Ultrasonic Touch Sensor With Rate-of-Change Water Detection
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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 functionality.
Innovation Solution
An ultrasonic touch sensor using capacitive micromachined ultrasonic transducers (CMUTs) that can differentiate between air and wet environments, employing a measurement signal rate of change threshold to switch operation modes and accurately detect touch events even when submerged in water.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive touch sensing is used, then touch detection functionality is provided, 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 transmits ultrasonic waves through the touch structure and detects reflected waves to determine touch events. This mechanical/acoustic approach is immune to water exposure, as the ultrasonic waves propagate through the solid touch structure regardless of external moisture, thereby resolving the reliability issue in wet environments.
Solution Approach 2:
The patent changes the sensing parameter from electrical capacitance to acoustic wave reflection. By measuring the reflected ultrasonic waves and their characteristics (such as amplitude, frequency, or time of flight), the system determines touch events. This parameter change makes the sensing mechanism independent of water exposure, as acoustic wave propagation through solids is not affected by external moisture.
2Measurement precision
If ultrasonic waves are transmitted through the touch structure, then touch events can be detected, but the sensor cannot distinguish between water presence and actual touch
Solution Approach 1:
The patent employs dynamic threshold adjustment based on environmental detection. The system first detects whether the touch structure is exposed to water by analyzing the reflected ultrasonic wave characteristics. Based on this environmental information, the system dynamically adjusts the touch detection threshold: using a first threshold when in air and a second, different threshold when in water. This dynamic adaptation enables accurate touch detection across varying environmental conditions without increasing structural complexity.
Solution Approach 2:
The system uses feedback from the reflected ultrasonic waves to determine both touch events and environmental conditions. By continuously monitoring the characteristics of reflected waves and comparing them against stored reference data or dynamic thresholds, the system feedback-adjusts its detection parameters. This feedback mechanism allows the sensor to distinguish between water presence and actual touch events, maintaining measurement precision without requiring additional complex sensing structures.
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 robust touch detection even in wet conditions by adapting its operation mode based on signal amplitude changes.
Implementation Method 1
Ultrasonic sensing relies on a transmission of an ultrasound wave directed at a touch structure, and reception and processing of a reflected waveform that is reflected back from the touch structure
Implementation Method 2
reception and processing of a reflected waveform that is reflected back from the touch structure
Implementation Method 3
A characteristic of the reflected waveform will depend on an existence or a non-existence of a touch event, and can be used to discriminate between the existence or the non-existence of the touch event
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.