Fundamental design of ultrasound focusing system using adaptive phononic metastructure

2022 Fiscal Year Final Research Report

• Project/Area Number: 18K04028
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 20010:Mechanics and mechatronics-related
• Research Institution: Jikei University School of Medicine
• Principal Investigator: UETA Tsuyoshi 東京慈恵会医科大学, 医学部, 教授 (30251185)
• Project Period (FY): 2018-04-01 – 2023-03-31
• Keywords: フォノニックレンズ / 点状散乱体 / 配置最適化 / 経頭蓋 / クロスバースイッチ / 積分方程式法 / 有限要素解析

Outline of Final Research Achievements

Fundamental research on a phononic lens that instantly and appropriately focuses an ultrasonic plane wave emitted from the outside of the skull at a moving focal point in the brain transcranially has been performed. Initially, I determined the distribution of materials with different impedances composing the lens using acoustic holography by the finite element method. Since it is difficult to optimize the structure of such a system instantly, however, we decided to construct a phononic lens by arranging bubbles in the water-like substance that covers the head. A bubble is modeled as a point-like scatterer, and the optimum arrangement of the scatterer is determined so that the sound field becomes maximum at the focal point in the skull and 0 elsewhere. It was shown that it is possible to realize a lens that can focus up to the diffraction limit in the direction perpendicular to the incident direction of ultrasonic waves and up to about twice of the limit in the incident direction.

Free Research Field

メタマテリアル

Academic Significance and Societal Importance of the Research Achievements

超音波平面波を頭蓋骨内に集束させるレンズは音響ホログラフィーの原理を用いて設計、製作され、集束特性が調べられていた。このレンズでは、頭蓋骨形状、焦点位置によりレンズを作り直す必要があった。本研究では、任意形状の頭蓋骨、移動する焦点に対して適時的に焦点を結ぶレンズを提案し、十分な機能を実現できることを示した。泡を適切に配列することでレンズとして機能させ得ること、その配列の最適化に用いる目的関数の定義、高速な音場の計算法の開発など学術的意義は大きい。得られた成果は脳梗塞の解消のみならず、近年精力的に研究されている超音波による脳刺激によるアルツハイマー病の治療にも応用でき、社会的波及効果も大きい。