Evaluation device for an NMR gyroscope, NMR gyroscope and method for evaluating a signal in an NMR gyroscope

Abstract

The invention relates to the evaluation of a signal from an NMR gyroscope. The time intervals of the zero points in the signal from a photodetector of the gyroscope are determined. Based on these time intervals, a rotation rate can be detected and, if necessary, its value can be determined.

Description

Technical field

[0001] The present invention relates to an evaluation device for an NMR gyroscope, and to an NMR gyroscope with such an evaluation device. The present invention further relates to a method for evaluating a signal in an NMR gyroscope. background

[0002] Numerous modern applications, such as navigation systems, require highly precise determination of rotation rates. Besides the currently used rotation rate sensors based on microelectromechanical systems (MEMS), so-called nuclear magnetic resonance gyroscopes, also known as NMR gyroscopes (NMR = nuclear magnetic resonance), have recently become available.

[0003] An exemplary setup of an NMR gyroscope and its operation is described in “MEMS Components for NMR Atomic Sensors” (RM Noor and AM Shkel; Journal of Microelectromechanical Systems, 27(6):1148-1159, Dec. 2018).

[0004] The publication DE 10 2020 208 340 A1 further describes an NMR gyroscope which is able to reduce the effects of external disturbances on the measurement result in a simple way. Disclosure of the invention

[0005] The present invention provides an evaluation device for an NMR gyroscope, an NMR gyroscope, and a method for evaluating a signal in an NMR gyroscope, comprising the features of the independent claims. Further advantageous embodiments are the subject of the dependent claims. Accordingly, the following is planned:

[0006] An evaluation device for an NMR gyroscope comprising an input interface and a processing unit. The input interface is designed to receive a signal from a photodetector of the NMR gyroscope. The processing unit is designed to detect zeros in the received signal from the photodetector. Furthermore, the processing unit is designed to determine the time interval between the detected zeros. In addition, the processing unit is designed to determine the rotation rate of the NMR gyroscope. Specifically, the processing unit is designed to determine the rotation rate of the NMR gyroscope using the determined time interval between the zeros in the received signal from the photodetector. Furthermore, the following is planned:

[0007] An NMR gyroscope with an evaluation device according to the invention. Finally, the following is planned:

[0008] A method for evaluating a signal in an NMR gyroscope. The method comprises a step for receiving a signal from a photodetector of the NMR gyroscope. Furthermore, the method comprises a step for detecting zeros in the received signal from the photodetector. In addition, the method comprises a step for determining the time interval between the detected zeros in the signal from the photodetector. Finally, the method comprises a step for determining the rotation rate of the NMR gyroscope using the determined time interval between the zeros in the received signal from the photodetector. Advantages of the invention

[0009] To evaluate the signals in an NMR gyroscope, conventional NMR gyroscopes integrate the signals from a photodetector over a predetermined period. If the signal is integrated over the period of the intrinsic Larmor frequency or a multiple thereof, the result of this integration is ideally zero without an external rotation rate. However, such approaches based on signal integration are very sensitive to noise. In particular, if the resulting detector signal contains significant noise, the superimposed noise can lead to a non-zero value for the integral, even without an external rotation rate.

[0010] It is therefore an idea of ​​the present invention to take this finding into account and to create an improved concept for evaluating the detector signals in an NMR gyroscope. For this purpose, it is provided that, instead of integrating the detector signals, an evaluation of the zero crossings of the detector signals is performed. It has been shown that even with noisy detector signals, the zero crossings can be evaluated very precisely. This increases the reliability of the evaluation. In particular, for example, the probability of an erroneously detected rotation rate can be reduced. Furthermore, the evaluation of the detector signal according to the invention can also be implemented by the NMR gyroscope particularly efficiently and simply.

[0011] To evaluate the detector signals, the time intervals of zero crossings within the detector signal are determined. These time intervals and the resulting period of the detector signal can be compared with the zero crossing corresponding to the period of the intrinsic Larmor frequency of the NMR gyroscope without a rotation rate. Furthermore, if a rotation rate is detected, the actual rotation rate can be determined very precisely and reliably.

[0012] According to one embodiment, the processing device is designed to detect rotation of the NMR gyroscope if the time interval between successive zeros deviates from a predetermined target value. The predetermined target value, which serves as a reference for this purpose, can be determined, for example, based on the period of the intrinsic Larmor frequency. If the determined time interval between adjacent zeros deviates from the predetermined target value, this indicates the presence of rotation or a rotation rate.

[0013] According to one embodiment, the processing device is designed to determine the rotation rate of the NMR gyroscope using the time interval between the zeros in the received signal from the photodetector. In particular, the value or direction of the rotation rate can be deduced from the difference between the determined time interval of the zeros and a predetermined time interval corresponding to the period of a non-rotating gyroscope.

[0014] According to one embodiment, the evaluation device includes a storage unit. The storage unit is designed to record data at predetermined times for zero crossings in the signal from the photodetector. The processing unit can then be configured to determine the rotation or rotation rate of the NMR gyroscope using the data stored in the storage unit. In this way, the evaluation of the signals from the NMR gyroscope can be performed particularly simply and efficiently without high computational effort.

[0015] According to one embodiment, the storage device is designed to provide data relating to the relationship between the time interval of zero crossings in the signal from the photodetector and a corresponding rotation rate. The processing device can then be configured to determine the rotation rate of the NMR gyroscope using the data stored in the storage device regarding the relationship between the time interval of zero crossings and the corresponding rotation rate. Thus, the specific value for the rotation rate, and optionally its direction, can be easily determined based on the calculated time interval of zero crossings.

[0016] According to one embodiment, the storage device is designed to store and provide the data in the form of a lookup table. This enables a particularly simple and efficient provision of the data required for evaluating the signals from the NMR gyroscope. Of course, any other suitable scheme for storing the required data is also possible.

[0017] According to one embodiment, the processing device is designed to determine a number of zero crossings in the signal from the photodetector within a predetermined time period. Furthermore, the processing device can be designed to determine the time interval between the zero crossings using the determined number of zero crossings within the predetermined time period. By evaluating a longer signal sequence over several periods, the accuracy for determining the zero crossings can be increased.

[0018] According to one embodiment, the evaluation device is implemented in a microchip. In particular, the evaluation device can be implemented on a microcontroller, an application-specific integrated circuit (ASIC), or an FPGA. Furthermore, any other implementations are also possible, especially in the form of integrated circuits or similar devices.

[0019] The above embodiments and further developments can be combined with one another as appropriate. Further embodiments, further developments, and implementations of the invention also include combinations of features of the invention described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In particular, those skilled in the art will also add individual aspects as improvements or additions to the respective basic forms of the invention. Brief description of the drawings

[0020] Further features and advantages of the invention are explained below with reference to the figures. These show: Fig. 1: a schematic representation of an NMR gyroscope with an evaluation device according to one embodiment; Fig. 2: a signal-time diagram of an output signal from an NMR gyroscope without rotation rate; Fig. 3: a signal-time diagram of an output signal from an NMR gyroscope with rotation rate; and Fig. 4: a flowchart as it underlies a method for evaluating a signal from an NMR gyroscope according to one embodiment. Description of embodiments

[0021] Fig. Figure 1 shows a schematic representation of an NMR gyroscope 2 with an evaluation device 1 according to one embodiment. Since the basic structure of such an NMR gyroscope 2 has been described, for example, in the publications mentioned in the introduction, the structure is only roughly explained here.

[0022] The NMR gyroscope 2 comprises a vapor cell 21 containing, for example, one or more alkali metals and one or more gases. For instance, the vapor cell can contain rubidium (Rb) and xenon (Xe). Furthermore, the xenon gas can contain two nuclear spin isotopes, 129Xe and 131Xe. The vapor cell 21 is irradiated from one direction with circularly polarized light by a first light source 22 (pump laser). Additionally, to read out the vapor cell 21, it is irradiated with linearly polarized light by a second light source 23 (probe laser). After passing through the vapor cell 21, this light can be detected and evaluated, optionally using a polarizing beam splitter cube 24, by means of a photodetector 25, in particular a balanced detector. For this purpose, the signal from the photodetector 25 can be fed to an evaluation device 1, which will be described in more detail below.The amplitude of the resulting Faraday rotation signal depends on a frequency detuning of the probe laser 23 with respect to the pump laser 22.

[0023] The evaluation device 1 thus evaluates the precession frequency of an atomic spin, for example the nuclear spin of xenon, in the vapor cell 21 based on the signal from the photodetector 25. The polarization vector of the probe laser 23 rotates according to the precession frequency of the xenon nuclear spin. To evaluate the precession frequency, the signal from the photodetector 25 is compared with an expected (sinusoidal) signal of a specific frequency. The frequency of the expected signal corresponds to the intrinsic Larmor frequency, which is derived from ωL=γB0 This results in B0 representing an applied static magnetic field at the steam cell 21. If an external rotation rate ω is present... rThis results in a frequency shift in the signal from the photodetector 25 according to ωL=γB0+ωr

[0024] From this, the current rotation rate of the NMR gyroscope 2 can be determined.

[0025] To detect whether a rotation rate is currently present, conventional approaches integrate the signal from the photodetector 25 over a period (or a multiple thereof) of the expected intrinsic Larmor frequency. If this integral is approximately zero, no rotation rate is detected. A value deviating from zero indicates a rotation rate. However, this approach carries the risk that, due to noise components in the signal from the photodetector 25, the value of the integral over a period can deviate significantly from zero even without a rotation rate. In this case, a rotation rate would consequently be erroneously detected. The evaluation device 1 of the gyroscope 2 according to the invention therefore uses a different approach to determine the rotation rate.

[0026] The evaluation device 1 comprises an input interface 11 at which the signal from the photodetector 25 can be received. This signal can then be evaluated by a processing unit 12. For this purpose, the processing unit 12 detects the zeros in the signal from the photodetector 25. Furthermore, the processing unit 12 can determine the time interval between successive zeros in the signal from the photodetector 25. For example, the number of zeros within a sequence of the signal from the photodetector 25 with a predetermined length can be determined. Alternatively, any other approach to determining the time interval between two successive zeros in the signal from the photodetector 25 is of course possible.

[0027] If the time interval between successive zeros in the signal from the photodetector 25 corresponds to the corresponding interval between zeros in a reference signal for the intrinsic Larmor frequency of a gyroscope 2 without a rotation rate, then it can be determined that there is currently no rotation rate. If the time interval between the zeros in the signal from the photodetector 25 deviates from this, then a rotation rate is detected. The current rotation rate can be determined from the deviation of the time interval between two successive zeros in the signal from the photodetector 25 and the time interval between successive zeros in the reference signal.

[0028] For simple and efficient processing, it is possible, for example, to provide a storage device 13 that supplies the necessary data for comparing the currently determined zeros and determining the rotation rate. For instance, the storage device 13 can provide data specifying the time interval between the zeros for the reference signal of the intrinsic Larmor frequency in a gyroscope 2 without a rotation rate. Thus, the currently determined time interval between two zeros in the signal from the photodetector 25 can be easily compared with the data provided by the storage device 13. Likewise, the storage device 13 can, for example, provide a lookup table that specifies the relationship between the deviation of the zeros between the signal from the photodetector 25 and the reference signal on the one hand, and the corresponding rotation rate on the other.In this way, after determining the time interval of the zeros in the signal from the photodetector 25, the current rotation rate of the NMR gyroscope 2 can be determined in a simple and efficient manner.

[0029] Fig. Figure 2 shows a schematic representation of the waveform of a signal 100 from the photodetector 25 in a gyroscope 2 without a rotation rate. A possible noise component in the signal 100 from the photodetector 25 is also shown. For comparison, the idealized waveform of a reference signal 200 is shown. It can be seen that the area components of the signal from the photodetector 25 in the positive and negative half-waves may not completely cancel each other out, and thus a resulting integral over one period may have a value other than zero. Furthermore, it can be seen that even with a noise component, the zeros correspond very well with the zeros of the reference signal.

[0030] Fig. Figure 3 shows a schematic representation of the waveform of a signal 101 from the photodetector 25 in a gyroscope 2 with a rotation rate. For clarity, the superposition with a noise component has been omitted. It can be seen that, due to the rotation rate, the positions and thus the time intervals between adjacent zeros deviate from the time intervals of the zeros in the reference signal. From this difference, a rotation / rotation rate can be detected and the value of the rotation rate determined.

[0031] Fig.Figure 4 shows a flowchart illustrating a method for evaluating a signal in an NMR gyroscope 2 according to one embodiment. The method can, in principle, comprise any steps suitable for implementing the evaluation device 1 and the gyroscope 2 described above. Similarly, the evaluation device 1 and the gyroscope 2 described above can also comprise any components that may be necessary for implementing the method described below.

[0032] In step S1, a signal is first received from a photodetector 25 of the NMR gyroscope 2. Then, in step S2, zeros in the received signal can be detected by the photodetector 25. Based on the detected zeros, a time interval between the detected zeros in the signal from the photodetector 25 can be determined in step S3.

[0033] In step S4, the rotation rate of the NMR gyroscope 2 can then be determined. This determination of the rotation or rotation rate of the NMR gyroscope 2 can be carried out using the determined time interval between the zeros in the received signal from the photodetector 25.

[0034] In summary, the present invention relates to the evaluation of a signal from an NMR gyroscope. The time intervals of the zero points in the signal from a photodetector of the gyroscope are determined. Based on these time intervals, a rotation rate can be detected and, if necessary, its value can be determined. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 208 340 A1

[0004] Cited non-patent literature

[0000] MEMS Components for NMR Atomic Sensors” (RM Noor and AM Shkel; Journal of Microelectromechanical Systems, 27(6):1148-1159, Dec. 2018

[0003]

Claims

[1] Evaluation device (1) for an NMR gyroscope (2), comprising: an input interface (11) designed to receive a signal from a photodetector (25) of the NMR gyroscope (2); a processing device (12) designed to detect zeros in an AC voltage component of the received signal from the photodetector (25), to determine a time interval between the zeros and to determine a rotation rate of the NMR gyroscope (2) using the determined time interval between the zeros in the received signal from the photodetector (25). [2] Evaluation device (1) according to claim 1, wherein the processing device (12) is designed to detect a rotation of the NMR gyroscope (2) if the time interval between successive zeros deviates from a predetermined target value. [3] Evaluation device (1) according to claim 1 or 2, wherein the processing device (12) is designed to determine a rotation rate of the NMR gyroscope using the time interval of the zeros in the received signal from the photodetector (25). [4] Evaluation device (1) according to one of claims 1 to 3, comprising a storage device (13) designed to store data at predetermined times for zero crossings in the course of the signal from the photodetector (25), wherein the processing device (12) is designed to determine the rotation and / or rotation rate of the NMR gyroscope (2) using the data stored in the storage device (13) at the times for the zero crossings. [5] Evaluation device (1) according to claim 4, wherein the storage device (13) is designed to provide data for a relationship between a time interval of the zero crossings in the course of the signal from the photodetector (25) and a corresponding rotation rate, wherein the processing device (12) is designed to determine the rotation rate of the NMR gyroscope (2) using the data stored in the storage device (13) about the relationship between the time interval of the zero crossings and the corresponding rotation rate. [6] Evaluation device (1) according to claim 4 or 5, wherein the storage device (13) is designed to store and provide the data in the form of a look-up table. [7] Evaluation device (1) according to one of claims 1 to 6, wherein the processing device (12) is designed to determine a number of zero crossings in the course of the signal from the photodetector (25) within a predetermined time period and to determine the time interval of the zero crossings using the determined number of zero crossings within the predetermined time period. [8] Evaluation device (1) according to any one of claims 1 to 7, wherein the evaluation device (1) is implemented in a microchip, in particular a microcontroller or an FPGA or an ASIC. [9] NMR gyroscope (2), with an evaluation device (1) according to any one of claims 1 to 8. [10] Method for evaluating a signal in an NMR gyroscope (2), comprising the steps: Receiving (S1) a signal from a photodetector (25) of the NMR gyroscope (2); Detecting (S2) zeros in an AC voltage component of the received signal from the photodetector (25); Determine (S3) a time interval between the detected zeros in the signal from the photodetector (25); and Determining (S4) a rotation rate of the NMR gyroscope (2) using the determined time interval between the zeros in the received signal from the photodetector (25).

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