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Current artificial magnetic conductor (AMC) designs use metallic patterns on rigid substrates and focus on shapes and sizes of AMC structures, rather than on material performance, which has hindered operation bandwidth and design flexibility. Here, we introduce printed graphene AMC-based broadband and flexible microwave radar absorbers, which not only redirect but also absorb the incident wave so to broaden the operation bandwidth. Contrasting to other reported works, the phase characteristics of the AMCs are realized through the control of the surface resistance provided by printed graphene laminates. We produced a variety of AMC structures, composed of printed graphene circular ring arrays with exactly the same shape and size, but different sheet resistances. By carefully designing the sheet resistance of printed graphene laminates, the optimized anti-phase reflection cancellation between AMCs can be achieved. With printed graphene AMCs and flexible dielectric substrate, the absorber presented in this work has a broadband effective absorption (above 90% absorptivity) from 7.58 GHz to 18 GHz, is polarization insensitive under normal incident and can work at relatively wide incident angles. Furthermore, this absorber is capable of bending easily with notable performance, which makes it ideal for applications with irregular and uneven shapes.

lass‐J GaN HEMT power amplifier (PA). A graphene resonant‐tunneling diode (RTD) NFC is proposed to provide negative differential resistance characteristics and to create an effective negative capacitance. The NFC is integrated in the input matching network of the Class‐J GaN HEMT PA to cancel out the transistor input parasitic capacitance so as to enhance PA bandwidth, efficiency, output power, and gain. The PA design is based on Cree's packaged GaN HEMT CGHV40030F biased with drain supply voltage of 50 V at quiescent drain‐to‐source current of 44 mA. The PA operates from 3.4 to 4.0 GHz with center frequency of 3.7 GHz. The effective negative capacitance of the NFC from 3.4 to 4.0 GHz stands at −3.3 to −6.0 pF. An effective capacitance of −3.7 pF has been obtained at 3.7 GHz. The PA has small signal gain of 16.1 dB at 3.7 GHz. Large signal simulation input power sweep from 1 to 33 dBm at 3.7 GHz, indicates that the PA has 57.8% drain efficiency, 54.7% power added efficiency (PAE), 44.6 dBm (28.8 W) output power and 11.6 dB transducer power gain at input power of 33 dBm.

Screen-printed graphene is integrated with multiple-input multiple-output (MIMO) technology to conquer the most concerned surge in electronic waste caused by the mass deployment of Internet of things (IoT) applications. A flexible MIMO antenna is implemented with simple fabrication process suitable for large-scale production by screen printing graphene highly conductive ink on paper substrate, ensuring high-speed 5G mass data wireless transmission without damaging the ecological environment. This environmental-friendly, low-cost, flexible and conformal MIMO antenna with orthogonal polarization diversity employs co-planar waveguide feed and planar pattern for achieving high space utilization and better integration in most scenarios, for instance, body centric networks and monitoring systems. Excellent performance has been achieved due to the high conductivity of the graphene: the fabricated antenna exhibits an average sheet resistance of 1.9 Ω s q − 1 . The bandwidth of the antenna ranges from 2.22 GHz to 3.85 GHz (53.71% fractional bandwidth), covering 4 G long term evolution, sub-6 GHz 5 G mobile communication networks, 2.5 and 3.5 GHz WiMAX, and 2.4 and 3.6 GHz WLAN. Within this range, the antenna exhibits effective radiation, also its envelope correlation coefficient remains below 0.2 × 10 − 6 , manifesting outstanding signal transmission quality in a variety of wireless networks. This work illustrates a novel aggregation of MIMO technology and graphene printing electronics, enabling cheap accessible and green MIMO antennas to be massively integrated in IoT applications.

This paper proposed a novel printed graphene based monopole antenna for UWB communication applications. Screen printed graphene laminate with the conductivity of 4.1×104 S/m is used in this paper to replace expensive metal inks. The CPW feed planar monopole antenna has a wideband characteristic from 5 GHz to 13.5 GHz and omnidirectional radiation patterns. Simulated and measured results are compared and discussed in this paper.

This paper presents the design, fabrication and measurement of a planar inverted F-shaped monopole antenna printed by graphene nanoflakes conductive ink. With the use of simple inverted-F shaped monopole structure, 2.4/5 GHz bands are excited to be used in WiFi band WLAN applications.

In this letter, a graphene nanoflakes printed antenna is presented. Graphene nanoflakes conductive ink has been screen-printed on paper substrate and compressed to achieve the conductivity of $\text{0.43} \times {\text{10}^{\text{5}}} \hbox{\,S/m}$ . Low-profile meandered-line dipole antenna has been fabricated as a proof of concept due to its electrically small size and simple structure. The maximum gain is measured to be ${-}\hbox{4 dBi}$ , the ${-} \hbox{10-dB}$ bandwidth ranges from 984 to 1052 MHz (6.67%), and the radiation pattern is verified as being typical radiation patterns of a dipole-type antenna. The radiation efficiency is 32%. The measurement results reveal that graphene nanoflakes printed antenna can provide practically acceptable return loss, gain, bandwidth, and radiation patterns for mid- and short-range RFID, and sensing applications. Furthermore, screen-printing technique employed in this work is of extremely low cost and capable of producing antennas in mass production.

This paper presents a design of transmission line based RF switch with graphene. The on-off states of the switch can be adjusted electrically due to the unique properties of monolayer graphene. The transmission between two ports varies more than 30dB when voltage changes from 0 to 30 V. The RF switch provides enough insertion loss and good isolation in on and off states.

Monolayer graphene microwave resonator and THz antenna are presented. CVD graphene is used for the microwave resonator fabrication and exfoliated graphene for he THz antennas. Raman spectroscopy has been adopted to confirm the layer number of graphene. The measurements were carried out for the resonator in the microwave spectrum, showing that graphene can work well as a resonating unit in the short-end resonating structure. The THz antenna has also been fabricated. The work presented here demonstrates that graphene can find its applications in developing graphene based devices at microwave and THz spectrums.

This study presents an effective method to model, analyse and design graphene metasurface-based terahertz (THz) absorbers using equivalent circuit model approach. Broadband and tunable absorbers consisting of graphene metasurface and metal-backed dielectric layer have been designed based on the formulas derived from this approach and verified by full-wave electromagnetic simulation. By properly constructing the graphene metasurface, broadband absorption over 70% fraction bandwidth has been achieved, showing that graphene can provide a wideband absorption in the low THz spectrum. Furthermore, tunability of the graphene metasurface has also been investigated. It is demonstrated that the absorption peak frequencies can be tuned while maintaining the peak absorption unchanged, which is highly desirable for THz sensing applications.

Design, fabrication and analysis of graphene based resonators at microwave frequencies are presented. Chemical Vapor Deposited (CVD) graphene is used to fabricate the resonating stub, where Raman spectroscopy has been adopted to confirm the layer number of graphene. The measurements were carried out from 12 GHz to 28 GHz. The results of graphene resonator's input impedance show that graphene could work well as a resonating unit in the short-end resonating structure, demonstrating that graphene based resonators can find a lot of applications in developing guided graphene based devices at microwave frequencies.

The potential of highly flexible and conductive graphene laminate is extended to the application of electromagnetic interference shielding. Graphene nanoflake-based conductive ink is printed on paper, and compressed to form a graphene laminate with a conductivity of 0.43 × 105 S/m. The shielding effectiveness is experimentally measured to be above 32 dB between 12 and 18 GHz, even though the thickness of the graphene laminate is only 7.7 µm. It is demonstrated that graphene has great potential in offering lightweight, low-cost, flexible and environmentally-friendly shielding materials.

This paper reports shielding effectiveness of screen printed graphene laminate for EMI applications. The graphene laminate was screen-printed on normal paper and cut to fit C band waveguide size (34.85 × 15.80 mm2) for measurement. The measurement results show that the average shielding effectiveness is above 32 dB across the whole C band, indicating that screen printed graphene laminate can be a viable alternative to printed metal to provide desired reflection loss.

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.

We report the initial study of the reconfigurable antenna composed of graphene, in which a coplanar waveguide (CPW)-fed circular slot antenna is presented. The simple circular antenna made of copper is connected with the graphene slot by a short circuiting stub, where the graphene slot can be tuned by DC voltage bias. When the graphene acts the metallic conductor or the lossy dielectric with different DC bias setting, the effective length of the proposed antenna is changed, as well as the resonant frequency. The attractive properties of the proposed antenna can find its applications for future graphene multi Terabit wireless data transmission and transparent all-graphene sensing systems.

This paper presents the design of a reconfigurable antenna design using graphene based switch, where its working frequencies can be adjusted by switching between on/off states. The switching comes from the varying conductivity of graphene biased by external voltage. The working frequency moves from 838 MHz to 1.588 GHz when voltage is applied to change chemical potential in the range from 0 to 0.8eV. The promising results provide an alternative using graphene in frequency reconfigurable antennas.

This paper presents the design of a reconfigurable planar antenna design using graphene based switch, where its working frequencies can be adjusted by applying different voltages to connect or disconnect four patch sections to a midsection of the planar antenna. The switching comes from the varying chemical potential in the range from 0 to 0.8eV of graphene biased by external voltage. The promising results provide an alternative using graphene in frequency reconfigurable antennas.

In this paper, we present the concept and design of beam scanning terahertz antenna based on graphene arrays. The main lobe direction is verified to be scannable with flexibility introduced by graphene. The working principle of the beam scanning is further studied based on secondary reflection theory. This work can be further extended to flexible metasurface/coding metamaterial based antennas with graphene.

This paper presents the design of a tunable attenuator with under-layer graphene, where its transmission properties can be adjusted electrically. Its tunability comes from the varying conductivity of graphene biased by external voltage. The forward transmission varies more than 60% when voltage is applied to change chemical potential in the range 0-0.8eV. The promising results provide an alternative using graphene for tunable transmission lines.

Graphene RF 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.

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 retur...

This paper proposes a new type of graphene based tunable radar absorbing screen. The absorbing screen consists of Hilbert curve metal strip array and chemical vapour deposition (CVD) graphene sheet. The graphene based screen is not only tunable when the chemical potential of the graphene changes, but also has broadband effective absorption. The absorption bandwidth is from 8.9GHz to 18.1GHz, ie., relative bandwidth of more than 68%, at chemical potential of 0eV, which is significantly wider than that if the graphene sheet had not been employed. As the chemical potential varies from 0 to 0.4eV, the central frequency of the screen can be tuned from 13.5GHz to 19.0GHz. In the proposed structure, Hilbert curve metal strip array was designed to provide multiple narrow band resonances, whereas the graphene sheet directly underneath the metal strip array provides tunability and averagely required surface resistance so to significantly extend the screen operation bandwidth by providing broadband impedance matching and absorption. In addition, the thickness of the screen has been optimized to achieve nearly the minimum thickness limitation for a nonmagnetic absorber. The working principle of this absorbing screen is studied in details, and performance under various incident angles is presented. This work extends applications of graphene into tunable microwave radar cross section (RCS) reduction applications.

In this work, we first screen print thin GO laminates on Kapton film and then chemically reduce to rGO with desired sheet resistance by controlling printing cycles and reduction time. The thin rGO laminates have a wide range of conductivity from 2.8 S m −1 up to 1.3×10 4 S m −1, exhibiting excellent consistency of electric performance even after 50000 times bending. Commonly used rGO reduction level characterization methods have been compared with the proposed sheet resistance method. It is revealed that the later has higher variation with reduction time, providing a new method for reduction monitoring of rGO. Benefiting from the tunability of its sheet resistance, the rGO laminate not only can be used in flexible electronic circuits as conductors or resistors, but also highly efficient to absorb microwave radiations with proper design. Therefore, a printed, three-layer, Jaumann structured microwave absorber has been designed, fabricated and characterised. The maximum microwave absorption rate is up to 99.9997% where the −10 dB fractional bandwidth is over 153%, which covers L, S and C bands. Moreover, the fabricated absorber can absorb efficiently even when the incident angle is as low as 20°. Full design procedure, simulation and measurement results are presented.

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.