High-intensity focused ultrasound (HIFU) is a breakthrough therapeutic technique used to treat tumors. The principle of this noninvasive, targeted treatment is much like that of focusing sunlight through a lens, using an ultrasonic transducer like a convex lens to concentrate ultrasound into a small focal region. In an article appearing this week in the Journal of Applied Physics, a multi-institutional team of researchers in China have now designed a semi-enclosed, spherical cavity transducer for potential application in HIFU that can generate a steady, standing-wave field with a subwavelength-scale focal region and extremely high ultrasound intensity.