THE INFLUENCE OF RF SWITCHES UPON THE PROPERTIES OF RECONFIGURABLE ANTENNAS. PART 1: SINGLE-FREQUENCY EXCITATION

2017 ◽  
Vol 76 (11) ◽  
pp. 963-981
Author(s):  
D. S. Gavva ◽  
E. A. Medvedev
Keyword(s):  
Reconfigurable Antennas ◽  
Single Frequency ◽  
Rf Switches ◽  
Frequency Excitation

Estimation of the Linearized Damping Coefficients of a Squeeze-Film Vibration Isolator

1987 ◽  
Vol 201 (3) ◽  
pp. 181-191 ◽  
Author(s):  
R Stanway ◽  
R Firoozian ◽  
J E Mottershead
Keyword(s):  
Single Frequency ◽  
Squeeze Film ◽  
Experimental Facility ◽  
Vibration Isolator ◽  
New Approach ◽  
Filtering Algorithm ◽  
Damping Coefficients ◽  
Performance Predictions ◽  
Frequency Excitation ◽  
Extract Information

In this paper the authors present experimental confirmation of the feasibility of a new approach to the estimation of the four damping coefficients associated with a squeeze-film vibration isolator. The design and construction of the experimental facility is described in detail. A time-domain filtering algorithm is applied to process the displacement responses to single-frequency excitation and thus extract information on the linearized dynamics of the squeeze-film. The estimated coefficients are validated by comparing performance predictions with those obtained from spectrum analysis and from short-bearing theory. The significance of the results is discussed and suggestions are made for further work in this area.

Two-Frequency Oscillation With Combined Coulomb and Viscous Frictions

2002 ◽  
Vol 124 (4) ◽  
pp. 537-544 ◽  
Author(s):  
Gong Cheng ◽  
Jean W. Zu
Keyword(s):  
Steady State ◽  
Dry Friction ◽  
Single Frequency ◽  
Friction Oscillator ◽  
One Stop ◽  
Frequency Excitation ◽  
Stop Motion ◽  
The One ◽  
Coulomb Dry Friction ◽  
Mass Spring

In this paper, a mass-spring-friction oscillator subjected to two harmonic disturbing forces with different frequencies is studied for the first time. The friction in the system has combined Coulomb dry friction and viscous damping. Two kinds of steady-state vibrations of the system—non-stop and one-stop motions—are considered. The existence conditions for each steady-state motion are provided. Using analytical analysis, the steady-state responses are derived for the two-frequency oscillating system undergoing both the non-stop and one-stop motions. The focus of the paper is to study the influence of the Coulomb dry friction in combination with the two frequency excitations on the dynamic behavior of the system. From the numerical simulations, it is found that near the resonance, the dynamic response due to the two-frequency excitation demonstrates characteristics significantly different from those due to a single frequency excitation. Furthermore, the one-stop motion demonstrates peculiar characteristics, different from those in the non-stop motion.

Dynamic analysis of nonlinear time-varying spur gear system subjected to multi-frequency excitation

2018 ◽  
Vol 25 (6) ◽  
pp. 1210-1226 ◽  
Author(s):  
Yi Yang ◽  
Mengjuan Xu ◽  
Yang Du ◽  
Pan Zhao ◽  
Yiping Dai
Keyword(s):  
Spur Gear ◽  
Numerical Results ◽  
Gear System ◽  
Working Environment ◽  
Single Frequency ◽  
Multiple Time Scales ◽  
Multiple Time ◽  
Time Varying ◽  
Harmonic Excitations ◽  
Frequency Excitation

Due to the complex working environment, gear systems always suffer from multiple excitations in actual engineering. This paper concerns the frequency response characteristics of a nonlinear time-varying spur gear system subjected to multi-frequency excitation. Firstly, a single degree-of-freedom gear pair model is established with consideration of the gear backlash, time-varying mesh stiffness and multiple harmonic excitations. Then, using the multiple time scales method, a comprehensive theoretical study is conducted to analyze various resonant cases including primary, parametric and combination resonances. Besides, parametric studies are accomplished to reveal the effects of the multi-frequency excitation on gear dynamics and to provide some useful references for reducing the vibration level. With the help of the fifth-order Runge–Kutta method, the numerical results are obtained to verify the validity of the analytical solutions and to emphasize the significances of the multi-frequency excitation. In addition, a comparison is performed between the numerical results and the published experimental results to validate the proposed gear model. Results show that the presence of the multi-frequency excitation will introduce the interaction between different harmonic excitations, which significantly affects the nonlinear vibration characteristics of a spur gear system. The proposed gear model with multi-frequency excitation could be more reliable and universal than that with single-frequency excitation. In addition, the results of parametric study could provide some suggestions to designers and researchers attempting to obtain desirable dynamic behaviors of a gear system subjected to multi-frequency excitation.

scholarly journals Analysis of RF Front-End Performance of Reconfigurable Antennas with RF Switches in the Far Field

2014 ◽  
Vol 2014 ◽  
pp. 1-14 ◽  
Author(s):  
Insu Yeom ◽  
Junghan Choi ◽  
Sung-su Kwoun ◽  
Byungje Lee ◽  
Changwon Jung
Keyword(s):  
Mobile Devices ◽  
Field Condition ◽  
Rf Mems ◽  
Reconfigurable Antennas ◽  
Reconfigurable Antenna ◽  
Far Field ◽  
Rf Switches ◽  
Mems Switches ◽  
Front End ◽  
Rf Front End

The RF front-end performances in the far-field condition of reconfigurable antennas employing two commonly used RF switching devices (PIN diodes and RF-MEMS switches) were compared. Two types of antennas (monopole and slot) representing general direct/coupled feed types were used for the reconfigurable antennas to compare the excited RF power to the RF switches by the reconfigurable antenna types. For the switching operation of the antennas, a biasing circuit was designed and embedded in the same antenna board, which included a battery to emphasize the antenna’s adaptability to mobile devices. The measurement results of each reconfigurable antenna (radiation patterns and return losses) are presented in this study. The receiving power of the reference antenna was measured by varying the transmitting power of the reconfigurable antennas in the far-field condition. The receiving power was analyzed using the “Friis transmission equation” and compared for two switching elements. Based on the results of these measurements and comparisons, we discuss what constitutes an appropriate switch device and antenna type for reconfigurable antennas of mobile devices in the far-field condition.

Single-frequency excitation wideband MRI (SE-WMRI)

2015 ◽  
Vol 42 (7) ◽  
pp. 4320-4328
Author(s):  
Edzer L. Wu ◽  
Yun-An Huang ◽  
Tzi-Dar Chiueh ◽  
Jyh-Horng Chen
Keyword(s):  
Single Frequency ◽  
Frequency Excitation

Calculating Scattering Spectra using Time-domain Modeling of Time-modulated Systems

2021 ◽  
Vol 35 (11) ◽  
pp. 1288-1289
Author(s):  
Adam Mock
Keyword(s):  
Time Domain ◽  
Single Frequency ◽  
Refractive Index Modulation ◽  
Domain Modeling ◽  
Resonant Structures ◽  
Theoretical Predictions ◽  
Time Domain Modeling ◽  
Scattering Spectra ◽  
Frequency Excitation ◽  
Frequency Mixing

Obtaining agreement between theoretical predictions that assume single-frequency excitation and finite-difference time-domain (FDTD) simulations that employ broadband excitation in the presence of time-varying materials is challenging due to frequency mixing. A simple solution is proposed to reduce artifacts in FDTD-calculated spectra from the frequency mixing induced by harmonic refractive index modulation applicable to scenarios in which second order and higher harmonics are negligible. Advantages of the proposed method are its simplicity and applicability to arbitrary problems including resonant structures.

The Testing and Approval of Aircraft Engine Mounted Accessories

1982 ◽  
Vol 196 (1) ◽  
pp. 57-64
Author(s):  
D S Pearson
Keyword(s):  
Gas Turbine ◽  
Aircraft Engine ◽  
Single Frequency ◽  
Turbine Engines ◽  
Severity Assessment ◽  
Gas Turbine Engines ◽  
Shaft Speed ◽  
Unified Approach ◽  
Frequency Excitation ◽  
Environmental Simulation

Vibration measurements on gas turbine engines are normally made using accelerometers. The environment to which engine accessories would be subject has been evaluated by comparing ‘g’ peaks in the frequency spectrum, individually, with empirical yardsticks of severity. Endurance approval testing of accessories to withstand the environment so characterized is normally conducted by applying unidirectional single frequency excitation to simulate engine conditions at a particular shaft speed. These procedures have proved inadequate in predicting failure or verifying corrective measures where accessory problems due to wear phenomena are concerned. This paper analyses reasons for this inadequacy in terms of measurement practice, engine severity assessment, environmental simulation and approval procedures. By recognizing the effect of multi-frequency vibration in three planes it further aims to provide a unified approach to accessory design and development by which service accessory reliability might be improved. Although at first sight more expensive, the approach described will in many cases reduce to previous practice. In cases where greater test expenditure is necessary, loopholes will have been plugged by which many expensive service problems previously escaped.

Sign in / Sign up

Export Citation Format

Share Document