Spatial Frequency Capacitive Motion Sensor for High Speed Tracking
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Solution Overview
Problem
Conventional motion sensors, such as optical and capacitive trackpads, face limitations in detecting high-speed motion due to large size requirements, high processing power needs, and security concerns related to fingerprint image capture and processing.
Innovation Solution
A spatial frequency-based capacitive motion sensor using an array of sense cells with processing circuitry that dynamically configures the array as a comb-filter to detect motion by measuring capacitance variations, reducing the required processing power and sensing area while avoiding fingerprint image detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a capacitive trackpad uses a large array of capacitive sensors to detect motion in multiple sequential locations, then the sensing area increases, but the device size becomes too large to fit into applications with limited surface area
Solution Approach 1:
The patent divides the sensing array into multiple smaller sub-arrays or zones, allowing motion detection to be performed in segments. This segmentation enables the system to detect motion across a large area while using a physically smaller sensor array, resolving the contradiction between sensing area and device size.
Solution Approach 2:
The patent transitions from detecting motion in sequential locations (requiring large spatial coverage) to detecting spatial frequency components of motion (transforming the problem into the frequency domain). This dimensional transformation allows accurate motion detection with a compact sensor array, as the spatial frequency analysis extracts motion information without requiring physical coverage of the entire motion path.
2Speed
If a capacitive trackpad uses a large array of capacitive sensors to detect high-speed motion, then the maximum detectable speed increases, but the sensing area and device size increase
Solution Approach 1:
The patent transforms the motion detection problem from the spatial domain to the frequency domain by analyzing spatial frequency components. This transformation enables high-speed motion detection with a compact array, as the frequency-based approach can capture rapid motion patterns without requiring proportional increases in sensor array size.
Solution Approach 2:
The patent dynamically adjusts parameters such as the sampling rate, analysis window size, and spatial frequency resolution to optimize detection of different motion speeds. By adapting these parameters, the system maintains high-speed detection capability while minimizing the required sensing area.
3Measurement precision
If fingerprint sensors are used to detect motion by comparing subsequent images with image correlation, then motion detection is achieved, but the processing time increases and maximum speed is limited
Solution Approach 1:
The patent extracts only the essential motion information from the sensor data by analyzing spatial frequency components, rather than performing full image correlation on complete fingerprint images. This extraction approach maintains motion detection accuracy while significantly reducing processing time, as it focuses computational effort on the relevant motion signals rather than entire images.
Solution Approach 2:
The patent uses simplified representations of motion data in the frequency domain instead of full image copies. By working with spectral components rather than complete images, the system achieves accurate motion measurement with reduced data processing requirements and faster execution.
4Loss of information
If fingerprint images are captured and processed for motion detection, then motion information is obtained, but security and privacy concerns arise from storing fingerprint images
Solution Approach 1:
The patent extracts only the motion-related spatial frequency components from the sensor data, discarding the biometric fingerprint image information. This extraction strategy enables accurate motion detection while eliminating security and privacy concerns associated with storing and processing fingerprint images, as only anonymized motion signals are retained.
Solution Approach 2:
The patent converts what would traditionally be considered loss of detailed image information into a benefit by deliberately avoiding capture and storage of biometric data. The system design transforms the potential harm of security risks into a protective feature, where the sensing and processing methodology inherently prevents biometric information from being stored or compromised.
5Measurement precision
If optical navigation sensors use a laser or LED light source and photodiode array, then motion detection is achieved, but the cost and size increase due to precision optical assembly requirements
Solution Approach 1:
The patent replaces the complex optical system (laser, mirrors, photodiode array) with a capacitive sensing system that uses electrical fields instead of light. This substitution eliminates the need for precision optical alignment and assembly while maintaining motion detection capability, significantly reducing device complexity and manufacturing cost.
Solution Approach 2:
The patent changes the fundamental detection parameter from optical properties (light reflection, speckle patterns) to electrical properties (capacitance variations). This parameter change enables motion detection through electrical field interactions with the finger, avoiding the need for complex optical components and simplifying the overall system design.
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 fast motion detection beyond 1,000 mm/second with a smaller sensing area and reduced processing power, addressing the limitations of existing sensors without security concerns related to fingerprint image processing.
Implementation Method 1
an array of sense cells to capacitively sense capacitance variations in a structure of a surface in proximity to the array
Data Source
AI summary
A spatial frequency based capacitive motion system and method of operating the same are disclosed. In one embodiment, the system includes an array of sense cells to sense capacitance variations induced by a detected surface in proximity to the array. The system further includes processing circuitry including one or more differential detectors and a processor to process output signals from the one or more differential detectors to measure displacement of the detected surface in a direction parallel to the array. Other embodiments are also disclosed.