EPR spectrometer having at least one pole piece made at least partially of a functional material

Abstract

An electron paramagnetic resonance (EPR) spectrometer comprising: a magnet system including at least one magnet and at least one pole piece, preferably a pair of pole pieces, for generating a magnetic field in a field of view in front of or between at least one pole piece, wherein the magnetic field is generated along the polar axis; a probe including a microwave resonator and at least one modulation or fast scanning coil for generating an additional time-varying magnetic field aligned along the polar axis, wherein the probe is arranged in the field of view, and a corresponding modulation or fast scanning coil is arranged between the microwave resonator and the corresponding pole piece; characterized in that for each pole piece having a modulation or fast scanning coil arranged between the pole piece and the microwave resonator, at least a portion of the pole piece facing the modulation or fast scanning coil is composed of a 10 4 Conductivity σ per sieve or less f And it has a saturation magnetic flux density of 0.2T or greater (BS). f It is made of functional materials. An EPR spectrometer is also proposed, which allows for a compact and inexpensive design, while allowing EPR to perform measurements with low energy consumption and low noise levels.

Description

Technical Field

[0001] This invention relates to an electron paramagnetic resonance (EPR) spectrometer, which has the following features:

[0002] - A magnet system comprising at least one magnet and at least one pole piece, preferably a pair of opposing pole pieces, for generating a magnetic field in the field of view in front of or between the pair of pole pieces.

[0003] The magnetic field is generated along the polar axis;

[0004] - The probe includes a microwave resonator and at least one modulation coil or fast scanning coil for generating an additional time-varying magnetic field aligned along the polar axis.

[0005] The probe is positioned within the field of view.

[0006] Furthermore, the corresponding modulation coil or fast scanning coil is arranged between the microwave resonator and the corresponding pole piece. Background Technology

[0007] This EPR spectrometer can be found in Gunnar Jeschke's lecture "Einführung in die ESR-Spektroskopie", Konstanz (DE) 1998 and 2006, page 88, Figure 4-2.

[0008] Electron paramagnetic resonance (EPR) spectroscopy is a powerful tool for studying samples with paramagnetic moments, particularly those with unpaired electrons. In EPR spectroscopy, the sample is typically subjected to microwave radiation of a constant frequency (also known as the B1 field) within a microwave resonator, while a background magnetic field (also known as the B0 field) generated by a magnetic system is scanned. The probe, which includes the microwave resonator with the sample, is exposed to this background magnetic field. Because the background magnetic field is scanned rather slowly, it is also referred to as the "static" magnetic field. The absorption of microwaves by the sample is measured and used to characterize the sample, particularly regarding its chemical state and molecular environment.

[0009] Continuous wave (CW) and rapid scan (RS) EPR methods further utilize periodically varying magnetic fields, which are respectively called modulation fields (B). mod ) and fast scan field (B RS The frequency of this changing magnetic field is typically between 5 kHz and 100 kHz. This changing magnetic field (also known as a time-varying magnetic field) is superimposed on the background magnetic field and is collinear with it. The changing magnetic field is usually generated by a set (pair) of coils, referred to as modulation coils or fast scanning coils, which are symmetrically placed between the pole shoes of the microwave resonator and the magnetic system, generating the background magnetic field in the field of view between the pole shoes.

[0010] Varying magnetic fields can improve EPR measurements. For example, modulation field B 调制 The purpose is to reduce the phase noise level and thus significantly improve the signal-to-noise ratio (SNR) of the transmitting and receiving systems by moving the source and detection subsystems from the 0Hz operating point (shot noise region) to higher levels (typically 5kHz to 100kHz (thermal noise region)), thereby increasing the SNR of EPR measurements. G. Jeschke (see above) discloses an EPR spectrometer comprising a pair of modulation coils attached to a microwave resonator arranged in the field of view of a magnet system comprising two magnets having a field of view between two pole shoes. Furthermore, US6,472,874 discloses an EPR imaging apparatus including modulation coils.

[0011] The pole pieces of a magnet system are generally used to guide and shape the background magnetic field in an EPR experiment; typically, the background magnetic field in the field of view needs to have good homogeneity and a strong magnetic field strength. The standard material for the pole pieces is iron.

[0012] However, when operating modulation or fast scanning coils, placing them near such pole shoes induces torsion currents in the conductor pole shoes. The magnetic fields generated by these so-called eddy currents change inversely to the magnetic field produced by the modulation coil, effectively reducing their efficiency and inductance. Therefore, it is necessary to increase the power input to the modulation or fast scanning coil to generate the desired magnetic field strength for the time-varying magnetic field.

[0013] As a side effect, increasing the power input at the modulation coil or fast scan coil also increases eddy currents in the walls of the microwave resonator. These AC-type eddy currents in the microwave resonator walls interact with the background magnetic field and can cause acoustic vibrations in the resonator walls. Furthermore, stronger current in the modulation coil also leads to stronger interaction with the background magnetic field, resulting in acoustic vibrations of the modulation coil. This combined vibration can cause detuning of the microwave resonator, which in turn can lead to noise in EPR experiments.

[0014] Furthermore, as an indirect effect, eddy currents in the pole shoes generate significant heat within the pole shoes and more generally in the magnet system. This can in turn lead to variations in the background magnetic field, resulting in noise effects in EPR experiments. Additionally, this heat can be introduced into the modulation coil and, together with it, into the walls of the microwave resonator via thermal conduction and / or radiation, in addition to the coil itself being additionally heated due to unfavorable changes in efficiency and inductance. This heat can cause thermal distortion in the modulation coil and microwave resonator components, which in turn can lead to resonator detuning-type thermal drift, potentially causing adverse conditions in the test sample. This heat also manifests as material structural weakening; therefore, the combination of stronger forces and material weakening results in stronger acoustic vibrations, which can further increase the noise level in EPR experiments through the mechanisms described above.

[0015] To minimize eddy currents in the pole shoes, the modulation coil or fast scanning coil can be positioned at a certain distance from the pole shoes. In the EPR spectrometer shown by G. Jeschke, as illustrated above, there is a large gap between the modulation coil and the pole shoes.

[0016] However, to do this, a relatively large field of view must be provided between the pole pieces, or a large air gap must be present. Increasing the air gap between the poles will require a significant increase in the size of the magnetic system, particularly its permanent magnets or electromagnets, when a specific strength and homogeneity of the background magnetic field is required. However, increasing the size of the magnetic system will greatly increase its manufacturing and operating costs.

[0017] US 5,124,651 A describes a human NMR scanner with a ferromagnetic frame, comprising a gradient coil. Multiple ferromagnetic elements are arranged side-by-side in a polarity region to limit eddy currents when the gradient coil is energized. Each ferromagnetic element includes a rod having a shortest dimension oriented perpendicular to the polar axis. In another variant, the ferromagnetic element comprises a stack of generally rectangular planes, wherein the planes of the stack are generally parallel to the polar axis.

[0018] A similar magnetic field generating device for MRI is known from US 5,283,544 A (also disclosed in EP 0 479 514 A), which uses pole shoes with stacked silicon steel sheets.

[0019] US 5,592,089 A describes another NMR imaging system for scanning the human body, having ferromagnetic poles equipped with an eddy current suppressing material having an initial permeability greater than 1000 and a resistivity less than 1000 microohms*cm. This material is designed to contain the magnetic field generated by the pulse gradient during MR imaging and suppress the eddy currents generated by the process.

[0020] US 5,061,897A (also disclosed as WO 91 / 14948A1) describes a medical NMR scanner in which gradient coils are arranged in a polar region of a device for generating a magnetic field, and in each of the polar regions a layer of magnetically conductive resistive material is positioned to limit eddy current generation in the polar region.

[0021] US 6,348,275 A describes a bulk amorphous metallic magnetic component that can be used specifically with magnetic resonance imaging systems.

[0022] US 6,093,232 discloses a method for manufacturing an iron-carbon compact that can be used as a flux concentrator.

[0023] The purpose of this invention

[0024] The object of this invention is to provide an EPR spectrometer that allows for a compact and inexpensive design, while enabling EPR measurements with low power consumption and low noise levels. Summary of the Invention

[0025] According to the present invention, this objective is achieved by the EPR spectrometer described at the beginning, characterized in that, for each of the pole shoes having a modulation coil or a fast scanning coil arranged between the pole shoes and the microwave resonator, at least a portion of the pole shoe facing the modulation coil or the fast scanning coil is composed of a 10 4 Conductivity σ per sieve or less f And it has a saturation magnetic flux density of 0.2 Tesla or greater (BS). f It is made of functional materials.

[0026] According to the present invention, each pole piece adjacent to the modulation coil or fast scanning coil is made of or equipped with a portion made of a functional material (also referred to as a surface portion). This functional material combines relatively low electrical conductivity with high saturation magnetic flux density, the electrical conductivity being approximately 10 times lower than that of typical ferrous metal materials used to manufacture conventional pole pieces. 4 The high saturation magnetic flux density is several times or more, roughly the same as that of typical ferrometallic materials. In other words, the functional material combines ferromagnetic properties with electrical insulating properties.

[0027] As a result, compared to the typical ferrous metal material, the eddy currents generated by the time-varying magnetic field or the corresponding current in the adjacent modulation coil or fast scanning coil are significantly reduced in the functional material or more generally in the pole shoe. The relatively low conductivity of the functional material in at least a portion (or surface portion) of the pole shoe minimizes the induced eddy currents. The Q factor (quality) of the modulation coil or fast scanning coil (i.e., the reciprocal of its total resistance at a given frequency) will be correspondingly higher, even when the coil is adjacent to the functional material.

[0028] Simultaneously, due to the permeability or saturation flux of the pole shoes, the pole shoes retain their ability to form and guide magnetic fields, respectively. Furthermore, modulation coils or fast scanning coils arranged close to the functional material can fully benefit from the permeability of the functional material, especially for achieving a high inductance value L of the coil. Note that, generally, the functional material as a whole exhibits soft magnetic properties.

[0029] The reduction in the amount of current required to operate the modulation coil or fast scan coil indirectly lowers the system noise level. Reduced eddy currents in the pole shoes will decrease ohmic heating caused by the pole shoes. Thermal instability and thermal deformation in all sections of the EPR spectrometer that could propagate heat will be reduced due to the reduced total amount of heat generated. Compared to using typical ferrous metal material for the entire nearby pole shoes, the pole shoes, the rest of the magnet system, the modulation coil or fast scan coil, and the microwave resonator will remain cooled or at least significantly cooler.

[0030] Reducing the current in the modulation coil can also directly reduce acoustic vibrations within the modulation coil. Furthermore, reducing eddy currents in the microwave walls caused by the modulation coil can also help reduce acoustic vibrations.

[0031] In summary, noise reduction can be achieved by 3 to 5 times, and sometimes up to 10 times, in practice compared to placing the traditional iron pole shoe near the modulation coil or fast scanning coil in an EPR spectrometer.

[0032] Meanwhile, the magnet system can remain very small, and therefore quite inexpensive (both in terms of construction and operation), because the field of view can be entirely devoted to the probe (including its modulation coil or fast scanning coil). In particular, there does not necessarily need to be a significant gap between the modulation coil or fast scanning coil and the pole shoes in order to minimize losses and noise.

[0033] The magnet (at least one magnet) of the magnet system can be a permanent magnet or a magnet (electromagnet) based on a resistance coil. Preferably, the at least one magnet is a permanent magnet or a permanent magnet combined with a resistance scanning coil.

[0034] Preferably, the magnet system includes a pair of magnets (permanent magnets or magnet coils) combined with a pair of pole shoes made of functional material and a pair of modulation coils or fast scanning coils.

[0035] The functional material has the required low electrical conductivity, at least in a plane perpendicular to the polar axis. Furthermore, the functional material has the high saturation magnetic flux, at least along the polar axis. Note that the functional material is generally isotropic, i.e., the electrical conductivity and saturation magnetic flux are the same regardless of orientation. Note that the functional material should be quasi-homogeneous with respect to the size proportions contained in the magnet system.

[0036] Typically, functional materials incorporate some structure (e.g., particles) of (primarily) ferromagnetic or subferromagnetic materials, resulting in sufficient permeability (typically at least 100 μ for low H values, and often at least 500 μ for overall functional materials). rel If the (first) material is conductive (as in the case of a ferromagnetic metal), the functional material may include a second electrically insulating material, thereby preventing the penetration of the structure (e.g., particles) of the first material, resulting in low overall material conductivity.

[0037] A magnet system typically includes a ferromagnetic yoke structure that connects the magnet (at least one magnet) to one or more pole pieces. The pole pieces are the ends of the magnet system facing the field of view or the probe. It is important to note that in the case of a pair of pole pieces, the field of view corresponds to the air gap between the pole pieces; in the case of a single pole piece, the field of view corresponds to the adjacent air space in front of the pole piece. Typically, one or more pole pieces are attached to the yoke structure, for example, using screws. The pole pieces often have a specific shape to homogenize the (background) magnetic field in the field of view. A typical magnet system also includes at least one, preferably two, scanning coils, which are typically wound around the yoke structure for (slowly) scanning the magnetic field generated by the magnet system (also called a "static field" because of the slow change).

[0038] A microwave resonator comprises a cavity surrounded by metal walls, in which a sample to be measured can be arranged. The microwave resonator is connected to a microwave source for applying microwave radiation (typically with a fixed frequency) to the microwave resonator.

[0039] Typically, the probe includes two modulation coils or fast scan coils (or even two modulation coils and two fast scan coils), the two modulation coils or fast scan coils being arranged symmetrically with respect to the microwave resonator; then each of the pair of pole shoes faces the modulation coil or fast scan coil (or both), and at least a portion of each pole shoe facing the corresponding modulation coil or fast scan coil is made of a functional material.

[0040] If the probe includes only one modulation coil or fast scan coil, then only one pole piece faces the modulation coil or fast scan coil, and only at least a portion of the pole piece facing the corresponding modulation coil or fast scan coil is made of a functional material.

[0041] Typically, if the coil must provide field modulation for the CW EPR method, the typical arrangement is a parallel LC tuner circuit, where the resonant frequency is between 5 kHz and 200 kHz.

[0042] Typically, one or more pole pieces face the field of view and have substantially flat surfaces oriented perpendicular to the polar axis. In the case of a pair of opposing pole pieces, the polar axis runs in a straight line from pole piece to pole piece across the field of view. The magnetic field generated by the magnet system and aligned with the polar axis is substantially homogeneous in the region of the microwave resonator (typically with a homogeneity of 100 ppm or better).

[0043] Preferred embodiments of the present invention

[0044] In a preferred embodiment of the EPR spectrometer of the present invention, the conductivity σ f 10 3 West / meter or smaller, and BS f The value is 0.5 Tesla or greater. Under these conditions, the eddy currents in one or more pole shoes can be further reduced, and exceptionally high magnetic field strengths can be established in the field of view.

[0045] In a preferred embodiment, the functional material is isotropic. This makes the fabrication of the functional materials and surface portions of the pole shoe, or the entire pole shoe, simple and easy to install. A specific orientation is not required, and undesirable distortion due to misalignment can be minimized.

[0046] In another preferred embodiment, the functional material comprises particles of ferromagnetic or subferromagnetic material dispersed in an electrically insulating matrix material. In particular, the functional material comprises soft magnetic particles of ferrite, metal, or metal alloy dispersed in a polymer matrix material. These materials can combine low electrical conductivity, high magnetic permeability, and saturation magnetic flux with isotropic properties. The electrical conductivity σ of the electrically insulating matrix material... 基体 10 4 10 sieves / meter or smaller, preferably 10 sieves / meter or smaller. 3 1000 A / m or less. Polymers are particularly inexpensive and easy to handle. Soft magnetic materials, specifically soft magnetic particles, have a coercive field strength of 1000 A / m or less. Soft magnetic materials also typically have a relative permeability of μ. rel At least 100 or even at least 500, typically 10 < μ rel <10 5 , or 100 < μ rel <10 5 .

[0047] In an advantageous embodiment, each of the pole shoes, having a modulation coil or fast scanning coil arranged between the pole shoe and the microwave resonator, is made entirely of a functional material. This is easy to manufacture and generally allows for better control over the shaping of the magnetic field in the field of view.

[0048] In an alternative preferred embodiment, for each pole shoe having a modulation coil or fast scanning coil arranged between the pole shoe and the microwave resonator, only a portion of the pole shoe facing the modulation coil or fast scanning coil is made of a functional material, and the remaining portion of the pole shoe that holds the functional material is made of a different material, specifically, a metallic material. This can reduce manufacturing costs where functional materials are expensive. It also simplifies the process of securing the portion (surface portion) of the pole shoe to the remaining portion (retainer), and simultaneously simplifies securing the pole shoe to the yoke structure. In the simplest case, the portion (made of functional material) can be glued to the remaining portion of the pole shoe (or the retainer).

[0049] In a preferred further development of the above embodiments, the portion of the pole shoe has a thickness T measured along the polar axis.

[0050] Where T ≥ 0.5 mm, preferably T ≥ 1.0 mm,

[0051] And / or wherein T ≤ 12.0 mm, preferably T ≤ 6.0 mm. With these dimensions, good eddy current reduction can be achieved with a relatively small amount of functional material, which is typically expensive.

[0052] In another further development, the portion of the pole shoe overlaps at least in a plane perpendicular to the polar axis with the entire modulation coil or fast scanning coil, preferably wherein the portion of the pole shoe extends beyond the modulation coil or fast scanning coil in the plane perpendicular to the polar axis. This optimizes eddy current reduction in the pole shoe. By making the functional material of the portion (surface portion) overlap with or even extend beyond the entire microwave resonator in a plane perpendicular to the polar axis, the (background) magnetic field can be homogenized within the microwave resonator; the material transition between the functional material and the remaining pole shoe material has little or no effect on the volume of the microwave resonator.

[0053] A further advantageous development specifies that the portion of the pole shoe is held in place by a press-fit insert within a frame structure of the remaining portion of the pole shoe, the frame structure being particularly a recess. This is easy to manufacture and facilitates good field homogeneity. The frame structure applies a clamping force to the insert, thereby holding the insert within the frame structure. The clamping force is typically in a plane perpendicular to the pole axis and compresses the insert. Typically, the pole shoe forms a recess with a closed circumferential edge surrounding the portion made of a functional material. Preferably, the remaining portion of the pole shoe is flush with the insert. Alternatively, the frame structure comprises only a plurality of opposing frame elements (protrusions) that clamp the insert.

[0054] In another further development, the aforementioned portion of the pole shoe is glued to the remaining portion of the pole shoe. This is particularly simple to implement.

[0055] A preferred further development specifies that the remainder of the pole shoe, and the portion not comprising the pole shoe, includes one or more openings through which a corresponding screw protrudes, wherein the screw is screwed into the yoke structure or permanent magnet of the magnet system. The threaded connection is particularly reliable and robust. Here, openings for the screw are required in the remainder, but not in the portion made of functional material (the surface portion), thus allowing for the easy use of brittle functional materials.

[0056] In a preferred embodiment, each modulation coil or fast scan coil is fixed to the pole piece it faces. This allows the modulation coil or fast scan coil to be very close to the pole piece, thereby optimizing the use of the space near the pole piece that is best suited for EPR measurements, particularly the space between the two opposing pole pieces (field of view or "air gap"). Alternatively, all modulation coils or fast scan coils can be fixed to the microwave resonator.

[0057] A preferred embodiment is one in which the EPR spectrometer comprises a pair of opposing pole shoes and a field of view having a width WAG along the polar axis, wherein 10 mm ≤ WAG ≤ 100 mm, preferably 20 mm ≤ WAG ≤ 60 mm. This compact design can be used according to the invention without the risk of inducing significant eddy currents in the pole shoes, thus resulting in low power consumption and low noise levels.

[0058] A particularly preferred embodiment is one in which the following applies to the distance DPC along the polar axis between the corresponding pole shoe and the modulation coil or fast scan coil it faces:

[0059] 0≤DPC≤2.0mm,

[0060] Preferably, 0 ≤ DPC ≤ 1.0 mm.

[0061] A preferred distance is 0 ≤ DPC ≤ 0.5 mm. These small distances allow for efficient use of the field of view without significant eddy currents caused by modulation or rapid scanning coils in the pole shoes.

[0062] The use of the EPR spectrometer of the present invention as described above in EPR measurements is also within the scope of the invention, wherein the sample is arranged in a microwave resonator, wherein a magnet system generates a magnetic field in the field of view along a magnetic axis, and wherein at least one modulation coil or fast scanning coil generates a time-varying additional magnetic field in the field of view along a polar axis, specifically wherein the time-varying additional magnetic field has a frequency between 5 kHz and 200 kHz. The additional magnetic field in the field of view will not induce eddy currents in the pole shoes or multiple pole shoes, or will only induce negligible eddy currents, thereby achieving low power consumption and low noise levels.

[0063] Further advantages can be drawn from the description and accompanying drawings. The features mentioned above and below can be used individually or in any combination according to the invention. The mentioned embodiments should not be construed as an exhaustive enumeration, but rather as exemplary features used to describe the invention. Attached Figure Description

[0064] Figure 1 A schematic cross-sectional view of a first embodiment of the EPR spectrometer of the present invention having a pair of modulation coils is shown;

[0065] Figure 2 A schematic cross-sectional view of a second embodiment of the single-sided EPR spectrometer of the present invention is shown, the spectrometer having a pole shoe and a single modulation coil;

[0066] Figure 3a This is a cross-sectional schematic diagram of the pole shoe used in this invention, which is attached to the magnetic yoke structure by adhesive bonding, wherein the pole shoe is made entirely of functional materials;

[0067] Figure 3b A schematic cross-section of the pole shoe used in this invention is shown, which is attached to the magnetic yoke structure by a threaded connection, wherein the pole shoe includes a portion made of a functional material glued to the rest of the pole shoe made of iron;

[0068] Figure 3c A schematic cross-section of the pole shoe for use in the present invention is shown, which is attached to the magnetic yoke structure by a threaded connection, wherein the pole shoe includes a portion made of a functional material that is clamped into a recess in the remaining portion of the pole shoe made of iron.

[0069] Figure 4a A schematic cross-section of the field of view of the EPR spectrometer of the present invention is shown, wherein a pair of modulation coils are arranged at a distance very close to a portion of the functional material of the pole shoe;

[0070] Figure 4bA schematic cross-section of the field of view of the EPR spectrometer of the present invention is shown, wherein a pair of modulation coils are directly attached to a portion of the pole shoe made of functional material;

[0071] Figure 5a A schematic cross-sectional view of the field of view of the EPR spectrometer is shown when using ferrous metal pole shoes at a short distance from the pole shoes (unlike the present invention).

[0072] Figure 5b shows a schematic cross-section of the field of view of an EPR spectrometer when using ferrous metal pole shoes (prior art) at a long distance from the pole shoes;

[0073] Figure 6 Using adjacent conventional ferrous metal pole shoes (dashed lines) and pole shoes made of the functional material according to the invention (solid curves), the relationship between impedance (ohms) and excitation frequency is shown for different distances of the modulation coil from the pole shoes, and the resonant frequency in the circuit including the modulation coil and capacitor is also shown; various curve markings indicate the distance between the coil and the polar material.

[0074] Figure 7 The relationship between the Q factor (which indicates the loss in the polar material) of the modulation coil and the distance of the modulation coil from the pole shoe is shown for resonant circuits using conventional ferrous metal pole shoes (dashed lines) and pole shoes made of functional materials (solid curves).

[0075] Figure 8 A schematic cross-section of a portion of the pole shoe used in this invention, made of a functional material, is shown. Detailed Implementation

[0076] Figure 1 A first embodiment of the EPR spectrometer 1 of the present invention is schematically shown. The EPR spectrometer 1 includes a magnet system 2 and a probe 3.

[0077] The magnet system 2 here comprises three magnets 4, namely permanent magnets 5 and two electromagnets 6a and 6b. The magnet system 2 also includes a yoke structure 7 made of ferromagnetic material, typically based on an iron alloy and having a generally C-shape, for guiding and enhancing the generated magnetic flux. The yoke structure may alternatively be shaped as a window frame, a can core, or any other suitable structure (not shown). Here, the electromagnets 6a, 6b, or their windings, are arranged on the upper and lower arms of the yoke structure 7, respectively. Figure 1 On the right side, at the opposite ends of the magnetic yoke structure 7, the magnetic yoke structure 7 is equipped with pole shoes 8a and 8b.

[0078] The permanent magnet 5 is integrated here onto the back of the yoke structure 7 (in Figure 1 (Middle left side).

[0079] Magnet system 2 generates a magnetic field (also called a background magnetic field, static magnetic field, or B0 field) in a field of view 9 between pole shoes 8a and 8b, which corresponds here to the air gap between the opposing pole shoes 8a and 8b. The magnetic field in field of view 9 is aligned with the polar axis PA, which is vertical and perpendicular to the surfaces 12a and 12b (“inner surfaces” 12a and 12b) of the pole shoes 8a and 8b facing field of view 9. Electromagnets 6a and 6b can be used to slowly change (or “scan”) the magnetic field during EPR measurements by means of appropriate current control; therefore, electromagnets 6a and 6b are also referred to as scanning coils.

[0080] In the field of view 9, a probe 3 is arranged, which here includes a microwave resonator 10, a pair of modulation coils 11a and 11b, and a housing 13 that houses the microwave resonator 10 and the modulation coils 11a and 11b. Inside the microwave resonator 10, which has metal walls, a sample volume portion 14 is arranged for arranging the sample 14a to be measured. Microwave radiation (also referred to as the B1 field) can typically be coupled to and from the microwave resonator 10 via waveguides (not shown here for simplicity) attached to the microwave source and the microwave detector.

[0081] In the illustrated embodiment, one of the modulation coils 11a, 11b is arranged between each of the pole shoes 8a, 8b and the microwave resonator 10. The pair of modulation coils 11a, 11b can generate an additional time-varying magnetic field along the polar axis PA, at least in the sample volume portion 14.

[0082] Furthermore, in the illustrated embodiment, the portions 15a, 15b of each pole shoe 8a, 8b facing the modulation coils 11a, 11b are made of materials with low conductivity (e.g., where σ0 = 0). f =10 2 (West / meter) and has a high saturation flux density (e.g., BS) f It is made of functional materials (represented by dots) with a strength of 0.5 Tesla.

[0083] The functional materials 15a and 15b prevent or at least minimize eddy current induction in the pole shoes 8a and 8b caused by the time-varying magnetic field generated by the modulation coils 11a and 11b. Note that the induced eddy currents not only generate ohmic losses, thus reducing the efficiency of the LC resonant cavity, but also generate a magnetic field opposite to the time-varying magnetic field that causes the eddy currents, thereby reducing the inductance of the coils. As a dual result of the application of the functional materials, since the losses caused by eddy currents in the polar materials are prevented or minimized, and only the inductance of the coils is advantageously increased, the current in the modulation coils 11a and 11b can be selected to a relatively small value to achieve the desired time-varying magnetic field strength at the location of the EPR sample, which reduces power consumption by a square factor. A first important result is that the acoustic vibration energy caused by the current in the coils 11a and 11b, as well as the ohmic losses as heat energy in the pole shoes 8a and 8b and the coils 11a and 11b, are also reduced, which leads to an advantageous reduction in noise in the EPR measurement on sample 14a. The second important result is that, in the compact design of the EPR spectrometer 1, the modulation coils 11a and 11b can be placed close to the pole shoes 8a and 8b, and higher performance and cost scores are achieved.

[0084] It should be noted that, according to the present invention, a fast scanning coil may be used instead of the modulation coils 11a and 11b, or in addition to the modulation coils 11a and 11b; the above description applies in a similar manner.

[0085] exist Figure 2 The image shows a second embodiment of the EPR spectrometer 1 of the present invention, which is a single-sided EPR spectrometer. This embodiment includes a magnet system 2 that generates a magnetic field in the probe 3 only from one side of the field of view 9 (in this case, from the top side). Arranging the magnet system 2 only on one side of the probe 3 is useful in very compact EPR devices such as chip-based EPR sensors.

[0086] exist Figure 2 In one embodiment, the probe 3 includes only one modulation coil 11a, which is positioned above the microwave resonator 10. In this case, it is sufficient to equip only one pole shoe 8a, positioned on the top side, with a component 15a made of functional material. The magnet system 2 can be composed of an electromagnet or permanent magnet combined with a scanning coil for CW applications.

[0087] However, a second pole shoe (not shown) can be arranged on the opposite side of pole shoe 8a, the second pole shoe being entirely made of materials with high conductivity (>>10). 4Made of conventional ferrous metal material (W / m). The arrangement of the second pole piece increases the homogeneity of the magnetic field in the field of view 9. The magnet system 2 may also be equipped with a yoke structure for returning the magnetic field to the magnet. The opposing second pole piece (not shown) is at least separated from the modulation coil 11a by the thickness of the microwave resonator 10 in the direction of the polar axis PA, so the local intensity of the time-varying magnetic field generated by the modulation coil 11a is generally much lower at the surface of the opposing second pole piece compared to the surface 12a of the pole piece 8a.

[0088] Figure 3a A first type of pole shoe 8a for use with the present invention is shown, for example in... Figure 1 It is used in the EPR spectrometer shown.

[0089] In the type shown, the pole shoe 8a is made entirely of functional material (indicated by dots, but this also applies to other examples). The pole shoe 8a is here glued to the end of the magnetic yoke structure 7.

[0090] Figure 3b A second type of pole shoe 8a is shown for use with the present invention, for example in... Figure 1 It is used in the EPR spectrometer shown.

[0091] Here, the pole shoe 8a includes a portion 15a made of a functional material and the remaining portion 16 (also called a retainer) made of a soft magnetic metallic material (here, iron). The portion 15a made of the functional material is glued to the remaining portion 16.

[0092] The remaining portion 16 of the pole shoe 8a includes an opening 17 through which a screw 18 protrudes. The screw 18 is screwed into a thread 19 located in the magnetic yoke structure 7.

[0093] Figure 3c A third type of pole shoe 8a is shown for use with the present invention, for example in... Figure 1 It is used in the EPR spectrometer shown.

[0094] Here, the pole shoe 8a includes a portion 15a made of a functional material and the remaining portion 16 (also called a retainer) made of a soft magnetic metallic material (here, iron). The remaining portion 16 forms a frame structure 20, which here has a recess with a circumferential edge into which the portion 15a has been pressed. Thus, the frame structure 20, which can be elastically deployed to a certain extent, applies some pressure to the component 15a along a clamping direction 21 perpendicular to the pole axis PA.

[0095] The remaining portion 16 of the pole shoe 8a also includes an opening 17 through which a screw 18 protrudes. The screw 18 is screwed into a thread 19 located in the magnetic yoke structure 7. The portion 15a here covers the screw 19 and the opening 17.

[0096] Figure 4a The field of view 9 of the EPR spectrometer of the present invention is illustrated by way of example, which is similar to... Figure 1 The embodiment shown.

[0097] In the example shown, there is a non-zero distance DPC between the pole shoe 8a and the modulation coil 11a it faces in the direction of the polar axis PA. Typically, this distance DPC is 2 mm or less. The distance DPC can be measured between the flat surface 12a of the pole shoe 8a or its portion 15a and the farthest part of the modulation coil 11a protruding towards the pole shoe 8a.

[0098] Furthermore, the portion 15a, made of functional material, has a thickness T measured along the polar axis PA. The thickness T is typically in the range of 1 mm to 6 mm. Such a thickness T is sufficient to reliably block eddies in the pole shoe 8a.

[0099] It should be noted that in the direction perpendicular to the polar axis PA, part 15a extends beyond the modulation coil 11a, and also extends beyond the microwave resonator 10.

[0100] The width WAG of the field of view 9 along the polar axis PA (i.e., the width of the air gap between the pole shoes 8a and 8b) is typically in the range of 10 mm ≤ WAG ≤ 100 mm, and preferably in the range of 20 mm ≤ WAG ≤ 60 mm.

[0101] Figure 4b The field of view 9 of the EPR spectrometer of the present invention is shown in another example.

[0102] In the example shown, the modulation coils 11a and 11b are directly attached to the pole shoes 8a and 8b; in other words, the distance along the polar axis PA between the pole shoes 8a and 8b and the modulation coils 11a and 11b they face is zero. This results in a very compact magnet system design.

[0103] As another particular feature, in the example shown, on the back of each part 15a, 15b made of functional material, a foil 22 made of a highly conductive material (e.g., copper) is attached, for example, the foil has a 10 7 A conductivity of 100 s / m or greater. In this way, the remaining eddy currents in the pole piece 8a can be captured in a defined manner, particularly at a relatively far distance from the modulation coils 11a, 11b.

[0104] Therefore, generally speaking, according to the present invention, a conductivity of 10 can be arranged on the side of at least a portion 15a, 15b of the pole shoes 8a, 8b away from the modulation coils 11a, 11b or the fast scanning coil. 7 A layer of highly conductive material with a diameter of 1000 m or more, particularly wherein the layer comprises, for example, a foil 22 made of copper.

[0105] exist Figure 5a In the middle, a similar example is shown. Figure 1 The field of view of the EPR spectrometer shown is shown in which the pole pieces 108a and 108b are not equipped with the functional material according to the invention, but are made of conventional iron material.

[0106] The magnet system 102 generates a background field B0, which is superimposed with a time-varying magnetic field 123 generated by the modulation coils 111a and 111b.

[0107] When conventional iron pole shoes 108a and 108b are used at the ends of the magnetic system 102, the time-varying magnetic field 123 generated by the modulation coils 111a and 111b induces eddy currents 124 in the nearby pole shoes 108a and 108b. These eddy currents 124 generate local magnetic fields opposite to the time-varying magnetic field 123, thus requiring an increase in the current intensity in the modulation coils 111a and 111b to achieve the desired field strength, at least within the sample volume portion 114. Furthermore, the pole shoes 108a and 108b become hot due to ohmic heating, and this heat can propagate throughout the setup, particularly into the modulation coils 111a and 111b and the microwave resonator 110, causing them to detune.

[0108] To avoid eddy currents in the pole shoes 108a and 108b, the width WAG' of the field of view 109 can be increased and the pole shoes 108a and 108b can be positioned at a greater distance DPC' from the modulation coils 111a and 11b, as shown in Figure 5b. However, to obtain the same magnetic field strength in the field of view 109 as before, a larger magnetic system 102 is typically required, which significantly increases the cost of the EPR spectrometer.

[0109] To demonstrate the benefits of this invention, a resonant circuit with a capacitor and modulation was fabricated, and the modulation coil was placed near a conventional ferrometallic pole piece or a pole piece made of (entirely) functional material, as this is an option of this invention. As the functional material, an epoxy resin with non-permeable ferrometallic particle inclusions (resistivity 0.5*10⁻⁶) has been used. 4 (Ohm*cm, saturation flux 2.03 Tesla).

[0110] Figure 6 The relationship between the excitation frequency (in kilohertz, kHz) on the horizontal axis and the measured impedance of the resonant circuit (in ohms) on the vertical axis is plotted. Dashed lines represent results using conventional iron pole shoes, and solid lines represent results using pole shoes made with the functional materials of this invention. The distance from the modulation coil to the pole shoe is 0 mm for the diamond-shaped markings, 2.5 mm for the square markings, 4 mm for the circular markings, and 6 mm for the triangular markings.

[0111] from Figure 6 As can be seen, for the iron pole shoe, the resonance curve (on the right) becomes flatter as the distance decreases. This further reduction in distance is a strong indication of increased eddy current damping in the iron pole shoe. On the other hand, for the pole shoe made of functional materials (on the left), the resonance curves are all sharp and almost independent of distance.

[0112] The inductance of the modulation coil is influenced by the surrounding material. Materials that allow for considerable eddy currents in the vicinity tend to decrease inductance, while materials with a ferromagnetic dielectric constant tend to increase inductance. For experiments with iron pole shoes, these two effects largely cancel each other out, while for experiments with pole shoes equipped with functional materials, the inductance increases significantly. As a result, the resonant frequency of experiments using pole shoes with functional materials is significantly lower than that of experiments using iron pole shoes (approximately 115 kHz for conventional pole shoes and approximately 90 kHz for the pole shoes of this invention).

[0113] Then for Figure 6 The resonance curve determines the Q factor. A low Q factor directly indicates strong damping, and vice versa.

[0114] exist Figure 7 In the diagram, the Q factor (dimensionless) is plotted on the vertical axis, while the horizontal axis represents the distance (in millimeters) from the modulation coil to the pole shoe in each case. The Q factor can be determined by Q = f0 / Δf, where f0 is the resonant frequency (the position of maximum amplitude in the resonance curve) and Δf is the width of the resonance curve relative to the maximum value under the condition of 3dB attenuation.

[0115] For the conventional iron pole shoe setup (dashed line), the Q factor is strongly dependent on distance, increasing from approximately 2.5 at zero distance to approximately 6.5 at a distance of 6.5 mm. In contrast, for the pole shoes of functional materials, the Q factor remains roughly constant between 7.5 and 8 for all studied distances.

[0116] Figure 8 The functional material in portion 15a of the pole shoe is shown. This functional material comprises a plurality of particles 23 of a ferromagnetic or ferrimagnetic material (e.g., iron), distributed within an electrically insulating matrix material 24, for example, made of a polymer, such as a polymer resin. The particles 23 do not permeate; that is, they do not form chains connecting the particles 23, but are isolated from each other by the matrix material 24. Therefore, the conductivity of the matrix material 24 dominates the conductivity of the functional material. However, the particles 23 can contribute to the overall permeability of the functional material in proportion to their proportion in the functional material. When the particles 23 are homogeneously distributed in the matrix material 24, the functional material exhibits isotropic electrical and magnetic properties.

[0117] List of reference numerals

[0118] 1 EPR spectrometer

[0119] 2 Magnet System

[0120] 3 probes

[0121] 4. Magnets

[0122] 5 permanent magnets

[0123] 6a, 6b Electromagnets

[0124] 7. Magnetic yoke structure

[0125] 8a, 8b Extreme Boots

[0126] 9 Field of view

[0127] 10 Microwave Resonators

[0128] 11a, 11b Modulation coils

[0129] Surfaces 12a and 12b

[0130] 13. Outer shell

[0131] 14 Sample volume

[0132] 14a Sample

[0133] 15a, 15b The functional material components of the extreme boots

[0134] 16. The rest of the extreme boots

[0135] 17 Opening

[0136] 18 screws

[0137] 19 Thread

[0138] 20. Frame Structure

[0139] 21 Clamping direction

[0140] 22 foil

[0141] 102 Magnet System

[0142] 108a, 108b Extreme Boots

[0143] 109 Field of View

[0144] 111a, 111b Modulation coils

[0145] 114 Sample volume

[0146] 123 Time-varying magnetic field

[0147] 124 Vortex

[0148] The distance between the DPC pole shoe and the (modulation or fast scan) coil

[0149] The distance between the DPC' pole shoe and the (modulation or fast scan) coil.

[0150] The thickness of the functional material portion of the T-boot

[0151] PA Polar Axis

[0152] WAG Field of View Width (along the polar axis)

[0153] WAG' Field of View Width (along the polar axis)

Claims

1. An EPR spectrometer (1), It has the following characteristics: -Magnetic system (2), the magnetic system comprising at least one magnet (4) and at least one pole shoe for generating a magnetic field in a field of view (9) in front of the at least one pole shoe, in, The magnetic field is generated along the polar axis (PA); - Probe (3), the probe comprising a microwave resonator (10) and at least one modulation coil (11a, 11b) or fast scanning coil for generating an additional time-varying magnetic field aligned along the polar axis (PA), The probe (3) is arranged in the field of view (9). Furthermore, a corresponding modulation coil (11a, 11b) or fast scanning coil is arranged between the microwave resonator (10) and the corresponding pole shoe; The EPR spectrometer (1) is configured in a parallel LC tuning circuit arrangement in continuous wave EPR, wherein the additional time-varying magnetic field with a frequency between 5 kHz and 200 kHz is generated during EPR measurement using at least one modulation coil (11a, 11b) or a fast scan coil. Wherein, for each pole piece having a modulation coil (11a, 11b) or a fast scanning coil arranged between the pole piece and the microwave resonator (10), at least a portion (15a, 15b) of the pole piece facing the modulation coil (11a, 11b) or the fast scanning coil is composed of a 10 4 Conductivity σ per sieve or less f And it has a saturation magnetic flux density of 0.2 Tesla or greater (BS). f Made of functional materials, Furthermore, the following applies to the distance DPC along the polar axis (PA) between the corresponding pole shoe and the modulation coil (11a, 11b) or fast scan coil that the pole shoe faces: 0≤DPC≤2.0mm.

2. The EPR spectrometer (1) according to claim 1, characterized in that, The magnet system (2) includes at least one magnet (4) and a pair of pole shoes for generating a magnetic field in the field of view (9) between the pole shoes.

3. The EPR spectrometer (1) according to claim 1, characterized in that, σ f 10 3 West / meter or smaller, and BS f It is 0.5 Tesla or more.

4. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, The functional material is isotropic.

5. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, The functional material includes particles (23) of ferromagnetic or subferromagnetic material dispersed in an electrically insulating matrix material (24).

6. The EPR spectrometer (1) according to claim 5, characterized in that, The functional material includes soft magnetic particles of ferrite, metal, or metal alloy dispersed in a polymer matrix material.

7. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, For each pole piece having a modulation coil (11a, 11b) or a fast scanning coil arranged between the pole piece and the microwave resonator (10), the pole piece is made entirely of the functional material.

8. The EPR spectrometer (1) according to claim 1, characterized in that, For each pole shoe having a modulation coil (11a, 11b) or a fast scanning coil arranged between the pole shoe and the microwave resonator (10), only a portion (15a, 15b) of the pole shoe facing the modulation coil (11a, 11b) or the fast scanning coil is made of the functional material, while the remaining portion (16) of the pole shoe to which the portion (15a, 15b) is fixed is made of a different material.

9. The EPR spectrometer (1) according to claim 8, characterized in that, The different materials mentioned are metallic materials.

10. The EPR spectrometer (1) according to claim 8, characterized in that, The portions (15a, 15b) of the pole shoe have a thickness T measured along the polar axis (PA). Where T≥0.5mm, And / or T≤12.0mm.

11. The EPR spectrometer (1) according to claim 10, characterized in that, T≥1.0mm and / or T≤6.0mm.

12. The EPR spectrometer (1) according to claim 8 or 10, characterized in that, The portions (15a, 15b) of the pole shoe overlap at least the entire modulation coil (11a, 11b) or fast scan coil in a plane perpendicular to the pole axis (PA).

13. The EPR spectrometer (1) according to claim 12, characterized in that, The portions (15a, 15b) of the pole shoe extend beyond the modulation coil (11a, 11b) or the fast scan coil in the plane perpendicular to the pole axis (PA).

14. The EPR spectrometer (1) according to any one of claims 8 to 11, characterized in that, The portions (15a, 15b) of the pole shoe are inserts held in the frame structure (20) of the remaining portion (16) of the pole shoe by press fitting.

15. The EPR spectrometer (1) according to claim 14, characterized in that, The frame structure is a recess.

16. The EPR spectrometer (1) according to any one of claims 8 to 11, characterized in that, The portions (15a, 15b) of the pole shoe are glued to the remaining portions (16) of the pole shoe.

17. The EPR spectrometer (1) according to any one of claims 8 to 11, characterized in that, The remaining portion (16) of the pole shoe, and the portion (15a, 15b) of the non-pole shoe, includes one or more openings (17), through which a corresponding screw (18) protrudes, wherein the screw (18) is screwed into the yoke structure (7) or permanent magnet (5) of the magnet system (2).

18. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, Each modulation coil (11a, 11b) or fast scan coil is fixed to the pole shoe it faces.

19. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, The EPR spectrometer (1) includes a pair of opposing pole shoes and the field of view (9) has a width WAG along the polar axis (PA). Where 10mm≤WAG≤100mm.

20. The EPR spectrometer (1) according to claim 19, characterized in that, 20mm≤WAG≤60mm.

21. The EPR spectrometer (1) according to any one of claims 1 to 3, characterized in that, The following applies to the distance DPC along the polar axis (PA) between the corresponding pole shoe and the modulation coil (11a, 11b) or fast scan coil that the pole shoe faces: 0≤DPC≤1.0mm.

22. The EPR spectrometer (1) according to claim 21, characterized in that, 0≤DPC≤0.5mm.

23. Use of the EPR spectrometer (1) according to any one of the preceding claims in EPR measurements, wherein a sample (14a) is arranged in the microwave resonator (10), wherein the magnet system (2) generates a magnetic field in the field of view (9) along the polar axis (PA), and wherein at least one modulation coil (11a, 11b) or fast scan coil generates an additional time-varying magnetic field in the field of view (9) along the polar axis (PA).

24. The use according to claim 23, characterized in that, The frequency of the additional time-varying magnetic field is between 5 kHz and 200 kHz.

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