Flow sensor comprising arrangement of a thermopile for a differential temperature measurement in the flow direction

Abstract

The invention relates to a flow sensor for measuring at least one flow parameter of a fluid. The flow sensor comprises a substrate and a thermal sensor, comprising a heating element for providing a thermal field and comprising a sensor component for detecting a temperature response of the thermal sensor depending on an influence of the flowing fluid on the thermal field. The sensor component comprises one or more thermocouples, the one or more thermocouples being positioned in a flow direction of the fluid for a differential temperature measurement. The invention further relates to a flow sensor arrangement, to a system comprising the flow sensor or the flow sensor arrangement and a fluid line, and to the use of the flow sensor.

Description

[0001] Flow sensor with arrangement of a thermo-column for differential temperature measurement along the flow direction

[0002] DESCRIPTION

[0003] The invention relates to a flow sensor for measuring at least one flow parameter of a fluid. The flow sensor comprises a substrate and a thermal sensor comprising a heating element for providing a heat field and a sensor component for detecting a temperature response of the thermal sensor as a function of the influence of the flowing fluid on the heat field. The sensor component comprises one or more thermocouples, wherein the one or more thermocouples are positioned along a flow direction of the fluid for differential temperature measurement.

[0004] Furthermore, the invention relates to a flow sensor arrangement, a system comprising the flow sensor or the flow sensor arrangement and a fluid line, and a use of the flow sensor.

[0005] Background and state of the art

[0006] Flow sensors are used in various applications involving flowing fluids and are particularly capable of measuring flow parameters of the fluid. For example, the velocity, flow direction, and / or viscosity of the fluid can be detected using a flow sensor, without being limited to these specific parameters.

[0007] In some applications, it is common to provide a so-called bypass configuration in which a fluid flow parameter is measured. In a bypass configuration, a flow restrictor or flow limiter is typically installed within a main channel through which the fluid flows. The main channel could be, for example, a pipeline for transporting a liquid or within an industrial plant. Furthermore, a bypass (also called a bypass channel or side channel) is fluidically connected to the main channel. The flow restrictor causes a pressure drop, resulting in a pressure differential in the main channel that depends on the fluid flow. With appropriate connections to the main channel upstream and downstream of the flow restrictor, the fluid is forced into the bypass by this pressure differential.The sensor used to measure the fluid can be positioned within or adjacent to the bypass. A bypass configuration ensures reliable fluid transfer to a sufficiently close location near the sensor, without requiring the sensor to be in the main channel and thus potentially disrupting the fluid flow. Furthermore, the fluid flow velocity in the bypass channel is directly dependent on the pressure differential created in the main channel by the flow restrictor. Therefore, measuring the fluid flow velocity in the bypass channel also allows for monitoring the fluid flow behavior in the main channel. A proven operating principle for flow sensors is the thermal measurement principle. In this case, the flow sensor typically comprises a heating element and at least one temperature sensor as a single sensor component.The heating element generates a heat field that can be detected by the temperature sensor. When a fluid flows, the heat field generated by the heating element is modulated. This modulation is detectable by the temperature sensor and depends on the fluid flow or its properties. A flow parameter can be determined from this modulation of the heat field. The described measurement principle is advantageous because it requires no mechanically moving components, thus achieving high robustness with minimal manufacturing effort.

[0008] Furthermore, thermal flow sensors can be provided using so-called MEMS (microelectromechanical systems), which have a very compact design (in the micrometer range) and excellent functionality, and can be produced at low manufacturing costs.

[0009] Furthermore, it is known in the prior art to use one or more temperature elements or thermopiles as a sensor component in order to perform temperature measurement of a heat field.

[0010] A miniaturized flow sensor comprising thermopiles is described, for example, in Billat et al. (2008). The flow sensor is structured as a wafer stack, meaning it comprises several wafers or substrates stacked on top of each other. Specifically, the flow sensor disclosed in Billat et al. (2008) includes a base substrate and a cap substrate, which are connected to each other. Openings are etched along the base substrate, serving as inlet and outlet regions for the fluid. The cap substrate is structured such that it has a cavity facing the base substrate. A flow channel is incorporated within the wafer stack, allowing the fluid to spread from the inlet region of the base substrate into the cavity of the cap substrate and then exit the flow sensor via the outlet region of the base substrate.A membrane is attached to the top of the lid substrate, on which a heating element and two thermopiles are located. The flow of fluid within the flow channel modulates the heat field provided by the heating element, which can be detected by the thermopiles.

[0011] In Liu et al., for example, a thermopile-based flow sensor for respiratory monitoring is described. The sensor described therein comprises a substrate onto which a layer system consisting of silicon dioxide, silicon nitride, and silicon dioxide is deposited. An n-doped silicon strip and a polysilicon strip are coated onto this layer system. A p-doped silicon strip and a polysilicon strip are then deposited over these strips on a silicon dioxide layer, with each pair of strips, comprising superimposed strips, being electrically contacted. The uppermost strips are subsequently passivated. A superimposed pair of strips acts as a thermopile. A heating element is positioned between the thermopiles. Thermocouples preferably comprise two measuring points, usually the ends, to perform a measurement.The first measuring junction of a thermocouple or thermopile is called the hot junction. The other end is similarly called the cold junction. The cold junction serves as a reference point for measuring temperature differences. A thermopile preferably comprises thermocouples connected electrically in series and thermally in parallel. When using a thermocouple or thermopile, the temperature difference between the hot junction and the cold junction is measured. The cold junction is often placed against a substrate, as the substrate acts as a heat sink. The hot junction, on the other hand, is oriented towards a heat field.As an output signal, thermocouples or thermopiles typically provide a thermoelectric voltage, i.e., an electrical voltage signal that is proportional to the temperature difference between the cold junction and the hot junction.

[0012] In the prior art, as illustrated, for example, in Fig. 1 of Billat et al. (2008), it is known to position two thermopiles above a flow channel such that both hot spots are located above and in thermal contact with the fluid flowing in the channel, while the cold spots are arranged above a substrate that can serve as a heat sink. The thermopiles are arranged such that the hot spot of a first thermopile is positioned upstream of the second thermopile. A heating element, for example in the form of a heating strip, is preferably positioned between the two thermopiles and generates a symmetrical heat field in the case of a stationary fluid.

[0013] Depending on the flow velocity or other flow parameters of the fluid, the heat field will shift towards the downstream hot spot of the second thermopile. In this case, the absolute temperature at the hot spot of the second thermopile (positioned downstream of the heating element) will be higher than the absolute temperature at the hot spot of the first thermopile (positioned upstream of the heating element).

[0014] Unlike simple temperature sensors, thermopiles always measure a temperature difference between the hot and cold junctions. When using two thermopiles, a first temperature difference ATi is measured between a hot junction positioned downstream of the heating element and a cold junction above the substrate, and a second temperature difference AT2 is measured between a hot junction positioned downstream of the heating element and a cold junction above the substrate.

[0015] AT1 denotes a temperature difference between a hot and cold junction of the first thermopile and can be measured directly via the thermopile's output voltage. Similarly, AT2 denotes a temperature difference between a hot and cold junction of a second thermocouple, which is proportional to the thermoelectric voltage of the thermopile. These temperature differences allow the determination of the temperature difference AT = AT2 - AT1 between the two hot junctions. It is advantageous that the cold junctions of both thermopiles are located above the substrate and are therefore essentially the same for both thermopiles. Based on the temperature difference AT, it is possible to determine fluid flow parameters, such as the flow velocity v. The flow velocity v is proportional to AT, so the flow rate can be determined from this: v ~ AT = AT2 - AT1.

[0016] Thermopiles are characterized by extremely low signal-to-noise ratio, enabling highly precise temperature difference determination between a hot and cold junction. By calculating the difference in the voltage signal or the difference between the two measured temperature differences AT2 and AT1, fluid flow parameters can be determined with high precision.

[0017] In the absence of flow, a heat field provided by a heating element is symmetrically distributed, and a temperature difference AT = AT2 - AT1 of essentially zero would be expected. If the fluid flows in such a way that it spreads towards the second thermocouple, the heat field provided by one heating element is shifted accordingly towards the second thermocouple. Spatial symmetry of the heat field is therefore no longer present, so that, as explained above, the temperature at the hot spot downstream of the heater (synonymous with heating element) of the second thermocouple is higher than the temperature at the hot spot upstream of the heater of the first thermocouple. Since the temperature differences are determined with respect to a substrate acting as a heat sink, the temperature difference AT2 will also be higher than AT1.

[0018] According to the invention, it was recognized that while the thermopiles themselves determine a temperature difference between the hot and cold junctions with high precision, determining a difference of temperature differences: AT = AT2 - AT1 can lead to a higher measurement fluctuation. Thus, a small difference between comparatively large temperature differences AT1 and AT2 can lead to a higher measurement uncertainty (see Fig. 1). In addition, the total thermal resistance of two thermocouples can add up to an increased noise source. Any temperature differences between the cold junctions, which act as heat sinks for the respective thermopiles, can also further impair the accuracy of measuring a flow-dependent shift of the measurement signal.

[0019] Furthermore, the provision of two opposing thermopiles, whose hot and cold points are located above the sensor channel and above the substrate respectively, occupies a considerable area, which also results in minimum requirements with regard to the flow channels - for example, their lengths.

[0020] In the prior art, several sensors and / or applications are known in which thermocouples or thermopiles are used.

[0021] US 2022 / 299427 A1 discloses a MEMS-based photoacoustic cell. Among other things, a sensor comprising a heating element, designed as a planar pad, and a multitude of temperature sensors configured as thermopiles is disclosed. The heating element and the temperature sensors are mounted on a partition or membrane such that apertures are located between the heating element and the multitude of temperature sensors. The heat flow from the central heating element to the temperature sensors is sensitive to gas flow through the aperture. The thermopiles are not positioned along the direction of gas flow to enable differential temperature measurement.

[0022] US 2023 / 358586 A1 deals with a device based on thermopile measurement. The device comprises a membrane on which a thermopile is mounted. The thermopile includes thermocouple measuring points. The measuring points are positioned along the flow direction of a fluid flowing above the thermopile. A heating element is mounted transversely to the structure of the thermopile.

[0023] WO 97 / 21986 A1 discloses a flow sensor. The flow sensor comprises a silicon membrane with heating resistors attached to its inner surface. Thermopiles, formed from strips of silicon and aluminum, are arranged between the heating resistors. Furthermore, contact surfaces are provided on the inner surface of the silicon membrane, allowing contact between the thermopiles and the heating resistors. The thermopiles are arranged perpendicular to the heating resistors.

[0024] US 2012 / 071783 A1 concerns a system for monitoring the position of the distal end of a tube relative to a blood vessel. A heating element is embedded in the tube to heat the outside of the distal end during operation. For this purpose, a power source supplies the heating element with a constant power during operation. A temperature sensor is configured to measure the temperature difference at points on either side of the heating element. For this purpose, the temperature sensor includes a thermopile consisting of a series of thermocouples arranged perpendicular to the heating element.

[0025] WO 2020 / 158155 A1 describes a detection device. The detection device comprises a heating element and a thermopile arranged symmetrically around the heating element. The detection device includes a substrate on which a film is applied. The heating element and the thermopiles are located on the film. The substrate has a cavity and an opening that is fluidically connected to the cavity. The flow occurs above the film and the substrate, respectively. The measuring points are aligned along a flow direction of the fluid, with a first hot junction of the thermopile preferably arranged upstream of the heating element, while a second hot junction is arranged downstream.

[0026] JP H05 99722 A discloses a flow sensor for measuring low flow rates. The flow sensor comprises an epitaxial layer on which a first and a second electrically conductive layer are deposited. The epitaxial layer is located on a silicon substrate. Glass is positioned above the electrically conductive layers. The individual electrically conductive layers function as thermocouples connected in series, with a heating element extending along the electrically conductive layer. The measurement points for detecting the flow are positioned along the direction of fluid flow. In particular, the cold and hot junctions of the thermocouples are arranged upstream and downstream of the heating element, respectively. Therefore, there is a need to provide improved or alternative flow sensors.

[0027] Object of the invention

[0028] The object of the invention is to eliminate disadvantages of prior art flow sensors. In particular, it is an object of the invention to provide a flow sensor that is characterized by high sensitivity and precise measurement results, while simultaneously being compact and easy to manufacture.

[0029] Summary of the invention

[0030] In a first aspect, the invention relates to a flow sensor for measuring at least one flow parameter of a fluid, comprising a thermal sensor comprising a heating element for providing a heat field and a sensor component for detecting a temperature response of the thermal sensor as a function of the influence of the flowing fluid on the heat field, wherein the sensor component comprises one or more thermocouples, characterized in that the one or more thermocouples are positioned along a flow direction of the fluid for differential temperature measurement. The flow sensor preferably comprises a substrate.

[0031] The flow sensor according to the invention offers advantages in a multitude of aspects. In particular, the arrangement of one or more thermocouples along the flow direction of the fluid for differential measurement reduces or eliminates factors that could impair sensitivity.

[0032] Positioning one or more thermocouples along the flow direction for differential temperature measurement allows for the determination of a relatively small temperature difference between two measuring points with high precision.

[0033] In contrast, as explained above, prior art methods have so far determined small temperature differences by comparing two large temperature differences, which negatively impacted the sensitivity of the measurement. However, according to the invention, positioning one or more thermocouples along the flow direction enables direct measurement of differential temperature.

[0034] This means, in particular, that a shift in the heat field provided by the heating element is directly determined as a temperature difference between the two measuring points of one or more thermocouples due to the fluid flow. The fluid flow can also be described as a flux field, which preferably refers to a vector field that specifically indicates the fluid flow velocity.

[0035] In preferred embodiments, the fluid flows in a flow channel. In this case, the fluid flow preferably takes place in a flow channel in which the flux field is also preferably present.

[0036] Preferably, the one or more thermocouples are positioned such that their sensitive measuring points are in thermal contact with the flowing fluid, with the thermocouples preferably positioned for differential temperature measurement along the flow direction of the fluid. This means that preferably a first measuring point of the one or more thermocouples is located upstream of the second measuring point of the one or more thermocouples. A displacement of a heat field due to the fluid flow can thus be directly detected based on the (voltage) signal of the one or more thermocouples, which is proportional to the temperature difference between the two measuring points.

[0037] This eliminates the need to install at least two thermocouples or thermopiles that detect the shift of the heat field by creating a difference in the (voltage) signals of the respective thermocouples or thermopiles.

[0038] The use of one or more thermocouples for direct differential temperature measurement along a flow direction of the fluid according to the invention represents a departure from previous flow sensors, which always used the ability of the thermocouples or thermopile to measure temperature differences in such a way that a (fluid- or measurement-sensitive) hot spot was arranged in thermal contact with the flowing fluid, while a (fluid-insensitive) cold spot was positioned in thermal contact with the substrate or support as a heat sink.

[0039] Instead, according to the invention, one or more thermocouples are brought directly into thermal contact with the flow field of the fluid for differential temperature measurement.

[0040] A thermal contact preferably refers to a sufficient transfer of heat between the heating element and the thermocouple, preferably a thermopile, particularly to its measuring points. This allows for the modulation of the heat field due to the fluid flow at a thermocouple, preferably a thermopile. The thermal contact thus refers in particular to the transport of thermal energy to the measuring points of a thermocouple, preferably a thermopile. It is known that heat transfer can occur through convection, thermal radiation, and / or thermal conduction. A thermal contact does not necessarily require direct contact. Instead, heat transfer to the thermocouple can also occur if an intermediate component, such as a heating element, is present.A thermally conductive area or a (at least partially thermally conductive) membrane is positioned between the heating element and the measuring points of one or more thermocouples, preferably a thermopile. Preferably, at least the measuring points of the thermocouple, preferably of the thermopile, are in thermal contact with the fluid, but not necessarily a central section of the thermocouple, preferably of the thermopile. A central section of the thermocouple, preferably of the thermopile, preferably refers to the section located between the first measuring point and the second measuring point.

[0041] Thus, the flow sensor according to the invention enables particularly high sensitivity. On the one hand, by positioning one or more thermocouples along the flow direction for differential temperature measurement, the displacement of the heat field can be measured directly at the flow field of the thermal sensor. On the other hand, the individual thermal resistances of the one or more thermocouples do not add up. Noise signals, in particular thermal noise, which can add up in the case of two thermocouples or thermopiles, are thereby significantly reduced.

[0042] Because no heat sink, such as the substrate, is required for differential temperature measurement, the dependence of the measurement on external temperatures, such as the substrate temperature and / or the ambient temperature, is eliminated or reduced. If these temperatures are subject to local fluctuations, the reference temperature can also fluctuate when using the cold junctions of the thermocouples or thermopiles in thermal contact with the substrate, negatively impacting measurement accuracy.

[0043] Instead, the flow sensor according to the invention enables a measurement specifically directed with respect to the displacement of the heat field by means of one or more thermocouples for differential temperature measurement, which minimizes noise sources or environmental influences.

[0044] Furthermore, the arrangement of one or more thermocouples along the flow direction for differential temperature measurement can be kept extremely compact. This eliminates the need to position the cold junctions of the thermocouples in thermal contact with the substrate. Instead, the thermocouples can be arranged, for example, essentially above or below a flow channel with minimal space requirements, provided the flow channel runs partially along or through a substrate of the thermal sensor (see also Fig. 2 or 3). A compact arrangement of the structural components of the thermal sensor for providing the flow sensor can also be advantageously achieved if the flow sensor is positioned within or adjacent to a flow channel located within a fluid line (see Fig. 7).A compact design of the flow sensor is also achieved when the flow of a fluid in the vicinity of the flow sensor is to be measured.

[0045] A simplified structural design of the thermal sensor also results from the elimination of the need for thermal grounding. Thermal grounding typically refers to a design of the flow sensor such that heat dissipation occurs in a way that interrupts unwanted heat paths which could, for example, distort the measurement. Advantageously, the effort required for such a design is eliminated, since a direct use of the temperature difference along the flow direction is possible, and thus the heat field is effectively utilized by the flow.

[0046] The flow sensor is used in particular for measuring at least one flow parameter of a fluid. The fluid preferably refers to a medium of which at least one flow parameter is to be measured by means of the flow sensor. The fluid is characterized in particular by its flowability and propagation capability. In particular, the fluid is capable of flowing or propagating in the vicinity of the flow sensor. The fluid is particularly capable of flowing through a preferred flow channel, which, for example, runs through the thermal sensor itself or a fluid line connected to the thermal sensor. The fluid itself preferably refers to a medium that can deform continuously under the influence of shear forces. In particular, the fluid can be a liquid or a gas. The direction in which the fluid propagates is referred to as the flow direction.The flow direction thus points in the direction in which a flow vector of the fluid is directed.

[0047] The flow direction of the fluid, of which at least one flow parameter can be detected by the flow sensor, is preferably determined by structural components of the flow sensor itself. In particular, if the flow sensor itself includes or is connected to a flow channel, the flow direction is defined by a line connecting an inlet or entry region (or inlet) and an outlet or exit region (or outlet) of the flow channel. Preferably, the flow direction can be formed by a difference vector, i.e., the difference between two position vectors (vectors with the same origin), one vector pointing towards the inlet and the other towards the outlet of the flow channel. Preferably, the flow direction is towards the outlet of the flow channel.For the differential temperature measurement according to the invention along the flow direction of the fluid, it is not significant which area is used for an inlet or outlet of the flow channel. What is crucial is that the flow direction can be specified by a difference vector between an inlet and an outlet of a flow channel, along which direction a differential measurement is performed. In this respect, a differential measurement between at least two measuring points of a thermocouple, preferably a thermopile, along the flow direction of the fluid is enabled by means of the preferred flow sensor. This means, in particular, that no differential measurement is performed along a line that runs perpendicular to the flow direction or to a connecting line or a difference vector between the inlet and outlet of the flow channel.If the flow channel is not part of the flow sensor, structural components on the flow sensor, such as connection components (e.g., adhesive pads, etc.) to a fluid line with a flow channel, can preferably define the positioning of at least two measuring points of a thermocouple, preferably a thermopile, with respect to the flow channel and thus the flow direction. In the case of wall flow or flow in the vicinity of the flow sensor, the flow sensor can also preferably include structural components that enable alignment with respect to the fluid flow direction. For example, the flow sensor can have connection components (e.g., adhesive pads, etc.) for mounting on a wall, which ensure alignment of the flow sensor and thus the thermocouples for differential temperature measurement along a fluid flow direction.

[0048] The at least one flow parameter preferably denotes a quantity with which the fluid can be characterized in its physical and / or chemical properties. Preferably, the flow parameter can be selected from a group comprising a flow velocity, a pressure, a volumetric flow rate, a flow frequency (in the case of an oscillating flow of the fluid), a concentration, and / or a composition of the fluid, without being limited to these preferred parameters. The flow sensor comprises a thermal sensor with which the flow can be detected.

[0049] The thermal sensor preferably comprises a heating element and a sensor component. The heating element serves in particular to provide a heat field. The heat field preferably refers to the heat emanating from the heating element. The heat field is thus transferred in such a way that the heat field of the heating element can propagate, particularly within a flow channel, and can be traversed by the fluid. The terms heat field and heat flow can be used synonymously in the context of the invention.

[0050] The fluid, through its flow, preferentially influences the heat field generated by the heating element. This influence, and the associated change in the heat field, is measurable by the sensor component of the thermal sensor. The change in the heat field due to the fluid flow can also be described as heat field modulation or heat flux modulation. The fluid's influence on the heat field, or the modulation, is reflected in a temperature response detected by the sensor component of the thermal sensor. In other words, the sensor component serves to detect a temperature response that, in turn, depends on the modulation of the heat field by the fluid.

[0051] The temperature response of the flow sensor preferably refers to a measurement signal acquired by the sensor component. The temperature response thus preferably represents a reaction of the thermal sensor, in particular the sensor component, with respect to the properties or flow of the fluid and its effect on the thermal field. The temperature response can preferably relate to a thermal quantity, which can be read out by the sensor component, such as the temperature itself. The temperature response can preferably refer to an electrical signal, which can preferably be described by an electrical voltage and / or an electrical current. In particular, the temperature response can refer to a voltage signal from one or more thermocouples, which is proportional to a temperature difference between two measuring points of the one or more thermocouples, which are preferably in thermal contact with the flowing fluid.

[0052] The flow sensor can be designed for different thermal measurement principles and / or preferably configured to operate, preferably using an electronic circuit, in one or more modes to measure at least one flow parameter.

[0053] For example, the flow sensor can be designed for a calorimetric measuring principle. A calorimetric measuring principle preferably utilizes the fact that the temperature profile around a heating element changes due to convection caused by the fluid flow. In the prior art, two sensor components are preferably positioned downstream and upstream of the heating element. Depending on the fluid flow, the temperature measured downstream and upstream of the heating element will differ. By measuring this temperature difference, a conclusion can be drawn about a flow parameter of the fluid. According to the invention, a sensor component comprising one or more thermocouples is used to perform a differential temperature measurement in the direction of fluid flow and thereby directly determine the difference between the temperature measured downstream and upstream of the heating element.

[0054] The heating element can be heated, for example, with a constant voltage, a constant current, a constant power, or to a constant temperature.

[0055] Furthermore, it may be preferable to design the flow sensor for a so-called time-of-flight (TOF) measurement principle. This preferably involves measuring the time between the moment a control signal is passed through the heating element and the time at which a maximum temperature rise is measured at the sensor component, for example, a temperature sensor, at a known distance from the heating element. The higher the flow rate, the shorter the TOF. In the context of the invention, the TOF measurement principle can be used to determine the time until the measured maximum temperature difference between one or more thermocouples is reached.

[0056] The flow sensor, in particular the temperature response of the thermal sensor, can preferably be used to determine further properties of the fluid, such as thermal conductivity, density, pressure, specific heat capacity, thermal conductivity, concentration and / or composition of the fluid.

[0057] It is known to those skilled in the art that, for example, an oscillating control signal can be used to preferably obtain a frequency-dependent temperature response in order to infer the thermal conductivity and / or volumetric heat capacity of a fluid. For instance, determining the phase between an oscillating control signal and a temperature response can be used, in particular, to determine the thermal conductivity. The amplitude of a temperature response under oscillating control can depend, in particular, not only on the thermal conductivity but also on the volumetric heat capacity. Therefore, the thermal conductivity and / or volumetric heat capacity of the fluid can be determined, for example, from the phase and amplitude of a temperature response to an oscillating control signal.These thermal parameters also allow conclusions to be drawn about, for example, the composition of the fluid and / or the concentration of a component within a fluid. If, for instance, the thermal conductivity and / or volumetric heat capacity of various components of a mixed fluid, e.g., a mixed gas, are known, the proportions of the individual components can be determined by measuring the thermal conductivity and / or volumetric heat capacity of the entire fluid.

[0058] The flow sensor preferably comprises a substrate. The substrate preferably serves as a support structure for the thermal sensor. Components of the thermal sensor, such as the heating element and / or one or more thermocouples, preferably a thermopile, can preferably be attached directly or indirectly to the substrate. A membrane can particularly preferably be held by the substrate, and the thermal sensor can be partially or completely mounted on this membrane.

[0059] The substrate can, for example, comprise a glass, a ceramic, and / or a semiconductor material, such as monosilicon, polysilicon, silicon carbide, silicon germanium, germanium, gallium arsenide, and / or gallium nitride. The substrate can preferably be single-layered (monolithic) or multi-layered (e.g., as a wafer stack).

[0060] In a preferred embodiment, at least one flow parameter of a fluid in the vicinity of the flow sensor can be measured using the flow sensor. In particular, at least one flow parameter of a wall or free flow of the fluid can be measured using the flow sensor. For example, the flow sensor can be positioned on or in a wall or similar structure to measure the flow in the vicinity of this wall.

[0061] Wall flow does not necessarily require an explicit path for fluid propagation. Therefore, wall flow can also refer to free flow. In wall flow, a flow can result, for example, from a spatially uneven pressure distribution, causing the flow to spread from an area of ​​higher pressure to an area of ​​lower pressure to equalize pressure. This can occur particularly with gas flows, such as air currents. Wall flow of a fluid can also occur as a result of external influences, for example, in bodies of water or rivers under investigation. In this case, the flow direction may be predetermined by the fluid under investigation, for example, by the course of a river.The flow sensor, and therefore the one or more thermocouples, are also designed in these cases to perform a differential measurement along the expected current direction.

[0062] In a preferred embodiment, the flow sensor is characterized in that the flowing fluid flows in a flow channel, wherein preferably the flow channel runs at least partially, preferably completely, through the substrate of the flow channel.

[0063] Advantageously, a particularly high degree of compactness can be achieved for the flow sensor if the flow channel runs at least partially, preferably completely, through the substrate.

[0064] It is preferred that the substrate is monolithic. Monolithic in this context preferably means that it is a single-piece substrate. Thus, in a monolithic design, the substrate preferably forms a single component.

[0065] The use of a monolithic substrate further increases the degree of compactness. Moreover, from a manufacturing and process engineering perspective, simple modifications can be made to the monolithic substrate, for example, at least partially, and preferably completely, embedding the flow channel in the substrate.

[0066] In a preferred embodiment, the flow sensor is positioned within or adjacent to a flow channel (see Fig. 7). In preferred embodiments, the flow channel is a component of a fluid line, with the flow sensor preferably being connected to the fluid line. In these embodiments as well, the fluid propagates within the flow channel, meaning that the flow channel, in particular, defines a flow direction for the fluid. The one or more thermocouples are positioned along the flow direction for differential measurement. A preferred first measuring point and a second measuring point of the one or more thermocouples for differential measurement are preferably positioned such that the first measuring point is located upstream of the second measuring point.Preferably, in this embodiment as well, the flow sensor has a substrate which serves as a support structure for components of the thermal sensor, preferably for the heating element and one or more thermocouples. Preferably, the substrate can comprise a cavity, wherein a membrane at least partially covers the cavity and supports components of the thermal sensor.

[0067] A thermocouple preferably refers to an arrangement comprising a pair of electrically conductive materials connected at one end, which, due to the thermoelectric effect, allows the measured temperature to be determined. Electrical energy is supplied when there is a temperature difference along the arrangement.

[0068] As explained above, one measuring point of the thermocouple is referred to as the hot junction, hot end, or by the English terms hot end or hot junction, and forms one end of the thermocouple. The other end, which is analogously referred to as the cold junction, cold end, or by the English terms cold end or cold junction, is, in the prior art, in particular a reference junction used to determine a temperature difference. Preferably, an electronic circuit and / or a processing unit for processing the temperature measurement is connected to the cold junction.

[0069] In the inventive arrangement of one or more thermocouples for differential measurement along the flow direction, preferably both the hot junction and the cold junction are used as measuring points and positioned for differential temperature measurement along the flow direction of the fluid.

[0070] Positioning one or more thermocouples for differential temperature measurement along the fluid flow direction preferably means that one of the hot junctions or cold junctions of the one or more thermocouples is arranged upstream or downstream with respect to the fluid flow direction, such that a flow-dependent displacement of a heating element's heat field can be determined by differential temperature measurement using the one or more thermocouples. The differential temperature measurement is intrinsically achieved through the measuring principle of the one or more thermocouples, which preferably provide a voltage signal as a measurement signal due to a thermoelectric effect, a signal that depends on the temperature difference between the hot junction and the cold junction.In contrast to prior art approaches, differential temperature measurement thus does not require the generation of a combined signal, such as a difference, from two separate sensor components, thereby reducing measurement noise as explained above. In a further preferred embodiment, the flow sensor is characterized in that the multiple thermocouples form a thermopile, such that the thermopile is positioned along the flow direction of the fluid for differential temperature measurement.

[0071] A thermopile is an element comprising multiple thermocouples. The thermocouples of the thermopile are preferably connected electrically in series and thermally in parallel. In preferred embodiments, the phrase "one or more thermocouples" thus refers to a thermopile in which the one or more thermocouples are connected together to generate a measurement signal.

[0072] Like a thermocouple, a thermopile comprises at least one hot junction at one end and at least one other end, a cold junction, which in the prior art serves in particular as a reference junction to detect a temperature difference. In the context of the invention, the at least one hot junction at one end and the at least one cold junction at another end are both used, as described, as measuring points for differential temperature measurement along the flow direction of the fluid. Preferably, a thermopile comprises several hot junctions and cold junctions of the respective thermocouples, preferably connected in parallel, as measuring areas. The measuring signal of the thermopile preferably reflects a temperature difference over the averaged temperature of the several hot junctions or the several cold junctions of the respective thermocouples.

[0073] In the context of the invention, a (first or second) measuring point of a thermopile preferably means the entirety of the measuring ranges of the several hot or cold points of the one or more thermocouples.

[0074] The use of thermopiles is particularly advantageous because connecting multiple thermocouples allows for a particularly informative signal. Specifically, the thermopile can utilize the increased thermal voltage resulting from the interconnected thermocouples, thus achieving an improved signal-to-noise ratio (compared to using a single thermocouple). The number of thermocouples forming a thermopile can preferably be 2, 3, 5, 10, 20, or more, and this number is preferably selectable depending on the dimensions (especially the width) of a flow channel and / or the desired measurement sensitivity.

[0075] In a further preferred embodiment, the flow sensor is characterized in that the differential temperature measurement takes place between a first measuring point and a second measuring point, wherein the first measuring point is located upstream of the second measuring point with respect to the flow direction of the fluid in the flow channel.

[0076] The first and second measuring points preferably define spatial sections between which a differential temperature measurement can be performed using one or more thermocouples. The first and second measuring points can preferably comprise one or more measuring sections of a thermocouple or a thermopile. With respect to a thermocouple, a first measuring point is preferably formed by a hot junction and a second measuring point by a cold junction (or vice versa). With respect to a thermopile comprising several thermocouples, a first measuring point is preferably formed by the multiple hot junctions of the respective thermocouples and a second measuring point preferably by the multiple cold junctions of the respective thermocouples (or vice versa). A temperature difference between the first and second measuring points can preferably be read out as a thermal voltage signal from the thermocouple or the thermopile.

[0077] Preferably, the first measuring point is arranged upstream of the second measuring point with respect to the fluid flow direction. This preferably means that the fluid passes the first measuring point before passing the second. In other words, the second measuring point is preferably located downstream of the first measuring point. In the case of a fluid flowing in the direction of flow, this preferably results in a shift of the heat field provided by the heating element towards the second measuring point. Therefore, it is preferred that a higher temperature is present at the second measuring point. In particular, the first measuring point can therefore comprise one or more cold junctions of a thermocouple or thermopile. The second measuring point can accordingly comprise one or more hot junctions of a thermocouple or thermopile.The terms upstream and downstream thus preferably denote directions with respect to the flow direction of the fluid. Downstream preferably means a position that lies in the direction of the fluid flow. Upstream preferably means a position that is against the flow direction of the fluid.

[0078] Preferably, the first and second measuring points are located along the fluid flow field in a preferred flow channel. It is therefore preferred that one or more cold junctions and also one or more hot junctions of a thermocouple or thermopile are located along the fluid flow field in a preferred flow channel. This allows a displacement of the heat field between the first and second measuring points to be measured directly along the flow field, enabling the determination of at least one fluid flow parameter by differential temperature measurement.

[0079] In a further preferred embodiment, the flow sensor is characterized in that the first measuring point and the second measuring point have a distance from each other of 0.5 - 1000 pm, preferably of 10 - 500 pm, particularly preferably of 20 - 200 pm.

[0080] The aforementioned preferred distances between measuring points have proven advantageous in that, firstly, a sufficient temperature difference between the positions of the first and second measuring points can be detected to enable sensitive differential temperature measurement. Secondly, the preferred distances between the first and second measuring points allow for a compact arrangement of one or more thermocouples with respect to a preferred flow channel of a flow sensor.

[0081] In another preferred embodiment, the flow sensor is characterized in that the heating element is positioned between the first measuring point and the second measuring point.

[0082] Positioning the heating element between the first and second measuring points ensures a particularly effective shift of the heat field provided by the heating element towards the second measuring point, caused by the flow. Only one heating element is required, and any flow-dependent shift of its heat field can be directly detected as a temperature difference between the second and first measuring points.

[0083] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor has an electronic circuit and / or is connected to an electronic circuit, wherein the electronic circuit is configured to control the heating element and / or to determine the at least one flow parameter of the fluid based on the measurement signals of the sensor component. In the context of the invention, a combination of an electronic circuit connected to a flow sensor can also be referred to as a flow sensor system comprising a flow sensor and an electronic circuit.

[0084] For the purposes of the invention, an electronic circuit preferably refers to an assembly of individual electrical or electromechanical elements into a functional arrangement. Preferably, the electronic circuit allows data or electrical signals to be sent, received, and / or processed.

[0085] Preferred electronic circuits include, without limitation, an integrated circuit (IC), application-specific integrated circuits (ASIC), a programmable logic device (PLD), a field programmable gate array (FPGA), a microprocessor, a microcomputer, a programmable logic controller and / or any other electronic, preferably programmable, circuit.

[0086] Preferably, the electronic circuit is configured to receive measurement data from the sensor component and / or to send control signals, for example control commands, to the heating element in order to generate the heat field.

[0087] Preferably, the electronic circuit can be configured to control the heating element based on the measurement data from the sensor component. More preferably, the electronic circuit is configured to send a command to the heating element to generate the heat field after a measurement by the sensor component, for example, to increase, maintain, or decrease the heat output. In particular, it may be preferred that the electronic circuit executes one or more of the aforementioned operating modes to measure at least one flow parameter based on the temperature response resulting from the influence of the fluid flow on the heat field. In preferred embodiments, the electronic circuit can also be configured to process the measurement data acquired by the sensor component with regard to modulating the heat field.Data processing preferably means that the electronic circuit is configured to perform calculations and / or computational steps, for example with regard to the recorded measurement data of the sensor component.

[0088] The electronic circuit can thus function as an evaluation, readout, and / or control unit, enabling the control of the heating element, the reading of the sensor component, and / or the evaluation of the measurement data. If evaluation is performed, the electronic circuit can also be referred to as a processing unit.

[0089] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor has a computing unit or is connected to a computing unit, wherein the computing unit is designed to determine the at least one flow parameter of the fluid on the basis of one or more thermocouples, preferably a thermopile, using an electrical measured quantity, preferably an electrical voltage and / or an electrical current.

[0090] The term "computing unit" preferably refers to any device or unit that can be configured to perform computational operations. Preferably, the computing unit is, for example, a processor, a processor chip, a microprocessor, and / or a microcontroller, preferably configured to evaluate the modulation of the thermal field. The computing unit can also preferably be a programmable printed circuit board. The computing unit can also preferably comprise a computer-usable or computer-readable medium, such as a hard drive, random access memory (RAM), read-only memory (ROM), flash memory, etc.

[0091] The process steps for determining at least one fluid flow parameter, as described herein, are preferably performed by the electronic circuit or computing unit. The phrase "is designed to do so" preferably means that computer code and / or software is installed on the electronic circuit or computing unit to perform the process step, for example, to verify the extent to which a modulation of the heat field was induced and which fluid parameters were responsible for this. The computer code and / or software for evaluating the modulation of the heat field can be written in any programming language or model-based development environment, e.g., in C / C++, C#, Objective-C, Java, Basic / VisualBasic, MATLAB, Simulink, StateFlow, LabView, and / or Assembler.

[0092] The computer code and / or software, preferably installed on the electronic circuit or processing unit, for the purpose of evaluating the modulation of the thermal field, can be considered a technical feature, since it utilizes a direct physical effect of the thermal sensor, such as the application of a control signal to a heating element or the detection of a temperature change by the sensor component. Functional descriptions of the computer code and / or software can therefore be considered preferred and defining embodiments of the invention.

[0093] In a further preferred embodiment, the flow sensor is characterized in that the heating element at least partially, preferably completely, covers a flow channel in a direction essentially orthogonal to the flow direction of the fluid, and the one or more thermocouples, preferably a thermopile, are positioned along the flow direction of the fluid in the flow channel such that the heating element is at least partially covered.

[0094] The embodiments may be particularly preferred for a flow sensor comprising a substrate in which the flow channel runs at least partially, preferably completely. However, it may also be preferred that the embodiments relate to a flow sensor in whose substrate the flow channel does not run, but which is arranged within or adjacent to a flow channel (for example, within a fluid line). In the latter case as well, the multiple thermocouples, preferably a thermopile, may be positioned, for example, along the flow direction of the fluid in the flow channel such that the heating element is at least partially covered.

[0095] The formulation, "the heating element covers the flow channel at least partially, preferably completely, in a direction essentially orthogonal to the flow direction of the fluid", preferably means that in a projection of the flow channel along its vertical dimension (height) the heating element covers at least partially, preferably completely, one dimension of the flow channel which is essentially orthogonal to the flow direction of the fluid (preferably a width).

[0096] The length of the flow channel preferably refers to its extent along the direction of fluid flow within the channel. The length of the flow channel thus preferably corresponds to a distance extending from an inlet region to an outlet region of the flow channel. Preferably, the length of the flow channel can substantially correspond to the length of a line connecting the inlet and outlet regions of the flow channel, for example, if the flow channel is substantially straight. It may also be preferred that the flow channel has a greater length than the line connecting the inlet and outlet regions, for example, if the flow channel is curved or winding.If the flow channel extends at least partially, preferably completely, through a substrate of the flow sensor, the inlet and outlet regions for the flow channel can, for example, be defined as corresponding openings in the substrate. The width and height of the flow channel preferably refer to a cross-sectional plane that is orthogonal to the vector of the fluid flow within the channel. While the height preferably refers to the extension of the channel from bottom to top or along the direction from a back to a front, the width of the flow channel preferably corresponds to a dimension that is orthogonal to the height. The product of width and height yields the cross-sectional area of ​​the flow channel. The heating element and the thermocouple or thermopile are preferably arranged above or below, or on a front or back side of, the flow channel.

[0097] The direction of the height, width, and / or length of a substrate of the flow sensor is preferably defined according to the height, width, and / or length of the flow channel. This preferably applies both to embodiments in which the flow channel is formed within the substrate of the flow sensor and to embodiments in which the flow sensor does not encompass the flow channel but is positioned within or adjacent to a flow channel, which may, for example, be located in a fluid line. In the latter embodiment, the length of the substrate can preferably correspond to the extent of the substrate along the flow direction of the fluid in the flow channel.

[0098] The width of the substrate preferably extends orthogonally to its length, with the thermal sensor and / or a membrane preferably arranged in the plane defined by the direction of the length and width. The height of the substrate preferably extends orthogonally to its length and width.

[0099] Complete coverage in this context means, in particular, that the heating element extends across the entire flow channel in a direction orthogonal to the fluid flow direction. In particular, the heating element preferably extends across the entire width of the flow channel.

[0100] Partial coverage preferably means a coverage of the flow channel along a direction orthogonal to the flow direction through the heating element by up to 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or more.

[0101] The at least partial coverage of the heating element by one or more thermocouples, preferably a thermopile, means in particular that, in a projection of the flow channel along its vertical dimension (height), the one or more thermocouples, preferably a thermopile, sweep over or intersect the heating element. In such a configuration, a first measuring point of the one or more thermocouples, preferably the thermopile, is preferably arranged upstream of the heating element, while a second measuring point of the one or more thermocouples, preferably the thermopile, is arranged downstream. An exemplary embodiment of this design is shown in Fig. 2.

[0102] This compact arrangement allows for a particularly precise determination of a fluid flow parameter using simple means, in which a flow-dependent displacement of a heat field is detected by measuring a temperature difference between the first measuring point and the second measuring point.

[0103] Terms such as "essentially", "approximately", etc. preferably describe a tolerance range of less than ± 20%, more preferably less than ± 10%, more preferably less than ± 5%, even more preferably less than ± 2%, and more preferably less than ± 1%, and particularly include the exact value. "Similarly" preferably describes quantities that are approximately equal. "Partially" preferably describes at least 5%, more preferably at least 10%, and more preferably at least 20%, and in some cases at least 40% (or more).

[0104] In a further preferred embodiment, the flow sensor is characterized in that the heating element is arranged essentially orthogonally to a flow direction of the fluid and the one or more thermocouples, preferably a thermopile, are arranged essentially parallel to a flow direction of the fluid on a substrate of the flow sensor.

[0105] The embodiments may also be particularly preferred for a flow sensor comprising a substrate in which the flow channel runs at least partially, preferably completely. However, it may also be preferred that the embodiments relate to a flow sensor in whose substrate the flow channel does not run, but which is arranged within or adjacent to a flow channel (for example, within a fluid line). In the latter case as well, the multiple thermocouples, preferably a thermopile, may be positioned, for example, along the flow direction of the fluid in a flow channel such that the heating element is at least partially covered.

[0106] A heating element positioned substantially orthogonal to the flow direction preferably means that the heating element is oriented substantially perpendicular to the flow direction along its length. Preferably, the heating element has an elongated extension where the dimension of one length is significantly larger than the cross-section of the heating element, for example by a factor of 2, 3, 5, 10 or more. The heating element can, for example, be configured as one or more heating wires. The heating element can preferably be located above or below the flow channel (i.e., preferably on the front or back side of the flow channel). It is also preferred that the heating element is positioned within the flow channel. In this embodiment, it is preferred that the heating element extends at least partially, preferably completely, across the width of the flow channel.

[0107] An orientation of one or more thermocouples substantially parallel to the flow direction preferably means that the longitudinal orientation of one or more thermocouples is substantially parallel to the flow direction. A longitudinal orientation of one or more thermocouples preferably means a connecting line between a hot junction and a cold junction of the one or more thermocouples. In the case of a thermopile with multiple thermocouples, these are preferably aligned parallel to each other, such that the longitudinal orientation of the thermopile corresponds to the longitudinal orientation of the individual thermocouples. If the thermocouples are not partially aligned parallel, the longitudinal orientation of the thermopile corresponds to the average of the longitudinal orientations of the respective thermocouples. Therefore, it is preferred that one or more thermocouples, preferably a thermopile, are oriented along a dimension corresponding to the length of the flow channel.

[0108] With this arrangement, the first and second measuring points are also located along a connecting line that is essentially parallel to the fluid flow direction. This arrangement allows for a particularly effective measurement of the flow-dependent displacement of the heat field for differential temperature measurement.

[0109] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor has two heating elements, which are preferably arranged substantially orthogonally to a flow direction of the fluid, and wherein one or more thermocouples, preferably a thermopile, are arranged substantially parallel to a flow direction of the fluid between the two heating elements.

[0110] As explained above, it may be preferable to position a heating element, arranged essentially orthogonally to the fluid flow direction, between the two measuring points of one or more thermocouples. The heating element preferably partially or completely covers the one or more thermocouples. If partial or complete coverage of the heating element by the one or more thermocouples is not desired, for example, to avoid direct temperature influence (i.e., preferably a temperature influence independent of the fluid), it may also be preferable to provide two heating elements. In Fig.Figure 6 shows such an embodiment in which two heating elements are arranged essentially orthogonally to a flow direction of the fluid, and in which one or more thermocouples are arranged essentially parallel to a flow direction of the fluid, between the two heating elements.

[0111] Along the flow direction of the fluid, it is therefore preferred that a first heating element is located upstream of a first measuring point of one or more thermocouples, preferably a thermopile, which in turn is located upstream of a second measuring point of one or more thermocouples, preferably a thermopile, which in turn is arranged upstream of the second heating element.

[0112] Both the first and the second heating element generate a heat field, whereby preferably a temperature increase due to the heat field is essentially only measurable at the nearest measuring points of the one or more thermocouples.

[0113] Due to the fluid flow along the flow direction, the heat field of the first heating element is shifted towards the one or more thermocouples, thus increasing the temperature in the region of the first (upstream) measuring point. Conversely, the heat field of the second heating element is shifted away from the one or more thermocouples, thus decreasing the temperature in the region of the second (downstream) measuring point.

[0114] Advantageously, a temperature difference between the first and second measuring points of one or more thermocouples, preferably a thermopile, can be measured, resulting from both effects. In this embodiment, a particularly sensitive measurement is thus possible, whereby parasitic heat transfer (via a different heat path than through the fluid) is avoided or at least reduced by arranging the heating elements at a suitable distance from the one or more thermocouples, preferably without overlap.

[0115] In a further preferred embodiment, the flow sensor is characterized in that the one or more thermocouples, preferably a thermopile, are positioned directly on the heating element, so that the one or more thermocouples, preferably the thermopile, contact the heating element.

[0116] Directly positioning one or more thermocouples, preferably a thermopile, directly on the heating element is characterized by a simple manufacturing process and compact dimensions along a vertical orientation. However, direct contact can disadvantageously lead to a direct transfer of heat from the heating element to the one or more thermocouples, i.e., independent of a heat path through the fluid, which can negatively affect the signal-to-noise ratio. In this case, direct thermal contact between the heating element and the one or more thermocouples, particularly the thermopile, is preferably not located in the area of ​​the measuring points, but rather, for example, only in a central region of the one or more thermocouples, particularly the thermopile, in order to reduce adverse effects on the signal-to-noise ratio.

[0117] In any case, this embodiment also shows good results and improvements compared to the use of two separate thermopiles, as was known in the prior art, due to the advantages in minimizing noise by means of a differential temperature measurement according to the invention using one or more thermocouples.

[0118] However, as explained below, it may be preferable to reduce or avoid direct contact between the heating element and the one or more thermocouples, including areas of the one or more thermocouples outside the measuring points.

[0119] In a further preferred embodiment, the flow sensor is characterized in that there is a vertical distance of 0.1 - 100 pm, preferably 0.5 - 50 pm, and particularly preferably 1 - 20 pm between the heating element and the one or more thermocouples, preferably a thermopile.

[0120] In a further preferred embodiment, the flow sensor is characterized in that a gap exists between the one or more thermocouples, preferably a thermopile, and the heating element, wherein the gap is preferably filled with an ambient fluid, preferably ambient air.

[0121] A vertical distance preferably refers to a distance along a vertical direction or height of a flow channel and / or substrate. The gap is also preferably located along a vertical direction, so that the gap thermally separates the heating element from the one or more thermocouples, preferably the thermopile.

[0122] A vertical distance between the heating element and one or more thermocouples exists particularly when a flow channel runs at least, preferably completely, through a substrate of the flow sensor. However, a vertical distance can also preferably exist when the flow sensor is positioned within or adjacent to a flow channel running in a fluid line. In this case, the vertical direction preferably refers to the vertical direction or height of the substrate.

[0123] The dimensions of the vertical distance or gap refer in particular to the vertical distances (from top to bottom) that the heating element and the one or more thermocouples have in those areas where the one or more thermocouples, preferably a thermopile, cover the heating element, i.e., in areas where, in a projection of the flow channel along its vertical dimension (height), the one or more thermocouples, preferably a thermopile, sweep over or intersect the heating element. Particularly preferably, specifications regarding the dimension of the vertical distance or gap correspond to an average value for the distance between the heating element and the one or more thermocouples in those areas.

[0124] For example, if the one or more thermocouples have an increased central area between the two measuring points along their length and the one or more thermocouples cover the heating element in the central area (see Fig. 4B), specifications regarding a vertical distance from the heating element to the one or more thermocouples refer to that central area.

[0125] The aforementioned preferred distance ranges for the vertical distance and also the provision of a gap have proven to be reliable in enabling a continued sufficient transmission of the displacement of the heat field to the one or more thermocouples, preferably a thermopile.

[0126] Advantageously, thermal insulation between the heating element and the one or more thermocouples, preferably a thermopile, can be increased both by the vertical distance, particularly with regard to the preferred dimensions, and by the gap. This results in reduced (direct) heat transfer from the heating element to the one or more thermocouples, preferably a thermopile, which occurs along a heat path independent of the fluid. Such heat transfer can also be described as parasitic heat transfer and increases thermal noise in the measurement signal of the sensor component, as explained above.

[0127] Including a gap between the heating element and one or more thermocouples, preferably a thermopile, is particularly advantageous in that it reduces Johnson noise. Johnson noise (also known as thermal noise or resistance noise), which is essentially white noise, refers to a noise signal that results from any ohmic resistance due to thermal electron movement. This creates a noise voltage across the resistance and limits the ability to work with small or weak measurement signals.

[0128] In the context of the invention, any noise voltage that may occur relates to the one or more thermocouples, preferably a thermopile. Direct heat transfer (independent of the fluid) from the heating element to the one or more thermocouples (for example, also in a central region between the measuring points) increases the (base) temperature of the one or more thermocouples, preferably the thermopile, and consequently the Johnson noise. By providing a gap or vertical space, however, heat conduction from the heating element is reduced, thus decreasing the thermal electron movement of the one or more thermocouples, preferably a thermopile, and consequently reducing Johnson noise. In this respect, the sensitivity of the flow sensor is advantageously increased.

[0129] Preferably, an ambient fluid, i.e., a fluid from the environment of the flow sensor, can be present in the gap. Particularly preferably, the ambient fluid is ambient air. The ambient fluid can preferably be introduced into the gap within a specific pressure range, for example, as a vacuum. The average person skilled in the art knows that a vacuum is not absolute, so a vacuum can be present down to a pressure range of up to 1 mbar (millibar), up to 10⁻⁶ 3 mbar, up to 10' 8 mbar, up to 10' 11 mbar, preferably below 10 11 mbar.

[0130] In a further preferred embodiment, the flow sensor is characterized in that an insulating layer is present between the thermopile and the heating element, wherein the insulating layer preferably comprises a material selected from a group comprising ceramic, glass, a polymeric material and / or a metal oxide, preferably an aluminum oxide, titanium oxide and / or silicon oxide.

[0131] The application of an insulating layer is another advantageous option for reliably ensuring thermal insulation between the heating element and the one or more thermocouples, preferably thermopiles. Analogous to providing a vertical gap or space, the insulating layer is preferably provided, in particular, in those areas where the one or more thermocouples, preferably a thermopile, cover the heating element, i.e., in areas where, in a projection of the flow channel along its vertical dimension (height), the one or more thermocouples, preferably a thermopile, overlap or intersect the heating element.

[0132] For example, if one or more thermocouples cover the heating element in a central area (between the measuring points) (see Fig. 3 and Fig. 4A), the insulating layer is preferably located in this central area. Preferably, the insulating layer is not located between the measuring points and a flow channel or fluid, so as not to impair the thermal contact between the measuring points and the fluid. The latter is particularly preferred if the flow sensor comprises a substrate and the flow channel runs at least partially, preferably completely, through the substrate. Applying an insulating layer between the heating element and the one or more thermocouples, preferably a thermopile, also prevents or at least reduces parasitic heat transfer (via a different heat path than through the fluid) and thus reduces Johnson noise.

[0133] The insulating layer can be provided, in particular, in those areas where the one or more thermocouples, preferably the thermopile, cover the heating element, i.e., in areas where, in a projection of the flow channel along its vertical dimension (height), the one or more thermocouples, preferably the thermopile, overlap or intersect the heating element. If, as shown in Fig. 3, the one or more thermocouples, preferably the thermopile, cover the heating element in a central region (between the measuring points), the insulating layer is preferably present at least in this central region. By applying an insulating layer between the heating element and the one or more thermocouples, parasitic heat transfer (via a heat path other than through the fluid) is advantageously avoided or at least reduced, thus reducing Johnson noise.

[0134] The aforementioned preferred materials for the insulating layer are particularly easy and cost-effective to process in semiconductor and / or microsystems technology and are also well suited for mass production. In particular, the aforementioned preferred materials for the insulating layer are also characterized by their good thermal insulation properties for the flow sensor in the context of the invention.

[0135] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor has a membrane which extends above the flow channel on a substrate.

[0136] The membrane is preferably held by at least two side walls of a support or support structure. The support or support structure may be enclosed by a substrate. Preferably, the support comprises four side walls on which the membrane is mounted. Preferably, the membrane is suspended across its entire surface within the remaining free area. The membrane's planar distribution indicates a lateral direction (width and / or height) of the flow sensor. The membrane preferably extends over a flow channel in the substrate, provided the flow channel runs through the substrate. If the flow channel is not formed within the substrate of the flow sensor, the membrane preferably extends above a cavity in the substrate.

[0137] The cavity preferably refers to a recess in the substrate or support structure that defines a void. The cavity or void can be open or closed to the surroundings of the flow sensor. The membrane is preferably held by the substrate or support structure in such a way that it extends over the cavity and defines an upper boundary of the cavity. The cavity is thus preferably located below the membrane and therefore below the thermal sensor. The support structure or substrate can preferably comprise one or more voids.

[0138] The planar design of the membrane preferably means that dimensions such as length and / or width are many times greater than a height or thickness perpendicular to them. Thus, the length and / or width can be greater than the thickness by a factor of 1.5, 2, 5, 10, 100, 1000, 10000 or more. Preferably, the thickness of the membrane is between 0.1 and 1000 pm, more preferably between 0.5 and 500 pm, particularly preferably between 1 and 300 pm, and most preferably between 5 and 200 pm.

[0139] The membrane is preferably configured in such a way that any vibrations caused by the fluid flow do not occur. Therefore, sufficient membrane stability is ensured, preventing any distortion of the measurement result due to modulation of the heat flow.

[0140] One, several, or all components of the thermal sensor can be positioned on the membrane.

[0141] Preferably, the flowing fluid flows in a flow channel, and the flow channel extends at least partially, preferably completely, through the substrate. Furthermore, it is preferred that the flow sensor has a membrane extending above the flow channel on the substrate.

[0142] Advantageously, the placement of the membrane above the flow channel achieves effective thermal insulation of the heating element and thermocouples from the substrate. This reduces heat loss into the substrate, improving energy efficiency and increasing sensitivity to flow changes.

[0143] Furthermore, the membrane enables precise positioning of the thermocouples upstream and downstream, which can be used for differential temperature measurement. This allows for particularly precise detection of temperature differences along the flow direction, leading to improved flow characterization.

[0144] The at least partial, preferably complete, integration of the flow channel into the substrate also allows for a particularly compact design of the flow sensor. This is especially advantageous for applications where installation space is severely limited, for example in medical technology, microfluidics, laboratory technology or industrial plants, without being limited to these exemplary applications.

[0145] Furthermore, the preferred design is compatible with established MEMS and / or semiconductor manufacturing technologies. This enables cost-effective mass production with high reproducibility and reliability.

[0146] In a preferred embodiment, the heating element is located on the membrane. Thus, the membrane preferably acts as an intermediate component between a flow channel and the heating element, particularly if the flow channel is formed within the substrate of the flow sensor (see Figs. 4A and 4B). The heat field provided by the heating element propagates across the membrane to the flow channel. The one or more thermocouples, preferably a thermopile, are also preferably located on the membrane. The heat field is modulated by the flow of fluid through the flow channel. This modulation of the heat field is measured by the one or more thermocouples, preferably by the thermopile, as described. At least one flow parameter of the fluid can be determined via the modulation of the heat field.

[0147] In a further preferred embodiment, the heating element is positioned below the membrane and within a flow channel, the flow channel preferably being formed in the substrate of the flow sensor (see Figs. 4C-4F). The one or more thermocouples, preferably a thermopile, are preferably located on the membrane. Due to the placement of the heating element within the flow channel, the fluid flows directly around the heating element. Advantageously, placing the heating element in the flow channel ensures a direct influence of the fluid on the heating element's thermal field. The modulation of the thermal field in the flow channel can be detected by the one or more thermocouples, preferably a thermopile, as described, which are located on the membrane.Furthermore, in this embodiment, the membrane can serve as a (partially) thermally insulating layer between the heating element and the one or more thermocouples to reduce thermal noise. However, thermal insulation by the membrane is preferably only provided if the membrane does not cause the same degree of thermal insulation at the measuring points of the one or more thermocouples. Otherwise, it is preferred that, if the membrane areas separate the measuring points from the fluid in the flow channel, the membrane does not have an excessively strong thermal insulating effect.

[0148] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor has a membrane which extends above a flow channel which is partially or completely present in the substrate of the flow sensor, wherein preferably one or more thermocouples, preferably a thermopile, are arranged above the membrane, wherein preferably a thermally conductive area, preferably a heat-conducting tube, is provided at a position of a measuring point of the one or more thermocouples, preferably a thermopile.

[0149] The preferred thermally conductive area serves in particular to improve thermal contact between a measuring point of one or more thermocouples and the fluid flowing in the flow channel. Any impairment of the thermal contact between the measuring point and the fluid caused by the membrane is specifically prevented by the incorporated thermally conductive areas at the measuring points of the one or more thermocouples.

[0150] In the context of the invention, a thermal contact preferably refers to a contact that enables heat transfer between the contacting components. An improved (e.g., direct) thermal contact is thus characterized by increased thermal conductivity, which allows for high heat transfer between the contacting components. By providing thermally conductive areas, the thermal contact at the measuring points of one or more thermocouples is advantageously improved to allow for particularly sensitive differential temperature measurement.

[0151] As a result, more accurate temperature readings can be obtained at the measuring points, allowing the precise determination of the temperature difference between a first and a second measuring point of one or more thermocouples, preferably a thermopile. In particularly preferred embodiments, the one or more thermocouples are located above the membrane, with the measuring points contacting the fluid in the flow channel via the thermally conductive areas, while the heating element is located below the membrane (see Figs. 4E, 4F). The thermally conductive areas have a higher thermal conductivity than the membrane material. In preferred embodiments, the thermally conductive areas preferably comprise a thermally conductive material, preferably with a thermal conductivity of 150 W / (m*K) (watts per meter Kelvin) to 500 W / (m*K).For example, the thermally conductive areas can be formed by silicon or metals, such as silver, copper, gold, and / or aluminum. In preferred embodiments, the thermally conductive areas can be designed as heat pipes, which preferably comprise entirely of a thermally conductive material or a rim of a thermally conductive material enclosing a cavity through which the fluid can propagate to the measuring point. The heat pipes can advantageously be provided using methods similar to those of semiconductor technology, such as vias made of (electrically) conductive material.

[0152] In a further preferred embodiment, the flow sensor is characterized in that the membrane comprises a dielectric material, preferably selected from a group comprising silicon nitride, silicon dioxide, aluminum oxide, aluminum nitride, polyimide and / or a polymeric material.

[0153] The preferred membrane materials have proven advantageous in that, in addition to their excellent design possibilities as mechanically stable and electrically non-conductive membranes, they also offer thermal insulation, thus reducing or preventing heat conduction through the membrane. This further improves the accuracy of the measurement results. Silicon nitride, for example, can be used as a preferred membrane material, having proven particularly advantageous with regard to processing, stability, and thermal properties.

[0154] In a further preferred embodiment, the flow sensor is characterized in that one or more connection pads are provided on a substrate for electrical contacting the heating element and / or the thermopile, wherein preferably an electrical connecting means is provided between the one or more connection pads, wherein the electrical connecting means is preferably selected from a group comprising one or more conductor tracks, conductor strips and / or wire connections, preferably wire bonds.

[0155] A connection pad preferably comprises an electrically conductive material, which is applied to a spatially restricted section of the flow sensor to enable electrical contact. Preferably, an insulating layer can be applied that delimits the section to be contacted in such a way that a free area remains. This free area can then be filled with the electrically conductive material.

[0156] Conductor tracks (also called conductive tracks or conductors) preferably refer to electrically conductive connections with a two-dimensional orientation, that is, along a plane, which can preferably also be called a conductor track or metallization plane. The connection between individual conductor track planes can preferably be provided by vias. To prevent short circuits or high leakage currents, a high degree of electrical insulation between the conductor tracks is preferred. Preferably, conductor tracks can be designed as elongated structures made of a conductive material, which have a significantly greater length (dimension along the electrical conductor) compared to their cross-sectional dimension. The conductor tracks can therefore also be referred to as conductor track strips, with a greater length than cross-sectional dimension.

[0157] Bond wires are an electrical connection method used particularly when components have been previously bonded. Bond wires are characterized by their exceptional thinness, which facilitates easy contact with component pins. A bond wire preferably has a diameter of approximately 15–500 pm, more preferably 15–100 pm, and most preferably 15–50 pm or 100–500 pm. A bond wire can be made of a material selected from the group consisting of gold, aluminum, copper, their compounds, and / or alloys.

[0158] A soldered connection preferably refers to an electrical connection made using a solderable material. The solderable material is preferably a material that melts after the application of a specific temperature, such that the melting process allows the material to spread and thus cover and / or fill a specific area. A preferred solder material may be selected from the group consisting of silver, copper, tin, zinc, their compounds, and / or alloys.

[0159] An electrically conductive adhesive is preferably characterized by the fact that solidification, and thus a permanent electrical connection, can be achieved without the application of pressure and / or heat. Instead, the electrically conductive adhesive solidifies after a specific time interval. An electrically conductive adhesive preferably comprises an adhesive and an electrically conductive filler. The adhesive may preferably be selected from the group consisting of epoxy (resin), silicone, acrylic, and / or bismaleimide. The electrically conductive filler may preferably be selected from the group consisting of gold, nickel, palladium, platinum, and / or silver.

[0160] A bump preferably refers to a substantially hump-shaped connecting element. The connecting element is characterized in particular by its hump-shaped design. This can be provided by electrically conductive material, especially by an electrically conductive adhesive and / or a solder material. Preferably, a plurality of bumps are used. Bumps can preferably be applied to an underside of the flow sensor to enable, for example, electrical contact with at least one section of a base plate. Bumps can preferably be applied by thin-film technology, electroplating, or stencil printing.

[0161] A via preferably refers to an essentially vertical electrical connection. Different levels of the flow sensor can be electrically connected to each other using a via. Preferably, to provide a via, a region of the substrate is removed, for example in the form of an essentially vertical cavity, and filled with a conductive material that extends vertically, i.e., along the height or thickness of the substrate.

[0162] The aforementioned preferred options for forming the connection have proven advantageous in that they are reliable and robust, and can be provided easily by a specialist using known state-of-the-art methods.

[0163] In another preferred embodiment, the flow sensor is characterized in that the heating element is an electrical heating element, preferably a heating resistor.

[0164] The heating element preferably refers to the component of the thermal sensor from which the heat field or heat flow originates by emitting thermal energy. An electric heating element preferably refers to a heating element capable of converting electrical energy into thermal energy, which is used as a heat field and transferred to the sensor component. In an electric heating element, the thermal energy or heat field is preferably generated by using an electrically conductive material through which an electric current flows and which is heated by Joule heating. A heating resistor has proven particularly suitable for this purpose, especially one comprising metallic alloys that do not melt and / or oxidize even at the particularly high temperatures they can generate.

[0165] In a further preferred embodiment, the flow sensor is characterized in that the heating element comprises a material selected from a group including silicon, polysilicon, aluminum, copper, gold, platinum, nickel, silver and / or tungsten, wherein the material preferably has a doping as a semiconductor material.

[0166] The preferred materials for the heating element, particularly the electric heating element, advantageously allow for a particularly high temperature without melting and / or chemical reactions (such as oxidation) of the heating element and / or other components. Furthermore, the preferred materials exhibit a high specific resistance, enabling a particularly compact design of the heating element. Doping, in the case of a semiconductor, allows for improved electrical conductivity and thus also improved heat transfer and convection from the heating element.

[0167] In a further preferred embodiment, the flow sensor is characterized in that it comprises a substrate with a front and a back side, and the thermal sensor is positioned on the front side of the substrate. Below the thermal sensor, within the substrate, is a flow channel, preferably formed by a partial removal of the substrate, starting from the back side. The flow channel has an inlet area for the fluid to enter the channel and an outlet area for the fluid to exit the channel, so that at least one flow parameter of the fluid can be measured based on the temperature response of the thermal sensor. The substrate is preferably monolithic.In this embodiment, a flow channel thus runs at least partially, preferably completely, through the substrate of the flow sensor.

[0168] Advantageously, the preferred flow sensor is characterized by a high degree of compactness. In particular, no multiple substrates or complex structures are required to provide a flow channel through which the fluid can flow. Instead, the flow channel of the flow sensor is preferably contained within a single substrate or wafer. This increases robustness and simplifies its fabrication. Furthermore, the preferred flow sensor advantageously has a low profile, which essentially corresponds to the height of the substrate or a flow channel formed within it. This allows for easy integration of the flow sensor, for example, into a base plate, enabling its use in a wide range of applications for measuring flowing fluids.

[0169] A further advantage of the preferred flow sensor is that it can be manufactured using simple and proven methods from semiconductor technology and / or microsystems technology. In particular, its manufacture is fast and cost-effective. The simplified manufacturing process results, among other things, from the fact that, if a monolithic substrate is used for the design of the flow channel, it is unnecessary to join different substrates together or to attach further components to one or more substrates. Instead of complex processes, the flow channel is formed by selectively removing material, preferably from the back side, within a monolithic substrate. This can essentially be accomplished in a single process step.The dimensions of the flow channel can be precisely adjusted to the desired application by removing the substrate, as explained below. This allows for the advantageous mass production of the flow sensor at low cost and with a high degree of reproducibility.

[0170] By creating the flow channel directly within the substrate through selective removal, a particularly fine structuring with high precision is advantageously possible. Furthermore, the precise design options of the preferred flow sensor, especially the flow channel, prevent undesirable turbulence that could occur within the flow channel, particularly at the inlet, and thus impair the measurement by the thermal sensor. In this respect, the preferred flow sensor can also achieve a high degree of sensitivity, enabling a particularly precise measurement of at least one flow parameter of the fluid.

[0171] Furthermore, the fluidic properties of the flow channel can be advantageously adjusted with particular precision and consistency. For example, the fluidic resistance of the flow channel according to the invention depends primarily on its width, which can be adjusted with extreme precision using known etching methods for the selective removal of the substrate. Error tolerances that could inherently arise during the formation of flow channels in composite stacks due to the joining technique are avoided. By forming the flow channel within the substrate, it can also be ensured that the dimensions of the flow channel remain constant and, in particular, are not influenced by the flow behavior of the fluid within the flow channel itself.

[0172] Furthermore, it is advantageous to provide particularly compact flow channels with widths of less than 100 pm, 50 pm, 30 pm or less.

[0173] Advantageously, an arrangement according to the invention of one or more thermocouples, which are positioned for differential temperature measurement along the flow direction of the fluid, can also be effectively positioned over such narrow flow channels in order to determine the flow parameters of a fluid as described.

[0174] The possibility of specifying a particularly precise fluidic resistance of the flow channel, which can be kept constant during the measurements, also means that the preferred flow sensor is particularly suitable for measuring fluid flows in a so-called bypass configuration.

[0175] In a bypass configuration, the flow of a fluid in a main channel is determined by measuring a pressure drop in a secondary channel, the so-called bypass. The bypass is typically fluidically connected to the main channel at an inlet and outlet, allowing the fluid to be introduced from the main channel into the bypass and a

[0176] The fluid can be returned from the bypass back to the main channel. Within the main channel itself, a flow restrictor is located between the inlet and outlet sections, causing a pressure drop. The pressure difference generated by the flow restrictor can be measured based on the resulting flow through the bypass channel, allowing conclusions to be drawn about the fluid's flow behavior within the channel.

[0177] In such a method, the measurement accuracy depends directly on the most precise possible setting of a fluidic resistance, which must also remain constant during the measurement to avoid distortions in the results. Both requirements can be easily and robustly ensured by the preferred flow sensor, whose flow channel is provided in a monolithic substrate.

[0178] In a further preferred embodiment, the flow sensor is characterized in that the flow channel has a height which essentially corresponds to a height of the monolithic substrate, wherein a width of the flow channel at its narrowest section is preferably smaller than the height of the flow channel, preferably by a factor of 1.5, 2, 3, 4, or more.

[0179] In a preferred embodiment, the preferred flow sensor is characterized in that the flow channel has a substantially constant width, for example of less than 500 pm, preferably less than 100 pm, 50 pm or less than 30 pm, and wherein the height of the flow channel preferably corresponds substantially to the height of the substrate.

[0180] In a further preferred embodiment, the preferred flow sensor is characterized in that the flow channel has at least one tapered and / or widened section, wherein the width of the tapered section is preferably less than 500 pm, preferably less than 100 pm, 50 pm or less than 30 pm, and wherein the height of the flow channel preferably corresponds substantially to the height of the substrate of the flow sensor.

[0181] The (minimum) width of the flow channel is preferably always smaller than the maximum height of the flow channel, which in particularly preferred embodiments is essentially constant and corresponds essentially to the height of the substrate or wafer. Preferably, the (minimum) width of the flow channel is smaller than the (maximum) height of the flow channel by at least a factor of 1.5, 2, 3, 4, or 5 or more. A minimum width preferably corresponds to the width of the flow channel at its narrowest point.

[0182] The (minimal) width of the flow channel is particularly important for the characteristics of the fluidic resistance. Accordingly, it may be preferable to provide a flow section with a constant width, preferably a small width compared to the height of the flow channel.

[0183] In this case, the thermal sensor is preferably positioned above any section of the flow channel, for example, in a central position with respect to an inlet or outlet region. A central positioning preferably means positioning the thermal sensor on the front side such that the thermal sensor is located substantially along half (the length) of the flow channel. It may also be preferred not to position the thermal sensor centrally on the front side of the substrate, but closer to the inlet or outlet region.

[0184] Providing a flow channel with an essentially constant width and height (corresponding to the height of the substrate) represents a particularly simple geometry for the flow channel, which both simplifies the manufacturing process and ensures a uniform, easily measurable flow behavior of the fluid within the flow channel.

[0185] Even for flow channels with a relatively small width, an arrangement of one or more thermocouples according to the invention can be advantageously positioned in a compact manner.

[0186] To increase the interaction area of ​​the thermal sensor with the fluid flowing in the flow channel, it may also be preferred to provide a widened section in the flow channel, wherein the widened section preferably has a greater width than other sections of the flow channel (such as, in particular, a tapered section). For embodiments of a flow channel in which the width varies, for example, to provide a widened section extending below the sensor component, it is further preferred that the height of the flow channel is essentially constant and corresponds to the height of the substrate or wafer.

[0187] In the case of a flow section with varying width, a tapered section preferably determines the fluidic resistance. A tapered section of the flow channel preferably refers to a section that has a smaller width compared to other sections of the flow channel.

[0188] In particular, this means that it is preferred that the flow channel does not have a constant cross-section. It is preferred that the flow channel has sections with different widths. The section of the flow channel with the smallest width can preferably be referred to as the tapered section in the context of the invention.

[0189] The height of the flow channel preferably corresponds substantially to the height of the substrate. In particular, the height of the flow channel corresponds substantially to the height of the substrate if the substrate was partially removed to create the flow channel. The height of the flow channel can also preferably be substantially the height of the substrate minus any remaining residual thickness. Thus, the height of the flow channel preferably refers to the dimension extending along the front and back of the substrate, i.e., between the side of the substrate where the thermal sensor is located and the opposite side from which the partial removal to create the flow channel was carried out. Preferably, the height of the flow channel is constant along its length or its course along the fluid direction.However, it may also be preferable for the height to vary. In the latter case, a maximum height preferably corresponds essentially to the height of the substrate.

[0190] In a further preferred embodiment, the flow sensor is characterized in that the flow sensor comprises a base plate, wherein the base plate has two openings which correspond to the inlet area for an inlet of the fluid into the flow channel and to the outlet area for an outlet of the fluid from the flow channel.

[0191] The base plate preferably refers to a component that acts as a support for a substrate, so that the substrate can be placed on the base plate.

[0192] Preferably, the back side of the substrate is attached to the base plate. The base plate comprises at least one, preferably two, openings, wherein in the latter case a first opening corresponds to the inlet region and a second opening to the outlet region of the flow channel. Here, "correspondence" preferably means that there is a fluidic connection between the inlet region and the first opening, as well as between the outlet region and the second opening of the base plate.

[0193] It may be preferred that the substrate is applied to the base plate in such a way that the inlet area is located essentially directly above the first opening of the base plate and the outlet area is located essentially directly above the second opening of the base plate. This allows for measurement by having the fluid first flow through the first opening of the base plate and the inlet area along the flow channel, and then exit the flow sensor after flowing through the outlet area and the second opening of the base plate. This embodiment is particularly preferred if the flow channel runs at least partially, and preferably completely, through a substrate of the flow sensor.

[0194] The inlet region represents a transition zone through which the fluid enters the flow channel from the surroundings of the flow sensor. Similarly, the outlet region represents a transition section of the flow channel through which the fluid can exit the channel. Therefore, when measuring at least one flow parameter with the flow sensor, it is preferred that the fluid flows into the flow channel from the inlet region and exits the flow channel from the outlet region.

[0195] In a further preferred embodiment, the flow sensor is characterized in that the base plate is essentially flat and forms a lower boundary of the flow channel and / or the base plate is a circuit carrier, preferably a printed circuit board.

[0196] A lower boundary of the flow channel preferably means that the base plate allows the flow channel to be covered from the rear. The base plate thus preferably forms a lower wall of the flow channel. While the flow channel is preferably laterally enclosed by a substrate, it is preferably bounded from above by a membrane and from below (except in the inlet and / or outlet areas) by the base plate.

[0197] The at least two openings on the base plate ensure that the fluid enters the flow channel via the inlet area and exits the flow channel via the outlet area.

[0198] A substantially flat design of the base plate on at least one side facing the substrate preferably means that the base plate has no unevenness, elevations, or depressions on the substrate-facing side, but is preferably essentially smooth to provide a smooth lower boundary of the flow channel. The side of the base plate facing away from the substrate may have such unevenness. Preferably, however, the base plate has an overall flat design in which the base plate has a substantially constant height or thickness. The height or thickness is preferably a multiple, more preferably by a factor of 2, 3, 4, 5, 10, or more, less than the length and / or width of the base plate.

[0199] Preferably, the base plate has a substantially uniform, flat geometric profile and, apart from the two openings, no further geometric structures. A substantially flat design of the base plate has proven advantageous for a precise fit between the substrate and the base plate.

[0200] Preferably, a bonding agent is applied between the back of the substrate and the side of the base plate facing the substrate, for example, on the base plate itself or on the back of the substrate, thereby connecting the flow sensor to the base plate. It is possible that some of the bonding agent, which may be an adhesive, for example, may penetrate into the flow channel. Consequently, the height of the flow channel would correspond to the height of the substrate minus the height of the bonding agent that penetrated. However, it is preferred that the height of the flow channel essentially corresponds to the height of the substrate. It is also preferred that the height of the flow channel is less than the height of the substrate. In particular, it is preferred that the bonding agent does not penetrate the flow channel substantially or only to a minimal extent.

[0201] In a further preferred embodiment, the flow sensor is characterized in that the substrate comprises a material selected from a group comprising glass, ceramics and / or a semiconductor material, wherein preferably the semiconductor material is selected from a group comprising monosilicon, polysilicon, silicon carbide, silicon germanium, germanium, gallium arsenide, gallium nitride and / or indium phosphide.

[0202] The aforementioned preferred materials for the insulating layer are particularly easy and cost-effective to process in semiconductor and / or microsystems technology and are also well-suited for mass production. These materials are also particularly well-suited for doping and / or coating to achieve the desired electrical, mechanical, thermal, and / or optical properties in specific areas. The aforementioned materials offer numerous advantages due to the applicability of standardized manufacturing techniques, which are also particularly suitable for the integration of other components, such as electronic circuits.

[0203] In another aspect, the invention relates to a flow sensor arrangement comprising a) a flow sensor as described above and b) a mainboard characterized in that the flow sensor is installed on the mainboard.

[0204] The average person skilled in the art recognizes that the explanations, technical features, definitions and advantages of the flow sensor and of preferred embodiments of the flow sensor also apply to the flow sensor arrangement according to the invention, and vice versa.

[0205] For the purposes of the invention, a flow sensor arrangement preferably refers to a device comprising at least the flow sensor and a mainboard. The mainboard preferably refers to a component that serves as a carrier for the flow sensor, so that the flow sensor can be placed on the mainboard.

[0206] In preferred forms, the flow sensor arrangement may also include a cover, for example a cap, which is connected to the main board in such a way that the flow sensor is enclosed within the housing-like components of the main board and cover.

[0207] Preferably, the back side of the flow sensor substrate is mounted on the main circuit board. In particular, the back side of a base plate can also be mounted on the main circuit board, with the substrate mounted on the base plate. The base plate preferably comprises two openings, wherein, in the latter case, a first opening corresponds to the inlet region and a second opening to the outlet region of the flow channel. Here, "correspondence" preferably means that there is a fluidic connection between the inlet region and the first opening, as well as between the outlet region and the second opening of the base plate.

[0208] It may be preferred that the substrate is applied to the base plate such that the inlet area is located essentially directly above the first opening of the base plate and the outlet area is located essentially directly above the second opening of the base plate. This allows for measurement using the flow sensor arrangement such that the fluid first flows through the first opening of the base plate and the inlet area along the flow channel, and then exits the flow sensor arrangement after flowing through the outlet area and the second opening of the base plate. The flow channel runs at least partially through the substrate of the flow sensor.

[0209] The mainboard preferably has mainboard openings that correspond to the openings in the base plate. The electronic circuit or processing unit can preferably be mounted on the mainboard, thus providing a data connection between the thermal sensor and the electronic circuit.

[0210] In another preferred embodiment, the flow sensor arrangement is characterized in that the main board is a circuit carrier, preferably a printed circuit board.

[0211] A circuit carrier preferably refers to a component comprising an electrically insulating material on which electrically conductive connections (traces) and / or electronic components or assemblies are located. A circuit carrier thus preferably refers to a carrier for electronic components or electrically conductive connections that serves both mechanical mounting and electrical connection. Since electronic components are preferably located on or in the circuit carrier, electrical connections are particularly prominent on or in the circuit carrier, mediated, for example, by wire bonds and / or traces. Therefore, the circuit carrier functions both as a mechanical support and as an electrical connection for realizing electrical functions. The electrical connections of the circuit carrier serve, in particular, for the electrical contacting of components.The insulating material of the circuit carrier preferably defines a basic shape of the circuit carrier, in particular to define a mechanical contact with the flow sensor.

[0212] A printed circuit board (PCB) is preferably used as the circuit carrier. A PCB preferably refers to the flat, well-known type of circuit carrier that includes electrical connections and provides mechanical support for surface-mounted and / or socketed components. Preferably, a PCB comprises fiberglass, an epoxy resin, and / or another composite material as insulating material. A PCB is advantageous in that the two openings corresponding to the inlet and outlet of the flow channel can be provided particularly easily.Furthermore, they are characterized by high stability, so that even the measurement of flows with high hydrodynamic pressure can still be carried out accurately and reliably using the flow sensor arrangement, without having to be exposed to the risk of possible mechanical deformations by the fluid and thus a falsification of measurement results.

[0213] Preferably, the circuit carrier, more preferably the printed circuit board, contains at least one electronic circuit which is electrically connected to the thermal sensor, preferably via a connection. The base plate in the form of a printed circuit board thus not only allows a fluidic connection of the flow sensor to a channel or container as a fluidic connection whose fluid content is to be measured, but can simultaneously provide control and / or evaluation electronics.

[0214] It is preferable that the connection between the base plate and the main board is made by means of a sealing ring, in particular a solder ring. Preferably, the solder ring can be connected to a further terminal to enable an electrical and mechanical connection between a flow sensor arrangement comprising the flow sensor and the base plate. The main board preferably has main board openings that correspond to the openings of the base plate. The electronic circuit is preferably mounted on the main board, thus providing a data connection between the thermal sensor of the flow sensor and the electronic circuit.

[0215] In another aspect, the invention relates to a system comprising a) a flow sensor according to the above or a flow sensor arrangement according to the above and b) a fluid line comprising a flow channel, wherein the fluid line and the flow sensor are connected to each other.

[0216] The average person skilled in the art will recognize that explanations, technical features, definitions and advantages of the flow sensor or flow sensor arrangement and of preferred embodiments of the flow sensor or flow sensor arrangement also apply to the system according to the invention, and vice versa.

[0217] A fluid line preferably refers to a device in which a fluid can spread. Thus, the fluid line can define a flow path for the fluid's propagation. For this purpose, the fluid line preferably comprises a cavity. In particular, the fluid line includes a flow channel. The cavity of the fluid line is specifically formed by the flow channel. The flow channel in the fluid line preferably forms a volume for the fluid's propagation.

[0218] In particular, the fluid line specifies a flow direction for the fluid, ensuring a flow through the fluid for influencing or modulating the heat field provided by the heating element.

[0219] It may be preferred that the fluid line forms a closed structure along its cross-section. In the context of the invention, this can also be referred to as a closed fluid line. A preferably present structure along its cross-section is an enclosure that completely encloses the fluid line. Exemplary embodiments of a closed fluid line include a pipe or a hose, but are not limited to these. It may also be preferred that the fluid line is at least partially open along its cross-section, i.e., that an enclosure in the cross-section is at least partially open, and therefore not necessarily completely closed.

[0220] Preferably, the flow sensor and the fluid line are connected in such a way that a fluid flowing through the flow channel can influence the heat field provided by the heating element in such a way that this influence or modulation can be detected by one or more thermocouples. For this purpose, it is particularly preferred that the sensor component of the flow sensor has thermal contact with the fluid flowing in the flow channel. This advantageously ensures that modulation of the heat field by the fluid can take place.

[0221] In a preferred embodiment, the flow sensor can be located within a fluid line (see Fig. 7). In particular, it is preferred that the flow sensor be located within the fluid line. This preferably ensures good thermal contact and prevents the fluid from influencing the heat field provided by the heating element.

[0222] It may also be preferred that the flow sensor is positioned in the fluid line such that it borders the flow channel. For example, it may be preferred that the flow sensor is inserted or embedded within a boundary of the fluid line. Furthermore, a section of this boundary may be open, particularly in the area of ​​the thermal sensor, to ensure stronger heat field transmission in a flow field and / or easier detection of heat field modulation.

[0223] Preferably, one or more thermocouples, preferably a thermopile, are arranged along the fluid flow direction, particularly along the flow channel of the fluid line, for differential measurement. For this purpose, a preferred first measuring point and a second measuring point of the one or more thermocouples are preferably positioned such that the first measuring point is located upstream of the second measuring point.

[0224] In a further embodiment, the system can also include a fluidic connection, wherein the fluidic connection enables a connection to a main channel, allowing the fluid to flow from the main channel into the flow channel via an inlet area and back into the main channel via an outlet area from the flow sensor. In this case, measuring the flow parameter in the flow channel preferably corresponds to measuring the flow parameter in a bypass channel.

[0225] In another aspect, the invention relates to the use of a flow sensor or a flow sensor arrangement or a system for measuring a flow parameter of a flowing fluid, preferably a fluid flowing in a flow channel.

[0226] The average person skilled in the art will recognize that the explanations, technical features, definitions and advantages of the flow sensor, the flow sensor arrangement and / or the system described above, as well as preferred embodiments thereof, also apply to use for measuring a flow parameter of a flowing fluid, preferably in a flow channel, and vice versa.

[0227] Preferably, the one or more thermocouples are positioned such that their sensitive measuring points are in thermal contact with the flowing fluid, with the thermocouples preferably positioned for differential temperature measurement along the flow direction of the fluid. This means that preferably a first measuring point of the one or more thermocouples is located upstream of the second measuring point of the one or more thermocouples. A displacement of a heat field due to the fluid flow can thus be directly detected based on the (voltage) signal of the one or more thermocouples, which is proportional to the temperature difference between the two measuring points.

[0228] Along a fluid flow direction, it is therefore preferred that a first measuring point of one or more thermocouples is arranged upstream of the second measuring point. Accordingly, a fluid flow, for example in a flow channel, causes the heat field to be shifted towards the second measuring point. Based on a temperature difference between the second measuring point and the first measuring point, it is possible to infer at least one flow parameter of the fluid.

[0229] In the case of a flow channel being formed in the substrate of the flow sensor, a fluid is preferably introduced into the flow channel for this purpose. This can be achieved in preferred configurations by means of a fluidic connection, which can, in particular, provide a connection to a main channel. Thus, the fluid can flow from the main channel into the flow channel via the fluidic connection and then back to the main channel via the fluidic connection. It is preferred that the first measuring point is positioned upstream of the second measuring point of one or more thermocouples, preferably a thermopile, along the flow channel on the substrate.

[0230] If no flow channel runs along the substrate of the flow sensor, the flow sensor can also be arranged such that the first and second measuring points of one or more thermocouples, preferably a thermopile, are in thermal contact with the fluid, which preferably flows in a flow channel. This ensures that a modulation of a heat field is generated by the flow, allowing the at least one flow parameter to be determined via a differential temperature measurement between a second and a first measuring point. Preferably, the flow sensor or a flow sensor arrangement can be installed within a fluid line, particularly within the flow channel, so that the fluid flows directly around the first and second measuring points.It may also be preferred that the flow sensor or flow sensor arrangement is positioned such that it adjoins a flow channel. For example, the flow sensor can be inserted into or embedded in the sheathing of a fluid line. It may also be preferred that the flow sensor is located on the outside of the sheathing of a fluid line. Furthermore, it may be preferred that a corresponding opening is provided in the sheathing to allow for improved thermal contact between the thermal sensor and the fluid.

[0231] In a preferred embodiment, the flow sensor, flow sensor arrangement or system is used to measure a flow parameter of a fluid in a main channel.

[0232] In this embodiment as well, a flow parameter of a fluid is preferably measured in a flow channel, whereby the flow channel itself does not constitute a main channel, but rather, based on the determination of a flow parameter of a fluid in the flow channel, conclusions can advantageously be drawn about a flow parameter in the main channel. This is preferably done by means of a so-called bypass configuration.

[0233] A bypass configuration preferably refers to the provision of a side channel (or bypass) to a main channel, into which the fluid to be measured can flow. The flow channel with which the thermal sensor is in thermal contact preferably forms the bypass. If the flow channel is formed within the flow sensor, the flow channel of the flow sensor forms the bypass or a section thereof. If the flow channel is formed in a fluid line to which the flow channel is connected, the fluid line forms the flow channel. A main channel in combination with a flow sensor or a flow sensor arrangement or system according to the invention, whose flow channel forms the bypass or a section thereof, is also referred to as a bypass configuration within the context of the invention.

[0234] In a bypass configuration, the fluid to be detected or measured flows within the main channel. The bypass is fluidically connected to the main channel, allowing fluid to be introduced from the main channel into the bypass and returned from the bypass back into the main channel. Furthermore, a flow restrictor is preferably located within the main channel in a bypass configuration.

[0235] Preferably, a flow restrictor is installed in the main channel and a fluidic connection between the flow sensor and the main channel is provided such that the inlet region of a flow channel borders a region of the main channel upstream of the flow restrictor, while the outlet region of the flow channel borders a region of the main channel downstream of the flow restrictor, so that a pressure difference across the flow restrictor can be measured by means of a flow of the fluid through the flow channel of the flow sensor.

[0236] The flow restrictor causes a pressure drop, creating a pressure difference, particularly between a section of the main channel at the inlet of the flow sensor (upstream of the flow restrictor) and a section of the main channel at the outlet of the flow sensor (downstream of the flow restrictor). This pressure difference forces the fluid into the bypass, with the magnitude of the pressure difference determining the flow velocity through the bypass. The fluid then flows from the main channel into the bypass and from the bypass back into the main channel.

[0237] The flow restrictor increases flow resistance within the main channel, resulting in a pressure differential. This can arise, without being limited to theory, from two effects. First, friction between the fluid and the surfaces of the flow restrictor (surfaces parallel to the flow) leads to a pressure drop that increases essentially linearly with the flow rate. Second, the end faces and their edges generate turbulence and thus a pressure drop that increases essentially quadratically with the flow rate. A pressure / flow characteristic curve therefore preferably comprises a combination of linear and quadratic components.

[0238] A flow restrictor may preferably be selected from a group comprising a measuring orifice (flow orifice) and / or a Venturi nozzle. It may also be preferred that the flow restrictor comprises a honeycomb structure or a vane structure. Preferably, the flow restrictor comprises the largest possible surface area oriented parallel to the flow direction within the main channel and the smallest possible cross-sectional area.

[0239] The bypass provides a fluidic connection to the main channel such that an inlet area of ​​the flow channel, for example, a flow channel in the substrate of the flow sensor, adjoins a region of the main channel upstream of the flow restrictor. An outlet area of ​​the flow channel, in turn, adjoins a region of the main channel downstream of the flow restrictor. Upstream and downstream are preferably defined with respect to the direction of fluid flow in the main channel. Positioning the inlet area upstream means that the inlet area is located upstream of the flow restrictor in the direction of fluid flow, while the outlet area is located downstream of the flow restrictor in the direction of fluid flow in the main channel. The pressure difference across or along the flow restrictor in the main channel can thus be measured by the flow sensor within the bypass.

[0240] The fluid flows from the main channel into the bypass. This is primarily due to the higher pressure at the inlet of the main channel compared to the outlet. This pressure difference results from the flow restrictor in the main channel and depends on the fluid's flow characteristics within the main channel, such as its flow velocity.

[0241] Within the bypass (or flow channel), the flow sensor, particularly the thermal sensor, can detect the fluid's influence on the heat field via the temperature response. This allows, for example, the determination of the fluid's flow behavior within the flow channel.

[0242] The temperature response, for example, is sensitive to the flow velocity in the bypass channel. Since the flow velocity in the bypass is directly related to the flow-dependent pressure difference in the main channel, this provides information about the flow in the main channel. The thermal sensor can also be used to obtain further properties or flow parameters of the fluid, such as heat capacity and / or thermal conductivity. This allows not only monitoring of the fluid's flow behavior in the main channel, but also of its composition.

[0243] In a further preferred embodiment, the use of the flow sensor, the flow sensor arrangement and / or the system is characterized in that the flow sensor is fluidically connected to a main channel via a fluidic connection.

[0244] Preferably, the fluidic connection allows a connection to a main channel, so that the fluid can flow from the main channel into the flow sensor via an inlet area and back into the main channel via an outlet area from the flow sensor.

[0245] In the context of the invention, the fluidic connection enables, in particular, a transition of the fluid from a main channel into the flow channel, which can be formed, for example, in a substrate of the flow sensor. If the flow channel is formed in the flow sensor, the transition specifically refers to an inflow of the fluid from the main channel into the flow sensor or the flow sensor assembly and an outflow of the fluid from the flow sensor or the flow sensor assembly back into the main channel. Thus, the fluidic connection defines a flow path for the fluid between the main channel and the flow sensor or the flow sensor assembly.

[0246] This allows for the advantageous optimization of the flow path between a main channel and the area of ​​the system where the measurement of at least one flow parameter is to be carried out. In particular, it can reduce or eliminate potential flow turbulence, enabling targeted, sensitive, and therefore reliable measurements.

[0247] In a further preferred embodiment, the flow sensor is connected to the fluidic connection via a base plate or a cover, wherein at least one opening is connected to the fluidic connection to provide an inlet area or an outlet area of ​​the flow sensor.

[0248] Therefore, a sufficiently stable connection between the fluidic port and the flow sensor or flow sensor assembly can be advantageously achieved. This can be done in particular by using a sealing material.

[0249] It may be preferred, for example, that the flow sensor, preferably comprising a base plate, is connected to a main circuit board. The main circuit board can be mounted on the base plate or the cover. The main circuit board preferably has main circuit board openings. The fluidic connection can preferably be connected to the main circuit board such that the fluid flows from the main channel through the fluidic connection and then via the inlet area into the flow channel. Subsequently, the fluid can exit the flow sensor via the main circuit board opening and the fluidic connection through the outlet area and return to the main channel. The electronic circuit can preferably be located on the main circuit board, which is connected to the flow sensor, in particular the thermal sensor, for controlling the heating element and / or evaluating the temperature response.

[0250] It may also be preferable for the flow sensor to be directly connected to a fluidic port, without a mainboard as an intermediate component. The connection between the flow sensor and the fluidic port can be facilitated via the base plate or the cover.

[0251] The fluidic connection preferably comprises a component that allows the fluid to pass into openings, for example, openings in the base plate and / or mainboard openings. The fluidic connection can preferably include one, two, or more connection areas designed to be connected to the openings of a base plate and / or mainboard openings, thereby providing a fluid connection, particularly to the inlet and outlet of the flow channel. Preferably, the fluidic connection can be formed by one or more pipes and / or hoses.

[0252] Preferably, the fluidic connection comprises a material selected from a group including plastic, plastic, metal and / or glass.

[0253] FIGURES

[0254] The aspects of the invention will be described below by way of example using figures, without being limited to these examples.

[0255] Brief description of the characters

[0256] Fig. 1 Schematic representation of a prior art measuring principle

[0257] Fig. 2-6 Schematic representation of preferred embodiments of the sensor according to the invention

[0258] Fig. 7 Schematic representation of a preferred embodiment of a system comprising a flow sensor and a fluid line

[0259] Detailed description of the figures

[0260] Fig. 1 illustrates a preferred thermal measurement principle from the prior art. For example, it is known in the prior art to position two thermopiles above a flow channel such that both hot spots are located above and in thermal contact with the fluid flowing in the channel, while the cold spots are arranged above a substrate that can serve as a heat sink. Here, the thermopiles are arranged such that the hot spot of a first thermopile is positioned upstream of the second thermopile. A heating element, for example in the form of a heating strip, is preferably positioned between the two thermopiles and generates a symmetrical heat field in the case of a stationary fluid (see temperature profile v=0).Depending on the flow velocity or other flow parameters of the fluid, the heat field will shift towards the downstream hot spot of the second thermopile (see temperature profile). In this case, the absolute temperature at the hot spot of the second thermopile (positioned downstream of the heating element) will be higher than the absolute temperature at the hot spot of the first thermopile (positioned upstream of the heating element).

[0261] Figure 1 shows the propagation of the heat field emanating from a heating element (not shown) and the temperature distribution along the flow direction (x-axis) in dashed lines. The position of the highest temperature or temperature plateau corresponds to the position of the heating element, while the temperature of the boundary regions preferably corresponds to the ambient temperature or the temperature at a heat sink (e.g., the substrate).

[0262] Unlike simple temperature sensors, thermopiles do not directly measure the temperature profile, but rather the temperature difference between the hot and cold junctions. The first measuring point of the thermocouple or thermopile is called the hot junction, hot end, or hot end. The other end is similarly called the cold junction, cold end, or cold end. The cold junction serves as a reference point for measuring the temperature difference.

[0263] When using two thermopiles, a first temperature difference ATi is measured between a hot spot positioned downstream of the heating element and a cold spot preferably above a substrate as a heat sink, and a second temperature difference AT2 is measured between a hot spot positioned downstream of the heating element and a cold spot preferably above a substrate as a heat sink.

[0264] AT1 denotes a temperature difference between a hot and cold junction of the first thermopile and can be measured directly via the thermopile's output voltage. Similarly, AT2 denotes a temperature difference between a hot and cold junction of a second thermocouple, which is proportional to the thermoelectric voltage of the thermopile.

[0265] Figure 1 illustrates AT1 and AT2. It is evident that AT1 and AT2, considered individually, allow the determination of the difference between the respective hot junctions of the first and second thermostatic junctions and the cold junctions.

[0266] The temperature differences also allow the determination of the temperature difference AT = AT2-AT1 between the two hot spots. It is advantageous that the cold spots of both thermopiles are located above the substrate and are therefore essentially the same for both thermopiles (see also Fig. 1, which shows that the temperature drops to the same value outside the heated area).

[0267] Based on the temperature difference AT, it is also possible to determine flow parameters of the fluid, such as the flow velocity v. The flow velocity v is proportional to AT, so the flow velocity can be determined from this: v ~ AT = AT2-AT1.

[0268] Thermopiles are characterized by extremely low signal-to-noise ratio, enabling highly precise temperature difference determination between a hot and cold junction. By calculating the difference in voltage signals or the difference between the two measured temperature differences AT2 and AT1, fluid flow parameters can be determined with high precision.

[0269] In the absence of flow, a heat field provided by a heating element is symmetrically distributed, and a temperature difference AT = AT2-AT1 of essentially 0 would be expected. This corresponds to the curve for v=0. Since there is no fluid flow at v=0, there is also no modulation of the heat field. Therefore, the heat field is symmetrical.

[0270] If the fluid flows in such a way that it spreads towards the second thermocouple, a heat field provided by one heating element is shifted accordingly towards the second thermocouple. This corresponds to the curve for v>0. Spatial symmetry of the heat field is therefore no longer present, so the temperature at the hot spot downstream of the heater in the second thermocouple is higher than the temperature at the hot spot upstream of the heater in the first thermocouple. Since the temperature differences are determined with respect to the same substrate as the heat sink, the temperature difference AT2 will also be higher than AT1.

[0271] According to the invention, it was recognized that while the thermopiles themselves can determine a temperature difference between the hot and cold junctions with high precision, determining a difference of temperature differences AT = AT2-AT1 can lead to a higher measurement fluctuation. Thus, a small difference between comparatively large temperature differences AT1 and AT2 can lead to a higher measurement uncertainty.

[0272] Furthermore, the combined thermal resistance of two thermocouples can increase the noise source. Any temperature differences between the cold junctions, which act as heat sinks for the respective thermopiles, can also further impair the accuracy of measuring a flow-dependent shift in the measurement signal.

[0273] Furthermore, the provision of two opposing thermopiles, whose hot and cold points are located above the sensor channel and above the substrate respectively, occupies a considerable area, which also results in minimum requirements with regard to the flow channels - for example, their lengths.

[0274] Therefore, there was a need to provide improved or alternative flow sensors.

[0275] Fig. 2 shows a preferred embodiment of a flow sensor 1 according to the invention as a top view, i.e., a view from above of a front face of the flow sensor 1. The flow sensor 1 for measuring at least one flow parameter of a fluid comprises a substrate 3 with a flow channel 11. Furthermore, the flow sensor 1 comprises a thermal sensor 5 including a heating element 7 for providing a heat field and a sensor component 9 for detecting a temperature response of the thermal sensor 5 as a function of the influence of the fluid flowing through the flow channel 11 on the heat field. The sensor component 9 comprises several thermocouples 10 forming a thermopile 23. The several thermocouples 10 are positioned along the flow direction SR of the fluid for differential temperature measurement.The thermal sensor 5, comprising the heating element 7 and the sensor component 9, is located above the flow channel 11 on a front side in the arrangement shown. Of course, an arrangement below the flow channel 11 on a rear side of the flow sensor 11 is also preferable. In particular, by arranging one or more thermocouples 10 along the flow direction SR of the fluid for differential measurement, factors that could impair sensitivity are reduced or eliminated.

[0276] The positioning of one or more thermocouples 10 along the flow direction SR for a differential temperature measurement enables the determination of a relatively small temperature difference between two measuring points M1 , M2 with high precision.

[0277] In contrast, as explained above, prior art methods have previously measured a small temperature difference by comparing two large temperature differences, which negatively impacted the sensitivity of the measurement. However, according to the invention, positioning one or more thermocouples 10 along the flow direction SR enables a direct measurement for differential temperature measurement.

[0278] This means, in particular, that a displacement of the heat field provided by the heating element 7 is determined directly as a temperature difference between the two measuring points M1, M2 of the one or more thermocouples 10, due to the flow of the fluid in the flow channel 11. The flow of the fluid in the flow channel 11 can also be described as a flux field, which preferably refers to a vector field that, in particular, indicates the flow velocity of the fluid within the flow channel 11. Preferably, the one or more thermocouples 10 are positioned such that their sensitive measuring points M1, M2 are in thermal contact with the flowing fluid, with the thermocouples 10 being positioned along the flow direction of the fluid for differential temperature measurement. That is, a first measuring point M1 of the one or more thermocouples 10 is located upstream of the second measuring point M2 of the one or more thermocouples 10.In this way, a shift of a heat field due to the flow of the fluid can be directly determined based on the (voltage) signal of one or more thermocouples 10, which is proportional to the temperature difference between the two measuring points.

[0279] A thermal contact preferably refers to a sufficient transfer of heat between the heating element 7 and the thermocouple 10, preferably a thermopile 23, particularly to its measuring points M1, M2. This allows a modulation of the thermal field due to the fluid flow at a thermocouple 10, preferably a thermopile 23, to be observed. The thermal contact thus refers in particular to the transport of thermal energy to the measuring points M1, M2 of the thermocouple 10, preferably the thermopile 23. A thermal contact does not necessarily require direct contact. Instead, heat transfer to the thermocouples 10 can also occur if an intermediate component, such as a thermally conductive area or a membrane (provided it is at least partially also thermally conductive), is placed between the heating element 7 and the measuring points M1, M2 of the thermocouples 10, preferably the thermopile 23.Preferably at least the measuring points M1 , M2 of the thermocouples 10, preferably of the thermopile 23, are in thermal contact with the fluid, but not necessarily a central area of ​​the thermocouples 10, preferably of the thermopile 23.

[0280] This eliminates the need to install at least two thermocouples 10 or thermopiles 23 that detect the shift of the heat field by forming a difference in the (voltage) signals of the respective thermocouples 10 or thermopiles 23.

[0281] The use of one or more thermocouples 10 according to the invention for direct differential temperature measurement along a flow direction SR of the fluid represents a departure from previous flow sensors, which always used the ability of the thermocouples 10 or thermopile 23 to measure temperature differences in such a way that a (fluid- or measurement-sensitive) hot spot was arranged in thermal contact with the flowing fluid, while a (fluid- or measurement-insensitive) cold spot was positioned in thermal contact with the substrate or support as a heat sink.

[0282] Instead, according to the invention, one or more thermocouples 10 are brought directly into thermal contact with the flow field of the fluid for differential temperature measurement.

[0283] Thus, the flow sensor 1 according to the invention enables a particularly high sensitivity. On the one hand, by positioning one or more thermocouples 10 along the flow direction SR, the displacement of the heat field can be measured directly at the flow field on the thermal sensor 5 for differential temperature measurement. On the other hand, the individual thermal resistances of the one or more thermocouples 10 do not add up. Noise signals, in particular thermal noise, which can add up in the case of two thermocouples 10 or thermopiles 23, are thus significantly reduced.

[0284] Because no heat sink, such as the substrate, is required for differential temperature measurement, the dependence of the measurement on external temperatures, such as the substrate temperature and / or the ambient temperature, is also eliminated or reduced. If these are subject to local fluctuations, the reference temperature can also fluctuate when using the cold junctions of the thermocouples or thermopiles in thermal contact with the substrate, which negatively affects the measurement accuracy.

[0285] Instead, the flow sensor 1, through the one or more thermocouples 10 for differential temperature measurement, enables a measurement specifically directed with respect to the displacement of the heat field, which minimizes noise sources or environmental influences.

[0286] Furthermore, the arrangement of the one or more thermocouples 10 along the flow direction SR for differential temperature measurement can be kept extremely compact. This advantageously eliminates the need to position cold junctions of the one or more thermocouples 10 in thermal contact with the substrate 3. Instead, the one or more thermocouples 10 can be arranged essentially above or below the flow channel 11, requiring minimal space.

[0287] A simplified structural design of the thermal sensor 5 also results from the elimination of the need for thermal grounding. Thermal grounding preferably refers to a design of the flow sensor 1 such that heat dissipation occurs in such a way that undesirable heat paths, which could, for example, distort the measurement, are interrupted. Advantageously, the effort required for such a design is eliminated, since a direct use of the temperature difference along the flow direction SR is possible, and thus the heat field is effectively utilized by the flow.

[0288] Fig. 3 shows another preferred embodiment of the flow sensor 1 as a top view, i.e., a view from above of a front face of the flow sensor 1. In the illustrated embodiment of the flow sensor 1, an insulating layer 13 is located between the thermopile 23 and the heating element 7. The insulating layer 13 is preferably located in a central region of the thermopile 23 and thus does not impair thermal contact between the measuring points M1 and M2 and the fluid in the flow channel.

[0289] The application of the insulating layer 13 is an advantageous option for reliably ensuring thermal insulation between the heating element 7 and the one or more thermocouples 10, preferably thermopiles 23, even in the central regions of the thermopile. Thus, the application of the insulating layer 13 between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23, also reduces Johnson noise. The insulating layer is therefore provided particularly in those areas where the one or more thermocouples 10, preferably the thermopile 23, cover the heating element 7, i.e., in areas where, in a projection of the flow channel along its vertical dimension (height), the one or more thermocouples 10, preferably the thermopile 23, overlap or intersect the heating element 7.

[0290] If, as shown in Fig. 3, the one or more thermocouples 10, preferably the thermopile 23, cover the heating element 7 in a central region (between the measuring points M1 and M2), the insulating layer 13 is preferably present at least in this central region. By applying an insulating layer 13 between the heating element 7 and the one or more thermocouples 10, parasitic heat transfer (via a different heat path than through the fluid) is advantageously avoided or at least reduced, thus reducing Johnson noise.

[0291] Fig. 4 shows in schematic form various embodiments of the flow sensor 1 in a cross-sectional view.

[0292] Fig. 4A shows the preferred embodiment of the flow sensor 1, in which the insulating layer 13 is located between a central region of the thermopile 23 and the heating element 7. Fig. 4A preferably depicts a sectional view of the flow sensor 1 along the flow direction SR of Fig. 3. The placement of the insulating layer 13 is an advantageous option for reliably ensuring thermal insulation between the heating element 7 and the one or more thermocouples 10, preferably thermopiles 23. By applying the insulating layer 13 between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23, Johnson noise is reduced.

[0293] The flow sensor 1 has a membrane 19 which extends above the flow channel 11 on the substrate 3. The membrane 19 serves in particular to cover the flow channel 11 and forms its upper boundary.

[0294] The membrane 19 is held by the substrate 3, which thus acts as a support for the substrate 3. Preferably, the membrane 19 has a planar configuration, which indicates a lateral direction of the flow sensor 1. The membrane 19 is preferably located above the flow channel 11. The planar configuration of the membrane 19 preferably means that dimensions such as length and / or width are many times greater than a height or thickness perpendicular to them. The membrane 19 is preferably configured such that any vibrations caused by the fluid flow are not transmitted or are transmitted only to a reduced extent. One or more or all components of the thermal sensor 5 can be positioned on the membrane 19. In preferred embodiments, the heating element is located on the membrane (see Figs. 4A and 4B). Thus, the membrane 19 then acts as an intermediate component between the flow channel 11 and the heating element 7.The heat field provided by the heating element 7 spreads across the membrane to the flow channel 11.

[0295] The one or more thermocouples 10, preferably a thermopile 23, are preferably also located on the membrane 19, with at least the measuring points M1 and M2 having thermal contact with the flow channel or fluid. The heat field is modulated as a result of the fluid flowing through the flow channel 11. The modulation of the heat field is measured by the one or more thermocouples 10, preferably by the thermopile 23, as described. At least one flow parameter of the fluid can be determined via the modulation of the heat field.

[0296] Fig. 4B shows another preferred embodiment of the flow sensor 1. In the illustrated embodiment of the flow sensor 1, there is a vertical gap between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23. This vertical gap preferably ranges from 0.1 to 100 pm, more preferably from 0.5 to 50 pm, and most preferably from 1 to 20 pm.

[0297] A vertical distance preferably refers to a distance along a vertical direction or height of the flow channel 11. The gap is also preferably located along a vertical direction, so that the gap thermally separates the heating element 7 from the one or more thermocouples 10, preferably the thermopile 23.

[0298] The dimensions of the vertical distance or gap refer in particular to the vertical distances (from top to bottom) that the heating element 7 and the thermocouples 10 have in those areas where the thermocouples 10, preferably a thermopile 23, cover the heating element 7, i.e., in areas where, in a projection of the flow channel 11 along its vertical dimension (height), the thermocouples 10, preferably a thermopile 23, sweep over or intersect the heating element 7. Particularly preferably, specifications regarding the dimension of the vertical distance or gap correspond to an average value for the distance between the heating element 7 and the one or more thermocouples 10 in those areas.

[0299] Provided that the thermocouples 10 have an increased central area between the two measuring points M1, M2 along their length and the thermocouples 10 cover the heating element 7 in the central area, as is the case in the present Fig. 4B, specifications regarding a vertical distance from the heating element 7 to the thermocouples 10 refer to that central area.

[0300] The aforementioned preferred distance ranges for the vertical distance and also the provision of a gap have proven to be reliable in enabling a continued sufficient transmission of the displacement of the heat field to the one or more thermocouples 10, preferably a thermopile 23.

[0301] Advantageously, the vertical distance, particularly with regard to the preferred dimensions, and the gap can increase thermal insulation between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23. This results in reduced heat transfer from the heating element 7 to the one or more thermocouples 10, preferably a thermopile 23, which occurs along a heat path independent of the fluid. Such heat transfer can also be described as paresial heat transfer and increases thermal noise in the measurement signal of the sensor component 9.

[0302] The inclusion of a gap between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23, is particularly advantageous in that Johnson noise is reduced.

[0303] Preferably, an ambient fluid, i.e., a fluid from the environment of the flow sensor, can be present in the gap. Particularly preferably, the ambient fluid is ambient air. The ambient fluid can preferably be introduced into the gap at a specific pressure range, for example, as a vacuum.

[0304] Fig. 4C shows another preferred embodiment of the flow sensor 1. Here, the heating element 7 is located below the membrane 19 and within the flow channel 11. The one or more thermocouples 10, preferably a thermopile 23, are located on the membrane 19. Due to the placement of the heating element 7 within the flow channel 11, the fluid flows directly around the heating element 7. Advantageously, placing the heating element 7 in the flow channel 11 ensures a direct influence of the fluid on the heat field of the heating element 7. The modulation of the heat field in the flow channel 11 can be detected by the one or more thermocouples 10, preferably a thermopile 23, as described above, which are located on the membrane 19. In addition, in this embodiment, the membrane 19 can serve as an insulating layer between the heating element 7 and the one or more thermocouples 10 to reduce thermal noise.

[0305] Fig. 4D shows a flow sensor 1 in which the heating element 7 is located below the membrane 19 and within the flow channel 11. The one or more thermocouples 10, preferably a thermopile 23, are located on the membrane 19. Furthermore, a gap exists between the one or more thermocouples 10, preferably the thermopile 23, as the sensor component 9, and the heating element 7. The gap is oriented vertically, thermally separating the heating element 7 from the one or more thermocouples 10, preferably the thermopile 23.

[0306] The dimensions of the vertical distance or gap refer in particular to the vertical distances (from top to bottom) that the heating element 7 and the thermocouples 10 have in those areas where the thermocouples 10, preferably a thermopile 23, as sensor component 9, cover the heating element 7, i.e., in areas where, in a projection of the flow channel 11 along its vertical dimension (height), the thermocouples 10, preferably a thermopile 23, sweep over or intersect the heating element 7. In particular, there is a raised central area between the measuring points M1 and M2 of the thermocouple 10. The thermocouples 10, preferably a thermopile 23, as sensor component 9, cover the heating element 7 in this central area. The specifications regarding a vertical distance from the heating element 7 to the thermocouples 10 as sensor component 9 refer to this central area.Advantageously, the gap can increase thermal insulation between the heating element 7 and the one or more thermocouples 10, preferably a thermopile 23, as sensor component 9. This results in reduced heat transfer from the heating element 7 to the one or more thermocouples 10, preferably a thermopile 23.

[0307] Figures 4E and 4F show another preferred embodiment of the flow sensor 1. In the illustrated embodiment, the flow sensor has a membrane 19 which extends above the flow channel 11 on the substrate 3. The one or more thermocouples 10, preferably a thermopile 23, are mounted above the membrane 19. At a measuring point of the one or more thermocouples 10, preferably a thermopile 23, a heat-conducting tube 21 is provided as a thermally conductive area. The thermally conductive area serves in particular to improve thermal contact between a measuring point of the one or more thermocouples 10 and the fluid flowing in the flow channel 11.Any potential impairment of the thermal contact between the measuring point and the fluid due to the membrane 19 is specifically avoided by the thermally conductive areas incorporated at measuring points M1 and M2 of the one or more thermocouples 10. As a result, more accurate temperature values ​​can be measured at measuring points M1 and M2, and thus the temperature difference between a first measuring point M1 and a second measuring point M2 of one or more thermocouples 10, preferably a thermopile 23, can be precisely determined. The one or more thermocouples 10 are located above the membrane 19, with the measuring points contacting the fluid in the flow channel via the heat-conducting tubes 21, while the heating element is located below the membrane 19.

[0308] In Fig. 4E, the heating element 7 is located directly below the membrane 19 and within the flow channel 11. In Fig. 4F, the heating element is located further below the membrane 19 and within the flow channel 11. The thermally conductive areas, referred to as heat pipes 21, preferably comprise a thermally conductive material entirely or an enclosing layer of a thermally conductive material, which encloses a cavity in which the fluid can propagate to the measuring point. The heat pipes 21 can advantageously be produced from (electrically) conductive material using methods similar to those used in semiconductor technology, such as through-hole plating.

[0309] Fig. 5 shows another preferred embodiment of the flow sensor 1. The flow sensor has two heating elements 7, in particular a first heating element 7a and a second heating element 7b, which are arranged substantially orthogonally to a flow direction SR of the fluid. The one or more thermocouples 10, preferably a thermopile 23, are preferably arranged substantially parallel to a flow direction SR of the fluid, between the two heating elements 7.

[0310] As explained above, it may be preferred to position a heating element 7, which is arranged substantially orthogonally to a flow direction SR of the fluid, between the two measuring points M1, M2 of one or more thermocouples 10. The one or more thermocouples 10 are preferably partially or completely covered by the heating element 7. If partial or complete coverage of the heating element by the one or more thermocouples is not desired, for example, to avoid direct temperature influence (i.e., preferably a temperature influence independent of the fluid), it may also be preferred to provide two heating elements.

[0311] Figure 5 shows such an embodiment in which two heating elements 7a, 7b are arranged essentially orthogonally to a flow direction SR of the fluid. The one or more thermocouples 10 are arranged essentially parallel to a flow direction SR of the fluid between the two heating elements 7a, 7b.

[0312] Along the flow direction SR of the fluid, it is therefore preferred that a first heating element 7a is located upstream of a first measuring point M1 of one or more thermocouples 10, preferably a thermopile 23, which in turn is located upstream of a second measuring point M2 of one or more thermocouples 10, preferably a thermopile 23, which in turn is arranged upstream of the second heating element 7b.

[0313] Both the first and the second heating element 7a, 7b generate a heat field, wherein preferably a temperature increase due to the heat field is essentially only measurable at the nearest measuring points M1, M2 of the one or more thermocouples 10.

[0314] Due to the fluid flow along the flow direction SR, the heat field of the first heating element 7a is displaced towards the one or more thermocouples 10, thus increasing the temperature in the region of the first (upstream) measuring point M1. Conversely, the heat field of the second heating element is displaced away from the one or more thermocouples 10, thus decreasing the temperature in the region of the second (downstream) measuring point M2.

[0315] Advantageously, a temperature difference between the first and second measuring points M1, M2 of the one or more thermocouples 10, preferably of the thermopile 23, can be measured, increased by both effects. In this embodiment, a particularly sensitive measurement can thus be carried out, whereby the arrangement of the heating elements 7 at a corresponding distance from the one or more thermocouples 10, preferably without overlap, avoids or at least reduces parasitic heat transfer (on a heat path other than through the fluid).

[0316] Fig. 6 shows a preferred embodiment of the flow sensor 1 in a three-dimensional view. The flow sensor 1 comprises a substrate 3 with a flow channel 11. Furthermore, the flow sensor 1 comprises a thermal sensor 5 including a heating element 7 for providing a heat field and a sensor component 9 for detecting a temperature response of the thermal sensor 5 as a function of the influence of the fluid flowing through the flow channel 11 on the heat field. The sensor component 9 comprises several thermocouples 10 forming a thermopile 23. The multiple thermocouples 10 are positioned along the flow direction SR of the fluid for differential temperature measurement.

[0317] The substrate 3 comprises a front and a back. The thermal sensor 5 is positioned on the front of the substrate 3, and the flow channel 11 is located below the thermal sensor 5 within the substrate 3. The flow channel 11 is formed by a partial removal of the substrate, starting from the back. The flow channel 11 has an inlet region 25 for the fluid to enter the flow channel and an outlet region 27 for the fluid to exit the flow channel 11, so that at least one flow parameter of the fluid can be measured based on the temperature response of the thermal sensor 5. The substrate 3 is preferably monolithic.

[0318] Advantageously, the preferred flow sensor 1 is characterized by a high degree of compactness. In particular, no multiple substrates 3 or complex structures are required to provide a flow channel 11 through which the fluid can flow. Instead, the flow channel 11 of the flow sensor 1 is preferably contained within a single substrate 3 or wafer. This increases its robustness and simplifies its fabrication. Furthermore, the preferred flow sensor 1 advantageously has a low height, which essentially corresponds to the height of the substrate 3 or of a flow channel 11 formed therein. Thus, the flow sensor 1 can be easily integrated, for example, into a base plate, so that it can be used for a wide variety of applications for measuring flowing fluids.

[0319] A further advantage of the preferred flow sensor 1 is that it can be manufactured using simple and proven methods from semiconductor technology and / or microsystems technology. In particular, its manufacture is fast and cost-effective. The simplified manufacturing process for the flow sensor 1 results, among other things, from the fact that, if a monolithic substrate 3 is used for the design of the flow channel 11, it is unnecessary to join different substrates together or to attach further components to one or more substrates. Instead of complex processes, the flow channel 11 is formed by selectively removing material, preferably from the back side, within a monolithic substrate 3. This can essentially be accomplished in a single process step.The dimensions of the flow channel can be precisely determined by adjusting the distance between the substrate 3 and the desired application. This allows for the advantageous mass production of the flow sensor 1 at low cost and with a high degree of reproducibility.

[0320] By forming the flow channel 11 directly within the substrate 3 by means of a partial removal, a particularly fine structuring with high precision is advantageously possible. Furthermore, the precise design option of the preferred flow sensor 1, especially the flow channel 11, allows for the avoidance of undesirable turbulence that could occur within the flow channel 11, particularly at the inlet region 25, and thus impair the measurement by the thermal sensor 5. In this respect, the preferred flow sensor 1 can also achieve a high degree of sensitivity, enabling a particularly precise measurement of at least one flow parameter of the fluid.

[0321] Furthermore, the fluidic properties of the flow channel 11 can be advantageously adjusted with particular precision and consistency. For example, the fluidic resistance of the flow channel 11 depends primarily on its width, which can be precisely controlled using known etching techniques for the selective removal of the substrate 3. This avoids inherent tolerances that could arise during the formation of flow channels 11 in composite stacks due to the joining technique. Moreover, by forming the flow channel 11 within the monolithic substrate 3, it can be ensured that the dimensions of the flow channel 11 remain constant and, in particular, are not influenced by the flow behavior of the fluid within the flow channel 11 itself.

[0322] Furthermore, particularly compact flow channels 11 with widths of less than 100 pm, 50 pm, 30 pm or less can advantageously be provided. Advantageously, the arrangement according to the invention of one or more thermocouples 10, preferably the thermopile 23, which are positioned for differential temperature measurement along the flow direction SR of the fluid, can also be effectively positioned via such a narrow flow channel 11 in order to determine the flow parameters of a fluid as described.

[0323] As illustrated in Fig. 6, it may be preferable to guide a heating element 7 with an elongated extension, where the dimension of one length is significantly larger than the cross-section of the heating element, for example by a factor of 2, 3, 5, 10 or more, across the width of the flow channel 11 in an orthogonal orientation to the flow direction SR. Corresponding connection pads 15 can also be positioned compactly on the substrate 3. A thermopile 23 is oriented for differential temperature measurement along the flow direction SR, with a first measuring point M1 positioned upstream of the heating element 7, while a second measuring point M2 is positioned downstream.An output signal of the thermopile 23 can be detected by means of corresponding connection pads 15, whereby, as described above, a displacement of a heat field by the flow of the fluid can be determined directly on the basis of the output signal of the thermopile 23, which is proportional to the temperature difference of the two measuring points M1 and M2.

[0324] Fig. 7 shows a preferred embodiment of a system 31. The system 31 comprises a flow sensor 1 and a fluid line 29, wherein the fluid line 29 and the flow sensor 1 are connected to each other.

[0325] The flow sensor 1 has a membrane 19 which is held by the substrate 3 and extends above a cavity of the flow sensor 1. The heating element 7 and the one or more thermocouples 10 are positioned on the membrane 19.

[0326] The flow channel 11 is a component of the fluid line 29. The fluid spreads within the flow channel 11, meaning that the flow channel 11, in particular, defines a flow direction for the fluid. The one or more thermocouples 10 are positioned along the flow direction SR for differential measurement. For this purpose, a first measuring point M1 and a second measuring point M2 of the one or more thermocouples 10 are preferably arranged such that the first measuring point M1 is positioned upstream of the second measuring point M2.

[0327] Reference symbol list

[0328] 1 flow sensor

[0329] 3 Substrat

[0330] 5 Thermal Sensor

[0331] 7 Heating element

[0332] 7a First heating element

[0333] 7b Second heating element

[0334] 9 Sensor component

[0335] 10 Thermocouple

[0336] 11 Flow channel

[0337] 13 Insulation layer

[0338] 15 connection pads

[0339] 17 Electrical connector

[0340] 19 Membran

[0341] 21 Heat pipe

[0342] 23 Thermopile

[0343] 25 Entrance area

[0344] 27 Exit area

[0345] 29 Fluid line

[0346] 31 System

[0347] M1 First measuring point

[0348] M2 Second measuring point

[0349] SR Flow direction Bibliography

[0350] Billat, S., et al. Monolithic integration of micro-channel on disposable flow sensors for medical applications. Sensors and Actuators A: Physical 145 (2008): 66-74.

[0351] Liu, Zemin, et al. "A Thermopile-Based Gas Flow Sensor with High Sensitivity for Noninvasive Respiration Monitoring." Micromachines 14.5 (2023): 910.

Claims

PATENT CLAIMS 1. Flow sensor (1) for measuring at least one flow parameter of a fluid comprising a substrate (3) and a thermal sensor (5) comprising a heating element (7) for providing a heat field and a sensor component (9) for detecting a temperature response of the thermal sensor (5) as a function of the influence of a flowing fluid on the heat field, wherein the sensor component (9) comprises one or more thermocouples (10), characterized in that the one or more thermocouples (10) are positioned for differential temperature measurement along a flow direction (SR) of the fluid.

2. Flow sensor (1 ) according to the previous claim characterized in that the flowing fluid flows in a flow channel (11), wherein preferably the flow channel (11) runs at least partially, preferably completely, through the substrate (3).

3. Flow sensor (1 ) according to one or more of the preceding claims characterized in that the multiple thermocouples (10) form a thermopile (23) such that the thermopile (23) is positioned for differential temperature measurement along the flow direction (SR) of the fluid.

4. Flow sensor (1) according to one or more of the preceding claims, characterized in that the differential temperature measurement is carried out between a first measuring point (M1) and a second measuring point (M2), wherein the first measuring point (M1) is located downstream of the second measuring point (M2) with respect to the flow direction (M2) of the fluid in the flow channel (11), wherein preferably the first measuring point (M1) and the second measuring point (M2) have a distance from each other of 0.5 - 1000 pm, preferably of 10 - 500 pm, particularly preferably of 20 - 200 pm.

5. Flow sensor (1) according to one or more of the preceding claims characterized in that the heating element (7) is positioned between the first measuring point (M1) and the second measuring point (M2).

6. Flow sensor (1) according to one or more of the preceding claims, characterized in that the flow sensor (1) has a processing unit, wherein the processing unit is designed to calculate, on the basis of an electrical measurement variable, preferably an electrical Voltage and / or an electric current, based on one or more thermocouples (10), preferably a thermopile (23), to determine at least one flow parameter of the fluid.

7. Flow sensor (1) according to one or more of the preceding claims, characterized in that the heating element (7) covers the flow channel (11) at least partially, preferably completely, in a direction substantially orthogonal to the flow direction (SR) of the fluid, and the one or more thermocouples (10), preferably a thermopile (23), are positioned along the flow direction (SR) of the fluid in the flow channel such that the heating element (7) is at least partially covered.

8. Flow sensor (1) according to one or more of the preceding claims, characterized in that the heating element (7) is arranged substantially orthogonally to a flow direction (SR) of the fluid and the one or more thermocouples (10), preferably a thermopile (23), are arranged substantially parallel to a flow direction of the fluid on the substrate (3) and / or the flow sensor (1) comprises two heating elements (7a, 7b), which are preferably arranged substantially orthogonally to a flow direction (SR) of the fluid, and wherein the one or more thermocouples (10), preferably a thermopile (23), are arranged substantially parallel to a flow direction (SR) of the fluid, between the two heating elements (7).

9. Flow sensor (1) according to one or more of the preceding claims, characterized in that the one or more thermocouples (10), preferably a thermopile (23), are positioned directly on the heating element (7), such that the one or more thermocouples (10), preferably the thermopile (23), contact the heating element (7), or a vertical distance of 0.1–100 pm, preferably 0.5–50 pm, and particularly preferably 1–20 pm is present between the heating element (7) and the one or more thermocouples (10), preferably a thermopile (23), or a gap is present between the one or more thermocouples (10), preferably a thermopile (9), and the heating element (7), wherein the gap is preferably filled with an ambient fluid, preferably ambient air, or an insulating layer (13) is present between the thermopile (9) and the heating element (7).wherein the insulating layer (13) preferably comprises a material selected from the group consisting of ceramics, glass, a polymeric material and / or a metal oxide, preferably an aluminum oxide, titanium oxide and / or silicon oxide.

10. Flow sensor (1) according to one or more of the preceding claims characterized in that the flow channel (11) extends at least partially, preferably completely, through the substrate (3) and the flow sensor (1) has a membrane (19) which extends above the flow channel (11) on the substrate (3), wherein the heating element (7) is preferably located on the membrane (19) so that heat is transferred to the fluid through the membrane (19) or the heating element (7) is placed below the membrane (19) and within the flow channel (11) so that the heating element (7) is preferably directly surrounded by the fluid in the flow channel (11).

11. Flow sensor (1) according to one or more of the preceding claims, characterized in that the flow channel (11) extends at least partially, preferably completely, through the substrate (3) and the flow sensor (1) has a membrane (19) which extends above the flow channel (11) on the substrate (3), wherein preferably one or more thermocouples (10), preferably a thermopile (23), are arranged above the membrane (19), wherein preferably at a position of a measuring point (M1, M2) of the one or more thermocouples (10), preferably a thermopile (23), a thermally conductive area, preferably a heat-conducting tube, is provided and / or one or more connection pads (15) are provided on the substrate (3) for electrical contacting the heating element (7) and / or the thermopile (9), wherein preferably an electrical connecting means (17) is provided between the one or more connection pads (15).wherein the electrical connecting element (17) is preferably selected from a group comprising one or more conductor tracks, conductor strips and / or wire connections, preferably wire bonds.

12. Flow sensor (1) according to one or more of the preceding claims, characterized in that the flow sensor comprises a substrate (3) with a front and a back, the substrate (3) is monolithic, and the thermal sensor (5) is positioned on the front of the substrate (3), and the flow channel (11) is located below the thermal sensor (5) within the substrate (3), which is preferably formed by a partial removal of the substrate (3), preferably starting from the back (R), wherein the flow channel (11) has an inlet region (25) for an inlet of the fluid into the flow channel (11) and an outlet region (27) for an outlet of the fluid from the flow channel (11), such that at least one flow parameter of the fluid can be measured on the basis of the temperature response of the thermal sensor (5).wherein preferably the flow sensor (1) comprises a base plate, the base plate having two openings which correspond to the inlet area (25) for an inlet of the fluid into the flow channel (11) and to the outlet area (27) for an outlet of the fluid from the flow channel (11).

13. Flow sensor arrangement comprising a) a flow sensor (1) according to one of the preceding claims 1-12 and b) a mainboard characterized in that the flow sensor (1) is installed on the mainboard.

14. System comprising a) a flow sensor (1 ) according to one or more of the preceding claims 1-12 or a flow sensor arrangement according to the preceding claim, and b) a fluid line (29) comprising a flow channel (11), wherein the fluid line (29) and the flow sensor (1) are connected to each other.

15. Use of a flow sensor (1) according to one or more of the preceding claims 1-12 for measuring at least one flow parameter of a flowing Fluids.

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