TECHNICAL FIELD

Aspects of the disclosure relate to electromagnetic impedance spectroscopy. In particular, aspects of the disclosure relate to an apparatus and related planar sensor system for use in characterizing selected portions of a material under test.

BACKGROUND

In U.S. Pat. No. 7,219,024 (which is hereby incorporated by reference in its entirety), a system is described for conducting electromagnetic impedance spectroscopy to non-invasively determine the in-place density (i.e., compaction) and moisture of various engineering materials with specific interest in soils. A fundamental component of this conventional system is the sensor system. Current testing standards for in-place soil testing, such as ASTM standard D1556 (for sand cone method), ASTM standard D6938 (for nuclear gauge method), and ASTM standard D7830 (for the method described in U.S. Pat. No. 7,219,024) do not provide a specific depth of soil to be tested. The physical design of the apparatus for the sand cone limits the testing depth to 4 to 6 inches, while the nuclear gauge provides for the placement of the radioactive source to a depth of 10 to 12 inches. Both the sand cone method and the nuclear gauge method require invasive procedures. In order to match the depth into the subsurface sampled by the accepted sand cone method, the sensor system disclosed in U.S. Pat. No. 7,219,024 must sample the soil to a depth of at least 4 inches below the surface. However, as noted herein, the nuclear gauge method provides for the placement of a radioactive source 10 to 12 inches into the soil. It may be beneficial for the sensor assembly to sample to a depth of at least 6 inches. However, the signals received by the current art in sensor systems from depths exceeding 4 inches have an unacceptable level of noise, which makes it difficult to accurately measure the soil impedance and determine the soil properties at that depth.

BRIEF SUMMARY

All examples and features mentioned below can be combined in any technically possible way.

Aspects of the disclosure provide for an electromagnetic sensor apparatus which overcomes the limitations in the current art to increase the depth of measurement into the surface and subsurface of a material under test (MUT) by reducing the noise of the received signals from greater depths. One implementation of the apparatus includes a sensor system including a transmitting electrode, a receiving electrode, and a backer ground plate that is configured to provide enclosed capacitive volume(s) above the transmitting electrode(s) and enclosed capacitive volume(s) above the receiving electrode(s). Various aspects focus on axisymmetric electrodes as described in U.S. Pat. No. 7,219,024, but additional aspects may utilize linear electrodes. The capacitive volumes may contain air or some other dielectric material.

The objective of the enclosed capacitive volumes is to isolate and control the effects of the field lines which emanate from both the transmitting electrode and the receiving electrode and go to the backer ground plate, and the field lines that pass through the soil and go to the backer ground plate. One group of field lines are proximate the transmitting electrode, transverse the soil at a shallow depth and interact with the backer ground plate in the region of the transmitting electrode. These field lines have greater strength (relative to other lines described herein) and are minimally modified by their route through the soil. Field lines will also penetrate deeply into the subsurface of the soil and interact with the backer ground plate in the region proximate the receiving electrode, as well as with the receiving electrode itself. These field lines will have less strength and are more affected (e.g., modified) by their route through the soil. In the sensor system of U.S. Pat. No. 7,219,024, the interaction of all of these field lines creates a varying field in the volume created by the electrodes and the intermediate ground. This varying field produces an uncontrolled parasitic capacitance that increases the noise level relative to the received signal, which inhibits accurate determination of the measured impedance. The creation of enclosed and separate capacitive volumes, the geometry and volumes of which can be designed to control the degree of the parasitic capacitance, can significantly reduce this problem.

The preceding description concerns the electromagnetic sensor described in U.S. Pat. No. 7,219,024 (hereby incorporated by reference in its entirety), which has a single transmitting electrode and a single receiving electrode in an axisymmetric configuration. However, aspects of the disclosure can be utilized to improve other sensor systems that have a single transmitting electrode and multiple receiving electrodes, such as the systems described in U.S. Pat. No. 9,804,112 (e.g., atFIG. 1). Additionally, aspects of the disclosure can be utilized to improve sensor systems having multiple transmitting and receiving electrodes, such as the systems described in U.S. Pat. No. 9,804,112 (e.g., atFIG. 2) or US Patent Publication No. 2016/0161624 (e.g., at FIG. 10), both of which are hereby incorporated by reference in their entirety.

Additional embodiments of the disclosure include use of a backer ground plate that is configured to provide enclosed capacitive volume(s) above each of the transmitting electrodes and enclosed capacitive volume(s) above each of the receiving electrodes, in configurations having a plurality of such electrodes.

In particular implementations, a sensor system includes: a planar array of at least two electrodes configured to be placed in electromagnetic communication with a material under test (MUT), wherein during operation of the planar array, at least one of the electrodes comprises a transmitting electrode for transmitting an electromagnetic signal over a range of frequencies through the MUT to at least one receiving electrode in the planar array; and a backer ground plate at least partially surrounding the at least two electrodes, the backer ground plate being electrically grounded and insulated from the at least two electrodes, wherein the backer ground plate extends from a plane formed by the at least two electrodes and separates the at least two electrodes to create at least one electrically isolated volume proximate to the at least two electrodes.

In additional particular implementations, a sensor system includes: an apparatus for communicating with a material under test (MUT), the apparatus having: a planar array of at least two electrodes configured to be placed in electromagnetic communication with the MUT, wherein during operation of the apparatus at least one of the electrodes comprises a transmitting electrode for transmitting an electromagnetic signal over a range of frequencies through the MUT to at least one receiving electrode in the planar array; and a backer ground plate at least partially surrounding the at least two electrodes, the backer ground plate being electrically grounded and insulated from the at least two electrodes, wherein the backer ground plate extends from a plane formed by the at least two electrodes and separates the at least two electrodes to create at least one electrically isolated volume proximate to the at least two electrodes; and a circuit coupled with the apparatus, the circuit configured to transmit a set of electromagnetic signals through the planar array to the MUT, and receive at least one return signal from the planar array.

In some cases, the backer ground plate is formed of an electrically conductive material.

In particular aspects, the backer ground plate includes a set of recesses corresponding with each of the at least two electrodes.

In certain implementations, the plane formed by the at least two electrodes is substantially parallel with a surface of the MUT.

In some aspects, the array of at least two electrodes includes axisymmetric circular electrodes.

In certain cases, the backer ground plate extends between neighboring electrodes in the array to the plane formed by the at least two electrodes.

In particular implementations, a first one of the at least two electrodes includes a central electrode and a second one of the at least two electrodes includes an outer electrode.

In some cases, the central electrode includes the transmitting electrode.

In certain aspects, the outer electrode includes the transmitting electrode.

In particular cases, the planar array of at least two electrodes is arranged in a linear configuration.

In some implementations, each of the at least two electrodes has a rectangular shape with rounded corners.

In certain implementations, any single electrode in the array includes the transmitting electrode and remaining electrodes in the array includes the at least one receiving electrode.

In particular cases, the transmitting electrode is selectable among the electrodes of the array, and is configured to change between the electrodes of the array.

In some aspects, the array includes a plurality of transmitting electrodes and a plurality of receiving electrodes.

In certain implementations, during operation of the apparatus, the planar array is in direct physical contact with the MUT and is electrically non-conductive with the MUT.

In particular aspects, the circuit includes a signal analyzer configured to compare the set of electromagnetic signals with the at least one return signal.

In some cases, the circuit further includes a computing device coupled with the signal analyzer, where the computing device is configured to determine a characteristic of the MUT based upon the comparison of the set of electromagnetic signals with the at least one return signal.

In certain aspects, determining the characteristic of the MUT includes: determining a difference in an aspect of the at least one return signal and an aspect of the set of electromagnetic signals; comparing the difference in the aspect to a predetermined threshold; and determining the characteristic of the MUT based upon the compared difference.

In some cases, during operation of the system, the planar array is in direct physical contact with the MUT and is electrically non-conductive with the MUT.

In certain aspects, the conductive backer ground plate extends between neighboring electrodes in the sensor array and defines a set of separate volumes corresponding with each of the at least two electrodes.

In particular implementations, the plane formed by the at least two electrodes and the conductive backer ground plate is substantially parallel with a surface of the MUT.

In some aspects, the array of at least two electrodes includes axisymmetric circular electrodes, where a first one of the at least two electrodes includes a central electrode and a second one of the at least two electrodes includes an outer electrode.

In certain implementations, the central electrode includes the transmitting electrode and wherein the outer electrode includes the receiving electrode.

In particular aspects, the central electrode includes the receiving electrode and wherein the outer electrode includes the transmitting electrode.

In some implementations, the planar sensor array is arranged in a linear rectangular configuration, where a first one of the at least two electrodes is a transmitting electrode and a second one of the at least two electrodes is a receiving electrode.

In certain aspects, a spacing of the conductive backer ground plate between the transmitting electrode and receiving electrode is sized to adjust for a depth of penetration and measurement into the MUT.

In particular implementations, each of the at least two electrodes has a rectangular shape with rounded corners.

In some cases, the array of at least two electrodes includes at least three electrodes arranged in a linear rectangular configuration.

In certain implementations, a single electrode in the planar sensor array includes the transmitting electrode and the remaining electrodes in the planar sensor array include the at least one receiving electrode.

In particular aspects, the planar sensor array includes a plurality of transmitting electrodes and a plurality of receiving electrodes.

In some cases, the transmitting electrode is selectable among the electrodes of the planar sensor array, and is configured to change between the electrodes of the planar sensor array.

In certain implementations, during operation of the apparatus, the planar sensor array is in direct physical contact with the MUT and is either electrically non-conductive with the MUT or electrically conductive with the MUT.

In particular cases, the circuit includes a signal generator operating over a range of frequencies for transmitting the electromagnetic signal from the transmitting electrode of the planar sensor system through the MUT and a signal analyzer configured to analyze the at least one return signal.

In some aspects, the circuit further includes a computing device coupled with the signal analyzer, where the computing device is configured to determine a physical property of the MUT based upon the transmitted electromagnetic signal and the at least one return signal.

In particular implementations, determining the physical property of the MUT includes: transmitting the electromagnetic signal over a range of frequencies from the transmitting electrode through the MUT to the receiving electrode; comparing the transmitted electromagnetic signal to the received signal to compute an electromagnetic property of the MUT; and correlating the computed electromagnetic property of the MUT with a physical property of the MUT to determine the physical property of the MUT.

In certain aspects, during operation of the system, the planar sensor array is in direct physical contact with the MUT and is either electrically non-conductive with the MUT or electrically conductive with the MUT.

In some cases, the conductive backer ground plate extends between neighboring electrodes in the sensor array in the plane of the electrodes and encompasses the electrodes to create a set of separate volumes corresponding with each of the at least two electrodes with the volumes for each electrode being individually optimized for minimal parasitic impedance.

In particular implementations, the plane formed by the at least two electrodes and the conductive backer ground plate is substantially parallel with a surface of the MUT.

In certain aspects, the array of at least two electrodes includes axisymmetric circular electrodes, wherein a first one of the at least two electrodes comprises a central electrode and a second one of the at least two electrodes comprises an outer electrode.

In some implementations, the array of at least two electrodes comprises axisymmetric circular electrodes, wherein the central electrode comprises the transmitting electrode and wherein the outer electrode comprises the receiving electrode.

In particular cases, the central electrode comprises the receiving electrode and the outer electrode comprises the transmitting electrode.

In some aspects, the planar array of two electrodes is arranged in a linear rectangular configuration with one being a transmitting electrode and one being a receiving electrode.

In certain implementations, the spacing of the conductive backer ground plate between the transmitting electrode and receiving electrode is sized to adjust for the depth of penetration and measurement into the MUT.

In particular aspects, each of the at least two electrodes has a rectangular shape with rounded corners.

In some cases, the planar array of at least three electrodes is arranged in a linear rectangular configuration.

In certain aspects, any single electrode in the array comprises the transmitting electrode and remaining electrodes in the array comprise the at least one receiving electrode.

In particular implementations, the array comprises a plurality of transmitting electrodes and a plurality of receiving electrodes.

In some aspects, the transmitting electrode is selectable among the electrodes of the array, and is configured to change between the electrodes of the array.

In particular cases, the circuit includes a signal generator and analyzer operating over a range of frequencies transmitting the electromagnetic signal from the transmitting electrode of the planar sensor system through the MUT and configured to receive the return signal to analyze the at least one return signal.

In certain implementations, the circuit further includes a computing device coupled with the signal generator and analyzer, wherein the computing device is configured to compute an electromagnetic characterization of the MUT and to correlate the computed electromagnetic characterization of the MUT to a physical property of the MUT.

In particular aspects, determining a physical characteristic of the MUT comprises: determining the electromagnetic characteristic of the MUT by transmitting an electromagnetic signal over a range of frequencies from the planar sensor system transmitting electrode through the MUT to the receiving electrode; comparing the transmitted signal to the received signal to compute an electromagnetic property of the MUT; developing an algorithm to correlate the computed electromagnetic property of the MUT with a physical property of the MUT; and applying the algorithm to a measured electromagnetic characteristic to determine the physical property.

Two or more features described in this disclosure, including those described in this summary section, may be combined to form implementations not specifically described herein.

The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features, objects and benefits will be apparent from the description and drawings, and from the claims.

