A Seminar Report on“Design and

Optimization of Low Cost Booster-Based HF RFID

Cards”

Submitted by :-
NAME :-AASHISH GHIMIRE
ID: 2016UEC1005
BATCH-EC-01

Under the guidance of

Dr. Ashish Kumar Ghunawat

Professor; Dept. of ECE,

MNIT, JAIPUR
ACKNOWLEDGEMENT

I would like to thank our Project Guide, Prof Dr. Ashish Kumar
Ghunawat his continuous support and encouragement in a
right way. It was he who provided an aim anddirection to
this project and constantly pushed me to work harder on it.
CONTENTS

1. INTRODUCTION
2. Non-Galvanic System
3. Booster-Based Cards
4. Design
5. Simulations and Measurements
6. Conclusion

1.INTRODUCTION
Radio Frequency Identification (RFID) technology had been the
focus of many researches for the past years. This is motivated
by its wide range of applications such as: biomedical sensors,
healthcare, tracking of goods, documents and animals … etc.
There are several challenges for RFID development such as
increasing the read range, lowering the cost of production,
enhancing robustness and reducing the size.
HF RFID systems operate at 13.56 MHz and is composed of a
reader that contains a coil (antenna) and a card that contains a
coil and chip. The communication between reader and card is
achieved through inductive coupling. There exist many
applications for such a technology, therefore, optimizing the
design of RFID systems has been a research focus for the past
recent years.
An HF RFID system is comprised of a reader coil which
transmits electromagnetic RF signals to a Proximity Integrated
Circuit Card (PICC). The communication between the reader
and card is achieved through inductive coupling where the card
contains a coil and chip. Conventionally, these two elements on
the card are connected galvanically through an electric wire.
However, this reduces the robustness of the card against
mechanical stress and increases the cost of production. We
have investigated the performance of a design [1] that utilizes a
lumped capacitor, booster coil and module in order to achieve a
non-galvanic coupling on the card. In the current work, we
propose a method for optimizing the parameters of that design
to achieve a maximum power transfer at the frequency of
operation and we also investigate the bandwidth capabilities.
2. Non-Galvanic System
An RFID card operates within a weak coupling range with
respect to the reader, where the coupling factor is in the range
of 0.05. Therefore, one can study the card on its own without
including the reader in order to simplify the analysis. A non-
galvanic card would be composed mainly of a module and an
additional circuitry. The module is composed of a chip and a
small coil denoted as module’s coil.

Fig. 1:Circuit model for non-galvanic card.

The lumped capacitor enhances the power transfer between the

reader and PICC. A module [2] is composed of a module coil
mounted with a chip and is placed on top of the secondary coil
to wirelessly couple the chip to the booster coil. Fig. 1 shows the
circuit model for the card where R1, L1 and C1 form the circuit
model of the primary coil. Similarly, R2, L2, and C2 are the
elements for the secondary coil. The capacitor CB is the lumped
capacitor placed within the booster coil.
Furthermore, Lm and Rm are the inductance and resistance of
the module coil. The simplified chip load is composed of the
capacitor Cc and the parallel resistance Rc. In this model, the
parasitic capacitance of the module coil is included also
within Cc.
The quality factor - bandwidth limit, composed of a matching
circuit and a shunt RC load, is known as the Bode-Fano
criterion .The Bode-Fano Limit. There exists a general limit
on the bandwidth over which an arbitrarily good impedance
match can be obtained in the case of a complex load
impedance. It is related to the ratio of reactance to resistance,
and to the bandwidth over which we desire to match the load.

Fig. Percentage of increase in bandwidth with respect to different matching circuit orders.

3. Booster-Based Cards
We propose a design for the PICC composed of two coils and a
lumped capacitor, to serve as a booster coil. The structure of
such a design where the two coils are named primary and
secondary coils. The points denoted by “1” and “2” in the figure
are connected together using a different layer. The coil-on-
module containing the module coil and chip is placed directly
on top of the secondary coil. The free space inside the
secondary coil can be used to glue the module. . The capacitor
in between the booster plays an important role where it creates
a series resonance circuit which enhances the coupling. It can
also be interpreted as a matching circuit that ensures maximum
transmission of energy between the reader and card.

Fig.(a)
Overview of non-galvanic RFID system (b) booster coil composed of primary,
secondary coils and a lumped capacitor.
The mutual inductances in (3) and (4) are almost identical to
that in equations (1) and (2), which was verified through
FastHenry [10]. Therefore, we can infer that the primary coil
dominates the coupling between the PCD and booster.
Similarly, the secondary coil has the highest contribution in the
mutual inductance to the module coil. So the function of the
booster can be clarified where the primary coil efficiently
couples information from the PCD and transfers it to the
secondary coil which efficiently communicates with the module
coil. There exists three additional coupling factors which have a
minor effect on the performance.
Fig .Representation of under-, critical- and over-coupling of a double tuned circuit.

4. Design
The use of Fast Henry, we choose the proper geometries for the first card, denoted by
“Card 1” that correspond to the previously calculated values, as indicated in Table I. The
variable ‘N’ indicates the number of turns, ‘a’ and ‘b’ are the width and length of the coil,
respectively. The track width and height are given by ‘w’ and ‘h’, and ‘g’ is the gap
between two adjacent wires. After determining the dimensions of the coils, the assumed
values of the parasitic elements (C1 , Rm , … ) can be calculated and reused
in (5) and (6). This iteration is repeated a couple of times for higher accuracy.
Furthermore, we manufacture two more cards where the only difference is in the
dimensions of the secondary coil. It is noted that the inductance value is still the
same 0.7 μH , however, we use different dimensions in order to increase the mutual
inductance M to the module’s coil. Table II, shows the dimension of the secondary coil
for “Card 2” and “Card 3”.

Table I: Dimensions of the primary, secondary and module coils (all values are in mm units).

Fig. 4 shows the geometry of the non-galvanic card based on the dimensions given
previously, created using HFSS. Table II represents all the coupling coefficients between
the reader and the non-galvanic PICC, calculated by FastHenry.
Table II: The mutual inductances between the reader antenna and PICC.

To create a comparison to the normal galvanic cards, we

designed a coil for direct connection to a 69 pF chip. The card is
composed of one coil with the dimensions of 50×80 mm, 3
turns, 0.3 mm track width, 0.3 mm gap and 0.035 mm track
height. This card is denoted as “Galvanic Card” and is shown
in Fig. 10. We have two prototypes; one with a chip and the
second with a lumped RC load. For a fair comparison, we used
an identical chip as in the modules. On the manufactured
galvanic cards, there are 2 pins which are placed only for
connecting the measurement probe and do not affect the card’s
operation. It is noted that HF RFID cards in the market usually
have higher resonance frequency (nearly 16 MHz) to adapt to
certain standardized constraints, which means trading off the
voltage at the chip side with the achieved bandwidth. However,
for the sake of fair comparison, we designed this galvanic card
to have a resonance frequency at 13.56 MHz similar to the
booster-based cards.
Fig. 10.Manufactured galvanic card with (a) a 69 pF chip (b) a lumped RC load.

Through utilizing FastHenry and HFSS, we calculate the value

of the circuit elements in Fig. 6. Table IV shows the values of all
circuit elements for Card 1. For Card 2 and Card 3, the only
difference is in the secondary coil. We have manufactured it to
have an inductance of nearly 0.7 μH and there is not a
significant change in the parasitic elements also. However, the
mutual inductance between the secondary coil and the reader
are changed where for Card 2, it is equal to 0.64 μH . Since the
secondary coil of Card 3 has more turns directly below the
module’s coil, it has the highest mutual inductance M=0.94 μH .

TABLE IV Circuit Elements Values for Booster-Based Card 1

5. Simulations and Measurements
In order to achieve practical results for the operation of our
booster-based cards in an actual RFID system, we include the
reader into our setup. The reference reader coil is specified at
the ISO/IEC 10373-6, where we use test Proximity Coupling
Device (PCD) layout 1 (available at Annex A [1]) for both
simulations and measurements. The standard defines a
measurement setup composed of a Test PCD assembly where
the reader coil and card are separated by distance of 37.5 mm.
The card under test is placed on the test PCD assembly and an
active probe is used to measure the voltage transferred from the
reader to the terminals of the chip or lumped load. In such a
setup, it is essential to use an active probe rather than a normal
passive probe, since the parasitic capacitance of such probes is
very low (~ 1 pF) in contrast to a (~ 10 pF) capacitance for
passive probes. Such high capacitance value would be relatively
close to the capacitance of the chip which means it would
detune the results. The reader is placed in the second slot at
the distance 37.5 mm. The second sense coil is located at the
last slot which is placed in accordance to the standard, but does
not influence the measurements in our setup.

Fig. 11.
Test setup to measure the transferred voltage to the chip on an RFID card.
Fig. 14.
Comparison of the voltage transferred to Card 1 with a module containing a lumped RC load
using measurements and simulations to that of a booster card without CB .

Table I shows five coupling coefficients which are used for the
ADS simulation of the RLC model given in Fig. 2. The main
contributing coupling coefficients - marked in red - are: the one
between the PCD and primary coil, and that between the
secondary and module coils. We can also notice that the value
of the coupling coefficient between L1 and LModhas a relatively
high value, however, it does not have a high contribution to the
performance in comparison to k2−Mod. Additionally, two more
coupling coefficients are represented in the table which add a
small contribution to the overall coupling of the system.
Fig. 5:
Magnitude of the transmission coefficient between the PCD (portl) and PICC (port2): comparison
between the measurement and simulations (ads, hfss).
6. Conclusion
We have presented a design for non-galvanic cards which
enhances the coupling through the use of a lumped capacitor.
Results of the RLC circuit simulation are aligned with HFSS
simulation and measurements, which verify the accuracy of the
RLC model. Moreover, the use of lumped capacitor enhances
coupling as the magnitude of transmission coefficient is
increased by almost 15 dB.

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