scholarly journals On negative induced polarization in frequency domain measurements

2020 ◽  
Author(s):  
Chen Wang ◽  
Andrew Binley ◽  
Lee D Slater
Keyword(s):  
Frequency Domain ◽  
Heterogeneous Media ◽  
Electric Circuit ◽  
Induced Polarization ◽  
Single Frequency ◽  
Phase Measurements ◽  
Resistivity Measurements ◽  
Phase Data ◽  
Phase Spectra ◽  
Electric Circuit Model

Summary Induced polarization (IP) has been widely used to non-invasively characterize electrical conduction and polarization in the subsurface resulting from an applied electric field. Earth materials exhibit a lossy capacitance defined by an intrinsic negative phase in frequency-domain IP (FDIP) or positive intrinsic chargeability in time-domain IP (TDIP). However, error-free positive apparent phase or negative apparent chargeability (i.e. negative IP effects) can occur in IP measurements over heterogeneous media. While negative IP effects in TDIP datasets have been discussed, no studies have addressed this topic in detail for FDIP measurements. We describe theory and numerical modeling to explain the origin of negative IP effects in FDIP measurements. A positive apparent phase may occur when a relatively high polarizability feature falls into negative sensitivity zones of complex resistivity measurements. The polarity of the apparent phase is determined by the distribution of subsurface intrinsic phase and resistivity, with the resistivity impacting the apparent phase polarity via its control on the sensitivity distribution. A physical explanation for the occurrence of positive apparent phase data is provided by an electric circuit model representing a four-electrode measurement. We also show that the apparent phase polarity will be frequency dependent when resistivity changes significantly with frequency (i.e. in the presence of significant IP effects). Consequently, negative IP effects manifest themselves in the shape of apparent phase spectra recorded with multi-frequency (spectral IP) datasets. Our results imply that positive apparent phase measurements should be anticipated and should be retained during inversion and interpretation of single frequency and spectral IP datasets.

CONTINUOUS SOUNDING‐PROFILING WITH A DIPOLE‐DIPOLE RESISTIVITY ARRAY

Geophysics ◽  
1968 ◽  
Vol 33 (5) ◽  
pp. 838-842 ◽  
Author(s):  
René Bodmer ◽  
Stanley H. Ward
Keyword(s):  
Frequency Domain ◽  
Induced Polarization ◽  
Inductive Coupling ◽  
Percentage Change ◽  
Single Frequency ◽  
Primary Reason ◽  
Electrode Arrays ◽  
Resistivity Sounding ◽  
The Earth ◽  
Percent Accuracy

Among the different four‐electrode arrays used in resistivity sounding and profiling, the dipole‐dipole array can provide, in some instances, advantages over the more conventional Schlumberger and Wenner configurations. Interpretation of data from Wenner and Schlumberger methods has been described by Compagnie Générale de Géophysique (1955), Mooney and Wetzel (1956), Zohdy (1964), and many others. The primary reason for using a dipole‐dipole array has been to minimize inductive coupling between the transmitting and receiving dipoles when performing frequency‐domain, induced‐polarization surveys (e.g., Marshall and Madden, 1959). This inductive coupling, as effected by the presence of the earth, produces spurious frequency‐dependent voltages in the measuring circuit. Such spurious voltages are small and only of importance when one wishes to calculate the percentage change in resistivity between two frequencies; they are usually much less than the 5 to 10 percent accuracy sought in most resistivity surveys. For this reason, and because the dipole‐dipole array leads to small measured potentials, it is seldom used in single‐frequency resistivity sounding or profiling. However, we shall demonstrate in this paper the manner in which the dipole‐dipole array may be used effectively for simultaneous sounding and profiling.

scholarly journals Improving DGNSS Performance through the Use of Network RTK Corrections

2021 ◽  
Vol 13 (9) ◽  
pp. 1621
Author(s):  
Duojie Weng ◽  
Shengyue Ji ◽  
Yangwei Lu ◽  
Wu Chen ◽  
Zhihua Li
Keyword(s):  
Carrier Phase ◽  
Local Area ◽  
Satellite System ◽  
High Accuracy ◽  
Single Frequency ◽  
Baseline Length ◽  
Low Latitude ◽  
Phase Measurements ◽  
Network Rtk ◽  
Global Navigation Satellite

The differential global navigation satellite system (DGNSS) is an enhancement system that is widely used to improve the accuracy of single-frequency receivers. However, distance-dependent errors are not considered in conventional DGNSS, and DGNSS accuracy decreases when baseline length increases. In network real-time kinematic (RTK) positioning, distance-dependent errors are accurately modelled to enable ambiguity resolution on the user side, and standard Radio Technical Commission for Maritime Services (RTCM) formats have also been developed to describe the spatial characteristics of distance-dependent errors. However, the network RTK service was mainly developed for carrier-phase measurements on professional user receivers. The purpose of this study was to modify the local-area DGNSS through the use of network RTK corrections. Distance-dependent errors can be reduced, and accuracy for a longer baseline length can be improved. The results in the low-latitude areas showed that the accuracy of the modified DGNSS could be improved by more than 50% for a 17.9 km baseline during solar active years. The method in this paper extends the use of available network RTK corrections with high accuracy to normal local-area DGNSS applications.

On: “Recent Advances and Applications in Complex Resistivity Measurements,” by K. L. Zonge and J. C. Wynn (GEOPHYSICS, Oct. 1975, p. 851–864)

Geophysics ◽  
1977 ◽  
Vol 42 (1) ◽  
pp. 120-121 ◽  
Author(s):  
P. H. Nelson ◽  
G. D. Van Voorhis
Keyword(s):  
Spectral Data ◽  
Induced Polarization ◽  
Complex Resistivity ◽  
Resistivity Measurements ◽  
Recent Advances ◽  
Measuring Techniques

In presenting a variety of induced polarization spectral data, Zonge and Wynn refer to a paper published earlier by us (Van Voorhis et al., 1973) which deals with the same topic. We feel Zonge and Wynn have misrepresented our measuring techniques, data, and conclusions in their references to our paper. Our principal objections center on three statements by the authors.

scholarly journals Photon Phase Shift Imaging Research on Frequency Domain Diffuse Optic Tomography

2021 ◽  
Author(s):  
huseyin ozgur kazanci
Keyword(s):  
Phase Shift ◽  
Frequency Domain ◽  
Laser Intensity ◽  
Model Problem ◽  
Modulation Frequency ◽  
Forward Model ◽  
Problem Solution ◽  
Inverse Problem Solution ◽  
Phase Data ◽  
Cartesian Coordinate

Abstract Diffuse optic imaging is an important biomedical optic research tool. Diffuse optic tomography (DOT) modality needs progressive philosophical approaches for scientific contribution. Technological developments and philosophical approaches should both go forward. Phase-shift based frequency domain (FD) diffuse optical tomography (FDDOT) method was well established in the literature. The instruments were tested for brain neurofunctional imaging. A mixture of AC laser intensity and phase data were used at these works. According to those works; deep volume resolution was improved by only using phase data. Because phase data is only related to the photon mean free path in imaging tissue media. Besides this advantage, laser intensity data is also affected by noisy background light and electrical artifacts. Another most important advantage of only using phase data can be explained as time-resolved temporal change can be directly related to phase shift of modulated frequency source. At this work, the frequency domain (FD) DOT imaging method which uses phase shift data were used for simulation phantom. Laser source-driven forward model problem weight matrix simulation data was given to the simple pseudo-inverse-based inverse problem solution algorithm for one inclusion example. The inclusion image was reconstructed and demonstrated successfully. Forward model problem weight functions inside the tissue simulation media were calculated and used based on the phase shifts at the same core modulation frequency. 100 MHz modulation frequency was selected due to its FDDOT standard. 13 sources and 13 detectors were placed on the back-reflected imaging surface. 40 x, y, z cartesian coordinate grid elements were used in the image reconstruction algorithm. Photon absorption coefficient: ma = 0.1 cm-1, and scattering coefficient: ms = 100 cm-1 values were set for background simulation phantom. One inclusion object was embedded inside the imaging tissue simulation phantom background. x, y, z cartesian coordinate grid sizes were selected for 100 mm for each direction. Photon phase shift fluencies were added to the forward model problem. The forward model problem was built according to the frequency domain photon migration diffusion approximation. Forward model problem photon fluencies were calculated according to the diffusion equation approximation. The simple pseudoinverse mathematical inverse problem solution algorithm was applied to test the results. The embedded inclusion object was reconstructed successfully with the high-resolution image quality. In general, DOT techniques suffer for the low image quality, but in this work, the high-quality image was reconstructed and demonstrated. The philosophical approach has future promising DOT imaging capability. The phase shift version of the FDDOT modality has an important advantage for future purpose.

scholarly journals Multifunctional Ultrahigh Sensitive Microwave Planar Sensor to Monitor Mechanical Motion: Rotation, Displacement, and Stretch

Sensors ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 1184 ◽  
Author(s):  
Mohammad Abdolrazzaghi ◽  
Mojgan Daneshmand
Keyword(s):  
Dynamic Range ◽  
Full Range ◽  
Electric Circuit ◽  
High Sensitivity ◽  
Parameter Extraction ◽  
Split Ring Resonator ◽  
Displacement Sensor ◽  
Rotation Sensor ◽  
Mechanical Deformations ◽  
Electric Circuit Model

This paper presents a novel planar multifunctional sensor that is used to monitor physical variations in the environment regarding distance, angle, and stretch. A double split-ring resonator is designed at 5.2 GHz as the core operating sensor. Another identical resonator is placed on top of the first one. The stacked configuration is theoretically analyzed using an electric circuit model with a detailed parameter extraction discussion. This design is first employed as a displacement sensor, and a compelling high sensitivity of 500 MHz/mm is observed for a wide dynamic range of 0-5 mm. Then, in another configuration, the stacked design is used as a rotation sensor that results in a high sensitivity of 4.5 MHz/ ° for the full range of 0-180 ° . In addition, the stacked resonator is utilized as a strain detector, and a 0–30% stretch is emulated with a linear sensitivity of 12 MHz/%. Measurements are well in congruence with simulated results, which proves the accurate functionality of the sensor in tracking mechanical deformations, all in a single compact contraption.

Frequency Domain Based Virtual Detector for Heterogeneous Media in Photoacoustic Imaging

2020 ◽  
Vol 6 ◽  
pp. 569-578
Author(s):  
Haoran Jin ◽  
Shuangli Liu ◽  
Ruochong Zhang ◽  
Siyu Liu ◽  
Yuanjin Zheng
Keyword(s):  
Frequency Domain ◽  
Heterogeneous Media ◽  
Photoacoustic Imaging
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