MEMS microphone with ventilation opening

Abstract

The invention relates to a MEMS microphone for detecting sound waves. The MEMS microphone includes a sensor and a housing. The housing surrounds an interior region of the MEMS microphone and has a vent that enables fluid communication between the interior region and an exterior region of the MEMS microphone. Wherein the sensor is a thermal sensor configured to measure acoustic waves from fluid flow through the vent, the acoustic waves causing a pressure difference between an inner region and an outer region of the MEMS microphone. Furthermore, the invention relates to a photoacoustic gas sensor, the sensor chamber of which likewise comprises a sensor and a housing, similar to a MEMS microphone, the housing surrounding the inner region of the sensor chamber and the sensor chamber having a vent allowing fluid communication between the inner region and the outer region of the sensor chamber. The sensor of the sensor chamber, similar to a sensor of a MEMS microphone, is a thermal sensor configured to measure acoustic waves as a function of fluid flow through the vent.

Description

Technical Field

[0001] This invention relates to a MEMS microphone for detecting sound waves. The MEMS microphone includes a sensor and a housing. The housing surrounds an internal region of the MEMS microphone and has a vent that enables fluid communication between the internal and external regions of the MEMS microphone. The sensor is a thermal sensor configured to measure sound waves caused by fluid flow through the vent, which induces a pressure difference between the internal and external regions of the MEMS microphone.

[0002] Furthermore, the present invention relates to a photoacoustic gas sensor, whose sensor chamber, similar to that of a MEMS microphone, includes a sensor and a housing, wherein the housing surrounds the internal region of the sensor chamber, and the sensor chamber has a vent that enables fluid communication between the internal and external regions of the sensor chamber. The sensor in the sensor chamber, similar to that of a MEMS microphone, is a thermal sensor configured to measure sound waves by means of fluid flow through the vent. Background Technology

[0003] Today, microsystems technology is used in many applications to manufacture compact electromechanical devices. Microsystems (MEMS) are thus manufactured to be extremely compact (in the micrometer range) while offering excellent functionality and ever-decreasing manufacturing costs.

[0004] MEMS technology offers a variety of driving mechanisms or sensing devices. In particular, MEMS technology offers promising possibilities for providing and operating sound pressure sensors, or microphones (also known as MEMS microphones).

[0005] For MEMS microphones, there are various conversion mechanisms that can convert the sound to be detected into a measurement signal. These mechanisms can be based on electrodynamic, electrical, piezoresistive, piezoelectric, optical, or capacitive mechanisms. For example, MEMS microphones based on the capacitive measurement principle are common.

[0006] The paper by Zawawi et al. (2022) includes an overview of known capacitive MEMS microphones in the prior art. Capacitive MEMS microphones typically have two parallel plates consisting of a vibrating or deflectable diaphragm and a backplate. The backplate is fixedly positioned along a substrate. The diaphragm deflects due to the action of sound waves, causing a change in the distance between the backplate and the diaphragm, resulting in a change in capacitance, from which the intensity of the sound wave can be inferred. The backplate may also have perforations, allowing air to flow between the diaphragm and the backplate. Perforations reduce acoustic noise and acoustic damping. Capacitive MEMS microphones have proven usable in numerous applications. However, for reliable operation of capacitive MEMS microphones, the areas of the backplate and diaphragm need to be set with exceptional precision, involving complex manufacturing processes. Furthermore, due to their structure, capacitive MEMS microphones often generate additional noise, such as due to perforations in the backplate (adding to acoustic noise), thus reducing the resolution of the measured signal.

[0007] The frequency range or band that a MEMS microphone can measure determines its suitability for the corresponding application. Typically, the sensitivity of MEMS microphones (especially condenser MEMS microphones) decreases below 100Hz and begins to rise between 4kHz and 6kHz due to Helmholtz resonance. The structure can be optimized to achieve a frequency band of 20Hz–20kHz to enable audio range detection. However, condenser MEMS microphones are generally not effective, especially for low frequencies (e.g., infrasound).

[0008] Another method for performing acoustic measurements is to use thermal sensors. Here, the velocity of molecules is measured, rather than (acoustic) pressure. For example, van Honschoten et al. (2005) disclosed a thermal flow sensor that can be used for acoustic measurements. The corresponding sensor consists of a “microflown” formed by an arrangement of three metal wires. The middle wire serves as a heating element, while the other two wires are positioned around the heating element and act as sensors. As air flows along the heating element, different measurements are obtained on the sensor. The flow rate can be inferred from the difference between these two results. In particular, sound intensity, acoustic impedance, and sound pressure can be measured. The sensor disclosed in van Honschoten et al. (2005) has a frequency band from 0 kHz to over 5 kHz, with a minimum provable particle velocity of approximately 70 nm / s in the 2 kHz to 5 kHz range.

[0009] Xu et al. (2022) also disclosed an arrangement that enables acoustic measurements using thermal sensors. This arrangement includes a cross-shaped heating element with four metal wires, each surrounded by thermal sensors arranged on a supporting substrate. Temperature sensors detect temperature changes through resistance variations. The heating element and temperature sensors are located above a backplate designed as a grid, acting as a heat sink and also acoustically transparent. This heat sink design allows for higher sensitivity in the z-axis. Suitable sensitivity was confirmed on all three Cartesian axes within the frequency range of 300Hz–5000Hz. However, below 300Hz, sensitivity along the z-axis is limited due to the grid-like backplate.

[0010] Due to its structure, MEMS microphones are also suitable for use in photoacoustic spectroscopy. The photoacoustic effect is utilized here to study gases. Energy is supplied rapidly and continuously by emitting light pulses within the medium. The resulting continuous alternation between heating and cooling causes alternating thermal expansion and contraction. These vibrations can be perceived as sound. For gas studies, the fact that gas molecules absorb light only at specific wavelengths or frequencies is utilized. These wavelengths or frequencies depend on the chemical structure and composition of the gas. To confirm a specific gas component in a gas mixture, light pulses whose frequencies are absorbed by only one type of molecule are used. The sound waves can be determined using a MEMS microphone. The higher the proportion of the gas being detected, the stronger the measurement signal at the MEMS microphone. In photoacoustic spectroscopy, low frequencies are frequently required for detection. For example, using thermal sensors known in the prior art, detection can be achieved by modulating the thermal field emitted by a heating element with sound waves.

[0011] For example, US10451589B2 discloses a detector for use in the field of PAS (Programmable Array of Sound-Induced Sensors). This detector includes a housing with an outer shell wall and a gas chamber disposed inside the housing. Furthermore, the gas chamber is configured to contain gas, wherein the outer shell wall has an opening providing a gas passage between the gas chamber and an outer surface. Additionally, an excitation element is present, configured to selectively excite specific types of gas molecules in the gas contained in the gas chamber in a time-varying manner, thereby generating sound waves. A MEMS microphone is used to detect the sound waves, wherein the MEMS microphone includes a mechanical structure that can be deflected by the sound wave to be detected.

[0012] WO2021 / 038099A1 discloses a photoacoustic gas sensor. This photoacoustic gas sensor includes a modulated infrared emitter, a detection chamber and a reference chamber that can be filled with gas, and a sensor channel connecting the detection chamber and the reference chamber. Furthermore, the photoacoustic gas sensor includes a sensor located in or adjacent to the sensor channel. The detection chamber, sensor channel, reference chamber, and sensor are arranged in a transverse plane substantially perpendicular to the radiation direction of the IR emitter. In one embodiment, the sensor is in the form of a capacitive microphone comprising a MEMS diaphragm. The MEMS diaphragm preferably also serves as an electrode, so that diaphragm vibrations caused by sound pressure waves can be measured by means of the (MEMS) electrode. In a preferred embodiment, the diaphragm may have holes for pressure equalization.

[0013] CA2200137A1 also demonstrates a photoacoustic gas sensor. This sensor includes a device for monitoring the functionality of a microphone and diaphragm located within the gas sensor. By monitoring the diaphragm, the microphone's sensitivity can be calibrated. Pressure modulation is performed via this device. The device includes a heating element, such as a wire, resistor, or heating film. Provided the diaphragm remains intact, the modulated heating of the air produces artificial pressure modulation not caused by the presence of a specific gas in the gas sensor's measuring chamber.

[0014] The method of detecting sound using the principle of thermal measurement is particularly advantageous due to the reduced noise effect and improved sensitivity. However, the corresponding sensors are highly sensitive to external influences. For example, even a small amount of dust or moisture inside the sensor can severely limit its operation, making sound measurements impossible or only unreliable.

[0015] Given the known solutions in the existing technology, there is a need to further optimize the structure and functional characteristics of MEMS microphones. Summary of the Invention

[0016] The object of this invention is to eliminate the known drawbacks of the prior art. In particular, the object of this invention is to provide a MEMS microphone that can guarantee persistent and reliable measurement of acoustic events, wherein the MEMS microphone is preferably characterized by reduced noise and high sensitivity over a wide frequency range.

[0017] The objective of this invention is achieved by the independent claims. Advantageous embodiments are disclosed in the dependent claims.

[0018] In a first aspect, the present invention relates to a MEMS microphone for detecting sound waves, comprising a sensor and a housing, wherein the housing surrounds an internal region of the MEMS microphone, and the MEMS microphone further has a vent that enables fluid communication between the internal region and an external region of the MEMS microphone, characterized in that the sensor is configured to measure sound waves based on fluid flow through the vent, the sound waves causing a pressure difference between the internal region and the external region of the MEMS microphone.

[0019] The MEMS microphone according to the invention utilizes the pressure difference between two regions (here, an inner region and an outer region) to cause fluid to flow in pressure equilibrium. This pressure difference specifically occurs when an acoustic event (i.e., an event that leads to the formation and propagation of sound waves) occurs. For example, it is possible that a higher pressure exists in the outer region or that a higher pressure is formed in the outer region due to an acoustic event. As a result, fluid flows from the outer region into the inner region through a vent.

[0020] The opposite can also occur. If the reference pressure in the internal region is higher than the pressure in the external region, a pressure difference will exist between the internal and external regions of the MEMS microphone. This pressure difference will cause fluid flow from the internal region to the external region.

[0021] Sensors can detect the resulting fluid flow, and thus infer acoustic events.

[0022] The MEMS microphone according to the present invention has a number of advantages.

[0023] In particular, the MEMS microphone according to the invention allows for the recording of high-resolution and particularly accurate measurement signals over a wide frequency range. Its compact and simple structure reduces factors that contribute to noise signals and thus distort the measurement signals. Therefore, compared to known condenser microphones, a perforated backplate, which could introduce noise due to the passage of sound waves, can be eliminated.

[0024] Furthermore, the MEMS microphone according to the invention is particularly suitable for detecting low-frequency sound waves, especially those below 100 Hz. Detecting such low-frequency acoustic events has proven difficult in the prior art. This is especially true for condenser microphones, which already have limitations when measuring sound waves below 100 Hz (see Shin et al. (2020)). This is primarily related to the back volume and the size of the sound inlet in condenser MEMS microphones. However, with the MEMS microphone according to the invention, the lower cutoff frequency can be advantageously kept particularly low, as further explained below. In particular, frequencies in the infrasound range can also be advantageously measured. Due to its ability to detect low frequencies, the MEMS microphone according to the invention has reliable applicability in the context of photoacoustic spectroscopy (PAS).

[0025] The possibility of sensitive measurement and higher resolution is primarily achieved through the potentially high acoustic impedance of the vent with a correspondingly small cross-section. Advantageously, even very small pressure differences can be detected in this way, thus making the sensor excellent for use as an acoustic detector (e.g., in photoacoustic gas sensors) for acoustic measurements.

[0026] The vent is preferably configured to correspond to the acoustic impedance, and the subsequent volume to correspond to the acoustic capacity or acoustic compliance. By appropriately selecting a small cross-section for the vent, a high acoustic impedance can be advantageously set. This allows for an extension of the measurement range with respect to low cutoff frequencies, or provides a smaller subsequent volume for the desired measurement frequency.

[0027] For the acoustic lower cutoff frequency ω, the following applies: ω = 1 (R S C bv ).

[0028] Voice and Appearance C bv Corresponding to the rear volume, the rear volume exists through the space between the carrier (for the thermal sensor) and the cover. The small cross-section of the vent allows for an advantageous reduction of the acoustic impedance R. S The acoustic impedance is set high. Therefore, even with a relatively small back volume, choosing a sufficiently high acoustic impedance can advantageously ensure a particularly low lower cutoff frequency. Furthermore, a high acoustic capacitance C can be set for MEMS microphones. bvSpecifically, this is determined by defining the volume of the internal region. The internal region preferably forms the area surrounded by the housing up to the vent. The internal region can preferably be considered as the rear volume of the MEMS microphone. A large rear volume and / or high acoustic impedance (especially determined by the construction of the vent) results in a particularly low cutoff frequency. Thus, the MEMS microphone can advantageously detect sounds even in the infrasound range (i.e., below 20 Hz, particularly preferably below 16 Hz). The lower cutoff frequency can, for example, have values ​​of 0.01 Hz–30 Hz (preferably 0.1 Hz–20 Hz, particularly preferably 1 Hz–15 Hz).

[0029] The lower cutoff frequency preferably represents a frequency below which the thermal sensor can measure fluid flow with reduced sensitivity under dynamic pressure fluctuations. The lower cutoff frequency is particularly determined by the acoustic impedance or fluid resistance and / or acoustic capacitance or back volume of the MEMS microphone, as described above.

[0030] The upper cutoff frequency preferably represents a frequency above which acoustic events can be measured with reduced sensitivity. While the lower cutoff frequency is determined by the structure of the MEMS microphone, particularly by the vents and housing, the upper cutoff frequency is preferably determined substantially by the sensor. In other words, the upper cutoff frequency is preferably related to the components and / or construction of the sensor. This will be illustrated exemplarily below with respect to a preferred embodiment where the sensor is a thermal sensor. Thus, in a preferred embodiment, the sensor can be a thermal sensor, which preferably has a heating element and a temperature sensor. The upper cutoff frequency may, for example, be affected by the thermal capacity of the temperature sensor or the thermal resistance of the diaphragm (on which the temperature sensor and / or heating element are located). The upper cutoff frequency may also depend, in particular, on the thermal diffusivity of the fluid in which the sound wave propagates. Thus, heat transfer through the fluid also at least jointly determines the upper cutoff frequency. For example, under high frequencies of pressure fluctuations and correspondingly rapid changes in thermal modulation, the temperature sensor may reach its measurement technology limit at which it can no longer distinguish such modulation. It should be noted in this regard that the modulation of the heat flow preferably occurs at a frequency twice the frequency of the acoustic signal. This is particularly relevant to the following: in both positive pressure cycles (pressure increases in the outer region, fluid flows into the inner region) and low pressure cycles (pressure decreases in the outer region, fluid flows out of the inner region), the temperature sensor detects lower temperatures due to the corresponding modulation of the heat flow. By providing a miniaturized temperature sensor, a high upper cutoff frequency can be advantageously achieved. The upper cutoff frequency can, for example, have values ​​greater than 1 kHz, greater than 10 kHz, and preferably greater than 100 kHz.

[0031] Therefore, a MEMS microphone can preferably achieve a very low lower cutoff frequency and a high upper cutoff frequency, thus providing a wide bandwidth within which sound waves can be reliably measured.

[0032] Therefore, the MEMS microphone according to the invention advantageously enables measurements over a particularly wide frequency band. The width of the frequency band can be determined by the difference between an upper cutoff frequency and a lower cutoff frequency. As mentioned above, the lower cutoff frequency preferably represents a frequency below which measurements can only be performed with reduced sensitivity. Similarly, the upper cutoff frequency represents a frequency above which measurements can only be performed with reduced sensitivity. The reduced sensitivity is preferably determined to be the maximum measurable value. This is equivalent to a decrease in sound level (e.g., sound pressure level) of approximately 3 dB.

[0033] Another advantage of MEMS microphones is that the amplitude and phase of sound waves can be inferred by measuring fluid flow. The MEMS microphone according to the invention is based on the detection of fluid flow caused by a pressure difference between an inner and outer region. This pressure difference is generated by sound waves, where fluid flow causes a pressure balance between the inner and outer regions. The MEMS microphone can thus identify the direction of fluid flow. For example, when sound waves impact the housing (preferably a robust cover), there may be higher pressure in the outer region. Therefore, fluid flows from the outer region to the inner region. Conversely, when the pressure in the outer region is lower, fluid flows from the inner region to the outer region to achieve pressure balance. Here, for example, it can be specified that fluid flow from the outer region to the inner region can be assigned a positive velocity, while fluid flow from the inner region to the outer region can be assigned a negative velocity or negative direction. Therefore, directional measurements can be performed, thereby obtaining more information about the phase and amplitude of the sound waves.

[0034] Furthermore, the compact structure allows for exceptionally robust MEMS microphones, which are further reduced to their sensitivity to external influences such as moisture and dust through the housing and the separation between the internal and external areas.

[0035] MEMS microphones preferably refer to microphones based on MEMS technology, and their sound-measuring or acoustic-measuring structures at least partially have dimensions in the micrometer range (1µm–1000µm). In the context of the invention, thermal sensors are preferably used as the acoustic-measuring structure. Therefore, it is preferred that at least the thermal sensor is based on MEMS technology and / or includes structures in the micrometer range.

[0036] The housing of a MEMS microphone preferably represents a stable and protective enclosure. Specifically, the housing protects the components of the MEMS microphone from foreign materials and / or damage. However, the housing can also perform other functions. For example, in addition to protection, the housing can provide support. Advantageously, omitting additional support structures reduces weight, the number of components, and assembly costs, thereby lowering the manufacturing cost of the MEMS microphone.

[0037] The housing preferably has a fastening area for connecting the thermal sensor to the housing. Options common in the prior art, such as brazing and / or bonding, can be used here. Such fastening options and methods are within the knowledge of those skilled in the art.

[0038] Specifically, the internal region of the MEMS microphone is surrounded by a housing. This internal region includes a spatial segment within the housing. Specifically, the internal region preferably includes the volume extending from the vent to the housing. Therefore, the vent preferably creates a separation between the internal and external regions of the MEMS microphone. Furthermore, a thermal sensor is preferably positioned adjacent to the vent to reliably detect fluid flow.

[0039] The outer region refers to the spatial region located outside the housing, i.e., preferably the (external) environment of the microphone. Acoustic events may occur in the outer region, propagating in the form of sound waves. When sound waves strike the MEMS microphone, they cause a pressure difference between the internal and outer regions, which, as mentioned above, causes fluid flow through the vents. Therefore, the MEMS microphone can detect sound waves by measuring the resulting fluid flow through the vents with high sensitivity (and advantageously even for lower frequencies) using a thermal sensor. In particular, the outer region refers to the environment of the MEMS microphone, which is open. An open environment preferably refers to a spatial region not surrounded by any structure of the MEMS microphone. The outer region preferably refers to a spatial region existing outside the housing of the MEMS microphone. The housing separates the outer region from the internal region of the MEMS microphone. Therefore, the MEMS microphone preferably has a housing that forms only one chamber and can be freely positioned in the environment to detect sound waves. This structure of the MEMS microphone also differs, for example, from the dual-chamber structure (with a reference chamber and a detection chamber) of the photoacoustic sensor known in WO2021 / 038099A1. For the photoacoustic sensor of WO2021 / 038099A1, although it is preferable to measure the fluid flow through the hole in the diaphragm between the detection chamber and the reference chamber, such a hole is not a vent that can connect to the external area in the sense of this invention.

[0040] A vent preferably represents a section of the MEMS microphone through which fluid communication is achieved between an external area and an internal area. Specifically, the vent separates the external and internal areas from each other. Fluid communication specifically means that fluid exchange can occur between the external and internal areas as long as a pressure difference exists between them. This pressure difference can be generated, in particular, by acoustic events or the impact of sound waves, where pressure is balanced via corresponding fluid flow through the vent. Sound waves are waves that propagate in the form of mechanical vibrations within an elastic medium (e.g., a fluid). Mechanical vibrations cause density fluctuations and, in particular, pressure fluctuations, which propagate in the fluid and thus form sound waves. Therefore, sound waves are also called sound pressure waves, which can be described, for example, by sound pressure and / or sound pressure level. Sound waves are caused by acoustic events that are the cause of their propagation. When a sound wave impacts the microphone, a pressure difference exists between the external and internal areas of the MEMS microphone. This pressure difference is balanced by fluid (in which the sound wave propagates) flowing from the external area into the internal area or vice versa. Although sound waves preferably refer to the propagation of vibrations rather than actual material flow, actual material flow is preferably occurring in fluid flow.

[0041] The fluid can be a liquid or a gas, such as air. Preferably, the vent forms an open section of the MEMS microphone, such as a hole in a diaphragm, the size of which can be adjusted according to measurements within the desired frequency band. The vent's design can influence the effect of fluid flow on the sensor. For the same DC fluid flow rate, a smaller vent cross-section results in a higher fluid velocity. As further explained below, for oscillating fluid flow of sound waves, a smaller cross-section may also reduce the flow velocity. The size of the vent cross-section can advantageously determine the effect of fluid flow on the sensor or the sensor's sensitivity.

[0042] Preferably, the vent is the only opening. Also preferably, the vent is formed by interconnected ribs, which are present, for example, within a diaphragm, on which the sensor is preferably located. Therefore, the vent can also preferably exist as a grid structure formed by ribs, such that fluid communication between the internal and external regions is still ensured through the gaps between the ribs. The gaps can, for example, have a square, rectangular, slit-shaped, circular, or elliptical cross-section. If this grid structure is located on the diaphragm (on which the heating element of the preferred thermal sensor is located), heat loss is advantageously reduced. The grid structure containing ribs provides high mechanical stability while reducing parasitic heat conduction. The grid structure can, for example, extend along a sub-region, such that the grid structure exists between the heating element and the temperature sensor.

[0043] Preferably, the sensor is positioned close enough to the vent (i.e., preferably less than 50 µm, more preferably less than 20 µm) to detect changes in fluid flow through the vent that depend on the sound waves. For example, the sensor may be located on a diaphragm adjacent to the opening forming the vent.

[0044] In the context of this invention, the sensor functions as a component, preferably configured to measure sound waves based on fluid flow through a vent. The sensor can preferably be any sensor capable of measuring fluid flow through a vent. Preferably, the sensor is a flow sensor. Particularly preferably, the sensor is a thermal sensor, wherein a thermal sensor preferably refers to a flow sensor that detects fluid flow through a thermal measurement principle. When using a preferred thermal sensor as the sensor, a heating element is particularly used, configured to provide heat flow, thereby inferring the fluid, and in particular, the sound waves, based on the modulation of the heat flow caused by the flow. As mentioned above, sound preferably refers to mechanical deformation propagating in a medium in the form of a wave. In a fluid (i.e., gas or liquid) as a medium, sound is always a longitudinal wave. The terms "sound" and "sound wave" can therefore be used synonymously. In a gas (such as air), sound can be described as a sound pressure wave superimposed on static air pressure. In sound waves, fluctuations in state quantities, including pressure and density, are generally small compared to their static values.

[0045] In another preferred embodiment, the MEMS microphone is characterized in that the sensor is a thermal sensor, which preferably includes a heating element and at least one temperature sensor, preferably two temperature sensors, so that the fluid flow through the vent can be measured by modulating the heat flow between the heating element and the temperature sensor.

[0046] In the context of this invention, a thermal sensor preferably refers to a sensor structurally based on MEMS technology and functionally based on the principle of thermal measurement. Preferably, the thermal sensor has a heating element, which, when triggered, can provide a heat flow towards the temperature sensor. The heat flow is modulated by the fluid flow through the vent based on the sound waves emitted, which can be identified by the temperature change measured at the temperature sensor.

[0047] Heat flux refers to the heat itself emitted from the heating element and transferred to the temperature sensor. Those skilled in the art know that heat itself is a form of energy. Fluid flow, particularly between the heating element and the temperature sensor, propagates through the heat flux via sound waves, thus influencing the heat flux. This influence, and the accompanying changes in heat flux caused by the fluid flow, can be detected by the temperature sensor; in the context of this invention, these changes in heat flux are referred to as modulation of the heat flux. Structurally, the thermal sensor includes components crucial to its function, including a heating element and a temperature sensor.

[0048] The heating element preferably represents a component of the thermal sensor from which heat flow is emitted by releasing thermal energy. Therefore, the heating element is particularly used to provide heat flow. The heating element may preferably exist as an electrothermal element. An electrothermal element preferably represents a heating element capable of converting electrical energy into thermal energy, which, in the context of this invention, serves as a heat flow and is transferred to the temperature sensor. In the electrothermal element, the thermal energy or heat flow is preferably generated by using a conductive material through which an electric current passes and which is heated by Joule heating.

[0049] The heating element can preferably be configured to emit a constant output of heat and thus a fixed heat flow at a constant heating temperature, thereby enabling a temperature sensor to detect the measured temperature. Due to the fluid flow, the heat flow is modulated, causing a change in the measured temperature at the temperature sensor. This change in measured temperature can be determined by the temperature sensor. In other words, the modulation of the heat flow is detected here by the change in the measured temperature at the temperature sensor. For example, the higher the sound pressure level of the propagating sound wave, the lower the temperature that can be measured at the temperature sensor. In other words, at high sound pressure levels, the difference from the base temperature is greater than in cases where the sound pressure level is lower. Acoustic parameters can be inferred from the difference between the base temperature and the measured temperature.

[0050] Similarly, it is also possible, for example, preferably, to adjust the thermal sensor to a constant measurement temperature at the temperature sensor. Here, the heating element is preferably configured to output heat, which ensures a constant measurement temperature at the temperature sensor. Modulation of the heat flow can occur due to fluid flow or the action of sound waves. However, the output heat or heating temperature can be readjusted by a control signal for the heating element to compensate for the thermal modulation and achieve a constant heat transfer to the temperature sensor, thereby keeping the measurement temperature at the temperature sensor constant. Therefore, the modulation of heat is detected by necessary adjustments to the heating element. For example, if the sound pressure level of the impacting sound wave is high, the control signal used to provide the heat flow from the heating element must be amplified in order to maintain a constant heat transfer.

[0051] Preferably, the heating element comprises a material selected from silicon, polycrystalline silicon, aluminum, copper, gold, platinum, nickel, silver, and / or tungsten, wherein preferably, the material is doped as a semiconductor material. The preferred material of the heating element advantageously allows for particularly high temperatures without melting processes and / or chemical reactions (e.g., oxidation) of the heating element and / or other components. Furthermore, the preferred material has a high resistivity, thereby enabling a particularly compact design of the heating element. In the case of a semiconductor, doping allows for better conductivity, and thus allows for better heat supply and convection from the heating element.

[0052] A temperature sensor refers to a component of a thermal sensor, specifically used to determine the modulation of heat flow and to measure temperature changes caused by the effect of fluid flow on heat flow. Preferably, the thermal sensor includes at least one heating element.

[0053] In other preferred embodiments, the thermal sensor may include two or more temperature sensors. In a preferred embodiment including two temperature sensors, it is preferable to position the heating element between the first and second temperature sensors. Particularly preferred is that the first and second temperature sensors are at substantially the same distance from the heating element. By installing at least two temperature sensors, the characteristics of the sound waves can be accurately inferred from the propagation time of heat transfer through the fluid flow to the first and second temperature sensors. Having substantially the same distance between the first and second temperature sensors and the heating element advantageously reduces inaccuracies in detecting fluid flow, as the measurements from the first and second temperature sensors can be better calibrated to each other. For example, it may be preferable here to have a vent only between the heating element and the first temperature sensor, such that the fluid flow modulates the heat flow, while the heat flow from the heating element to the second temperature sensor is substantially independent of the fluid flow, and allows for reference measurements.

[0054] In another preferred embodiment, the MEMS microphone is characterized in that the temperature sensor is selected from thermocouples, thermopile, thermistors and / or diodes.

[0055] A thermocouple preferably represents an arrangement comprising a pair of conductive materials connected to each other at one end, and allows the inference of the measured temperature based on the thermoelectric effect. Electrical energy is provided when a temperature difference exists along this arrangement.

[0056] A thermopile preferably represents an element having multiple thermocouples. The thermocouples in a thermopile are preferably connected in electrical series and thermal parallel.

[0057] A thermistor preferably refers to a component containing resistance whose resistance value changes repeatably with temperature. Based on its temperature characteristics, thermistors are classified into negative temperature coefficient (NTC) thermistors and positive temperature coefficient (PTC) thermistors, both of which can be used in thermal sensors. NTC thermistors have a negative temperature coefficient and conduct electricity better in a hot state than in a cold state. PTC thermistors have a positive temperature coefficient and conduct electricity better in a cold state than in a hot state.

[0058] Diodes can also be advantageously used as temperature sensors. For example, the forward voltage of a diode changes substantially linearly with temperature. The higher the temperature, the lower the forward voltage, and vice versa. Therefore, changes in temperature can be inferred from changes in the forward voltage.

[0059] The aforementioned preferred components have proven suitable for use as temperature sensors and are capable of reliably measuring temperature by modulating the heat flow through fluid flow or sound waves.

[0060] In another preferred embodiment, the MEMS microphone is characterized in that the sensor (preferably a thermal sensor) is mounted on a diaphragm, wherein the diaphragm exists on a carrier containing a cavity, and the diaphragm extends over the cavity.

[0061] The carrier preferably represents the support structure of the sensor. In other words, the carrier is preferably a frame structure that is essentially formed by the continuous outer edges (in the form of sidewalls) of an open planar region. This frame structure is preferably stable and resistant to bending. In the case of an angular frame shape (triangular, quadrilateral, hexagonal, or general polygonal outline), the individual lateral regions (preferably forming the frame structure) are specifically referred to as sidewalls.

[0062] The diaphragm is preferably held by at least two sidewalls of a carrier. Preferably, the carrier comprises four sidewalls on which the diaphragm is mounted. Preferably, the diaphragm is planarly suspended within an open plane. The planar design of the diaphragm preferably means that dimensions such as length and / or width are many times greater than the height or thickness orthogonal to it. Thus, the length and / or width can be 1.5 times, 2 times, 5 times, 10 times, 100 times, 1000 times, 10000 times, or more than the thickness. Preferably, the thickness of the diaphragm is between 0.1µm and 1000µm, more preferably between 0.5µm and 500µm, particularly preferably between 1µm and 300µm, and very particularly preferably between 5µm and 200µm.

[0063] In another preferred embodiment, the diaphragm comprises a material selected from conductive and / or dielectric materials, wherein preferably, the conductive material is selected from semiconductors and / or metals, particularly from silicon, polycrystalline silicon, graphene, and chalkogenidides, wherein preferably, the dielectric material is selected from silicon nitride, silicon dioxide, aluminum oxide, aluminum nitride, polyimide, and / or polymer materials.

[0064] Preferred materials for the diaphragm have proven advantageous because, in addition to their good formability as a sufficiently mechanically stable diaphragm, they provide thermal insulation, thereby reducing or avoiding thermal conduction caused by the diaphragm. In particular, parasitic thermal conduction via the diaphragm can be minimized or eliminated. This is especially advantageous when the sensor is a thermal sensor. Parasitic thermal conduction specifically means the possibility of undesirable thermal conduction, particularly via the diaphragm, which can also be detected by the temperature sensor of the thermal sensor. Due to parasitic thermal conduction, the sensitivity to heat flow modulation via fluid flow is adversely reduced. Advantageously, particularly through the thickness of the material and / or the diaphragm, the temperature sensor exhibits particularly high sensitivity to heat flow modulation, and other heat and / or temperature effects do not, or only lessen, reduce the sensitivity of the temperature sensor.

[0065] In another preferred embodiment, the MEMS microphone is characterized in that the housing has a sound inlet, allowing sound waves to propagate from the outer region to the inner region, and in a flow technique, first through the sound inlet and then through the vent, wherein preferably, the cross-section of the sound inlet is larger than the cross-section of the vent.

[0066] The sound inlet preferably refers to an opening present in the housing of the MEMS microphone. Preferably, in the direction of fluid flow, the sound inlet is located before the fluid flow passes through or traverses the thermal sensor, particularly for modulating the heat flow provided by the heating element.

[0067] The vent is preferably located after the sound inlet in the flow direction toward the interior of the MEMS microphone. Therefore, sound waves first impact the sound inlet from the external region, and then fluid flow can enter the internal region of the MEMS microphone through the vent. The sound inlet is preferably formed as an opening on the housing of the MEMS microphone. The vent may preferably be provided as an opening or hole in a diaphragm on which a thermal sensor is located.

[0068] In another preferred embodiment, the MEMS microphone is characterized in that the cross-sectional area of ​​the vent is 1µm²–100000µm², preferably 1µm²–1000µm², and / or the shape of the vent is selected from semicircular, circular, elliptical, triangular, quadrilateral, polygonal or slit-shaped.

[0069] The preferred cross-sectional area size and / or the preferred vent design shape have proven advantageous because they enable a transition of fluid flow into or out of the MEMS microphone, allowing sound to be detected via the fluid flow using a thermal sensor. By selecting the cross-sectional size, for example, the intensity of the heat flow provided by the heating element can be set, particularly at the expected sound pressure level, when using a thermal sensor as the sensor. In particular, the velocity of the fluid flow through the vent can be set by the vent size design. Thus, the effect on the fluid flow passing through the heat flow can be set by the cross-section and / or shape, thereby setting the measurement range of the sensor. In particular, the vent design allows for the influence of the acoustic impedance of the MEMS microphone. The acoustic impedance is preferably determined by the sum of the acoustic impedance passing through the sound inlet and the vent. This, in turn, allows for adjustment of the cutoff frequency. Given that the vent preferably has a significantly smaller cross-section than the sound inlet, the vent design is crucial for setting the acoustic impedance of the MEMS microphone.

[0070] Acoustic resistance R passing through the vent ak It can be expressed as the ratio of sound pressure Δp to sound flow rate Q, where sound flow rate represents the area integral of the sound velocity: .

[0071] The sound resistance is inversely proportional to the cube of the width w and length l of the vent: , Where n represents the number of ventilation openings.

[0072] The velocity of fluid flow can be expressed as the ratio of sound flow rate to the area or cross-sectional area A of the vent: .

[0073] Area A specifically represents the product of the vent's length l and width w: A = l*w*n.

[0074] Therefore, the speed is proportional to the square of the width: .

[0075] The fluid flow velocity ν increases with the square of the width w. Therefore, the larger the vent width w, the greater the fluid flow velocity and the greater the modulation of the heat flow to the thermal sensor.

[0076] The relationship described applies in particular to so-called AC (altering current) flow, which here exists as fluid flow caused by the pressure difference between the internal and external regions of the MEMS microphone.

[0077] In another preferred embodiment, the MEMS microphone is characterized in that the vent exists as a hole in a diaphragm on which a thermal sensor is located, wherein preferably the vent is located between the temperature sensor and the heating element of the thermal sensor.

[0078] Here, the fluid flow is transverse to the direction of heat flow propagation. The heat flow propagates from the heating element to the temperature sensor. Since the fluid flow used for pressure balancing either flows from the inner region to the outer region or vice versa, the direction of fluid propagation is essentially perpendicular to the direction of heat flow propagation from the heating element to the temperature sensor. The corresponding arrangement of the direction of fluid flow and the direction of heat flow from the heating element to the temperature sensor is used to clarify the meaning of "transverse" in this context. The heat flow is modulated by the fluid flow, and this modulation can be detected by the temperature sensor; for example, the stronger the fluid flow, the greater the temperature drop.

[0079] Preferably, the vent is formed by a single hole on the diaphragm. The cross-section of the hole therefore corresponds to the cross-section of the vent. Also preferably, multiple holes are present, forming the vent. Here, the cross-section of the vent is derived from the sum of the cross-sections of all the holes.

[0080] As described above, the vent can be formed by a grille structure containing ribs, wherein the ribs form gap areas that provide openings.

[0081] The preferred embodiment for providing the vents advantageously allows for a particularly process-efficient approach because one or more holes can be provided on the diaphragm using a simple and proven method, on which thermal sensors are arranged. Furthermore, since fluid flow can enter the internal region or exit to the external region via the vents, the heat flow provided by the preferred heating element can be modulated transversely to the direction of fluid flow. Additionally, a preferred carrier (on which the diaphragm with the holes provided as vents is located) can be easily integrated into the housing, enabling separation between the internal and external regions.

[0082] In a preferred embodiment, the hole may also be in the form of a slit, with a length (in the depth direction of the figures below) greater than 100 µm or greater than 1 mm, and a width less than 20 µm, preferably less than 10 µm. The width preferably represents the dimension (in the cross-sectional plane) perpendicular to the fluid flow velocity vector, and this dimension is the minimum dimension of the vent. The length represents the dimension in the cross-sectional plane perpendicular to both the width and the fluid flow velocity vector.

[0083] In a preferred embodiment, two temperature sensors, namely a first temperature sensor and a second temperature sensor, are provided, arranged spaced apart from the heating element. A vent is located, for example, between the heating element and the first temperature sensor. The heat flow is modulated by fluid flow so that a (first) heat flow can be detected at the first temperature sensor, having an intensity lower than a (second) heat flow detected by the second temperature sensor and not modulated by fluid flow. In a preferred embodiment, two, three, four, five, ten, or more such temperature sensor pairs can also be arranged, for example, if the aperture is designed in the shape of an elongated slit with a length (in the depth direction of the figures below) greater than 100 µm, preferably greater than 1 mm.

[0084] In another preferred embodiment, the MEMS microphone is characterized in that the vent exists as a channel in which a sensor is located, preferably a thermal sensor, and particularly preferably, the thermal sensor includes a first temperature sensor for measuring a first temperature and a second temperature sensor for measuring a second temperature, along the channel, and a heating element disposed between the first and second temperature sensors. In this embodiment, the vent is formed by an open cross-section of the channel (particularly at the height of the thermal sensor).

[0085] The channel preferably represents a spatial segment formed as an elongated section of the housing. For this purpose, the housing may preferably include a sub-segment as its boundary. An elongated segment preferably means that its length (i.e., the dimension along the fluid flow direction) is greater than its width and / or height (i.e., the dimension substantially orthogonal to the fluid flow direction). The length of the channel may preferably be 1.5, 2, 3, 4, 5, 10, or more times greater than its width and / or height. A thermal sensor can be disposed within the channel to detect fluid flow. A vent is correspondingly present as a sub-segment of the channel, which is retained between the thermal sensor and the housing. Within the channel, there is a vertical extension of at least one component of a MEMS microphone, such as a vertical extension of a carrier, on which a diaphragm for positioning the thermal sensor is preferably present, such that the remainder of the spatial segment is used for the vent. In particular, when the channel is provided as an elongated segment, the fluid flow is along the direction of heat flow propagation from the heating element to one or more temperature sensors. In other words, providing a vent through the channel specifically allows fluid flow to pass through the thermal sensor in the direction of heat flow. Therefore, the propagation of heat along the flow or direction of flow preferably means that the direction vector of the fluid flow is substantially parallel to the direction of heat propagation.

[0086] As described above, when providing vents through holes in a diaphragm, the heat flow is preferably modulated transversely to the fluid flow. In this embodiment, the heat flow is preferably modulated along the direction of fluid flow through the channel used to provide the vents.

[0087] The thermal sensor may preferably include a first temperature sensor and a second temperature sensor, and a heating element located between them. Therefore, when fluid flows from the outer region to the inner region of the MEMS microphone, the fluid flow first passes through the first temperature sensor and then flows through the heating element to the second temperature sensor. As a result, the heat flow along the fluid flow is promoted, such that the heat flow from the heating element towards the second temperature sensor is greater than the heat flow towards the first temperature sensor (opposite to the direction of fluid flow). Therefore, the temperature measurable at the second temperature sensor will be higher than the temperature measurable at the first temperature sensor. The degree of differential measurement or difference between the temperatures of the first and second temperature sensors allows for the inference of parameters of the sound waves causing the fluid flow. When the fluid flows from the inner region to the outer region, the fluid flow will correspondingly promote the heat flow from the heating element to the second temperature sensor. A correspondingly reversed temperature difference can be observed between the second and first temperature sensors. Through differential measurement, particularly reliable results can be advantageously obtained because, for example, temperature fluctuations that equally affect both temperature sensors can be averaged out.

[0088] A channel specifically represents a flow path along which fluid flow can propagate to achieve pressure balance between internal and external regions, allowing a thermal sensor to be positioned within the channel to measure the modulation of heat flow in the direction of fluid flow.

[0089] The channel can be formed, for example, by parallel longitudinal segments of the housing, which enable elongated fluid communication between the outer and inner regions of the housing. A thermal sensor can be positioned accordingly within the channel, such that the remaining area between the thermal sensor and the channel sidewall forms a vent. The cross-section of the remaining area thus corresponds to the cross-section of the vent. The length of the channel is preferably chosen such that the thermal sensor can be positioned within the channel.

[0090] In a preferred embodiment, the channel may have a length, for example, ranging from 10µm to 500µm (preferably 20µm–400µm, or 50µm–200µm). The height of the channel is preferably in the range of 2µm–100µm, and particularly preferably between 5µm–50µm.

[0091] The width of the channel is preferably 1µm–1mm, more preferably 5µm–100µm. In the cross-sectional view of the following figures, the length and height are shown schematically (not necessarily to scale), while the width corresponds to the (not visible) drawing depth in the figures.

[0092] As described above, the vent is preferably present as a section or remaining area of ​​the channel, which remains between the thermal sensor and the housing. In particular, the remaining area is the spatial area of ​​the channel, which exists between the thermal sensor and / or the component on which the thermal sensor is mounted and the housing (especially the housing portion providing the channel).

[0093] In a preferred embodiment where the vent is located on the housing or formed by a channel and fluid flows thereby along the heat flow, the output signal of the thermal sensor, acting as the sensor, can have a frequency substantially the same as the sound wave causing the fluid flow. In the case of a preferred aperture on the diaphragm used to provide the vent, where the fluid flow is transverse to the heat flow of the thermal sensor, the frequency of the output signal will preferably be substantially twice the frequency of the sound wave, i.e., the output signal will have a frequency of approximately 2f (where f represents the sound wave frequency).

[0094] In another preferred embodiment, the MEMS microphone is characterized in that a diaphragm spans a recess in the housing, such that the diaphragm can be deflected when detecting sound waves.

[0095] A diaphragm is a component of a MEMS microphone that can be deflected by sound waves. Preferably, the diaphragm is located within a recess in the housing or is formed by a segment of the housing that has lower stiffness compared to the rest of the housing. Lower stiffness can be achieved, for example, by making a portion of the housing have a smaller thickness than the rest of the housing.

[0096] In a preferred embodiment, the diaphragm is formed of a thin, layered acoustic diaphragm disposed within a recess in the housing. The acoustic diaphragm is preferably designed to receive sound waves. The acoustic diaphragm is preferably thin enough to bend and vibrate under the influence of pressure changes induced by the sound waves. Therefore, sound waves striking the MEMS microphone cause the acoustic diaphragm to vibrate.

[0097] The preferred diaphragm, as an additional component on the housing, advantageously functions as an acoustic compensator, thereby optimizing the sensitivity of the MEMS microphone. Consequently, the effects of low-frequency acoustic events (such as door noise, wind noise, and / or blast noise) can be advantageously reduced, resulting in improved acoustic waveforms.

[0098] Furthermore, through the deflection of the diaphragm and the resulting vibration, additional measurement signals can be advantageously captured besides those detected by the thermal sensor. The thermal sensor's measurement signal is a result of fluid flow, while the diaphragm's measurement signal is generated by pressure fluctuations of sound waves impacting the MEMS microphone. Therefore, with a diaphragm, the thermal sensor can perform both flow-based measurements via fluid flow and pressure-based measurements via diaphragm vibration. This allows for better inference of the acoustic parameters of the sound waves. The second measurement signal through the diaphragm can be detected using different operating principles, as will be further explained below.

[0099] In another preferred embodiment, the MEMS microphone is characterized in that it includes a diaphragm, such that when detecting sound waves, a second measurement signal can be detected by deflection of the diaphragm, preferably based on the principle of capacitance or piezoelectric measurement.

[0100] The second measurement signal here refers to the measurement signal of the sound wave generated by the deflection of the diaphragm under the action of the sound wave, which is added to the (first) measurement signal of the thermal sensor. In other words, the first measurement signal can be detected by the thermal sensor of the MEMS microphone, for example by the modulation of heat flow caused by the fluid flow through the vent. The second measurement signal can be detected by the deflection of the diaphragm, in particular by the effect of the sound pressure or sound pressure level of the sound wave.

[0101] Thus, the MEMS microphone provides two measurement signals that allow the sound waves to be inferred.

[0102] Therefore, the first measurement signal detects sound based on the measurement of particle motion or fluid flow, while the second measurement signal detects sound as pressure fluctuations that cause the diaphragm to deflect.

[0103] Advantageously, the (first) measurement signal of the thermal sensor and the second measurement signal due to diaphragm deflection complement each other in terms of sensitivity across different frequency ranges. As described above, the first measurement signal of the thermal sensor can advantageously and reliably detect low-frequency sounds, particularly sounds below 100 Hz, and even more preferably below 20 Hz, while the second measurement signal based on diaphragm deflection can reliably measure sounds with frequencies above 1 kHz, above 10 kHz, or even ultrasound (above 20 kHz).

[0104] Any possible upper limit cutoff frequency that limits the sensitivity of thermal sensors for higher frequency sound measurements can be advantageously compensated for by providing a deflectable diaphragm.

[0105] Therefore, MEMS microphones can cover a wider frequency band, allowing for a variety of possible applications for different frequency ranges.

[0106] The second measurement signal is preferably detected by capacitance, piezoelectricity, optical or piezoresistive methods.

[0107] In capacitive readout or detection, the principle of capacitance measurement is used, for example, by detecting the deflection of the diaphragm relative to a backplate. In another preferred embodiment, the MEM microphone is characterized in that, for recording a second measurement signal, a backplate is fixedly mounted in a position spaced apart from the diaphragm, such that the distance between the diaphragm and the backplate can be measured by changes in sound waves and capacitance changes can be measured, wherein the backplate is preferably perforated and extends over the entire diaphragm.

[0108] The above-described embodiment enables capacitive reading of impacting acoustic waves. The fixed mounting of the backplate specifically means that the backplate is fixedly positioned, particularly preventing movement due to impacting acoustic waves or fluid flow. Conversely, the diaphragm is deflectable upon fluid flow or acoustic wave impact. Therefore, when an acoustic wave impacts the diaphragm and pressure changes cause deflection or bulging, a change in distance occurs between the diaphragm and the backplate. The arrangement including the diaphragm and backplate can be approximated as a parallel-plate capacitor. Thus, the capacitance is higher when the distance decreases and correspondingly lower when the distance increases. An electrical measurement signal can be read from the capacitance, which infers acoustic parameters, such as sound pressure levels, from the measured capacitance change due to distance variations. Preferably, one or more electrical contact pads are present to enable the acquisition of electrical measurement signals based on capacitance changes. Preferably, an oscillating capacitance change occurs due to diaphragm vibration, which can be acquired via one or more connection pads for oscillating current.

[0109] Preferably, the backplate is perforated. The term "perforated" preferably means that the backplate has perforations, which refer to openings. The perforations allow sound to pass through, thereby achieving further pressure equalization, so that even very high sound pressure levels can be detected without causing contact between the diaphragm and the backplate. The perforations in the backplate dampen sound waves that impact the diaphragm.

[0110] Detection or reading via piezoelectric means refers to the piezoelectric measurement principle. Therefore, it is preferable that the diaphragm contains a piezoelectric material. Due to the deflectability of the diaphragm, the piezoelectric material undergoes a shape change, thereby generating a voltage that can be acquired and allows inference of the sound pressure or sound pressure level that caused the shape change of the diaphragm.

[0111] In another preferred embodiment, the MEMS microphone is characterized in that it includes a diaphragm made of a conductive material and / or a dielectric material, wherein preferably, the material of the diaphragm is selected from the group consisting of conductive materials selected from silicon (especially monocrystalline or polycrystalline silicon), aluminum, nickel, copper, titanium, silver and / or gold, which may optionally be used in combination with a dielectric material, wherein preferably, the dielectric material is in contact with one or more electrodes.

[0112] The conductive material is advantageously particularly suitable for capacitively reading acoustic waves impacting the diaphragm. With a conductive material, an electric field is formed between the diaphragm and the backplate, causing changes in capacitance due to changes in distance. If the diaphragm contains a dielectric material, it is preferable to provide one or more electrodes through which capacitive reading is achieved. Providing one or more electrodes is also preferred when the diaphragm preferably contains a dielectric material capable of readability.

[0113] In another preferred embodiment, the MEMS microphone is characterized in that it includes a diaphragm that can be deflected by sound waves, wherein the diaphragm includes a sheet, the thermal sensor is mounted on the sheet, and the vent exists as a hole in the sheet.

[0114] In this embodiment, a first (sound) measurement signal dependent on fluid flow through the vent and a second (sound) measurement signal dependent on diaphragm deflection can be advantageously detected by a single component. Therefore, the deflectable diaphragm can preferably also function as a (thermal) diaphragm for a thermal sensor. Thus, with a single component, the first measurement signal can be achieved by a thermal sensor mounted on the diaphragm, and the second measurement signal by diaphragm deflection. In other words, in the described embodiment, sound measurement by diaphragm deflection is combined with sound measurement by means of a thermal sensor. Advantageously, the frequency band in which sound measurements can be performed is broadened, thereby expanding the measurement range of detectable acoustic events. In particular, a positive shift of the upper cutoff frequency is achieved, enabling reliable detection of high frequencies, except for particularly low frequencies.

[0115] The aforementioned preferred features regarding providing a preferred thermal sensor to measure fluid flow through the orifice and regarding providing a deflectable diaphragm for measurement by, for example, piezoelectric or capacitive methods are similarly applicable.

[0116] For example, preferably, the thermal sensor is mounted on a diaphragm, which preferably exists as a membrane. The membrane is preferably mounted on a carrier. The thermal sensor may preferably include a temperature sensor and a heating element. A vent is preferably present on the membrane and disposed between the heating element and the temperature sensor. A backplate may preferably be spaced apart from the membrane, such that the diaphragm, as a membrane, is designed to be read capacitively by changes in the distance between the membrane and the backplate. Thus, two measurement signals can be advantageously detected: one is a measurement signal obtained by fluid flow on the thermal sensor, and the other is a pressure measurement by acoustic waves that cause the membrane to deflect.

[0117] In the context of this invention, the terms "membran" and "diaphragm" preferably refer to components that perform different functions in a MEMS microphone. Membranes are particularly used as carriers for thermal sensors and are therefore also referred to as thermal diaphragms or carrier diaphragms. As mentioned above, for (thermal) carrier diaphragms, materials that provide thermal insulation in addition to sufficient mechanical stability are therefore preferred. This advantageously reduces or avoids undesirable (parasitic) heat conduction caused by the diaphragm. If a low deflection capability is desired for the (thermal) carrier diaphragm, the material can preferably be selected such that its specific thermal conductivity is as low as possible. For thin films, in a preferred form, low deflection capability can also be achieved through high mechanical tensile stress.

[0118] The diaphragm preferably refers to a component in a MEMS microphone that can deflect sound waves. For this purpose, the diaphragm is preferably designed to be thin enough to bend and vibrate under the influence of pressure changes induced by sound waves. Therefore, the diaphragm is preferably vibrating when excited by sound waves. Thus, the diaphragm can also preferably be called an acoustic diaphragm or acoustic sheet.

[0119] Therefore, when the (first) thermal diaphragm is specifically used as a carrier of the thermal sensor and is preferably mechanically stable enough not to be deflected by sound waves, the (second) acoustic diaphragm or diaphragm is preferably characterized by its deflectability.

[0120] In a preferred embodiment, the diaphragm can be under tensile stress, where the mechanical deflection capability is dominated by the tensile stress. In this case, the deflection capability is preferably inversely proportional to the stress and the diaphragm thickness. In another preferred embodiment, the diaphragm can also be suspended substantially without stress, where the deflection capability of the diaphragm is substantially determined by its thickness d, and is preferably proportional to 1 / d³.

[0121] In some implementations, the diaphragm and diaphragm are separate components of the MEMS microphone. This is preferably the case in the following implementations: where the diaphragm, or acoustic diaphragm, spans a recess in the housing, while the (thermal) diaphragm is used to position a thermal sensor for measuring fluid flow through a vent (see Figure 2).

[0122] In other embodiments, the diaphragm may comprise or form a sheet. This is preferably the case in embodiments where the MEMS microphone is configured to detect sound based on two measurement principles or two signals. Here, the diaphragm can serve as an acoustic diaphragm whose deflection due to sound waves can be detected, for example, by capacitance. Simultaneously, at least one region of the diaphragm can preferably serve as a carrier for a (thermal) diaphragm and a thermal sensor that detects fluid flow through holes or vents in the diaphragm (see, for example, Figure 5A). In some embodiments, the (thermal) carrier diaphragm and the deflectable diaphragm (or acoustic diaphragm) can be formed from the same component. If this component serves simultaneously as a thermal carrier diaphragm and a deflectable acoustic diaphragm or diaphragm, a thin layer with a low specific thermal conductivity (thermally insulating) can be preferably selected, for example, under the lowest possible tensile stress (allowing for mechanical deflection). Those skilled in the art can select appropriate material properties and thicknesses to define corresponding functions for the thermally insulating (carrier) diaphragm and / or the deflectable acoustic diaphragm or diaphragm.

[0123] In another preferred embodiment, the MEMS microphone includes electronic circuitry. This electronic circuitry may preferably be selected from: ASICs (application-specific integrated circuits), computing units, integrated circuits (ICs), programmable logic devices (PLDs), field-programmable gate arrays (FPGAs), microprocessors, microcomputers, stored program controllers, and / or other electronic circuit elements.

[0124] The electronic circuitry is preferably configured to control and / or read out the thermal sensor and / or the diaphragm. Control of the thermal sensor may, for example, involve the provision of heat flow, particularly by controlling a heating element. Reading out the thermal sensor includes, for example, measuring the temperature at a first temperature sensor and / or a second temperature sensor and thereby detecting heat flow modulation caused by fluid flow. Control of the diaphragm may, for example, involve adjusting its stiffness or deflection capability and / or its basic deflection relative to its initial position. Reading out the diaphragm preferably includes detecting the deflection of the diaphragm in order to, for example, infer the acoustic parameters of the sound waves.

[0125] Preferably, an electrical connection exists between the electronic circuitry and the diaphragm and / or the thermal sensor. This electrical connection can be formed, for example, through wires (especially bonding wires), conductor traces, conductor trace lines, and / or vias. Furthermore, the electronic circuitry is preferably located inside the housing. This allows for a simple and compact implementation of the electrical connection to the electronic circuitry.

[0126] In another aspect, the present invention relates to a photoacoustic gas sensor comprising a modulated transmitter and a gas-fillable sensor chamber, wherein the sensor chamber is located in the optical path of the transmitter such that the transmitter can excite the gas in the sensor chamber to form sound waves by modulated emitted radiation, wherein the sensor chamber includes a sensor and a housing, wherein the housing surrounds an internal region of the sensor chamber and the sensor chamber has a vent that enables fluid communication between the internal and external regions of the sensor chamber, wherein the sensor is a thermal sensor configured to measure the sound waves based on fluid flow through the vent, the sound waves causing a pressure difference between the internal and external regions of the sensor chamber.

[0127] Those skilled in the art will recognize that the photoacoustic gas sensor and MEMS microphone according to the present invention are based on the same inventive concept. For the MEMS microphone, the housing defines an internal region and an external region, wherein vents enable fluid communication and provide thermal sensors to detect acoustic events in the MEMS microphone's environment (i.e., the external environment) based on fluid flow through the vents.

[0128] For photoacoustic gas sensors, the housing of the sensor chamber defines an internal and external region, where vents (in the sensor chamber) enable fluid communication and provide thermal sensors to detect acoustic events (PAS signals) in the internal region of the sensor chamber based on fluid flow through the vents.

[0129] Those skilled in the art will also recognize that the technical features, definitions, and advantages disclosed for MEMS microphones and their preferred embodiments are equally applicable to the photoacoustic gas sensor of the present invention, and vice versa. For example, the vents of the sensor chamber can be formed in a similar manner by holes in a diaphragm that spans a sound inlet or opening in the housing. Similarly, descriptions, for example, concerning the provision of a thermal sensor, (thermal) diaphragm, housing, deflectable diaphragm, etc., disclosed for MEMS microphones are similarly applicable to gas sensors (particularly their sensor chambers), and will not be repeated here to avoid repetition. Furthermore, the photoacoustic gas sensor may preferably include electronic circuitry. This electronic circuitry may preferably be configured for controlling and / or reading the thermal sensor, diaphragm, and / or modulated transmitter.

[0130] Therefore, the present invention also advantageously provides an alternative photoacoustic gas sensor capable of detecting particularly low frequencies, especially in the infrasound range, which is particularly important in photoacoustic spectroscopy.

[0131] The basic principles and main components of photoacoustic gas sensors are known to those skilled in the art. A modulated transmitter generates electromagnetic radiation and is preferably arranged and configured such that the radiation emitted by the transmitter substantially or at least partially irradiates the gas to be analyzed in the analytical volume.

[0132] Modulated irradiation occurs when the irradiation is modulated using a wavelength corresponding to the absorption spectrum of a molecule of a gas component in the gas mixture. This leads to heating and cooling processes, the timescale of which reflects the modulation frequency of the radiation. According to the photoacoustic effect, the heating and cooling processes cause the gas component to expand and contract, thereby exciting it to form a sound pressure wave with a frequency essentially equal to the modulation frequency. This sound pressure wave, also known as a PAS signal, can be measured using a thermal sensor. The pressure of the sound wave generated by modulation absorption is proportional to the concentration of the gas component being detected or absorbed. The modulated emitter specifically irradiates the internal region of the sensor chamber.

[0133] In a preferred embodiment, the photoacoustic gas sensor includes an optical or spectral filter present in the optical path of the transmitter, such that when the transmitter is turned on, a gas component in the sensor chamber corresponding to the filtered light is excited, generating a pressure proportional to the concentration of that gas component in the sensor chamber. Periodic sound pressure is generated in the sensor chamber by modulation from the IR transmitter; this sound pressure is measured by a thermal sensor based on fluid flow through a vent to the external area.

[0134] Various emitters are preferably suitable as radiation sources for the above-described applications. For example, thermal emitters, lasers, LEDs, or infrared light sources can be used as emitters.

[0135] The transmitter is modulated, meaning that, preferably, the intensity of the emitted radiation, more preferably the intensity of the beam, can be controlled to vary over time. Modulation should preferably cause a change in intensity over time as a measurable variable. This means, for example, that there is a difference between the weakest intensity measured during the measurement period and the strongest intensity measured during the same period, a difference greater than the sensitivity of the equipment typically used to measure or determine the intensity for this radiation spectrum and application. Preferably, the difference between the strongest and weakest adjustable intensities is significantly greater than 2 times, more preferably 4 times, 6 times, or 8 times. Particularly preferably, the intensity of the modulated beam is modulated for one or more predetermined resonant wavelengths.

[0136] Therefore, a modulated emitter preferably refers to a device that emits electromagnetic radiation within a wavelength range of a specific spectrum. This spectrum is specifically selected such that it corresponds to the preferred application area of ​​the emitter, namely PAS. Particularly preferred are the vibrational excitations of gas molecules in the reference gas to be analyzed and / or detected, depending on whether the gas molecules correspond to the preferred spectral range.

[0137] Preferably, the sensor chamber is located in the optical path of the transmitter. This preferably means that the intensity of the light beam substantially or at least partially illuminates the transmitter-facing side of the sensor chamber. Partially preferably means at least 40%, more preferably at least 50%, at least 60% or more.

[0138] In a preferred embodiment, the sensor chamber is an open system with one or more openings allowing the gas to be analyzed to flow into or diffuse into the sensor chamber. These openings may be vents, or additional openings may exist within the sensor chamber.

[0139] According to the PAS measurement method, the (additional) opening can preferably be designed to be reclosable, thereby allowing the gas to be replaced. However, it is also preferable, for example, during the manufacturing process, to fill the chamber with reference gas once and then not replace or replenish it. Preferably, gas flow can also be achieved, for example, by having the detection chamber include at least two openings.

[0140] Preferably, a continuous or discontinuous gas flow into the sensor chamber can be achieved, for example, through a first opening as an inlet and a second opening as an outlet, such as during a filling or gas exchange phase. During the measurement phase, the gas flow can be interrupted, for example. Preferably, different gases can be analyzed at different time points, wherein a purge gas can preferably be introduced between two analytes to remove any residual gas in the volume.

[0141] If the detection chamber is at least partially open relative to the environment, for example through an opening of a required size, permanent gas exchange with the environment can be advantageously achieved, wherein the detection chamber is filled by interaction with the gaseous atmosphere of the environment.

[0142] Preferably, the spectrum of the modulated transmitter and / or optical filter is coordinated with the excitation frequency of the gas component to be detected in the sensor chamber.

[0143] In a preferred embodiment, the photoacoustic gas sensor is characterized in that the sensor chamber is filled with a reference gas, and the gas to be analyzed is located in the optical path between the transmitter and the sensor chamber, such that the proportion of the reference gas in the gas to be analyzed can be measured by a thermal sensor based on the generation of sound pressure waves in the sensor chamber.

[0144] Therefore, photoacoustic sensors are designed to detect gas components along the measurement path between the modulated transmitter and the sensor chamber.

[0145] If molecules corresponding to the reference gas molecules enter the optical path between the sensor chamber and the modulated emitter, the radiation will undergo at least partial modulation absorption. Therefore, the intensity of radiation illuminating the sensor chamber decreases for the wavelength range of the reference gas molecule absorption spectrum. Correspondingly, the acoustic pressure wave generated within the sensor chamber by the excitation of the reference gas molecules also decreases. As a result, the thermal sensor measures a weakened or attenuated PAS signal. The degree of weakening or attenuation allows for the inference of the proportion of reference gas located in the optical path or measurement path.

[0146] As described above, by means of a thermal sensor, preferably comprising a heating element and at least one temperature sensor, acoustic events or PAS signals can be inferred by measuring the modulation of heat flow caused by fluid flow. Due to its high sensitivity, this measurement principle allows for the advantageous detection of extremely small concentrations of reference gas molecules in the environment of the photoacoustic gas sensor.

[0147] In another preferred embodiment, the photoacoustic gas sensor is characterized in that the transmitter is located in the outer region of the sensor chamber, and the housing has at least a partially transparent section located in the optical path of the transmitter.

[0148] By using at least partially transparent sections, radiation emitted by the transmitter can pass through, enabling photoacoustic excitation of the gas components within the sensor chamber. Transparency refers to the optical property that allows radiation to penetrate the section. In the case of near-complete transparency, reflection and / or absorption occur little or no. Partial transparency allows only a portion of the incident radiation to pass through the section. For example, the section may have 100% transparency for essentially complete transparency, or 90%, 80%, 70%, 60%, 50%, or lower for partial transparency. Transparency preferably relates to the wavelength range of the radiation emitted by the transmitter.

[0149] In a preferred embodiment, the at least partially transparent segment may be a spectral filter, or the spectral filter may be additionally disposed in the optical path between the transmitter and the sensor chamber. The wavelength or wavelength range of the filter is preferably coordinated with the absorption spectrum of the gas component to be analyzed or the reference gas. For example, the transmitter may emit infrared radiation over a wide wavelength range of 1 µm to 10 µm, while the at least partially transparent segment and / or spectral filter is designed to allow a wavelength range of approximately 4.2 µm to pass through for photoacoustic excitation of carbon dioxide in the gas component to be analyzed or the reference gas. Therefore, the wavelength range to be set and the placement of the at least partially transparent segment or spectral filter depend on the selection and / or composition of the gas molecules to be excited.

[0150] For filters, different implementation methods can be considered depending on the application.

[0151] For example, a Fabry-Perot filter can be used. Such a filter can be used, for example, to select a very narrow spectrum. Preferably, the Fabry-Perot interferometer on which the filter is based is tunable, for example, by temperature tunability or by mechanical adjustment. Thus, the desired spectrum can be flexibly selected from the original beam. Suitable thin-film filters can also preferably be used. These thin-film filters are particularly easy to manufacture and very compact. Flexible combinations of thin-film filters or thin-film filters tunable by, for example, temperature methods are also advantageous. Filters for other characteristics of IR radiation (e.g., polarization) can also be used, and these filters are preferably also part of the cover element.

[0152] For at least partially transparent sections of the sensor chamber housing, it is preferable to enable irradiation of the gas within the sensor chamber by means of modulated infrared radiation. The transmitter can be positioned relative to the sensor chamber as needed. Preferably, the transmitter is positioned such that the thermal sensor within the sensor chamber is not directly affected by infrared radiation, thereby minimizing the impact of infrared radiation on thermal measurements.

[0153] In some implementations, the transmitter and sensor chamber can preferably be positioned separately and independently (see [link to implementation]). Figure 6 A). Preferably, the sensor chamber contains a reference gas, which is detected by a photoacoustic gas sensor in the measurement path between the IR transmitter and the sensor chamber.

[0154] If the gas to be detected enters the optical path or measurement path between the transmitter and the sensor chamber, it will be absorbed by radiation. This results in a more attenuated PAS signal in the sensor chamber, which weakens the fluid flow through the vent. The concentration of the gas component to be detected in the measurement path between the transmitter and the sensor chamber can be inferred from the degree of attenuation. Here, a narrowband transmitter is preferably used to excite only the gas component to be detected as much as possible.

[0155] In this embodiment, the photoacoustic gas sensor also has an advantageous flexible design, which allows for the optimal location of the transmitter, for example, depending on the specific conditions of the room where the photoacoustic gas sensor is to be installed.

[0156] Alternatively, it is preferable to integrate the transmitter and sensor chamber together in the housing of the photoacoustic gas sensor (see Figure 6B).

[0157] In another preferred embodiment, the photoacoustic gas sensor is characterized in that the transmitter and the sensor chamber are surrounded by a housing of the photoacoustic sensor, the housing comprising the housing of the sensor chamber.

[0158] Preferably, the transmitter is mounted within the same housing as the gas sensor containing the sensor chamber. The sensor chamber may also preferably have at least a partially transparent section that simultaneously defines a partition wall within the gas sensor housing. The interior region of the sensor chamber continues to be defined by the housing of the sensor chamber. The exterior region of the sensor chamber can refer, on one hand, to the area outside the sensor chamber but still within the photoacoustic sensor housing. On the other hand, the exterior region can also refer to the exterior region of the photoacoustic sensor housing or the environment. The latter is preferred, such that the vent preferably allows for fluid communication between the interior region of the sensor chamber and both the exterior regions of the sensor chamber and the photoacoustic sensor.

[0159] Through such a vent or one or more additional openings, the gas to be detected can enter the sensor chamber from the environment, thereby exciting the gas components to be detected into PAS within the sensor chamber.

[0160] Furthermore, this implementation allows for reliable protection of the transmitter and also offers a high degree of compactness.

[0161] The aspects of the invention will be described in more detail below with the aid of the accompanying drawings, but are not limited thereto. Attached Figure Description

[0162] Figure 1 A schematic diagram of a preferred embodiment of the MEMS microphone according to the present invention includes a thermal sensor configured to measure sound waves based on fluid flow through a vent.

[0163] Figure 2 : A schematic diagram of a preferred embodiment of a MEMS microphone, which includes a vent and a deflectable diaphragm.

[0164] Figure 3 : A schematic diagram of a preferred embodiment of a MEMS microphone, wherein a vent exists as a hole in a diaphragm, and a thermal sensor is located on the diaphragm.

[0165] Figure 4 : A schematic diagram of a preferred embodiment of a MEMS microphone, wherein a thermal sensor is disposed within a channel and a vent is formed as an open cross-section of the channel at the height of the thermal sensor.

[0166] Figure 5 A schematic diagram of a preferred embodiment of a MEMS microphone, comprising a diaphragm deflectable by sound waves, wherein the diaphragm includes a sheet, a thermal sensor is mounted on the sheet, and a vent exists as a hole in the sheet.

[0167] Figure 6A schematic diagram of a preferred embodiment of the photoacoustic gas sensor according to the present invention includes a thermal sensor configured to measure a PAS signal based on fluid flow through a vent in the sensor chamber. Detailed Implementation

[0168] Figure 1 A schematic diagram of a preferred embodiment of a MEMS microphone 1 according to the present invention is shown, the MEMS microphone being used to detect sound waves. The MEMS microphone 1 has a sensor and a housing 5. The housing 5 surrounds an internal region 7. Furthermore, the MEMS microphone 1 has a vent 11 that enables fluid communication between the internal region 7 and an external region 9. The sensor is a thermal sensor configured to measure the sound waves causing a pressure difference between the internal region 7 and the external region 9 of the MEMS microphone 1 based on the fluid flow through the vent 11.

[0169] The MEMS microphone 2 according to the present invention utilizes the pressure difference between two different regions (here, the inner region 7 and the outer region 9) to cause fluid to flow in order to balance the pressure.

[0170] When sound waves strike the MEMS microphone 2, a pressure difference can occur. For example, a higher pressure may exist in the outer region 9, or a higher pressure may be created in the outer region 9 due to an acoustic event. The higher pressure in the outer region 9... Figure 1 In A, the variable p + Δp is used, where Δp represents the pressure difference between the pressure in the outer region and the reference pressure p in the inner region 7. This causes fluid flow from the outer region 9 to the inner region 7 through the vent 11. This fluid flow can be detected by a sensor, thereby allowing the inference of the sound waves causing the flow. The fluid flow is indicated here by arrows. In the context of this invention, a positive velocity v > 0 is preferably assigned to the fluid flow from the outer region 9 to the inner region 7 of the MEMS microphone 1.

[0171] Figure 1 B illustrates the opposite situation. Here, a pressure difference exists between the inner region 7 and the outer region 9 of the MEMS microphone 1, where the reference pressure p in the inner region 7 is higher than the pressure p-Δp in the outer region 9. Due to this pressure difference, fluid flow occurs from the inner region 7 to the outer region 9. In the context of this invention, this flow direction and velocity are preferably specified as negative, i.e., v < 0.

[0172] Figure 1Figure C shows a circuit diagram intended to illustrate in more detail the functional principle of the MEMS microphone 2 according to the present invention, which has a vent 11. The vent 11 corresponds to acoustic impedance, while the rear volume corresponds to acoustic capacitance or acoustic compliance. This can preferably be described by a first-order low-pass filter (comprising resistors and capacitors). The lower cutoff frequency is preferably derived from ω = 1 / (R·C), where R is acoustic impedance and C is acoustic capacitance. The acoustic capacitance preferably corresponds to the rear volume, while the acoustic impedance can advantageously be set high by the small cross-section of the vent. Therefore, a large rear volume and / or high acoustic impedance results in a particularly low cutoff frequency. Thus, the MEMS microphone 1 can advantageously detect sounds even at frequencies in the infrasound range.

[0173] The upper cutoff frequency preferably represents a frequency above which acoustic events can be measured with reduced sensitivity. While the lower cutoff frequency is determined by the structure of the MEMS microphone, particularly by the vents and housing, the upper cutoff frequency is preferably determined substantially by the sensor. In cases where a thermal sensor is used as the sensor, the upper cutoff frequency may be affected, for example, by the thermal capacitance of the temperature sensor or the thermal resistance of the diaphragm (on which the temperature sensor and / or heating element are located). A high upper cutoff frequency can also be advantageously achieved by providing a miniaturized temperature sensor.

[0174] Therefore, the MEMS microphone 1 can preferably achieve a particularly low lower cutoff frequency and a high upper cutoff frequency, thus providing a wide bandwidth within which sound waves can be reliably measured.

[0175] Figure 2 A preferred embodiment of the MEMS microphone 1 according to the present invention is shown, including a vent 11 and a deflectable diaphragm 17. According to... Figure 2 A. The diaphragm 17 can span an opening in the housing 5, allowing it to deflect when detecting sound waves. The deflection of the diaphragm 17 and the resulting vibration advantageously allow the detection of additional measurement signals beyond those detectable by the thermal sensor. The thermal sensor's measurement signal is a result of fluid flow, while the diaphragm 17's measurement signal is generated by pressure fluctuations of the sound waves impacting the MEMS microphone 1. Therefore, with the diaphragm 17, the thermal sensor can perform both flow-based measurements via fluid flow and pressure-based measurements via the vibration of the diaphragm 17. This allows for a better deduction of the acoustic parameters of the sound waves.

[0176] Figure 2 The corresponding circuit diagram was drawn in C. Figure 1As in the illustrated implementation, vent 11 represents acoustic resistance, while the rear volume in the internal region 7 represents acoustic capacity. In addition to the rear volume, diaphragm 17 also functions as a capacitive component.

[0177] Figure 3 A preferred embodiment of the MEMS microphone 1 according to the present invention is schematically shown, wherein a vent 11 exists as an aperture in a diaphragm 19, and a thermal sensor 3 is located on the diaphragm. The MEMS microphone 1 includes a housing 5 that surrounds an internal region 7. Furthermore, the MEMS microphone 1 has a vent 11 that enables fluid communication between the internal region 7 and the external region 9 of the MEMS microphone 1. The thermal sensor 3 is configured to measure the acoustic waves causing a pressure difference between the internal region 7 and the external region of the MEMS microphone 1 based on the fluid flow through the vent 11. For this purpose, the thermal sensor 3 has a heating element 13 and a temperature sensor 15. The vent 11, as an aperture in the diaphragm 19, is located between the heating element 13 and the temperature sensor 15. Heat flow propagates from the heating element 13 to the temperature sensor 15. Since the fluid flow for pressure balancing either flows from the internal region to the external region or vice versa, the direction of fluid propagation is substantially perpendicular or transverse to the direction of heat flow from the heating element 13 to the temperature sensor 15. The heat flow is modulated by the fluid flow, and this modulation can be detected by a temperature sensor; for example, the stronger the fluid flow, the greater the temperature drop.

[0178] The diaphragm 19, including the thermal sensor 3, is held by the carrier 25 and extends above the cavity 27.

[0179] Figure 4 A schematic illustration shows another preferred embodiment of the MEMS microphone 1. Here, a thermal sensor 3 is located within the channel 20. The thermal sensor includes a first temperature sensor 15 for measuring a first temperature, a second temperature sensor 15 for measuring a second temperature, and a heating element 13, wherein the heating element 13 is arranged between the first temperature sensor 15a and the second temperature sensor 15b. In this embodiment, the vent 11 is therefore formed by an open cross-section of the channel 20 at the height of the thermal sensor 3. The channel represents a spatial segment formed as an elongated segment of the housing 5. For this purpose, the housing 5 may include a portion of the segment as its edge, thereby forming the channel 20 as an elongated segment. The thermal sensor 3 is arranged within the channel 20, and the vent 11 exists as a portion of the channel 20, which remains open between the thermal sensor 3 and the housing 5.

[0180] Channel 20 specifically represents a path along which fluid flow for pressure equilibrium between the inner region 7 and the outer region 9 propagates, allowing the thermal sensor 3 to be positioned within channel 20, thereby enabling measurement of the thermal flux modulation of the thermal sensor 3. Channel 20 is formed here by parallel longitudinal sections of the housing 5, which enable elongated fluid communication between the outer and inner regions of the housing 5.

[0181] The thermal sensor 3 can be positioned accordingly in the channel 20, such that the remaining area between the thermal sensor 3 and the sidewall of the channel 20 forms a vent 11. The cross-section of the opening in the remaining area therefore corresponds to the cross-section of the vent 11.

[0182] When the channel is configured as an elongated segment, the fluid flow follows the direction of heat propagation from the heating element 13 to the temperature sensor 15. In other words, providing a vent through the channel specifically allows the fluid flow to pass through the heat sensor in the direction of heat flow. The fluid flow is represented here by the arrow and the letter q. When the fluid flow q flows from the outer region 9 into the inner region 7 of the MEMS microphone 1, the fluid flow first passes through the first temperature sensor 15a, and then the fluid flows along the second temperature sensor 15b.

[0183] As a result, heat flow is promoted along the fluid flow direction, such that the heat flow from heating element 13 towards the second temperature sensor 15b is higher than the heat flow towards the first temperature sensor 15a (opposite to the fluid flow direction). Therefore, the temperature measurable at the second temperature sensor 15b will be higher than the temperature measurable at the first temperature sensor 15a. The degree of temperature difference between the first temperature sensor 15a and the second temperature sensor 15b can then be used to infer the parameters of the sound waves that cause the fluid flow.

[0184] exist Figure 4 In B, the flow rate q is plotted relative to the frequency f, where f c This indicates the upper cutoff frequency of the MEMS microphone. MEMS microphone 1 can achieve an upper cutoff frequency f. c Moving in the positive direction creates a wider frequency band in which measurements can be taken.

[0185] Figure 5A schematic diagram illustrates another preferred embodiment of the MEMS microphone 1. In this embodiment, the MEMS microphone 1 includes a diaphragm such that, upon detection of sound waves, a second measurement signal can be detected by deflection of the diaphragm, for example, based on capacitive or piezoelectric measurement principles. For this purpose, a backplate 21 is positionally mounted on a base 23, spaced apart from the deflectable diaphragm 17, such that the distance between the diaphragm 17 and the backplate 21 can be varied by sound waves, allowing capacitance changes to be measured. The backplate 21 is perforated and extends over the entire diaphragm 17. The diaphragm 17 includes a membrane 19 on which a thermal sensor 3 is mounted, wherein a vent 11 exists as a hole in the membrane 19.

[0186] In this embodiment, it is advantageous to detect a first (sound) measurement signal that depends on the fluid flow through the vent and a second (sound) measurement signal that depends on the deflection of the diaphragm 17 by a single component.

[0187] The second measurement signal represents the measurement signal generated by the deflection of the diaphragm 17 under the action of sound waves, which is obtained additionally to the (first) measurement signal of the thermal sensor. In other words, the first measurement signal can be detected by the thermal sensor 3 of the MEMS microphone 1, particularly by the thermal flow modulation caused by the fluid flow above the vent 11. The thermal sensor 3 here includes a heating element 13 and a temperature sensor 15, which are similar in nature to... Figure 3 The illustrated embodiment includes a vent 11, which serves as an opening. As described above, the first measurement signal is measured based on the modulation of heat flow by fluid flow, and is indicated in this figure by a double arrow and the letter q.

[0188] The second measurement signal can be detected by the pressure-related deflection of the diaphragm 17, particularly by the effect of the sound pressure or sound pressure level (Schalldruckpegel) of the sound wave. The second measurement signal obtained by the deflection of the diaphragm 17 is indicated by a double arrow and the letter p. Thus, two measurement signals can be read from the MEMS microphone 1, allowing the inference of the sound wave. Advantageously, the measurement signal from the thermal sensor 3 and the second measurement signal obtained by the deflection of the diaphragm 17 complement each other, forming a broadband MEMS microphone 1. Figure 5 Table B illustrates the frequency correlation between the measurement signals (flow rate q) from the thermal sensor and the measurement signals (pressure p) from the deflectable diaphragm.

[0189] Advantageously, the (first) measurement signal (flow rate q) of the thermal sensor and the second measurement signal (pressure p) deflected by the diaphragm complement each other in terms of sensitivity across different frequency ranges. The first measurement signal of the thermal sensor can advantageously and reliably detect low-frequency sounds, particularly sounds below 20 Hz, while the second measurement signal based on the deflection of the diaphragm 17 can reliably measure sounds with higher frequencies.

[0190] Figure 6 A preferred embodiment of a photoacoustic gas sensor 29 is schematically illustrated. The photoacoustic gas sensor 29 includes a modulated emitter 31 and a gas-fillable sensor chamber 30. The sensor chamber 30 is located in the optical path of the emitter 29, such that the emitter 31 can excite the gas in the sensor chamber 30 to generate sound waves by means of modulated emitted radiation. The sensor chamber 30 includes a sensor and a housing 5, wherein the housing 5 surrounds an internal region 7 of the sensor chamber 30. The sensor chamber 30 has a vent 11 that allows fluid communication between the internal region 7 and the external region 9 of the sensor chamber 30. The sensor is a thermal sensor 3, configured to measure the sound waves causing a pressure difference between the internal region 7 and the external region 9 of the sensor chamber 30 based on the fluid flow through the vent 11.

[0191] exist Figure 6 In A, the transmitter 31 is positioned in the outer region 9 of the sensor chamber 30. The housing 5 has at least a partially transparent section 33 located in the optical path of the transmitter 31. By arranging the transmitter 31 in the optical path toward the at least partially transparent section of the housing 5, it is ensured that sound waves and fluid flow can be generated within the sensor chamber 30 and thus in the inner region 7.

[0192] Preferably, a reference gas is present in the sensor chamber 30, corresponding to the gas to be analyzed in the optical path between the transmitter 31 and the sensor chamber 30, such that the proportion of the reference gas in the gas to be analyzed can be measured by a thermal sensor based on the formation of acoustic pressure waves in the sensor chamber. If molecules corresponding to the molecules of the reference gas enter the optical path between the sensor chamber 30 and the modulated transmitter 30, at least partially modulated absorption of the radiation occurs. Therefore, for the wavelength range of the absorption spectrum of the reference gas molecules, the intensity of the radiation irradiating the sensor chamber decreases. Accordingly, the acoustic pressure waves generated in the sensor chamber by the excitation of the molecules of the reference gas also decrease. As a result, a weakened or reduced PAS signal is measured by a thermal sensor. The degree of reduction or attenuation allows the proportion of the reference gas located in the optical path or measurement path to be inferred accordingly.

[0193] exist Figure 6In B, the transmitter 31 and the sensor chamber 30 are contained within the housing 5 of the photoacoustic sensor 29. Specifically, the transmitter 31 is mounted within the housing 5 of the photoacoustic sensor 29, which contains the sensor chamber 30.

[0194] The sensor chamber 30 has at least a partially transparent section that simultaneously defines a partition wall within the housing 5 of the photoacoustic sensor 29. The interior region of the sensor chamber 30 continues to be defined by the housing of the sensor chamber 30. The exterior region of the sensor chamber 30 can refer, on one hand, to the area located outside the sensor chamber 30 but still within the housing of the photoacoustic sensor 29. On the other hand, the exterior region can also refer to the exterior region of the housing 5 of the photoacoustic sensor 30 or the environment. As shown, the latter is preferred, allowing the vent 11 to enable fluid communication between the interior region of the sensor chamber 30 and the exterior regions of both the sensor chamber 30 and the photoacoustic sensor 29.

[0195] Through such a vent 11 or one or more additional openings, the gas to be detected can enter the sensor chamber 30 from the environment, thereby exciting the components of the gas to be detected into PAS within the sensor chamber 30.

[0196] Preferably, the wavelength of the modulated transmitter 31 and / or the optical filter is coordinated with the absorption spectrum of the gas component to be detected in the sensor chamber 30.

[0197] If the irradiation is modulated using a wavelength corresponding to the absorption spectrum of a molecule present in the gas mixture, modulation absorption occurs, leading to heating and cooling processes whose timescale reflects the modulation frequency of the radiation. According to the photoacoustic effect, the heating and cooling processes cause the gas component to expand and contract, thereby exciting it into a sound pressure wave with a substantially modulated frequency. This sound pressure wave, also known as a PAS signal, can be measured using the thermal sensor 3. Here, specifically, due to the pressure difference between the inner region 7 and the outer region 9, a fluid flow is generated through the vent 11, which can be measured based on the modulation of the heat flow between the heating element 13 and the temperature sensor 15.

[0198] List of reference numerals 1: MEMS microphone 3: Thermal sensor 5: Casing 7: Internal area 9: External Area 11: Ventilation opening 12: Sound Inlet 13: Heating element 15: Temperature sensor 15a: First temperature sensor 15b: Second temperature sensor 17: Diaphragm 19: Membrane 20: Channel 21: Back panel 23: Base 25: Carrier 27: Cavity 29: Photoacoustic gas sensor 30: Sensor chamber 31: Transmitter 33: At least partially transparent sections.

[0199] References Zawawi, Siti Aisyah, et al. "A review of MEMS capacitivemicrophones." Micromachines 11.5 (2020): 484. van Honschoten, Joost W., et al. "Optimization of a thermal flowsensor for acoustic particle velocity measurements." Journal of microelectromechanical systems 14.3 (2005): 436-443. Xu, Xiang-Yuan, et al. "A monolithic three-dimensional thermalconvective acoustic vector sensor with acoustic-transparent heat sink." JASAExpress Letters 2.4 (2022): 044001. Shin, Kumjae, et al. "A modeling and feasibility study of a micro-machined microphone based on a field-effect transistor and an electret for alow-frequency microphone." Sensors 20.19 (2020): 5554.

Claims

1. A MEMS microphone (1) for detecting sound waves, the MEMS microphone comprising a sensor and a housing (5), wherein, The housing (5) encloses the internal area (7) of the MEMS microphone (1), and the MEMS microphone (1) also has a vent (11) that enables fluid communication between the internal area (7) and the external area (9) of the MEMS microphone (1). Its features are, The sensor is configured to measure the acoustic waves that cause the pressure difference between the internal region (7) and the external region (9) of the MEMS microphone (1) based on the fluid flow through the vent (11).

2. The MEMS microphone (1) according to the preceding claim. Its features are, The sensor is a thermal sensor (3), preferably, the thermal sensor includes a heating element (13) and at least one temperature sensor (15), thereby enabling the measurement of fluid flow through the vent (11) by modulating the heat flow between the heating element (13) and the temperature sensor (11), preferably, the thermal sensor includes a heating element and two temperature sensors.

3. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The sensor is mounted on a diaphragm (19), preferably a thermal sensor (3) is mounted on the diaphragm (19), wherein the diaphragm (19) exists on a carrier (25) including a cavity (27), and the diaphragm (19) extends over the cavity (27). Preferably, the diaphragm (19) comprises a material selected from conductive and / or dielectric materials. Preferably, the conductive material is selected from semiconductors and / or metals, and in particular, the conductive material is selected from silicon, polycrystalline silicon, graphene, and chalcogenides. Preferably, the dielectric material is selected from silicon nitride, silicon dioxide, aluminum oxide, aluminum nitride, polyimide and / or polymer materials.

4. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The housing (5) has a sound inlet (12) that allows sound waves to propagate from the outer region (9) to the inner region (7) and flow first through the sound inlet (12) and then through the vent (11). Preferably, the cross-section of the sound inlet (12) is larger than the cross-section of the vent (11).

5. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The vent (11) has a diameter of 1µm. 2 -100000µm 2 The cross-sectional area of ​​the vent (11) is preferably 1µm. 2 -1000µm 2 The cross-sectional area, and / or the vent (11) has a shape selected from semicircular, circular, elliptical, triangular, quadrilateral, polygonal or slit shape.

6. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The vent (11) exists as a hole in the diaphragm (19), and the thermal sensor (3) is located on the diaphragm. Preferably, the vent (11) is located between the temperature sensor (15) and the heating element (13) of the thermal sensor (9).

7. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The vent (11) exists as a channel, and the sensor is installed in or on the channel, wherein, preferably, the sensor is a thermal sensor (3), wherein, particularly preferably, the thermal sensor (3) includes a first temperature sensor (15a) for measuring a first temperature and a second temperature sensor (15b) for measuring a second temperature and a heating element (13) along the channel, wherein the heating element (13) is arranged between the first temperature sensor (15a) and the second temperature sensor (15b).

8. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The diaphragm (17) spans the recess of the housing, such that the diaphragm (17) is deflectable when detecting sound waves.

9. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The MEMS microphone (1) includes a diaphragm (17) such that when detecting sound waves, a second measurement signal can be detected by deflection of the diaphragm (17). Preferably, the second measurement signal is detected based on a capacitive, piezoelectric, piezoresistive, or optical measurement principle.

10. The MEMS microphone (1) according to the preceding claim. Its features are, In order to record the second measurement signal, a back plate is fixedly mounted in a position spaced apart from the diaphragm (17) such that the distance between the diaphragm (17) and the back plate (21) can change due to sound waves and the capacitance change can be measured, wherein, preferably, the back plate (21) is perforated and extends over the entire diaphragm (17).

11. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The MEMS microphone includes a diaphragm (17) made of conductive and / or dielectric material, wherein, preferably, the material of the diaphragm (17) is selected from silicon, aluminum, nickel, copper, titanium, silver and / or gold, and optionally, the material is used in combination with a dielectric material, wherein, preferably, the dielectric material is in contact with one or more electrodes.

12. The MEMS microphone (1) according to one or more of the preceding claims. Its features are, The MEMS microphone (1) includes a diaphragm (17) capable of deflecting sound waves, wherein the diaphragm (17) includes a sheet (19), the thermal sensor (3) is mounted on the sheet, and the vent (11) exists as a hole in the sheet (19).

13. A photoacoustic gas sensor (29), the photoacoustic gas sensor comprising a modulated transmitter (31) and a sensor chamber (30) capable of being filled with gas, wherein, The sensor chamber (30) exists in the optical path of the transmitter (29), enabling the transmitter (31) to excite the gas in the sensor chamber (30) to generate sound waves by means of radiation that can be emitted in a modulated manner. The sensor chamber (30) includes a sensor and a housing (5), wherein the housing (5) surrounds the internal region (7) of the sensor chamber (30), and the sensor chamber (30) has a vent (11) that enables fluid communication between the internal region (7) and the external region (9) of the sensor chamber (30). Its features are, The sensor is a thermal sensor (3) configured to measure the acoustic waves that cause a pressure difference between the inner region (7) and the outer region (9) of the sensor chamber (30) based on the fluid flow through the vent (11).

14. The photoacoustic gas sensor (29) according to the preceding claim. Its features are, The transmitter (31) is positioned in the outer region (9) of the sensor chamber (30) and the housing (5) has at least a partially transparent section (33) located in the optical path of the transmitter (31).

15. The photoacoustic gas sensor according to claim 13, Its features are, The transmitter (31) and the sensor chamber (30) are surrounded by the housing of the photoacoustic gas sensor, the housing of the photoacoustic gas sensor including the housing (5) of the sensor chamber (30).

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