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M. Pesic, W. Pachler, S. Rampetzreiter, H. Arthaber:
"Modeling and Design of Small, Passive, and Standard-compliant Proximity Coupling Transponders";
Talk: 2020 IEEE International Conference on RFID (RFID), Orlando, Florida, USA; 09-28-2020 - 10-16-2020; in: "2020 IEEE International Conference on RFID (RFID)", (2020), ISBN: 978-1-7281-5576-0; 7 pages.

Proximity coupling (13.56 MHz) RFID transpondersof today utilize small form factor antennas and are passive interms of power supply. They are predominantly used in smartwearables (e.g., watches, bracelets, rings). Such transponder sizesdemand careful design regarding energy transfer and longestachievable operating distance, so that compliance to standards (e.g., EMVCo) can be maintained.
This work compares three design approaches for thesetransponders: IC-only tuning, optimized tuning, and powermatching, along with their advantages, disadvantages, and rea-soning behind the choice of right transponder components(antenna and IC). A simulation framework based on linear andnonlinear modeling is also presented. It offers more degrees offreedom in searching for the optimal design and predicts the mostimportant figue of merit for these transponders: the minimum operating magnetic fiel strength (H_min).
Compared to measurements, our framework was able topredict H_min with an accuracy of under 0.1 A/m. The three designapproaches were applied on rectangular 20x25 mm transpondersthat were modeled within the framework and subsequentlyfabricated. Using power matching (H_min=0.78 A/m, Q=27.64)resulted in a significan improvement over IC-only tuning(H_min=1.71 A/m, Q=3.98) and optimized tuning (H_min=1.31 A/m,Q=5.02). An even smaller (20x20 mm) transponder with powermatching was still able to fulfil EMVCo compliance and achieve a reading distance of 7 cm with a typical payment reader.

http://dx.doi.org/10.1109/RFID49298.2020.9244912