Tire Pressure Sensor Phase Modulation Accuracy
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Solution Overview
Problem
Existing tire pressure sensors lack accuracy in measuring tire pressure using RFID technology, as they rely on frequency shifts that are not reliably indicative of pressure changes due to variations in capacitance.
Innovation Solution
A tire pressure sensor utilizing a parallel resonant circuit with a capacitive pressure sensor connected via switches, generating distinct RF signals based on pressure-induced capacitance changes, allowing for precise pressure determination through frequency differences measured by a reader circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a passive RFID transponder is used for tire pressure monitoring, then power consumption is reduced and the device is simplified, but measurement precision deteriorates because frequency shifts are not reliably indicative of pressure changes
Solution Approach 1:
The patent changes the measurement parameter from frequency shift to phase shift. The transponder modulates the phase of the RF signal in response to pressure changes detected by the capacitive sensor, rather than changing frequency. This phase modulation provides more reliable and precise pressure measurement while maintaining the passive operation of the transponder.
2Loss of information
If frequency shift modulation is used to transmit pressure data, then the transponder can communicate pressure information, but measurement precision worsens due to capacitance variations that are not reliably indicative of pressure changes
Solution Approach 1:
The patent changes the modulation parameter from frequency to phase. The capacitive pressure sensor detects pressure changes and modulates the phase of the RF signal accordingly. This phase modulation technique provides more reliable pressure information transmission because phase changes are more directly and reliably correlated with capacitance changes than frequency shifts are.
3Adaptability or versatility
If a capacitive pressure sensor is integrated into the resonant circuit, then pressure measurement capability is added, but device complexity increases due to additional components and calibration requirements
Solution Approach 1:
The patent merges the capacitive pressure sensor directly into the resonant tank circuit of the transponder. The sensor capacitor becomes part of the resonant circuit, eliminating the need for separate sensing and communication circuits. This integration reduces overall device complexity while adding pressure sensing capability, as the same circuit components serve dual purposes.
Solution Approach 2:
The resonant circuit serves multiple functions: it acts as both the communication carrier wave generator and the pressure sensing element. The capacitive sensor integrated into the tank circuit allows the same circuit to both transmit data and measure pressure, reducing the need for additional dedicated components and simplifying the overall device architecture.
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 solution enables accurate tire pressure measurement by generating and interpreting specific frequency shifts, improving measurement accuracy and allowing for calibration to correct for external influences, thereby providing reliable pressure data.
Implementation Method 1
a parallel resonant circuit comprising an inductor and a first capacitor for generating a first radio frequency (RF) signal
Implementation Method 2
a second capacitor coupled across the parallel resonant circuit by a first switch in a first position with generating a second RF signal
Implementation Method 3
A capacitive pressure sensor is coupled across the parallel resonant circuit by the first switch in a second position for generating a third frequency RF signal
Data Source
AI summary
A tire pressure sensor has an RFID (radio frequency identification) device having a parallel resonant circuit including an inductor and a first capacitor for generating a first radio frequency (RF) signal for transmission to a reader circuit, and a second capacitor coupled across the parallel resonant circuit by a first switch in a first position and generating a second RF signal for transmission to the reader circuit. A capacitive pressure sensor is coupled across the parallel resonant circuit by the first switch in a second position for generating a third frequency RF signal for transmission to the reader, wherein a difference in frequency between the first and third RF signals is indicative of a pressure of a tire.