An apparatus may include a one- or two-dimensional array of micromechanical ultrasonic transducer (PMUT) elements positioned below, beside, with, on, or above a backplane of a visual display. The backplane may be a thin-film transistor (TFT) backplane. The array of PMUT elements may be a piezoelectric micromechanical ultrasonic transducer (PMUT) array or a capacitive micromechanical ultrasonic transducer (CMUT) array. The PMUT array may be configurable to operate in modes corresponding to multiple frequency ranges. When operating in the low-frequency mode, the apparatus may be capable of gesture detection. A high-frequency mode may include a fingerprint sensor mode or a stylus detection mode.