Conductivity Of Vanadium Dioxide Research Articles

Temperature-tunable terahertz metamaterial device based on VO2 phase transition principle.

Terahertz devices play an irreplaceable role in the development of terahertz technology. However, at present, it is difficult for most natural materials to respond in the terahertz band, making the devices made of them perform poorly. In order to realize the diversity and tunability of device functions, we designed a terahertz metamaterial device composed of the thermally-induced phase change material VO2. The device structure is composed of a Au bottom layer, a SiO2 dielectric layer and a VO2 top layer. Through software simulation, we found that when T = 313 K, the device has complete reflection ability in the whole terahertz band. When T = 342 K, the average absorptivity is above 95% in the ultra-wide band range of 4.71-9.41 THz, and the absorptivity reaches an amazing 0.99999 at 6.31 THz. Thus, the maximum thermal modulation range of the device is 0.001-0.99999. The Bruggeman effective medium theory clarifies the phase transition characteristics of vanadium dioxide. The Drude model establishes the functional relationship between the conductivity of vanadium dioxide and temperature. The basic principle of high absorption was described using the impedance matching theory. We also drew the electric field intensity diagram during the temperature rise of the device to further confirm the reason for the change in the device performance. In addition, the influence of the absence of different structural layers on the absorptivity was simulated, which reflected the role of each layer structure more intuitively. We also explored the influence of the geometric size of the device on the absorptivity, which provided a certain reference value for practical application. In short, we have designed a tunable terahertz device with simple structure, high absorptivity, and wide absorption bandwidth, which can be used in the fields of energy collection, electromagnetic stealth, and modulation.

Development of a terahertz metamaterial polarization converter with multiple tuning modes based on graphene and vanadium dioxide

A dynamically tunable terahertz metamaterial polarization converter is proposed. By manipulating the Fermi level of graphene and the conductivity of vanadium dioxide (VO2) flexibly, multiple tuning modes for polarization conversion performance are realized. First, while graphene is in the metallic or insulating state, we can achieve an ideal broadband reflective or an ideal broadband transmissive polarization converter respectively. By manipulating the conductivity of VO2, a modulation depth of 80 % for intensity of the reflected polarization conversion rate (PCRr) and that of 70 % for bandwidth of the transmissive polarization conversion rate (PCRt) can be achieved. Then, while VO2 is in the insulating state, we obtain another broadband transmissive polarization converter. Similarly, we can achieve PCRt intensity modulation by manipulating the Fermi level of graphene. While VO2 is in the metallic state, the device can switch from a broadband polarization converter to a narrow one as the Fermi level of graphene increases. Finally, by manipulating graphene and VO2 simultaneously, the central frequency modulation of PCRt can be obtained with the bandwidth keeping unchanged. Compared with the ones reported recently, our device has some advantages on tuning mode, relative bandwidth, and polarization conversion performance.

Transformation of twin-peak electromagnetically induced transparency to twin-peak electromagnetically induced absorption based on magnetic dipole and dielectric resonator

This paper puts forward the transmission from twin-peak electromagnetically induced transparency (EIT) to twin-peak electromagnetically induced absorption (EIA), while it is rare to see the transformation between EIT and EIA in metastructure (MS) in one device in previous articles. With the incidence of TE waves, two transparent windows are generated, ranging from 0.382 THz to 0.986 THz which are separated by 0.604 THz, when the conductivity of vanadium dioxide (VO2) is set to 10 S/m. Two peaks reach 0.864 and 0.934, respectively, accompanied by the largest group delays of the two peaks being 7.55 and 4.54 ps. In addition, VO2 blocks in the metallic state will affect interference paths between energy levels, contributing to the formation of EIA, then maintaining a common absorption of 0.607 at 0.429 THz and 0.904 at 0.678 THz. Under the combined action of the dielectric resonator and metal resonator, the conversion from bimodal EIT to bimodal EIA is hardly been researched, at the same time, the adoption of the circuit model and the four-level theory proves the rationality of the model. The transformation from EIT to EIA is aroused by changing the state of VO2, promising broad prospects in multifunctional devices.

Individually tunable array reflector for amplitude and phase modulation.

Based on graphene's phase modulation property and vanadium dioxide's amplitude modulation property, we developed an array reflector for terahertz frequencies that is individually adjustable. Starting with a theoretical analysis, we look into the effects of voltage on the Fermi level of graphene and temperature on the conductivity of vanadium dioxide, analyze the beam focusing characteristics, and finally link the controllable quantities with the reflected beam characteristics to independently regulate each cell in the array. The simulation findings demonstrate that the suggested array structure can precisely manage the focus point's position, intensity, and scattering degree and that, with phase compensation, it can control the wide-angle incident light. The array structure offers a novel concept for adjustable devices and focusing lenses, which has excellent potential for study and application.

Tunable Dual-Broadband Terahertz Absorber with Vanadium Dioxide Metamaterial

A dual broadband terahertz bifunction absorber that can be actively tuned is proposed. The optical properties of the absorber were simulated and numerically calculated using the finite-difference time-domain (FDTD) method. The results show that when the conductivity of vanadium dioxide is less than S/m, the absorptance can be continuously adjusted between 2% and 100%. At vanadium dioxide conductivity greater than S/m, the absorption bandwidth of the absorber can be switched from 3.4 THz and 3.06 THz to 2.83 THz and none, respectively, and the absorptance remains above 90%. This achieves perfect modulation of the absorptance and absorption bandwidth. The physical mechanism of dual-broadband absorptions and perfect absorption is elucidated by impedance matching theory and electric field distribution. In addition, it also has the advantage of being polarization insensitive and maintaining stable absorption at wide angles of oblique incidence. The absorber may have applications in emerging fields such as modulators, stealth and light-guided optical switches.

Terahertz phase shifter based on phase change material-metasurface composite structure

With its rapid development, the terahertz technology is widely used in radar, imaging, remote sensing and data communication. As one of terahertz wave devices, the terahertz phase shifter has become a research hotspot. The existing phase shifters have the disadvantages of large volume, high power consumption and small phase shifting. In the present work, a tunable terahertz phase shifter with liquid crystal and vanadium dioxide is proposed. It is composed of an upper vanadium dioxide embedded metal layer, a liquid crystal, a lower vanadium dioxide embedded metal layer, and a silicon dioxide substrate in sequence from top to bottom. The liquid crystal is sandwiched between the upper and lower vanadium dioxide embedded metal layer. The phase of the device can be controlled by both the phase transition characteristics of vanadium dioxide and the birefringence of liquid crystal. By changing the external applied temperature, the conductivity of vanadium dioxide is changed, and the phase of the device shifts accordingly. Likewise the refractive index of the liquid crystal changes under different externally applied voltages. Finally, the phase of the proposed device can be effectively controlled in a terahertz range by both externally applied temperature and voltage. The phase shift characteristics of the device are analyzed by using software CST studio. The results verify that the terahertz phase shifter can achieve a maximum phase shift of 355.37° at <i>f</i> = 0.736 THz and a phase shift is larger than 350° in a range of 0.731–0.752 THz (bandwidth 22 GHz). Therefore, compared with the traditional phase shifter, this kind of phase change material-metasurface composite structure provides a new idea for flexibly manipulating the terahertz beam. And it is expected to be widely used in terahertz imaging, terahertz wireless and other fields.

Terahertz Absorber With Reconfigurable Bandwidth Based on Isotropic Vanadium Dioxide Metasurfaces

The design of a broadband tunable absorber is proposed based on a thin vanadium dioxide metasurface, which is composed of a simple array of vanadium dioxide and a bottom gold film. When the conductivity of vanadium dioxide is equal to 2000 Ω -1 cm -1 , simulated absorptance exceeds 90% with 71% bandwidth from 0.47 to 0.99 THz and full width at half maximum is 98% from 0.354 to 1.036 THz with center frequency of 0.695 THz. Simulated results show that absorptance peak can be tuned from 5% to 100% when the conductivity changes continually from 10 Ω -1 cm -1 to 2000 Ω -1 cm -1 . The designed absorber may have useful applications in terahertz spectrum such as energy harvesting, thermal emitter, and sensing.

Tunable Toroidal Dipolar Resonance for Terahertz Wave Enabled by a Vanadium Dioxide Metamaterial

An active toroidal switch is numerically presented in a terahertz metamaterial. Transmission of toroidal dipole can be tuned by the conductivity of vanadium dioxide, and its modulation depth can be up to 32%. The resonance of toroidal dipole is verified by the distribution of electric current. Due to the unique field distribution of the toroidal mode, the proposed design may find potential applications in enhanced absorption and sensing.

Terahertz toroidal metamaterial with tunable properties.

We present a tunable metamodulator to work at terahertz frequencies by employing the dependency of toroidal dipolar resonance on the conductivity of vanadium dioxide. Numerical results show that toroidal dipolar resonance in the proposed planar structure can be observed around 0.288 THz in transmission spectrum. From the distribution of the anti-phase current flowing in the symmetric split ring resonator, the formation of toroidal dipole is validated. Our design may have potential applications in advanced terahertz devices, such as filter, plasmonic sensor, and fast switch.