An end effector includes a first portion having a first specific acoustic impedance value, and a second portion having a second specific acoustic impedance value less than the first specific acoustic impedance value. The first portion may include a proximal end segment and a distal end segment. The proximal end segment and the distal end segment are composed of a first material. The second portion may include an insert segment composed of a second material. The insert segment is located between the proximal end segment and the distal end segment along the longitudinal axis of the end effector. The insert segment functions to bridge or fill a nodal energy gap defined by the end effector.