Printed electronics offer a breakthrough in the penetration of information technology into everyday life. The possibility of printing electronic circuits will further promote the spread of the Internet of Things applications. Inks based on graphene have a chance to dominate this technology, as they potentially can be low cost and applied directly on materials like textile and paper. Here we report the environmentally sustainable route of production of graphene ink suitable for screen-printing technology. The use of non-toxic solvent Dihydrolevoglucosenone (Cyrene) significantly speeds up and reduces the cost of the liquid phase exfoliation of graphite. Printing with our ink results in very high conductivity (7.13 × 104 S m−1) devices, which allows us to produce wireless connectivity antenna operational from MHz to tens of GHz, which can be used for wireless data communication and energy harvesting, which brings us very close to the ubiquitous use of printed graphene technology for such applications.

In this paper, we demonstrate realization of printable radio frequency identification (RFID) antenna by low temperature processing of graphene ink. The required ultra-low resistance is achieved by rolling compression of binder-free graphene laminate. With compression, the conductivity of graphene laminate is increased by more than 50 times compared to that of as-deposited one. Graphene laminate with conductivity of 4.3 × 104 S/m and sheet resistance of 3.8 Ω/sq (with thickness of 6 μm) is presented. Moreover, the formation of graphene laminate from graphene ink reported here is simple and can be carried out in low temperature (100 °C), significantly reducing the fabrication costs. A dipole antenna based on the highly conductive graphene laminate is further patterned and printed on a normal paper to investigate its RF properties. The performance of the graphene laminate antenna is experimentally measured. The measurement results reveal that graphene laminate antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns, making it ideal for low cost printed RF applications, such as RFID tags and wearable wireless sensor networks.

In this paper, we report highly conductive, highly flexible, light weight and low cost printed graphene for wireless wearable communications applications. As a proof of concept, printed graphene enabled transmission lines and antennas on paper substrates were designed, fabricated and characterized. To explore its potentials in wearable communications applications, mechanically flexible transmission lines and antennas under various bended cases were experimentally studied. The measurement results demonstrate that the printed graphene can be used for RF signal transmitting, radiating and receiving, which represents some of the essential functionalities of RF signal processing in wireless wearable communications systems. Furthermore, the printed graphene can be processed at low temperature so that it is compatible with heat-sensitive flexible materials like papers and textiles. This work brings a step closer to the prospect to implement graphene enabled low cost and environmentally friendly wireless wearable communications systems in the near future.

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In this work, the relative dielectric permittivity of graphene oxide (GO), both its real and imaginary parts, have been measured under various humidity conditions at GHz. It is demonstrated that the relative dielectric permittivity increases with increasing humidity due to water uptake. This finding is very different to that at a couple of MHz or lower frequency, where the relative dielectric permittivity increases with decreasing humidity. This GO electrical property was used to create a battery-free wireless radio-frequency identification (RFID) humidity sensor by coating printed graphene antenna with the GO layer. The resonance frequency as well as the backscattering phase of such GO/graphene antenna become sensitive to the surrounding humidity and can be detected by the RFID reader. This enables battery-free wireless monitoring of the local humidity with digital identification attached to any location or item and paves the way for low-cost efficient sensors for Internet of Things (IoTs) applications.

Graphene RF Q1 and microwave passive components such as coplanar waveguide transmission lines, open/short-circuited resonators and wideband antenna on paper substrate were designed, screen printed and characterized in this work. The experimental results demonstrate that the screen printed graphene passive components can be used for RF signal transmitting, processing and radiating/ receiving; revealing that graphene ink can be a low cost alternative to much more expensive metal nanoparticle inks, such as silver nanoparticle ink. The screen printed graphene is processed at low temperature so that it is compatible with heat-sensitive flexible materials like papers, PTFE (Polytetrafluoroethylene) and textiles. The screen printed graphene passive components reported here are of high conductivity, high flexibility, light weight and low cost, making them ideal candidate for low cost wearable electronics. This work makes it prospective to manufacture RF and microwave passive components in mass production by screen printing in much lower cost to any other known techniques.

Screen-printed graphene near field communication (NFC) tag antenna is integrated with inkjet-printed WS2 photodetector on paper substrate to fabricate battery-free wireless photosensor. A sequential multi-stack printing is employed for the wireless photosensor fabrication: the NFC tag antenna is first screen-printed with graphene conductive ink and then the photodetector is inkjet-printed with transition metal dichalcogenides (TMDs) WS2 ink as photoactive component. High responsivity and sensitivity are observed for the WS2 photodetector, which acts as photoactive thermistor of the NFC sensor IC chip. The highly conductive graphene nanoflakes ink enables the screen-printed graphene NFC tag antenna to withdraw sufficient power wirelessly from the reader to power the sensor IC chip. This work demonstrates a prospective approach to manufacture 2D materials enabled electronics where the electronic circuits (normally having a large size) can be realized by mass production screen printing and the sensing component (normally having a small size) can be produced by inkjet printing, enabling low cost and simple fabrication methods, compatible with flexible substrates such as paper.

A battery free wearable sensing device with temperature and sweat sensors embedded into and powered by a smart textile NFC antenna available for both NFC readers and NFC enabled smart phones, which can take part in various medical applications such as daily healthcare, fever detection and wound healing monitoring. Take-Home Messages  In this manuscript, body temperature and sweat sensors are integrated with a textile NFC antenna, which eliminates the need for external batteries and realizes real-time wireless monitoring.  This paper has presented design, fabrication implementation, measurements and real-life applications of smart textile NFC antennas and a battery-free wireless NFC body temperature and sweat sensing device, aiming for truly ubiquitous wireless health and wellbeing monitoring.  The proposed device targets at body temperature and sweat loss monitoring for daily healthcare, systemic hyperthermia from fever, sweating symptoms caused by various kinds of infection, inflammation and trauma and wound healing monitoring.  Different from conventional battery enabled and wire connected sensors, the significance of this work is by applying textile NFC as a communication interface as well as a wireless power harvester, battery-free realtime body temperature and sweat monitoring has been realized simultaneously.  Apart from the device itself, an App has also been developed on Android system for the sensor data to be accessed by smart phones.