Near-Field Chipless Radio-Frequency Identification (RFID) Sensing and Identification System with Switching Reading

Abstract

A chipless radio-frequency identification (chipless-RFID) and sensing system, where tags are read by proximity (near-field) through a switch, is presented. The tags consist of a set of identical resonant elements (split-ring resonators or SRRs), printed or etched at predefined and equidistant positions, forming a linear chain, each SRR providing a bit of information. The logic state (‘1’ or ‘0’) associated with each resonator depends on whether it is present or not in the predefined position. The reader is an array of power splitters used to feed a set of SRR-loaded transmission lines (in equal number to the number of resonant elements, or bits, of the tag). The feeding (interrogation) signal is a harmonic (single-tone) signal tuned to a frequency in the vicinity of the fundamental resonance of the SRRs. The set of SRR-loaded lines must be designed so that the corresponding SRRs are in perfect alignment with the SRRs of the tag, provided the tag is positioned on top of the reader. Thus, in a reading operation, as long as the tag is very close to the reader, the SRRs of the tag modify (decrease) the transmission coefficient of the corresponding reader line (through electromagnetic coupling between both SRRs), and the amplitude of the output signal is severely reduced. Therefore, the identification (ID) code of the tag is contained in the amplitudes of the output signals of the SRR-loaded lines, which can be inferred sequentially by means of a switching system. Unlike previous chipless-RFID systems based on near-field and sequential bit reading, the tags in the proposed system can be merely positioned on top of the reader, conveniently aligned, without the need to mechanically place them across the reader. Since tag reading is only possible if the tag is very close to the reader, this system can be also used as a proximity sensor with applications such as target identification. The proposed chipless-RFID and sensing approach is validated by reading a designed 4-bit tag. For identification purposes, this system is of special interest in applications where a low number of bits suffice, and tag reading by proximity is acceptable (or even convenient). Applications mostly related to secure paper, particularly involving a limited number of items (e.g., exams, ballots, etc.), in order to provide authenticity and avoid counterfeiting, are envisaged. As a proximity sensor, the system may be of use in detecting and distinguishing different targets in applications such as smart packaging.

Chipless-RFID: A Review and Recent Developments

“…With this approach, the number of achievable bits is only limited by the area occupied by the tags and the ID code is contained in the amplitude modulated signal generated by the tags. Such tags typically consist of a chain of either resonant elements [42,43,44,45,46,47,48,49] or metallic strips [50,51,52], etched or printed at predefined and equidistant positions on a dielectric substrate. Basically, in a tag reading operation, the tag is mechanically displaced over the sensitive part of the reader.…”

Time-Domain-Signature Chipless RFID Tags: Near-Field Chipless-RFID Systems With High Data Capacity

“…Similar to frequency-domain chipless-RFID systems, which can be applied to sensors [77]- [84], the proposed time-domain near-field chipless-RFID system can be also used for sensing purposes (e.g., proximity sensors with ID code [85], or motion control devices [70], [71]), but such applications are out of the scope of this article, entirely focused on identification.…”

Strategies to Enhance the Data Density in Synchronous Electromagnetic Encoders

“…For example, there are sensors that exploit coupling modulation [75][76][77][78][79], whereas other sensors are based on frequency variation [80]. In such sensors, a resonant (movable) element is displaced over a transmission line structure (typically, the resonator in motion is displaced in a plane parallel to the one of the line, but there are also realizations, where the resonator displaces vertically [79,81]). Although these sensors are relatively simple, their input dynamic range is usually very limited, since it is of the order of the size of the resonant elements.…”