Acoustic Touch Sensing Using Piezoelectric Transducers

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Solution Overview

Problem

Capacitive-type touch sensing systems face performance issues due to interference from metal housing and are sensitive to water, making them unsuitable for wet environments, while resistive touch sensing systems have limitations on surface types and water resistance.

Innovation Solution

Acoustic touch sensing systems using piezoelectric transducers to transmit ultrasonic waves and detect object interactions through time-of-flight, acoustic image reconstruction, or reflection attenuation, allowing for touch detection on various surfaces, including metal and glass, and insensitivity to water.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If capacitive-type touch sensing systems are used, then touch detection capability is provided, but performance is reduced due to interference from metal housing and sensitivity to water

Engineering Contradiction:

Improvetouch sensing reliabilityVSAvoidinterference from metal housing and water sensitivity

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The patent replaces capacitive sensing (which relies on electrical fields) with acoustic sensing using piezoelectric transducers that generate and detect ultrasonic waves. This mechanical/acoustic approach is immune to electromagnetic interference from metal housing and unaffected by water, as acoustic waves propagate through the solid structure rather than through air or fluid media where they would be attenuated by water.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces piezoelectric transducers as intermediary elements that convert electrical signals to acoustic waves and back. These transducers are coupled to the device housing to form an acoustic sensing system that mediates between the user's touch and the detection system, providing reliable operation in environments where direct capacitive sensing fails.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Reliability

If resistive touch sensing systems are used, then touch detection is provided, but surface type limitations and water resistance issues occur

Engineering Contradiction:

Improvetouch detection capabilityVSAvoidsurface type compatibility

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The acoustic touch sensing system using piezoelectric transducers can be integrated into various device surfaces including metal housings, glass panels, and plastic components. The system is not limited to specific surface types as it senses vibrations and acoustic waves transmitted through the structure itself, making it universally applicable across different materials and device designs.

Inventive Principle:

Principle #6Universality (Multi-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

Enables reliable touch sensing in wet conditions and on surfaces where capacitive or resistive systems fail, providing a robust and versatile solution for touch input detection.

Implementation Method 1

Acoustic touch sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface

Methodology Applied

Scientific EffectPiezoelectric effect: Piezoelectric Effect

Implementation Method 2

As the wave propagates along the surface, one or more objects (e.g., finger, stylus, etc.) in contact with the surface can interact with the transmitted wave causing attenuation, redirection and/or reflection

Methodology Applied

Scientific EffectUltrasonic wave propagation: Ultrasound

Implementation Method 3

The location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave

Methodology Applied

Scientific EffectTime-of-flight measurement: Time of Flight

Data Source

PatentUS20230022492A1Methodology and application of acoustic touch detection

Publication Date: 2023.01.26 APPLE INC

AI summary

Acoustic touch detection (touch sensing) system architectures and methods can be used to detect an object touching a surface. Position of an object touching a surface can be determined using time-of-flight (TOF) bounding box techniques, or acoustic image reconstruction techniques. Acoustic touch sensing can utilize transducers, such as piezoelectric transducers, to transmit ultrasonic waves along a surface and/or through the thickness of an electronic device. Location of the object can be determined, for example, based on the amount of time elapsing between the transmission of the wave and the detection of the reflected wave. An object in contact with the surface can interact with the transmitted wave causing attenuation, redirection and/or reflection of at least a portion of the transmitted wave. Portions of the transmitted wave energy after interaction with the object can be measured to determine the touch location of the object on the surface of the device.