enhance the sensitivity and resolution of the high-voltage sensor.

Holographic otoscope for nanodisplacement measurements of surfaces under dynamic excitation.

We describe a novel holographic otoscope system for measuring nanodisplacements 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 the 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. SCANNING 33: 342-352, 2011.

The case of a spherical wave front for the generalized Lorenz-Mie theory including a comparison to experimental data

Abstract Scattering light from a spherical particle located on-axis to an electromagnetic spherical wave is numerically predicted using the generalized Lorenz–Mie theory (GLMT). The model is compared to the classical Lorenz–Mie theory, plane wave case, and to experimental in-line Fraunhofer holograms of spherical particles, showing good agreement. Fundamental questions germane to velocimetry applications and seeding particle positioning are discussed.

Analysis of the spectral characteristics of piezoelectrically driven dual and triple-period optical fibre Bragg gratings

Abstract A report on the analysis of the spectral characteristics obtained from uniform optical fibre Bragg gratings driven by piezoelectric ceramics is given for both dual and triple-period fibre gratings. Experimental results show that in principle the reflection spectrum of the variable dual-period fibre grating has an adjustable transmission bandpass. It is also demonstrated how the bandwidth of a variable triple-period OFBG may be piezoelectrically adjusted from ∼0.21 nm to ∼0.8 nm. Calculated spectral characteristics are in good agreement with measured ones.

Measurement of Young's modulus in an elastic material using 3D digital holographic interferometry.

Digital holographic interferometry using three different illumination directions is applied to quantify in full field of view the deformation of an elastic membrane under a given vibration frequency. The technique allows the separation of the object microdisplacements components in the x, y, and z directions, and the resulting data is used to find the membrane Youngs modulus. The latter was compared with the result obtained using the theory of thin plates for a clamped circular membrane under a uniformly distributed load, reaching a 95% agreement. Validation of the results between these methods shows the reliability of DHI to measure the mechanical properties of an elastic material.