In this study, in practice based on at-sea experiment it is confirmed that bi-directional communication by time reversal can be achieved and it is proved that time reversal communication is superior to the conventional method.

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The method to derive attenuation coefficient of thin materials from group delay spectrum was proposed and applied to the interpretation of the abnormal behavior of the group delay spectrum of a real thin material. As a result, the possibility that the absorption of wave energy is not negligible in thin materials was also shown.

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In order to clarify the process of the mechanical effect caused by micro-bubbles, detailed behaviors of a single bubble adhered to solid surface were optically observed using an ultra high-speed camera. The changing pressure from the bubble to the surface was simultaneously observed by a thin piezoelectric transducer. At the time of collpse, we confirmed the radiation of a micro-jet from the bubble, which was followed by a counter-jet. An impulsive positive pressure to the surface was also observed synchronously with the collapse motion. This pressure seems to come from the jet flow or the violent vibration of the bubble.

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The automatic resonance frequency control was tried by using the GIC circuit. Moreover, the sensitivity decrease correction was examined by the transducer that controlled the resonance frequency by using the GIC circuit.

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Highly c-axis oriented LiNbO_3 (006) thin films with thickness of 2.5 μm have been successfully grown on SiO_2/Si substrates with a ZnO buffer layer by XeCl excimer pulsed laser deposition (PLD) technique. The full width at half maximum intensity (FWHM) of LiNbO_3 (006) peak of the sample fabricated under the optimum deposition parameters is only 0.18°. The center frequency and phase velocity of the LiNbO_3/ZnO/SiO_2/Si substrate with line width of 4μm is 188 MHz and 3010 m/s, respectively.

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The anisotropy and distribution of fast wave speeds in bovine cancellous bone were investigated. The results show bone anisotropy strongly affects the sound speeds, which seems to cause various difficulties in vivo assessment. In addition, fast wave speeds were strongly related to the averaged trabecular length.

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We proposed CBCE method as a new imaging method which is effective to obtain the physiological information in detail such as microvascular blood flow. This study experimentally confirmed the sum frequency components in the ultrasonic waves scattered at the microbubbles in the region of the crossed two beams formed by ultrasonic waves of 2 and 3 MHz.

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