10 MHz용 압전 HIFU 트랜스듀서의 음향 및 온도 특성에 대한 유한요소해석
Finite element analysis for acoustic and temperature characteristics of a piezoelectric HIFU transducer at 10 MH
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초록
압전 HIFU 트랜스듀서는 바이오 의료분야에 적용되고 있는 새로운 기술로 발생한 초음파 에너지를 열로 변환하여 사용하는 디바이스이다. 최근 HIFU 디바이스는 7MHz 이상의 고 작동 주파수를 갖는 디바이스를 개발하는 추세이다. 본 논문에서는 유한요소법을 이용해 10MHz 작동주파수를 갖는 HIFU 트랜스듀서에 의해 발생된 tissue에서의 음압 및 온도분포를 계산하고, 압력의 focusing 특성 등을 분석하였다. HIFU의 형상변수로는 압전소재 두께, 렌즈 형상, 물높이, 필름의 두께 등을 고려하였다. 그 결과, 디바이스의 발생 음압은 렌즈의 HL/RL 비가 증가함에 따라 증가하다 일정한 값에 도달하는 경향을 보이고 있다. 그러나 디바이스의 focusing 면적은 렌즈의 HL/RL 비가 증가함에 급격하게 감소하는 특성을 보이고 있다. 최적 형상을 갖는 HIFU 디바이스의 경우, 최대 음압 및 온도는 각각 19MPa 및 65도 정도로 분석되었다. 또한 축방향 및 이와 수직한 방향에서 -3dB 초점 거리는 각각 2.3mm 및 0.23mm 정도인 것으로 나타났다
Abstract
A high intensity focuses ultrasound (HIFU) is one of the emerging technologies in the biomedical field. The piezoelectric HIFU transducer is a device that utilizes the thermal energy generated by high ultrasound energy. Recently an operating frequency of the HIFU transducer is to expand above a 7 MHz. In this study, the acoustic pressures and temperature distributions in the tissue that generated by the HIFU transducer at 10 MHz were calculated with the finite element method. In addition, the pressure focusing characteristics of the device were analyzed. The geometrical variables are the piezo-material thickness, lens shape, water height, and film thickness. The results shown that the acoustic pressure increased and saturated gradually when the height/radius (HL/RL) ratio of the lens increased. Moreover, the focal area was gradually decreases with HL/RL ratio of the lens. In case of the optimized HIFU transducer, the maximum pressure and temperature were analyzed about 19 MPa and 65°C respectively. And the -3 dB focused distances in the axial and lateral direction are around 2.3 mm and 0.23 mm respectively.
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