Acoustic Touch Sensor Isolation Layer for Metal Housing Reflections
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Solution Overview
Problem
Capacitive-type touch sensing systems face performance issues due to conductive, electrically-floating objects such as water droplets, and are unsuitable for metal housing surfaces, limiting their use in wet environments or submerged applications.
Innovation Solution
Acoustic touch sensing systems utilizing piezoelectric transducers to transmit ultrasonic waves and determine object position via time-of-flight techniques, which are insensitive to water contact and can operate on metal or glass surfaces, incorporating isolation and absorption layers to mitigate reflections and ringing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitive-type touch sensing systems are used, then touch detection capability is provided, but performance is reduced due to water droplets and conductive objects
Solution Approach 1:
The patent replaces capacitive sensing (electrical field-based) with acoustic sensing (ultrasonic wave-based). The acoustic touch sensor transmits ultrasonic waves through the housing and detects reflections from touching objects, making the system insensitive to water droplets and conductive objects that interfere with capacitive sensing.
Solution Approach 2:
The patent introduces an isolation layer as an intermediary between the acoustic touch sensor and the housing. This layer acoustically isolates the sensor from reflections generated by the housing structure, eliminating harmful reflections that would interfere with touch detection accuracy.
2Adaptability or versatility
If acoustic touch sensing is implemented on metal housing, then versatility is improved, but reflections from housing interfere with sensing accuracy
Solution Approach 1:
The patent introduces an isolation layer as an intermediary between the acoustic touch sensor and the housing. This layer acoustically isolates the sensor from reflections generated by the housing structure, eliminating harmful reflections that would interfere with touch detection accuracy.
Solution Approach 2:
The patent extracts the harmful reflection paths by placing absorption material within the housing cavity. This material absorbs ultrasonic waves before they can reflect off the housing surfaces and return to the sensor, removing the interference source from the system.
3Measurement precision
If isolation layers are added to reduce reflections, then sensing accuracy is improved, but device complexity increases
Solution Approach 1:
The isolation layer serves multiple functions simultaneously: it acoustically isolates the sensor from housing reflections, provides mechanical mounting for the sensor assembly, and can be integrated into existing device structures. This multi-functionality reduces the need for additional separate components.
Solution Approach 2:
The patent modifies the acoustic impedance parameters of the interface between sensor and housing by introducing the isolation layer. This changes the acoustic transmission characteristics to minimize reflections while maintaining a simple structural implementation.
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
Enables reliable touch sensing in wet conditions and on previously unsuitable surfaces by accurately detecting object positions and reducing interference from water and housing reflections, enhancing usability in diverse environments.
Implementation Method 1
Acoustic touch sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface
Implementation Method 2
transmit ultrasonic waves along a surface and/or through the thickness of one or more materials
Implementation Method 3
The position of an object touching a surface can be determined using time-of-flight (TOF) techniques
Implementation Method 4
an object (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave, causing a reflection of at least a portion of the transmitted wave
Implementation Method 5
coupled to a housing of the electronic device by a second adhesive layer that provides an acoustic isolation between the transducer assembly and the housing based on an impedance mismatch between the second adhesive layer and the housing
Implementation Method 6
an absorption layer that converts incident acoustic energy into heat, thus preventing the incident acoustic energy from becoming reflected acoustic energy that can return to the transducer
Data Source
AI summary
Acoustic touch sensing system architectures and methods for acoustic touch sensing can be used to detect a position of an object touching a surface. Acoustic touch sensing can utilize transducers (e.g., piezoelectric) to simultaneously transmit ultrasonic waves along a surface and through a thickness of a material. The location of the object can be determined based on the amount of time elapsing between the transmission of the waves and receipt of the reflected waves. In some examples, an acoustic touch sensing system can be insensitive to water contact on the device surface, and thus acoustic touch sensing can be used for touch sensing in devices that may become wet or fully submerged in water. In some examples, techniques such as isolation and absorption of acoustic energy can be used to mitigate acoustic energy reflected by portions of the electronic device and interfere with the acoustic touch sensing operation.