Methods of distinguishing among touch events using piezoelectric micromechanical sensing
A method of distinguishing between a first-type touch event and a second-type touch event is disclosed. A force-measuring and touch-sensing system includes piezoelectric force-measuring elements (PFEs) and piezoelectric ultrasonic transducers (PUTs), wherein each PUT can be configured as a transmitter (PUT transmitter) and/or a receiver (PUT receiver). The force-measuring and touch-sensing system is configured at a sense region. Each PUT transmitter transmits ultrasound signals towards the sense region and voltage signals are generated at the PUT receivers in response to ultrasound signals arriving from the sense region. Voltage signals are generated at PFEs in response to a low-frequency mechanical deformation of the respective piezoelectric capacitors. An event is determined to be a first-type touch event or a second-type touch event depending on a PUT data decrease and a magnitude of PFE data.
1 . A method of distinguishing between a first-type touch event and a second-type touch event at a sense region, the method comprising:
configuring a system at the sense region, the system comprising:
at least one piezoelectric micromechanical force-measuring element (PMFE), each PMFE comprising a respective piezoelectric capacitor; and
at least one piezoelectric micromechanical ultrasonic transducer (PMUT), each PMUT comprising a respective piezoelectric capacitor, each PMUT being configured as a PMUT transmitter and/or a PMUT receiver, the PMUT transmitter(s) numbering at least one, and the PMUT receiver(s) numbering at least one;
transmitting, by each PMUT transmitter, ultrasound signals of a frequency F 1 , in longitudinal mode(s) propagating along a direction approximately normal to a plane of the respective piezoelectric capacitor towards the sense region;
reading, by a signal processing circuitry, voltage signals from the PMUT receiver(s) generated in response to ultrasound signals of the frequency F 1 arriving at the PMUT receiver(s) from the sense region;
reading, by the signal processing circuitry, voltage signals from the PMFE(s) generated in response to a low-frequency mechanical deformation of the respective piezoelectric capacitor(s);
processing the voltage signals from the PMUT receiver(s) to obtain PMUT digital data;
processing the voltage signals from the PMFE(s) to obtain PMFE digital data;
determining that an event at the sense region is the first-type touch event if (1a) the PMUT digital data decrease by at least a minimum decrease percentage of a predetermined dynamic range in a moving time window of a predetermined duration, and (2a) a magnitude of the PMFE digital data is greater than a PMFE threshold value; and
determining that the event is the second-type touch event if (1a) the PMUT digital data decrease by at least the minimum decrease percentage of the predetermined dynamic range in the moving time window of the predetermined duration, and (2b) the magnitude of the PMFE digital data is not greater than the PMFE threshold value,
wherein:
the first-type touch event comprises a first object contacting the sense region and the second-type touch event comprises a second object contacting the sense region.
2 . The method of claim 1 , wherein the first object is a digit and the first object contacting the sense region comprises the digit touching the sense region.
3 . The method of claim 2 , wherein the first object contacting the sense region comprises the digit pressing and releasing the sense region.
4 . The method of claim 1 , wherein the second object is a liquid droplet, and the second object contacting the sense region comprises the liquid droplet landing on the sense region.
5 . The method of claim 1 , further comprising:
determining that the event is neither the first-type touch event nor the second-type touch event if (1b) the PMUT digital data do not decrease by at least the minimum decrease percentage of the predetermined dynamic range in the moving time window of the predetermined duration.
6 . The method of claim 1 , wherein the minimum decrease percentage is at least 1%.
7 . The method of claim 6 , wherein the minimum decrease percentage is at least 2%.
8 . The method of claim 1 , wherein the predetermined dynamic range is a dynamic range of the PMUT digital data under application of a force in a range of 0.5 N to 10 N at the sense region.
9 . The method of claim 1 , wherein the predetermined duration is in a range of 100 ms to 300 ms.
10 . The method of claim 1 , wherein the PMFE threshold value is at least five times a standard deviation of a noise level of the PMFE digital data.
11 . The method of claim 1 , wherein:
the PMUT(s) and PMFE(s) are located at respective lateral positions along a piezoelectric layer, each of the PMUT(s) and the PMFE(s) comprising a respective portion of the piezoelectric layer, the PMUT(s) and the PMFE(s) being part of an integrated circuit.
12 . The method of claim 11 , wherein the signal processing circuitry is part of the integrated circuit.
13 . The method of claim 1 , wherein a closest distance between the at least one PMFE and the at least one PMUT is 5 mm or less.