scholarly journals Modelling of High-Frequency Roughness Scattering from Various Rough Surfaces through the Small Slope Approximation of First Order

2012 ◽  
Vol 02 (01) ◽  
pp. 1-11 ◽  
Author(s):  
Virginie Jaud ◽  
Cedric Gervaise ◽  
Yann Stephan ◽  
Ali Khenchaf
Keyword(s):  
High Frequency ◽  
Rough Surfaces ◽  
First Order

scholarly journals A Capacitively-Fed Inverted-F Antenna for Displacement Detection in Structural Health Monitoring

Sensors ◽  
2020 ◽  
Vol 20 (18) ◽  
pp. 5310
Author(s):  
Songtao Xue ◽  
Zhiquan Zheng ◽  
Shuai Guan ◽  
Liyu Xie ◽  
Guochun Wan ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Resonant Frequency ◽  
Current Distribution ◽  
Health Monitoring ◽  
High Frequency ◽  
Relative Displacement ◽  
Displacement Sensor ◽  
First Order ◽  
High Frequency Structure Simulator ◽  
Dimensional Parameters

This paper presents a capacitive displacement sensor based on a capacitively fed inverted-F antenna (CFIFA) for displacement detection. The sensor is composed of a grounded L-shape patch and a rectangular upper patch, forming a capacitor between them. The asymmetric dipole model is adopted to explain the frequency shift and current distribution of the proposed antenna sensor at its first-order resonance. The numerical simulation of the CFIFA using the Ansoft high-frequency structure simulator (HFSS) software is carried out to optimize the dimensional parameters, allowing the antenna to perform better. Two sets of CFIFAs are fabricated and tested for verification. Results show that the CFIFA has a good linear relationship between its first resonant frequency and the relative displacement, and is capable of a long range of displacement measuring.

An improved solution to the fourth moment equation for intensity fluctuations

1983 ◽  
Vol 386 (1791) ◽  
pp. 461-474 ◽  
Keyword(s):  
High Frequency ◽  
Correction Term ◽  
Approximate Solutions ◽  
Moment Equation ◽  
Solution Procedure ◽  
Fourth Moment ◽  
Basic Solution ◽  
Numerical Work ◽  
First Order ◽  
First Order Correction

An approximate solution is presented for the fourth moment equation that describes fluctuations of intensity in a wave propagating through a randomly fluctuating medium. The solution is valid for high frequency or relatively strong fluctuations in the medium. The solution procedure is straightforward and at zero order agrees with previously derived approximate solutions. However, the present method is much more direct and more easily extended to complicated problems. Indeed, the first order correction to this basic solution is also determined and it is found that significantly better agreement with previous numerical work is obtained. In addition, knowledge of the correction term allows approximate estimates to be made for the error involved in using the basic solution.

scholarly journals The energetics of flow through a rapidly oscillating tube with slowly varying amplitude

2011 ◽  
Vol 369 (1947) ◽  
pp. 2989-3006 ◽  
Author(s):  
Robert J. Whittaker ◽  
Matthias Heil ◽  
Sarah L. Waters
Keyword(s):  
Flow Structure ◽  
Energy Budget ◽  
High Frequency ◽  
Axial Flow ◽  
Multiple Scale ◽  
Amplitude Equations ◽  
Long Wavelength ◽  
First Order ◽  
Collapsible Tubes ◽  
Flow Through

Motivated by the problem of self-excited oscillations in fluid-filled collapsible tubes, we examine the flow structure and energy budget of flow through an elastic-walled tube. Specifically, we consider the case in which a background axial flow is perturbed by prescribed small-amplitude high-frequency long-wavelength oscillations of the tube wall, with a slowly growing or decaying amplitude. We use a multiple-scale analysis to show that, at leading order, we recover the constant-amplitude equations derived by Whittaker et al . (Whittaker et al. 2010 J. Fluid Mech. 648 , 83–121. ( doi:10.1017/S0022112009992904 )) with the effects of growth or decay entering only at first order. We also quantify the effects on the flow structure and energy budget. Finally, we discuss how our results are needed to understand and predict an instability that can lead to self-excited oscillations in collapsible-tube systems.

HIGH FREQUENCY LIMITS OF THE TWO-ELECTRON PHOTOIONIZATION CROSS SECTIONS

2002 ◽  
Vol 09 (02) ◽  
pp. 1161-1166 ◽  
Author(s):  
R. KRIVEC ◽  
M. YA. AMUSIA ◽  
V. B. MANDELZWEIG
Keyword(s):  
Wave Function ◽  
Excited States ◽  
Cross Sections ◽  
High Frequency ◽  
Nuclear Charge ◽  
Principal Quantum Number ◽  
Dipole Approximation ◽  
Wave Functions ◽  
Initial State ◽  
First Order

Several cross sections of two-electron processes at high but nonrelativistic photon energies ω are considered, which are expressed solely via the initial state wave function of the ionized two-electron object. The new high precision and locally correct nonvariational wave functions describing the ground and several lowest excited states of H -, He and helium-like ions are used in calculations of different cross sections in the pure dipole approximation and with account of first order corrections in ω/c2, and a number of the cross sections' ratios. The dependencies of all these quantities on the nuclear charge Z and the principal quantum number n (for 1 < n < 5) of the initial state excitation are studied.

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