Under water touch detection with ultrasonic sensors using capacitive micromachined ultrasonic transducers (cmuts)

An ultrasonic touch sensor, comprising:

• a touch structure comprising a touch surface, configured to receive a touch, and a touch interface at the touch surface;
• a mode detection circuit configured to:
• configure the ultrasonic touch sensor into a first operation mode based on a surrounding environment of the ultrasonic touch sensor being an air environment, or
• configure the ultrasonic touch sensor into a second operation mode based on the surrounding environment of the ultrasonic touch sensor being a liqiud environment;
• and
• a sensor circuit configured to:
• receive a measurement signal representative of an ultrasonic reflected wave produced by a reflection of an ultrasonic wave transmitted at the touch structure, and
• determine whether a no-touch event or a touch event has occurred at the touch surface based on the measurement signal and whether the ultrasonic touch sensor is operating in the first operation mode or the second operation mode.

A method, comprising:

• receiving, by a sensor circuit of an ultrasonic touch sensor, a first measurement signal, associated with the ultrasonic touch sensor being submerged in liquid, or a second measurement signal, associated with the ultrasonic touch sensor being exposed to air,
• wherein the first measurement signal is representative of a first ultrasonic reflected wave produced by a reflection of a first ultrasonic transmit wave at a touch surface of a touch structure of the ultrasonic touch sensor when the ultrasonic touch sensor is submerged in liquid, or
• wherein the second measurement signal is representative of a second ultrasonic reflected wave produced by a reflection of a second ultrasonic transmit wave at the touch surface when the ultrasonic touch sensor is exposed to air;
• and
• determining, by the sensor circuit, whether a no-touch event or a touch event has occurred at the touch surface while the touch surface is submerged in liquid based on whether the first measurement signal satisfies a first threshold, or
• determining whether the no-touch event or the touch event has occurred at the touch surface while the touch surface is exposed to air based on whether the second measurement signal satisfies a second threshold different than the first threshold.