Gas concentration measurement using thermoacoustic sound waves

Abstract

Gas sensor with the following features: a stoker, a recipient, and a space arranged between the heater and the receiver, wherein the heater is designed to generate a thermoacoustic sound wave propagating through the space using an excitation signal, and wherein the receiver is designed to receive the thermoacoustic sound wave that has propagated through the room and to convert it into a received signal that has a time-dependent shift relative to the excitation signal and thus provides information about a gas concentration in the room; and a gas concentration determination circuit designed to determine a phase shift between the received signal and a heater signal, or, based on the received signal, a travel time of the thermoacoustic wave through the room, each of which is a measure of the gas concentration in the room; and a thermal conductivity determination circuit designed to determine the thermal conductivity of the room, which depends on the gas concentration in the room, using the heater signal, where the heater signal is the excitation signal or a temperature signal indicating the temperature of the heater.

Description

Technical field

[0001] This disclosure relates to gas sensors and methods for determining gas concentration using thermoacoustic sound waves. Furthermore, this disclosure relates to robust H2 sensors that enable integrated measurement of thermal conductivity, speed of sound, and / or temperature. Background of the invention

[0002] Gas sensors are a class of sensors used in many applications. In the process industry, gas sensors can be used for process monitoring or quality assurance; in the field of safety technology, gas sensors serve, for example, for explosion protection, poison control, or leak detection.

[0003] Another important application area for gas sensors is the automotive industry. Besides solutions such as lambda sensors in gasoline engines, there are particular challenges in the field of gas sensor technology with regard to fuel cell vehicles.

[0004] With the increasing prevalence of fuel cells in the automotive sector, the demand for suitable sensors, for example for monitoring and control, may rise. Since this can be a safety-relevant component of the system, the requirements for bringing a long-term stable, reliable, yet cost-effective gas sensor, such as a hydrogen sensor, to market can be very high.

[0005] Gas sensors can be adapted to the specific properties of the gas being detected. In the case of hydrogen, these properties can include the following aspects: - Hydrogen, for example, can only form the H2 state under atmospheric conditions. - For example, due to its property as the smallest atom, hydrogen can exhibit rapid effusion and diffusion, which can lead to a change in the chemical and physical properties of a substrate material. Hydrogen can be chemically very active, so that it forms a strongly reducing element, e.g. a reducing agent. - Hydrogen can exhibit a flammability within limits of 4-75% or 18-59%.

[0006] Other properties of gases, including hydrogen, are described in the Fig. 3-5 times.

[0007] Fig. Figure 3 shows a plot of different sound velocities, for example in ms, for various gases.

[0008] Fig. Figure 4 shows a plot of specific heat capacities, for example in kJkgK, for various gases.

[0009] Fig. Figure 5 shows a plot of thermal conductivities, for example in WmK, for various gases.

[0010] It should be noted that the gas sensors presented below, in accordance with the disclosure, may be based on one or more of the properties, property distinctions, or aspects described above. Individual properties or aspects, for example of hydrogen, may be used in gas sensors according to the disclosure. State of the art

[0011] The following describes some conventional gas sensors, such as hydrogen gas sensors, and their basic principles. Furthermore, the following description can provide a technological overview of gas sensors.

[0012] Previous solutions for sensors, for example hydrogen gas sensors, include sensors that are based on physical or chemical properties, for example.

[0013] One such physical property is thermal conductivity. Thermal conductivity can be measured, for example, using the 3-omega method. This method measures temperature oscillations, such as those caused by periodic, applied heating, and determines the thermal conductivity from their frequency dependence. The excitation can be applied at a high frequency, for example, in the kilohertz range. Detecting a harmonic, such as the third harmonic, can then provide a measure of the gas's thermal conductivity. Furthermore, to measure thermal conductivity, a large contact area can be subjected to a constant power, with the contact area being cooled differently depending on the gas concentration. This cooling effect is due to the gas concentration-dependent thermal conductivity, allowing the gas concentration to be deduced from the thermal conductivity.

[0014] Another physical property can be an acoustic one. A suitable sensor can, for example, utilize the change in the speed of sound using ultrasonic TOF (Time of Flight). In this method, an emitted ultrasonic signal can be reflected by a gas to be detected, and the gas can be identified from the time of flight or signal transit time.

[0015] Gas sensors based on chemical properties can include sensors with catalytic combustion. These can consist of coils coated (e.g., with PT) in a ceramic matrix. Furthermore, a temperature increase can occur due to the catalytic combustion. Such a sensor can comprise a detector element, which contains the catalytic material, and a compensation element. A combustible gas to be detected can combust at the detector element, causing a temperature increase and thus increasing the resistance of the detector element. In the compensation element, the temperature and resistance remain approximately constant. The evaluation of the detector element and the compensation element can be performed using a bridge circuit. The difference between the two elements can then be used to deduce the type of gas or its concentration.

[0016] Other gas sensors based on chemical properties can include semiconductors. A gas can alter the electrical properties of, for example, integrated semiconductor elements, so that the gas or its concentration can be deduced from the changes in electrical properties.

[0017] Semiconductors or semiconductor elements can include, for example, the following: - Schottky diodes, for example with a semiconductor substrate, an insulating layer and a metal layer applied to the insulating layer, - pn transition diodes, for example with an n-doped semiconductor substrate, a p-doped semiconductor layer and a metal layer applied to the p-doped semiconductor layer, - MOS transistors, for example, with an n-doped semiconductor substrate, an S- (e.g., Source) and a D- (e.g., Drain) terminal in the semiconductor substrate, and an insulating layer applied to the n-doped semiconductor substrate and the S- and D- terminals, and a metal layer applied to the insulating layer.

[0018] Gas sensors based on chemical properties can also rely on chemically resistive principles or effects (or chemi-resistive, MOX, e.g., metal oxide-semiconductor gas sensors). Such gas sensors can be based on the change in resistance of a chemically active coating. Electrons can be donated or accepted, or materials and substances that act as electron donors or acceptors can be used. For example, some materials change their conductivity in the presence of a gas. A material might adsorb oxygen molecules onto its surface. In this process, electrons can be donated from the material to the oxygen atoms until an equilibrium is reached. A reduced gas to be detected can be oxidized by the adsorbed oxygen, so that an electron is donated back to the material, thus changing the material's conductivity. Through the resistance or...Changes in conductivity can then be used, for example, to infer the nature of the gas or its concentration.

[0019] Gas sensors based on chemical properties can also include Pd-based sensors. Such sensors can rely on the change in mechanical properties, e.g., mechanical stress, strain, and / or dimension, through the absorption of a gas to be detected.

[0020] Furthermore, previous solutions are based, for example, on a sensor system with several discrete sensors (e.g. humidity sensor, temperature sensor, thermal conductivity sensor, MOX sensor), whose output signals are processed in a central control unit.

[0021] Reference is made to further approaches from the state of the art: US patent 2019 / 0310229A1 describes a gas sensor with a vibrator mounted on a resonator and incorporating a heating element. The vibrator can generate sound waves, which can be converted into an electrical signal by a transducer. This allows the presence of a gas to be detected.

[0022] US Patent 2,653,471 A describes a device for analyzing gases. The device comprises an oscillator, a thermophone connected to the oscillator and located in a first chamber, a microphone with an amplifier, and a second chamber connected to the first chamber via a channel. A gas to be analyzed is supplied via a line. To identify the gas, three parameters are determined: an amplitude, a resonant frequency, and a parameter indicating the sharpness of the resonance. Knowing any two of these parameters, a measurement of a gas can be performed based on a predetermined relationship between the parameters (see Fig. 1f) are assigned.

[0023] DE 10 2018 206 669 B3 describes a fluid sensor with a housing and a thermal emitter arranged in the housing, which is configured to emit a first thermal radiation into a detection volume of the housing containing a measuring gas at a first power level during a measurement interval and to emit the first thermal radiation at a reduced first power level or not at all during an intermediate interval arranged outside the measurement interval.

[0024] With regard to the foregoing, it should be noted that a gas sensor as disclosed may include one or more aspects, properties or functionalities of the sensors or sensor principles described above. Summary of the invention

[0025] The inventors have recognized that previous approaches have several drawbacks, for example regarding long-term stability, reliability, and cost. Therefore, there is a need to provide robust gas sensors with good integration potential and low cost.

[0026] Examples according to the present disclosure provide a gas sensor with a heater, a receiver, and a space arranged between the heater and the receiver. The heater is designed to generate a thermoacoustic sound wave propagating through the space using an excitation signal. The receiver is designed to receive the thermoacoustic sound wave that has propagated through the space and convert it into a received signal that has a time-of-flight shift relative to the excitation signal and thus provides information about a gas concentration in the space. The gas sensor further comprises a gas concentration determination circuit designed to determine a phase shift between the received signal and a heater signal, or, based on the received signal, a time of flight of the thermoacoustic wave through the space, each of which is a measure of the gas concentration in the space.The gas sensor further includes a thermal conductivity determination circuit designed to determine the thermal conductivity of the room, which depends on the gas concentration in the room, using the heater signal, where the heater signal is the excitation signal or a temperature signal indicating a temperature of the heater.

[0027] Further examples according to the present disclosure provide a method for determining a gas concentration. The method comprises applying an excitation signal to a heater to generate a thermoacoustic sound wave that propagates through a space located between the heater and a receiver, and receiving the thermoacoustic sound wave at the receiver to generate a received signal. The method further comprises determining a time-of-flight-dependent displacement between the heater signal and the received signal, and determining the gas concentration in the space using the determined time-of-flight-dependent displacement. The method also comprises determining the thermal conductivity of the space, which depends on the gas concentration in the space, using the heater signal. The heater signal is either the excitation signal or a temperature signal indicating the temperature of the heater.

[0028] The present invention provides a gas sensor and a method for determining a gas concentration according to the independent claims. Further developments of the invention are defined in the dependent claims. All embodiments and examples of the description that are not within the scope of the claims are not part of the invention and serve only for illustration.

[0029] Examples according to the present disclosure are based on the core idea that a time-of-flight shift of a received signal to an excitation signal, and thus information about a gas concentration in a room, can be acquired in such a way that the structures used can further be used to acquire another parameter that can contain information about a gas to be detected. In this process, a heater generates a thermoacoustic sound wave using the excitation signal, which, after propagating through the room with the gas concentration to be detected, is converted by the receiver into the received signal. The time-of-flight shift can be, for example, according to Fig. 3. This is caused by the different speeds of sound of the thermoacoustic sound wave depending on the gas concentration in the room. For example, such a method can be particularly advantageous for gases that have a characteristic speed of sound, such as hydrogen or helium (see e.g. Fig. 3) In other words, the speed of sound of the thermoacoustic sound wave can be used to determine the gas concentration due to the relationship between gas concentration and speed of sound.

[0030] The excitation signal can be, for example, a high-frequency signal (e.g., in the range of 10 kHz). Furthermore, the excitation signal can be a periodic signal, a pulse, or a sequence of pulses. In the case of a single pulse, a simple measurement of the pulse's transit time can be performed. In the case of a periodic excitation signal, the transit-time-dependent shift can be due to a phase shift of the thermoacoustic sound wave, resulting from the gas-dependent sound velocities in space. Additionally, a superposition of frequencies within a short pulse, followed by a transit-time measurement, is also possible.

[0031] Since, according to the disclosure, a thermoacoustic sound wave is generated by a heater, the structures used, such as the heater, can also be used to detect another parameter that may contain information about a gas to be detected, such as its thermal conductivity. Thus, examples from the disclosure make it possible to detect multiple parameters in an integrated sensor.

[0032] Due to the disclosed concept of generating the thermoacoustic sound wave using the heater, a corresponding gas sensor can be particularly robust and reliable, for example, because it eliminates moving parts. In contrast to generating a sound wave using, for example, a membrane, a heater can, in addition to having a lower probability of mechanical failure, also be produced more cost-effectively.

[0033] Furthermore, a gas sensor as disclosed enables an evaluation of the received signal with low computational effort, since the determination of the time-of-flight-dependent displacement can be carried out with simple calculations and, in particular in systems with low computing capacities, the evaluation of the time-of-flight-dependent displacement may only include a determination of the signal transit time, for example of a pulse signal generated by the heater. Character description

[0034] Examples according to the present disclosure are explained in more detail below with reference to the accompanying figures. With regard to the schematic figures shown, it should be noted that the functional blocks depicted are to be understood both as elements or features of the device according to the disclosure and as corresponding process steps of the process according to the disclosure, and corresponding process steps of the process according to the disclosure can also be derived from them. They show: Fig. 1 a schematic side view of an example of a gas sensor according to the present disclosure; Fig. 2 a schematic side view of an extended example of a gas sensor according to the present disclosure; Fig. 3 a plot of sound velocities for different gases; Fig. 4 a plot of specific heat capacities for different gases; Fig. 5. A plot of thermal conductivities for various gases; Fig. 6 a schematic side view of an example of a gas sensor according to the present disclosure with a microphone diaphragm; Fig. 7 a schematic top view of the example of the gas sensor from Fig. 6; Fig. 8 a schematic signal profile of the received signal and the heater signal according to an example in the present disclosure; Fig. 9 a schematic side view of an example of a gas sensor according to the present disclosure with a temperature sensor; and Fig. 10 a schematic top view of the example of the gas sensor from Fig. 9. Detailed description of the examples according to the figures

[0035] Before examples of the present invention are explained in detail below with reference to the drawings, it should be noted that identical, functionally equivalent or equivalent elements, objects and / or structures in the different figures are provided with the same or similar reference numerals, so that the description of these elements shown in different examples is interchangeable or can be applied to one another.

[0036] Fig. Figure 1 shows a schematic side view of an example of a gas sensor according to the present disclosure.

[0037] Fig. Figure 1 shows a gas sensor 100 with a heater 110 and a receiver 120. A space 130 is arranged between the heater 110 and the receiver 120, in which a thermoacoustic sound wave 140 propagates.

[0038] The receiver 120 can include a microphone or microphone diaphragm and / or a temperature sensor, e.g., with a thin diaphragm. The heater 110 can be a heating structure formed within a MEMS element, for example, a conductive trace.

[0039] The heater 110 generates a thermoacoustic sound wave 140, propagating through room 130, using an excitation signal. Due to gases or gas concentrations and the resulting changes in sound velocity within room 130, the thermoacoustic sound wave 140 undergoes a time-of-flight shift, e.g., a delay. The thermoacoustic sound wave 140 is received by the receiver 120 and converted into a received signal. This time-of-flight shift of the thermoacoustic sound wave 140 results in a time-of-flight shift of the received signal relative to the excitation signal. By evaluating this time-of-flight shift, information about the gas concentration in room 130 can be determined.

[0040] Before the detailed explanation of the other figures, further examples and aspects and / or variations of examples and aspects according to the present revelation will first be described below.

[0041] In further examples according to the present disclosure, the receiver includes a microphone. The microphone may be a microphone diaphragm. Microphones constitute sophisticated sensor elements whose signals can be amplified and analyzed using simple methods for subsequent processing. Furthermore, in addition to extracting frequency or phase information, e.g., to determine the time-of-flight shift, microphones also enable the evaluation of amplitude information, for example, with regard to signal attenuation, thus allowing further analyses, for example, concerning the gas-dependent thermal conductivity of the space located between the heater and the receiver.

[0042] In further examples according to the present disclosure, the receiver includes a temperature sensor. The temperature sensor can be a thin membrane. Furthermore, such a temperature sensor can include a temperature-sensitive sensor element, e.g., in the form of a bridge, or a bridge within a recess of a sensor structure of the temperature sensor. Such a sensor element can be designed as a conductor with temperature-dependent resistance, so that an incident thermoacoustic wave can lead to heating and thus a detectable change in resistance.

[0043] By using a temperature sensor, the thermal conductivity of the space between the heater and the receiver can be determined. The thermal conductivity of the space depends on the gas concentration within it. Therefore, by determining the thermal conductivity, the gas concentration can be inferred, either in addition to determining the gas concentration by measuring the speed of sound (via a time-of-flight-dependent displacement caused by the temperature sensor), or solely by determining the gas concentration. Furthermore, temperature sensors can be designed without moving parts, making them more robust and reliable than, for example, a microphone diaphragm.

[0044] In examples according to the present disclosure, the gas sensor has a gas concentration determination circuit designed to determine a phase shift between the received signal and a heater signal, or, based on the received signal, a transit time of the thermoacoustic wave through the room, each of which is a measure of the gas concentration in the room.

[0045] In the case of a periodic heater signal, the gas concentration determination circuit can have a phase detector to determine a time-of-flight-dependent shift between the heater signal and the received signal in the form of a phase shift.

[0046] In alternative examples, the heater signal can be a pulse or a pulsed signal. The gas concentration determination circuit can then determine the signal's propagation time based on the time difference between the received signal and the heater signal, or based on the received signal and a time information component. This time information can be the time of transmission of the pulse or pulsed signal, so that, with information about the signal's arrival time provided by the received signal, the time difference between transmission and reception of the pulse or pulsed signal, and thus the signal propagation time or the propagation time-dependent shift, can be determined.

[0047] The gas concentration determination circuit can be integrated into the gas sensor, allowing the gas sensor to output a signal indicating the gas concentration. Alternatively, the gas concentration determination circuit can be located outside the sensor, enabling the gas sensor to output a signal that allows for the determination of the gas concentration.

[0048] The gas concentration determination circuit allows a relationship to be established between the speed of sound of a thermoacoustic wave and a gas concentration, see for example Fig. 3. can be used. In particular, for gases with characteristic sound speeds, a measure of the gas concentration can be determined with, for example, low susceptibility to error.

[0049] In examples according to the present disclosure, the heater signal is the excitation signal or a temperature signal indicating the heater's temperature. By using the excitation signal as the heater signal, a signal for evaluation is available without further effort, for example, with regard to additional hardware. The temperature signal can also be used to determine the thermal conductivity of the space adjacent to the heater. If it is possible to determine the heater's temperature, this can improve the accuracy of an evaluation, since the measurement can, for example, mitigate the influence of model inaccuracies or tolerances.For example, under ideal conditions, the thermoacoustic sound wave emitted by the heater can be calculated as a function of the excitation signal, allowing changes in the thermoacoustic sound wave due to gas concentration to be calculated using the received signal. However, due to model inaccuracies or heater tolerances, this relationship may not correspond to ideal conditions, such as standard conditions, meaning that a calculated emitted thermoacoustic sound wave does not necessarily correspond to the actually emitted thermoacoustic sound wave. Measuring the heater's temperature can therefore reduce these uncertainties.

[0050] Examples according to the present disclosure include gas sensors in which the electrical resistance of the heater is temperature-dependent and which are designed to generate the temperature signal as a function of the heater's electrical resistance. The temperature dependence of the heater's electrical resistance can, for example, be determined a priori, so that the actual determination of the heater's temperature during operation can be implemented using, for example, a simple current or voltage measurement. Either a current can be applied and a voltage measured, or a voltage can be applied and a current measured. For example, by using a stored temperature-current or voltage table, the heater's temperature can be determined with little or no computational effort.

[0051] In examples according to the present disclosure, the gas sensor further comprises a thermal conductivity determination circuit designed to determine, using the heater signal, the thermal conductivity of the room, which depends on the gas concentration in the room.

[0052] If the heater signal includes a temperature signal indicating the heater's temperature, the thermal conductivity can be determined based on the heat energy or heat output radiated by the heater. The heater's temperature depends on the radiated heat. The radiated heat energy or heat output, in turn, depends on the thermal conductivity of the room. Therefore, if, for example, the material and geometric information of the heater and the room is known, the thermal conductivity can be deduced from the heater's temperature. For instance, a high heater temperature might indicate low thermal conductivity in the room, while a low heater temperature might indicate high thermal conductivity.

[0053] In other words, a known power output can be applied to the heater. From measuring the heater's temperature, the radiated heat energy or heat output can be deduced, and thus the thermal conductivity in the room.

[0054] Alternatively or additionally, by knowing the excitation signal and, for example, a model of the heater, one can deduce the expected temperature of the heater and compare it with the actual temperature of the heater. From this, one can infer the radiated heat and thus the thermal conductivity of the room.

[0055] In further examples, the amplitude of the thermoacoustic sound wave received by the receiver can be determined and compared with the corresponding output amplitude of the thermoacoustic sound wave emitted by the heater, e.g., calculated via the relationship between the thermoacoustic sound wave and the excitation signal or determined from a corresponding temperature signal from the heater, in order to draw conclusions about the thermal conductivity of the room. Furthermore, the temperature signal can be used with other known methods, e.g., the 3-omega method, to draw conclusions about the thermal conductivity of the room.

[0056] The thermal conductivity determination circuit can be integrated into the gas sensor or located outside the sensor, so that the gas sensor can be designed to output a signal indicating the thermal conductivity or enabling the determination of the thermal conductivity.

[0057] In addition to determining the speed of sound, measuring thermal conductivity offers a way to determine gases or gas concentrations. By measuring thermal conductivity alongside the speed of sound, a redundant and therefore particularly robust gas sensor can be implemented, which is especially advantageous in safety-critical applications. Besides using the excitation signal to determine thermal conductivity, the temperature signal can also be used additionally or alternatively.

[0058] In examples according to the present disclosure, the gas sensor includes a driver circuit designed to apply the excitation signal to the heater. The driver circuit can be designed to apply different excitation signals to the heater, such as pulses or periodic excitation signals. Furthermore, the driver circuit can be designed to switch between different excitation signals, for example, to enable different types of evaluation, thereby reducing sources of error in transmission or evaluation. In addition, the driver circuit can be designed to generate the excitation signal.

[0059] In examples according to the present disclosure, at least the heater, the receiver, and the space arranged between the heater and the receiver are integrated into a microsystem or MEMS system (micro-electro-mechanical systems). Microsystems or MEMS systems can include systems with dimensions in the micrometer range and below, for example, with dimensions smaller than 100 µm or smaller than 1 µm. Thus, the terms microsystems or MEMS systems used here also include systems whose structures have dimensions in the nanometer range, which are also referred to as NEMS systems, i.e., nanoelectromechanical systems.

[0060] MEMS systems further include systems with electrical and mechanical components, including stationary mechanical components. In general, examples according to the present disclosure include gas sensors that are integrated or semi-integrated into microsystems or MEMS systems, whereby such systems do not necessarily have to include moving elements.

[0061] Such systems can further be realized using one or more wafers, e.g., Si or SiO wafers, by bulk micromechanics or surface micromechanics. For example, the structures can be fabricated using semiconductor technology methods in the nanometer and / or micrometer range, and the structures can also incorporate materials other than semiconductors. Furthermore, the thermal conductivity determination circuit and / or the gas concentration determination circuit and / or driver circuit can also be integrated. Examples according to the present disclosure thus include integrated microstructures, e.g., microstructures with an integrated or partially integrated gas sensor, or with integrated elements or sub-elements of the gas sensor.

[0062] A high degree of integration facilitates the miniaturization of the gas sensor or parts thereof. Furthermore, an integrated design can reduce costs and enable comprehensive solutions with extensive functionality.

[0063] In examples according to the present disclosure, the microsystem or MEMS system has a first connection for applying the excitation signal to the heater and a second connection for outputting the received signal.

[0064] Such a choice of interfaces allows for good modularity of the gas sensor and / or the overall system. This enables, for example, the use of different driver circuits to generate the excitation signal and / or different circuits to analyze the received signal, depending on the application. Furthermore, this concept facilitates easy integration into a higher-level system.

[0065] In examples according to the present disclosure, the heater is arranged on a first side of a cavity in the microsystem, and the receiver has a membrane that is spaced apart from the heater and arranged on a second side of the cavity in the microsystem or MEMS system. The second side of the cavity can, for example, be a side opposite the first side of the cavity.

[0066] Such an arrangement of heater and membrane allows for good sensitivity of the gas sensor despite the limited installation space of the microsystem or MEMS system. This is because, for example, the thermoacoustic sound wave travels the greatest possible distance, considering the available space, before striking the membrane. This allows for sufficient compensation for the influence of a gas in the cavity on the thermoacoustic sound wave, such as signal delay or a reduction in signal amplitude, in order to obtain a meaningful result for the gas concentration.

[0067] In examples according to the present disclosure, the heater signal is a periodic signal, and determining the propagation-time-dependent shift involves determining a phase shift between the received signal and the heater signal. Excitation with a periodic heater signal can, for example, be achieved energetically efficiently using a resonant circuit, so that a gas sensor according to the disclosure can have low energy consumption.

[0068] In examples according to the present disclosure, determining the transit-time-dependent displacement involves determining the transit time of the thermoacoustic sound wave through space. By determining the transit time of the thermoacoustic sound wave, the speed of sound and thus the gas concentration can be deduced. Furthermore, by analyzing the thermoacoustic sound wave, a potential source of error in the conversion of the thermoacoustic sound wave into a received signal can be reduced or circumvented.

[0069] Further aspects according to the present revelation will be described below with reference to the other figures.

[0070] Fig. Figure 2 shows a schematic side view of an extended example of a gas sensor according to the present disclosure.

[0071] Fig. 2 shows the arrangement from Fig. Figure 1, comprising the heater 110, the receiver 120 (which may include a microphone and / or a temperature sensor), and the space 130 located between the heater and the receiver, as well as the thermoacoustic sound wave 140, an excitation signal 210, and a reception signal 220. Furthermore, a gas concentration determination circuit 230 and the associated signals, on the basis of which the phase shift or transit time is determined, are shown. To determine the phase shifts or transit time of the thermoacoustic sound wave, a reception signal 220 and the heater signal 250 can be used as input. In examples, time information can be used instead of the heater signal to determine the transit time.

[0072] The heater signal 250 can include the excitation signal 210 or the temperature signal 260, which indicates the temperature of the heater 110. These possibilities for the heater signal 250 are indicated in the figure by a signal switch 240. The signal switch 240 serves only to illustrate the possible signal inputs of the gas concentration determination circuit 230, so that in some examples only one of the two signal paths may be implemented, or both signal paths may be implemented.

[0073] Fig. Figure 2 also shows a thermal conductivity determination circuit 270 for determining the thermal conductivity of room 130. The input signal of the thermal conductivity determination circuit 270 is the heater signal 250. Examples of the circuit shown in Figure 2 are also shown. Fig. The thermal conductivity determination circuit 270 can be omitted in the sensor shown in Figure 2.

[0074] Furthermore, it shows Fig. 2. A driver circuit 280, and a microsystem or MEMS system 290 into which the heater 110, the receiver 120, and the space 130 between the heater and the receiver are integrated. It should be noted, however, that further elements may also be integrated into the microsystem or MEMS system 290, for example, the gas concentration determination circuit 230, and / or the thermal conductivity determination circuit 270, and / or the driver circuit 280. The microsystem or MEMS system 290 further comprises a first terminal 300 and a second terminal 310, wherein the excitation signal 210 is present at the first terminal 300 and the receive signal 220 is output at the second terminal 310. In examples where further components are integrated into the microsystem or MEMS system 290, the terminals 300 and 310 need not be provided.

[0075] The driver circuit 280 is designed to apply the excitation signal 210 to the heater 110. In some examples, the driver circuit 280 can also generate the excitation signal 210. The excitation signal 210 can be a single pulse, a sequence of pulses, a superposition of frequencies in a short pulse, or a periodic signal, for example, a continuous signal.

[0076] The excitation signal 210 can have a frequency in the kilohertz range, for example, around 10 kHz. Using the excitation signal 210, the heater 110 generates a thermoacoustic sound wave 140 that propagates through the room 130. The thermoacoustic sound wave 140 travels through the room 130 at a speed of sound. This speed of sound depends on the gas(es) or their concentrations in the room 130; see, for example, [reference to relevant figure]. Fig. 3. Furthermore, the thermal conductivity of the space 130 can influence the thermoacoustic sound wave 140 with respect to the gas(es). The receiver 120 converts the influenced thermoacoustic sound wave 140 into a received signal 220. The received signal 220 is output at the second terminal 310. The analysis of the received signal 220 is performed in the gas concentration determination circuit 230.

[0077] In the gas concentration determination circuit 230, a phase shift between the received signal 220 and the heater signal 250 or a transit time of the thermoacoustic wave 140 is determined on the basis of the received signal 220 and the heater signal 250, at least on the basis of the received signal 220.

[0078] In the thermal conductivity determination circuit 270, the thermal conductivity of the room, which depends on the gas concentration in the room, is determined based on the heater signal 250. For example, a signal amplitude of the thermoacoustic wave 140 could be determined from the heater signal 250 and compared with the amplitude of the thermoacoustic wave upon arrival at the receiver 120, e.g., using a temperature sensor in the receiver, in order to determine, for example, signal attenuation and the thermal conductivity, and from this, in turn, to deduce the gas concentration in the room.

[0079] Alternatively or additionally, the amount of heat, or heat output, dissipated from heater 110 through room 130 can be determined in order to infer the thermal conductivity. This can be done by comparing the temperature of heater 110 with a model, which allows for the inference of the thermal conductivity. Furthermore, the specified 3-omega method can also be applied.

[0080] The results from the gas concentration determination circuit 230 and the thermal conductivity determination circuit 270 can be further processed in their respective determination circuits, for example, to determine the gas concentration in room 130. However, the results can also be further processed in one or more additional circuit sections outside of the respective determination circuit. Furthermore, the gas concentration results from both determination circuits can be combined to determine an overall result, for example, by averaging.

[0081] Fig. Figure 6 shows a schematic side view of an example of a gas sensor according to the present disclosure with a microphone diaphragm. Fig. Figure 7 shows a schematic top view of the example gas sensor from Fig. 6.

[0082] Fig. 6 and Fig. Figure 7 shows a gas sensor 600 with a heater structure 610 and a microphone diaphragm 620, which are attached to a support structure 630. The heater structure 610 can be an embodiment of a previously described heater. A space 130 is arranged between the heater structure 610 and the microphone diaphragm 620. The support structure 630 can be formed by structured and / or unstructured layers of a microsystem or MEMS system. A thermoacoustic wave 140, indicated by an arrow, propagates in the space. The heater structure 610 is configured as a bridge formed by a conductor track, but can also be configured as a diaphragm. The microphone diaphragm 620 has a circular cross-section with a circular recess 640 in the center. The bridge of the heater structure 610 is arranged such that it intersects the recess 640 of the microphone diaphragm 620 at its center.

[0083] The heater structure 610 can be heated electronically in pulsed fashion. This cyclical heating generates a thermoacoustic sound wave 140 in the vicinity of the heater structure 610. The thermoacoustic sound wave 140 is picked up by the microphone diaphragm 620, which is integrated in the second layer below the heater structure 610. The speed of sound can be derived from a time-of-flight-dependent shift, e.g., a phase shift, of the thermoacoustic sound wave 140 picked up by the microphone diaphragm 620 or of the received signal, which depends on the signal's travel time, for example, the travel time of the thermoacoustic sound wave 140. The speed of sound can then be used to infer the presence of a gas or a gas concentration.The Gas Sensor 600 can form a fully integrated sensor system with which the temperature, thermal conductivity and speed of sound within a gas mixture, for example in room 130, can be measured.

[0084] Examples of the present disclosure, for example using the one contained in the Fig. 6 and Fig. The sensor shown in Figure 7 enables a method with the following features: stimulation of a heater structure 610, for example with a frequency of ~10 kHz, generation of a thermoacoustic sound wave 140, propagation of the sound wave at the speed of sound, detection of the sound wave with a microphone diaphragm 620 or a microphone, determination of a phase shift (e.g., Φ) or a transit time or delay of the acoustic signal depending on the speed of sound. In addition, in some examples, the sensor can be configured to detect thermal conductivity, and thus the gas sensor can function as a thermal conductivity sensor.

[0085] Fig. Figure 8 shows a schematic signal waveform of the received signal and the heater signal according to an example from the present disclosure. The heater signal can be the excitation signal or the temperature of the heater. The received signal can be the microphone signal, or the signal picked up by the microphone diaphragm, or another temperature signal, e.g., a temperature signal from the receiver, such as a temperature sensor that forms the receiver or is part of the receiver. Furthermore, Figure 8 shows Fig. 8 an example of a time-dependent shift, e.g. a phase shift, e.g. Φ between excitation and received signal.

[0086] The propagation delay can be determined from the heater and receiver signals, which in turn allows conclusions to be drawn about the speed of sound of the thermoacoustic wave in the room. From this, it is possible to infer the presence of a gas or a gas concentration in the room.

[0087] In the case of a periodic heater signal, as in Fig. As shown in Figure 8, the transit-time-dependent shift can be determined in the form of a phase shift. For this purpose, the gas concentration determination circuit can include a phase detector to determine the phase shift by comparing the heater signal, for example in the form of the excitation signal or the heater temperature, with the received signal.

[0088] It should be noted that the signal profiles are according to Fig. Figure 8 represents only exemplary scenarios. The heater signal can also be a single pulse or a sequence of pulses, and the received signal a correspondingly delayed signal. In this case, the propagation delay-dependent shift can be determined as a signal propagation time or signal delay. For this purpose, the heater signal and the received signal can be compared in the gas concentration determination circuit. The shift can then be determined from the time difference between the two signals.

[0089] Another, simpler approach involves evaluating the received signal together with a time signal in the gas concentration determination circuit. This time signal could be the time of the heater signal or, for example, the time of transmission of the thermoacoustic wave. Based on this time signal or the transmission time, the propagation delay can be determined according to the arrival time of the received signal or the received signal itself.

[0090] Fig. Figure 9 shows a schematic side view of an example of a gas sensor according to the present disclosure with a temperature sensor. Fig. Figure 10 shows a schematic top view of the example of the gas sensor from Fig. 9.

[0091] Fig. 9 and Fig. Figure 10 shows a gas sensor 900, comprising a heater structure 610 and a temperature sensor 910, for example, with a thin membrane, which are attached to a support structure 630. The heater structure 610 can be an embodiment of a previously described heater; furthermore, the temperature sensor 910 can, for example, form the previously described receiver or be part of the receiver. The temperature sensor comprises a sensor structure 930 and a sensor element 940. A space 130 is arranged between the heater structure 610 and the temperature sensor 910. The support structure 630 can be formed by structured and / or unstructured layers of a microsystem or MEMS system. A thermal sound wave 920, indicated by an arrow, propagates in the space. The heater structure 610 can form a temperature emitter. The temperature sensor 910 has a round cross-section with a round recess in which the sensor element 940 is arranged.The sensor element 940 is designed as a bridge and exhibits a temperature-dependent resistance. The heater structure 610 is also designed as a bridge and is arranged such that the bridge of the heater structure 610 intersects the recess of the temperature sensor 910 centrally and perpendicularly to the sensor element 940 of the temperature sensor 910.

[0092] The temperature sensor 910 or the sensor element 940 can have a low heat capacity and can be used to detect the thermoacoustic sound wave that has propagated through the space. The temperature sensor 910 can also follow the frequency of the temperature transmitter, for example, the heater structure 610. For example, the heater structure 610 can emit a thermal sound wave 920, excited by an excitation signal with a specific frequency, so that after the thermal sound wave 920 has passed through the space between the heater structure 610 and the temperature sensor 910, the wave reaches the temperature sensor 910, where, for example, the frequency of the received signal of the temperature sensor corresponds to the frequency of the heater structure 610 or the temperature transmitter.

[0093] Furthermore, the gas sensor 900 can have a frequency range from one or a few hertz up to 100 kHz; for example, the temperature sensor 910 or the sensor element 940 can only follow the temperature emitter 610 within such a frequency range. Frequency ranges can describe frequencies of the excitation signal and / or the received signal.

[0094] The time-dependent signal shift or phase shift and the signal level, e.g., the amplitude of the signal, for example, the received signal or temperature signal at the temperature sensor, for example, between temperature emitter and temperature sensor, depends on the thermal conductivity of the gas and also on pressure and temperature.

[0095] Thus, given, for example, known pressure and temperature, the relationship with thermal conductivity can be determined, e.g., according to... Fig. 5 can be inferred from a gas or the concentration of the gas in the room.

[0096] Examples of the present disclosure, for example using the one contained in the Fig. 9 and Fig. The 10 sensors shown enable a method with the following features: Stimulation of the heater structure 610, for example with a frequency ~10 kHz, generation of a thermal sound wave 920, propagation of the thermal sound wave at the speed of sound, detection of the sound wave with the temperature sensor 910 and / or with the sensor element 940, determination of a phase offset or phase shift (e.g. Φ) or a transit time or transit time delay of the acoustic signal depending on the speed of sound.

[0097] A gas sensor according to Fig. 9 and Fig. 10 can enable a simple design of the gas sensor, so that the gas sensor is, for example, less complicated, e.g., with regard to manufacturing or susceptibility to interference, e.g., compared to the presented design of the Fig. 6 and Fig. It can be 7.

[0098] All the materials, environmental influences, electrical properties and optical properties listed herein are to be regarded as examples and not as exhaustive. Conclusions and further remarks

[0099] In general, examples according to the present disclosure create gas sensors with several fundamental, physically based, and therefore, for example, very robust measurement methods. Furthermore, these measurement methods, or elements of gas sensors according to the disclosure, can be combined in a microsystem or a MEMS chip based on these measurement methods. Examples according to the present disclosure also enable a high degree of integration and the combination of multiple measurement principles.

[0100] Examples according to the present disclosure enable the reduction of systems, such as gas sensors, to a minimum, for example with regard to dimensions or manufacturing and / or integration effort. For example, complex PCB-based structures could be integrated into a chip package using the gas sensor according to the disclosure.

[0101] In general, examples according to the present disclosure create gas sensors in which a thermoacoustic sound wave, which is generated during the measurement of thermal conductivity, is simultaneously used to measure the speed of sound.

[0102] Examples according to the present disclosure create systems, e.g. integrated systems, e.g. systems with an integrated or semi-integrated gas sensor, which can be implemented in a small form, e.g. with small dimensions or dimensions, and can have a low complexity.

[0103] Examples according to the present disclosure provide gas sensors comprising a heater structure which is excited by an excitation signal, e.g., with a high frequency, to emit a thermoacoustic wave, and in which the thermoacoustic wave passes through a space containing a gas concentration to be detected. Subsequently, in some examples, the thermoacoustic wave is converted by a receiver into a received signal, which is evaluated with respect to both the thermal conductivity and the speed of sound of the gas-filled space. Alternatively, in some examples, the received signal can be evaluated only with respect to the speed of sound, and the thermal conductivity is determined based on the heater signal, which may include the excitation signal of the heater structure or its temperature.

[0104] In examples according to the present disclosure, the Omega-3 method can be used to determine the thermal conductivity, e.g. in addition to a determination of the speed of sound of the thermoacoustic wave according to the disclosure.

[0105] In general, in examples according to the present disclosure, a predetermined power is applied to the heating structure and a temperature is measured to determine the thermal conductivity. The measured temperature depends on the gas concentration.

[0106] Examples according to the present disclosure create robust H2 sensors.

[0107] Examples according to the present disclosure create gas sensors which are based on the combination of a determination of a thermal conductivity and a speed of sound, using a thermoacoustic sound wave.

[0108] In some examples, a processing circuit, such as a gas concentration determination circuit or a thermal conductivity determination circuit, can be implemented using any suitable circuit structure, such as microprocessor circuits, ASIC circuits, CMOS circuits, and the like. In others, the processing circuit can be implemented as a combination of hardware structures and machine-readable instructions. For example, the processing circuit can include a processor and a memory device that stores machine-readable instructions which provide the described functionalities and, when executed by the processor, lead to the execution of the procedures described herein.In examples, the storage device can be implemented by any suitable storage device, such as ROM, PROM, EPROM, EEPROM, flash memory, FRAM (ferroelectric RAM), MRAM (magnetoresitive RAM), or phase-change RAM. Implementation alternatives

[0109] Although some aspects have been described in connection with a device, it is understood that these aspects also constitute a description of the corresponding process, so that a block or component of a device can also be understood as a corresponding process step or as a feature of a process step. Similarly, aspects described in connection with or as a process step also constitute a description of a corresponding block, detail, or feature of a corresponding device. Some or all of the process steps can be performed by (or using) a hardware apparatus, such as a microprocessor, a programmable computer, or an electronic circuit. In some examples, some or more of the key process steps can be performed by such an apparatus.

[0110] The examples described above merely illustrate the principles of the present invention. It is understood that modifications and variations of the arrangements and details described herein will be obvious to other people skilled in the art. Therefore, it is intended that the invention be limited only by the scope of protection set forth in the following claims and not by the specific details presented herein by way of description and explanation of the examples.

Claims

[1] Gas sensor with the following features: a stoker, a recipient, and a space arranged between the heater and the receiver, wherein the heater is designed to generate a thermoacoustic sound wave propagating through the space using an excitation signal, and wherein the receiver is designed to receive the thermoacoustic sound wave that has propagated through the room and to convert it into a received signal that has a time-dependent shift relative to the excitation signal and thus provides information about a gas concentration in the room; and a gas concentration determination circuit designed to determine a phase shift between the received signal and a heater signal, or, based on the received signal, a travel time of the thermoacoustic wave through the room, each of which is a measure of the gas concentration in the room; and a thermal conductivity determination circuit designed to determine the thermal conductivity of the room, which depends on the gas concentration in the room, using the heater signal, where the heater signal is the excitation signal or a temperature signal indicating the temperature of the heater. [2] Gas sensor according to claim 1, wherein the receiver has a microphone. [3] Gas sensor according to claim 1, wherein the receiver has a temperature sensor. [4] Gas sensor according to one of claims 1 to 3, wherein the electrical resistance of the heater is temperature-dependent, the gas sensor being designed to generate the temperature signal depending on the electrical resistance of the heater. [5] Gas sensor according to any one of claims 1 to 4, comprising a driver circuit designed to apply the excitation signal to the heater. [6] Gas sensor according to any one of claims 1 to 5, wherein at least the heater, the receiver and the space arranged between the heater and the receiver are integrated into a microsystem or MEMS system. [7] Gas sensor according to claim 6, wherein the microsystem or MEMS system has a first connection for applying the excitation signal to the heater and a second connection for outputting the received signal. [8] Gas sensor according to claim 6 or 7, wherein the heater is arranged on a first side of a cavity in the microsystem or MEMS system and the receiver has a membrane which is spaced apart from the heater on a second side of the cavity in the microsystem or MEMS system. [9] Method for determining a gas concentration, comprising the following features: Applying an excitation signal to a heater to generate a thermoacoustic sound wave that propagates through a space located between the heater and a receiver, Receiving the thermoacoustic sound wave at the receiver to generate a received signal, Determining a time-of-flight-dependent shift between a heater signal and the received signal, and Determining the gas concentration in the room using the determined transit-time-dependent displacement and Determination of the thermal conductivity of the room, which depends on the gas concentration in the room, using the heater signal; wherein the heater signal is the excitation signal or a temperature signal indicating a temperature of the heater. [10] Method according to claim 9, wherein the heater signal is a periodic signal and determining the time-of-flight-dependent shift involves determining a phase shift between the received signal and the heater signal. [11] Method according to claim 9, wherein determining the transit-time dependent displacement comprises determining a transit time of the thermoacoustic sound wave through the space. [12] Method according to any one of claims 9 to 11, wherein the electrical resistance of the heater is temperature-dependent and the temperature signal is generated as a function of the electrical resistance of the heater.

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