Xianjun Huang

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.

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.

Graphene radio frequency and microwave passive components for low cost wearable electronics

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.

Low Phase Noise Free-Running Oscillator Based on High Selectivity Bandpass Filter Using Composite Right/Left-Handed Transmission Line

This letter presents a novel low phase noise freerunning oscillator based on a high selectivity bandpass filter (BPF) using a composite right/left-handed transmission line (CRLH TL). The oscillator is designed at the spectrum-based quality factor (Qs) peak frequency to achieve low phase noise performance. Ata center frequency of 2.05 GHz, the oscillator demonstrates, experimentally, a phase noise of -150.4 dBc/Hz at 1 MHz frequency, offset with a figure of merit(FOM) of -207.2 dBc/Hz, less than -32 dBm spurious harmonics, and total oscillator power consumption of 6.1 mW from a 2 V supply voltage.

Low-Power and Wideband LC-VCO for WiMAX in CMOS Technology

This work presents an ultralow phase-noise and wide turning-range voltage-controlled oscillator (VCO) for 5.72GHz WiMAX applications. The fully integrated VCO is designed and simulated using 130-nm CMOS technology. Instead of using the conventional diode-based varactor in the tank design, high-performance body-grounded NMOS transistors are employed as effective varactors. A controlled self-biasing current source is implemented to avoid higher power supply sensitivity and higher up-conversion of flicker noise. The proposed VCO-measured results demonstrate a worst case phase noise of -132.68dBc/Hz at 1MHz frequency offset with an excellent figure of merit (FOM), which is -201.6dBc/Hz under a power consumption of 2.21mW. The VCO shows a tuning range of approximately 37.59%.

Miniaturized via-less ultra-wideband bandpass filter based on CRLH-TL unit cell

In this paper, a new via-less ultra-wideband (UWB) bandpass filter design based on a composite right/left-handed transmission line (CRLH-TL) unit cell is presented. Microstrip capacitive patch is used to provide virtual ground and replace the via in the conventional CRLH TL. Via fabrication complexity can be avoided for large-scale and cost-effective production by using microstrip patch. By cascading the interdigital coupled line with a low-pass filter (LPF) based on symmetrical split ring resonator (SSRR) defected ground structure (DGS), an UWB frequency response is achieved. SSRR DGS was used to obtain wider upper-stopband and sharp roll-off rate. The filter has compact size (15.6 × 13 mm2) and exhibits a rejection level greater than 20 dB at both upper and lower stopband. The filter has an insertion loss of 0.9 dB, a return loss better than 14 dB, and a fractional bandwidth of more than 100% at center frequency of 6.8 GHz.

Wide tuning range voltage controlled oscillator (VCO) with minimized phase noise variation in nanoscale CMOS technology

A cross-coupled differential VCO with low phase noise variation is presented. The VCO core adopts a metal-oxide-metal (MOM) digital switching capacitor array (DSCA), which is connected in series and in parallel to the nMOS varactor in order to reduce the KVCO variation. For further gain linearity, wider tuning range and minor phase noise variations, this varactor bank is connected in parallel to three nMOS varactor pairs. Each pair is biased at a different voltage. The proposed VCO has been designed and implemented in UMC 130-nm, 6-metal CMOS technology and operates from 3.45 GHz to 6.23 GHz with 55.6% tuning range, phase noise variations ranging between -134 dBc/Hz and -130.8 dBc/Hz and power consumption below 6 mW at supply voltage of 3.2 V. The simulated phase noise at 1 MHz offset is 132.4 dBc/Hz at 5.0 GHz and a good FOM performance of approximately 204.5 dBc/Hz is achieved.

Low-phase noise variation VCO implementing resistorless digitally controlled varactor

A novel resistorless digital capacitor switching array (DCSA) has been implemented into a wideband CMOS VCO for 5-GHz WiMAX/WLAN applications. The proposed DCSA is added both in series and parallel to nMOS varactors. Based on this, a wideband VCO is achieved, which not only exhibits lower phase noise in comparison with reported state-of the-art wideband VCOs, but also has low phase noise variation of less than 5 dBc/Hz. In addition, it has demonstrated low power consumption, improved linearity of the f-V curve and extended tuning range. The proposed VCO has been designed using UMC 130 nm CMOS technology. It operates from 3.65 GHz to 6.34 GHz, with a phase noise of -132.70 dBc/Hz at 1 MHz offset, a figure of merit (FoM) of -202.9 dBc/Hz, less than -41 dBm spurious harmonics and total VCO core power consumption of 2.88 mW from a 3.2 V supply voltage.