Abstract: A method and apparatus for coupling ultrasonic energy into a clad or unclad waveguide include using phased array techniques to increase the area and intensity of radiation into the waveguide. An array of ultrasound transducers is positioned at the exterior of the waveguide and at dissimilar distances from the end of the waveguide. The transducers are individually fired by applying separate phase-shifted excitation signals. The phase shifting achieves a selected phase-differential relationship with respect to signals applied to adjacent transducers. The selected phase-differential relationship defines an angle of radiation into the waveguide. In the preferred embodiment, the apparatus is a medical device, such as an angioplasty device or ultrasound imaging device.