Device and method for electromagnetic characterization of a medium using a non-contact resonator, and related objects and resonators - Patents.com

Abstract

The present invention relates to a method and system for characterizing media, particularly dielectric media, using a multi-frequency resonator located at a distance from the region to be characterized and remotely excited and interrogated by inductive coupling with a probe. A reader measures the complex impedance of the probe via a single channel when the probe is coupled to said resonator and the resonator magnetically interacts with the region to be characterized. The impedance is spectrally analyzed to extract individual complex impedances for each resonant frequency of the resonator. These individual impedances are processed to calculate electrical properties such as the dielectric constant and / or conductivity of the medium, providing information about the nature and / or changes of the medium. The present invention also relates to a multi-frequency resonator applied in such a system or method.

Description

[Technical field]

[0001] The present invention relates to a method and system for characterizing media, particularly dielectric media, using a multi-frequency resonator located at a distance from the region to be characterized and remotely excited and interrogated by inductive coupling with a probe. A reader measures the complex impedance of the probe via a single channel when the probe is coupled to the resonator and the resonator magnetically interacts with the region to be characterized. The impedance is spectrally analyzed to extract individual complex impedances for each resonant frequency of the resonator. These individual impedances are processed to calculate electrical properties such as the permittivity and / or conductivity of the medium, providing information about the nature and / or changes of the medium.

[0002] The invention also relates to a multi-frequency resonator for application in such a system or method.

[0003] The resonator typically comprises multiple split transmission lines, each in a self-closing pattern, each determining a different resonant frequency from the others, either nested within one another or nested such as single-turn or multi-turn concentric split rings. [Background technology]

[0004] In many areas where non-destructive testing is performed, for example for medical diagnostics or quality control, it is desirable to characterize a medium through its electromagnetic properties, especially for "dielectric" media, which are usually poor electrical conductors, such as composite substances, organic and inorganic media, and composite materials.

[0005] This electromagnetic characterization involves, among other things, quantifying the interaction of the electromagnetic fields passing through the medium being characterized.

[0006] For this purpose it is known to use passive sensors using a transmission line coupled to a resonant antenna. A particular sensor of this type is the LC passive sensor with a capacitive effect that can be remotely interrogated. This communication uses electrical resonance as a means of remote interrogation, similar to RFID tags, and is disclosed in "Electronics for RFID Tags", Vol. 1, No. 1, pp. 1171-1175, 2002.

[0007] However, most of the existing characterization sensors, such as coaxial sensors, microwave antennas, or circular transmission lines (or SRRs: split-ring resonators), operate in contact with the medium under test, operate at relatively high frequencies, about hundreds of MHz to tens of GHz, and are usually only capable of measuring the dielectric constant.

[0008] In the medical imaging field, passive antennas have been developed for non-invasive characterization of specific tissues, for example, in Non-Patent Document 2, a microwave (GHz order) antenna for breast cancer detection is disclosed, or in Non-Patent Document 3, a high-frequency antenna (MHz order) for imaging devices such as MRI is disclosed.

[0009] These applications use a passive antenna known as a multi-turn transmission line resonator (or "MTLR"), which has been around for about 20 years and is made from a single, segmented transmission line with multiple circular turns, and which has a specific resonant frequency.

[0010] This type of resonator is described, for example, in "Electromagnetic Field Measurements," IEEE Transactions on Physics, Vol. 13, No. 1, pp. 1171-1175, 2002. These radio frequency ("RF") antennas are used to detect nuclear magnetic resonance (NMR) signals emitted by molecules in the human body exposed to a strong magnetic field.

[0011] This type of multi-turn transmission line resonator (MTLR) has been used for several years now, at least since 2014, for contactless measurement of the dielectric properties of organic and inorganic media via inductive coupling. This is described, for example, in: For the characterization of biological tissues, see Non-Patent Document 5. - For the evaluation of dielectric inclusions in the medium, see Non-Patent Document 6. - For burn depth assessment in organic tissues, see Non-Patent Document 7. - For evaluation of yogurt gelation, see Non-Patent Document 8.

[0012] This type of sensor has a characteristic resonant frequency at which it exhibits high sensitivity when operated and excited.

[0013] However, this type of characterization is not always accurate in obtaining specific properties of the investigated environment, for example with regard to the nature and composition of the medium or its structural properties, especially in complex and / or changing media.

[0014] One object of the present invention is to overcome all or part of the drawbacks of the prior art. In particular, a more accurate and / or more diverse characterization of the properties (e.g. composition, water content, physicochemical and biological changes, etc.) and / or structure of a medium, e.g. more accurate investigation of electrical properties at different time and spatial scales, is required. Also, an increased flexibility of its implementation is required, e.g. to allow easier and less invasive measurements that are more suitable for a functional context or more indicative of the state or changes of the investigated environment. [Prior art documents] [Non-patent literature]

[0015] [Non-Patent Document 1] Huang et al.'s paper "LC Passive Wireless Sensors Toward a Wireless Sensing Platform: Status, Prospects, and Challenges" (Journal of Microelectromechanical Systems, vol.25, no.5, pp.822-841, 2016) [Non-Patent Document 2] Paper by Modiri et al. “Review of breast screening: Toward clinical realization of microwave imaging: Toward” (Medical Physics, vol.44, no.12, e446-e458, 2017) [Non-Patent Document 3] Gruber et al.'s paper "RF coils: A practical guide for nonphysicists" (Journal of Magnetic Resonance Imaging, vol.48, no.3, pp.590-604, 2018) [Non-Patent Document 4] Serfaty, N. Haziza, L. Darrasse and S. Kan, "Multiturn split-conductor transmission-line resonators," Magnetic Resonance in Medicine, vol. 38, no. 4, pp. 687-689, 1997. [Non-Patent Document 5] Masilamany et al. (2014)'s paper "Wireless implementation of high sensitivity radiofrequency probes for the dielectric characterization of biological tissues" (IEEE MeMeA 2014 - IEEE International Symposium on Medical Measurements and Applications, Proceedings, 2014, pp.1-6) [Non-Patent Document 6] A. Pasquier, Y. Le Diraison, S. Serfaty and P.-Y. Joubert's 2018 paper "Multi-frequency detection of a dielectric object using flexible contactless RF sensors for tissue diagnosis" (2020 42nd Annual International Conference of the IEEE Engineering in Medicine & Biology Society (EMBC), 2020, pp.4105-4108, doi: 10.1109 / EMBC44109.2020.9175769) [Non-Patent Document 7] Dinh, Serfaty, & Joubert's 2019 paper "Non-Contact Radiofrequency Inductive Sensor for the Dielectric Characterization of Burn Depth in Organic Tissues" (Sensors, 19(5), p.1220) [Non-Patent Document 8] Dinh, Bore, Serfaty & Joubert's 2017 paper "Non invasive evaluation of yogurt formation using a contactless radiofrequency inductive technique" (Stud. Appl. Electromagn. Mech. Electromagn. Nondestruct. Eval. Vol.42, pp.42 298-305 (2017)) [Non-Patent Document 9] E. Hammerstad and O. Jensen, “Accurate Models for Microstrip Computer-Aided Design.,” IEEE MTT-S International Microwave Symposium Digest, vol. 1, no. 12, pp. 107‐409, 1980, issn: 0149645X. doi: 10.1109 / mwsym.1980.1124303.(Reference

[22] ) [Non-Patent Document 10] Y. Luo, X. Wang, and X. Zhou, “Inductance calculations for circular coils with rectangular cross section and parallel axes using inverse mellin transform and generalized hypergeometric functions,” IEEE Transactions on Power Electronics, vol. 32, no. 2, pp. 1367‐1374, 2017, issn: 08858993. doi: 10.1109 / TPEL.2016.2541180.(Reference

[23] ) [Non-Patent Document 11] BCR Paul, “The concept of “partial” inductance,” pp. 195-245 (Reference

[24] ) [Non-Patent Document 12] JT Conway, “Analytical solutions for the self-and mutual inductances of concentric coplanar disk coils,” IEEE Transactions on Magnetics, vol. 49, no. 3, pp. 1135‐1142, 2013, issn: 00189464. doi: 10.1109 / TMAG.2012.2229287.(Reference

[25] ) [Non-Patent Document 13] G. Masilamany, PY Joubert, S. Serfaty, B. Roucaries, and Y. Le Diraison, “Radiofrequency inductive probe for non-contact dielectric characterizations of organic medium,” Electronics Letters, vol. 50, no. 7, pp. 496-497, 2014, issn: 00135194. doi: 10.1049 / el.2014.0558. [Online]. Available: http: / / digital-library.theiet.org / content / journals / 10.1049 / el.2014.0558. (Reference

[26] ) Summary of the Invention

[0016] To this end, the present invention provides a method for characterizing at least one region in a medium to be characterized, the method comprising at least the following steps:

[0017] The probe is inductively coupled in a non-contact manner to a number of transmission lines arranged to have mutually different resonant frequencies at the same time. These transmission lines together form a multi-frequency resonator, which is located in the vicinity of the area under investigation but does not require contact with the area under investigation, with which the transmission lines interact. These lines typically also interact with each other. Thus, each of these transmission lines, or "TLRs" (transmission-line resonators), can be considered an "element transmission line" or "element resonator" within such a multi-frequency resonator.

[0018] Measuring (104) the impedance change of the multi-frequency resonator in the form of a single signal constituting a single measurement channel using a reader that interacts with the probe, which may be an external device connected thereto, such as a conventional vector network analyzer, or may be integrated into all or part of the probe.

[0019] Processing (103) the measurements of the impedance change, including a spectral analysis (103) as a function of frequency, to determine a number of individual impedances (Zm1 to Zm8) measured for a number of measurement frequencies (fm1 to fm8, respectively). This spectral analysis is typically a vector analysis giving the modulus, offset, frequency, phase, real and / or imaginary parts of the impedance. This is performed over a broadband, for example in one or more segments, to cover all expected resonant frequencies.

[0020] The measurement frequencies are defined around the resonant frequencies, in particular by means of an analytical model, and are usually determined relative to the resonant frequencies, for example in a number of bands corresponding to one of the resonant frequencies, in particular in a band including such a resonant frequency.

[0021] Processing (104) one or more of the individual impedances to extract one or more electrical properties of the area under study.

[0022] Typically, each of these transmission lines is formed along a "nearly closed" path, i.e., a path that self-closes while leaving a non-conductive interruption called a "gap." The line can take on a variety of shapes and sizes while still maintaining a self-closing linear path sufficient to radiate the magnetic field.

[0023] This gives, for example, a quantity proportional to the conductivity and / or permittivity of the medium for this frequency in this region.

[0024] Typically, these frequencies are determined by characteristics such as the dimensions and materials of the resonator lines, their arrangement relative to one another and to any substrate, and the dimensions and properties of such substrate.

[0025] Based on this type of characteristic, the inventors have identified a model capable of predicting the resonant frequencies of a multi-frequency resonator.

[0026] Another model is used to extract the value of a complex (in the mathematical sense) electrical property from the impedance value measured by the reader.

[0027] The present invention provides a method for implementing a non-contact inductive device for the characterization of complex dielectric media. It concerns a simple passively emitting multi-resonator that can be interrogated and excited remotely by inductive coupling at low financial and environmental cost. Such a device is referred to herein as a "multi-frequency resonator" or "WMFR" (wireless multifrequency resonator).

[0028] It exhibits high selectivity and interacts with the surrounding environment by radiating electromagnetic waves, allowing its spectral breadth to be controlled to non-contactly monitor complex dielectric properties. In the presence of a variable electromagnetic field, typically generated by a nearby excitation coil, referred to herein as a "probe", this high quality factor device resonates at multiple distinct frequencies, predetermined by the size of the conductive tracks (typically rings). These tracks can be viewed as interwoven radiating transmission lines.

[0029] Conversely, the WMFR generates a magnetic field for each of these frequencies, whose spectral response is modulated by the dielectric properties of the surrounding medium, called the "medium under investigation." The equivalent impedance around each resonant frequency can then be measured via inductive coupling with the probe.

[0030] That is, the present invention makes it possible to obtain more diverse and / or more accurate information, especially on the mesoscopic scale, ie in the range of about millimeters to centimeters.

[0031] By its construction, such a WMFR is a passive resonator with N resonant frequencies, which are tunable by the size of the transmission line. Interrogation of the resonator to access its impedance spectrum is typically performed using a single measurement channel, for example with a vector network analyzer, by simply measuring the impedance between the terminals of the probe's inductive circuit.

[0032] Because the resonators are passive, remotely interrogable, cheap and compact, they can be easily integrated into the medium under investigation and, if necessary, permanently, e.g., portable or even implantable, especially for medical applications or object degradation monitoring.

[0033] It can be fabricated on planar and flexible supports, thus minimizing invasiveness. It can be produced relatively simply and cheaply, especially using flexible and proven printed circuit board technology. It can therefore be integrated into numerous structures. It can also be fabricated using microtechnology on biocompatible polymers for biological or medical applications.

[0034] Such a measurement technique is non-invasive, multi-frequency, without contact with the medium under investigation. As the multi-frequency resonators themselves are passive, they can be integrated into structures, containers or packaging, for example for quality control or monitoring the degradation of objects. They can also be attached to plants, for example to monitor their growth or ripening. They can be worn as accessories or clothing, or implanted in living organisms, for example for medical or wellness applications. They can also be disposable, for example in medical dressings or food packaging. In use, the WMFR can be associated with simple and remote single-channel reader electronics, allowing the spectral analysis of the desired dielectric properties.

[0035] Unlike conventional sensors or systems for dielectric characterization of a medium (e.g., microwave antennas that require electrical coupling to a transmission line or electrical connection), such multi-frequency WMFRs are passive and can be remotely queried in the context of use disclosed herein.

[0036] Since WMFRs are not in contact with the medium, measurements are not perturbed by the quality of the contact between the sensor and the medium under investigation, as is the case with capacitive sensors or bioimpedance electrodes. Furthermore, since WMFRs allow for simultaneous multi-frequency measurements, the associated characterization system allows for a more robust estimation of the desired dielectric properties.

[0037] Having access to the dielectric parameters of the medium at multiple frequencies not only improves the quality of the characterization, but also makes it possible, if necessary, to calibrate the WMFR using one or more analysis frequencies against potentially problematic influences for the measurement, e.g. large temperature changes, changes in the distance between the WMFR and the investigated medium, or changes in the volume of the measured quantity.

[0038] The geometric variations associated with the various resonating elements of a WMFR allow one to envisage devices in which the investigation region, particularly in terms of depth, depends directly on the properties of the elements brought into resonance.

[0039] Specifically, for a resonant antenna, the penetration depth of the magnetic field generated in the medium is directly related to its diameter. Here, the various resonant elements (various transmission lines) of the WMFR have different dimensions from each other, e.g., due to nesting, so that each has a different inspection depth, giving the investigation a tomographic character. This proves to be particularly advantageous in many cases, e.g., when detecting and / or locating dielectric anomalies in a medium, such as tumors in tissue or cracks in concrete or steel.

[0040] In comparison, methods such as coaxial sensors and capacitive sensors require contact with the medium. Moreover, radio frequency and microwave antennas require electrical connections for use. It should also be noted that most of these sensors, especially coaxial sensors and microwave antennas, operate at frequencies from hundreds of MHz to tens of GHz, i.e., higher frequencies than the methods disclosed herein. Thus, they have access to the dielectric parameters of the medium, which are essentially related to the relative permittivity of the medium, but have difficulty in measuring the electrical conductivity of the medium.

[0041] There are many fields in which the present invention can be used, including, but not limited to, the following: Agri-food sector: plant characterization and animal health monitoring, food process monitoring and e.g. monitoring of growth, maturation, moisture content, ageing, especially storage, transportation, packaging and freshness and quality control of food products during natural or accelerated / artificial maturation. In the health field, by characterizing biological tissues via their dielectric properties: detection of lesions such as tumors or other internal lesions, characterization of lesions such as tumors, injuries, burns, skin diseases and monitoring their changes over time.

[0042] Geophysical materials characterization for the characterization of various types of soft materials or soils, cosmetics, etc.

[0043] Integrated health monitoring (or structural health monitoring) for various types of objects or operations: civil engineering, aerospace, etc. In particular, for all media with low electrical conductivity, such as carbon, concrete, wood, composites, etc.

[0044] Many of these applications, or others, can take the form of connected objects that participate in or provide such functionality.

[0045] Various specific features of the invention are described below, which may be combined with one another or taken separately.

[0046] According to one particular aspect of the invention, the individual impedances of the different resonant frequencies, or respective electrical properties extracted therefrom, are combined to provide a characterization of the area under investigation at different distances from the multi-frequency resonator, which can, for example, provide imaging and / or tomography of the area under investigation.

[0047] In particular, the size of the antenna directly affects the penetration depth and therefore the location of the interrogation region in terms of depth.

[0048] According to another feature, the individual impedances of a number of different resonant frequencies, or respective electrical properties extracted therefrom, are combined to provide a more accurate characterization of the same part of the investigated area, for example using values ​​obtained from different frequencies to provide more accurate values ​​of the electrical properties, or for example using different frequencies to extract different properties that apply to the same investigated area, thus giving more accurate information about said area.

[0049] According to yet another feature, the method is used to generate multiple characterizations at different time points, thereby providing monitoring over time of an area of ​​interest where at least one material or object is being altered.

[0050] According to yet another specific feature, the method implements one or more multi-frequency resonators incorporated or embedded in an object or system to characterize an area of ​​interest, including materials belonging to said object and / or materials in contact with or in the vicinity of said object and / or interfaces between said materials. According to this specific feature, the method is performed to obtain a plurality of time-distributed characterizations of said area of ​​interest, thereby monitoring changes in the area of ​​interest over time.

[0051] This makes it possible, for example, to monitor the state of a material, such as its airtightness, to monitor the emergence of new materials or phenomena, or to monitor the static or dynamic properties of fluids or solids located in the vicinity of or passing in contact with the object.

[0052] [Systems and devices implementing the method] According to another aspect of the invention, there is provided a system for non-contact characterization of at least one region in a medium to be characterized, referred to as an area of ​​interest, comprising: - at least one transmission line resonator (linear but not necessarily straight), which is intended to be placed in the vicinity of said area of ​​interest, but does not necessarily have to be in contact with said area of ​​interest. - Probes positioned as follows: on the other hand, coupled via inductive coupling to the resonator by an inductive loop circuit; and On the other hand, it interacts with at least one reader (usually via an electrical connection; the reader may or may not be integrated in the same housing as the probe).

[0053] According to the invention, the resonator comprises a number of transmission lines arranged to have different resonant frequencies, thereby forming a multi-frequency resonator, which transmission lines interact with the area under investigation and usually also with each other, typically resulting in changes in the individual responses of said transmission lines, in particular in terms of resonant frequency and the bandwidth around this resonant frequency.

[0054] This same probe is arranged to simultaneously interact with the entire multi-frequency resonator, i.e. the assembly formed by the multiple lines. The reader is arranged to interact with the probe so as to implement the method disclosed herein. The electrical properties provided by this method are used to characterize the medium in the region of interest.

[0055] Typically, the element transmission lines are formed by conductive tracks deposited on two opposing faces of a low-loss planar insulating substrate. These conductive tracks are preferably positioned relative to each other such that one or more interruptions on one face do not face one or more gaps on the other face. However, it is also possible to use only one track for each transmission line.

[0056] In the claimed system, the multi-frequency resonator comprises a number of separate and unconnected transmission lines, each formed by at least one conductive track, usually formed in a planar or non-planar shape, e.g. on a flexible two-dimensional dielectric substrate, with a low or no electrical conductivity. The track is formed along a "nearly closed" path, i.e. a path that self-closes while leaving non-conductive interruptions. The track can take on various shapes and sizes, while maintaining a self-closing linear path sufficient to radiate a magnetic field.

[0057] This type of transmission line is, for example, a circular track in a shape known as a "split ring". Other patterns are envisaged and may be circular or other shapes, rounded or not, spiral or variable radius.

[0058] Preferably, each line comprises two tracks formed on each of two opposing faces of the same substrate, opposed and angularly offset from one another.

[0059] Among the transmission lines, different resonant frequencies are typically obtained by giving them different dimensions. Alternatively, or in combination, these frequency differences are obtained by different combinations of one or more parameters selected from the following: track length, track path geometry (typically radius), track width, track thickness, track material properties, substrate thickness, and substrate material properties.

[0060] It is also envisaged to manufacture element transmission lines having one or more openings, i.e. element transmission lines formed by multiple tracks that are not connected to each other but are sufficiently close and / or intertwined with each other to radiate at the same frequency into the same spatial region.

[0061] It is also envisioned to fabricate element transmission lines with more than one layer, or even a single layer.

[0062] According to one particular feature, all or part of the transmission lines of the multi-frequency resonators each form a substantially closed path of a single turn, typically a circular split ring of a single turn.

[0063] Alternatively, or in combination, the use of multi-turn paths, for example continuous helical or discontinuous offset, is also envisaged and is used in a particularly known manner.

[0064] According to another particular feature, the multi-frequency resonator comprises a number of conductive tracks of substantially closed shape enclosed within one another.

[0065] According to yet another particular feature, the multi-frequency resonator comprises a plurality of transmission lines, separate and unconnected from one another, each formed by a conductive track made on a two-dimensional insulating substrate, which in particular are paired with one another on both sides of said substrate, angularly offset opposite one another and along a "quasi-closed", in particular circular, path. According to this particular feature, at least two transmission lines of different frequencies are arranged so as not to nest within one another and are called separate. The probe comprises an inductive loop circuit, the shape of which is arranged so as to obtain simultaneous inductive coupling to said two separate transmission lines. In particular, a conductive loop is formed with a single-turn or multi-turn protrusion, arranged so as to be able to place a protrusion on each of said separate transmission lines. It can for example be in a daisy pattern, the different petals of which each cover one of the split rings of a resonator with a plurality of separate split rings.

[0066] According to yet another specific feature, the multi-frequency resonator comprises a plurality of transmission lines separate and unconnected from one another, each transmission line being formed by conductive tracks (c14a, c14b) along an "approximately closed", in particular circular, path, on the same plane or on the same two-dimensional insulating substrate.

[0067] All or some of the lines may be non-coplanar with respect to one another.

[0068] For example, they are arranged on separate substantially parallel planes (or two-dimensional surfaces), which are for example strictly parallel to each other or which form an angle of less than 45°, in particular less than 20°, or even less than 5°, relative to each other.

[0069] Each line may have a three-dimensional path, i.e. a path that is not described in a simple two-dimensional surface, provided that this path is capable of radiating a directional magnetic field with magnetic flux lines that pass in common through the various transmission lines. For example, it may take the form of a helical arrangement on a cone, a circular ring around an axis but with varying axial position along its path.

[0070] As another example, they may be positioned on two dimensional planes or surfaces that are not parallel to one another, for example to couple to different inductive loops or portions of the probe in different orientations.

[0071] According to a preferred embodiment, this multi-frequency resonator comprises a number of mutually separate and unconnected transmission lines, each formed by a conductive track made on the same two-dimensional insulating substrate, each along a "nearly closed" path, for example a single-turn, in particular a circular path, which are arranged inside each other, in particular concentrically with each other.

[0072] According to yet another aspect of the invention, there is provided a transmission line resonator device, of a type capable of communicating with an inductive loop probe via inductive coupling and adapted to interact with said probe, to be excited by said probe, said resonator according to this aspect comprising a number of transmission lines of substantially closed shape enclosed inside one another, in particular concentric circles, arranged together to form a multi-frequency resonator suitable for implementation within a system or method disclosed herein.

[0073] According to one particular feature, each transmission line forms a single turn.

[0074] [Embedded resonator] According to another aspect of the invention, there is provided an object or system including at least one transmission line resonator including a plurality of transmission lines arranged to have different resonant frequencies, thereby forming a multi-frequency resonator, the transmission lines interacting with an area of ​​interest and typically also with each other.

[0075] According to this aspect, the multi-frequency resonator is arranged to form an inductive coupling with an inductive loop probe and interacts with said probe to: - forming a characterization system as disclosed herein, the system being arranged to characterize an area of ​​interest within the medium to be characterized (which may be remote from said resonator); and / or - Implemented in the manner disclosed herein. Typically, this region of investigation includes materials belonging to said object and / or materials in contact with or in the vicinity of said object and / or interfaces between said materials.

[0076] In this way, an "embedded object" or "embedded system" is obtained, which can be monitored in a regular or continuous manner, for example in multiple or difficult to access locations, by a separate or integrated reader, in a very regular manner, since the one or more resonators remain in a very stable position relative to the object or system thus embedded.

[0077] According to one particular feature, the object or system includes at least one probe arranged to communicate via inductive coupling with a multi-frequency resonator, said multi-frequency resonator and said probe being arranged to form a characterization system as disclosed herein or to be implemented in a characterization method as disclosed herein.

[0078] Various embodiments of the invention are provided that incorporate any of the various features described herein in all possible combinations. [Brief description of the drawings]

[0079] Other features and advantages will become apparent from the detailed description of entirely non-limiting embodiments and from the accompanying drawings, in which: [Figure 1a] FIG. 1a is a scaled top view of a multi-frequency resonator according to an exemplary embodiment of the present invention, illustrating a resonator having four nested single-turn circular meshes. [Figure 1b] FIG. 1b is a scaled top view of a multi-frequency resonator according to an exemplary embodiment of the invention, illustrating a resonator having eight nested single-turn circular meshes. [Diagram 2] 2 is a scaled top view showing a multi-frequency resonator having four nested circular meshes, one of which is single turn and the others are multi-turn, according to one exemplary embodiment of the invention. [Figure 3a] FIG. 3a is a partial schematic top, cross-sectional and exploded perspective view of an example of a single-turn circular element transmission line (or TLR) that can be used in a multi-frequency resonator according to one exemplary embodiment. [Figure 3b] FIG. 3b is a diagram illustrating an example of a single-turn circular element transmission line (or TLR) that can be used in a multi-frequency resonator according to one exemplary embodiment, and is a circuit diagram of the interaction between the TLR, inductive control loop, and vector network analyzer of FIG. 3a taken individually. [Figure 4] Figure 4 shows a partial schematic top view and cross-sectional view of a multi-gap element transmission line (or TLR) partially having six circular transmission lines, each of which has a decreasing radius and is arranged concentrically with respect to each other and offset by 60°. Each line is formed by two tracks arranged on one of the two faces of an insulating thin substrate, the two tracks facing each other and offset angularly with respect to each other. [Diagram 5]FIG. 5 is a scale perspective view of a test bench for characterizing the liquid contents of an insulating container by interrogating through the bottom wall of the container using the resonator of FIG. 1b having eight resonant frequencies. [Figure 6] FIG. 6 is an equivalent circuit diagram of a resonator with three resonant frequencies, showing its interaction with the probe and the medium being characterized. [Figure 7] FIG. 7 shows curves of the modulus of the measured impedance Zmes with frequency for the eight resonators of FIG. 1b, with a close-up of the overall and low intensity peaks. [Figure 8] FIG. 8 shows curves for the four resonators of FIG. 1a at no load, showing the real part of the measured impedance Zmes versus frequency, according to a simulation. [Figure 9] FIG. 9 shows simulated curves similar to those of FIG. 8 for the eight resonators of FIG. 1b. [Figure 10] FIG. 10 is a graph showing a comparison of experimentally obtained resonant frequencies, semi-analytically modeled resonant frequencies, and simulated resonant frequencies, where FIG. 10(a) is a graph showing the case of the four-frequency resonator of FIG. 1a, and FIG. 10(b) is a graph showing the case of the eight-frequency resonator of FIG. 1b. [Figure 11] FIG. 11 is a graph showing, separately for each of the four meshes of the four-frequency resonator of FIG. 1a, the induced resistance as a function of the conductivity of the medium to be characterized, formed by an aqueous solution of NaCl. [Figure 12] FIG. 12 is a flow chart that illustrates a schematic of the operation of a characterization method according to some exemplary embodiments of the present invention. [Figure 13] 13 is a top view of a multi-frequency resonator with four frequencies interrogable by the same probe, in accordance with an exemplary embodiment of the present invention, where the resonator includes two meshes nested within each other and two other meshes that are not nested. [Figure 14]Figure 14 is a top view showing a multi-frequency resonator interrogable by the same probe, in an exemplary embodiment of the invention, where the resonator includes three separate groups, each containing four transmission lines nested within each other. [Figure 15] FIG. 15 is a cross-sectional view of one embodiment of the present invention for non-contact characterization of the contents of a magnetic field permeable container. [Figure 16] FIG. 16 is a cross-sectional view of an exemplary embodiment of the present invention for non-contact characterization of the contents of a container with a resonator embedded in the thickness of its wall. [Figure 17] FIG. 17 is a cross-sectional view of an exemplary embodiment of the present invention for non-contact characterization of the condition of the inner surface of a tank having multiple resonators embedded in its wall. [Figure 18] FIG. 18 illustrates the use of a matrix device including multiple multi-frequency resonators, each with its own individual probe, to characterize an in vivo organism, both graphically and over time, in accordance with an exemplary embodiment of the present invention. [Figure 19] 19 is a cross-sectional view illustrating the use of a device including a multi-frequency resonator and its unique individual probes to monitor the time course of a biological object undergoing degradation (in this example, a veal steak), according to an exemplary embodiment of the present invention. [Figure 20] FIG. 20 is a graph showing the inductance induced in the object of FIG. 19 versus time. [Figure 21] FIG. 21 is a graph showing the resistance induced in the object of FIG. 19 versus time. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] Detailed Description and Exemplary Embodiments with Reference to the Figures The WMFR itself is a passive structure consisting of a combination of split transmission-line resonant passive structures, which can be represented by as many coupled RLC circuits as there are transmission lines implemented. These individual transmission lines are referred to herein as TLRs (transmission-line resonators), or "meshes" because they correspond to a circuit mesh in an equivalent circuit diagram such as Figure 6.

[0081] Figures 1a and 1b show examples of multi-frequency resonators according to embodiments of the present invention. Figure 1a shows an example of a multi-frequency resonator MR1 having four nested concentric single-turn lines M11-M14. Figure 1b shows an example of a multi-frequency resonator MR2 having eight nested concentric single-turn lines M21-M28.

[0082] FIG. 2 shows another example of a multi-frequency resonator MR3 having four nested concentric lines M31-M34, one of which, M32, is single turn and the others, M31, M33, M34, are multi-turn.

[0083] Figure 3a shows the three-dimensional arrangement of one of the transmission lines of such a resonator, in this case the largest single-turn line M14 of the resonator of Figure 1a. As can be seen from the cross-section, this "transmission line", considered here as a single element, is formed by two interrupted (or "open") circular tracks, one circular track disposed on each of the two faces of a thin dielectric or insulating substrate (in this example, a flexible Kapton substrate). Each open track in the line has an interruption or space, referred to herein as a "gap", e.g., referenced G14 for this line.

[0084] The transmission line may be fabricated as a single track, but for greater efficiency it is preferably arranged in face-to-face groups of equal sized tracks.

[0085] In embodiments with two (or more) tracks, they are preferably planar and parallel to each other and / or radially identical, here ensured by arranging them on both sides of the substrate, although any other technical solution allowing this arrangement to be obtained can also be used.

[0086] Typically, the various tracks forming the same transmission line are arranged opposite each other such that their respective gaps are angularly offset from one another. In this example, the gap G14 in the upper track (which is referred to here as M14, as is the transmission line to which it belongs) is located facing the solid part of the opposite track M14'. Similarly, the gap G14' in the lower track M14' is arranged facing the solid part of the upper track M14. Preferably, each of the gaps is located as far as possible in angle from one or more gaps in the opposite track, in this case diametrically opposed.

[0087] The offset between the two faces allows for differential mode compensation, resulting in maximization of the common mode current, as opposed to conventional resonators which attempt to minimize the common mode current.

[0088] These two tracks together form a single transmission line M14 with a single resonant frequency, which is determined inter alia by the geometry of these tracks.

[0089] FIG. 4 shows another example of a transmission line M1 operating at a single resonant frequency, called multi-opening or "multi-gap". Each face of the substrate d1 has a track M1 (and M1') consisting of multiple parts that are not connected to each other. In this example, there are six parts M1a-M1f, which are partially circular with decreasing radius, arranged concentrically with each other and offset by 60°. Each of these parts is formed by two tracks arranged on one of the two faces of the insulating thin substrate, facing each other and angularly offset. Each track has a gap, for example the gap of the track M1a is G1a. On the opposite face of the substrate, the associated multi-part track M1' has the same arrangement of six parts, but its gaps are angularly offset with respect to the gaps of the multi-part track M1. Thus, the gap G1a' of the part M1a' of the face shown on the right is offset by 30° with respect to the gap G1a of the other face. Each of these gaps G1a and G1a' thus faces a solid part of the opposite track. This design has multiple track sections that are not connected to each other, but their nested arrangement allows them to operate together as a single transmission line with a single resonant frequency. This multi-section or multi-opening line can also be used in place of a single section line, as one of the lines of a multi-frequency resonator, and in any of their possible combinations.

[0090] Figure 6 shows a circuit diagram of the interaction illustrating the implementation of this type of structure in an experimental setup combining, on the one hand, a vector analyzer connected and, on the other hand, a remote excitation / read coil placed in the vicinity of the medium under investigation (see Figures 5 and 15-19).

[0091] The analytical models were validated experimentally and by finite element numerical modeling from HFSS. The complete models allow the WMFR to be sized and the desired spectroscopic response to be selected. They also allow the extraction of the impedance induced in the environment surrounding the WMFR resonator, which represents a complex dielectric property. These models were verified by a test bench with an accuracy of a few percent.

[0092] The step of extracting the inductive impedance of the medium around each resonant frequency is carried out using a complex fitting algorithm for fitting between the interaction model derived from the diagram in Figure 3a and the measured data. As an example, we show the conductivity spectrum of an organic medium (veal steak) left at room temperature for 5 days, measured using a WMFR with 8 resonances between 20 MHz and 350 MHz (Figure 5). The conductivity as a function of frequency and time is observed.

[0093] [Modeling and Resonance of Element Transmission Lines (TLR)] The resonance conditions of this elemental transmission line, or TLR, can be determined from a semi-analytical model that includes the components and geometry of the resonator.

[0094] For example, for a circular single-turn transmission line (TLR) as in FIG. 3a, the following components and geometries are used: - Outer diameter: R ext - Track width: d - Conductor thickness: th cond - Dielectric thickness: th dielec

[0095] For circular, multi-turn transmission lines such as lines M31, M33, and M34 of resonator MR3 in FIG. 2, other parameters must also be taken into account: - Number of turns: N t - Track distance - Number of openings (gaps): n

[0096] The set of these parameters contributes to the resonance condition of the element transmission line and is written according to the following equation:

[0097]

number

[0098] During the ceremony, - "ω" is the angular frequency - "n" is the number of openings - "Λ" is the equivalent total inductance of the resonator - "Z" is the characteristic impedance of the transmission line - "E re " is the effective dielectric constant of the line - "x l " is the average track length - "c" is the speed of light in a vacuum

[0099] Based on this relationship and on the basis of the studies carried out in

[22] ,

[23] ,

[24] and

[25] (described in the appendix) which allow to determine the coupling between the transmission lines and the characteristic impedance, it is possible to determine the resonant frequency of the TLR, its total inductance L et , and the equivalent capacitance C can be determined in advance. Such a semi-analytical model (SAM) was written here in the Matlab environment.

[0100] On this basis, it is possible to complete the equivalent RLC circuit diagram of this element resonator by estimating the overall equivalent resistance R based on considerations of the track geometry, especially the conductors used, and the surface condition of the track, as we have shown in

[26] (listed in the appendix), although the latter determination remains quite empirical.

[0101] In order to fully characterize the element resonator, and to obtain better accuracy for the determination of R, it is proposed here to derive the equivalent resistance R from measurements of the resonance quality factor Q.

[0102] The implementation of such a TLR (single line resonator) as a resonant inductive sensor has been described and published by the inventors in

[12] ,

[26] and

[27] (listed in the attached documents). The implementation consists of exciting the resonator by inductive coupling using a remote control loop connected to a vector network analyzer (VNA, e.g. HP4195A analyzer), as shown in Figure 5.

[0103] The VNA sends out a high-frequency signal that powers the excitation loop. The magnetic flux from this loop induces, by magnetic coupling, a current in the track of the nearby TLR, the strength of which increases the closer it is to the resonance of the TLR. Conversely, the TLR generates a magnetic field, which "modifies" the behavior of the loop and induces a change in its impedance. Since the loop is connected to the VNA, it is possible to measure its impedance near the resonance frequency of the TLR. From this analysis, it is possible to extract information about the magnetic interaction between the TLR and its immediate environment, via a non-contact inductive coupling. This loop can be considered as a control probe that excites and "reads" the TLR by its simultaneous excitation and measurement. Thus, as explained in

[26] , the idea is to transmit as much power as possible by the probe without the coupling between the probe and the TLR interfering with the operation of the TLR. Therefore, the probe is sized to operate below its self-resonant frequency (staying in the frequency range where it is purely inductive), its diameter is smaller than the inner diameter of the TLR it interacts with, and it is placed at a close distance to the TLR to ensure sufficient coupling with the TLR. All the interactions that occur between the TLR, the control probe, and the VNA are summarized in the equivalent circuit diagram in Figure 4.

[0104] This diagram in Figure 4 shows two magnetically coupled electrical meshes. One of the meshes, Z1, corresponds to a TLR that is modeled as a resonant circuit with distributed constants L1, C1, and R1. It has a total impedance Z S Circuit L s and R s The probe is inductively coupled to the probe, whose element is experimentally determined and can be written as: Z S =R S +j2πfL

[0105]

number

[0106] The current in the branch associated with the resonator is denoted by i1, and the voltage across its terminals is denoted by v1. For the branch corresponding to the probe, s and v s The coupling coefficient between the two circuits is k S1 The probe is connected to the RF source of the VNA and has an impedance between its terminals, Z mes This can be easily explained from the different elements of the diagram in Figure 4 according to the following equation, according to reference

[26] :

[0107]

number

[0108] This formula allows predicting the behavior of a TLR-probe combination depending on the frequency used.

[0109] The interaction between the excitation probe and the TLR can also be modeled using numerical calculations carried out using the finite element numerical modeling software distributed under the name "HFSS" by Ansys, Inc. These simulations also make it possible to determine the resonant frequency of a TLR with a given geometry and set of parameters through this calculation of the frequency response of the system.

[0110] Experimental measurements were performed on two batches of six single-turn and single-opening TLRs fabricated and varnished as two-layer printed circuit boards (PCBs) on flexible Kapton substrates. The substrates had a relative dielectric constant of ε r = 3.4, thickness th diel = 50μm, the conductor used for the transmission line has a thickness of th cond = 35 μm of copper.

[0111] The various TLRs in the two batches differ from each other in track width and outer diameter.

[0112] For each of the 12 TLRs considered, we determined the expected theoretical resonant frequency using the analytical model (SAM) described above. Furthermore, the resonant frequencies of the various fabricated TLRs were measured. Two series of measurements were performed. In batch 1, the probe was a loop of 11 mm diameter, circular in cross section and made of 1.5 mm copper wire, placed at a distance of 5 mm from the TLR. In batch 2 of the element resonators, the loop was of the same type but with a diameter of 14 mm, and the distance between the loop and the TLR was kept the same.

[0113] The four TLRs in batch 1 have the following characteristics:

[0114] [Table 1]

[0115] The eight TLRs in batch 2 have the following characteristics:

[0116] [Table 2]

[0117] Numerical simulations of the TLRs using HFSS have also been performed, showing overall very good agreement between the expected theoretical resonant frequencies (according to SAM) and the measurements: in fact, for both batches, the average deviation observed is less than 6%.

[0118] Finally, numerical simulations using HFSS of a TLR excited by a probe with the same size and distance parameters as the experimental tests were performed. The calculated impedance spectra allowed to extract the resonant frequencies of the considered set of TLRs and probes. Again, a very good fit was observed between the HFSS simulation results and the experimental measurements, with an average deviation of less than 10%.

[0119] In conclusion, a comparison was made between the TLR model and experimental measurements for the element resonator. They showed that both models used (semi-analytical "SAM" and numerical "HFSS") are relevant for the study of the behavior of TLRs, especially in the frequency range from 20 MHz to 300 MHz. Moreover, although the semi-analytical model used does not take into account the presence of an excitation coil in the calculation of the resonant frequency of the TLR, the latter determination remains very close to the experimentally observed one. This indicates that the influence of the excitation coil on the characteristics of the TLR is small, which is advantageous in terms of simplification from a practical point of view.

[0120] [Multi-frequency non-contact resonator (WMFR)] In the example presented here, a non-contact resonator (WMFR) is formed of a multiple element resonator, or TLR, with a common substrate. This WMFR consists of conductive open tracks, for example made of copper, deposited on either of two opposing faces of a low dielectric loss substrate (for example Kapton, or FR4). The configuration of these tracks relative to each other (length, spacing, thickness, type of conductor, gap width) and the type of substrate used (loss, thickness) determine the different resonant frequencies associated with the various components of the WMFR, which can range from a few MHz to hundreds of MHz depending on the geometry chosen, thereby covering a very wide frequency spectrum in the RF range. Thus, many geometric arrangements of the conductive tracks of the WMFR are conceivable, thus offering a wide range of diverse performance levels suited to different applications. The position of the gaps in the various coupled transmission lines that make up the WMFR does not affect the resonant frequencies observed. It is preferable to have the gaps distributed uniformly in order to homogenize the magnetic flux generated by the WMFR, if necessary.

[0121] WMFR is based on the combination of multiple element TLRs, all excited by the same probe. When N TLRs arranged in this way are excited by a probe, all the magnetic couplings involved can be represented using the equivalent circuit diagram in Figure 5.

[0122] In this equivalent circuit diagram, each of the N elements TLR has a coupling coefficient k Sj (j∈{1,2,...,N}) with a coupling coefficient k mn (m ≠ n and (m,n) ∈ {1,2,...,N}) are magnetically coupled to each of the other TLRs. In each branch, the current flowing through it is i j and the voltage between each terminal is v j The interactions among the N+1 meshes in Fig. 5 can be written in the form of a matrix system inspired by

[15] .

[0123]

number

[0124] In the formula, when a ≠ b,

[0125]

number

[0126] and

[0127]

number

[0128] It is.

[0129] TLR j The equivalent electrical parameter L j and C j is calculated analytically via the semi-analytical model SAM as described above, and the resistance R j is the quality factor Q of each element TLR taken individually j The mutual value M between the two resonators is estimated from the measurement of ab , ((a,b)∈{1,2,...,N}) are determined using the analytical formula in

[25] , and the mutual interaction value M Sj is determined using the literature

[24] . Now that all the elements of the matrix system of equations (1.3.2.1) have been determined, we can invert the system to obtain

[0130]

number

[0131] In the formula, element y ij are the coefficients of the inverse matrix, which are of the same order as the admittance. Impedance Z mes can be extracted from equation (1.3.2.2) as follows:

[0132]

number

[0133] As an example, Figure 7 shows the impedance Z seen by the excitation coil, analytically determined using Equation 1.3.2.3, for a WMFR consisting of the combination of eight TLRs from batch 2 forming the eight-line multi-frequency resonator MR2 (or “WMFR-8”) of Figure 1b. mes The numerical results are shown below.

[0134] Therefore, Figure 7 shows the Z mes The presence of eight resonance peaks at eight resonance frequencies fr1 to fr8 is observed, reflecting the contributions of the eight TLRs that make up WMFR-8.

[0135] [Coexistence of TLR within WMFR] HFSS simulations were used to study how the element TLRs in the WMFR enter into resonance. For this, the surface distribution of currents in the vicinity of the resonance frequencies of the various TLRs was calculated. In the case of the multi-frequency resonator MR1 (or WMFR-4) in Fig. 1a, the current densities were calculated for four operating frequencies: 20 MHz, 45 MHz, 90 MHz and 206 MHz. It can be seen that for each of these selected operating frequencies, the strongest current passes through the TLR whose theoretical resonance frequency is closest to the operating frequency. Thus, this simulation clearly shows that each TLR constituting the WMFR is indeed selectively "activated" by the excitation coil when the latter is operating at the correct tuning frequency (close to but different from its natural resonance frequency).

[0136] This confirms that, despite the existence of coupling between the element TLRs, multiple different TLRs can coexist within a WMFR without compromising their respective resonances.

[0137] [Complex impedance of WMFR] The complex impedance Z of the two WMFRs under consideration mesTwo broadband HFSS simulations were performed to determine, This was calculated for the bench in Figure 5 without load, i.e. without any vessel or medium under investigation.

[0138] Figure 8 shows the results of the real part of the impedance measured as a function of frequency for the multi-frequency resonator MR1 with four element transmission lines (i.e. WMFR-4 type) of Figure 1a. The geometric characteristics are those of the four TLRs of batch 1 mentioned above, namely M11, M12, M13, M14.

[0139] Figure 9 shows the results of the real part of the impedance measured as a function of frequency for the multi-frequency resonator MR2 with eight element transmission lines (i.e. WMFR-8 type) of Figure 1b. The geometric characteristics are those of the eight TLRs of batch 2 mentioned above, namely M21, M22, M23, M24, M25, M26, M27, M28.

[0140] These simulations also show that the resonances of the various TLRs involved are clearly observable, one peak per TLR, and linking them in the form of a WMFR does not destroy their individual resonances.

[0141] These results show that it is possible to predict the behavior of the multi-resonant system formed by the WMFR: useful information is thus extracted from the difference between the unloaded impedance and the impedance in the presence of the medium under investigation.

[0142] [Test bench] Figure 5 shows two examples of WMFRs MR1 ​​and MR2 with four and eight resonances shown in Figure 1a and Figure 1b, respectively, with the same parameters as in the simulation, i.e., the relative dielectric constant ε r = 3.4, thickness th diel = 50 μm substrate, and thickness th cond Figure 1 shows the test bench used to implement the design with a = 35 μm element transmission line (TLR). The inductive loop parameters are the same as above.

[0143] The first, WMFR-4, consists of four MTLRs from batch 1, and the second, WMFR-8, consists of eight MTLRs from batch 2. Experimental implementations were carried out in a wide frequency band ranging from a few MHz to 400 MHz.

[0144] As in the case of the model, the presence of resonance peaks that could be attributed to each TLR that composes the WMFR is observed. Moreover, when comparing the observed resonance values ​​for the two WMFRs with those provided by the semi-analytical model SAM shown above (the matrix of equation (1.3.2.1) gives equation (1.3.2.3)), and the numerical (HFSS) model, a very good fit between the experimental and model values ​​is again observed. Indeed, for WMFR-4, an average deviation of 8% is observed between the data determined by HFSS and the measured data, and an average deviation of about 4.5% is observed between the analytical model and the measurements in Table 1. For WMFR-8, these average deviations are about 8% and 9%, respectively, in Table 2.

[0145] FIG. 10 shows, in the form of curves, a comparison of the frequency peaks observed for the various TLRs of each multi-frequency resonator MR1 and MR2.

[0146] These results show that it is in fact quite possible to exploit the resonances of different MTLRs that compose a WMFR: the observed resonant frequencies of the multi-frequency resonator are slightly different from the resonant frequencies of the TLRs taken alone, due to the coupling that occurs between these TLRs.

[0147] However, it is entirely possible to predict these couplings through analytical or numerical modeling, and thus the resulting resonant frequencies observed for WMFRs.

[0148] Furthermore, it should be noted that these couplings do not negate the resonant properties of the TLRs that make up the WMFR (single turn in this case). They all have resonant frequencies that can be determined in advance and quality factors that are close to those measured with a single TLR. It is therefore entirely conceivable to use WMFRs as multi-frequency resonators in a manner similar to a single TLR for characterizing dielectric media.

[0149] For the WMFR-4 and WMFR-8 measured at no load, the observed resonant frequencies and characteristics are as follows:

[0150] [Table 3]

[0151] [Table 4]

[0152] [Methods for characterizing dielectric media] For non-contact multi-frequency characterization of an electrical medium, the implementation places the WMFR assembly MR2 and excitation coil S1 in close proximity to the dielectric medium 91 to be characterized, and measures the impedance Z over a wide frequency band using a VNA from the excitation coil. mes Measure.

[0153] 5 shows the placement of a WMFR in the presence of a homogeneous dielectric medium 91 contained in a container such as a glass dish 81. An excitation coil S1 is placed as a probe. A network analyzer (VNA) S0 is connected to this probe to provide (102) an excitation current and measure (104) its impedance.

[0154] The characterization of this dielectric medium is possible through the relationship between the dielectric properties of the medium surrounding the WMFR and the magnetic field induced in it by the WMFR. It has been established, especially in the literature

[16] , that the complex dielectric properties of an organic medium are very good indicators of its physicochemical or pathophysiological state. These properties express how the medium dissipates the electromagnetic energy transmitted to it, via its electrical conductivity σ (S / m), and how it stores the transmitted energy, via its relative permittivity εr (dimensionless), as described in the literature

[28] . The evaluation of these dielectric properties by frequency, especially in the high frequency range (from a few MHz to several hundred MHz), is particularly relevant in providing information on the state of the organic matter, as described in the literature

[29] . The relationship between the dielectric properties of the medium and the magnetic field radiated by the WMFR is, according to the literature

[30] , expressed as the impedance Z of the investigated medium, m It is expressed by the formula:

[0155]

number

[0156] In the formula, Z m corresponds to the impedance of the dielectric medium, σ is the electrical conductivity, ε r is the relative dielectric constant, ε0 is the dielectric constant of a vacuum,

[0157]

number

[0158] is the vector potential associated with the magnetic field generated by the WMFR, I is the current through the WMFR, and ω is the angular frequency. Conversely, the magnetic field, and therefore the impedance of the WMFR, is modulated by the surrounding dielectric medium.

[0159] The configuration of FIG. 5 can be represented diagrammatically by the equivalent electrical circuit shown in FIG.

[0160] This equivalent circuit diagram shows the WMFR MR2 and its various components: the TLRs M21-M28, the excitation coil S1 connected to the VNA S0, and the complex impedance R m , L m This summarizes the magnetic and electrical interactions occurring between the various interrelated elements of the dielectric medium modeled by

[81] . As in the case of TLRs interacting with a dielectric medium, a simplifying assumption can be made that the excitation coil is not directly coupled to the medium, as described in

[31] .

[0161] However, each TLR in the WMFR has a coupling coefficient k mj The TLRs are then coupled to the medium via the excitation coil and the other TLRs as described above. The coupling between the various TLRs and the medium is then j The impedance of the branch related to R j , L j , C j The complex impedance Z induced by the medium applied to mj We further simplify by assuming that the matrix representing all connections can be written as

[0162]

number

[0163] In the formula, when a ≠ b, M ab =M ba and

[0164]

number

[0165] and

[0166]

number

[0167] It is.

[0168] By inverting this matrix system for all frequencies in the range, we obtain the impedance Z mes Furthermore, it is possible to extract narrow frequency bands B j By noting that, we can easily express the impedance "seen" by the excitation coil, considering only the "active" branch in this frequency band. j Impedance Z at mes is expressed as follows:

[0169]

number

[0170] In practice, the parameters of the medium induced in each branch R mj and L mj For each frequency band, B j Z measured at mes can be estimated using a complex fitting algorithm for fitting between the experimental data of and the model of equation (1.3.5.3) for the same frequency band, where the quantity R j , L j , C j and Z S (unloaded probe impedance) is pre-determined. Now, as described in

[12] , the element R at the resonant frequency of the TLR in question is mj and L mj The value of is related on the one hand to the dielectric properties of the medium (i.e., its electrical conductivity (σ)) and on the other hand to the dielectric permittivity (ε r ) which in turn is related to the induced impedance at N resonant frequencies in the WMFR, by using equation (1.3.5.3) it is possible to derive therefrom information about the dielectric parameters of the medium at as many analysis frequencies as there are resonators in the WMFR.

[0171] [Characterization of NaCl aqueous solution] FIG. 11 shows separately for each of the four meshes of the four transmission lines of the four-frequency resonator MR1 of FIG. 1a the resistance induced as a function of the conductivity of the medium to be characterized, formed by an aqueous solution of sodium chloride.

[0172] The solutions used are conductive saline solutions (deionized water + NaCl) in various proportions to obtain a medium with electrical properties (electrical conductivity or dielectric permittivity) that are adjustable and shown in the table.

[0173] Each of these solutions is placed in turn in a glass dish 81 with a fixed volume of 700 ml. For each solution, multiple Z mes A measurement is taken.

[0174] After implementing the WMFR for all of the calibrated dielectric solutions, the complex impedance induced by the medium around each resonant frequency (element R i and L i ) is estimated.

[0175] For each resonant frequency of the multi-frequency resonator, the results already observed for a simple MTLR are returned. On the one hand, the resistance induced in the medium R i On the other hand, there is a linear relationship between the change in the inductance L induced in the medium and the electrical conductivity of the medium. i There is a linear relationship between the dielectric permittivity of the medium and the dielectric constant of the medium. These linearities are graphically highlighted by the curves in Figure 11.

[0176] Therefore, WMFR-4 has two parameters of interest, L i and R i Through extraction of the , it is observed that the ,frequency is sensitive at each resonance to very small changes in the ,permittivity and conductivity in homogeneous media.,Similar results are observed for the WMFR-8.

[0177] Thus, a WMFR with N element transmission lines forms a device that allows for N simultaneous analyses of a medium, correspondingly enriching the dielectric characterization of the medium.

[0178] The invention is therefore particularly advantageous for the analysis of organic media whose variation with frequency in their dielectric parameters is known to be a particularly relevant marker of their physicochemical state, or pathophysiology.

[0179] [Research into changes in meat pieces] As shown in Fig. 19, such a multi-frequency resonator and its individual probes S1 can be used to investigate the electrical properties of objects placed in a container without contacting or accessing the inside of the container, such as the case for example of food products 94 moving on a conveyor of an agricultural production chain as they pass over a resonator MR2 integrated or attached to a support 61. The contactless investigation capability in depth thus allows the product 94 to be investigated to a considerable depth, as shown by the region R3.

[0180] As a validation test, the multi-frequency resonator MR2 (WMFR-8) in Figure 1b was used to study the decomposition of a veal steak (15 cm long, 2 cm thick, and 7 cm wide). The steak was placed in the glass dish shown in Figure 5 and then subjected to a Z mes was measured on days 0, 1, 2, and 5. By day 5, the steaks were in an advanced state of degradation with changes in appearance visible to the naked eye, including the presence of liquid, and changes in shape and color.

[0181] Figure 20 shows the inductance L induced in the steak over time and for different frequencies. i This provides this information for different depths in the investigated region R3. Figure 21 shows the induced resistance R i , and a similar curve showing

[0182] The advantage of such a multi-frequency measurement can be seen in Figures 20 and 21. In fact, these two figures show the relationship between the two parameters of interest, R i and L i These, as is well known, are the σ and ε r It is observed that the dielectric properties of the veal steak change with the length of decomposition. In fact, the induced inductance value L for each frequency i appears to increase with time and frequency with relatively significant differences. Similarly, the induced resistance R i For , we can see a very clear difference between the D+5 curve and the other curves, especially at the lowest frequency of 22MHz, and not so much at the highest frequency. Furthermore, from D+1 to L i and R i A change in the D+5 curve becomes evident, which becomes more pronounced over time, and it can be seen that the curve for D+5 is very different from the others. Thus, the decomposition phenomenon can be monitored by the WMFR from the very beginning and continued until the advanced stages. These results confirm that this WMFR multi-frequency sensor is capable of non-invasive and non-contact monitoring of the properties of organic dielectric media in real time.

[0183] FIG. 12 shows an example of how such a multi-frequency resonator MR1 can be implemented for different characterization applications, for example as shown in FIG.

[0184] The resonator is positioned (101) at a suitable distance from the region to be investigated, e.g. removably or embedded in a nearby object. Before or at the time of the measurement, the inductive part of the probe S1 is temporarily or permanently positioned at a suitable distance from the resonator MR1, e.g. so that it is itself embedded.

[0185] The probe S1 is excited by the reader S0 in order to obtain an inductive coupling (102) between the probe and the resonator MR1, which performs a measurement (104) of the complex impedance of the assembly formed by the resonator MR1 and the region under investigation R1.

[0186] This complex impedance is spectrally processed to obtain individual impedances Zm1 to Zm4 measured for each measurement frequency fm1 to fm4.

[0187] From these individual impedances Zm1-Zm4, individual electrical properties P1-P4 of the medium in the region of interest for different measurement frequencies fm1-fm4 are extracted (105), for example by combining the method described herein with methods described in the accompanying literature or known to those skilled in the art.

[0188] These individual electrical properties are then used to characterize the medium 91 in the region of interest R1, for example based on known data or relationships, or by comparing or calibrating with known data or recorded data for calibration, for example using known statistical methods for processing with reference data, in particular neural networks.

[0189] 13 and 14 show other embodiments of a resonator and a probe inductively coupled thereto. In these examples, spatially separate, non-nested individual transmission lines (TLRs) are coupled to the same probe S2.

[0190] In this example, the probe S2 includes a single inductive circuit that is formed from a number of separate portions S21, S22, S23, which can be visually likened to the petals of a daisy.

[0191] In FIG. 13, the multi-frequency resonator MR4 has two single-turn circular lines M42 and M41, separate from each other, and two other single-turn circular lines M43 and M44, concentric with each other and separate from the other two. These four lines M41-M44 are spatially divided into three groups, typically on the same plane, each having a different individual resonance and thus able to interact with the medium under investigation in three different sub-regions. This arrangement makes it possible to use a large number of different lines, without being limited by their size as would be the case, for example, if they were arranged concentrically with each other. These different groups are each placed on the axis of one of the petals of the probe S2, exciting and measuring them strictly simultaneously. Thus, these four element transmission lines together form a single four-frequency resonator MR4, or WMFR-4.

[0192] In FIG. 14, the multi-frequency resonator MR5 has three groups M511, M512, M513 with four single-turn circular lines that are different from each other and concentric with each other. These different groups M511, M512, M513 are each located on one axis of the petals of the probe S2, which excites and measures them strictly simultaneously. Thus, these three groups together form a single resonator MR5 with four frequencies, or WMFR-4, if these three groups are identical. This arrangement makes it possible to investigate a larger area with the same frequencies. If the three groups are different from each other, for example in terms of thickness, material, or spacing of the tracks, this arrangement also makes it possible to combine a larger number of frequencies. In this case, up to 12 frequencies can be combined.

[0193] Any type of TLR can be combined in this type of arrangement to create a single multi-frequency resonator, provided that they are coupled to a single identical probe, thereby having their overall impedance measured via a single channel. EXAMPLES

[0194] In the embodiment of Fig. 15, the resonator MR1 is used for contactless characterization of the contents 91 of a container 81 that is permeable to magnetic fields, for example a non-magnetic or thin container. In this embodiment, the resonator MR1 is mounted on a fixed support 61 over which the different containers whose contents are to be characterized, for example for quality control or identification, pass. The resonator allows contactless characterization of an area R1 of each container 81 that passes successively over it.

[0195] 16 shows one implementation in which the resonator MR1 is integrated into the container 82, in this case embedded in its wall. In this way, it is possible to monitor the region R2 of the contents 91 at any point in the course of its evolution, without opening the container 82.

[0196] FIG. 17 shows one implementation in which a number of multi-frequency resonators MR7a-MR7h are embedded in a wall of a tank (e.g. tank 83 for fuel 92 closed with cap 831) at multiple locations. These multi-frequency resonators are excited by a series of probes S7a-S7h, respectively, which are for example integrated in a continuous plate or embedded or attached to the outer wall of the tank. These resonators are sized and positioned to characterize the medium present in a series of regions R7a-R7h, which for example cover the region of the interface between the tank wall and the fuel. Periodically or permanently characterizing these interface regions makes it possible to monitor the presence or changes of any bacterial film 928 that may occur or promote corrosion at any corrosion points.

[0197] Figure 18 shows one implementation where a matrix device containing multiple multi-frequency resonators MR8a-MR8h, each with its own individual probe S8a-S8h, is placed implanted in a living organism (in this case a mouse 93). If desired, the probes can also be placed in a separate device and the resonators can also be directly implanted in the mouse's body. Such a system allows a graphical characterization of the time evolution of all or part of the mouse's body by a matrix arrangement of resonators, each investigating a different region R8a-R8h. For example, the diffusion of an injected compound anywhere in the organism or the time evolution of the state of a particular organ can be monitored and visualized. Such an implantation configuration allows the device to be worn on the mouse and its parameters monitored throughout the day during the mouse's waking activity.

[0198] [References] References

[22] E. Hammerstad and O. Jensen, “Accurate Models for Microstrip Computer-Aided Design.,” IEEE MTT-S International Microwave Symposium Digest, vol.1, no.12, pp.107‐409, 1980, issn: 0149645X.doi: 10.1109 / mwsym.1980.1124303. Reference

[23] Y. Luo, X. Wang, and X. Zhou, “Inductance calculations for circular coils with rectangular cross section and parallel axes using inverse mellin transform and generalized hypergeometric functions,” IEEE Transactions on Power Electronics, vol.32, no.2, pp.1367‐1374, 2017, issn: 08858993. doi: 10.1109 / TPEL.2016.2541180. Reference

[24] B.C.R. Paul, “The concept of “partial” inductance,” pp.195‐245, Reference

[25] J.T. Conway, “Analytical solutions for the self-and mutual inductances of concentric coplanar disk coils,” IEEE Transactions on Magnetics, vol.49, no.3, pp.1135‐1142, 2013, issn: 00189464. doi: 10.1109 / TMAG.2012.2229287. Reference

[26] (Non-patent Document 9) G. Masilamany, P.Y. Joubert, S. Serfaty, B. Roucaries, and Y. Le Diraison, “Radiofrequency inductive probe for non-contact dielectric characterizations of organic medium,” Electronics Letters, vol.50, no.7, pp.496‐497, 2014, issn: 00135194. doi: 10.1049 / el.2014.0558. [Online]. Available: http: / / digital-library.theiet.org / content / journals / 10.1049 / el.2014.0558.

Claims

1. 1. A method for characterizing at least one region in a medium to be characterized, comprising at least the following steps: a step of simultaneously inductively coupling (102) a probe to a number of transmission lines (M11-M14, M21-M28) arranged to have mutually different resonant frequencies (fr1-fr8), in a non-contact manner, said transmission lines together forming a multi-frequency resonator, which is located in the vicinity of the area under investigation but does not necessarily have to be in contact with the area under investigation, said transmission lines interacting with the area under investigation (and usually with each other); - measuring (104) said change in impedance of said multi-frequency resonator using a reader interacting with said probe; - processing (103) the measurements of said impedance changes, including a spectral analysis (103) as a function of frequency, thereby determining a number of individual impedances (Zm1-Zm8) measured for a number of measurement frequencies (fm1-fm8, respectively); - processing (104) one or more of said individual impedances to extract one or more electrical properties of said area of ​​interest; The method includes:

2. 2. The method of claim 1, wherein the individual impedances, or the respective electrical properties extracted therefrom, of a plurality of different resonant frequencies are combined to provide a characterization of the investigated area at different distances from the multi-frequency resonator.

3. 3. The method of claim 1 or 2, wherein the individual impedances, or the respective electrical properties extracted therefrom, of a number of different resonant frequencies are combined to provide a more accurate characterization of the same portion of the investigated area.

4. The method according to claim 1 or 2, which is used to generate a plurality of characterizations at different time points, thereby providing monitoring over time of an area of ​​investigation (R3, R71-R7h, R8a-R8h) in which at least one material or object is being changed (931).

5. 3. A method according to claim 1 or 2, comprising implementing one or more multi-frequency resonators (MR1, MR7a to MR7h, MR8a to MR8h) integrated or embedded in an object (61, 82, 83) or a system for characterizing an area of ​​interest, said area of ​​interest includes materials belonging to said object (82) and / or materials (92, 93) in contact with said object (61, 83) or in said vicinity (931) and / or an interface (928) between said materials (92 and 83), A method is performed to obtain a plurality of time-distributed characteristic evaluations of said area of ​​interest, thereby monitoring changes in said area of ​​interest (R7a-R7h, R3) over time.

6. A system for the contactless characterization of at least one region, called a region of interest (R1, R2, R3, R7, R8), in a medium to be characterized (91, 92, 93, 94), comprising: at least one transmission line resonator (MR1 to MR8) intended to be placed in said vicinity of the area under investigation, but without necessarily being in contact with said area under investigation; on the one hand, coupled via inductive coupling to said resonator by an inductive loop circuit (S1, S7, S8), and on the other hand, a probe arranged to interact with at least one reader (S0), the resonator comprises a plurality of transmission lines (M11-M14, M21-M28, M31-M34) arranged to have mutually different resonant frequencies (fr1-fr8), thereby forming a multi-frequency resonator (MR1-MR8), the transmission lines interacting with the area of ​​interest; the probe is positioned to interact with the entire multi-frequency resonator; A system, wherein the reader is arranged to interact with the probe to perform the method of claim 1.

7. 7. The system of claim 6, wherein the multi-frequency resonators (MR1, MR2, MR3) comprise a plurality of transmission lines (M11-M14, M21-M28, M31-M34) that are separate and unconnected from one another, each transmission line being formed by at least one conductive track formed on a two-dimensional dielectric substrate along a substantially closed path.

8. A system according to claim 6 or claim 7, wherein all or part of the transmission lines of the multi-frequency resonators (MR1, MR2) form substantially closed paths (M11-M14, M21-M28, M32) of a single turn each, typically forming a single-turn circular split ring.

9. 8. The system of claim 7, wherein the multi-frequency resonator comprises a plurality of conductive tracks (M11-M14, M21-M28, M31-M34, M43-M44) of substantially closed shape surrounded by each other.

10. A system according to claim 6 or 7, in which the multi-frequency resonators (MR4, MR5) comprise a plurality of mutually separate and unconnected transmission lines, each formed by conductive tracks (c14a, c14b) fabricated on a two-dimensional insulating substrate (d1), which are in particular paired with each other on either side of said substrate, angularly offset opposite each other along a "substantially closed", in particular circular, path, At least two transmission lines of different frequencies are arranged so that they are not nested within each other and are called separate. The probe (S2) includes an inductive loop circuit of the above shape arranged so as to obtain inductive coupling to the two separate transmission lines simultaneously, in particular a system in which a conductive loop is formed having a single turn (S21, S23) or multi-turn (S22) protrusion arranged so as to be able to place a protrusion on each of the separate transmission lines (M41, M42, M43 and M44, respectively).

11. 8. A system according to claim 6 or claim 7, wherein the multi-frequency resonator comprises a plurality of transmission lines which are separate and unconnected from one another, each transmission line being formed by conductive tracks (c14a, c14b) along an "almost closed" path, on the same plane or on the same two-dimensional insulating substrate.

12. 8. A system according to claim 6 or 7, wherein the multi-frequency resonator comprises a plurality of transmission lines which are separate and unconnected from one another, each formed by a conductive track fabricated on the same two-dimensional insulating substrate along a respective single-turn "near-closed" path, A system in which the transmission lines are arranged inside one another, in particular concentrically with one another.

13. A transmission line resonator device of the type described above, capable of communicating with an inductive loop probe via inductive coupling and adapted to be excited by and interact with said probe, comprising: A device comprising a plurality of transmission lines of substantially closed shape enclosed inside one another, in particular concentric circles, which are arranged together to form a multi-frequency resonator suitable for implementation in a system as described in claim 6 or in a method as described in claim 1.

14. 14. The device of claim 13, wherein each transmission line forms a single turn.

15. A system (17, 18) including an object (61, 82, 83), said system or object including at least one transmission line resonator, said resonator including a plurality of transmission lines arranged to have mutually different resonant frequencies (fr1-fr8), thereby forming multi-frequency resonators (MR1, MR7a-MR7h, MR8a-MR8h), said transmission lines interacting with said area of ​​interest, The multi-frequency resonator forms a system according to claim 6, or is implemented in a method according to claim 1, arranged to form an inductive coupling with an inductive loop probe (S1, S7a-S7h, S8a-S8h) and arranged to interact with said probe and thereby characterize a region of interest (R2, R7a-R7h, R8a-R8h) in a medium to be characterized, The system, wherein the area under investigation includes materials belonging to the object (82), and / or materials (92, 93) in contact with the object (61, 83) or materials (931) in its vicinity, and / or the interface (928) between the materials (92 and 83).

16. 16. The system of claim 15, comprising at least one probe (S8a to S8h) arranged to communicate with said multi-frequency resonator (MR8a to MR8h, respectively) via inductive coupling.

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