Ultrasonic sensor system and multi-layer stiffener for foldable display

An apparatus comprising:

• an ultrasonic sensor stack configured to transmit and receive ultrasonic waves;
• a foldable display stack comprising a first stiffener;
• a second stiffener between the ultrasonic sensor stack and the foldable display stack;
• and
• a first adhesive layer between the second stiffener and the first stiffener, wherein a multi-layer stiffener is formed by at least the first stiffener, the second stiffener, and the first adhesive layer, wherein each of the first stiffener and the second stiffener has a Young's modulus greater than about 10 GPa, and an acoustic impedance value of greater than about 8.0 MRayls.

A method comprising:

• controlling, via a control system, an ultrasonic transceiver layer of an ultrasonic sensor stack to transmit ultrasonic waves through at least a multi-layer stiffener and one or more display stack layers of a foldable display, the multi-layer stiffener including a first stiffener layer of the foldable display, a second stiffener layer, and an adhesive layer between the first and second stiffener layer;
• receiving, by the control system and from the ultrasonic sensor stack, ultrasonic sensor signals corresponding to reflections of transmitted ultrasonic waves from a portion of a target object positioned on an outer surface of an apparatus that includes the ultrasonic sensor stack;
• and
• performing, by the control system, an authentication process based, at least in part, on the ultrasonic sensor signals.