Modern Physics Letters B

A perfect dual-band optical absorber is designed and measured. A low absorption peak (P1) and two high absorption peaks (P2 and P3) are obtained. The P1 peak is excited by the resonance of internal surface plasmon (ISP) mode. The P2 peak is resulted by the coupling of local surface plasma (LSP) modes and the resonance of ISP mode. The P3 peak is excited by the resonance of ISP mode. The damping constant of the gold film is optimization calculated in simulations. Measured results indicate that high absorption performed is obtained with different dielectric layers. The measured metamaterial absorber displays high absorption performed at TM and TE configurations. Moreover, the proposed metamaterial absorber is sensitivity on the change of the refractive index of the environmental media.

A color-tunable phosphor based on Tb${}^{3+}$/Eu${}^{3+}$ co-doped GdNbO₄ were synthesized by a traditional solid-state reaction method. X-ray powder diffraction (XRD), diffuse reflectance spectra, photoluminescence spectra and decay curves were utilized to characterize the as-prepared phosphors. XRD result indicated that various concentrations Tb${}^{3+}$/Eu${}^{3+}$ single-doped and co-doped phosphors were well indexed to the pure GdNbO₄ phase. The GdNbO₄ host was proved to be a self-activated phosphor with broad absorption range from 200 nm to 325 nm. When Tb${}^{3+}$ ions were added into the host lattice, the energy transferring from host to Tb${}^{3+}$ was identified. And the broad absorption in the UV region was changed and enhanced. Therefore, we selected Tb${}^{3+}$ as the sensitizer ion, and adjusted red component from Eu${}^{3+}$ to control the emission color. The energy transfer from Tb${}^{3+}$ to Eu${}^{3+}$ was confirmed based on the luminescence spectra and decay curves. Furthermore, the energy transmission mechanism was deduced to be the dipole–quadrupole interaction. On the whole, the obtained GdNbO₄, GdNbO₄:Tb${}^{3+}$, and GdNbO₄:Tb${}^{3+}$, Eu${}^{3+}$ phosphors may have potential application in the UV white-light-emitting diodes (w-LEDs) and display devices.

Based on nonlocal strain gradient theory, wave propagation in fluid-conveying viscoelastic single-walled carbon nanotubes (SWCNTs) is studied in this paper. With consideration of thermal effect and surface effect, wave equation is derived for fluid-conveying viscoelastic SWCNTs under longitudinal magnetic field utilizing Euler–Bernoulli beam theory. The closed-form expressions are derived for the frequency and phase velocity of the wave motion. The influences of fluid flow velocity, structural damping coefficient, temperature change, magnetic flux and surface effect are discussed in detail. SWCNTs’ viscoelasticity reduces the wave frequency of the system and the influence gets remarkable with the increase of wave number. The fluid in SWCNTs decreases the frequency of wave propagation to a certain extent. The frequency (phase velocity) gets larger due to the existence of surface effect, especially when the diameters of SWCNTs and the wave number decrease. The wave frequency increases with the increase of the longitudinal magnetic field, while decreases with the increase of the temperature change. The results may be helpful for better understanding the potential applications of SWCNTs in nanotechnology.

In this paper, a very low 1/f noise integrated Wheatstone bridge magnetoresistive sensor ASIC based on magnetic tunnel junction (MTJ) technology is presented for high sensitivity measurements. The present CMOS instrumentation amplifier employs the gain-boost folded-cascode structure based on the capacitive-feedback chopper-stabilized technique. By chopping both the input and the output of the amplifier, combined with MTJ magnetoresistive sensitive elements, a noise equivalent magnetoresistance 1 nT/Hz${}^{1/2}$ at 2 Hz, the equivalent input noise spectral density 17 nV/Hz${}^{1/2}$(@2Hz) is achieved. The chip-scale package of the TMR sensor and the instrumentation amplifier is only about 5 mm × 5 mm × 1 mm, while the whole DC current dissipates only 2 mA.

This study investigates the sensing applications of metamaterial (MTM) structures in the terahertz (THz) region and is based on a broadside-coupled diamond and square-ring resonator (DSRR) structures. The resonators are designed and simulated as sensors in detail. Compared with single-sided sensors, the sensing capability of double-sided sensors provide an enhancement with respect to the sensitivity. To analyze the structure as sensor, the changes in the transmission resonance are investigated as a function of the permittivity and thickness of overlayer for the single- and double-sided MTM. The results demonstrate that this design can provide good sensitivity when sensing the chemical or biological agents that are resonant in the terahertz region of the electromagnetic spectrum. These types of designs can be employed in the many sensing applications that are of interest in the THz region.

In this paper, using a cross-shaped complementary Indium Tin Oxide (ITO)-based metasurface design, the transmission of THz radiation is shown to be filtered within the 3 dB level from maximum in the frequency range of interest ($\sim$333 GHz). Various metasurface structures primarily composed of cross-shaped openings with a 400 micron unit cell size are patterned on top of 1750 micron thick fused silica substrates. They are patterned using UV lithography methods after the films were grown using DC sputtering. The fabricated structures were characterized using Terahertz Time Domain Spectroscopy (THz-TDS) measurement technique. The measured transmission agrees well with the simulation of the structure for four different samples with different geometries. These results suggest that metasurface and/or metamaterial patterns based on ITO in visibly transparent media can be utilized for filtering of frequencies in the long wavelength spectrum. These types of filters can be very useful in the near future for THz communication and security applications.

A novel superconducting tilting-pad bearing was proposed for the advanced research of reusable liquid hydrogen turbopump in liquid rocket. The bearing is a combination of superconducting magnetic bearing and hydrodynamic fluid-film bearing. Since the viscosity of cryogenic fuel to activate superconducting state and form hydrodynamic fluid-film is very low, bearing clearance will be very small. This study focuses on the investigation of superconducting levitation force in this kind of small clearance superconductor–magnet system. Based on Bean critical state model and three-dimensional finite element method, an analysis method is presented to obtain the levitation force under such situation. Since the complicated operational conditions and structural arrangement for application in liquid rocket, center lines of bulk superconductor and magnet rotor will usually be in non-coaxial state. Superconducting levitation forces in axial direction and radial direction under non-coaxial situation are also analyzed by the presented method.

A principle of an acoustic Eaton lens array and its application as a removable tsunami wall is proposed theoretically. The lenses are made of expandable rubber pillars or balloons and create a stop-band by rotating the incoming tsunami wave and reduce the pressure by canceling each other. The diameter of each lens is larger than the wavelength of the tsunami near the coast, that is, order of a kilometer. The impedance matching on the border of the lenses results in a little reflection. Before a tsunami, the balloons are buried underground in shallow water near the coast in folded or rounded form. Upon sounding of the tsunami alarm, water and air are pumped into the pillars, which expand and erect the wall above the sea level within a few hours. After the tsunami, the water and air are released from the pillars, which are then buried underground for reuse. Electricity is used to power the entire process. A numerical simulation with a linear tsunami model was carried out.

Compared without electroless Ni–P alloy coating on the SiCp/Al composites, the paper describes the effect of Ni–P deposited layer on the microstructure evolution, shear strength, airtightness and fracture behavior of vacuum brazed joints. Void free and compact reaction layers along the 6063Al/Ni–P deposited layer/filler metal interfaces indicated that the joints exhibit high airtightness with He-leakage less than $2.0\times 10^{-8}$ $\mathrm{\text{Pa}}\cdot {\mathrm{\text{m}}}^3/\mathrm{\text{s}}$. Energy Dispersive X-ray Spectroscopy (EDS) analysis showed that the reaction layers mainly included brittle Al–Ni and Al–Cu–Ni intermetallics, where fracture occurred in priority and the shear strength was less than 90 MPa. However, without Ni–P alloy coating, sound joints with high shear strength of 100.1 MPa but low airtightness with He-leakage higher than $1.45\times 10^{-7}\mathrm{\text{Pa}}\cdot {\mathrm{\text{m}}}^3/\mathrm{\text{s}}$ were also obtained at 590${}^{\circ }$C for soaking time of 30 min. In this case, a few holes that occurred along the filler metal/SiC particle interface significantly decreased the compactness of the joints. Therefore, according to the requirements in practical applications, suitable choice was provided in this research.

In this paper, an innovative design approach is proposed to solve time-varying dynamical equation, including matrix inverse equation and Sylvester equation. Based on the precondition of the existing solution of time-varying dynamical equation, different from previous approach to solve unknown matrix, an optimal design principle is used to solve the unknown variables. A performance index is introduced based on the inherent properties of the time-varying dynamical equation and Euler equation. The solution of time-varying dynamical equation is converted to an optimal problem of performance index. Furthermore, convergence and sensitivity to additive noise are also analyzed, and simulation results confirm that the method is feasible and effective. Especially, in simulations we design a tunable positive parameter in the dynamic optimization model. The tunable parameter is not only helpful to accelerate its convergence but also reduce its sensitivity to additive noise. Meanwhile the comparative simulation results are shown for the convergence accuracy and robustness of this method.

Based on the study of the material matching and structure cooperating, this paper mainly explores a new packaging structure with low thermal mismatches which can enhance the accuracy and stability of the resonant pressure sensor. According to the finite element simulation, the rule of the coefficient of thermal expansion (CTE) and the depth of the groove on the substrate, which has an influence on the temperature sensitivity, could be obtained. By analyzing the effect of temperature on the resonant frequency, it shows the temperature sensitivity of the new packaging structure is −0.97 Hz/${}^{\circ }$C in 20 kPa, under the temperature range of 30${}^{\circ }$C to 80${}^{\circ }$C. After analyzing resonant frequency stability at different temperatures, it is found that the time for achieving stability at different temperatures of the new packaging structure is at least 10 min less than that of TO packaging structure. The average frequency’s relative variation ratio of the new packaging structure at different temperatures remains roughly the same, and the variation range is within ±0.005% as time changes. These results indicate that the new packaging structure has the characteristic of great temperature-immunization.

We presented a pure-shear film bulk acoustic resonator (FBAR) and investigated its sensing characteristics in viscous liquids. In the resonator, the electrodes were located on the surface of c-axis-oriented AlN film to generate the lateral electric field and excite the shear acoustic resonance. Compared with the typical quasi-shear film bulk acoustic resonator based on inclined c-axis-oriented AlN or ZnO piezoelectric film, the proposed device exhibits significantly higher Q-factors and a notably improved detection limit, particularly in water and viscous liquids. The frequency shifts show a linear dependency on the square root of the product of the liquid viscosity and density of the glycerol solution in the viscosity range of 1–5 mPa$\cdot$s. Furthermore, we measured the mass sensitivity through real-time monitoring of the frequency change during the volatilization process of the loaded saline solutions. The proposed device shows the mass sensitivity of 465 Hz$\cdot$cm²/ng and the mass resolutions of 0.17 ng/cm² in air, 0.25 ng/cm² in water and 2.08 ng/cm² in 50% glycerol solution, respectively. The obtained results clearly indicate that the proposed device is capable of using in liquid phase detection with high sensitivity requirements.