Piezoelectric Transducers for Touch Confirmation on Large Surfaces
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Capacitive touch sensors face challenges with increased complexity, cost, and reliability issues on large touch surfaces, particularly with conductive materials and in wet conditions, and struggle to distinguish between hovering and touching objects.
Innovation Solution
Employing piezoelectric transducers around the perimeter of a touch surface to complement capacitive sensors, using active or passive sensing modalities to detect touches through ultrasonic waves, time-of-flight principles, or low-frequency signals, enhancing touch detection accuracy and reliability.
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 power consumption
Solution Approach 1:
The patent replaces capacitive sensing (electrical field-based) with piezoelectric sensing (mechanical stress-based). Piezoelectric transducers convert mechanical stress from touch into electrical signals, eliminating the need for numerous capacitive sensors and their associated complex ASIC circuits. This substitution reduces device complexity while maintaining large touch surface area.
Solution Approach 2:
The piezoelectric transducer array provides multiple functions: touch detection, touch location determination, and confirmation of actual contact versus hovering. A single piezoelectric sensor can replace multiple capacitive sensors, reducing the overall number of components while maintaining comprehensive touch sensing capability across large surfaces.
2Adaptability or versatility
If capacitive touch sensors are used with conductive touch surfaces, then touch detection is enabled, but metallic surfaces shield the finger from sensor electrodes making detection unreliable
Solution Approach 1:
The patent replaces capacitive sensing (which relies on electrical field coupling) with piezoelectric sensing (which relies on mechanical stress). Since piezoelectric transducers detect physical contact through stress-induced charge generation, they are not affected by the shielding effect of conductive surfaces. This allows reliable touch detection on metallic and other conductive touch surfaces.
3Ease of operation
If capacitive touch sensors are used in wet conditions, then touch detection may occur, but smeared water causes shielding effects making tracking unreliable
Solution Approach 1:
The patent replaces capacitive sensing with piezoelectric sensing, which detects mechanical stress from actual contact. Water or moisture does not interfere with the mechanical stress detection mechanism, allowing reliable touch tracking in wet conditions where capacitive sensors fail due to shielding effects from water layers.
4Measurement precision
If capacitive touch sensors are used to detect touches, then touch detection is provided, but false detections occur when objects hover without actual contact
Solution Approach 1:
The patent replaces capacitive sensing (detects electrical field changes from proximity) with piezoelectric sensing (detects mechanical stress from contact). Piezoelectric transducers only generate signals when actual physical contact applies stress to the sensor, eliminating false detections from hovering objects while maintaining accurate detection of genuine touches.
5Ease of manufacture
If capacitive touch sensors are placed below thick touch surface materials, then touch detection is enabled, but detection accuracy decreases due to distance from the touch point
Solution Approach 1:
The patent replaces capacitive sensing (which degrades with distance due to field attenuation) with piezoelectric sensing (which responds to mechanical stress transmitted through the structure). Piezoelectric transducers mounted on the housing can detect touches through the touch surface materials regardless of thickness, as mechanical stress transmits effectively through solid structures, maintaining detection accuracy while providing manufacturing flexibility.
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 piezoelectric transducers provide accurate touch confirmation and location, reduce complexity and cost, and improve reliability on large touch surfaces, including those with conductive materials and in wet conditions, while minimizing false detections.
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. 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.
Implementation Method 2
the PE transducers can be configured for passive sensing which means that all the PE transducers will operate in 'listening-only' mode and none of them will be driven with any signal. A touching object generates time-varying stress on the touch surface and can cause acoustic waves to propagate within the touch surface.
Implementation Method 3
If no object is in contact with the touch surface, the ultrasonic wave will propagate with minimal reflections, and after impinging on distal surfaces (e.g., surfaces on the opposite side of the touch surface from the PE transducer), will reflect back to the PE transducer. The TOF of the reflected ultrasonic wave can be measured and used to determine whether an object was present.
Implementation Method 4
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.
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.