NFC Distance Sensing Using RF-Off Ringing Under Metal Interference
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Solution Overview
Problem
NFC technology is limited by the interference of metal objects, which affect communication performance and hinder accurate distance measurement and object detection.
Innovation Solution
An NFC system that processes RF-off ringing signals to determine distance and object characteristics by analyzing signal features such as phase-mean-phase (PMP) and phase-circular-variance (PCV) using a signal processor and look-up tables to map these features to distance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NFC readers use traditional RF communication methods, then communication can be established with NFC tags, but metal objects interfere with the radio field and prevent accurate distance measurement and object detection
Solution Approach 1:
The patent converts the harmful effect of metal objects on RF fields into a beneficial measurement mechanism. By detecting RF-off ringing signals that occur when metal objects are present in the NFC field, the system transforms interference into a detectable phenomenon that enables distance measurement and object detection. The ringing signal characteristics (frequency, amplitude, decay rate) provide information about the metal object's presence and position.
Solution Approach 2:
The patent replaces traditional continuous RF transmission methods with an RF-off detection approach. Instead of continuously transmitting RF signals and measuring responses, the system transmits RF pulses and measures the ringing signals that occur during the off-period between pulses. This substitution enables detection of metal objects and distance measurement that was not possible with conventional continuous transmission methods.
2Use of energy by moving object
If NFC readers transmit continuous RF fields for communication, then data exchange with NFC tags is enabled, but power consumption increases and distance measurement capability is lost
Solution Approach 1:
The patent implements periodic RF pulse transmission instead of continuous transmission. The NFC reader transmits RF pulses at specific intervals, creating periodic on-off cycles. During the off-periods, the system measures RF-off ringing signals to detect metal objects and determine distance. This periodic approach reduces power consumption compared to continuous transmission while enabling distance measurement capabilities.
Solution Approach 2:
The patent maintains continuous useful action by utilizing both the RF-on transmission period for communication and the RF-off period for measurement. Instead of losing the off-period as wasted time, the system continuously measures ringing signals during off-periods, enabling simultaneous communication and distance measurement functions without requiring separate operational modes.
3Reliability
If NFC readers use low-power RF transmissions for communication, then energy efficiency is improved, but the ability to detect metal objects and measure distance is hindered
Solution Approach 1:
The patent enables the NFC reader to self-diagnose the presence and position of metal objects by analyzing RF-off ringing signals generated during normal operation. The system uses its own transmitted RF pulses to create measurable ringing effects when metal objects are present, eliminating the need for separate detection hardware or additional power-consuming detection modes. The low-power RF transmissions serve dual purposes: communication and metal object detection.
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 high-resolution, low-power distance measurement and object detection, allowing applications like door status monitoring and liquid level sensing with improved accuracy and reliability.
Implementation Method 1
a transmitter configured to transmit a radio frequency transmitted field and a receiver configured to receive from an antenna one or more response signals in response to the radio frequency transmitted field transmitted by the transmitter
Implementation Method 2
processing the one or more response signals to determine a first value of a first signal feature of the one or more response signals
Data Source
AI summary
A device may include a data storage device storing a first look-up table that contains a plurality of distance mappings that each associate a value of a first signal feature with a distance value. An NFC reader is configured to communicate with an NFC tag includes: an antenna, a transmitter that is configured to use the antenna to transmit a radio frequency transmitted field, a receiver configured to receive from the antenna one or more response signals in response to the radio frequency transmitted field transmitted by the transmitter, and a signal processor configured to: process the one or more response signals to determine a first value of the first signal feature, access the first look-up table to determine a first distance mapping that associates the value of the first signal feature with a first distance, and generate an output signal based upon the first distance.