DOI: 10.3179/jjmu. JJMU.R.59 ◇ STATE OF THE ART 超音波測定技術の進歩 ◇ チタン前面板裏面に水熱合成チタン酸ジルコン酸鉛を成膜した 耐音響キャビテーションハイドロホン 椎葉 倫久1 岡田 長也2 内田 武吉3 黒澤 実4 竹内 真一5 抄 録 近年，高強度の超音波を用いた様々な治療法や診断法が利用されている．しかし，強力な超音波を生体内に照射す るためには，生体への安全性の観点からも，また効率的な利用という観点からも正確な音場，音圧，音響強度の計 測が重要である．我々は，チタン製前面板（受音面）の裏面に水熱合成チタン酸ジルコン酸鉛（PZT）多結晶膜を 成膜し，音響キャビテーションの発生を伴う強力な超音波の音場で測定をしても壊れないように工夫した耐音響キャ ビテーションの堅牢型ハイドロホンの開発を行ってきた．しかし，低固有音響インピーダンス背板を用いた従来の 堅牢型ハイドロホンでは受波感度が高周波領域ほど低下してしまい，実際の超音波波形を十分な忠実度で表現でき ないという問題点があった．そのため，Mason の等価回路に基づく数値シミュレーションを実施して周波数特性 の改善策を検討した結果，固有音響インピーダンスが約 20 MRayl の背板材料を用いることでフラットな受信感度 の周波数特性を得られることがわかった．我々は固有音響インピーダンスが 20 MRayl 付近の背板を有する新しい 堅牢型ハイドロホンを開発した．新しい堅牢型ハイドロホンでは受波感度が高周波領域で低下することを抑制でき た．このハイドロホンを用いると従来の堅牢型ハイドロホンよりも忠実に超音波波形の非線形歪を表現できること がわかった．強力な超音波により音響キャビテーションが発生している超音波洗浄器の水槽内で，各ハイドロホン の超音波曝露実験を行った結果，新しい堅牢型ハイドロホンは市販のハイドロホンの約 10 倍の耐久性を持ってい ると考えられた． Development of anti-acoustic cavitation hydrophone with hydrothermally synthesized lead zirconate titanate poly-crystalline film Michihisa SHIIBA1, Nagaya OKADA2, Takeyoshi UCHIDA3, Minoru KUROSAWA4, Shinichi TAKEUCHI5 Abstract Recently, a number of diagnosis and treatment methods employing high-intensity ultrasound have been developed and used clinically. However, it is important from the standpoint of protecting human tissue and the standpoint of effective utilization of high-intensity ultrasound to accurately measure sound field, sound pressure, and acoustic intensity. Thus, we have been developing an anti-cavitation hydrophone that can withstand measurement in a high-intensity ultrasound field with inertial acoustic cavitation by deposition of a hydrothermally synthesized lead zirconate titanate（PZT）polycrystalline film on the reverse side of the titanium front plate. However, our conventional anti-cavitation hydrophone with low specific acoustic impedance backing had limitations, i.e., the receiving sensitivity decreased with an increase in frequency, and it could not describe the actual ultrasound waveform with high fidelity. Therefore, we considered improving the frequency characteristics of the receiving sensitivity by performing numerical simulations based on the Mason’s equivalent circuit model and one-dimensional acoustic transmission line model. It was found that flat frequency characteristics of the receiving sensitivity could be obtained by using a backing with about 20 MRayl specific acoustic impedance. We then developed a new anti-cavitation hydrophone using a backing with about 20 MRayl specific acoustic impedance based on the simulated results. The decrease in receiving sensitivity in the high-frequency range could be suppressed in our newly fabricated anti-cavitation hydrophone. Furthermore, durability tests of each hydrophone under ultrasound exposure were performed in a water tank containing ultrasound cleaner with generation of inertial acoustic cavitation. It was found that our new anti-cavitation hydrophone had a 10-fold longer lifetime as compared with a commercial needle-type hydrophone. Keywords hydrophone, hydrothermally synthesized lead zirconate titanate（PZT）polycrystalline film, Ti front plate, backing material, high-intensity ultrasound 1 桐蔭横浜大学大学院・日本学術振興会特別研究員 DC，2本多電子株式会社，3産業技術総合研究所計測標準研究部門，4東京工業大学大 学院，5桐蔭横浜大学 1 Toin University of Yokohama・Research Fellow of Japan Society for the Promotion of Science, 1614 Kurogane, Aoba, Yokohama, Kanagawa 225︲8503, Japan; 2Honda Electronics Company Limited, 20 Oyamazuka, Oiwa, Toyohashi, Aichi 441︲3193, Japan; 3National Institute of Advanced Industrial Science and Technology, 1︲1︲1 Umezono, Tsukuba, Ibaraki 305︲8568, Japan; 4Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama, Kanagawa 226︲8503, Japan; 5Toin University of Yokohama, 1614 Kurogane, Aoba, Yokohama, Kanagawa 225︲8503, Japan Received on April 10, 2014; Accepted on May 8, 2015 J-STAGE. Advanced published. date: August 10, 2015 Jpn J Med Ultrasonics
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