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The use of therapeutic focused ultrasound requires control of the focal position for different treatment regions. In this study, a piezoelectric ultrasonic transducer of plano-concave form was designed, and the change of the focal position depending on the frequency of the driving signal of the fabricated transducer was experimentally investigated. PVA gel and thermochromic liquid crystal film were used to observe the thermal distribution in the focal region caused by focused ultrasound produced by the transducer. The ability to control the position of the focal region between (62 and 154) % of the geometric focal length of the transducer, depending on the input signal frequency change, was confirmed. The change of acoustic field distribution, which was calculated using the transfer function of the vibration element distributed on the surface of the transducer as the source strength, showed good agreement with the change of temperature distribution experimentally observed. |
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