title: Design and Fabrication of Double-Focused Ultrasound Transducers to Achieve Tight Focusing.
abstract: Beauty treatment for skin requires a high-intensity focused ultrasound (HIFU) transducer to generate coagulative necrosis in a small focal volume (e.g., 1 mm³) placed at a shallow depth (3-4.5 mm from the skin surface). For this, it is desirable to make the F-number as small as possible under the largest possible aperture in order to generate ultrasound energy high enough to induce tissue coagulation in such a small focal volume. However, satisfying both conditions at the same time is demanding. To meet the requirements, this paper, therefore, proposes a double-focusing technique, in which the aperture of an ultrasound transducer is spherically shaped for initial focusing and an acoustic lens is used to finally focus ultrasound on a target depth of treatment; it is possible to achieve the F-number of unity or less while keeping the aperture of a transducer as large as possible. In accordance with the proposed method, we designed and fabricated a 7-MHz double-focused ultrasound transducer. The experimental results demonstrated that the fabricated double-focused transducer had a focal length of 10.2 mm reduced from an initial focal length of 15.2 mm and, thus, the F-number changed from 1.52 to 1.02. Based on the results, we concluded that the proposed double-focusing method is suitable to decrease F-number while maintaining a large aperture size.
authors: Department of Electronic Engineering, Sogang University, Seoul 04107, Korea. jhjang@sogang.ac.kr.
authors: Jihun
authors: J
authors: Jang
authors: Department of Electronic Engineering, Sogang University, Seoul 04107, Korea. jhchang@sogang.ac.kr.|Department of Biomedical Engineering, Sogang University, Seoul 04107, Korea. jhchang@sogang.ac.kr.|Sogang Institutes of Advanced Technology, Sogang University, Seoul 04107, Korea. jhchang@sogang.ac.kr.
authors: Jin Ho
authors: JH
authors: Chang
mesh_terms: D006801:Humans; D012867:Skin / Q000528:radiation effects*; D012879:Skin Physiological Phenomena / Q000528:radiation effects*; D013499:Surface Properties / Q000528:radiation effects; D014159:Transducers; D014464:Ultrasonic Therapy / Q000379:methods*; D014463:Ultrasonography / Q000295:instrumentation*
keywords: 1-3 piezo-composite; acoustic lens; double-focusing; press-focusing; skin disease treatment; therapeutic ultrasound transducer