sensor

Abstract

The present invention provides a sensor capable of effectively detecting the fluorescence intensity of an element having a color center. [Solution] The sensor 1 comprises an element 10 that emits fluorescence upon irradiation with excitation light and has a color center, an antenna 20 that radiates microwaves to the element 10, an optical system 30 that irradiates the element 10 with excitation light, and a photosensor 40 that receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence. The element 10 is a plate-shaped member and has an irradiation surface 10a to which excitation light is irradiated and an emission surface 10b on the opposite side of the irradiation surface 10a from which fluorescence is emitted. The antenna 20 is formed of a plate-shaped member with a through hole 23a, the through hole 23a is positioned between the element 10 and the photosensor 40, and the photosensor 40 is positioned to face the emission surface 10b of the element 10.

Description

[Technical Field]

[0001] This invention relates to a sensor. [Background technology]

[0002] Conventionally, optically detected magnetic resonance (ODMR) techniques using materials such as diamond containing nitrogen and lattice defects (NV centers) are known. In this technique, as described later, the magnetic field received by the object being measured can be measured based on the resonance frequency of the ODMR spectrum.

[0003] Non-Patent Document 1 discloses a method in which microwaves are irradiated onto a diamond element using a microwave antenna, the diamond element is excited with 532 nm laser light, and the red fluorescence emitted from the diamond element is detected. Non-Patent Document 2 discloses a method in which microwaves are irradiated onto a diamond element using a microwave antenna, 532 nm laser light is irradiated onto the surface of the diamond element through a multimode fiber, and the red fluorescence emitted from the diamond element is detected with a fluorescence probe. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] RL Patel et al., "Subnanotesla Magnetometry with a Fiber-Coupled Diamond Sensor", PHYSICAL REVIEW APPLIED, October 2020, Vol. 14, Issue 4 [Non-Patent Document 2] Y. Gao et al., "Research and Experiment on the System of Miniaturized Diamond NV Center Ensemble Magnetometer Based on Fiber Coupling", 2021 IEEE 15th International Conference on Electronic Measurement & Instruments (ICEMI), October 2021 [Overview of the project] [Problems that the invention aims to solve]

[0005] In Non-Patent Document 1, the red fluorescence of the diamond element is blocked by a microwave antenna, and therefore the red fluorescence emitted from the diamond element is detected by a photodetector through a fiber, dichroic mirror, and filter. In Non-Patent Document 2, the red fluorescence of the diamond element is also blocked by a microwave antenna, and therefore the red fluorescence emitted from the diamond element is detected by a fluorescence probe through a multimode fiber. However, in the conventional technology, since the red fluorescence is detected through a fiber or the like, it was not possible to directly detect the red fluorescence emitted from the element. Therefore, in the conventional technology, there was a risk that a sufficient signal-to-noise ratio could not be obtained.

[0006] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a sensor capable of effectively detecting the fluorescence intensity of an element having a color center. [Means for solving the problem]

[0007] A sensor according to an aspect of the present invention comprises an element that emits fluorescence upon irradiation with excitation light and has a color center, an antenna that radiates microwaves to the element, and an optical system that irradiates the element with excitation light. The sensor includes a photosensor that receives the fluorescence emitted from the element and detects the intensity of the fluorescence. The element is a plate-shaped member and has an irradiation surface to which the excitation light is irradiated, and an emission surface on the opposite side of the irradiation surface from which the fluorescence is emitted. The antenna is formed of a plate-shaped member with a through hole. The through hole is located between the element and the photosensor. The photosensor is located facing the emission surface of the element. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sensor capable of effectively detecting the fluorescence intensity of an element having a color center. [Brief explanation of the drawing]

[0009] [Figure 1] This is a perspective view showing a sensor according to one embodiment. [Figure 2] This is a plan view showing an example of the inside of a sensor with the top panel removed. [Figure 3] A side view showing a sensor according to one embodiment. [Figure 4] This diagram schematically shows the structure of a diamond element having an NV center. [Figure 5] This figure shows the valence band and conduction band of a diamond element with an NV center. [Figure 6] This figure shows the energy levels between the ground state and excited state of a diamond element having an NV center. [Figure 7] This is the ODMR spectrum when no magnetic field is applied to the element (Bext=0). [Figure 8] This graph shows the relationship between the magnetic field applied to the element and the ground state energy levels (ms = -1, 0, +1). [Figure 9]ODMR spectra when no magnetic field is applied to the element (Bext = 0) and when a magnetic field is applied to the element (Bext > 0). [Figure 10] FIG. 3 is a perspective view showing an example of an antenna according to an embodiment. [Figure 11] FIG. 6 is a side view showing an example of a through-hole provided in the antenna. [Figure 12] FIG. 9 is a plan view showing a state where fluorescence passes through the through-hole. [Figure 13] FIG. 12 is a side view showing another example of a through-hole provided in the antenna. [Figure 14] FIG. 15 is a side view showing another example of a through-hole provided in the antenna. [Figure 15] FIG. 18 is a side view showing another example of a through-hole provided in the antenna. [Figure 16] FIG. 21 is a side view showing another example of a through-hole provided in the antenna. [Figure 17] FIG. 24 is a side view showing another example of a through-hole provided in the antenna. MODE FOR CARRYING OUT THE INVENTION

[0010] Hereinafter, the sensor according to the present embodiment will be described in detail with reference to the drawings. Note that the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

[0011] FIG. 1 is a perspective view showing a sensor 1 according to an embodiment. FIG. 2 is a plan view showing an example of the inside of the sensor 1 with the top plate 63 removed. FIG. 3 is a side view showing the sensor 1 according to an embodiment. The sensor 1 according to the present embodiment is a current sensor that measures a current flowing through a bus bar B such as a power supply path or a switchboard. As shown in FIGS. 1 to 3, the sensor 1 according to the present embodiment includes an element 10, an antenna 20, a microwave generator 26, an optical system 30, an optical sensor 40, a control arithmetic processing unit 45, and a holder 60.

[0012] The element 10 according to this embodiment emits fluorescence upon irradiation with excitation light. The element 10 is a diamond element having an NV center and is positioned in close proximity to one side of the busbar B. The element 10 is a plate-shaped member with a rectangular shape in plan view. The element 10 is attached to the tip of the optical fiber 32 of the optical system 30 and has an irradiation surface 10a to which excitation light is irradiated. The element 10 has a first emission surface 10b on the side opposite to the irradiation surface 10a from which fluorescence is emitted. The element 10 also has a second emission surface 10c that connects the irradiation surface 10a and the first emission surface 10b and from which fluorescence is emitted. The irradiation surface 10a and the first emission surface 10b are parallel surfaces, and the second emission surface 10c is a surface perpendicular to the irradiation surface 10a and the first emission surface 10b and extends in the thickness direction of the element 10. The second emission surface 10c is formed from four surfaces, and the area of ​​each surface is smaller than the area of ​​the irradiation surface 10a and the first emission surface 10b.

[0013] Antenna 20 radiates microwaves onto element 10. Optical system 30 irradiates element 10 with excitation light. Photosensor 40 receives fluorescence emitted from element 10 and detects the intensity of the fluorescence. Control processing unit 45 controls the microwave generator 26 and optical system 30 and calculates at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, strain, etc., of the object to be measured, based on the output signal detected by photosensor 40. Holder 60 is attached to the surface of busbar B and houses and fixes element 10.

[0014] As shown in Figure 4, the NV center has a structure in which one carbon atom in the diamond crystal structure is replaced by a nitrogen atom, and a vacancy is located adjacent to the replaced nitrogen atom. Because the NV center has a long spin coherence time at room temperature and atmospheric pressure, it can perform highly sensitive measurements even under normal conditions.

[0015] As shown in Figure 5, diamond is a wide-bandgap semiconductor with a bandgap width of approximately 5.5 eV, but its ground state is located 2.6 eV from the conduction band, and its excited states are also within the bandgap.

[0016] As shown in Fig. 6, an NV center (NV - ) with one negative charge has a triplet state with magnetic quantum numbers m S = -1, 0, +1 in the ground state, and the spin sublevels with m S = ±1 are degenerate when the magnetic field is 0. When the electron is in the ground state with m S = 0 and the element 10 is irradiated with green excitation light, the electron transitions from the ground state to the excited state and then returns to the ground state while emitting red fluorescence. However, when a microwave of 2.87 GHz corresponding to the energy difference between m S = 0 and m S = ±1 is applied to the element 10 and the element 10 is irradiated with green excitation light when the electron is in the state with m S = ±1, the proportion of non-radiative transitions increases. That is, the intensity of the red fluorescence is lower when the electron is excited from m S = ±1 than when it is excited from m S = 0. Therefore, as shown in Fig. 7, when the frequency of the microwave is the resonance frequency of the NV center, the intensity of the red fluorescence emitted from the NV center decreases. Thus, by utilizing the characteristics of ODMR, the spin state of the NV center can be detected with light and microwaves.

[0017] On the other hand, as shown in Figs. 8 and 9, when a magnetic field parallel to the NV axis is applied to the element 10, the levels of m S = -1 and m S = +1 are Zeeman split, and the resonance frequency varies in proportion to the magnetic field strength. Therefore, by obtaining the difference between the microwave frequency of the fluorescence intensity minimum at m S = -1 and the microwave frequency of the fluorescence intensity minimum at m S = +1, the magnetic field strength applied to the element 10 can be measured.

[0018] Antenna 20 radiates microwaves to element 10. Antenna 20 radiates frequency-variable microwaves to element 10. Microwaves are supplied to antenna 20 by microwave generator 26. Antenna 20 is electrically connected to a feed line 27 such as a coaxial cable, and a frequency-variable high-frequency current is supplied from microwave generator 26 via the feed line 27. As will be described later, antenna 20 is formed of a plate-shaped member with a through hole 23a. The through hole 23a is located between element 10 and optical sensor 40, and optical sensor 40 is positioned facing the first emission surface 10b of element 10. Antenna 20 covers the first emission surface 10b and the second emission surface 10c of element 10 with space between them, and optical sensor 40 is positioned on the side of antenna 20 opposite to element 10.

[0019] As shown in Figure 10, the antenna 20 is formed into a rectangular loop shape by bending, for example, a roughly rectangular plate-shaped conductor. Such an antenna 20 is low-cost and can reduce unevenness in the distribution of microwaves applied to the element 10. The element 10 is arranged inside the loop-shaped antenna 20. The antenna 20 includes a first metal plate 21, a second metal plate 22, a third metal plate 23, a fourth metal plate 24, and a fifth metal plate 25. The first metal plate 21, the second metal plate 22, the third metal plate 23, the fourth metal plate 24, and the fifth metal plate 25 are all flat plates. The first metal plate 21 is connected to the second metal plate 22, and the second metal plate 22 is connected to the third metal plate 23. The third metal plate 23 is connected to the fourth metal plate 24, and the fourth metal plate 24 is connected to the fifth metal plate 25.

[0020] In the planar direction, one end of the first metal plate 21 is a free end, and the other end of the first metal plate 21 is connected to the second metal plate 22. In the planar direction, one end of the second metal plate 22 is connected to the first metal plate 21, and the other end of the second metal plate 22 is connected to the third metal plate 23. In the planar direction, one end of the third metal plate 23 is connected to the second metal plate 22, and the other end of the third metal plate 23 is connected to the fourth metal plate 24. In the planar direction, one end of the fourth metal plate 24 is connected to the third metal plate 23, and the other end of the fourth metal plate 24 is connected to the fifth metal plate 25. In the planar direction, one end of the fifth metal plate 25 is connected to the fourth metal plate 24, and the other end of the fifth metal plate 25 is a free end.

[0021] The first metal plate 21 and the fifth metal plate 25, and the third metal plate 23 and the fifth metal plate 25 are arranged facing each other with a space in between. The second metal plate 22 and the fourth metal plate 24 are also arranged facing each other with a space in between. The first metal plate 21 has a feed point, to which a feed line 27 is connected. A high-frequency current is supplied from the microwave generator 26 to the antenna 20 via the feed line 27 and the feed point. The element 10 is arranged in the space enclosed by the second metal plate 22, the third metal plate 23 and the fourth metal plate 24. The third metal plate 23 is positioned facing the first emission surface 10b of the element 10 and covering the first emission surface 10b. The second metal plate 22 and the fourth metal plate 24 are positioned facing the second emission surface 10c of the element 10, respectively, and are positioned to cover each second emission surface 10c. The third metal plate 23 is provided with a through-hole 23a through which fluorescence emitted from the element 10 passes. In this embodiment, the through-hole 23a is a single square through-hole when viewed from the thickness direction of the third metal plate 23. The fifth metal plate 25 has a power supply line insertion hole 25a through which the power supply line 27 is inserted, and an optical fiber insertion hole 25b through which the optical fiber 32 is inserted. The power supply line insertion hole 25a is a power supply point connected to, for example, the outer conductor of a coaxial cable.

[0022] The optical system 30 irradiates the element 10 with excitation light. The optical system 30 irradiates the element 10 with green light as the excitation light. The optical system 30 includes a light source 31 and an optical fiber 32. The light source 31 may include, for example, a laser diode and emit laser light. The light emitted from the light source 31 may have a peak in intensity that shows its maximum value in the range of 500 nm to 560 nm. The optical fiber 32 guides the light emitted from the light source 31 to the element 10. Specifically, the light source 31 is provided at one end of the optical fiber 32, and the element 10 is provided at the other end of the optical fiber 32. The light emitted from the light source 31 is then irradiated onto the element 10.

[0023] The light sensor 40 receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence. The light sensor 40 may include a photodiode, and the red fluorescence emitted from the element 10 may be detected by the photodiode. The light sensor 40 outputs an output signal corresponding to the detected fluorescence intensity to the control processing unit 45.

[0024] The control processing unit 45 controls the microwave generator 26 and the optical system 30, and calculates at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, and strain of the object to be measured, based on the output signal detected by the optical sensor 40. The control processing unit 45 is equipped with a computer including a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and loads a program stored in ROM into RAM and executes it with the CPU.

[0025] The holder 60 includes a base plate 61, a plurality of support columns 62, and a top plate 63. The base plate 61 is attached in contact with the surface of the busbar B. In this embodiment, the base plate 61 is integrally formed with the plurality of support columns 62, and the plurality of support columns 62 support the top plate 63. The holder 60 also has an element housing section 64, a power supply line insertion section 65, and an optical fiber insertion section 66. The element housing section 64, the power supply line insertion section 65, and the optical fiber insertion section 66 are spaces formed between the base plate 61, the support columns 62, and the top plate 63.

[0026] The holder 60 houses the element 10 and the antenna 20. The element housing section 64 houses the element 10, and the position of the element 10 is fixed relative to the position of the holder 60. The antenna 20 is also housed in the element housing section 64, and the antenna 20 is fixed to the holder 60. The feed line 27 is inserted through the feed line insertion section 65. The optical fiber 32 is inserted through the optical fiber insertion section 66. The tip of the optical fiber 32 is positioned in the element housing section 64.

[0027] In this embodiment, the holder 60 has a rectangular parallelepiped shape and is made of a resin material, but the shape of the holder 60 and the material used to form it are not particularly limited. For example, the holder 60 may be made of a material such as ceramic.

[0028] Sensor 1, configured as described above, irradiates the NV center of element 10 with green excitation light and simultaneously radiates microwaves to the NV center of element 10 while modulating the frequency of the microwaves. By utilizing the characteristics of ODMR, the magnetic field around busbar B can be measured.

[0029] In this embodiment, the case where sensor 1 is a current sensor has been described. Sensor 1 can be used, for example, as a battery sensor to evaluate the remaining battery level of an electric vehicle by measuring the current flowing through busbar B. However, sensor 1 may also measure at least one physical quantity selected from the group consisting of magnetic field, electric field, temperature, strain, etc., using ODMR.

[0030] Furthermore, although the element 10 according to this embodiment is a diamond element having an NV center, it may also be an element having a color center such as an SnV center, a SiV center, or a GeV center. An SnV center is a structure in which one carbon atom in the diamond crystal is replaced by tin (Sn), and a vacancy is adjacent to the replaced Sn. A SiV center is a structure in which one carbon atom in the diamond crystal is replaced by Si, and a vacancy is adjacent to the replaced Si. A GeV center is a structure in which one carbon atom in the diamond crystal is replaced by Ge, and a vacancy is adjacent to the replaced Ge.

[0031] Furthermore, the sensor 1 according to this embodiment may include a magnet (not shown) for applying a bias magnetic field to the element 10. When a bias magnetic field is applied to the element 10, as described above, m S = +1 and m S The -1 level undergoes Zeeman splitting, and the splitting width increases in proportion to the strength of the bias magnetic field. Therefore, by applying a sufficiently large bias magnetic field to element 10 relative to the current flowing through busbar B, the direction of the current can be detected. The magnitude of the magnet's bias magnetic field should be adjusted as appropriate depending on the current detection range. The magnet is located at element 10. <111> A bias magnetic field may be applied parallel to the direction.

[0032] The magnet may include at least one of a permanent magnet and an electromagnet. The permanent magnet may include at least one selected from the group consisting of neodymium magnets, samarium cobalt magnets, ferrite magnets, and alnico magnets. The magnet includes a pair of magnets, which may be arranged so as to sandwich the element 10 with a space between them. The magnet may be located inside the holder 60 and housed and fixed within the holder 60, or it may be located outside the holder 60 and fixed to an optical base plate (not shown). When the magnet is fixed to the holder 60, fluctuations in the magnetic field applied to the element 10 can be suppressed. When the magnet is fixed to the holder 60, it is preferable that the magnet includes a samarium cobalt magnet. Although samarium cobalt magnets have weaker magnetic force than neodymium magnets, their Curie temperature is higher than that of neodymium magnets, and they can maintain a high magnetic force even under conditions where the optical fiber 32 is in a high-temperature environment. The magnet is a ring-shaped magnet with a through-hole, through which the optical fiber 32 may be inserted. In other words, the ring-shaped magnet may surround the optical fiber 32. This allows for efficient use of space, thus reducing the size of the sensor 1.

[0033] As described above, the sensor 1 according to this embodiment comprises an element 10 that emits fluorescence upon irradiation with excitation light and has a color center, an antenna 20 that radiates microwaves to the element 10, and an optical system 30 that irradiates the element 10 with excitation light. The sensor 1 includes a photosensor 40 that receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence. The element 10 is a plate-shaped member and has an irradiation surface 10a to which excitation light is irradiated, and a first emission surface 10b on the opposite side of the irradiation surface 10a from which fluorescence is emitted. The antenna 20 is formed of a plate-shaped member with a through hole 23a. The through hole 23a is located between the element 10 and the photosensor 40. The photosensor 40 is located facing the first emission surface 10b of the element 10.

[0034] As described above, in the sensor 1 according to this embodiment, the through-hole 23a is positioned between the element 10 and the photosensor 40. The photosensor 40 is positioned to face the first emission surface 10b of the element 10. With this configuration, as shown in Figure 12, fluorescence emitted from the first emission surface 10b of the element 10 passes through the through-hole 23a and is detected by the photosensor 40. In other words, fluorescence emitted from the front of the element 10, rather than the side, can be detected by the photosensor 40. Therefore, in the sensor 1 according to this embodiment, the fluorescence intensity of the element 10 having a color center can be effectively detected, and for example, the signal-to-noise ratio can be improved.

[0035] The optical system 30 may include an optical fiber 32, and the element 10 may be attached to the tip of the optical fiber 32. With this configuration, the excitation light can be reliably irradiated onto the element 10, and the intensity of the fluorescence emitted from the element 10 can be increased.

[0036] As shown in Figure 11, in this embodiment, the through-hole 23a is a single square through-hole when viewed from the thickness direction of the plate-shaped member forming the antenna 20, but the number and shape of the through-holes 23a are not limited to this form. Specifically, the antenna 20 only needs to have at least one through-hole 23a, and may have multiple through-holes 23a. For example, as shown in Figure 13, the antenna 20 may have two rectangular through-holes 23a that are short in the vertical direction, arranged in a vertical direction. Also, as shown in Figure 14, the antenna 20 may have five rectangular through-holes 23a that are short in the vertical direction, arranged in a vertical direction. Also, as shown in Figure 15, the antenna 20 may have one circular through-hole 23a. Also, as shown in Figure 16, the antenna 20 may have multiple circular through-holes 23a arranged in the vertical and planar directions. Also, as shown in Figure 17, the antenna 20 may have five rectangular through-holes 23a that are long in the vertical direction, arranged in a planar direction.

[0037] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of Symbols]

[0038] 1 sensor 10 elements 10a Irradiation surface 10b 1st exit surface 20 antennas 23a Through hole 30 Optical system 32 optical fibers 40 Light Sensors

Claims

1. An element that emits fluorescence upon irradiation with excitation light and has a color center, The element is provided with an antenna that emits microwaves, An optical system for irradiating the element with the excitation light, A light sensor that receives the fluorescence emitted from the element and detects the intensity of the fluorescence, Equipped with, The element is a plate-shaped member having an irradiation surface to which the excitation light is irradiated, and an emission surface on the opposite side of the irradiation surface from which the fluorescence is emitted. The antenna is formed from a plate-shaped member having a through hole, The through hole is positioned between the element and the optical sensor. The light sensor is positioned so as to face the emission surface of the element.

2. The optical system includes optical fibers, The sensor according to claim 1, wherein the element is attached to the tip of the optical fiber.

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