Mitra Akbari

Fabrication and Characterization of Graphene Antenna for Low-Cost and Environmentally Friendly RFID Tags

We present the fabrication and testing of graphene-based dipole antennas on cardboard, which is a promising low-cost, recyclable, and flexible substrate for future wireless electronics. The letter presents the details of the manufacturing, as well as results from the measurements and simulations. The measured sheet resistance of graphene antenna is 1.9 Ω/sq. Overall, a graphene-based planar dipole antenna with the length of 143 mm achieved the measured total efficiency of 40% and the realized gain of - 2.18 dBi at 889 MHz. Moreover, a passive ultra-high-frequency radio-frequency tag based on a graphene dipole antenna on cardboard achieved the attainable read range of more than 5 m at 950 MHz.

Toward Graphene-Based Passive UHF RFID Textile Tags: A Reliability Study

This paper discusses the fabrication, wireless performance, and reliability of graphene-based passive ultrahigh-frequency radio-frequency identification (RFID) tags on a fabric substrate. The conductive ink comprising functionalized graphene nanoplatelets is deposited directly on a cotton fabric substrate to fabricate the tag antennas. After attaching the chips, the tag performance is evaluated through wireless tag measurements before and after high-humidity conditions, bending, and stretching. Initially, the peak read range of the tag is about 1.6 m, which increases to 3.2 m in 100% humidity conditions. Additionally, after drying, the performance of the tag returns back to normal. In a bending test, the read range of a bent tag decreases below 1 m. Furthermore, the read range of the tag in a nonbended state gradually decreases and is about 1.1 m after 100 bending cycles. According to our measurements, stretching has a serious detrimental effect on these tags and they cannot be considered stretchable. However, these initial results show that this low-cost and eco-friendly graphene RFID tag has a remarkable and unique response to moisture and high reliability in harsh bending conditions. Overall, it also has a strong potential to be used in future wearable sensor applications.

Sensitivity enhancement of flexible gas sensors via conversion of inkjet-printed silver electrodes into porous gold counterparts

This work describes a facile, mild and general wet chemical method to change the material and the geometry of inkjet-printed interdigitated electrodes (IDEs) thus drastically enhancing the sensitivity of chemiresistive sensors. A novel layer-by-layer chemical method was developed and used to uniformly deposit semiconducting single-wall carbon nanotube (SWCNT)-based sensing elements on a Kapton® substrate. Flexible chemiresistive sensors were then fabricated by inkjet-printing fine-featured silver IDEs on top of the sensing elements. A mild and facile two-step process was employed to convert the inkjet-printed dense silver IDEs into their highly porous gold counterparts under ambient conditions without losing the IDE-substrate adhesion. A proof-of-concept gas sensor equipped with the resulting porous gold IDEs featured a sensitivity to diethyl ethylphosphonate (DEEP, a simulant of the nerve agent sarin) of at least 5 times higher than a similar sensor equipped with the original dense silver IDEs, which suggested that the electrode material and/or the Schottky contacts between the electrodes and the SWCNTs might have played an important role in the gas sensing process.

3D-Printed Graphene Antennas and Interconnections for Textile RFID Tags: Fabrication and Reliability towards Humidity

We present the possibilities of 3D direct-write dispensing in the fabrication of passive UHF RFID graphene tags on a textile substrate. In our method, the graphene tag antenna is deposited directly on top of the IC strap, in order to simplify the manufacturing process by removing one step, that is, the IC attachment with conductive glue. Our wireless measurement results confirm that graphene RFID tags with printed antenna-IC interconnections achieve peak read ranges of 5.2 meters, which makes them comparable to graphene tags with epoxy-glued ICs. After keeping the tags in high humidity, the read ranges of the tags with epoxy-glued and printed antenna-IC interconnections decrease 0.8 meters and 0.5 meters, respectively. However, after drying, the performance of both types of tags returns back to normal.

Characterization of graphene-based inkjet printed samples on flexible substrate for wireless sensing applications

Inkjet printing is one of the emerging methods for fabrication of electronic devices. The important issue in this area is developing nanomaterial-based inks for different applications such as gas sensors for environmental monitoring. In particular, graphene-based materials have recently gained interest due to their extraordinary properties. However, graphene has hydrophobic nature resulting in poor solubility in the most of the solvents. In order to solve this problem, graphene oxide is mostly used instead of graphene. To retrieve the conductivity, the printed samples are reduced to remove the oxygen containing groups. The major contribution of this paper is focused on the production of conductive graphene-based patterns on the flexible kapton substrate utilizing thermal reduction process. Both printed samples and inks were characterized and analyzed to enhance the quality of printing. The effect of different parameters such as surface modification, annealing condition, thermal reduction atmosphere, setting of inkjet printer, and concentration of ink were investigated. The characterization part includes analysis of the morphology, sheet resistance, conductivity, and viscosity of ink. This work is an important step for future research on the development of wireless graphene-based gas sensors.

3D Printed and Photonically Cured Graphene UHF RFID Tags on Textile, Wood, and Cardboard Substrates

This paper introduces 3D direct writing and microdispensing of graphene ultrahigh frequency (UHF) radio-frequency-identification (RFID) antennas on textile, wood, and cardboard substrates, subsequently cured either by conventional oven or photonically by pulsed Xenon flashes. Photonic-cured passive UHF RFID graphene tags on cardboard, wood, and textile substrates achieve read ranges of 5.4, 4.6, and 4 meters, respectively. These results are superior to those achieved by the oven-cured tags that featured read ranges of 4.8, 4.5, and 3.6 meters, respectively. This work presents the first integration of 3D printing and photonic curing of graphene antennas on low-cost versatile substrates.

Implementation and performance evaluation of graphene-based passive UHF RFID textile tags

In this paper, we investigate the fabrication and wireless performance of graphene-based passive UHF RFID textile tags. Two different graphene-based inks were used to fabricate identical antennas on a fabric substrate by doctor blading technique. The performance of the tags was evaluated with wireless measurements throughout the UHF RFID frequency band. Based on our results, the graphene-based tags showed attainable read ranges of 1.6 and 2.4 meters. According to these first results, these tags have a great potential in future wearable applications along with cost-effective and eco-friendly aspects.

Strain reliability and substrate specific features of passive UHF RFID textile tag antennas

We investigate the strain reliability of passive UHF RFID tags based on antennas printed on two structurally dissimilar textiles. The performance of the tags under strain and during repeated stretching cycles is evaluated through wireless measurements. Initially, both tags achieve read ranges of 9.5 meters and retain high readable ranges under notable, 20%, strain. Our results from a cyclic strain test evidence that the fabric substrate structure and elasticity play an important role in the reliability and recovery of printed thick-film conductors.

The possibilities of graphene-based passive RFID tags in high humidity conditions

In this paper, we study the wireless response and reliability of graphene-based passive UHF RFID tags in high humidity conditions. The functional graphene ink is deposited directly on cardboard substrate to fabricate the RFID tag and the tag performance is evaluated through wireless tag measurements before and after high humidity conditions. Initially the peak read range of the tag is about 2.7 meters, which increases to 3.2 meters in high humidity conditions. Additionally, after drying, the performance of the tag returns back to normal. The results show that this low-cost and eco-friendly graphene RFID tag has a remarkable and unique response to moisture and has a strong potential to be used in future humidity sensor applications.

Flash reduction of inkjet printed graphene oxide on flexible substrates for electronic applications

Graphene based nanomaterials open a new horizon in the electronic devices due to the unique and superior properties of graphene. The deposition of graphene based materials has significant effects on their final properties. Moreover, deposited graphene based samples are reduced by chemical or thermal reduction methods. To save time and energy compared to conventional approaches, advanced methods such as photonic curing have been recently developed and reported. The aim of our study is to fabricate thin layer of reduced graphene oxide on the flexible substrate which can be used as a sensing part in mechanical, environmental or biological sensors. The graphene oxide dispersion in deionized water was inkjet printed on oxygen plasma treated polyimide substrate (Kapton, TM), and then reduced by Xenon flash. The energy of each pulse, pulse amplitude and width were adjusted to achieve the optimum flash settings for inkjet-printed graphene oxide. The cured samples were characterized to observe influence of different processing conditions of the reduced GO films.