EAS Detection Threshold Adjustment for Booster Bag Shielding
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Solution Overview
Problem
Existing electronic article surveillance (EAS) systems are vulnerable to circumvention by metal-lined 'booster bags' that act as Faraday cages, shielding tags from detection, leading to false negatives or false alarms when passing through automatic doors with metal parts.
Innovation Solution
A method involving demodulating signals received by antennas to detect base levels and predict a lower threshold, allowing for real-time detection of metal objects like booster bags by evaluating signal transitions and setting alarm detectors accordingly, even when automatic doors are opening, thereby improving detection reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a metal-lined booster bag is used to shield tags, then electromagnetic shielding effectiveness is improved, but detection reliability deteriorates
Solution Approach 1:
The system performs preliminary actions by detecting door movement patterns and adjusting detection parameters before the actual detection of metal objects. The base level detection and threshold adjustment occur proactively based on door state, ensuring the system is prepared to accurately detect booster bags even when doors are moving, thus maintaining detection reliability despite shielding attempts.
2Measurement precision
If detection sensitivity is increased to detect booster bags, then detection capability is improved, but false alarms increase
Solution Approach 1:
The system dynamically adjusts detection thresholds and parameters based on real-time door state and signal base levels. Instead of using fixed sensitivity settings, the detection threshold adapts to current environmental conditions, allowing high detection sensitivity while dynamically controlling false alarm rates through context-aware parameter adjustment.
Solution Approach 2:
The system continuously monitors signal base levels and uses this feedback to adjust detection thresholds in real-time. By comparing current signals against dynamically updated base levels and thresholds, the system maintains optimal detection sensitivity while reducing false alarms through continuous adaptive feedback control.
3Area of stationary object
If detection occurs during door movement, then detection coverage is improved, but signal interference increases
Solution Approach 1:
The system extracts and separates door movement signals from metal object detection signals by detecting base level changes. By identifying and isolating the characteristic signal patterns caused by door movement, the system can distinguish these from actual metal object signals, maintaining detection coverage during door operation while filtering out interference through signal separation.
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
This method enhances the ability to accurately detect booster bags and other metal objects at the moment they pass through automatic doors, reducing false alarms and improving the reliability of EAS systems by processing signals in real-time and adjusting thresholds based on door states.
Implementation Method 1
The detection system for such tags emits, by a transmitting antenna, periodic tonal bursts at about e.g. 58 kHz, the same as the resonance frequency of the amorphous strips. This causes the strip to vibrate longitudinally by magnetostriction
Implementation Method 2
The vibration causes a change in magnetization in the amorphous strip, which induces an AC voltage in a receiving antenna
Implementation Method 3
When a tagged good is placed in a booster bag, the booster bag will act as a Faraday cage, shielding the tags from the detection system's transmitting and receiving antennas
Data Source
AI summary
A method of detecting a metal object in a detection zone between a transmitting antenna (101) and a receiving antenna (102) installed in proximity of an automatic door (105; 106), the method comprising: demodulating an amplitude modulated signal received via the receiving antenna to provide a first signal; and on a recurring basis: detecting a first base level of the first signal at a point in time when the first signal is settled at a magnitude at or about the first base level, and following a first signal transition of the first signal, detecting a second base level of the first signal at a point in time when the first signal is settled at a magnitude at or about the second base level; predicting a lower base level to be the lowest of the first base level and the second base level and setting a first threshold value, which is set relative to and lower than the lower base level predicted; and evaluating whether the first signal falls below the first threshold value and setting a first alarm detector at a point in time, while the first signal is below the first threshold value. Thereby it is possible to detect a metal object, such as a ‘booster bag’, in a detection zone in proximity of automatic doors even at the very moment the automatic door opens.