Deep eutectic solvent microwave sensor for the detection of at least one target gas, communicating system comprising it, and associated characterization method

Abstract

Deep eutectic solvent microwave sensor for the detection of at least one target gas, communicating system comprising it, and associated characterization method. The invention relates to a microwave sensor (2) for the detection of at least one target gas, comprising: a substrate (4); a microwave device (5) printed on the substrate (4) and having a deposition opening (7); and a liquid substance (8) sensitive to at least one target gas, said liquid substance (8) being disposed in the deposition opening (7) so as to be in contact with the microwave device (5), the liquid substance (8) being of the deep eutectic solvent type and chosen such that the presence of at least one target gas causes at least one of a modification of the dielectric characteristics and a modification of the electrical characteristics of the liquid substance (8), causing a modification of the distribution parameters of the microwave device (5).Figure to be published with the abbreviation: Figure 1.

Description

Title of the invention: Deep eutectic solvent microwave sensor for the detection of at least one target gas, communicating system comprising it, and associated characterization method

[0001] The present invention relates to the field of gas microwave sensors, and relates in particular to a deep eutectic solvent type liquid microwave sensor for the detection of at least one target gas, to a communicating system comprising such a microwave sensor, and to a method for characterizing at least one deep eutectic solvent type liquid using such a microwave sensor.

[0002] The development of microwave gas sensors has generated considerable interest in numerous application areas, such as the protection of military personnel in combat zones, air quality monitoring, etc. Gas sensors, which by definition combine a receiver (or sensitive layer) with a transducer that transforms the physical or chemical interaction of gaseous species with the sensitive layer into an analyzable signal, exclusively use receivers based on solid sensitive layers. These layers are capable of interacting with a gaseous species to be detected through physical interactions and / or chemical reactions that lead to a modification of the electrical or dielectric characteristics of the solid sensitive layer, which is then translated into a physical quantity. Thus, the choice of the solid sensitive layer is essential in any sensor development.The solid light-sensitive coatings currently available on the market are varied and fall into several categories based on their composition and chemical structure. These include, among others, metal / metal oxide nanostructures, polymer nanostructure-based light-sensitive coatings, organic-inorganic composites, and organometallic structures.

[0003] The aforementioned solid sensitive layers make it possible to detect many pollutants or gases such as ammonia, hydrogen disulfide, nitrogen monoxide or dioxide, carbon monoxide, volatile organic compounds (VOCs), hydrochloric acid, etc.

[0004] In particular, solid sensitive layers based on inorganic metal oxides such as zinc oxide (ZnO), ammonia-sensitive titanium dioxide (TiO2), iron oxides (Fe2O3 / Fe2O4), or silicon dioxide (SiO2) possess very good detection capabilities due to the variable oxygen stoichiometry at the surface and their resulting electrical characteristics. However, this type of sensor generally operates at high temperatures, which leads to drifts due to due to oxidation of the reference electrode. This implementation difficulty prevents low-cost industrialization. Conductive polymers, on the other hand, are often used as a sensitive layer for VOC detection, although water present in the atmosphere significantly destabilizes the system, thus limiting the sensitivity of the sensors.

[0005] The present invention aims to resolve the drawbacks of the prior art by proposing a gas microwave sensor whose sensitive layer is at least a sensitive liquid substance of the deep eutectic solvent type integrated into a microwave device.

[0006] The gas microwave sensor according to the present invention thus uses a bio-based, eco-responsible, easily synthesized, and easily depositable sensitive layer on the surface of the microwave device, which makes it possible to obtain a low-complexity, reversible and low-cost microwave sensor.

[0007] Wireless gas sensors sensitive to potentially dangerous and / or polluting gases such as, for example, hydrochloric acid, sulfur dioxide, ammonia or volatile organic compounds (VOCs), or even deadly gases such as warfare gases, can thus be developed, these sensors being selective and discriminating the targeted gaseous species.

[0008] The present invention therefore relates to a microwave sensor for the detection of at least one target gas, characterized in that it comprises: a substrate; at least one microwave device printed on the substrate, said at least one microwave device having at least one deposition opening;and at least one liquid substance sensitive to at least one target gas, said at least one liquid substance being disposed in at least one deposition opening so as to be in contact with at least one microwave device, the at least one liquid substance being of the deep eutectic solvent type and chosen such that the presence of at least one target gas causes at least one of the following to be a change in the dielectric characteristics and a change in the electrical characteristics of the at least one liquid substance, causing a change in the distribution parameters of the at least one microwave device when a microwave signal is applied thereto.

[0009] Thus, combining a sensitive liquid substance of the deep eutectic solvent type with a microwave device makes it possible to detect the presence of a target gas, which may be a lethal, potentially hazardous, and / or polluting gas. Indeed, a change in the distribution parameters of the microwave device when the sensitive liquid substance interacts with the target gas allows the microwave sensor to detect the presence of the target gas.

[0010] The microwave device (also called a microwave device) is printed on the substrate and is configured to operate in the microwave / microwave. It can, for example, be one of a transmission line, a delay line, a resonator, a filter, a coupler and / or an antenna.

[0011] At least one liquid substance is disposed in at least one deposition opening so as to bring into contact the two parts of the microwave device separated by the deposition opening.

[0012] Scattering parameters (also called diffraction parameters or S parameters) are used in microwave, electrical, and electronic applications to describe the electrical behavior of linear power networks as a function of input signals. A microwave device is modeled, by the scattering parameters, as a set of ports. Each port corresponds to a transmission line or the equivalent of a transmission line of a propagating mode of a waveguide. For a microwave device having one input (designated 1) and one output (designated 2), the scattering parameters are thus Su (input reflection coefficient), Si2 (reverse transmission coefficient), S2i (forward transmission coefficient), and S22 (output reflection coefficient).

[0013] The present invention thus implements, for the first time, a sensitive layer in liquid form made of a deep eutectic solvent. Deep eutectic solvents constitute a new type of emerging, eco-friendly solvent known for their low toxicity, non-volatility, and low production cost, since most of them are made from readily available natural products. They are defined by the formation of a molecular network resulting from non-covalent associations governed by hydrogen bonds between hydrogen bond acceptors and hydrogen bond donors, and by electrostatic interactions.On the one hand, their very low volatility, their high viscosity (which prevents the spread of the droplet deposited on the surface of the microwave device), and their interactions with ionic entities (dipoles) make them excellent candidates for the fabrication of sensitive layers whose variation in electrical and / or dielectric characteristics directly impacts the microwave signals applied to the microwave device. On the other hand, the reversible absorption capacity of certain gases, such as hydrochloric acid (HCl), ammonia (NH3), or sulfur dioxide (SO2), by deep eutectic solvents has been demonstrated by differential physicochemical measurements of the interacting gaseous species.

[0014] Furthermore, the means used for depositing the liquid sensitive substance into the deposition opening formed on the microwave device is easily and inexpensively implemented. Indeed, for example, a positive displacement micropipette (ideal for sampling viscous liquids) is sufficient to draw the required volume of liquid sensitive substance to be deposited into the deposition opening of the hy- device. frequency.

[0015] Although the system has demonstrated a certain degree of reversibility, the liquid sensing substance nevertheless loses its effectiveness with use. However, it can easily be removed from the deposition opening and replaced with a new drop of liquid sensing substance when its effectiveness reaches a predefined threshold value. This avoids the need to manufacture a new gas microwave sensor.

[0016] The deposition opening formed in the microwave device allows for the localization and delimitation of the deposition zone of the liquid sensitive substance on the substrate, in order to ensure the optimal operation of the microwave sensor.

[0017] Furthermore, the deposition aperture is created in the microwave device in order to disrupt its operation. Indeed, the location of the liquid sensitive substance in the deposition aperture and the evolution of this liquid sensitive substance following an external perturbation (presence of gaseous species, temperature change, etc.) makes it possible to extract the evolution of the electrical and / or dielectric characteristics of the liquid sensitive substance and to use the device as a gas-sensitive sensor.

[0018] The dielectric characteristics of the sensitive liquid substance which vary in the presence of at least one target gas can, for example, be the dielectric permittivity (er) and the tangent of the dielectric loss angle (tgô), as well as the absorption damping constant (a), these three parameters er, tgô and a evolving as a function of the gaseous environment of the sensitive liquid substance, its temperature and the operating frequency of the microwave device.

[0019] The electrical characteristics of the sensitive liquid substance which vary in the presence of at least one target gas may, for example, be resistivity or conductivity or resistance per square.

[0020] The present invention uses the specific response of the liquid sensitive substance integrated into the microwave device and is based on the evolution of the distribution parameters Sy (namely, the reflection parameters or coefficients Su and S22, and the transmission parameters or coefficients Si2 and S2i) of the microwave device when the liquid sensitive substance interacts with a specific gaseous species.

[0021] According to a particular feature of the present invention, each deep eutectic solvent-type liquid substance is one of:

[0022] - a mixture of choline chloride and urea in a molar ratio 1:2;

[0023] - a mixture of choline chloride and thiourea in a molar ratio of 1:1;

[0024] - a mixture of choline chloride and glycerol in a molar ratio of 1:1;

[0025] - a mixture of choline chloride and ethylene glycol in one of the ratios molars 1:2 and 1:1;

[0026] - a mixture of choline chloride and glycerol in one of the molar ratios 1:2 and 1:1;

[0027] - a mixture of choline chloride and malonic acid in one of the ratios molars 1:2 and 1:1;

[0028] - a mixture of thymol and a fatty acid, such as hexanoic acid, heptanoic acid, octanoic, nonanoic, or decanoic, in one of the molar ratios 1:2 and 1:1; and

[0029] - a mixture of menthol and a fatty acid, such as hexanoic acid, heptanoic acid, octanoic, nonanoic or decanoic, in one of the molar ratios 1:2 and 1:1.

[0030] Thus, each sensitive liquid substance of the deep eutectic solvent type is formed by a mixture, liquid at room temperature, of two compounds (namely, a hydrogen bond donor and a hydrogen bond acceptor) in the exact proportion that corresponds to the eutectic point.

[0031] According to a particular feature of the present invention, in each storage opening, one is provided between a textile soaked in at least one liquid substance, and a cavity containing at least one liquid substance.

[0032] Thus, either the textile (such as a felt) placed on the substrate in the deposition opening so as to be in contact with the printed microwave device is soaked with the liquid sensitive substance, or the cavity in the substrate forming the deposition opening is directly filled with the liquid sensitive substance so that the latter is in contact with the printed microwave device.

[0033] According to a particular feature of the present invention, the substrate is made of polytetrafluoroethylene, and at least one microwave device is made of copper and printed on the substrate.

[0034] By way of example, the substrate can be made of polytetrafluoroethylene (PTFE) having a thickness of 0.5 mm, a dielectric permittivity er = 2.1 and a loss angle tangent tgô = 103.

[0035] In addition, also by way of example, at least one microwave device can be made of copper 18 pm thick.

[0036] According to a particular feature of the present invention, at least one microwave device is a transmission line with an impedance of 50 Ohms, and at least one deposition opening is a break formed on the transmission line with an impedance of 50 Ohms.

[0037] Thus, the interruption on the transmission line forms an interval or space, also called a gap, which serves as a deposition zone for the liquid sensitive substance.

[0038] By way of example, the transmission line may have a length of 30 mm and a width of 1.8 mm, with a 200 pm interruption at mid-length of the transmission line.

[0039] According to a particular feature of the present invention, at least one microwave device is a 50 Ohm impedance transmission line from which extends at least one stub to form at least one quarter-wave stub resonator whose stub has a break as a deposition opening.

[0040] Thus, the interruption on the stub of the resonator forms a gap which serves as a deposition zone for the liquid sensitive substance.

[0041] By way of example, the resonator transmission line may have a length of 30 mm and a width of 1.8 mm, and the quarter-wave stub of the resonator may have a length of 10 mm and a width of 0.08 mm, with an 80 pm break approximately halfway along the length of the stub.

[0042] According to a particular feature of the present invention, several stubs extend from the 50 Ohm impedance transmission line to form several quarter-wave stub resonators, each quarter-wave stub resonator having, as a deposition opening, a break formed on its stub, a different deep eutectic solvent-type liquid substance being disposed in each of the stub break-type deposition openings.

[0043] Thus, this microwave device of the resonator type with several quarter-wave stubs allows the deposition of several different liquid sensing substances (namely, a distinct liquid sensing substance in each deposition orifice), thereby increasing the selectivity of the microwave sensor. Indeed, the deposition of several liquid sensing substances on the microwave device makes it possible to obtain a transmitted signal characteristic of the target gas by obtaining a specific resonant frequency and amplitude. This is the average resonant frequency of all the liquid sensing substances combined.

[0044] The present invention also relates to a communicating system for the detection of at least one target gas, characterized in that it comprises a microwave sensor as described above and a transmitting antenna connected to at least one microwave device of the microwave sensor, the at least one liquid substance of the microwave sensor being chosen such that the presence of at least one target gas causes at least one of a change in the dielectric characteristics and a change in the electrical characteristics of the at least one liquid substance, causing a change in the distribution parameters of the communicating system when a microwave signal is applied to at least one microwave device of the microwave sensor.

[0045] Thus, the transmitting antenna of the communicating system allows the result of the detection, by the microwave sensor, of at least one target gas to be transmitted wirelessly in the presence of the latter in the environment of the microwave sensor.

[0046] The microwave sensor can be connected to the transmitting antenna either phy- sically, or by coupling.

[0047] The communicating system thus makes it possible to transmit the detection information, and consequently the nature of the detected gas(s), instantaneously to a dedicated microwave receiving system. Furthermore, the communicating system is reusable, even after the detection of a target gas.

[0048] According to a particular feature of the present invention, the transmitting antenna is one of a horn antenna and a printed radiating element antenna.

[0049] In the case of a printed radiating element antenna (also called a plate antenna or patch antenna), the radiating element of the antenna can be printed on the same substrate as the microwave device.

[0050] The present invention also relates to a communicating system for the detection of at least one target gas, characterized in that it comprises a microwave sensor as described above, of which at least one microwave device is a printed radiating element transmitting antenna in which at least one deposition opening is formed, the at least one liquid substance of the microwave sensor being chosen such that the presence of at least one target gas causes at least one of a modification of the dielectric characteristics and a modification of the electrical characteristics of the at least one liquid substance, causing a modification of the distribution parameters of the communicating system when a microwave signal is applied to the printed radiating element transmitting antenna.

[0051] Thus, the radiating element of the patch antenna is printed on the substrate, and the deposition opening(s) formed in the radiating element of the antenna allow the deposition of one or more liquid sensitive substances on the microwave device.

[0052] The patch antenna thus plays both the role of microwave device for the microwave sensor and the role of transmitting antenna for the communicating system.

[0053] The patch-type transmitting antenna of the communicating system allows the result of the detection, by the microwave sensor, of at least one target gas to be transmitted wirelessly in the presence of the latter in the environment of the microwave sensor.

[0054] The communicating system thus makes it possible to transmit the detection information, and consequently the nature of the detected gas(s), instantaneously to a dedicated microwave receiving system. Furthermore, the communicating system is reusable, even after the detection of a target gas.

[0055] According to a particular feature of the present invention, the communicating system further comprises a Peltier temperature control device configured, after absorption of at least one target gas by at least one liquid substance of the microwave sensor, to heat and then cool the microwave sensor frequency so as to cause the desorption of at least one target gas within at least one liquid substance, causing a return of the distribution parameters of the communicating system to the initial state before absorption.

[0056] Thus, the Peltier temperature control device allows the communicating system to be temperature regulated. Indeed, after detection of the target gas, it heats and then cools the communicating system in order to regenerate the liquid sensitive substance of the microwave sensor.

[0057] The present invention further relates to a method for characterizing at least one liquid substance of the deep eutectic solvent type sensitive to at least one target gas, using a microwave sensor as described above, characterized in that said method comprises the following steps: - applying, using a network analyzer, a microwave signal to at least one microwave device of the microwave sensor; - measuring, using the network analyzer, the distribution parameters of the microwave signal at different absorption times of at least one target gas by at least one liquid substance of the deep eutectic solvent type of the microwave sensor;and - define, using numerical simulation software, one of the dielectric and electrical characteristics of at least one deep eutectic solvent-type liquid substance using the distribution parameters measured at different absorption times, said dielectric characteristics including at least the dielectric permittivity and the tangent of the dielectric loss angle.

[0058] The microwave sensor according to the invention can thus also be used for microwave characterization of the sensitive liquid substance of the deep eutectic solvent type, either pure or after its interaction with a specific gaseous species, through the evolution of its intrinsic electrical and / or dielectric characteristics.

[0059] The characterization method according to the present invention is simple and efficient, unlike existing techniques. Indeed, the complex structure of deep eutectic solvents and their formulation based on non-covalent interactions make them very difficult to characterize using the most common existing physicochemical methods in laboratories. Studies of their physicochemical properties, including their viscosity, water content (percentage) via the Karl Fischer method, and density, are more generally employed. A recent study also made it possible to characterize deep eutectic solvents in the gas phase using mass spectrometry. Infrared (IR) and Nuclear Magnetic Resonance (NMR) techniques are also used to study the interactions between certain deep eutectic solvents and other products such as water.Methods of difference. Neutron fractions associated with molecular modeling have also been proposed, but they remain confined to the expertise of highly specialized research units.

[0060] The present invention makes it possible to obtain efficiently, reliably and reproducibly the intrinsic electrical and / or dielectric characteristics of each deep eutectic solvent (and their evolution when subjected to a gas) by means of the analysis of the microwave signal of the microwave device and a rapid back-simulation by means of a numerical simulation software.

[0061] To better illustrate the object of the present invention, we will describe below, by way of illustration and not limitation, preferred embodiments, with reference to the attached drawings.

[0062] On these drawings:

[0063] [Fig. 1] represents a communicating system according to a first embodiment of the present invention;

[0064] [Fig.2] represents a communicating system according to a second embodiment of the present invention;

[0065] [Fig.3] represents a communicating system according to a third embodiment of the present invention;

[0066] [Fig.4] represents a communicating system according to a fourth embodiment of the present invention;

[0067] [Fig.5] represents a communicating system according to a fifth embodiment of the present invention;

[0068] [Fig.6] represents a microwave device according to a sixth embodiment of the present invention;

[0069] [Fig.7] represents curves illustrating experimental measurements, as a function of the frequency, the amplitude of the transmission coefficient S2i of a microwave device of the quarter-wave stub resonator type according to the invention under different conditions of exposure to the target gas;

[0070] [Fig.8] represents curves illustrating simulated and experimental measurements of the evolution, as a function of frequency, of the amplitude of the transmission coefficient S2i of a microwave transmission line type device at 50 Ohms according to the invention under different conditions of exposure to the target gas;

[0071] [Fig.9] represents curves illustrating experimental measurements of the evolution, depending on the frequency, the difference in amplitude of the AS2i transmission coefficient of a quarter-wave stub resonator microwave device according to the invention under different exposure conditions to the target gas; and

[0072] [Fig. 10] represents curves illustrating experimental measurements of the evolution, as a function of frequency, of the reflection coefficient Su and the gain of the system com communicating the [Fig.4] under different conditions of exposure to the target gas.

[0073] If we refer to [Fig. 1], we can see that it represents a communicating system 1 for the detection of at least one target gas, according to a first embodiment of the present invention.

[0074] The communicating system 1 includes a microwave sensor 2 and a transmitting antenna 3.

[0075] The microwave sensor 2 comprises a substrate 4 on which a microwave device 5 is printed.

[0076] The microwave device 5 according to the first embodiment is a 50 Ohm impedance transmission line printed on the substrate 4, one 5a of the ends of the transmission line being configured to be connected to a network analyzer (RA) capable of applying a microwave signal on the transmission line, and the other 5b of the ends of the transmission line being connected to the transmitting antenna 3 via a connecting cable 6, the transmitting antenna 3 according to the first embodiment being a horn antenna.

[0077] It should be noted that the transmitting antenna 3 could also be connected to the microwave device 5 wirelessly by coupling, without departing from the scope of the present invention.

[0078] The microwave device 5 has a deposition opening 7 which is a break formed on the transmission line of impedance 50 Ohms, separating the transmission line into two portions on either side of the deposition opening 7.

[0079] By way of example, the transmission line may have a length of 30 mm and a width of 1.8 mm, with a deposition opening 7 of 200 pm at mid-length of the transmission line.

[0080] Furthermore, also by way of example, the substrate 4 can be made of polytetrafluoroethylene (PTFE) having a thickness of 0.5 mm, a dielectric permittivity er = 2.1 and a loss angle tangent tgô = 103, and the microwave device 5 can be made of copper 18 pm thick.

[0081] A cavity is provided in the substrate 4 at the level of the deposition opening 7, such that the deposition opening 7 serves as a deposition zone for a liquid substance 8 sensitive to at least one target gas.

[0082] It should be noted that a textile (such as a felt) could also be inserted at the level of the deposit opening 7 and soaked with the liquid substance 8 sensitive to at least one target gas, without departing from the scope of the present invention.

[0083] A drop (for example, with a volume of 15 pL) of the liquid substance 8 is deposited (for example, using a positive displacement micropipette) into the cavity of the deposition opening 7 so as to be in contact with the microwave device 5, with the two portions of the transmission line that are on either side of the opening of depot 7.

[0084] The liquid substance 8 is of the deep eutectic solvent type and is chosen such that the presence of at least one target gas in the environment of the microwave sensor 2 causes at least one of a change in the dielectric characteristics and a change in the electrical characteristics of the liquid substance 8, causing a change in the Sy distribution parameters of the microwave device 5 when a microwave signal is applied to it via the network analyzer.

[0085] The deep eutectic solvent-type liquid substance 8 may, for example, be one of:

[0086] - a mixture of choline chloride and urea in a molar ratio of 1:2;

[0087] - a mixture of choline chloride and thiourea in a molar ratio of 1:1;

[0088] - a mixture of choline chloride and glycerol in a molar ratio of 1:1;

[0089] - a mixture of choline chloride and ethylene glycol in one of the ratios molars 1:2 and 1:1;

[0090] - a mixture of choline chloride and glycerol in one of the molar ratios 1:2 and 1:1;

[0091] - a mixture of choline chloride and malonic acid in one of the ratios molars 1:2 and 1:1;

[0092] - a mixture of thymol and a fatty acid, such as hexanoic acid, heptanoic acid, octanoic, nonanoic or decanoic, in one of the molar ratios 1:2 and 1:1; and

[0093] - a mixture of menthol and a fatty acid, such as hexanoic, heptanoic, octanoic, nonanoic or decanoic, in one of the molar ratios 1:2 and 1:1.

[0094] The deep eutectic solvent-type liquid substance 8 is thus formed by a mixture, liquid at room temperature, of two compounds (namely, a hydrogen bond donor and a hydrogen bond acceptor) in an exact proportion that corresponds to the eutectic point.

[0095] The deposition opening 7 formed in the microwave device 5 allows for the localization and delimitation of the deposition area of ​​the liquid sensitive substance 8 on the substrate 4, in order to ensure the optimal operation of the microwave sensor 2.

[0096] Furthermore, the deposition opening 7 created in the microwave device 5 makes it possible to disrupt the operation of the microwave sensor 2. Indeed, the localization of the liquid sensitive substance 8 in the deposition opening 7 and the evolution of the electrical and / or dielectric characteristics of this liquid sensitive substance 8 following an external disturbance (presence of gaseous species, evolution of temperature, etc.) makes it possible to use the device as a gas-sensitive sensor.

[0097] The dielectric characteristics of the liquid sensitive substance 8 that vary in the presence of at least one target gas may, for example, be the permittivity di electric (er) and the tangent of the dielectric loss angle (tgô), as well as the absorption damping constant (a), these three parameters er, tgô and a evolving as a function of the gaseous environment of the sensitive liquid substance 8, its temperature and the working frequency of the microwave device 5.

[0098] The electrical characteristics of the sensitive liquid substance 8 which vary in the presence of at least one target gas may, for example, be resistivity or conductivity or resistance per square.

[0099] The communicating system 1 uses the specific response of the sensitive liquid substance 8 integrated into the microwave device 5 and is based on the evolution of the distribution parameters Sy (namely, the reflection parameters or coefficients Su and S 22, and the transmission parameters or coefficients Si2 and S2i) of the microwave device 5 when the sensitive liquid substance 8 interacts with one or more lethal, potentially dangerous and / or polluting target gases (such as SO2 or HCl).

[0100] The transmitting antenna 3 of the communicating system 1 allows the detection information and consequently the nature of the detected gas(s) to be transmitted directly into free space instantly to a dedicated microwave receiving system (not shown in [Fig.1]).

[0101] The communicating system 1 may further include a Peltier temperature control device (not visible in [Fig.1]) configured, after absorption of at least one target gas by the liquid substance 8 of the microwave sensor 2, to heat and then cool the microwave sensor 2 so as to cause the desorption of at least one target gas within the liquid substance 8 in order to regenerate the latter, thus causing a return of the distribution parameters of the microwave device 5 to the initial state before absorption, thus allowing the communicating system 1 to be reusable.

[0102] The Peltier temperature control device can either be a separate Peltier effect cell arranged so as to be able to heat and then cool the whole microwave sensor 2, or be a Peltier effect cell integrated into the substrate 4 in which case the microwave device 5 is directly printed on the surface of the Peltier effect cell.

[0103] If we refer to [Fig.2], we can see that a communicating system 11 is represented there according to a second embodiment of the present invention.

[0104] The common elements between the first embodiment of the invention in [Fig.1] and this second embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

[0105] The communicating system 11 according to the second embodiment is identical to communicating system 1 according to the first embodiment, except that the microwave device 15 according to the second embodiment is a 50 Ohms impedance transmission line 15a from which extends a stub 15b to form a quarter wave stub resonator whose stub 15b has a break as a deposition opening 17.

[0106] One 15c of the ends of the transmission line 15a is configured to be connected to a network analyzer (not shown in [Fig.2]) capable of applying a microwave signal to the microwave device 15, and the other 15d of the ends of the transmission line 15a is connected to the horn-type transmitting antenna 3 via the connecting cable 6.

[0107] A cavity is provided in the substrate 4 at the level of the deposition opening 17, such that the deposition opening 17 serves as a deposition zone for the liquid substance 8 sensitive to at least one target gas.

[0108] It should be noted that a textile (such as a felt) could also be inserted at the deposit opening 17 and soaked with the liquid substance 8 sensitive to at least one target gas, without departing from the scope of the present invention.

[0109] A drop of the liquid substance 8 is deposited (for example, using a positive displacement micropipette) into the cavity of the deposition opening 17 so as to be in contact with the stub 15b of the microwave device 15.

[0110] By way of example, the transmission line 15a of the resonator may have a length of 30 mm and a width of 1.8 mm, and the quarter-wave stub 15b of the resonator may have a length of 10 mm and a width of 0.08 mm, with a deposition aperture 17 of approximately 80 pm at mid-length of the stub 15b.

[0111] Referring to [Fig.3], one can see that a communicating system 21 is represented therein according to a third embodiment of the present invention.

[0112] The common elements between the first embodiment of the invention in [Fig.1] and this third embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

[0113] The communicating system 21 according to the third embodiment is identical to the communicating system 1 according to the first embodiment, except that the transmitting antenna 23 according to the third embodiment is a printed radiating element antenna (also called a patch antenna) whose radiating element is printed on the substrate 4 and connected to the end 5b of the microwave device 5 of the 50 Ohm transmission line type.

[0114] Referring to [Fig.4], one can see that a communicating system 31 is represented there according to a fourth embodiment of the present invention.

[0115] The common elements between the third embodiment of the invention on the [Fig.3] and this fourth embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

[0116] The communicating system 31 according to the fourth embodiment is identical to the communicating system 21 according to the third embodiment, except that the microwave device 35 according to the fourth embodiment comprises a transmission line 15a and a quarter-wave stub 15b to form a quarter-wave stub resonator.

[0117] One end 15c of the transmission line 15a is configured to be connected to a network analyzer (not shown in [Fig. 4]) capable of applying a microwave signal to the microwave device 35, and the other end 15d of the transmission line 15a is connected to one side of the patch-type transmitting antenna 23. The stub 15b is connected to the opposite side of the patch-type transmitting antenna 23 and has a break as a dropout 17.

[0118] During an experimental measurement, the communicating system 31 according to the fourth embodiment was evaluated during the application of a microwave signal at 2.45 GHz. The evolution of the reflection coefficient (Su), the gain, the efficiency and the radiation pattern was measured after deposition of a drop of deep eutectic solvent (namely, a mixture of choline chloride and urea in a molar ratio 1:2) in the deposition aperture 17 of the microwave device 35, and then after this deep eutectic solvent was subjected to a gas (namely, HCl vapors). A mismatch was observed in the communicating system 31 at the time of the deposition of the deep eutectic solvent droplet, thus degrading the quality of the transmission of the signal at 2.45 GHz, this mismatch becoming more significant during the absorption of HCl vapors by the deep eutectic solvent and during the increase in exposure time.Furthermore, it was observed that when antenna 23 is subsequently heated to 250°C (a deliberately high temperature to observe a significant effect; however, a lower temperature could be used simply to trigger the desorption process), the desorption of HCl species within the deep eutectic solvent leads to a readjustment of the communicating system 31, and a higher-quality microwave signal is again transmitted at 2.45 GHz. Thus, the communicating system 31 is indeed fully reversible.

[0119] Referring to [Fig.5], one can see that a communicating system 41 is represented therein according to a fifth embodiment of the present invention.

[0120] The common elements between the fourth embodiment of the invention in [Fig.4] and this fifth embodiment of the invention bear the same reference number, and will not be described in more detail here when they are of identical structures.

[0121] The communicating system 41 according to the fifth embodiment is identical to the communicating system 31 according to the fourth embodiment, except that the microwave device 45 according to the fifth embodiment is a printed radiating element transmitting antenna 23 to which a transmission line 15a is connected.

[0122] One 15c of the ends of the transmission line 15a is configured to be connected to a network analyzer (not shown in [Fig.5]) capable of applying a microwave signal to the microwave device 45, and the other 15d of the ends of the transmission line 15a is connected to the patch-type transmitting antenna 23.

[0123] In addition, three deposition openings 47 are formed in the printed radiating element of the transmitting antenna 23, and thus allow the deposition of one or more liquid sensitive substances of the deep eutectic solvent type on the surface of the microwave device 45.

[0124] It should be noted that any number of deposition openings 47 could be formed in the printed radiating element of the transmitting antenna 23, without departing from the scope of the present invention.

[0125] The patch-type transmitting antenna 23 thus acts both as a microwave device 45 for the microwave sensor 2 and as a transmitting antenna for the communicating system 4L

[0126] The deposition apertures 47 are thus directly incorporated into the printed radiating element of the transmitting antenna 23 in order to accommodate the deep eutectic solvent(s). Advantageously, the deposition apertures 47 are located in the areas of the antenna 23 where the current densities are maximum so that the modification of the electrical and / or dielectric characteristics of the deep eutectic solvent(s) has the maximum impact on the microwave signal generated by the communicating system 4L

[0127] Referring to [Fig.6], we can see that a microwave device 55 is shown there according to a sixth embodiment.

[0128] In this sixth embodiment, the microwave device 55 consists of a transmission line 55a with an impedance of 50 Ohms from which three stubs 55b, 55c and 55d extend so as to form three quarter-wave stub resonators connected in series.

[0129] A first cavity-type deposit opening 57a is formed on the first stub 55b, a second cavity-type deposit opening 57b is formed on the second stub 55c, and a third cavity-type deposit opening 57c is formed on the third stub 55d.

[0130] A first liquid substance of the deep eutectic solvent type 8a is deposited in the first deposition opening 57a, a second liquid substance of the deep eutectic solvent type 8b is deposited in the second deposition opening 57b, and a third liquid substance of the deep eutectic solvent type 8c is deposited in the third deposition opening 57c, the first, second and third liquid substances of the deep eutectic solvent type 8a, 8b and 8c being different from each other.

[0131] The microwave device 55 according to the sixth embodiment thus allows the deposition of various deep eutectic solvents in order to increase the selectivity of the microwave sensor 2. The deposition of several liquid sensitive substances 8a, 8b, and 8c onto the microwave device 55 makes it possible to obtain a transmitted signal characteristic of the target gas by obtaining a specific resonant frequency and amplitude. This is in fact the average resonant frequency of the set of liquid sensitive substances 8a, 8b, and 8c combined.

[0132] It should be noted that any number of stubs could also extend from the transmission line 55a, depending on the number of deep eutectic solvents to be deposited, without departing from the scope of the present invention.

[0133] By way of example, the first liquid substance 8a may be a mixture of choline chloride and urea (ChCl / U) in a molar ratio of 1:2, the second liquid substance 8b may be a mixture of choline chloride and thiourea (ChCl / ThU) in a molar ratio of 1:1, and the third liquid substance 8c may be a mixture of choline chloride and glycerol (ChCl / Gly) in a molar ratio of 1:1.

[0134] As shown in Table 1 below, these three liquid substances 8a, 8b, and 8c have different dielectric signatures (er and tgô) and reactivity to HCl. This leads to different resonance frequencies and amplitudes. For example, after 15 minutes of exposure to HCl, the resonance frequencies of ChCl / U, ChCl / ThU, and ChCl / Gly are 4.89 GHz, 5.11 GHz, and 6.29 GHz, respectively, with resonance amplitudes of -6.1 dB, -7.3 dB, and -5.5 dB, respectively.

[0135] [Tables 1] — Dielectric permittivity (er) Loss angle tangent (tangh) Resonance frequency (GHz) Resonance amplitude (dB) ChCl / U Without HCl 4.2 + 0.2 0.7 + 0.035 6.70 -8.6 With HCl t= 4 min 6.0 + 0.2 0.9 + 0.035 5.46 -6.8 With HCl t= 15 min 6.5 + 0.2 1.5 + 0.035 4.89 -6.1 ChCl / Th U Without HCl 3.9 + 0.2 0.5 + 0.035 6.92 -10.5 With HCl t= 4 min 6.5 + 0.2 0.6 + 0.035 6.11 -8.0 With HCl t= 15 min 9.0 + 0.2 1.0 + 0.035 5.11 -7.3 ChCl / Gly Without HCl 2.9 + 0.2 0.7 + 0.035 7.37 -8.9 With HCl t= 4 min 2.95 + 0.2 0.7 + 0.035 7.21 -8.2 With HCl t= 15 min 3.6 + 0.2 1.2 + 0.035 6.29 -5.5

[0136] To verify the functionality of such a microwave device 55, simulations were performed. In the case of a microwave device 55 with three sensitive layers (ChCl / U, ChCl / ThU, and ChCl / Gly), the resonance frequency is 5.22 GHz. This is the average resonance frequency of the three deep eutectic solvents combined. The resonance amplitude is -26.1 dB.

[0137] It should be noted that, in the case of a microwave device 55 with two sensitive layers (ChCl / U and ChCl / Gly), the resonance frequencies and amplitudes are respectively equal to 5.19 GHz and -18.1 dB. These results thus lead to obtaining a specific resonance frequency and resonance amplitude characteristic of the exposed gas (here HCl).

[0138] It should also be noted that the amplitude of a microwave device 55 with two or three sensitive layers is three times (or even four times) lower than that of microwave devices with a single sensitive layer. This makes it possible to consider using these devices for antenna development. Such a low amplitude would lead to the antenna stopping over a very wide band.

[0139] The microwave sensor 2 according to the present invention can also be used to carry out a process for characterizing at least one deep eutectic solvent-type liquid substance 8 sensitive to at least one target gas, comprising the following steps: applying, using a network analyzer, a microwave signal to the microwave device 5, 15, 35, 45 or 55 of the microwave sensor 2; measuring, using the network analyzer, the distribution parameters of the microwave signal at different absorption times of at least one target gas by at least one deep eutectic solvent-type liquid substance 8 of the microwave sensor 2; and obtaining, using numerical simulation software, the dielectric characteristics or the electrical characteristics of at least one deep eutectic solvent-type liquid substance 8 from the distribution parameters measured at the different absorption times.

[0140] Referring to [Fig.7], we can see that it shows curves illustrating experimental measurements, as a function of frequency, of the amplitude of the transmission coefficient S2i of the microwave device 15 of the quarter-wave stub resonator type according to the second embodiment, under different conditions of exposure to the target gas.

[0141] The curve Cn corresponds to the condition in which the deposition opening 17 is not loaded such that air is present at the level of the deposition opening 17, a resonance frequency of 9.20 GHz is then obtained.

[0142] Curve C12 corresponds to the condition in which the deposition opening 17 is loaded with a water droplet (15 pl), a resonance frequency of 4.28 GHz is then obtained.

[0143] The Cn curve corresponds to the condition in which the deposition opening 17 is loaded with a drop (15 pL) of deep eutectic solvent of the ChCl / U type in the absence of HCl gas in the environment, a resonance frequency of 6.70 GHz is then obtained.

[0144] The CU curve corresponds to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / U type and after an exposure time of 4 minutes to HCl gas vapors, a resonance frequency of 5.76 GHz is then obtained.

[0145] The curve Ci5 corresponds to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / U type and after an exposure time of 15 minutes to HCl gas vapors, a resonance frequency of 4.89 GHz is then obtained.

[0146] It can thus be observed that the deposition of the deep eutectic solvent in the deposition aperture 17 of the quarter-wave stub resonator leads to a first shift in the resonance frequency of the stub, explained by the modification of the effective permittivity undergone by the microwave device 15. When the eutectic solvent When the deep element is exposed to a gas such as HCl vapors, a new frequency shift is observed, accompanied by a decrease in the amplitude of the resonance peak. The effect intensifies with exposure time and is explained by an evolving modification of the dielectric characteristics of the deep eutectic solvent.

[0147] This phenomenon is characteristic of the behavior of a charged quarter-wave stub resonator; however, the shifts in resonance frequencies and the decrease in the amplitude of the resonance peaks are specific to each deep eutectic solvent. These observed differences allow for the dielectric characterization and definition of deep eutectic solvents by determining their dielectric permittivity (er) and their loss angle tangent (tan θ) from back-simulations performed with numerical simulation software such as CST Microwave Studio®. This method is a simple, reliable, reproducible, and low-cost way to characterize and identify a deep eutectic solvent by extracting the pair (er, tan θ) specific to each solvent from microwave measurements. Furthermore, regardless of the microwave device used, deep eutectic solvents have shown high sensitivity to HCl vapors.Thus, the use of these materials as a liquid sensitive layer in the development of microwave gas sensors is demonstrated.

[0148] Referring to [Fig.8], we can see that it shows curves illustrating simulated and experimental measurements of the evolution, as a function of frequency, of the amplitude of the transmission coefficient S2i of a microwave device 5 of the 50 Ohm transmission line type according to the first embodiment, under different conditions of exposure to the target gas.

[0149] The C2i curve and the C22 curve correspond, respectively, to an experimental measurement and a back-simulated measurement in the condition in which the deposition opening 7 is loaded with a drop (15 pL) of deep eutectic solvent of the ChCl / U type in the absence of HCl gas in the environment, er = 4.2 and tgô = 0.7 are then obtained.

[0150] Curve C23 and curve C24 correspond, respectively, to an experimental measurement and a back-simulated measurement in the condition in which the deposition opening 7 is loaded with the drop of deep eutectic solvent of the ChCl / U type and after an exposure time of 15 minutes to HCl gas vapors, er = 6.5 and tgô = 1.5 are then obtained.

[0151] In order to clarify the behavior of the deep eutectic solvent when subjected to HCl vapors, a kinetic study of HCl absorption and desorption was carried out using a 50 Ohm transmission line type microwave device 5 and focusing on three specific frequencies (100 MHz: the radio frequency, 1 GHz: an intermediate frequency, and 2.45 GHz: the WiFi frequency). The The microwave device 5, a 50-ohm transmission line type, was preferred to the microwave device 15, a quarter-wave stub resonator type, because its microwave behavior is analogous to that of a capacitor and is therefore simpler to process. Indeed, at low frequencies, the signal is not transmitted (the amplitude S2i is less than -20 dB), and at high frequencies, the behavior of the microwave device 5 is close to that of a short circuit.

[0152] It is thus observed that the absorption of HCl vapors by the deep eutectic solvent results in a significant increase in the microwave signal transmitted at low frequency and a better signal transmitted at high frequencies.

[0153] Heating at the end of absorption may be useful to accelerate the desorption process of HCl.

[0154] Referring to [Fig.9], it can be seen that it shows curves illustrating experimental measurements of the evolution, as a function of frequency, of the difference in amplitude of the transmission coefficient AS2i of the microwave device 15 of the quarter-wave stub resonator type according to the second embodiment, under different conditions of exposure to the target gas.

[0155] Curve C3i corresponds to the condition in which the deposition opening 17 is loaded with a drop (15 pL) of deep eutectic solvent of the ChCl / U type and after an exposure time of 4 minutes to HCl gas vapors.

[0156] Curve C32 corresponds to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / U type and after an exposure time of 15 minutes to HCl gas vapors.

[0157] It can be observed that the shape of the obtained kinetic curves is comparable to a damped sinusoidal function. Modeling has thus made it possible to extract two new constants: a damping constant α, and the amplitude A of the damped sinusoidal function. It has been found that these constants depend on the operating frequency of the stub resonator and the selected deep eutectic solvent, thus enabling a new method for differentiating these sensitive compounds.

[0158] The dielectric characteristics obtained, as well as the understanding and control of the microwave behavior of deep eutectic solvents, have thus confirmed the implementation of such a sensitive material for the development of communicating microwave systems based on printed sensor antennas.

[0159] Referring to [Fig. 10], it can be seen that it shows curves illustrating experimental measurements, as a function of frequency, amplitude of reflection coefficient Su and gain of communicating system 31 according to the fourth embodiment, under different conditions of exposure to the target gas.

[0160] The graphical representations Dla and Dlb correspond, respectively, to the amplitude of the reflection coefficient Su and the gain of the antenna 23 of the communicating system 31 according to the fourth embodiment, during a first phase of absorption of HCl.

[0161] The DI 1b curve corresponds to the condition in which the deposition opening 17 is not charged such that air is present at the level of the deposition opening 17.

[0162] The DI la and D12b curves correspond to the condition in which the deposition opening 17 is loaded with a drop of deep eutectic solvent of the ChCl / ThU type and in the absence of HCl gas in the environment.

[0163] Curves D12a and D13b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after an exposure time of 5 minutes to HCl gas vapors.

[0164] Curves D13a and D14b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after an exposure time of 10 minutes to HCl gas vapors.

[0165] Curves D14a and D15b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after an exposure time of 15 minutes to HCl gas vapors.

[0166] The graphical representations D2a and D2b correspond, respectively, to the amplitude of the reflection coefficient Su and the gain of the antenna 23 of the communicating system 31 according to the fourth embodiment, during a desorption phase triggered by heating after the first phase of absorption of HCl.

[0167] Curve D21b corresponds to the condition in which the deposition opening 17 is not charged such that air is present at the level of the deposition opening 17.

[0168] Curves D21a and D22b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and in the absence of heating.

[0169] Curve D22a corresponds to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a heating time of 5 minutes.

[0170] Curves D23a and D23b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a heating time of 10 minutes.

[0171] Curves D24a and D24b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a heating time of 15 minutes.

[0172] The graphical representations D3a and D3b correspond, respectively, to the amplitude of the reflection coefficient Su and the gain of the antenna 23 of the communicating system 31 according to the fourth embodiment, during a second phase HCl absorption after the heating-triggered desorption phase.

[0173] Curve D31b corresponds to the condition in which the deposition opening 17 is not loaded such that air is present at the level of the deposition opening 17.

[0174] Curves D31a and D32b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and before the second phase of HCl absorption.

[0175] Curves D32a and D33b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a second exposure time of 5 minutes to HCl gas vapors.

[0176] Curves D33a and D34b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a second exposure time of 10 minutes to HCl gas vapors.

[0177] Curves D34a and D35b correspond to the condition in which the deposition opening 17 is loaded with the deep eutectic solvent droplet of the ChCl / ThU type and after a second exposure time of 15 minutes to HCl gas vapors.

[0178] Fig. 10 as a whole thus represents the evolution of the parameter Su and the gain of the antenna 23 of the communicating system 31 during three different phases, namely a first absorption phase where the liquid substance of the deep eutectic solvent type ChCl / ThU, once deposited in the deposition opening 17, is exposed to HCl for 15 minutes, a second phase called desorption, where the system is heated to 200°C and finally, a second phase of HCl absorption of 15 minutes.

[0179] All the numerical values ​​of interest, including the theoretically expected gain losses during the mismatch phase between the network analyzer and the antenna 23, are grouped in Table 2 below. These mismatch losses are a function of the reflection coefficient Su at the input of the antenna 23 and are calculated as follows:

[0180] P^-101og(l-|SHj 2 )

[0181] These theoretical losses are compared to those measured.

[0182] [Tables2] — Su (dB) Gain (dBi) Efficiency (%) Losses due to expected misadventures (dB) Actual losses (dB) ChCl / ThU -13.8 0.72 25 / / 1st addition of HCl ChCl / ThU + HCl t= 3.5 2 5 min -0.4 ChCl / ThU + HCl t= 10 min -6.4 -4.51 7.7 1.13 5.22 ChCl / ThU + HCl t= 15 min -5.6 -5.51 6.4 1.38 6.22 Heating ChCl / ThU + / HCl- t6= ChCl / ThU + HCl t= 10 min -9.7 −0.05 21 0.49 0.77 ChCl / ThU + HCl t= 15 min -11.1 1.09 26 0.36 0.38 2nd addition of HCl, 0.3 min 0.38 t=ThU 23 0.34 0.32 ChCl / ThU + HCl t= 10 min −8.0 −0.53 18 0.76 1.25 ChCl / ThU + HCl t= 15 min −6.8 −2.23 12 1.01 2.95

[0183] Thus, it can be observed that during the first absorption phase, the antenna's Su parameter increases while its gain decreases. Therefore, the absorption of HCl by ChCl / ThU leads to a degradation in the performance of antenna 23. Indeed, by comparing the expected mismatch losses with the measured losses, the experimental losses are always greater than the calculated ones. This leads to the conclusion that the mismatch of antenna 23 is largely induced by the increased losses of the sensitive liquid substance 8 when it absorbs HCl. Furthermore, the study of efficiencies confirms this observation once again. Indeed, after deposition of ChCl / ThU in the deposition aperture 17, the efficiency of antenna 23 is 25%. However, after 15 minutes of exposure to HCl, the efficiency will reach a value of 6.4%.

[0184] Furthermore, the desorption of HCl triggered by a heating step of the system The 200°C heating of a communicating system 31 confirms the reversibility of a communicating system 31 using a deep eutectic solvent as the sensitive liquid substance 8. Indeed, after 15 minutes of heating, the antenna 23 returns almost to its initial state in terms of gain, reflection coefficient, and efficiency. Finally, during the second phase of HCl absorption, a mismatch in the antenna is still observable, but the phenomenon is less intense than during the first phase. In fact, during the first absorption phase, after 15 minutes, the reflection coefficient and the antenna gain reach values ​​of -5.6 dB and -5.51 dBi, respectively, compared to -6.8 dB and -2.23 dBi in the case of the second absorption phase. Thus, it is observed that ChCl / ThU, as a sensitive liquid substance 8, loses efficiency during its use.It is understood that the particular embodiments which have just been described have been given by way of indication and not limitation, and that modifications may be made without departing from the present invention.

Claims

Claims

1. Microwave sensor (2) for the detection of at least one target gas, characterized in that it comprises: - a substrate (4); - at least one microwave device (5; 15; 35; 45; 55) printed on the substrate (4), said at least one microwave device (5; 15; 35; 45; 55) having at least one deposition opening (7; 17; 47; 57a, 57b, 57c); and - at least one liquid substance (8; 8a, 8b, 8c) sensitive to the at least one target gas, said at least one liquid substance (8; 8a, 8b, 8c) being arranged in the at least one deposition opening (7; 17; 47; 57a, 57b, 57c) so as to be in contact with the at least one microwave device (5; 15; 35; 45; 55), the at least one liquid substance (8; 8a, 8b, 8c) being of deep eutectic solvent type and chosen so that a presence of the at least one target gas causes at least one of a modification of the dielectric characteristics and a modification of the electrical characteristics of the at least one liquid substance (8; 8a, 8b, 8c), causing a modification of the distribution parameters of the at least one microwave device (5; 15; 35; 45; 55) when a microwave signal is applied to it.

2. Microwave sensor (2) according to claim 1, characterized in that each deep eutectic solvent type liquid substance (8; 8a, 8b, 8c) is one of: - a mixture of choline chloride and urea in a molar ratio of 1:2; - a mixture of choline chloride and thiourea in a molar ratio of 1:1; - a mixture of choline chloride and glycerol in a molar ratio of 1:1; - a mixture of choline chloride and ethylene glycol in one of the molar ratios 1:2 and 1:1; - a mixture of choline chloride and glycerol in one of the molar ratios 1:2 and 1:1; - a mixture of choline chloride and malonic acid in one of the molar ratios 1:2 and 1:1; - a mixture of thymol and a fatty acid, such as hexanoic acid, heptanoic, octanoic, nonanoic or decanoic acid, in one of the molar ratios 1:2 and 1:1; and - a mixture of menthol and a fatty acid, such as hexanoic, heptanoic, octanoic, nonanoic or decanoic acid, in one of the molar ratios 1:2 and 1:

1.

3. Microwave sensor (2) according to claim 1 or 2, characterized in that, in each deposit opening (7; 17; 47; 57a, 57b, 57c), one of a textile soaked in at least one liquid substance (8; 8a, 8b, 8c) and a cavity containing the at least one liquid substance (8; 8a, 8b, 8c) is provided.

4. Microwave sensor (2) according to one of claims 1 to 3, characterized in that the substrate (4) is made of polytetrafluoroethylene, and the at least one microwave device (5; 15; 35; 45; 55) is made of copper and printed on the substrate (4).

5. Microwave sensor (2) according to one of claims 1 to 4, characterized in that the at least one microwave device (5) is a transmission line with an impedance equal to 50 Ohms, and the at least one deposit opening (7) is an interruption formed on the transmission line with an impedance of 50 Ohms.

6. Microwave sensor (2) according to one of claims 1 to 4, characterized in that the at least one microwave device (15; 35) is a transmission line with an impedance equal to 50 Ohms (15a) from which at least one stub (15b) extends to form at least one quarter-wave stub resonator, the stub (15b) of which has an interruption as a deposition opening (17).

7. A microwave sensor (2) according to claim 6, characterized in that a plurality of stubs (55b, 55c, 55d) extend from the 50 Ohm impedance transmission line (55a) to form a plurality of quarter-wave stub resonators, each quarter-wave stub resonator having, as a deposition opening (57a, 57b, 57c), an interruption formed on its stub (55b, 55c, 55d), a different deep eutectic solvent-like liquid substance (8a, 8b, 8c) being disposed in each of the stub interruption-like deposition openings (57a, 57b, 57c).

8. Communicating system (1; 11; 21; 31) for the detection of at least one target gas, characterized in that it comprises a microwave sensor (2) according to one of claims 1 to 7 and a transmitting antenna (3; 23) connected to the at least one microwave device (5; 15; 35; 55) of the microwave sensor (2), the at least one liquid substance (8; 8a, 8b, 8c) of the microwave sensor (2) being chosen such that a presence of the at least one target gas causes at least one of a modification of the dielectric characteristics and a modification of the electrical characteristics of the at least one liquid substance (8; 8a, 8b, 8c), causing a modification of the distribution parameters of the communicating system (1; 11; 21; 31) when a microwave signal is applied to the at least one microwave device (5; 15; 35; 55) of the microwave sensor (2).

9. Communicating system (1; 11; 21; 31) according to claim 8, characterized in that the transmitting antenna is one of a horn antenna (3) and a printed radiating element antenna (23).

10. Communicating system (41) for detecting at least one target gas, characterized in that it comprises a microwave sensor (2) according to one of claims 1 to 4, the at least one microwave device (45) of which is a printed radiating element transmitting antenna (23) in which the at least one deposition opening (47) is formed, the at least one liquid substance (8) of the microwave sensor (2) being chosen so that a presence of the at least one target gas causes at least one of a modification of the dielectric characteristics and a modification of the electrical characteristics of the at least one liquid substance (8), causing a modification of the distribution parameters of the communicating system (41) when a microwave signal is applied to the printed radiating element transmitting antenna (23).

11. Communicating system (1; 11; 21; 31; 41) according to one of claims 8 to 10, characterized in that it further comprises a Peltier effect temperature regulation device configured, after absorption of the at least one target gas by the at least one liquid substance (8; 8a, 8b, 8c) of the microwave sensor (2), to heat and then cool the microwave sensor (2) so as to cause the desorption of the at least one target gas within the at least one liquid substance (8; 8a, 8b, 8c), causing a return of the distribution parameters of the communicating system (1; 11; 21; 31; 41) to the initial state before absorption.

12. Method for characterizing at least one liquid substance of deep eutectic solvent type (8; 8a, 8b, 8c) sensitive to at least one target gas, using a microwave sensor (2) according to one of the claims indications 1 to 7, characterized in that said method comprises the following steps: - applying, using a network analyzer, a microwave signal to the at least one microwave device (5; 15; 35; 45; 55) of the microwave sensor (2); - measuring, using the network analyzer, the distribution parameters of the microwave signal at different absorption times of the at least one target gas by the at least one liquid substance of deep eutectic solvent type (8; 8a, 8b, 8c) of the microwave sensor (2); and - defining, using digital simulation software, one of the dielectric characteristics and the electrical characteristics of the at least one deep eutectic solvent type liquid substance (8; 8a, 8b, 8c) using the distribution parameters measured at the different absorption times, said dielectric characteristics comprising at least the dielectric permittivity and the tangent of the dielectric loss angle.

Images