Diamond spin sensor and diamond spin sensor system

Abstract

This diamond spin sensor includes: a diamond that includes a color center having electron spin; and a heat transfer part that contacts the diamond. The heat transfer part is fixed to an object, and at least one of a magnetic field, the current, and the temperature of the object is detected by irradiating a color sensor with excitation light and then measuring the fluorescence emitted from the color center.

Description

Diamond spin sensor and diamond spin sensor system

[0001] This disclosure relates to a diamond spin sensor and a diamond spin sensor system. This application claims priority to Japanese Patent Application No. 2023-100678, filed on June 20, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] In power cables installed at high altitudes such as steel towers as power transmission and distribution facilities, devices equipped with temperature detectors, current detectors, etc. are installed in the power cables for the purpose of maintenance and management, abnormality detection, etc. For example, Patent Document 1 listed below discloses a configuration in which an optical sensor (utilizing the Faraday effect or the Pockels effect) is installed on the high-voltage side to detect fault locations in power transmission and distribution lines, etc., and the detected optical signal is transmitted to a monitoring and control system on the ground side via an optical fiber in an optical fiber-embedded insulator.

[0003] A diamond spin sensor system using the NV center of diamond (i.e., NV center) is known as a sensor for detecting magnetic fields, currents, temperatures, etc. The NV center, which is formed by nitrogen occupying a substitutional position of carbon in diamond and a vacancy adjacent to the nitrogen, becomes negatively charged (this state is called NV － The NV center has a ground state in which the spin S is triplet (i.e., the spin S is S=1). When the NV center is excited with a wavelength of 532 nm (i.e., green light), it emits fluorescence with a wavelength of 637 nm (i.e., red light). The intensity of the fluorescence changes depending on the spin state, and the spin state changes due to magnetic resonance between a magnetic field applied to the NV center and microwaves or radio waves, so it can be used as a magnetic sensor.

[0004] For example, a diamond spin sensor system includes a diamond substrate containing NV centers, an optical system that transmits excitation light from a light source and irradiates the NV centers, an optical system that collects fluorescence from the NV centers and transmits it to a photodetector, and a waveguide that transmits microwaves from a power source and irradiates the NV centers. For example, Non-Patent Document 1 below discloses a configuration in which a diamond sensor is mounted on a coplanar waveguide and microwaves are irradiated. The diamond substrate has a rectangular parallelepiped shape, and excitation light is irradiated from the side of the diamond substrate, while fluorescence is collected from above the diamond substrate.

[0005] Japanese Patent Application Laid-Open No. 2003-35852

[0006] Yuta Masuyama, Yuji Hatano, Takayuki Iwasaki, Mutsuko Hatano, "High-sensitivity macro-diamond magnetometer using coplanar waveguides," Proceedings of the 79th Autumn Meeting of the Japan Society of Applied Physics (published September 5, 2018). Takaaki Oka, Ippei Nakamura, Hiroki Morishita, Masanori Fujiwara, Shiro Saito, Norikazu Mizuochi, "Temperature sensing using diamond NV center ensemble," Proceedings of the 78th Autumn Meeting of the Japan Society of Applied Physics (published August 25, 2017).

[0007] A diamond spin sensor according to one aspect of the present disclosure is a diamond spin sensor including a diamond having a color center with electronic spin and a heat transfer part in contact with the diamond, wherein the heat transfer part is fixed to an object, and at least one of the magnetic field, current, and temperature of the object is detected by measuring the fluorescence emitted from the color center after excitation light is irradiated onto the color center.

[0008] FIG. 1 is a block diagram showing the configuration of a diamond spin sensor system according to a first embodiment. FIG. 2 is a perspective view showing the configuration of the sensor unit (i.e., the diamond spin sensor) shown in FIG. 1. FIG. 3 is a perspective view showing how the heat transfer unit shown in FIG. 2 is arranged on a power transmission line. FIG. 4 is a three-view diagram showing the shape of the diamond in the sensor unit and the relative positioning of the diamond and the optical waveguide. FIG. 5 is a cross-sectional view showing the sensor unit according to a first modified example fixed to a power transmission line. FIG. 6 is a three-view diagram showing the shape of the diamond included in the sensor unit according to a second modified example and the relative positioning of the diamond and the optical waveguide. FIG. 7 is a block diagram showing the configuration of a diamond spin sensor system according to a second embodiment. FIG. 8 is a perspective view showing the configuration of the sensor unit (i.e., the diamond spin sensor) shown in FIG. 7. FIG. 9 is a two-view diagram (plan view and front view) showing the relative positions of the diamond and the optical waveguide used in the experiment. FIG. 10 is a table showing sample information and experimental results. FIG. 11 is a cross-sectional view showing the heat transfer unit used in the experiment attached to the power transmission line being measured. Fig. 12 is a cross-sectional view showing a state in which a heat transfer unit different from that shown in Fig. 11 used in the experiment is attached to the power transmission line to be measured. Fig. 13 is a cross-sectional view showing a state in which a heat transfer unit different from that shown in Figs. 11 and 12 used in the experiment is attached to the power transmission line to be measured. Fig. 14 is a table showing sample information and experimental results.

[0009] [Problem to be Solved by the Present Disclosure] A power cable is a cylindrical single wire or a twisted wire made by twisting together multiple single wires, and is not coated. In order to measure the temperature of a power cable using a sensor (e.g., a thermocouple), the sensor must be stably fixed to the power cable. For example, a sensor is attached by tying it to the power cable to measure the temperature. However, with such an attachment method, it is not easy to closely attach the sensor to the power cable to be measured and stably fix it for a long period of time. A similar problem occurs when a diamond containing an NV center is used as a sensor.

[0010] Therefore, an object of the present disclosure is to provide a diamond spin sensor and a diamond spin sensor system that can be stably fixed to an object to be measured.

[0011] Effect of the Present Disclosure According to the present disclosure, it is possible to provide a diamond spin sensor and a diamond spin sensor system that can be stably fixed to an object to be measured.

[0012] [Description of Embodiments of the Present Disclosure] The contents of the embodiments of the present disclosure will be listed and described below. At least some of the embodiments described below may be combined in any combination.

[0013] (1) A diamond spin sensor according to a first aspect of the present disclosure includes a diamond having a color center with electronic spin and a heat transfer part in contact with the diamond. The heat transfer part is fixed to an object, and at least one of the object's magnetic field, current, and temperature is detected by measuring the fluorescence emitted from the color center after irradiation with excitation light. This allows the diamond spin sensor to be stably fixed to the object to be measured. Therefore, stable detection of physical states (voltage, current, temperature, etc.) is possible. Furthermore, since the sensor element includes a diamond that can withstand harsh environments, physical states can be detected even in harsh environments.

[0014] (2) In the above (1), the object can be a linear member, a cylindrical member, or a stranded member, thereby enabling the physical state (voltage, current, temperature, etc.) of a power cable in a power transmission facility to be detected as the measurement object.

[0015] (3) In the above (2), the diamond may have a flat main surface, the object may be a cylindrical member or a twisted wire member, the heat transfer part may have a curved surface, the main surface may be in contact with a surface of the heat transfer part other than the curved surface, and the curved surface may be in contact with a side surface of the cylindrical member or twisted wire member. This allows the diamond spin sensor to be fixed in close contact with the object to be measured.

[0016] (4) In the above (3), the diamond may further have a side surface perpendicular to the main surface, and the side surface of the diamond may receive the excitation light and emit fluorescence. This allows the diamond and the optical fiber, which is an optical waveguide that propagates the excitation light and fluorescence, to be stably fixed to the object to be measured. This allows the excitation light and fluorescence to be transmitted through a single optical waveguide.

[0017] (5) In the above (3), the diamond may further have a side surface perpendicular to the main surface and a back surface parallel to the main surface, and the side surface of the diamond may be incident with excitation light, and the back surface may emit fluorescence. This increases the efficiency of collecting fluorescence emitted from the color center of the diamond.

[0018] (6) In the above (3), the diamond may be plate-shaped, and the shape of the main surface may be a right-angled isosceles triangle. This allows the diamond to be stably fixed to the heat transfer part.

[0019] (7) In any one of the above (1) to (6), the object may be an uncoated power line, and the heat transfer part may be formed of a metal that does not cause galvanic corrosion when in contact with the power line. This makes it possible to suppress the occurrence of corrosion, i.e., galvanic corrosion, that occurs due to a potential difference between dissimilar metals when joining them.

[0020] (8) In the above (7), the heat transfer portion may be made of aluminum or copper. This allows the diamond spin sensor to be stably fixed to the power cable made of aluminum or copper, and further suppresses the occurrence of electrolytic corrosion.

[0021] (9) In any one of (1) to (8) above, a microwave circuit may be further included, and the diamond may have a flat main surface and a back surface parallel to the main surface, with the microwave circuit disposed on the main surface and a metal disposed on the back surface. This allows the magnetic field to be calculated from the distance between two valleys in the frequency spectrum observed when microwaves are irradiated. A compact diamond spin sensor can be realized without the need for a separate mechanism for irradiating microwaves.

[0022] (10) In the above (1) or (2), an optical waveguide for transmitting excitation light may be further included, and the optical waveguide may be a light guide or an optical fiber, and the thickness of the diamond may be 1 / 2 or more and 2.5 times or less of the diameter of the optical waveguide. This makes it possible to detect the physical state of the measurement object.

[0023] (11) In the above (10), the diamond may have a flat main surface, the shape of the main surface may be a right triangle, and the central axis of the optical waveguide may be arranged parallel to a line that bisects the interior angle that is a right angle of the main surface at the portion where the end face of the optical waveguide contacts the diamond. This allows the physical state of the measurement object to be detected efficiently.

[0024] (12) In the above (11), the shape of the main surface may be a right-angled isosceles triangle, and the height to the apex of the right-angled isosceles triangle may be at least twice the thickness of the diamond. This allows the physical state of the measurement object to be detected efficiently.

[0025] (13) In the above (11) or (12), the diamond may further have a side surface perpendicular to the main surface and a back surface parallel to the main surface, and the excitation light may be incident on the diamond from the side surface, and the diamond may further include a detection unit for detecting fluorescence emitted from the back surface. This allows the physical state of the measurement object to be detected efficiently.

[0026] (14) In the above (13), the detection unit may include a photodiode onto which the fluorescence emitted from the back surface is directly incident, thereby enabling efficient detection of the physical state of the measurement object.

[0027] (15) In the above (13), an optical fiber that transmits the fluorescence to the detection unit and an optical system that collects the fluorescence emitted from the back surface at the end face of the optical fiber may be further included, thereby enabling efficient detection of the physical state of the measurement object.

[0028] (16) In the above (11) or (12), the diamond may further have a side surface perpendicular to the main surface, the excitation light may be incident on the diamond from the side surface, and a detection unit may further be included that detects the fluorescence emitted from the side surface. This allows the physical state of the measurement object to be detected efficiently.

[0029] (17) In any one of (13) to (16) above, the angle between the normal to the side surface and the central axis of the optical waveguide may be the Brewster angle, which allows the excitation light to be efficiently incident into the diamond without being reflected by the side surface, thereby improving the efficiency of generating fluorescence.

[0030] (18) A diamond spin sensor system according to a second aspect of the present disclosure includes the diamond spin sensor according to any one of (1) to (17) above, and a control power supply unit that generates excitation light and detects fluorescence. This allows the diamond spin sensor to be stably fixed to the object to be measured. Therefore, it is possible to stably detect physical states (voltage, current, temperature, etc.). Furthermore, since the sensor element includes diamond that can withstand harsh environments, it is possible to detect physical states in harsh environments.

[0031] [Details of the embodiments of the present disclosure] In the following embodiments, the same components are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0032] 1, a diamond spin sensor system 100 according to a first embodiment of the present disclosure includes a sensor unit 102, an optical waveguide 104, and a control power supply unit 106. The sensor unit 102 is a NV － The sensor unit 102 includes a diamond 110 including a center (hereinafter referred to as an NV center), and a heat transfer unit 112. The sensor unit 102 is also called a diamond spin sensor. The optical waveguide 104 includes a medium that transmits light and is coated with a resin or the like. The optical waveguide 104 is, for example, an optical fiber. The optical waveguide 104 may also be, for example, an optical guide having a structure in which optical fibers are bundled together. The optical waveguide 104 transmits light in both directions.

[0033] Referring to FIG. 2 , the heat transfer unit 112 of the sensor unit 102 includes a first member 150 and a second member 152. The power transmission line 900 is a linear or cylindrical single wire made of, for example, aluminum or copper, or a stranded wire formed by twisting single wires, and is not coated. The heat transfer unit 112 is fixed around the power transmission line 900. A diamond 110 is disposed on the heat transfer unit 112. As described below, the diamond 110 is formed in the shape of a triangular prism plate. That is, the height of the triangular prism is the thickness of the plate. Of the two triangular planes of the diamond 110, the first plane (hereinafter referred to as the main surface) is in contact (i.e., surface contact) with the heat transfer unit 112. The diamond 110 is fixed to the heat transfer unit 112 by a fixing member 154 disposed opposite the heat transfer unit 112 (specifically, the first member 150) with the diamond 110 sandwiched therebetween. That is, of the two triangular flat surfaces of diamond 110, the second flat surface (hereinafter referred to as the back surface) is in contact (i.e., surface contact) with fixing member 154. For example, diamond 110 can be fixed to heat transfer part 112 by fixing fixing member 154 to heat transfer part 112 with screws. Fixing member 154 can be made of, for example, ceramics or resin. As the resin, one with high discharge resistance is preferable, and for example, PEEK (Poly Ether Ether Ktone) can be used.

[0034] Referring to FIG. 3 , the first member 150 and the second member 152 each have a curved surface that can be placed in close contact with the cylindrical side surface of the power transmission line 900, which may be a solid or stranded wire. The first member 150 and the second member 152 each have a plurality of holes (e.g., through-holes) that can be inserted and fastened around the power transmission line 900 with screws. For example, when a male screw is inserted and fastened in the direction of the arrow, the first member 150 may have a through-hole, and the second member 152 may have a female thread that can fasten the male screw. For example, the curved surfaces of the first member 150 and the second member 152 may be semi-cylindrical, with a radius equal to the radius of the cylindrical side surface of the power transmission line 900. This allows the heat transfer unit 112 to be placed in close contact with the power transmission line 900 and stably fixed. That is, the sensor unit 102 may be stably fixed to the power transmission line 900.

[0035] The first member 150 and the second member 152 may be formed from metal, ceramic, or resin. When measuring the temperature of the power transmission line 900 using the diamond 110, the first member 150 and the second member 152 are preferably formed from a metal with high thermal conductivity. This allows the temperature of the diamond 110 to quickly equalize with that of the power transmission line 900, thereby enabling accurate temperature detection of the power transmission line 900. Furthermore, when the first member 150 and the second member 152 are formed from a metal, the first member 150 and the second member 152 may be formed from the same material as the power transmission line 900. For example, if the power transmission line 900 is formed from aluminum, the first member 150 and the second member 152 are formed from aluminum, and if the power transmission line 900 is formed from copper, the first member 150 and the second member 152 are formed from copper. This prevents the occurrence of galvanic corrosion (i.e., corrosion caused by a potential difference when dissimilar metals are joined).

[0036] When detecting a magnetic field or a current, the first member 150 and the second member 152 may be made of ceramics or resin. The resin is preferably one with high discharge resistance, such as PEEK.

[0037] Referring to Figure 4, as described above, diamond 110 is formed in the shape of a plate having two parallel planes (i.e., a main surface and a back surface). The shape of the two parallel planes is, for example, a right-angled isosceles triangle. Diamond 110 has three side surfaces that are perpendicular to the main surface and the back surface. Of the three side surfaces, side surface 110C is where the end face of optical waveguide 104 is located. As a result, as will be described later, excitation light 304 enters the interior of diamond 110 from side surface 110C. Fluorescence 306 emitted from the NV center within diamond 110 is output to the outside of diamond 110 from side surface 110C and propagates through optical waveguide 104.

[0038] Thus, the sensor unit 102 includes a diamond 110 having an NV center and a heat transfer unit 112 in contact with the diamond 110. The heat transfer unit 112 includes a first member 150 and a second member 152 as a mechanism for closely attaching the sensor unit 102 to the power transmission line 900, which is the object of measurement. At least one of the magnetic field, current, and temperature of the object of measurement (i.e., the magnetic field due to the object of measurement, the current flowing through the object of measurement, and the temperature of the object of measurement) is detected by measuring the fluorescence emitted from the NV center after irradiating the NV center with excitation light. This allows the sensor unit 102, which is a diamond spin sensor, to be stably fixed to the object of measurement. Therefore, stable detection of physical states (such as voltage, current, and temperature) is possible. Because the sensor element includes a diamond 110 that can withstand harsh environments, physical states can be detected even in harsh environments.

[0039] As described above, the physical state (voltage, current, temperature, etc.) of the power transmission line 900 in the power transmission facility, which is a linear member, a cylindrical member, or a stranded member, can be detected as the measurement object.

[0040] As described above, the first member 150 and the second member 152 included in the heat transfer unit 112 each have a curved surface, the main surface of the diamond 110 contacts a surface of the heat transfer unit 112 that is different from the curved surface, and the curved surface is abutted against and fixed to the side surface of the cylindrical or stranded member of the power transmission line 900. This allows the sensor unit 102 to be fixed in close contact with the power transmission line 900, which is the object to be measured.

[0041] As described above, diamond 110 has a side surface 110C perpendicular to first surface 110A (main surface), and excitation light is incident on side surface 110C, which emits fluorescence. This allows the excitation light and fluorescence to be transmitted through a single optical waveguide 104 (e.g., an optical fiber).

[0042] Although the above description has been given of the case where excitation light is incident on the side surface 110C and fluorescence is emitted from the side surface 110C, the present invention is not limited to this. For example, excitation light may be incident on the side surface 110C and fluorescence may be emitted from the second surface 110B (back surface). In this case, the fixing member 154 shown in FIG. 2 may be formed from a material (e.g., resin) that transmits fluorescence, and a fluorescence detection unit such as a photodiode may be embedded inside the fixing member 154. This can increase the efficiency of collecting fluorescence emitted from the NV center of the diamond 110. Furthermore, an optical waveguide (e.g., an optical fiber) that transmits the fluorescence emitted from the second surface 110B (back surface) to the detection unit, and an optical system (e.g., a lens) that collects the fluorescence emitted from the second surface 110B may be provided at the end face of the optical waveguide.

[0043] As described above, the diamond 110 has a plate shape, and the first surface 110A is a right-angled isosceles triangle, which allows the diamond 110 to be stably fixed to the heat transfer portion 112.

[0044] Returning to FIG. 1 , the control power supply unit 106 irradiates the diamond 110 with excitation light and detects fluorescence emitted from the diamond 110. The control power supply unit 106 includes an excitation light generator 120, a filter 122, a focusing element 124, a long-pass filter (LPF) 126, a light detector 128, and a control unit 130. The control unit 130 includes a central processing unit (CPU), a memory unit, and a wireless communication unit (none of which are shown). The processing performed by the control unit 130, which will be described later, is realized by the CPU reading and executing a program pre-stored in the memory unit. As will be described later, the control unit 130 acquires a signal (i.e., fluorescence intensity) detected by the light detector 128 and transmits it to an external device via the wireless communication unit. The external device calculates physical conditions (e.g., magnetic field and temperature) from the detection signal of the light detector 128 received from the control unit 130.

[0045] The excitation light generating unit 120 generates excitation light 304 for exciting the NV center of the diamond 110 under the control of the control unit 130. The control unit 130 supplies, for example, a voltage to the excitation light generating unit 120 at a predetermined timing to cause the excitation light generating unit 120 to emit light. The excitation light 304 is green light (i.e., wavelength 490 nm to 560 nm). The excitation light 304 is preferably laser light, and the excitation light generating unit 120 is preferably a semiconductor laser (e.g., emitted light wavelength 532 nm).

[0046] The filter 122 is an element for separating the excitation light 304 incident from the excitation light generating unit 120 and the light emitted from the diamond (i.e., the fluorescent light 306). For example, the filter 122 is a filter that cuts off (i.e., reflects) light with wavelengths equal to or less than a predetermined wavelength and passes light with wavelengths greater than the predetermined wavelength, or a bandpass filter that passes light with wavelengths within a predetermined wavelength range and cuts off (i.e., reflects) light with wavelengths outside the predetermined wavelength range. Generally, the wavelength of the excitation light is shorter than that of the fluorescent light, so such a configuration is preferable. The filter 122 is preferably a dichroic mirror with this function.

[0047] The focusing element 124 focuses the excitation light 304 input from the filter 122. The focusing element 124 is, for example, a spherical lens. The focusing element 124 inputs as much of the excitation light 304 diffused and output from the excitation light generating unit 120 as possible into the end of the optical waveguide 104. The optical waveguide 104 has a first end and a second end, and transmits the excitation light 304 incident on the first end from the focusing element 124 to the second end. The optical waveguide 104 also transmits the emitted light (i.e., fluorescence 306) from the diamond incident on the second end to the first end and outputs it.

[0048] The LPF 126 is a long-pass filter that passes light with wavelengths equal to or greater than a predetermined wavelength and cuts (e.g., reflects) light with wavelengths smaller than the predetermined wavelength. Diamond radiation is red light and passes through the LPF 126, but the excitation light 304 output from the excitation light generator 120 has a shorter wavelength and does not pass through the LPF 126. This prevents the excitation light 304 emitted from the excitation light generator 120 from being detected by the photodetector 128 and becoming noise, thereby reducing the detection sensitivity of the diamond radiation (i.e., fluorescence 306). The photodetector 128 generates and outputs an electrical signal corresponding to the incident light. The photodetector 128 is, for example, a photodiode. The output signal from the photodetector 128 is acquired by the control unit 130. As described above, the signal acquired by the control unit 130 is transmitted to an external device via the wireless communication unit of the control unit 130. This allows the external device to calculate the physical conditions (for example, magnetic field and temperature) at the location where the diamond 110 is located from the output signal received from the light detection unit 128.

[0049] The diamond spin sensor system 100 is installed in power transmission equipment (e.g., overhead power transmission equipment) and is used for maintaining and managing power cables and detecting abnormalities. That is, the sensor unit 102 is installed on the power transmission line 900, and the control power supply unit 106 is installed on the steel pole of the steel tower. The optical waveguide 104 connecting the sensor unit 102 and the control power supply unit 106 is fixed to the arm of the steel tower or the like.

[0050] Using the NV center, the magnetic field can be calculated from changes in the ESR (Electron Spin Resonance) spectrum. It is also known that the resonance frequency of the NV center has temperature dependence in the range from 120 K to 700 K. For example, as disclosed in Non-Patent Document 2, temperature can be measured from changes in the ODMR (Opticaly Detected Magnetic Resonance) signal strength near the resonance frequency.

[0051] The diamond 110 in the sensor unit 102 detects the magnetic field generated by the current flowing through the power line 900 or the fluorescence corresponding to the temperature of the power line 900. The detection signal is transmitted via the optical waveguide 104 to the control power supply unit 106, which then transmits it to a device on the ground. This allows the magnetic field or temperature at the location where the diamond 110 is located to be detected. The sensor unit 102 and a portion of the optical waveguide 104 are located in the vicinity of the power line 900, where high voltages of several thousand kV (e.g., 6,600 kV) or more are transmitted, i.e., in a harsh high-voltage environment, while the control power supply unit 106 is located in a normal environment away from the power line 900. The diamond 110 and optical waveguide 104 included in the sensor unit 102 are not affected by the environment even when placed in a high-voltage environment. The control power supply unit 106 is located in a normal environment. This allows for a diamond spin sensor system with a long product life and easy maintenance. Note that a "harsh environment" refers to an environment that is difficult for humans to enter, such as a high-voltage environment around power transmission line 900 in FIG. 3 . A "normal environment" refers to an environment other than a "harsh environment." In a harsh environment, at least one of electric field strength, magnetic field strength, temperature, and pressure is greater than in a normal environment (for example, by one or more orders of magnitude).

[0052] (First Modification) In the above, the sensor unit 102 is fixed to the power transmission line 900 so that the first member 150 and the second member 152 sandwich the power transmission line 900. However, this is not limiting. If the diameter of the power transmission line 900 is larger than the size of the sensor unit 102, the sensor unit 102 may be fixed to the power transmission line 900 using a strip-shaped member. Referring to FIG. 5 , the sensor unit 140 includes a diamond 110, a heat transfer unit 160, and a fixing member 162, and is fixed to the power transmission line 900 by a strip-shaped fixing member 164. The heat transfer unit 160 corresponds to the heat transfer unit 112 shown in FIG. 2. The heat transfer unit 160 has a curved surface that fits closely to the side surface of the power transmission line 900. The heat transfer unit 160 is made of the same material as the heat transfer unit 112. The fixing member 162 corresponds to the fixing member 154 shown in FIG. 2. The band-shaped fixing member 164 is formed in a band shape having a predetermined width from a flexible resin or the like, which allows the sensor unit 140 to be fixed in close contact with the side surface of the power transmission line 900, which is larger than the sensor unit 140. Therefore, the diamond 110 can stably detect the magnetic field, current, temperature, and the like.

[0053] (Second Modification) In the above, the main surface and back surface of the plate-shaped diamond 110 are triangular in shape, and excitation light is incident perpendicularly on the side surface. However, this is not limited to this. The main surface and back surface of the diamond 110 may also be polygonal in shape with four or more sides. Furthermore, excitation light may be incident obliquely on the side surface of the diamond 110. Referring to FIG. 6, the diamond 114 has a first surface 114A (main surface), a second surface 114B (back surface), and a side surface 114C. The first surface 114A and the second surface 114B are rectangular in shape. The excitation light 304 propagated by the optical waveguide 104 is irradiated onto the side surface 114C and enters the interior of the diamond 114 from the side surface 114C. The end surface of the optical waveguide 104 is inclined with respect to the central axis of the optical waveguide 104 and is in close contact with the side surface 114C. Fluorescence 306 generated within diamond 114 is emitted from side surface 114 C to the outside of diamond 114 , enters the end face of optical waveguide 104 , and propagates through optical waveguide 104 .

[0054] In the arrangement shown in FIG. 6 , the angle φ that the end face of the optical waveguide 104 makes with the central axis is the complementary angle of θ, expressed as φ=π / 2−θ (rad), where θ is the angle between the excitation light 304 and the side surface 114C (the angle between the normal to the side surface 114C and the excitation light 304). The incident angle θ is preferably the Brewster angle. The Brewster angle refers to the angle of incidence at which the reflected light intensity of p-polarized light becomes zero. In other words, when the diamond 114 (i.e., the side surface 114C) and the optical waveguide 104 are arranged so that the incident angle θ is the Brewster angle, the excitation light 304 that propagates through the optical waveguide 104 and is irradiated onto the side surface 114C can be efficiently incident into the diamond 114 without being reflected by the side surface 114C. This improves the efficiency of fluorescence generation by the NV center.

[0055] Second Embodiment In the first embodiment, the diamond spin sensor system that does not use microwaves has been described, whereas the diamond spin sensor system according to the second embodiment uses microwaves.

[0056] Referring to FIG. 7 , a diamond spin sensor system 200 according to a second embodiment of the present disclosure includes a sensor unit 202, an optical waveguide 104, a control power supply unit 106, a modulation signal generating unit 204, an optical modulation unit 206, and an optical waveguide 208. The diamond spin sensor system 200 is the diamond spin sensor system 100 shown in FIG. 1 , with the sensor unit 202 replacing the sensor unit 102 and adding a modulation signal generating unit 204, an optical modulation unit 206, and an optical waveguide 208. The sensor unit 202 includes a diamond 110, a heat transfer unit 112, and a photoelectric conversion unit 210. The sensor unit 202 is the sensor unit 102 shown in FIG. 1 with the addition of a photoelectric conversion unit 210. In FIG. 7 , elements with the same reference numerals as those in FIG. 1 have the same functions as those in FIG. 1 . Therefore, redundant description will not be repeated. In addition to the above functions, the control unit 130 also has the function of controlling the modulation signal generating unit 204. That is, a program for controlling the modulation signal generating unit 204 is stored in a storage unit included in the control unit 130, and the program is executed by a CPU included in the control unit 130.

[0057] Referring to FIG. 8 , the heat transfer unit 112 of the sensor unit 202 includes a first member 150 and a second member 152. A diamond 110 is disposed on the heat transfer unit 112. The diamond 110 is formed in the shape of a triangular prism plate. Of the two triangular flat surfaces of the diamond 110, a first surface 110A (main surface) is in contact (i.e., surface contact) with the heat transfer unit 112. A photoelectric conversion unit 210 is disposed on the diamond 110. That is, of the two triangular flat surfaces of the diamond 110, a second surface 110B (rear surface) is in contact (i.e., surface contact) with the photoelectric conversion unit 210. The diamond 110 and the photoelectric conversion unit 210 are fixed to the heat transfer unit 112 by a fixing member 154 disposed opposite the heat transfer unit 112 (specifically, the first member 150) with the diamond 110 and the photoelectric conversion unit 210 sandwiched therebetween.

[0058] Returning to FIG. 7 , under the control of the control unit 130, the modulation signal generation unit 204 generates a signal of a predetermined frequency (i.e., microwave frequency band) and inputs it to the optical modulation unit 206. The optical modulation unit 206 amplitude-modulates the light of the predetermined frequency using the signal supplied from the modulation signal generation unit 204, and generates and outputs modulated light. That is, the signal output by the modulation signal generation unit 204 is a modulation signal used to generate modulated light. The frequency of the signal output by the modulation signal generation unit 204 is a modulation frequency. The light of the predetermined frequency to be modulated is a carrier wave. The modulated light generated by the optical modulation unit 206 is transmitted to the photoelectric conversion unit 210 of the sensor unit 202 via the optical waveguide 208. The optical waveguide 208 is, for example, an optical fiber.

[0059] The photoelectric conversion unit 210 converts the modulated light transmitted through the optical waveguide 208 into an electrical signal (i.e., photoelectric conversion) and outputs it. As a result, an electrical signal having the frequency of the carrier wave (i.e., microwave frequency band) is generated from the modulated light, and is irradiated as an electromagnetic wave to the diamond 110. The electromagnetic wave irradiated to the diamond 110 is used for magnetic resonance of the NV center.

[0060] The control unit 130 controls the excitation light generating unit 120 to output excitation light 304 for a predetermined time (e.g., period t1) at a predetermined timing. The control unit 130 controls the modulation signal generating unit 204 to output electromagnetic waves from the photoelectric conversion unit 210 for a predetermined time (e.g., period t2) at a predetermined timing. Any appropriate pulse sequence may be used during period t2. This allows the excitation light and electromagnetic waves to be combined temporally and spatially and irradiated onto the diamond 110. The control unit 130 captures the output signal from the light detecting unit 128 at a predetermined timing (e.g., within period t3) and stores it in the memory unit.

[0061] For example, after irradiating the diamond 110 (i.e., the NV center) with 2.87 GHz microwaves, it is excited by irradiating it with green excitation light. As a result, the transition when the spin of the NV center returns to the ground state includes a transition that does not emit light (i.e., fluorescence), so the intensity of the observed emitted light decreases. Therefore, two valleys (i.e., signal drops) are observed in the ESR spectrum. The distance Δf (i.e., frequency difference) between the two observed valleys depends on the magnetic field strength at the position of the diamond 110. The control unit 130 transmits the output signal of the light detection unit 128 to an external device via a wireless communication unit, and the external device can calculate Δf and calculate the magnetic field from Δf.

[0062] The above describes a case where microwaves are optically transmitted and converted into electromagnetic waves (microwaves) by the photoelectric conversion unit 210, but this is not limiting. Microwaves may also be generated using an electromagnetic wave generator. The generated microwaves are transmitted to the diamond 110 via a microwave transmission line (e.g., a coaxial cable) and irradiated onto the diamond 110 via a microwave circuit. The microwave circuit may be a circuit such as a coplanar line or a microstrip line. For example, a microwave circuit is formed directly on the first surface 110A (main surface) of the diamond 110 shown in FIG. 4 by patterning metal. A metal is deposited on the entire second surface 110B (rear surface) of the diamond 110 by vapor deposition and used as an earth. This allows microwaves to penetrate into the diamond 110. A power cable may be placed on either the main surface side or the rear surface side. The metal forming the microwave circuit is a non-magnetic, low-resistance metal such as gold (Au), silver (Ag), copper (Cu), or aluminum (Al). When the patterned first surface 110A (main surface) is positioned facing the power transmission line 900 (see, for example, Figure 2), fluorescence cannot be detected from the second surface 110B (back surface) on which the metal is arranged. In this case, fluorescence is detected from the same side surface as the incident surface of the excitation light. Because the metal is arranged on the back surface, the fluorescence emitted from the NV center of the diamond 110 is efficiently emitted from the side surface. In this way, by forming a microwave circuit on the surface of the diamond 110, there is no need to provide a separate mechanism for irradiating microwaves, and a compact diamond spin sensor can be realized.

[0063] In the above, a case where a diamond element having an NV center is used in a diamond spin sensor has been described, but this is not limiting. Any diamond element having a color center with electronic spin will suffice. A color center with electronic spin is a center that forms a spin triplet state and emits light when excited, with the NV center being a typical example. In addition, it is known that color centers with electronic spin also exist in silicon-vacancy centers (i.e., Si-V centers), germanium-vacancy centers (i.e., Ge-V centers), and tin-vacancy centers (i.e., Sn-V centers). Therefore, diamond elements including these may be used instead of diamond elements including NV centers to form a diamond spin sensor.

[0064] (Example) Experimental results are shown below. As described above, a diamond spin sensor system including a heat transfer section was used to measure the magnetic field and temperature of an object to be measured. The diamond used in the experiment was prepared as follows. That is, a diamond containing 30 ppm of substitutional nitrogen was synthesized by a high-temperature, high-pressure method and formed into a 2 mm x 2 mm square with a thickness of 0.1 mm to 2 mm. An electron beam with an energy of 3 MeV was applied to the obtained diamond at a speed of 1 x 10 １８ cm －２ After irradiation with a dose of 1000 kJ / cm, the diamond was annealed at 950°C for 1 hour. － It was confirmed by ODMR spectroscopy (optically detected magnetic resonance spectroscopy) that a color center having the above spin can be formed and that the magnetic field and temperature can be detected by the spin.

[0065] The produced diamond was processed into a triangular prism and used as diamond 110 in the arrangement shown in Figure 2. The magnetic field and temperature were measured using two measurement methods (Measurement A and Measurement B described below). Measurement A used the phenomenon of a decrease in fluorescence intensity when a constant intensity excitation light source was irradiated onto the diamond and the magnetic field was detected by observing the fluorescence (magnetic field detection using only the excitation light source). Since the magnetic field is detected by changes in fluorescence intensity, if the change in fluorescence intensity becomes small and is buried in noise, it is determined that magnetic field detection is impossible. Measurement B used a method in which a microwave was irradiated onto the diamond in the configuration shown in Figure 1, and the distance (frequency difference) between the two peaks of the ODMR spectrum obtained by changing the microwave frequency irradiated and detecting the fluorescence intensity was converted into the magnetic field (magnetic field detection using ODMR spectrum). In Measurement B, if the change in fluorescence intensity becomes small and is buried in noise, it is determined that magnetic field detection is impossible. Temperature was measured using ODMR spectrum, as in Measurement B.

[0066] A diamond was placed on a cylindrical or twisted wire-shaped measurement object via a heat transfer unit (see Figure 2). Both the main and side surfaces of the diamond, which had been machined into a triangular prism shape, were polished to a mirror finish (specifically, the arithmetic mean roughness after polishing, Ra, < 5 nm). The side surfaces were perpendicular to the main surface. Polishing to Ra < 5 nm improved the fluorescence collection efficiency.

[0067] Various diamonds with triangular prism shapes but different dimensions were fabricated and used for experiments. The main surface of the triangular diamond was placed in contact with the flat surface of the heat transfer unit, and an optical waveguide (specifically, an optical fiber with a core diameter of 200 μm) for transmitting excitation light and fluorescence was placed thereon. Referring to FIG. 9 , the shape of the diamond 400 used in the experiment and the positional relationship between the diamond 400 and the optical fiber 410 serving as the optical waveguide will be described. The diamond 400 has a triangle ABC (main surface) with vertices A, B, and C in plan view. The optical fiber 410 was positioned so that excitation light was incident on the diamond 400 from a side surface 402 including one base BC of the triangle ABC. The triangle ABC was designed so that the intersection 406 between the perpendicular line from vertex A to base BC and the base BC was located near the midpoint 404 of base BC. The angle (interior angle) D of vertex A was designed to be approximately 90°. Note that angle D at vertex A is considered to be a right angle, and the length from intersection 406 to vertex A is referred to as the height to the vertex of the right-angled isosceles triangle.

[0068] Measurement results using diamonds 400 of various dimensions are shown in Figure 10. The table in Figure 10 shows the measured fluorescence intensity, whether magnetic detection was possible, and whether the temperature of the object to be measured was accurately measured. The fluorescence intensity represents the percentage of the intensity of the excitation light, which is the incident light. In the table in Figure 10, E1 (%) represents the ratio of the distance b between the midpoint 404 and the intersection point 406 to half the length a of the base BC. E2 (%) represents the ratio of the distance c (perpendicular distance) between the central axis of the optical fiber 410 and the midpoint 404 to half the length a of the base BC. F (mm) represents the height (i.e., thickness) of the triangular prism-shaped diamond 400. In the columns for the results of Measurement A and Measurement B, "pass" indicates that the measurement was successful, and "fail" indicates that the measurement was not successful.

[0069] From Figure 10, it can be seen that measurement is possible as long as the angle D of vertex A is within the range of 90°±10°. Furthermore, it can be seen that measurement is possible if E1-E2 is 10% or less, i.e., if the deviation between the perpendicular line from vertex A to base BC and the central axis of optical fiber 410 is 10% or less. This means that the central axis of optical fiber 410 needs to be approximately parallel to the line bisecting angle D of vertex A (the line connecting point A and midpoint 404). It can also be seen that measurement is possible as long as the thickness F of diamond 400 is 50% or more of the optical fiber core diameter (200 μm). That is, the thickness F of diamond 400 needs to be at least half the diameter φ of the optical waveguide and not more than 2.5 times the diameter φ of the optical waveguide. Furthermore, under the same conditions as Sample No. 1 shown in Figure 10, different materials were prepared, with the height to the vertex of the right-angled isosceles triangle being 0.8, 1, 2 (Sample No. 1), and 4 times the thickness F of the diamond, and the fluorescence intensity was confirmed. As a result, the results of Measurement A and Measurement B were acceptable for samples where the height to the apex of the right-angled isosceles triangle was more than twice the thickness F of the diamond. Samples where the height to the apex of the right-angled isosceles triangle was more than twice the thickness F of the diamond had a fluorescence intensity of 80% or more. In contrast, samples where the height to the apex of the right-angled isosceles triangle was less than 1 time the thickness F of the diamond had an extremely low fluorescence intensity of 10% or less.

[0070] The influence of the shape of the heat transfer part on the measurement was evaluated. Specifically, heat transfer parts with different shapes of the part that comes into contact with the cylindrical measurement object (power transmission line) were fabricated. Referring to FIG. 11 , a heat transfer part 420 including a first member 422 and a second member 424 was fabricated. Screws or the like were inserted into the through holes 426, and the first member 422 and the second member 424 were attached to a cylindrical measurement object 910 with a radius R. Furthermore, the NV fabricated as described above was － The diamond including the center was placed on the first member 422 as shown in Fig. 2, and the temperature was measured. The portions where the first member 422 and the second member 424 contact the measurement object 910 are flat (radius ∞).

[0071] 12, a heat transfer unit 430 including a first member 432 and a second member 434 was fabricated. The first member 432 and the second member 434 have a cross section perpendicular to the axis of the measurement object 910 that is an arc 438, and the radius of the arc 438 is r (r>R). The first member 432 and the second member 434 were attached to the measurement object 910 by inserting a screw or the like into the through hole 436. Furthermore, the NV fabricated as described above was － The diamond including the center was placed on the first member 432 as shown in Fig. 2, and temperature measurement was performed. Referring to Fig. 13, a heat transfer unit 440 including a first member 442 and a second member 444 was fabricated. The first member 442 and the second member 444 have a cross section perpendicular to the axis of the measurement object 910 that is an arc, and the radius of the arc is equal to the radius R of the measurement object 910. The first member 442 and the second member 444 were attached to the measurement object 910 by inserting a screw or the like into the through hole 446. Furthermore, the NV fabricated as described above was － The diamond including the center was placed on the first member 442 as shown in FIG. 2, and the temperature was measured.

[0072] In a room temperature environment of 25°C, the temperature of the measurement object 910 was maintained at 150°C, and temperature measurement was performed using Measurement B (measurement by ODMR spectrum) using a diamond placed on the first member. The results are shown in Figure 14. The measured fluorescence intensity represents the ratio (%) of the intensity of the excitation light, which is the incident light. The "Judgment" column indicates the reliability of the measurement results. α indicates high measurement accuracy, while reliability decreases in the order of α, β, and γ. Figure 14 shows that if the difference (r-R) between the radius r of the arc formed in the heat transfer section and the radius R of the measurement object 910 is 20% or less of radius R (see Samples No. 21 to 23), the error in the measured temperature is within 10°C.

[0073] Although the present disclosure has been described above by explaining the embodiments, the above-described embodiments are merely examples, and the present disclosure is not limited to only the above-described embodiments. The scope of the present disclosure is defined by the claims in the scope of the claims, taking into consideration the description of the detailed description of the invention, and includes all modifications within the meaning and scope equivalent to the wordings described therein.

[0074] 100, 200 Diamond spin sensor system 102, 140, 202 Sensor unit 104, 208 Optical waveguide 106 Control power supply unit 110, 114, 400 Diamond 110A, 114A First surface 110B, 114B Second surface 110C, 114C, 402 Side surface 112, 160, 420, 430, 440 Heat transfer unit 120 Excitation light generating unit 122 Filter 124 Light collecting element 126 LPF 128 Light detecting unit 130 Control unit 150, 422, 432, 442 First member 152, 424, 434, 444 Second member 154, 162 Fixing member 164 Strip-shaped fixing member 204 Modulation signal generating unit 206 Optical modulation section 210 Photoelectric conversion section 304 Excitation light 306 Fluorescence 404 Midpoint 406 Intersection 410 Optical fiber 426, 436, 446 Through hole 438 Circular arc 900 Power transmission line 910 Measurement object A, B, C Points a Length b, c Distance D Angle R, r Radius θ Incident angle

Claims

1. Diamonds having color centers with electron spin, A diamond spin sensor including a heat transfer part in contact with the diamond, The heat transfer unit is fixed to the object, The magnetic field, current, and temperature of the object are detected by measuring the fluorescence emitted from the color center after the color center is irradiated with excitation light. The diamond has a flat main surface, The object is a linear member, a cylindrical member, or a stranded wire member. The heat transfer section has a curved surface, The main surface is in contact with the surface of the heat transfer part other than the curved surface. The curved surface is a diamond spin sensor that contacts the side surface of the object.

2. The diamond further has a side perpendicular to the main surface, The diamond spin sensor according to claim 1, wherein the side surface of the diamond is incident on the excitation light and emits fluorescence.

3. The diamond further has a side surface perpendicular to the main surface and a back surface parallel to the main surface, The surface of the diamond is to which the excitation light is incident, The diamond spin sensor according to claim 1, wherein the back surface emits the fluorescence.

4. The aforementioned diamond is in the form of a plate, The diamond spin sensor according to any one of claims 1 to 3, wherein the shape of the main surface is a right-angled isosceles triangle.

5. A diamond having a color center with electron spin, A diamond spin sensor including a heat transfer part in contact with the diamond, The heat transfer unit is fixed to the object, The magnetic field, current, and temperature of the object are detected by measuring the fluorescence emitted from the color center after the color center is irradiated with excitation light. The aforementioned object is an uncovered power transmission line, The heat transfer section is made of a metal that does not cause electrolytic corrosion when in contact with the power transmission line, in the diamond spin sensor.

6. The diamond spin sensor according to claim 5, wherein the heat transfer section is formed of aluminum or copper.

7. It further includes a microwave circuit, The diamond has a flat main surface and a back surface parallel to the main surface. The microwave circuit is arranged on the main surface. The diamond spin sensor according to any one of claims 1 to 3, 5, and 6, wherein a metal is arranged on the back surface.

8. The optical waveguide for transmitting the excitation light further includes, The optical waveguide is an optical guide or an optical fiber. The diamond spin sensor according to any one of claims 1 to 3, 5, and 6, wherein the thickness of the diamond is 1 / 2 or more of the diameter of the optical waveguide and 2.5 times or less of the diameter.

9. A diamond having a color center with electron spin, A diamond spin sensor including a heat transfer part in contact with the diamond, The heat transfer unit is fixed to the object, The magnetic field, current, and temperature of the object are detected by measuring the fluorescence emitted from the color center after the color center is irradiated with excitation light. The optical waveguide for transmitting the excitation light further includes, The optical waveguide is an optical guide or an optical fiber. The diamond has a flat main surface, The shape of the main surface is a right triangle, In a diamond spin sensor, the central axis of the optical waveguide is positioned parallel to a straight line that bisects the interior angle perpendicular to the main surface in the portion where the end face of the optical waveguide contacts the diamond.

10. The shape of the main surface is a right-angled isosceles triangle. The diamond spin sensor according to claim 9, wherein the height to the vertex of the right-angled isosceles triangle is more than twice the thickness of the diamond.

11. The diamond further has a side surface perpendicular to the main surface and a back surface parallel to the main surface, The excitation light is incident on the diamond from the side, The diamond spin sensor according to claim 9 or claim 10, further comprising a detection unit for detecting fluorescence emitted from the back surface.

12. The diamond spin sensor according to claim 11, wherein the detection unit includes a photodiode to which the fluorescence emitted from the back surface is directly incident.

13. An optical fiber for transmitting the fluorescence to the detection unit, The diamond spin sensor according to claim 11, further comprising an optical system for collecting the fluorescence emitted from the back surface at the end face of the optical fiber.

14. The diamond further has a side perpendicular to the main surface, The excitation light is incident on the diamond from the side, The diamond spin sensor according to claim 9 or claim 10, further comprising a detection unit for detecting fluorescence emitted from the aforementioned side.

15. The diamond spin sensor according to claim 11, wherein the angle between the normal to the side surface and the central axis of the optical waveguide is the Brewster angle.

16. A diamond spin sensor according to any one of claims 1 to 3, 5, 6, 9 and 10, A diamond spin sensor system including a control power supply unit that generates the excitation light and detects the fluorescence.