RFID (radio-frequency identification) is a wireless technology that can be used for various purposes, including identification, monitoring, sensing, and security. RFID tags typically have an antenna (for interaction with the reader) as well as a silicon integrated circuit (IC), or chip, on which data is stored. Despite chipped-RFID tags are inexpensive (usually a few Euro cents), in many situations, this cost can account for a major portion of the item price, preventing this technology from becoming adopted more and more.
To overcome chipped-cost RFID’s limitations, substantial work has been dedicated to chipless-RFID in the previous decade, with chips being substituted with printed encoders. When contrasted to silicon ICs, such encoders are often built on plastic substrates utilizing printing methods such as inkjet printing (or huge manufacturing operations such as rotogravure, screen printing, etc.) utilizing conductive inks. Printed encoders, on the other hand, take up a lot of space (roughly equivalent to the number of bits) and have a limited data storage capacity when comparing to the 96 bits of regulated passive RFID technology operating in the Ultra-High Frequency (UHF) band as well as with a small range.
As a result, numerous attempts have been made to improve the datastore capacity and read distances of chipless-RFID devices in recent years.
- Chipless-RFID systems can be implemented in two ways: in the time domain or the frequency domain. The majority of systems in the former approach use time-domain reflectometry (TDR), in which the ID code is determined by the echoes created by the tag (a delaying line with reflectors at specific points) in response to a short pulse (interrogation signal). Despite their competitiveness, TDR tags based on surface acoustic wave (SAW) technologies are unsuitable for normal printing procedures.
- The frequency-domain Chipless RFID systems rely on printed tags made up of a series of resonant elements adjusted to different frequencies. Each resonator in these tags offers a bit of information, a ‘1’ or ‘0’ based on whether the resonator is functioning or detuned. The interrogating signal is a multi-frequency signal that should cover the tag’s whole spectral bandwidth. The number of bits determines the frequency sweep necessary for the interrogation signal. As a result, with a simple and low-cost reader, certain limits cannot be exceeded.
What is new with this Chipless-RFID Sensing and Identifying Mechanism?
A novel time-domain chipless-RFID sensing and identifying system, theoretically similar to the previous model, is proposed in a recent study on chipless RFID systems, where tag reading doesn’t require tag motion. The tags in this proposed format are the same as those used during near-field chipless-RFID, i.e., linear chains of matching resonators (present or not, at predetermined and equidistant points).
Previous chipless-RFID methods rely on near-field coupling and consecutive bit reading in the time domain demand the tags to be manually put over the reader for tag reading; however, tag motion is not required in the system described in this study. Time-division multiplexing is accomplished using a switch controlled by a microcontroller that gives the logic state of each bit sequentially. The intensity of the signal presented at the output side of each channel line of the reader provides this logic state. Since the system reads tags based on proximity, it can also be used as a proximity sensor with identifying capabilities.
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