Ultrasonic Touch Sensor Capacitive Cross-Talk Glove Detection
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Solution Overview
Problem
Ultrasonic touch sensors fail to detect touch events accurately when a user is wearing a glove, as the glove does not adequately absorb the ultrasound wave, leading to misinterpretation of touch events as no-touch events.
Innovation Solution
The ultrasonic touch sensor employs capacitive cross-talk by capacitively coupling a transmitter and receiver with a capacitive path, using an excitation signal to induce capacitive cross-talk, which is monitored to differentiate between touch and no-touch events, including indirect touches, by forming a second capacitive path through the user to ground, reducing cross-talk and improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If ultrasonic touch sensing is used to detect touch events, then touch detection capability is provided, but detection accuracy deteriorates when user is wearing a glove
Solution Approach 1:
The patent introduces capacitive cross-talk as an intermediary mechanism to detect touch events. Instead of relying solely on ultrasound wave absorption, the system uses the capacitive coupling between transmitter and receiver that is modulated by touch events. The capacitive cross-talk signal serves as an intermediary indicator that can detect both direct touches and indirect touches (through gloves), resolving the accuracy issue while maintaining detection capability
Solution Approach 2:
The patent substitutes the mechanical ultrasound wave absorption mechanism with an electrical capacitive coupling mechanism. By replacing the reliance on acoustic wave absorption properties with electrical capacitive cross-talk measurement, the system can detect touch events more accurately regardless of whether the user is wearing a glove, as the capacitive path is formed through the user's body to ground
2Measurement precision
If capacitive cross-talk is used to detect touch events, then detection accuracy is improved, but device complexity increases
Solution Approach 1:
The patent makes the capacitive path serve multiple functions: it provides both the ultrasonic transmission medium and the capacitive coupling path for cross-talk detection. The same capacitive coupling that enables ultrasound transmission also serves as the sensing mechanism for touch detection through capacitive cross-talk, eliminating the need for separate sensing structures and reducing overall device complexity
Solution Approach 2:
The system uses the excitation signal itself to induce capacitive cross-talk that serves as the detection mechanism. The transmitter's excitation signal automatically creates the capacitive cross-talk effect in the receiver without requiring additional active components or complex circuitry, allowing the system to self-generate the detection signal
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
This approach enables the ultrasonic touch sensor to accurately discriminate between touch and no-touch events, including those involving gloves, enhancing the sensor's reliability and accuracy in detecting both direct and indirect touches.
Implementation Method 1
the transmitter and the receiver are coupled by a capacitive path
Implementation Method 2
the excitation signal induces a capacitive cross-talk on the capacitive path
Implementation Method 3
the transmitter is configured to receive the excitation signal and transmit the ultrasonic transmit wave towards the touch structure based on the excitation signal
Implementation Method 4
the receiver is configured to receive an ultrasonic reflected wave produced by a reflection of the ultrasonic transmit wave at the touch structure
Data Source
AI summary
A touch sensor includes a touch structure; a signal generator configured to generate an excitation signal; a transmitter configured to receive the excitation signal and transmit an ultrasonic transmit wave towards the touch structure based on the excitation signal; a receiver configured to receive an ultrasonic reflected wave produced by a reflection of the ultrasonic transmit wave at the touch structure, wherein the transmitter and the receiver are coupled by a capacitive path, the receiver is configured to be influenced by the excitation signal whereby the excitation signal induces a capacitive cross-talk on the capacitive path, and the receiver is configured to generate a measurement signal representative of the capacitive cross-talk; and a measurement circuit coupled to the receiver and configured to perform a comparison of the measurement signal with a threshold to determine whether a no-touch event or a touch event has occurred at the touch interface.