RF Facial Movement Detection Using Resonant LC Sensing
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Solution Overview
Problem
Conventional LC resonant drive circuits in Mixed Reality (MR) devices require high power-supply levels to achieve sufficient resolution for facial movement detection, which reduces battery life and increases system complexity.
Innovation Solution
A low power efficient RF facial movement detection system using a pulse driver that generates pulse signals below the battery voltage, an LC filter with a high quality factor, and a coupling capacitor to amplify AC voltage at a resonant frequency, eliminating the need for high voltage power supplies and reducing circuit complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional LC resonant drive circuits use high power-supply levels to maximize signal amplitude, then measurement precision is improved, but use of energy increases and device complexity increases
Solution Approach 1:
The patent employs resonant oscillation of the LC circuit at its natural frequency to amplify the sensed signal. By driving the circuit at resonance, the system achieves maximum signal amplitude with minimal input energy, eliminating the need for high power-supply levels while maintaining measurement precision.
Solution Approach 2:
The patent changes the operating parameters by using a resonant frequency drive approach instead of conventional high-power continuous drive. The LC circuit is tuned to resonate at a specific frequency, allowing the system to achieve high signal amplitude through resonant buildup rather than high input power, thus reducing power consumption while maintaining signal resolution.
2Measurement precision
If conventional LC resonant drive circuits use high power-supply levels, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent extracts and eliminates the need for high voltage power supply circuits and complex signal conditioning stages by using resonant amplification. The LC resonance circuit itself provides the necessary signal amplification, removing the need for additional high-power components and simplifying the overall system architecture.
Solution Approach 2:
The LC resonance circuit serves multiple functions simultaneously: it acts as the sensing element, the amplification stage, and the signal source. This multi-functionality eliminates the need for separate high-power supply circuits and complex signal conditioning hardware, reducing device complexity while maintaining measurement precision.
3Use of energy by moving object
If pulse driver operates below battery voltage, then use of energy is reduced, but output signal amplitude decreases
Solution Approach 1:
The pulse driver excites the LC circuit at its resonant frequency, causing the circuit to oscillate with large amplitude despite low input energy. The resonant oscillation naturally amplifies the signal, allowing the system to achieve high output signal amplitude while operating the pulse driver below battery voltage, thus reducing power consumption.
Solution Approach 2:
The patent changes the approach from direct high-power amplification to resonant amplification. By tuning the LC circuit to resonate at the driving frequency, the system achieves high output signal amplitude through energy accumulation during oscillation cycles, rather than requiring high instantaneous power input, enabling low-voltage operation with sufficient output amplitude.
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 system achieves high output signals with low input signals, reducing power consumption and extending battery life while maintaining signal quality, thereby enhancing system performance and user experience.
Implementation Method 1
The capacitance of the antenna varies responsive to facial movements of the user based on the varying distance of the antenna to the user's skin
Implementation Method 2
An LC filter receives the pulse signals and generates a transient response based on a capacitance value associated with an antenna
Implementation Method 3
A coupling capacitor AC couples the output of the LC filter to other system components, where the AC coupled output of the LC filter includes a detected signal amplitude and a detected signal phase
Data Source
AI summary
The techniques disclosed herein provide low power, efficient systems, devices and circuits that detect facial movements of a user of a Mixed Reality (MR) device. An example battery operated system includes a pulse driver that generates pulse signals at a set frequency, while operated below the battery voltage. An LC filter receives the pulse signals and generates a transient response based on a capacitance value associated with an antenna. The capacitance of the antenna varies responsive to facial movements of the user based on the varying distance of the antenna to the users skin. A coupling capacitor AC couples the output of the LC filter to other system components, where the AC coupled output of the LC filter includes a detected signal amplitude and a detected signal phase of the LC filter responsive to facial movements of the user.