Wireless Impedance Sensor Self-Test for Eye-Mountable Devices
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Solution Overview
Problem
Existing eye-mountable devices face challenges in accurately detecting eyelid overlap due to the conductivity of tear film, which interferes with capacitive sensing, leading to errors in accommodation control mechanisms, particularly in devices relying on photodetection or capacitive sensing.
Innovation Solution
The implementation of an impedance sensor with an oscillator circuit that uses wireless inductive coupling to distinguish between tear film and eyelid overlap, employing a secondary electrode to impart impedance changes for self-testing and feedback control, ensuring accurate accommodation adjustments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If capacitive sensing is used to detect eyelid overlap, then the device can monitor accommodation, but the conductivity of tear film interferes with sensing accuracy
Solution Approach 1:
The patent introduces an intermediary wireless load (secondary electrode system) that couples between the impedance sensor and the eyelid/tear film interface. This intermediary allows the sensor to indirectly measure impedance changes caused by eyelid overlap without being directly affected by the conductive tear film, thereby resolving the interference problem while maintaining measurement precision.
Solution Approach 2:
The patent replaces the direct capacitive sensing mechanism with an inductive coupling system using wireless electromagnetic fields. Instead of relying on direct electrical contact through the conductive tear film, the system uses electromagnetic induction to transfer signals, substituting a mechanical/electrical contact-based system with a field-based system that is immune to tear film conductivity issues.
2Reliability
If built-in self-test mechanisms are added to ensure functional integrity, then reliability improves, but device complexity increases
Solution Approach 1:
The patent makes the secondary electrode system serve multiple functions: it acts as both the wireless load for impedance sensing and the test object for self-testing. The same hardware infrastructure is used for both normal operation and self-diagnosis, eliminating the need for separate dedicated test components and thereby improving reliability without proportionally increasing device complexity.
Solution Approach 2:
The patent implements a self-service mechanism where the device automatically tests its own impedance sensor functionality using its existing wireless load infrastructure. The system performs self-diagnosis without requiring external testing equipment or additional specialized test components, thereby improving reliability while minimizing the increase in device complexity.
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 solution provides reliable and repeatable self-testing of impedance sensors, reducing errors and maintaining accurate accommodation control by efficiently differentiating between tear film and eyelid overlap, thus enhancing the functionality of eye-mountable devices.
Implementation Method 1
an impedance sensor with an oscillator circuit that uses wireless inductive coupling to distinguish between tear film and eyelid overlap
Implementation Method 2
an impedance sensor with an oscillator circuit that uses wireless inductive coupling
Data Source
AI summary
An apparatus with a built-in self-test includes a sensor electrode, an impedance sensor coupled to the sensor electrode to measure a test impedance of the sensor electrode as influenced by an external load, a secondary electrode disposed adjacent to the sensor electrode to inductively couple with the sensor electrode and influence the external load on the sensor electrode, a first switch coupled to the secondary electrode to selectively change a second impedance of the secondary electrode, and a controller coupled to the impedance sensor and the first switch. The controller includes logic for adjusting the first switch to wirelessly load the sensor electrode with the secondary electrode in a predetermined impedance state, measuring the test impedance with the impedance sensor while the secondary electrode is in the predetermined impedance state, and comparing the measured test impedance against a threshold impedance range to perform a self-test.