A focused annular ultrasound transducer design based on a planar lens

Acoustic lenses are widely used in focused ultrasound transducers to produce high acoustic intensity at the focal point. However, acoustic lenses are usually curved or curled, and when air or bubbles gather near the curved surface, the transducer may be damaged as a result of heating or cavitation. In addition, their non-planar structure may cause difficulties to develop multilayer lens to reduce the F-number further. In this work, we develop a focused annular ultrasound transducer with a planar acoustic lens, which is made of a velocity gradient matching layer. KLM model simulation is used to design the piezoelectric part of the transducer. Finite element analysis (FEA) simulation is used to predict the acoustic field distribution, following by hydrophone measurement verification using a motion stage. The result shows that the planar lens achieves a focusing distance of 62 mm, with a lower F-Number of 2.81 comparing to the natural focusing at 78.5mm.