EAS Pedestal Backfield Reduction via Signal Level Adjustment
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Solution Overview
Problem
Electronic Article Surveillance (EAS) systems face issues with undesired alarms due to electromagnetic energy radiating into backfields, which can lead to false detection of markers outside the intended detection zone, necessitating a solution that does not compromise detection performance.
Innovation Solution
The method involves measuring and comparing tag responses at two pedestals to determine the relative signal strength, reducing the exciter drive signal for the pedestal with the lesser response, and adjusting the electromagnetic field to minimize backfield interference, allowing for precise location determination of tags within the detection zone.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the electromagnetic field intensity is increased to improve detection sensitivity, then detection precision is improved, but backfield interference increases causing false alarms
Solution Approach 1:
The patent applies different signal levels to different spatial zones by using two pedestals with different exciter signal levels. The first pedestal uses a higher signal level for the first signal level zone, while the second pedestal uses a lower signal level for the second signal level zone. This creates localized field intensity optimization - strong enough to detect tags in the primary detection zone but weak enough to minimize backfield interference and false alarms.
Solution Approach 2:
The patent changes the parameter of exciter signal level between the two pedestals. The first pedestal operates at a first exciter signal level while the second pedestal operates at a second exciter signal level that is lower than the first. This parameter differentiation allows the system to maintain detection sensitivity in the primary zone while reducing backfield effects that cause false alarms.
2Object-affected harmful factors
If a single pedestal transmits and the other receives to reduce backfield alarms, then false alarms are reduced, but pedestal separation must be reduced compromising detection zone coverage
Solution Approach 1:
Rather than making both pedestals identical in function (both transmit or both receive), the patent assigns different signal levels to different pedestals. Both pedestals can transmit simultaneously, but the second pedestal uses a lower exciter signal level. This creates localized field zones where the first pedestal covers a larger area with higher power, while the second pedestal provides supplementary coverage with lower power, reducing backfield interference without sacrificing overall detection zone coverage.
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 approach effectively reduces undesired alarms by accurately determining the location of tags within the detection zone, preventing false alarms and maintaining system performance without adding new hardware or increasing costs.
Implementation Method 1
A reduced level exciter drive signal is then applied to the exciter coil at the first pedestal so as to produce an electromagnetic exciter field in the detection zone
Implementation Method 2
markers which respond in some known electromagnetic manner to the interrogation signal
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4B
AI summary
Method for reducing undesired alarms in an electronic article surveillance (EAS) system involves measuring a tag response at a first and second pedestal to obtain contemporaneous first and second tag responses. The tag responses are compared to evaluate relative signal strength and thereby discern a lesser signal strength tag response. A reduced level exciter drive signal is applied to a selected one of the first and second pedestals associated with the lesser signal strength tag response. A. detection zone is then monitored to determine the occurrence of a third tag response resulting from the reduced level exciter signal. The approximate location of the tag in relation to the first and second pedestals is determined based on the first, second, and third tag responses.