Large Frequency Range Research Articles

Unsteady aerodynamic modeling methodology based on dynamic mode interpolation for transonic flutter calculations

A new unsteady aerodynamic modeling methodology for calculating transonic flutter characteristics is presented. The main idea of the methodology is to obtain the unsteady flow response to small amplitude periodic deformations of a structure over a large range of oscillation frequencies through the interpolation of the most dominant fluid dynamic modes obtained from Dynamic Mode Decomposition (DMD) of a few reference unsteady simulations at different oscillation frequencies. These simulations can be carried out by solving the Euler or RANS equations. The methodology can then be used to obtain a frequency-domain generalized aerodynamic force matrix, and stability analysis can be performed using standard flutter analysis methods such as the p-k method. The proposed methodology provides a very good estimate of the flutter boundary for the 2D Isogai airfoil and 3D AGARD 445.6 wing models, but at a lower computational cost than the traditional higher-fidelity Fluid–Structure Interaction (FSI) simulations.

Research on bandgap property of a novel small size multi-band phononic crystal

A novel small size multi-band gaps phononic crystal (hPC) composed of the periodic plumbum and aluminum mass has been investigated in this paper, we calculated the dispersion relations and the displacement fields with finite element method (FEM). The influences of the geometrical parameters and materials parameters on the band structure are further investigated. We studied the influence factors of band gap by the model of origin anti-resonance. There are many flat bands in the characteristic frequency curve. The band gap covers a large range in low frequency.

Analysis of dynamic mechanical properties of photochemically crosslinked poly(isobornylacrylate-co-isobutylacrylate) applying WLF and Havriliak-Negami models

Chemically crosslinked poly (isobornylacrylate-co-isobutylacrylate) was elaborated by radical photo-copolymerization of isobornylacrylate and isobutylacrylate monomers in a 4:1 mass ratio, by adding a crosslinking agent at low concentration. The obtained copolymer was characterized by Fourier transform infrared spectroscopy for structural analysis, by differential scanning calorimetry for the determination of the glass transition temperature, and by thermogravimetric analysis to investigate thermal degradation effects. Storage modulus, dissipation modulus and tan delta were evaluated by dynamic mechanical analysis and modeled using different physical approaches such as the time-temperature superposition principle and the Havriliak-Negami model. The Cole-Cole curve was fitted with the Havriliak-Negami model yielding five parameters which were used to calculate the dynamic mechanical properties of the copolymer over a large frequency range from 1.03 × 10−4 Hz to 7.58 × 107 Hz. Calculated elastic and dissipative moduli agree well with the experimental data.

Application of the Modal Approach for Prediction of Forced Response Amplitudes for Fan Blades

Forced response is the main reason for high cycle fatigue in turbomachinery. Not all resonance points in the operating range can be avoided especially for low order excitation. For highly flexible carbon fiber reinforced polymer (CFRP) fans, an accurate calculation of vibration amplitudes is required. Forced response analyses were performed for blade row interaction and boundary layer ingestion (BLI). The resonance points considered were identified in the Campbell diagram. Forced response amplitudes were calculated using a modal approach and the results are compared to the widely used energy method. For the unsteady simulations, a time-based linearization of the unsteady Reynolds average Navier–Stokes equations were applied. If only the resonant mode was considered, the forced response amplitude from the modal approach was confirmed with the energy method. Thereby, forced response due to BLI showed higher vibration amplitudes than for blade row interaction. The impact of modes which are not in resonant to the total deformation were investigated by using the modal approach, which so far only considers one excitation order. A doubling of vibrational amplitude was shown in the case of blade row interaction for higher rotational speeds. The first and third modeshapes as well as modes with similar natural frequencies were identified as critical cases. The behavior in the vicinity of resonance shows high vibration amplitudes over a larger frequency range. This is also valid for high modes with many nodal diameters, which have a greater risk of critical strain.

Sensitive label-free and compact ultrasonic sensor based on double silicon-on-insulator slot micro-ring resonators

We propose a new label-free ultrasonic sensor, which comprises a slot wave-guide and double silicon-on-insulator (SOI) slot micro-ring resonators. The all-optical sensors do not suffer from electromagnetic interference. We choose to integrate a silicon slot double micro-ring (SDMR) resonators in an acoustically resonant membrane. Optimization of the several key structural parameters is investigated to achieve the mode-field distributions of transmission spectrum based on Comsol Multiphysics software. Our numerical studies show that the proposed ultrasonic sensor offers higher sensitivity and a larger detection frequency range than conventional piezoelectric based ultrasound transducer. For a SDMR system with an area of 15μm×30μm, sensitivity as high as 2453.7mV/kPa, and over a bandwidth range of 1-150MHz. The sensitivity value is 36 times higher than that of single slot micro-ring ultrasonic sensor. The theoretical Q -factor of the SDMR can be approximately 1.24×106 with bending radius of 5μm. The investigation on the SDMR system is a valuable exploration of the photo-acoustic microscopy for the ultra-high Q factor and large frequency range.

Effect of Gamma Radiation Induced on Structural, Electrical, and Optical Properties of N, N′-Dimethyl-3,4,9, 10-Perylenedicarboximide Nanostructure Films

N,N′-Dimethyl-3,4,9,10-perylenedicarboximide (PTCDI-C1) thin films were first prepared by thermal evaporation technique. Then, the prepared films were irradiated with gamma rays at room temperature with different absorbed doses. The structure of PTCDI-C1 films at different doses of gamma radiation was elucidated by x-ray diffraction. The results confirmed that PTCDI-C1 film has a nanostructure morphology. The grain size was observed to decrease slightly with increasing the gamma radiation doses. The temperature dependence of the electrical conductivity was measured in the temperature range of 293–423 K. It was found that the obtained activation energy of PTCDI-C1 films decreased with increasing gamma radiation dose. The optical parameters were obtained using spectrophotometric measurements. The single oscillator model of Wemple–Didomenico was adopted to study the normal dispersion of refractive index. The optical dispersion parameters of PTCDI-C1 films such as dispersion energy, oscillator energy and the high frequency dielectric constant were calculated. Furthermore, the nonlinear susceptibility values of PTCDI-C1 films at different gamma radiation dose were calculated. Also, the dielectric constants of the films were investigated in a large range of frequencies. The fundamental band gap energy values (3.91 eV Eg2 > 50 kGy).

Superconducting coplanar microwave resonators with operating frequencies up to 50 GHz

We demonstrate the operation of superconducting coplanar microwave resonators in a very large frequency range up to 50 GHz. The resonators are fabricated from niobium thin films on sapphire substrates and have fundamental frequencies of 5 GHz or 10 GHz. We study numerous harmonics of the resonators at temperatures between 1.5 K and 6 K, and we determine quality factors of up to 22 600 at 1.5 K. As an example for spectroscopy applications of such resonators we detect the superconducting transition of a bulk tin sample at multiple probing frequencies.

3D harmonic modeling of eddy currents in segmented conducting structures

PurposeThe purpose of this paper is to describe a semi-analytical modeling technique to predict eddy currents in three-dimensional (3D) conducting structures with finite dimensions. Using the developed method, power losses and parasitic forces that result from eddy current distributions can be computed.Design/methodology/approachIn conducting regions, the Fourier-based solutions are developed to include a spatially dependent conductivity in the expressions of electromagnetic quantities. To validate the method, it is applied to an electromagnetic configuration and the results are compared to finite element results.FindingsThe method shows good agreement with the finite element method for a large range of frequencies. The convergence of the presented model is analyzed.Research limitations/implicationsBecause of the Fourier series basis of the solution, the results depend on the considered number of harmonics. When conducting structures are small with respect to the spatial period, the number of harmonics has to be relatively large.Practical implicationsBecause of the general form of the solutions, the technique can be applied to a wide range of electromagnetic configurations to predict, e.g. eddy current losses in magnets or wireless energy transfer systems. By adaptation of the conductivity function in conducting regions, eddy current distributions in structures containing holes or slit patterns can be obtained.Originality/valueWith the presented technique, eddy currents in conducting structures of finite dimensions can be modeled. The semi-analytical model is for a relatively low number of harmonics computationally faster than 3D finite element methods. The method has been validated and shown to be computationally accurate.

150 km fast BOTDA based on the optical chirp chain probe wave and Brillouin loss scheme.

Distributed long-range Brillouin optical time domain analysis (BOTDA) is an extremely time-consuming sensing scheme, which requires frequency mapping of the Brillouin spectrum and a large number of average times. Here, we propose a fast long-range BOTDA based on the optical chirp chain (OCC) probe wave and Brillouin loss scheme. The OCC-modulated probe wave is enabled by cascading fast-frequency-changing microwave chirp segments head-to-tail, which covers a large frequency range around the anti-Stokes frequency relative to the pump wave. The combination of the OCC technique and Brillouin loss scheme provides several advantages, i.e., fast measurement, a high Brillouin threshold, no additional amplification scheme, and freedom from the nonlocal effect. In the experiment, 6m spatial resolution, 3.2s measurement time, and 3MHz measurement precision were achieved over a 150km single-mode fiber.

Finite-frequency noise of interacting single-electron emitters: Spectroscopy with higher noise harmonics

We derive the symmetrized current-noise spectrum of a quantum dot, which is weakly tunnel-coupled to an electron reservoir and driven by a slow time-dependent gate voltage. This setup can be operated as an on-demand emitter of single electrons into a mesoscopic conductor. By extending a real-time diagrammatic technique which is perturbative in the tunnel coupling, we obtain the time-resolved finite-frequency noise as well as its decomposition into noise harmonics in the presence of both strong Coulomb interaction and slow time-dependent driving. We investigate the noise over a large range of frequencies and point out where the interplay of Coulomb interaction and driving leads to unique signatures in finite-frequency noise spectra, in particular in the first harmonic. Besides that, we employ the first noise harmonic as a spectroscopic tool to access individual fluctuation processes. We discuss how the inverse noise frequency sets a time scale for fluctuations, which competes with time scales of the quantum-dot relaxation dynamics as well as the driving.

Odd-frequency superconducting pairing in junctions with Rashba spin-orbit coupling

We consider normal-superconductor (NS) and superconductor-normal-superconductor (SNS) junctions based on one-dimensional nanowires with Rashba spin-orbit coupling and proximity-induced $s$-wave spin-singlet superconductivity and analytically demonstrate how both even- and odd-frequency and spin-singlet and -triplet superconducting pair correlations are always present. In particular, by using a fully quantum mechanical scattering approach, we show that Andreev reflection induces mixing of spatial parities at interfaces, thus being the unique process which generates odd-frequency pairing; on the other hand, both Andreev and normal reflections contribute to even-frequency pairing. We further find that locally neither odd-frequency nor spin-triplet correlations are induced, but only even-frequency spin-singlet pairing. In the superconducting regions of NS junctions, the interface-induced amplitudes decay into the bulk, with the odd-frequency components being generally much larger than the even-frequency components at low frequencies. The odd-frequency pairing also develops short and long-period oscillations due to the chemical potential and spin-orbit coupling, respectively, leading to a visible beating feature in their magnitudes. Moreover, we find that in short SNS junctions at $\pi$-phase difference and strong spin-orbit coupling, the odd-frequency spin-singlet and -triplet correlations strongly dominate with an alternating spatial pattern for a large range of sub-gap frequencies.

Broadband efficient vortex beam generation with metallic helix array

Vortex beams with orbital angular momentum are characterized by a helical phase front and a phase singularity at the beam center. Such beams have various intriguing applications, such as optical communications, particle trapping, and high resolution imaging. Generating a vortex beam by exploiting the geometric phase has attracted great interest, due to its spin-to-orbital conversion feature and device versatility. To meet the requirements of applications such as optical communications and make the devices more user-friendly, vortex beam generation needs to be efficient in a large frequency range. The efficient bandwidth of the optical element is critical here, since the geometric phase is frequency independent. In this work, we design and fabricate a broadband efficient reflective vortex beam generator based on a metallic helix array, which has a uniform efficient co-circular-polarization reflection property. Vortex beams with arbitrary topological charge can be generated with such devices. The measured efficiency of our device is above 58.4%, with the relative bandwidth of 64.52%.

GlucoCEST imaging with on-resonance variable delay multiple pulse (onVDMP) MRI.

To examine the detection sensitivity for the rapidly exchanging hydroxyl protons of D-glucose using the recently developed on-resonance variable delay multi-pulse (onVDMP) chemical exchange saturation transfer (CEST) technique. The onVDMP method was applied for the detection of water signal changes upon venous D-glucose infusion in mice with 9L glioma xenografts. The effect size of onVDMP MRI during infusion was compared with that of conventional continuous wave (CW) CEST MRI. Both methods highlighted the tumor and the blood vessels on D-glucose infusion. In interleaved studies, the mean signal changes detected by onVDMP were found to be 1.8 times higher than those by CW-CEST, attributed to its high labeling efficiency for fast exchanging protons and the labeling of the OH protons over a larger frequency range. The onVDMP method is a more sensitive technique for the detection of exogenous CEST agents with fast-exchanging protons compared to CW-CEST MRI.

Quantum depletion and superfluid density of a supersolid in Raman spin-orbit-coupled Bose gases

We theoretically investigate a three-dimensional weakly interacting Bose gas with one-dimensional Raman-type spin-orbit coupling at zero temperature. By employing an improved ansatz, including high-order harmonics in the stripe phase, we show that the critical transition from the stripe to the plane-wave phases is shifted to a relatively larger Rabi frequency compared to the prediction by previous work [Li $\textit{et al.}$, Phys. Rev. Lett. $\textbf{108}$, 225301 (2012)] using a first-order stripe ansatz. We also determine the quantum depletion and superfluid density over a large range of Rabi frequency in different phases. The depletion exhibits an intriguing behavior with a discontinuous jump at the transition between the stripe and plane-wave phases, and a maximum at the transition between the plane-wave and zero-momentum phases. The superfluid density is derived through a phase-twist method. In the plane-wave and zero-momentum phases, it is significantly suppressed along the spin-orbit-coupling direction and vanishes at the transition, consistent with a recent work [Zhang $\textit{et al.}$, Phys. Rev. A $\textbf{94}$, 033635 (2016)], while in the stripe phase, it smoothly decreases with increasing Rabi frequency. Our predictions would be useful for further theoretical and experimental studies of the exotic supersolid stripe phase.

A Handheld Electronics Module for Dielectrophoretic Impedance Measurement of Cancerous Cells in the Microchip

This study proposes a handheld electronics module integrated with the microchip that utilizes dielectrophoretic (DEP) impedance measurement for characterizing of cancerous cell lines. The microchip consists of circle-on-line-shaped interdigitated microelectrodes, which were used for DEP concentration and impedance sensing of cells within a chamber, patterned by standard microfabrication processes. The handheld electronics module was built for measuring impedance of cancerous cells in the microchip. It can provide sinusoidal electrical signals in a large range of frequencies. The analyzed results demonstrate a high-sensitivity impedance measurement. Meanwhile, the linear relationships between the admittance variation and the number of cell were observed for both two human lung cell lines, namely A549 human lung carcinoma cells and MRC-5 human lung epithelial cells. The difference in the slopes of these characteristic lines could be used to distinguish two stages of lung cells. The proposed device is simple to operate, has high sensitivity, inexpensive and portable.

Multi-mode tunable absorber based on graphene metamaterial

In this paper, a novel design of metamaterial absorber (MA) with multi modes and tunability characteristics in terahertz (THz) range is presented. The MA consists of patterned gold-graphene on the top layer, graphene sheet and gold ground separated by SiO2. The chemical potential of patterned graphene and graphene sheet can be tuned independently. Thus, the regulation flexibility of MA is greatly enhanced. For demonstration, the proposed MA is investigated using circuit analogy method and the distributions of the electric field are also discussed in detail to explore underlying mechanism. Numerical calculations are stimulated in a commercial full-wave solver and indicate that the proposed MA possesses excellent absorption properties. There are three perfect absorption (≥99.2%) modes at 2.4 THz, 4.2 THz and 7.2 THz respectively. Under the regulation of chemical potential, the proposed MA could serve as single-frequency or dual-frequency absorber without change of physical structure. When working as single-frequency absorber, the MA could be regulated between different modes during a large frequency range and the absorption peaks could also be regulated within the same mode during a relative smaller frequency range. Furthermore, the MA has two absorption peaks at 2.4 THz and 7.2 THz (≥95%) simultaneously as dual-frequency absorber. The proposed MA shows promising application potentials due to the flexible modulation and functions and this work provides a new perspective for the design of tunable THz absorbers based on graphene.

A Broadband Dual-Polarized Antenna With Front-to-Back Ratio Enhancement Using Semicylindrical Sidewalls

A novel dual-polarized antenna, with a large bandwidth and a high front-to-back ratio, is proposed in this communication. The antenna is composed of printed dipoles and tapered baluns above a square ground plane to yield a wide bandwidth. Semicylindrical walls are loaded on the edge of the ground plane to suppress the back lobe and produce a stable gain. Backward radiation is suppressed by the diffraction effect of the semicylindrical sidewalls. Simulation shows that the back-lobe level can be reduced below −13 dB in a large frequency range without degrading the antenna bandwidth. The proposed antenna is fabricated and the measured results show that it has an impedance bandwidth of 69.6% (1.46–3.02 GHz) for voltage standing wave ratio <1.5. Within the bandwidth, the gain varies between 7.1 and 8.4 dBi, and the front-to-back ratio is above 20 dB. The proposed antenna is suitable for outdoor base station applications, and the back-lobe suppression technique can be applied easily to base station antennas.

Ferroelastic relaxation at 20 GHz evidenced by large frequency range picosecond acoustics

We present a method to perform elastic measurements on a thin-film as a function of frequency between a few GHz and a few hundred GHz. The technique is mainly based on Picosecond Acoustics (PA), which is an ultrafast optical technique that realizes pulse-echo measurements in the hypersonic range. Here, we combine gold layers serving as transducers and several opto-acoustic detection mechanisms to extend the PA technique to the lowest accessible frequencies (a few GHz) up to hundreds of GHz. We can therefore use the same technique on the same material to explore its elastic properties at a certain frequency over a very large frequency range. We have then applied this technique to explore the elastic properties of a lead zirconate titanate thin film from 3 to 80 GHz. We report a 9% increase in the longitudinal sound velocity above 20 GHz, which corresponds to a 19% increase in the C33 elastic modulus. We interpret such an observation as a direct evidence of ferroelastic domain wall relaxation.

Polymer Optical Fiber Bragg Gratings in CYTOP Fibers for Angle Measurement with Dynamic Compensation.

This paper demonstrates the use of polymer optical fiber Bragg gratings (POFBGs) for angle measurements over a range of different oscillatory frequencies. The POFBGs are inscribed in low-loss, cyclic transparent amorphous fluoropolymers (CYTOP) and are imprinted using the direct-write, plane-by-plane femtosecond laser inscription method. As the polymer has a viscoelastic response and given that the Young’s modulus depends on the oscillatory frequency, a compensation technique for sensor frequency cross-sensitivity and hysteresis is proposed and verified. Results show that the proposed compensation technique is able to provide a root mean squared error (RMSE) reduction of 44%, and a RMSE as low as 2.20° was obtained when compared with a reference potentiometer. The hysteresis reduction provided by the proposed technique is 55%, with hysteresis <0.01. The results presented in this paper can pave the way for movement analysis with POFBG providing higher sensitivity and low hysteresis over a large range of motion frequencies.

Optimal sponge layer for water waves numerical models

We present the system of linear equations to be solved to evaluate the reflection coefficient at a sponge layer boundary with damping forces ρfSL=−ρβu, where β is the sponge layer function. The case of 2D waves is discussed in details and different sponge layer functions are proposed. The linear system is solved using the finite element method (FEM) at low computational cost compared to the target simulations. This method should enable the design of efficient sponge layer for any full Navier–Stokes solvers. The linear model results solved with a FEM solver are compared here to SPH simulations with good agreement. The linear model is then used to determine the reflection coefficient for different power sponge functions, length and dissipation coefficient using the FEM solver.The linear model solved by a simple FEM solver can be used to evaluate the suitable dissipation coefficients for waves ranging from shallow to deep water for a given sponge layer length. The coefficient depends on the non-dimensional frequency for Ω=ωd/g<2. A table of suitable parameters for different sponge layer functions is provided over a large range of non-dimensional frequency and sponge layer length. A 3D application of waves is also presented with 45° incidence angle.