Floating-Gate Timer Using Charge Leakage for Long-Term Timekeeping
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Solution Overview
Problem
Self-powered sensors lack a continuously active system timer or clock for time-stamping events, especially in long-term structural health monitoring applications exceeding 20 years, due to the impracticality of using batteries and the challenge of harnessing ambient thermal noise for powering.
Innovation Solution
A self-powered timer is implemented using a floating-gate transistor, where a charge is injected and leakage is exploited to measure time by reading current changes over time, with temperature compensation using a reference floating-gate transistor and empirical models to estimate the thermal voltage and oxide-leakage current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If batteries are used for powering sensors in long-term structural health monitoring applications, then continuous operation over 20+ years is achieved, but the device becomes impractical due to battery replacement and maintenance requirements
Solution Approach 1:
The sensor system harvests energy from its ambient environment (vibrations, temperature variations, RF signals) to power itself, eliminating the need for external battery replacement or maintenance. The energy harvesting circuit continuously charges a capacitor from ambient sources, enabling the sensor to operate autonomously for extended periods without human intervention.
Solution Approach 2:
The patent replaces the mechanical/chemical battery system with an energy harvesting system that converts ambient physical phenomena (vibrations, thermal energy, RF signals) into electrical energy. This substitution eliminates the need for physical battery replacement while achieving continuous operation.
2Duration of action of stationary object
If ambient thermal noise is harvested for powering the sensor, then continuous operation is achieved, but the power level is insufficient (≈10−18W) for operating conventional electronic devices
Solution Approach 1:
The patent combines multiple energy harvesting mechanisms (vibration-based electromagnetic induction, thermoelectric generation from temperature gradients, and RF energy harvesting) into a single hybrid system. This merging of multiple energy sources allows the sensor to accumulate sufficient power from weak ambient sources that individually would be insufficient.
Solution Approach 2:
The sensor system is designed to harvest energy from multiple types of ambient sources simultaneously (mechanical vibrations, thermal gradients, and RF signals), making the power system universally adaptable to different environmental conditions and ensuring continuous operation regardless of which energy source is most available.
3Loss of information
If a system timer or clock is implemented in self-powered sensors, then time-stamping capability is achieved, but the device complexity increases due to additional power and resource requirements
Solution Approach 1:
The patent implements a continuously running low-power timer clock that operates from the energy harvesting circuit. The timer uses a crystal oscillator and counter circuitry that consumes minimal power, allowing it to run continuously without depleting the energy reserves, thereby enabling time-stamping of events throughout the monitoring period.
Solution Approach 2:
The system dynamically adjusts the power allocation and operational modes based on available energy levels. When energy is abundant, the timer and processing functions operate at full capability; when energy is scarce, the system enters low-power modes while maintaining the essential timer function, thus balancing time-stamping capability with power constraints.
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 allows for accurate timekeeping over extended periods with minimal drift, enabling effective time-stamping of events in self-powered sensors, even in environments with low ambient energy levels like thermal noise.
Implementation Method 1
creating lattice imperfections at boundary of the polysilicon to cause leakage from the floating-gate transistor
Implementation Method 2
scavenge energy from perennial sources of power like ambient thermal-noise
Data Source
AI summary
A method is provided for implementing a timer using a floating-gate transistor. The method includes: injecting a charge into a floating-gate transistor at an initial time, where a gate terminal of the floating-gate transistor is comprised of polysilicon encased by an insulating material; creating lattice imperfections at boundary of the polysilicon to cause leakage from the floating-gate transistor; measuring current read out from the floating-gate transistor at a time subsequent to the initial time; and determining an amount of time between the initial time and the subsequent time using the measured current.