This paper details high time-resolution flow field measurements in a micro-pipe made by a micro digital holographic particle tracking velocimetry (micro-DHPTV) method. The system consists of an objective lens, a high-speed camera and a single high-frequency double pulsed laser. The volume of the system is 409.6 µm × 92 µm × 92 µm. It is illuminated by a laser beam with a pulse length of 58 ns, a resolution time of 100 µs and a repetition rate of 1 kHz. 104 velocity vectors could be obtained instantaneously in the micro-pipe. Particle positions in the three-dimensional field are reconstructed by a computer-generated hologram. The time evolution of a three-dimensional water flow in a micro-pipe of 92 µm inner diameter is obtained successfully using the micro-DHPTV system. The error of reconstruction in the z-direction is evaluated by analysing the traverse of particles on a glass plate and obtaining the velocity error in the z-direction by uncertainty analysis.

We have developed a parallel algorithm for microdigital-holographic particle-tracking velocimetry. The algorithm is used in (1) numerical reconstruction of a particle image computer using a digital hologram, and (2) searching for particles. The numerical reconstruction from the digital hologram makes use of the Fresnel diffraction equation and the FFT (fast Fourier transform), whereas the particle search algorithm looks for local maximum graduation in a reconstruction field represented by a 3D matrix. To achieve high performance computing for both calculations (reconstruction and particle search), two memory partitions are allocated to the 3D matrix. In this matrix, the reconstruction part consists of horizontally placed 2D memory partitions on the x-y plane for the FFT, whereas, the particle search part consists of vertically placed 2D memory partitions set along the z axes. Consequently, the scalability can be obtained for the proportion of processor elements, where the benchmarks are carried out for parallel computation by a SGI Altix machine.

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We have designed a special purpose computer system for digital holographic particle tracking velocimetry (DHPTV). We present the pipeline for calculating the intensity of an object from a hologram by fast Fourier transform in an FPGA chip. This system uses four FPGA chips and can make 100 reconstructed images from a 256x256-grid hologram in 266 msec. It is expected that this system will improve the efficiency of analysis in DHPTV.

Digital holographic particle tracking velocimetry (PTV) is developed by single high-speed camera and single double pulsed laser with high frequency pulses. This system can directly capture 1000 hologram fringe images for 1 second through a camera computer memory. The 3-D particle location is made of the reconstruction by using a computer hologram algorithm in a personal computer. This system can successfully be applied to instantaneous 3-D velocity measurement in the water flow with a square obstacle, and can obtain an average of 300 instantaneous velocity vectors.Holographic particle image velocimetry has been adopted using photographic film. 1-3) This system has high quality flow information and recording of an instantaneous 3-D velocity field illuminated by one beam line. These characteristics are a big advantage over other particle image velocimetry (PIV) method. However the technique takes up most of the reconstruction process time, and it is difficult to capture the time evolution of a particle image by a single frame recording of instantaneous particles dispersed in a flow field. On the other hand, digital holographic techniques easily capture the time evolution of particles by digital camera. But they are only used for in-line holograms 4,5) due to the limitation of digital camera resolutions, and require high-speed computer performance to reconstruct particle location by a computer hologram algorithm. Furthermore, the computational cost is increased if it is used for reconstruction of particles by a high-speed camera owing to the increase in the fringe image frame. However, the particle field of the high-speed reconstruction has recently been successful using the fast fourier transform (FFT) technique with Fresnel diffraction equation for the computer hologram calculation 4,5) However, the result by the FFT method 5) was only used for the evaluation of reconstruction of steady particles. Therefore, the digital holographic particle tracking velocimetry (PTV) system has not been used with the FFT algorithm. Moreover, we did not know that a digital holographic PTV system existed to measure with the time evolution of particles and the velocity vector. Therefore, we developed a complete digital holographic PTV system without photographic film, and the 3D velocity vectors in our system can be taken by one high speed digital camera. Furthermore, the 3D vectors obtained have time evolutions with the repetition time of 1 KHz; that is, high speed measurements in fluids can be obtained. The present system is applied to measure instantaneous 3-D velocity vectors by tracking tracer particles in a water flow field with a square. Figure 1 shows the optical setup. The optical system consists of a single high-speed camera, a single laser, one filter, one beam expander, and one mirror. Nd:YLF laser (Photonic Industries DS20-527, ¼ 527 nm) is used as a light source, which gives a pair of laser pulses at a repetition rate of 1 kHz. The hologram fringe images are captured through a high-resolution digital CCD camera (Visionr...