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In this paper, we report a therapeutic ultrasonic transducer with a sub-wavelength periodic structure, by which ultrasonic focusing and temperature elevation have been significantly enhanced compared to a conventional concave transducer with the same size. Enhanced acoustic focusing was demonstrated by both measuring and simulating acoustic pressure and temperature elevation. Compared to the conventional concave transducer, the proposed transducer exhibited stronger capacity in elevating acoustic pressure and temperature rise in the focal region, in which extraordinary acoustic transmission close to Wood's anomaly could be modulated by the spherically curved surface. This work is believed to possess great clinical potential in the safe and efficient application of ultrasonic therapy. [ABSTRACT FROM AUTHOR]

Resolution of high intensity focused ultrasound (HIFU) focusing is limited by the wave diffraction. We have developed a spherical cavity transducer with two open ends to improve the focusing precision without sacrificing the acoustic intensity (App Phys Lett 2013; 102: 204102). This work aims to theoretically and experimentally investigate the frequency dependence of the acoustic field generated from the spherical cavity transducer with two open ends. The device emits high intensity ultrasound at the frequency ranging from 420 to 470 kHz, and the acoustic field is measured by a fiber optic probe hydrophone. The measured results shows that the spherical cavity transducer provides high acoustic intensity for HIFU treatment only in its resonant modes, and a series of resonant frequencies can be choosen. Furthermore, a finite element model is developed to discuss the frequency dependence of the acoustic field. The numerical simulations coincide well with the measured results. [ABSTRACT FROM AUTHOR]