Battery Charger for Low-Power RF Energy Harvesting
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Solution Overview
Problem
Existing RF energy harvesting technologies face challenges in efficiently harvesting and storing low-power ambient RF energy, particularly in environments with bursty and power-limited Wi-Fi signals, due to voltage and power limitations, which hinder the operation of digital circuitry and wireless sensors.
Innovation Solution
A battery charger system that includes a boost converter and battery charging circuit optimized for input power levels below −20 dBm, utilizing a transistor-based control mechanism to trickle charge a battery, which has a lower self-discharge rate than capacitors, enabling efficient energy storage and utilization for sensor operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If RF energy harvesting is performed at low power levels (below -20 dBm), then energy can be harvested from ambient Wi-Fi signals, but the rectified energy is both power limited and voltage limited, making it insufficient to operate digital circuitry
Solution Approach 1:
The patent transforms the harvested RF energy parameters through a boost converter that increases voltage from the low voltage output of the rectifier to a higher voltage suitable for operating digital circuitry. This parameter transformation enables the system to operate at power levels below -20 dBm while still providing sufficient voltage for digital operations
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the rectifier and the digital circuitry. The capacitor accumulates energy from the bursty RF signals and provides stable power delivery, bridging the gap between intermittent low-power RF input and continuous digital circuit requirements
2Quantity of substance
If energy is stored in a capacitor, then energy can be accumulated from RF signals, but the stored energy is consumed by circuit leakage in between RF transmission bursts
Solution Approach 1:
The patent changes the energy storage medium from a capacitor with high leakage to a battery with low self-discharge rate. This parameter change in the storage medium's discharge characteristics allows energy to be retained much longer between RF transmission bursts, reducing energy loss while maintaining storage capability
3Loss of energy
If a battery is used for energy storage, then energy can be stored with lower self-discharge rate, but the system requires voltage boosting and control mechanisms to charge the battery from low-power RF signals
Solution Approach 1:
The patent combines the voltage boosting function and battery charging control into an integrated system. The boost converter simultaneously performs voltage transformation and provides the necessary control logic for battery charging, merging multiple functions into a unified circuit that reduces overall system complexity despite the added battery storage component
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 effectively harvests and stores RF energy, providing a stable power source for sensors and communication units, even in environments with low and bursty RF energy availability, thereby extending the operational duration of wireless sensors and reducing maintenance needs.
Implementation Method 1
a boost converter to transform the low voltage RF energy into higher voltage suitable for battery charging
Implementation Method 2
rectification of the RF power incident on an antenna into DC charge on a capacitor
Data Source
AI summary
A battery charger for charging a battery is disclosed. In one embodiment, the battery charger comprises an input for receiving a first voltage and for coupling to a positive terminal of the battery; a first transistor having a first gate, a first drain and a first source, wherein the first gate is for coupling to a charging signal for the battery and the first drain is coupled to the battery negative terminal and, the first transistor to cause energy to be transferred from the input into the battery when turned on; and a group of transistors coupled to the first transistor and the input to control when the first transistor is turned on, wherein the group of transistors comprises a second transistor having a second gate coupled to the input and coupled to a third transistor to turn off the third transistor after a delay occurs after the voltage on the input reaches a predetermined level, and further herein the third transistor causes the first transistor to turn on when the third transistor is turned off.