| CPC G06V 40/1306 (2022.01) [B06B 1/0688 (2013.01)] | 29 Claims |

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1. A foldable display device, comprising:
a display system including a display stack;
an ultrasonic fingerprint sensor system including an ultrasonic fingerprint sensor system stack; and
a stiffener layer residing between the display stack and the ultrasonic fingerprint sensor system stack, the stiffener layer having a stiffener layer thickness configured to allow the ultrasonic fingerprint sensor system to operate in a near-field mode having a peak frequency in a range from 1 megahertz (MHz) to 6 MHz, wherein the stiffener layer thickness corresponds to a transmission coefficient in a range from 10 percent to 30 percent for ultrasonic waves in the range from 1 MHz to 6 MHz.
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