An ultrasonic transducer is disclosed, which includes one or more ultrasonic emitting units. Wavefront of the ultrasonic waves emitted by said one or more ultrasonic emitting units is sphere with equal radius, additionally said one or more ultrasonic emitting units can reflect ultrasound. Said one ultrasonic emitting unit is configured to form a spherical surface resonant cavity, or said more ultrasonic emitting units are configured to form a spherical surface resonant cavity together. The internal cavity of said spherical surface resonant cavity has a spherical shell-shape or a cross-sectional spherical shell-shape with a spherical center. The ultrasound emitted by said one or more ultrasonic emitting units focuses on the spherical center of said spherical surface resonant cavity. The ultrasonic transducer could be not only provided with a large ultrasonic emitting area and a great focal gain that render the energy of the ultrasonic focus enhanced dramatically, but also practically immune to work frequency of an ultrasonic source.
