Fully Printed Dual-Layer Depolarizing Chipless RFID Tag for Wearable Applications

Abstract

This work presents a cross-polar dual-layer chipless radio-frequency identification (RFID) tag based on a laddershaped resonator design. An integrated ground plane enables direct attachment to human skin without performance deterioration. Simulations show that the ladder-shaped resonator provides several advantages over traditional L-shaped and straight resonators, including a strong cross-polar radar cross section (−23.4 dBsm), third-order harmonics, orientation insensitivity, and compact size (0.062 λ 2 ). The effects of the ground plane shape on the surface current distribution are investigated, and a circular tag of 20 mm radius is designed using ladder resonator groups and frequency shift encoding to provide an active area of 96.45 bits/λ 2 and a unit frequency of 6.03 bits/GHz. The tag substrate is three-dimensionally (3D) printed with metallic resonator patterns that are subsequently screen-printed on the substrate. The maximum read range is measured at 40 mm using a cross-shaped, dual-polarized Vivaldi antenna connected to a network analyzer. The measured characteristics in free space are in good agreement with the simulation results, and practical onbody performance tests for the manufactured prototype using simulation and direct measurements indicate that the tag performance remains stable for both free space and on-body cases. The fully printed fabrication process makes the proposed tag design suitable for mass production at a low cost.

Wireless Technologies in Flexible and Wearable Sensing: From Materials Design, System Integration to Applications

“…[38,39] However, microchips inevitably increase the complexity of the fabrication of RFID tags and generally lead to rigidity. On the contrary, chipless RFID tags can be realized in a relatively simple process, [40] significantly lowering fabrication costs. More importantly, tailoring the dielectric property of the substrates or the electrical conductivity of the conductors induces the shift of the tag response, which enables chipless RFID ideal for sensing various external stimuli, such as humidity, [41,42] temperature, [43,44] and mechanical strain.…”

Hybrid Encoding Method for Radio Frequency Identification in the Internet of Things Systems

“…RFID systems are classified according to the tag detection distance by the reader, the operating frequency range, using the chip or chipless tag and having a power supply or not [21][22][23]. In an active RFID system, the required energy to activate the tag is supplied from an external power supply (such as a battery), whereas in a passive RFID system, tag energy is supplied from reader signals, where the tag does not have any built-in power supply [24][25][26][27][28].…”

“…This ID is retrieved via the RF signals exchanged between a reader and a tag. [25][26][27][28][29][30]. The RFID tags are classified in terms of information transmission methods.…”

“…In fact, information transmission via responses to the signals sent by a reader can be in either retransmission or backscatter methods. The retransmission-based tags need specific antennas to send and receive signals in their structures; however, information transmission and responses to the signals of a reader are emitted in the backscatter tags without needing any antennas [25]. The RFID tags are categorized as LF, HF, UHF, and UWB classes based on the working frequency domain.…”