排序方式: 共有91条查询结果,搜索用时 46 毫秒
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Y. Pennec M. Beaugeois B. Djafari-Rouhani R. Sainidou A. Akjouj J.O. Vasseur L. Dobrzynski E.H. El Boudouti J.-P. Vilcot M. Bouazaoui J.-P. Vigneron 《Photonics and Nanostructures》2008,6(1):26-VII
We report numerical simulations, based on a finite difference time domain (FDTD) method, of light propagation in two-dimensional semiconductor micro-optical waveguides coupled to one or several lateral stubs. It is shown that when the stub is covered with a perfectly metallic thin layer, the transmission spectrum contains several narrow dips. Such simulation of the metallic coating can be used in the far infrared frequency domain, far from the optical regime. We propose a selective filtering device based on the interaction between several stubs. Inserting an appropriate defect stub between a set of periodical stubs leads to a tunnelling transmission, with a narrow peak inside the gap. This filtering phenomenon is used to propose a demultiplexer based on a Y-shaped waveguide for separating signals with different frequencies. Finally, we show that the filtering effect of a stub can also be reproduced when the metal is described in the frame of a Drude model instead of being perfect, which makes plausible the realization of the above devices in the near optical regime. 相似文献
72.
Zhi Yan Yi Ming Mi Zhi Tang Song Wei Li Liu Hong Ji Song Lin Feng 《Physica B: Condensed Matter》2007,400(1-2):38-41
ZnO-based film bulk acoustic resonator (FBAR) was fabricated with many ZnO/Pt layers by magnetron sputtering. All the layers are good crystallized and highly textured. By crystallographic test, the orientation fluctuation of Pt layer increases with increasing film thickness or stack layers, whereas that of ZnO layer decreases slightly. It is consistent with ZnO grain c-axis tilting observed using transmission electron microscopy. Due to these good quality layers, the device has a high resonate frequency of 3.94 GHz. 相似文献
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The paper reviews the state-of-art for micro optical fluidic systems (MOFS), or optofluidics, which employs optics and fluidics
in a microsystem environment to perform novel functionalities and in-depth analysis in the biophysical area. Various topics,
which include the introduction of MOFS in biomedical engineering, the implementation of near-field optics and also the applications
of MOFS to biophysical studies, are discussed. Different optical detection techniques, such as evanescent wave, surface plasmon
resonance, surface enhanced Raman scattering, resonators and transistors, have been studied extensively and integrated into
MOFS. In addition, MOFS also provides a platform for various studies of cell biophysics, such as cell mass determination and
cell Young’s modulus measurement.
Figure Cell encapsulation and trapping for refractive index measurement in MOFS 相似文献
74.
We study the effects of electrodes of nonuniform thickness on thickness-shear vibration frequencies and mode shapes of quartz resonators. This paper extends a previous paper from electrodes of stepped thickness to continuously varying thickness. Numerical results for electrodes of linearly varying thickness are presented. The results show that strong energy trapping can be achieved and adjusted using electrodes with variable thickness. 相似文献
75.
Effect of RF coil excitation on field inhomogeneity at ultra high fields: a field optimized TEM resonator 总被引:2,自引:0,他引:2
Tamer S. Ibrahim Robert Lee Brian A. Baertlein Amir M. Abduljalil Hui Zhu Pierre-Marie L. Robitaille 《Magnetic resonance imaging》2001,19(10):1339-1347
In this work, computational methods were utilized to optimize the field produced by the transverse electromagnetic (TEM) resonator in the presence of the human head at 8 Tesla. Optimization was achieved through the use of the classical finite difference time domain (FDTD) method and a TEM resonator loaded with an anatomically detailed human head model with a resolution of 2 mm × 2 mm × 2 mm. The head model was developed from 3D MR images. To account for the electromagnetic interactions between the coil and the tissue, the coil and the head were treated as a single system at all the steps of the model including, numerical tuning and excitation. In addition to 2, 3, 4, 6, and 10-port excitations, an antenna array concept was utilized by driving all the possible ports (24) of a 24-strut TEM resonator. The results show that significant improvement in the circularly polarized component of the transverse magnetic field could be obtained when using multiple ports and variable phase and fixed magnitude, or variable phase and variable magnitude excitations. 相似文献
76.
《Magnetic resonance in chemistry : MRC》2018,56(3):153-163
We present the development of a portable dynamic nuclear polarization (DNP) instrument based on the PCI eXtensions for Instrumentation platform. The main purpose of the instrument is for study of 1H polarization enhancements in solution through the Overhauser mechanism at low magnetic fields. A DNP probe set was constructed for use at 6.7 mT, using a modified Alderman–Grant resonator at 241 MHz for saturation of the electron transition. The solenoid for detection of the enhanced 1H signal at 288 kHz was constructed with Litz wire. The largest observed 1H enhancements (ε) at 6.7 mT for 14N‐CTPO radical in air saturated aqueous solution was ε~65. A concentration dependence of the enhancement is observed, with maximum ε at 5.5 mM. A low resonator efficiency for saturation of the electron paramagnetic resonance transition results in a decrease in ε for the 10.3 mM sample. At high incident powers (42 W) and long pump times, capacitor heating effects can also decrease the enhancement. The core unit and program described here could be easily adopted for multi‐frequency DNP work, depending on available main magnets and selection of the “plug and play” arbitrary waveform generator, digitizer, and radiofrequency synthesizer PCI eXtensions for Instrumentatione cards. 相似文献
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