Graphene metasurface-based switchable terahertz half-/quarter-wave plate with a broad bandwidth

Metasurfaces incorporating graphene hold great promise for the active manipulation of terahertz waves. However,it remains challenging to design a broadband graphene-based terahertz metasurface with switchable functionality of half-wave plate(HWP) and quarter-wave plate(QWP). Here, we propose a graphene–metal hybrid metasurface for achieving broadband switchable HWP/QWP in the terahertz regime. Simulation results show that, by varying the Fermi energy of graphene from 0 eV to 1 eV, the function of the reflective metasurface can be switched from an HWP with polarization conversion ratio exceeding 97% over a wide band ranging from 0.7 THz to 1.3 THz, to a QWP with ellipticity above 0.92over 0.78 THz–1.33 THz. The sharing bandwidth reaches up to 0.52 THz and the relative bandwidth is as high as 50%.We expect this broadband and dynamically switchable terahertz HWP/QWP will find applications in terahertz sensing,imaging, and telecommunications.

Electrically triggered dual-band tunable terahertz metamaterial band-pass filter based on Si_3N_4–VO_2–Si_3N_4 sandwich

We experimentally demonstrate an electrically triggered terahertz(THz) dual-band tunable band-pass filter based on Si_3 N_4–VO_2–Si_3 N_4 sandwich-structured hybrid metamaterials. The insulator–metal phase transition of VO_2 film is induced by the Joule thermal effect of the top metal layer. The finite-integration-time-domain(FITD) method and finite element method(FEM) are used for numerical simulations. The sample is fabricated using a surface micromachining process,and characterized by a THz time-domain-spectrometer(TDS). When the bias current is 0.225 A, the intensity modulation depths at two central frequencies of 0.56 THz and 0.91 THz are about 81.7% and 81.3%, respectively. This novel design can achieve dynamically electric–thermo–optic modulation in the THz region, and has potential applications in the fields of THz communications, imaging, sensing, and astronomy exploration.

Silicon micropillar electrodes of lithiumion batteries used for characterizing electrolyte additives

The 100 crystal-oriented silicon micropillar array platforms were prepared by microfabrication processes for the purpose of electrolyte additive identification. The silicon micropillar array platform was used for the study of fluorinated vinyl carbonate(FEC), vinyl ethylene carbonate(VEC), ethylene sulfite(ES), and vinyl carbonate(VC) electrolyte additives in the LiPF_6 dissolved in a mixture of ethylene carbonate and diethyl carbonate electrolyte system using charge/discharge cycles, electrochemical impedance spectroscopy, cyclic voltammetry, scanning electron microscopy, and x-ray photoelectron spectroscopy. The results show that the silicon pillar morphology displays cross-shaped expansion after lithiation/delithiation, the inorganic lithium salt keeps the silicon pillar morphology intact, and the organic lithium salt content promotes a rougher silicon pillar surface. The presence of poly-(VC) components on the surface of FEC and VC electrodes allows the silicon pillar to accommodate greater volume expansion while remaining intact. This work provides a standard, fast, and effective test method for the performance analysis of electrolyte additives and provides guidance for the development of new electrolyte additives.

Switchable terahertz polarization converter based on VO_(2)metamaterial

A switchable terahertz(THz)polarization converter based on vanadium dioxide(VO_(2)) metamaterial is proposed.It is a 5-layer structure which containing metal split-ring-resonator(SRR),the first polyimide(PI)spacer,VO_(2) film,the second PI spacer,and metal grating.It is an array structure and the period in x and y directions is 100μm.The performance is simulated by using finite integration technology.The simulation results show that,when the VO_(2) is in insulating state,the device is a transmission polarization converter.The cross-linear polarization conversion can be realized in a broadband of0.70 THz,and the polarization conversion rate(PCR)is higher than 99%.Under thermal stimulus,the VO_(2) changes from insulating state to metallic state,and the device is a reflective polarization converter.The linear-to-circular polarization conversion can be successfully realized in a broadband of 0.50 THz,and the PCR is higher than 88%.

A Comprehensive Evaluation Method for Sensing Characteristics of Multi-Peak Terahertz Metamaterials Sensor in Polarization Mode

In this study,the multi-peak terahertz metamaterials sensors are designed and fabricated,whose structures are the asymmetrical single split ring(SSR)and three split rings(TSR).The resonant formation and sensing mechanism of the two structures are investigated by using the finite-difference time-domain(FDTD)method.Vitamin B6(VB6)and its reactants with bovine serum protein(BSA)are tested as the medium,and the sensing experiments of the SSR and TSR are carried out.The experimental and simulation results indicate the consistent law,which is the sensitivity of the resonance in the transverse magnetic(TM)mode is much greater than that in the transverse electric(TE)mode.According to the weighted average method and the law for unequal precision measuring,the quality factor of the resonance is used as the weighting coefficient to calculate the comprehensive evaluation parameter(CEP)of the multi-peak metamaterials sensors in the TE and TM modes based on the experimental data.When the CEP and frequency shifts are as the evaluation parameter in experiments,the law’s variation of the CEP is consistent with that of the frequency shift,indicating that it is feasible to characterize the sensing characteristics of metamaterials with the CEP,which presents simplified characteristics of multi-peak metamaterials at different polarization modes.The method implies that the different influencing factors may be integrated into the CEP with the idea of weight,which promotes the practical application of the metamaterials sensor.The revelation of the sensing law also provides a method for the design of the terahertz metamaterials sensor with the high sensitivity.