Piezoelectric Touch Sensing on Large and Conductive Surfaces
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Solution Overview
Problem
Capacitive touch sensors face challenges with increased complexity, cost, and reliability issues due to the need for multiple sensors on large touch surfaces, inability to detect touches on conductive surfaces, and false detections from hovering objects, especially with thick materials or gloved fingers.
Innovation Solution
Employing piezoelectric transducers around the perimeter of a touch surface to complement capacitive sensors, using active and passive sensing modalities to confirm and locate touches, including time-of-flight, tomography, and absorption principles to detect ultrasonic wave reflections and absorptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If capacitive touch sensors are used on large touch surfaces, then touch detection capability is provided, but the number of sensors increases leading to increased ASIC size, I/O, cost, and integration complexity
Solution Approach 1:
The patent replaces capacitive sensing (electrical field-based) with piezoelectric sensing (mechanical stress-based). Piezoelectric transducers convert mechanical stress from touch directly into electrical signals, eliminating the need for complex capacitive sensor arrays and associated ASIC infrastructure. This substitution reduces integration complexity while maintaining large touch surface capability.
Solution Approach 2:
The piezoelectric transducer array serves multiple functions: primary touch detection, touch location determination, and validation of capacitive sensor readings. This multi-functionality reduces the need for separate systems and simplifies the overall architecture compared to using only capacitive sensors across large surfaces.
2Reliability
If capacitive touch sensors are used, then touch detection is enabled, but they cannot detect touches on conductive surfaces due to shielding effect
Solution Approach 1:
The patent replaces capacitive sensing with piezoelectric sensing, which detects mechanical stress waves rather than electrical field changes. Since piezoelectric transducers respond to physical touch forces regardless of the electrical properties of the touching object or surface, they work reliably on conductive surfaces, metal surfaces, and even wet surfaces where capacitive sensors fail due to shielding effects.
3Measurement precision
If capacitive touch sensors are used, then touch detection is provided, but false detections occur from hovering objects and thick gloves
Solution Approach 1:
The patent replaces capacitive sensing with piezoelectric sensing that detects actual mechanical contact through stress wave generation. Piezoelectric transducers only respond when physical force is applied to the surface, not when objects merely hover nearby. This mechanical-based detection eliminates false positives from hovering objects and works reliably even when users wear thick gloves, as the mechanical stress from the touch is transmitted through the glove material.
4Strength
If capacitive touch sensors are placed below thick touch surface materials, then protection is provided, but touch detection reliability decreases
Solution Approach 1:
The patent replaces capacitive sensing with piezoelectric sensing that detects mechanical stress waves. Since mechanical stress waves propagate effectively through solid materials including thick protective layers, the piezoelectric transducers can be positioned behind protective surfaces and still reliably detect touches. The mechanical energy from the touch transmits through the protective material to generate detectable stress waves in the piezoelectric elements.
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
Enhances touch detection accuracy, reduces complexity and cost, and improves reliability on large and conductive surfaces by using piezoelectric transducers, minimizing false detections and enabling detection through gloves or on wet surfaces.
Implementation Method 1
one or more piezoelectric transducers can be configured for active sensing which involves actively driving at least one PE transducer with some desired waveform
Implementation Method 2
When a TOF modality is employed, one or more PE transducers can be configured to transmit an ultrasonic wave into and across the touch surface. If no object is in contact with the touch surface, the ultrasonic wave will propagate with minimal reflections, and after impinging on distal surfaces, will reflect back to the PE transducer. However, if an object is present, due to acoustic impedance mismatches between the touch surface and the touching object, the ultrasonic wave will reflect back to the PE transducer sooner than if no object were present.
Implementation Method 3
When a tomography modality is employed, one or more PE transducers can be configured as a PE transmitter to transmit an ultrasonic wave into and across the touch surface. If no object is in contact with the touch surface, the ultrasonic wave will propagate with minimal reflections until it is received at one or more PE transducers configured as a PE receiver. However, if an object is present, some of the energy of the ultrasonic wave will be absorbed by the object, and some of the energy will pass through the object and be detected at a PE receiver. However, the energy level of the attenuated ultrasonic waves received at the PE receiver will drop.
Data Source
AI summary
Examples of the disclosure are directed to the use of one or more piezoelectric (PE) transducers for detecting one or more touches on a surface. In some embodiments, the one or more PE transducers can complement a capacitive touch sensor array and provide a confirmation that a touch has in fact occurred, and can provide a secondary determination of touch location. In some examples, the one or more PE transducers can be formed on, or as part of, a flex circuit that is adhered to a housing or other structure to which the touch surface is affixed. The flex circuit can be formed as a strip upon which the one or more PE transducers are attached, and can be shaped and sized (optionally with a fold to create a tail for electrical connections) to adhere to an inner or outer surface of the housing.