Abstract: A touch sensor includes a touch structure including a touch interface and an inner interface arranged opposite to the touch interface; a capacitive ultrasonic transmitter arranged inside an enclosed interior volume and configured to transmit an ultrasonic transmit wave towards the touch structure; a capacitive ultrasonic receiver arranged inside the enclosed interior volume and configured to receive at least one ultrasonic reflected wave produced from the ultrasonic transmit wave via internal reflection; a coupling medium that fills an area between the inner interface and the capacitive ultrasonic receiver, wherein an external force applied to the touch interface is configured to impart an internal pressure onto the capacitive ultrasonic receiver through the coupling medium; and a sensor circuit configured to convert the at least one ultrasonic reflected wave into a measurement signal and detect the external force based on the measurement signal.

Abstract: A method for calibrating an ultrasonic touch sensor includes generating a sequence of excitation signals, including sweeping a signal parameter such that the signal parameter is set to different parameter values; sequentially transmitting the plurality of ultrasonic transmit waves based on the sequence of excitation signals; receiving a plurality of ultrasonic reflected waves; generating a plurality of measurement signals representative of the plurality of ultrasonic reflected waves, wherein each measurement signal corresponds to a respective ultrasonic reflected wave of the plurality of ultrasonic reflected waves; determining a cumulative signal energy for each measurement signal; determining which measurement signal out of the plurality of measurement signals has a highest cumulative signal energy; and configuring, for a touch detection operation, the signal parameter with the parameter value that corresponds to the measurement signal having the highest cumulative signal energy.