Force sensing in touch sensor by directivity control of transmit transducers

A touch sensor includes a touch structure arranged over an ultrasound port; an array of transceiver transducers arranged inside the ultrasound port and configured to generate a main directivity lobe directed at a touch interface, receive an ultra-sonic reflected wave produced at least in part by internal reflection of the main directivity lobe at the touch interface, and convert the ultra-sonic reflected wave into at least one measurement signal; a controller configured to modulate a directivity characteristic of the main directivity lobe by selectively activating the transmit transducers; and a receiver circuit configured to determine a size of a contact patch of a touch event present at the touch interface based on the at least one measurement signal and the directivity characteristic of the main directivity lobe, and determine an amount of contact force applied during the touch event based on the size of the contact patch.