Sensing method and system

Abstract

A method and sensing system for determining an electromagnetic property of a material is disclosed. The method and system comprise applying a first time varying magnetic field at a modulation frequency to the material located in a sensing region and operating a resonant detection circuit at an operating frequency higher than the modulation frequency where the resonant detection circuit is for sensing a material response upon application of the first time varying magnetic field to the material in the sensing region. The method and system further comprise determining an impedance characteristic of the resonant detection circuit; and then processing the impedance characteristic to determine the electromagnetic property of the material.

Description

SENSING METHOD AND SYSTEMPRIORITY DOCUMENTS

[0001] The present application claims priority from Australian Provisional Patent Application No. 2024904048 titled “SENSING METHOD AND SYSTEM” and fded on 6 December 2024, the content of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure relates to the sensing of one or more electromagnetic properties of a material. In a particular form, the present disclosure relates to determining the electromagnetic properties of an ore material as part of an ore processing system.BACKGROUND

[0003] Sensing the electromagnetic properties of a sample material can be important in many applications. In one example, a target material may be identified by its inherent electromagnetic properties from other materials that are generated by mining activities. These electromagnetic properties can vary in the presence of a magnetic field for magnetoactive materials. This provides a further means of discrimination. Example target materials of interest include different types of iron ore, sulfide minerals or other magnetoactive materials which will need to be distinguished from gangue material generated in the mining process. In other examples, the gangue material may be magnetoactive and the requirement is to distinguish the magnetoactive gangue material from the target of material which is not.

[0004] Mining activities will typically generate bulk material which must be transported from the ore body for characterisation and further processing. Determining early on in this process to what extent the bulk material contains the relevant target material or materials will ensure that further processing maximises the amount of target material retrieved from the ore body. Such materials are often transported in great quantities and at speed on conveyor belts or as slurries in pipes.

[0005] As would be appreciated, this presents significant challenges to any sensing arrangement that is attempting to determine the electromagnetic property of a material that is being transported in this manner as the sensor will optimally need to penetrate the bulk material to determine its properties but also be reliable in the rugged mining environment where any stoppages in processing of ore can have significant cost implications.SUMMARY

[0006] In a first aspect, the present disclosure provides a method for determining an electromagnetic property of a material, comprising: applying a first time varying magnetic field at a modulation frequency to the material located in a sensing region; operating a resonant detection circuit at an operating frequency higher than the modulation frequency, the resonant detection circuit for sensing a material response upon application of the first time varying magnetic field to the material in the sensing region; determining an impedance characteristic of the resonant detection circuit; and processing the impedance characteristic to determine the electromagnetic property of the material.

[0007] In another form, operating the resonant detection circuit at the operating frequency comprises generating a second time varying magnetic field at the operating frequency in the sensing region.

[0008] In another form, determining the impedance characteristic comprises: determining an input impedance of the resonant detection circuit; and determining the impedance characteristic based on the input impedance of the resonant detection circuit.

[0009] In another form, the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining a resistance characteristic of the inductive component.

[0010] In another form, the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining an inductance characteristic of the inductive component.

[0011] In another form, determining an input impedance of the resonant detection circuit comprises: determining a first sensed circuit signal and a second sensed circuit signal; processing the first sensed circuit signal and the second sensed circuit signal to generate a processed first sensed circuit signal and a processed second sensed circuit signal; and determining the input impedance based on the processed first sensed circuit signal and the processed second circuit signal.

[0012] In another form, processing the first sensed circuit signal and the second sensed circuit signal to generate processed first and second sensed circuit signals comprises determining low and high frequencycomponents of the first and second processed sensed circuit signals respectively and wherein determining the input impedance comprises determining an average input impedance based on the low frequency components of the first and second processed sensed circuit signals and a high frequency input impedance based on the high frequency components of the of the first and second processed sensed circuit signals.

[0013] In another form, determining the low and high frequency components of the first and second processed sensed circuit signals respectively comprises enhancing sideband information near to the operating frequency in the first and second sensed circuit signals.

[0014] In another form, enhancing sideband information near to the operating frequency comprises: determining low and high frequency components of the respective processed sensed circuit signals by down-converting a respective sensed circuit signal to form down-converted in-phase and quadrature signal components having a frequency range corresponding to a sideband information frequency range of interest; demodulating down-converted in-phase and quadrature signal components to generate respective demodulated low frequency and high frequency in-phase and quadrature components; amplifying the high frequency demodulated in-phase and quadrature components; determining the low frequency component of the respective processed sensed circuit signal from the demodulated low frequency in-phase and quadrature components; and determining the high frequency component of the respective processed sensed circuit signal from the demodulated amplified high frequency in-phase and quadrature components.

[0015] In another form, the sideband information frequency range of interest corresponds to a factor times the modulation frequency, wherein the factor corresponds to a number of sidebands of interest.

[0016] In another form, the first sensed circuit signal corresponds to a forward voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a reflected voltage signal of the resonant detection circuit and determining the input impedance comprises initially determining a reflection coefficient of the resonant detection circuit.

[0017] In another form, the first sensed circuit signal corresponds to a voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a current signal of the resonant detection circuit and determining the input impedance comprises determining a ratio of the voltage signal to the current signal.

[0018] In another form, operating a resonant detection circuit at the operating frequency comprises operating the resonant detection circuit at a resonant frequency of the resonant detection circuit.

[0019] In another form, operating the resonant detection circuit at the resonant frequency comprises modifying the operating frequency to compensate for changes in the resonant frequency to maintain a real impedance for the resonant detection circuit.

[0020] In another form, operating a resonant detection circuit at the resonant frequency comprises modifying the resonant detection circuit and corresponding resonant frequency to compensate for changes in the resonant frequency.

[0021] In another form, modifying the resonant detection circuit and corresponding resonant frequency comprises modifying a capacitive component of the resonant detection circuit.

[0022] In another form, the method further comprises determining an initial resonant frequency for the resonant detection circuit where a characteristic material is initially sensed without applying the first time varying magnetic field at the modulation frequency.

[0023] In another form, the electromagnetic property comprises an indication of a magnetoresistance of the material.

[0024] In another form, the electromagnetic property comprises an indication of a magnetic susceptibility of the material.

[0025] In another form, the electromagnetic property comprises an indication of the magnetic susceptibility’s dependence on the first time varying magnetic field.

[0026] In another form, processing the impedance characteristic to determine the electromagnetic property of the material comprises: determining spectral characteristics of the impedance characteristic with respect to the modulation frequency; and analysing the spectral characteristics to classify the material.

[0027] In another form, determining the spectral characteristics of the impedance characteristic with respect to the modulation frequency comprises determining one or more of peak values, amplitudes or phases of harmonics of a frequency spectrum to determine a signature for the material.

[0028] In another form, analysing the spectral characteristics to classify the material comprises comparing the determined signature to previously determined signatures to classify the material.

[0029] In another form, analysing the spectral characteristics to classify the material comprises determining any one or more of:a grade of material; a type of material; a concentration of a mineral or mineral phase in the material; elemental or mineral components of the material; a presence of a trace element in the material; or a particle size of the material.

[0030] In another form, analysing the spectral characteristics to classify the material comprises determining ratios of selected harmonics of the frequency spectrum.

[0031] In another form, orientations of the first time varying magnetic field and the second time varying magnetic field are aligned with each other.

[0032] In another form, orientations of the first time varying magnetic field and the second time varying magnetic field are orthogonal to each other.

[0033] In another form, the method further comprises generating the first time varying magnetic field at the modulation frequency by a first conductive coil and generating the second time varying magnetic field at the operating frequency by a second conductive coil.

[0034] In another form, the first and second conductive coils substantially surround the sensing region.

[0035] In another form, one or both of the first and second conductive coil is in the form of a solenoidal, Helmholtz or Saddle coil.

[0036] In another form, the material traverses the sensing region.

[0037] In another form, the operating frequency is at least two orders of magnitude greater than the modulation frequency.

[0038] In a second aspect, the present disclosure provides a sensing system for determining an electromagnetic property of a material, comprising: a magnetic field generator for applying a first time varying magnetic field at a modulation frequency to the material located in a sensing region; a resonant detection circuit operating at an operating frequency higher than the modulation frequency, the resonant detection circuit for sensing a material response upon application of the first time varying magnetic field to the material in the sensing region;a circuit characterisation arrangement for determining an impedance characteristic of the resonant detection circuit; and an electromagnetic property processor for processing the impedance characteristic to determine the electromagnetic property of the material.

[0039] In another form, operating at the operating frequency comprises generating a second time varying magnetic field at the operating frequency in the sensing region.

[0040] In another form, determining the impedance characteristic by the circuit characterisation arrangement comprises: determining an input impedance of the resonant detection circuit; and determining the impedance characteristic based on the input impedance of the resonant detection circuit.

[0041] In another form, the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining a resistance characteristic of the inductive component.

[0042] In another form, the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining an inductance characteristic of the inductive component.

[0043] In another form, determining an input impedance of the resonant detection circuit by the circuit characterisation arrangement comprises: a first circuit signal sensor for determining a first sensed circuit signal; a second circuit signal sensor for determining a second sensed circuit signal; a signal processing arrangement for processing the first sensed circuit signal and the second sensed circuit signal to generate a processed first sensed circuit signal and a processed second sensed circuit signal; and determining the input impedance based on the processed first sensed circuit signal and the processed second circuit signal.

[0044] In another form, processing the first sensed circuit signal and the second sensed circuit signal to generate processed first and second sensed circuit signals comprises determining low and high frequency components of the first and second processed sensed circuit signals respectively and wherein determining the input impedance comprises determining an average input impedance based on the low frequency components of the first and second processed sensed circuit signals and a high frequency input impedance based on the high frequency components of the of the first and second processed sensed circuit signals.

[0045] In another form, determining the low and high frequency components of the first and second processed sensed circuit signals respectively comprises enhancing sideband information near to the operating frequency in the first and second sensed circuit signals.

[0046] In another form, enhancing sideband information near to the operating frequency comprises: determining low and high frequency components of the respective processed sensed circuit signals by down-converting a respective sensed circuit signal to form down-converted in-phase and quadrature signal components having a frequency range corresponding to a sideband information frequency range of interest; demodulating down-converted in-phase and quadrature signal components to generate respective demodulated low frequency and high frequency in-phase and quadrature components; amplifying the high frequency demodulated in-phase and quadrature components; determining the low frequency component of the respective processed sensed circuit signal from the demodulated low frequency in-phase and quadrature components; and determining the high frequency component of the respective processed sensed circuit signal from the demodulated amplified high frequency in-phase and quadrature components.

[0047] In another form, the sideband information frequency range of interest corresponds to a factor times the modulation frequency, wherein the factor corresponds to a number of sidebands of interest.

[0048] In another form, the first sensed circuit signal corresponds to a forward voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a reflected voltage signal of the resonant detection circuit and determining the input impedance comprises initially determining a reflection coefficient of the resonant detection circuit.

[0049] In another form, the first sensed circuit signal corresponds to a voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a current signal of the resonant detection circuit and determining the input impedance comprises determining a ratio of the voltage signal to the current signal.

[0050] In another form, the resonant detection circuit is operated at a resonant frequency of the resonant detection circuit.

[0051] In another form, operating the resonant detection circuit at the resonant frequency comprises modifying the operating frequency to compensate for changes in the resonant frequency to maintain a real impedance for the resonant detection circuit.

[0052] In another form, operating a resonant detection circuit at the resonant frequency comprises modifying the resonant detection circuit and corresponding resonant frequency to compensate for changes in the resonant frequency.

[0053] In another form, modifying the resonant detection circuit and corresponding resonant frequency comprises modifying a capacitive component of the resonant detection circuit.

[0054] In another form, the sensing system further comprises determining an initial resonant frequency for the resonant detection circuit where a characteristic material is initially sensed without applying the first time varying magnetic field at the modulation frequency.

[0055] In another form, the electromagnetic property comprises an indication of a magnetoresistance of the material.

[0056] In another form, the electromagnetic property comprises an indication of a magnetic susceptibility of the material.

[0057] In another form, the electromagnetic property comprises an indication of the magnetic susceptibility’s dependence on the first time varying magnetic field.

[0058] In another form, processing the impedance characteristic to determine the electromagnetic property of the material by the electromagnetic property processor comprises: determining spectral characteristics of the impedance characteristic with respect to the modulation frequency; and analysing the spectral characteristics to classify the material.

[0059] In another form, determining the spectral characteristics of the impedance characteristic with respect to the modulation frequency comprises determining one or more of peak values, amplitudes or phases of harmonics of the frequency spectrum to determine a signature for the material.

[0060] In another form, analysing the spectral characteristics to classify the material comprises comparing the determined signature to previously determined signatures to classify the material.

[0061] In another form, analysing the spectral characteristics to classify the material comprises determining any one or more of: a grade of material; a type of material; a concentration of a mineral or mineral phase in the material;elemental or mineral components of the material; a presence of a trace element in the material; or a particle size of the material.

[0062] In another form, analysing the spectral characteristics to classify the material comprises determining ratios of selected harmonics of the frequency spectrum.

[0063] In another form, orientations of the first time varying magnetic field and the second time varying magnetic field are aligned with each other.

[0064] In another form, orientations of the first time varying magnetic field and the second time varying magnetic field are orthogonal to each other.

[0065] In another form, the magnetic field generator comprises a first conductive coil for generating the first time varying magnetic field at the modulation frequency and the resonant detection circuit comprises a second conductive coil for generating the second time varying magnetic field at the operating frequency.

[0066] In another form, the first and second conductive coils substantially surround the sensing region.

[0067] In another form, one or both of the first and second conductive coil is in the form of a solenoidal, Helmholtz or Saddle coil.

[0068] In another form, the material traverses the sensing region.

[0069] In another form, the operating frequency is at least two orders of magnitude greater than the modulation frequency.

[0070] In a third aspect, the present disclosure provides a sensing system comprising means to carry out the method in accordance with the first aspect.BRIEF DESCRIPTION OF DRAWINGS

[0071] Embodiments of the present disclosure will be discussed with reference to the accompanying drawings wherein:

[0072] FIG. 1 is a flowchart for a method for determining an electromagnetic property of a material in accordance with some embodiments;

[0073] FIG. 2 is a system overview diagram of an example sensing system for determining an electromagnetic property of a material in accordance with some embodiments;

[0074] FIG. 3 is a system overview diagram of a magnetic field generator in accordance with some embodiments;

[0075] FIG. 4 is a system overview diagram of a resonant detection circuit in accordance with some embodiments;

[0076] FIGS. 5A and 5B show two example magnetic field configurations for a sensing system in accordance with some embodiments;

[0077] FIG. 6 is a circuit schematic diagram of a resonant detection circuit in accordance with some embodiments;

[0078] FIG. 7 is a circuit schematic diagram of another resonant detection circuit in accordance with some embodiments;

[0079] FIG. 8 is a flowchart of a method for determining an impedance characteristic of the resonant detection circuit in accordance with some embodiments;

[0080] FIG. 9 is a flowchart of a method for determining an input impedance of the resonant detection circuit in accordance with some embodiments;

[0081] FIG. 10 is a flowchart of a method for processing the first and second circuit signals and then determining an input impedance based on these processed signals according to some embodiments;

[0082] FIG. 11 is a flowchart of a method for enhancing sideband information near to the operating frequency in accordance with some embodiments;

[0083] FIG. 12 is a system overview diagram of a circuit characterisation arrangement in accordance with some embodiments;

[0084] FIG. 13 is a system overview diagram of a signal processing arrangement for enhancing sideband information near to the operating frequency in accordance with some embodiments;

[0085] FIG. 14 is a flowchart of a method for processing the impedance characteristic to determine the electromagnetic property of the material in accordance with some embodiments;

[0086] FIG. 15 is a plot of the variation in — r as a function of time for bismuth in accordance with some o embodiments;A

[0087] FIG. 16 is a plot of the variation in — r as shown in FIG. 15 over a reduced time scale and also o showing the first time varying magnetic field being applied at the modulation frequency in accordance with some embodiments;Ar

[0088] FIG. 17 is plot of the FFT of the variation in — r in FIG. 16 in accordance with some o embodiments;

[0089] FIGS. 18(a) and (b) are plots of the variation in — r and respectively for a sensing system with O ‘-‘Q no material in the sensing region in accordance with some embodiments;Ar

[0090] FIG. 19(a) shows a plot of the variation in — r (raw and filtered), FIG. 19(b) is a plot of the o spectral characteristics of (a), and FIG. 19(c) is a plot showing the variation in the height of the first and second harmonics as a function of modulation frequency in accordance with some embodiments;Ar

[0091] FIGS. 20(a) and (b) are respectively plots of the variation in — r and the associated spectral o composition of a pyrite material as determined by a sensing system in accordance with some embodiments;

[0092] FIGS. 21(a) and (b) are respectively plots of the variation in and the associated spectral composition of a pyrite material as determined by a sensing system in accordance with some embodiments;Ar

[0093] FIG. 22 comprises plots of the determined resistance characteristic — r for goethite and the oassociated spectral composition as well as the determined inductance characteristic for goethite and theassociated spectral composition in accordance with some embodiments;Ar

[0094] FIG. 23 comprises plots of the determined resistance characteristics — r for hematite and the o associated spectral composition as well as the determined inductance characteristic for goethite and theassociated spectral composition in accordance with some embodiments;

[0095] FIG. 24 is a plot of the — second harmonic peak values versus the — second harmonic peak oro values for a variety of different iron ore materials as determined by a sensing system in accordance with some embodiments; and

[0096] FIG. 25 is a figurative view of a sensing system employed in an ore processing application in accordance with some embodiments.DESCRIPTION OF EMBODIMENTS

[0097] Techniques are disclosed for sensing one or more electromagnetic properties of a material which may be employed in a mining environment for processing certain types of ore material to identify those materials having electromagnetic characteristics indicative of a particular ore type, mineral concentration, particle size, impurity content or grade. In some embodiments, spectral analysis techniques in accordance with the sensing techniques of the present disclosure may be used to distinguish different mineral grades or types based on their spectral signature. The disclosed techniques are particularly beneficial, as they allow for the high throughput or on-line processing of significant quantities of bulk material where often the sensing environment will be challenging.

[0098] Referring now to FIG. 1, there is shown a flowchart of a method 100 for determining or sensing an electromagnetic property of a material. By way of overview, method 100 comprises (at block 110) applying a first time varying magnetic field to the material at a modulation frequency.

[0099] In one example, as will be seen below, the first time varying magnetic field may be generated by an inductive component such as a first conductive coil which is driven by a current source having an alternating waveform in the form of an oscillating or periodic wave generated at the modulation frequency. The waveform may be selected from any periodic waveform including, but not limited to: sine wave, square wave, triangle wave, sawtooth wave, or arbitrary repeating waveform.

[0100] In various examples, the material whose electromagnetic property or properties are being determined or characterised is arranged to be located within the first conductive coil during the sensing process. At block 120, method 100 comprises operating a resonant detection circuit at an operating frequency higher than the modulation frequency where the resonant detection circuit is configured to sense a material response resulting from the application of the first time varying magnetic field (eg, from the first conductive coil) to the material in the sensing region.

[0101] In one example, operating the resonant detection circuit at an operating frequency comprises generating a second time varying magnetic field at an operating frequency at or near the resonant frequency of the resonant detection circuit (which may change). In various examples, the secondtime varying magnetic field may be generated by an inductive component forming a component of the resonant detection circuit which may take different forms as will be seen below.

[0102] Method 100 further comprises determining an impedance characteristic (at block 130) of the resonant detection circuit and then processing the impedance characteristic (at block 140) to determine the electromagnetic property of the material.

[0103] Referring now to FIG. 2, there is shown an example sensing system 200 for determining an electromagnetic property of a material 280 in accordance with some embodiments. In various examples, system 200 may be configured to implement or carry out method 100 as illustrated in FIG. 1 (and also FIGS. 8, 9 and 11 referred to below).

[0104] In this example, sensing system 200 comprises a magnetic field generator 210 for applying a first time varying magnetic field 211 at a modulation frequency to the material 280 located in sensing region 270 and resonant detection circuit 220 operating at an operating frequency higher than the modulation frequency, the resonant detection circuit for sensing a material response upon application of the first time varying magnetic field 211 to the material 280 in the sensing region 270.

[0105] In one example, resonant detection circuit 220 generates a second time varying magnetic field 221 at an operating frequency at or near the resonant frequency in the sensing region 270. Sensor system 200 further comprises a circuit characterisation arrangement 230 for determining an impedance characteristic of the resonant detection circuit 220 and an electromagnetic property processor 240 for processing the impedance characteristic to determine the electromagnetic property of the material 280.

[0106] Referring now to FIG. 3, there is shown a system overview diagram of a magnetic field generator 300 according to some embodiments. In one example, magnetic field generator 300 may comprise the magnetic field generator 210 shown in FIG. 2.

[0107] Magnetic field generator 300 in this example comprises a controller 310, power supply 320 and an inductive component 330 and a capacitive component 340 in series with the inductive component 330 to assist in varying the modulation frequency. In various examples, inductive component 330 includes, but is not limited to: a resonator element such as loop-gap resonator; or to a conductive coil based component such as solenoid, Helmholtz coil, or saddle coil.

[0108] Controller 310 functions to control power supply 320 to generate an alternating current to drive inductive component 330 at a selected modulation frequency. In one example, controller 310 may be further operable to select the waveform of the alternating current source as described above. In one example, the controller may be an arbitrary waveform generator or similar. In another example, controller310 may be a data processor operating in accordance with programmed instructions. In various examples, the functionality of controller 310 and power supply 320 may be integrated into a single component. 3

[0109] Referring back to FIG. 2, magnetic field generator 210 (eg, magnetic field generator 300) is arranged so that the generated time varying magnetic field 211 is applied to the material 280 in the sensing region 270. In the example of magnetic field generator 300, where the inductive component 330 defines an encompassed region (eg, a conductive coil or the like) the encompassed region of the magnetic field generator 300 may be arranged so that the sensing region 270 is within the encompassed region. As will be described below with respect to FIG. 25 which depicts a sensing system 2500 directed to measuring the electromagnetic property of a material as part of an ore processing operation, an inductive component in the form a solenoid coil may be arranged so that the material is conveyed within and along an axial direction of the coil.

[0110] As would be appreciated, the time varying magnetic field 211 generated by magnetic field generator 210 may be applied over a larger region than the sensing region 270 and the inductive component 330 generating the time varying magnetic field 211 need not necessarily encompass or have sensing region 280 located within the inductive component 330.

[0111] In one example, the modulation frequency is selected from an audio frequency (AF) range. In various examples, the modulation frequency may be selected from one of the following frequency ranges including, but not limited to: less than 1 Hz, 1 Hz - 100 Hz, 100 Hz - 1 kHz, 1 kHz - 5 kHz, or greater than 5 kHz.

[0112] Selection of the modulation frequency will generally include a consideration of the characteristics of the magnetic field generation. As an example, where the magnetic field is generated by a conductive coil, the modulation frequency may be selected to minimise skin depth effects which will generally increase resistance, power loss and undesirable magnet heating with increasing frequency. Additionally, selecting too high a modulation frequency may result in high voltages on the electromagnetic circuit generating the time varying magnetic field, that is also undesirable.

[0113] In other applications, where the material whose electromagnetic properties are being determined in the sensing region is moving with respect to the first time varying magnetic field, eg material being moved on a conveyer at a speed of approximately 2 m.s1(eg, see FIG. 25 dealing with ore processing or more generally where a material sample such as from a drill core is being conveyed), then another consideration may be that the material is subjected to at least a minimum number of periods of oscillation of the magnetic field (eg, 10) as the material traverses the sensing region which may imply a minimum modulation frequency.

[0114] Referring now to FIG. 4, there is shown a system overview diagram of a resonant detection circuit 400 according to some embodiments. In one example, resonant detection circuit 400 may comprise the resonant detection circuit 220 shown in FIG. 2.

[0115] Resonant detection circuit 400 in this example comprises a controller 410, a power supply 420, a capacitive component 440 and an inductive component 430 for generating a time varying magnetic field or flux operable to couple to the material in the sensing region. In various examples, inductive component 430 includes, but is not limited to: a resonator element such as loop-gap resonator; or to a conductive coil based component such as solenoid, Helmholtz coil, or saddle coil.

[0116] Controller 410 functions to control power supply 420 to together generate an alternating voltage to drive the resonant detection circuit to operate at the operating frequency (e.g., at or near the resonant frequency of the resonant detection circuit 400 which will increase the sensitivity of the circuit).

[0117] In one example, controller 410 may be further operable to select the waveform and frequency of the alternating voltage. In one example, the controller 410 may be an arbitrary waveform generator or similar. In another example, controller 410 may be a data processor operating in accordance with programmed instructions. In various examples, the functionality of controller 410 and power supply 420 may be integrated into a single power driving component.

[0118] Referring back to FIG. 2, resonant detection circuit 220 (eg, resonant detection circuit 400) is arranged so that the generated oscillating time varying magnetic field 221 is applied to the material 280 in the sensing region 270. In the example of resonant detection circuit 400, the inductive component 430 of the resonant detection circuit 400 may be arranged so that the sensing region 270 is encompassed with the inductive component 430.

[0119] As will be described below with respect to FIG. 25 which depicts a sensing system 2500 directed to measuring the electromagnetic property of a material as part of an ore processing operation, the inductive component 430 of the resonant detection circuit which in this example is a conductive coil in the form of a solenoid may be arranged so that the material may be conveyed within and along an axial direction of the solenoid and additionally within the conductive coil responsible for generating the first time varying magnetic field at the modulation frequency.

[0120] Referring now to FIGs. 5A and 5B, there are shown two example magnetic field configurations 500, 550 for a sensing system according to some embodiments. In these examples, and by reference to FIGs. 3 and 4, inductive component 330 of magnetic field generator 300 comprises a Helmholtz coil 510 having a magnetic field orientation 515 and inductive component 430 of resonantdetection circuit 400 comprises a solenoid coil 520 having a magnetic field orientation 525. As would be appreciated, the Helmholtz and solenoid coils may be interchanged in other examples.

[0121] As can be seen by inspection, the orientations of the generated magnetic fields may be generally orthogonal to each other (eg, magnetic field configuration 500) or parallel to each other (eg, magnetic field configuration 550). In various examples, one or both of the magnetic field directions may align with a direction of travel of a sample material (as indicated by arrow 540). In other examples, the orientations of the magnetic fields may be at an angle between 0° and 90° with respect to each other.

[0122] In various examples, the resonant frequency is selected from a radio frequency (RF) range. In various examples, the resonant frequency may be selected from one of the following frequency ranges including, but not limited to: less than 1 MHz, 1 MHz - 10 MHz, 10 MHz - 20 MHz, 20 MHz - 30 MHz, 30 MHz - 40 MHz, 40 MHz - 50 MHz or greater than 50 MHz.

[0123] Selection of the resonant frequency will generally include a consideration that a lower frequency will allow sensing to a greater penetration depth into the sample to more uniformly measure a bulk sample. Lower sample loss, however, results in lower overall sensitivity as compared to a higher sample loss which will boost sensitivity which will be obtained at a higher frequency. Another factor which may be considered when configuring the resonant detection circuit is to include high inductance to minimise signal loss and thermal noise.

[0124] As will be seen below, the resonant detection circuit impedance characteristics may change as part of the sensing process and these changes may require compensation to maintain performance of the circuit (eg, changing the operating frequency). Determining any compensation will be assisted generally by having a simpler resonant detection circuit configuration involving less components as the circuit may be characterised more easily to determine the required compensation as compared to more complex circuits involving a larger number of components.

[0125] Referring now to FIG. 6, there is shown an example circuit schematic diagram of a resonant detection circuit 600 according to some embodiments. In this example, resonant detection circuit 600 is in the form of a capacitive L-network comprising an inductive component in the form of a conductive coil 650. The circuit is subdivided into a lossless series element 610 with reactance Xsand a “tank” circuit 640, which is the parallel-resonant arrangement containing an inductive component in the form of the sensor conductive coil 650 having inductance L and resistance r, resonated with a capacitive component in the form of capacitor C. The generally complex impedance of the tank circuit is denoted ZT-

[0126] Referring now to FIG. 7, there is shown a circuit schematic diagram of another resonant detection circuit 700 according to some embodiments.

[0127] In this example, resonant detection circuit 700 is in the form of a magnetically coupled network adopted to resonate an inductive component in the form of coil 750. Resonant detection circuit 700 is split into a series “feed” component 710 and atank component 740 acting as the “secondary” circuit that is magnetically coupled with the feed component through a mutual inductance M. In this example, feed component 710 is lossless and has zero reactance, so that it provides no contribution to the resonant detection circuit 700 input impedance Zin. Similar to “tank” circuit 640, tank component 740 comprises an inductive component in the form of the sensor conductive coil 750 having inductance L and a resistance r, resonated with a capacitive component in the form of capacitor C.

[0128] This will be true for a selected operating frequency but only an approximation over a band of frequencies. Additionally, the mutual inductance is limited to portions of the tank that have no coupling to the material that is measured. This means that the value for M is fixed regardless of the resistance or reactance changes imparted by the material that is to be measured.

[0129] Resonant detection circuit (eg, circuits 600, 700) further comprises an alternating voltage source (eg, AC voltage sources 620, 720) that generates in this example a sinusoidally alternating voltage that functions to drive the circuit to operate at a resonant frequency.

[0130] As will be appreciated, resonant detection circuits 600, 700 embody the design approach referred to above, being examples of circuit design having a smaller number of circuit elements involving principally reactive components which may be configured to generate a desired impedance.

[0131] In other examples, resonant detection circuit 220 may be based on a bridge circuit configuration.

[0132] Referring back to FIG. 1, at block 130 an impedance characteristic of the resonant detection circuit is determined. In various examples, as will be described below, the impedance characteristic may be a resistance characteristic and / or an inductance characteristic of the inductive component of the resonant detection circuit.

[0133] Referring now to FIG. 8, there is shown a flowchart of a method 800 for determine the impedance characteristic according to some embodiments. At block 810, the input impedance of the resonant detection circuit is determined and then at block 820 the impedance characteristic is determined based on the determined input impedance.

[0134] Referring now to FIG. 9, there is shown a flowchart of a method 900 for determining an input impedance of a resonant detection circuit according to some embodiments. Method 900 comprises at block 910 determining a first sensed circuit signal Cx(t) and a second sensed circuit signal C2(t) and then processing the first sensed circuit signal and the second sensed circuit signal to generate processed first and second sensed signals (t) and C2(t) . At block 920, the input impedance of the resonant detection circuit is then determined based on the processed first sensed circuit signal (t) and the processed second circuit signal C2(t) .

[0135] Referring now to FIG. 10, there is shown a flowchart of a method 1000 for processing the first and second circuit signals Cx(t), C2(t) and then determining an input impedance based on these processed signals according to some embodiments. At block 1010, method 1000 comprises determining low and high frequency components of the first and second processed sensed circuit signals respectivelyand C2(t), C2(t)). At block 1020, an average input impedance Zinis determined based on the low frequency components of the first and second processed sensed circuit signalsand C2(t) and at block 1030, a high frequency input impedance Zmis determined based on the high frequency components of the first and second processed sensed circuit signalsand C2(t).

[0136] In this context, the term “low frequency” refers to frequencies at or below the modulation frequency. The low frequency components in the sensed circuit signals may be generated by external noise sources to any sensing apparatus, drift in the sensing apparatus, or in the example of where the material is moving with respect to the sensing apparatus (eg, material being transported on a conveyer) this will appear as variable electromagnetic characteristics over the timescale that the material transitions through the sensing apparatus or where the composition of the material changes.

[0137] By contrast, the term “high frequency” refers to the region of the demodulated spectrum corresponding to a frequency range above the modulation frequency that contains sideband peaks resulting from the non-linear material response of the material that may be used to characterise electromagnetic properties of the material.

[0138] As will be seen below, average input impedance Zmmay be used to broadly characterise the resonant detection circuit such as shifts in the resonant frequency and the high frequency input impedance Zmmay be used to determine impedance characteristics of the inductive component relevant to the electromagnetic property of the material in the sensing region.

[0139] In one example, the material response detected by the resonant detection circuit relevant to the one or more electromagnetic properties of the material is contained in a sideband information frequency range of interest near to the operating frequency of the resonant “carrier” signal.

[0140] This sideband information is generated from the non-linear interaction in the material of the first time varying magnetic field applied at the modulation frequency and the resonant detection circuit operating at or near the resonant frequency (eg, through generating a second time varying magnetic field at this resonant frequency in the sensing region). In various examples, this sideband information will contain a collection of sidebands in the spectrum that are offset in frequency from the operating frequency, with the offset frequency being equal to multiples of the applied modulation frequency.

[0141] Accordingly, in one example, determining the low and high frequency components of the first and second sensed circuit signals respectively comprises enhancing sideband information near to the operating frequency in the first and second processed sensed circuit signals.

[0142] Referring now to FIG. 11, there is shown a flowchart of a method 1100 for enhancing sideband information near to the operating frequency according to some embodiments.

[0143] Method 1100 comprises at block 1110 down-converting the sensed circuit signal (ie, could be either the first or second sensed circuit signal) to form down -converted in-phase and quadrature signal components having a frequency range corresponding to a sideband frequency range of interest, ie, C* (t) and C^ (t) where i = 1, 2 corresponds to the first or second sensed circuit signal. This step recognises that the amplitude of the sidebands in the material response may be small compared to the amplitude of the resonant frequency. This will also assist in reducing the measurement dynamic range required to analyse the sidebands.

[0144] In one example, the sideband information frequency range of interest relative to the operating frequency will correspond to a factor times the modulation frequency where the factor corresponds to the number of sidebands of interest. In various examples, the number of sidebands of interest may be selected from the ranges of 1-10 sidebands, 10-20 sidebands, 20-30 sidebands, 30-40 sidebands, 40-50 sidebands, or greater than 50 sidebands.

[0145] In this manner, the sidebands will appear as features in the frequency spectrum of the demodulated signal in a frequency range corresponding to the order of magnitude and / or phase of the modulation frequency and these features may be quantified by spectral analysis techniques such as Fourier methods and the like.

[0146] At block 1120, method 1100 comprises demodulating the down-converted in-phase and quadrature signal components to generate respective demodulated “low” frequency and “high” frequency in-phase and quadrature components, ie,LF(t). C-Q HF(t).

[0147] At block 1130, method 1100 comprises applying a gain factor G to amplify the high frequency demodulated in-phase and quadrature components, C*HF(t) and C*Q HF(t).

[0148] As noted above, the sideband peaks will be in the high frequency band. In this example, the high frequency component is separately amplified. This will assist the subsequent analogue to digital conversion process as the high frequency part of the spectrum will be resolvable with the available dynamic range without saturation which could occur if both the low frequency and high frequency components were amplified together.

[0149] At block 1140, method 1100 comprises determining the low frequency component of the respective processed sensed circuit signalfrom the demodulated low frequency in-phase and quadrature components C* LF(0, iQ LF(t)- In one example, this will involve digitising the low frequency in-phase and quadrature components and then generating the equivalent signal based on the digitised in- phase and quadrature components in the standard manner where:

[0150] and:

[0151] At block 1150, method 1100 comprises determining the high frequency component of the respective processed sensed circuit signalfrom the demodulated amplified high frequency in- phase and quadrature components Gone example, this will involve digitising the amplified high frequency in-phase and quadrature components and then generating the equivalent signal based on the digitised in-phase and quadrature components in the standard manner as outlined above for the low frequency case.

[0152] As will be discussed below, the first and second processed low frequency sensed circuit signals may be employed to determine the “average” input impedance of the resonant detection circuit,while the first and second processed high frequency sensed circuit signals will contain the sideband information.

[0153] In various examples, interpreting the sideband information is assisted by maintaining the average input impedance Zmas a constant (eg, a real value) or have any deviations corrected for.

[0154] In one example, the first sensed circuit signal corresponds to the forward voltage at the resonant detection circuit and the second sensed circuit signal corresponds to the reflected voltage signal of the resonant detection circuit. In this example, processing the first sensed circuit signal and the second sensed circuit signal to determine the input impedance comprises in part determining the reflection coefficient T of the resonant detection circuit and then determining the average input impedance based on the reflection coefficient where the reflection coefficient F of the resonant detection circuit may be determined as the ratio of the processed low frequency first and second sensed circuit signals as follows:

[0155] The average input impedance Zinof the resonant detection circuit may then be defined as:

[0156] where Zs is the characteristic frequency of the transmission lines adopted in the system.

[0157] In another example, the first sensed circuit signal corresponds to the voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to the current signal of the resonant detection circuit. In this example, processing the first sensed circuit signal and the second sensed circuit signal to determine the input impedance comprises in part determining the average input impedance Zmdirectly as the ratio of the voltage signal to the current signal as follows:

[0158] Referring back to FIG. 8, following determining the input impedance at block 810, then at block 820 the impedance characteristic is determined based on the input impedance. In various examples, the impedance characteristic may be a resistance characteristic and / or an inductance characteristic of an inductive component of the resonant detection circuit (eg, conductive coil) of that defines any sensing region containing the material whose properties are being determined.

[0159] In one example, where the resonant detection circuit is a capacitive L-network circuit (eg, see resonant detection circuit 600 in FIG. 6) and the operating frequency is fixed (ie, single frequencyAT" mode) then the impedance characteristics comprising the resistance characteristic — r (where r is the o resistance of the inductive component of the resonant detection circuit) and / or the inductance characteristic (where L refers to the inductance of the inductive component of the resonant detection circuit coil) may be found based on AZm(ie, the difference between the high frequency input impedance Zinand the starting impedance Zinowhich in this example is set to Ro= 50 Q and is assumed to be maintained as purely real) in accordance with the following:

[0160] In this example, the capacitances C and Csand initial quality factor Qoare known

[0161] In another example, where there may be a relatively large change in r or L of the inductive component then a frequency shift A&> from the initial operating frequency &)0to a>' for the next measurement may be required to the operating frequency to establish or maintain a purely real impedance for subsequent measurements and allow uncorrected use of the sideband information. This operation can then be repeated as necessary over time as the sensor and load characteristics vary. The operating frequency shift A&> required may be determined as follows

[0162] Where: Zin= Rin+ jXinandEqn. 10

[0163] Where CO T is the resonant frequency of the tank circuit (see Fig 6) and:Eqn. 11

[0164] In this case, the values for 80. Lo. r0and Qowill change and require updating before substituting into Eqns. 6, 7 and 8 for the next iteration as follows:Qo' = )'CRno(l + 8'2) + 8' Eqn. 12c r _Rin(1 +So2) p 12dR° ~ I+QQ2 EQN'D

[0165] In another example, the resonant characteristics of the resonant detection circuit may be periodically monitored and the frequency shift Ao> updated as required.

[0166] In this manner, maintaining the operating frequency at the detection circuit resonant frequency will involve modifying the operating frequency to compensate for changes introduced by the sensing process (eg, movement of the material with respect of the sensing region, change in type of material etc).

[0167] In the example, where the operating frequency is adjusted to provide a purely real impedance of the resonant detection circuit, this will involve introducing frequency shifts of the operating frequency as referred to above which are based on an understanding of the operating characteristics of the resonant detection circuit to maintain the real impedance. By ensuring that the operating frequency is applied at the resonant frequency this allows essentially a real time determination of the circuit impedance and from this the electromagnetic property of the material being sensed while still maintaining high frequency resolution.

[0168] In another example, such as where there has been a long term drift in resonant frequency of the resonant detection circuit then the resonant detection circuit may be modified to change the resonant frequency such as by modifying or changing a capacitive component of the resonant detection circuit.

[0169] This may be contrasted to approaches which involve operating a detection circuit over a range of frequencies that encompass the resonant frequency and then attempting to determine the inductor impedance from the multitude of detection circuit impedances measured at different frequencies. Not only does this approach prevent rapid real time measurement, the inductor and circuit impedances may change while the frequency sweep is occurring meaning that any measurement will not be a reliable quantification of the sample. Additionally, these approaches typically assume that the detection circuit is properly tuned to one specific real impedance for at least one frequency in the swept frequency band, which is not normally guaranteed without cumbersome modification of the resonant circuit.

[0170] Even if this could be achieved by adopting complicated feedback mechanisms to the detection signal this still does not account for the sample changing (eg, moving) during the frequency sweep. Increasing the speed of the frequency sweep in an attempt to address these issues results, however, in low frequency resolution and correspondingly poor resolution in determining the properties of any material that is being attempted to be sensed.

[0171] In another example, where the resonant detection circuit is a magnetically coupledAT" network (eg, see resonant detection circuit 700 in FIG. 7) then the resistance (ie — r ) and inductance (ie, o7^) of the resonant detection circuit inductive component may be determined as follows:

[0172] by reading off the real and imaginary components on each side of Eqn. 13.

[0173] Referring now to FIG. 12, there is shown a system overview diagram of a circuit characterisation arrangement or module 1200 for determining an impedance characteristic of a resonant detection circuit according to some embodiments. In one example, circuit characterisation arrangement 1200 may comprise the circuit characterisation arrangement 220 shown in FIG. 2.

[0174] In this example, circuit characterisation arrangement 1200 comprises a first circuit signal sensor 1210A for measuring or determining a first sensed circuit signal Cx(t) and a second circuit signal sensor 1210B for measuring or determining a second sensed circuit signal C2(t) and respective signal processing arrangements 1220A, 1220B for processing the first sensed circuit signal and the second sensed circuit signal.

[0175] Circuit characterisation arrangement 1200 further comprises input impedance determining arrangement 1230 to determine the input impedance based on the processed first sensedcircuit signal and the processed second sensed circuit signal to determine the input impedance and impedance characteristic determining arrangement 1240 to determine the impedance characteristic based on the input impedance determined by input impedance determining arrangement 1230

[0176] In one example, signal processing arrangements 1220A, 1220B are operable to determining low and high frequency components of the first and second sensed circuit signals respectively and the input impedance determining arrangement 1230 determines an average input impedance based on the low frequency components of the first and second sensed circuit signals and a high frequency input impedance based on the high frequency components of the of the first and second sensed circuit signals following processing.

[0177] In one example, determining the low and high frequency components of the first and second sensed circuit signals comprises signal processing arrangements 1220A, 1220B being operable to enhance sideband information near to the modulation frequency in the first and second sensed circuit signals.

[0178] Referring now to FIG. 13, there is shown a system overview diagram of a signal processing arrangement 1300 for enhancing sideband information near to the operating frequency in accordance with some embodiments. In various examples, signal processing arrangement 1300 may be configured to implement or carry out method 1100 as illustrated in FIG. 11 and comprise part of the signal processing arrangement 1220A, 1220B shown in FIG. 12.

[0179] As would be appreciated, and as describe below, there will be two signal processing arrangements 1300 operating in parallel to process both sensed signals. Signal processing arrangement 1300 first comprises a down-converter 1310 operating on sensed circuit signal 1311 and in this example having as its local oscillator input the operating frequency 1312 to form down-converted in-phase (I) and quadrature (Q) signal components having a frequency range corresponding to the modulation frequency.

[0180] Signal processing arrangement 1300 then comprises a demodulator 1320 generate respective demodulated “low” frequency and “high” frequency in-phase and quadrature components (ILF, IHF, QLF and QHF). where “low frequency” refers to spectral components at or below the modulation frequency and “high frequency” refers to the region of the demodulated spectrum corresponding to a frequency range containing sideband peaks or information proximal to the modulation frequency as has been described previously.

[0181] The demodulated “high” frequency down -converted in-phase and quadrature components are than amplified by amplifier 1330 (eg, by gain factor G) to generate GXIHF and G / Qm .

[0182] Finally digitiser 1340 (in this example) converts each of the low frequency and amplified high frequency in-phase and quadrature analogue component signals to a respective digital representation (eg, by a suitable analogue to digital conversion arrangement) and then processing these digital representations by a data processor to recombine the low frequency in-phase and quadrature signals to generate the low frequency component of the respective sensed circuit signal and further to recombine the amplified high frequency in-phase and quadrature signals to generate the high frequency component of the respective sensed circuit signal.

[0183] Referring back to FIG. 12, circuit characterisation arrangement 1200 further comprises input impedance determining arrangement 1230 to determine the input impedance based on the processed first sensed circuit signal and the processed second sensed circuit signal to determine the input impedance as previously described depending on whether the first sensed circuit signal corresponds to the forward voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to the reflected voltage signal of the resonant detection circuit in which case the reflection coefficient of the resonant detection circuit is initially determined and an average input impedance is determined based on the low frequency components of the first and second sensed circuit signals and a high frequency input impedance is determined based on the high frequency components of the of the first and second sensed circuit signals.

[0184] Alternatively, if the first sensed circuit signal corresponds to the voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to the current signal of the resonant detection circuit then determining the input impedance comprises determining the ratio of the voltage signal to the current signal.

[0185] As referred to above, impedance characteristic determining arrangement 1240 determines an impedance characteristic based on the input impedance determined by input impedance determining arrangement 1230. In various examples, the impedance characteristic may be the resistance and / or inductance characteristic of the inductive component of the resonant detection circuit which is determined from the high frequency input impedance of the resonant detection circuit based on Eqns. 6 to 8 or 13 as previously described.

[0186] In one example, impedance characteristic determining arrangement 1240 is configured to determine the frequency shift Am required to ensure that the operating frequency is as close as possible to the resonant frequency of the resonant detection circuit as previously described (see Eqn. 9), and in some examples, to maintain a real impedance for the resonant detection circuit at the operating frequency.

[0187] As would be appreciated, the various components of circuit characterisation arrangement 1200 may be implemented as analogue or digital processes. In one example, an analogue signal ismaintained until the signal recombination following the down-converting and demodulation processing steps (achieved by hardware processing) which occurs digitally following an analogue to digital conversion of the in-phase and quadrature processed signals (eg, see blocks 1110 to 1130 in FIG. 11).

[0188] Referring back to FIG. 1, following determination of the impedance characteristic (eg, resistance characteristic — r and / or inductance characteristic y^) at block 140 this impedance characteristic O ‘-‘Q may be processed to determine the electromagnetic property of the material. In one example the electromagnetic property of the material is an indication of the magnetoresistance which is generallyAT" related to the determined impedance characteristic — r . o

[0189] In another example, the electromagnetic property of the material is an indication of themagnetic susceptibility which is generally related to the determined impedance characteristic Inanother example, the electromagnetic property of the material is an indication of the magnetic susceptibility’s dependence on the first time varying magnetic field (ie, magneto-susceptibility) applied at the modulation frequency.

[0190] As would be appreciated, and in accordance with the present disclosure, the electromagnetic property need not be determined in an absolute sense but may be characterised in a relative sense in that materials or morphologies of materials (eg, different particle sizes) having a differing magnetoresistance (as an example) may be distinguished based on the determined impedance AT" characteristic — r for each material. Similarly, materials having a different magnetic susceptibility or omagneto-susceptibility may be distinguished based on the determined impedance characteristic for each material. Additionally, different combinations of materials (and associated morphologies) may also be characterised based on the determined impedance characteristic.

[0191] Referring now to FIG. 14, there is shown a flowchart of a method 1400 for processing the impedance characteristic to determine the electromagnetic property of the material according to some embodiment. In one example. At block 1410, the spectral characteristics of the impedance characteristic with respect to the modulation frequency are determined and at block 1420 the spectral characteristics are analysed to classify the material.

[0192] In one example, determining the spectral characteristics of the impedance characteristic with respect to the modulation frequency comprises determining one or more of peak values, amplitudes or phases of harmonics of the frequency spectrum to determine a signature for the material.

[0193] In another example, analysing the spectral characteristics to classify the material comprises comparing the determined signature to previously determined signatures to classify the material.

[0194] In various examples, analysing the spectral characteristics to classify the material comprises determining any one or more of a grade of material, a type of material, a concentration of a mineral or mineral phase in the material, elemental or mineral components of the material, a presence of a trace element in the material; or a particle size of the material.

[0195] In another example, analysing the spectral characteristics to classify the material comprises comparing the ratios of selected harmonics of the frequency spectrum.

[0196] Referring again to FIG. 2, in one example the various aspects of determining the electromagnetic property of the material based on the determined impedance characteristic of the resonant detection circuit may be carried out by electromagnetic property processor 240 of sensing system 200 which includes one or more data processors 241 configured to configured to receive and process the impedance characteristic of the resonant detection circuit to determine the electromagnetic property in accordance with the present disclosure. Electromagnetic property processor 240 may be any computing device or system computer system, such as a workstation, desktop computer, server, laptop, handheld computer, tablet computer, mobile computing or communication device, VR device or VR component (eg, headset, camera, etc) or other form of computing or telecommunications device that is capable of communication and that has sufficient processor power and memory capacity to perform the operations described in this disclosure.

[0197] In this example, electromagnetic property processor 240 includes storage 242 that may include one or more storage devices or non-transitory computer-readable media having encoded on the media one or more computer-executable instructions or software for implementing techniques as variously described in this disclosure. The storage 242 may include a computer system memory or random access memory, such as a durable disk storage (which may include any suitable optical or magnetic durable storage device, eg, RAM, ROM, Flash, USB drive, or other semiconductor-based storage medium), a hard-drive, CD-ROM, or other computer readable media, for storing data and computer-readable instructions or software that implement various embodiments as taught in this disclosure.

[0198] Storage 242 may include other types of memory as well, or combinations. The storage device may be provided on electromagnetic property processor 240 or provided separately or remotely. The non-transitory computer-readable media may include, but are not limited to, one or more types of hardware memory, non-transitory tangible media (for example, one or more magnetic storage disks, oneor more optical disks, one or more USB flash drives), and the like. The non transitory computer-readable media included in the electromagnetic property processor 240 may store computer-readable and computer-executable instructions or software for implementing various embodiments. The computer- readable media may be provided on the electromagnetic property processor 240 or provided separately or remotely from the electromagnetic property processor 240.

[0199] The one or more data processors 241 are configured for executing computer-readable and computer-executable instructions or software stored in the storage 242 and other programs for controlling system hardware. Virtualization may be employed in the electromagnetic property processor 240 so that infrastructure and resources may be shared dynamically. For example, a virtual machine may be provided to handle a process running on multiple processors so that the process appears to be using only one computing resource rather than multiple computing resources. Multiple virtual machines may also be used with one processor. In other examples, a distributed electromagnetic processing system may be provided including a plurality of such electromagnetic property processors 240.

[0200] A user may interact with the electromagnetic property processor 240 through a display 244, such as a screen or monitor, including an augmented reality display device, which may display one or more user interfaces provided in accordance with some embodiments. The output device 244 may also display other aspects, elements or information or data associated with some embodiments.Electromagnetic property processor 240 may include input or input / output devices 243 for receiving input from a user, for example, a keyboard, a joystick, a game controller, a pointing device (eg, a mouse, a user's finger interfacing directly with a touch-sensitive display device, etc.), or any suitable user interface, including an AR headset. The electromagnetic property processor 240 may include other suitable conventional I / O peripherals.

[0201] Electromagnetic property processor 240 may run any suitable operating system including, but not limited to, any embedded operating system, any real-time operating system, any open source operating system, any proprietary operating system, any operating systems for mobile computing devices, or any other operating system capable of running on electromagnetic property processor and performing the operations described in this disclosure. In an embodiment, the operating system may be run on one or more cloud machine instances.

[0202] In other embodiments, the functional components / modules of electromagnetic property processor 240 may be implemented with hardware, such as gate level logic (eg, FPGA) or a purpose-built semiconductor (eg, ASIC). Still other embodiments may be implemented with a microcontroller having several input / output ports for receiving and outputting data, and several embedded routines for carrying out the functionality described in this disclosure. In a more general sense, any suitable combination of hardware, software, and firmware can be used, as will be apparent.

[0203] As will be appreciated in light of this disclosure, the functionality of electromagnetic property processor 240 may be implemented in software, such as a set of instructions (eg, HTML, XML, C, C++, object oriented C, BASIC, Python, MATLAB, Labview, etc.) encoded on any computer readable medium or computer program product (eg, hard drive, server, disc, or other suitable non-transitory memory or set of memories), that when executed by one or more processors, cause the various methodologies provided in this disclosure to be carried out.AT"

[0204] Referring now to FIG. 15, there is shown a plot 1500 of the variation in — r as a function o of time for bismuth according to some embodiments. Bismuth is a material that is known to exhibit strong magnetoresistance at room temperature. In this example, a modulation frequency of 0.05 Hz was adopted.AT"Plot 1500 shows the variation of — r comparing the use of a single operating frequency (see 1510) as o compared to where a range of operating frequencies as closed to the resonant frequency (in this case10 MHz) is adopted (see 1520) and shows the good agreement between both methods (NOTE: there is an intended Y-axis offset). An estimate of the magnetoresistance coefficient based was calculated which compared to favourably to the published value.AT"

[0205] FIG. 16 is a plot 1600 of the variation in — r 1610 as shown in FIG. 15 over a reduced o time scale and also showing the first time varying magnetic field 1620 being applied at the modulation frequency according to some embodiments.

[0206] In accordance with the present disclosure, the impedance characteristic in the form of the AT" resistance characteristic — r is processed to determine the spectral characteristics, eg, by a fast Fourier o transform (FFT) which may be analysed to classify the material. This is shown in FIG. 17 which shows a A plot 1700 of the FFT of the variation in — r in FIG. 16. As can be seen by inspection, plot 1700 shows a o pronounced second harmonic 1710 relative to the modulation frequency which may be used to classify the material.Ar

[0207] Referring now to FIGS. 18(a) and (b) there is shown a plot 1800 of the variation in — r and oa plot 1840 of the variation in for a sensing system with no material in the sensing region according tosome embodiments showing that the signals are much smaller than those obtained from magnetoactive materials such as bismuth and pyrite.

[0208] In various examples, it may be important to characterise any sensing apparatus without a sample to check for possible sources of interference with and ensure the measured signals are due to a material and not something inherent from the sensor setup.

[0209] In another example, an initial resonant frequency for the resonant detection circuit will be determined using a characteristic material similar to the material that is to be measured without applying the first time varying magnetic field at the modulation frequency to determine an expected baseline condition for when the material is actually measured in operation. r

[0210] FIG. 19(a) shows a plot 1900 of the variation in — r (raw and filtered), (b) is a plot 1920 of o spectral characteristics of (a), and (c) is a plot 1940 showing the variation in the height of the first and second harmonics as a function of modulation frequency according to some embodiments.

[0211] In this example, a 46.2 mT magnetic field is applied at a modulation frequency of 1 Hz to a sensing region containing a 25 mb, 126.2 g sample of powdered bismuth and the resonant detection circuit was operating in single frequency mode at an operating frequency of 10 MHz. Plot 1900 shows the AT" variation in — r based on the raw data 1910 as compared to the processed or filtered data 1915 which has o been processed to enhance the sideband peaks close to the modulation frequency.

[0212] FIG. 19(c) shows the change in amplitude of the 1stand 2ndharmonics of the signal as a function of modulation frequency of the applied magnetic field. As would be appreciated, the second harmonic is evidence of a non-linear effect being measured. Any harmonic other than the 1stharmonic is evidence of a non-linear effect that is related to electromagnetic properties of a material that changes with the applied magnetic field.

[0213] Referring now to FIGS. 20(a) and (b) there are shown respectively plots 2000, 2040 ofAT" the variation in — r and the associated spectral composition of a pyrite material as determined by a sensing o system according to some embodiments. Also shown in FIG. 20(a) is a plot of the first time varying magnetic field 2010 having a modulation frequency of 0.05 Hz. Pyrite (FeS2) is a sulphide mineral that may incorporate economically important elements (eg, gold, nickel, cobalt) as impurities is its crystalline structure

[0214] FIGS. 21(a) and (b) are the equivalent to the plots shown in FIG. 20(a) and (b) but thistime showing the variation in (ie, plot 2100) and the associated spectral composition (ie, plot 2140).

[0215] As can be seen by comparison with the — and spectral composition plots 1800, 1840 shown in FIGS. 18(a) and 18(b) respectively, for an equivalent set of measurement parameters but where no material is being measured, the — and spectral composition plots 2040, 2140 for pyrite each showa distinctive signal or spectral signature that may be used to either separate sulphides from wastematerials in ore processing or to detect the presence of impurities in sulphides such cobalt and nickel which alters the electromagnetic properties of pyrite and the measured spectral signature. In this example, the expected response to the applied magnetic field should be an even function and accordingly the harmonics of interest will be the even harmonics

[0216] Referring now to FIG. 22, there are shown plots of the determined resistanceAT" characteristic — r for goethite (plot 2200) and the associated spectral composition (plot 2220) as well as the odetermined inductance characteristic for goethite (plot 2240) and the associated spectral composition (plot 2260) according to some embodiments.

[0217] Referring now to FIG. 22, there are shown plots of the determined resistanceAT" characteristics — r for hematite (plot 2300) and the associated spectral composition (plot 2320) as well as o the determined inductance characteristic for goethite (plot 2340) and the associated spectral composition (plot 2360) according to some embodiments.

[0218] As can be determined by inspection from FIGS. 22 and 23, the sensed signal results for hematite measured in accordance with the present disclosure is significantly larger than for goethite for equivalent measurement setup. In addition, the spectral signatures as determined from the spectral compositions of each material for each determined impedance characteristic are different providing an additional means to distinguish these materials.

[0219] Referring now to FIG. 24, there is shown a plot 2400 of second harmonic peak values versus the — r second harmonic peak values for a variety of different iron ore materials as determined by a o sensing system according to some embodiments. In this example, the first time varying magnetic field was applied with a modulation frequency of 0.05 Hz implying second harmonic peak values corresponding to a frequency of 0.1 Hz.

[0220] The different iron ore materials measured may be categorised into four groups comprising itabirite (indicated as IHF, IGF and IHC), martite (indicated as MGD, M2H, MGM, MGF), goethite (indicated as GOV, GOL), and gangue / waste (indicated as PHY, CLA). Iron ores are known to exhibit permeabilities that change with magnetic fields as well as magnetoresistance.

[0221] As can be seen by inspection, the four different groups of iron ore materials occupy unique regions on the plot allowing these materials to be separately identified in accordance with the present disclosure. The goethite group 2410 has a comparably weak response for — and (ie, bottomleft). The itabirites group 2420 by contrast has a strong response for — r and — . The martite group 2430 O ‘-‘Q are distinguishable from each other but also form a clear group near the centre of plot 2400. As can be AT" seen the gangue material group 2440 has relatively low values of — r . o

[0222] Referring now to FIG. 25, there is shown a figurative view of a sensing system 2500 applied to an ore processing application according to some embodiments. In this example, material 2580 to be measured or sensed is transported by a conveyer system 2590 incorporate a moving belt 2591. As would be appreciated, material 2580 may be transported by other arrangements such as through the use of a moving slurry being conveyed in a trough, chute, trench or pipe.

[0223] Sensing system 2500 comprises a magnetic field generator 2510 having a first conductive coil 2511 for generating a first time varying magnetic field in a sensing region 2570 defined within the first conductive coil 2511 at a modulation frequency. Sensing system 2500 further comprises a resonant detection circuit 2520 having a second conductive coil 2521 that surrounds the sensing region 2570 and which generates a second time varying magnetic field at a resonant frequency of the detection circuit.

[0224] In this example, second conductive coil 2521 is located within and co-axial to the first conductive coil 2511 so that the material may be conveyed within and along an axial direction of both coils.

[0225] Sensor system 2500 further comprises a circuit characterisation arrangement 2530 that functions to determine an impedance characteristic of the resonant detection circuit in accordance with the present disclosure. As discussed, in various examples the impedance characteristic may comprise the resistance or inductance of the resonant detection circuit. As the material 2580 interacts with both time varying magnetic fields, one or more impedance characteristics of the resonant detection circuit will vary. In one example, the operating frequency of the resonant detection circuit 2520 is continuously modified so that the sensing system 2500 may effectively operate at or near the resonant frequency of the resonant detection circuit 2520 in accordance with the present disclosure .

[0226] Following determination of the impedance characteristic, electromagnetic property processor 2540 then determines the electromagnetic property of the material 2580. In accordance with the present disclosure, this may comprise determining an indication of an electromagnetic property such as the magnetoresistance or magnetic permeability of the material or in another aspect a spectral signature may be determined that can be compared to previously determined signatures to assist in identifying or classifying the material in accordance with its electromagnetic properties.

[0227] As would be appreciated, this online determination of an electromagnetic property of a material which may further use to identify or classify the material may be beneficially adopted in ore processing application. As shown in FIG. 25, the material 2580 being conveyed on the conveyer may be separated or sorted into different types of material 2592, 2593 based on a classification signal from sensing system 2500.

[0228] In an embodiment such as shown in Figure 25, the material of interest passes through the sensing region and the characteristic high frequency impedances may be measured, as in the example for pyrite in Figures 20 or 21. In the simplest example, the amplitude of one sideband is found to be proportional to the amount of pyrite present in the sample on belt. When this amplitude is normalised by the weight of material on the belt, obtained from another instrument such as a belt-weigher as an example, the concentration of the mineral pyrite may be determined.

[0229] An essentially real-time decision may then be made to keep or reject the sample based on a few seconds of measurement time by sensor systems in accordance with the present disclosure based on the determined pyrite concentration. In other examples, a mineral type, grade or other characteristic of the material may also be determined. In other examples, sensor systems in accordance with the present disclosure may be adapted to monitor for magnetoactive contaminants or in another example for determining particle sizes (in the range of 100’s of um) during processing.

[0230] More complicated determinations may also be made by combining information from multiple sidebands of both components of impedance (ie, resistance and inductance). In Figure 24 the 2ndharmonic of response for is plotted and regions representing different types of iron ore aredetermined. This would allow decisions of routing the ore based on ore type to be made in accordance with the present disclosure. Still further combinations are possible, including adding corrections from other data modalities such as temperature or operating frequency if the ore response is sensitive to these parameters. In other examples, more complicated correlation schemes or similar may be used to determine the ratios of mixtures of ore types present in the sample.

[0231] As would be appreciated, sensing systems and methods in accordance with the present disclosure may be directed to any application involving determining an electromagnetic property of a material. In one non-limiting example, also related to a mining application, the methods and systems of the present disclosure may be used to analyse an ore sample (eg, a drill core sample or drill chips) to determine the prospectivity of a region by such as by determining one or more of a grade or type of the sample material, a concentration of a mineral or mineral phase in the sample material, elemental or mineral components of the sample material a presence of a trace element in the sample material, or a particle size of the sample material.

[0232] The methodologies described in the present disclosure may be implemented by various means depending upon applications according to particular examples. For example, such methodologies may be implemented in hardware, firmware, software, optical componentry, or combinations of these implementation aspects. In a hardware implementation, for example, a processing unit may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, electronic devices, signal generators, analogue -to-digital convertors (ADCs) or other devices units designed to perform the functions as described.

[0233] Some portions of the detailed description included in the present disclosure are presented in terms of algorithms or symbolic representations of operations on binary digital signals stored within a memory of a specific apparatus or special purpose computing device or platform. In the context of this particular disclosure, the term specific apparatus or the like includes a general purpose computer once it is programmed to perform particular operations pursuant to instructions from program software. Algorithmic descriptions or symbolic representations are examples of techniques used by those of ordinary skill in the signal processing or related arts to convey the substance of their work to others skilled in the art. An algorithm is here, and generally, is considered to be a self-consistent sequence of operations or similar signal processing leading to a desired result.

[0234] In this context, operations or processing involve physical manipulation of physical quantities. Typically, although not necessarily, such quantities may take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared or otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to such signals as bits, data, values, elements, symbols, characters, terms, numbers, numerals, or the like. It should be understood, however, that all of these or similar terms are to be associated with appropriate physical quantities and are merely convenient labels. Unless specifically stated otherwise, as apparent from the discussion herein, it is appreciated that throughout this specification discussions utilising terms such as "processing," "computing," "calculating," "determining" or the like refer to actions or processes of a specific apparatus, such as a special purpose computer or a similar special purpose electronic computing device. In the context of this specification, therefore, a special purpose computer or a similar special purpose electronic computing device is capable of manipulating or transforming signals, typically represented as physical electronic or magnetic quantities within memories, registers, or other information storage devices, transmission devices, or display devices of the special purpose computer or similar special purpose electronic computing device.

[0235] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that such prior art forms part of the common general knowledge.

[0236] It will be understood that the terms “comprise” and “include” and any of their derivatives (e.g. comprises, comprising, includes, including) as used in this specification, and the claims that follow, is to be taken to be inclusive of features to which the term refers, and is not meant to exclude the presence of any additional features unless otherwise stated or implied.

[0237] In some cases, a single embodiment may, for succinctness and / or to assist in understanding the scope of the disclosure, combine multiple features. It is to be understood that in such a case, these multiple features may be provided separately (in separate embodiments), or in any other suitable combination. Alternatively, where separate features are described in separate embodiments, these separate features may be combined into a single embodiment unless otherwise stated or implied. This also applies to the claims which can be recombined in any combination. That is a claim may be amended to include a feature defined in any other claim. Further a phrase referring to “at least one of’ a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

[0238] It will be appreciated by those skilled in the art that the disclosure is not restricted in its use to the particular application or applications described. Neither is the present disclosure restricted in its preferred embodiment with regard to the particular elements and / or features described or depicted herein. It will be appreciated that the disclosure is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope as set forth and defined by the following claims.

Claims

CLAIMS1. A method for determining an electromagnetic property of a material, comprising: applying a first time varying magnetic field at a modulation frequency to the material located in a sensing region; operating a resonant detection circuit at an operating frequency higher than the modulation frequency, the resonant detection circuit for sensing a material response upon application of the first time varying magnetic field to the material in the sensing region; determining an impedance characteristic of the resonant detection circuit; and processing the impedance characteristic to determine the electromagnetic property of the material.

2. The method of claim 1, wherein operating the resonant detection circuit at the operating frequency comprises generating a second time varying magnetic field at the operating frequency in the sensing region.

3. The method of any one of the preceding claims, wherein determining the impedance characteristic comprises: determining an input impedance of the resonant detection circuit; and determining the impedance characteristic based on the input impedance of the resonant detection circuit.

4. The method of claim 3, wherein the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining a resistance characteristic of the inductive component.

5. The method of claim 3, wherein the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining an inductance characteristic of the inductive component.

6. The method of any one of claims 3 to 5, wherein determining an input impedance of the resonant detection circuit comprises: determining a first sensed circuit signal and a second sensed circuit signal; processing the first sensed circuit signal and the second sensed circuit signal to generate a processed first sensed circuit signal and a processed second sensed circuit signal; and determining the input impedance based on the processed first sensed circuit signal and the processed second circuit signal.

7. The method of claim 6. wherein processing the first sensed circuit signal and the second sensed circuit signal to generate processed first and second sensed circuit signals comprises determining low and high frequency components of the first and second processed sensed circuit signals respectively and wherein determining the input impedance comprises determining an average input impedance based on the low frequency components of the first and second processed sensed circuit signals and a high frequency input impedance based on the high frequency components of the first and second processed sensed circuit signals.

8. The method of claim 7, wherein determining the low and high frequency components of the first and second processed sensed circuit signals respectively comprises enhancing sideband information near to the operating frequency in the first and second sensed circuit signals.

9. The method of claim 8, wherein enhancing sideband information near to the operating frequency comprises: determining low and high frequency components of the respective processed sensed circuit signals by down-converting a respective sensed circuit signal to form down-converted in-phase and quadrature signal components having a frequency range corresponding to a sideband information frequency range of interest; demodulating down-converted in-phase and quadrature signal components to generate respective demodulated low frequency and high frequency in-phase and quadrature components; amplifying the high frequency demodulated in-phase and quadrature components; determining the low frequency component of the respective processed sensed circuit signal from the demodulated low frequency in-phase and quadrature components; and determining the high frequency component of the respective processed sensed circuit signal from the demodulated amplified high frequency in-phase and quadrature components.

10. The method of claim 9, wherein the sideband information frequency range of interest corresponds to a factor times the modulation frequency, wherein the factor corresponds to a number of sidebands of interest.

11. The method of any one of claims 6 to 10, wherein the first sensed circuit signal corresponds to a forward voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a reflected voltage signal of the resonant detection circuit and determining the input impedance comprises initially determining a reflection coefficient of the resonant detection circuit.

12. The method of any one of claims 6 to 10, wherein the first sensed circuit signal corresponds to a voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to acurrent signal of the resonant detection circuit and determining the input impedance comprises determining a ratio of the voltage signal to the current signal.

13. The method of any one of claims 1 to 12, wherein operating a resonant detection circuit at the operating frequency comprises operating the resonant detection circuit at a resonant frequency of the resonant detection circuit.

14. The method of claim 13, wherein operating the resonant detection circuit at the resonant frequency comprises modifying the operating frequency to compensate for changes in the resonant frequency to maintain a real impedance for the resonant detection circuit.

15. The method of any one of claims 1 to 14, wherein operating a resonant detection circuit at the resonant frequency comprises modifying the resonant detection circuit and corresponding resonant frequency to compensate for changes in the resonant frequency.

16. The method of claim 15, wherein modifying the resonant detection circuit and corresponding resonant frequency comprises modifying a capacitive component of the resonant detection circuit.

17. The method of any one of claims 1 to 16, comprising determining an initial resonant frequency for the resonant detection circuit where a characteristic material is initially sensed without applying the first time varying magnetic field at the modulation frequency.

18. The method of any one of claims 1 to 17, wherein the electromagnetic property comprises an indication of a magnetoresistance of the material.

19. The method of any one of claims 1 to 18, wherein the electromagnetic property comprises an indication of a magnetic susceptibility of the material.

20. The method of claim 19, wherein the electromagnetic property comprises an indication of the magnetic susceptibility’s dependence on the first time varying magnetic field.

21. The method of any one of claims 1 to 20, wherein processing the impedance characteristic to determine the electromagnetic property of the material comprises: determining spectral characteristics of the impedance characteristic with respect to the modulation frequency; and analysing the spectral characteristics to classify the material.

22. The method of claim 21, wherein determining the spectral characteristics of the impedance characteristic with respect to the modulation frequency comprises determining one or more of peakvalues, amplitudes or phases of harmonics of a frequency spectrum to determine a signature for the material.

23. The method of claim 22, wherein analysing the spectral characteristics to classify the material comprises comparing the determined signature to previously determined signatures to classify the material.

24. The method of any one of claims 21 to 23, wherein analysing the spectral characteristics to classify the material comprises determining any one or more of: a grade of material; a type of material; a concentration of a mineral or mineral phase in the material; elemental or mineral components of the material; a presence of a trace element in the material; or a particle size of the material.

25. The method of any one of claims 22 to 24, wherein analysing the spectral characteristics to classify the material comprises determining ratios of selected harmonics of the frequency spectrum.

26. The method of any one of claims 2 to 25, wherein orientations of the first time varying magnetic field and the second time varying magnetic field are aligned with each other.

27. The method of any one of claims 2 to 25, wherein orientations of the first time varying magnetic field and the second time varying magnetic field are orthogonal to each other.

28. The method of any one of claims 2 to 27, further comprising generating the first time varying magnetic field at the modulation frequency by a first conductive coil and generating the second time varying magnetic field at the operating frequency by a second conductive coil.

29. The method of claim 28, wherein the first and second conductive coils substantially surround the sensing region.

30. The method of claim 28 or 29, wherein one or both of the first and second conductive coil is in a form of a solenoidal, Helmholtz or Saddle coil.

31. The method of any one of claims 1 to 30, wherein the material traverses the sensing region.

32. The method of any one of claims 1 to 31, wherein the operating frequency is at least two orders of magnitude greater than the modulation frequency.

33. A sensing system for determining an electromagnetic property of a material, comprising: a magnetic field generator for applying a first time varying magnetic field at a modulation frequency to the material located in a sensing region; a resonant detection circuit operating at an operating frequency higher than the modulation frequency, the resonant detection circuit for sensing a material response upon application of the first time varying magnetic field to the material in the sensing region; a circuit characterisation arrangement for determining an impedance characteristic of the resonant detection circuit; and an electromagnetic property processor for processing the impedance characteristic to determine the electromagnetic property of the material.

34. The sensing system of claim 33, wherein operating at the operating frequency comprises generating a second time varying magnetic field at the operating frequency in the sensing region.

35. The sensing system of claim 33 or 34, wherein determining the impedance characteristic by the circuit characterisation arrangement comprises: determining an input impedance of the resonant detection circuit; and determining the impedance characteristic based on the input impedance of the resonant detection circuit.

36. The sensing system of claim 35, wherein the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining a resistance characteristic of the inductive component.

37. The sensing system of claim 35, wherein the resonant detection circuit comprises an inductive component and determining the impedance characteristic comprises determining an inductance characteristic of the inductive component.

38. The sensing system of any one of claims 35 to 37, wherein determining an input impedance of the resonant detection circuit by the circuit characterisation arrangement comprises: a first circuit signal sensor for determining a first sensed circuit signal; a second circuit signal sensor for determining a second sensed circuit signal; a signal processing arrangement for processing the first sensed circuit signal and the second sensed circuit signal to generate a processed first sensed circuit signal and a processed second sensed circuit signal; and determining the input impedance based on the processed first sensed circuit signal and the processed second circuit signal.

39. The sensing system of claim 38, wherein processing the first sensed circuit signal and the second sensed circuit signal to generate processed first and second sensed circuit signals comprises determining low and high frequency components of the first and second processed sensed circuit signals respectively and wherein determining the input impedance comprises determining an average input impedance based on the low frequency components of the first and second processed sensed circuit signals and a high frequency input impedance based on the high frequency components of the first and second processed sensed circuit signals.

40. The sensing system of claim 39, wherein determining the low and high frequency components of the first and second processed sensed circuit signals respectively comprises enhancing sideband information near to the operating frequency in the first and second sensed circuit signals.

41. The sensing system of claim 40, wherein enhancing sideband information near to the operating frequency comprises: determining low and high frequency components of the respective processed sensed circuit signals by down-converting a respective sensed circuit signal to form down-converted in-phase and quadrature signal components having a frequency range corresponding to a sideband information frequency range of interest; demodulating down-converted in-phase and quadrature signal components to generate respective demodulated low frequency and high frequency in-phase and quadrature components; amplifying the high frequency demodulated in-phase and quadrature components; determining the low frequency component of the respective processed sensed circuit signal from the demodulated low frequency in-phase and quadrature components; and determining the high frequency component of the respective processed sensed circuit signal from the demodulated amplified high frequency in-phase and quadrature components.

42. The sensing system of claim 41, wherein the sideband information frequency range of interest corresponds to a factor times the modulation frequency, wherein the factor corresponds to a number of sidebands of interest.

43. The sensing system of any one of claims 38 to 42, wherein the first sensed circuit signal corresponds to a forward voltage signal of the resonant detection circuit and the second sensed circuit signal corresponds to a reflected voltage signal of the resonant detection circuit and determining the input impedance comprises initially determining a reflection coefficient of the resonant detection circuit.

44. The sensing system of any one of claims 38 to 42, wherein the first sensed circuit signal corresponds to a voltage signal of the resonant detection circuit and the second sensed circuit signalcorresponds to a current signal of the resonant detection circuit and determining the input impedance comprises determining a ratio of the voltage signal to the current signal.

45. The sensing system of any one of claims 33 to 44, wherein the resonant detection circuit is operated at a resonant frequency of the resonant detection circuit.

46. The sensing system of claim 45, wherein operating the resonant detection circuit at the resonant frequency comprises modifying the operating frequency to compensate for changes in the resonant frequency to maintain a real impedance for the resonant detection circuit.

47. The sensing system of any one of claims 33 to 46, wherein operating a resonant detection circuit at the resonant frequency comprises modifying the resonant detection circuit and corresponding resonant frequency to compensate for changes in the resonant frequency.

48. The sensing system of claim 47, wherein modifying the resonant detection circuit and corresponding resonant frequency comprises modifying a capacitive component of the resonant detection circuit.

49. The sensing system of any one of claims 33 to 48, comprising determining an initial resonant frequency for the resonant detection circuit where a characteristic material is initially sensed without applying the first time varying magnetic field at the modulation frequency.

50. The sensing system of any one of claims 33 to 49, wherein the electromagnetic property comprises an indication of a magnetoresistance of the material.

51. The sensing system of any one of claims 33 to 50, wherein the electromagnetic property comprises an indication of a magnetic susceptibility of the material.

52. The sensing system of claim 51, wherein the electromagnetic property comprises an indication of the magnetic susceptibility’s dependence on the first time varying magnetic field.

53. The sensing system of any one of claims 33 to 52, wherein processing the impedance characteristic to determine the electromagnetic property of the material by the electromagnetic property processor comprises: determining spectral characteristics of the impedance characteristic with respect to the modulation frequency; and analysing the spectral characteristics to classify the material.

54. The sensing system of claim 53, wherein determining the spectral characteristics of the impedance characteristic with respect to the modulation frequency comprises determining one or more of peak values, amplitudes or phases of harmonics of a frequency spectrum to determine a signature for the material.

55. The sensing system of claim 54, wherein analysing the spectral characteristics to classify the material comprises comparing the determined signature to previously determined signatures to classify the material.

56. The sensing system of any one of claims 53 to 55, wherein analysing the spectral characteristics to classify the material comprises determining any one or more of: a grade of material; a type of material; a concentration of a mineral or mineral phase in the material; elemental or mineral components of the material; a presence of a trace element in the material; or a particle size of the material.

57. The sensing system of any one of claims 54 to 56, wherein analysing the spectral characteristics to classify the material comprises determining ratios of selected harmonics of the frequency spectrum.

58. The sensing system of any one of claims 34 to 57, wherein orientations of the first time varying magnetic field and the second time varying magnetic field are aligned with each other.

59. The sensing system of any one of claims 34 to 57, wherein orientations of the first time varying magnetic field and the second time varying magnetic field are orthogonal to each other.

60. The sensing system of any one of claims 34 to 59, wherein the magnetic field generator comprises a first conductive coil for generating the first time varying magnetic field at the modulation frequency and the resonant detection circuit comprises a second conductive coil for generating the second time varying magnetic field at the operating frequency.

61. The sensing system of claim 60, wherein the first and second conductive coils substantially surround the sensing region.

62. The sensing system of claim 60 or 61, wherein one or both of the first and second conductive coil is in a form of a solenoidal, Helmholtz or Saddle coil.

63. The sensing system of any one of claims 33 to 62, wherein the material traverses the sensing region.

64. The sensing system of any one of claims 33 to 63, wherein the operating frequency is at least two orders of magnitude greater than the modulation frequency.

65. A sensing system comprising means to carry out the method of any one of claims 1 to 32.

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