The Experts below are selected from a list of 43080 Experts worldwide ranked by ideXlab platform
R Mittra - One of the best experts on this subject based on the ideXlab platform.
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efficient computation of Resonant Frequencies and quality factors of cavities via a combination of the finite difference time domain technique and the pade approximation
IEEE Microwave and Guided Wave Letters, 1998Co-Authors: S Dey, R MittraAbstract:An efficient method for analyzing cavity structures by using the fast Fourier transform (FFT)/Pade technique, in combination with the finite-difference time-domain (FDTD) method, is presented. Without sacrificing the accuracy of the results, this new method significantly reduces the computational time compared to that needed where the conventional FFT algorithm is used. The usefulness of this approach is demonstrated by modeling a lossy cavity and computing its Resonant Frequencies as well as Q.
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a study of the nonorthogonal fdtd method versus the conventional fdtd technique for computing Resonant Frequencies of cylindrical cavities
IEEE Transactions on Microwave Theory and Techniques, 1992Co-Authors: P H Harms, Jinfa Lee, R MittraAbstract:The nonorthogonal finite-difference-time-domain (FDTD) technique is used to compute the Resonant Frequencies of dielectric-filled cylindrical cavities. Because the method is based on the nonorthogonal coordinate system, it is not restricted to specific geometries, e.g. rectangular or axially symmetric geometries, and is suitable for analyzing cavities of arbitrary shape. The advantages of this technique over the conventional FDTD algorithm with a staircase grid are shown in a convergence study, where the two methods are used to compute the dominant Resonant frequency of a cylindrical cavity. The accuracy of the technique for calculating the Resonant Frequencies of the first few modes is demonstrated by comparing the results obtained with this technique with those derived by using two versions of the finite element method in the frequency domain. >
L P B Katehi - One of the best experts on this subject based on the ideXlab platform.
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design of reconfigurable slot antennas
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: Dimitrios Peroulis, K Sarabandi, L P B KatehiAbstract:In this paper the design of a compact, efficient and electronically tunable antenna is presented. A single-fed Resonant slot loaded with a series of PIN diode switches constitute the fundamental structure of the antenna. The antenna tuning is realized by changing its effective electrical length, which is controlled by the bias voltages of the solid state shunt switches along the slot antenna. Although the design is based on a Resonant configuration, an effective bandwidth of 1.7:1 is obtained through this tuning without requiring a reconfigurable matching network. Four Resonant Frequencies from 540-890 MHz are selected in this bandwidth and very good matching is achieved for all Resonant Frequencies. Theoretical and experimental behavior of the antenna parameters is presented and it is demonstrated that the radiation pattern, efficiency and polarization state of the antenna remain essentially unaffected by the frequency tuning
Yuhsi Huang - One of the best experts on this subject based on the ideXlab platform.
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theoretical analysis and experimental measurement of flexural vibration and dynamic characteristics for piezoelectric rectangular plate
Sensors and Actuators A-physical, 2017Co-Authors: Yuhsi HuangAbstract:Abstract In this study, we investigate the out-of-plane vibration characteristics of a piezoelectric rectangular plate from theoretical analysis, numerical calculation and experimental measurement. The Resonant Frequencies and mode shapes of the piezoelectric rectangular plate with free boundary condition are analyzed in detail. The analytical solutions based on the superposition method are compared with two different techniques to confirm the validity. One is the numerical computation base on the finite element method (FEM), the other is experimental measurement. For experimental technique, two methods are used to validate the theoretical result, one is amplitude-fluctuation electronic speckle pattern interferometer (AF-ESPI) technique, and the other is laser Doppler vibrometry (LDV). This study uses a special configuration of electrodes for piezoelectric plates in experimental measurement of AF-ESPI to improve the electromechanical coupling efficiency of transverse vibration. It can be seen that specific vibration modes are easily excited by manipulating the configuration of electrodes. The superposition method is used to solve the out-of-plane displacement field and Resonant Frequencies for the piezoelectric plate. According to the explicit out-of-plane displacement field solution, the analytical results of mechanical and electric fields are also presented in explicit forms. It is shown that the comparison between theoretical analysis, numerical computations and experimental measurement in terms of the Resonant Frequencies and corresponding mode shapes are with good agreement.
Ivo Stachiv - One of the best experts on this subject based on the ideXlab platform.
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nanocantilevers with adjustable static deflection and significantly tunable spectrum Resonant Frequencies for applications in nanomechanical mass sensors
Nanomaterials, 2018Co-Authors: Ivo Stachiv, P SittnerAbstract:Nanocantilevers have become key components of nanomechanical sensors that exploit changes in their Resonant Frequencies or static deflection in response to the environment. It is necessary that they can operate at a given, but adjustable, Resonant frequency and/or static deflection ranges. Here we propose a new class of nanocantilevers with a significantly tunable spectrum of the Resonant Frequencies and changeable static deflection utilizing the unique properties of a phase-transforming NiTi film sputtered on the usual nanotechnology cantilever materials. The reversible frequency tuning and the adjustable static deflection are obtained by intentionally changing the Young’s modulus and the interlayer stress of the NiTi film during its phase transformation, while the usual cantilever elastic materials guarantee a high frequency actuation (up to tens of MHz). By incorporating the NiTi phase transformation characteristic into the classical continuum mechanics theory we present theoretical models that account for the nanocantilever frequency shift and variation in static deflection caused by a phase transformation of NiTi film. Due to the practical importance in nanomechanical sensors, we carry out a complete theoretical analysis and evaluate the impact of NiTi film on the cantilever Young’s modulus, static deflection, and the Resonant Frequencies. Moreover, the importance of proposed NiTi nanocantilever is illustrated on the nanomechanical based mass sensors. Our findings will be of value in the development of advanced nanotechnology sensors with intentionally-changeable physical and mechanical properties.
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Simultaneous determination of the residual stress, elastic modulus, density and thickness of ultrathin film utilizing vibrating doubly clamped micro-/nanobeams
AIP Publishing LLC, 2016Co-Authors: Ivo Stachiv, Tehua Fang, Chih-yun Kuo, Vincent MortetAbstract:Measurement of ultrathin film thickness and its basic properties can be highly challenging and time consuming due to necessity of using several very sophisticated devices. Here, we report an easy accessible Resonant based method capable to simultaneously determinate the residual stress, elastic modulus, density and thickness of ultrathin film coated on doubly clamped micro-/nanobeam. We show that a general dependency of the Resonant Frequencies on the axial load is also valid for in-plane vibrations, and the one depends only on the considered vibrational mode. As a result, we found that the film elastic modulus, density and thickness can be evaluated from two measured in-plane and out-plane fundamental Resonant Frequencies of micro-/nanobeam with and without film under different prestress forces. Whereas, the residual stress can be determined from two out-plane (in-plane) measured consecutive Resonant Frequencies of beam with film under different prestress forces without necessity of knowing film and substrate properties and dimensions. Moreover, we also reveal that the common uncertainties in force (and thickness) determination have a negligible (and minor) impact on the determined film properties. The application potential of the present method is illustrated on the beam made of silicon and SiO2 with deposited 20 nm thick AlN and 40 nm thick Au thin films, respectively
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mass detection in viscous fluid utilizing vibrating micro and nanomechanical mass sensors under applied axial tensile force
Sensors, 2015Co-Authors: Ivo Stachiv, Tehua Fang, Yeauren JengAbstract:Vibrating micro- and nanomechanical mass sensors are capable of quantitatively determining attached mass from only the first three (two) measured cantilever (suspended) Resonant Frequencies. However, in aqueous solutions that are relevant to most biological systems, the mass determination is challenging because the quality factor (Q-factor) due to fluid damping decreases and, as a result, usually just the fundamental Resonant Frequencies can be correctly identified. Moreover, for higher modes the resonance coupling, noise, and internal damping have been proven to strongly affect the measured resonances and, correspondingly, the accuracy of estimated masses. In this work, a technique capable of determining the mass for the cantilever and also the position of nanobeads attached on the vibrating micro-/nanomechanical beam under intentionally applied axial tensile force from the measured fundamental flexural Resonant Frequencies is proposed. The axial force can be created and controlled through an external electrostatic or magnetostatic field. Practicality of the proposed technique is confirmed on the suspended multi-walled carbon nanotube and the rectangular silicon cantilever-based mass sensors. We show that typically achievable force resolution has a negligibly small impact on the accuracy of mass measurement.
Ian J Craddock - One of the best experts on this subject based on the ideXlab platform.
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finite difference time domain simulation of the earth ionosphere Resonant cavity schumann resonances
IEEE Transactions on Antennas and Propagation, 2005Co-Authors: A Soriano, J A Porti, E A Navarro, D L Paul, J A Morente, Ian J CraddockAbstract:This paper presents a numerical approach to study the electrical properties of the Earth's atmosphere. The finite-difference time-domain (FDTD) technique is applied to model the Earth's atmosphere in order to determine Schumann Resonant Frequencies of the Earth. Three-dimensional spherical coordinates are employed and the conductivity profile of the atmosphere versus height is introduced. Periodic boundary conditions are implemented in order to exploit the symmetry in rotation of the Earth and decrease computational requirements dramatically. For the first time, very accurate FDTD results are obtained, not only for the fundamental mode but also for higher order modes of Schumann resonances. The proposed method constitutes a useful tool to obtain Schumann Resonant Frequencies, therefore to validate electrical models for the terrestrial atmosphere, or atmospheres of other celestial bodies.
