Zhirun Hu

Binder-free highly conductive graphene laminate for low cost printed radio frequency 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 retur...

Highly Flexible and Conductive Printed Graphene for Wireless Wearable Communications Applications

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.

Stepping toward standard methods of small-signal parameter extraction for HBTs

An improved HBT small-signal parameter extraction procedure is presented in which all the equivalent circuit elements are extracted analytically without reference to numerical optimization. Approximations required for simplified formulae used in the extraction routine are revised, and it is shown that the present method has a wide range of applicability, which makes it appropriate for GaAs and InP-based single and double HBTs. Additionally, a new method is developed to extract the total delay time of HBTs at low frequencies, without the need to measure h/sub 21/ at very high frequencies and/or extrapolate it with -20 dB/dec roll-off. The existing methods of finding the forward transit time are also modified to improve the accuracy of this parameter and its components. The present technique of parameter extraction and delay time analysis is applied to an InGaP/GaAs DHBT and it is shown that: (1) variations of all the extracted parameters are physically justifiable; (2) the agreement between the measured and simulated S- and Z-parameters in the entire range of frequency is excellent; and (3) an optimization step following the analytical extraction procedure is not necessary. Therefore, we believe that the present technique can be used as a standard extraction routine applicable to various types of HBTs.

On the study of left-handed coplanar waveguide coupler on ferrite \r\nsubstrate

This paper introduces a 3 dB tunable symmetric left handed coupled line coupler implemented on ferrite substrate. The proposed coupler is realized in LH coplanar waveguide configuration constructed using interdigital capacitors and meandered line inductors. The analytical analysis and the numerical verification of the proposed couple line coupler are presented. The full wave numerical simulation results for different DC magnetic bias indicate that a tunable left handed coupled line coupler propagation with transmission coefficient up to 3 dB and isolation level more than 25 dB over a wide bandwidth can be achieved.

Miniaturized Composite Right/Left-Handed Stepped-Impedance Resonator Bandpass Filter

In this letter, a microstrip Stepped Impedance Resonator (SIR) bandpass filter (BPF) based on Composite Right/Left-Handed (CRLH) transmission lines is presented for the first time. Supported by theory, full-wave simulations and measurements, operational principle of the filter is explained and results are analysed. Also, comparison is made between this filter and its conventional right-handed (RH) counterpart. For the same centre frequency, fractional bandwidth and stop-band attenuation, the CRLH SIR BPF presented here proves to surpass its conventional counterpart in terms of size, being about 80% smaller, without degradation of performance. The CRLH SIR BPF is also significantly more controllable in its dimensions and response due to the fact that more elementary parameters are available in CRLH configuration.

Graphene Nanoflakes Printed Flexible Meandered-Line Dipole Antenna on Paper Substrate for Low-Cost RFID and Sensing Applications

In this letter, a graphene nanoflakes printed antenna is presented. Graphene nanoflakes conductive ink has been screenprinted on paper substrate and compressed to achieve the conductivity of 0.43 × 105 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 -4 dBi, the -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 midand short-range RFID, and sensing applications. Furthermore, screenprinting technique employed in this work is of extremely low cost and capable of producing antennas in mass production.

A compact dual band meta-material antenna for wireless applications

This paper presents a compact dual band metamaterial antenna for WiMAX applications. The reported antenna was based on using a metamaterial modified left handed transmission line unit cell. The designed antenna was introduced to operate with the WiMAX lower 2.4 GHz band and upper 5.8 GHz band. The designed antenna has the advantages of its compact size (only 2 × 3) cm2. Compared to the conventional patch length, the designed patch radiator is only 25% at 2.4 GHz and 60% 5.8 GHz. The antenna designed was discussed theoretically and its performance was verified using the electromagnetic full wave simulations. The results confirm that the antenna can introduce the dual bands operation with return loss better than 15 dB at each operating band. Moreover, the radiation pattern is almost omnidirectional at the two bands.

Design and Analysis of Tunable Left Handed Zeroth-Order Resonator on Ferrite Substrate

This paper presents, for the first time, a tunable left handed coplanar waveguide zeroth-order resonator on a ferrite substrate. Analysis and design procedures of the proposed resonator are introduced. The proposed resonator is designed to be tuned over the frequency band from 3 to 4.85 GHz with lower than 3-dB insertion loss and better than 10-dB return loss. The dimensions of the proposed resonator are 8.3 times 20 mm. The advantages of the proposed resonator are its tuning capability in addition to its compact size.

Graphene based tunable fractal Hilbert curve array broadband radar absorbing screen for radar cross section reduction

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.

Multi-Band Functional Tunable LH Impedance Transformer

This paper presents, for the first time, the analysis and design performance of tunable left handed coplanar waveguide transformer designed on a ferrite substrate. The proposed transformer is studied analytically and verified numerically. Results show that the proposed transformer has tunable dual band of operation with frequency tuning range from 2.35 GHz to 3.85 GHz with return loss from 10 dB to 25 dB. Such tunability can be achieved by changing the DC magnetic bias. The advantages of the proposed transformer are its tuning capability, its multi functionality operation, and its compact size.