Papers by Keyword: Resonant Frequency

Abstract: The radio frequency (RF) performances of MEMS suspended spiral inductor under high overload environments are studied. Firstly, a suspended spiral inductor and its MEMS surface micromachining process which is compatible with CMOS process are developed. Then, the mechanical responses and RF performances of the inductor are simulated by ANSYS and HFSS, respectively. The simulation results show that, as the overload increases, the inductance and quality factor decrease significantly when the frequency band is closed to the resonant frequency but have no significant change when the frequency band is much lower than resonant frequency_; the resonant frequency of the suspended inductor decreases monotonically with the increase of overload. A modified lumped parameter model is utilized to illustrate the simulation results, which theoretically indicates that the substrate loss is more severe than the ohmic loss as the overload increases.

Abstract: A circular high electron mobility transistor (C-HEMT) prepared on the AlGaN/GaN membrane surface has been investigated and its potential for pressure sensing has been already demonstrated. The key issue in the design process of such heterostructure based MEMS sensors is the stress engineering. This way we can scale the sensor performance, measured pressure range and sensitivity. Especially, the knowledge of the exact value of the residual stress in membranes (caused by deposition process) helps us to optimize the sensing devices. In this work, the residual stress determination method in gallium nitride circular shaped membrane is reported. It is shown that resonant frequency method using Laser Doppler Vibrometry (LDV) for membrane vibration measurement seems to be an appropriate technique to determine the residual stress in micro-scale membranes. Circularly shaped AlGaN/GaN micro-membranes are excited by acoustic short time pulse. The decay oscillating motion of the membrane is recorded by oscilloscope. By FFT spectral analysis of the signals the resonance frequencies are obtained. For the sample studied, the natural frequency mode resonance peak is used to define the residual stress level. To verify the observed stress in investigated membranes, prestressed modal analysis in finite element method (FEM) code ANSYS is performed. The stress extracted from the measured frequency is taken as an initial stress state of the modelled membrane. Experimentally obtained shock spectra are compared with that computed by FEM simulation.

Abstract: In order to improve the energy harvesting efficiency of piezoelectric cantilever beam (PCB) in the environment. This paper presents a new type of piezoelectric cantilever beam which is the single-sided trapezoidal loop shaped PCB. By theory analysis, the equivalent circuit model was established, resonant angular frequency is inversely proportional to the length of cantilever beam. Based on finite element analysis method, the piezoelectric performance of single-sided trapezoidal loop shaped PCB and that of single-sided rectangular loop shaped PCB are compared with the same areas. The analysis results show that the coupling voltage of the former is larger, the output power of single-sided trapezoidal loop shaped PCB is improved, and the theoretical derivation of the inverse relationship between the frequency and length is verified.

Abstract: Inverted-F antenna loaded meander-line was studied by using High Frequency Structure Simulator V11(hereinafter referred to as HFSS V11). Research had focused on main performance parameters of Inverted-F antenna which loaded different number of meander-lines and different height of meander-lines. According to research, main performance parameters of inverted-F antenna, such as resonant frequency, resonance impedance and S₁₁ parameter of resonance point could be adjusted effectively. Inverted-F antenna could be miniaturized effectively by selecting appropriate number and height of meander-lines. The technology of loaded meander-line is a kind of simple and effective way that can be applied to the RFID field and other areas that have high requirements for miniaturization of antenna.

Abstract: This research proposes a novel piezoelectric harvester structure which is constructed by a cantilever base beam and piezoelectric elements bonded with the base beam in a certain manner. By changing the electrical boundary conditions of the piezoelectric elements, the resonant frequency of the beam structure changes accordingly. Two kinds of manners in which piezoelectric elements are bonded with the beam are investigated and compared with ANSYS simulations and experiments. The results showed that the embedded manner surpasses the surface-bonded manner with the frequency variation ratio of 3.17%.

Abstract: This paper proposes a matter of permittivity measurement method which based on the microwave antennas resonant characteristics. The basic principle of measuring permittivity was analyzed by the antenna resonance theory. The simulation model has been build and analyzed by Ansoft HFSS simulation software. The relationship between different permittivity and the antennas resonant frequency was given. The experimental model was designed and the experimental data of sample was measured. The experimental and simulation data are compared and discussed. Results show that the simulation and experimental results are consistent well; the antenna resonance method to measure the permittivity is feasible.

Abstract: Micromechanical calculations and elasticity standard relations are used to predict the elastic properties of porous alumina, zirconia and kaolin-based ceramics, as well as the high-temperature Young moduli of alumina-zirconia and alumina-mullite composites. The predictions are compared with experimental results obtained via impulse excitation. It is found that the Young moduli of highly porous (cellular) alumina ceramics can be predicted via the Gibson-Ashby power-law relation, whereas for partially sintered kaolin-based ceramics our exponential relation, albeit better than the Gibson-Ashby relation, does not give a satisfactory prediction. However, once the Young moduli are known, the shear and bulk moduli can be reliably predicted in both cases, based on rough information on the Poisson ratio. The temperature dependence of the Youngs moduli of two-phase composites can be quite precisely predicted as soon as the master curves of the constituent phases and the type of porosity (convex, concave, or saddle-point) are known.

Abstract: Resonant properties of a Microwave cavity with ceramic material for a new type of rubidium clock is studied by mode matching method. In order to study main factors influencing resonant characteristics, resonant frequencies of TE₀₁₁ mode are calculated. In addition, the effect of the ceramic material on resonant frequency are also analyzed. This work is of great significance for cavity design and theory perfection in atomic clock.

Abstract: The dynamic stability of a timber shell roof structure of the Palasport located in Bologna, has been investigated by means of reduced 1/30 scale model tested on seismic shaking table at Dynamic Testing Laboratory of IZIIS, Skopje, Macedonia. The model was physically modeled according to similitude lows and Buckingham's theorem as an artificial mass simulation model, using the same material as for the prototype structure. The supporting structure of the model was constructed by 26 micro-concrete foundations, 52 micro-concrete columns and 52 steel braces. The roof structure made of wooden lamellar beams forming triangles. The roof consists of a central cylindrical part and 2 lateral spherical parts. The connection between the beams was made by steel rings. The total number of the wooden beams was 550 forming 203 internal and external joints. The model was tested in vertical and horizontal direction considering various loading conditions: symmetrical and non-symmetrical. After definition of dynamic characteristics of the model, it was subjected to seismic excitation of Ancona, as well as Montenegro earthquakes. It was found out that the cylindrical part is more flexible than the spherical one. The largest amplitudes during the tests were obtained in vertical direction. The highest stress concentration was at the cylindrical central arches. The asymmetric load produced more unfavorable behavior than the symmetric one.

Abstract: The gyroscopes have been used as a suitable inertial instrument for the navigation guidance and attitude controls. The accuracy as very sensitive sensor is limited by the lock-in region (dead band) due to the frequency coupling between two counter-propagating waves at low rotation rates. This frequency coupling gives no phase difference, and an angular increment is not detected. This problem can be overcome by mechanically dithering the gyroscope. This paper presents the design method of mechanical dither by the theoretical considerations and the verification of the theoretical equations through FEM applications. As a result, comparing to the past result, the maximum prediction error of resonant frequency was within 3 percent and peak dither rate was within 5 percent. It was found that the theoretical equations can be feasible for the mechanical performance of dither.