Ultrasonic backer for bias transfer systems

Embodiments herein comprise a printing apparatus having a media path and a printing engine along the media path. The printing engine comprises a back up roll having an outer surface and an inner surface, a bias roll adjacent the outer surface of the back up roll, a photoreceptor belt, and a transfer belt. The bias roll is positioned with respect to the back up roll to form a nip between the bias roll and the back up roll. A portion of the photoreceptor belt is in the nip between the bias roll and the back up roll, and a portion of the transfer belt is in the nip between the bias roll and the photoreceptor belt. A transducer (e.g., an ultrasonic piezoelectric device) is contacting the inner surface of the back up roll. The transducer is physically connected to the back up roll in a manner such that the transducer transfers vibrations to the back up roll and to the photoreceptor belt. For example, in one embodiment, the transducer contacts and is physically biased against the inner surface of the back up roll.