scholarly journals Approximating spheroid inductive responses using spheres

Geophysics ◽  
2006 ◽  
Vol 71 (2) ◽  
pp. G21-G25 ◽  
Author(s):  
J. Torquil Smith ◽  
H. Frank Morrison
Keyword(s):  
Magnetic Fields ◽  
Time Domain ◽  
High Frequency ◽  
Transverse Direction ◽  
High Permeability ◽  
Frequency Limit ◽  
Aspect Ratios ◽  
Oblate Spheroids ◽  
Prolate Spheroids ◽  
The Time Domain

Spheroid responses are important as limiting cases when modeling inductive responses of isolated metallic objects such as unexploded military ordnance. The response of high-permeability ([Formula: see text] ≥ 50) conductive spheroids of moderate aspect ratios (0.25–4) to excitation by uniform magnetic fields in the axial or transverse direction is approximated by the response of spheres of appropriate diameters, of the same conductivity and permeability, with magnitude rescaled based on the differing volumes, dc magnetizations, and high-frequency limit responses of the spheres and modelled spheroids. In the frequency domain, the scaled sphere responses agree within 5% of complex magnitudes for prolate spheroids and within 7% for oblate spheroids. The approximation is more accurate for source magnetic fields in the spheroid's shorter direction than in the spheroid's longer direction. In the time domain, the approximation describes spheroid responses over five decades of time after transmitter shutoff, with a maximum discrepancy of 20%.

Measurement of Strain Induced by Impact with Fiber Bragg Grating

2008 ◽  
Vol 381-382 ◽  
pp. 435-438
Author(s):  
Ping Yu Zhu ◽  
D. Liu ◽  
Y. Lin
Keyword(s):  
Composite Material ◽  
Fiber Bragg Grating ◽  
Time Domain ◽  
High Frequency ◽  
Impact Test ◽  
Bragg Grating ◽  
Experiment Data ◽  
Frequency Limit ◽  
Fiber Bragg Grating Sensors ◽  
Frequency Components

After deriving the propagation formula of stress wave through incident bar, the measured signals both in horizontal impact test and drop impact tests are investigated with novel fiber Bragg grating sensors(FBGs). Especially those strain signals from FBGs which mounted on the surface of an incident bar are studied. The signals in impactor and the FBGs embedded in the composite material under similar test condition are compared. The dropping and impacting models have been setup. The experiment data measured in a lab are analyzed both in time-domain and in frequency domain. Those ultra-high frequency components in the above strain signals can not be obtained by current FBG measurement system due to frequency limit of the demodulation system. Further study to improve the frequency of demodulation system will be done in next step.

Radiation in Materials

2019 ◽  
pp. 303-365
Author(s):  
Richard Freeman ◽  
James King ◽  
Gregory Lafyatis
Keyword(s):  
Magnetic Fields ◽  
Time Domain ◽  
Measurement Techniques ◽  
Group Versus ◽  
Index Of Refraction ◽  
The Real ◽  
Versus Phase ◽  
Fundamental Relationship ◽  
Electric And Magnetic Fields ◽  
The Time Domain

The interaction of electromagnetic radiation and matter is examined, specifically electric and magnetic fields in materials with real and imaginary responses: under certain conditions the fields move through the material as a wave and under others they diffuse. The movement of a pulse of radiation in dispersive materials is described in which there are two wave velocities: group versus phase. The reflection of light from a sharp interface is analyzed and the Fresnel reflection/transmission equations derived. The response of materials to applied electric and magnetic fields in the time domain are correlated to their frequency response of the material’s polarization. The generalized Kramers–Kronig equations are derived and their applicability as a fundamental relationship between the real and imaginary parts of any material’s polarizability is discussed in detail. Finally, practical measurement techniques for extracting the real and imaginary components of a material’s index of refraction are introduced.

Time domain waveform inversion—A frequency domain view: How well we need to match waveforms?

1991 ◽  
Vol 81 (6) ◽  
pp. 2351-2370
Author(s):  
Zoltan A. Der ◽  
Robert H. Shumway ◽  
Michael R. Hirano
Keyword(s):  
Time Domain ◽  
High Frequency ◽  
Waveform Inversion ◽  
Quantitative Measure ◽  
Domain Modeling ◽  
Low Frequencies ◽  
Waveform Modeling ◽  
Time Domain Modeling ◽  
Frequency Components ◽  
The Time Domain

Abstract Waveform modeling in the time domain matches the various frequency components of seismic signals unevenly; the agreement is better at low frequencies and becomes progressively worse towards higher frequencies. The net effect of this kind of time-domain modeling is that the resolution in the spatial details of the source is less than optimal since the high-frequency components of the signal with their short wavelengths to resolve finer details do not fit the data. These problems are demonstrated by numerical simulations and by the reanalysis of some aspects of the El Golfo earthquake in using a new seismic imaging technique based on a generalization of an f-k algorithm. This procedure computes a statistic that can be used to derive confidence limits of the parameters sought in the inversion, thus providing a quantitative measure of the uncertainties in the results.

Development of High Frequency Virtual Thermocouples

2017 ◽  
Author(s):  
James Braun ◽  
Shengqi Lu ◽  
Guillermo Paniagua
Keyword(s):  
Frequency Response ◽  
Time Domain ◽  
High Frequency ◽  
Conjugate Heat Transfer ◽  
Numerical Procedure ◽  
Navier Stokes ◽  
Digital Compensation ◽  
Fine Wire ◽  
The Time Domain ◽  
Thermocouple Probe

This paper presents a numerical procedure to enhance the frequency response of temperature probes equipped with two thermocouple junctions of different diameter. The output of the two thermocouples exposed to the same flow transient can be used to predict the output of a virtual smaller thermocouple, which cannot be physically realized. The approach is demonstrated numerically, with the aid of conjugate heat transfer simulations performed with 3D Unsteady Reynolds Averaged Navier-Stokes. The dual junction thermocouple with wire diameters of 50 μm, 25 μm were exposed to several inlet temperatures and pressures to analyze the overall recovery factor. Then multiple unsteady tests were performed. The analysis of those transient tests was used to determine the transfer function in the time domain between the two wires and to perform a digital compensation to predict the performance of a much thinner wire thermocouple. This method was assessed by recovering the theoretical response of the 12.5 μm thermocouple with our dual-junction thermocouple probe for several pressures and wall temperatures. Finally, the procedure was applied to a virtual fine wire thermocouple of 6 μm and a frequency response around 700 Hz.

Noncausality of the discrete‐time magnetotelluric impulse response

Geophysics ◽  
1992 ◽  
Vol 57 (10) ◽  
pp. 1354-1358 ◽  
Author(s):  
Gary D. Egbert
Keyword(s):  
Magnetic Fields ◽  
Frequency Domain ◽  
Impulse Response ◽  
Discrete Time ◽  
Time Domain ◽  
Linear Relation ◽  
External Source ◽  
The Time Domain ◽  
Treat All ◽  
Time Invariant

Under the assumption that the external source magnetic fields are uniform, the electric (E) and magnetic (H) fields observed at the surface of the conducting earth satisfy a time‐invariant linear relation, which may be expressed as multiplication in the frequency domain, [Formula: see text], Eq. (1), or as convolution in the time domain, [Formula: see text], Eq. (2). Here the tilde denotes quantities in the frequency domain; e.g., [Formula: see text] is the frequency‐domain magnetotelluric (MT) impedance, and Z the corresponding time‐domain impulse response. For simplicity in the following discussion, I treat all quantities as scalars, although the operations in equations (1) and (2) generally involve vectors and tensors.

scholarly journals Study of railway curve squeal in the time domain using a high-frequency vehicle/track interaction model

2018 ◽  
Vol 431 ◽  
pp. 177-191 ◽  
Author(s):  
J. Giner-Navarro ◽  
J. Martínez-Casas ◽  
F.D. Denia ◽  
L. Baeza
Keyword(s):  
Time Domain ◽  
High Frequency ◽  
Interaction Model ◽  
The Time Domain ◽  
Curve Squeal
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