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In order to investigate the impact of design parameters (depth, width, and location) of the single-circumferential groove (SCG) on tip leakage flow (TLF) reduction in a transonic turbine stage, a systematic investigation was conducted by high-precision numerical simulation method. The numerical results show that the introduction of SCG could improve the stage efficiency (η) of turbine significantly. The optimal design parameters of depth coefficient (ζ), width (W), and location (L) were ζ = 3, W = W3, and L = 20%Cax (where Cax denotes the axial chord of the blade), which could reduce tip clearance leakage rate (m*) by 28.9% and improve the η by 0.56%. The implementation of flow field display methods reveals that the introduction of SCG influences the formation and development of the vortex system at the rotor tip region. The circumferential groove vortex (CGV), induced by SCG, divided the tip leakage vortex (TLV) into two segments TLV_1 and TLV_2 due to its blocking effect. TLV_1 interacted with the passage vortex (PV) and depress the strength of PV. Meantime, TLV_2 would regenerate from the trailing edge of SCG, due to its limited development range and insufficient growth, the strength and scale of TLV_2 were weakened. Given that the TLF passing through SCG flows in an opposite direction to the original TLF, the SCG at appropriate location could lead to a fact that the net flow rate of the leakage flow reached the minimum value, thereby considerably reducing the m* and flow loss caused by TLF. [ABSTRACT FROM AUTHOR]

We demonstrate a dielectric metamolecule composed of ceramic and ferrite, which can be regarded as an equivalent LC circuit. When temperature varies, inductance is adjusted via the active ambient effective permeability of the metamolecule, thus counteracting the frequency drift caused by the temperature coefficient of the ceramic. The introduction of the ferrite meta-atom permits magnetic tunability, widening the working band of the filter. Additionally, the metamolecule inherits the high Q-value of the ceramic resonator. This work opens up an opportunity for realizing miniaturized, thermostable, tunable microwave filters with high-Q values in the fields of communication. [ABSTRACT FROM AUTHOR]

Actively controllable material properties are desirable for applications in materials science and microwave engineering. We design and fabricate a magnetically-coupled metamolecule with ferrite for X-band microwave frequencies that shows tunable responses to external magnetic fields. When compared with the metamolecule's magnetic Mie resonance, superior field sensitivity is observed in the vicinity of the Fano resonance through analysis of the transmission spectra. The mechanism is investigated by emulating the field distributions, and the phenomenon is attributed to specially coupled magnetic dipoles. The simulation results are verified experimentally. This work substantiates the metamaterial's enhanced electromagnetic properties for potential application to tunable microwave devices. [ABSTRACT FROM AUTHOR]

The Mie resonance of two dielectric meta-atoms causes a destructive coupling effect between them and results in hybridization induced transparency in the metamolecule. By actively adjusting the temperature, permittivities of the dielectric with opposite temperature coefficients vary in contrary trends, appearing as the field redistribution in each meta-atom. At the same time, two collective modes of the metamolecule behave as addition and subtraction of magnetic fields in meta-atoms. Combining both the intrinsic properties of materials and the collective properties of the coupling "dimer" system together, varying degrees of asymmetry of the metamolecule are obtained as the temperature changes. Since the intensity of the excited magnetic field can reflect the resonance amplitudes of the metamolecule onto the incident wave, the ratio of the transmission amplitudes of the two collective modes changes in a manner similar to the average magnetic field intensity of the metamolecule in two hybridized modes. Based on this behavior, we propose a method to estimate the degree of asymmetry of the metamolecule according to the field distribution intensity. [ABSTRACT FROM AUTHOR]

Spin valve sensors are used to measure on chip, the deflection of microelectromechanical system resonators (bridges or cantilevers), with nm resolution. A spin valve sensor (10 × 2 µm², MR = 6.5%) was placed 3.2 µm away and 2.8 µm below the central region of an a-Si:H bridge, with a 1.2 µm air gap. The bridge movement was controlled by an applied voltage on the gate. In the undeflected state, a Co[sub 78]Pt[sub 22] micromagnet (0.2 µm × 18 µm × 15 µm, M[sub r]t = 12.5 memu/cm²) deposited on top of the bridge, and saturated in an external field, creates a fringe field in the sensor shifting the transfer curve. An external bias field was then used to linearize the sensor response. Final sensor output versus bridge gate voltage was obtained using a low frequency square-wave gate excitation voltage (1 Hz). Bridge deflections from a few nm to 0.23 µm were detected. [ABSTRACT FROM AUTHOR]

Exchange enhancement through thermal anneal in bottom-pinned Mn[sub 76]Ir[sub 24] spin valves is investigated. Samples were fabricated by ion beam deposition (IBD), post-annealed in vacuum (10[sup -6] Torr) at 270 °C for 10 min, then cooled in a 3 kOe applied field. For a bilayer structure, glass/Ta 40 Å/NiFe 30 Å/MnIr 60 Å/CoFe 25 Å/Ta 40 Å, the exchange field (H[sub ex]) reaches 1148 Oe (J[sub ex]=0.4 erg/cm[sup 2]) after anneal. X-ray diffraction (XRD) analysis shows strong enhancement of <111> texture upon anneal, while grain size obtained from XRD and transmission electron microscopy for as-deposited and annealed states shows no major change. With increasing MnIr thickness, the exchange field decreases, and blocking temperature (T[sub b]) increases, reaching 295 °C for t[sub MnIr]=180 Å. Spin valves built with the same exchange bilayer (Ta 20 Å/NiFe 30 Å/MnIr 60 Å/CoFe 25 Å/Cu 22 Å/CoFe 20 &A! ring;/NiFe 40 Å/Ta 40 Å) show H[sub ex]=855 Oe (J[sub ex]=0.3 erg/cm[sup 2]) and magnetoresistance (MR)=7.1%. The incorporation of nano-oxide layers in spin valves increases the MR signal to 11%. No signal degradation is found in these specular structures for anneals up to 310 °C. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A magnetic tunable Fano-resonant metamaterial structure with enhanced nonreciprocity at microwave frequencies has been designed and investigated. The metamolecule has been implemented by using a dielectric cube and a magnetically biased ferrite. The Fano resonances originate from mode coupling between two constituents. The structure possesses a nonreciprocal feature since the external field breaks the time-reversal symmetry, and the Fano-type interference further enhances the nonreciprocal nature of biased ferrite. We are able to manipulate the Fano modes by adjusting the applied magnetic field. Simulation results suggest that the proper permittivity of the dielectric cube will optimize the nonreciprocal contrast. The magnetically tunable feature of the proposed metamaterial can potentially be applied to design dynamically controlled switches and isolators. [ABSTRACT FROM AUTHOR]