NMR detector

Abstract

To increase detection sensitivity of a nuclear magnetic resonance (NMR) signal by suppressing occurrence of distortion of a static magnetic field when a sample coil composed of a superconductor is used.SOLUTION: A sample coil 16 includes: a first coil unit 38 including a coil composed of a superconductor; and a second coil unit 40 including a coil composed of a superconductor. The first coil unit 38 and the second coil unit 40 apply a high-frequency magnetic field to a sample 18 and detects a nuclear magnetic resonance (NMR) signal from the sample 18. A coil included in the first coil unit 38 is disposed without crossing the sample 18 when viewed from a direction orthogonal to a surface in which the first coil 38 is formed. A coil included in the second coil unit 40 is disposed without crossing the sample 18 when viewed from a direction orthogonal to a surface in which the second coil unit 40 is formed.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to NMR detectors for use in NMR instruments. [Background technology]

[0002] 2. Description of the Related Art A nuclear magnetic resonance (NMR) apparatus is known as a magnetic resonance measuring apparatus.

[0003] In an NMR instrument, an NMR probe is placed in a static magnetic field. The NMR probe includes a sample coil for transmission and a sample coil for reception. The sample coil irradiates a high-frequency magnetic field to a sample during transmission and detects the NMR signal of the sample during reception.

[0004] To perform NMR measurements of a solution sample with the highest possible sensitivity, the NMR measurements are performed using an NMR device that uses a cryogenic NMR probe. In general, the Q value of the sample coil is increased by cooling the sample coil to cryogenic temperatures to reduce the electrical resistance of the sample coil. This increases the SNR (signal to noise ratio). In other words, cooling the sample coil to cryogenic temperatures increases the detection sensitivity of the sample coil, thereby increasing the SNR. The Q value is expressed by the following formula: Q=2πfL / R where f is the resonant frequency, L is the inductance of the sample coil, and R is the resistance of the sample coil.

[0005] Conventionally, a copper sample coil is used as the sample coil. The sample coil is cooled to a temperature of about 20 K by a cooling system. This allows for NMR measurements with higher sensitivity than NMR probes at room temperature.

[0006] To measure NMR signals, a radio-frequency magnetic field with a frequency equal to the sample's inherent resonant frequency is irradiated onto the sample via a cryogenic NMR probe. The sample coil and sample are placed in a static magnetic field generated by a superconducting magnet. If the static magnetic field is inhomogeneous in the active region of the sample, the NMR spectrum may be distorted or the NMR signal itself may not be detected. To avoid this, the static magnetic field is usually maintained uniform by adjusting the static magnetic field distribution using a magnetic modulation coil.

[0007] Conventionally, a copper sample coil irradiates the sample with the radio frequency magnetic field required for NMR excitation, oriented perpendicular to the static magnetic field. When a uniform radio frequency magnetic field is irradiated onto the sample and a uniform static magnetic field is applied to the sample, the NMR signal is detected by the sample coil. The detected NMR signal is processed by a spectrometer to produce an NMR spectrum.

[0008] However, even if a copper sample coil is cooled, there is a limit to how much the electrical resistance of the sample coil can be reduced, and therefore there is a limit to how much the detection sensitivity of the NMR signal can be increased.

[0009] Therefore, attempts are being made to improve the detection sensitivity of NMR signals by using a sample coil made of a superconductor.

[0010] However, superconductors can only be deposited on planar substrates, and the Meissner effect, which is specific to superconductors, significantly distorts the static magnetic field, which can lead to distortions in NMR spectra.

[0011] In this regard, US Pat. No. 5,399,633 describes a coil arrangement having an additional superconductor structure, which compensates for disturbing effects caused by the magnetization of a superconductor separated from the resonator.

[0012] Moreover, Patent Document 2 describes an RF receiving coil device having a planar substrate element on which a superconductor structure is arranged. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] JP 2003-202367 A [Patent Document 2] JP 2002-341001 A Summary of the Invention [Problem to be solved by the invention]

[0014] As described above, sample coils using superconductors have been proposed, but the sample coils according to the conventional techniques have the following problems.

[0015] As in the case of detecting an NMR signal using a copper sample coil, in order to detect an NMR signal, the following conditions (1) to (3) must be satisfied. (1) Irradiate the sample with a uniform and as strong a radio-frequency magnetic field as possible. (2) Irradiating the sample with a radio frequency magnetic field having the same frequency as the resonant frequency of the nuclide being measured. (3) Do not distort the static magnetic field.

[0016] However, when a sample coil made of a superconductor is used, the static magnetic field is significantly distorted due to the Meissner effect, which is specific to superconductors, and as a result, there is a possibility that distortions will occur in the NMR spectrum.

[0017] In addition, the higher the Q value of the sample coil, the stronger the effect of the dielectric loss of the sample on the electric field concentration area of ​​the sample coil, and therefore, when a sample is inserted into the NMR probe (specifically, when a sample is inserted into the space surrounded by the sample coil), the Q value of the sample coil decreases significantly.

[0018] Depending on the degree of the decrease in the Q value, the Q value of a sample coil made of a superconductor may decrease to the same level as that of a copper sample coil. Therefore, unless the problem of the decrease in the Q value is solved, there will be no point in using a superconductor as a sample coil.

[0019] An object of the present disclosure is to increase the detection sensitivity of NMR signals while suppressing the occurrence of distortion in the static magnetic field when a sample coil made of a superconductor is used. [Means for solving the problem]

[0020] One aspect of the present disclosure is an NMR detector that irradiates a high-frequency magnetic field onto a sample placed in a static magnetic field and detects NMR signals from the sample, comprising: a first coil unit including a coil made of a superconductor; and a second coil unit including a coil made of a superconductor, the second coil unit being arranged opposite the first coil unit with the sample in between, wherein the first coil unit and the second coil unit irradiate a high-frequency magnetic field onto the sample and detect NMR signals from the sample, and the coil included in the first coil unit is arranged so as not to intersect with the sample when viewed from a direction perpendicular to the plane formed by the first coil unit, and the coil included in the second coil unit is arranged so as not to intersect with the sample when viewed from a direction perpendicular to the plane formed by the second coil unit.

[0021] The first coil unit may include a first coil and a second coil arranged at a distance from the first coil by at least the width of the sample, and the second coil unit may include a third coil and a fourth coil arranged at a distance from the third coil by at least the width of the sample.

[0022] Each of the first coil, the second coil, the third coil and the fourth coil may include an electric field concentration portion.

[0023] The first coil, the second coil, the third coil and the fourth coil each may include a portion close to the sample and a portion far from the sample, and the electric field concentration portion may be formed in the portion far from the sample.

[0024] The electric field concentration portion may have a shape in which a plurality of coil elements overlap in a plane.

[0025] The electric field concentration portion may have a shape corresponding to a resonance frequency of the sample.

[0026] Each of the first coil, the second coil, the third coil and the fourth coil may include a current concentrating portion.

[0027] The first coil, the second coil, the third coil and the fourth coil each may include a portion close to the sample and a portion far from the sample, and the current concentration portion may be formed in the portion close to the sample.

[0028] The first coil, the second coil, the third coil and the fourth coil may each have a total length of half the wavelength of a radio frequency magnetic field irradiated to the sample.

[0029] The first coil, the second coil, the third coil and the fourth coil may each be a coil disposed on a planar substrate, and a folded-back portion of an inner periphery of the coil may have a curved shape. Effect of the Invention

[0030] According to the present disclosure, when a sample coil made of a superconductor is used, it is possible to increase the detection sensitivity of NMR signals while suppressing the occurrence of distortion in the static magnetic field. [Brief description of the drawings]

[0031] [Figure 1] FIG. 1 is a diagram showing an NMR apparatus according to an embodiment. [Diagram 2] FIG. 2 is a perspective view showing a sample coil according to an embodiment. [Diagram 3] FIG. 2 is a diagram showing the sample coil according to the embodiment as viewed from the X direction. [Figure 4] FIG. 2 is a perspective view showing a sample coil according to an embodiment. [Diagram 5] FIG. 2 is a diagram showing the first coil unit according to the embodiment as viewed from the X direction. [Figure 6] FIG. [Figure 7] FIG. 13 is a diagram showing a virtually exploded state of an electric field concentration portion. [Figure 8] FIG. 2 is a diagram showing an equivalent circuit of a coil. [Figure 9] FIG. [Figure 10] FIG. [Figure 11] FIG. [Figure 12] FIG. 11 is a perspective view showing a sample coil according to a comparative example. [Figure 13] FIG. 13 is a diagram showing a sample coil according to a comparative example when viewed from the X direction. [Figure 14] 11A and 11B are diagrams showing calculation results of the distribution of a high-frequency magnetic field generated by a sample coil according to an embodiment. [Figure 15] FIG. 13 is a diagram showing the measurement results of a static magnetic field. [Figure 16] FIG. 1 shows the distribution of signal intensity versus chemical shift. [Figure 17] FIG. 13 is a diagram showing the measurement results of a loaded Q value. [Figure 18] FIG. 13 is a diagram showing a current distribution according to a comparative example. [Figure 19] FIG. 4 is a diagram showing a current distribution according to the embodiment. [Figure 20] FIG. 13 is a diagram showing the distribution of current generated in a folded portion of a coil. [Figure 21] FIG. 13 is a diagram showing the distribution of current generated in a folded portion of a coil. [Figure 22] FIG. 13 is a diagram showing the distribution of current generated in a folded portion of a coil. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] An NMR apparatus according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing an NMR apparatus 10. The NMR apparatus 10 is an apparatus that measures an NMR signal generated from a sample.

[0033] The NMR apparatus 10 includes a static magnetic field generator. The static magnetic field generator includes a superconducting magnet 12 and generates a static magnetic field B0. A vertically extending cavity is formed in the center of the static magnetic field generator. The NMR probe 14 has a cylindrical shape that also extends vertically, and is inserted into the cavity of the static magnetic field generator. The NMR probe 14 is a probe for use at extremely low temperatures.

[0034] A detection circuit is provided in the NMR probe 14. The detection circuit is a tuning and matching circuit, and includes a sample coil 16, a variable tuning capacitor, a variable matching capacitor, etc. The variable tuning capacitor and the variable matching capacitor provide tuning and matching, and optimize the characteristics of the detection circuit.

[0035] The sample coil 16 is disposed around the sample 18 within the NMR probe 14. The sample coil 16 irradiates the sample 18 with a high-frequency magnetic field B1 and detects an NMR signal generated from the sample 18. The sample coil 16 is made of a superconductor.

[0036] The magnetic field modulation coil 20 is disposed between the superconducting magnet 12 and the NMR probe 14. The magnetic field modulation coil 20 is a coil for adjusting the distribution of the static magnetic field B0.

[0037] The inside of the NMR probe 14 is maintained at a vacuum by a vacuum pumping system 22. In addition, the inside of the NMR probe 14 is cooled by a cooling system 24. For example, the sample coil 16 and its surroundings are cooled to a temperature of about 20 K. This realizes an NMR probe 14 for use at extremely low temperatures.

[0038] When measuring an NMR signal, a high-frequency oscillator 26 generates a high-frequency current having a frequency equal to the inherent resonant frequency of the sample 18. The high-frequency current is adjusted to an appropriate value by an attenuator 28 and supplied to the sample coil 16 via the NMR probe 14.

[0039] The sample coil 16 and the sample 18 are placed in the static magnetic field B0 generated by the superconducting magnet 12. If the static magnetic field B0 is non-uniform in the active region of the sample 18, the measured NMR spectrum may be distorted or the NMR signal itself may not be detected. To avoid these problems, the distribution of the static magnetic field B0 is adjusted by the magnetic field modulation coil 20.

[0040] The sample coil 16 irradiates the sample 18 with a radio frequency magnetic field B1 required for NMR excitation in a direction perpendicular to the direction of the static magnetic field B0. When the uniform radio frequency magnetic field B1 is irradiated to the sample 18 and the uniform static magnetic field B0 is applied to the sample 18, an NMR signal is detected by the sample coil 16. The sample coil 16 corresponds to an example of an NMR detector.

[0041] The NMR signal detected by the sample coil 16 is amplified by the low-temperature preamplifier 30 and the preamplifier 32. The personal computer 36 applies signal processing such as Fourier transform to the amplified signal to generate an NMR spectrum. For example, the NMR spectrum is displayed on a display.

[0042] The configuration other than the sample coil 16 may be a known configuration.

[0043] The sample coil 16 will be described below with reference to Fig. 2 and Fig. 3. Fig. 2 is a perspective view showing the sample coil 16. Fig. 3 is a view of the sample coil 16 as viewed from the X direction. Fig. 3 shows a first coil unit 38 and a sample 18.

[0044] 2 and 3, a three-dimensional orthogonal coordinate system is defined, which is made up of mutually orthogonal X-axis, Y-axis, and Z-axis. The direction of the static magnetic field B0 coincides with the positive direction of the Z-axis.

[0045] The sample coil 16 includes a first coil unit 38 and a second coil unit 40. The first coil unit 38 and the second coil unit 40 are arranged facing each other with the sample 18 (more specifically, a sample tube that stores the sample 18) between them. The first coil unit 38 and the second coil unit 40 are arranged at a distance from each other along the X-axis.

[0046] The first coil unit 38 includes a planar substrate 42, a coil 44, and a coil 46. The second coil unit 40 includes a planar substrate 48, a coil 50, and a coil 52.

[0047] The coil 44 corresponds to an example of a first coil. The coil 46 corresponds to an example of a second coil. The coil 50 corresponds to an example of a third coil. The coil 52 corresponds to an example of a fourth coil.

[0048] For example, the planar substrates 42 and 48 are sapphire substrates. The planar substrates 42 and 48 are disposed opposite each other with the sample 18 (more specifically, a sample tube storing the sample 18) therebetween. The planar substrates 42 and 48 are disposed with a gap between them along the X-axis.

[0049] For example, the planar substrate 42 and the planar substrate 48 are arranged parallel to each other. As a result, the first coil unit 38 and the second coil unit 40 are arranged parallel to each other. The planar substrate 42 and the planar substrate 48 may be arranged strictly parallel to each other (i.e., parallel in a mathematical sense), or may not be arranged strictly parallel to each other. For example, the planar substrates 42 and 48 may be arranged at an angle deviated from parallel in a mathematical sense within a range in which the detection sensitivity of the NMR signal is allowed. In other words, the first coil unit 38 and the second coil unit 40 may be arranged at an angle deviated from parallel in a mathematical sense within a range in which the detection sensitivity of the NMR signal is allowed. In the example shown in FIG. 2 and FIG. 3, the plane formed by the planar substrate 42 is the YZ plane. The same applies to the planar substrate 48.

[0050] The coils 44, 46 are formed on the planar substrate 42. The coils 50, 52 are formed on the planar substrate 48. The coils 44, 46, 50, 52 are made of a superconductor such as YBCO (yttrium-based superconductor, YBa2Cu3O7). For example, the coils 44, 46 are formed on the planar substrate 42, and the coils 50, 52 are formed on the planar substrate 48 by processes such as film formation and etching.

[0051] Each of the coils 44, 46 has a shape wound on the planar substrate 42. Each of the coils 50, 52 has a shape wound on the planar substrate 48. The coils 44, 46, 50, 52 have the same shape and size. For example, the number of turns of each of the coils 44, 46, 50, 52 is one turn. Of course, the number of turns is not limited, and the number of turns may be multiple turns.

[0052] The first coil unit 38 and the second coil unit 40 each irradiate the sample 18 with a high frequency magnetic field B1 and detect an NMR signal from the sample 18. The first coil unit 38 and the second coil unit 40 are arranged parallel to each other, so that a high frequency magnetic field B1 having a direction perpendicular to the direction of the static magnetic field B0 is irradiated. In the example shown in Figures 2 and 3, the direction of the high frequency magnetic field B1 coincides with the negative direction of the Y axis.

[0053] The coils 44 and 46 are arranged on the planar substrate 42 in a mutually inverted manner with the Z axis as the central axis. The coil 46 is also arranged on the planar substrate 42 at a position away from the coil 44 in the Y direction by at least the width of the sample 18. That is, the coils 44 and 46 are arranged on the planar substrate 42 (i.e., in the YZ plane) at a position where they do not overlap with the sample 18. In other words, the coils 44 and 46 are arranged at a position where they do not intersect with the sample 18 when viewed from a direction perpendicular to the planar substrate 42 (i.e., the X direction). As a result, the coils included in the first coil unit 38 are arranged so as not to intersect with the sample 18 when viewed from a direction perpendicular to the plane formed by the first coil unit 38 (i.e., the YZ plane) (i.e., the X direction).

[0054] The coils 50 and 52 are arranged on the planar substrate 48 in a mutually inverted manner with the Z-axis as the central axis. The coil 52 is also arranged on the planar substrate 48 at a position away from the coil 50 in the Y direction by at least the width of the sample 18. That is, the coils 50 and 52 are arranged on the planar substrate 48 (i.e., in the YZ plane) at a position that does not overlap with the sample 18. In other words, the coils 50 and 52 are arranged at a position that does not intersect with the sample 18 when viewed from a direction perpendicular to the planar substrate 48 (i.e., the X direction). As a result, the coils included in the second coil unit 40 are arranged so as not to intersect with the sample 18 when viewed from a direction perpendicular to the plane formed by the second coil unit 40 (i.e., the YZ plane) (i.e., the X direction).

[0055] By arranging the coils included in the first coil unit 38 and the coils included in the second coil unit 40 so as not to intersect with the sample 18 when viewed from the X direction, it is possible to reduce distortion of the static magnetic field B0 formed in the region where the sample 18 is placed. This effect will be described in detail later.

[0056] Coil 44 and coil 50 are disposed opposite each other along the X-axis. Coil 44 and coil 50 are disposed parallel to each other. Similarly, coil 46 and coil 52 are disposed opposite each other along the X-axis. Coil 46 and coil 52 are disposed parallel to each other.

[0057] Coil 44 and coil 52 are disposed at diagonal positions relative to each other with respect to the X-axis. Similarly, coil 46 and coil 50 are disposed at diagonal positions relative to each other with respect to the X-axis. For example, coil 44 and coil 52 are disposed with sample 18 therebetween. Similarly, coil 46 and coil 50 are disposed with sample 18 therebetween.

[0058] Each of the coils 44, 46, 50, and 52 includes an electric field concentration portion 54. Each of the coils 44, 46, 50, and 52 includes a portion close to the sample 18 and a portion far from the sample 18. The electric field concentration portion 54 is formed in the portion far from the sample 18. Each of the coils 44, 46, 50, and 52 also includes a current concentration portion 56. The current concentration portion 56 is formed in the portion close to the sample 18. Hereinafter, the portion close to the sample 18 will be referred to as the "near portion," and the portion far from the sample 18 will be referred to as the "far portion."

[0059] The near portions are the inner portions of the coils 44, 46, 50, and 52. The far portions are the outer portions of the coils 44, 46, 50, and 52. For example, the electric field concentration portion 54 is formed at the center of the outer portions of the coils 44, 46, 50, and 52. The current concentration portion 56 is formed at the center of the inner portions of the coils 44, 46, 50, and 52.

[0060] In the coils 44 and 46, the portions facing each other correspond to the near portions. Similarly, in the coils 50 and 52, the portions facing each other correspond to the near portions.

[0061] The far portion of coil 44 is the portion opposite the near portion of coil 44 along the Y axis. The far portion of coil 46 is the portion opposite the near portion of coil 46 along the Y axis. The far portion of coil 50 is the portion opposite the near portion of coil 50 along the Y axis. The far portion of coil 52 is the portion opposite the near portion of coil 52 along the Y axis.

[0062] The electric field concentration portion 54 of the coil 44 and the electric field concentration portion 54 of the coil 50 are formed at positions facing each other along the X-axis. The electric field concentration portion 54 of the coil 46 and the electric field concentration portion 54 of the coil 52 are formed at positions facing each other along the X-axis.

[0063] The electric field concentration portion 54 of the coil 44 and the electric field concentration portion 54 of the coil 52 are formed at positions diagonal to each other with respect to the X-axis. The electric field concentration portion 54 of the coil 46 and the electric field concentration portion 54 of the coil 50 are formed at positions diagonal to each other with respect to the X-axis.

[0064] The current concentrating portion 56 of the coil 44 and the current concentrating portion 56 of the coil 50 are formed at positions facing each other along the X-axis. The current concentrating portion 56 of the coil 46 and the current concentrating portion 56 of the coil 52 are formed at positions facing each other along the X-axis.

[0065] The current concentration portion 56 of the coil 44 and the current concentration portion 56 of the coil 52 are formed at positions diagonal to each other with respect to the X-axis. The current concentration portion 56 of the coil 46 and the current concentration portion 56 of the coil 50 are formed at positions diagonal to each other with respect to the X-axis.

[0066] The coils 44, 46, 50, and 52 function as superconducting resonators and are magnetically coupled to each other. The coupled state is shown in FIG. 4. FIG.

[0067] The coupling a1 is a magnetic coupling between the coil 44 and the coil 46. The coupling a2 is a magnetic coupling between the coil 50 and the coil 52. The couplings a1 and a2 can be said to be couplings in the horizontal direction.

[0068] The coupling b1 is a magnetic coupling between the coil 44 and the coil 50. The coupling b2 is a magnetic coupling between the coil 46 and the coil 52. The couplings b1 and b2 can be said to be couplings in the facing direction.

[0069] Coupling c1 is a magnetic coupling between coil 44 and coil 52. Coupling c2 is a magnetic coupling between coil 46 and coil 50. Couplings c1 and c2 can be said to be diagonal couplings.

[0070] As described above, the coils 44, 46, 50, and 52 are magnetically coupled to each other. Therefore, when high-frequency currents are applied to the coils 44, 46, 50, and 52, the coils 44, 46, 50, and 52 resonate with each other, and a uniform high-frequency magnetic field B1 (i.e., a high-frequency composite magnetic field) can be generated.

[0071] The configuration of the electric field concentration portion 54 will be described below with reference to Figs. 5 to 7. Fig. 5 is a view of the first coil unit 38 as viewed from the X direction. Fig. 5 shows the coils 44, 46, but does not show the planar substrate 48. Fig. 6 is an enlarged view of the electric field concentration portion 54. Fig. 7 is a view showing a virtually exploded state of the electric field concentration portion 54. Note that the coils 50, 52 also have the same shape as that shown in Fig. 5.

[0072] The electric field concentration portion 54 has a shape in which a plurality of coil elements overlap in a plane. For example, the electric field concentration portion 54 has a comb shape.

[0073] 6, the electric field concentration portion 54 includes coil elements 54a to 54f. The coil elements 54a to 54f each have a linear shape and overlap one another within the planar substrate 48.

[0074] The number and shape of the coil elements are merely examples. In the example shown in Fig. 6, the electric field concentration portion 54 is formed by six coil elements, but the electric field concentration portion 54 may be formed by fewer than six coil elements or more than six coil elements. Some or all of the coil elements may be formed in a curved shape.

[0075] 7, for example, coil elements 54a, 54b, and 54c are formed at one end of coil 44, and coil elements 54d, 54e, and 54f are formed at the other end of coil 44. As indicated by the arrows in FIG 7, by interlocking these ends, coil elements 54a to 54f overlap one another, and as a result, electric field concentration portion 54 is formed.

[0076] The dielectric loss of the sample 18 affects the electric field concentration part of the sample coil. To explain in detail, when a high-frequency AC electric field is applied to the dielectric, the dipoles constituting the dielectric try to follow the reversal of the electric field. As a result, heat is generated by friction between the dipoles, and this heat becomes thermal noise and causes loss. This heat affects the electric field concentration part, thereby decreasing the Q value. Therefore, in the past, when the sample 18 is inserted into the NMR probe 14, the Q value of the sample coil decreases. In contrast, in this embodiment, since the electric field concentration part 54 is formed in a distant part, the effect of the dielectric loss of the sample 18 on the electric field concentration part 54 can be suppressed compared to when the electric field concentration part 54 is formed in a close part. As a result, the decrease in the Q value when the sample 18 is inserted into the NMR probe 14 can be suppressed.

[0077] 8 shows the equivalent circuits of the coils 44, 46, 50, and 52. R indicates resistance, L indicates inductance (inductance coefficient), and C indicates capacitance (electrostatic capacitance).

[0078] 6 and 7, the length (length in the Z direction) of each of the coil elements 54a to 54f is length a. In other words, the length of the portions where the coil elements 54a to 54f mesh with each other is length a. As shown in Fig. 6, the distance between the coil elements (distance in the Y direction) is distance d. The thickness (thickness in the X direction) of each of the coils 44, 46, 50, and 52 is thickness t.

[0079] The resonant frequency f of the sample coil 16 is expressed by the following formula (1), and the capacitance C is expressed by the following formula (2). ε is the dielectric constant (constant). S is the area (length a × thickness t). Since the thickness t of each of the coils 44, 46, 50, and 52 is very thin, the capacitance C is expressed by formula (2).

number

number

[0080] Changing the resonance frequency f will be described with reference to Figures 9 and 10. Figure 9 is an enlarged view of electric field concentration portion 54A. Figure 10 is an enlarged view of electric field concentration portion 54B.

[0081] Electric field concentration portions 54A and 54B are an example of electric field concentration portion 54, and are composed of coil elements 54a to 54f. The only difference between electric field concentration portion 54A and electric field concentration portion 54B is the length a of each of coil elements 54a to 54f. Length a of the coil elements of electric field concentration portion 54A is shorter than length b of the coil elements of electric field concentration portion 54B.

[0082] The shorter the length a of the coil element, the smaller the capacitance C (see equation (2)), and as a result, the higher the resonant frequency f (see equation (1)). Conversely, the longer the length a of the coil element, the larger the capacitance C, and as a result, the lower the resonant frequency f.

[0083] That is, the resonant frequency f of the sample coil 16 having the electric field concentration portion 54A is higher than the resonant frequency f of the sample coil 16 having the electric field concentration portion 54B. In other words, the sample coil 16 having a high resonant frequency f is formed by the electric field concentration portion 54A, and the sample coil 16 having a low resonant frequency f is formed by the electric field concentration portion 54B.

[0084] When electric field concentration portion 54A is used as the electric field concentration portion, the same electric field concentration portion 54A is formed in each of coils 44, 46, 50, and 52. When electric field concentration portion 54B is used as the electric field concentration portion, the same electric field concentration portion 54B is formed in each of coils 44, 46, 50, and 52.

[0085] As described above, the resonant frequency f of the sample coil 16 can be changed simply by changing the length a of each of the coil elements of the coils 44, 46, 50, and 52. Therefore, the resonant frequency f of the sample coil 16 can be changed without changing the size of the coils 44, 46, 50, and 52.

[0086] For example, when a general spiral coil is used as a sample coil, the number of turns of the spiral coil must be changed to change the resonant frequency. Specifically, in order to achieve a low resonant frequency, the number of turns must be increased. However, the more the number of turns is increased, the larger the size of the spiral coil becomes. Since the space for accommodating the sample coil is limited, when using a sample coil having a low resonant frequency, it is necessary to secure the space for the sample coil. Or, since the space is limited, the resonant frequency that can be realized is limited.

[0087] In contrast to this, in this embodiment, the resonant frequency f of the sample coil 16 can be changed by simply changing the length a of the coil element, without changing the sizes of the coils 44, 46, 50, and 52.

[0088] For example, the electric field concentration portion 54 has a shape according to the resonance frequency of the sample 18. In other words, the length a of the coil element is set to a length that can realize a resonance frequency f equal to the resonance frequency of the sample 18 to be measured. In this way, by using a sample coil 16 in which the length a of the coil element is changed according to the sample 18, it becomes possible to perform NMR measurement of various samples 18 simply by changing the sample coil 16. For example, by changing the length a according to a nuclide such as 13C, 19F, 15N, or 31P, it becomes possible to perform NMR measurement of each nuclide.

[0089] Hereinafter, current concentration portion 56 will be described with reference to Fig. 11. Fig. 11 is a development view of coil 44. The state of coil 44 shown in Fig. 11 is a state in which coil 44 is developed linearly with coil elements 54a-54c constituting electric field concentration portion 54 and coil elements 54d-54f constituting electric field concentration portion 54 virtually separated from each other.

[0090] A waveform 58 is a schematic representation of the waveform of a high-frequency current. A waveform 60 is a schematic representation of a half-wavelength of the high-frequency current.

[0091] The overall length of coil 44 is determined so that coil 44 resonates at half the wavelength (λ / 2) of the high-frequency current (high-frequency magnetic field B1) supplied to coil 44. For example, the overall length of coil 44 has a length of half the wavelength of the high-frequency current (high-frequency magnetic field B1). As a result, when high-frequency current is supplied to coil 44, the current is concentrated in the center of the linear coil 44. This portion is current concentration portion 56.

[0092] Coil 44 is formed on planar substrate 42 so that the center of coil 44 (i.e., current concentrating portion 56) when coil 44 is virtually extended in a straight line is located near sample 18. The same is true for coils 46, 50, and 52. In this way, current concentrating portions 56 of coils 44, 46, 50, and 52 are located near sample 18.

[0093] By arranging the current concentrating portion 56 at a position close to the sample 18, a stronger radio frequency magnetic field B1 can be irradiated onto the sample 18 compared to a case in which the current concentrating portion 56 is arranged at a position farther from the sample 18.

[0094] Here, a sample coil according to a comparative example will be described with reference to Fig. 12 and Fig. 13. Fig. 12 is a perspective view of the sample coil according to the comparative example. Fig. 13 is a view of the sample coil according to the comparative example as viewed from the X direction.

[0095] 12, a sample coil 100 according to the comparative example includes a first coil unit 102 and a second coil unit 104. The first coil unit 102 and the second coil unit 104 are disposed with a sample 18 therebetween.

[0096] The first coil unit 102 includes a planar substrate 106 and a coil 108. The second coil unit 104 includes a planar substrate 110 and a coil 112. For example, the planar substrates 106 and 110 are sapphire substrates. The coils 108 and 112 are made of a superconductor and have a wound shape. The coils 108 and 112 have the same shape.

[0097] When the coil 108 is viewed from the X direction perpendicular to the planar substrate 106, the coil 108 has a shape that intersects with the sample 18. Similarly, when the coil 112 is viewed from the X direction perpendicular to the planar substrate 110, the coil 112 has a shape that intersects with the sample 18.

[0098] 13, the coil 108 includes two electric field concentration portions 114. One electric field concentration portion 114 is formed in an upper portion of the coil 108, and the other electric field concentration portion 114 is formed in a lower portion of the coil 108. When the coil 108 is viewed from the X direction, the two electric field concentration portions 114 are formed at positions intersecting with the sample 18. Like the coil 108, the coil 112 also includes two electric field concentration portions 114. When the coil 112 is viewed from the X direction, the two electric field concentration portions 114 are formed at positions intersecting with the sample 18.

[0099] In the sample coil 100 according to the comparative example, when the coils 108, 112 are viewed from the X direction, the electric field concentration portion 114 intersects with the sample 18. That is, the region in which the static magnetic field B0 is formed intersects with the coils 108, 112 (specifically, the electric field concentration portion 114). As a result, distortion occurs in the static magnetic field B0, and a uniform static magnetic field B0 cannot be formed.

[0100] In contrast, according to the sample coil 16 of the present embodiment, since the sample coil 16 does not cross the sample 18, distortion does not occur in the static magnetic field B0 or ​​the occurrence of distortion can be suppressed. As a result, a uniform static magnetic field B0 can be formed.

[0101] The distribution of the high frequency magnetic field B1 generated by the sample coil 16 will be described with reference to Fig. 14. Fig. 14 shows the calculation results of the distribution of the high frequency magnetic field B1.

[0102] As an example, a three-dimensional electromagnetic field simulator (CST Studio Suite, AET) was used to calculate the distribution of the high-frequency magnetic field B1 generated by the sample coil 16. Fig. 14 shows the distribution of the high-frequency magnetic field B1 as viewed from the Z direction. The arrows shown in Fig. 14 indicate the direction of the high-frequency magnetic field B1. The shading of the arrows indicates the strength of the high-frequency magnetic field B1.

[0103] In the region where the sample 18 is placed (region surrounded by a circle), the direction of the high frequency magnetic field B1 coincides or nearly coincides with the direction of the Y axis and is constant. The strength of the high frequency magnetic field B1 is also constant or nearly constant. Thus, it can be seen that a uniform high frequency magnetic field B1 is formed in the region where the sample 18 is placed.

[0104] The measurement results of the static magnetic field B0 will be described with reference to Fig. 15. Fig. 15 shows the measurement results of the static magnetic field B0. The horizontal axis indicates the distance in the Z direction. The vertical axis indicates the strength of the static magnetic field B0. The position of Z=0 is the center of the area where the sample 18 is placed.

[0105] Graph 62 is a graph according to a comparative example. That is, when the sample coil 100 according to the comparative example is used, a static magnetic field B0 having the distribution shown in graph 62 is formed. Graph 64 is a graph according to the embodiment. That is, when the sample coil 16 according to the embodiment is used, a static magnetic field B0 having the distribution shown in graph 64 is formed.

[0106] As shown in graph 62, when the sample coil 100 according to the comparative example is used, the distortion of the static magnetic field B0 is large. On the other hand, as shown in graph 64, when the sample coil 16 according to the embodiment is used, the distortion of the static magnetic field B0 is small, and the occurrence of distortion is suppressed.

[0107] For example, it is required that the distortion of the static magnetic field B0 is within ±1.9 μT in as wide a range as possible in the Z-axis direction. In the comparative example, this requirement is not met, and therefore distortion occurs in the NMR spectrum. On the other hand, according to the present embodiment, this requirement can be met, and therefore no distortion occurs in the NMR spectrum, or the occurrence of such distortion can be suppressed.

[0108] The intensity of the detected NMR signal will be described with reference to Fig. 16. Fig. 16 shows the distribution of signal intensity versus chemical shift. The horizontal axis indicates the chemical shift of the high frequency magnetic field B1. The vertical axis indicates the intensity of the detected NMR signal.

[0109] Graph 66 is a graph according to a comparative example. That is, when the sample coil 100 according to the comparative example is used, an NMR signal having the signal intensity shown in graph 66 is detected. Graph 68 is a graph according to the embodiment. That is, when the sample coil 16 according to the embodiment is used, an NMR signal having the signal intensity shown in graph 68 is detected.

[0110] When the sample coil 100 according to the comparative example is used, as described above, the distortion of the static magnetic field B0 is large. Therefore, the intensity of the detected NMR signal is low and the distribution of the NMR signal is split. As a result, the NMR spectrum is split and the intensity is low.

[0111] In contrast, when the sample coil 16 according to the embodiment is used, the distortion of the static magnetic field B0 is smaller than that of the comparative example. Therefore, the intensity of the detected NMR signal is higher than that of the comparative example. In addition, no split occurs in the distribution of the NMR signal. As a result, the split of the NMR spectrum is suppressed, and a high-intensity NMR spectrum is obtained.

[0112] The measurement results of the loaded Q factor will be described with reference to Fig. 17. Fig. 17 shows the measurement results of the loaded Q factor. The vertical axis represents the loaded Q factor.

[0113] Graphs 70 and 72 are loaded Q values ​​measured when the sample 18 is not inserted in the NMR probe 14. Graph 70 is a graph according to the embodiment. That is, the loaded Q value shown in graph 70 was measured when the sample coil 16 according to the embodiment was used. Graph 72 is a graph according to a comparative example. Here, a copper sample coil was used as the sample coil according to the comparative example. The loaded Q value shown in graph 72 was measured when the copper sample coil was used.

[0114] Graphs 74 and 76 are loaded Q values ​​measured when the sample 18 was inserted into the NMR probe 14. Here, a heavy solvent sample (D2O) was used as the sample 18. Graph 74 is a graph according to the embodiment. That is, the loaded Q value shown in graph 74 was measured when the sample coil 16 according to the embodiment was used. Graph 76 is a graph according to a comparative example. That is, the loaded Q value shown in graph 76 was measured when a copper sample coil was used.

[0115] As graphs 70 and 72 show, the loaded Q factor according to the embodiment is higher than the loaded Q factor according to the comparative example when the sample 18 is not inserted into the NMR probe 14. Here, the loaded Q factor according to the embodiment is about 28 times higher than the loaded Q factor according to the comparative example.

[0116] As shown in graphs 74 and 76, the loaded Q factor according to the embodiment is higher than the loaded Q factor according to the comparative example, even when the sample 18 is inserted into the NMR probe 14. Here, the loaded Q factor according to the embodiment is about 20 times higher than the loaded Q factor according to the comparative example.

[0117] As described above, when the sample coil 16 according to the embodiment is used, a high loaded Q value can be maintained even when the sample 18 is inserted into the NMR probe 14. Therefore, the detection sensitivity of the NMR signal can be improved compared to the comparative example.

[0118] 2, 3, 5, and 11, in this embodiment, the current concentration portion 56 is formed in a portion close to the sample 18 (i.e., the inner portion of each of the coils 44, 46, 50, and 52). As a result, the current concentration portion 56 formed in the portion close to the sample 18 is formed at a position farther from the inner wall surface of the NMR probe 14 than when the current concentration portion 56 is formed in a portion far from the sample 18 (i.e., the outer portion of each of the coils 44, 46, 50, and 52). In this way, it is possible to reduce eddy currents generated on the inner wall surface of the NMR probe 14. As a result, it is possible to reduce the influence of conductor loss on the sample coil 16 from the inner wall surface, and it is possible to suppress a decrease in the Q value of the sample coil 16 due to conductor loss.

[0119] The eddy current generated on the inner wall surface of the NMR probe 14 will be described with reference to Fig. 18 and Fig. 19. Fig. 18 shows a current distribution according to a comparative example. Fig. 19 shows a current distribution according to the embodiment. Each current distribution is a result of analysis by an electromagnetic field simulator.

[0120] The inner wall surface 78 is the inner wall surface of the NMR probe 14. The magnitude of the eddy current generated on the inner wall surface 78 is represented by shading.

[0121] The current concentrating portion of the sample coil 100 according to the comparative example is disposed at a position close to the inner wall surface 78. In contrast, the current concentrating portion 56 of the sample coil 16 according to the embodiment is disposed at a position farther from the inner wall surface 78 than in the comparative example.

[0122] When the sample coil 100 according to the comparative example was used, the current distribution shown in Fig. 18 was generated. When the sample coil 16 according to the embodiment was used, the current distribution shown in Fig. 19 was generated.

[0123] In the comparative example, large eddy currents are generated on the inner wall surface 78. In contrast, in this embodiment, the eddy currents generated on the inner wall surface 78 are smaller than those generated in the comparative example. Therefore, according to this embodiment, the effect of conductor loss on the sample coil 16 from the inner wall surface 78 can be reduced, and a decrease in the Q value of the sample coil 16 can be suppressed.

[0124] Normally, the higher the Q value of the sample coil, the greater the eddy currents generated on the inner wall surface 78, which causes conductor loss and reduces the Q value of the sample coil. According to this embodiment, the generation of eddy currents can be suppressed, and therefore the reduction in the Q value of the sample coil 16 can be suppressed.

[0125] The following describes the configuration of the inner periphery of the coils 44, 46, 50, and 52. Here, the configuration of the inner periphery of the coils 44 and 46 will be described with reference to FIG.

[0126] Coil 44 has one turn and is configured to define an inner periphery 44a in coil 44. Similarly, coil 46 has one turn and is configured to define an inner periphery 46a in coil 46. Inner periphery 44a is the portion of coil 44 that runs along the inside of the wound coil. Inner periphery 46a is the portion of coil 46 that runs along the inside of the wound coil.

[0127] The folded portion 44b of the inner circumferential portion 44a is not shaped at a right angle but is shaped like a curve. The inner circumferential portion 44a has two folded portions 44b, and each folded portion 44b is shaped like a curve. Each folded portion 46b of the inner circumferential portion 46a is also shaped like a curve but is not shaped like a right angle. The coils 50 and 52 also have an inner circumferential portion, and each folded portion of the inner circumferential portion is shaped like a curve but is not shaped like a right angle.

[0128] If the folded portion has a right angle (i.e., a shape having an angle of 90°), the current may concentrate at the folded portion, and the superconducting state may be destroyed. If the folded portion has a curved shape as in the present embodiment, the current can be prevented or suppressed from concentrating at the folded portion, and the destruction of the superconducting state can be prevented or suppressed.

[0129] The current concentration at the folded portion will be described with reference to Figures 20 to 22. Figures 20 to 22 show the distribution of current generated in coils 44, 46, 50, and 52. The current distribution is the result of analysis using an electromagnetic field simulator. The magnitude of the current is expressed by shading.

[0130] FIG. 20 shows the distribution of current generated in the folded portion 46b for each of "R=0" ("R0" in FIG. 20), "R=1.0" ("R1.0" in FIG. 20), "R=0.5" ("R0.5" in FIG. 20), and "R=0.25" ("R0.25" in FIG. 20). R represents the radius of curvature. The current distribution for "R0" is the current distribution when the folded portion 46b has a right-angled shape. The current distributions for "R1.0", "R0.5", and "R0.25" are the current distributions when the folded portion 46b has a curved shape.

[0131] FIG. 21 shows the current distribution for "R0". FIG. 22 shows the current distribution for "R0.5". As shown in FIG. 21, when the shape of the turn-back portion 46b is a right angle, the current concentrates at the turn-back portion 46b. In contrast, as shown in FIG. 22, when the shape of the turn-back portion 46b is a curved shape, the current concentration at the turn-back portion 46b can be suppressed. For example, the magnitude of the current can be suppressed to about 60% of the magnitude of the current at "R0". As a result, the destruction of the superconducting state due to the current concentration can be prevented or suppressed. Although the distribution of the current generated at the turn-back portion 46b is shown in FIG. 20 to FIG. 22, the same results can be obtained for the other turn-back portions.

[0132] The effects of the sample coil 16 according to this embodiment will be summarized below.

[0133] Since the sample coil 16 (specifically, the coils 44, 46, 50, and 52) does not intersect with the sample 18, the occurrence of distortion of the static magnetic field B0 can be suppressed.

[0134] Since the electric field concentration portion 54 is formed at a position far from the sample 18, it is possible to suppress a decrease in the Q value of the sample coil 16 when the sample 18 is inserted into the NMR probe 14. As a result, it is possible to suppress a decrease in detection sensitivity caused by the insertion of the sample 18.

[0135] By changing the length a of the coil elements that make up the electric field concentration portion 54, the resonant frequency of the sample coil 16 can be changed without changing the overall size of the sample coil 16.

[0136] Since the current concentration portion 56 is formed in a position close to the sample 18, a uniform and strong radio frequency magnetic field B1 can be irradiated onto the sample 18. In addition, since the current concentration portion 56 is formed in a position away from the inner wall surface of the NMR probe 14, the influence of conductor loss from the inner wall surface can be reduced.

[0137] As described above, according to this embodiment, it is possible to improve the detection sensitivity of NMR signals without compromising the effect obtained by forming the sample coil 16 from a superconductor. [Explanation of symbols]

[0138] 16 sample coil, 38 first coil unit, 40 second coil unit, 42, 48 planar substrate, 44, 46, 50, 52 coil, 54 electric field concentration portion, 56 current concentration portion.

Claims

1. An NMR detector for irradiating a high frequency magnetic field onto a sample placed in a static magnetic field and detecting an NMR signal from the sample, A first coil unit including a coil made of a superconductor; a second coil unit including a coil made of a superconductor, the second coil unit being disposed opposite the first coil unit with the sample therebetween; Including, the first coil unit and the second coil unit irradiate the sample with a radio frequency magnetic field and detect an NMR signal from the sample; a coil included in the first coil unit is arranged so as not to intersect with the sample when viewed from a direction perpendicular to a plane formed by the first coil unit; a coil included in the second coil unit is arranged so as not to intersect with the sample when viewed from a direction perpendicular to a plane formed by the second coil unit; NMR detector.

2. 2. The NMR detector according to claim 1, The first coil unit is A first coil; a second coil disposed at a position spaced apart from the first coil by at least the width of the sample; Including, The second coil unit is A third coil; a fourth coil disposed at a position spaced apart from the third coil by at least the width of the sample; Including, NMR detector.

3. 3. The NMR detector according to claim 2, Each of the first coil, the second coil, the third coil, and the fourth coil includes an electric field concentration portion. NMR detector.

4. 4. The NMR detector according to claim 3, each of the first coil, the second coil, the third coil, and the fourth coil includes a portion close to the sample and a portion remote from the sample; The electric field concentration portion is formed in a portion far from the sample. NMR detector.

5. 4. The NMR detector according to claim 3, The electric field concentration portion has a shape in which a plurality of coil elements are overlapped in a plane. NMR detector.

6. 6. The NMR detector according to claim 5, The electric field concentration portion has a shape according to a resonance frequency of the sample. NMR detector.

7. 3. The NMR detector according to claim 2, Each of the first coil, the second coil, the third coil, and the fourth coil includes a current concentrating portion. NMR detector.

8. 8. The NMR detector according to claim 7, each of the first coil, the second coil, the third coil, and the fourth coil includes a portion close to the sample and a portion remote from the sample; the current concentration portion is formed in a portion close to the sample, NMR detector.

9. 9. The NMR detector according to claim 8, a total length of each of the first coil, the second coil, the third coil, and the fourth coil is half the wavelength of a high frequency magnetic field irradiated to the sample; NMR detector.

10. 3. The NMR detector according to claim 2, The first coil, the second coil, the third coil, and the fourth coil are each a coil arranged on a planar substrate, and a folded portion of an inner periphery of the coil has a curved shape. NMR detector.

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