1. An electronic device configured to identify a user, the electronic device comprising: a display; a cover above the display; a first array of ultrasonic transducers arranged along a first side of the display, the first array of ultrasonic transducers configured to produce a first bulk wave transverse to a plane of the cover; a first mode converter formed as a convex contoured region that connects an outer surface of the cover and an adjacent side surface of the electronic device, the first mode converter configured to convert the first bulk wave into a surface wave in the cover, wherein a set of scattered waves comprising a scattered wave pattern are created by a user touch on the cover; a second mode converter arranged along a second side of the display, the second mode converter configured to convert at least a portion of the set of scattered waves into a second bulk wave transverse to the plane of the cover; a second array of ultrasonic transducers arranged along the second side of the display, the second array of ultrasonic transducers configured to receive the second bulk wave and produce an output associated with the scattered wave pattern that corresponds to fingerprint characteristics of the user; and a processing unit configured to distinguish the user from other users based on the output.