FR3114152A1 - Device and method for detecting hydrogen - Google Patents

Abstract

The invention relates to a hydrogen detection device (1) comprising at least one ultrasonic transmitter (10), at least one ultrasonic receiver (20), together defining a measurement space (40), and a processing (30) capable of determining, from a characteristic signal supplied by the ultrasonic receiver (20), a value characteristic of the presence of hydrogen in the measurement space (40). The ultrasound transmitter (10) is configured to emit ultrasound waves (45) at a frequency greater than or equal to 2 MHz, and the processing unit (30) is configured to determine the characteristic value of the presence of hydrogen based on an attenuation value of the ultrasonic wave emitted by the ultrasonic transmitter (10), said attenuation value being determined from a characteristic amplitude value of the ultrasonic wave ( 45) received. Figure for abstract: figure 1

Description

Device and method for detecting hydrogen

The invention relates to the field of detecting hydrogen in a gaseous medium, such as the atmosphere of a confined space of a storage place for chemical and/or radioactive products or a fuel tank.

The invention thus more particularly relates to a hydrogen detection device and a hydrogen detection method.

State of the prior art

As demonstrated by the inventors in their work presented by L. Iglesias et. al as part of the conference "16 ^th International Workshop on Nanomechanical Sensors" which took place between June 19 and 21, 2019 in Lausanne, Switzerland, it is possible to use ultrasound to monitor the composition of a gaseous medium . Indeed, the composition of the gaseous medium directly influencing the speed of propagation of the ultrasonic waves of the latter, it is possible to obtain information on the composition of the gaseous medium from measurements of the time of flight of the ultrasonic waves.

Thus, the inventors have been able to demonstrate that with such time-of-flight measurements, it is possible, when the gaseous medium has a binary composition whose components are known, to determine the respective proportion of the components of the gaseous medium. It would therefore be possible, for a relatively simple composition of a gaseous medium to be monitored, to use such measurements to detect the presence of hydrogen.

Nevertheless, in the context of the monitoring of a gaseous medium, such as the atmosphere of a confined space of a storage place for chemical and/or radioactive products or a fuel tank, the gaseous composition can be relatively complex. and may vary over time. As a result, the use of ultrasound as proposed by the inventors in their work presented in Lausanne in 2019 does not seem appropriate due to this complexity.

Thus, there is currently no hydrogen detection device based on ultrasound that is suitable for monitoring gaseous media with a relatively complex composition.

The invention aims to remedy this drawback and thus aims to provide a hydrogen detection device which allows the detection of hydrogen in a gaseous medium having a relatively complex composition.

The invention relates for this purpose to a hydrogen detection device comprising:
- at least one ultrasonic transmitter able to emit ultrasonic waves,
- at least one ultrasonic receiver capable of measuring a characteristic value of an ultrasonic wave, the ultrasonic transmitter and the receiver being arranged so as to define a measurement space between them and such that an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasonic receiver after passing through the measurement space,
- a processing unit capable of determining, from at least one characteristic value measured by the ultrasonic receiver when receiving an ultrasonic wave emitted by the ultrasonic transmitter, a characteristic value of the presence of hydrogen in the measurement space.

The ultrasonic transmitter is configured to emit ultrasonic waves at a frequency greater than or equal to 2 MHz, the frequency preferably being greater than 2.5 MHz,

the processing unit being configured to determine the characteristic value of the presence of hydrogen on the basis of an attenuation value of the ultrasound wave emitted by the ultrasound emitter, said attenuation value being determined from the characteristic amplitude value of the ultrasonic wave received.

The inventors have discovered that with an ultrasonic wave frequency greater than or equal to 2 MHz, the attenuation value of the ultrasonic wave varies mainly with the hydrogen content in the measurement space. Therefore, a hydrogen detection device will make it possible to obtain effective detection of hydrogen, with a reduced influence of the rate of other gases that may be found in the measurement space. The device according to the invention is therefore perfectly functional, even in the context of the detection of hydrogen in gaseous media having a relatively complex composition.

It will be noted that to provide such detection, a simple placement of the detection device in the gaseous medium with the measurement space in fluid communication with the gaseous medium allows monitoring of said gaseous medium.

The attenuation value can be determined from a ratio between a characteristic amplitude value of the ultrasonic wave received and a characteristic amplitude value of at least one ultrasonic wave previously determined in the absence of hydrogen in the measurement space.

By using such a characteristic value ratio, it is possible to overcome the characteristics of the elements of the detector, such a ratio depending solely on the characteristics of the gaseous medium and the dimensioning of the measurement space.

The characteristic value of the presence of hydrogen can be an estimated value of the quantity of hydrogen present in the measurement space.

In this way, it is possible to precisely identify the risks associated with such a presence of hydrogen.

The ultrasonic transmitter can be configured to emit ultrasonic waves at at least a first frequency and a second frequency, at least one of the first and second frequencies of which is greater than or equal to 2 MHz,
the processing unit being preferably configured to determine the characteristic value of the presence of hydrogen on the basis of attenuation values obtained respectively at the first and at the second frequency.

In this way it is possible to obtain a more precise characteristic value of the presence of hydrogen.

The processing unit may be capable of providing a value characteristic of the presence of at least one gas other than hydrogen, the at least one other gas being preferably selected from carbon dioxide and methane.

In this way, it is possible to identify the risks associated with any type of gaseous contamination of the gaseous medium.

The processing unit can furthermore be configured to identify the nature of the possible contaminating gas among hydrogen and the at least one other gas from the attenuation values determined, the processing unit further being configured to determine the characteristic value of the presence of said contaminant gas among hydrogen and the at least one other gas after identification of the possible contaminant gas from at least one determined attenuation value among the determined attenuation values for the first and second frequency.

With such identification, it is possible to provide a particularly versatile detection device, since it is possible to identify contamination for a contaminant gas and to know the nature of said contaminant gas.

The processing unit can be configured to determine at least two attenuation parameters including:
- a sign of the attenuation value determined for one of the first and second frequencies,
- a sign of the difference between the attenuation value determined for the first frequency and the attenuation value determined for the second frequency,
the nature of the possible contaminant gas among hydrogen and the at least one other gas being identified from said attenuation parameters.

In this way, the nature of the contaminating gas can be identified with simple parameters.

The attenuation value may be a frequency normalized attenuation value.

When determining the characteristic value of the presence of said contaminant gas from hydrogen and the at least one other gas after identification of the possible contaminant gas, the determined attenuation value used can be chosen by the unit of treatment from among those determined for the first and second frequency depending on the nature of any contaminant gas identified.

In this way, it is possible to identify the characteristic value of the presence of said contaminant gas with precision whatever the nature of the latter.

At least one of the ultrasonic transmitter and the ultrasonic receiver may include at least one capacitive micro-machined transducer (cMUT).

Such micro-machined capacitive transducers are particularly advantageous in the context of the invention, in particular when they comply with the teaching of document FR 2962926, since they give access to a wide operating frequency range, both for transmission and reception of ultrasonic waves with particularly optimized integration. Thus, the industrialization of a device according to the invention is made particularly easy.

The invention further relates to a method for detecting hydrogen from a hydrogen detection device, the hydrogen detection device comprising:
- at least one ultrasonic transmitter able to emit ultrasonic waves,
- at least one ultrasonic receiver capable of supplying at least one characteristic signal of an ultrasonic wave, the ultrasonic transmitter and the ultrasonic receiver being arranged so as to define a measurement space and such that an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasonic receiver after passing through the measurement space,
- a processing unit capable of determining, from the at least one characteristic signal supplied by the ultrasound receiver during an emission of ultrasound by the ultrasound emitter, a value characteristic of the presence of hydrogen in the measurement space,
the method comprising the following steps:
- emission of at least one ultrasonic wave by the ultrasonic transmitter, the ultrasonic wave having a frequency greater than or equal to 2 MHz, the frequency preferably being greater than 2.5 MHz, with a given amplitude,
- supply, by the ultrasonic receiver when receiving the at least one ultrasonic wave emitted by the ultrasonic transmitter, of at least one characteristic signal of the at least one ultrasonic wave,
- determination of the characteristic value of the presence of hydrogen by the processing unit on the basis of the amplitude characteristic of the ultrasonic wave received.

Since such a method can be implemented by a device according to the invention, it benefits from the same advantages.

The following steps may also be provided:
- emission of at least one other ultrasonic wave by the ultrasonic transmitter, the other ultrasonic wave having a second frequency,
- Supply, by the ultrasonic receiver when receiving the other ultrasonic wave emitted by the ultrasonic transmitter, of at least one characteristic signal of the other ultrasonic wave,
wherein during the step of determining the characteristic value of the presence of hydrogen, the processing unit is configured to determine the characteristic value of the presence of hydrogen on the basis of a first and a second value d attenuation obtained respectively at the first and at the second frequency.

During the step of determining the characteristic value of the presence of hydrogen by the processing unit, a value characteristic of the presence of a gas other than hydrogen can also be determined.

The present invention will be better understood on reading the description of exemplary embodiments, given purely for information and in no way limiting, with reference to the appended drawings in which:

FIG. 1 illustrates a hydrogen detection device according to the invention.

FIG. 2 graphically illustrates the evolution of the variation of the attenuation coefficient ΔαGaz of an ultrasonic wave as a function of the ultrasound frequency obtained for a hydrogen detection device according to the invention, this for hydrogen, carbon dioxide and methane.

FIG. 3 graphically illustrates the evolution of the variation of the attenuation coefficient ΔαGaz of an ultrasonic wave, this for a gaseous medium consisting of nitrogen into which hydrogen has been introduced intermittently.

FIG. 4 graphically illustrates the evolution of the variation of the attenuation coefficient ΔαGaz of an ultrasonic wave, this for a gaseous medium consisting of nitrogen into which carbon dioxide has been introduced intermittently.

FIG. 5 graphically illustrates the evolution of the variation of the attenuation coefficient ΔαGaz of an ultrasonic wave for a gaseous medium consisting of nitrogen into which methane has been introduced intermittently.

FIG. 6 graphically illustrates the evolution of the variation of the attenuation coefficient i illustrated in FIG. 2 after frequency normalization, said variation of the normalized attenuation coefficient being denoted Δαn.

FIG. 7 graphically illustrates the evolution of the variation of the attenuation coefficient ΔαGaz of an ultrasonic wave, this for a gaseous medium consisting of nitrogen into which hydrogen has been introduced intermittently, the detection device comprising for these measurements of the ultrasonic transducers, for the ultrasonic transmitter and receiver, the transduction surface of which is, for the first and second curves, 27 µm by 37 µm, and, for the third curve, 27 µm by 27 µm .

Identical, similar or equivalent parts of the different figures bear the same reference numerals so as to facilitate passage from one figure to another.

The different parts shown in the figures are not necessarily shown on a uniform scale, to make the figures more readable.

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

FIG. 1 illustrates a hydrogen detection device 1 according to the invention, such a hydrogen detection device 1 being suitable for providing hydrogen detection based on a measurement of attenuation of ultrasonic waves 45 during their passing through a space to be monitored 40.

The detection device hydrogen according to the invention

Such a hydrogen detection device 1 comprises:
- at least one ultrasonic transmitter 10 able to emit ultrasonic waves 45,
- at least one ultrasonic receiver 20 capable of supplying a characteristic signal of an ultrasonic wave 45, the ultrasonic transmitter 10 and the ultrasonic receiver 20 being arranged so as to define the space to be monitored 40 and that an ultrasonic wave 45 emitted by the ultrasonic transmitter 10 is received by the ultrasonic receiver 20 after passing through the measurement space 40,
- a processing unit 30 capable of determining, from at least one characteristic signal supplied by the ultrasonic receiver 20 upon receipt of an ultrasonic wave 45 emitted by the ultrasonic transmitter, a characteristic value of the presence of hydrogen in the measuring space 40.

When setting up the detection device 1 in the context of monitoring a gaseous medium, the detection of hydrogen in the gaseous medium can be carried out by placing the detection device 1 with its measurement space 40 in fluid communication with the gaseous medium. In this way, the measurement space 40 and the gaseous medium are able to share the same atmosphere with an identical gaseous composition.

More specifically and as illustrated in Figure 1, the ultrasound transmitter 10 according to this first embodiment, comprises:
- a plurality of first ultrasound transducers 11 capable of emitting ultrasound,
- a first support 12 on which is arranged the plurality of ultrasonic transducers 11 and,
- a first amplification unit 15 configured to generate, from a control signal from the processing unit 30, a supply voltage of the plurality of ultrasonic transducers 11.

According to an advantageous possibility of the invention, the first ultrasonic transducers 11 are cMUT transducers, for micro-machined capacitive transducers, as described in document FR 2962926. In accordance with the teaching of this document, the first cMUT transducers according to this embodiment of the invention, each comprise a membrane and have a resonance frequency of this membrane. The resonant frequency of the membrane is chosen to be higher than the frequency of the ultrasonic waves to be generated. This resonance frequency can thus be 125% to 200% of the maximum frequency of the ultrasonic waves to be generated.

Thus, for example, for a maximum frequency of the ultrasonic waves to be generated equal to 3 MHz, the ultrasonic transducers according to this first embodiment can have a resonance frequency which is between 3.75 MHz and 6 MHz.

In accordance with the invention, the ultrasound transmitter 10 is configured to emit ultrasound waves at a frequency greater than or equal to 2 MHz, the frequency preferably being greater than 2.5 MHz, with a given amplitude A ₀ .

Such first ultrasonic transducers 11 are particularly advantageous in the present embodiment since they allow the generation of ultrasonic waves over a relatively large frequency range.

Of course, such a configuration is only provided by way of example and other types of ultrasonic transducers can be used without departing from the scope of the invention. It will be noted in particular that according to the possibility of the invention in which the ultrasound transmitter 10 is configured to emit ultrasound waves at at least a first frequency and a second frequency, that it is possible as a variant and without the It is outside the scope of the invention that the ultrasonic transmitter 10 comprises at least two types of ultrasonic transducers, a first type adapted to the first frequency and a second type adapted to the second frequency.

The first ultrasound transducers 11 are arranged on the first support 12 so as to define a first wall of the space to be monitored 40.

As shown in Figure 1, the ultrasonic receiver 20 includes:
- a plurality of second ultrasonic transducers 21 able to receive ultrasonic waves and to generate from said ultrasonic waves, a measurement signal corresponding to the ultrasonic waves received,
- a second support 22 on which is arranged the plurality of ultrasonic transducers 21 and,
- a DC power supply 23, capable of supplying the second ultrasonic transducers 21 with a DC voltage,
- a second amplification unit 25 configured to amplify the measurement signal supplied by the plurality of second ultrasonic transducers 21.

According to one possibility of the invention, the second ultrasonic transducers 21 can be of a type identical to the first ultrasonic transducers 11. Thus, in the present embodiment, and as shown in FIG. 1, the second ultrasonic transducers 11 are cMUTs, for micro-machined capacitive transducers, in accordance with the teaching of document FR 2962926.

Of course, as a variant and without departing from the scope of the invention, the second ultrasonic transducers 21 can be of another type. Similarly, according to the possibility of the invention in which the ultrasonic transmitter 10 is configured to emit ultrasonic waves at at least a first frequency and a second frequency, it is possible as a variant and without it departs from the scope of the invention, that the ultrasonic receiver 20 comprises at least two types of ultrasonic transducers 21, a first type matched to the first frequency and a second type matched to the second frequency.

The second ultrasonic transducers 21 are arranged on the second support 22 opposite the first ultrasonic transducers 11 so that the second support 22 defines a second wall of the space to be monitored 40. Thus the first and the second support 12 , 22 together define, by the space they delimit between them, the space to be monitored 40.

Of course, such an arrangement of the ultrasonic transmitter 10 and the ultrasonic receiver 20 is provided by way of example only and is in no way limiting. Other arrangements are perfectly possible as long as the ultrasonic transmitter and the ultrasonic receiver 20 are arranged to define the measurement space 40 and as long as an ultrasonic wave emitted by the ultrasonic transmitter is received by the ultrasound receiver after passing through the measurement space 40.

The second ultrasonic transducers 21 are supplied with voltage by the DC power supply 23 and the measurement signal generated by the second transducers when an ultrasonic wave is received is amplified by the second amplification unit 25. This measurement signal thus amplified forms a characteristic signal of the ultrasonic wave emitted by the ultrasonic transmitter 10.

The measurement signal is supplied by the second amplifier 25 to the processing unit 30.

The processing unit 30 is configured to determine the characteristic value of the presence of hydrogen on the basis of an attenuation value of the ultrasound wave emitted by the ultrasound emitter, said attenuation value being determined at from a characteristic amplitude value of the ultrasonic wave received.

Principle of measurement implemented in the context of the invention

Figure 1 illustrates the principle of such a determination. The processing unit 30 supplying the control signal to the first amplification unit 15 which in turn supplies the first ultrasonic transducers 11, an emitted ultrasonic wave 45 will have an amplitude A ₀ corresponding to the following equation:

With S the amplitude of the control signal, H _{Amp 1} the transfer function of the first amplification unit 15, H _Emits the transfer function of the first ultrasonic transducers 11.

The ultrasonic wave 45 during its transit in the measurement space 40 will present an attenuation H _Gas directly proportional to the distance d traveled and depending on the composition of the gas located in the measurement space 40. Such an attenuation H _Gas can be calculated with the following equation:

With α _Gas a gas attenuation coefficient corresponding to the composition of the gas located in the measurement space 40 and A the amplitude of the ultrasonic wave received by the second ultrasonic transducers 21.

Thus, the amplitude A of the ultrasonic wave received by the second ultrasonic transducers will therefore be equal to:

Concerning the detector, the characteristic signal supplied by the ultrasonic receiver to the processing unit will be dependent both on the transfer function H _recept of the second ultrasonic transducers 21 and on the transfer function H _Amp2 of the second unit d 'amplification. The characteristic signal S _{C aract} therefore responds to the following equation:

In other words, from the characteristic signal S _{C aract} and a given control signal S, and knowing all the transfer functions of each of the elements 11, 15, 21, 25 of the detection device 1, it is possible to determine the attenuation H _Gas = of the ultrasonic wave 45 during its transit in the measurement space 40.

Nevertheless, according to one possibility of the invention, in order to guard against the need to characterize the transfer function of each of the elements 11, 15, 21, 25 of the detection device 1, it is possible to use a reference measurement , S_Refbeforehand with a reference gas, such as a gas that does not contain hydrogen. According to this possibility the variation of the attenuation coefficient Δα_Gas= α_Gas– α_Ref between the gas and the reference gas can be obtained with the following formula:

S _Ref being the characteristic signal recovered by the processing unit 30 during the prior reference measurement, and is the reference measurement.

Thus, with such a detection device 1 and by using a prior reference measurement, it is easy to determine a variation of the attenuation coefficient Δα_Gas = α_Gas– α_Refas an attenuation value.

From this principle and within the framework of the invention, the inventors have demonstrated that for ultrasound frequencies greater than or equal to 2 MHz, or even greater than or equal to 2.5 MHz, the variation of the attenuation coefficient Δα _Gas is mainly related to hydrogen concentration. To obtain such a result, as illustrated in FIG. 2, the inventors have studied the variation of the attenuation coefficient Δα _Gas for different gases likely to contaminate the measurement space as a function of the frequency of the ultrasonic wave 45.

For this demonstration, the inventors used the following configuration:
- an AGILENT™ E5061B network analyzer as the first amplifier 15 to generate an electrical excitation of 800 mV peak-to-peak which is amplified with a gain of 100 to reach 80 V peak-to-peak and to which is added a DC component of 40 V,
- a DC power supply 23 configured to apply a DC voltage of 70 V to the second ultrasonic transducers 21,
- a second amplifier 25 supplied by a COOKNELL™ charge amplifier, the network analyzer making it possible to measure the characteristic signal supplied by the second amplifier 25.

In this demonstrator used by the inventors to illustrate the principle of the invention, the AGILENT™ E5061B network analyzer provides part of the functions of the processing unit 30.

Thus, figure 2 shows the evolution of the variation Δα_Gasfor a nitrogen gas into which was respectively introduced 1% hydrogen (curve 101), 1% carbon dioxide (curve 102) and 1% methane (curve 103) and, the reference measurement having been carried out for uncontaminated nitrogen gas, i.e. substantially pure nitrogen. For a 2 MHz ultrasonic wave, the variation of the attenuation coefficient Δα_Gasis of the order of 7 m^-1for hydrogen, 101, while it is less, in absolute value, than 3 m^-1for carbon dioxide, 102, and methane, 103. For an ultrasonic wave of 2.5 MHz, the variation of the attenuation coefficient Δα_Gasis of the order of 10 m^-1 for hydrogen, 101, while this same variation remains less than 3 m^-1, in absolute value, for carbon dioxide, 102, and methane, 103. It can be seen in Figure 2 that this selectivity for hydrogen increases with frequency, especially for frequencies above 3 MHz, or even at 3.5 MHz, even 4 MHz.

It should be noted that, unless otherwise specified, all of the gas proportion values provided above and in the rest of this document are molar proportions, such a molar gas proportion corresponding directly to the same volume proportion value .

Thus, any variation in attenuation coefficient Δα _Gas obtained for an ultrasonic wave frequency greater than or equal to 2 MHz can therefore be attributed to the presence of hydrogen in the measurement space 40, since a significant quantity of another gas (e.g. more than double for carbon dioxide and a frequency of 2 MHz, and triple for carbon dioxide and a frequency of 2.5 MHz) to obtain a really significant variation of this same variation of the attenuation coefficient Δα _Gas .

During this same study, at the origin of the invention, the inventors also demonstrated that, as illustrated in Figure 3, the variation of the attenuation coefficient Δα _Gas evolves linearly with the presence of hydrogen this regardless of the frequency of the ultrasonic wave. To do this, the inventors introduced into an atmosphere consisting of nitrogen in turn 4% hydrogen, 3% hydrogen, 2% hydrogen, 1% hydrogen, and again 4%, this over a given time range, the nitrogenous atmosphere of the measurement space 40 being re-established between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient Δα _Gas was determined for three ultrasonic wave frequencies, 2 MHz (curve 111), 3.6 MHz (curve 112) and 4.1 MHz ( curve 113) throughout these introductions of hydrogen.

We can thus see that the variation of the attenuation coefficient Δα_Gasevolves linearly with the amount of hydrogen introduced, whatever the ultrasonic wave frequency used. Indeed, from these measurements, the inventors measured a sensitivity of 0.062 cm^-1.%^-1at 2 MHz, a sensitivity of 0.175 cm^-1.%^-1at 3.6 MHz and a sensitivity of 0.211 cm^-1.%^-1 at 4.1MHz.

In addition, as shown in Figures 4 and 5, the inventors have also discovered that if the variation of the attenuation coefficient Δα _Gas changes predominantly with the proportion of hydrogen in the measurement space 40 for the frequencies ultrasonic waves above 2 MHz, the evolution of the variation of this attenuation coefficient Δα _Gas with the frequency of the ultrasonic wave is characteristic of the contaminant gas added in the measurement space 40.

This can thus be seen in FIG. 4, which shows the result of measurements during which the inventors introduced into an atmosphere consisting of nitrogen in turn 4% carbon dioxide, 3% carbon dioxide, 2% carbon, 1% carbon dioxide, and once again 4% carbon dioxide over a given time range, the nitrogenous atmosphere of the measurement space 40 being re-established between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient Δα _Gas was determined for three ultrasonic wave frequencies, 2 MHz (curve 121), 3.6 MHz (curve 122) and 4.1 MHz ( curve 123) throughout these introductions of carbon dioxide.

For carbon dioxide, the inventors have thus identified that the variation of the attenuation coefficient Δα _Gas evolves linearly with the quantity of carbon dioxide found in the measurement space 40, this with a positive leading coefficient, and that, as for hydrogen, this same variation of the attenuation coefficient Δα _Gas increases when the frequency of the ultrasonic wave 45 increases.

Regarding methane, as shown in Figure 5 which illustrates the result of measurements during which the inventors introduced into an atmosphere consisting of nitrogen in turn 4% methane, 3% methane, 2% methane, 1 % of methane, and once again 4% of methane over a given time range, the nitrogenous atmosphere of the measurement space 40 being re-established between two introductions. During these introductions, the evolution of the variation of the attenuation coefficient Δα _Gas was once again determined for three ultrasonic wave frequencies, 2 MHz (curve 131), 3.6 MHz (curve 132) and 4, 1 MHz (curve 133) throughout these methane introductions.

For methane, the variation of the attenuation coefficient Δα_Gasalso varies linearly with the quantity of methane, the directing coefficient being negative contrary to hydrogen and carbon dioxide (the attenuation decreases when more methane is introduced), and that this same variation of the attenuation coefficient Δα_Gas increases, in absolute value, when the frequency of the ultrasonic wave 45 increases.

The result of all these measurements is summarized in the following table which presents the sensitivity of the variation of the attenuation coefficient with respect to the proportion of hydrogen, carbon dioxide and methane, this for three ultrasonic wave frequencies studied and the selectivity of hydrogen towards carbon dioxide and methane

_H2
in cm ^-1 .% ^-1 _CO2
in cm ^-1 .% ^-1 CH ₄
in cm ^-1 .% ^-1 _H2 selectivity
opposite CO ₂ /CH ₄ F1=2MHz 0.062 0.0195 -0.0073 3.2/-8.5 F2=3.6MHz 0.175 0.024 -0.015 7.3/-11.7 F3=4.1MHz 0.211 0.0335 -0.0195 6.3/-10.8

From this principle, the processing unit 30 is therefore capable of determining, from the characteristic signal S _{C aract} , an attenuation value of the ultrasonic wave, such as for example the variation of the attenuation coefficient Δα _Gas or the variation of the attenuation coefficient Δα _Gas multiplied by d, and to determine from said attenuation value a characteristic value of the presence of hydrogen. This characteristic value of the presence of hydrogen can be a state of the presence of hydrogen or an estimated quantity of hydrogen present in the measurement space.

In the case where the characteristic value of the presence of hydrogen is a state of presence, this state of presence can be a Boolean variable presenting a false state, in the absence of hydrogen, and which changes to the true state when the attenuation value exceeds a threshold value corresponding to a quantity of interest of hydrogen present in the measurement space 40. Such a quantity of interest of hydrogen can be for example a quantity considered to be of concern, for example 1% of hydrogen, and characteristic of a significant contamination of the measurement space 40 and therefore of the gaseous medium, or even a quantity of hydrogen considered to be at risk from which a risk of explosion cannot be excluded, such than for example 4% hydrogen. As a variant, the characteristic value can be a state variable with several states corresponding to several thresholds for the presence of hydrogen, such as for example a first threshold of suspicion of contamination, for example 1% of hydrogen, a second threshold of confirmed contamination, for example 2% hydrogen, and a third alert threshold during which, for example, an alarm, for example sound and/or light, is triggered, this third threshold possibly being for example 4%.

Of course, it is also possible, within the scope of the invention, for the processing unit 30 to be capable of determining several characteristic values comprising a status value, as explained in the previous paragraph, and a quantity of estimated hydrogen.

Variant of the invention in the context of contamination binary

It should be noted that according to a variant of the invention, in the case where the measurement space 40 is likely to be contaminated by two contaminant gases (binary composition), one of which is hydrogen, it is possible to use the possibility of the invention to determine the contamination respectively of the measurement space 40 by these two contaminant gases, one of which is hydrogen.

According to this variant, the ultrasonic transmitter 10 is configured to emit ultrasonic waves at at least a first frequency and a second frequency with the first frequency which is greater than or equal to 2 MHz and the second frequency which is preferably less than 2 MHz.

According to the principle already explained, the processing unit 30 is configured to determine, on the basis of the attenuation value determined for the ultrasonic wave at the first frequency, a value characteristic of the presence of hydrogen in space measurement 40. Indeed, the influence of hydrogen contamination being preponderant for ultrasonic wave frequencies above 2 MHz, the possible presence of the other gas does not have to be taken into account.

The characteristic value of the presence of hydrogen having been determined, the processing unit 30 can be configured to determine, on the basis of the attenuation value determined for the ultrasonic wave at the second frequency and by correcting the influence of hydrogen from the value characteristic of the presence of hydrogen, a value characteristic of the presence of the other gas.

It will be noted that this other gas, according to a preferred application of the invention, can be chosen from carbon dioxide and methane. The values provided in table 1 can be used in particular to correct the influence of hydrogen.

It can also be noted that such a variation of the attenuation coefficient Δα _Gas with the frequency of the ultrasonic wave and with the quantity of gas which is, as the inventors have discovered, characteristic of the contaminant gas, can also be used for the identification of a contaminant gas introduced into the measurement space.

Possibility of identification of contamination

Thus, according to this possibility of the invention, from the results presented above in the part " measuring principle implemented in the context of the invention " , the inventors have developed a method for identifying the contaminant gas based on the fact that the evolution of the variation of this attenuation coefficient Δα _Gas with the frequency of the ultrasonic wave is characteristic of the contaminant gas.

In the context of this possibility of identifying contamination, the inventors have retained the variation of the normalized attenuation in frequency Δα _n as the attenuation value, with respect to the variation of attenuation “not normalized in frequency", which makes it possible to better highlight the specificities of each of the gases considered (hydrogen, methane and carbon dioxide). This so-called normalized frequency attenuation value Δα _n is equal to the value of the variation of the attenuation coefficient Δα _Gas divided by the frequency f. Of course, the use of the normalized attenuation variation in frequency Δα _n as an attenuation value within the framework of this possibility of identification is only provided by way of example and other values d attenuation, such as the attenuation variation Δα _Gas , which is therefore “non-standardized in frequency”, can of course also be used in the context of such a possibility.

Indeed, figure 6, which illustrates the evolution of the variation of the normalized attenuation coefficient in frequency Δα_not as a function of frequency (the curves 141, 142 and 143 corresponding to an introduction of respectively 1% hydrogen, 4% carbon dioxide and 4% methane), shows that, with the variation of the normalized attenuation coefficient Δα_notas an attenuation value, we obtain for a first and a second frequency at 2 MHz and 3.6 MHz:
- for hydrogen, curve 141 shows an attenuation value, the normalized attenuation variation in frequency Δα_nothaving a positive sign (both at 2 MHz and 3.6 MHz) and a positive variation of this same attenuation value when passing from the first to the second frequency,
- for carbon dioxide, curve 142 shows an attenuation value, the normalized attenuation variation in frequency Δα_{not ,}having a positive sign (both at 2 MHz and 3.6 MHz) and a negative variation of this same attenuation value when passing from the first to the second frequency,
- for methane, curve 143 shows an attenuation value, the normalized attenuation variation in frequency Δα_not, presenting a negative sign (both at 2 MHz and at 3.6 MHz) and a negative variation of this same attenuation value when passing from the first to the second frequency.

Thus, in the event of observation of a variation in the attenuation of an ultrasonic wave in the measurement chamber and therefore of a potential contamination of the gaseous medium by a contaminant gas, from two attenuation parameters alone, the sign of the normalized attenuation variation in frequency Δα _n (both at the first frequency and at the second frequency) and the sign of the evolution of the normalized attenuation variation in frequency Δα _n between the first and the second frequency, it is easy to determine the nature of the contaminating gas present in the gaseous medium.

According to this possibility, the processing unit 30 can be configured to authorize the implementation of an identification method comprising the following steps:
- emission by the ultrasonic transmitter 10 of a first and a second ultrasonic wave respectively at the first and the second frequency,
- measurement of a characteristic signal by the ultrasonic receiver 20 of respectively the first and the second ultrasonic wave,
- determination of a first and a second attenuation value, here the normalized attenuation variations at the first and second frequencies Δα _n (f1) and Δα _n (f2), respectively from respectively the first and second signals characteristics measured,
- calculation of at least one characteristic value of the change in attenuation between the first and the second attenuation value, here a difference between the normalized attenuation variations at the first and second frequencies,
- identification of the nature of the possible contaminant gas on the basis of the characteristic value of the attenuation evolution and at least one of the first and the second attenuation value (Δα _n (f2)- Δαn(f1)), this for example from attenuation parameters,
- determination of a value characteristic of the presence of any identified gas.

In the context of the invention, the first frequency is a frequency greater than or equal to 2 MHz, this so as to allow, according to the principle of the invention, the detection of the presence of hydrogen.

In order to allow the nature of the possible contaminant gas to be identified, the processing unit 30 can thus be configured to determine at least two attenuation parameters including:
- a sign of the attenuation value determined for one of the first and second frequencies, here the sign of the normalized attenuation variation in frequency Δα _n either at the first frequency or at the second frequency Sign( Δα _n (f1 or f2),
- a sign of the difference between the attenuation value determined for the first frequency and the attenuation value determined for the second frequency, said difference corresponding to a characteristic value of the change in attenuation between the first and the second value of attenuation which are here the variations of normalized attenuation in frequency Δα _n , Sign(Δα _n (f2) - Δα _n (f1)).

Of course, these two parameters are only provided by way of example, other attenuation parameters can be envisaged without departing from the scope of the invention. It will be noted in particular, in the case where one is interested in a larger number of contaminating gases, that it is perfectly possible to use a slope value at the first frequency or even, when a leak is proven, a variation ratio between the normalized frequency attenuation variation at the first frequency Δα _n (f1) and the normalized frequency attenuation variation at the second frequency Δα _n (f2).

Once a contaminant gas has been identified, the processing unit 30 can also be configured to determine a value characteristic of the presence of the identified contaminant gas. Such a value characteristic of the presence of the contaminant gas can be determined from at least one of the attenuation value determined for the first frequency and the attenuation value determined for the second frequency. Advantageously, the attenuation value used to determine the characteristic value of the presence of the contaminant gas may be the attenuation value among the attenuation value determined for the first and the second frequency which is expected as having the sensitivity the most important for the contaminant gas identified the corresponding frequency is called adapted frequency. It will be noted that in the present embodiment, an attenuation value at a third frequency equal to 4.1 MHz has also been determined, the selection thus being made between the attenuation values determined for the first to the third frequency.

Thus, according to this possibility of this present embodiment, the ultrasonic transmitter 10 can be configured to emit at least a third ultrasonic wave at a third frequency distinct from the first and from the second frequency. The ultrasonic receiver 20 is configured to supply at least a third characteristic signal of respectively the third ultrasonic wave, and the adapted frequency is one of at least the first to the third ultrasonic frequency.

In order to illustrate such a possibility, the inventors have implemented the principle of operation of such a method for monitoring a measurement space for contamination with hydrogen, carbon dioxide and methane from the measurements presented within the framework of figures 3, 4 and 5. Thus, from these measurements, it was possible to show the result of such a process within the framework of respective introductions of 1%, 2%, 3% and 4% hydrogen, carbon dioxide and methane in the measurement space 40 which has a nitrogenous atmosphere.

For each quantity of contaminant gas, on the basis of the results illustrated in FIGS. 3, 4 and 5, the attenuation values of the first ultrasonic wave are those corresponding to ultrasonic waves whose frequency is equal to 2 MHz, and those of the second ultrasonic wave are those corresponding to ultrasonic waves whose frequency is equal to 3.6 MHz. The first frequency is thus 2 MHz and the second frequency is 3.6 MHz, these two frequencies being, in accordance with the principle of the invention, both greater than or equal to 2 MHz.

From these attenuation values, the inventors were able to determine for each quantity of contaminant gas:
- a first sign of the normalized attenuation value at the first frequency (in other words, if the normalized attenuation variation in frequency Δα _n (f1) at the first frequency increases or decreases during the introduction of the contaminant gas), And
- A second sign of the difference Δα _n (f2)-Δα _n (f1) between the attenuation value (here the variations of the normalized frequency attenuation coefficient Δα _n ) determined for the second frequency and for the first frequency.

As indicated previously, the expected signs for each of the three contaminant gases were determined from Figure 6, namely:
- a first and a second positive sign for hydrogen,
- a first positive sign and a second negative sign for carbon dioxide,
- a first and a second negative sign for methane.

In the same way, on the basis of Table 1, the appropriate frequency has been defined for each of the contaminant gases to determine the characteristic value of the presence of said contaminant gas, here the proportion of gas in the measurement space 40. Thus for hydrogen it is the third frequency which is 4.1 MHz (much higher than 2 MHz according to the invention) and for methane it is the second frequency 3.6 MHz and for carbon dioxide this is the first frequency which is 2 MHz.

It will be noted that in the context of the invention, it would have been perfectly possible to use a frequency lower than 2 MHz in order to promote sensitivity to carbon dioxide and methane.

Mix introduced Measure Determination by 30 Gas Quantity (%) Sign of Δα _not (f1) Sign of Δα _not (f2)-Δα _not (f1) suitable frequency MHz Gas identified Estimated quantity (%) H ₂ 1 + + 4.1 H ₂ 0.98 2 + + 4.1 1.99 3 + + 4.1 2.98 4 + + 4.1 4.04 CO ₂ 1 + - 2 CO ₂ 1.18 2 + - 2 1.94 3 + - 2 3.15 4 + - 2 3.88 CH ₄ 1 - - 3.6 CH ₄ 1.02 2 - - 3.6 1.79 3 - - 3.6 3.24 4 - - 3.6 3.93

It can be seen that by applying the process according to this possibility compatible with the invention, each of the contaminating gases has indeed been identified and the proportions determined are close to the expected values showing the correct operation of the process.

Of course, such an implementation of the identification method is only provided as an example of this possibility compatible with the invention and is therefore in no way limiting. Thus, it is possible, without departing from the scope of the invention, to use more than two ultrasonic wave frequencies in order to determine the attenuation parameters making it possible to discriminate the nature of the contaminant gas, or even to 'use other types of variations than those described above (in particular using an attenuation value or attenuation difference, or even attenuation variation difference as such, rather than signs as used in Table 2).

It will also be noted that it is perfectly possible, on the basis of the present teaching and using algorithms of the deep learning type (better known by its English name "deep learning"), to be able to identify a large number of contaminating gases likely to contaminate, and even simultaneous contamination by several contaminating gases, this in addition to the detection of hydrogen.

In addition, while this document focuses on the detection of hydrogen and possible contaminant gas in a gaseous medium to be monitored and on the determination of the quantity of hydrogen and possible contaminant gas present in this same gaseous medium, in the context of the practical implementation of such a device, the processing unit 30 can be configured to detect such contamination or a suspicion of contamination from the detection of an attenuation variation at least one ultrasonic wave, such as the first and the second ultrasonic wave. According to this possibility, some, or all, of the hydrogen detection steps can be implemented only in the case of the detection of such contamination or of a suspicion of contamination of the gaseous medium to be monitored (the setting implementation of these steps not being necessary in the event that there is no contamination). In the same way, some of the stages of the detection of a possible contamination of the gaseous medium can be common with that of the detection of hydrogen (in particular those concerning the emission of the ultrasonic wave and the measurement of the characteristic signal of the latter).

In this way, the principle of measurement discovered by the inventors, based on the variation of the attenuation of the ultrasonic waves with the frequency of the ultrasonic wave and according to the composition of the atmosphere located in the measurement space 40, is particularly reliable. As shown in FIG. 7, in order to demonstrate the reliability provided by the inventors and show the reproducibility of such an attenuation value, the inventors have reproduced a measurement of attenuation variation Δα _Gas within the framework of an introduction of hydrogen in accordance with the measurement shown in FIG. 3 a first time with an ultrasonic emitter having a surface of 27 μm by 37 μm, as shown by curve 151, with an ultrasonic emitter having a surface of 27 μm by 27 µm, curve 152, and a second time with an ultrasound emitter having a surface of 27 µm by 27 µm, curve 153. It can be seen that these curves are superimposed and therefore show the reliability of this measurement whether in the scope of the invention or of the possibility compatible with the invention. Such reliability is perfectly compatible with the field of securing buildings and workers in which the invention falls.

It will further be noted that in the present embodiment, the ultrasonic transmitter 10 and the ultrasonic receiver 20 have a configuration in which they face each other in order to define the measurement space 40 Of course, other configurations can be envisaged without departing from the scope of the invention, as long as in these configurations, the arrangement of the ultrasonic transmitter 10 and of the ultrasonic receiver 20 makes it possible to define the measurement space 40. It will be noted in particular that it is possible to use one or more walls able to reflect ultrasonic waves in order to use other configurations.

Thus, according to a variant of the invention and of the possibility compatible with the invention, the ultrasonic transmitter 10 and the ultrasonic receiver 20 can use the same ultrasonic transducer(s) in combination with a wall capable of reflecting the ultrasound, the ultrasound transducers allowing, within the framework of the ultrasound transmitter 10, to emit the ultrasound wave(s) 45 in the form of wave trains, and allowing, after reflection of said wave trains by said wall , to measure a characteristic signal of said wave trains. It should be noted that in this configuration, the ultrasonic wave traverses the measurement space twice and therefore presents, as a result, a double attenuation to which are added the losses related to the reflection on the wall.

Similarly, according to another similar variant based on the use of a reflecting wall, the transducers of each of the ultrasonic transmitter 10 and of the ultrasonic receiver 20 can be arranged on the same support. Here too, with such a configuration, the ultrasonic wave travels the measurement space twice and therefore presents, as a result, a double attenuation to which are added the losses related to the reflection on the wall.

Claims (11)

Hydrogen detection device (1) comprising:
- at least one ultrasonic transmitter (10) able to emit ultrasonic waves (45),
- at least one ultrasonic receiver (20) capable of supplying at least one characteristic signal of an ultrasonic wave (45), the ultrasonic transmitter (10) and the ultrasonic receiver (20) being arranged so as to define a measurement space (40) and that an ultrasonic wave (45) emitted by the ultrasonic transmitter (10) is received by the ultrasonic receiver (20) after passing through the measurement space (40 ),
- a processing unit (30) capable of determining, from the characteristic signal provided by the ultrasonic receiver (20) upon receipt of an ultrasonic wave (45) emitted by the ultrasonic transmitter (10), a value characteristic of the presence of hydrogen in the measurement space (40),
The detection device (1) being characterized in that :
- the ultrasonic transmitter (10) is configured to emit ultrasonic waves (45) at a frequency greater than or equal to 2 MHz, the frequency preferably being greater than 2.5 MHz,
- the processing unit (30) is configured to determine the characteristic value of the presence of hydrogen on the basis of an attenuation value of the ultrasonic wave emitted by the ultrasonic transmitter (10), said value attenuation being determined from a characteristic amplitude value of the ultrasonic wave (45) received. Hydrogen detection device (1) according to Claim 1, in which the attenuation value is determined from a ratio between a characteristic value of amplitude of the ultrasonic wave received and a characteristic value of amplitude d at least one ultrasonic wave previously determined in the absence of hydrogen in the measurement space (40). Hydrogen detection device (1) according to Claim 1 or 2, in which the characteristic value of the presence of hydrogen is an estimated value of the quantity of hydrogen present in the measurement space (40). Hydrogen detection device (1) according to any one of Claims 1 to 3, in which the ultrasonic transmitter (10) is configured to emit ultrasonic waves at at least a first frequency and a second frequency of which at least least one of the first and second frequencies is greater than or equal to 2 MHz,
wherein the processing unit (30) is preferably configured to determine the characteristic value of the presence of hydrogen on the basis of attenuation values obtained respectively at the first and at the second frequency. Hydrogen detection device (1) according to Claim 4, in which the processing unit (30) is able to supply a value characteristic of the presence of at least one gas other than hydrogen, the at least another gas being preferably selected from carbon dioxide and methane. Hydrogen detection device (1) according to Claims 4 and 5, in which the processing unit (30) is further configured to identify the nature of the possible contaminant gas among hydrogen and the at least one other gas from the determined attenuation values, the processing unit (30) being further configured to determine the characteristic value of the presence of said contaminant gas from among hydrogen and the at least one other gas after identification of the possible contaminant gas from at least one attenuation value determined from among the attenuation values determined for the first and the second frequency. Hydrogen detection device (1) according to claim 6, in which the processing unit (30) is configured to determine at least two attenuation parameters including:
- a sign of the attenuation value determined for one of the first and second frequencies,
- a sign of the difference between the attenuation value determined for the first frequency and the attenuation value determined for the second frequency,
the nature of the possible contaminant gas among hydrogen and the at least one other gas being identified from said attenuation parameters. Hydrogen detection device (1) according to claim 7, in which when determining the characteristic value of the presence of said contaminant gas among hydrogen and the at least one other gas after identification of the possible contaminant gas , the determined attenuation value used is chosen by the processing unit from among those determined for the first and second frequencies as a function of the nature of any contaminant gas identified. A method of detecting hydrogen from a hydrogen detection device (1), the hydrogen detection device comprising:
- at least one ultrasonic transmitter (10) able to emit ultrasonic waves (45),
- at least one ultrasonic receiver (20) capable of supplying at least one characteristic signal of an ultrasonic wave (45), the ultrasonic transmitter (10) and the ultrasonic receiver (20) being arranged so as to define a measurement space (40) and that an ultrasonic wave (45) emitted by the ultrasonic transmitter (10) is received by the ultrasonic receiver (20) after passing through the measurement space (40 ),
- a processing unit (30) capable of determining, from the at least one characteristic signal supplied by the ultrasound receiver (20) during an emission of ultrasound (45) by the ultrasound transmitter ( 20), a value characteristic of the presence of hydrogen in the measurement space (40),
The process comprising the following steps:
- emission of at least one ultrasound wave (45) by the ultrasound transmitter (10), the ultrasound wave (45) having a frequency greater than or equal to 2 MHz, the frequency preferably being greater than 2.5 MHz , with a given amplitude,
- supply, by the ultrasonic receiver (20) when receiving the at least one ultrasonic wave emitted by the ultrasonic transmitter (10), at least one characteristic signal of the at least one wave ultrasound,
- determination of the characteristic value of the presence of hydrogen by the processing unit (30) on the basis of the amplitude characteristic of the ultrasonic wave received. Detection method according to claim 9, in which the following steps are further provided:
- emission of at least one other ultrasonic wave (45) by the ultrasonic transmitter (10), the other ultrasonic wave (45) having a second frequency,
- supply, by the ultrasonic receiver (20) when receiving the other ultrasonic wave emitted by the ultrasonic transmitter (10), at least one signal characteristic of the other ultrasonic wave,
wherein in the step of determining the hydrogen presence characteristic value, the processing unit (30) is configured to determine the hydrogen presence characteristic value based on a first and a second attenuation value obtained respectively at the first and at the second frequency. Detection method according to claim 10, in which during the step of determining the characteristic value of the presence of hydrogen by the processing unit (30), a value characteristic of the presence of a gas other than hydrogen.