Nobuyuki Masuda

Special-purpose computer for holography HORN-3 with PLD technology

Abstract We have designed and built a special-purpose computer for holography, HORN-3 (HOlographic ReconstructioN) using PLD (Programmable Logic Device) technology. We could integrate a pipeline to calculate hologram into one PLD chip, so that we can readily parallelize the system. By mounting two of the PLD chips on a PCI (Peripheral Component Interconnect) universal board, HORN-3 calculates light intensity at high speed of about 1.2 G flops. The cost of HORN-3 board is 200,000 Japanese yen (1600 US dollar). We obtained 1024× 768 grids hologram from a virtual 3D-image composed of 2500 points in about 60 sec with the HORN-3 system.

Effects of Bjerknes Forces on Gas-Filled Microbubble Trapping by Ultrasonic Waves.

When gas-filled microbubbles flow into an ultrasonic wavefield, the microbubbles interact with the ultrasonic waves and aggregate into large masses of bubbles. Those bubbles are trapped against the surrounding liquid flow by ultrasonic waves. In this paper, the microbubble trapping by an ultrasonic wavefield are discussed both from theoretical and experimental viewpoints. Both, the microbubble aggregation by ultrasonic-wave secondary Bjerknes force and the microbubble trapping by ultrasonic-wave primary Bjerknes force are considered. The dynamics of microbubbles inside an ultrasonic wavefield are observed using two different types of gas-filled microbubbles with corresponding mean diameters of 20 µm and 1.3 µm.

Trapping of Micrometer Size Bubbles by Ultrasonic Waves

An ultrasonic trapping method of small objects is applied to micrometer size bubbles. The experiments are carried out using an ultrasonic contrast agent of mean diameter 1.3 µm. An ultrasonic focused wave of opposite phase with frequency 5 MHz is applied to produce sequential traps for the microbubble flow. It is found that the microbubbles aggregate forming large masses of bubbles which are trapped inside the ultrasonic wave field. The effects of viscosity of the surrounding liquid are also examined.

Characterization of secondary ultrasonic waves radiated from bubbles based on small-bubble trapping pattern analysis

When a microbubble oscillates under an ultrasonic wave, the bubble radiates a secondary ultrasonic wave around it. This wave produces the secondary Bjerknes force between the neighboring bubbles and it assists in the aggregation of bubbles to make bubble clouds if the phases of the vibrations are the same. In this paper, a novel technique to characterize the secondary ultrasonic wave radiated from a bubble is proposed. This method is based on the observation of the interference fringe pattern which is produced by small bubbles trapped around the bubble of interest. A method to estimate the frequency, phase and amplitude of the secondary ultrasonic wave is discussed. Experiments are carried out for bubbles produced by an ultrasonic wave contrast agent. The results show that aggregated bubbles of a few tens of micrometers radiate approximately 7th- to 8th-order harmonic waves at 200 kPa sound pressure.

Effects of Red Blood Cells on Ultrasonic Wave Microbubble Trapping

One of the problems in microbubble trapping by ultrasonic waves when applied to in vivo experiments is the existence of red blood cells (RBCs). It is expected that the amount of microbubbles which are trapped by acoustic radiation forces decrease because the RBCs in the liquid act as obstacles when the bubbles produce the bubble clouds. In this study, the effects of RBCs on microbubble trapping are examined experimentally. The results for different RBCs concentrations are shown. The dependency of the ultrasonic wave frequency on ultrasonic wave microbubble trapping is also presented.

Autoencoder-based holographic image restoration

We propose a holographic image restoration method using an autoencoder, which is an artificial neural network. Because holographic reconstructed images are often contaminated by direct light, conjugate light, and speckle noise, the discrimination of reconstructed images may be difficult. In this paper, we demonstrate the restoration of reconstructed images from holograms that record page data in holographic memory and quick response codes by using the proposed method.

In Situ Characterization of Microbubble Oscillation by Bubble Aggregation Pattern Analysis

When micro bubbles flow into an ultrasonic wave field, the microbubbles often produce bubble aggregation. The aggregated bubbles create an inherent aggregate pattern depending on the bubbles, ultrasonic wave frequency and sound pressure. To evaluate the microbubble aggregation, which is produced by ultrasonic waves, the Bjerknes force which is produced by aggregated bubbles is derived. We assume that 2n+1 bubbles are aligned with a separation shorter than the wavelength and that they oscillate independently producing secondary ultrasonic waves around the bubbles. The relative phase between the secondary wave radiation of the aggregated bubbles and the radial oscillation of a single neighboring bubble is an important parameter for characterizing the bubble aggregation. Based on this discussion, a novel method of measuring the relative phase between the secondary wave radiation and the radial oscillation is proposed. This method is applied to micro bubbles with polyvinyl chloride shells.

Acceleration of computer-generated hologram by Greatly Reduced Array of Processor Element with Data Reduction

Abstract. We have implemented a computer-generated hologram (CGH) calculation on Greatly Reduced Array of Processor Element with Data Reduction (GRAPE-DR) processors. The cost of CGH calculation is enormous, but CGH calculation is well suited to parallel computation. The GRAPE-DR is a multicore processor that has 512 processor elements. The GRAPE-DR supports a double-precision floating-point operation and can perform CGH calculation with high accuracy. The calculation speed of the GRAPE-DR system is seven times faster than that of a personal computer with an Intel Core i7-950 processor.

Digital holographic high-speed 3D imaging for the vibrometry of fast-occurring phenomena

Digital holography allows production of high-speed three-dimensional images at rates over 100,000 frames per second; however, simultaneously obtaining suitable performance and levels of accuracy using digital holography is difficult. This problem prevents high-speed three-dimensional imaging from being used for vibrometry. In this paper, we propose and test a digital holography method that can produce vibration measurements. The method is based on single-shot phase-shifting interferometry. Herein, we imaged the surface of a loudspeaker diaphragm and measured its displacement due to the vibrations produced by a frequency sweep signal. We then analyzed the frequency of the experimental data and confirmed that the frequency spectra inferred from the reconstructed images agreed well with the spectra produced by the sound recorded by a microphone. This method can be used for measuring vibrations with three-dimensional imaging for loudspeakers, microelectromechanical systems, surface acoustic wave filters, and biological tissues and organs.

Speeding up image quality improvement in random phase-free holograms using ringing artifact characteristics

A holographic projector utilizes holography techniques. However, there are several barriers to realizing holographic projections. One is deterioration of hologram image quality caused by speckle noise and ringing artifacts. The combination of the random phase-free method and the Gerchberg-Saxton (GS) algorithm has improved the image quality of holograms. However, the GS algorithm requires significant computation time. We propose faster methods for image quality improvement of random phase-free holograms using the characteristics of ringing artifacts.