Three-dimensional Imaging Method Using Spherical Ultrasound Wave Generated by Laser Breakdown

1 Introduction

Ultrasounds imaging with ring array probe is effective in several fields such as medical diagnostic or industry etc [1]. Under the condition that optical measurement is impossible, for instance, inside of blood vessel or in muddy water at industrial plant, the ultrasound imaging is effective means. However, ultrasound wave generated by current transducer has certain extent of directivity. Hence, wide measurement area cannot be obtained. Therefore, to obtain wide measuring area and clear reconstructed image, the purpose of this research is designing the three-dimensional imaging method using perfectly spherical ultrasound wave which is generated by Laser breakdown.

2 Laser Breakdown

Laser breakdown is the phenomenon that laser causes plasma with being condensed by some optical lenses. This phenomenon generates light and acoustic wave. Generated wave contains both audible frequency and inaudible frequency, and the wave is perfectly spherical. Figure1 shows appearance of laser breakdown generating equipment, and figure2 is a snapshot of laser breakdown.

Figure1 Figure2

3 Experiment

In this experiment I try to reconstruct a image of hexagonal wrench. (Figure3) And I

used a needle hydrophrone to measure the echo. Reconstructing three-dimensional image by Synthetic aperture Beamforming, it’s necessary to measure several points. So in this experiment I established 5x5 points of measuring points. (Figure4)

Figure3

Figure4

4 Result

4.1 Result of Measurement

Figure5 shows a waveform of the echo from one of measurement points. There are three peaks in the graph. The First biggest peak is direct wave from sound source. The second peak is the echo from the wrench, and the third peak is echo from walls of water bath.

Figure5

4.2 Reconstructed Image

Reconstructed image of hexagonal wrench is shown on figure6 and figure7. Figure6 correspond to figure3 and figure7 correspond to figure4.

Figure6 Figure7

5 Conclusion

In this experiment, I can’t show clear reconstructed images. There is difficulty of measuring the breakdown point in the measuring system and keeping the sensor exact location. Another problem is difficulty of distinction between the echo from target and the echo from another object such as wall of water bath. This problem is conflict of the merit and demerit using perfectly spherical wave.

6 Future Work

l Distinction the echo from target and echo from walls

l Improvement of Reconstructing algorithm

Reference

[1] A. Matani, M. Nambu, A. Kondo. O. Oshiro and K. Chihara: A Method for Measurement with High Resoluton Using Ultrasound Spherical Waves: Jpn.J.Appl. Phys.Vol36,pp.3255-3259(1997)