Wireless Sensor Impedance Sensing for Passive RFID
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Solution Overview
Problem
Current wireless sensors, particularly RFID tags, face limitations in efficiently sensing multiple environmental conditions and providing accurate, real-time data without the need for batteries, as they often rely on indirect sensing methods or require complex circuitry for direct sensing, which increases costs and complexity.
Innovation Solution
The development of wireless sensors that incorporate a sensing element and a power supply impedance altering element, capable of changing RF characteristics and impedance to accurately sense conditions such as moisture, temperature, and pressure, using back-scattering and power harvesting circuits to generate digital values representative of sensed conditions, allowing for multiple sensing options with reduced complexity and cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If passive RFID tags are used for wireless sensing, then battery-free operation is achieved, but sensing accuracy and reliability deteriorate due to indirect sensing methods
Solution Approach 1:
The sensing element utilizes the RF power supply circuit's own impedance changes to perform sensing, eliminating the need for separate sensing circuits. The power supply circuit serves dual purposes: providing power and enabling sensing through its inherent impedance variations when environmental conditions affect the sensing element.
Solution Approach 2:
The RF power supply circuit is designed to perform multiple functions simultaneously - it provides power to the passive tag and also serves as the sensing mechanism. The same circuit that converts RF signals to DC power also detects environmental conditions through impedance changes, reducing overall system complexity.
2Measurement precision
If direct sensing circuits are added to passive RFID tags, then sensing accuracy improves, but device complexity and cost increase
Solution Approach 1:
The sensing function is merged with the power supply circuit by placing the sensing element in parallel with the rectifying diode. This integration eliminates the need for separate sensing circuits, reducing component count and system complexity while maintaining direct sensing capability.
Solution Approach 2:
The power supply circuit performs dual duty by both providing power and enabling sensing through its impedance characteristics. The sensing element's interaction with the power supply circuit creates measurable impedance changes that indicate environmental conditions, making the power circuit self-sufficient for both functions.
3Adaptability or versatility
If multiple sensing elements are added to a single wireless sensor, then sensing versatility improves, but device complexity increases
Solution Approach 1:
Multiple sensing elements (moisture sensor, temperature sensor, pressure sensor) are integrated into a single passive wireless sensor unit, all utilizing the same RF power supply and back-scattering communication mechanism. This allows one sensor to perform multiple sensing functions without requiring separate power or communication circuits for each sensor type.
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, accurate, and cost-effective sensing of various environmental conditions, including moisture, temperature, and pressure, using a single wireless sensor, facilitating real-time data collection and processing without the need for batteries, thereby enhancing monitoring capabilities in diverse applications.
Implementation Method 1
The power supply circuit includes one or more diodes and one or more capacitors. The diode(s) function to rectify the AC signal and the capacitor(s) filter the rectified signal to produce the DC power supply voltage
Implementation Method 2
The power supply circuit includes one or more diodes and one or more capacitors. The diode(s) function to rectify the AC signal and the capacitor(s) filter the rectified signal to produce the DC power supply voltage
Implementation Method 3
using back-scattering and power harvesting circuits to generate digital values representative of sensed conditions
Data Source
AI summary
A wireless sensor includes a radio frequency (RF) front end and a sensing integrated circuit (IC). The RF front end includes an antenna that is operable to transceive RF signals and a tuning circuit. The sensing IC includes a power supply. The sensing IC is operable to detect an impedance change of the power supply. The sensing IC is further operable to convert the impedance change into a digital value. The sensing IC is further operable to output, via the antenna, the digital value.