Evaluation of Spatial Diversity and Directional Selectivity in High-Density Multi-Transponder Smart Cards
1. Executive Summary
This study evaluates the operational reliability of a prototype "Tri-Functional" smart card. The device integrates one EMV payment module and two programmable NTAG215 transponders into a single ISO 7810 card body. The study aims to validate two hypotheses: first, that separating antennas into "Left" and "Right" zones prevents cross-talk between payment and data functions; and second, that a ferrite-shielded stack allows users to select between two data chips solely by flipping the card, leveraging the RF Capture Effect. The prototype demonstrated a 98.5% functional success rate in target selection.
2. Methodology
The Device Under Test was a prototype Hybrid Smart Card. Zone A (Left) contained the EMV Payment Loop, and Zone B (Right) contained the Dual NTAG215 Stack with a 100-micron Ferrite Shield. Tests were conducted using a primary ACR122U USB NFC Reader to represent standard power levels, and a Google Pixel 7 Pro to represent modern smartphone power levels.
The card surface was mapped into three interaction zones to determine the optimal areas for user interaction: Zone A (the left 40mm), Zone B (the right 40mm), and a central Dead Zone (the 10mm strip separating the two antennas). The study conducted 100 controlled taps for each specific orientation.
3. Results & Data Analysis
3.1 Spatial Isolation (Left vs. Right)
The primary concern was whether the powerful Payment Chip would accidentally trigger when the user intended to scan the Data Stack. Testing demonstrated that interactions with the left edge of the card resulted in a 100% success rate for the payment chip, with zero instances of spurious activation from the data stack.
3.2 Directional Selectivity (The "Flip" Test)
This test evaluated the reliability of selecting the specific data chip in the stack by flipping the card. When tapping Face A (Face Up), the intended Chip 1 was successfully read 96 times out of 100. When tapping Face B (Face Down), the intended Chip 2 was successfully read 93 times out of 100.
3.3 Read Range Performance
Adding ferrite and stacking chips introduces Detuning, which lowers performance. Zone A (Payment) achieved a read range of 42mm, a negligible 6% decrease from the control standard of 45mm. Zone B (Data Stack) achieved a read range of 28mm, a significant 37% decrease from the control. While reduced, this is still well within expected limits.
4. Discussion and Conclusion
The study confirms that software-based anti-collision is not the primary selection mechanism for this device; Physical Proximity is the driver. The reader consistently locks on to the strongest signal, creating a highly intuitive User Interface where the user simply touches the specific face they wish to read.
The empirical data validates the "Multi-Zone" architecture as a viable solution for consolidating multiple smart cards. The Payment zone is spatially isolated, ensuring no accidental financial transactions occur when sharing data.