Chapter 6. Real Time PGSE NMR Through Direct Acquisition of Averaged Propagators in the Time Domain Using Pulsed Second Order Magnetic Fields

2016 ◽  
pp. 194-225
Author(s):  
Wilfred Kittler ◽  
Sergei Obruchkov ◽  
Mark Hunter ◽  
Petrik Galvosas
Keyword(s):  
Magnetic Fields ◽  
Real Time ◽  
Time Domain ◽  
Second Order ◽  
The Time Domain ◽  
Pgse Nmr

scholarly journals A Multimodal Feature Fusion-Based Deep Learning Method for Online Fault Diagnosis of Rotating Machinery

Sensors ◽  
2018 ◽  
Vol 18 (10) ◽  
pp. 3521 ◽  
Author(s):  
Funa Zhou ◽  
Po Hu ◽  
Shuai Yang ◽  
Chenglin Wen
Keyword(s):  
Deep Learning ◽  
Fault Diagnosis ◽  
Real Time ◽  
Time Domain ◽  
Feature Fusion ◽  
Rotating Machinery ◽  
Time Domain Data ◽  
Diagnosis Method ◽  
The Time Domain ◽  
Potential Frequency

Rotating machinery usually suffers from a type of fault, where the fault feature extracted in the frequency domain is significant, while the fault feature extracted in the time domain is insignificant. For this type of fault, a deep learning-based fault diagnosis method developed in the frequency domain can reach high accuracy performance without real-time performance, whereas a deep learning-based fault diagnosis method developed in the time domain obtains real-time diagnosis with lower diagnosis accuracy. In this paper, a multimodal feature fusion-based deep learning method for accurate and real-time online diagnosis of rotating machinery is proposed. The proposed method can directly extract the potential frequency of abnormal features involved in the time domain data. Firstly, multimodal features corresponding to the original data, the slope data, and the curvature data are firstly extracted by three separate deep neural networks. Then, a multimodal feature fusion is developed to obtain a new fused feature that can characterize the potential frequency feature involved in the time domain data. Lastly, the fused new feature is used as the input of the Softmax classifier to achieve a real-time online diagnosis result from the frequency-type fault data. A simulation experiment and a case study of the bearing fault diagnosis confirm the high efficiency of the method proposed in this paper.

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.

Second-Order Fourier Synthesis of Broadband Acoustic Signals Using Normal Modes

1997 ◽  
Vol 05 (04) ◽  
pp. 355-370 ◽  
Author(s):  
E. K. Skarsoulis
Keyword(s):  
Time Domain ◽  
Normal Modes ◽  
Acoustic Signals ◽  
Second Order ◽  
Single Frequency ◽  
Closed Form Expression ◽  
Fourier Synthesis ◽  
Eigenvalues And Eigenfunctions ◽  
Intermediate Order ◽  
The Time Domain

A scheme for approximate normal-mode calculation of broadband acoustic signals in the time domain is proposed based on a second-order Taylor expansion of eigenvalues and eigenfunctions with respect to frequency. For the case of a Gaussian impulse source a closed-form expression is derived for the pressure in the time domain. Using perturbation theory, analytical expressions are obtained for the involved first and second frequency-derivatives of eigenvalues and eigenfunctions. The proposed approximation significantly accelerates arrival-pattern calculations, since the eigenvalues, the eigenfunctions and their frequency-derivatives need to be calculated at a single frequency, the central frequency of the source. Furthermore, it offers a satisfactory degree of accuracy for the lower and intermediate order modes. This is due to the fact that essential wave-theoretic mechanisms such as dispersion and frequency dependence of mode amplitudes are contained in the representation up to a sufficient order. Numerical results demonstrate the efficiency of the method.

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%.

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.

Discuss about Fast Response Performance of under-Damped Second-Order System in Time Domain

2013 ◽  
Vol 655-657 ◽  
pp. 2202-2206
Author(s):  
Yuan Sheng Wang ◽  
Gui Ying Lu ◽  
Juan Yu ◽  
Bo Li
Keyword(s):  
Time Domain ◽  
Input Signal ◽  
Damping Ratio ◽  
Fast Response ◽  
Second Order ◽  
Order System ◽  
Peak Time ◽  
Response Performance ◽  
The Time Domain ◽  
The Relationship

Influence of the damping ratio on the response fast performance to under-damped second-order system in the time domain has been discussed. The relationship between peak time and the input signal, the adjust time, and the system type has been analyzed. The response’s fast performance indicators are relative, and it is related to the input signal, the response of the system, and the type of system and its initial states. In conclusion, the peak time and the adjust time cannot reach a minimum at the same time. The fast response issue must be discussed in relation to specific cases, and it cannot be generalized.

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