Response characteristics of coincident loop transient electromagnetic systems

Geophysics ◽  
1982 ◽  
Vol 47 (9) ◽  
pp. 1325-1330 ◽  
Author(s):  
P. Weidelt
Keyword(s):  
Step Function ◽  
Voltage Response ◽  
Complex Frequency ◽  
Induced Voltage ◽  
Response Characteristics ◽  
Transient Electromagnetic ◽  
Driving Current ◽  
Occasional Occurrence ◽  
Frequency Independent ◽  
Independent Distribution

The occasional occurrence of persistent sign reversals in coincident loop transient electromagnetic (TEM) measurements stimulates an investigation of possible causes for this effect. By examining the response in the complex frequency plane near the spectrum of freely decaying current modes, it is shown that for any physically reasonable frequency‐independent distribution of electrical conductivity and magnetic permeability the voltage response to a step function driving current is of one sign only. Moreover, under the conditions mentioned above, the logarithm of the induced voltage is a decreasing convex function of time. These characteristics are retained for more general time functions of the driving current. The conservation of sign for frequency‐independent material parameters supports the assumption of IP effects as a possible mechanism for sign reversals. The latter point is illustrated by a simplified example.

The use and misuse of apparent resistivity in electromagnetic methods

Geophysics ◽  
1986 ◽  
Vol 51 (7) ◽  
pp. 1462-1471 ◽  
Author(s):  
Brian R. Spies ◽  
Dwight E. Eggers
Keyword(s):  
Apparent Resistivity ◽  
Early Time ◽  
Asymptotic Formulas ◽  
Voltage Response ◽  
Late Time ◽  
Induced Voltage ◽  
Resistivity Curve ◽  
Transient Electromagnetic ◽  
Electromagnetic Methods ◽  
Tem Method

Problems and misunderstandings arise with the concept of apparent resistivity when the analogy between an apparent resistivity computed from geophysical observations and the true resistivity structure of the subsurface is drawn too tightly. Several definitions of apparent resistivity are available for use in electromagnetic methods; however, those most commonly used do not always exhibit the best behavior. Many of the features of the apparent resistivity curve which have been interpreted as physically significant with one definition disappear when alternative definitions are used. It is misleading to compare the detection or resolution capabilities of different field systems or configurations solely on the basis of the apparent resistivity curve. For the in‐loop transient electromagnetic (TEM) method, apparent resistivity computed from the magnetic field response displays much better behavior than that computed from the induced voltage response. A comparison of “exact” and “asymptotic” formulas for the TEM method reveals that automated schemes for distinguishing early‐time and late‐time branches are at best tenuous, and those schemes are doomed to failure for a certain class of resistivity structures (e.g., the loop size is large compared to the layer thickness). For the magnetotelluric (MT) method, apparent resistivity curves defined from the real part of the impedance exhibit much better behavior than curves based on the conventional definition that uses the magnitude of the impedance. Results of using this new definition have characteristics similar to apparent resistivity obtained from time‐domain processing.

scholarly journals Simulation Research and Application on Response Characteristics of Detecting Water-filled Goaf by Transient Electromagnetic Method

2021 ◽  
Author(s):  
Tingye Qi ◽  
Xiaoming Pei ◽  
Guorui Feng ◽  
Huiru Wei
Keyword(s):  
Numerical Simulation ◽  
Coal Mine ◽  
Water Inrush ◽  
Electromagnetic Method ◽  
Transient Electromagnetic Method ◽  
Induced Voltage ◽  
Measuring Point ◽  
Response Characteristics ◽  
Transient Electromagnetic ◽  
Water Accumulation

Abstract Water inrush disasters poses a great threat to the safe exploitation of coal resources. To solve this problem, the transient electromagnetic method(TEM) was proposed to accurately detect the water accumulation in the goaf. The electromagnetic response characteristics of different water-filled goaves were studied by electromagnetic field theory, numerical simulation and field verification. Through the models of 100% water accumulation, 50% water accumulation, 0% water accumulation, 100% water accumulation with collapsed rock, 50% water accumulation with collapsed rock and 0% water accumulation with collapsed rock goaf, the characteristics of induced voltage attenuation curves were studied. Meanwhile, the relationship between the attenuation voltage value and area of the transmitting coil and the depth of the goaf were also simulated. The results illustrate that the attenuation curve of induced voltage presented a regular exponential decay form in the 0% water accumulation model but existed abnormal exaltation for voltage in water-filled model. Through the linear fitting curve, it can be seen that the abnormal intensity of the induced voltage becomes stronger as the distance between the measuring point and the center of the target decrement. Moreover, the abnormal amplitude of the induced voltage increases with the rise of the water accumulation and collapsed rock will weakly reduce the low-resistance anomalous effect on the water-accumulated goaf. In addition, the response value of the attenuation voltage increased in second-order as the area of the transmitting coil increases, but decreased in third-order as the depth of the target body increases. The field detection results of the Majiliang coal mine also confirmed the theoretical analysis and the numerical simulation. The conclusions had important guiding significance for accurate detection of coal mine goaf.

Positivity of the coincident loop transient electromagnetic response

Geophysics ◽  
1984 ◽  
Vol 49 (2) ◽  
pp. 194-194 ◽  
Author(s):  
D. Guptasarma
Keyword(s):  
Magnetic Permeability ◽  
Decay Curve ◽  
Electromagnetic Response ◽  
Field Observations ◽  
Induced Voltage ◽  
Linear Medium ◽  
System A ◽  
Transient Electromagnetic ◽  
Maximum Value ◽  
Frequency Independent

Field observations with a coincident loop transient EM frequently show that the measured decaying voltage changes its sign during the decay, reaches a maximum value with this changed sign, and then decays to zero. This change of sign has been ascribed to special distributions of magnetic permeability or conductivity (Spies, 1980), as well as to the presence of electrochemical polarizability (Lee, 1975, 1981). Gubatyenko and Tikshayev (1979) showed, however, that for any frequency‐independent linear medium the induced voltage caused by a step current excitation is always of one sign. Weidelt (1982) extended the results of Gubatyenko and Tikshayev (1979), and established further constraints on the slope and curvature of the decay curve. It is thus quite clear that with a coincident loop system a change of the polarity of the decaying voltage cannot be caused by any distribution of conductivity or permeability in the ground.

Using an induction coil sensor to indirectly measure the B-field response in the bandwidth of the transient electromagnetic method

Geophysics ◽  
2000 ◽  
Vol 65 (5) ◽  
pp. 1489-1494 ◽  
Author(s):  
Richard S. Smith ◽  
A. Peter Annan
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Indirect Measurement ◽  
Rate Of Change ◽  
Induction Coil ◽  
Voltage Response ◽  
Magnetic Field Data ◽  
Transient Electromagnetic ◽  
Different Characteristics ◽  
The Magnetic Field

The traditional sensor used in transient electromagnetic (EM) systems is an induction coil. This sensor measures a voltage response proportional to the time rate of change of the magnetic field in the EM bandwidth. By simply integrating the digitized output voltage from the induction coil, it is possible to obtain an indirect measurement of the magnetic field in the same bandwidth. The simple integration methodology is validated by showing that there is good agreement between synthetic voltage data integrated to a magnetic field and synthetic magnetic‐field data calculated directly. Further experimental work compares induction‐coil magnetic‐field data collected along a profile with data measured using a SQUID magnetometer. These two electromagnetic profiles look similar, and a comparison of the decay curves at a critical point on the profile shows that the two types of measurements agree within the bounds of experimental error. Comparison of measured voltage and magnetic‐field data show that the two sets of profiles have quite different characteristics. The magnetic‐field data is better for identifying, discriminating, and interpreting good conductors, while suppressing the less conductive targets. An induction coil is therefore a suitable sensor for the indirect collection of EM magnetic‐field data.

Pioneering Application of Corona Charge-Kelvin Probe Metrology to Noncontact Characterization of In0.53 Ga0.47 As/Al2O3/HfO2 Stack

2014 ◽  
Vol 1691 ◽  
Author(s):  
Alexandre Savtchouk ◽  
John D’Amico ◽  
Marshall Wilson ◽  
Jacek Lagowski ◽  
Wei-E Wang ◽  
...  
Keyword(s):  
High Mobility ◽  
Dielectric Surface ◽  
Differential Capacitance ◽  
Voltage Response ◽  
Induced Voltage ◽  
Kelvin Probe ◽  
Dielectric Characterization ◽  
High K ◽  
Corona Charge

ABSTRACTWe report the first successful application of corona charging noncontact C-V and I-V metrology to interface and dielectric characterization of high-k/III-V structures. The metrology, which has been commonly used in Si IC manufacturing, uses incremental corona charge dosing, ΔQC, on the dielectric surface, and the measurement of surface voltage response, ΔVS, using a Kelvin-probe. Its application to In0.53Ga0.47As with a high-k stack required modifications related to the effects of dielectric trap induced voltage transients. The developed Corona Charge-Kelvin Probe Metrology adopted strictly differential measurements using ΔQC and ΔV, and corresponding differential capacitance rather than measurements based on total global charge, Q, and voltage, V, values.Electrical characterization data including interface trap density, electrical oxide thickness, and dielectric leakage are presented for a sample containing an In0.53 Ga0.47 As channel overlaid with a bilayer (2nm Al2O3/5nm HfO2) dielectric stack that is considered to be very promising for application in performance NFETs with high-mobility channels.

scholarly journals Structural and Mechanical Characteristics of a Capsule-Type Soft Pneumatic Actuator with Large Thrust Force and High-Contraction Ratio

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Qing Zhu ◽  
Qingyun Liu ◽  
Mingxing Yang ◽  
Xingsong Wang
Keyword(s):  
Thrust Force ◽  
Tracking Error ◽  
Step Function ◽  
Pneumatic Actuator ◽  
Response Characteristics ◽  
Capsule Type ◽  
Effective Contact ◽  
Contraction Ratio ◽  
Drive Systems ◽  
Fiber Materials

A capsule-type soft pneumatic actuator (CTSPA) was molded with hyperelastic material (latex) and subjected to deformations. In order to provide a large thrust force and limit the direction of expansion and contraction, the actuator was covered by fiber materials and driven by compressed air. Soft pneumatic actuator, belonging to flexible drive, showed nonlinear characteristics. In this study, with theoretical and experimental methods, a static mathematical model of CTSPA was established to analyze the relationship between the inflation pressure, driving force, and deformations. Furthermore, we experimentally explored the response characteristics of CTSPA by using a unit step function. The hysteresis was significantly affected by air pressure, loading size, and effective contact area of the actuator. Finally, the actuator realized a compatible position tracking performance of 1 Hz and a low average tracking error of 0.3°. The study provides a basis for studying the control methods and state maintenance of flexible drive systems.

scholarly journals Numerical Simulation of Transient Electromagnetic Response of Unfavorable Geological Body in Tunnel

2011 ◽  
Vol 90-93 ◽  
pp. 37-40 ◽  
Author(s):  
Lu Bo Meng ◽  
Tian Bin Li ◽  
Zheng Duan
Keyword(s):  
Numerical Simulation ◽  
Finite Element ◽  
Electromagnetic Field ◽  
Electromagnetic Response ◽  
Detection Distance ◽  
Geological Body ◽  
Response Characteristics ◽  
Finite Element Software ◽  
Transient Electromagnetic ◽  
Field Decay

To investigate the transient electromagnetic method of response characteristics in the tunnel geological prediction, the finite element numerical simulation of unfavorable geological body of different location, different resistivity sizes, different shapes, and different volume size were carried out by ANSYS finite element software. The results show that secondary electromagnetic field of different location of unfavorable geological body have same decay rate, when detection distance from 30m to 70m, transient electromagnetic responses are strongest, followed distance from 10m to 30m and from 70m to 90m. The shape, volume and resistivity of unfavorable geological body have strong influence on transient electromagnetic response, unfavorable geological body more sleek, the greater the volume and the smaller the resistivity of unfavorable geological body, the secondary electromagnetic field decay slower.

scholarly journals A MEMS Ultra-Wideband (UWB) Power Sensor with a Fe-Co-B Core Planar Inductor and a Vibrating Diaphragm Capacitor

Sensors ◽  
2021 ◽  
Vol 21 (11) ◽  
pp. 3858
Author(s):  
Sujitha Vejella ◽  
Sazzadur Chowdhury
Keyword(s):  
Microelectromechanical Systems ◽  
Ultra Wideband ◽  
Induced Voltage ◽  
Adhesively Bonded ◽  
Capacitance Change ◽  
Frequency Independent ◽  
Power Sensor ◽  
Footprint Area ◽  
Microfabrication Techniques ◽  
2D Array

The design of a microelectromechanical systems (MEMS) ultra-wideband (UWB) RMS power sensor is presented. The sensor incorporates a microfabricated Fe-Co-B core planar inductor and a microfabricated vibrating diaphragm variable capacitor on adhesively bonded glass wafers in a footprint area of 970 × 970 µm2 to operate in the 3.1–10.6 GHz UWB frequency range. When exposed to a far-field UWB electromagnetic radiation, the planar inductor acts as a loop antenna to generate a frequency-independent voltage across the MEMS capacitor. The voltage generates a coulombic attraction force between the diaphragm and backplate that deforms the diaphragm to change the capacitance. The frequency-independent capacitance change is sensed using a transimpedance amplifier to generate an output voltage. The sensor exhibits a linear capacitance change induced voltage relation and a calculated sensitivity of 4.5 aF/0.8 µA/m. The sensor can be used as a standalone UWB power sensor or as a 2D array for microwave-based biomedical diagnostic imaging applications or for non-contact material characterization. The device can easily be tailored for power sensing in other application areas such as, 5G, WiFi, and Internet-of-Things (IoT). The foreseen fabrication technique can rely on standard readily available microfabrication techniques.

Discussions and Communications: Propagation of Transient Electromagnetic Waves in a Conducting Medium

Geophysics ◽  
1955 ◽  
Vol 20 (4) ◽  
pp. 959-961 ◽  
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Electromagnetic Waves ◽  
Step Function ◽  
Conducting Medium ◽  
Initial Value ◽  
Transient Electromagnetic ◽  
Ramp Function

Wait (1951) has calculated the transient electric fields for several types of step-function current sources placed inside a conducting medium. Now any generated pulse will require a finite build-up time to reach its final magnitude from its initial value of zero. In most cases, this type of pulse may be very well approximated by a ramp-function pulse (Figure 1). Expressions for the electric field of this type of pulse will be deduced in the following analysis.

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