Radio Frequency Identification (RFID) has revolutionized the tracking practice for many industries, as it offers a quicker way to track multiple items over long distances. RFID is a highly versatile technology with applications throughout tracking businesses – from baggage handling, controlling manufacturing processes to real-time tracking of inventory. While it can offer considerable benefits, it does come with some limitations and challenges, such as read range limitations, sensitivity to the types and shape of surrounding materials, orientation, and positioning, etc.
To successfully optimize RFID deployment and take full advantage of what this technology has to offer, careful system design must be undertaken with focus on antennas and the surrounding electromagnetic environment.
HFWorks Modeling of RFID Systems
To contribute to this research effort, we used our electromagnetic virtual prototyping software, HFWorks, to study the effect of metals, liquids, and dielectric materials on the tag performance. Moreover, we examined the read range of the tag under various conditions.
The Performance of Tag and Reader Antennas
An RFID system consists of a tag and a reader. The tag is composed of a chip and an antenna. The design of the tag and reader antennas was obtained from the two journal papers [1] and [2]. For the tag, NXP SL3S1213 UCODE G2iL chip is used. The IC chip has a power sensitivity of -18 dBm (- 48 dB).
The (left) Top View and (right) Bottom View of the Reader Antenna
Tag Antenna Reader and Tag Antennas
The tag and reader antennas are simulated, the following results are obtained:
Return Loss of the Reader and Tag Antennas
Electric Field Animation of the Reader and the Tag Antennas
3D Gain Pattern of the Tag Antenna
3D Gain Pattern of the Reader Antenna
2D Gain Pattern of the Reader and Tag Antennas
From the return loss plot, we can notice both the tag and reader antennas resonate at the same UHF frequency of 868 MHz. The reader has a directional radiation pattern, whereas the tag has an omnidirectional radiation pattern as illustrated in the 2D radiation figure.
The Effect of Dielectric Materials, Metals and Liquids
Antennas do not function independently of surrounding objects. The objects can destruct the performance of the antenna. In RFID systems, the object materials should have a minimum effect on the operation of the tag antenna so that the reading stability remains intact. The behavior of the tag antenna, however, varies when it is mounted on different objects.
Return Loss of the Tag Mounted on Different Objects
Far Field Results Table for the Tag Unattached to Objects
Far Field Results Table for the Tag on a Stainless-Steel
Far Field Results Table for the Tag on Filled Plastic Water Bottle
We can notice from the above plot that the dielectric materials such as glass and plastic decrease the read range of the tag due to frequency shift of the resonance frequency. On the other hand, metallic objects and liquids seriously degrade the impedance matching, the radiation efficiency, and the read range of the tag antenna, as can be observed in the above tables. Metals reflect a part of the radiated electromagnetic waves, whereas liquids absorb some of them. The radio-frequency electromagnetic field of the reader powers the tag -passive tags- and allows the RFID reader to communicate with the tag. The presence of the metals and liquids can prevent the chip from receiving enough energy. Consequently, the communication between the reader and tag may break down.
Read Range of the Tag under Different Conditions
The tag antenna and the chip sensitivity play a major role in the performance of an RFID system, namely, the read range. There are several factors that affect the readability of the tag. These include impedance matching between the tag and the IC chip, the gain of the tag and the reader antennas, the power sensitivity of the chip and the surrounding objects. By performing a parameterization study, the read range of the tag under different conditions is obtained. The results are displayed below:
Read Range of the Tag on Different Objects
The tag has a read range of 2.5 m unattached to objects and 2 m in an empty plastic bottle. The read range drastically decreases to 1 m in an empty metallic bottle and to less than 1 m in a filled plastic water bottle.
Conclusion
RFID systems, pivotal for modern tracking applications, are influenced significantly by their deployment environments. This study, utilizing HFWorks software, emphasizes the necessity of meticulous system design, focusing on antennas and their electromagnetic interactions. Through simulated scenarios involving various materials, we demonstrate the substantial impact on tag performance and read range. This exploration underlines the importance of adapting RFID systems to their specific operational contexts, ensuring optimal performance amidst the challenges posed by surrounding materials.
References
[1] B. Shrestha, A. Elsherbeni, L. Ukkone, 2011, “ UHF RFID reader antenna for near-field and far-field operations”
[2] M. Tariqul Islam, T. Alam, I. Yahya and M. Cho, 2018, “Flexible Radio-Frequency Identification (RFID) Tag Antenna for Sensor Applications”
