Sensor arrangement

Abstract

The invention relates to a sensor arrangement having at least one sensor unit and an evaluator, the at least one sensor unit being thermally energizable by means of a heater; wherein the sensor unit is designed to carry out an oscillating behavior depending on a gas property of a gas surrounding the sensor unit, in particular a thermal conductivity and / or a volumetric heat capacity and / or a temperature and / or a pressure, the sensor unit being excited by an excitation frequency, and wherein a first excitation frequency or a first evaluation frequency is used for a first measurement, and wherein a second excitation frequency or evaluation frequency is used for a second measurement wherein the first excitation frequency is different from the second excitation frequency or wherein the first evaluation frequency is different from the second evaluation frequency; and wherein the evaluator is designed to determine the thermal conductivity on the basis of the first measurement and to determine the volumetric heat capacity on the basis of the second measurement.

Description

Field of the Invention

[0001] Embodiments of the present invention relate to sensor arrangements and corresponding evaluation methods. Further embodiments relate to flow sensors having corresponding sensor arrangements and / or pressure sensors having corresponding sensor arrangements. Background Art

[0002] The output signal of a thermal flow sensor (usually a flow sensor) is affected not only by the flow rate (l / min), but also by the properties of the gas, e.g., such as density ρ, thermal conductivity k, and / or specific heat capacity c of the flowing medium. The gas properties in turn depend on the temperature and pressure. For example, if the gas composition, temperature, and / or pressure change with a constant flow rate, the output signal will also change, which may be misinterpreted as a change in the flow rate. Therefore, the thermal flow sensor is either calibrated for the gas / gas mixture or the gas properties must be determined by additional additional sensors to compensate the generated output signal using an algorithm. The signal compensation is more accurate when the sensor is directly adjacent to the flow sensor.

[0003] Therefore, the prior art is to calibrate the flow sensor to the gas properties (known pressure, temperature, and gas composition), or to allow signal compensation by additional independent MEMS sensors (environmental sensors). According to the prior art, sensors with different measurement principles must be integrated. In a typical sensor arrangement with low complexity, the thermal conductivity and volumetric heat capacity are not easily determined and thus cannot be calibrated. Therefore, an improved method is needed. Summary of the Invention

[0004] Embodiments of the present invention are based on the object of providing a concept that allows for the determination of volumetric heat capacity and thermal conductivity in a reliable and accurate manner using a measurement arrangement of low complexity.

[0005] This object is achieved by the subject matter of the independent claims.

[0006] Embodiments of the present invention provide a sensor arrangement, which includes at least one sensor unit and an evaluator. The at least one sensor unit can be thermally excited by a heater or can be excited to perform thermal oscillations. The sensor unit is configured to form a corresponding (thermal) oscillation behavior according to the gas properties of the gas around the sensor unit, in particular the thermal conductivity and / or the volume heat capacity and / or the temperature and / or the pressure. According to an embodiment, the heater, which is exemplarily implemented as a self-supporting bridge structure, performs oscillations. The sensor unit is excited by an excitation frequency, wherein a first excitation frequency or a first evaluation frequency is used for a first measurement, and wherein a second excitation frequency or a second evaluation frequency is used for a second measurement. The first excitation frequency is different from the second excitation frequency, and the first evaluation frequency is different from the second evaluation frequency. The evaluator is configured to determine the thermal conductivity based on the first measurement and to determine the volume heat capacity based on the second measurement. It should be noted here that according to an embodiment, the first excitation frequency and / or the second excitation frequency can be greater than or equal to 0 Hz. This also means that for the first measurement, the excitation (or the excitation for the second measurement) can occur at 0 Hz, which means that, for example, a DC current can be used for excitation. For example, the first excitation frequency is equal to 0, wherein the excitation energy for the first measurement is greater than 0. In the second measurement, for example, a second excitation frequency greater than 0 Hz is used. According to an embodiment, the second excitation frequency can of course be equal to 0 Hz, that is, a second measurement is performed using an excitation energy greater than 0, wherein in this case, a first measurement is performed using an excitation frequency greater than 0.

[0007] Embodiments of the present invention are based on the following finding: under different excitations, for example, using different excitation frequencies, which are associated with different physical groups, differential sensitivities to different physical parameters can be implemented, that is, for group 1 (including thermal conductivity) and for group 2 (including volume heat capacity). Due to the different excitations / different excitation frequencies and also due to the different evaluation frequencies, different high sensitivities to different physical parameters are formed, which allows the independent determination of the volume heat capacity cv and the thermal conductivity k. Here, the (single) sensor operates in a first frequency range, exhibits high sensitivity to the thermal conductivity k and at the same time exhibits low cross-sensitivity to the volume heat capacity cv. For the second measurement, the (same) sensor operates in a certain frequency range, exhibits high sensitivity to the volume heat capacity cv and at the same time exhibits low cross-sensitivity to the thermal conductivity k.

[0008] In other words, this means that, according to an embodiment, two measurements are performed using different excitations. Measurement 1 can be performed using a first excitation, for example, which includes a first excitation frequency, while a different excitation, for example, a larger or smaller excitation frequency, i.e., a different excitation frequency, is used to perform Measurement 2. Alternatively, it is also conceivable that Excitation 1 includes a DC excitation (excitation frequency equal to 0), while Measurement 2 is performed using a different excitation with an excitation frequency greater than 0. Another alternative is to evaluate the sensor at different evaluation frequencies.

[0009] According to an embodiment, the first excitation frequency differs from the second excitation frequency by at least a factor of 2 or at least a factor of 4, or even at least a factor of 10. Similarly, the first evaluation frequency and the second evaluation frequency can differ by at least a factor of 2, at least a factor of 4, or at least a factor of 8. Here, fixed first and second excitation frequencies or fixed first and second evaluation frequencies can be used.

[0010] According to an embodiment, the excitation frequency is determined as a function of the cut-off frequency of the sensor. For example, the first excitation frequency can be at least a factor of 2 or at least a factor of 4 smaller than the cut-off frequency of the sensor, where the second excitation frequency is at least a factor of 2 or at least a factor of 4 larger than the cut-off frequency of the sensor. According to an alternative / additional embodiment, the evaluation frequency can be at least a factor of 2 or at least a factor of 4 smaller than the cut-off frequency of the sensor, while the second evaluation frequency is at least a factor of 2 or at least a factor of 4 larger than the cut-off frequency of the sensor.

[0011] According to an embodiment, the result is the difference in sensitivity between the two measurements. For example, the sensitivity to volumetric heat capacity in the second measurement may be at least a factor of 3, at least a factor of 4, or at least a factor of 5 higher than the sensitivity to volumetric heat capacity in the first measurement. The sensitivity to thermal conductivity in the second measurement may be at least a factor of 1.1 or at least a factor of 1.2 higher than the sensitivity to thermal conductivity in the second measurement.

[0012] According to an embodiment, in the first measurement and the second measurement, or in the above special cases, in at least one of the two measurements, the sensor unit is excited by the excitation frequency. For example, periodic excitation can be performed by a square wave voltage. According to a further embodiment, it is also conceivable to configure the excitation frequency to be variable, for example, as a Chirp signal or as a Dirac signal. Here, different evaluation frequencies are selected for the first measurement and the second measurement for evaluation.

[0013] The common point of the above two variants is that, according to a further embodiment, the measurements can be performed at different time points (Measurement 1 is performed at time point t1, and Measurement 2 is performed at time point t2).

[0014] Sensor: According to an embodiment, the sensor unit may include a cavity having a heater, or a heat sink (or heating fins spaced apart from the heat sink) having spaced-apart heaters. The heater or heating fins may be configured to perform thermal oscillations, thereby forming (thermal) oscillation behavior. According to an embodiment, it is also conceivable that the heater is formed by heating fins, such as in the form of a self-supporting structure or a self-supporting bridge structure.

[0015] According to a further embodiment, the sensor unit includes a detector configured to detect the oscillation behavior. The detector may be arranged independently of the heater. According to a further embodiment, the detector may also be integrated in the heater as follows. The heater is excited to perform (thermal) oscillations, whereupon a resistance evaluation of the temperature signal can then be performed in the same heater. According to an embodiment, a current flows through the heater, which is made of, for example, metal or another electrically conductive material.

[0016] According to an embodiment, the evaluator is configured to determine the oscillation behavior of the sensor using the dynamic temperature response and / or using the amplitude and / or using the frequency and / or using the phase. According to an embodiment, the evaluator may be implemented as an ASIC. Here, the ASIC may be integrated in a chip or monolithically integrated in a chip that also houses the sensor unit.

[0017] Another embodiment provides a flow sensor that includes a corresponding sensor arrangement. The flow sensor is configured to determine the flow rate (volumetric flow rate or gas flow rate) taking into account the determined thermal conductivity and volumetric heat capacity. It is advantageous to perform the determination in a compensated manner here.

[0018] Another embodiment provides a pressure sensor that is configured to determine the pressure taking into account the volumetric heat capacity and / or the thermal conductivity.

[0019] In both applications of the pressure sensor and the flow sensor just mentioned, it is advantageous that, by determining the thermal conductivity and the heat capacity, the correct volumetric flow rate or the correct pressure can still be determined even if the gas or gas mixture may be unknown.

[0020] Another embodiment provides a method that includes the following steps:

[0021] - exciting the sensor (10) with an excitation frequency, where a first excitation frequency or a first evaluation frequency is used for a first measurement (M1), and where a second excitation frequency or a second evaluation frequency is used for a second measurement (M2), where the first excitation frequency is different from the second excitation frequency, or where the first evaluation frequency is different from the second evaluation frequency; and

[0022] - Determine the thermal conductivity (k) based on the first measurement (M1) and determine the volumetric heat capacity (cv) based on the second measurement (M2). According to a further embodiment, the method may be computer-implemented. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Before discussing embodiments of the present invention with reference to the drawings below, it should be noted that elements and structures with the same effect have the same reference numerals, and thus their descriptions are mutually applicable or interchangeable.

[0024] Figure 1a and 1b schematically shows, in a sectional view ( Figure 1a ) and a top view ( Figure 1b ), the sensor unit used in an embodiment;

[0025] Figures 2a - 2q shows a schematic view of the sensor unit used in an extended embodiment;

[0026] Figure 3a and 3b shows a schematic embodiment of a sensor arrangement including two sensor units according to a comparative aspect;

[0027] Figure 3c and 3d shows a schematic view for illustrating the potential sensor unit sizes according to an embodiment;

[0028] Figure 4a and 4b shows a schematic view discussing the sensitivity to thermal conductivity and volumetric heat capacity for two sensor units according to a comparative aspect;

[0029] Figure 5 shows a schematic circuit block diagram of a sensor unit including an evaluation electronic device according to a main embodiment;

[0030] Figure 6a and 6b shows a schematic view discussing the sensitivity to thermal conductivity and volumetric heat capacity for two sensor units according to an embodiment;

[0031] Figure 7a and 7b shows a schematic view for showing the sensitivity plotted against frequency to discuss potential configurations according to an embodiment;

[0032] Figure 8 shows a schematic view for showing the dependence between sensor sensitivity and the measurement gas;

[0033] Figure 9a 、 9b 、9c and 9d show schematic views of potential applications according to an embodiment; and

[0034] Figures 10a - 10c A schematic diagram showing an evaluator according to an extended embodiment is shown. Detailed description

[0035] Figure 1a A cross-sectional view of the sensor unit 10 is shown, and Figure 1b A top view is shown. The sensor unit 10 includes a heater 12 which is arranged, for example, as a self-supporting structure above a cavity 14. The cavity 14 can be embedded, for example, in a silicon substrate 16. The heater 12 can be excited to perform thermal oscillations by excitation of a driving frequency. Here, for example, an alternating voltage or current having a corresponding frequency flows through the heater. Starting from the excitation, the result is a frequency-dependent temperature overshoot, or, where applicable, a low-pass behavior. This temperature overshoot or low-pass behavior depends on geometric parameters and material properties. Basic geometric parameters are, for example, the height 12h of the heater, the width 12b of the heater, and the length 121 of the heater. Another parameter is the volume of the cavity 14, which basically depends on the height 14d of the cavity. The silicon substrate 16 or the lower side of the cavity 14 serves as a heat absorber for the heater 12, wherein the heat transfer in the heat absorber depends on the thickness 14d of the cavity 14.

[0036] The sensor unit 10 excited to oscillate in this way is configured to oscillate at a corresponding frequency. This frequency depends on the physical parameters of the surrounding gas on one side of the cavity 14 and on the side opposite the cavity 14 (for example, this side serves as the measurement side). For example, influencing factors are temperature, pressure, but especially thermal conductivity and volumetric heat capacity. Conversely, this allows determination of these physical parameters of thermal conductivity and / or volumetric heat capacity starting from the oscillation behavior of the heater. Here, the oscillation behavior is monitored, for example, by a detector (not shown).

[0037] The determination method is as follows:

[0038] - The heater is periodically excited (by current or voltage) and heated (Joule heating).

[0039] - The temperature of the heater changes and depends on the heat exchange with the surrounding gas (the gas to be analyzed / the gas surrounding the self-supporting thermal structure 12).

[0040] - Thermal conductivity and volumetric heat capacity affect the dynamic heat dissipation to the gas.

[0041] - Therefore, the dynamic temperature response (such as amplitude and phase) of the heater 12 can be measured, and for detection, resistance or thermoelectric monitoring of the thermal response can be performed. For example, the following heat transfer temperature T is obtained. T = function (L, h, b, d, k h , c vh , k gas , cvgas ) with the following alternative parameters: R heater = L / (h * b * k h ); C heater = c vh * b * h * L; R gas = d / (L * b * k gas ); C gas = d * b * L * cv gas .

[0042] If the gas exhibits different k gas and cv gas , the amplitude and dynamic behavior vary with frequency. The system exhibits high-pass behavior, i.e., the temperature decreases with increasing frequency and the phase shift increases with increasing frequency. In addition to the sensor-set dimensions, this frequency-dependent behavior may also depend on the gas properties. If an equilibrium is assumed between the width b of the heater and the scale factor of the width b gas of the effective heat transfer area to the gas, the cut-off frequency is described by the following relationship. For b gas = b, the scale factor can be eliminated and the following applies:

[0043]

[0044] It can be concluded therefrom that the lower the cut-off frequency, the lower the thermal conductivity and the higher the volume heat capacity. This means that an increase in pressure reduces the cut-off frequency of the system. An increase in temperature increases the cut-off frequency of the system. From a physics perspective, this background led to the discovery of the present invention, i.e., by using two sensor units with different set dimensions (possibly with different drive frequencies), for example, as Figure 3a or as shown in 3b, the thermal conductivity k gas or S k and the volume heat capacity S cv or cv gas can be determined independently of each other. Here, for example, a sensor with high sensitivity to thermal conductivity is combined with a sensor with high sensitivity to volume heat capacity.

[0045] According to an embodiment, the sensor includes at least one separate heating element, the surrounding gas volume of which is periodically heated and the temperature response of the heating element is determined. According to an embodiment, the sensor is read out equivalently or independently of each other by a temperature-dependent resistor and / or a thermal element:

[0046] ■ Variant 1, see Figure 5 and 6: scanning at least one sensor at two fixed frequencies or within two frequency ranges, where the sensitivity differences of the thermal sensor to thermal conductivity and volume heat capacity are large enough

[0047] ■ Variant 2: Two or more sensors (sensor array) are configured by geometric parameter variations (length, width, layer thickness, shape, height of the cavity) and / or different material properties such that the thermal coupling to the heat sink is different and combined, so that when operating in one or more selected frequency ranges or at a fixed frequency, the sensitivity to thermal conductivity and volumetric heat capacity varies sufficiently

[0048] Figure 3a A sensor arrangement 20 including a first sensor 10a and a second sensor 10b is shown as a comparative example. It can be recognized that the sensors are sized differently, where the basic principle corresponds to Figure 1a and Figure 1b the basic principle. Both sensor units 10a and 10b face the gas to be inspected, with their sides facing away from the cavity, or both sensor units 10a and 10b are embedded in the device for gas exchange, for example, with a dry gas without particles.

[0049] Potential variation parameters for the different sizing of (the two) sensor units are, for example:

[0050] ● Geometric parameters (length, width, layer thickness)

[0051] ● The heater can be formed by several heaters (e.g., two heaters in parallel, a combination of several types of heaters)

[0052] ● Types of heaters (holes, e.g., honeycomb structure, with film, curved, …)

[0053] ● Materials / material combinations (thermal properties, passivation, etc.)

[0054] Figure 3 shows a slightly different setup, where the sensors 10a and 10b in the sensor arrangement 20’ are indirectly coupled via an enclosed volume. This enclosed volume has the reference numeral 15 and is encapsulated relative to the environment by a membrane 17. The gas to be measured or the medium, liquid or particulate - contaminated gas to be measured acts on the membrane 17.

[0055] It can be clearly recognized that in Figure 3a the embodiment and Figure 3b the embodiment, the sizing of the sensor units 10a and 10b is different. This means that different sensitivities will be produced for the quantity to be measured with respect to the volumetric heat capacity cv and the thermal conductivity k. For example, when looking at Figure 4a and 4b , this principle can be clearly seen.

[0056] Figure 4a Shows the sensitivity S to thermal conductivity plotted against frequency for two different sensors k whileFigure 4b Shows the sensitivity S to the volumetric heat capacity plotted again against frequency for the same two sensors cv . It can be seen that sensor 2 is more sensitive than sensor 1, especially in the frequency range of 10 - 100 Hz, where sensor 1 shows increased sensitivity over the entire frequency range or at least up to 1000 Hz. In these examples, the sensitivity difference between sensor 1 and sensor 2 is not significant, so the operating points of sensors 1 and 2 are important here. For example, if the operating point is chosen to be 350 Hz, then sensor 1 is preferred in terms of the sensitivity to thermal conductivity. It should be noted here that the discussion of the operating point is only exemplary and varies from sensor to sensor. In Figure 4b the figure of cv , the sensitivity S to the volumetric heat capacity is plotted for two sensors 1 and 2 cutoff，S2 . It can be seen that there is significantly higher sensitivity in sensor 2 compared to sensor 1. Here, the operating point will be selected in the range between 350 and 1000 Hz, and sensor 2 operates at the cut-off frequency f

[0057] . In this range, sensor 1 preferably shows good sensitivity to thermal conductivity, so that when the two sensors are operated at the same excitation or evaluation frequency, two different sensors can be used to independently determine the volumetric heat capacity and thermal conductivity from each other. cutoff,S2 below (e.g., at 1 / 3 of the cut-off frequency f cutoff，S2 ) to determine the thermal conductivity. Sensor 2 will operate in the range at or slightly above the cut-off frequency f cutoff，S2 to determine the volumetric heat capacity.

[0058] The result is different operating modes corresponding to different comparative examples:

[0059] - Different set sizes + different frequencies

[0060] - Different set sizes + same frequencies

[0061] Evaluation: When talking about frequency in the embodiments, the excitation frequency or the evaluation frequency can be assumed. For example, a sensor can be excited at one frequency and evaluated at another frequency. For example, this is advantageous when using a chirp signal or a Dirac signal and is subjected to different frequencies. Alternatively, a fixed excitation frequency can be used for both sensors or for the respective sensors 10a and 10b or for two measurements.

[0062] The common point of the above comparison examples is that two thermal sensors or at least two thermal sensors are excited and read out independently of each other, so that the different sensitivities of two sensors that are operated differently or implemented differently can be utilized. The sensitivity can be calculated as follows:

[0063]

[0064] As described above, the sensitivity can be adjusted via the operating point.

[0065] The common point of all the above comparison examples is that at least two sensors / sensor units with different set sizes (e.g., differing by at least one order of magnitude) are combined. For example, these can be integrated (i.e., monolithically) on a silicon chip, so as to form different dynamic behaviors with heat propagation in the gas. Different operating points, similar to the different sizes / set sizes of the sensors, provide a basis for allowing the determination of the gas properties by utilizing the amplitude and / or phase position of the heater to be determined through dynamic excitation.

[0066] The typical sizes of the sensor units will be indicated below as exemplary examples. Here, all the sizes can occur combinatorially or individually:

[0067] ■ Length of the heater: 10 - 1000 μm

[0068] ■ Width of the heater: 1 - 200 μm

[0069] ■ Width of heat transfer: 1 - 500 μm

[0070] ■ Height of the heater: 0.1 - 2 μm

[0071] ■ Height of the cavity: 0.05 - 500 μm

[0072] Using these sizes, sensor units with different set sizes can be manufactured, and thus, different oscillation behaviors are generated. The oscillation behavior is particularly represented by the cut-off frequency f cutoff to represent. In Figure 3c four different sensors are listed and shown in the corresponding graphs (amplitude vs. phase and phase vs. frequency), which have different cut-off frequencies and thus different oscillation behaviors. It can be recognized that by changing the cavity height d, a significant shift of, for example, 10 times the cut-off frequency can be achieved. The sensor is configured for a constant pressure of, for example, 1 bar and a varying temperature in the range of 10 to 60 °C. Even with a constant temperature (e.g., 24 °C) and a varying pressure in the range of 0.5 to 3.0 bar, the results are similar, as can be recognized in Figure 3d Four sensors are also shown here, where it can again be recognized that the cavity height (usually the height of the heating element above the radiator) has an impact on the cut-off frequency fcutoff Has a significant impact.

[0073] Excitation: In the above comparative example, for example, it has been assumed that the heater is periodically excited by a square wave signal and a sine signal, where the responsiveness of the heater, i.e., the oscillation behavior or thermal oscillation behavior of the heater, can be monitored by only a few thermal elements or resistance changes. For example, at an excitation of 1 kHz, the result of the modeling is that the amplitude (and phase) of the heater shows a dependence on the gas pressure for a gas volume (d = 50 μm, b = 20 μm) (large), and is insensitive to temperature changes. The amplitude of the heater shows a dependence on the gas temperature for a gas volume (d = 5 μm, b = 5 μm) (small), but is insensitive to pressure changes. In this example, it is also shown that it is advantageous to preferably combine two or more sensor units with different set dimensions (d, b, L) on the chip, and, in addition to determining the volume heat capacity and thermal conductivity, it also allows providing a wide range of sensors for different measured quantities of temperature and pressure. According to the comparative example, a gas-independent wide-range pressure sensor (from a few millibars to a few bars) can be provided without any mechanical components (diaphragm). Of course, using this comparative example, the gas properties (determining the thermal conductivity and volume heat capacity) can also be determined. In the next step, this allows determining the so-called temperature conductivity or the product of density and thermal conductivity. Note: Temperature conductivity is defined as thermal conductivity / (density * specific heat capacity), i.e., a = k / (ρ * c). These quantities can be advantageously used for precise on-chip signal compensation in flow sensors or pressure sensors, as will be discussed below with reference to FIG. 9. It should also be noted here that in order to provide sensors with different set dimensions, the geometry of the heater can also be varied. Bent shapes, honeycomb heating structures, thermal mirrors, as discussed in connection with FIG. 2, are conceivable.

[0074] According to an embodiment, an arrangement of the sensors of FIG. 3 or 5 using a microtechnology manufacturing method can be produced to be compatible with another (thermal) sensor process, thus providing a high degree of integration for multi-parameter applications (such as gas composition and flow rate). Due to the small dead volume, this arrangement can additionally be operated as highly dynamic. According to an embodiment, an isolated heating structure surrounded by gas is realized by sacrificial layer technology (surface micromachining) or bulk micromachining (dry etching,...). The heating element provided in this way can be periodically heated by Joule heating. At the same time, the temperature response of the heater is monitored. This arrangement allows for significant miniaturization of the sensor structure. The properties of the gas affect the resulting temperature response (amplitude, phase shift) of the heating element. Due to the small space requirements, several of these sensors can be easily integrated with a wafer-level thermal flow sensor. In addition, only the thermal conversion principle is employed. This combination makes the system unique.

[0075] According to the comparative example, the sensor is sufficiently insensitive and can operate in the same frequency range, for example, if the resulting cut-off frequencies differ by at least a factor of 10 due to changes in geometric parameters (length, width, layer thickness, shape, height of the cavity) and / or different material properties.

[0076] Examples of reducing the cut-off frequency

[0077] - Increase the length of the heater

[0078] - Increase the height of the cavity.

[0079] According to an embodiment, by using an excitation below the cut-off frequency, a high sensitivity to thermal conductivity is obtained. For a high sensitivity to volumetric heat capacity, an excitation above the cut-off frequency is advantageous.

[0080] ■ The gas properties can be derived using the signal amplitude and / or phase shift

[0081] ■ The measured gas properties (k and cv) are used for direct signal compensation in the heat flux sensor and / or for determining the gas composition and pressure

[0082] According to an embodiment, by specifically changing the excitation or the excitation frequency, certain sensor geometries become selective to the measured quantity and insensitive to certain cross-influences. This applies to different sensor geometries, but also to the same sensor geometry. Thus, the embodiment provides a sensor system including a sensor unit and an evaluator, as will be shown in reference Figure 5 shown.

[0083] Figure 5 A sensor unit 10 including a heater 12, a cavity 14, and a substrate 16 is shown, together with an evaluator 50. The evaluator 50 is used to drive the sensor unit 10 and is configured to drive the sensor unit with at least two different excitation variations, for example, by two different excitation frequencies. For example, for certain environmental conditions, a sensor with a cut-off frequency can be excited by a frequency significantly lower than the cut-off frequency, for example, at half (1 / 2) or one-third (1 / 3) or one-fourth (1 / 4) of the cut-off frequency (first measurement), and for a second measurement, it can be excited by an excitation frequency significantly higher than the cut-off frequency, for example, at twice or three times the cut-off frequency (preferably 3 to 20 times the cut-off frequency). This means that, generally, the first measurement and the second measurement taken at different time points are different because different excitation frequencies are used, preferably an excitation frequency less than 1 / 2 or less than 1 / 4 of the cut-off frequency and / or an excitation frequency greater than three times the cut-off frequency. Thus, the sensor unit 10 can be operated at different operating points.

[0084] As can be seen from Figure 6a and 6bAs can be seen, operations at different operating points allow for different sensitivities to thermal conductivity and volumetric heat capacity. Accordingly, the evaluator 50 is configured to determine the thermal conductivity by a first measurement (operating point below the cut-off frequency) and to determine the volumetric heat capacity by a second measurement (operating point above the cut-off frequency). Figure 6a and 6b The figures of Figure 6a and 6b show two exemplary selected operating points or frequencies for the two measurements. This operating mode is advantageous because the volumetric heat capacity and the thermal conductivity can be determined independently of each other using only a single sensor. The advantage of the variant of Figure 3 is that the measurements are carried out simultaneously, whereas in Figure 5 the measurements are carried out serially, i.e. at different points in time.

[0085] According to an embodiment, the sensor can, for example, exhibit sufficient insensitivity to the cross-influence of gas properties that will not be measured in the current measurement, for example, if it is operated in a first frequency range that is approximately 4 times lower than the cut-off frequency in the first measurement and, for the second measurement, in a second frequency range that is approximately 4 times higher than the cut-off frequency of the sensor system.

[0086] According to an embodiment, the excitation frequency for determining the thermal conductivity can be lower than the cut-off frequency, such as less than 1 / 4 or less than 1 / 2. According to a further embodiment, the excitation frequency for determining the volumetric heat capacity can be higher than the cut-off frequency, such as about 3 to 20 times higher, or, generally, 2 or 3 times higher. In these regions, the sensitivities S k and S cv are different. According to an embodiment, the cut-off frequency depends on the size of the sensor or the implementation of the sensor. This means that, according to an embodiment, taking into account the above-described dependence on the cut-off frequency, the operating points for the first measurement and the second measurement will be selected differently, and the correlation between the sensor set size and the selection of the operating point will be applied.

[0087] According to an embodiment, regardless of the set size of the structure, a high sensitivity to thermal conductivity can be obtained at low frequencies. According to an embodiment, the frequency can also be f = 0, which corresponds to DC operation. This means that the excitation frequency is in the range f ≥ 0, i.e. close to zero, for example. According to an embodiment, the excitation frequencies are different, i.e. have different amplitudes. According to an embodiment, at high frequencies, the structure is insensitive to thermal conductivity (S k is close to 0). According to a further embodiment, the sensitivity to the volumetric heat capacity can include a local maximum.

[0088]

[0089] It is known from the literature that specific optimization (both geometry and frequency) is not possible based on a parametric model. Subsequently, it is necessary to find suitable optimum values for the operating points of the sensor arrangement.

[0090] Regarding the determination of the sensitivity to thermal conductivity and volumetric heat capacity, refer to the above formula and discuss it in conjunction with FIG. 3.

[0091] According to a further embodiment, the sensor 10 can also be excited with a varying signal (such as a Dirac signal) instead of changing the excitation frequency with two fixed frequencies. For example, it can then be evaluated at different frequencies at which the corresponding sensitivities to thermal conductivity and volumetric heat capacity are formed. This principle has been discussed in conjunction with FIG. 3 (see "Evaluation"), but according to the embodiment, it can be transferred to Figure 5 the implementation of. The potential variations of the excitation signal have been discussed in conjunction with FIG. 3 (see "Excitation"). Regarding the dependence on the sensor size, refer to the set size variations in FIG. 3.

[0092] According to an embodiment, Figure 2a one of the sensors of -q can be used as the sensor 10.

[0093] It will be combined with Figure 9a and, in particular, in combination with Figure 9b -d, discuss Figure 5 the application of the sensor system of. For example, Figure 5 the sensor system in or in combination with Figure 5 the operating method for operating the sensor discussed can be used for a wide range of sensors, such as wide range pressure sensors. Furthermore, according to a further embodiment, Figure 5 the sensor system in or the corresponding operating method can also be used for flow measurement (compensated flow sensor) or for applications compensating pressure sensors.

[0094] Regarding excitation, it should also be mentioned that, for example, it is possible to alternate and jump between two frequencies to achieve high sensitivity to thermal conductivity and volumetric heat capacity (such as a pure sine signal or using harmonics). At least two different excitations are used for one, two or more sensors (depending on the setting of FIG. 3 or Figure 5 ). The result is a modulated periodic excitation with two evaluation frequencies for thermal conductivity and volumetric heat capacity. In addition to the sine-shaped excitation, potential periodic signal shapes are square wave signals or sawtooth signals.

[0095] Different sensor units will be discussed below with reference to Figure 2a -o, and these sensor units can all be used in the above examples (embodiment or comparative example).

[0096] Figure 2a Shows Figure 1a and 1b the known sensor 10 in, which has a heater 12 above the cavity 14. In Figure 2bIn [the figure], a bent heater 12' above the cavity 14 is shown. In the embodiment, it is shown that different set dimensions are achieved by varying the different geometries of the heater 12', because the heater 12' is significantly longer than the heater 12. Both the heaters 12 and 12' are self-supporting structures or self-supporting bridge structures located above the cavity 14.

[0097] Figure 2c A self-supporting bridge structure is also shown, but the cross-section of the feeder line is increased. This means that the temperature point of the heater 12” is formed at the center. In Figure 2d a similar temperature point is also formed in the heater 12” in [the figure], because the bent shape is specifically arranged at the center of the cavity. Here, the cavity 14' is enlarged relative to Figure 2b the cavity 14 in [the figure]. Figure 2a 、 2b All the previous variants of 2c and 2d have one thing in common, that is, the cavity is basically rectangular. However, as shown, for example, in Figure 2e the figure, this is not absolutely necessary.

[0098] Figure 2e A sensor unit including a circular cavity 14” and a spiral heater 12”” is shown, which has a two-dimensional appearance.

[0099] As previously mentioned, for example, the heater includes a type of self-supporting bridge structure, such as seen in Figure 2a 、 Figure 2c or Figure 2d the figure. The heater exemplarily includes a conductive material, which emits corresponding Joule energy when an electric current flows through it. In this case, the conductive material, such as a metal, for example, forms a self-supporting structure. According to a further embodiment, it is also conceivable to provide additional support structures, for example, by means of a membrane or a perforated membrane. According to an embodiment, the self-supporting structure can be clamped on one or both sides, or generally, on several sides. A structure clamped on one side is also called a heating fin.

[0100] According to an embodiment, as shown in Figure 2g the figure, in the structure 12””, it is also conceivable to perforate the heating fin, or generally, the self-supporting structure. The increase in the perforated structure 12”” is as shown in Figure 2f the figure. It can be recognized that hexagonal openings are provided here.

[0101] According to a further embodiment, two heaters 12a and 12b can be arranged above the cavity 14, as can be seen in Figure 2hRecognized in the figure. The heaters can be the same or different. The heaters 12a and 12b shown here are parallel to each other and are arranged above the radiator at the bottom of the chamber 14 or the chamber 14 at equal spaced heights. According to a further embodiment, it is also conceivable that the two heaters 12a and 12b cross above the chamber 14 such that the two heaters 12a and 12b are arranged at different heights.

[0102] According to a further variant, separate chambers 14a and 14b can be provided for each of the heaters 12a and 12b, as Figure 2j shown in the figure.

[0103] In the above embodiments, it is assumed that the chamber 14 or 14a or 14b, or rather the bottom of the chamber, serves as the radiator. This means that the distance is decisive for the oscillation behavior, and thus this distance can be used to dimension the individual sensor units differently. According to a further embodiment, it is also conceivable to introduce alternative or additional radiators in addition to the heaters, as Figure 2k shown in the figure. In addition to the heater 12 arranged above the chamber 14, an additional radiator is provided, for example made of metal, having the reference numeral 13 here. The two radiators can also be formed by two substrates 16a and 16b surrounding the heater 12a. A chamber is formed between the two substrates 16a and 16b, and the heater 12 is located in this chamber. Multiple radiators 16a, 16c, and 16d are used as Figure 2m shown in the figure. In this embodiment, a spacer layer 17 is applied to the substrate, and this layer 17 includes a recess below the heater 12, thereby forming a chamber below the heater 12. Transverse to the heater 12, radiators 16c1 and 16c2 are provided at the same level as the heater 12.

[0104] Figure 2n A further variant is shown. Here, several heaters 12* are applied to the substrate surface of the substrate 16 as parallel structures / heating fins spaced apart from the substrate 16. The heaters 12* of the substrate are implemented as heating fins having a significantly widened fulcrum relative to the heating fins. This is particularly due to manufacturing technology factors. Figure 2o Another heater manufactured and implemented in a similar manner is shown. Here, the heating fin again has the reference numeral 12*. Figure 2n and 2o The variants of are so-called surface micromechanics.

[0105] In summary, it can be said that most different embodiments can be used, such as honeycomb structures, membranes (with / without holes), additional elements for actively transferring heat to the measurement gas (such as aluminum), curved arrangements, etc. The potential arrangements of alternative detectors will be discussed below.

[0106] Figure 2pThe heater 12 is shown in combination with the detector 18. These two elements are arranged next to each other at the same level above the cavity 14, i.e., at equal intervals.

[0107] Figure 2q The heater 12 is shown, and the detector 18 is arranged on the heater 12, separated by an insulating layer. The insulating layer has the reference numeral 18i. It is advantageous here that the excitation and the detection occur close to each other, where, however, the excitation and the detection are independent. For example, according to an embodiment, there are the following detection variants:

[0108] ● The resistive detector is stacked above the heater and separated by an insulating layer

[0109] ● The resistive detector is arranged next to the heater (parallel, around the heater, …)

[0110] ● A thermal element can be used similarly to the resistive detector.

[0111] Alternatively, the heater itself can be used as a detector, for example, by evaluating the electrical response signal. This means that, according to a further embodiment, the excitation and the detection can be performed by the same element (Joule heating of the heater and resistive evaluation of the temperature signal). This variant is not described here.

[0112] In FIG. 7, the manner of using the frequency-dependent sensitivity S of the material property change of the heating structure is shown k of.

[0113] Reference Figure 7a and Figure 7b , Figure 7a shows the sensitivity of kh with frequency for each of two different sensors, Figure 7b shows the sensitivity of cv with frequency for each of two different sensors h of, and the embodiments of one or both sensors in the embodiment according to FIG. 3 or according to Figure 5 are discussed.

[0114] Figure 7a shows the influence of the thermal conductivity of the sensor signal on the frequency-dependent sensitivity S k of. These two sensors have the same settings, but the thermal conductivity k h of the heating structure of sensor 1 is lower than that of sensor 2. Figure 7b shows the influence of the thermal conductivity of the sensor signal on the frequency-dependent sensitivity S k of. These two sensors have the same settings, however, the volume heat capacity cv h of the heating structure of sensor 1 is lower than that of sensor 2.

[0115] Sensor 1 and measurement M1 are sensitive to k, while sensor 2 and measurement M2 are insensitive to k. Two different solutions can be applied here, namely:

[0116] a) Solution at a lower frequency (f << f cutoff or f → 0)

[0117] b) Solution at a higher frequency within the cut-off frequency range (0.5*f < f cutoff ).

[0118] For a), the following three optimization methods are obtained:

[0119] ■ Optimize the ratio of the cavity: d1 / d2 > 20

[0120] ■ Optimize the ratio of the thermal conductivity of the heater: k h1 / k h2 < 0.05

[0121] ■ Optimize the ratio of the product of the layer thickness and width of the heater:

[0122] (b1*h1) / (b2*h2) < 0.2 (prerequisite: the heat transfer area to the gas is equal).

[0123] For solution b), the following optimization method is obtained:

[0124] Optimize the ratio of the product of the volume heat capacity and height of the heater:

[0125] (cv h1 *h1) / (cv h2 *h2) < 0.25

[0126] It should be noted here that the above optimization methods should all be understood as specific embodiments, so that further variants of the optimization can be envisioned according to further embodiments.

[0127] According to the embodiment, the geometry of the gas can be adjusted. The higher k gas , the larger the cavity. Doubling k gas results in d becoming four times as large. The smaller k gas , the higher cv ga x, and the smaller the selected frequency.

[0128] Starting from the requirement that sufficient sensitivity to cv can be achieved through sensor 1 or measurement M1 and the requirement that sufficient insensitivity to cv can be obtained through sensor 2 or measurement M2, for higher frequencies within the cut-off frequency range, the following solution can be selected.

[0129] When combining these two applications and considering what can be obtained from Figure 7a and 7bWhen considering the teachings that can be recognized, according to the embodiments, it should be noted that preferably the thermal conductivity is evaluated below the cut-off frequency, while the volumetric heat capacity is evaluated above the cut-off frequency.

[0130] As mentioned above, the gas composition affects all measurements and, therefore, also affects the output signal of the heat flux sensor, as can be seen from Figure 8 it.

[0131] Figure 8 shows the sensor signal as a function of the flow rate measured for different gas compositions. The result is a large number of characteristic curves. This shows that in order to determine the characteristic curves in the flow sensor, it is necessary to preferably establish the relevant gas parameters directly near the heat flux sensor. While taking into account the above teachings, the gas composition can be easily and effectively established using FIG. 3 or Figure 5 a variant thereof.

[0132] According to the embodiments, these microtechnology sensors in FIG. 3 and Figure 5 can be used both for signal compensation in the heat flux sensor in the case of changing gas media and operating parameters (pressure, temperature), and also provide a way to determine the volumetric heat capacity, thermal conductivity, temperature, and pressure as separate sensors.

[0133] The result is the application of an inline-capable flow sensor, providing a way for signal compensation. Figure 9a shows a flow sensor 70 composed of an actual flow sensor 72 and a sensor arrangement 1 including two sensor chips 10a and 10b. The sensor 1 has several gas parameter sensitive sensors and is located in the cavity of the chip 72, i.e., the current-limiting region. A heat flux sensor is provided on the surface of the sensor 70, and the heat flux sensor has a membrane with holes for gas exchange.

[0134] Transferred to Figure 5 the functions in the variant of the sensor in are schematically shown in Figure 9b it. Figure 9b shows two sensors 10 and 72. The k of the known gas mixture 3 is determined by the sensor 10a (first measurement M1). In addition, ρ*c is determined by the same sensor 10 for the same gas mixture 3 (first measurement M2). These two determined parameters can be transmitted to the evaluation device of the flow sensor 72 for compensation, and the evaluation device determines the flow rate of the gas mixture 3. The compensation can be performed, for example, through a look-up table to determine the compensated flow rate.

[0135] For a known gas mixture 3 (with known thermal conductivity and volumetric heat capacity at a reference temperature and reference pressure), the following method can be applied:

[0136] - Evaluation of the output signal of measurement M1 (amplitude of the temperature response), which is proportional to the thermal conductivity. The thermal conductivity depends on the temperature and is used to determine the average gas temperature.

[0137] - The output signal of sensor 10a obtained from measurement M1 is used to compensate the output signal (amplitude) of sensor signal 10b. The output signal of sensor 10b for measurement M2 depends on the volumetric heat capacity. The density can be determined by compensation and is used to determine the pressure.

[0138] According to a further embodiment, the gas temperature T = f(k gas ) can be determined based on the sensor value of measurement M1, and the pressure p = f(cv gas ) can be determined by the sensor signal of measurement M2. In both variants, a look-up table can be used. It should be noted here that this is not absolutely necessary for the gas mixture to be understood (see Figure 9c ).

[0139] For example, using another sensor 75, i.e., a temperature sensor, the gas composition can also be determined based on the sensor signal of measurement M1, based on the unknown mixture 3*. The known gas composition vol.% = f(k gas ), and using the sensor signal of measurement M2, the corrected flow rate can be determined, as discussed above (using the flow sensor 72).

[0140] As Figure 9d shows, a temperature sensor is not absolutely necessary because using two measurements to determine two values k and ρc based on the unknown gas mixture 3* is sufficient to compensate the flow rate of the flow sensor 72. The feature here is that the temperature, pressure, and gas composition are not directly determined, and these are not absolutely necessary for absolute signal compensation.

[0141] The above discussion shows that further comparative examples relate to a flow sensor with the sensor arrangement of FIG. 3. Here, for example, sensor 10a exhibits high sensitivity to the thermal conductivity, and sensor 10b exhibits high sensitivity to the volumetric heat capacity. According to an embodiment, the sensor 10 with the evaluator 50 in Figure 5 can also be used because using two measurements (measurement M1 and measurement M2 at two different / continuous time points t1, t2) can correspondingly determine the same parameters during operation.

[0142] A further embodiment relates to a pressure sensor that determines the compensated pressure with known parameters k and ρ*c.

[0143] It should be noted here that preferably the thermal conductivity is evaluated below the cut-off frequency, as from Figure 7a and 7bwhich can be recognized.

[0144] Another embodiment relates to a method for operating a sensor arrangement. According to an embodiment, an operating point can be determined here. The method for determining the optimal sensor configuration can be implemented as follows:

[0145] To configure the sensor / sensor arrangement, for example for a general measurement range, according to an embodiment, a self-regulating method can be used to find the operating point:

[0146] ■ Sensor geometry: Create and change the structure for operation at the same frequency

[0147] ■ Sensor operation: Frequency scanning to determine the gas-dependent operating point (also depending on pressure / temperature) → For the highest sensitivity difference between sensor groups 1 and 2, find the local maximum.

[0148] To determine the operating point of the sensor arrangement for the measured quantity (thermal conductivity or volume heat capacity) in the multi-dimensional parameter domain highest of the best sensitivity, changes in thermal conductivity (such as temperature change, gas composition) and / or volume heat capacity (such as pressure, gas composition) must be induced: This can be done at the calibration measurement station of the configured sensor arrangement. However, even at a non-optimal operating point, the measured quantity can be determined, that is, the sensor arrangement can also be used in a non-calibrated state.

[0149] According to an embodiment, a sensor chip, such as Figure 5 the sensor chip of or the sensor chip of FIG. 3, includes an evaluator. Preferably, one or more sensors are fabricated on a common chip. According to the compatibility with the manufacturing process of the heat flux sensor, the flow sensor can be fabricated on the same chip. According to another embodiment, the ASIC can also be fabricated on the same chip. The ASIC or generally, the evaluation electronics, is configured to easily process the combination of signals of several sensors for the dynamic on-chip signal compensation of the heat flux sensor. Thus, a highly miniaturized sensor with high dynamic performance and the potential for monolithic integration is provided.

[0150] According to an embodiment, one or more sensors and one and / or more sensors combined with the evaluator are monolithically integrated. Here, either only sensors for determining gas parameters are provided, or the sensors can be extended by pressure sensors or flow sensors.

[0151] Reference will be made Figure 10a 、 10b and 10c to discuss the extended embodiments related to the evaluation. Figure 10a The layout of the potentially adoptable heating element 10* is shown. It should be noted here that according to an embodiment, this layout can also be applied to the above embodiments.Figure 9b A diagram obtained by FFT is shown to illustrate this embodiment. Figure 10c A diagram (voltage on frequency) is shown to illustrate two evaluation signals or evaluation frequencies.

[0152] Figure 10a A layout 10* is shown, which has one or more heaters 12* (such as metal wires), these heaters can be arranged on an optional film 14m (which covers the cavity), and a thermal element 18* for temperature detection of the heating element 12*. A periodic current with circular frequency Ω is fed in the metal wire: I(t) = IO × cos(Ωt). The thermal power fed in the heating wire is equal to: P(t)I 2 ×R = I(t) 2 ×R = (IO 2 ×R / 2) × (1 + cos(2Ωt)), where R is the resistance of the heater 12*. Since the power is fed at the same frequency as the power supply signal, the temperature of the heater will change: T(t) = T0(t) × ΔTXcos(2Ωt + Φ). The amplitude ΔT and the phase shift Φ relative to the fed power depend on the thermal conductivity of the material and the frequency Ω. T0 is the zero position of the temperature oscillation and depends on the power and the coupling between the sample and the environment. The temperature oscillation of the heating wire causes its resistance to oscillate. The discussion of coupling or causing thermal oscillation will be applied to the above embodiment.

[0153] Starting from the thermal oscillation excited in this way, the heating element, here the heating element 12*, can be excited at only one frequency (such as 1 kHz). In this embodiment, the evaluation frequency is evaluated at two points, for example, at the 0th harmonic and the 2nd harmonic. The 0th harmonic oscillation is also called the DC signal. The second is called the 2-omega signal. The evaluation by FFT analysis is as Figure 10b shown. In the FFT analysis, different harmonic oscillations are formed. First, the 0-omega signal and the 2-omega signal are of interest, here denoted as AB1 and AB2. AB1 represents the 0-omega signal or the DC signal and is used as a measure of T0. AB2 represents the 2-omega signal and is used as a measure of ΔT. The result is the temperature signal T(t) = T0(t) + ΔT × cos(2ΩT + Φ). According to another embodiment, for example, another harmonic signal or other frequency signal, such as the 1-omega signal, can be used. It should be noted here that in Figure 10b the embodiment shown in, an excitation of 10 Hz is used. In this embodiment, the evaluation frequencies are 0 Hz and 20 Hz.

[0154] In Figure 10cIn it, the 0-omega signal and the 2-omega signal within the frequency range are shown. Starting from this figure, the 0-omega signal (DC signal) can be used as a measure of thermal conductivity, while the higher-frequency 2-omega signal represents a measure of temperature conductivity and volumetric heat capacity.

[0155] This means that the above embodiments have shown that when two evaluation frequencies are to be used, the 0 Hz frequency can also be used as an evaluation frequency. This procedure has been proven to be applicable to the first measurement in order to achieve high sensitivity to thermal conductivity (DC component) and high sensitivity to volumetric heat capacity when using only a single excitation frequency.

[0156] According to an embodiment, the evaluation using two evaluation frequencies can be performed by FFT analysis. According to an embodiment, FFT analysis of harmonic temperature signals (such as 2x excitation frequency and 0x excitation frequency (DC signal)) can be executed. According to another embodiment, one detector measures the DC signal, while another detector measures the harmonic signal. Figure 10a Multiple detectors combined with a heating element are shown in it, where this only represents an exemplary case.

[0157] The comparative example provides a sensor arrangement that includes at least two highly miniaturized sensors having a thermal operating principle for determining respective gas properties (volumetric heat capacity cv (product of density and specific heat capacity) or thermal conductivity k). These thermal sensors are configured such that at least one component exhibits high sensitivity to one gas property, while at least one other component exhibits high sensitivity to another gas property. The challenge lies in producing a structure that is sensitive to gas properties while minimizing cross-sensitivity. As mentioned above, gas properties depend not only on composition but also on temperature and pressure. However, this influence varies greatly and can be used to indirectly determine pressure and temperature by employing several combined gas property sensors. A small change in pressure (Ap < 10 bar) in the first approximation only causes a change in gas density. However, in the first approximation, a temperature change (AT < 50K) has an impact on density and thermal conductivity. However, the specific heat capacity remains almost unaffected by changes in pressure and temperature.

[0158] Description of the variables used above:

[0159] - Dimensions of the heater: L, b, h

[0160] - Height of the cavity: d

[0161] - Material properties of the heater: cv h 、k h

[0162] - Gas properties k, cv, or, for the sake of clarity, k gas 、cvgas

[0163] - Sensitivity S to the properties of the gas k 、S cv

[0164] - Width b of the effective heat transfer area to the gas gas

[0165] - Cut-off frequency f cutoff or f cutoff，S1

[0166] Although some aspects are described in the context of an apparatus, it should be understood that these aspects also represent a description of the corresponding method, and thus the blocks or structural components of the apparatus should also be understood as corresponding method steps or features of method steps. Similarly, aspects described in the context of method steps or as method steps also represent a description of the corresponding blocks or details or features of the corresponding apparatus. Some or all of the method steps may be performed by (or using) a hardware device, such as a microprocessor, a programmable computer, or an electronic circuit. In some embodiments, some or several of the most important method steps may be performed by such a device.

[0167] According to specific implementation requirements, embodiments of the present invention may be implemented in hardware or software. It may be implemented when using a digital storage medium, such as a floppy disk, a DVD, a Blu-ray disc, a CD, a ROM, a PROM, an EPROM, an EEPROM, or a flash memory, a hard disk, or any other magnetic or optical memory on which an electronically readable control signal is stored, and the electronically readable control signal can cooperate with a programmable computer system or cooperate with a programmable computer system to perform the corresponding method. This is why the digital storage medium can be computer-readable.

[0168] Therefore, some embodiments according to the present invention include a data carrier that includes an electronically readable control signal that can cooperate with a programmable computer system to perform any method described herein.

[0169] Generally, embodiments of the present invention may be implemented as a computer program product having program code that, when the computer program product runs on a computer, the program code effectively performs any method.

[0170] For example, the program code may also be stored on a machine-readable carrier.

[0171] Other embodiments include a computer program for performing any of the methods described herein, the computer program being stored on a machine-readable carrier. In other words, an embodiment of the method of the present invention is a computer program having program code that, when the computer program runs on a computer, is used to perform any of the methods described herein.

[0172] Accordingly, another embodiment of the method of the present invention is a data carrier (or digital storage medium or computer-readable medium) on which a computer program for performing any of the methods described herein is recorded.

[0173] Accordingly, another embodiment of the method of the present invention is a data stream or signal sequence representing a computer program for performing any of the methods described herein. The data stream or signal sequence can be configured to be transmitted, for example, via a data communication link (such as via the Internet).

[0174] Another embodiment includes a processing device, such as a computer or a programmable logic device, which is configured or adapted to perform any of the methods described herein.

[0175] Another embodiment includes a computer on which a computer program for performing any of the methods described herein is installed.

[0176] Another embodiment according to the present invention includes an apparatus or system configured to transmit a computer program for performing at least one of the methods described herein to a receiver. For example, the transmission can be electronic or optical. For example, the receiver can be a computer, a mobile device, a storage device, or a similar device. For example, the apparatus or system can include a file server for transmitting the computer program to the receiver.

[0177] In some embodiments, a programmable logic device (such as a field programmable gate array, FPGA) can be used to perform some or all of the functions of the methods described herein. In some embodiments, the field programmable gate array can cooperate with a microprocessor to perform any of the methods described herein. Alternatively, a microcontroller (such as a PSoC, programmable system on chip) and / or locking technology can be used. Generally, in some embodiments, these methods are performed by any hardware device, which can be general-purpose hardware, such as a computer processor (CPU), or can be hardware dedicated to the method, for example, an ASIC.

[0178] The above embodiments merely illustrate the principles of the present invention. It should be understood that other technicians in the art will understand the modifications and variations of the arrangements and details described herein. This is why the present invention is intended to be limited only by the scope of the following claims, rather than by the specific details presented in the description and discussion of the embodiments herein.

Claims

1. A sensor arrangement comprising at least one sensor unit and an evaluator (50); wherein the at least one sensor unit can be thermally excited by a heater (12); wherein the sensor unit is configured to form an oscillatory behavior based on the gas properties of the gas surrounding the sensor unit, in particular the thermal conductivity (k) and / or the volumetric heat capacity (cv) and / or the temperature and / or the pressure; wherein the sensor unit is excited by at least one excitation frequency, and wherein a first excitation frequency or a first evaluation frequency is used for a first measurement, and wherein a second excitation frequency or a second evaluation frequency is used for a second measurement (M2); Among them, the first excitation frequency being different from the second excitation frequency, or wherein the first evaluation frequency is different from the second evaluation frequency; and wherein the evaluator (50) is configured to determine the thermal conductivity (k) of the surrounding gas based on the first measurement (M1) and to determine the volumetric heat capacity (cv) of the surrounding gas based on the second measurement (M2).

2. The sensor arrangement according to claim 1, wherein the first excitation frequency and / or the second excitation frequency is greater than or equal to 0 Hz; wherein the first excitation frequency is equal to 0 Hz and the excitation energy used for the first measurement (M1) is greater than 0, or wherein the second excitation frequency is equal to 0 Hz and the excitation energy used for the second measurement (M2) is greater than 0.

3. The sensor arrangement according to claim 1 or 2, wherein the first excitation frequency differs from the second excitation frequency by at least a factor of 2, at least a factor of 4 or at least a factor of 8; and / or wherein the first evaluation frequency differs from the second evaluation frequency by at least a factor of 2, at least a factor of 4 or at least a factor of 8.

4. The sensor arrangement according to any one of the preceding claims, wherein, The first excitation frequency or the first evaluation frequency and the second excitation frequency or the second evaluation frequency are each defined by a fixed frequency.

5. The sensor arrangement according to any one of the preceding claims, wherein the first excitation frequency is at least a factor of 2 or at least a factor of 4 smaller than the cut-off frequency of the sensor (10), and wherein the second excitation frequency is at least a factor of 2 or at least a factor of 4 greater than the cut-off frequency of the sensor (10); and / or wherein the first evaluation frequency is at least a factor of 2 or at least a factor of 4 smaller than the cut-off frequency of the sensor (10), and wherein the second evaluation frequency is at least a factor of 2 or at least a factor of 4 greater than the cut-off frequency of the sensor (10).

6. The sensor arrangement according to any one of the preceding claims, wherein the sensor unit comprises a cavity (14) having a heater (12), or a radiator having spaced-apart heaters (12), or heating fins spaced apart from a radiator; and / or wherein the heater (12) or the heating fins are configured to thermally oscillate so as to form the oscillatory behavior; and / or wherein the heater (12) is formed by heating fins or a self-supporting structure or a self-supporting bridge structure.

7. The sensor arrangement according to any one of the preceding claims, wherein the sensor unit comprises a detector configured to detect the oscillatory behavior.

8. The sensor arrangement according to any one of the preceding claims, wherein the sensitivity to the volumetric heat capacity (c v ) in the second measurement (M2) is at least 3 times, at least 4 times or at least 5 times higher than the sensitivity to the volumetric heat capacity (c v ) in the first measurement (M1); and / or The sensitivity to the thermal conductivity (k) in the first measurement (M1) is at least 1.1 times or at least 1.2 times higher than the sensitivity to the thermal conductivity (k) in the second measurement (M2).

9. The sensor arrangement according to any one of the preceding claims, wherein the evaluator (50) is configured to periodically excite the sensor unit.

10. The sensor arrangement according to any one of the preceding claims, wherein the sensor unit is excited by a varying excitation frequency, in particular a CHIRP signal or a DIRAC signal.

11. The sensor arrangement according to any one of the preceding claims, wherein the evaluator (50) determines the oscillation behavior of the sensor (10) using the dynamic temperature response and / or using the amplitude and / or using the frequency and / or using the phase.

12. The sensor arrangement according to any one of the preceding claims, wherein the evaluator (50) is implemented as an ASIC, and the ASIC is integrated in a chip or a monolithic chip accommodating the sensor unit.

13. The sensor arrangement according to any one of the preceding claims, wherein the first evaluation frequency and / or the second evaluation frequency is greater than or equal to 0 Hz; and / or wherein the evaluator includes an FFT; or wherein the evaluator includes an FFT and the first measurement occurs at a first evaluation frequency equal to 0 Hz and / or the second evaluation frequency is greater than or equal to 0 Hz or is 1-OMEGA, 2-OMEGA or 3-OMEGA.

14. A flow sensor, comprising the sensor arrangement according to any one of the preceding claims, wherein the flow sensor is configured to determine the flow rate taking into account the determined thermal conductivity (k) and the volumetric heat capacity (cv).

15. A pressure sensor, comprising the sensor arrangement according to any one of claims 1 to 13, wherein the pressure sensor is configured to determine the pressure taking into account the volumetric heat capacity (cv) and the thermal conductivity (k).

16. A method for evaluating (50) the sensor arrangement according to any one of claims 1 to 13, comprising the following steps: Exciting the sensor (10) by an excitation frequency, wherein a first excitation frequency or a first evaluation frequency is used for the first measurement (M1), and wherein a second excitation frequency or a second evaluation frequency is used for the second measurement (M2), wherein the first excitation frequency is different from the second excitation frequency, or wherein the first evaluation frequency is different from the second evaluation frequency; and Determining the thermal conductivity (k) based on the first measurement (M1), and determining the volumetric heat capacity (cv) based on the second measurement (M2).

17. A computer program for performing the method according to claim 16 when a computer runs an evaluator (50).

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