Some Modifications of Toroidal Long-Range-Focusing Transducers for Sidelobe Reduction

Ultrasound focusing transducers with a toroidal radiating surface can generate a narrow-beam ultrasound over a large depth, while they produce high-level sidelobes. In this paper two types of modified toroidal transducers are proposed with improved sidelobe characteristics; one is a concave-toroidal hybrid transducer and the other is a dual-phase toroidal transducer. These transducers exhibit almost the same beamwidth characteristics as toroidal ones and a reduced fractional sidelobe level of 15–20% in a certain axial range, in contrast with 30–40% for toroidal transducers.