System for detecting electron paramagnetic resonance

Abstract

The invention relates to a system (100) for detecting electron paramagnetic resonance, comprising at least: - a first injection-locked oscillator (102) which includes at least one inductive element (106) and is configured to be magnetically coupled to a sample (104) in which electron paramagnetic resonance is intended to be detected by the system for detecting electron paramagnetic resonance; - a frequency synthesiser (108) which is configured to generate and output a first periodic signal on an injection input of the first injection-locked oscillator; and - a device (110) for detecting a phase difference between the first periodic signal and an output signal of the first injection-locked oscillator.

Description

[0001] Title: ELECTRONIC PARAMAGNETIC RESONANCE DETECTION SYSTEM

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The field of the invention is that of Electronic Paramagnetic Resonance (EPR) detection systems (also called ESR for "Electron Spin Resonance") used in particular for applications of integrated physical instrumentation on a chip and with low consumption. The invention can be applied in particular to the fields of the medical sector, nuclear security, agri-food, semiconductors and even batteries.

[0004] STATE OF THE ART

[0005] EPR is a technique used in spectroscopy to study systems with unaffected electronic spins. Its principle consists of immersing the sample to be studied in a static magnetic field which will induce the lifting of spin degeneracy (Zeeman effect) of the sample material. Transitions are then induced within the material by absorption of an electromagnetic wave whose photon energy corresponds exactly to the energy difference of the states. In practice, magnetic fields of the order of Tesla and electromagnetic waves whose frequencies are of the order of tens of GHz are generally used to cause this phenomenon. The material to be studied is placed in a cavity whose dimensions determine the frequency of the electromagnetic wave in play, then this cavity is subjected to the magnetic field, the intensity of which is modified until a resonance is detected in the material studied.Because EPR has no influence on diamagnetic matter, it is extremely sensitive to minimal amounts of magnetic elements, which can therefore be detected without having to subtract the influence of the diamagnetic matter. EPR therefore makes it easy to identify free radicals naturally present in the material of the sample studied or caused by ionizing radiation in this material (and which are representative of the nature of the material of the sample studied), defects in solids and semiconductors, or even transient species produced in energy storage systems such as batteries, fuel cell membranes, electrolyzers, etc.Until recently, EPR was a technique used only in research laboratories due to the size and weight of the devices enabling its implementation, as well as the difficulty of inserting a sample into the small cavity of such a device using this technique.

[0006] The paper by J. Handwerker et al., "28.2 A 14GHz battery-operated point-of-care ESR spectrometer based on a 0.13pm CMOS ASIC," 2016 IEEE International Solid-State Circuits Conference (ISSCC), San Francisco, CA, USA, 2016, pp. 476-477, proposes a spectrometer addressing the above issues and using VCO (Voltage-Controlled Oscillator) based integrated circuit technology. This is a device whose frequency can be directly controlled by applying a variable voltage and which allows generating / detecting the interaction between a sample and a microwave. Thanks to the frequency sweep performed by the VCO, it is possible to use a constant static magnetic field produced by permanent magnets, which drastically reduces the size and power consumption of the device. The sample is placed on the inductance of the VCO which is in free oscillation mode.By varying the free oscillation frequency of the VCO, when it approaches the RPE, a coupling due to the RPE then induces a non-monotonic variation of the free oscillation frequency of the VCO.

[0007] Such a spectrometer does not require magnetic field scanning by electromagnet (which is heavy and a big energy consumer) and does not require the sample to be positioned inside a cavity. It has the advantage of being miniature, autonomous and easily transportable. Such a spectrometer increases the range of EPR applications.

[0008] However, in such a spectrometer, the oscillator is free, which adds its own phase noise to the signal to be measured. In addition, FM modulation coupled with lock-in detection is used to reduce low-frequency noise. The detected signal is frequency-divided and brought back to an intermediate frequency through a mixer and a reference signal. A significant limitation of this spectrometer is therefore that the phase noise of the VCO induces noise on the VCO frequency, and therefore limits the detection sensitivity that can be obtained. DISCLOSURE OF THE INVENTION

[0009] The present invention aims to remedy all or part of the drawbacks of the state of the art cited above, and in particular to propose an electronic paramagnetic resonance detection system which can be compact, autonomous, transportable, and having better detection sensitivity than a spectrometer carrying out EPR detection via a variation of the free oscillation frequency of a VCO.

[0010] For this purpose, the invention proposes an electronic paramagnetic resonance detection system comprising at least: a frequency synthesizer configured to generate and deliver a first periodic injection signal Sinj; a first injection-locked oscillator including at least one inductive element configured to be magnetically coupled to a sample in which an electronic paramagnetic resonance is intended to be detected by the electronic paramagnetic resonance detection system, the first oscillator comprising an injection input receiving the first signal Sinj and delivering an output signal having an output pulsation locked to that of the injected signal Sinj; and a device for detecting the phase difference between the output signal of the first injection-locked oscillator and a reference signal S ref, the reference signal and said first periodic signal being obtained from the same initial periodic signal produced by a periodic signal generation circuit.

[0011] The system according to the invention proposes to perform RPE detection by an injection-locked oscillator, or ILO (Injection-Locked Oscillator). An ILO corresponds to an oscillator which, in the absence of an injection signal applied at the input, generates at the output a signal at a natural oscillation frequency, called the self-oscillation frequency, which depends in particular on the value of a control signal applied to a control input of the 1 LO. When an injection signal is applied to an injection input of the 1 LO and this signal satisfies certain conditions, such as for example having a frequency of value close to that of the self-oscillation frequency and a sufficient amplitude level, the 1 LO locks onto the frequency of the injection signal, so that its oscillation frequency is dependent on the frequency to which the 1 LO is locked. The ILO then copies the phase properties of the injection signal, in particular the phase noise.In the proposed system, the first ILO is configured to lock and copy the first periodic signal (applied to the injection input of the first ILO) in frequency and phase, and therefore in phase noise. By modifying the frequency of the first periodic signal, the frequency of the output signal of the first ILO is also modified, and the phase difference between the output signal of the first ILO and the first periodic signal is then constant. This phase difference follows a monotonic curve as a function of the frequency variation of the first periodic signal. However, when an EPR occurs, the magnetic coupling that occurs between the sample and the inductance of the first ILO has the effect of modifying the natural frequency of the first ILO, and therefore of modifying the phase difference between the output signal of the first ILO and the first periodic signal.The frequency at which the RPE occurs is then determined by identifying a non-monotonic variation in the phase difference between the output signal of the first ILO and the first periodic signal.

[0012] Thus, because the first ILO is locked to the first periodic signal, the proposed system achieves low phase noise, which results in a significant improvement in detection sensitivity compared to the system using a VCO to perform RPE detection.

[0013] Furthermore, such a detection system is perfectly compatible with a design allowing it to be compact, autonomous and easily transportable.

[0014] In addition to the advantages mentioned above, the proposed system can be used to perform continuous monitoring of RPE. It can also be coupled to other sensors present in the vicinity. Finally, the proposed system is compatible with use in a dirty (from a chemical and / or radiological point of view) and / or confined environment. Advantageously, the phase difference detection device can comprise at least one analog-to-digital converter configured to receive as input at least the output signal of the first injection-locked oscillator.

[0015] In a particular configuration, the phase difference detection device may further comprise a digital processing device configured to analyze the phase of the output signal of the digitally converted first injection-locked oscillator. In a second embodiment, the electron paramagnetic resonance detection system may further comprise a second injection-locked oscillator comprising an injection input coupled to the output of the frequency synthesizer, and the phase difference detection device may be configured to receive as input the output signals of the first and second injection-locked oscillators.

[0016] This second embodiment proposes to use a second ILO which is not magnetically coupled to the sample. Thus, the output signal of the second ILO is not affected or disturbed by EPR phenomena, and can thus serve as a reference to which the output signal of the first ILO can be compared. The detection of a disturbance due to EPR is therefore facilitated compared to the first embodiment in which a single ILO is used.

[0017] In this second embodiment, and when the phase difference detection device comprises the analog-to-digital converter, the analog-to-digital converter may be configured to also receive as input the output signal of the second injection-locked oscillator, and the phase difference detection device may further comprise a digital processing device configured to compare the phase of the output signal of the first digitally converted injection-locked oscillator and the phase of the output signal of the second digitally converted injection-locked oscillator.

[0018] In a variant of the second embodiment, the phase difference detection device may comprise at least one mixer configured to multiply the output signals of the first and second injection-locked oscillators with each other. In this case, the detection system may further comprise a low-pass filter coupled to an output of the mixer.

[0019] Furthermore, in this variant of the second embodiment, and when the phase difference detection device comprises the analog-to-digital converter, this converter can be configured to receive at least one output signal from the mixer as input or, when the electronic paramagnetic resonance detection system comprises the low-pass filter, an output signal from the low-pass filter. In such a configuration, it is possible to perform EPR detection by sampling the output signal from the low-pass filter statically and therefore without having to use an analog-to-digital converter operating at high frequency. In a particular embodiment, the frequency synthesizer can comprise a first frequency multiplier comprising at least:

[0020] - a periodically repeated oscillation train generator configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi, of duration less than Ti = 1 / Fi and repeated periodically at frequency Fi, with N an integer greater than 1;

[0021] - a third injection-locked oscillator having an injection input coupled to an output of the periodically repeated oscillation train generator, and having an output coupled to the injection input of the first injection-locked oscillator.

[0022] In this particular embodiment, it is possible to use a source generating a periodic signal of frequency Fi lower than that of the first periodic signal serving as an injection signal to the first ILO. The value of the multiplication coefficient between the frequency Fi and that of the first periodic signal serving as an injection signal to the first ILO is also easily configurable.

[0023] In this particular embodiment, the frequency multiplier may further comprise a signal amplifier having an input coupled to the output of the periodically repeated oscillation train generator and having an output coupled to the injection input of the third injection-locked oscillator.

[0024] In a third embodiment, the frequency synthesizer may comprise first and second frequency multipliers each comprising at least:

[0025] - a periodically repeated oscillation train generator configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi, of duration less than Ti = 1 / Fi and repeated periodically at frequency Fi, with N an integer greater than 1;

[0026] - a third injection-locked oscillator having an injection input coupled to an output of the periodically repeated oscillation train generator; an output of the third injection-locked oscillator of the first frequency multiplier being coupled to the injection input of the first injection-locked oscillator, and an output of the third injection-locked oscillator of the second frequency multiplier being coupled to the injection input of the second injection-locked oscillator.

[0027] With this third embodiment, it is possible to use a source generating a periodic signal of frequency Fi lower than that of the periodic signals serving as injection signals to the first and second ILOs. In addition, the value of the multiplication coefficient between the frequency Fi and that of the periodic signals serving as injection signals to the first and second ILOs is easily configurable. Furthermore, this third embodiment can make it possible to further reduce the phase noise obtained at the output when the mixer performs a multiplication of the output signals of the first and second ILOs with each other because this mixing eliminates the phase noise coming from the frequency synthesizer.

[0028] In a variant of the third embodiment, the frequency synthesizer may comprise first and second frequency multipliers each comprising at least:

[0029] - a generator of a train of periodically repeated oscillations configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi when the generator is part of the first frequency multiplier and substantially equal to M.Fi when the generator is part of the second frequency multiplier, of duration less than Ti = 1 / Fi and repeated periodically at the frequency Fi, with N and M integers greater than 1;

[0030] - a third injection-locked oscillator having an injection input coupled to an output of the periodically repeated oscillation train generator; an output of the third injection-locked oscillator of the first frequency multiplier being coupled to the injection input of the first injection-locked oscillator, and an output of the third injection-locked oscillator of the second frequency multiplier being coupled to the injection input of the second injection-locked oscillator.

[0031] In this variant of the third embodiment, the multiplication factors of the first and second frequency multipliers may be different. Thus, it is possible to digitize the signal to be analyzed at a non-zero frequency which makes it possible to obtain vector information (amplitude and phase) of the signal extracted after mixing. In addition, this frequency can be placed beyond a few MHz which makes it possible to overcome 1 / f noise (flicker noise).

[0032] Advantageously, each of the first and second frequency multipliers may further comprise a signal amplifier having an input coupled to the output of the periodically repeated oscillation train generator and having an output coupled to the injection input of the third injection-locked oscillator.

[0033] The frequency synthesizer may further comprise a generator of the first periodic signal of frequency Fi, an output of which is coupled to an input of the generator of a train of periodically repeated oscillations of the first frequency multiplier or, when the frequency synthesizer comprises the first and second frequency multipliers, to inputs of the generators of a train of periodically repeated oscillations of the first and second frequency multipliers.

[0034] Throughout the text of this application, the term "coupled" can designate either a direct connection between two elements, without an intermediate element between them, or an indirect connection between these two elements, that is to say a connection formed through at least one intermediate element.

[0035] BRIEF DESCRIPTION OF THE FIGURES

[0036] Other advantages, aims and particular characteristics of the present invention will emerge from the following non-limiting description of at least one particular embodiment of the devices and methods which are the subject of the present invention, with reference to the appended drawings, in which:

[0037] - figure 1 schematically represents an electronic paramagnetic resonance detection system, object of the present invention, according to a first embodiment;

[0038] - figure 2 represents an example of an output signal delivered by an electronic paramagnetic resonance detection system, object of the present invention, according to the first embodiment;

[0039] - Figure 3 schematically represents an electronic paramagnetic resonance detection system, object of the present invention, according to a second embodiment; - Figure 4 represents examples of signals obtained in an electronic paramagnetic resonance detection system, object of the present invention, according to the second embodiment;

[0040] - figure 5 schematically represents an electronic paramagnetic resonance detection system, object of the present invention, according to a variant of the second embodiment;

[0041] - figure 6 represents an example of an output signal delivered by an electronic paramagnetic resonance detection system, object of the present invention, according to the variant of the second embodiment represented in figure 5;

[0042] - figure 7 schematically represents an electronic paramagnetic resonance detection system, object of the present invention, according to a third embodiment;

[0043] - Figure 8 represents examples of signals obtained in an electronic paramagnetic resonance detection system, object of the present invention, according to the third embodiment;

[0044] - Figure 9 represents examples of signals obtained in an electronic paramagnetic resonance detection system, object of the present invention, according to a variant of the third embodiment.

[0045] Identical, similar or equivalent parts of the different figures described below bear the same numerical references so as to facilitate the transition from one figure to another.

[0046] The different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable.

[0047] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other.

[0048] DETAILED DESCRIPTION OF THE INVENTION

[0049] An exemplary embodiment of an electron paramagnetic resonance detection system 100, according to a first embodiment, is described below in connection with FIG. 1.

[0050] The system 100 comprises a first injection-locked oscillator, or ILO, 102 including at least one inductive element configured to be magnetically coupled to a sample 104 in which an electron paramagnetic resonance is intended to be detected by the system 100. In FIG. 1, the inductive element of the first ILO 102 is symbolized by a rectangle designated by the reference 106 and on which the sample 104 is disposed.

[0051] As an example, the first ILO 102 may be realized as described in the document "A Multichannel Programmable High Order Frequency Multiplier for Channel Bonding and Full Duplex Transceivers at 60 GHz Band," A. Siligaris et al., 2020 IEEE Radio Frequency Integrated Circuits Symposium (RFIC), Los Angeles, CA, USA, 2020, pp. 259-262, doi: 10.1109 / RFIC49505.2020.9218433.

[0052] In general, an injection-locked oscillator (ILO) is an unstable active device crossed by a current lo generating at its output a periodic signal So of natural pulsation 00 dependent on its resonator, and which, when injected (by means of an active injection device) by a periodic signal Sinj of pulsation 0j n j close to 0o, is locked by Sinj so that So then has a pulsation E nj. The output pulsation of the injection-locked oscillator ILO being locked to that of the injected signal Sinj, only its phase 0 SS depends on the state of its resonator according to the Adler formula given below (see (1) and (2)).

[0053] The system 100 also comprises a frequency synthesizer 108 configured to generate and output a first periodic signal, called Sinj in FIG. 1. The output of the frequency synthesizer 108 is coupled to an injection input of the first ILO 102. In FIG. 1, the control input of the first ILO 102 to which a control signal, called V tU ne_io2, allowing the control of the natural oscillation frequency, or self-oscillation frequency, of the first ILO 102 is not shown. When using the system 100, the control signal V tU ne_io2 applied to the control input of the first ILO 102 sets in particular its self-oscillation frequency to a value close to the frequency of the first periodic signal Sinj.

[0054] The system 100 also comprises a device 110 for detecting the phase difference between the first periodic signal Sinj and an output signal, called Sdet in FIG. 1, delivered by the first ILO 102.

[0055] Advantageously, the device 110 comprises at least one analog-digital converter receiving as input the output signal Sdet from the first ILO 102. In the proposed system 100, the first ILO 102 is used as an RPE detector.

[0056] As previously stated, the control signal V tUne_io2 applied to the control input of the first ILO 102 is such that the first ILO 102 locks and copies the first periodic signal Sinj in frequency and phase, and therefore in phase noise. If the frequency Finj of the first periodic signal Sinj applied to the injection input of the first ILO 102 is modified, the output frequency of the first ILO 102 is also modified. The phase difference between the output signal of the first ILO 102, i.e. the signal Sdet, and the injected signal, corresponding to the first periodic signal Sinj, is constant when the first ILO 102 is locked to the injected signal. When the frequency Finj of the injected signal Sinj varies, the phase difference between the signal Sdet and the signal Sinj follows a monotonic curve, noted (Dss and which depends in particular on the locking conditions of the first ILO 102. The value of

[0057] (Dss is given by the following relation:

[0058] (j> ss = arcsm

[0059] With GOO the free oscillation pulsation of the first ILO 102 in the absence of a signal applied to its injection input, inj the pulsation of the injected signal Sinj and GOL the locking range of the first ILO 102. This locking range GOL can be expressed by the following relation

[0060] Relation (1) is verified under the condition of having |ÛJ0— < ) L . In relation (2), Q is the quality factor of the resonator of the first ILO 102 and depends on the values ​​of the inductive element 106, of C which is the variable capacitance of the resonator fixing the free oscillation frequency of the first ILO 102, not shown in figure 1, through the control signal V tUne_io2, not shown here. Q also depends on R, the resistance of the resonator of the first ILO 102 not shown in Figure 1, reflecting the ohmic losses of the resonator. In relation (2), lo is the free oscillation current of the first ILO 102 when the Sinj signal is absent and finally, IINJ is the injection current of the Sinj signal into the first ILO 102 when it is injected.

[0061] The phase difference (Dss) depends on the natural frequency of the first ILO 102. However, in the presence of an EPR phenomenon, the magnetic coupling which takes place between the sample 104 and the inductance of the first ILO 102 has the effect of modifying the natural frequency of the first ILO 102 (the value of JO depends in particular on the value of the inductive element of the first ILO 102) and therefore of modifying (ss). Thus, the system 100 performs phase detection of an ILO disturbed by a magnetic field at the frequency at which the EPR occurs, due to the coupling of the sample 104 with the inductance of the first ILO 102.

[0062] Figure 2 illustrates the signal (Dss) obtained at the output of an exemplary embodiment of the system 100 by varying the frequency Finj of the signal Sinj between 13.5 GHz and 14.5 GHz. During this variation in the frequency of the signal Sinj, the frequency of the first ILO 102, and therefore of the signal Sdet, monotonically follows the frequency of the signal Sinj, but the phase of the output signal exhibits a non-monotonic variation around the frequency at which the EPR occurs, for example in the form of one or more glitches appearing on the curve around the frequency at which the EPR occurs. The frequency(ies) at which this or these glitch(es) appear are representative of the nature of the sample 104, and it is this signature of the material(s) of the sample 104 which is detected by the system 100 in order to analyze the sample 104.

[0063] In a particular configuration, the device 110 may further comprise a digital processing device configured to analyze the phase of the digitally converted signal Sdet and the phase of the digitally converted signal Sinj. For example, the digital processing device may calculate a parameter A(D = phase(Sdet) - phase(Sinj).

[0064] An exemplary embodiment of an electron paramagnetic resonance detection system 100, according to a second embodiment, is described below in connection with FIG. 3.

[0065] As in the first embodiment, the system 100 comprises the first ILO 102 whose inductive element 106 is magnetically coupled to the sample 104, the frequency synthesizer 108 and the phase difference detection device 110.

[0066] In this second embodiment, the system 100 further comprises a second ILO 112 comprising an injection input coupled to the output of the frequency synthesizer 108. This second ILO 112 is for example similar to the first ILO 102.

[0067] The second ILO 112 includes at least one inductive element, designated by the reference 114 in FIG. 3. Unlike the inductive element 106 of the first ILO 102, the inductive element 114 of the second ILO 112 is not configured to be magnetically coupled to the sample 104. In FIG. 3, the control input of the second ILO 112 to which a control signal, called V tU ne_ii2, allowing the control of the natural oscillation frequency, or self-oscillation frequency, of the second ILO 112 is not shown. When using the system 100, the control signal V tUne_ii2 applied to the control input of the second ILO 112 sets in particular its self-oscillation frequency to a value close to the frequency of the first periodic signal Sinj.

[0068] The phase difference detection device 110 is configured to receive as input the output signals of the first and second ILOs 102, 112. The output signal of the second ILO 112 is called S re f.

[0069] Advantageously, the analog-digital converter of the device 110 also receives as input the output signal S re f of the second ILO 112, and the device 110 comprises a digital processing device configured to compare the phase of the output signal Sdet of the digitally converted first ILO 102 and the phase of the output signal S re f of the second ILO 112 digitally converted.

[0070] In this second embodiment, the second ILO 112 receives as input the same injection signal Sinj as the first ILO 102 and operates in parallel with the first ILO 102. Because the inductive element 114 of the second ILO 112 is not magnetically coupled to the sample 104, the second ILO 112 copies as output the frequency and the phase of the injection signal Sinj without exhibiting any disturbance due to the EPR. Thus, the phase of the output signal Sref delivered by the second ILO 112 follows a monotonic curve with respect to the frequency Finj of the injection signal Sinj, while the first ILO 102 behaves as previously described for the first embodiment. The second ILO 112 not undergoing the EPR disturbance forms a reference ILO while the first ILO 102 undergoing the EPR disturbance forms a detection ILO.The RPE is detected here by calculating the difference between the phase of the output signal Sdet delivered by the first ILO 102 and that of the output signal S. re f delivered by the second ILO 112, this phase difference AO therefore being expressed by the relation AO = phase(Sdet) - phase(S re f).

[0071] The left curves visible in Figure 4 represent the evolution of the phases of the output signals Sdet and S ref by varying the frequency Finj of the signal Sinj between 13.5 GHz and 14.5 GHz. The variation due to the EPR is well detected and identified by the glitch appearing on the right corresponding to the phase of the signal Sdet. The curve corresponding to the phase of the signal Sref is on the other hand totally monotonous over the entire range of variation of the frequency Finj of the signal Sinj, without the presence of glitch because the inductance of the second ILO 112 is not disturbed by the EPR. On the right-hand curve, the phase difference AO obtained for this variation of frequency Finj of the signal Sinj is strongly disturbed at the frequency at which the variation due to the EPR is detected.

[0072] An exemplary embodiment of an electronic paramagnetic resonance detection system 100, according to a variant of the second embodiment, is described below in connection with FIG. 5.

[0073] Compared to the system 100 according to the second embodiment previously described in connection with FIG. 3, the phase difference detection device 110 of the system 100 comprises a mixer 116 configured to multiply the output signals of the first and second ILOs 102, 112 with each other, i.e. the signals Sdet and S re f. This multiplication of the signals Sdet and S re has the result of creating, at the output of the mixer 116, a signal whose value depends on the phase shift between the signals Sdet and S re f.

[0074] In the embodiment shown in Figure 5, the device 110 also comprises a low-pass filter 118 coupled to the output of the mixer 116. In the example of Figure 5, this low-pass filter is formed by a capacitor. This low-pass filter 118 makes it possible to keep only the static component of the product of the signals Sdet and S ref, and to reject the higher harmonics (Finj, 2 *Finj, 3* Finj, ...).

[0075] Although not visible in Figure 5, the device 110 may also include an analog-digital converter receiving as input the output signal of the low-pass filter 118 (or the output signal of the mixer 116 when the device 110 does not include the low-pass filter 118) and performing an analysis of the resulting static signal.

[0076] Figure 6 represents an example of a signal, called MIX OUT, obtained at the output of the low-pass filter 118. In this signal, the strong variation obtained corresponds to the detection of the variation due to the RPE.

[0077] An exemplary embodiment of an electron paramagnetic resonance detection system 100, according to a third embodiment, is described below in connection with FIG. 7.

[0078] As in the second embodiment previously described, the system 100 comprises the first ILO 102 whose inductive element 106 is magnetically coupled to the sample 104, the second ILO 112 whose inductive element 114 is not magnetically coupled to the sample 104, the frequency synthesizer 108 and the phase difference detection device 110. In the example of FIG. 7, the device 110 is similar to that previously described in connection with FIG. 5.

[0079] In this third embodiment, the frequency synthesizer 108 comprises first and second frequency multipliers each comprising:

[0080] - a generator (designated by the reference 120 for the first frequency multiplier and 122 for the second frequency multiplier) of a train of periodically repeated oscillations configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi, of duration less than Ti = 1 / Fi and repeated periodically at the frequency Fi, with N an integer greater than 1;

[0081] - a third ILO (designated by the reference 124 for the first frequency multiplier and 126 for the second frequency multiplier) of which an injection input is coupled to an output of the generator 120, and respectively 122, and of which the output is coupled to the injection input of the first ILO 102 for the first frequency multiplier or of the second ILO 112 for the second frequency multiplier, respectively. Each of the third ILOs 124, 126 delivers on its output the signal Sinj.

[0082] In the exemplary embodiment described in connection with FIG. 7, each of the first and second frequency multipliers further comprises a signal amplifier (designated by the reference 128 for the first frequency multiplier and 130 for the second frequency multiplier) one input of which is coupled to the output of one of the generators 120, 122 and one output of which is coupled to the injection input of one of the third ILOs 124, 126.

[0083] The third ILOs 124, 126 are for example similar to the first and second ILOs 102, 112. The generators 120, 122 are for example produced as described in document EP 2 786492 Bl.

[0084] In the example of Figure 7, the frequency synthesizer 108 also comprises a generator 132 of the first periodic signal of frequency Fi.

[0085] In this third embodiment, the use of the first and second frequency multipliers makes it possible to synthesize a periodic signal of frequency Fi (obtained at the output of the generator 132) at low frequency and to reach, at the input of the mixer 116, high frequencies while maintaining low consumption and phase noise. For example, the generator 132 can be configured to generate a periodic signal of frequency Fi of the order of, or equal to, 500 MHz. In addition, the use of the generators 120, 122 coupled to the third ILOs 124, 126 makes it possible to program the value of the multiplication factor N, resulting in the frequency Finj. The first and second ILOs 102, 112 are here locked to the same harmonic N of the input frequency Fi.For example, the input frequency Fi can be around 500 MHz and each of the frequency multipliers can be programmed to deliver a frequency injection signal Finj corresponding for example to 28. ème harmonic of the frequency Fi, i.e. approximately 14 GHz. In this case, by varying the value of Fi around 500 MHz, the frequency of the injection signals applied at the input of the first and second ILOs 102, 112 varies around 14 GHz (28* Fi). The injection signals Sinj obtained at the output of the first and second ILOs 102, 112 are coherent with respect to the frequency signal Fi delivered by the generator 132 and their respective phase noises therefore remain coherent with each other and identical. Thus, the first and second ILOs 102, 112 have phase noises that are coherent with each other and their mixing by the mixer 116 has the effect of subtracting this phase noise coming from the frequency signal Fi.

[0086] The left curve visible in Figure 8 represents the phase difference AO between the signal Sdet and the signal S re f. (AO = phase(Sdet) - phase(S re f)) obtained in this third embodiment by varying the frequency Fi between 480 MHz and 520 MHz and which, as in the previous embodiments, is strongly disturbed at the frequency at which the variation due to the RPE is detected. The right-hand curve of Figure 8 represents the MIX OUT signal obtained at the output of the low-pass filter 118 of the system 100 according to the third embodiment. In this signal, the amplitude of which is in Volts because the phase difference between the signals Sdet and S ref is directly translated into a static DC signal by the mixer 116, the strong variation obtained corresponds to the detection of the variation due to the RPE. In a variant, the system 100 according to the third embodiment can carry out the detection of the RPE at an intermediate frequency (Fl) by mixing the signals of the first and second ILOs 102, 112 at different frequencies while maintaining coherence between these signals. This is done by configuring one of the two frequency multipliers at the N ème harmonic, while the other string is programmed to an M ème harmonic different from N ème harmonic, with for example M = Nl. For example, the first frequency multiplier can be programmed such that the Finji frequency of the injection signal delivered at the output of the ILO 124 Sinji corresponds to the 28 èmeharmonic (N = 28) of the frequency Fi, i.e. varies around 14 GHz when the frequency Fi varies around 500 MHz, and the second frequency multiplier can be programmed such that the frequency Fj n j2 of the injection signal delivered at the output of the ILO 126 Sj n j2 corresponds to 27 ème harmonic (M = 27) of the frequency Fi, that is to say varies around 13.5 GHz when the frequency Fi varies around 500 MHz. This has the effect of obtaining, at the output of the mixer 116, a mixing product whose Fl is located at FFI = (28-27)*Fi = Fi, and therefore equal to 500 MHz in the example described previously.

[0087] The left curve visible in Figure 9 represents the phase difference AO (AO = phase(Sdet) - phase(S ref)) obtained in this variant of the third embodiment by varying the frequency Fi between 480 MHz and 520 MHz and which, as in the previous embodiments, is strongly disturbed at the frequency at which the variation due to the RPE is detected. The right-hand curve of Figure 9 represents the phase of the MIX OUT signal obtained at the output of the low-pass filter 118 of the system 100 according to this variant of the third embodiment. Indeed, the MIX OUT signal being at the intermediate frequency Fl (for example 500 MHz), the phase difference between the signals Sdet and S re f is reported on the phase of the MIX OUT signal. This phase is extracted after digital post-processing by the device 110 which may include at least one analog-digital converter. In this signal, the strong variation obtained corresponds to the detection of the variation due to the RPE.

[0088] The use of a frequency multiplier can be envisaged in a system 100 not comprising the second ILO 112, that is to say as a variant of the first embodiment previously described in connection with FIG. 1. In this case, the frequency synthesizer 108 comprises at least:

[0089] - a periodically repeated oscillation train generator configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi, of duration less than Ti = 1 / Fi and repeated periodically at frequency Fi, with N an integer greater than 1;

[0090] - an injection-locked oscillator having an injection input coupled to an output of the periodically repeated oscillation train generator, and having an output coupled to the injection input of the first ILO 102.

[0091] The frequency synthesizer 108 may also comprise the generator 132 of the first periodic signal of frequency Fi, an output of which is coupled to the input of the generator of a train of periodically repeated oscillations.

[0092] Generally speaking, as appears from reading the above-mentioned exemplary embodiments, the phase difference detection device receives on the one hand the detection signal Sdet and on the other hand a signal which is taken as a reference by the detection device to analyze the phase of the detection signal. This other signal, which can generally be called the “reference signal” Sref for the detection device, is in practice obtained from the same initial periodic signal. In the first exemplary embodiments, this same initial periodic signal is the signal Sinj produced by the frequency synthesizer 108. In the following examples, this initial periodic signal is produced by the generator 132.The fact that the detection signal Sdet and the reference signal both come from the same initial periodic signal makes it possible to have two signals presenting correlated noises and consequently, the phase detection device can subtract the correlated noises to ultimately obtain a better measurement.

Claims

CLAIMS 1. Electronic paramagnetic resonance detection system (100), characterized in that it comprises at least: a frequency synthesizer (108) configured to generate and deliver a first periodic injection signal Sinj; a first injection-locked oscillator (102) including at least one inductive element (106) configured to be magnetically coupled to a sample (104) in which an electronic paramagnetic resonance is intended to be detected by the electronic paramagnetic resonance detection system (100), the first oscillator comprising an injection input receiving the first signal Sinj and delivering an output signal having an output pulsation locked to that of the injected signal Sinj and; a phase difference detection device (110) between the output signal of the first injection-locked oscillator (102) and a reference signal (S ref ; Sinj), the reference signal and said first periodic signal being obtained from the same initial periodic signal produced by a periodic signal generation circuit (108; 132).

2. Electronic paramagnetic resonance detection system (100) according to claim 1, further comprising means for varying the frequency of the first periodic injection signal Sinj and a processing device for detecting a non-monotonic variation in the phase of the output signal of the injection-locked oscillator (102) around at least one frequency at which the paramagnetic resonance occurs.

3. Electronic paramagnetic resonance detection system (100) in which the phase difference detection device (110) comprises at least one analog-to-digital converter configured to receive as input at least the output signal of the first injection-locked oscillator (102).

4. The electron paramagnetic resonance detection system (100) of claim 3, wherein the phase difference detection device (110) further comprises a digital processing device configured to analyze the phase difference phase between the output signal of the first injection-locked oscillator (102) and said digitally converted reference signal.

5. Electronic paramagnetic resonance detection system (100) according to one of the preceding claims, wherein the phase difference detection device (110) is configured to receive as input the output signal of the first injection-locked oscillator (102) and said first periodic signal produced by said frequency synthesizer (108).

6. Electron paramagnetic resonance detection system (100) according to one of claims 1 to 4, further comprising a second injection-locked oscillator (112) comprising an injection input coupled to the output of the frequency synthesizer (108), and wherein the phase difference detection device (110) is configured to receive as input the output signals of the first and second injection-locked oscillators (102, 112).

7. Electronic paramagnetic resonance detection system (100) according to claims 3 and 6, wherein the analog-to-digital converter is configured to also receive as input the output signal of the second injection-locked oscillator (112), and wherein the phase difference detection device (110) further comprises a digital processing device configured to compare the phase of the output signal of the first digitally converted injection-locked oscillator (102) and the phase of the output signal of the second digitally converted injection-locked oscillator (112).

8. The electron paramagnetic resonance detection system (100) of claim 6, wherein the phase difference detection device (110) comprises at least one mixer (116) configured to multiply the output signals of the first and second injection-locked oscillators (102, 112) with each other.

9. The electron paramagnetic resonance detection system (100) of claim 8, further comprising a low-pass filter (118) coupled to an output of the mixer (116).

10. Electronic paramagnetic resonance detection system (100) according to claim 3 and according to one of claims 8 or 9, wherein the analog-digital converter is configured to receive as input at least one output signal from the mixer (116) or, when the electronic paramagnetic resonance detection system (100) comprises the low-pass filter (118), an output signal from the low-pass filter (118).

11. Electronic paramagnetic resonance detection system (100) according to one of claims 1 to 4, wherein the frequency synthesizer (108) comprises a first frequency multiplier comprising at least: a periodically repeated oscillation train generator (120, 122) configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N. Fi, of duration less than Ti = 1 / Fi and periodically repeated at the frequency Fi, with N integer greater than 1; a third injection-locked oscillator (124, 126) having an injection input coupled to an output of the periodically repeated oscillation train generator (120, 122), and having an output coupled to the injection input of the first injection-locked oscillator (102).

12. The electron paramagnetic resonance detection system (100) of claim 11, wherein the frequency multiplier further comprises a signal amplifier (128, 130) having an input coupled to the output of the periodically repeated oscillation train generator (120, 122) and having an output coupled to the injection input of the third injection-locked oscillator (124, 126).

13. Electronic paramagnetic resonance detection system (100) according to one of claims 6 to 10, wherein the frequency synthesizer (108) comprises first and second frequency multipliers each comprising at least: a generator of a train of periodically repeated oscillations (120, 122) configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N.Fi, of duration less than Ti = 1 / Fi and periodically repeated at the frequency Fi, with N integer greater than 1; a third injection-locked oscillator (124, 126) having an injection input coupled to an output of the periodically repeated oscillation train generator (120, 122); wherein an output of the third injection-locked oscillator (124) of the first frequency multiplier is coupled to the injection input of the first injection-locked oscillator (102), and wherein an output of the third injection-locked oscillator (126) of the second frequency multiplier is coupled to the injection input of the second injection-locked oscillator (112).

14. Electron paramagnetic resonance detection system (100) according to one of claims 6 to 10, wherein the frequency synthesizer (108) comprises first and second frequency multipliers each comprising at least: a periodically repeated oscillation train generator (120, 122) configured to receive as input a periodic signal of frequency Fi and to generate as output a periodic signal corresponding to a train of oscillations of frequency substantially equal to N. Fi when the generator is part of the first frequency multiplier and substantially equal to M. Fi when the generator is part of the second frequency multiplier, of duration less than Ti = 1 / Fi and periodically repeated at the frequency Fi, with N and M integers greater than 1; a third injection-locked oscillator (124, 126) having an injection input coupled to an output of the periodically repeated oscillation train generator (120, wherein an output of the third injection-locked oscillator (124) of the first frequency multiplier is coupled to the injection input of the first injection-locked oscillator (102), and wherein an output of the third injection-locked oscillator (126) of the second frequency multiplier is coupled to the injection input of the second injection-locked oscillator (112).

15. The electron paramagnetic resonance detection system (100) of claim 13 or 14, wherein each of the first and second frequency multipliers further comprises a signal amplifier (128, 130) having an input coupled to the output of the periodically repeated oscillation train generator (120, 122) and having an output coupled to the injection input of the third injection-locked oscillator (124, 126).

16. Electronic paramagnetic resonance detection system (100) according to one of claims 11 to 15, wherein the frequency synthesizer (108) further comprises a generator (132) of the first periodic signal of frequency Fi, an output of which is coupled to an input of the periodically repeated oscillation train generator (120) of the first frequency multiplier or, when the frequency synthesizer (108) comprises the first and second frequency multipliers, to inputs of the periodically repeated oscillation train generators (120, 122) of the first and second frequency multipliers.

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