Magnetic field surge detection device, detection method, and power equipment equipped with the same

Abstract

To detect magnetic field surges in a short-time and in a measurement range of wide magnetic field strength.SOLUTION: A magnetic field surge detection device 10 includes: an electromagnetic wave irradiation unit 2 that repeatedly irradiates a quantum sensor element 1 with an electromagnetic wave for manipulating an electron spin state of the quantum sensor element 1 that changes due to interaction with a magnetic field to be detected in a pulse sequence in which a time τ for observing free induction decay of the electron spin state is determined according to a temporal change rate of the magnetic field surge strength; and a magnetic field surge detection unit 3 that repeatedly detects the magnetic field surge based on changes in a plurality of electron spin states after the interaction with the magnetic field.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to technology using quantum sensors, and more particularly to a magnetic field surge detection device and method using quantum sensors, and to electric power equipment equipped with a magnetic field surge detection device. [Background technology]

[0002] Electricity is indispensable in modern society, and power facilities have become an essential part of the infrastructure. Once power facilities, including power transmission and transformation equipment such as transformers and switchgears, are in operation, there are few opportunities to shut them down, and if a failure occurs in such power facilities, the impact on society would be significant.

[0003] When a surge occurs in power equipment, which is an abnormal overvoltage or overcurrent that flows in a short period of time due to the effects of lightning strikes or other events, it can cause the power equipment to malfunction. To protect power equipment from malfunctions caused by surges, lightning arresters known as surge protective devices (SPDs) are connected to the power equipment. When a lightning strike or other event occurs, the lightning arresters themselves safely malfunction, bypassing the surge current and protecting the power equipment.

[0004] In recent years, diamond has also been attracting attention as a material for sensor elements that measure magnetic fields. Complex defects called nitrogen-vacancy centers can be found in the crystal structure of diamond. These nitrogen-vacancy centers consist of a pair of a nitrogen atom that replaces a carbon atom in the crystal lattice, and a vacancy (missing a carbon atom) located adjacent to the nitrogen atom; they are also called NV centers (Nitrogen Vacancy centers). In addition to NV centers, complex defects called silicon-vacancy centers and germanium-vacancy centers can also be found in the crystal structure of diamond. These complex defects, including NV centers, are called color centers.

[0005] The NV center is in a state where an electron is trapped in a vacancy (negative charge state, hereafter referred to as "NV - In this NV state, the electron spin exhibits a magnetic property. - is the state in which no electrons are captured (neutral state, hereafter referred to as "NV 0 NV exhibits a long transverse relaxation time (decoherence time, hereafter referred to as "T2") compared to NV. - In the electron spin state of NV, after the magnetization of the electron spins aligned in the vertical direction of the external magnetic field (hereinafter referred to as the "quantization axis") is tilted to the transverse direction, the individual spins are displaced due to the precession of the individual spins, and it takes a long time for the overall transverse magnetization to disappear. - exhibits a long T2 value even at room temperature (approximately 300 K).

[0006] NV - The electron spin state of diamond changes in response to an external magnetic field, and this electron spin state can be measured at room temperature. Therefore, diamond containing NV centers can be used as a material for magnetic field sensor elements.

[0007] For example, Patent Document 1 discloses a method for measuring an AC magnetic field by magnetic resonance of electron spins in diamond, in which a pulse sequence based on the spin echo method is applied to the spins.

[0008] For example, Patent Document 2 discloses a method for measuring an AC magnetic field by optically detected magnetic resonance (ODMR) of electron spins in diamond. NV centers are excited by laser light, and magnetic resonance signals (phase information) related to the spin state are detected by measuring changes in the intensity of fluorescence emitted from the NV centers.

[0009] In addition to sensors using diamond color centers, there are various other types of sensors used as magnetic field sensor elements, such as sensors using color centers in silicon carbide (SiC), optically pumped atomic magnetometers (OPMs), and superconducting quantum interference devices (SQUIDs). These diamond color centers, silicon carbide color centers, optically pumped magnetometers, and superconducting quantum interference devices are called quantum sensors because they measure physical quantities using quantum effects. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-103171 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-75964 Summary of the Invention [Problem to be solved by the invention]

[0011] When a surge current occurs due to a lightning strike or other cause, not only does the surge current flow through equipment and cause it to malfunction, but a high-intensity magnetic field is generated around the equipment in an extremely short time, within about 1 ms (millisecond). This sudden increase in magnetic field strength caused by the generation of a surge current (hereinafter referred to as a magnetic field surge) can cause malfunctions in operating power equipment.

[0012] Although lightning arresters can bypass surge currents by safely failing themselves, they cannot protect power equipment from such instantaneous, high-intensity magnetic fields. Even if a lightning arrester bypasses the surge current, the bypassed surge current still generates a magnetic field surge around the arrester. Therefore, there is a need to develop a device that can output an electrical signal to activate an interlock function that stops the operation of power equipment within an extremely short time, approximately 1 ms, after the occurrence of a surge current.

[0013] In order to detect magnetic field surges and activate the interlock function, the magnetic field sensor must be able to measure both the magnetic field generated when the power equipment is in stable operating condition and the high-intensity magnetic field that suddenly increases due to the generation of surge current. However, the range of magnetic field strength that can be measured by previously known magnetic field sensors is narrow, making it difficult to detect the rise of a magnetic field surge that suddenly increases in an extremely short time of approximately 1 ms and activate the interlock function. As a sign of a magnetic field surge, it is necessary to detect magnetic field surges in a short time and over a wide measurement range of magnetic field strength.

[0014] An object of the present invention is to detect a magnetic field surge in a short time and over a wide measurement range of magnetic field strength. [Means for solving the problem]

[0015] The present invention for solving the above problems includes, for example, the following aspects. (Section 1) an electromagnetic wave irradiation unit that repeatedly irradiates the quantum sensor element with electromagnetic waves for manipulating the electron spin state of the quantum sensor element, which changes due to interaction with the magnetic field to be detected, in a pulse sequence in which the time τ for observing the free induction decay of the electron spin state is determined according to the time rate of change of the surge strength of the magnetic field; a magnetic field surge detector that repeatedly detects a surge in the magnetic field based on changes in the plurality of electron spin states after interacting with the magnetic field; A magnetic field surge detection device comprising: (Section 2) The magnetic field surge detection unit a magnetic field strength calculation unit that calculates the strength of the magnetic field based on each of the plurality of electron spin states after the interaction; a differential property calculation unit that calculates a time differential property of the intensity of the magnetic field based on the intensities of the plurality of magnetic fields; Including, Item 2. The magnetic field surge detector according to item 1, wherein the magnetic field surge is detected based on the calculated differential characteristic. (Section 3) The differential characteristic calculation unit

number

[0016] According to the present invention, magnetic field surges can be detected in a short time and over a wide measurement range of magnetic field strength. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a diagram schematically illustrating a general configuration of a magnetic field surge detector 10 according to an embodiment of the present invention. [Figure 2] FIG. 2 is a diagram schematically illustrating an example of a specific configuration of the magnetic field surge detector 10 shown in FIG. [Figure 3] 1 is a schematic diagram of an electric power facility 9 equipped with a magnetic field surge detection device 10 according to an embodiment of the present invention. [Figure 4] 1 is a schematic diagram of an electric power facility 9 equipped with a magnetic field surge detection device 10 according to an embodiment of the present invention. [Figure 5] FIG. 1 is a diagram schematically showing the energy levels of electrons in the NV-center of diamond. [Figure 6] This is an exemplary pulse sequence for sensing a magnetic field using an optically detected magnetic resonance (ODMR) method, and is a pulse sequence that includes two π / 2 pulses to observe a free induction decay (FID) signal. [Figure 7] 1 is a diagram for explaining the magnetic field surge detection concept of the present invention. FIG. [Figure 8] 1 is a diagram for explaining the magnetic field surge detection concept of the present invention. FIG. [Figure 9] 1 is a flowchart illustrating the steps of a magnetic field surge detection method according to an embodiment of the present invention. [Figure 10] This is an exemplary pulse sequence for sensing a magnetic field using an optically detected magnetic resonance (ODMR) method, and is a pulse sequence for observing a free induction decay (FID) signal using a pulse sequence including a single π pulse. [Figure 11] 10 shows the results of a numerical simulation of a surge magnetic field according to the first embodiment. [Figure 12] 10 shows the results of a numerical simulation of a surge magnetic field according to the first embodiment. [Figure 13] 10 shows the results of a numerical simulation of a surge magnetic field according to Example 2. [Figure 14] 10 shows the results of a numerical simulation of a surge magnetic field according to Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals will denote the same or similar components, and therefore, redundant descriptions of the same or similar components will be omitted.

[0019] In this specification, a physical quantity refers to a quantity whose dimensions are determined under a certain system in physics and which can be expressed as a multiple of a defined physical unit. Examples of physical quantities include magnetic fields, electric fields, temperature, and mechanical quantities (mechanical stress, pressure, etc.). Magnetic fields, electric fields, and mechanical quantities include physical quantities that do not change over time and physical quantities whose direction repeatedly changes over time. In other words, magnetic fields include static magnetic fields and AC magnetic fields, electric fields include electrostatic fields and AC electric fields, and mechanical quantities include static mechanical quantities and AC mechanical quantities.

[0020] [Device configuration] Fig. 1 is a diagram schematically showing the general configuration of a magnetic field surge detector 10 according to one embodiment of the present invention. Fig. 2 is a diagram schematically showing an example of the specific configuration of the magnetic field surge detector 10 shown in Fig. 1.

[0021] The magnetic field surge detector 10 (hereinafter simply referred to as the detector 10) includes a sensor element 1, an electromagnetic wave irradiator 2, and a magnetic field surge detector 3. In this embodiment, the sensor element 1 is attached to the tip of a probe 11 of the detector 10.

[0022] The sensor element 1 is a quantum sensor element. In this embodiment, the sensor element 1 is a diamond crystal having a color center, and an NV center is used as the color center. The NV center is a complex (complex defect) of nitrogen (N) substituting a carbon atom and a vacancy (V) adjacent to the nitrogen. In this embodiment, the sensor element 1 is generated in advance by a known method in a predetermined region on the diamond crystal 12. Illustratively, the region contains approximately several thousand particles (concentration: 1×10 12 / cm -3 ) A plurality of sensor elements 1 are generated. In this embodiment, the sensor elements 1 are ensemble NV centers.

[0023] The electron spin state of the sensor element 1 is changed by an interaction 8 with an object 9. In this embodiment, the object 9 is an electric power facility, and the interaction 8 is an interaction due to a magnetic field. When the interaction 8 is due to a magnetic field, the electron spin state of the color center of the sensor element 1 changes to a state that corresponds to the strength of the magnetic field generated around the object 9, which is the electric power facility.

[0024] The electromagnetic wave irradiating unit 2 irradiates the sensor element 1 with electromagnetic waves for manipulating the electron spin state of the sensor element 1 by magnetic resonance. As an example, in this embodiment, the electromagnetic wave irradiating unit 2 includes a known microwave (MW) oscillator 21, a switch 22 for irradiating the electromagnetic waves in a pulsed form, and an amplifier 23. The switch 22 and the amplifier 23 may have any configuration. In this embodiment, the electromagnetic wave irradiating unit 2 irradiates the sensor element 1 with electromagnetic waves in a pulsed form for manipulating the electron spin state of the sensor element 1.

[0025] The electromagnetic wave pulse sequence irradiated by the electromagnetic wave irradiating unit 2 to the sensor element 1 can be any of various pulse sequences for generating magnetic resonance. Apart from the present invention, for example, when sensing an AC magnetic field by optically detected magnetic resonance (ODMR) of electron spins in the sensor element, the sensor element is irradiated with electromagnetic waves by a pulse sequence based on the Hahn echo method of the spin echo method. Furthermore, when sensing a static magnetic field by optically detected magnetic resonance, the sensor element is irradiated with electromagnetic waves by a pulse sequence based on the Ramsey method of the spin echo method.

[0026] In the present invention, a pulse sequence for observing a free induction decay (FID) signal is used in order to detect a magnetic field surge in a short time and over a wide measurement range (dynamic range) of magnetic field strength. Such a pulse sequence for observing a free induction decay signal is even simpler than pulse sequences based on the Hahn echo method or the Ramsey method, which are exemplified as examples of pulse sequences used in detecting magnetic resonance signals. The reason for using a pulse sequence for observing a free induction decay signal is that, in the present invention, it is important to detect a magnetic field surge at its rising time, and the accuracy of the magnetic field strength when a magnetic field surge occurs is not important.

[0027] Therefore, in the present invention, the electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves using a pulse sequence in which the time τ for observing the free induction decay of the electron spin state of the sensor element 1 is determined according to the temporal rate of change of the strength of the magnetic field surge. In this embodiment, a pulse sequence including two π / 2 pulses is used. The time τ between the π / 2 pulses is determined according to the temporal rate of change of the strength of the magnetic field surge to be detected. In another embodiment, a pulse sequence including a single π pulse is used. The time τ after the single π pulse is determined according to the temporal rate of change of the strength of the magnetic field surge to be detected. The innovations applied to the pulse sequence will be described later with reference to FIGS. 6 to 8.

[0028] The electromagnetic wave irradiating unit 2 irradiates the sensor element 1 with electromagnetic waves through an antenna 14 for irradiating electromagnetic waves that is arranged in the vicinity of the sensor element 1. The antenna 14 is formed on the diamond crystal 12 using a conductive metal, for example, by lithography technology.

[0029] The magnetic field surge detection unit 3 detects a magnetic field surge based on a change in the state of multiple electron spins of the sensor element 1 after the change occurs due to an interaction 8 with the object 9. In this embodiment, the magnetic field surge is detected based on the time differential property of the strength of the magnetic field generated around the object 9, which is power equipment. The magnetic field surge detection unit 3 includes a light irradiation unit 31, a detection unit 32, and a data processing unit 33.

[0030] The frequency of the electromagnetic waves irradiated by the electromagnetic wave irradiator 2 to the sensor element 1 is preset to an on-resonance frequency corresponding to the energy difference between the spin states in the sensor element 1, and the magnetic field surge detector 3 measures the electronic spin state of the sensor element 1 on-resonance. In this state, if a magnetic field surge occurs in the magnetic field generated around the power equipment, a change occurs in the energy difference between the spin states in the sensor element 1, resulting in a shift in the resonant frequency. In other words, when a magnetic field surge occurs, the magnetic field surge detector 3 measures the electronic spin state of the sensor element 1 off-resonance. The magnetic field surge detector 3 detects the magnetic field surge based on the changes in multiple electronic spin states measured off-resonance, including changes based on the off-resonance state.

[0031] The light irradiating unit 31 irradiates the sensor element 1 with light for reading out phase information of the electron spin state of the sensor element 1 after interacting with the object 9. The light irradiating unit 31 also irradiates the sensor element 1 with light for initializing the electron spin state of the sensor element 1. As an example, in this embodiment, the light irradiating unit 31 includes a light source 311, an acousto-optical modulator (AOM) 312, and an objective lens 313. The acousto-optical modulator 312 and the objective lens 313 can have any configuration.

[0032] The light source 311 emits light for reading out phase information of the electron spin state of the sensor element 1 after interaction with the object 9. The light source 311 also emits light for exciting and initializing the electron spin state of the sensor element 1. The wavelength of the light emitted by the light source 311 is determined depending on the type of the sensor element 1. In this embodiment, the light source 311 emits laser light with a wavelength of 532 nm (green). For example, various known laser generating devices can be used as the light source 311. In this embodiment, the light source 311 is a semiconductor laser that emits green laser light.

[0033] The objective lens 313 focuses the light emitted from the light source 311 and irradiates it onto the area on the diamond crystal 12 where the sensor element 1 is being generated. Illustratively, the spot size of the laser light focused on the diamond crystal 12 has a diameter of about 2 μm. As the spot size of the laser light decreases, the intensity of the laser light per unit area increases, and the efficiency of the photocurrent generated in the conduction band of the diamond also increases.

[0034] 2, the spot of the laser light is positioned so as to cover the area where the sensor element 1 is generated on the diamond crystal 12. Preferably, the spot of the laser light can be positioned at a position offset from approximately the center of the area where the sensor element 1 is generated.

[0035] The detection unit 32 detects changes occurring in the sensor element 1. In this embodiment, the detection unit 32 detects the light emitted from the sensor element 1, and detects a magnetic resonance signal as a change in light emission intensity by a known optically detected magnetic resonance (ODMR) method. In this case, the detection unit 32 can be, for example, a known photodiode. The photodiode can be, for example, an avalanche photodiode.

[0036] In this embodiment, the electromagnetic wave for operation is irradiated in a pulsed form in the electromagnetic wave irradiation unit 2. Therefore, in this embodiment, specifically, detection is performed by the Pulsed Optically Detected Magnetic Resonance (pODMR) method.

[0037] The data processing unit 33 is connected to the detection unit 32, reads out phase information of the electron spin state of the sensor element 1 after interacting with the object 9 from the changes detected by the detection unit 32, and detects a magnetic field surge based on the read out phase information. The data processing unit 33 includes a magnetic field strength calculation unit 331, a differential characteristic calculation unit 332, and an alarm unit 333.

[0038] The data processing unit 33 may be, for example, a known general-purpose computer or various information terminal devices such as a smartphone. The data processing unit 33 may be configured as an integral part of the detection device 10, or, as shown in the figure, may be provided externally to the detection device 10 and connected to the detection device 10 via a wired or wireless network 99.

[0039] The magnetic field strength calculation unit 331 calculates the strength of the magnetic field for each of the plurality of electron spin states after the interaction based on the respective electron spin states.

[0040] The differential property calculation unit 332 calculates a time differential property of the magnetic field strength based on the intensities of the multiple magnetic fields. In this embodiment, the differential property calculation unit 332 calculates the differential property based on a mathematical formula described later with reference to FIG.

[0041] When a magnetic field surge is detected, the alarm unit 333 outputs, for example, an alarm signal to stop the operation of the power equipment 9. The alarm signal can be an electric signal (i.e., an interlock signal) for activating an interlock function that stops the operation of the power equipment 9. The alarm signal can also be transmitted, for example, via the network 99 to a computer device (not shown) that centrally manages the operation status of other power equipment, to stop the operation of the other power equipment.

[0042] 3 and 4 are schematic diagrams of an electric power facility 9 equipped with a magnetic field surge detection device 10 according to one embodiment of the present invention. As the electric power facility 9, a current transformer 9a is illustrated in FIG. 3, and a voltage transformer 9b is illustrated in FIG. 4. The locations of the detection device 10 illustrated in these figures are merely examples.

[0043] The detection device 10 is disposed in a position where it can sense the magnetic field generated around the power equipment 9 (9a, 9b). Preferably, the detection device 10 is disposed so that the axis along which the sensor element 1 senses the magnetic field is aligned with the direction of the magnetic field generated around the power equipment 9.

[0044] [Detection principle] In the present invention, the quantum sensor 1 is used to measure the strength of the magnetic field generated around the target electric power equipment 9. This allows for highly sensitive detection of magnetic field surges. The magnetic resonance signal used to calculate the magnetic field strength is detected by the optically detected magnetic resonance (ODMR) method. This allows for contactless detection of magnetic field surges without direct electrical connection to the target electric power equipment 9.

[0045] In the present invention, a pulse sequence of electromagnetic waves for manipulating the electron spin state is devised for use in measuring magnetic resonance signals. This allows magnetic field surges to be detected in a short time and over a wide measurement range of magnetic field strength. In the pulse sequence of electromagnetic waves irradiated onto the quantum sensor 1, the time τ for observing the free induction decay of the electron spin state of the sensor element 1 is determined according to the temporal rate of change of the magnetic field surge strength. In other words, the measurement range (dynamic range) of the magnetic field strength is determined by adjusting the time τ according to the temporal rate of change of the magnetic field surge strength. When a pulse sequence including two π / 2 pulses is used, the time τ is the time between the π / 2 pulses. When a pulse sequence including a single π pulse is used, the time τ is the time after the single π pulse. Note that the time τ is shorter than the coherence time T2 (transverse relaxation time T2).

[0046] In the following, we first explain the principle and procedure for detecting magnetic resonance signals using optically detected magnetic resonance (ODMR), and then explain how to calculate the magnetic field strength from the detected magnetic resonance signals. Next, we explain the concept of detecting magnetic field surges based on the principle of detecting magnetic resonance signals and the method for calculating the magnetic field strength.

[0047] <Detection of magnetic resonance signals by optically detected magnetic resonance (ODMR)> Figure 5 shows the NV of diamond. - FIG. 2 is a diagram schematically illustrating the energy levels of electrons at the center.

[0048] In this embodiment, the NV center of diamond is used as the sensor element 1. The ground state of the NV center has a magnetic quantum number m s = -1, 0, +1 spin triplet states, and in the steady state at room temperature, all levels are equally distributed in the ground state.

[0049] Ground state magnetic quantum number m s When irradiated with a laser beam with a wavelength of 532 nm (green), the electron in the state m transitions to an excited state, emitting red fluorescence and exhibiting a magnetic quantum number m s =0 ground state.

[0050] On the other hand, the magnetic quantum number m in the ground state s When an electron with a magnetic quantum number m = 0 is irradiated with microwaves with a resonant frequency of 2.87 GHz, electron spin resonance (ESR) occurs, and the magnetic quantum number m s The magnetic quantum number m s When irradiated with a laser beam with a wavelength of 532 nm (green), the electrons with magnetic quantum number m s = 0. This series of processes is a non-radiative transition that does not emit fluorescence.

[0051] In this way, the process of emitting red fluorescence occurs when magnetic resonance occurs and the electrons have a magnetic quantum number m s This is unlikely to occur when the magnetic quantum number m s The doubly degenerate ground states of = ±1 are split by Zeeman splitting in proportion to the strength of the external magnetic field, so the fluorescence intensity also changes as the electron's magnetic quantum number m s = ±1. Therefore, when the microwave frequency is swept around 2.87 GHz, the magnetic resonance signal can be detected as a point where the red fluorescence intensity decreases.

[0052] Fig. 6 shows an exemplary pulse sequence for sensing a magnetic field using an optically detected magnetic resonance (ODMR) method. The pulse sequence of the operating electromagnetic wave shown in Fig. 6 is a pulse sequence including two π / 2 pulses for observing a free induction decay (FID) signal.

[0053] State I represents the state in which the electron spins are initialized by laser light irradiation. In the Bloch sphere, which is a notation for representing quantum states on a unit sphere, the electron spins are aligned along the z-axis, which is the quantization axis.

[0054] Next, in state II, a π / 2 pulse is applied to tilt the electron spins along the quantization axis to a plane perpendicular to the quantization axis. The electron spins are tilted to the xy plane of the Bloch sphere. After that, in state III, the electron spins tilted to the xy plane are dephased while rotating in the xy plane of the Bloch sphere due to interaction with the magnetic field for a predetermined time τ. The strength of the interaction corresponds to the strength of the magnetic field felt by the electron spins. In this state III, the electron spins are dephased while rotating in the xy plane of the Bloch sphere due to interaction with the magnetic field. This process is observed as a free induction decay (FID) signal in the subsequent state V.

[0055] After a certain time τ has elapsed while the phase is being relaxed in state III, a π / 2 pulse is applied in state IV to project the relaxed electron spins onto the quantization axis. The electron spins, which were located within the xy plane of the Bloch sphere, are projected onto the z-axis, which is the quantization axis, and aligned along the z-axis.

[0056] Thereafter, in state V, the sensor element is irradiated with laser light and the light emitted from the sensor element is detected, thereby reading out the phase information of the electron spin state after the interaction.

[0057] In the pulse sequence including two π / 2 pulses shown in Figure 6, electron spins relax while rotating in the xy plane of the Bloch sphere in state III, and in magnetic resonance imaging, the signal generated when the electron spins relax is detected as a magnetic resonance signal. The time τ between the π / 2 pulses corresponds to the period in state III during which the electron spins relax, and this time τ determines the sensitivity of the measurement. This is because the degree to which the electron spins relax due to interaction with a magnetic field corresponds to the strength of the magnetic field felt by the electron spins.

[0058] In the present invention, the time τ for observing the free induction decay of the electron spin state of the sensor element 1 is determined according to the rate of change over time of the magnetic field surge strength. The matters to be considered in determining the time τ will be described later with reference to FIGS. 7 and 8.

[0059] <Method for calculating magnetic field strength based on magnetic resonance signals> In the optically detected magnetic resonance (ODMR) method, phase information (magnetic resonance signal) of the electron spin state of the sensor element 1 after interaction with the object 9 is detected as a change in emission intensity. The detected phase information corresponds to the physical quantity of the object. Therefore, by appropriately processing the detected phase information of the electron spin state after interaction, the physical quantity of the object can be calculated. The physical quantity of the object can be calculated based on the Hamiltonian of the electron spin.

[0060] Electron spin Hamiltonian H gs is expressed by the following formula:

number

[0061] First term

number

[0062] The second and third terms are due to dipole interactions (i.e., spin-spin interactions).

number

number

[0063] Thus, the strength of the magnetic field can be calculated based on the first term, the strength of the temperature and mechanical quantities can be calculated based on the second term, and the strength of the electric field can be calculated based on the third term.

[0064] <Magnetic field surge detection concept> 7 and 8 are diagrams for explaining the magnetic field surge detection concept of the present invention.

[0065] Fig. 7 shows a schematic diagram of a magnetic field surge occurring in a magnetic field generated around a power facility, which is an object 9. In Fig. 7, the upper part shows the magnetic field generated around the power facility, which is an object 9, and the lower part shows an exemplary pulse sequence when sensing the magnetic field by a method using optically detected magnetic resonance (ODMR).

[0066] Fig. 8 is an enlarged view of the portion surrounded by a dashed line in the pulse sequence shown in the lower part of Fig. 7. Symbols I to V shown in Fig. 8 correspond to states I to V of the pulse sequence shown in Fig. 6.

[0067] In the present invention, the strength of the magnetic field generated around the target object 9, which is the power equipment, is measured. The measurement of the magnetic field strength is performed by measuring magnetic resonance signals using the pulse sequences exemplified in, for example, FIGS. 7 and 8 (more specifically, FIG. 6). Whether a magnetic field surge is occurring is determined by comparing the magnetic resonance signals in the previous pulse sequence with the magnetic resonance signals in the current pulse sequence. For example, the magnetic field strength is calculated for each of these magnetic resonance signals, and the time-differential characteristics of the magnetic field strength are calculated based on the magnetic field strength in the previous pulse sequence and the magnetic field strength in the current pulse sequence. If the time-differential characteristics of the magnetic field strength exceed, for example, a predetermined threshold, it is determined that a sudden increase in magnetic field strength (i.e., a magnetic field surge) is occurring, and an electrical signal is output to activate an interlock function that stops operation of the power equipment.

[0068] The number of magnetic field strength data used for comparing magnetic resonance signals, i.e., comparing magnetic field strengths, may be one for one sequence or multiple for multiple sequences. When multiple data for multiple sequences are used for comparing magnetic field strengths, for example, the average value of the multiple magnetic field strength data may be calculated and used.

[0069] In this embodiment, a sudden increase in magnetic field strength is determined based on the time differential characteristics of the magnetic field strength.

number

[0070] As shown in Figure 7, time t0 indicates the current time when the measurement was made, and time t i indicates a future time (i.e., the past). M and P are determined depending on the rate of change over time of the strength of the magnetic field surge to be detected.

[0071] Considering noise in measurements due to the influence of the geomagnetic field, it is preferable that the differential characteristic shown in Equation 1 satisfy the condition of Equation 2 shown below, where T is the magnitude of the geomagnetic field [unit: nT (nanotesla)].

number

[0072] When using a pulse sequence including two π / 2 pulses, each time t i Data on magnetic field strength at B i represents the integrated value of the magnetic field strength felt by the electron spin during the time τ between two π / 2 pulses. When using a pulse sequence including a single π pulse, i Data on magnetic field strength at B i represents the measurable range of the frequency shift during irradiation of a single π pulse.

[0073] [Detection Procedure] FIG. 9 is a flowchart showing the steps of a magnetic field surge detection method according to one embodiment of the present invention.

[0074] In step S1, the sensor element 1 is irradiated with laser light to initialize the electron spin of the color center (NV center) of the sensor element 1. Then, the electron spin of the initialized NV center is caused to interact with the magnetic field generated around the object 9. After the interaction is allowed to continue for a sufficient period of time, the electron spin state of the NV center becomes a state corresponding to the strength of the magnetic field. The state of step S1 corresponds to state I of the pulse sequence shown in FIG. 6. If a magnetic field surge occurs in the magnetic field generated around the object 9, the electron spin of the initialized NV center interacts with the magnetic field including the magnetic field surge and becomes a state corresponding to the strength of the magnetic field including the magnetic field surge.

[0075] In step S2, magnetic field sensing is performed by irradiating the sensor element 1 with electromagnetic waves for spin manipulation. In this embodiment, magnetic field sensing is performed by irradiating two π / 2 pulses according to the pulse sequence shown in Fig. 6. That is, in this embodiment, the electron spin state of the NV center is manipulated to correspond to states II to IV of the pulse sequence shown in Fig. 6.

[0076] In step S3, the sensor element 1 is irradiated with laser light and changes occurring in the sensor element 1 are detected, thereby reading out phase information of the electron spin state after the interaction. In this embodiment, the phase information of the electron spin state after the interaction is read out by detecting light emitted from the sensor element 1. The phase information of the electron spin state after the interaction is detected by the detection unit 32 as changes in emission intensity by optically detected magnetic resonance (ODMR). The state in step S3 corresponds to state V of the pulse sequence shown in FIG. 6.

[0077] In step S4, it is determined whether the series of measurement processes from steps S1 to S3 has been repeatedly executed a predetermined number of times. If the series of measurement processes has been repeatedly executed a predetermined number of times (Yes in step S4), the process of step S5 is executed. If the series of measurement processes has not been repeatedly executed a predetermined number of times (No in step S4), the process is executed again from step S1. In this embodiment, the predetermined number of times corresponds to the number of data points required to calculate the temporal differential characteristics of the magnetic field strength expressed by equation 1 or equation 2, and corresponds to the sum of M and P in equation 1 or equation 2. The range of multiple pulse sequences corresponding to the sum of M and P can be expressed as a determination time window for calculating the temporal differential characteristics of the magnetic field strength and detecting a magnetic field surge. In other words, in this embodiment, the temporal differential characteristics of the magnetic field strength are repeatedly monitored within the time range included in the width of the determination time window.

[0078] In step S5, for each of the plurality of electron spin states after the interaction, the strength of the magnetic field is calculated based on each electron spin state.

[0079] The strength of the magnetic field is calculated from the phase information of the electron spin state after the interaction read out in step S3. The phase information of the electron spin state after the interaction detected by the detection unit 32 corresponds to the magnetic field of the object 9. Therefore, the strength of the magnetic field can be calculated by appropriately processing the phase information of the detected electron spin state after the interaction. For example, the strength of the magnetic field of the object 9 can be calculated by finding the probability that the electron spin state after the interaction will be the ground state. The strength is calculated using the Hamiltonian H of the electron spin gs This can be done based on the term due to the Zeeman effect.

[0080] In step S6, the time differential characteristic of the magnetic field strength is calculated based on the intensities of the plurality of magnetic fields. In this embodiment, the time differential characteristic of the magnetic field strength is calculated based on Equation 1.

[0081] In step S7, a magnetic field surge is detected based on the differential characteristic. For example, it is determined whether the magnitude of the differential characteristic calculated in step S6 is equal to or greater than a predetermined threshold value.

[0082] If a magnetic field surge is detected (Yes in step S8), an alarm signal is output in step S9 to stop operation of the power equipment 9. The alarm signal can be an electrical signal (i.e., an interlock signal) for activating an interlock function that stops operation of the power equipment 9. The alarm signal is transmitted, for example, to a computer device that centrally manages the operation status of other power equipment, for example, via a network 99. Upon receiving the alarm signal, the centralized management computer device transmits an electrical signal (i.e., an interlock signal) to the other power equipment to activate an interlock function that stops operation of the power equipment. Upon receiving the interlock signal, each piece of power equipment stops operation.

[0083] If no magnetic field surge is detected (No in step S8), the process is repeated from step S1 to detect the magnetic field surge. Note that if no magnetic field surge is detected (No in step S8) and the process is repeated from step S1, the time width of the magnetic field strength monitored by the determination time window mentioned in the description of step S4 is shifted back by the time of one pulse sequence.

[0084] [effect] As described above, the present invention makes it possible to detect magnetic field surges in a short time and over a wide range of magnetic field strengths, thereby enabling the activation of an interlock function that stops the operation of power equipment in an extremely short time after the occurrence of a surge current.

[0085] In this invention, the strength of the magnetic field generated around the target electric power equipment is measured using a quantum sensor. This makes it possible to detect magnetic field surges with high sensitivity. The magnetic resonance signal used to calculate the magnetic field strength is detected by the optically detected magnetic resonance (ODMR) method. This makes it possible to detect magnetic field surges contactlessly without directly connecting electrically to the target electric power equipment.

[0086] In this invention, we devise an electromagnetic wave pulse sequence for manipulating the electron spin state when measuring magnetic resonance signals, which enables us to detect magnetic field surges in a short time and over a wide measurement range of magnetic field strength.

[0087] [Other forms] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

[0088] In the above-described embodiment, a pulse sequence including two π / 2 pulses as illustrated in FIG. 6 is used, but the pulse sequence for observing the free induction decay (FID) signal is not limited to this pulse sequence. Instead of a pulse sequence including two π / 2 pulses, a pulse sequence including a single π pulse as illustrated in FIG. 10 can be used. The time τ after the single π pulse is determined according to the temporal rate of change of the intensity of the magnetic field surge to be detected. By utilizing the off-resonance effect, the present invention can function even if a pulse sequence including a single π pulse is used instead of a pulse sequence including two π / 2 pulses. This is because the magnetic field surge is detected by the off-resonance effect.

[0089] When using a pulse sequence including a single π pulse as illustrated in FIG. 10, it is preferable that the time τ after the single π pulse is shorter than the coherence time T2 (transverse relaxation time T2) and as long as a magnetic field surge can be detected.

[0090] Fig. 10 shows an exemplary pulse sequence for sensing a magnetic field using an optically detected magnetic resonance (ODMR) method. The operational electromagnetic pulse sequence shown in Fig. 10 includes a single π pulse, allowing for the observation of a short magnetic field surge.

[0091] State I represents the state in which the electron spins are initialized by laser light irradiation. In the Bloch sphere, which is a notation for representing quantum states on a unit sphere, the electron spins are aligned along the z-axis, which is the quantization axis.

[0092] Next, a π pulse is applied in state II' to flip the electron spin along the z-axis. The flipped electron spin then dephases in state III' due to interaction with the magnetic field for a predetermined time τ. In the presence of a strong magnetic field surge, the electron spin in state II' is no longer flipped due to the off-resonance effect, and the unflipped spin information is observed as a strong magnetic field surge.

[0093] Thereafter, in state IV', the sensor element is irradiated with laser light and the light emitted from the sensor element is detected, thereby reading out the phase information of the electron spin state after the interaction.

[0094] In the above-described embodiment, the magnetic resonance signal used to calculate the magnetic field strength is detected by optically detected magnetic resonance (ODMR), but the method used to detect the magnetic resonance signal is not limited to optically detected magnetic resonance (ODMR). Instead of optically detected magnetic resonance (ODMR), the magnetic resonance signal can also be detected by, for example, electrically detected magnetic resonance (EDMR). In this case, a pair of measurement electrodes for detecting the magnetic resonance signal is electrically connected to the sensor element 1. A bias voltage is applied between the pair of measurement electrodes, and an electric field is applied to the sensor element 1 through the measurement electrodes.

[0095] In the above-described embodiment, a magnetic field surge is detected based on the time differential characteristics of the strength of the magnetic field generated around the target object 9, which is the power equipment. However, the method of detecting a magnetic field surge is not limited to this. For example, whether a magnetic field surge is occurring can also be determined by comparing the measured value of the magnetic field strength in the current pulse sequence with the measured value of the magnetic field strength in the previous pulse sequence. For example, if the ratio of these measured values ​​exceeds a threshold, it is determined that a sudden increase in the magnetic field strength (i.e., a magnetic field surge) is occurring, and an electrical signal is output to activate an interlock function that stops operation of the power equipment.

[0096] In the above-described embodiment, the magnetic field surge detection device 10 detects a magnetic field surge occurring around the power equipment 9, and although a current transformer 9a and a voltage transformer 9b are exemplified as examples of the power equipment 9, the power equipment 9 is not limited to these. The power equipment 9 can include, for example, power transmission and transformation equipment such as a transformer and a switchgear.

[0097] [Example] Examples of the present invention will be described below to clarify the features of the present invention. [Example]

[0098] In Example 1, a numerical simulation of a free induction decay (FID) signal was carried out.

[0099] Numerical simulation conditions The pulse sequence was a simple FID sequence, and since each measurement relies on a single sequence, no accumulation of magnetic resonance signals was performed.

[0100] The assumed conditions (a) to (h) for the sensor element sample and pulse sequence are as follows:

[0101] (a) Coherence time T2 is 100 ns (nanoseconds). (b) The diameter of the laser spot is 10 μm, and the NV center density “NV” is 3 × 10 16 cm-3 Therefore, the number of NV centers in a spherical volume is approximately 15 × 10 6 Depending on the NV center sample used, the NV center density "NV" can be as high as 1 × 10 19 cm -3 It may be possible to improve up to (c) The contrast between spin states is approximately 1% (d) On average, 0.1 photons per readout per NV center. (e) The pulse sequence for measuring the FID signal was a pulse sequence including two π / 2 pulses as shown in FIG. (f) The laser pulse length is 30 μs, the waiting time between the laser pulse and the first π / 2 pulse is 1 μs, the π / 2 pulse length is 40 ns, and the delay between these pulses is approximately 10 ns. (g) M = 3 (covers approximately 100 μs), P = 31 (covers approximately 1 ms), T = 0.3 mT (millitesla). The surge waveform is triangular with a rise time of 1 μs and a fall time of 100 μs. (h) The measurements were simulated using a Hamiltonian for the spin. Therefore, important effects such as off-resonance effects were fully taken into account. Regarding the noise in the measurements, only the main noise source, shot noise, was considered.

[0102] Numerical simulation results 11 and 12 are the results of a numerical simulation of a surge magnetic field according to Example 1, showing the simulation results of a surge of a magnetic field B of 0.5 mT at time t=20 ms. In FIG. 11, (A) is the simulation result of intensity, and (B) is the result of filtering the result of (A) using Equation 2. In FIG. 12, (A) is the simulation result of a magnetic field, and (B) is the result of filtering the result of (A) using Equation 2.

[0103] In Figure 11(A), the solid line shows the intensity measured ignoring shot noise, and the plot indicated by the cross "x" shows the intensity measured including shot noise. In Figure 12(A), the solid line shows the magnetic field, and the plot indicated by the cross "x" shows the measured magnetic field converted from the intensity measurement.

[0104] As shown in Figure 12(B), in the example shown in Example 1, a 2 mT surge was detected within approximately 40 μs (microseconds), demonstrating that magnetic field surges can be detected by utilizing the off-resonance effect. This off-resonance effect can also be obtained for magnetic fields higher than 2 mT, such as 20 mT or 200 mT. As long as measurements are performed based on the off-resonance effect, the absolute value of the surge magnetic field is not important. Therefore, measurements using the off-resonance effect are shown to be suitable for monitoring surge magnetic fields that rapidly increase over time. [Example]

[0105] In Example 2, a pulse sequence different from that of Example 1 was used to perform a numerical simulation of a free induction decay (FID) signal in the same manner as in Example 1, and changes in response time were examined. Specifically, instead of the pulse sequence including two π / 2 pulses used in Example 1 as exemplified in Fig. 6, a pulse sequence including a single π pulse as exemplified in Fig. 10 was used to perform a numerical simulation of a free induction decay (FID) signal.

[0106] 13 and 14 show the results of a numerical simulation of a surge magnetic field according to Example 2. In Fig. 13, (A) shows the simulation result of intensity, and (B) shows the simulation result of the magnetic field. In Fig. 14, (A) shows the result of filtering the result of Fig. 13(A) using Equation 2, and (B) shows the result of filtering the result of Fig. 13(B) using Equation 2.

[0107] 14(B), in the example shown in Example 2, it was shown that it was possible to detect a magnetic field surge of 2 mT within about 17 μs. In Example 2, the response time was about 16.5 μs, which was faster than the response time of about 48.5 μs in Example 1. [Explanation of symbols]

[0108] 1. Sensor element (Nuclear-Voltage center in diamond) 2 Electromagnetic wave irradiation section 3 Magnetic field surge detector 8 Interaction 9(9a,9b) Electric power equipment (current transformers, voltage transformers) 10 Magnetic field surge detector 11 Probe 12 Diamond Crystal 14 Antenna 21 Microwave (MW) Oscillator 22 Switch 23 Amplifier 31 Light irradiation unit 311 Light source 312 Acousto-optic Modulator (AOM) 313 Objective Lens 32 Detection unit 33 Data Processing Unit 331 Magnetic Field Strength Calculation Unit 332 Differential characteristic calculation section 333 Alarm section 99 Network

Claims

1. an electromagnetic wave irradiation unit that repeatedly irradiates the quantum sensor element with electromagnetic waves for manipulating the electron spin state of the quantum sensor element, which changes due to interaction with the magnetic field to be detected, in a pulse sequence in which the time τ for observing the free induction decay of the electron spin state is predetermined according to the time rate of change of the strength of the surge of the magnetic field; a magnetic field surge detector that repeatedly detects a surge in the magnetic field based on changes in the plurality of electron spin states after interacting with the magnetic field; Equipped with The magnetic field surge detection unit a magnetic field strength calculation unit that calculates the strength of the magnetic field based on each of the plurality of electron spin states after the interaction; a differential property calculation unit that calculates a time differential property of the intensity of the magnetic field based on the intensities of the plurality of magnetic fields; Including, Detecting a surge in the magnetic field based on the calculated differential characteristic; The differential characteristic calculation unit [Equation 1] Calculating the differential characteristic based on where i is an integer value greater than or equal to 0, B i is the strength of the magnetic field at time t i , M is the number of data points containing a potential surge, and P is the number of data points before the potential surge.

2. The magnetic field surge detection unit a light irradiation unit that irradiates the quantum sensor element with light for reading information on the phase of the electron spin state after interacting with the magnetic field; a detection unit that detects a change that occurs in the quantum sensor element due to the irradiation of the light; further comprising The magnetic field strength calculation unit 2. The magnetic field surge detector according to claim 1, wherein the phase information is read from the detected change, and the intensity of the magnetic field is calculated based on the read phase information.

3. 3. The magnetic field surge detector according to claim 1, wherein the magnetic field surge detector further includes an alarm unit that outputs an alarm signal when a surge of the magnetic field is detected.

4. 4. The magnetic field surge detection device according to claim 1, wherein the electromagnetic wave irradiation unit repeatedly irradiates the electromagnetic wave to the quantum sensor element in a pulse sequence in which the time τ between π / 2 pulses is predetermined according to the temporal change rate of the strength of the magnetic field surge.

5. The electromagnetic wave irradiation unit repeatedly irradiates the electromagnetic wave to the quantum sensor element in a pulse sequence in which the time τ after a single π pulse is predetermined according to the temporal change rate of the strength of the magnetic field surge. The magnetic field surge detection device according to any one of claims 1 to 3.

6. a step of repeatedly irradiating the quantum sensor element with electromagnetic waves for manipulating the electron spin state of the quantum sensor element, which changes due to interaction with the magnetic field to be detected, in a pulse sequence in which the time τ for observing the free induction decay of the electron spin state is predetermined according to the time rate of change of the surge of the magnetic field; repeatedly detecting the magnetic field surges based on changes in the plurality of electron spin states after interacting with the magnetic field; Including, The step of repeatedly detecting magnetic field surges comprises: calculating the strength of the magnetic field based on each of the plurality of electron spin states after the interaction; calculating a differential property of the magnetic field strength with respect to time based on the plurality of magnetic field strengths; Including, Detecting a surge in the magnetic field based on the calculated differential characteristic; The step of calculating the differential characteristic includes: [Equation 2] Calculating the differential characteristic based on where i is an integer value greater than or equal to 0, B i is the strength of the magnetic field at time t i , M is the number of data points containing a potential surge, and P is the number of data points before the potential surge.

7. The step of repeatedly detecting magnetic field surges comprises: irradiating the quantum sensor element with light for reading out information on the phase of the electron spin state after interacting with the magnetic field; detecting a change in the quantum sensor element caused by the irradiation of light; further comprising The step of calculating the strength of each magnetic field includes:

7. The magnetic field surge detection method according to claim 6, further comprising the steps of: reading out information about the phase from the detected change; and calculating the intensity of the magnetic field based on the read-out information about the phase.

8. An electric power facility comprising the surge detection device according to any one of claims 1 to 5.

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