Method for measuring a rotation rate using a nuclear magnetic resonance gyroscope and nuclear magnetic resonance gyroscope

Abstract

Method (100) for measuring a rotation rate using a nuclear magnetic resonance gyroscope (200) comprising a vapor cell (10) containing atoms with atomic nuclei having a non-zero magnetic moment (27), wherein in an initialization phase (24) a static bias magnetic field (12) is generated along a first axis (13) of the nuclear magnetic resonance gyroscope (200), and wherein the magnetic moments (27) of the atoms are polarized by optical pumping by means of irradiation with first laser light (16), wherein in a measurement phase (26) the static bias magnetic field (12) is generated along the first axis (13), and wherein a resonance frequency is determined by means of irradiation with second laser light (18) along a second axis (19) of the nuclear magnetic resonance gyroscope (200), wherein during the initialization phase (24) and the measurement phase (26) a static Bias magnetic field (12) transverse first alternating magnetic field (14) is generated,wherein a pulse phase (25) is provided between the initialization phase (24) and the measurement phase (26), wherein in the pulse phase (25) a pulse of a second alternating magnetic field (20) is coupled along a third axis (21) of the nuclear magnetic resonance gyroscope (200).

Description

[0001] The present invention relates to a method for measuring a rotation rate using a nuclear magnetic resonance gyroscope, wherein the nuclear magnetic resonance gyroscope comprises a vapor cell containing atoms with nuclei having a non-zero magnetic moment. Furthermore, the present invention relates to a nuclear magnetic resonance gyroscope comprising a vapor cell containing atoms with nuclei having a non-zero magnetic moment. State of the art

[0002] In the field of navigation, there is an increasing need for gyroscopes capable of precisely measuring rotation rates. Highly accurate rotation rate sensors based on optical resonators are already installed in aircraft. However, such optical resonators are bulky and expensive to manufacture.

[0003] For autonomous driving and flying, as well as for applications with poor GPS, radar, and similar system connectivity, such as underwater navigation, highly accurate onboard sensors are required. At the same time, size and required installation volume play a crucial role. Particularly in autonomous driving, it must be ensured that the vehicle can be safely stopped or brought to a halt based on inertial sensors. Currently available sensors do not meet the required specifications. In particular, existing sensors lack the necessary drift stability.

[0004] To enable purely inertial navigation even for longer distances, such as in tunnels or urban canyons, a significant reduction in the noise of gyroscopes would also be desirable.

[0005] In the prior art, so-called nuclear magnetic resonance (NMR) gyroscopes are known. NMR gyroscopes are based on the evaluation of nuclear magnetic resonance signals from atomic nuclei with a non-zero magnetic moment. Such NMR gyroscopes exhibit increased drift stability and higher accuracy compared to current MEMS gyroscopes, particularly those used in the automotive industry. Optically pumped gyroscopes based on a vapor cell are also part of the prior art. In these, the spin precession ω is used. mess The data was read out in a steam cell. The spin precession is caused by a superposition of the Larmor precession ω. larmor and an external rotation ω R Given. The external rotation ω R represents an additional rotation, which can be derived from the equation ω mess = ω larmor ± ω R can be determined.

[0006] A laser frequency stabilization system used for a nuclear magnetic resonance gyroscope is disclosed in CN 105352490 A. The nuclear magnetic resonance gyroscope operates at a high temperature. A PWM pulse generator is used to generate a heating signal to control the temperature of the nuclear magnetic resonance gyroscope. The heating signal affects the laser signal, reducing its frequency, stability, and precision, and a non-heating period is additionally delayed after the generation of a heating pulse signal. Temperature control of the nuclear magnetic resonance gyroscope is performed during the heating signal period, and laser frequency stabilization control of the nuclear magnetic resonance gyroscope is performed during the non-heating signal period.

[0007] In the prior art, continuous measurement methods for nuclear magnetic resonance gyroscopes are known in which the magnetic moments of the atomic nuclei are simultaneously polarized by optical pumping and the nuclear magnetic resonance signal is read out. With continuous measurement methods, the maximum signal amplitude, and thus the signal-to-noise ratio and the achievable sensitivity, are limited. Disclosure of the invention

[0008] The present invention is based on the objective of providing a method for measuring a rotation rate using a nuclear magnetic resonance gyroscope, by means of which the maximum signal amplitude can be increased and thus the signal-to-noise ratio and the achievable sensitivity can be improved.

[0009] To solve the problem underlying the invention, a method for measuring a rotation rate using a nuclear magnetic resonance gyroscope is proposed, wherein the nuclear magnetic resonance gyroscope comprises atoms with atomic nuclei having a non-zero magnetic moment, including a vapor cell, wherein the method comprises an initialization phase and a measurement phase, wherein in the initialization phase a static bias magnetic field is generated along a first axis of the nuclear magnetic resonance gyroscope, and wherein the magnetic moments of the atoms are polarized by optical pumping by means of irradiation, preferably along the first axis, of circularly polarized first laser light, wherein in the measurement phase the static bias magnetic field is generated along the first axis, and wherein a resonance frequency is determined by means of irradiation along a second axis of the nuclear magnetic resonance gyroscope of preferably linearly polarized second laser light.wherein a first alternating magnetic field transverse to the static bias magnetic field is generated during the initialization phase and the measurement phase, wherein it is further provided that a pulse phase is provided temporally between the initialization phase and the measurement phase, wherein in the pulse phase a pulse of a second alternating magnetic field is coupled along a third axis of the nuclear magnetic resonance gyroscope.

[0010] The first laser light is preferably generated by a pump laser of the nuclear magnetic resonance gyroscope. The second laser light is preferably generated by a probe laser of the nuclear magnetic resonance gyroscope.

[0011] The static bias magnetic field, the transverse first alternating magnetic field, and the second alternating magnetic field are generated specifically at the location of the steam cell. The first laser light and the second laser light are also coupled specifically into the steam cell.

[0012] In contrast to the prior art, the method according to the invention does not involve continuous measurement. Instead, in an initialization phase, the magnetic moments of the atoms are first polarized by optical pumping using the first laser light in the static bias magnetic field. The first alternating magnetic field serves to synchronize the spin precession of the polarized magnetic moments. The initialization phase is followed by a pulse phase in which a pulse of a second alternating magnetic field is coupled in along a third axis. The pulse of the second alternating magnetic field along the third axis causes the nuclear spins of the atomic nuclei to be brought into a coherent superposition of the "up" and "down" states with respect to the first axis. In this superposition state of the atoms, measurements can be taken with a high amplitude. After the pulse phase, the measurement phase follows, in which a resonance frequency is determined by irradiation with a second laser light.

[0013] In the method according to the invention, the strength of the static bias magnetic field determines only the duration of the required pulse of the second alternating magnetic field and the length of the measurement period during the measurement phase. However, the strength of the static bias magnetic field has no influence on the bandwidth. The sensitivity and the signal-to-noise ratio are significantly increased because the spins, and thus the magnetic moments, of the atomic nuclei are completely aligned along the sensitive axis.

[0014] Preferably, the first laser light, especially the pump laser, is switched off during the measurement phase.

[0015] As soon as the pump laser stops, and the first laser light is thus switched off, a period of time on the order of the coherence time, which is usually a few seconds, is available for the pulse phase and for the measurement phase.

[0016] During the determination of the resonance frequency in the measurement phase, the polarization of the magnetic moments is lost through various relaxation mechanisms, and the system must be repolarized before another measurement can be taken.

[0017] In principle, it is possible for a measurement, in particular the determination of the resonance frequency, to take place even during the initialization phase. Measurement during the initialization phase enables precise timing of the pulse during the pulse phase.

[0018] Furthermore, it is fundamentally possible that the first alternating magnetic field is switched off during the initialization phase and / or during the measurement phase.

[0019] Furthermore, the second laser light can also be switched off during the initialization phase.

[0020] Preferably, the first axis is a z-axis, the second axis is an x-axis, and the third axis is a y-axis. Particularly preferably, the first, second, and third axes are mutually orthogonal.

[0021] In other words, during the initialization phase, a static bias magnetic field is generated along the z-axis, and the magnetic moments of the atoms are polarized by optical pumping through the irradiation of, preferably circularly polarized, first laser light along the first axis or the z-axis. During the measurement phase, the static bias magnetic field is also generated along the first axis or the z-axis. Additionally, during the measurement phase, a resonance frequency is determined by irradiating, preferably linearly polarized, second laser light along the x-axis. In the pulse phase provided between the initialization and measurement phases, a pulse of the second alternating magnetic field is coupled in along the y-axis.

[0022] Preferably, the static bias magnetic field, the first laser light, and the second laser light are switched off during the pulse phase. Furthermore, the first alternating magnetic field is preferably switched off during the pulse phase.

[0023] For this purpose, a control unit, in particular control electronics, can preferably be provided, which is designed in particular for a rapid switching on and off of the bias magnetic field and the first alternating magnetic field.

[0024] A further advantage is that at the beginning of the pulse phase, the first alternating magnetic field is designed at a predetermined phase angle.

[0025] In particular, the first alternating magnetic field is switched off before the pulse of the second alternating magnetic field is coupled in.

[0026] The first alternating magnetic field is stopped at a specific phase angle. This makes it possible to couple a well-defined pulse of the second alternating magnetic field along the third axis, enabling a precise projection of the nuclear spins or magnetic moments onto the sensitive axis.

[0027] The previously described, preferably planned measurement during the initialization phase can be used for calibration to compensate for shifts. Such shifts can be caused by a slow switch-off of the magnetic fields. This is possible because the measurement signal during the initialization phase provides information about the current orientation of the nuclear spins or magnetic moments.

[0028] After the end of the pulse phase, the static bias magnetic field and the first alternating magnetic field transverse to the static bias magnetic field are rebuilt for the measurement phase.

[0029] Preferably, the frequency of the second alternating magnetic field corresponds to a Larmor frequency of the atomic nuclei. Because the frequency of the second alternating magnetic field corresponds to a Larmor frequency of the atomic nuclei, the nuclear spins of the atomic nuclei can be brought into a coherent superposition of the "up" and "down" states with respect to the first axis or the z-axis.

[0030] It is preferably provided that the duration of the pulse of the second alternating magnetic field corresponds to a phase change of π / 2, wherein the amplitude of the second alternating magnetic field is further preferably set such that the product of a gyromagnetic ratio of the atomic nuclei and the duration of the pulse is π / 2.

[0031] It is advantageously possible to provide that the strength of the static bias magnetic field is at least 10 nT, preferably at least 100 nT, and more preferably at least 1 µT. Furthermore, the strength of the static bias magnetic field can be between 10 nT and 100 nT, particularly if high coherence is present.

[0032] Because the pulse of the second alternating magnetic field during the pulse phase means that the proportion of the nuclear spin orientation along the sensitive axis no longer depends on the magnitude of the static bias magnetic field, measurements can be taken at significantly higher static bias magnetic fields without losing signal amplitude. Increasing the strength of the static bias magnetic field also increases the fundamental frequency, enabling faster signal processing and thus higher bandwidths.

[0033] Preferably, the procedure is repeated after the measurement phase, starting with the initialization phase.

[0034] During the readout phase of the measurement, the polarization is lost through various relaxation mechanisms, and the system must be repolarized before another measurement can be performed. Therefore, the procedure can always be repeated after the measurement phase, starting with the initialization phase.

[0035] To provide continuous measurement of a rotation rate, two magnetic resonance gyroscopes can be used, with the two magnetic resonance gyroscopes operating alternately during the measurement and pulse phases. This ensures that one of the magnetic resonance gyroscopes is always measuring in the highly sensitive range.

[0036] Furthermore, it is preferably provided that the steam cell contains two nuclear spin isotopes, in particular 129 Xe and 131Xe is included. The use of two nuclear spin isotopes allows for the elimination of interfering components. The pulse scheme remains unchanged due to the antiparallel behavior of the magnetic moments of 129 Xe and 131 Xe exist. The pulse durations must be adjusted according to the different gyromagnetic properties of the nuclear spin isotopes.

[0037] Another solution to the problem underlying the invention consists of a nuclear magnetic resonance gyroscope comprising a vapor cell containing atoms with nuclei having a non-zero magnetic moment, a coil system for generating a static bias magnetic field along a first axis and for generating a first alternating magnetic field transverse to the static bias magnetic field, a first laser, in particular a pump laser, for generating first laser light, a second laser, in particular a probe laser, for generating second laser light, wherein it is provided that the coil system of the nuclear magnetic resonance gyroscope is configured to generate a second alternating magnetic field along a third axis, and that a control unit is provided which is configured to carry out a previously described method for controlling the coil system.

[0038] The first laser is preferably aligned along the first axis. The second laser is preferably aligned along the second axis.

[0039] Preferably, the first axis is a z-axis, the second axis is an x-axis, and the third axis is a y-axis. Particularly preferably, the first, second, and third axes are mutually orthogonal.

[0040] The control unit is preferably also designed to control the first laser and the second laser.

[0041] All functions, features and designs described above regarding the procedure can also be transferred to the nuclear magnetic resonance gyroscope in a correspondingly analogous manner.

[0042] In particular, it is thus provided that the atoms have two nuclear spin isotopes, preferably 129 Xe and 131 Xe, include.

[0043] The invention is explained in more detail below with reference to the accompanying figures. These show Fig. 1. A flowchart of a procedure for measuring a rotation rate using a nuclear magnetic resonance gyroscope, Fig. 2 a nuclear magnetic resonance gyroscope, Fig. 3a - 3e an alignment of magnetic fields and of laser light radiation during individual phases of the procedure for measuring a rotation rate using a nuclear magnetic resonance gyroscope, Fig. 4. A first temporal switching diagram of the magnetic fields and the laser light radiation during individual phases of the process. Fig. 5 a second temporal switching scheme of the magnetic fields and the laser light radiation during individual phases of the process, and Fig. 6 a third temporal switching scheme of the magnetic fields and the laser light radiation during individual phases of the process.

[0044] Fig. Figure 1 shows a flowchart of a method 100 for measuring a rotation rate using a nuclear magnetic resonance gyroscope 200 in accordance with the invention. Fig. Figure 2 schematically shows a nuclear magnetic resonance gyroscope 200 trained for carrying out procedure 100.

[0045] The in Fig. The nuclear magnetic resonance gyroscope 200 shown in Figure 2 comprises a vapor cell 10 containing atoms with nuclei possessing a non-zero magnetic moment. Furthermore, the nuclear magnetic resonance gyroscope 200 comprises a coil system 11 for generating a static bias magnetic field 12 along a first axis 13 and for generating a first alternating magnetic field 14 transverse to the static bias magnetic field 12, a first laser 15 aligned along the first axis 13, configured as a pump laser 15a, for generating first laser light 16, and a second laser 17, configured as a probe laser 17a, for generating second laser light 18 along a second axis 19. The coil system 11 of the nuclear magnetic resonance gyroscope 200 is also configured for generating a second alternating magnetic field 20 along a third axis 21. The first axis 13, the second axis 19 and the third axis 21 are orthogonal to each other in pairs.The first axis 13 corresponds to the z-axis, the second axis 19 corresponds to the x-axis, and the third axis 21 corresponds to the y-axis of a coordination system 22 attributable to the nuclear magnetic resonance gyroscope 200. The nuclear magnetic resonance gyroscope 200 also includes a control unit 23. The control unit 23 is configured to control the coil system 11, the first laser 15, and the second laser 17 in order to carry out a method 100 for measuring a rotation rate in accordance with the invention.

[0046] The procedure 100 comprises an initialization phase 24, a pulse phase 25 and a measurement phase 26. In Fig. Figures 3a to 3e schematically depict the orientation of the static bias magnetic field 12, the first alternating magnetic field 14 transverse to the static bias magnetic field 12, the first laser light 16, the second laser light 18, and the second alternating magnetic field 20 for the individual phases 24, 25, and 26. Furthermore, in Fig. Figures 3a to 3e show the orientation of the spins or magnetic moments 27 of the atoms. Accompanying this is a figure that shows... Fig. 4 a temporal switching scheme of the magnetic fields 12, 14, 20 of the first laser light 16 and the second laser light 18. In the Fig. 5 and Fig. 6 Variants for the temporal switching scheme of the magnetic fields 12, 14, 20 of the first laser light 16 and the second laser light 18 are shown.

[0047] Referring to the flowchart according to Fig. 1. The procedure 100 begins in a first procedure step S1 with the initialization phase 24. In the initialization phase 24, according to Fig. 3a and Fig. 4. The static bias magnetic field 12 and the first alternating magnetic field 14 are switched on. Furthermore, the first laser light 16 is switched on. The atoms in the vapor cell 10 are pumped by means of the first laser light 16. The spins or magnetic moments 27 of the atoms precess around the first axis 13. Optionally, the second laser light 18 can also be switched on in order to carry out measurements for calibration purposes during the initialization phase 24. According to the variants according to the Fig. 5 and Fig. 6. The second laser light 18 can also be switched off during the initialization phase 24. Specifically in the variant after Fig. 5. The first alternating magnetic field 14 can also be switched off during the initialization phase 24. At the beginning of the pulse phase 25, which occurs in a second process step S2, the static bias magnetic field 12, the first alternating magnetic field 14, the first laser light 16, and the second laser light 18 are switched off. The first alternating magnetic field 14 is stopped at a specific phase, as described in Fig. 3b shown. In pulse phase 25, a pulse of the second alternating magnetic field 20 is coupled along the third axis 21 of the nuclear magnetic resonance gyroscope 200. This causes, as shown in Fig. 3c and Fig. 3d shows a coherent superposition of the “up” and “down” states of the spins or magnetic moments 27 with respect to the first axis 13. In a third process step S3, the measurement phase 26 is carried out, in which the static bias magnetic field 12, the first alternating magnetic field 14 and the second laser light 18 are switched on ( Fig. 3e and Fig. 4). in the variant according to Fig. 5 the first alternating magnetic field 14 in the measurement phase 26 can also be switched off.

[0048] Due to the coherent superposition of the "up" and "down" states of the spins or magnetic moments 27, measurements can be taken with a high amplitude. This is evident from the signal waveform 28 according to Fig. 4 is recognizable in measurement phase 26. During measurement phase 26, the polarization of the magnetic moments 27 is lost through various relaxation mechanisms, and the system must be repolarized before another measurement can be performed. Accordingly, the procedure begins 100 after Fig. 4 again with an initialization phase 24. In the variant after Fig. 5 is the first alternating magnetic field 14 switched off in the renewed initialization phase 24. In the variant according to Fig. In the first alternating magnetic field 14 is switched on in the re-initialization phase 24, and the second laser light 18 is switched off in the re-initialization phase 24.

[0049] In the variant according to Fig. 5. By switching off the first alternating magnetic field 14 in the initialization phase 24 and in the measurement phase 26, and by switching off the second laser light 18 in the initialization phase 24, continuous readout is avoided, i.e., also in the initialization phase 24. This has the advantage that no broadening of the resonance occurs and thus a signal with a larger amplitude can be measured.

[0050] In the variant according to Fig. 6 the first alternating magnetic field 14 is applied, but to improve the signal amplitude the second laser light 18 is switched off. 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] CN 105352490 A

[0006]

Claims

[1] Method (100) for measuring a rotation rate using a nuclear magnetic resonance gyroscope (200), wherein the nuclear magnetic resonance gyroscope (200) comprises a vapor cell (10) containing atoms with atomic nuclei having a non-zero magnetic moment (27), wherein the method comprises an initialization phase (24) and a measurement phase (26), wherein in the initialization phase (24) a static bias magnetic field (12) is generated along a first axis (13) of the nuclear magnetic resonance gyroscope (200), and wherein the magnetic moments (27) of the atoms are polarized by optical pumping by means of irradiation, preferably along the first axis (13), of circularly polarized first laser light (16), wherein in the measurement phase (26) the static bias magnetic field (12) is generated along the first axis (13), and wherein by means of irradiation along a second axis (19) of the nuclear magnetic resonance gyroscope (200) of, preferably linearly polarized,a resonance frequency is determined using the second laser light (18), whereby a first alternating magnetic field (14) transverse to the static bias magnetic field (12) is generated during the initialization phase (24) and the measurement phase (26), , characterized by , that a pulse phase (25) is provided between the initialization phase (24) and the measurement phase (26), wherein in the pulse phase (25) a pulse of a second alternating magnetic field (20) is coupled along a third axis (21) of the nuclear magnetic resonance gyroscope (200). [2] Method (100) according to claim 1, characterized by , that the first axis (13) is a z-axis, that the second axis (19) is an x-axis, and that the third axis (21) is a y-axis. [3] Method (100) according to claim 1 or 2, characterized by , that during the pulse phase (25) the static bias magnetic field (12), the first alternating magnetic field (14), the first laser light (16) and the second laser light (18) are switched off. [4] Method (100) according to claim 3, characterized by , that at the beginning of the pulse phase (25) the first alternating magnetic field (14) is switched off at a predetermined phase angle. [5] Method (100) according to any of the aforementioned claims, characterized by , that the frequency of the second alternating magnetic field (20) corresponds to a Larmor frequency of the atomic nuclei. [6] Method (100) according to any of the aforementioned claims, characterized by , that a duration of the pulse of the second alternating magnetic field (20) corresponds to a phase change of π / 2, wherein preferably an amplitude of the second alternating magnetic field (20) is set such that the product of a gyromagnetic ratio of the atomic nuclei and the duration of the pulse is π / 2. [7] Method (100) according to any of the aforementioned claims, characterized by , that the strength of the static bias magnetic field (12) is at least 10 nT, preferably at least 100 nT, more preferably at least 1µT. [8] Method (100) according to any of the aforementioned claims, characterized by , that the procedure (100) is repeated after the measurement phase (26) beginning with the initialization phase (24). [9] Nuclear magnetic resonance gyroscope (200) comprising a vapor cell (10) containing atoms with nuclei having a non-zero magnetic moment (27), a coil system (11) for generating a static bias magnetic field (12) along a first axis (13) and for generating a first alternating magnetic field (14) transverse to the static bias magnetic field (12), a first laser (15), in particular a pump laser (15a), for generating first laser light (16), a second laser (17), in particular a probe laser (17a), for generating second laser light (18), characterized by, that the coil system (11) of the nuclear magnetic resonance gyroscope is configured to generate a second alternating magnetic field (20) along a third axis (21), and that a control unit (23) is provided which is configured to carry out a method (100) according to one of the preceding claims to control the coil system (11). [10] Nuclear magnetic resonance gyroscope (200) according to claim 9, characterized by that the atoms have two isotopes, preferably 129 Xe and 131 Xe, include.

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