An ultrasonic surgical instrument includes a handle assembly, a waveguide extending distally therefrom to an end effector, an ultrasonic transducer assembly supported by the handle assembly, and a drive signal antenna. The ultrasonic transducer assembly includes a transducer, a horn extending distally from the transducer, an electrode antenna disposed about and operably coupled to the transducer, and an outer casing enclosing the transducer, the electrode antenna, and a portion of the horn. Another portion of the horn extends distally from the outer casing to operably connect to the waveguide. The drive signal antenna is disposed externally of and adjacent to the ultrasonic transducer assembly and is configured to contactlessly transmit a drive signal through the outer casing to the electrode antenna to thereby energize the transducer such that ultrasonic energy is transmitted from the horn along the waveguide to the end effector for treating tissue therewith.