Piezoelectric Touch Sensor Impedance Scanning
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Solution Overview
Problem
Existing touch sensing devices face challenges in accurately detecting the position and force of input objects, particularly those with insulating properties, due to transient electric charges in piezoelectric materials and the complexity of routing numerous wires for large sensor arrays.
Innovation Solution
A touch sensing device with a configuration of first and second electrodes and a piezoelectric material between them, where the processing system applies a time-varying electrical excitation signal to detect impedance changes, allowing for independent measurement of forces across a two-dimensional array of sensing elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a two-dimensional array of piezoelectric sensors is constructed with separate sense electrodes for each sensor, then the measurement precision for position and force is improved, but the device complexity and wiring requirements increase significantly
Solution Approach 1:
The patent merges the function of multiple separate sense electrodes into a single shared sense electrode that can detect forces from multiple piezoelectric sensors sequentially. This is achieved through time-multiplexed scanning of the electrode array, where each sensor is excited and measured in turn using the same readout electrode, thereby reducing the number of wires required while maintaining the ability to measure forces across the entire sensor array with high precision
2Adaptability or versatility
If piezoelectric materials are used to sense input objects, then the detection of insulating objects is improved, but the transient nature of generated charge prevents detection of stationary objects
Solution Approach 1:
The patent applies periodic action by using time-varying excitation signals that are repeatedly applied to the piezoelectric sensors at a scanning rate. Instead of relying on a single transient charge generation event, the system periodically re-excites the sensors and measures the response over multiple cycles. This allows the system to detect both moving objects (which generate transient charges) and stationary objects (which maintain consistent impedance characteristics) by comparing the sensor response across multiple periodic measurement cycles
3Measurement precision
If capacitive sensing techniques are used, then the detection of conductive objects is improved, but the detection of insulating objects becomes ineffective
Solution Approach 1:
The patent employs a composite sensing approach that combines piezoelectric sensing elements with capacitive sensing electrodes in a layered structure. The piezoelectric layer provides force sensing capability and works with insulating objects, while the capacitive electrodes provide position detection capability. This composite structure allows the system to detect both conductive and insulating objects effectively by utilizing the complementary strengths of both sensing mechanisms simultaneously across the same device area
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 detection of stationary and moving objects, including those with insulating properties, by measuring impedance changes, thereby improving accuracy and reducing the need for extensive wiring.
Implementation Method 1
Some touch sensing devices have used piezoelectric materials to sense the presence and force or pressure from an input object. Such devices generally rely on the piezoelectric effect, which causes an electric charge to form in the piezoelectric material when a force is applied.
Implementation Method 2
the processing system applies a time-varying electrical excitation signal to detect impedance changes, allowing for independent measurement of forces across a two-dimensional array of sensing elements
Data Source
AI summary
Embodiments of the disclosure generally provide an integrated input device that is configured to sense the position and amount of force applied by input objects that are in contact with an input region of an input device. The input device is generally configured to sense the position and amount of force applied by an input object that is in contact with the input region using a piezoelectric material. The input device generally includes a plurality of electrodes that are positioned to measure an electrical characteristic of the piezoelectric layer at different points within the input region to determine the position and/or amount of applied force. The input device may also include one or more components that are able to simultaneously or sequentially sense the position of an input object using a touch sensing technique independent of the electrical properties of the piezoelectric material to sense the input object position.