Differential target antenna coupling (DTAC) data corrections

• US 10,520,630 B2
• Filed: 07/09/2019
• Issued: 12/31/2019
• Est. Priority Date: 10/11/2016
• Status: Active Grant

• Current Assignee: Arizona Board of Regents (University of Arizona)
• Original Assignee: Arizona Board of Regents (University of Arizona)
• Inventors: Sternberg, Ben K.
• Primary Examiner(s): Assouad, Patrick
• Assistant Examiner(s): Pretlow, Demetrius R
• Application Number:
  US16/506,771
• Publication Number:
  US 20190331823A1
• Time in Patent Office: 175 Days
• Field of Search: 324377
• CPC Class Codes: G01R 23/02 Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
• CPC Class Codes: G01R 29/0892 Details related to signal analysis or treatment; presenting results, e.g. displays; measuring specific signal features other than field strength, e.g. polarisation, field modes, phase, envelope, maximum value
• CPC Class Codes: G01V 3/104 using several coupled or uncoupled coils G01V3/101 takes precedence
• CPC Class Codes: G01V 3/12 operating with electromagnetic waves operating with millimetre waves G01V8/005
• CPC Class Codes: G01V 3/38 Processing data, e.g. for analysis, for interpretation, for correction

Abstract

The present invention features a unique system of interdependent methods to greatly improve data acquired via the Differential Target Antenna Coupling (“DTAC”) method, which transmits electromagnetic (“EM”) fields and measures the primary EM field and the secondary EM fields generated in subsurface targets. These new data correction techniques provide improvements, in orders of magnitude, to the measured DTAC response accuracy. This improvement allows for greater depth of investigation, improved target location, and enhanced target characteristics.

Claims

1. A method for reducing a primary electromagnetic (“

EM”

) field presence at a receiver antenna of a subsurface imaging and detection system to effectively enhance a dynamic range of a series of measurements of a target in a subsurface environment, the method comprising;

(a) providing a tilt table (100) comprising;

(i) an x-axis linear adjustment (104) operatively connected to an x-axis receiver-coil (102) at a first point of attachment (106), wherein the first point of attachment (106) is an end of the x-axis receiver-coil (102), wherein the x-axis linear adjustment (104) operates to pivot the x-axis receiver-coil (102) about a center point (110) on the x-axis linear adjustment (104); and

(ii) a y-axis linear adjustment (114) operatively connected to a y-axis receiver-coil (112) at a second point of attachment (116), wherein the second point of attachment (116) is an end of the y-axis receiver-coil (112), wherein the y-axis linear adjustment (114) operates to pivot the y-axis receiver-coil (112) about a center point (110) on the y-axis linear adjustment (114),

wherein the receiver antenna comprises the x-axis receiver-coil (102) and the y-axis receiver-coil (112), wherein the center point (110) of the x-axis motorized linear (104) adjustment and the center point (110) of the y-axis linear adjustment (114) is a common point (110), wherein the x-axis linear adjustment (104) is positioned orthogonal to the y-axis linear adjustment (114),

wherein the tilt table (100) operates to tilt the x-axis receiver-coil (102) up and down via the x-axis linear adjustment (104) and the tilt table (100) operates to tilt the y-axis receiver-coil (112) up and down via the y-axis linear adjustment (114);

(b) calculating a null angle relative to a current orientation of the x-axis receiver-coil (102) and the y-axis receiver-coil (112); and

(c) adjusting the current orientation of the x-axis receiver-coil (102) and the y-axis receiver-coil (112) to reflect the null angle,

wherein a primary EM field is transmitted by a transmitter-coil of the subsurface imaging and detection system into the subsurface environment, wherein a secondary EM field is produced as a result of interactions between the primary EM field and said environment, wherein the receiver antenna records a set of data values associated with the secondary EM field for a plurality of receiver antenna rotational directions and a plurality of received frequencies, wherein data values associated with the primary EM field are integrated into the set of data values associated with the secondary EM field as a result of a presence of the primary EM field at the receiver antenna, wherein the tilt table (100) uses the null angle calculated for each of the plurality of receiver antenna rotational directions to adjust the current orientation of the x-axis receiver-coil (102) and the y-axis receiver-coil (112) to reflect the null angle, thereby placing the x-axis receiver-coil (102) and the y-axis receiver-coil (112) in a null-coupling orientation at each receiver antenna rotational direction and effectively reducing the presence of the primary EM field at the receiver antenna.

2. The method of claim 1, wherein a linear motion control of the x-axis linear adjustment (104) and the y-axis linear adjustment (114) is motorized.

3. The method of claim 1, wherein a calibration of the x-axis receiver-coil (102) and the y-axis receiver-coil (112) is performed such that the x-axis receiver-coil (102) and the y-axis receiver-coil (112) are aptly coupled to the transmitter-coil,

wherein the x-axis receiver-coil (102) and the y-axis receiver-coil (112) are aptly coupled to the transmitter-coil when the orientation of the x-axis receiver-coil (102) and the y-axis receiver-coil (112) are shifted about 6°

off the null-coupling orientation, wherein said shift effectively maintains a coupling of the x-axis receiver-coil (102) and the y-axis receiver-coil (112), as well as a near-null coupling of the transmitter-coil with the x-axis receiver-coil (102) and y-axis receiver-coil (112).

4. The method of claim 1, wherein a method is provided to monitor changes in a receiver response for simultaneous calibration of the receiver, the method comprising:

(a) transmitting a calibrating signal into the x-axis receiver-coil (102) and the y-axis receiver-coil (112), wherein the calibrating signal is offset in frequency from the secondary EM field; and

(b) normalizing a set of received data signals of the secondary EM field by the calibrating signal such that a change in the receiver response is removed,

wherein a vertical calibration coil (118) is operatively coupled to the receiver for transmitting the calibrating signal, wherein the vertical calibration coil (118) is offset from the x-axis and the y-axis receiver coils (102, 112), wherein a high output-impedance amplifier drives the vertical calibration coil (118) through a low-capacitance cable to eliminate changes in responses of the x-axis and the y-axis receiver coils (102, 112) caused by the vertical calibration coil (118).