The design, fabrication and cold test of a high frequency system (HFS) for an H-band (220-325GHz) sheet beam travelling wave tube (SB-TWT) is presented in this paper. The HFS was composed of a 90-period double-staggered grating waveguide and a pair of identical L-shaped couplers with Bragg reflectors and matching steps. The HFS was manufactured by Nano-CNC machining and its electromagnetic properties were measured by using a vector network analyzer. The measured S-parameters were in good agreement with the simulated ones, which predicted a 3 dB bandwidth of ~47.0 GHz. The maximum value of the measured transmission coefficient S21 was -4.9 dB and the in-band port reflection S11 was around -15.0 dB. Based on the cold testing-based HFS, simulations of the beam wave interaction predicted a stable output power of over 55.1 W in the frequency range of 230-280 GHz. In addition, the instabilities of the beam wave interaction were investigated in the simulation.

Developing highly efficient anchoring materials to suppress sodium polysulfides (NaPSs) shuttling is vital for the practical applications of sodium sulfur (Na-S) batteries. Herein, we systematically investigated pristine graphene and metal-N₄@graphene (metal = Fe, Co, and Mn) as host materials for sulfur cathode to adsorb NaPSs via first-principles theory calculations. The computing results reveal that Fe-N₄@graphene is a fairly promising anchoring material, in which the formed chemical bonds of Fe-S and N-Na ensure the stable adsorption of NaPSs. Furthermore, the doped transition metal iron could not only dramatically enhance the electronic conductivity and the adsorption strength of soluble NaPSs, but also significantly lower the decomposition energies of Na₂S and Na₂S₂ on the surface of Fe-N₄@graphene, which could effectively promote the full discharge of Na-S batteries. Our research provides a deep insight into the mechanism of anchoring and electrocatalytic effect of Fe-N₄@graphene in sulfur cathode, which would be beneficial for the development of high-performance Na-S batteries.

LiNi_0.5Mn_1.5O₄ (LNMO) is a potential cathode material for lithium-ion batteries with outstanding energy density and high voltage plateau (>4.7 V). However, the interfacial side reaction between LNMO and the liquid electrolyte seriously causes capacity fading during cycling at the high voltage. Here, p-toluenesulfonyl isocyanate (PTSI) is used as the electrolyte additive to overcome the above problem of LNMO. The results show that the specific capacity of LNMO/Li cell with 0.5 wt.% PTSI at the first cycle is effectively enhanced by 36.0 mAh/g and has better cycling performance than that without PTSI at 4.98 V. Also, a stable solid electrolyte interface (SEI) film derived from PTSI is generated on the electrode surface, which could alleviate the strike of hydrofluoric acid (HF) caused by electrolyte decomposition. These results are explained by the molecular structure of PTSI, which contains SO₃. The S=O groups can delocalize the nitrogen nucleus to block the reactivity of PF₅.

Terahertz has significant potential applications in biosensing, but its detection sensitivity still needs to be improved. Metamaterials can effectively improve terahertz sensing sensitivity due to their field-enhancing properties. In this work, we designed and fabricated a double-open hexagonal ring metamaterial with a high refractive index sensitivity of 430 GHz/RIU. The resonant properties of metamaterials were demonstrated by both simulations and experiments. The sensing performance were tested with different concentrations of glucose and bovine serum protein solutions. The results showed that the sensitivity of the metamaterial to glucose and bovine serum protein solution reached 0.37 GHz/(mg/dL) and 36.44 GHz/(mg/mL), respectively, while the detection limits of glucose and bovine serum protein solution reached 9.867 mg/dL and 0.16 mg/mL, respectively. The proposed metamaterial sensor has potential application scenarios in the terahertz biomedical field.

Optically clear adhesive (OCA) has been widely used in flexible devices, where wavy stripes that cause troublesome long-term reliability problems often occur. The complex mechanical behavior of OCA should be studied, as it is related to the aforementioned problems. Therefore, it is necessary to establish reasonable mechanical constitutive models for deformation and stress control. In this work, hyperelastic and viscoelastic mechanical tests were carried out systematically and relative constitutive models of OCA material were established. We found that temperature has a great influence on OCA’s mechanical properties. The stress and modulus both decreased rapidly as the temperature increased. In the static viscoelasticity test, the initial stress at 85 °C was only 12.6 kPa, 57.4% lower than the initial stress at 30 °C. However, in the dynamic test, the storage modulus monotonically decreased from 1666.3 MPa to 0.6628 MPa as the temperature rose, and the decline rate reached the maximum near the glass transition temperature (T_g = 0 °C). The test data and constitutive models can be used as design references in the manufacturing process, as well as for product reliability evaluation.