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

Abstract

Deep eutectic solvent microwave sensor for detecting at least one target gas, communicating system comprising same, and associated characterization method The invention relates to a microwave sensor (2) for detecting 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 the at least one target gas, said liquid substance (8) being arranged in the deposition opening (7) so as to be in contact with the microwave device (5), the liquid substance (8) 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 liquid substance (8), causing a modification of the distribution parameters of the microwave device (5).Figure to be published with the abstract: Figure 1.

Description

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

[0001] The present invention relates to the field of microwave gas sensors, and relates in particular to a microwave sensor with a liquid substance of the deep eutectic solvent type 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 liquid substance of the deep eutectic solvent type using such a microwave sensor.

[0002] The development of microwave gas sensors has attracted widespread interest in many 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 device that transforms the physical or chemical interaction of the gaseous species with the sensitive layer into an analyzable signal, exclusively use receivers based on solid sensitive layers. The latter are capable of interacting with a gaseous species to be detected via physical interactions and / or chemical reactions that lead to a modification of the electrical or dielectric characteristics of the solid sensitive layer that will translate into a physical quantity. Thus, the choice of the solid sensitive layer is essential in any sensor development.The solid sensitive layers currently available on the market are varied and can be divided into several categories depending on their composition and chemical structure. These include, among others, metal / metal oxide nanostructures, sensitive layers based on polymer nanostructures, organic-inorganic composites and organometallic structures.

[0003] The aforementioned solid sensitive layers make it possible to detect numerous 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 oxide such as zinc oxide (ZnO), titanium dioxide (TiO2) sensitive to ammonia NH3, iron oxides (Fe2O3 / Fe2O4) or silicon dioxide (SiO2) have very good detection capabilities linked to the variable stoichiometry of oxygen on the surface and to their resulting electrical characteristics. On the other hand, this type of sensor generally operates at high temperature, which leads to drifts due to the oxidation of the reference electrode. This difficulty of implementation prevents low-cost industrialization. Conductive polymers are often used as a sensitive layer for the detection of VOCs, although the water present in the atmosphere strongly 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 microwave gas sensor whose sensitive layer is at least one sensitive liquid substance of the deep eutectic solvent type integrated in a microwave device.

[0006] The microwave gas sensor according to the present invention thus uses a bio-sourced, eco-responsible, easily synthesizable, and easily deposited 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 ones such as combat gases, can thus be developed, these sensors being selective and discriminating the targeted gas species(s).

[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 the at least one target gas, said at least one liquid substance being arranged in the at least one deposition opening so as to be in contact with the at least one microwave device, the at least one liquid substance 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, causing a modification of the distribution parameters of the at least one microwave device when a microwave signal is applied thereto. ;

[0009] Thus, the association of a liquid sensitive substance of deep eutectic solvent type with a microwave device makes it possible to detect the presence of a target gas, the latter being able to be a lethal, potentially dangerous and / or polluting gas. Indeed, a modification of the distribution parameters of the microwave device when the liquid sensitive substance interacts with the target gas allows the microwave sensor to detect the presence of the target gas.

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

[0011] The at least one liquid substance is arranged in the 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 microwaves, electricity or electronics to describe the electrical behavior of linear electrical networks as a function of input signals. A microwave device is modeled, by the distribution parameters, by 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 an input (designated 1) and an output (designated 2), the distribution parameters are thus Su (input reflection coefficient), Si2 (reverse transmission coefficient), S2i (direct transmission coefficient) and S22 (output reflection coefficient).

[0013] The present invention thus implements, for the first time, a sensitive layer in liquid form formed from a deep eutectic solvent. Deep eutectic solvents constitute a new variety of emerging solvents, eco-responsible and known for their low toxicity, their non-volatility and their low production cost, since they are, for the majority of them, formed from easily accessible natural products. They are defined through the formation of a molecular network resulting from non-covalent associations governed by hydrogen bonds between hydrogen bond acceptors and hydrogen bond donors and electrostatic interactions.On the one hand, their very low volatility, their high viscosity (which prevents the spreading of the drop deposited on the surface of the microwave device) and their interactions with ionic entities (dipoles) make them very good candidates for the development 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 highlighted by differential physicochemical measurements of the interacting gaseous species.

[0014] Furthermore, the means used for depositing the liquid sensitive substance in the deposition opening formed on the microwave device is easily achievable at low cost. Indeed, it is sufficient, for example, to use a positive displacement micropipette (ideal for sampling a viscous liquid) to sample the required volume of liquid sensitive substance to be deposited in the deposition opening of the microwave device. perfrequency.

[0015] Although the system has demonstrated a certain reversibility, the liquid sensitive substance still loses its effectiveness as it is used. However, it can easily be removed from the deposition opening and replaced by a new drop of liquid sensitive substance, when its effectiveness reaches a predefined threshold value. This thus makes it possible to avoid the manufacture of a new microwave gas sensor.

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

[0017] Furthermore, the deposition opening is created in the microwave device in order to disturb the operation of the latter. Indeed, the location of the liquid sensitive substance in the deposition opening and the evolution of this liquid sensitive substance following an external disturbance (presence of gaseous species, evolution of the temperature, 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 liquid sensitive substance which vary in the presence of the at least one target gas may, 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 liquid sensitive substance, its temperature and the working frequency of the microwave device.

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

[0020] The present invention uses the specific response of the liquid sensitive substance integrated in 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 characteristic of the present invention, each liquid substance of deep eutectic solvent type is one of:

[0022] - a mixture of choline chloride and urea in a molar ratio of 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 a 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 a hexanoic acid, heptanoic acid, octanoic, nonanoic or decanoic, in one of the molar ratios 1:2 and 1:1.

[0030] Thus, each liquid sensitive substance of 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 which corresponds to the eutectic point.

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

[0032] Thus, either the textile (such as a felt) arranged 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 characteristic of the present invention, the substrate is made of polytetrafluoroethylene, and the at least one microwave device is made of copper and printed on the substrate.

[0034] For 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] Furthermore, also by way of example, the at least one microwave device may be made of 18 μm thick copper.

[0036] According to a particular characteristic of the present invention, the at least one microwave device is a transmission line with an impedance equal to 50 Ohms, and the at least one deposition opening is an interruption 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] For 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 characteristic of the present invention, the at least one microwave device is a transmission line of impedance 50 Ohms from which at least one stub extends to form at least one quarter-wave stub resonator whose stub has an interruption 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] For example, the resonator transmission line may be 30 mm long and 1.8 mm wide, and the resonator quarter-wave stub may be 10 mm long and 0.08 mm wide, with an 80 pm break approximately halfway along the stub.

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

[0043] Thus, this quarter-wave multi-stub resonator type microwave device allows the deposition of several different liquid sensitive substances (i.e., a distinct liquid sensitive substance in each deposition opening), which makes it possible to increase the selectivity of the microwave sensor. Indeed, the deposition of several liquid sensitive substances on the microwave device makes it possible to obtain a transmitted signal characteristic of the target gas by obtaining a specific resonance frequency and amplitude. This is the average resonance frequency of all the liquid sensitive substances combined.

[0044] The present invention also relates to a communicating system for detecting at least one target gas, characterized in that it comprises a microwave sensor as described above and a transmitting antenna connected to the at least one microwave device of the microwave sensor, the at least one liquid substance of the microwave sensor 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, causing a modification of the distribution parameters of the communicating system when a microwave signal is applied to the at least one microwave device of the microwave sensor.

[0045] Thus, the transmitting antenna of the communicating system makes it possible to transmit wirelessly the result of the detection, by the microwave sensor, of the at least one target gas 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- exclusively, or by coupling.

[0047] The communicating system thus makes it possible to transmit the detection information and consequently the nature of the gas(es) detected instantly to a dedicated microwave reception system. In addition, the communicating system is reusable, even after detection of a target gas.

[0048] According to a particular characteristic 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, the at least one microwave device of which is a printed radiating element transmitting antenna in which the at least one deposition opening is formed, the at least one liquid substance of the microwave sensor 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, 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 a microwave device for the microwave sensor and the role of a transmitting antenna for the communicating system.

[0053] The patch-type transmission antenna of the communicating system makes it possible to wirelessly transmit the result of the detection, by the microwave sensor, of the at least one target gas 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 gas(es) detected instantly to a dedicated microwave reception system. In addition, the communicating system is reusable, even after detection of a target gas.

[0055] According to a particular characteristic of the present invention, the communicating system 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 of the microwave sensor, to heat and then cool the microwave sensor. frequency so as to cause the desorption of the at least one target gas within the 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 effect temperature control device makes it possible to regulate the temperature of the communicating system. In fact, after detecting the target gas, it makes it possible to heat and then cool 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 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 the 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 the at least one target gas by the at least one liquid substance of deep eutectic solvent type of the microwave sensor;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 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.;

[0058] The microwave sensor according to the invention can thus also be used for the microwave characterization of the liquid sensitive substance of 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 effective, unlike existing techniques. Indeed, the complex structure of deep eutectic solvents and their shaping based on non-covalent interactions make them very difficult to characterize with the existing physicochemical means most widely used in laboratories. It is in fact studies of their physicochemical properties including, among other things, their viscosity, their water charge (percentage) via the Karl Fischer method and their density, which are more generally implemented. A recent study has also made it possible, via mass spectrometry, to structurally characterize deep eutectic solvents in the gas phase. 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, for example.Methods of dif . neutron fraction associated with molecular modeling have also been proposed, but they remain confined to the know-how of highly specialized research units.

[0060] The present invention makes it possible to obtain efficiently and in a reliable and reproducible manner 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 retro-simulation by means of digital simulation software.

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

[0062] In 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, of the amplitude of the transmission coefficient S2i of a quarter-wave stub resonator type microwave device 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 the frequency, of the amplitude of the transmission coefficient S2i of a 50 Ohm transmission line type microwave device according to the invention under different conditions of exposure to the target gas;

[0071] [Fig.9] represents curves illustrating experimental measurements of the evolution, as a function of the frequency, of the difference in amplitude of the transmission coefficient AS2i of a quarter-wave stub resonator type microwave device according to the invention under different conditions of exposure 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 com system communicating with [Fig.4] under different conditions of exposure to the target gas.

[0073] If we refer to [Fig. 1], we can see that there is shown 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 comprises 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 transmission line with an impedance of 50 Ohms printed on the substrate 4, one 5a of the ends of the transmission line being configured to be connected to a network analyzer (AR) capable of applying a microwave signal to the transmission line, and the other 5b of the ends of the transmission line being connected to the transmission antenna 3 via a connection cable 6, the transmission 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 an interruption 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] For example, the transmission line may have a length of 30 mm and a width of 1.8 mm, with a deposition aperture 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 tangent of the loss angle tgô = 103, and the microwave device 5 can be made of copper 18 μm thick.

[0081] A cavity is provided in the substrate 4 at 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 deposition 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, of a volume of 15 pL) of the liquid substance 8 is deposited (for example, using a positive displacement micropipette) in 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 which are on either side of the opening of deposit 7.

[0084] The liquid substance 8 is of the deep eutectic solvent type and is chosen so that a presence of the at least one target gas in the environment of the microwave sensor 2 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 Sy of the microwave device 5 when a microwave signal is applied thereto 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 a hexanoic acid, heptanoic acid, octanoic, nonanoic or decanoic acid, in one of the molar ratios 1:2 and 1:1; and

[0093] - a mixture of menthol and a fatty acid, such as a 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 the exact proportion which corresponds to the eutectic point.

[0095] The deposition opening 7 formed in the microwave device 5 makes it possible to ensure the location and delimitation of the deposition zone of the liquid sensitive substance 8 on the substrate 4, in order to ensure 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 location 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 the temperature, etc.) makes it possible to use the device as a gas-sensitive sensor.

[0097] The dielectric characteristics of the liquid sensitive substance 8 which vary in the presence of the 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 according to the gaseous environment of the liquid sensitive substance 8, its temperature and the working frequency of the microwave device 5.

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

[0099] The communicating system 1 uses the specific response of the liquid sensitive substance 8 integrated in 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 liquid sensitive 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 makes it possible to transmit directly into free space the detection information and consequently the nature of the gas(es) detected instantaneously to a dedicated microwave receiving system (not shown in [Fig.l]).

[0101] The communicating system 1 may further comprise a Peltier effect temperature regulation device (not visible in [Fig.l]) configured, after absorption of the 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 the 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 effect temperature control device can either be a separate Peltier effect cell arranged so as to be able to heat and then cool the entire 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 there is represented a communicating system 11 according to a second embodiment of the present invention.

[0104] The elements common to the first embodiment of the invention in [Fig.l] 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 the communicating system 1 according to the first embodiment, except that the microwave device 15 according to the second embodiment is a 50 Ohm impedance transmission line 15a from which a stub 15b extends to form a quarter-wave stub resonator whose stub 15b has an interruption 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 connection cable 6.

[0107] A cavity is provided in the substrate 4 at 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 level of the deposition 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] For 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 80 pm approximately halfway along the length of the stub 15b.

[0111] If we refer to [Fig.3], we can see that there is shown a communicating system 21 according to a third embodiment of the present invention.

[0112] The elements common to the first embodiment of the invention in [Fig.l] 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] If we refer to [Fig.4], we can see that there is represented there a communicating system 31 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 15c of the ends 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 15d of the ends of the transmission line 15a is connected to one of the sides 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 an interruption as a deposition opening 17.

[0118] In an experimental measurement, the communicating system 31 according to the fourth embodiment was evaluated when applying a microwave signal at 2.45 GHz. The evolution of the reflection coefficient (Su), the gain, the efficiency as well as the radiation pattern was measured after depositing a drop of deep eutectic solvent (namely, a mixture of choline chloride and urea in a 1:2 molar ratio) in the deposition opening 17 of the microwave device 35, then after this deep eutectic solvent was subjected to a gas (namely, HCl vapors). A mismatch of the communicating system 31 was observed at the time of deposition of the drop of deep eutectic solvent, thus degrading the quality of the signal transmission at 2.45 GHz, this mismatch becoming more significant during the absorption of the HCl vapors by the deep eutectic solvent and during the increase in the exposure time.Furthermore, it has been observed that, when the antenna 23 is then heated to a temperature of 250°C (a deliberately high temperature to observe a significant effect, it would however be possible to use a lower temperature to only trigger the desorption phenomenon), the desorption of the HCl species within the deep eutectic solvent leads to a readjustment of the communicating system 31 and a better quality microwave signal is again transmitted at 2.45 GHz. Thus, the communicating system 31 is indeed completely reversible.

[0119] If we refer to [Fig.5], we can see that there is shown a communicating system 41 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 15 a 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 is noted that any number of deposition apertures 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 transmission antenna 23 thus plays both the role of microwave device 45 for the microwave sensor 2 and the role of transmission antenna for the communicating system 4L.

[0126] The deposition openings 47 are thus directly included in the printed radiating element of the transmitting antenna 23 in order to accommodate the deep eutectic solvent(s) therein. Advantageously, the deposition openings 47 are located in the zones 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] If we refer 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 of impedance 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-like deposition opening 57a is formed on the first stub 55b, a second cavity-like deposition opening 57b is formed on the second stub 55c, and a third cavity-like deposition opening 57c is formed on the third stub 55d.

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

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

[0132] It is 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] For example, the first liquid substance 8a may be a mixture of choline chloride and urea (ChCl / U) in a 1:2 molar ratio, the second liquid substance 8b may be a mixture of choline chloride and thiourea (ChCl / ThU) in a 1:1 molar ratio, and the third liquid substance 8c may be a mixture of choline chloride and glycerol (ChCl / Gly) in a 1:1 molar ratio.

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

[0135] [Tables 1] — Dielectric permittivity (er ) Tangent of the loss angle (tgô) Resonant frequency (GHz) Resonant 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] In order to verify the functionality of such a 55 microwave device, simulations were carried out. In the case of a 55 microwave device 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 equal to -26.1 dB.

[0137] It should be noted that, in the case of a 55 microwave device 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 resonance frequency and a specific 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 for microwave devices having a single sensitive layer. This makes it possible to consider the use of these devices for antenna development. Such a low amplitude would lead to the stopping of the operation of the antenna over a very wide band.

[0139] The microwave sensor 2 according to the present invention can also be used to carry out a method for characterizing at least one liquid substance of deep eutectic solvent type 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 the at least one target gas by the at least one liquid substance of deep eutectic solvent type 8 of the microwave sensor 2; and obtaining, using digital simulation software, the dielectric characteristics or the electrical characteristics of the at least one liquid substance of deep eutectic solvent type 8 from the distribution parameters measured at the different absorption times.

[0140] If we refer to [Fig.7], we can see that curves are shown there illustrating experimental measurements, as a function of the frequency, of the amplitude of the transmission coefficient S2i of the quarter-wave stub resonator type microwave device 15 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 drop of water (15 pl), a resonance frequency of 4.28 GHz is then obtained.

[0143] The curve Cn 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 drop of deep eutectic solvent 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] Curve Ci5 corresponds to the condition in which the deposition opening 17 is loaded with the drop of deep eutectic solvent of the ChCl / U type and after an exposure time of 15 minutes to the HCl gas vapors, a resonance frequency of 4.89 GHz is then obtained.

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

[0147] This phenomenon is characteristic of the behavior of a loaded 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 make it possible to characterize and define deep eutectic solvents dielectrically by determining their dielectric permittivity (er) and their loss angle tangent (tgô) from retrosimulations carried out with numerical simulation software such as CST Microwave Studio® software. This method is a simple, reliable, reproducible and low-cost way to characterize and identify a deep eutectic solvent by extracting the pair (er , tgô) specific to each from microwave measurements. In addition, regardless of the microwave device used, deep eutectic solvents have shown high sensitivity to HCl vapors.Thus, the use of these materials as liquid sensitive layer in the development of microwave gas sensors is demonstrated.

[0148] If we refer to [Fig.8], we can see that curves are shown there illustrating simulated and experimental measurements of the evolution, as a function of the 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] Curve C2i and curve C22 correspond, respectively, to an experimental measurement and a retrosimulated 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 retrosimulated 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 the absorption and desorption of HCl was carried out using the 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). 50 Ohm transmission line type microwave device 5 was preferred to the quarter-wave stub resonator type microwave device 15 because its microwave behavior is similar to that of a capacitor and is therefore simpler to process. Indeed, at low frequencies, the signal is not transmitted (the amplitude S 2i is less than -20 dB), and at high frequencies, the behavior of microwave device 5 is similar 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 in order to accelerate the HCl desorption process.

[0154] If we refer to [Fig.9], we can see that curves are shown there illustrating experimental measurements of the evolution, as a function of the frequency, of the difference in amplitude of the transmission coefficient AS2i of the quarter-wave stub resonator type microwave device 15 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 drop of deep eutectic solvent of the ChCl / U type and after an exposure time of 15 minutes to HCl gas vapors.

[0157] It can be seen that the shape of the kinetic curves obtained is comparable to a damped sinusoidal function. Modeling has thus made it possible to extract two new constants: a damping constant a, as well as the amplitude A of the damped sinusoidal function. It has been found that these constants are dependent on the working frequency of the stub resonator and the selected deep eutectic solvent, thus allowing a new method of 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] If we refer to [Fig. 10], we can see that curves illustrating experimental measurements are represented therein, as a function of the frequency, the amplitude of the reflection coefficient Su and the gain of the 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] Curve DI 1b corresponds to the condition in which the deposition opening 17 is not charged such that air is present at the deposition opening 17.

[0162] Curves D11a and D12b 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 drop of deep eutectic solvent 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 drop of deep eutectic solvent 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 drop of deep eutectic solvent 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 to 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 HCl absorption phase.

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

[0168] Curves D21a and D22b correspond to the condition in which the deposition opening 17 is loaded with the drop of deep eutectic solvent 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 drop of deep eutectic solvent 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 drop of deep eutectic solvent 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 drop of deep eutectic solvent 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 to the gain of the antenna 23 of the communicating system 31 according to the fourth embodiment, during a second phase HCl absorption after the desorption phase triggered by heating.

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

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

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

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

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

[0178] [Fig. 10] as a whole thus represents the evolution of the parameter Su and of 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 HCl absorption phase 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 together 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 Misalignments (dB) Actual Losses (dB) ChCl / ThU -13.8 0.72 25 / / 1st Addition of HCl ChCl / ThU + HCl 3,9 1 2 5 min -0.8 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 seen that during the first absorption phase, the Su parameter of the antenna increases while its gain decreases. Thus, the absorption of HCl by ChCl / ThU leads to a degradation of the performance of the antenna 23. Indeed, by comparing the expected mismatch losses with those measured, it is found that the experimental ones are always greater than those calculated. This leads to the conclusion that the mismatch of the antenna 23 is induced largely by the increase in losses of the sensitive liquid substance 8 when it absorbs HCl. Furthermore, the study of the efficiencies once again confirms this observation. Indeed, after deposition of ChCl / ThU in the deposition opening 17, the efficiency of the antenna 23 is 25%. However, after 15 minutes of exposure to HCl, the efficiency will reach a value of 6.4%.

[0184] In addition, the desorption of HCl triggered by a heating step of the system communicating 31 of 200°C confirms the ability of a communicating system 31 using a deep eutectic solvent as sensitive liquid substance 8 to be reversible. Indeed, it is observed that 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 of the antenna is still observable but the phenomenon is less intense than during the first phase. Indeed, during the first absorption kinetics, after 15 minutes, the reflection coefficient and the gain of the antenna 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 kinetics. Thus, it is observed that ChCl / ThU, as sensitive liquid substance 8, loses its efficiency during its use.It is understood that the particular embodiments which have just been described have been given for informational and non-limiting purposes, and that modifications may be made without departing from the present invention.

Claims

Claims

1. Microwave sensor (2) for detecting 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.

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