Principles of spatial surface electric field filtering in magnetotellurics: Electromagnetic array profiling (EMAP)

Geophysics ◽  
1992 ◽  
Vol 57 (4) ◽  
pp. 603-622 ◽  
Author(s):  
Carlos Torres‐Verdín ◽  
Francis X. Bostick
Keyword(s):  
Electric Field ◽  
Spatial Filtering ◽  
Depth Of Penetration ◽  
Pass Filter ◽  
Lateral Electric Field ◽  
Field Response ◽  
Low Pass ◽  
Surface Electric Field ◽  
Subsurface Resistivity ◽  
Dipole Length

Electromagnetic Array Profiling (EMAP) is an adaptation of magnetotellurics to overcome spatial aliasing effects associated with the sampling of the surface electric field. Undersampling lateral electric field variations can result in misleading geoelectric interpretations of the subsurface, particularly under the common presence of static distortion. In the EMAP field procedure, electric dipoles are positioned end‐to‐end along a continuous survey path; this configuration, in addition to reducing aliasing effects, lends itself to low‐pass filtering of the lateral electric field variations. We show that lengthening an electric dipole can reduce the static effect due to confined resistivity anomalies smaller than a dipole length. This modification of the sensor characteristics involves a spatial filtering process in which the cutoff wavenumber is inversely proportional to the length of the dipole. However, excessively long dipoles may not prove appropriate at high frequencies where the objective is to sense geoelectric features smaller than a dipole length. Thus, an array of adjacent dipoles along the survey path allows us to control the characteristics of the low‐pass filter employed to reduce static effects. A standard dipole length should be comparable with the shallowest depth of penetration at the highest frequency. The survey path, on the other hand, should be long enough to allow the suppression of static effects due to geoelectric structure of size comparable to the depth of penetration at the lowest frequency. Previously, we showed that a profile of the subsurface resistivity distribution can be estimated by inverting the inductive part of the surface electric field response derived from spatial filtering. For this purpose, the suggested wavenumber filter is one for which the cutoff wavenumber decreases with decreasing values of frequency, just in the same way the subsurface resistivity distribution is naturally averaged at depth to produce its inductive surface electric field response. Hence, the EMAP field procedure for the measurement of lateral electric field variations is suitable for an inversion of this type. We introduce a data‐adaptive spatial filtering technique that responds to changes in local average resistivity at a given frequency to estimate both effective depth of response and resistivity along the survey path. Application of this filtering procedure shows encouraging results in the interpretation of data simulated numerically from two‐dimensional models possessing different degrees of structural complexity. We also present results from a field study carried out in the northern basin and range geological province of Nevada.

Implications of the Born approximation for the magnetotelluric problem in three‐dimensional environments

Geophysics ◽  
1992 ◽  
Vol 57 (4) ◽  
pp. 587-602 ◽  
Author(s):  
Carlos Torres‐Verdín ◽  
Francis X. Bostick
Keyword(s):  
Magnetic Field ◽  
Electric Field ◽  
Born Approximation ◽  
Transfer Functions ◽  
Pass Filter ◽  
Near Surface ◽  
Low Pass ◽  
Surface Electric Field ◽  
Subsurface Resistivity ◽  
Lateral Variations

A first‐order Born approximation is obtained for the integral equations governing the surface magnetotelluric response over a three‐dimensional earth. Although accurate only in cases of low resistivity contrasts, the resulting expressions: (1) exhibit a linear relationship between a spatial perturbation in subsurface resistivity and the ensuing perturbation on the surface field response, and, more importantly, (2) allow arbitrary degrees of complexity in the geometrical characteristics of the subsurface. The linear system solutions derived from the Born approximation are studied by examining the properties of their associated kernels. These kernels may be thought of as a suite of horizontal magnetotelluric “wavelets” weighting the subsurface resistivity distribution at different depth levels. Analytical expressions for the wavelets are obtained in the wavenumber domain, thus generating a suite of magnetotelluric “transfer functions.” Expressions for the latter are particularized to the cases of one‐ and two‐dimensional geolectric media yielding results consistent with the characteristics of the magnetotelluric fields known to hold in these low‐order environments. Inspection of the electric transfer functions reveals severe sensitivity to near‐surface lateral variations of resistivity, which persists even at deep sensing frequencies. This near‐surface sensitivity is the result of an additive term in the electric field transfer functions, the static component, acting as a spatial highpass filter of the lateral variations of surface resistivity. A second additive component in the electric transfer functions, the induction component, functions as a spatial lowpass filter of the lateral variations in subsurface resistivity, and is primarily responsible for the inductive part of the surface electric field response. A common problem in magnetotelluric interpretation, the electric static effect can be reduced by inverting the role of the static component, i.e., by spatially low‐pass filtering the surface electric field. The suggested low‐pass filter for such an operation is one for which the cutoff wavenumber increases with frequency and is therefore insensitive to the response from the induction component. Low‐pass filtering of the surface electric field is best implemented in the field if the electric dipoles are deployed end‐to‐end continuously along a survey path. The magnetic field transfer functions, on the other hand, exhibit a single induction term with band‐pass filter properties which may actually lead to some amount of local distortion on the measured surface magnetic field. We propose to reduce this distortion by referring all electric field measurements to the primary magnetic field within the survey area. The primary magnetic field components, in turn, can be estimated by the spatial average of the magnetic measurements acquired at an array of magnetic stations. The suggested procedures for both the acquisition and processing of natural electric and magnetic field data encompass altogether a novel adaptation of the magnetotelluric method.

Electrical conductivity and capacitance spectra of Bi1.37Sm0.13Zn0.92Nb1.50O6.92 pyrochlore ceramic in the range of 0–3 GHz

2014 ◽  
Vol 07 (02) ◽  
pp. 1450018 ◽  
Author(s):  
A. F. Qasrawi ◽  
Faten M. Bzour ◽  
Eman O. Nazzal ◽  
A. Mergen
Keyword(s):  
Electrical Conductivity ◽  
Electric Field ◽  
Dielectric Breakdown ◽  
Microwave Cavity ◽  
Frequency Range ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Microwave Cavities ◽  
Rejection Filter ◽  
Low Pass

In this work, the electrical properties of samarium-doped bismuth niobium zinc oxide ( Sm -doped BZN ) pyrochlore ceramics are investigated by means of temperature dependent electrical conductivity and capacitance spectroscopy in the frequency range of 0–3 GHz. It was observed that the novel dielectric Sm - BZN ceramic exhibits a temperature and electric field dependent dielectric breakdown. When measured at 300 K, the breakdown electric field is 1.12 kV/cm and when heated the breakdown temperature is ~ 420 K. The pyrochlore is thermally active above 440 K with conductivity activation energy of 1.37 eV. In addition, the room temperature capacitance spectra reflected a resonance–antiresonance switching property at 53 MHz when subjected to an AC signal of low power of 5 dBm. Furthermore, when the Sm - BZN ceramics are used as microwave cavity and tested in the frequency range of 1.0–3.0 GHz, the cavity behaves as low pass filter with wide tunability up to a frequency of 1.91 GHz. At this frequency it behaves as a band rejection filter that blocks waves of 1.91 GHz and 2.57 GHz frequencies. These properties of the Sm -doped BZN are promising as they indicate the usability of the ceramics in digital electronic circuits as resonant microwave cavities suitable for the production of low pass/rejection band filters.

Design and Implementation of a Kind of Ship Underwater Electric Field Signal Collection Equipment Hardware

2014 ◽  
Vol 945-949 ◽  
pp. 2102-2105 ◽  
Author(s):  
Xiao Bei Wang ◽  
Li Xia ◽  
Xiang Jun Wang ◽  
Yi Liu
Keyword(s):  
Electric Field ◽  
Low Noise ◽  
Electric Signal ◽  
Instrumentation Amplifier ◽  
Signal Acquisition ◽  
Three Dimension ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Signal Collection ◽  
Low Pass

Based on the characteristics that ship underwater electric signal is waek, a kind of ship underwater electric signal acquisition equipment of hardware structure is designed. With instrumentation amplifier of high-precision and low noise and low pass filter module, the electric field signal collected by three dimension sensor is filtered and amplified. It ensures the integrity and validity of acquisition signal.

Off-Axis Digital Holographic Reconstruction Based on the Spatial Filtering of the Hologram Illuminated with the Reference Wave

2013 ◽  
Vol 760-762 ◽  
pp. 502-506
Author(s):  
Yan Xu ◽  
Pei Zhen Qiu
Keyword(s):  
Spatial Filtering ◽  
Image Plane ◽  
Zero Order ◽  
Real Image ◽  
Pass Filter ◽  
Low Pass Filter ◽  
The Real ◽  
Low Pass ◽  
Spectrum Characteristic ◽  
Holographic Reconstruction

In order to eliminate the zero-order and conjugate image in off-axis digital holography, a new method based on the spatial filtering of the hologram illuminated with the reference (written as RIh) wave is proposed. By using RIhand the low-pass filter to do the convolution operation, the real image of the object without the zero-order and conjugate image is directly obtained. Simultaneously, the real image always appears in the center of the reconstructed image plane. The spectrum characteristic of RIhis analyzed. A comparative analysis of the spectrum characteristics of the hologram and RIhis discussed. The theoretical and experiment results show that: this method requires only one hologram, and do once Fourier transform. The process of designing filtering window is simple and convenient.

The Effect of Roughness Features on Mos Surface Electric Field and Fowler-Nordheim Tunneling Behavior

1997 ◽  
Vol 473 ◽  
Author(s):  
Heng-Chih Lin ◽  
Edwin C. Kan ◽  
Toshiaki Yamanaka ◽  
Simon J. Fang ◽  
Kwame N. Eason ◽  
...  
Keyword(s):  
Electric Field ◽  
Three Dimensional ◽  
Tunneling Current ◽  
Gate Oxide ◽  
Oxide Thickness ◽  
Interface Roughness ◽  
Normal Electric Field ◽  
Surface Electric Field ◽  
Tunneling Behavior ◽  
Nordheim Tunneling

ABSTRACTFor future CMOS GSI technology, Si/SiO2 interface micro-roughness becomes a non-negligible problem. Interface roughness causes fluctuations of the surface normal electric field, which, in turn, change the gate oxide Fowler-Nordheim tunneling behavior. In this research, we used a simple two-spheres model and a three-dimensional Laplace solver to simulate the electric field and the tunneling current in the oxide region. Our results show that both quantities are strong functions of roughness spatial wavelength, associated amplitude, and oxide thickness. We found that RMS roughness itself cannot fully characterize surface roughness and that roughness has a larger effect for thicker oxide in terms of surface electric field and tunneling behavior.

Design of Programmable Wideband Low Pass Filter with Continuous-Time/Discrete-Time Hybrid Architecture

2017 ◽  
Vol E100.C (10) ◽  
pp. 858-865 ◽  
Author(s):  
Yohei MORISHITA ◽  
Koichi MIZUNO ◽  
Junji SATO ◽  
Koji TAKINAMI ◽  
Kazuaki TAKAHASHI
Keyword(s):  
Discrete Time ◽  
Continuous Time ◽  
Hybrid Architecture ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Low Pass
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