M. Pilar Arroyo

Recent Developments of PIV towards 3D Measurements

This chapter reviews the different techniques that have been proposed in the last few years for turning PIV into a 3D velocimetry technique. Any technique capable of simultaneously measuring more than one plane is included. In expanding normal-viewing PIV depth increases from dual-plane PIV, multiple-plane PIV in its version of digital image plane holography to adjustable-depth volume PIV methods like defocus-evaluating PIV, tomographic PIV, and off-axis holography. Other volume holographic setups utilize reusable real-time recording material (polarization multiplexing with bacteriorhodopsin), explore digital in-line holography and promise extensions to even deeper volumes (light-in-flight holography). The principles, the present state-of-the-art and some ideas on future developments are presented.

Shifted knife-edge aperture digital in-line holography for fluid velocimetry

We describe a digital holography technique that, with the simplicity of an in-line configuration, produces holograms where the real and virtual images are completely separated, as in an off-axis configuration. An in-line setup, in which the object is imaged near the sensor, is modified by placing a shifted knife-edge aperture that blocks half the frequency spectrum at the focal plane of the imaging lens. This simple modification of the in-line holographic configuration allows discriminating the virtual and real images. As a fluid velocimetry technique, the use of this aperture removes the minimum defocusing distance requisite and reduces the out-of-plane velocity measurement errors of classical in-line holography. Results with different test objects are shown.

Parallel resolution of the 3D Helmholtz equation based on multi‐graphics processing unit clusters

The resolution of the 3D Helmholtz equation is required in the development of models related to a wide range of scientific and technological applications. For solving this equation in complex arithmetic, the biconjugate gradient (BCG) method is one of the most relevant solvers. However, this iterative method has a high computational cost because of the large sparse matrix and the vector operations involved. In this paper, a specific BCG method, adapted for the regularities of the Helmholtz equation is presented. This BCG is based on the implementation of a novel format (named ‘Regular Format’) that allows the storage of the large sparse matrix involved in the sparse matrix vector product in a compact form. The contribution of this work is twofold: (1) decreasing the memory requirements of the 3D Helmholtz equation using the ‘Regular Format’ and (2) speeding up the resolution of the equation using high performance computing resources. A hybrid Message Passing Interface (MPI)‐graphics processing unit CUDA GPU parallelization that is capable of solving complex problems in short time has carried out (Fast‐Helmholtz). Fast‐Helmholtz combines optimizations at Message Passing Interface and GPU levels to reduce communications costs and to improve the exploitation of GPU architecture. This strategy makes it possible to extend the dimension of the Helmholtz problem to be solved, thanks to the relevant reduction of memory requirements and runtime. Copyright

Endoscopic digital holography for measuring flows in opaque vessels

In this work a new application of digital holography for the study of cardio vascular diseases is proposed. The simultaneous measurement of the blood flow velocity and the vein wall deformation can be obtained by combining digital holography and endoscopy. Endoscopes are used for the illumination and recording of digital holograms inside a vein model. Two different endoscopes have been used in different vein models in order to test the technique performance. Preliminary results of flow velocity and wall deformation are presented.

Dual holographic interferometry for measuring the three velocity components in a fluid plane

A technique that allows one to measure simultaneously the three velocity components in a fluid plane is presented. One obtains the quantitative information from only one holographic recording by combining two different reconstruction processes. As both processes use an interferometric comparison of two waves, we refer to this technique as dual holographic interferometry. The far-field fringe pattern that is obtained when reconstruction is made with an expanded laser beam allows one to determine the in-plane velocity components. The image-field fringe pattern that is obtained when a pointwise laser beam is used for reconstruction contains information about an out-of-plane velocity component. As the two reconstruction processes have different sensitivities, two different ways to combine them are proposed. The system has been demonstrated in a fluidlike solid object and in a convective flow.

Application of digital speckle interferometry to visualize surface changes in metallic samples immersed in Cu(NO3)2 solutions

Abstract. Digital speckle pattern interferometry (DSPI) has been applied to analyze surface corrosion processes in a metallic sample immersed in a 0.1 M Cu(NO3)2 solution. The corrosion process induces changes in the surface and in the solution refractive index. A detailed analysis of the DSPI measurements has been performed to obtain a two-dimensional visualization of the surface changes and an evaluation of the refractive index changes of the solution. The possibilities of DSPI for measuring surface changes in these conditions have been analyzed.

PIV and digital holography for measuring blood flows and vessel wall dynamics

In this work endoscopy has been combined with high speed PIV and holographic interferometry for flow velocity and wall deformation measurement of different vessels. Endoscopes have been used for illumination and/or recording of PIV images and digital holograms. High speed PIV has been applied to evaluate the influence of an antithrombotic filter in a vena cava model flow. Qualitative wall deformation has been obtained using digital holography in a vein model and in a real sheep aorta.

Force plate for measuring small animal forces by digital speckle pattern interferometry

This paper presents a force plate specially designed for measuring ground reaction forces in small animals. Digital Speckle Pattern Interferometry (DSPI) is used to measure the plate deformation produced by the animal. Elasticity theory is used to obtain force magnitude and application position from the vertical displacement field measured with DSPI. The force plate has been tested with static weights of 5g and 10g at various locations on the plate. Some experiments with 20g body weight transgenic mice are also reported.

Multiplexed two in-line holographic recordings for flow characterization in a flexible vessel

The simultaneous presence of the real and virtual images in the hologram reconstruction is inherent in the in-line holography. This drawback can be overcome with a shifted knife-edge aperture at the focal plane of the imaging lens. The shifted aperture DIH produces holograms where the real and virtual images are completely separated. In this paper we propose a modification of the shifted aperture DIH that allows recording two holograms simultaneously using one camera, while retaining the simplicity of the in-line configuration and the advantage of the shifted-aperture strategy. As in typical stereoscopy, the advantage of this configuration is limited by the angle between the two illuminating beams, and therefore the aperture size. Some improvement on the out-of-plane resolution can be expected from a combined analysis of the multiplexed holograms. In order to compare this technique with other in-line holographic configurations, several experiments have been performed to study the spatial resolution along the optical axis. The capabilities of the different techniques for characterizing the flow in a flexible and transparent model of a carotid bifurcation are also investigated.

Simultaneous shape and deformation measurements in a blood vessel model by two wavelength interferometry

Holographic techniques have been used to measure the shape and the radial deformation of a blood vessel model and a real sheep aorta. Measurements are obtained from several holograms recorded for different object states. For each object state, two holograms with two different wavelengths are multiplexed in the same digital recording. Thus both holograms are simultaneously recorded but the information from each of them is separately obtained. The shape analysis gives a wrapped phase map whose fringes are related to a synthetic wavelength. After a filtering and unwrapping process, the 3D shape can be obtained. The shape data for each line are fitted to a circumference in order to determine the local vessel radius and center. The deformation analysis also results in a wrapped phase map, but the fringes are related to the laser wavelength used in the corresponding hologram. After the filtering and unwrapping process, a 2D map of the deformation in an out-of-plane direction is reconstructed. The radial deformation is then calculated by using the shape information.