CMUT Ultrasonic Touch Sensing With Adaptive Wet-Mode Switching
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Solution Overview
Problem
Capacitive touch sensors fail to operate reliably when exposed to water, leading to false signals and interrupted touch detection.
Innovation Solution
An ultrasonic touch sensor using capacitive micromachined ultrasonic transducers (CMUTs) that can differentiate between touch and no-touch events, even when submerged in water, by employing a configurable operation mode based on the rate of change in signal amplitude and a threshold, enabling robust touch detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive touch sensing is used, then touch detection can be implemented, but the sensor fails to operate reliably when exposed to water
Solution Approach 1:
The patent replaces capacitive touch sensing with ultrasonic touch sensing. The ultrasonic sensor uses acoustic waves to detect touch events by measuring changes in reflected wave patterns, eliminating the capacitive sensing mechanism that fails in wet environments. This substitution fundamentally resolves the water compatibility issue while maintaining touch detection functionality.
Solution Approach 2:
The patent implements mode switching between first and second operation modes based on environmental conditions. The measurement circuit detects water presence through rate-of-change analysis of the measurement signal and transitions between modes accordingly. This parameter change approach allows the sensor to adapt its detection parameters based on whether it is operating in air or water, maintaining reliability across different environments.
2Reliability
If ultrasonic sensing is used to detect touch events, then water exposure no longer causes false signals, but the device complexity increases due to mode switching capability
Solution Approach 1:
The measurement circuit is designed with dynamic adaptability through mode switching. The circuit automatically transitions between first and second operation modes based on real-time detection of water presence via rate-of-change analysis. This dynamic behavior allows the system to optimize its performance for different environments without requiring separate fixed circuits for each mode, managing complexity through intelligent adaptability rather than parallel dedicated paths.
Solution Approach 2:
The measurement circuit performs self-diagnosis and self-adjustment by monitoring the measurement signal for rate-of-change characteristics that indicate water presence. When water is detected, the circuit automatically switches to the appropriate operation mode without external intervention. This self-service capability reduces the need for external control mechanisms and simplifies the overall system architecture despite the added functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ultrasonic touch sensor effectively discriminates between touch and no-touch events, ensuring reliable operation even in wet environments by adapting its mode of operation to account for rapid changes in signal amplitude caused by water contact.
Implementation Method 1
An ultrasonic transmitter arranged within the package cavity, wherein the ultrasonic transmitter is configured to transmit at least one ultrasonic transmit wave toward the touch structure
Implementation Method 2
an ultrasonic receiver arranged within the package cavity, wherein the ultrasonic receiver is configured to receive ultrasonic reflected waves produced by a plurality of reflections of the at least one ultrasonic transmit wave and generate a measurement signal representative of the ultrasonic reflected waves
Implementation Method 3
the measurement circuit is configured to acquire a first plurality of samples of the measurement signal, calculate a rate of change of the first plurality of samples, perform a first comparison based on the rate of change and a rate of change threshold
Data Source
AI summary
An ultrasonic touch sensor includes a touch structure comprising a touch surface configured to receive a touch; an ultrasonic transmitter configured to transmit at least one ultrasonic transmit wave toward the touch structure; an ultrasonic receiver configured to receive ultrasonic reflected waves produced by a plurality of reflections of the at least one ultrasonic transmit wave and generate a measurement signal representative of the ultrasonic reflected waves; and a measurement circuit configurable in a first operation mode corresponding to an air environment and a second operation mode corresponding to a wet environment. The measurement circuit is configured to calculate a rate of change of a plurality of samples of the measurement signal, perform a first comparison based on the rate of change and a rate of change threshold, and operate in the second operation mode based on the rate of change satisfying the rate of change threshold.