Simulatoins of time reversal communication considering current flow are executed. It is shown that the flow-induced effect can be compensated and communication can be achieved by the proposed method. Simulations with other various conditions will be carried out and at-sea experiments under current flow will be performed.

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The influence on the sound field of the consecutive IWs was examined. The sound field without IW and with IWs were compared, and the sound field having different intervals of IWs are compared respectively. As a result, the position between the position of sound field without IW and the internal wave fields is important in the sound field formation. Moreover, considering from the states of the phase, the shifting to the low-order mode by the refraction to the upper side and to the high-order mode by the refraction to the lower side became clear.

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High frequency communication devices including thin film surface acoustic wave (SAW) filter, film bulk acoustic resonator (FBAR), as well as microelectromechanical systems (MEMS) use piezoelectric thin films (PZT, LiNbO_3, AlN, ZnO) as actuating elements. However, sound velocity of polycrystalline piezoelectric films is sometimes different from that calculated using published single-crystal elastic constants. There is reason to believe that that was caused by grain boundaries. In this work, elastic constants of thin films were calculated by using a composite model. In addition, because complex elastic constants were introduced in the calculation, propagation loss was evaluated, and a good result was obtained.

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Aluminum oxide (Al_2O_3) films have been successfully deposited on ST-cut quartz substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al_2O_3 films to quartz substrates The Al_2O_3 thin films increase the surface acoustic wave (SAW) velocity sufficiently, and they can be used for improvement of the performance of the SAW devices. The effect of accelerating SAW by the Al_2O_3 thin films has been measured and discussed. The results show that SAW phase velocity in the Al_2O_3/quartz structure increases with inserting an Al_2O_3 film. It is observed that the 1.45μm thick Al_2O_3 film is able to speed up SAW by 3.28% at 271 MHz for Al_2O_3/quartz sample.

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A transition bandwidth between a transmission (Tx: 1850-1910MHz) and a receiving (Rx: 1930-1990MHz) of Personal Communication Services (PCS) handy phone in US is very narrow as 20MHz compared with other systems. Authors have already realized the 5.0×5.0×1.7 or 3.0×2.5×1.2mm^3 size SAW duplexer for US-PCS which has a good temperature coefficient of frequency (TCF) by using the SH wave on flattened-SiO_2/Cu-electrode/36〜48° YX-LiTaO_3 structure and Rayleigh wave on SiO_2/Cu-electrode/120〜128° YX-LiNbO_3 structure. Though the surface of above-mentioned structures is the flattened SiO_2, authors also studied the shape of the surface of the SiO_2. As a result, in addition to increase of reflection coefficient, the TCF and power durability have been improved by making convex portions on the surface of the SiO_2 over the IDT's gap.

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Radio frequency filters with a narrow band width.and high attenuations are required in recent years. One of the substrates with a suitable coupling factor and an excellent TCF for this filter is a ZnO film/Al electrode/quartz substrate. However, the reflection coefficient of this substrate has not reported, and both the RF SAW filter and the multiple mode resonator one using this substrate have not been reported. In this report, an RF narrow band SAW resonator filter composed of the ZnO/high density metal electrode/quartz structure was realized to obtain a suitable reflection coefficient, and it has minimum insertion loss of 2.08 dB, bandwidths of 3.9MHz (0.054%), and excellent TCF of 4.0ppm/℃.

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This paper discusses the application of Cu-grating/15°YX-LiNbO_3(15-LN)-substrate structure to the development of wideband Double-Mode SAW (DMS) filters. This structure seems suitable for the current purpose because of its distinctive features such as extremely large electromechanical coupling factor (circa 30%) and small attenuation with propagation. We applied the pitch modulation technique for the design of IDTs to arrange multiple resonances properly. This arrangement is essential for the realization of flat and wide passband. The result indicates relative bandwidth more than 12% and good out of band rejection are simultaneously achievable. A DMS filter was fabricated on Cu-grating/15-LN substrate. The measured result agreed well with the design, and the passband width of 11.9% and the minimum insertion loss of 1.7 dB were obtained at 900 MHz range.

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