A coupler includes a first portion and a second portion, and defines a passageway configured to fixedly receive a proximal end portion of a transmission member. The first portion is configured to be coupled to an ultrasonic energy source. The coupler is configured to transfer at least a portion of an ultrasonic vibration produced by the ultrasonic energy source to the transmission member. Furthermore, the first portion and the second portion are collectively configured to adjust a resonant frequency of the transmission member to correspond to a vibrational frequency of the ultrasonic vibration produced by the ultrasonic energy source. In some embodiments, the portion of the ultrasonic vibration includes a linear component. In such embodiments, the first portion and the second portion are collectively configured to transform at least a portion of the linear component of the ultrasonic vibration into a torsional component within the transmission member.
