Xunjun He

Dual-Band Terahertz Metamaterial Absorber with Polarization Insensitivity and Wide Incident Angle

This paper presents the design, simulation and mea- surement of a dual-band terahertz metamaterial absorber with polarization-insensitivity and wide incident angle. The unit cell of the metamaterial consists of top resonator structures and low metal- lic ground plane, separated by an isolation material spacer to realize both electric and magnetic resonances. The physical mechanism of dual-band absorption and the sensitivity to the polarization direction and incident direction of the EM wave are theoretically investigated by simulating the x-component and normal component electric fleld distribution, current distribution on ERRs and metallic ground plane, and distribution of power ∞ow and loss at the resonance frequencies as well as difierent modes EM waves, based the FDTD calculated method, respectively. The results show that the absorber is not only correctly coupling to the incident electric fleld and magnetic fleld, but also can trap the input power into speciflc positions of the devices and ab- sorb it, besides insensitivity to the polarized angle and incident angle. Moreover, the experiment demonstrates that the absorber achieves two strong absorptions of 82.8% and 86.8% near 1.724 and 3.557THz.

Electrically tunable terahertz wave modulator based on complementary metamaterial and graphene

In this paper, we design and numerically demonstrate an electrically controllable light-matter interaction in a hybrid material/metamaterial system consisting of an artificially constructed cross cut-wire complementary metamaterial and an atomically thin graphene layer to realize terahertz (THz) wave modulator. By applying a bias voltage between the metamaterial and the graphene layer, this modulator can dynamically control the amplitude and phase of the transmitted wave near 1.43 THz. Moreover, the distributions of current density show that this large modulation depth can be attributed to the resonant electric field parallel to the graphene sheet. Therefore, the modulator performance indicates the enormous potential of graphene for developing sophisticated THz communication systems.

Tunable ultrasensitive terahertz sensor based on complementary graphene metamaterials

In this paper, we propose an ultrasensitive terahertz sensor based on the complementary graphene metamaterial composed of wire-slot and split-ring resonator slot array structure. The destructive interference between two resonators gives rise to a reflection peak enabling ultrasensitive sensing, and a sensitivity of 177.7 GHz per RIU and FOM of 59.3 can be obtained for the proposed sensor. More importantly, this sensor can not only enhance the absorption of biomolecules and sensing performance, but also dynamically tune the sensing range by shifting the Fermi energy. In addition, the influences of the lateral displacement on the sensing performance are also investigated to improve the sensitivity of the sensor. Therefore, this method opens up opportunities for efficiently sensing several organic and explosive molecules and biomolecules.

Design and analysis of a novel low actuation voltage capacitive RF MEMS switches

The novel design of capacitive RF MEMS switches using torsion spring is presented and analyzed in this paper. The RF MEMS switches not only have ordinary folded suspending beams, but also add torsion springs. The simulation results show that compared with ordinary bending deflection, the torsion deflection is sensibly influenced by the ratio of the arm width (b) and the arm thickness (t), so the actuation voltage (VT) of the RF MEMS capacitive switches which have both the ordinary bending deflection and added torsion deflection will be obviously depressed. At same time, the theory analysis shows that the lower VT can be obtained with longer torsion arm length (LD), longer driven arm length (LD).By optimizing the structure design of RF MEMS switches, when LT, LD, b and t are 180 um, 120 um, 5 um and 1 um, respectively, the area actuation electrodes is 120times120 um2, the actuation voltages of RF MEMS switches is 1.5 V by computer simulating.

Electrically active manipulation of electromagnetic induced transparency in hybrid terahertz metamaterial

In this paper, we numerically demonstrate that an actively controllable electromagnetic induced transparency (EIT) behavior can be obtained in a hybrid terahertz metamaterial. A unit cell of the hybrid metamaterial consists of a metallic split-ring resonator surrounded by a concentric graphene close-ring resonator, serving as superradiant and subradiant modes, respectively. The EIT-like effect results from the destructive interference caused by strong near field coupling between superradiant and subradiant mode resonators. A classical two-particle model is employed to theoretically study EIT-like behavior in the hybrid metamaterial, and the analytic results agree excellently with our numerical results. More importantly, by tuning Fermi energy based on electrical doping, the hybrid metamaterial can realize switching, modulation, and slow-light capabilities. Therefore, these results would exhibit potential applications in light storage and compact devices.

Sensitivity-enhanced temperature sensor by hybrid cascaded configuration of a Sagnac loop and a F-P cavity

A hybrid cascaded configuration consisting of a fiber Sagnac interferometer (FSI) and a Fabry-Perot interferometer (FPI) was proposed and experimentally demonstrated to enhance the temperature intensity by the Vernier-effect. The FSI, which consists of a certain length of Panda fiber, is for temperature sensing, while the FPI acts as a filter due to its temperature insensitivity. The two interferometers have almost the same free spectral range, with the spectral envelope of the cascaded sensor shifting much more than the single FSI. Experimental results show that the temperature sensitivity is enhanced from −1.4 nm/°C (single FSI) to −29.0 (cascaded configuration). The enhancement factor is 20.7, which is basically consistent with theoretical analysis (19.9).

Surface Plasmon Resonant THz Wave Transmission on Carbon Nanotube Film

The properties of the terahertz resonant surface plasmons wave on the carbon nanotube film and dielectric interface have been investigated. As a first step towards engineering terahertz SPPs-like surface modes, we present a computer experiment to demonstrate that the carbon nanotube film surface can also be employed to concentrate and guide the terahertz SPPs wave. The carbon nanotube film is modeled in an experimentally realizable geometry. It is shown that a unique electromagnetic surface mode in terahertz region can be supported along the carbon nanotube film/dielectric interface when the free-space broadband terahertz pulse is incident on the carbon nanotube film with subwavelength gratings. Comparing with noble metals, plasmonic nano-structure materials based on carbon nanotube film offer a potentially more versatile approach to engineering tightly confined surface modes in the THz regime.

Properties of carbon nanotubes loop antenna at Terahertz range

It is the first time this paper investigates the fundamental characteristics of the loop antenna formed single-walled carbon nanotubes from 1.0∼10 terahertz frequency region using finite integral methods. The armchair single-walled carbon nanotubes can be considered due to their metallic conducting. The surface current dense, electric field and magnetic field distribution, scattering coefficient, input admittance, radiation patterns and gain are presented and compared to carbon nanotubes dipole antenna with the same size of the perimeter of the loop antenna. The results demonstrate that carbon nanotubes loop antenna with a radius of 15 µm takes on the resonant frequency properties from 7.35 terahertz to 7.46 terahertz in the center frequency of 7.4 terahertz, corresponding scattering coefficient less than −10dB. The maximum gain of carbon nanotubes loop antenna is 5.7 dB. All results is can be used for the design of carbon nanotubes antenna in the terahertz region.

High-sensitive dual-band sensor based on microsize circular ring complementary terahertz metamaterial

Abstract Recently, resonance sensing based on the terahertz metamaterials has attracted considerable attentions due to the enhancement and confinement of local fields in microsize gap of resonant structures. Here, a high-sensitive dual-band sensor based on the complementary terahertz metamaterial composed of microsize circular ring gap array is proposed to detect the thickness and refractive index of thin film. The structure of this sensor is polarization insensitive dual-band operating mode and can be easily filled by the biomolecules. Simulation results demonstrate that the dual-band resonances are very sensitive to the dielectric variation, and the sensitivity levels of 99 GHz/refractive index unit (RIU) for mode f1 and 242 GHz/RIU for mode f2 are obtained and further enhanced by optimizing structures. Therefore, this structure can exhibit promising application for monitoring thin film thickness.

Influence of Wafer Level Packaging Modes on RF Performance of MEMS Phase Shifters

With RF MEMS technology rapid development, the distributed RF MEMS phase shifters have exhibited excellent RF performance, such as high isolation, high phase shifts, low insertion loss and wide bandwidth operation features at high frequency. However, the applications of RF MEMS phase shifter are hampered by the lack of production-worthy wafer level packaging. Therefore, the problems on packaging solved are very stringent. This paper mainly investigates on the influence of wafer level packaging modes on the RF performance of distributed RF MEMS phase shifters. The insertion loss S21, return loss S11 and phase shifts parameters are analyzed using 3D electromagnetic simulation tool - microwave studio (CST). Simulation results show that the insertion loss of the distributed RF MEMS phase shifters for bonding wafer packaging and wafer level micropackaging is -0.59dB and -0.061dB at l0GHz, -0.79dB and -0.25dB at 50 GHz, respectively. The return loss -11.8366dB and -26.66906dB at l0GHz, -14.50227dB and -32.30596dB at 50GHz, and the phase shift is 170.78deg and 161.82deg at 50GHz, respectively. Therefore, we concluded that different wafer level packaging modes distinctly affect the microwave performance of the distributed RF MEMS phase shifters. Comparing the RF performance parameters of two modes, the wafer level micropackaging mode shows excellent RF performance (the average insertion loss of -0.ldB and the average return loss of deg22 dB) and no resonances at 1-60 GHz, and adapted to the packaging of distributed RF MEMS phase shifters