sensor

Abstract

The present invention provides a sensor capable of suppressing fluctuations in the magnetic field applied from a magnet to 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, a first emission surface 10b on the opposite side of the irradiation surface 10a from which fluorescence is emitted, and a second emission surface 10c that connects the irradiation surface 10a and the first emission surface 10b from which fluorescence is emitted. The antenna 20 is formed of a plate-shaped member and covers the first emission surface 10b of the element 10, and the photosensor 40 is positioned to face the second emission surface 10c.

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] Patent Document 1 discloses that a 532 nm green laser is continuously irradiated onto a diamond element having an NV center, and the excited NV center returns to the ground state through both radiative and non-radiative transitions, emitting red fluorescence in the case of a radiative transition. In Patent Document 1, the red fluorescence emitted from the diamond element is detected by a photodiode via a dichroic mirror and a notch filter. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] X. Zhang et al., "Battery Characterization via Eddy-Current Imaging with Nitrogen-Vacancy Centers in Diamond", Applied Sciences, 2021, Vol. 11, Issue 7 [Overview of the project] [Problems that the invention aims to solve]

[0005] As described in Patent Document 1, in a device using a diamond element with an NV center, fluorescence emitted from the diamond element is detected using a dichroic mirror. However, in such a device, the optical path including the dichroic mirror and the detection unit including the photodiode are fixed on an optical base plate, which may result in a large device.

[0006] This invention has been made in view of the problems of the prior art described above. The object of this invention is to provide a sensor using an element having a color center that can be miniaturized. [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 excitation light is irradiated, a first emission surface on the opposite side of the irradiation surface from which fluorescence is emitted, and a second emission surface connecting the irradiation surface and the first emission surface from which fluorescence is emitted. The antenna is formed of a plate-shaped member and covers the first emission surface of the element. The photosensor is positioned facing the second emission surface. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a sensor using an element having a color center that enables miniaturization of the detection mechanism. [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 and circuit board removed. [Figure 3] This is a plan view showing an example of the inside of a sensor with the top panel removed. [Figure 4] It is a side view showing a sensor according to an embodiment. [Figure 5] It is a diagram schematically showing the structure of a diamond element having an NV center. [Figure 6] It is a diagram showing the valence band and conduction band of a diamond element having an NV center. [Figure 7] It is a diagram showing the energy levels of the ground state and excited state of a diamond element having an NV center. [Figure 8] It is an ODMR spectrum when no magnetic field is applied to the element (Bext = 0). [Figure 9] It is a graph showing the relationship between the magnetic field applied to the element and the energy levels of the ground state (ms = -1, 0, +1). [Figure 10] It is an ODMR spectrum when no magnetic field is applied to the element (Bext = 0) and when a magnetic field is applied to the element (Bext > 0). [Figure 11] It is a perspective view showing an example of an antenna according to an embodiment.

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 be different 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 from which the top plate 63 and the circuit board 41 are removed. FIG. 3 is a plan view showing an example of the inside of the sensor 1 from which the top plate 63 is removed. FIG. 4 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 the current flowing through a bus bar B such as a power supply path or a switchboard. As shown in FIGS. 1 to 4, 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 disposed close to one surface of the bus bar B. The element 10 is a plate-shaped member having 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 on which excitation light is irradiated. The element 10 has a first emission surface 10b on the surface opposite to the irradiation surface 10a, from which fluorescence is emitted. Further, the element 10 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 extending in the thickness direction of the element 10. The second emission surface 10c is formed of four surfaces, and the area of each surface is smaller than the areas of the irradiation surface 10a and the first emission surface 10b.

[0013] The antenna 20 radiates microwaves to the element 10. The optical system 30 irradiates the element 10 with excitation light. The optical sensor 40 receives the fluorescence emitted from the element 10 and detects the intensity of the fluorescence. The control arithmetic 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 a magnetic field, an electric field, a temperature, a strain, etc. of a measurement target based on the output signal detected by the optical sensor 40. The holder 60 is attached to the surface of the bus bar B and houses and fixes the element 10.

[0014] As shown in FIG. 5, the NV center has a structure in which one carbon is replaced by nitrogen in the diamond crystal structure and a vacancy is arranged at a position adjacent to the replaced nitrogen. Since the NV center has a long spin coherence time at room temperature and atmospheric pressure, highly sensitive measurement can be performed even in a normal environment.

[0015] As shown in FIG. 6, diamond is a wide-gap semiconductor having a bandgap width of about 5.5 eV, but the ground state is at a position 2.6 eV from the conduction band, and the excited state is also within the bandgap.

[0016] As shown in Fig. 7, 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 device 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 device 10 and the device 10 is irradiated with green excitation light in a state where the electron has 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. 8, 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. 9 and 10, when a magnetic field parallel to the NV axis is applied to the device 10, the levels of m S = -1 and m S = +1 are Zeeman split, and the resonance frequency fluctuates in proportion to the magnetic field strength. Therefore, by obtaining the difference between the microwave frequency at the minimum fluorescence intensity at m S = -1 and the microwave frequency at the minimum fluorescence intensity at m S = +1, the magnetic field strength applied to the device 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.

[0019] As shown in Figure 11, 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 fifth metal plate 25 has a power supply line insertion hole 25a through which a power supply line 27 is inserted, and an optical fiber insertion hole 25b through which an 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 is mounted on the holder 60. Specifically, the light sensor 40 is provided on the circuit board 41, and the circuit board 41 is mounted by being sandwiched between the support column 62 and the top plate 63 of the holder 60. The circuit board 41 has an amplification circuit that amplifies the output signal according to the intensity of the fluorescence output from the light sensor 40. The light sensor 40 outputs an output signal according 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, a first emission surface 10b on the opposite side of the irradiation surface 10a from which fluorescence is emitted, and a second emission surface 10c that connects the irradiation surface 10a and the first emission surface 10b from which fluorescence is emitted. The antenna 20 is formed of a plate-shaped member and covers the first emission surface 10b of the element 10. The photosensor 40 is positioned facing the second emission surface 10c.

[0034] Element 10 emits red fluorescence not only from the first emission surface 10b but also from the second emission surface 10c. On the other hand, the antenna 20 is formed of a plate-shaped member and covers the first emission surface 10b of element 10. However, the light sensor 40 is positioned opposite the second emission surface 10c and is positioned to receive the light emitted from element 10. Therefore, the light sensor 40 can receive the fluorescence emitted from element 10. With this arrangement, fluorescence from element 10 can be detected by the light sensor 40 without using a dichroic mirror. Thus, in the sensor 1 using an element with a color center, the detection mechanism can be miniaturized.

[0035] Sensor 1 may include a holder 60 that houses the element 10 and the antenna 20. The light sensor 40 may be attached to the holder 60. With this configuration, the fluorescence emitted from the element 10 can be reliably received by the light sensor 40.

[0036] 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.

[0037] Sensor 1 may include an amplification circuit that amplifies the output signal according to the fluorescence intensity output from the photosensor 40. The fluorescence intensity emitted from the second emission surface 10c of element 10 is smaller than the fluorescence intensity emitted from the first emission surface 10b of element 10. However, by using an amplification circuit that amplifies the output signal from the photosensor 40, the signal-to-noise ratio of sensor 1 can be improved compared to the case where a dichroic mirror is used.

[0038] 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]

[0039] 1 sensor 10 elements 10a Irradiation surface 10b 1st exit surface 10c 2nd exit surface 20 antennas 30 Optical system 32 optical fibers 40 Light Sensors 60 holder

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, a first emission surface on the opposite side of the irradiation surface from which the fluorescence is emitted, and a second emission surface connecting the irradiation surface and the first emission surface from which the fluorescence is emitted. The antenna is formed of a plate-shaped member and covers the first emission surface of the element, The aforementioned light sensor is positioned to face the second emission surface.

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.

3. The sensor comprises a holder that houses the button and the antenna. The sensor according to claim 1 or 2, wherein the optical sensor is attached to the holder.

4. The sensor according to claim 1 or 2, further comprising an amplification circuit for amplifying an output signal corresponding to the intensity of the fluorescence output from the light sensor.

Images