RFID Tag Power Prioritization Using Field Strength Sensing
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Solution Overview
Problem
Existing RFID systems lack an effective method to quantify RF field strength as a function of induced current, which hinders the ability to maximize received power with minimal power loss and efficiently vary the input impedance during normal operation.
Innovation Solution
A sensing system for RFID systems that includes a tank circuit with selectively variable impedance and a detector circuit to quantify RF field strength, allowing the RFID reader to dynamically adjust the impedance and sense environmental changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage quantization is used to match tank circuit frequency to transmission frequency, then frequency matching is achieved, but received power maximization is not effectively achieved because voltage quantization is only indirectly related to received signal field strength
Solution Approach 1:
The patent replaces voltage-based frequency matching with a current-based field strength detection system. A detector circuit measures the actual RF induced current, which directly correlates to received signal field strength. This substitution of measurement basis (from voltage to current) enables direct quantization of field strength, providing more accurate feedback for impedance adjustment and power maximization.
Solution Approach 2:
The patent implements a feedback mechanism where the detector circuit continuously monitors RF induced current and provides quantized field strength information back to the impedance control system. This feedback loop enables dynamic adjustment of tank circuit impedance to maximize received power based on actual field conditions rather than relying solely on frequency matching.
2Power
If dynamic impedance variation is implemented to maximize received power, then power transfer efficiency improves, but system complexity increases due to additional detector circuit and control mechanisms
Solution Approach 1:
The detector circuit serves multiple functions: it detects RF induced current for field strength quantization, provides feedback for impedance control, and can trigger alerts when field strength exceeds thresholds. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall system complexity while achieving dynamic power optimization.
Solution Approach 2:
The patent changes the measurement parameter from voltage to current for field strength detection. By monitoring RF induced current directly, the system achieves more accurate field strength quantization with a relatively simple detector circuit implementation, avoiding the need for complex voltage-based indirect measurement systems while enabling effective impedance control.
3Measurement precision
If RF induced current is used as the basis for field strength quantization, then direct measurement of received signal strength is achieved, but additional detector circuitry is required
Solution Approach 1:
The patent merges the field strength detection function with the existing power management and control circuits. The detector circuit that measures RF induced current is integrated into the tag's existing architecture, sharing components and control logic with other system functions. This merging approach enables direct field strength measurement without proportionally increasing overall circuit 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
Enables efficient quantization of RF field strength, allowing for optimal power transfer and impedance adjustment, thereby maximizing received power while minimizing power loss and effectively sensing environmental changes.
Implementation Method 1
the amplitude modulated (AM) signal broadcast by the reader in an RFID system will be electromagnetically coupled to a conventional antenna, and a portion of the current induced in a tank circuit
Data Source
AI summary
A method includes transmitting, by a radio frequency identification (RFID) reader, a series of RF signals to RFID tags in a time sequence. A first RF signal includes a first message for responding when received signal strength corresponds to a first power level and a second RF signal includes a second message for responding when the received signal strength of the RF signal corresponds to a second power level. The method further includes receiving, by the RFID reader, a first set of responses from a first set of RFID tags that received the first and second RF signals at a received signal strength corresponding to the first power level. The method further includes receiving, by the RFID reader, a second set of responses from a second set of RFID tags that received the first and second RF signals at a received signal strength corresponding to the second power level.