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Proceedings of the 42nd European Microwave Conference
FEM Modeling of Gigahertz TEM Cells for
Susceptibility Analysis of RFID Products
Wilmar Heuvelman, Rick Janssen Ralph Prestros
Central R&D BU-Identification
NXP Semiconductors B.V. NXP Semiconductors Austria GmbH
Eindhoven, the Netherlands Gratkorn, Austria
[email protected], [email protected] [email protected]
Abstract-- This paper presents a novel simulation methodology to wave is the TEM (transverse electromagnetic) wave within a
model the coupling between a GTEM cell and an RF-ID antenna. GTEM (gigahertz transverse electromagnetic) cell, because it
This model can further be used in a simulation test bench to locally corresponds to a plane wave from DC to several GHz.
verify the susceptibility of contactless RFID cards to RF Besides the fact that it is difficult to generate the approximation
interference from mobile phone transmissions. In this test bench of a plane wave over such a wide band within an anechoic
the immunity test signals are injected into the contactless smart chamber even with several antennas, most anechoic chambers
card under design within a model of a GTEM cell. A GTEM cell are not really anechoic anymore below 30 MHz. In
is used for this purpose because it is the only real-life test comparison, such a GTEM cell is a low cost and well
environment that allows exposing the DUT with a localized plane
established test environment in Electromagnetic Compatibility
wave from 13.56 MHz up to multi-GHz frequencies. Our
(EMC) testing and described in various EMC standards [2].
proposed methodology has been well verified by comparing
simulations with measurements. In this paper a simulation methodology is proposed, based
on well-verified measurements, that calculates the scattering
Keywords--Gigahertz transverse electromagnetic (GTEM) cell, (S-)parameters between the feed port of a GTEM cell and the
numerical simulation, Finite Element Methods (FEM), feed port of a prototype Proximity Integrated Circuit Card
Electromagnetic Compatibility (EMC), RFID. (PICC) coil antenna (see Fig. 1). This S-parameter model can
be further used in a test bench to verify the EMI susceptibility
I. INTRODUCTION of an RFID proximity integrated circuit. This simulation
Contactless payment/banking card transactions can be method enables either the IC or antenna designer to verify, at
protected against nearly all kinds of fraud by the use of a so- an early stage, the susceptibility of RFID products to any
called crypto tunnel. Such a crypto tunnel is an encapsulation electromagnetic interferer (such as EMI from a GSM signal).
of the data transfer over different public (wireless) networks The S-parameter model from the simulation can be validated
from the CPU of a contactless smart card directly to the credit using S-parameters obtained from measurements.
card provider. Such a crypto tunnel is required if e.g. a
GSM/GPRS enabled Point-of-Sale terminal or a Near Field
Communication (NFC) enabled phone is used as a terminal of a
continuous cell phone connection. During the entire smart card
transaction the RFID circuit is exposed to the wireless
connection, which can interfere with the smart card. Therefore
credit card providers and banks demand proper
Electromagnetic Interference (EMI) susceptibility testing from
the smart card industry with a special focus on the frequency
bands of mobile devices.
Until now such tests have been performed with real-life
contactless readers based on the transformer principle operating
at 13.56 MHz [1] and a simple dipole antenna has been used to
emit the interference signal. The disadvantage of such a
configuration is to setup a proper simulation environment due Figure 1. Orientation of the PICC Antenna inside the GTEM Cell, including
the fields.
to the complexity caused by the fact that the field distribution is
strongly dependent on the distance from the antenna. In
This paper is organized as follows: in section II the
contrast, the simplest simulation setup is a homogenous plane
wave that is incident on the contactless smart card, as it is individual components of the test bench are described;
available in FDTD (Finite-Difference Time-Domain) 3D EM section III shows how the simulation setup is used in real-life
simulators. The practical implementation of such a test bench is to test contactless chip-card prototypes against EMI; in
not possible, because a true plane wave does not exist. section IV the simulation setup is described; finally, in
Therefore the best approximation of a true homogenous plane section V the measurement setup is described that is used to
978-2-87487-027-9