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Broad-band measurements of dielectric permittivity in coaxial line using partially filled circular waveguide
摘要： The full-wave analysis was applied for a coaxial line (i.e., transmission line) that has a “short-circuited” discontinuity. The discontinuity has a radius less than or equal to the inner radius of the coaxial line. The “sample region” can be considered as a partially filled circular waveguide. Such a structure is very practical and is of particular interest for the dielectric spectroscopy applications. It takes into account the inhomogeneous field distribution, which is the limiting factor for the determination of high dielectric permittivity values at microwave frequencies. The direct problem was solved by using the mode-matching technique, and the relationship between the complex reflection coefficient and the dielectric permittivity of the cylindrical sample was obtained. By solving the inverse problem, it is possible to obtain the complex dielectric permittivity from the experimental values of the scattering matrix. The results were verified by the finite element modeling of the system and applied for particular materials. The correspondence between these approaches is excellent. This method is very suitable for the determination of permittivity, which exceeds several thousands (it is applicable for any type of material). It extends the frequency range where the permittivity can be determined reliably. There is no necessity to prepare samples with different geometries (i.e., surface area and thickness).
关键词： dielectric permittivity,coaxial line,circular waveguide,mode-matching technique,finite element modeling
更新于2025-09-23 15:21:01
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[ASME ASME 2014 International Mechanical Engineering Congress and Exposition - Montreal, Quebec, Canada (Friday 14 November 2014)] Volume 10: Micro- and Nano-Systems Engineering and Packaging - Effect of Imperfections on Fused Silica Shell Resonators
摘要： Axisymmetric shell resonators have been attractive candidates for high performance MEMS vibratory gyroscopes because of their high quality factor, low sensitivity to environmental vibrations and electrostatic tuning capability. Fused silica shell resonators made by blow torch molding with high quality factor could perform as high performance MEMS gyroscopes. Despite such advantageous features, the performance of these is limited by geometric imperfections that occur during fabrication. This paper investigates effect of geometric asymmetries such as height and radius imperfections, notch, and mass imbalance in the rim of gyroscopes on the split in the natural frequencies of the n=2 wineglass modes. Numerical simulation shows that perfect fused silica shell has 13929 Hz natural resonance frequencies without any frequency split. Analysis of imperfect shell reveals that frequency split is very sensitive to edge geometric imperfection and mass imbalance in the rim. On the other hand, ??? is not very sensitive to the notch in the rim of shell and height imperfection less than 40????.
关键词： Frequency Split,Geometric Imperfection,MEMS Gyroscope,Shell Resonators,Mode Matching
更新于2025-09-23 15:21:01
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On the attenuation of fluida??structure coupled modes in a non-planar waveguide
摘要： In this article, the attenuation of ?uid–structure coupled modes of non-planar waveguide involving cavities is discussed. The physical problem is modeled to illustrate the scattering behavior of acoustic waves in a ?exible waveguide composed of thin elastic elements having edges or joints and structural discontinuities. The ?uid–structure coupled waveforms scatter after interacting with the discontinuities and edges of the underlying structure. An appropriate choice of edges offers scattering or resonance processes, which also guide ?uid–structure coupled waves. The mode-matching technique, together with low-frequency approximation, is used to determine velocity potentials. The guiding structure is then analyzed and validated through scattering energy functionals by varying the dimensions of the cavities and the wave frequency. The results are formulated and analyzed by tuning the device using an appropriate choice of edge conditions, dimension of cavities, and wave frequencies, thereby validating the obtained solutions. These descriptions are very useful for the active control measure of structural vibrations.
关键词： cavities,mode-matching,Attenuation,non-planar waveguide,?uid structure
更新于2025-09-23 15:19:57
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A Mode-Matching Solution for the Study of Cylindrical Waveguide Bifurcation via Closed-Form Coupling Integrals
摘要： In this paper, we present a mode-matching technique formulation for the rigorous electromagnetic analysis of a circular waveguide bifurcated into circular and coaxial domains. A generalized scattering matrix is obtained for relating the modal field amplitudes in each of the waveguides, and we were able to obtain closed-form solutions for all the associated coupling integrals. We present a series of validation results showing that the technique introduced in this work can model accurately and efficiently a class of cylindrical waveguide devices.
关键词： multifurcated waveguide,Mode-matching technique,generalized scattering matrix
更新于2025-09-23 15:19:57
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Dynamic mode matching of internal and external cavities for enhancing the mode-hop-free synchronous tuning characteristics of an external-cavity diode laser
摘要： This paper proposed an external-cavity diode laser (ECDL) that has low-frequency tuning (< 10 Hz) ability using the synchronous tuning principle. However, during high-frequency tuning, the mechanical vibration of the external-cavity system inherent in the ECDL is excited, which will break the mode matching of the internal and external cavities and greatly decrease the mode-hop-free (MHF) tuning range of the ECDL. To obtain a wide MHF range at high-frequency tuning, we used an active internal-cavity mode control method with an inductance–resistance–capacitance (LRC) filter to implement the dynamic mode matching of the internal and external cavities. After using the LRC filter, the experimental results indicated that the MHF tuning range at high-frequency tuning was significantly improved and a maximum wavelength tuning rate of 6.21 THz/s was obtained at tuning frequency of 30 Hz using an uncoated laser diode with a central wavelength of 785 nm.
关键词： mode-hop-free tuning,dynamic mode matching,synchronous tuning,LRC filter,external-cavity diode laser
更新于2025-09-12 10:27:22
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New Insight into Complex Mode Matching Method for Modeling and Simulation of Surface-Emitting Grating Couplers
摘要： A complex mode matching method is investigated for modeling and simulation of surface-emitting grating couplers. It is noted that the degree of accuracy for the complex modes obtained numerically plays significant role in determining the overall accuracy of the mode matching method, regardless of the number of modes used in the mode expansion. Furthermore, a reduced two-dimensional (2D) model by using the effective index method is shown to yield highly accurate results in comparison with the full three-dimensional (3D) model for practical grating couplers, which allows huge saving in computational resources for performance simulation and design optimization. Lastly, we employ a robust genetic algorithm (i.e., the particle swarm method) for optimization against grating period for maximum coupling efficiency to a single mode optical fiber and produces results consistent with those reported in literature.
关键词： radiation coupling,Integrated optics devices,mode-matching method
更新于2025-09-09 09:28:46