Shield Electrode Enhances Capacitive Skimmer Detection Distance
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Solution Overview
Problem
Current capacitive sensor systems for detecting skimmers at self-service terminals have limited skimmer detection distance due to the presence of a ground plane, which reduces the magnitude of the projected electric field and limits their effectiveness.
Innovation Solution
Incorporating a shield electrode between the transmit electrode and the ground plane, driven by the same signal as the transmit electrode, to minimize signal leakage and enhance the projected electric field magnitude without increasing signal strength, thereby improving skimmer detection distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a ground plane is used on the transmit electrode printed circuit board to prevent false triggering by movement behind the front fascia, then false alarm reduction is improved, but skimmer detection distance is limited
Solution Approach 1:
A shield electrode is introduced as an intermediary element between the transmit electrode and the ground plane. This shield electrode is driven by the same signal as the transmit electrode, creating a capacitive shield that prevents signal leakage to the ground plane while maintaining the electric field projection in the forward direction. The shield electrode acts as a mediator that resolves the conflict between needing a ground plane for stability and avoiding signal leakage that limits detection distance.
2Reliability
If the ground plane is placed close to the transmit electrode to reduce sensitivity to movement behind the electrode, then reliability is improved, but the magnitude of the projected electric field is reduced
Solution Approach 1:
The shield electrode serves as a capacitive barrier between the transmit electrode and ground plane, allowing the ground plane to remain close to the transmit electrode for stability while preventing capacitive signal leakage. The shield electrode is driven at the same potential as the transmit electrode, creating a virtual extension that maintains electric field magnitude in the forward direction without the ground plane interfering.
3Length of stationary object
If signal strength is increased to enhance the projected electric field magnitude, then skimmer detection distance is improved, but signal leakage to the ground plane increases
Solution Approach 1:
The shield electrode introduces a capacitive barrier that blocks signal leakage to the ground plane. This allows the system to maintain or increase signal strength for enhanced detection distance without the penalty of increased leakage, as the shield electrode captures and redirects the electric field lines away from the ground plane and toward the forward detection zone.
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 configuration allows for a larger projected electric field in front of the transmit electrode, enhancing skimmer detection capabilities without triggering false alarms from internal movements, thus improving the overall effectiveness of the fraud detection system.
Implementation Method 1
the shield electrode is driven by the same signal as the transmit electrode... to enhance the projected electric field magnitude
Implementation Method 2
Capacitive sensor-based skimmer detection systems typically identify the presence of a skimmer by detecting a change in a projected electric field coupling between a transmit electrode and a receive electrode
Data Source
AI summary
A system and method for detecting a foreign object is disclosed. A transmit assembly has a transmit electrode, a ground plane, and a shield electrode positioned between the transmit electrode and the ground plane. Drive circuitry applies a predetermined fixed signal to the transmit electrode and to the shield electrode. A receive assembly is positioned adjacent to the transmit assembly and has a receive electrode. Detection circuitry is coupled to the receive electrode and generates a receive signal based the predetermined fixed signal applied to the transmit electrode. A controller monitors the receive signal to determine when a foreign object has been placed in proximity to the transmit assembly and/or the receive assembly.