Photoacoustic gas sensor and pressure sensor

Abstract

A MEMS photoacoustic gas sensor and a pressure sensor, the photoacoustic gas sensor including a first membrane and a second membrane opposite to the first membrane and separated from the first membrane by a sensing volume. The MEMS photoacoustic gas sensor includes an electromagnetic source and communicates with the sensing volume to deflect the first membrane and the second membrane.

Description

Technical Field

[0001] The present disclosure relates to a MEMS photoacoustic gas sensor and a MEMS pressure sensor. The present disclosure also relates to a dual membrane photoacoustic spectrometer (PAS) sensor. Background Art

[0002] With the development of the mobile device, home automation, and automotive industries, the sensing of environmental parameters such as noise, sound, temperature, and gas has become increasingly important. The concentration of harmful gases may be caused by pollution and the malfunction of specific devices. At the same time, air quality has a great impact on well-being. Therefore, gas detection using inexpensive, readily available, and connectable sensors is an upcoming topic. Summary of the Invention

[0003] Therefore, an object of the embodiments is to provide a device that allows for the precise measurement of environmental parameters.

[0004] According to one embodiment, a microelectromechanical system (MEMS) photoacoustic gas sensor includes a first membrane and a second membrane, the second membrane being opposite to the first membrane and separated from the first membrane by a sensing volume. The MEMS photoacoustic gas sensor includes an electromagnetic source in communication with the sensing volume. By using a membrane structure having two membranes, both of which are adapted to move or deflect, where the movement is guided in opposite directions such that the membranes move towards or away from each other, a high signal amplitude can be obtained, which allows for the precise determination of environmental parameters by the photoacoustic gas sensor.

[0005] An embodiment provides a MEMS pressure sensor that includes a first membrane and a second membrane, the second membrane being separated from the first membrane by a sensing volume. The MEMS pressure sensor includes a circuit configured to measure the capacitance between the first membrane and the second membrane. Similarly, by having two deflectable membranes that deflect in opposite directions, environmental parameters, namely pressure, can be precisely measured.

[0006] The present disclosure also defines further embodiments. Brief Description of the Drawings

[0007] Embodiments are described herein with reference to the drawings, in which:

[0008] Figure 1 A schematic block diagram of a MEMS photoacoustic gas sensor according to one embodiment is shown;

[0009] Figure 2a A schematic side view of a portion of a MEMS photoacoustic gas sensor having a rear volume in addition to a front volume according to one embodiment is shown;

[0010] Figure 2b Shows Figure 2aSchematic side view of part of a MEMS photoacoustic gas sensor being subject to interference arriving through the front volume;

[0011] Figure 3 Schematic side view showing a MEMS photoacoustic gas sensor having a so-called bottom port configuration according to an embodiment;

[0012] Figure 4 Schematic side view showing a MEMS photoacoustic gas sensor according to an embodiment, in which the electromagnetic source is supported by a semiconductor substrate;

[0013] Figure 5 Schematic side view showing part of a MEMS photoacoustic gas sensor including a backplate structure according to an embodiment;

[0014] Figure 6 Schematic side view showing part of another MEMS photoacoustic gas sensor according to an embodiment;

[0015] Figure 7 Schematic side view showing a MEMS photoacoustic gas sensor including at least a third membrane according to an embodiment;

[0016] Figure 8 Schematic side view showing part of a MEMS photoacoustic gas sensor according to an embodiment, which is implemented to independently measure the deflection of a membrane relative to a fixed backplate structure; and

[0017] Figure 9 Schematic side view showing part of a MEMS photoacoustic gas sensor including a circuit according to an embodiment. Detailed Description

[0018] Identical or equivalent elements or elements having the same or equivalent functions are denoted by the same or equivalent reference numerals in the following description, even if they appear in different drawings.

[0019] In the following description, numerous details are set forth to provide a more thorough explanation of the embodiments. However, those skilled in the art should understand that the embodiments can be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form rather than in detail to avoid obscuring the embodiments. Additionally, unless otherwise specifically stated, the features of the different embodiments described below can be combined with each other.

[0020] In the following, reference is made to measurement environmental parameters. Some embodiments relate to measuring the concentration of a specific gas and / or the presence of a specific substance or material in a gas. Such measurements can be performed by using a microelectromechanical system (MEMS) implemented as a photoacoustic gas sensor. This can also be referred to as a photoacoustic spectrometer (PAS) sensor. Such a sensor can be used for gas sensing and can include a back volume, a sensing volume, and two membranes therebetween. A specific type of gas (at least having a concentration or being a pure gas) disposed in the sensing volume can be excited by using radiation, thereby dynamically causing deflection of the membranes. Such deflection can be evaluated and associated with the specific gas. That is, different gases or different concentrations therein can result in different behaviors of the membranes, the different behaviors are measured, and therefrom the gas or its concentration between the membranes is inferred.

[0021] Figure 1 A schematic block diagram of a MEMS photoacoustic gas sensor 10 according to one embodiment is shown. The MEMS photoacoustic gas sensor 10 can include a substrate 12, which can be formed at least in part by using a semiconductor material. For example, the substrate 12 can include a silicon material. Alternatively or additionally, the substrate 12 can include a different semiconductor material, such as gallium arsenide, etc. The substrate 12 can be formed or shaped by using an additive process (e.g., growing a corresponding structure). Alternatively or additionally, a subtractive process (e.g., an etching process) can be used such that the structure of the substrate 12 is retained from a larger body.

[0022] The MEMS photoacoustic gas sensor includes a first membrane 141 and a second membrane 142 opposite the first membrane 141. The membranes 141 and 142 can be separated from each other by a sensing volume 16. The sensing volume 16 can allow gas or its particles to move from a front volume 18 outside the sensing volume 16 into the sensing volume 16, for example, based on diffusion and / or based on a slow exchange of gas between the front volume 18 and the sensing volume 16, where "slow" is understood to mean a non-acoustic speed.

[0023] The MEMS photoacoustic gas sensor 10 includes an electromagnetic source 22 in communication with the sensing volume 16. The electromagnetic source can be configured to generate and / or emit energy 24 into the sensing volume 16, thereby exciting the gas and / or particles in the sensing volume 16. That is, the electromagnetic source can be configured and / or arranged to deflect the first membrane 141 and / or the second membrane 142. Both membranes 141 and 142 can deflect relative to the substrate, for example, along the same direction z. By exciting the sensing volume 16, a relative movement of the membranes 141 and 142 with respect to each other can be produced. For example, the membrane 141 can deflect in the negative z direction while, at the same time, due to the expansion within the sensing volume 16, the membrane 142 deflects in the positive z direction. Alternatively, the membrane 141 can move in the positive z direction while, at the same time, the membrane 142 moves in the negative z direction.

[0024] The electromagnetic source 22 can be configured to dynamically emit energy 24 so as to generate dynamic movement of membranes 141 and 142 such that the described movement can be understood as vibrations of membranes 141 and 142, wherein corresponding vibrations are generated to indicate the reverse with respect to the respective other membrane 141 or 142.

[0025] Evaluating the relative movement (e.g., by evaluating the voltage or capacitance between membranes 141 and 142) can allow for precise measurement of the sensing volume 16 by means of a relatively high-amplitude relative movement (compared to the movement of only one movable or deflectable membrane with respect to the stator electrodes). At the same time, this configuration allows for high robustness against acoustic noise, such as that which can propagate through the front volume 18 to the membrane arrangement 141 and 142. Such acoustic noise (e.g., sound pressure) can cause membranes 141 and 142 to deflect in the same direction, which can be easily distinguished from the movement generated by the electromagnetic source 22, allowing for simple compensation.

[0026] Membranes 141 and 142 can comprise a semiconductor material, such as a silicon material, e.g., crystalline or polycrystalline silicon. The semiconductor material can be a doped semiconductor material in order to obtain conductive properties that allow the structure to be used as an electrode. Alternatively or additionally, a conductive layer can be arranged at the semiconductor material, e.g., a layer comprising a metallic material (e.g., gold, silver, aluminum, copper, etc.).

[0027] The electromagnetic source 22 can be configured to generate and / or emit energy 24 as electromagnetic energy. For example, the electromagnetic source 22 can be implemented as an infrared source configured to emit energy 24 as an infrared signal. For example, the electromagnetic source 22 can be a heater. The electromagnetic source 22 can comprise a conductive material (e.g., doped silicon material or conductive material arranged on the surface of a substrate material) configured to increase in temperature in response to an electric current.

[0028] Figure 2a A schematic side view of a portion of a MEMS photoacoustic gas sensor 20 according to one embodiment is shown, which, compared to the MEMS photoacoustic gas sensor 10, also has a rear volume 26 in addition to the front volume 18. The difference between the front volume 18 and the rear volume 26 is that the fluid or gas to be measured and disturbances can reach membranes 141 and 142 at the front volume 18, while being largely or completely blocked (at least in part) by the rear volume 26. The heater 22 is part of the MEMS photoacoustic gas sensor 20 but is not shown in Figure 2a is shown.

[0029] In Figure 2a membranes 141 and 142 are also shown in the deflected states 14'1 and 14'2, which can be obtained by excitation of the electromagnetic source 22.

[0030] In order to avoid high pressure in the rear volume 26, the substrate 12 forming the rear volume 26 can comprise one or more openings allowing for air flow.

[0031] In other words, the photoacoustic signal can generate pressure within the sensing volume 16. This causes the membrane to move in the opposite direction.

[0032] Figure 2b is shown Figure 2a A schematic side view of a portion of the MEMS photoacoustic gas sensor 20 showing interference 28 arriving through the front volume 18. The interference 28 can include an external pressure, such as an acoustic pressure, etc. The interference 28 can cause deflections 14'1 and 14'2 of the membranes 141 and 142 in the same direction (e.g., positive z). Compared with Figure 2a the opposite movement in Figure 2a this movement can keep the measured value of the measurement signal 32 between the membranes 141 and 142 without a significant effect. For example, when compared with Figure 2b in Figure 2a the movement can keep the capacitance between the membranes 141 and 142 unchanged or can cause a small change, where

[0033] That is to say, the specific design of the MEMS photoacoustic gas sensor described herein can be used to eliminate noise. The embodiments relate to the so-called open system PAS sensor concept and reduce the sensitivity of such systems to acoustic noise.

[0034] According to one embodiment, the MEMS photoacoustic gas sensor 20 is modified such that the mechanical stiffness of the membrane 141 and the mechanical stiffness of the membrane 142 are implemented in different ways, i.e., the mechanical stiffnesses of both can vary relative to each other. For example, the mechanical stiffnesses can be selected such that an acoustic signal (e.g., the interference 28 passing from the front volume 28 through the sensing volume 16 to the rear volume 26) causes the membranes 141 and 142 to have the same deflection amplitude within a tolerance range of, for example, ±10%, ±7% or ±5%. For example, the attenuation of the acoustic signal by the sensing volume 16 that reduces the mechanical force on the membrane 141 and the membrane 142 can be easily determined, and can be taken into account by selecting the mechanical stiffness of the membrane 141 and / or 142 such that there is the same deflection (at least within the tolerance range) at least for the reference force amplitude.

[0035] In other words, the pressure of the acoustic signal can cause the membranes to move in the same direction. The photoacoustic signal and the acoustic signal can be easily distinguished.

[0036] Figure 3FIG. 0 shows a schematic side view of a MEMS photoacoustic gas sensor 30 according to one embodiment. A sensing volume may be arranged between volumes 18 and 26, and volumes 18 and 26 are shown, for example, as a so-called bottom port configuration, i.e., the front volume 18 is respectively arranged below the rear volume 26 and the sensing volume 16. It should be noted that expressions such as left, right, bottom, or top are only for explanation, and by rotating the device, the meaning of such descriptions can be easily changed. For example, the MEMS photoacoustic gas sensor 30 can be modified to close the housing 34 in the region of the front volume 18, and by opening the housing 34, gases and / or interferences can reach the membranes 141 and 142 through the rear volume 26, thereby changing the configuration to a top port configuration and interchanging the meanings of the front volume and the rear volume.

[0037] Alternatively or additionally, membrane 141 and / or membrane 142 may include openings (e.g., ventilation holes 361 - 364), and for each of membranes 141 and 142, the number of openings is more than one, more than five, more than ten, or even more.

[0038] One or more optional openings 361 and 362 in membrane 141 may fluidly couple the front volume 18 with the sensing volume 16, i.e., an exchange of fluid (i.e., gas) may occur between volumes 16 and 18. The exchange of gas molecules can be adjusted (e.g., by the number and / or size of openings 361 and / or 362) to allow the transmission of gas molecules, particularly the gas molecules detected by the MEMS photoacoustic gas sensor. Instead or additionally, one or more openings 363 and 364 in membrane 142 may fluidly couple the rear volume 26 with the sensing volume 16. According to one embodiment, openings 361 - 364 are each formed with a size to block audio frequencies. The number and the common, grouped different or even individual sizes of the openings can be designed in the following way: to obtain optimization to block audio frequencies and allow gas diffusion into the sensing volume. For example, a trade-off can be made between one or more large openings for rapid gas exchange and small openings for good blocking of audio frequencies. The openings allow the exchange of fluid into the sensing volume 16, thereby allowing modification of the measurement in a modified environment while avoiding acoustic short circuits, thus allowing high-quality measurements.

[0039] As Figure 1 、 Figure 2a 、 Figure 2b and Figure 3 As shown, the substrate 12 may include an opening 38, and may additionally support membranes 141 and 142 in such a way that membranes 141 and 142 cover the opening 38.

[0040] Figure 4Shows a schematic side view of a MEMS photoacoustic gas sensor 40 according to an embodiment, wherein the electromagnetic source 22 is supported by the semiconductor substrate 12. This allows on the one hand to obtain a compact device and on the other hand to generate a direction along which the energy 24 is emitted. For example, the semiconductor substrate can be used as a reflector or a director of the energy 24. Optionally, the electromagnetic source can be covered by a cover layer 42 (e.g., a filter for filtering or passing a specific wavelength). Instead or additionally, the cover layer 42 can provide chemical and / or electrical and / or physical protection for the electromagnetic source 22.

[0041] Figure 5 Shows a schematic side view of a part of a MEMS photoacoustic gas sensor 50 according to an embodiment. The MEMS photoacoustic gas sensor 50 may include an electrode structure 44, e.g., a backplane structure that can be considered immovable when compared to the movable or deflectable membranes 141 and 142. The backplane structure 44 can be arranged between the membranes 141 and 142 in the sensing volume 16. By implementing the backplane structure 44 as another electrode, two measurement signals 321 and 322 can be independently measured between the membrane 141 and the backplane structure 44 and between the membrane 142 and the backplane structure 44, respectively. This can allow for high-precision measurements. The backplane structure 44 may include an opening 46, the size of which can be larger compared to the opening 36 to avoid acoustic blockage, especially to prevent the generation of pressure between the membranes 141 and 142 and the backplane structure 44.

[0042] As described in connection with different MEMS photoacoustic gas sensors, the MEMS photoacoustic gas sensor 50 includes an electromagnetic source 22 not shown and can be further arranged such that the sensing volume 16 is arranged between a first volume and a second volume (e.g., a front volume and a back volume).

[0043] Figure 6 Shows a schematic side view of a part of a MEMS photoacoustic gas sensor, i.e., the electromagnetic source 22 is not shown. Compared to the MEMS photoacoustic gas sensor 50, the MEMS photoacoustic gas sensor 60 may include connectors 481 - 483 mechanically coupled between the membranes 141 and 142. For example, the connectors 481 - 483 can pass through the opening 46 of the backplane structure 44. Alternatively, the MEMS photoacoustic gas sensor 60 can be implemented without the backplane structure 44. In both configurations, the MEMS photoacoustic gas sensor 60 allows for a low deflection amount in the area of the connectors 481 - 483.

[0044] Optionally, the connectors can divide the sensing volume 16 into a plurality of partial sensing volumes 16 a -16 d . The electromagnetic source can be configured to cause alternating bending of adjacent or neighboring parts of the membranes 141 and 142 in neighboring partial sensing volumes. For example, the membranes 141 and 142 can be in the partial sensing volume 16a -16 d deflect towards each other within one of a , and can deflect away from each other within adjacent partial sensing volumes. To cause alternating bending, the electromagnetic source can be controlled to provide a transient power signal that can vary in amplitude and / or time, such as a sine signal or a rectangular chopped signal. Some partial sensing volumes 16 a -16 d can be arbitrary and can be selected, for example, by mechanical parameters. For example, the distance between the connectors 481 - 483 can be selected such that bending with the maximum or minimum amplitude occurs within the partial sensing volume.

[0045] Alternatively or additionally, the distance between the connectors 481 - 483 and / or the size of the partial sensing volume 16 a -16 d can be selected taking into account the resonant frequency obtained based on the size of the partial sensing volume 16 a -16 d The connectors 481 - 483, which can be arranged in any number and / or any geometric form, can be electrically insulating or, alternatively, can be conductive.

[0046] Figure 7 shows a schematic side view of a MEMS photoacoustic gas sensor 70 according to an embodiment. When compared with the MEMS photoacoustic gas sensors 10, 20, 30, 40, 50, and 60, the MEMS photoacoustic gas sensor 70 can include at least a third membrane 143, which is arranged opposite to the membrane 142 and forms an additional sensing volume 162, added to the sensing volume 161 between the membranes 141 and 142. For example, considering the size and / or the gas contained therein or the material sensitive to the sensing volumes 161 and 162, the sensing volumes 161 and 162 can be different from each other. For example, different measurements can be performed in the different sensing volumes 161 and 162. Optionally, the MEMS photoacoustic gas sensor 70 can include another electromagnetic source, which is configured to emit corresponding energy at different energy levels, simultaneously in different wavelength ranges or different frequencies, or at different times, compared with the electromagnetic source 22.

[0047] The MEMS photoacoustic gas sensor 70 can be formed monolithically in the same way as the MEMS photoacoustic gas sensors 10, 20, 30, 40, 50, and / or 60 by the layering and structuring of semiconductor materials.

[0048] According to one embodiment, the sensing volumes 161 and 162 may be arranged adjacent to each other and separated by the membrane 142. According to another embodiment, the sensing volumes 161 and 162 may be arranged spaced apart from each other, for example by yet another fourth membrane, such that the two sensing volumes 161 and 162 may be excited independently of each other because each sensing volume is surrounded by a pair of membranes specifically associated with that sensing volume. Alternatively, by arranging a fourth or even greater number of membranes, a greater number of sensing volumes may be generated.

[0049] In one or more of the sensing volumes 161 and 162, a backplate structure may be arranged.

[0050] Figure 8 A schematic side view of a portion of a MEMS photoacoustic gas sensor 80 is shown, where the electromagnetic source 22 is again not shown. Compared to other MEMS photoacoustic gas sensors described herein, the MEMS photoacoustic gas sensor 80 may be implemented to independently measure the deflection of the membrane 141 relative to the fixed backplate structure 441 and additionally measure the deflection of the membrane 142 relative to another fixed backplate structure 442. The positions of the associated backplate structures 441, 442 below or above the respective membranes 141, 142 may be independently selected. This may allow for high selectivity in evaluating the measurement results. This also allows for the fabrication of a first (e.g., upper) group (membrane 142, fixed backplate structure 442, and adjacent substrate 122) and a second (e.g., lower) group (membrane 141, fixed backplate structure 441, and adjacent substrate 121) in separate manufacturing processes. For example, these groups may be joined together by a bonding process.

[0051] Figure 9 A schematic side view of a portion of a MEMS photoacoustic gas sensor 90 according to one embodiment is shown. For example, the MEMS photoacoustic gas sensor 90 may include the MEMS photoacoustic gas sensor 10, where, alternatively or additionally, any other MEMS photoacoustic gas sensor described herein may be arranged. Furthermore, the MEMS photoacoustic gas sensor 90 includes circuitry, such as a processor, configured to process at least one signal (e.g., measurement signal 32) generated by the deflection of the membranes 141 and 142, such as a central processing unit (CPU) or a microcontroller or an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA). For example, the circuitry 52 may be configured to correlate the measurement signal 32 with the properties of the fluid in the sensing volume 16.

[0052] The embodiments described herein are described in connection with a MEMS photoacoustic gas sensor. According to a further embodiment, a MEMS pressure sensor is provided. As described in connection with the MEMS photoacoustic gas sensor, the MEMS pressure sensor according to an embodiment may include a first and a second membrane spaced apart from each other to form a sensing volume therebetween. The pressure sensor may include circuitry configured to measure the capacitance between the first and the second membrane, for example by using circuitry 52. That is, instead of evaluating the deflection of membranes 141 and 142 in opposite directions, the deflection in the same direction may also be evaluated, wherein the deflection may be associated with the pressure acting on the sensing volume 16.

[0053] The PAS sensors described herein may include a sensing volume and a back volume, and optionally a front volume. A membrane is placed between the back volume and the sensing volume. A second membrane is placed between the sensing volume and the environment (front volume). The movement of the membranes may be coupled mechanically (e.g., by using a connecting member) or by an intermediate air or fluid coupling. Due to the arrangement of the membranes, the photoacoustic signal may be distinguished from the acoustic noise. When compared to a solution with a second device for noise cancellation, the embodiments allow for precise measurements to be obtained using the same device, thus avoiding the need for additional devices for calibration. Optionally, an electromagnetic source (e.g., an infrared emitter) and the two membranes may be implemented in one chip, resulting in a smaller package size.

[0054] Embodiments may include three possible main components that are connected in an easily constructible setup and may enhance the functionality of the sensor. The first component is a bulk silicon frame with Bosch holes to generate cavities for the membranes. The second component may be a first membrane or thin structure aligned over the cavities or holes of the first component. Additionally, the third component may be a second membrane or thin structure aligned over the cavities or holes described in association with the first component. The membrane is located above the first membrane.

[0055] Optionally, other components may be added. Among them, a backplane structure is present between the membranes for more complex readout. Instead of or in addition to this, connection elements may be arranged between the membranes to enhance the uniform movement of the membranes under the influence of acoustic noise, such as connecting members.

[0056] Embodiments allow for the detection of the movement of the membranes achieved by capacitive, piezoelectric, or inductive readout. The diffusion of gas into the sensing volume may be achieved through ventilation holes in the two membranes. The same ventilation holes may be used for static pressure compensation. Optionally, the emitter is placed on the same chip next to the membrane stack.

[0057] Further described in the main body: The described embodiment can form the sensing sub - part, i.e., the component, of a photoacoustic spectrometer (PAS) sensor. This arrangement can also be used as a slow - transient pressure sensor. In the target PAS sensor, the read - out can be achieved via a pressure - sensitive membrane. To distinguish the desired sensor signal from the noise, two membranes can be used to implement differential read - out. The embodiment relates to a concept, a sensor, and a method for implementing differential read - out via two membranes positioned one after another (as opposed to being arranged side - by - side). The sensing volume can be arranged between the membranes. Acoustic noise can cause the membranes to deflect in the same direction, while the photoacoustic signal can cause the membranes to deflect in opposite directions. Thus, the noise signal and the sensor signal can be distinguished.

[0058] The embodiment allows for obtaining a miniaturized PAS sensor. Such a sensor can be used in an environment with acoustic noise (e.g., speech, music, ambient noise, etc.).

[0059] Although some aspects are described in the context of a device, it is evident that these aspects also represent a description of a corresponding method, where a block or a device corresponds to a method step or a feature of a method step. Similarly, aspects described in the context of method steps also represent a description of corresponding blocks or items or features of a corresponding device.

[0060] The above - mentioned embodiments are merely illustrative of the principles of the present disclosure. It should be understood that modifications and variations to the arrangements and details described herein will be apparent to those skilled in the art. Therefore, it is limited only by the scope of the upcoming patent claims, rather than by the specific details presented in the description and explanation of the embodiments herein.

Claims

1. A MEMS photoacoustic gas sensor, comprising: a first membrane (141); a second membrane (142), opposite to the first membrane (141) and separated from the first membrane (141) by a sensing volume (16); and an electromagnetic source (22), in communication with the sensing volume (16), wherein the electromagnetic source is configured to generate and / or emit energy into the sensing volume, thereby exciting a gas and / or particles in the sensing volume to generate a pressure within the sensing volume such that the first membrane and the second membrane move in opposite directions, and wherein the movement results in a measurement signal of the photoacoustic gas sensor.

2. The sensor according to claim 1, wherein the first membrane (141) is disposed between the sensing volume (16) and a first volume (18), and the second membrane (142) is disposed between the sensing volume (16) and a third volume (28).

3. The sensor according to claim 2, wherein the first volume (18) is a front volume and the third volume (28) is a rear volume; or wherein the first volume (18) is a rear volume and the third volume (28) is a front volume.

4. The sensor according to claim 3, wherein a first stiffness of the first membrane (141) and a second stiffness of the second membrane (142) are selected such that an acoustic signal propagating from the front volume through the sensing volume (16) to the rear volume causes deflections of the first membrane (141) and the second membrane (142) of the same magnitude within a tolerance range.

5. The sensor according to any one of claims 2 to 4, wherein the first membrane (141) includes at least one first opening (361) fluidly coupled to the first volume (18) and the sensing volume (16), and the second membrane (142) includes at least one second opening (363) fluidly coupled to the third volume (28) and the sensing volume (16).

6. The sensor according to claim 5, wherein the at least one first opening (361) and the at least one second opening (363) are each sized to block acoustic frequencies and are implemented to be fluidly coupled to the first volume (18) and the sensing volume (16) to permit transmission of gas molecules.

7. The sensor according to claim 1, further comprising: A backplate (44), disposed between the first membrane (141) and the second membrane (142) and separated from the first membrane (141) and the second membrane (142).

8. The sensor according to claim 1 further comprises: One or more connectors (48), mechanically coupled between the first membrane (141) and the second membrane (142).

9. The sensor according to claim 8, wherein the one or more connectors (48) are conductive.

10. The sensor according to claim 8, wherein the one or more connectors (48) are electrically insulating.

11. The sensor according to any one of claims 7 to 10, wherein the one or more connectors (48) divide the sensing volume (16) into a plurality of partial sensing volumes (16a - 16d), and the electromagnetic source (22) is configured to cause alternating bending of the first membrane (141) and the second membrane (142) in adjacent partial sensing volumes.

12. The sensor according to claim 1, wherein the first membrane (141) is supported by a semiconductor substrate (12), and the semiconductor substrate (12) has an opening (38) over which the first membrane (141) is disposed.

13. The sensor according to claim 12, wherein the electromagnetic source (22) is supported by the semiconductor substrate (12).

14. The sensor according to claim 1, wherein the electromagnetic source (22) is an infrared source.

15. The sensor according to claim 1, wherein the electromagnetic source (22) is a heater.

16. The sensor according to claim 1, wherein the sensing volume (16) is a first sensing volume (161), and the sensor further comprises at least a third membrane (143) which, together with the first membrane (141) and the second membrane (142), forms at least a part of a stack and defines a second sensing volume (162) in the stack.

17. The sensor according to claim 1 further comprises: A circuit (52), configured to process at least one signal (32) generated by a first deflection (14'1) of the first membrane (141) and a second deflection (14'2) of the second membrane (142).

18. A MEMS pressure sensor, comprising: A first membrane (141); A second membrane (142), separated from the first membrane (141) by a sensing volume (16); A circuit (52), configured to measure the capacitance between the first membrane (141) and the second membrane (142); and An electromagnetic source (22), in communication with the sensing volume (16), wherein the electromagnetic source is configured to generate and / or emit energy into the sensing volume so as to excite gases and / or particles in the sensing volume, generating a pressure within the sensing volume such that the first membrane and the second membrane move in opposite directions, and wherein the movement results in a measurement signal of the MEMS pressure sensor.

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