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Papers by Dan Borza
Optics and Lasers in Engineering, 2006
High-resolution time-averaged speckle interferometry and quasi-binary electronic speckle interfer... more High-resolution time-averaged speckle interferometry and quasi-binary electronic speckle interferometry are two methods used in mechanical vibration measurement. The first method is used to increase the spatial resolution of time-average patterns. Detecting with subpixel resolution the minima of the Bessel-type fringes becomes thus possible. The second method is used to obtain a high contrast of the fringe pattern and a measurement range doubled with respect to that of traditional time-average holography. Quasi-binary fringes are loci of constant sign of the Bessel function modulating the object image. The two methods are closely related and based on a common principle. The objectives of the paper are to extend these methods to Fresnel digital holography and to propose a new data processing algorithm, allowing using the time-average hologram for calculating the unwrapped vibration-related phase map. The phase is calculated by local inversion of the Bessel function. Quantitative data processing is possible for both undersampled and oversampled fringe patterns. Only the basic holographic equipment is used, without any stroboscopic or modulating devices. r
Proceedings of Spie the International Society For Optical Engineering, 2008
Piezoelectric actuators are widely used active devices able to perform static and dynamic displac... more Piezoelectric actuators are widely used active devices able to perform static and dynamic displacements in the micrometer and submicrometer range. Both the magnitudes and the directions of these displacements and forces applied to devices acted upon must be strictly controlled. Different actuators have been studied by using speckle interferometry. The results of the study show that some actuator designs lead to unexpected shapes of the deformed actuator. As a consequence, these actuators have an unsuitable behaviour, which may consist in uncontrolled directions of the forces applied, in unconveniant deformations of the structures acted upon, or in stress concentrations which are dangereous for the actuator itself. Several holographic and shearographic speckle interferometry techniques are used throughout the study, so as to allow separate measurement of orthogonal components of the displacement maps and an estimation of their spatial derivatives. Results of other experimental investigations show deformations which are convenient and may be used in the development of sensors and actuators.
Abstract Holography, along with other coherent optical techniques, has already been proved to be ... more Abstract Holography, along with other coherent optical techniques, has already been proved to be an effective technique in non-destructive testing of composites. One of the difficulties of holographic non-destructive testing is finding the stressing technique able to produce ...
The paper describes a technique for measuring the whole field of vibration amplitudes of mechanic... more The paper describes a technique for measuring the whole field of vibration amplitudes of mechanical components observed with real-time holographic interferometry. A real-time static fringe pattern is imposed by a translation of the hologram and forms a set of lining-up fringes. Analysis of holographic observation of vibrating objects in the presence of these lining-up fringes yields a simple relation for determining vibration amplitudes. The resulting fringe spacing is that of time-average holography, so that the sensitivity of the real-time method is increased by a factor of 2 by imposing the lining-up fringes. The method may be applied without the use of real-time plate holders or stroboscopic equipment.
Optics and Lasers in Engineering, 2006
High-resolution time-averaged speckle interferometry and quasi-binary electronic speckle interfer... more High-resolution time-averaged speckle interferometry and quasi-binary electronic speckle interferometry are two methods used in mechanical vibration measurement. The first method is used to increase the spatial resolution of time-average patterns. Detecting with subpixel resolution the minima of the Bessel-type fringes becomes thus possible. The second method is used to obtain a high contrast of the fringe pattern and a measurement range doubled with respect to that of traditional time-average holography. Quasi-binary fringes are loci of constant sign of the Bessel function modulating the object image. The two methods are closely related and based on a common principle. The objectives of the paper are to extend these methods to Fresnel digital holography and to propose a new data processing algorithm, allowing using the time-average hologram for calculating the unwrapped vibration-related phase map. The phase is calculated by local inversion of the Bessel function. Quantitative data processing is possible for both undersampled and oversampled fringe patterns. Only the basic holographic equipment is used, without any stroboscopic or modulating devices. r
Proceedings of Spie the International Society For Optical Engineering, 2008
Piezoelectric actuators are widely used active devices able to perform static and dynamic displac... more Piezoelectric actuators are widely used active devices able to perform static and dynamic displacements in the micrometer and submicrometer range. Both the magnitudes and the directions of these displacements and forces applied to devices acted upon must be strictly controlled. Different actuators have been studied by using speckle interferometry. The results of the study show that some actuator designs lead to unexpected shapes of the deformed actuator. As a consequence, these actuators have an unsuitable behaviour, which may consist in uncontrolled directions of the forces applied, in unconveniant deformations of the structures acted upon, or in stress concentrations which are dangereous for the actuator itself. Several holographic and shearographic speckle interferometry techniques are used throughout the study, so as to allow separate measurement of orthogonal components of the displacement maps and an estimation of their spatial derivatives. Results of other experimental investigations show deformations which are convenient and may be used in the development of sensors and actuators.
Abstract Holography, along with other coherent optical techniques, has already been proved to be ... more Abstract Holography, along with other coherent optical techniques, has already been proved to be an effective technique in non-destructive testing of composites. One of the difficulties of holographic non-destructive testing is finding the stressing technique able to produce ...
The paper describes a technique for measuring the whole field of vibration amplitudes of mechanic... more The paper describes a technique for measuring the whole field of vibration amplitudes of mechanical components observed with real-time holographic interferometry. A real-time static fringe pattern is imposed by a translation of the hologram and forms a set of lining-up fringes. Analysis of holographic observation of vibrating objects in the presence of these lining-up fringes yields a simple relation for determining vibration amplitudes. The resulting fringe spacing is that of time-average holography, so that the sensitivity of the real-time method is increased by a factor of 2 by imposing the lining-up fringes. The method may be applied without the use of real-time plate holders or stroboscopic equipment.