Photoacoustic gas sensor device

Abstract

A photoacoustic gas sensor device for determining a value indicative of the presence or concentration of a component in a gas, comprising a measurement cell (2) enclosing a measurement volume (3) and a gas-permeable region (4) in the measurement cell (2) for letting gas into the measurement volume (3). An electromagnetic radiation source (7) is arranged to emit electromagnetic radiation (8) into the measurement volume (3), and a pressure sensor (6) is arranged to measure acoustic waves (9) generated by the component in response to absorption of the electromagnetic radiation (8) by the component in the measurement volume (3). In one aspect, the gas-permeable region (4) is represented by a porous gas-permeable membrane (5) having an average pore size between 10 nm and 1 µm. In another aspect, the gas-permeable region (4) is represented by a region of the measurement cell (2) comprising a hole (211) through other gas-tight material of the measurement cell (2), the hole (211) having a diameter between 100 nm and 10 µm.

Description

Technical Field

[0001] The present invention relates to a photoacoustic gas sensor device configured to determine the presence or concentration of a component (particularly CO2) in an indicator gas. Background Technology

[0002] Photoacoustic gas sensors rely on physical effects, such as the absorption of infrared radiation by molecules of a component of interest in a gas (e.g., CO2), causing the molecules to transition to an excited state. Subsequently, heat is generated due to the non-radiative decay of the excited state (e.g., due to molecular collisions), leading to an increase in pressure. By modulating the absorbed infrared radiation at a modulation frequency, the pressure changes at that frequency. This pressure change can be measured by a pressure sensor. The concentration of the component is proportional to the magnitude of the pressure change.

[0003] The measuring cell requires a ventilated area to allow the target gas to enter. This ventilated area is expected to meet several requirements: it is desirable that the ventilated area allows sufficient exchange of the target gas between the outside (as the surrounding environment) and the inside (also known as the measuring volume) of the measuring cell. On the other hand, it is undesirable for pressure changes within the measuring cell, which are caused by photoacoustic effects and represent temporary overpressure, to escape through the ventilated area, otherwise the signal detected by the pressure sensor would be less significant. Simultaneously, it is desirable that pressure changes outside the measuring cell (such as ambient noise) do not migrate into the measuring cell, thereby interfering with and distorting the photoacoustic effects caused by the components in the target gas.

[0004] Therefore, the object of the present invention is to provide a photoacoustic gas sensor device with a breathable area that satisfies at most these different conditions. Summary of the Invention

[0005] This objective is achieved by a photoacoustic gas sensor device according to the first and second aspects of the invention, as claimed in independent claims 1 and 12.

[0006] A photoacoustic gas sensor device for determining the presence or concentration of a component in an indicator gas includes a measuring cell that seals the measuring volume. The device also includes an electromagnetic radiation source for emitting electromagnetic radiation into the measuring volume, and a pressure sensor arranged to measure acoustic waves generated by the component in response to absorption of the electromagnetic radiation by the component in the measuring volume. Preferably, the electromagnetic radiation source and the pressure sensor are arranged within the measuring cell. Therefore, the photoacoustic response within the measuring cell is caused by irradiation by the gas present in the measuring volume and is measured by the pressure sensor.

[0007] The photoacoustic effect is based on the mechanism by which molecules of a gaseous component of interest (e.g., CO2) absorb electromagnetic radiation (infrared radiation in one example). This absorption leads to the generation of heat due to non-radiative attenuation (e.g., through collisions between molecules of the gaseous component and / or through collisions between molecules of the gaseous component and different molecules), which in turn causes an increase in pressure within the measurement volume. Pressure modulation is achieved by modulating the intensity of the electromagnetic radiation at a modulation frequency. This pressure modulation, represented by a pressure change (i.e., sound waves), can be measured by a pressure sensor. The magnitude of the pressure change can then be used to determine a value indicating the presence or concentration of the component, i.e., the concentration of the component. It can be assumed that the magnitude is proportional to the amount of electromagnetic radiation absorbed by the component, and therefore, if all other factors (e.g., the average optical path length in the measurement volume) remain constant, then it is proportional to the concentration of the component in the gas.

[0008] To allow the gas to be investigated to enter the measuring cell, a permeable area is provided in the measuring cell, while the rest of the measuring cell is preferably made airtight.

[0009] According to the first aspect of claim 1, the breathable area is represented by a porous breathable membrane. Thus, the breathable membrane includes pores created by the properties of the membrane material or by the manufacturing process. Preferably, the porous breathable membrane is attached to the measuring cell and covers the openings in the measuring cell.

[0010] The average pore size of the porous breathable membrane is between 10 nm and 1 μm, preferably between 20 nm and 200 nm. Preferably, the porosity of the porous breathable membrane is between 20% and 90%, particularly between 20% and 50%. In summary, for a pressure difference of 10 mbar, the permeability, especially that resulting from the average pore size, porosity, and pore structure, is preferably low, particularly around 0.03 l / (hrcm). 2 ) and 2l / (hr cm 2 The value is between 0.03 l / (hr cm), preferably between 0.03 l / (hr cm). 2 ) and 0.4 l / (hr cm 2 The small pore size and low porosity (especially related to a specific pore structure) result in such low permeability and desired degradation characteristics. Moreover, the low porosity leads to a mechanically stable membrane and avoids membrane buckling.

[0011] To meet different objectives, it was found that determining the parameter size in this way improves the attenuation characteristics of porous breathable membranes: a relatively large measurement volume, a thick membrane, a small number of pores, and a small pore size. Conversely, determining the parameter size supports a small diffusion time: a relatively small measurement volume, a thin membrane, a large number of pores, and a large pore size. However, it was also found that the attenuation characteristics of porous breathable membranes have a strong non-linear relationship with the pore size, while the diffusion time has a linear relationship with the pore size. In particular, for decreasing the pore size, the attenuation increases strongly non-linearly. This leads to the finding that membrane materials preferably include multiple small-sized pores, rather than membrane materials with fewer but larger pores. This approach ensures sufficient attenuation of external noise. At the same time, due to the migration through the porous breathable membrane, the photoacoustic pressure change within the measurement cell is attenuated, and the time constant (also known as the response time or sensor) for gas diffusion into the measurement volume is relatively short. Therefore, by applying the above-mentioned average pore size, the greatest achievement is obtained for different requirements in the breathable region.

[0012] The desired attenuation characteristics primarily affect high-frequency pressure changes because pressure changes caused by the photoacoustic effect occur within a certain frequency range or at a given frequency. At least, the desired attenuation characteristics apply to this frequency range. The frequency range to be attenuated is at least higher than the frequency of the pressure changes responsible for the exchange of gaseous media in the measurement volume. The former is more suitable in the Hz and kHz range, while the latter is more suitable in the sub-Hz range. In this context, a porous membrane with a suggested average pore size acts as a low-pass filter for pressure changes. Considering the specially designed average pore size, slow pressure changes causing gas exchange in the measurement cell can pass through the porous membrane, while pressure changes at higher frequencies are attenuated or blocked by the porous membrane. Therefore, higher-frequency sounds caused by the photoacoustic effect are damped or blocked from escaping from the measurement volume to the outside through the porous membrane. On the other hand, the low-pass filter characteristics of the porous membrane also attenuate or block such higher-frequency pressure changes from entering the measurement volume from the outside. Therefore, noise in the frequency range that would otherwise affect the measurement within the measurement volume is also attenuated by the porous membrane. Thus, even in the relevant spectrum, the pressure sensor signal is largely unaffected by such external noise. In one embodiment, strong attenuation of higher frequency pressure changes may be sufficient when limited to the relevant frequency range, since the signal supplied by the pressure sensor is preferably filtered by a narrow bandpass filter near the relevant frequency in any case.

[0013] In summary, porous breathable membranes advantageously serve as decoupling elements between the measurement volume and the environment surrounding the measurement cell. Sound waves in the relevant frequency range of photoacoustic emission within the measurement cell, generated by electromagnetic radiation stimulating the target gas components, are attenuated or blocked by the porous breathable membrane and thus prevented from leaving the measurement volume. Meanwhile, noise from the surrounding environment is attenuated or blocked from entering the measurement volume by the porous breathable membrane.

[0014] By using a porous, breathable membrane, controlled vents (such as valves) can be avoided in the measurement cells, which is desirable given that valves require considerable space and active control.

[0015] Preferably, the porous permeable membrane comprises or is made of one of sintered metals, ceramics, and polymers. Preferably, a material comprising PTFE or composed thereof is used for the membrane. This material includes pores within a desired range, particularly porosity within a desired range. This material is obtained by expanding sheets of material, or by a process such as sintering or molding raw granular material, or by any other means of obtaining a porous material. Particularly in the case of PTFE, the membrane is heat-resistant, which allows for reflow soldering of the membrane to the measuring cells and / or reflow soldering of the entire device.

[0016] The volume measurement dimension is preferably within 0.03 cm. 3 and 8cm 3 Between, preferably within 0.08cm 3 and 1cm 3 Between, and preferably 0.2 cm 3 These dimensions are preferred for providing small-sized sensors that are also suitable for portable applications and / or for saving space in measuring devices.

[0017] In embodiments with circular venting regions, the diameter of the venting region is preferably between 0.2 mm and 4 mm, and more preferably between 0.5 mm and 2 mm. In different embodiments with non-circular venting regions, the size of the venting regions is preferably within the same range. This size is due to the total measurement volume and to prevent membrane bulging or buckling that could affect the measurement results. Furthermore, it has the advantage of exposing a sufficient area of ​​the porous material.

[0018] The membrane thickness is preferably between 50 μm and 400 μm, and more preferably between 100 μm and 300 μm. Similarly, the thickness affects both diffusion time and attenuation, and is selected in conjunction with the preferred average pore size.

[0019] Preferably, the target time constant for diffusion is less than 100 s, and more preferably less than 70 s. The preferred time constant representing attenuation (especially acoustic attenuation) is preferably greater than 10 s. -2 s.

[0020] Preferably, the measuring cell includes at least a substrate and a measuring cell body (e.g., cap-shaped), the measuring cell body preferably being attached to a substrate that is preferably planar. These components at least help the measuring cell to confine the measuring volume within its interior.

[0021] Preferably, the substrate is a printed circuit board (PCB), for example, made of FR4. In different embodiments, the substrate is made of a ceramic material that provides high mechanical stability. In further embodiments, the substrate is part of a system-in-package (SiP), or a SiP substrate. The electromagnetic radiation source and pressure sensor are preferably arranged on the front side of the substrate facing the measurement volume, and thus arranged in the measurement cell.

[0022] Regarding the measuring cell body, preferably, at least a major portion (i.e., at least 50%) of its inner surface facing the measuring volume is made of a reflective material. That is, a portion or the entire inner surface is preferably made of a reflective material, either by applying a reflective coating to the core of the measuring cell body, or by making the measuring cell body itself a reflective material. In the latter embodiment, the measuring cell body may be made of a sheet metal, for example by deep drawing. Sheets have the advantage of mechanical stability even at low thicknesses and exhibit high reflectivity to electromagnetic radiation even without any further coating. In earlier embodiments, the core of the measuring cell body is made of a non-reflective or low-reflective material (e.g., plastic), for example by injection molding, and a reflective coating is applied to the inner surface. Generally, the reflective material is preferably a metal, or a metal-filled polymer, or metallized or mirrored glass, or another material with high reflectivity (particularly for the wavelength of the emitted radiation). The reflective material may be, for example, one or more of gold, aluminum, nickel, and copper. These materials are particularly useful in cases where a reflective coating is applied to the core.

[0023] Regarding the location of the porous breathable membrane within or at the measurement cell, three preferred options are listed below:

[0024] In the first variant, a porous breathable membrane is arranged relative to the measuring cell body. The measuring cell body includes an opening defining a breathable area. The opening is covered by the porous breathable membrane. The porous breathable membrane is preferably attached to the measuring cell body, particularly by one of gluing, injection molding, casting, brazing, and welding. Thus, apart from the opening covered by the porous breathable membrane, all other components contributing to the measuring cell (i.e., the substrate and the remainder of the measuring cell body) are preferably hermetically sealed and hermetically assembled, allowing the target gas to enter the measuring volume only through the breathable area. Note that, considering the porous breathable membrane is preferably attached to the measuring cell body via its edges, preferably, the porous breathable membrane extends beyond the size of the opening. The geometry of the porous breathable membrane can differ from the geometry of the opening, as long as the opening is completely covered by the porous breathable membrane during installation. The porous breathable membrane can be attached to the measuring cell body from the inside, i.e., the porous breathable membrane is attached to the inner surface of the measuring cell body. In different embodiments, the porous breathable membrane is attached to the body of the measuring cell from the outside, that is, the porous breathable membrane is attached to the outer surface of the body of the measuring cell.

[0025] According to the second variant, all these features and interpretations also apply when openings are provided in the substrate. Given that electronic components such as electromagnetic radiation sources and pressure sensors are preferably reflow soldered to the substrate, it is preferable that the porous venting membrane is also reflow soldered in a co-assembly step with the electronic components when attached to the substrate. For this purpose, it is preferable that the porous venting membrane includes, for example, metallization at its edges, through which the porous venting membrane is soldered to the substrate. In one embodiment, the openings can even be arranged below the electronic components located on the substrate to ensure sufficient ventilation between the openings and the electronic components, which is preferably achieved through the distance between them.

[0026] In the third variant, an opening is provided between the substrate and the measuring cell body. Similarly, the opening is covered by a porous breathable membrane, which is now preferably attached to both the measuring cell body and the substrate, particularly by one of gluing, injection molding, casting, brazing, and welding.

[0027] The following preferred embodiments are designed to prevent the porous breathable membrane from bulging or buckling. Bulging of the porous breathable membrane can be caused by pressure changes inside or outside the membrane. If the pressure change occurs outside the membrane, its buckling may not coincide with gas diffusion through the membrane. This can lead to a reduction in the photoacoustic signal detected by the pressure sensor. This drawback can be avoided or mitigated when the porous breathable membrane is supported by a means that holds the membrane in a rigid planar position.

[0028] In its first embodiment, a support layer is attached to a porous breathable membrane and serves as a mechanical support. In a variation, the support layer is an adhesive layer by which the porous breathable membrane is attached to the measuring cell. Thus, the adhesive support layer functions dually. It serves as a means of attachment to the porous breathable membrane and as a mechanical support after curing or annealing. Where the support layer is arranged between the membrane and the measuring cell and extends across the entire surface of the membrane, it is preferable that the support layer includes one or more pores arranged to allow gas to enter the measuring volume as it passes through the porous breathable membrane. Regarding manufacturing, it is preferable to first attach the support layer to the porous breathable membrane. Secondly, the support layer is structured while residing on the porous breathable membrane, for example, to create one or more pores in the support layer but not in the porous breathable membrane. Thirdly, the membrane-support layer combination is attached to the measuring cell body by means of the adhesive support layer, such that the opening is covered. Finally, the adhesive support layer can be cured or annealed. Thus, in this embodiment, the support layer is arranged between the porous breathable membrane and the measuring cell / opening.

[0029] In different embodiments, the support structure is arranged on the membrane and faces the sensor's surrounding environment during installation. In one embodiment, this support structure may be a lattice structure, for example, made of metal. Thus, the lattice structure is first attached to a first side of the porous breathable membrane. Then, the lattice structure-membrane assembly is attached to the measuring cell by means of an adhesive, which is attached to the side of the porous breathable membrane opposite to the first side.

[0030] In the third embodiment, bulging of the porous breathable membrane is prevented by dividing the opening in the measuring cell into multiple drill holes with a diameter smaller than the intended single opening. The porous breathable membrane is attached to the measuring cell in the area with the multiple drill holes and covers all the drill holes. Similarly, the porous breathable membrane can be attached to the measuring cell, for example, by an adhesive.

[0031] As described in one of the above embodiments, the inner surface of the measurement cell body is at least partially (but more preferably completely) made of a reflective material or reflective coating. Assuming the porous breathable membrane material is non-reflective, the breathable area represented by the openings covered by the porous breathable membrane typically does not have reflective properties. Therefore, the breathable area constitutes a non-reflective area, which leads to a reduction in the overall reflectivity of the measurement cell, thereby reducing the average optical path length and thus lowering the signal-to-noise ratio (SNR).

[0032] For this reason, reflectors can be provided to at least partially shield the permeable area, which in turn increases the overall average reflectivity within the measurement cell. Assuming that the gas entering through the membrane should reach the measurement volume, such reflectors are preferably arranged inside the measurement cell and spaced apart from the openings and the membrane. The reflectors reflect electromagnetic radiation back to the measurement volume, radiation that would otherwise be absorbed or permeate through the porous permeable membrane.

[0033] According to the second aspect claimed in claim 12, the permeable area of ​​the photoacoustic gas sensor device is represented by an area of ​​the measuring cell containing a hole through the wall of the measuring cell, rather than by a membrane covering the opening. The diameter of the hole is between 100 nm and 10 μm. Thus, the measuring cell itself (i.e., its wall) is perforated by a hole having the aforementioned specified diameter. In another embodiment of the second aspect, the hole is located in a small plate, i.e., the hole passes through the small plate. The small plate covers the opening in the measuring cell. As described in the context of the first aspect, the opening may also be located, if applicable, at one of the measuring cell body, the substrate, or between the measuring cell body and the substrate. Furthermore, other features of the membrane covering the opening in the first aspect (e.g., the size of the opening or the mounting of the membrane) may also be applied to the small plate covering the opening.

[0034] Note that the diameter differs from the average pore size of the membrane mentioned in the first aspect of the invention. However, the considerations and advantages of the second aspect of the invention are the same as those of the first aspect. Therefore, unless specific to membranes, all statements made in the context of the first aspect should be considered as disclosed also in the context of the second aspect.

[0035] Regarding the second aspect, it is preferable that the number of holes is relatively large and the diameter of the holes is relatively small, as described above. Preferably, the number of holes is in the range of 50 to 200,000, and more preferably between 100 and 10,000.

[0036] Note that the holes may be provided in the body of the measuring cell and / or the substrate. The holes may be densely arranged in an area corresponding to the venting area of ​​a given diameter in the first aspect. Alternatively, the holes may be arbitrarily distributed on the measuring cell.

[0037] Preferably, it is assumed that all holes have a uniform length and a uniform diameter. Otherwise, an average value will be applied, aiming to satisfy the range conditions described above. In one embodiment, the thickness of the measuring cell (i.e., its wall) defining the ventilated area is between 1 μm and 1 mm, and thus represents the average hole length.

[0038] For high attenuation, a relatively long hole with a relatively small diameter is preferred. The time constant characterizing the attenuation properties of the hole is given by τ = k*V*l_c / r_c. 2 Let k be a constant, V be the measured volume, l_c be the length of the hole, and r_c be the radius of the hole. For diffusion through the hole, the time constant is τ = k * V * l_c / r_c. 4For rapid gas diffusion through a porous, permeable membrane, short pores with large diameters are preferred. Similarly, the range of pore diameters chosen is based on the understanding that the attenuation factor increases faster than the diffusion time decreases as the diameter decreases. Specifically, attenuation increases non-linearly with decreasing diameter, while diffusion decreases linearly. However, the determination of the pore length and its diameter depends not only on diffusion and attenuation considerations but also on manufacturing constraints. For manufacturability reasons, the aspect ratio of the pore diameter to its length is preferably less than 20.

[0039] Preferably, the hole is a capillary. Preferably, the hole is created by, for example, etching into a semiconductor material, or by laser or by ion bombardment.

[0040] The following embodiments are explicitly applicable to two aspects of the present invention.

[0041] Specifically, the pressure sensor can be a microphone, particularly a microphone that is sensitive only to a specific frequency range around the modulation frequency. In different embodiments, the pressure sensor is a pressure sensor.

[0042] In a preferred embodiment, the electromagnetic radiation is infrared radiation. This means that the electromagnetic radiation source is an infrared radiation source configured to emit infrared radiation. Infrared radiation is preferably defined as radiation with wavelengths in the range between 700 nm and 1 mm. In another embodiment, the electromagnetic radiation source is a source for emitting radiation with wavelengths in the range between 100 nm and 700 nm. In one embodiment, the electromagnetic radiation source may be a heater, in another embodiment a laser, and in yet another embodiment an LED. A heater may also be considered a broadband radiation source, while a laser and an LED may be considered narrowband radiation sources. Preferably, the electromagnetic radiation emitted by the electromagnetic radiation source is emitted only in a frequency band that matches the absorption peak of the gas component of interest. A frequency band is considered a subrange of the electromagnetic spectrum, preferably symmetrical about the wavelength representing the absorption peak, with a maximum / minimum band limit of + / - 15% of the wavelength representing the absorption peak.

[0043] In one embodiment, the photoacoustic gas sensor device is used as a CO2 sensor. In that case, the infrared radiation band is centered at a wavelength of approximately 4.3 μm. Preferably, this band has a full width at half maximum (FWHM) of less than 0.5 μm, which can be understood as a narrow band. For example, the narrow band source may include a metasurface resonator and may be implemented, for example, as an LED. In another embodiment, the electromagnetic radiation source includes a broadband emitter covered by a wavelength-selective bandpass filter configured to filter out out-of-band electromagnetic radiation. A broadband emitter is defined as emitting radiation with a wide spectrum, such as across the entire infrared spectrum, or for example, between 0.8 μm and 10 μm. Such a broadband emitter may specifically be an infrared emitter, such as a heater.

[0044] In embodiments, the photoacoustic sensor device further includes an integrated circuit, also known as a chip, particularly an ASIC, which preferably includes the function of a controller for photoacoustic sensing, configured to control an electromagnetic radiation source. The integrated circuit is preferably disposed on the front side of a substrate. The integrated circuit is preferably configured to control the intensity of the electromagnetic radiation to be modulated using a modulation frequency. The modulation frequency is between 1 Hz and 100 Hz, preferably between 10 Hz and 200 Hz, more preferably between 20 Hz and 60 Hz, for example 40 Hz, and particularly for heaters that switch the electromagnetic radiation source at the modulation frequency, if applicable. Low modulation frequencies below 100 Hz are advantageous for generating large photoacoustic signals.

[0045] Preferably, the integrated circuit is configured to receive a measurement signal from a pressure sensor and determine a value indicating the presence or concentration of a component based on the measurement signal, preferably including signal processing such as linearization and / or compensation. Specifically, this value is determined based on the amplitude of the measurement signal (e.g., loudness in the case of sound waves). Preferably, the measurement signal is band-filtered around the modulation frequency. This increases the robustness of the determination because sound waves with other frequencies are not taken into account.

[0046] In embodiments, the photoacoustic sensor device further includes another sensor for sensing temperature, humidity, pressure, and one or more of the different components in the gas. Thus, this other sensor can be implemented as one or more of the following: a pressure sensor, a gas pressure sensor, another microphone, or another gas sensor (e.g., a metal oxide type or an electrochemical type). This other sensor can be disposed on or integrated into the front side of the substrate. Preferably, the other sensor is located within the measurement cell. In the presence of other sensors, the integrated circuit is preferably configured to compensate for values ​​indicating the presence or concentration of a component based on measurements from the other sensor. Therefore, the influence of environmental conditions on the measurement of the component can be reduced or eliminated. This compensation makes the resulting concentration values ​​more accurate and reliable, or in other words, the gas sensor device can be applied in varying environmental conditions.

[0047] Preferably, all electrical and electronic components of the photoacoustic sensor device (collectively referred to as electrical components) are mounted on the front side of the substrate and are preferably arranged in the measurement cell. At least the pressure sensor, electromagnetic radiation source, and possibly the main body of the measurement cell are surface-mounted on the front side of the substrate. Preferably, all electronic components are surface-mounted on the front side of the substrate, making the photoacoustic gas sensor device an SMD (surface-mount device).

[0048] Preferably, the back side of the substrate includes only contacts for electrically connecting the photoacoustic gas sensor device to the carrier. In an embodiment, the contacts include a connection pad grid array (LGA) pads arranged for SMD assembly and / or reflow soldering. This facilitates customer assembly of the device with other components. Other contact options may include DFN, QFN, or slot holes.

[0049] In a preferred embodiment, a reflective shield is provided that divides the measurement volume into a first volume and a second volume. The pressure sensor and the electromagnetic radiation source are preferably arranged in the first volume on the front side of the substrate. Although the actual photoacoustic conversion mainly occurs in the second volume in this arrangement, it is still reasonable to refer to the combination of the first and second volumes as the measurement volume, considering that the pressure sensor, as the measurement entity, is located in the first volume. The reflective shield preferably includes an aperture, through which electromagnetic radiation generated by the electromagnetic radiation source is transmitted to the second volume; this aperture is preferably a single aperture. Therefore, dividing the measurement volume into a first volume and a second volume does not imply that the two volumes are sealed to each other. Instead, the second volume is communicatively coupled to the first volume and specifically coupled to the pressure sensor arranged therein. This allows the pressure sensor to detect changes in sound caused by the absorption of electromagnetic radiation by the component of interest in the first volume. Therefore, the communicative coupling is preferably acoustic coupling, and preferably includes pressure changes in the second volume that can be detected by the pressure sensor arranged in the first volume. In one embodiment, acoustic coupling can be achieved through a single aperture in the reflective shield.

[0050] At least a portion of the surface of the reflective shield facing the second volume is made of a material that reflects electromagnetic radiation, particularly electromagnetic radiation of a specific wavelength or frequency band emitted by an electromagnetic radiation source. The wavelength or frequency band of the emitted radiation preferably coincides with, or includes, a wavelength or frequency band that is readily absorbed by the components in the gas.

[0051] To achieve the aforementioned objective of providing good reflectivity characteristics in the second volume, it is preferable that at least a major portion (i.e., at least 50% of this surface) of the reflective shield facing the second volume is made of a reflective material. However, to further increase the reflectivity in the second volume, it is even more preferable that the entire surface of the reflective shield facing the second volume is made of a reflective material. Preferably, the aim is to maximize the surface of the defined second volume having reflective material. As for the material providing reflectivity, it refers to the material listed for measuring the reflectivity of the cell body.

[0052] Therefore, the second volume is designed to provide optimal reflection of the emitted radiation. The electronic components, including the pressure sensor and the electromagnetic radiation source, are physically separated from the second volume, which serves as the primary space for photoacoustic conversion. Thus, any non-reflective surfaces of the electronic components no longer affect the radiation path, and therefore do not interfere with the photoacoustic response or reduce the sensitivity of the measurement signal. Furthermore, the high reflectivity of the inner surface of the measurement cell reduces the pressure signal offset caused by photoacoustic effects occurring in the solid material (e.g., on the surface of the measurement cell body).

[0053] Preferably, the thickness of the reflective shield is between 30 μm and 1 mm, particularly between 50 μm and 200 μm. This thickness will not significantly affect the size of the photoacoustic sensor device, which is expected to remain small.

[0054] Preferably, the ratio of the second volume to the first volume is at least 1.5, preferably at least 2, preferably at least 3, and preferably at least 5. Such a ratio is preferred because, given that only the second volume is radiated, the photoacoustic effect primarily occurs in the second volume. On the other hand, a large first volume reduces pressure changes, which will result in a less significant signal supplied by the pressure sensor. Furthermore, given that gas enters the first volume through corresponding openings, a large first volume will substantially affect the diffusion of gas into the second volume.

[0055] Preferably, the permeable region is provided within the portion defining the first volume of the measuring cell. Given that the vast majority of electromagnetic radiation is reflected in the second volume rather than the first, this arrangement of the permeable region reduces the severe exposure of the porous, permeable membrane, which acts as a non-reflective surface, to electromagnetic radiation. This increases the average reflectivity within the measuring cell, which in turn increases the absorption of reflected light / radiation by gaseous components such as CO2.

[0056] In one embodiment, the planar extensions of the reflective shield and the planar extensions of the substrate are aligned parallel to each other. The holes in the reflective shield are preferably aligned perpendicularly to an electromagnetic radiation source disposed on the substrate, and particularly perpendicularly to its active region. The electromagnetic radiation source and the pressure sensor face the reflective shield.

[0057] In one embodiment, in addition to the pressure sensor and electromagnetic radiation source, integrated circuits and / or other sensors (if any) are also arranged on the front side of the substrate in the first volume, and preferably facing the reflective shield. In another embodiment, all electrical components are arranged in the first volume, and preferably facing the reflective shield.

[0058] Preferably, the measuring cell body and the substrate are connected in an airtight manner, for example, by gluing or welding. Advantageously, the measuring cell is soundproof except for vented areas (if any) for gas to enter. In a preferred embodiment, the measuring cell body is mounted to the substrate by means of a snap-fit ​​engagement. Preferably, the measuring cell body includes one or more clip arms, and the substrate includes one or more corresponding holes for the one or more clip arms to pass through. Preferably, the snap-fit ​​engagement is designed to soundproofly mount the measuring cell body to the substrate.

[0059] It should be understood that, where applicable, all embodiments of the first aspect should also be disclosed in conjunction with the second and third aspects of the invention. Attached Figure Description

[0060] Embodiments, aspects, and advantages of the present invention will become clear from the following detailed description. Detailed description is given with reference to the accompanying drawings, which illustrate:

[0061] Figures 1 to 3 and Figures 7 to 9 Each is a cross-sectional view of a photoacoustic gas sensor device including a membrane according to an embodiment of the present invention.

[0062] Figures 4 to 6 Each of these is a membrane arrangement used in a photoacoustic gas sensor device according to an embodiment of the present invention, shown as a top view in Figure a) and a cross-sectional view in Figure b).

[0063] Figure 10 This is a cross-sectional view of a photoacoustic gas sensor device including a hole according to an embodiment of the present invention, and

[0064] Figure 11 It is illustrated in, for example, in Figure 10 The diagram illustrates the effects of various parameters of the hole solution applied in the embodiments. Detailed Implementation

[0065] The same elements are indicated by the same reference numerals in all the accompanying drawings.

[0066] Figure 1 A schematic cross-sectional view of a photoacoustic gas sensor device according to an embodiment of the present invention is shown.

[0067] The device includes a substrate 1, such as a printed circuit board (PCB), having a front side 11 and a back side 12 opposite to the front side 11. A measurement cell body 21 is mounted on the front side 11 of the substrate 1, and the substrate 1 and the measurement cell body 21 together form a measurement cell 2 that encloses a measurement volume 3. The measurement cell 2 includes a venting region 4, which includes an opening 41 in the measurement cell body 21, the opening 41 being covered by a porous venting membrane 5 to allow gas exchange between the measurement volume 3 and the surrounding environment, and in particular to allow the gas to be measured to enter the measurement volume 3 such that the concentration of the component of interest in the gas in the measurement volume 3 is similar to that in the surrounding environment.

[0068] Both the pressure sensor 6 (such as a MEMS microphone or pressure sensor) and the electromagnetic radiation source 7 (an infrared source in this example) are located on the front side 11 of the substrate 1 inside the measurement cell 2. The electromagnetic radiation source 7 includes an active region 71 that emits electromagnetic radiation (i.e., infrared radiation in this example) as indicated by arrow 8. The infrared source emits infrared radiation in this frequency band, wherein the intensity of the infrared radiation is modulated as described above. The infrared radiation is selectively absorbed by molecules of the gas component of interest.

[0069] In this embodiment, a reflective shield 17 is provided in the measurement cell 2. The reflective shield 17 currently extends in a plane parallel to the plane of the substrate 1. The reflective shield 17 is attached to or integrally formed with the measurement cell body 21. The reflective shield 17 divides the measurement volume 3 into a first volume 31 between the substrate 1 and the shield 17, and a second volume 32 between the shield 17 and the measurement cell body 2. The reflective shield 17 includes an aperture 18 currently aligned with the infrared source 7, such that infrared radiation 8 can be emitted from the infrared source 7 through the aperture 18 into the second volume 32.

[0070] Preferably, the surface 171 of the shield 17 facing the second volume 32 is made of a material that reflects electromagnetic radiation emitted by the electromagnetic radiation source 7. This is indicated by the arrows representing the electromagnetic radiation 8 reflected in the second volume 32 after being emitted from the infrared source 7. The absorption rate of infrared radiation 8 is increased by increasing the average optical path length of infrared radiation 8 within the measuring volume 3. This is achieved by selecting a material that is reflective, at least for the inner surface 212 of the measuring cell body 21. In the case of a coating, the reflective coating can be made of metals such as gold, aluminum, nickel, or copper. In this way, the total reflectivity within the second volume 32 increases, which leads to more accurate measurements of component concentration. The increase in the average optical path length (particularly in contrast to the linear optical path in conventional photoacoustic gas sensors) is illustrated in the various figures by the multiple reflections of infrared radiation 8. Here, the photoacoustic effect begins to take effect: molecules of the gas component of interest (e.g., CO2) in the second volume 32 absorb the electromagnetic radiation, resulting in the production of heat and thus an increase in pressure. Pressure modulation can be achieved by modulating the intensity of the electromagnetic radiation in the infrared source 7 with a modulation frequency.

[0071] This pressure modulation or pressure change (i.e., sound wave) can be measured by the pressure sensor 6. In this example, the aperture 18 in the reflective shield 17 allows this sound wave generated in the second volume 32 to reach the first volume 31 and thus the pressure sensor 6. For this purpose, a gap is provided between the reflective shield 17 and the electromagnetic radiation source 7. The sound wave is... Figure 1 Reference numeral 9 in the figure indicates this. Thus, by means of the aperture 18 in the shield 17, the second volume 32, in which absorption and sound wave generation mainly occur, is coupled in communication to the first volume 31 and the pressure sensor 6. Thus, in this example, not only does electromagnetic radiation enter the second volume 32 through the aperture 18, but sound waves also propagate from the second volume 32 to the first volume 31 and reach the pressure sensor 6.

[0072] Although in different embodiments the reflective shield may be mounted to the substrate 1, in other embodiments such a reflective shield 17 is not provided at all, and the measured volume 3 is uniform.

[0073] In addition to the electromagnetic radiation source 7 and the pressure sensor 6, additional components are arranged on the front side 11 of the substrate 1 inside the measuring cell 2. These components include an integrated circuit 14, such as an ASIC, which is preferably configured to control the electromagnetic radiation source 7, for example, by applying intensity modulation to infrared radiation emitted at a modulation frequency. The modulation frequency can be within the audible spectrum, for example, between 20 Hz and 20 kHz, or up to 100 kHz, or even as low as 5 Hz. The integrated circuit 14 is also configured to receive measurements from the pressure sensor 6, and values ​​for determining the concentration of gas components based on these measurements, for example, by using a predefined or resettable calibration function that links the measurements to the concentration values ​​of the gas components. The values ​​of the gas component concentrations can be output via a digital interface (e.g., an I2C interface) and can be values ​​from one or more other sensors (if any).

[0074] In this example, another sensor 13 is arranged on the front side 11 of the substrate 1 within the measuring cell 2. This other sensor 13 is advantageously one or more of the following: a temperature sensor, a humidity sensor, a combined temperature / humidity sensor, a pressure sensor, particularly a barometric pressure sensor, another microphone, and another gas sensor, such as a metal oxide type or an electrochemical type. The gas concentration value can be compensated for, for example, the effects of temperature and / or humidity, through integrated circuit 14, by means of the measured values ​​of temperature and / or humidity and / or any other parameters measured by such other sensors. Therefore, the influence of environmental conditions on component measurements can be reduced or eliminated.

[0075] Additional electronic components 15 may be arranged on the front side 11 of the substrate 1 within the measurement cell 2. These additional electronic components 15 may include passive components or auxiliary electronic devices, such as capacitors and resistors, as needed.

[0076] On the back side 12 of substrate 1, connection pad grid array (LGA) pads 16 are arranged for customer SMD assembly and reflow soldering. Other contacts (such as DFN, QFN, or slot holes) are also possible.

[0077] In one example, the component to be measured is CO2. Measurement results are possible within the range of 0 to 10,000 ppm, 0 to 40,000 ppm, or 0 to 60,000 ppm CO2.

[0078] The proposed photoacoustic gas sensor device (e.g., such as...) Figure 1 (As shown) can be constructed with a small shape factor, such that the total size of the measurement cell is 0.2 cm. 3 Therefore, it is significantly smaller and less expensive to manufacture than conventional photoacoustic gas sensors or NDIR-based gas sensors.

[0079] Figure 2 A cross-sectional view of another photoacoustic gas sensor device including a membrane 5 according to an embodiment of the present invention is illustrated. For illustrative purposes, details are omitted. Figure 1 Some of the attached figure labels. (and) Figure 1 Compared to the previous embodiment, the porous breathable membrane 5 is now at least partially shielded from the inside. For this purpose, a reflector 28 is arranged inside the measuring cell 2. At least a portion of the reflector 28 is spaced apart from the opening 41. The reflector 28 is arranged and configured to reflect electromagnetic radiation back into the measuring volume 3, which would otherwise be absorbed by or transmitted through the porous breathable membrane 5. This function is indicated by arrow 8, which represents the electromagnetic radiation reflected by the reflector 28 in the region of the opening 41. The surface of the reflector 28 facing the measuring volume 3 has reflective properties for electromagnetic radiation 8.

[0080] In this example, reflector 28 is integrally formed with the measuring cell body 21. It is assumed that the interior of the measuring cell body 21 is made of or coated with a reflective material. Reflector 28 can be manufactured by cutting or stamping a tongue or flap into the measuring cell body 21 at a desired location in the opening 41. The flap or tongue remains attached to the rest of the measuring cell body 21 and is pressed into the interior of the measuring cell 2.

[0081] Figure 3 Implementation examples and Figure 1 The difference in this embodiment lies in the different location of the opening 41 in the measuring cell 2. The venting area 4 (and therefore the opening 41) is still arranged within the measuring cell body 21. However, instead of... Figure 1 and Figure 2 The measuring cell body 2, which was originally positioned at the top, is now arranged laterally within the sidewall. Furthermore, opening 41 now provides access to the first volume 31 instead of the second volume 32. Similarly, opening 41 is covered by a porous, breathable membrane 5.

[0082] In this arrangement, since the vast majority of electromagnetic radiation 8 is emitted into and reflected in the second volume 32, the film 5, as a non-reflective surface, is less exposed to electromagnetic radiation 8. This increases the average reflectivity in the measuring cell 2, which in turn increases the absorption of reflected light / radiation by gaseous components (such as CO2). Means used to increase reflectivity, such as... Figure 2 The reflector 28 in the membrane 5. In addition, undesirable photoacoustic reactions at the surface of the membrane 5 are reduced or avoided.

[0083] It may be undesirable for the buckling or bulging of the porous breathable membrane to adversely affect the measurement. Figures 4 to 6Each of the figures illustrates a means for improving the mechanical stability of a porous, breathable membrane used in a photoacoustic gas sensor device according to an embodiment of the invention, with a top view in Figure a) and a cross-sectional view along line A-A' in Figure b).

[0084] Figure 4 The illustration shows a porous breathable membrane 5 attached to the measuring cell body 21 or substrate 1, preferably attached externally. An opening 41 in the measuring cell body 21 is covered by the porous breathable membrane 5, the size of which extends the opening 41 to provide sufficient material for attaching the porous breathable membrane 5 to the measuring cell body 21. In this example, the porous breathable membrane 5 is square in shape, while the opening 41 is circular. Attachment is accomplished by an adhesive layer that also serves as a support layer 51. The support layer 51 is preferably structured to include holes 511. The support layer 51 is then preferably applied to the porous breathable membrane 5. Given that the support layer 51 is preferably airtight, the holes 511 allow gas passing through the porous breathable membrane 5 to enter the measuring volume 3 through the opening 41. Thus, the adhesive support layer 51 serves not only to attach the porous breathable membrane 5 to the measuring cell body 21 or substrate 1, but also as its mechanical support and thus to prevent buckling and bulging. The adhesive support layer 51 is preferably hardened or annealed to provide sufficient rigidity and adhesion.

[0085] Figure 5 Another variant is illustrated. Similarly, the porous breathable membrane 5 is attached to the measuring cell body 21 or substrate 1, preferably externally. Likewise, the opening 41 in the measuring cell body 21 or substrate 1 is covered by the porous breathable membrane 5, the size of which extends the opening 41 to provide sufficient material for attaching the porous breathable membrane 5 to the measuring cell body 21 or substrate 1. Attachment is also accomplished by means of an adhesive (now referred to as 53). However, in this case, the adhesive 53 does not additionally act as a support for the porous breathable membrane 5 and is only applied to the edge sections of the porous breathable membrane 5 through which it is attached to the measuring cell body 2 or substrate 1. Instead, a lattice structure 54 provides mechanical stability and is attached to the first side of the porous breathable membrane 5 facing the outside of the device. To create this arrangement, it is preferred to first attach the lattice structure 54 to the porous breathable membrane 5, and then attach this combination to the measuring cell body 21 or substrate 1 by means of the adhesive 53. Note that, for illustrative purposes, the lattice period in Figure b) does not match the lattice period shown in Figure a).

[0086] exist Figure 6In this embodiment, the previous single opening 41 is now replaced and represented by a plurality of drill holes 411 or openings in the measuring cell body 21 or substrate 1. The porous breathable membrane 5 is attached to the measuring cell body 21, for example, by means of an adhesive not shown, and covers the plurality of drill holes 411. In this example, the plurality of smaller drill holes prevent the porous breathable membrane 5 from bulging or wobbling, given that it spans a plurality of smaller drill hole diameters rather than a large drill hole diameter.

[0087] Figure 7 A cross-sectional view of a photoacoustic gas sensor device including a membrane according to an embodiment of the present invention is shown again. In this embodiment, a reflective shield 17 is integrally formed with the measuring cell body 2. Here, the measuring cell body 21 includes a frame 221 and a cover 222 that acts as a lid. An opening 41 is now provided in the cover 222, and a porous, breathable membrane 5 is attached to the peripherally facing top side of the cover 222. In this embodiment, the frame 221, the cover 222, and the reflective shield 17 (if any) may all be made of a reflective material (e.g., metal). However, in different embodiments, one or more of the frame 221, the cover 222, and the reflective shield 17 (if any) may include a plastic core and a reflective coating (where desired). For illustrative purposes, the integrated circuit 14, one or more other sensors 13, and components from... Figure 1 Any other electronic component 15 known in the embodiments.

[0088] Figure 8 Implementation examples and Figure 1 The difference in this embodiment is that a permeable region 4 is now provided between the substrate 1 and the measuring cell body 21. Due to the construction of the measuring cell body 21 (and specifically its frame 221), a horizontal opening 41 is formed between the front side 11 of the substrate 1 and the bottom surface of the frame 221 when the frame 221 is clamped to the substrate 1. This opening 41 preferably takes the shape of a ring around the measuring volume 3 and is filled with a ring of, for example, a porous permeable membrane material. Thus, the gas to be measured enters laterally into the measuring volume 3 through the opening 41 between the measuring cell body 21 and the substrate 1, and diffuses from the first volume 31 through the hole 18 into the second volume 32, where it encounters electromagnetic radiation 8. This process occurs in... Figure 8 The dotted arrow indicates the measurement volume 3. In this embodiment, cover 222 is understood to seal the measurement volume 3 from the top. In this embodiment, the coverage area of ​​the substrate 1 matches the coverage area of ​​the measurement cell body 2, allowing the measurement cell body 2 to be easily attached to the substrate 1 using snap-fit ​​fitting 25.

[0089] Figure 9 The embodiments are similar to Figure 1The embodiment is described above. However, the venting region 4 is now located in the substrate 1 in the form of a through-hole opening 41. Thus, the gas to be measured enters the measuring volume 3 through the opening 41 in the substrate 1 and diffuses from the first volume 31 through the hole 18 into the second volume 32, where it encounters electromagnetic radiation 8. The porous venting membrane 5 is now attached to the substrate 1, and preferably to the front side 11 of the substrate 1 facing the first volume 31. In a different embodiment, the porous venting membrane 5 is attached to the back side 12 of the substrate 1.

[0090] Figure 10 A cross-sectional view of a photoacoustic gas sensor device according to an embodiment of the present invention is shown, now including holes 211 instead of a porous breathable membrane. Thus, the breathable region 4 in this embodiment is represented by the region of the measuring cell 2, specifically the region of the measuring cell body 21, which contains holes 211 through the walls of the measuring cell body 21, which are otherwise made of an airtight material. The diameter d_c of the hole 211 is between 100 nm and 10 μm. The length l_c of the hole 211 is between 1 μm and 1000 μm. Meanwhile, the dimension l_h represents the thickness of the measuring cell body 21 at least in the breathable region 4. The number of holes 211 is between 50 and 15000. A magnified view illustrates a portion of the breathable region 4 in more detail.

[0091] exist Figure 11 The figure illustrates the effects of different parameters related to the hole, for example, applicable to Figure 10The embodiment shown is illustrated. In this example, 100 holes present in measurement cell 2, representing the venting area, are investigated for attenuation and diffusion. Assuming that the diameter and length of the holes are consistent across all 100 holes, the x-axis represents the different diameters d_c of the holes (in μm). The y-axis represents the time constant τ in seconds, representing the low-pass filter time constant. Each graph depicts the time constant τ with respect to the hole diameter d_c for a given hole length l_c. Dashed graphs show the time constant τ of the diffusion process through the hole, while straight graphs represent the time constant of the low-pass filter for reference attenuation. The appropriate hole size (i.e., hole diameter d_c and hole length l_c) can be selected as follows: a diffusion time τ of up to 60 seconds is considered acceptable, and from a manufacturing perspective, an aspect ratio of hole length l_c to hole diameter d_c of up to 20 is considered acceptable. From the perspective of attenuation, represented by the time constant of the low-pass filter for a straight line, a reasonably low time constant is desired so that higher frequency pressure changes are filtered by the set of holes. On the other hand, the minimum time constant of the low-pass filter is considered to be within the range of 0.1 s, represented by the thick dashed horizontal line. These choices result in a preferred range of hole diameters d_c, shown in the thickened segment of the straight line for each hole length l_c. The ellipse surrounding the range of hole diameters d_c and hole lengths l_c, for a number of 100 holes, this combination of dimensions results in the desired diffusion and attenuation characteristics.

[0092] While embodiments of the invention have been shown and described above, it should be understood that the invention is not limited thereto, but may be practiced and implemented differently in other ways within the scope of the following claims.

Claims

1. A photoacoustic gas sensor device for determining a value indicative of the presence or concentration of a component in a gas, the photoacoustic gas sensor device comprising: a measurement cell (2) enclosing a measurement volume (3), a gas-permeable region (4) in the measurement cell (2) for letting gas into the measurement volume (3), an electromagnetic radiation source (7) arranged to emit electromagnetic radiation (8) into the measurement volume (3), and a pressure sensor (6) arranged to measure acoustic waves (9) generated by a component in response to absorption of the electromagnetic radiation (8) by the component in the measurement volume (3), wherein the gas-permeable region (4) is represented by a porous gas-permeable membrane (5), wherein the average pore size of the porous gas-permeable membrane (5) is between 10 nm and 1 pm, wherein the porosity of the porous gas-permeable membrane (5) is between 20% and 50%, where the dimensions of the measurement volume (3) are between 0.03 cm 3 and 8 cm 3 . wherein the diameter of the gas-permeable region (4) is between 0.2 mm and 4 mm.

2. The photoacoustic gas sensor device according to claim 1, wherein the average pore size of the porous gas-permeable membrane (5) is between 20 nm and 200 nm, and wherein the electromagnetic radiation source (7) and the pressure sensor (6) are arranged in the measurement cell (2).

3. The photoacoustic gas sensor device according to claim 1, where the dimensions of the measurement volume (3) are between 0.08 cm 3 and 1 cm 3 ​ wherein the diameter of the gas-permeable region (4) is between 0.5 mm and 2 mm.

4. The photoacoustic gas sensor device according to claim 1, wherein the porous air-permeable membrane (5) comprises or consists of one of the following: sintered metal, ceramic, polymer, and wherein the thickness of the porous gas-permeable membrane (5) is between 50 pm and 400 pm.

5. The photoacoustic gas sensor device according to claim 1, where the dimensions of the measurement volume (3) are 0.2 cm 3 , wherein the porous gas-permeable membrane (5) comprises PTFE, and wherein the thickness of the porous gas-permeable membrane (5) is between 100 pm and 300 pm.

6. The photoacoustic gas sensor device according to claim 1, comprising a substrate (1), and a measurement cell body (21), the substrate (1) and the measurement cell body (21) defining the measurement volume (3), wherein the measurement cell body (21) comprises an opening (41), wherein the opening (41) is covered by the porous gas-permeable membrane (5), and wherein the porous gas-permeable membrane (5) is attached to the measurement cell body (21).

7. The photoacoustic gas sensor device according to claim 6, wherein the porous gas-permeable membrane (5) is attached to the measurement cell body (21) by one of gluing, injection, casting, soldering and welding.

8. The photoacoustic gas sensor device according to claim 6, wherein the measurement cell body (21), the substrate (1) and other components defining the measurement volume (3) are made of a gas-tight material and are assembled in a gas-tight manner.

9. The photoacoustic gas sensor device according to claim 1, a substrate (1), and a measurement cell body (21), the substrate (1) and the measurement cell body (21) defining the measurement volume (3), wherein the substrate (1) comprises an opening (41), wherein the opening (41) is covered by the porous gas-permeable membrane (5), and wherein the porous gas-permeable membrane (5) is attached to the substrate (1).

10. The photoacoustic gas sensor device according to claim 9, wherein the measurement cell body (21), the substrate (1) and other components defining the measurement volume (3) are made of a gas-tight material and are assembled in a gas-tight manner.

11. The photoacoustic gas sensor device according to claim 9, wherein the porous gas-permeable membrane (5) comprises a metallization welded to the substrate (1).

12. The photoacoustic gas sensor device according to claim 1, comprising a substrate (1), and a measurement cell body (21), the substrate (1) and the measurement cell body (21) defining a measurement volume (3), wherein an opening (41) between the measurement cell body (21) and the substrate (1) is covered by the porous gas-permeable membrane (5), and wherein the porous gas-permeable membrane (5) is attached to one or more of the measurement cell body (21) and the substrate (1).

13. The photoacoustic gas sensor device according to claim 12, wherein, wherein the measurement cell body (21), the substrate (1) and other components defining the measurement volume (3) are made of a gas-tight material and are assembled in a gas-tight manner, except for the opening (41).

14. The photoacoustic gas sensor device according to claim 12, wherein the porous gas-permeable membrane (5) is attached to one or more of the measurement cell body (21) and the substrate (1) by one of gluing, injection, casting, soldering and welding.

15. The photoacoustic gas sensor device according to claim 1, comprising a support layer (51) attached to the porous gas-permeable membrane (5).

16. The photoacoustic gas sensor device according to claim 15, wherein the support layer (51) is an adhesive layer and the porous gas-permeable membrane (5) is attached to the measurement cell (2) by means of the adhesive layer.

17. The photoacoustic gas sensor device according to claim 15, wherein the support layer (51) is gas-tight and comprises one or more holes (511) arranged to allow a gas to enter the measurement volume (3) when passing through the porous gas-permeable membrane (5).

18. The photoacoustic gas sensor device according to claim 1, comprising a lattice structure (54) attached to a first side of the porous gas-permeable membrane (5), wherein the porous gas-permeable membrane (5) is attached to the measurement cell (2) by means of an adhesive (53) arranged on a second side of the porous gas-permeable membrane (5) opposite the first side.

19. The photoacoustic gas sensor device according to any one of claims 6 to 11, wherein the opening (41) is represented by a plurality of drillings (411) in one or more of the measurement cell body (21) and the substrate (1), wherein the porous gas-permeable membrane (5) is attached to the measurement cell body (21) or the substrate (1), respectively, to cover the plurality of drillings (411).

20. The photoacoustic gas sensor device according to any one of claims 6 to 14, comprising a reflector (28) arranged inside the measurement cell (2) and spaced apart from the opening (41) for reflecting electromagnetic radiation back into the measurement volume (3) that would otherwise be absorbed by or transmitted through the porous gas-permeable membrane (5).

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