Humidity-Sensing Chipless RFID Tag with Enhanced Sensitivity Using an Interdigital Capacitor Structure

Abstract

An eight-bit chipless radio frequency identification tag providing humidity sensing and identification information is proposed. A compact, enhanced-sensitivity resonator based on an interdigital capacitor (IDC) structure is designed for humidity sensing, whereas seven electric-field-coupled inductor capacitor (ELC) resonators are used for identification information. These eight resonators are placed in a two-by-four array arrangement. A step-by-step investigation for the effect of varying the number of elements and array configuration on the resonant frequency and radar cross-section (RCS) magnitude of the IDC resonator is conducted. The RCS value of the resonant peak frequency for the IDC resonator increases as the number of array elements placed nearby increases due to the mutual coupling among the elements, and the increase in the RCS value becomes larger as the number of arrays increases in the vertical direction. Polyvinyl alcohol (PVA) is coated on the IDC-based resonator at a thickness of 0.02 mm. A non-reflective temperature and humidity chamber is fabricated using Styrofoam, and the relative humidity (RH) is varied from 50% to 80% in 10% intervals at 25 °C in order to measure a bistatic RCS of the proposed tag. The humidity sensing performance of the IDC resonator in the proposed tag is measured by the shift in the resonant peak frequency and the RCS value, and is compared with a single ELC resonator. Experiment results show that when RH increased from 50% to 80%, the sensitivities of both the resonant peak frequency and the RCS value of the IDC resonator were better than those of the ELC resonator. The variation in the RCS value is much larger compared to the resonant peak frequency for both IDC and ELC resonators. In addition, the resonant peak frequency and RCS value of the PVA-coated IDC-based resonator change, whereas those of the other seven resonators without a PVA coating do not change.

Internal Damage Detection of Composite Structures Using Passive RFID Tag Antenna Deformation Method: Basic Research

“…The results of this technique showed a good correlation with actual fatigue crack growth obtained from visual inspection. To improve efficiency and gain a competitive advantage, major airports and airlines adopted RFID technology, which was developed and used as an early-stage technology on the Internet of Things (IoT) [22]-a core technology of the fourth industrial revolution. The airports and airlines used RFID in various processes [23]: baggage handling and tracking [24], monitoring of individual aircraft parts and supply chains [25,26], and as health monitoring systems [26][27][28][29].…”

Compact Wideband Tapered Slot Antenna Using Fan-Shaped and Stepped Structures for Chipless Radio-Frequency-Identification Sensor Tag Applications

“…Among the various methods realizing chipless RFID tags, a microwave resonator-based method has been actively investigated. The microwave resonator-based method can be divided into time domain, frequency domain, and hybrid methods depending on the domain in which electromagnetic wave signals are used [ 56 , 57 ]. Frequency domain methods can be divided into a retransmission-based method using transmitting and receiving antennas combined with resonators and a back scattering-based method using only resonators.…”

Microwave Humidity Sensor for Early Detection of Sweat and Urine Leakage

“…Planar microwave sensors can be fabricated by means of either subtractive (e.g., photoetching or milling) or additive (e.g., inkjet-printing, screen-printing, or 3D-printing) processes. Moreover, planar microwave sensors are compatible with many other technologies such as microfluidics, micromachining, textiles, etc., and can be equipped with functional films, that make these sensors of interest in applications as diverse as liquid sensing [3][4][5][6][7], bio-sensing [8,9], gas sensing [10][11][12][13][14][15][16], wearables [17,22], measurement of physical variables (such as temperature or ambient humidity [23][24][25]), etc. Nevertheless, the most canonical application of planar microwave sensors is the dielectric characterization of materials (permittivity measurements [7], [26][27][28]).…”