Sensor system for monitoring the characteristics of a dewar tank

Abstract

This system provides a sensor for monitoring the characteristics of a dewar tank. [Solution] The sensor system includes a sensor arrangement comprising a first magnetic field sensor and a first permanent magnet element, and a controller. The first magnetic field sensor is connected to the controller. The first magnetic field sensor is configured to be mounted on the outer shell 22 of the dewar tank 20. The first permanent magnet element is configured to be mounted on the inner shell 21 or outer shell of the dewar tank. The first magnetic field sensor and the first permanent magnet element are configured to be positioned in close proximity to each other when mounted on the dewar tank, so that the magnetic field sensor can detect the magnetic field generated by the first permanent magnet element. The controller is configured to measure the magnetic field of the first permanent magnet element via the first magnetic field sensor and to infer at least one characteristic of the dewar tank based on the detected magnetic field of the first permanent magnet element.

Description

[Technical Field]

[0001] This disclosure relates to a sensor system for a fluid tank, and more specifically, to a sensor system for monitoring the characteristics of a dewar tank. [Background technology]

[0002] In light of the increasing emphasis on environmental protection, alternative propulsion sources for aircraft are being developed. These alternative propulsion sources may utilize alternative fuels other than kerosene, such as liquid hydrogen, which cannot be stored in conventional fuel tanks. Therefore, hydrogen fuel or other liquid-gas fuels must be stored in appropriate tanks (such as dewar tanks), and these tanks must be able to withstand, for example, the internal pressure and low temperatures (20K) required to store the gas in liquid form. However, for safety reasons, it is also necessary to be able to accurately monitor specific tank characteristics, such as the fuel tank's fill level and temperature, at all times.

[0003] For example, the fill level of a fluid tank can currently be determined indirectly by measuring the weight of the tank or by monitoring the amount of fluid leaking from the tank. However, these methods may be inaccurate or unsuitable for aircraft applications. For example, it is not easy to implement soft suspension (such as that found in weighing scales) in mobile vehicles. In aircraft, for example, altitude changes occur, and in the ascending or descending sections of such an aircraft, the gravity vector on the fuel tank may not be constant, making it difficult to determine accurate weight values ​​and, consequently, fill levels. Similar challenges arise in curved flight sections where the aircraft's flight vector changes. Furthermore, detection solutions, such as those currently used for kerosene detection in aircraft wings, cannot be used in hydrogen tanks for safety reasons (separation of electronics from hydrogen is required) and thermal insulation (leakage) reasons.

[0004] Therefore, in several patent applications by the applicant, non-intrusive sensing systems for cryogenic tanks for measuring the fill level of hydrogen tanks, particularly in aircraft applications, have already been described. One of these solutions is the interpretation of measurements based on vibration. Prior to these inventions, the technical options available for this purpose were very limited.

[0005] For example, the applicant's patent application (Patent Document 1) (briefly described below) describes a general method for determining the filling level of a fluid tank by monitoring the resonant frequency of the fluid tank, which illustrates the concept and gauging principle.

[0006] (Patent Document 1) describes a fill level monitoring device for liquid tanks such as hydrogen tanks, a hydrogen tank equipped with such a fill level monitoring device, and an aircraft equipped with such a hydrogen tank. The fill level monitoring device uses a signal source and an excitation element to transmit a vibration load having multiple frequency components to the container. The resonant frequency of the container depends on the fill level of the container. After the excitation element transmits the vibration load to the container, a sensing element measures the vibration inside the container. A processing unit performs spectral analysis of the input signal from the signal source and the vibration signal from the sensing element, and extracts the resonant frequency by comparing the spectral functions of the input signal and the vibration signal. The resonant frequency of the container further depends on the spatial localization of the container. A fill level display unit calculates the current fill level of the container from the extracted resonant frequency and the spatial localization signal from the spatial localization sensor by correlating the collected data with reference data.

[0007] In addition to the above, liquid hydrogen (LH2) for aviation purposes is preferably stored in cylindrical dewar-type tanks, the cylindrical axis of which is horizontal to the ground, although other shapes are also possible. Such a dewar tank includes an inner shell and an outer shell. The inner shell contains the liquid hydrogen. The outer shell surrounds the inner shell. The space between the inner and outer shells is filled with a high vacuum. To minimize LH2 leakage and maintain the required cryogenic temperature as best as possible, the tanks are welded during manufacturing.

[0008] Preferably, when monitoring the characteristics of the tank (to determine the fill level, measure the temperature, or for any other purpose), these characteristics must be monitored in the inner shell in direct contact with the LH2. This creates a problem where, when replacement / maintenance is required of any equipment installed inside the tank, specifically on the inner shell (e.g., vibration sensors used to determine the fill level by measurement based on vibrations at resonant frequencies, as described in (Patent Document 1), or temperature sensors), the tank must be completely dismantled and cut open. Therefore, in-line maintenance / repair of such elements is impossible, and downtime and the cost of performing such operations are significantly increased. The materials used in the manufacture of Dewar tanks are non-magnetic, such as aluminum, non-magnetic stainless steel alloys, and CFRP, which are permeable to magnetic fields. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2023 / 217807A1 brochure [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] The objective is to provide a sensor system for monitoring the characteristics of a dewar tank, which enables simple and time-saving maintenance by allowing the active component to be replaced in the event of a sensor component failure, specifically without disassembling and cutting open the dewar tank. [Means for solving the problem]

[0011] This objective is achieved by the subject matter of the independent claim. Further embodiments are described in the dependent claims and the following description.

[0012] According to a first embodiment, a sensor system is provided for monitoring the characteristics of a dewar tank having an inner shell and an outer shell. The sensor system includes a sensor arrangement including a first magnetic field sensor and a first permanent magnet element, and a controller. The first magnetic field sensor is connected to the controller. The first magnetic field sensor is configured to be mounted on the outer shell of the dewar tank. The first permanent magnet element is configured to be mounted on either the inner or outer shell of the dewar tank. The first magnetic field sensor and the first permanent magnet element are configured to be located in close proximity to each other when mounted on the dewar tank, so that the magnetic field sensor can detect the magnetic field generated by the first permanent magnet element. The controller is configured to measure the magnetic field of the first permanent magnet element via the first magnetic field sensor and to infer at least one characteristic of the dewar tank based on the detected magnetic field of the first permanent magnet element.

[0013] As shown in the introduction, liquid hydrogen (or, in principle, any other cryogenic fluid) can preferably be filled into a dewar tank having an inner shell and an outer shell. When the inner and outer shells of the dewar tank are assembled, a high vacuum exists between them for adiabatic purposes. Active sensors installed on the inner shell may need to be replaced or maintained at some point after assembly, which is difficult because it would require disassembling and cutting open the dewar tank. The present invention avoids this by not installing active components on the inner shell. Instead, all active components are placed on the outer shell, and only non-active components that do not require replacement or maintenance, such as permanent magnet elements, or in some embodiments, superconducting elements, are placed on the inner shell. The disclosed sensor system takes advantage of the fact that magnetic fields can pass through metal (specifically, the metal used in the manufacture of the dewar tank).

[0014] The sensor arrangement includes at least one magnetic field sensor and at least one permanent magnet element, which together constitute a functional sensor for measuring, for example, vibration or temperature of an inner shell containing a fluid filler. Such vibration measurements can be used, for example, to measure the filler level by monitoring the resonant frequency, as shown in the introduction. It should be understood that in some embodiments, the sensor system may include multiple sensor arrangements, as will be further described below with respect to one embodiment.

[0015] In its simplest form, such a sensor configuration includes one magnetic field sensor and one permanent magnet element. The permanent magnet element is located in the upper part of the inner shell, and the magnetic field sensor is positioned in the upper part of the outer shell, specifically above or at least near the permanent magnet element, so as to be able to detect the magnetic field of the permanent magnet element. The magnetic field sensor is connected to a controller, which performs the function of evaluating the measurement data. The magnetic field sensor can be any suitable sensor, such as a fluxgate sensor, Hall effect sensor, magnetoresistive sensor, inductive sensor, SQUID (superconducting quantum interference device) sensor (if the requirements are met), photo-excited magnetometer, Wiegand sensor, magneto-optical sensor, or any other suitable type of magnetic field sensor. However, this enumeration is essentially illustrative and not limiting.

[0016] The permanent magnet element can be any suitable permanent magnet, depending on the application, such as a samarium-cobalt magnet (SmCo magnet), a neodymium-iron-boron magnet (NdFeB magnet), or any other suitable permanent magnet. For example, SmCo magnets exhibit relatively stable magnetization at extremely low temperatures, making them particularly useful in applications where stable magnetization is required, such as vibration measurements. On the other hand, NdFeB magnets are more sensitive to temperature changes. Sintered NdFeB magnets exhibit a negative dependence of their residual magnetic field on temperature (typically -0.1% / K around room temperature). This means that the magnetic field increases when the temperature is lowered to about 140K, and then begins to decrease due to the spin rearrangement process. Therefore, such NdFeB magnets are particularly useful for temperature measurements because their magnetic field is very sensitive to temperature changes.

[0017] Generally, permanent magnet elements generate a static magnetic field (under stable conditions, such as stable temperature conditions, e.g., NdFeB magnets). This static magnetic field can be used for vibration measurement, for example, as follows: Since the permanent magnet element is located on the inner shell, when the inner shell vibrates, the permanent magnet element also vibrates in sync. Next, the inner shell vibrates relative to the outer shell. Since the magnetic field sensor is installed near the permanent magnet element, specifically on the outer shell above the permanent magnet element, the magnetic field lines of the permanent magnet element (naturally, closed magnetic field lines extending from the north pole to the south pole of the permanent magnet element) penetrate the magnetic field sensor in different ways depending on the relative position of the inner shell (including the permanent magnet element) with respect to the outer shell (including the magnetic field sensor). In other words, when the inner shell vibrates relative to the outer shell, a change in the magnetic field occurs due to the change in the relative position of the inner shell with respect to the outer shell. The magnetic field sensor detects this change in the magnetic field, and by tracking this change over time, a time-series signal of vibration can be obtained from the magnetic field sensor. Next, as shown in the introduction, such a time-series signal can be used, for example, in filling level monitoring measurement as described in the application of (Patent Document 1).

[0018] In the case of temperature measurement, specifically, if the magnetization of a permanent magnet element is extremely sensitive to temperature changes, a magnetic field sensor can detect changes in magnetic field strength and / or changes in the direction / shape of magnetic field lines resulting from such changes. The corresponding measurement signal can then be correlated with different temperatures, for example, based on calibration, based on a physical model, by machine learning, or by any other suitable method.

[0019] The above use cases of vibration and temperature measurement are essentially just examples. In principle, the sensor system can also be used to measure other characteristics of the Dewar tank. For example, when the inner shell is slightly deformed due to a pressure increase, the arrangement of the inner shell relative to the outer shell changes (slightly), and as a result, the magnetic field at the position of the corresponding magnetic field sensor also changes. Therefore, such a change can also be detected by the magnetic field sensor and can be correlated with the internal pressure of the Dewar tank, for example, by calibration, by a physical model, by machine learning, or by any other suitable method. Other use cases are also conceivable. Therefore, the present disclosure is not limited to any one of these use cases.

[0020] In another example, corresponding measurements can also be realized by installing both the magnetic field sensor and the permanent magnet element adjacent to each other on the upper part of the outer shell with a certain gap. In such a configuration, another additional passive element (such as a superconducting element) that distorts the magnetic field lines is installed below the permanent magnet element and / or below the magnetic field sensor. Then, the magnetic field sensor tracks the change in the magnetic field lines that are closed in a different form due to the presence of the superconducting element. Also in this case, these changes are directly correlated with the relative movement / position of the inner shell and the outer shell.

[0021] In any of the configurations described in this specification, the positions and shapes of all necessary permanent magnet elements, superconducting elements, etc. need to be optimized with respect to the resolution and dynamic range of the magnetic field sensor.

[0022] According to one embodiment, at least one characteristic includes at least one of the temperature of the Dewar tank and at least one filling level of the Dewar tank based on at least one vibration mode of the Dewar tank that correlates with the filling level.

[0023] Vibration and temperature measurements themselves are described in more detail above. To measure the filling level by vibration mode, for example, the suspension mode (vibration mode of the suspension element) or the horizontal vibration mode (vibration mode corresponding to vibrations propagating horizontally within the dewar tank) is particularly useful in determining the filling level of the dewar tank, because, as explained in the applicant's previous patent applications, these modes have a high correlation with the filling level of the dewar tank.

[0024] According to another embodiment, the first permanent magnet element is one of the types of samarium cobalt magnets (SmCo magnets) and neodymium iron boron magnets (NdFeB magnets).

[0025] SmCo magnets exhibit relatively stable magnetization at cryogenic temperatures, particularly at the temperatures used for liquid hydrogen. Therefore, SmCo magnets are particularly useful when such stable magnetization is required, for example, for vibration measurements. On the other hand, NdFeB magnets are more sensitive to temperature changes. This characteristic can be utilized, for example, for temperature measurement.

[0026] According to another embodiment, the sensor arrangement further includes a second permanent magnet element of a type different from the first permanent magnet element. Both the first permanent magnet element and the second permanent magnet element are configured to be attached to the inner shell of the dewar tank.

[0027] Specifically, can both the first permanent magnet element and the second permanent magnet element be associated with a single magnetic field sensor (i.e., install both permanent magnet elements on the inner shell near the magnetic field sensor so that the magnetic field sensor can detect the magnetic fields of both permanent magnet elements), or can each of the first permanent magnet element and the second permanent magnet element be associated with an individual magnetic field sensor. In the former case, the individual signals detected by the single sensor from the two permanent magnet elements can be distinguished by, for example, a corresponding data analysis algorithm based on calibration. In the latter case, the individual signals can be directly distinguished by the signals of the individual magnetic field sensors.

[0028] Specifically, the first and second permanent magnet elements (or more precisely, their magnetizations) may have different sensitivities / characteristics with respect to the characteristics of the dewar tank being monitored. For example, the first permanent magnet element may be an SmCo magnet (stable to temperature changes), and the second permanent magnet element may be an NdFeB magnet (temperature sensitive). However, other combinations are also possible. Such combinations of different types of permanent magnet elements can provide additional information to improve the accuracy of the corresponding measurements. Furthermore, such combinations can add redundancy.

[0029] According to another embodiment, the sensor arrangement further includes a second magnetic field sensor. The first permanent magnet element is configured to be positioned below the first magnetic field sensor. The second permanent magnet element is configured to be positioned below the second magnetic field sensor.

[0030] This configuration allows for direct differentiation of the magnetic signals from both permanent magnet elements, as described above.

[0031] According to another embodiment, the first permanent magnet element is of a type that is stable with respect to temperature changes. The second permanent magnet element is of a type that is relatively sensitive to temperature changes.

[0032] In this configuration, the presence of two types of permanent magnet elements (provided both have been previously calibrated individually for temperature) can provide additional information to improve the accuracy of the measurement system. Furthermore, the two different permanent magnet elements may be sensitive to temperature changes in different temperature ranges (e.g., with relatively large magnetic field gradients with respect to temperature), thereby extending the overall sensitivity range of the sensor configuration to temperature changes. The "more sensitive" nature of the second permanent magnet element to temperature changes could mean that while the first permanent magnet element is largely unresponsive to such temperature changes, the second permanent magnet element is not, or that the second permanent magnet element is sensitive to temperature changes over a wider temperature range.

[0033] In another embodiment, the first permanent magnet element is a samarium cobalt magnet (SmCo magnet). The second permanent magnet element is a neodymium iron boron magnet (NdFeB magnet).

[0034] According to another embodiment, the sensor system further includes a superconducting element that becomes superconducting at cryogenic temperatures. Both the first magnetic field sensor and the first permanent magnet element are configured to be mounted adjacent to each other on the outer shell of the dewar tank. The superconducting element is configured to be mounted on the inner shell of the dewar tank below the first permanent magnet element and / or below the magnetic field sensor.

[0035] In this configuration, both the magnetic field sensor and the permanent magnet element are positioned in close proximity to each other on the outer shell, allowing for replacement / maintenance without dismantling the dewar tank if necessary. To ensure that monitoring of the inner shell's relative movement to the outer shell (or any other suitable property of the inner shell as described herein) is still possible, a superconducting element that becomes superconducting at cryogenic temperatures is positioned below the magnetic field sensor, below the permanent magnet element, or below both, instead of the permanent magnet element.

[0036] Generally, superconductors exert a unique influence on magnetic field lines, primarily through the Meissner-Ochsenfeld effect, which actively rejects magnetic fields. This behavior differs depending on whether the material is a type I or type II superconductor. The Meissner-Ochsenfeld effect can be explained as follows: When a material transitions to a superconducting state, it completely rejects magnetic field lines from within. This occurs regardless of whether the magnetic field is applied before or after the transition. This effect arises because an electric current is formed on the surface of the superconductor, thereby generating a magnetic field that precisely cancels out the external magnetic field. Therefore, the magnetic field disappears inside the superconductor.

[0037] In type I superconductors, magnetic fields below a critical threshold are completely eliminated. When a magnetic field exceeds this threshold, the superconductor loses its superconducting properties and returns to a normal conducting state. Examples of type I superconductors include pure metals such as mercury or lead.

[0038] Type II superconductors exhibit two critical magnetic field strengths. Below the lower critical magnetic field, they behave similarly to Type I superconductors (completely rejecting the magnetic field). Between the lower and upper critical magnetic fields, Type II superconductors enter a mixed state, meaning they are surrounded by superconducting regions, and magnetic field lines penetrate the superconductor in the form of flux vortices. Above the upper critical magnetic field, the material returns to a normal conducting state. Examples of Type II superconductors include high-temperature superconductors such as YBCO (yttrium barium copper oxide).

[0039] In summary, in relation to this embodiment of the present invention, the superconductor has the effect of repelling (shielding by the Meissner effect) magnetic field lines. Furthermore, in type II superconductors, magnetic field lines can penetrate as quantization vortices. Overall, these effects result in distortion of magnetic field lines generated by the permanent magnet element. This distortion depends on the relative arrangement between the superconducting element and the permanent magnet element. Thus, since the superconducting element is located on the inner shell and the permanent magnet element is located on the outer shell, the relative movement of the inner shell to the outer shell affects the magnetic field lines detected / measured by the magnetic field sensor on the outer shell. Furthermore, the superconducting effect also depends on the temperature within the superconducting range, thereby allowing for the detection of temperature changes, for example.

[0040] By using a superconducting element on the inner shell and a permanent magnet element on the outer shell, the permanent magnet element can be replaced if it becomes demagnetized for any reason (for example).

[0041] According to another embodiment, the sensor system includes at least two sensor arrangements.

[0042] For example, multiple sensor arrangements (each configured as described in relation to any one of the embodiments described herein; that is, depending on the use case, the individual sensor arrangements may be configured differently from each other, or all sensor arrangements may be of the same type) can be arranged at different locations on the dewar tank, for example, spaced apart from each other in the circumferential direction of the dewar tank.

[0043] By placing sensors at different locations on the cylindrical wall of a dewar tank, for example, displacement and temperature can be monitored at different points. For example, by using a long filter in a certain time domain (to reduce the effects of random vibrations and readout noise) on the data collected at each detection point (i.e., from each sensor placement), the deviation from the expected cross-section of the inner shell can be estimated, which enables monitoring of deformation and stress, for example. Furthermore, by using an appropriate model (or, for example, a machine learning algorithm trained with appropriate training data), the internal pressure can also be estimated.

[0044] According to another embodiment, the sensor arrangement further includes a magnetic shield for shielding the magnetic field sensor and / or permanent magnet element from stray magnetic fields.

[0045] Since stray magnetic fields can be detected by magnetic field sensors, they may distort the measurement characteristics. Therefore, to obtain accurate measurement results, magnetic field sensors can be shielded from such stray magnetic fields by, for example, using a cap made of a highly permeable material such as mu-metal (nickel-iron soft magnetic material) or any other suitable material, which is placed above the corresponding magnetic field sensor. Since permanent magnet materials are placed below or next to the magnetic field sensor, such shielding can also shield the permanent magnet elements from stray magnetic fields that could demagnetize them.

[0046] According to a second embodiment, a hydrogen tank is provided. The hydrogen tank is a dewar tank for holding liquefied hydrogen, and includes a dewar tank having an inner shell and an outer shell, and a sensor system according to any one of the embodiments described herein.

[0047] According to a third embodiment, a vehicle is provided. The vehicle includes an airframe and a hydrogen tank as described herein. A sensor system is configured to monitor the hydrogen level in the fluid container.

[0048] Vehicles can be of any kind, including aircraft, automobiles, road vehicles such as semi-trucks or trucks, water vehicles such as boats or ships, spacecraft, or any other suitable vehicle.

[0049] According to one embodiment, the vehicle is an aircraft.

[0050] In summary, this disclosure provides a sensor system for monitoring specific properties of a dewar tank. Such properties may include, but are not limited to, vibration, temperature, pressure, deformation, stress, and any other conceivable quantities measurable by the sensor arrangement of the disclosed sensor system. For example, vibration measurement can be used to determine the fill level of a dewar tank by monitoring vibration modes sensitive to the fill level. Since all active components (magnetic field sensors) are located on the outer shell of the dewar tank, these components can be easily replaced / maintained without cutting open or dismantling the dewar tank, thereby enabling measurement / monitoring of dewar tank properties from the inner shell while reducing system complexity and maintenance time.

[0051] The following describes exemplary embodiments in more detail with reference to the attached figures. The illustrations are schematic and not to scale. The same reference numerals refer to the same or similar elements. [Brief explanation of the drawing]

[0052] [Figure 1] This is a schematic diagram of a hydrogen tank in the form of a dewar tank that can use the sensor system disclosed herein. [Figure 2] Figure 1 is a schematic diagram of at least a portion of a sensor system mounted on a dewar tank, and includes a sensor arrangement having a first magnetic field sensor and a first permanent magnet element in a first exemplary configuration. [Figure 3]Figure 1 is a schematic diagram of at least a portion of a sensor system mounted on a dewar tank, and includes a sensor arrangement having a first magnetic field sensor, a first permanent magnet element, and a superconducting element according to a second exemplary configuration. [Figure 4] Figure 1 is a schematic diagram of at least a portion of a sensor system mounted on a dewar tank, and includes a sensor arrangement having a first magnetic field sensor, a second magnetic field sensor, a first permanent magnet element, and a second permanent magnet element according to a third exemplary configuration. [Figure 5] This is a schematic diagram of a dewar tank equipped with four sensors. [Figure 6] This is a circuit diagram of an example magnetic field sensor. [Figure 7] This is a schematic diagram of an aircraft equipped with a hydrogen tank having a sensor system according to one of the embodiments described herein. [Modes for carrying out the invention]

[0053] Figure 1 shows a schematic diagram of a hydrogen tank 30 in the form of a dewar tank 20. The dewar tank 20 includes an inner shell 22 and an outer shell 21. A high vacuum 26 exists between the inner shell 22 and the outer shell 21 for insulating purposes to maintain the cryogenic temperature inside the dewar tank 20. The inner shell 22 is the wall of the fluid container, and a fluid (in this case, hydrogen) can be stored inside it. The dewar tank 20 is shown to have a filling containing liquid hydrogen 24 in the liquid phase and gaseous hydrogen 23 in the gas phase. It should be understood that this disclosure is not limited to hydrogen tanks and is applicable to any dewar tank 20 for any fluid. A gas / liquid interface 25 separates the liquid hydrogen 24 and gaseous hydrogen 23. In state-of-the-art technology, corresponding sensors such as vibration sensors or temperature sensors need to be attached to the inner shell 22 to monitor characteristics such as filling level, temperature, and pressure, because this inner shell is in contact with the filling of the dewar tank 20. However, in this state, the dewar tank must be disassembled when replacing / maintaining the corresponding sensor, as further explained above in this specification.

[0054] To avoid such disassembly, Figure 2 shows a first configuration of the sensor system 10 according to this disclosure, usable in the dewar tank 20 of Figure 1. The sensor system 10 includes a sensor arrangement 16 (shown by a dashed ellipse). The sensor arrangement 16 includes a first magnetic field sensor 11 and a first permanent magnet element 12 (multiple magnetic field sensors 11 and multiple permanent magnet elements 12 may be used, as will be apparent from the description of Figure 4 and the further description above). The first permanent magnet element 12 is located in the vacuum 26 (see Figure 1) above the inner shell 22 of the dewar tank 20 (Figure 1). The first magnetic field sensor 11 is located near, specifically above, the first permanent magnet element 12, so that the first magnetic field sensor 11 can measure / detect the magnetic field generated by the first permanent magnet element 12. The first magnetic field sensor 11 is connected to a controller 13, which performs the function of evaluating the measurement values ​​of the magnetic field sensor 11. Controller 13 can be any suitable controller, such as a general-purpose computer having a CPU and memory components, FPGA, ASIC, or any other suitable device. Furthermore, Controller 13 can be, for example, part of the flight computer of an aircraft 40 (Figure 7).

[0055] Since the permanent magnet element 12 is attached to the inner shell 22 and the magnetic field sensor 11 is attached to the outer shell 11, the relative movement of the inner shell 22 with respect to the outer shell 21 is directly converted into the relative movement of the first permanent magnet element 12 with respect to the first magnetic field sensor 11. Therefore, for example, if the inner shell 22 vibrates relative to the outer shell 21, the magnetic field measured by the first magnetic field sensor 11 will be deflected in conjunction with these vibrations (the permanent magnet element 12 generates a static magnetic field, and the relative position of the permanent magnet element 12 with respect to the magnetic field sensor 11 changes in conjunction with the vibrations). Furthermore, the magnetization of the first permanent magnet element may also depend, for example, on the temperature of the inner shell (which is in direct thermal contact with the permanent magnet element 12), and as a result, the magnetic field at the position of the magnetic field sensor 11 changes with temperature changes. This fact can be used to infer the temperature of the inner shell 12 from the magnetic field measured by the magnetic field sensor 11.

[0056] The first permanent magnet element 12 can be selected according to the characteristics to be monitored. Examples of suitable permanent magnet elements 12 include, for example, samarium cobalt magnets (SmCo magnets) or neodymium iron boron magnets (NdFeB magnets). For example, SmCo magnets are particularly useful in vibration measurements (e.g., measurement of filling levels based on vibration modes correlated with filling levels) because their magnetization is relatively stable even at extremely low temperatures. On the other hand, NdFeB magnets are particularly useful in temperature measurements, as described in more detail above, because they are more sensitive to temperature changes.

[0057] The sensor system 10 in Figure 2 allows for easy maintenance or replacement of the magnetic field sensor 11 (as the active element of the sensor system 10) without disassembling the dewar tank 20, if necessary.

[0058] Figure 3 shows another configuration of the sensor system 10 having a different sensor arrangement 16. Unlike the sensor arrangement 16 in Figure 2, in sensor arrangement 16, both the first magnetic field sensor 11 and the first permanent magnet element 12 are positioned side by side with a gap / distance between them in the outer shell 21 of the dewar tank 20. In addition, a superconducting element 14 is installed on the inner shell 22 of the dewar tank 20 below the first permanent magnet element 12. The superconducting element 14 becomes superconducting at extremely low temperatures, as described in more detail above. The permanent magnet element 12 (like any magnet) generates closed magnetic field lines. These magnetic field lines are affected / strained by the superconducting element 14, depending on the position of the superconducting element 14 relative to the first permanent magnet element 12 and the first magnetic field sensor 11. Therefore, when the inner shell 22 is displaced relative to the outer shell 21 (for example, by vibration), the magnetic field measured by the first magnetic field sensor 11 changes in conjunction with the relative movement of the inner shell 22 to the outer shell 21 due to these vibrations. Furthermore, since the superconducting effect of the superconducting element 14 also depends on temperature (within the superconducting range), temperature changes can also be detected, for example, by the configuration shown in Figure 3. This is because the shape of the magnetic field lines of the first permanent magnet element 12 depends on the temperature of the superconducting element 14 that is in direct contact with the inner shell 22. By using the superconducting element 14 on the inner shell 22 and the permanent magnet element 12 on the outer shell 21, the permanent magnet element 12 can be easily replaced if it becomes demagnetized for any reason (for example).

[0059] Figure 4 shows another possible configuration of the sensor arrangement 16 of the sensor system 10. The configuration in Figure 4 differs from the configuration in Figure 2 in that a second permanent magnet element 12 and a second magnetic field sensor 11 are present. The second magnetic field sensor 11 is also mounted on the outer shell 11 at a distance from the first magnetic field sensor 11, and the second permanent magnet element 12 is also mounted on the inner shell 21 at a distance from the first permanent magnet element 12. The first magnetic field sensor 11 is mounted above the first permanent magnet element 12, and the second magnetic field sensor 11 is mounted above the second permanent magnet element 12. The first magnetic field sensor 11 detects the magnetic field of the first permanent magnet element 12, and the second magnetic field sensor 11 detects the magnetic field of the second permanent magnet element 12. It should be understood that there may also be only one magnetic field sensor 11 configured to detect the magnetic fields of both the first and second permanent magnet elements 12. In such cases, the individual signals can be distinguished by a data analysis algorithm.

[0060] Specifically, the first permanent magnet element 12 and the second permanent magnet element 12 (or more precisely, their magnetizations) may have different sensitivities / characteristics with respect to the characteristics of the dewar tank 20 being monitored. For example, the first permanent magnet element 12 may be an SmCo magnet (stable to temperature changes), and the second permanent magnet element 12 may be an NdFeB magnet (temperature sensitive). However, other combinations are also possible. Such combinations of different types of permanent magnet elements 12 can provide additional information to improve the accuracy of the corresponding measurements. Furthermore, such combinations can add redundancy.

[0061] The first permanent magnet element 12 may be a type that is stable to temperature changes. The second permanent magnet element 12 may be a type that is relatively sensitive to temperature changes. In this configuration, the presence of two types of permanent magnet elements 12 (both of which have been previously and individually calibrated for temperature) can provide additional information to improve the accuracy of the measurement system. The two different permanent magnet elements 12 may be sensitive to temperature changes in different temperature ranges (for example, with a relatively large magnetic field gradient with respect to temperature), thereby extending the sensitivity range of the entire sensor arrangement 16 to temperature changes. The second permanent magnet element being "more sensitive" to temperature changes may mean that the second permanent magnet element 12 is not as unresponsive to such temperature changes as the first permanent magnet element 12, or it may mean that the second permanent magnet element 12 is sensitive to temperature changes over a wider temperature range.

[0062] Furthermore, Figure 4 also shows that, as further explained above, a magnetic shield 15 is provided above each magnetic field sensor 11 to shield the magnetic field sensor 11 and / or permanent magnet element 12 from stray magnetic fields. Although shown only in Figure 4, it should be understood that such a magnetic shield may also exist in the configurations of Figures 2, 3, and 5, which are not explicitly shown or explained in those figures.

[0063] Figure 5 is a cross-section of the dewar tank 20 along the cutting line AA of Figure 1. Furthermore, Figure 5 shows a sensor system 10 having four sensor arrangements 16 arranged at equal intervals on the circumference of the dewar tank 20. Although Figure 2 shows the sensor arrangements 16, each sensor arrangement 16 in Figure 5 can be embodied according to any one of the configurations described herein, specifically any one of the configurations in Figures 2, 3, and 4. Furthermore, depending on the use case, all sensor arrangements 16 may be of the same type, or some or all of the sensor arrangements 16 may be of different types. Moreover, it should be understood that more or fewer than four sensor arrangements 16 are available, and that the individual sensor arrangements 16 do not necessarily have to be arranged at equal intervals on the circumference of the dewar tank 20. Furthermore, at least some of the sensor arrangements 16 may not even be arranged in the same longitudinal position along the length of the dewar tank 20. In any configuration described herein, the position, shape, quantity, arrangement, etc., of all necessary permanent magnet elements 12, superconducting elements 14, and any other elements should be optimized with respect to the resolution and dynamic range of the magnetic field sensor 11, as well as with respect to the use case, i.e., with respect to which characteristics to monitor.

[0064] By installing sensor arrays 16 at different locations on the cylindrical wall of the dewar tank 20, for example, displacement and temperature can be monitored at different locations. For example, by using a long filter in a certain time domain (to reduce the effects of random vibrations and readout noise) on the data collected at each detection point (i.e., from each sensor array 16), the deviation of the inner shell 21 from the expected cross-section can be estimated, thereby enabling monitoring of deformation and stress, for example. Furthermore, by using an appropriate model (or, for example, a machine learning algorithm trained with appropriate training data), the internal pressure can also be estimated.

[0065] FIG. 6 shows an exemplary circuit of the magnetic field sensor 11 that can be used in any of the embodiments described herein. The exemplary magnetic field sensor 11 generates a current I based on induction caused by a magnetic field change resulting from the relative displacement between the outer shell 22 and the inner shell 21. d It includes a coil 17 that generates a current I d . Further, a constant drive current I L is applied to the coil 17, generating a magnetic field that repels the magnetic field of the corresponding permanent magnet element 12. Thus, due to the relative movement of the outer shell 22 and the inner shell 21, a repulsive force is generated, and thus the magnetic field of the coil of the coil 17 changes with time. This change in the magnetic field is proportional to the change in the electrical impedance Z (t) of the coil 17 and can be used as the output signal of the magnetic field sensor 11.

[0066] Specifically, the drive current I d causes the coil 17 to generate a magnetic field. When this magnetic field configuration changes, for example, due to an external magnetic field (such as the magnetic field generated by the permanent magnet element 12), an additional induced current I c is induced in the coil 17 and added to the drive current I d / subtracted from the drive current I d . Then, the resulting current (I d ±I c ) flows through the resistor 18, causing a voltage drop, which can be measured by a voltmeter (or a similar voltage measuring device) 27. The voltmeter 27 can be, optionally, either implemented by the controller 13 (see FIGS. 2, 3, 4) or an individual device connected to the controller 13. The measured voltage drop is proportional to the distance between the coil 17 and the permanent magnet element 12 located on the inner shell 22 (e.g., FIGS. 2, FIG. 4) or the outer shell (e.g., FIG. 3). Thus, by monitoring this voltage drop, the dynamics of the tank can be monitored, as described in more detail above herein. An optional amplifier 19 can also be used to amplify the measured voltage drop.

[0067] However, it should be understood that any other type of magnetic field sensor 11 can be used, such as fluxgate sensors, Hall effect sensors, magnetoresistive sensors, inductive sensors, SQUID (superconducting quantum interference device) sensors (if the requirements are met), photoexcited magnetometers, Wiegand sensors, magneto-optical sensors, and any other suitable type of magnetic field sensor 11.

[0068] Figure 7 shows an aircraft 40 having a fuselage 41 and a hydrogen tank 30 in the form of a dewar tank 20, such as the dewar tank 20 in Figure 1, located within the fuselage 41. The dewar tank 20 is equipped with a sensor system 10 according to any one of the embodiments described herein.

[0069] It should be noted that “comprising” or “including” does not exclude other elements or steps, and “one” or “a” does not exclude multiple. Furthermore, it should be noted that any feature or step described in relation to any of the embodiments described above can be used in combination with any feature or step of any other embodiment described above. Reference numerals in the claims should not be considered limiting. [Explanation of Symbols]

[0070] 10 Sensor Systems 11 Magnetic field sensor 12 Permanent magnet elements 13 Controllers 14 Superconducting Elements 15 Magnetic Shielding 16 Sensor placement 17 coils 18 resistor 19 Amplifier 20 Dewar Tanks 21 Inner shell 22 Outer shell 23. Gaseous hydrogen 24 Liquid Hydrogen 25 Gas / Liquid Interface 26 Vacuum 27 Voltmeters / Voltage Measuring Devices AA cutting line 30 hydrogen tanks 40 Vehicles / Aircraft 41 aircraft I c induced current I d Drive current

Claims

1. A sensor system (10) for monitoring the characteristics of a dewar tank (20) having an inner shell (21) and an outer shell (22), A sensor arrangement (16) including a first magnetic field sensor (11) and a first permanent magnet element (12), Controller (13) and A sensor system (10) including, The first magnetic field sensor (11) is connected to the controller (13), The first magnetic field sensor (11) is configured to be attached to the outer shell (22) of the dewar tank (20), The first permanent magnet element (12) is configured to be attached to the inner shell (21) or the outer shell (22) of the dewar tank (20), The first magnetic field sensor (11) and the first permanent magnet element (12) are configured to be positioned close to each other when mounted on the dewar tank (20), so that the magnetic field sensor (11) can detect the magnetic field generated by the first permanent magnet element (12). Sensor system (10) wherein the controller (13) is configured to measure the magnetic field of the first permanent magnet element via the first magnetic field sensor (11) and to infer at least one characteristic of the dewar tank (20) based on the detected magnetic field of the first permanent magnet element (12).

2. The above at least one characteristic is, The temperature of the Dewar tank (20), and The filling level of the dewar tank (20) is determined based on at least one vibration mode of the dewar tank (20) that correlates with the filling level. A sensor system (10) according to claim 1, comprising at least one of the following.

3. The first permanent magnet element (12) is Samarium cobalt magnets (SmCo magnets), and Neodymium iron boron magnet (NdFeB magnet) A sensor system (10) according to claim 1 or 2, which is one of the types of the sensor system.

4. The sensor arrangement (16) further includes a second permanent magnet element (12) of a different type from the first permanent magnet element (12), The sensor system (10) according to any one of claims 1 to 3, wherein both the first permanent magnet element (12) and the second permanent magnet element (12) are configured to be attached to the inner shell (21) of the dewar tank (20).

5. The sensor arrangement (16) further includes a second magnetic field sensor (11), The first permanent magnet element (12) is configured to be positioned below the first magnetic field sensor (11), The sensor system (10) according to claim 4, wherein the second permanent magnet element (12) is configured to be positioned below the second magnetic field sensor (11).

6. The first permanent magnet element (12) is of a type that is stable with respect to temperature changes. The sensor system (10) according to claim 4 or 5, wherein the second permanent magnet element (12) is of a type that is relatively sensitive to temperature changes.

7. The first permanent magnet element (12) is a samarium cobalt magnet (SmCo magnet), The sensor system (10) according to claim 6, wherein the second permanent magnet element (12) is a neodymium iron boron magnet (NdFeB magnet).

8. A sensor system (10) according to any one of claims 1 to 3, further comprising a superconducting element (14) that becomes superconducting at extremely low temperatures, Both the first magnetic field sensor (11) and the first permanent magnet element (12) are configured to be mounted adjacent to each other on the outer shell (22) of the dewar tank (20). Sensor system (10) wherein the superconducting element (14) is configured to be attached to the inner shell (21) of the dewar tank (20) below the first permanent magnet element (12) and / or below the magnetic field sensor (11).

9. A sensor system (10) according to any one of claims 1 to 8, comprising at least two sensor arrangements (16).

10. The sensor system (10) according to any one of claims 1 to 9, wherein the sensor arrangement (16) further includes a magnetic shield (15) for shielding the magnetic field sensor (11) and / or the permanent magnet element (12) from a stray magnetic field.

11. A dewar tank (20) for holding liquefied hydrogen, comprising a dewar tank (20) having an inner shell (21) and an outer shell (22), A sensor system (10) according to any one of claims 1 to 10 and A hydrogen tank (30) including this.

12. The aircraft (41) and, The hydrogen tank (30) according to claim 11 and A vehicle (40) including, A vehicle (40) in which the sensor system (10) is configured to monitor the hydrogen filling level (210) of a fluid container (200).

13. The vehicle (40) according to claim 12, which is an aircraft (40).

Images