G. N. de Oliveira

Dynamic moiré patterns for profilometry applications

In the present work is proposed that dynamic moire-like fringe patterns produced by photorefraction, with low spatial frequencies, could be used for profile determination of small objects. The Fourier transform profilometry technique is applied in the projected moire fringe pattern onto an object surface. Basically, the Fourier transform of the projected fringes is obtained. After that, a phase map is generated. Then, the optical profile of object is obtained using phase unwrapping. So, the entire process can be indicated to measure, with good accuracy degree, profile of small objects in sub-micrometer scale in optical mechanical systems.

Shear strain determination of the polymer polydimethysiloxane (PMDS) using digital image correlation in different temperatures

In the present work a digital image correlation (DIC) method is used in order to analyze the adhesive shear modulus of poly-dimethylsiloxane (PDMS) submitted to different loads and temperatures. This is an optical-numerical full-field surface displacement measurement method. It is based on a comparison between two images of a specimen coated by a random speckled pattern in the undeformed and in the deformed states. A single lap joint testing is performed. This is a standard test specimen for characterizing adhesive properties and it is considered the simplest form of adhesive joints. For the single lap joint specimen, steel adherends are bonded using a flexible rubber elastic polymer (PDMS), which is a commercially available silicone elastic rubber

Photorefractive holographic moiré-like patterns for secure numerical code generation

In this Letter, low-frequency photorefractive holographic moiré fringe patterns are proposed as secure numerical code generators that could be useful for storage or data transmission. These dynamic moiré patterns are holographically obtained by the superposition of two or more sinusoidal gratings with slightly different pitches. The Bi(12)TiO(20) photorefractive crystal sample is used as holographic medium. An optical numerical base was defined with patterns representing the 0, 1 and -1 digits as bits. Then, the complete set of these optical bits is combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code is simple, robust and extremely secure, then could be used efficiently as standard numerical identification in robotic vision or eventually in storage or transmission of secure numerical data.

Digital holographic interferometry applied to mixed-mode fracture analysis

In the present work digital holographic interferograms obtained by digital Fourier transform holography are used to analyze fracture propagation. Digital holography is a non-contact optical technique that consists in recording digitally a hologram with a CCD sensor as holographic media. The image reconstruction of the object is obtained numerically. Holographic interferograms are obtained by superposition of two holograms of object, being the first one in its initial state and the second one after some modification produced in this object. Basically, the main purpose is to use interferograms for investigating mixed-mode I/II fracture. Tests on cracked specimen under combined loading are performed.

Dynamic moiré patterns and Michelson fringe patterns for profilometry: a results comparative analysis

In the present work we present a simple comparative analysis of the results in the optical Fourier transform profilometry which fringe projection is produced by two different methods, dynamic moire-like patterns and Michelson interferometer. First, the Fourier transform profilometry technique is applied in the projected moire fringe pattern onto an object surface. Then, this result is compared to the Michelson fringe pattern projection in the same method of profilometry that is applied using the same test object. We have conclude that dynamic moire-like fringe patterns could be used with some advantages, comparatively to the results obtained by the classical Michelson fringe patterns.

Photorefractive moiré-like patterns for the multifringe projection method in Fourier transform profilometry

In the present paper, the method of simultaneous moire-like fringe pattern projection for Fourier transform profilometry is described. The photorefractive holographic interferometric process produces controlled moire-like patterns with two or more different variation directions. Each low spatial frequency fringe pattern is experimentally obtained as a result of the superposition of two high spatial frequency sinusoidal gratings, with slightly different pitches, for each fringe variation direction. These dynamic moire-like patterns are induced due to an optical holographic beating of the sinusoidal induced gratings in the volume of the photorefractive Bi₁₂TiO₂₀ (BTO) crystal sample used as dynamic holographic medium. Two or more moire-like fringe patterns, with at least two different variation directions, simultaneously (or not), are projected onto the object surface. Thus, this is the 2D fringe projection stage of our proposed Fourier transform procedure to determine the profile of a simple object.

Digital holographic moiré pattern for optical numerical code generation

In the present paper low frequency moire fringe patterns are used as secure numerical code generator. These moire patterns are experimentally obtained by the superposition of two sinusoidal gratings with slightly different pitches. The Bi 12 TiO 20 photorefractive crystal sample is used as holographic medium An optical numerical base was defined with patterns representing 0,1 and -1 digits like bits. Then, the complete set of these optical bits are combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code could be used as standard numerical identification in robotic vision or in transmition of security numerical keys.

Photorefractive moiré like pattern as optical numerical code generator

In the present letter low frequency moiré fringe patterns are used as secure numerical code generator. These moiré patterns are experimentally obtained by the superposition of two sinusoidal gratings with slightly different pitches. The Bi12TiO20 photorefractive crystal sample is used as holographic medium An optical numerical base was defined with patterns representing 0,1 and -1 digits like bits. Then, the complete set of these optical bits are combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code could be used as standard numerical identification in robotic vision or in transmition of security numerical keys.In the present letter low frequency moire fringe patterns are used as secure numerical code generator. These moire patterns are experimentally obtained by the superposition of two sinusoidal gratings with slightly different pitches. The Bi12TiO20 photorefractive crystal sample is used as holographic medium An optical numerical base was defined with patterns representing 0,1 and -1 digits like bits. Then, the complete set of these optical bits are combined to form bytes, where a numerical sequence is represented. The results show that the proposed numerical code could be used as standard numerical identification in robotic vision or in transmition of security numerical keys.

Analysis of cantilever beam test using digital holography

In the present work an interferometric approach based on the implementation of a digital holography setup is discussed. It is used to determine interferograms of materials under small deformations. In order to do this, a fixed-free cantilever beam subjected to a concentrated force applied at the free end is taken into account. The experimental procedure to estimate displacements is carried out using digital Fourier transform holography (DFTH) technique. This is obtained making a very simple modification in the classical setup architecture of the DFTH setup. It is also demonstrated the easy and practical viability of the setup in an interferometric application for mechanical parameters determination.

Simple optical setup implementation for digital Fourier transform holography

In the present work a simple implementation of Digital Fourier Transform Holography (DFTH) setup is discussed. This is obtained making a very simple modification in the classical setup arquiteture of the Fourier Transform holography. It is also demonstrated the easy and practical viability of the setup in an interferometric application for mechanical parameters determination. The work is also proposed as an interesting advanced introductory training for graduated students in digital holography.