Shigeru Murata

Potential of digital holography in particle measurement

This paper describes the potential power of digital holography in particle measurement and its expected development in the near future. In digital holography, image reconstruction is carried out numerically on a computer using observed hologram patterns and some quantitative information can be derived from the reconstructed images. In this paper, the basic concept and procedure of digital in-line holography are shown mainly for particle depth measurement and the performance test results obtained in numerical simulations and experiments are demonstrated to examine the potential of the present method.

Spatial Phase-Shifting Digital Holography for Three-Dimensional Particle Tracking Velocimetry

This paper presents a holographic technique for three-dimensional particle tracking. The complex amplitude on an image sensor is measured with two pairs of spatially phase-shifted digital holograms captured in a short time interval using a phase-shifting technique. Pairs of digital holograms are used to track small tracer particles in three-dimensional space and the phase-adjusted complex amplitude is employed in numerical image reconstruction to accurately detect the particles. The performance of the method is evaluated by numerical simulation. In order to demonstrate the feasibility of the method for real flow measurement, it is applied to the velocity measurement of tracer particles in a small water channel along which a high voltage is applied. The resulting components of the velocity vector in three-dimensional space are compared to those obtained using a conventional single-shot phase-shifting technique.

A Comparative Study of the PIV and LDV Measurements on a Self-induced Sloshing Flow

Particle Imaging Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) measurements on a self-induced sloshing flow in a rectangular tank had been conducted in the present study. The PIV measurement result was compared with LDV measurement result quantitatively in order to evaluate the accuracy level of the PIV measurement. The comparison results show that the PIV and LDV measurement results agree with each other well in general for both mean velocity and fluctuations of the velocity components. The average disagreement level of the mean velocity between PIV and LDV measurement results was found to be within 3% of the target velocity for the PIV system parameter selection. Bigger disagreements between the PIV and LDV measurement results were found to concentrate at high shear regions. The spatial resolution and temporal resolution differences of the PIV and LDV measurements and the limited frames of the PIV instantaneous results were suggested to be the main reasons for the disagreement.

Particle depth measurement based on depth-from-defocus

An optical and digital method has been developed for the detection of the depth of small particles distributed in 3D space and its performance has been examined in numerical simulations and experiments. The present method is based on depth-from-defocus in which the depth of particle is detected from the image blur of the particle. The results of numerical simulations show that low-pass filtering is effective for the reduction of error. In the experiments with a single 3CCD color camera, it is found that the RMS error of the present method is 1.81 mm for the depth range of 40 mm.

Phase retrieval method for digital holography with two cameras in particle measurement.

This paper presents a phase retrieval method for digital holography with two high-speed cameras in particle measurement. The conditions for recording two holograms are derived theoretically. We focus in particular on the distance between the two holograms. The relative misalignment of the two holograms is also evaluated by numerical simulations. Finally, we experimentally compared settling particles reconstructed by the presented method and the Gabor method.

Calibration along the depth direction in tomographic digital holography

This paper proposed the detection method for the depth position of a dot to calibrate along the depth direction of two cameras, which is performed with obtaining the reconstruction distances to match the reconstructed volumes at each camera. We determined the reconstruction distance of each camera by using the dot-array plate and the proposed detection method of a dot. The reconstruction distance is calculated as the position that the variance of the real and the imaginary part of dots becomes a minimum value. We investigate the effect of dot spacing in the dot-array plate by comparing the error between the calculated distance and the true distance in numerical simulation. In addition, the effect of this method is also experimentally confirmed.

Three-Dimensional Measurement of Interaction Between a Circular Cylinder and Surrounding Flow by Digital Holographic Particle Tracking Velocimetry

As an example of Flow-Induced Vibration (FIV), an interaction between a circular cylinder and a surrounding flow is measured by Digital Holographic Particle Tracking Velocimetry (DH PTV). Tracer particles having two different diameters are dispersed in a cylinder and pipe flow. The cylinder, containing dispersed tracer particles, is made of an acrylic transparent resin and is attached to an inner wall of the pipe. In order to suppress a difference in the refractive index between the cylinder and fluid, the acrylic pipe is filled with a refractive-index-matching liquid having the same refractive index as the cylinder (1.49). The holographic pattern of the tracer particles dispersed in both the cylinder and fluid is measured by digital in-line holography. The three-dimensional position of particles is detected by reconstructed holographic patterns at each time step. Three-dimensional velocity of a surrounding flow and three-dimensional vibration of the cylinder are derived by using a Self-Organizing Map (SOM). Vector fields for the vibrating cylinder and surrounding flow are individually identified from the difference in the particle size detected by digital holography.Copyright

Noninvasive evaluation system of fractured bone based on speckle interferometry

This paper presents a noninvasive evaluation system of fractured bone based on speckle interferometry using a modified evaluation index for higher performance, and the experiments are carried out to examine the feasibility in evaluating bone fracture healing and the influence of some system parameters on the performance. From experimental results, it is shown that the presence of fractured part of bone and the state of bone fracture healing are successfully estimated by observing fine speckle fringes on the object surface. The proposed evaluation index also can successfully express the difference between the cases with cut and without it. Since most system parameters are found not to affect the performance of the present technique, the present technique is expected to be applied to various patients that have considerable individual variability.

Stress Measurement of Cantilever Beam under Dynamic Load by Holographic Particle-Tracking Velocimetry

In this study, we observe the time-series of the stress field of a cantilever beam subjected to a dynamic load by using holographic Particle-Tracking Velocimetry (PTV). The beam (elastic modulus 2822 MPa, 3.95×20.45×2.99 mm3) is composed of a transparent acrylic resin containing dispersed tracer particles (average diameter: 60 µm).　The cantilever beam is subjected to a dynamic load (0 N to 10 N over 10 sec) at the tip. We compare the experimental and analytical values of the deflection at t = 10 sec. The RMS error is 24.5 µm with respect to the maximum deflection value of 657 µm.

Calibration of particle position on digital holography using transparent resin block with dispersed particles

This paper describes the use of a Calibration Block (CB) for evaluating the accuracy of digital holography in particle position measurement. CB made of acrylic has three layers and the gap between the layers is filled with transparent resin. The refractive index of the resin and the layers is almost the same (1.49). Fin Block (FB), which is not filled with resin, is introduced in order to evaluate effects of the resin. The fringe edges of several holographic patterns are observed by using three kinds of CB and FB. Each layer is coated with spherical particles (diameter: 16.36 ± 0.42 μ m). The influence of multiple scattering on the detected depth of the particles is evaluated by changing the number density of particles. Three kinds of CB and FB are prepared (averaged particle density in the holographic pattern; 83.2, 166.5 and 249.7). The fringe edges of the holographic patterns generated in CB and FB are observed, respectively. It is found that the fringe edges of CB are clearer than FB. Also, Multiple scattering acts as a source of background noise with high spatial frequency, which has almost the same frequency as that of the particle diffraction on the fringe patterns, and reduces the effective signal-to-noise ratio of the holographic pattern. CB can be used to evaluate the influence of multiple scattering on the detected particle depth.