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

Abstract

The invention relates to a microwave sensor (2) for detecting at least one target gas, the sensor 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, the 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 a deep eutectic solvent and chosen such that the presence of the at least one target gas causes at least one of a change in the dielectric characteristics or a change in the electrical characteristics of the liquid substance (8), resulting in a change in the distribution parameters of the microwave device (5).

Description

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 deep eutectic solvent type liquid substance microwave sensor for detecting 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 substance 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 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 through 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-state sensitive layers currently available on the market are varied and can be divided into several categories based 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 above-mentioned solid sensitive layers can 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 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 their resulting electrical characteristics. On the other hand, this type of sensor generally operates at high temperatures, 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 sensitive layers for the detection of VOCs, although water present in the atmosphere strongly destabilizes the system, thus limiting the sensitivity of the sensors.

[0005] The present invention aims to solve 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 disposed 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 combination of a liquid sensitive substance of the 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 range. 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, and electronics to describe the electrical behavior of linear electrical networks as a function of input signals. A microwave device is modeled, by the scattering 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 with an input (designated 1) and an output (designated 2), the scattering parameters are thus S 11 (input reflection coefficient), S 12(reverse transmission coefficient), S 21 (direct transmission coefficient) and S 22 (reflection coefficient at the output).

[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 collect the required volume of liquid sensitive substance to be deposited in the deposition opening of the microwave device.

[0015] Although the system has demonstrated a certain reversibility, the liquid sensing substance still loses its effectiveness over time. 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 thus eliminates the need to manufacture a new microwave gas sensor.

[0016] The deposition opening formed in the microwave device ensures the localization and delimitation of the deposition area 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 disrupt 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 (ε r ) and the tangent of the dielectric loss angle (tgδ), as well as the absorption damping constant (α), these three parameters ε r , tgδ and α evolving according to 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 S ij(namely, the reflection parameters or coefficients S 11 and S 22 , and the transmission parameters or coefficients S 12 and S 21 ) 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 deep eutectic solvent type liquid substance 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 molar ratios 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 molar ratios 1:2 and 1:1;

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

[0029] - 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.

[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 ε r = 2.1 and a tangent of the loss angle tgδ = 10 -3 .

[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 deposit opening is an interruption formed on the transmission line with an impedance of 50 Ohms.

[0037] Thus, the interruption in 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 be 30 mm long and 1.8 mm wide, with a 200 µm break halfway along 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 resonator stub forms a gap which serves as a deposition zone for the liquid sensitive substance.

[0041] As an 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 µm 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-like liquid substance being disposed in each of the stub interruption-like 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 separate liquid sensitive substance in each deposition opening), which increases 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 together.

[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 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 physically or by coupling.

[0047] The communicating system thus makes it possible to transmit 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 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.

[0054] The communicating system thus makes it possible to transmit 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 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 allows the temperature of the communicating system to be regulated. In fact, after detecting the target gas, it allows the communicating system to be heated and then cooled in order to regenerate the sensitive liquid 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 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 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. Indeed, studies of their physicochemical properties including, among other things, their viscosity, their water charge (percentage) via the Karl Fischer method and their density 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.Neutron diffraction methods 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 efficiently, reliably and reproducibly obtain 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 accompanying drawings.

[0062] On these drawings:

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

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

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

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

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

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

[0069] represents curves illustrating experimental measurements, as a function of frequency, of the amplitude of the transmission coefficient S 21of a quarter-wave stub resonator type microwave device according to the invention under different conditions of exposure to the target gas;

[0070] represents curves illustrating simulated and experimental measurements of the evolution, as a function of frequency, of the amplitude of the transmission coefficient S 21 of a 50 Ohm transmission line type microwave device according to the invention under different conditions of exposure to the target gas;

[0071] represents curves illustrating experimental measurements of the evolution, as a function of frequency, of the difference in amplitude of the transmission coefficient ΔS 21 of a quarter-wave stub resonator type microwave device according to the invention under different conditions of exposure to the target gas; and

[0072] represents curves illustrating experimental measurements of the evolution, as a function of frequency, of the reflection coefficient S 11 and the gain of the communicating system under different conditions of exposure to the target gas.

[0073] Referring to the, it can be seen 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 is 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 be 30 mm long and 1.8 mm wide, with a deposition aperture 7 of 200 µm at mid-length of the transmission line.

[0080] Furthermore, also by way of example, the substrate 4 may be made of polytetrafluoroethylene (PTFE) having a thickness of 0.5 mm, a dielectric permittivity ε r = 2.1 and a tangent of the loss angle tgδ = 10 -3 , and the microwave device 5 can be made of 18 µm thick copper.

[0081] A cavity is provided in the substrate 4 at the deposition opening 7, such that the deposition opening 7 serves as a deposition area 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 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 μL) 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 deposition opening 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 results in 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 S ij 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 molar ratios 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 molar ratios 1:2 and 1:1;

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

[0094] The deep eutectic solvent-like 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 localization and delimitation of the deposition zone 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 location of the liquid sensitive substance 8 in the deposition opening 7 and the change in the electrical and / or dielectric characteristics of this liquid sensitive substance 8 following an external disturbance (presence of gaseous species, change in 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 dielectric permittivity (ε r ) and the tangent of the dielectric loss angle (tgδ), as well as the absorption damping constant (α), these three parameters ε r, tgδ and α evolving as a function of 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 S ij (namely, the reflection parameters or coefficients S 11 and S 22 , and the transmission parameters or coefficients S 12 and S 21) of the microwave device 5 when the liquid sensitive substance 8 interacts with one or more deadly, 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 instantly to a dedicated microwave receiving system (not shown).

[0101] The communicating system 1 may further comprise a Peltier effect temperature regulation device (not visible in the) 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 temperature control device may either be a separate Peltier cell arranged to be capable of heating and then cooling the entire microwave sensor 2, or it may be a Peltier cell integrated into the substrate 4 in which case the microwave device 5 is directly printed on the surface of the Peltier cell.

[0103] Referring to the, it can be seen that there is shown a communicating system 11 according to a second embodiment of the present invention.

[0104] The common elements between the first embodiment of the invention 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 the) 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 area 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 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 be 30 mm long and 1.8 mm wide, and the quarter-wave stub 15b of the resonator may be 10 mm long and 0.08 mm wide, with a deposition aperture 17 of 80 µm approximately mid-length of the stub 15b.

[0111] Referring to the, it can be seen that there is shown a communicating system 21 according to a third embodiment of the present invention.

[0112] The common elements between the first embodiment of the invention 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 the, it can be seen that there is shown a communicating system 31 according to a fourth embodiment of the present invention.

[0115] The common elements between the third embodiment of the invention 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 the) 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 in turn 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 (S 11), gain, efficiency and radiation pattern were 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, and 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] Referring to the, it can be seen 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 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 the) 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] Furthermore, 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 transmitting antenna 23 thus plays both the role of microwave device 45 for the microwave sensor 2 and the role of transmitting antenna for the communicating system 41.

[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 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 41.

[0127] Referring to the, it can be seen 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-like liquid substance 8a is deposited in the first deposition opening 57a, a second deep eutectic solvent-like liquid substance 8b is deposited in the second deposition opening 57b, and a third deep eutectic solvent-like liquid substance 8c is deposited in the third deposition opening 57c, the first, second, and third deep eutectic solvent-like 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 all the liquid sensitive substances 8a, 8b and 8c combined.

[0132] It is noted that any number of stubs could also extend from 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 presented in Table 1 below, these three liquid substances 8a, 8b and 8c have a dielectric signature (ε r and tgδ) as well as different 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] Dielectric permittivity (ε r )Tangent of the loss angle (tgδ)Resonance frequency (GHz)Resonance amplitude (dB)ChCl / USoHCl4.2 ± 0.20.7 ± 0.0356.70-8.6With HCl t= 4 min6.0 ± 0.20.9 ± 0.0355.46-6.8With HCl t= 15 min6.5 ± 0.21.5 ± 0.0354.89-6.1ChCl / ThUSoHCl3.9 ± 0.20.5 ± 0.0356.92-10.5With HCl t= 4 min6.5 ± 0.20.6 ± 0.0356.11-8.0With HCl t= 15 min9.0 ± 0.21.0 ± 0.0355.11-7.3ChCl / GlyWithout HCl2.9 ± 0.20.7 ± 0.0357.37-8.9With HCl t= 4 min2.95 ± 0.20.7 ± 0.0357.21-8.2With HCl t= 15 min3.6 ± 0.21.2 ± 0.0356.29-5.5

[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 is also worth noting 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 with 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 antenna stopping operation 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 numerical 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 the, we can see that it shows curves illustrating experimental measurements, as a function of the frequency, of the amplitude of the transmission coefficient S 21 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 C curve 11 corresponds to the condition in which the deposition opening 17 is not charged such that air is present at the deposition opening 17, a resonance frequency of 9.20 GHz is then obtained.

[0142] The C curve 12 corresponds to the condition in which the deposition opening 17 is loaded with a drop of water (15 µl), a resonance frequency of 4.28 GHz is then obtained.

[0143] The C curve 13corresponds to the condition in which the deposition opening 17 is loaded with a drop (15 µL) 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 C curve 14 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] The C curve 15 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 explained by the modification of the effective permittivity undergone by the microwave device 15. When the deep eutectic solvent is subjected to a gas such as HCl vapors, a new frequency shift is observed to which is added a reduction in the amplitude of the resonance peak. The effect intensifies with the 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 make it possible to characterize and define deep eutectic solvents dielectrically by determining their dielectric permittivity (ε r ) and their loss angle tangent (tgδ) from back simulations performed 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 through the extraction of the couple (ε r, tgδ) specific to each from microwave measurements. Moreover, regardless of the microwave device used, deep eutectic solvents showed high sensitivity to HCl vapors. Thus, the use of these materials as a liquid sensitive layer in the development of microwave gas sensors is therefore demonstrated.

[0148] If we refer to the, 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 S 21 of a 50 Ohm transmission line type microwave device 5 according to the first embodiment, under different conditions of exposure to the target gas.

[0149] The C curve 21 and curve C 22correspond, respectively, to an experimental measurement and a back-simulated measurement under the condition in which the deposition opening 7 is loaded with a drop (15 µL) of deep eutectic solvent of the ChCl / U type in the absence of HCl gas in the environment, ε r = 4.2 and tgδ = 0.7 are then obtained.

[0150] The C curve 23 and curve C 24 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, ε r = 6.5 and tgδ = 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 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). The 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 analogous to that of a capacitor and is therefore simpler to process. Indeed, at low frequencies, the signal is not transmitted (the amplitude S 21 is less than -20 dB), and in high frequencies, the behavior of the microwave device 5 approaches 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 frequencies and a better signal transmitted at high frequencies.

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

[0154] If we refer to the, we can see that it shows curves illustrating experimental measurements of the evolution, as a function of frequency, of the difference in amplitude of the transmission coefficient ΔS 21 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] The C curve 31corresponds to the condition in which the deposition opening 17 is loaded with a drop (15 µL) of deep eutectic solvent of the ChCl / U type and after an exposure time of 4 minutes to HCl gas vapors.

[0156] The C curve 32 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.

[0157] It can be seen 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, 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 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] If we refer to the, we can see that it shows curves illustrating experimental measurements, as a function of the frequency, of the amplitude of the reflection coefficient S 11 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 D1a and D1b correspond, respectively, to the amplitude of the reflection coefficient S 11 and to 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 D11b 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 S 11 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 S 11 and to the gain of the antenna 23 of the communicating system 31 according to the fourth embodiment, during a second phase of absorption of HCl 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 absorption phase 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 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 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 HCl gas vapors.

[0178] The whole thus represents the evolution of the parameter S 11 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 HCl absorption phase of 15 minutes.

[0179] All 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 S 11 at the input of antenna 23 and are calculated as follows:

[0180]

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

[0182] S 11 (dB)Gain(dBi)Efficiency (%)Expected mismatch losses (dB)Actual losses(dB)ChCl / ThU-13,80,7225 / / 1 er addition of HClChCl / ThU + HCl t= 5 min-8.9-2.47120,593.19ChCl / ThU + HCl t= 10 min-6.4-4.517,71,135.22ChCl / ThU + HCl t= 15 min-5.6-5.516.41,386.22HeatingChCl / ThU + HCl t= 5 min-6.2 / / 1.20 / ChCl / ThU + HCl t= 10 min-9.7-0.05210,490.77ChCl / ThU + HCl t= 15 min-11.11.09260,360,382 èmeaddition of HClChCl / ThU + HCl t= 5 min-11.20.39230,340.32ChCl / ThU + HCl t= 10 min-8.0-0.53180.761.25ChCl / ThU + HCl t= 15 min-6.8-2.23121.012.95

[0183] Thus, we can see that during the first absorption phase, the parameter S 11of 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. In addition, 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] Furthermore, the desorption of HCl triggered by a heating step of the communicating system 31 by 200°C makes it possible to confirm the capacity 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 a sensitive liquid substance 8, loses its effectiveness 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

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 thereto.; Microwave sensor (2) according to claim 1, characterized in that each deep eutectic solvent 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, 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.; Microwave sensor (2) according to claim 1 or 2, characterized in that, in each deposition 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. 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). 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. 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). 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). Communicating system (1; 11; 21; 31) for detecting 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 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 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). 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). 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). 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 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. 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 claims 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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