Device for the excitation of a magnetic or at least magnetisable sample and method for the reduction of penetration

Abstract

The invention relates to a device and a method for the excitation of a sample by means of at least one time-varying magnetic field (110), comprising a current source (400) for generating a time-varying current, a transmitting coil (300) acting on a sample volume (102) for receiving a sample, for generating a time-varying transmitting magnetic field (110) as a function of the current generated in the transmitting coil (300) by the current source (400) connected to the transmitting coil (300), a measuring coil system (103, 104, 105) having a receiving coil (104) for generating an induction voltage that can be induced in the receiving coil (104) as a function of a sample magnetic field and the transmitting magnetic field (110), and having at least one compensation coil (103, 105), which is connected in series with the receiving coil (104) in reverse polarity, for at least partial compensation of the induction voltage generated in the receiving coil (104) by the transmitting magnetic field (110), at least one measuring electronics (500), with which the induction voltage generated in the measuring coil system (103, 104, 105) can be measured, at least one tuning unit (100 / 101, 200 / 201) that is electrically coupled without contact to the measuring coil system (103, 104, 105) and / or the transmitting coil (300) by at least one coupling element (101) and with which the at least partial compensation of the induction voltage generated in the receiving coil (300) by the transmitting magnetic field (103) can be influenced, wherein the tuning unit (100 / 101) comprises an element, the impedance of which is changed at least once with respect to an original impedance, or the impedance of which can be adjusted several times, in particular reversibly.

Description

[0001] Device for the excitation of a magnetic or at least magnetizable sample and method for punch-through reduction

[0002] The invention relates to a device for exciting a sample, in particular a magnetic or at least magnetizable sample, in particular particles, by means of at least one time-varying, in particular oscillating, magnetic field, comprising a current source for generating a time-varying current, a transmitting coil acting on a sample volume for receiving a sample for generating a time-varying transmitting magnetic field as a function of the current generated in the transmitting coil by the current source connected to the transmitting coil, a measuring coil system with a receiving coil for generating an induction voltage that can be induced in the receiving coil as a function of a sample magnetic field and the transmitting magnetic field, and with at least one compensation coil that is connected in series with the receiving coil in reverse polarity,for at least partially compensating the induction voltage generated in the receiving coil by the transmitting magnetic field, at least one measuring electronics unit with which the induction voltage generated in the measuring coil system can be measured, in particular stored and evaluated, at least one tuning unit that is electrically coupled to the measuring coil system and / or the transmitting coil via at least one coupling element and with which the at least partial compensation of the induction voltage generated in the receiving coil by the transmitting magnetic field can be influenced. Preferably, in one possible application, the transmitting coil acting on a sample volume for receiving a sample is arranged around a sample volume.

[0003] The invention also relates to a method for reducing the induction voltage generated by the transmitting magnetic field in the measuring coil system of such a device, in particular for reducing the penetration in such a device.

[0004] The device of the invention is preferably a device for performing Magnetic Particle Imaging (MPI) or Magnetic Particle Spectroscopy (MPS).

[0005] Using this principle, concentrations of magnetic or at least magnetizable particles, especially nanoparticles, such as preferably iron oxide, can be measured in a test volume. This test volume can be located outside a transmitting coil or inside a transmitting coil, in particular on the axis of a transmitting coil, as is known and also the case with the invention.

[0006] In the device of the invention, in addition to the transmitting coil, at least one coil arrangement is preferably provided for generating a location-dependent, preferably static magnetic field, in particular with which the measured sample volume can be defined, wherein it can preferably be provided that the coil arrangement can be displaced in order to spatially displace the sample volume.

[0007] In the device of the invention, preferably alternatively or cumulatively to the aforementioned embodiment, at least one magnet, preferably a pair of magnets, is additionally provided for generating a location-dependent, static magnetic field, which assumes the value zero at a point or along a path, preferably in the form of a line, in particular within the measured sample volume and assumes values ​​other than zero outside of this point or this path. Here, too, it can preferably be provided that the at least one magnet, preferably a permanent magnet, in particular the pair of magnets, is displaceable in order to spatially displace the sample volume. The sample magnetic field, like the transmitting magnetic field, represents a varying magnetic field, wherein the sample magnetic field is the magnetic field generated by the sample, e.g., which is generated by the movement of magnetic particles or by the magnetization of magnetizable material (e.g.sample), is generated by e.g. the varying transmitting magnetic field of the transmitting coil acting on the sample or e.g. by a macroscopic movement of the sample within a static magnetic field.

[0008] In the invention, the receiving coil is preferably arranged around the sample volume, particularly like the transmitting coil. However, in the case of a "single-sided MPI," it can also be provided that the sample or sample volume is arranged outside the transmitting coil and / or the receiving coil.

[0009] Preferably, the receiving coil is coaxial with the transmitting coil, wherein both coils more preferably overlap at least partially.

[0010] The problem here is that the sample magnetic field is small compared to the transmitting magnetic field and the voltage induced by the sample magnetic field in the measuring coil system is therefore also small compared to the voltage induced by the transmitting magnetic field in the measuring coil system.

[0011] It is therefore difficult to discriminate the induction voltage generated by the sample from the induction voltage generated by the transmitting magnetic field.

[0012] The measuring coil system comprising a receiving coil and at least one compensation coil is also referred to as a gradiometer arrangement. This known coil arrangement ensures that the voltages induced in the receiving coil and the at least one compensation coil by the varying transmitted magnetic field at least partially cancel each other out.

[0013] This process is called punch-through reduction and further causes the induction voltage generated directly by the transmitting magnetic field to be reduced in the measuring coil system compared to the induction voltage generated by the sample, in particular that generated by the particle magnetic field of moving magnetic particles or by the changing magnetization of magnetic / magnetizable particles.

[0014] To achieve this, it is known that the receiving coil and the at least one compensation coil must be adjusted with respect to their relative positions to each other, in particular also to the transmitting coil. In particular, this can change the amplitude of the induction voltage generated in the compensation coil. The goal is that the amplitudes of the induction voltages generated by the transmitting magnetic field in the receiving coil and in the sum of all compensation coils are equal, the induction voltages continue to have opposite signs, and the induction voltages can thus, at least theoretically, cancel each other out.

[0015] Preferably, the at least one compensation coil can be arranged offset in the axial direction relative to the receiving coil, in particular with the receiving coil surrounding the sample volume. Thus, the magnetic field generated by the excited sample acts at least predominantly on the receiving coil, so that the induced voltage from this magnetic field is largely uncompensated by the induced voltage from the at least one compensation coil.

[0016] Furthermore, the at least one compensation coil can be tilted in its axial direction relative to the axial direction of the receiving coil. The offset and / or tilt can be adjustable or at least adjusted to achieve a reduction in penetration with this gradiometer arrangement.

[0017] The induction voltage directly generated by the transmitting magnetic field can typically be attenuated by up to 80 dB in the measuring coil system.

[0018] As mentioned above, the geometrical positional change of the compensation coil(s) and the receiving coil relative to each other essentially only influences the amplitude of the induced voltages. However, due to remaining phase errors / phase differences in the induced voltages from the receiving coil and the at least one compensation coil, a theoretically complete reduction in penetration cannot be achieved in practice.

[0019] However, a further improvement in the reduction of penetration is possible with a coordination unit of the type mentioned above.

[0020] A device of the type mentioned above is known, for example, from publication US 2019 / 0064289 A1. This document describes a device for performing magnetic particle imaging (MPI) or magnetic particle spectroscopy (MPS), in which the tuning unit is designed as a movable, short-circuited coil, which, in one possible embodiment, is magnetically coupled in a contactless manner, particularly inductively, to the measuring coil system and / or the transmitting coil by itself as a coupling element.

[0021] It is mentioned in the publication that the penetration reduction can be tuned and improved even more finely by translation and rotation of the tuning unit, i.e. by movements or changes in position relative to the measuring coil system and / or the transmitting coil, which are also carried out in the case of at least one compensation coil.

[0022] The publication mentioned mentions a penetration reduction of approximately 90 dB.

[0023] The problem here is that, due to the inherently electrically non-changeable tuning unit, even with the known tuning unit, essentially only further, in particular finer, amplitude changes of the induction voltages are possible, but it is still not possible to sufficiently influence occurring phase errors / phase differences, so that the penetration reduction continues to be subject to strict limits.

[0024] Against this background, it is an object of the invention to provide a device and a method for operating a device with which a further optimization of the punch-through reduction can be achieved, in particular with which phase mismatches / phase differences between the induction voltages of the receiving coil and the at least one compensation coil can be reduced.

[0025] Preferably, a device and the method should be usable in Magnetic Particle Imaging (MPI) or Magnetic Particle Spectroscopy (MPS), since all these devices and methods use the excitation of samples, such as particles or other matter in a varying magnetic field.

[0026] This object is achieved according to the invention in a device mentioned at the outset in that the tuning unit comprises an element which is either changed at least once in its impedance compared to an original impedance, or which is adjustable in its impedance several times, in particular reversibly.

[0027] In the method, the object is achieved by reducing a phase mismatch between the induction voltages generated by the transmitting magnetic field in the receiving coil and the at least one compensation coil by changing the impedance of at least one element of the tuning unit.

[0028] The invention has the effect that the tuning unit can not only be changed in its geometric position relative to the measuring coil system and / or the transmitting coil for the purpose of tuning, as in the cited prior art, but moreover the total impedance of the tuning unit can be influenced according to the invention and thus the impedance of the tuning unit as an influenceable electrical variable can contribute to improving the punch-through reduction, because the impedance opens up the possibility of influencing the current flowing in the tuning unit and its phase position to the voltage induced in the measuring coil system.

[0029] It is preferably provided that the aforementioned element of the tuning unit is the at least one coupling element of the tuning unit and / or at least one impedance element present in the tuning unit in addition to the at least one coupling element, in particular which is electrically connected in series or parallel with the at least one coupling element.

[0030] By means of the at least one coupling element of the tuning unit, which preferably enables inductive and / or capacitive coupling, the tuning unit is coupled to the other magnetic fields acting in the device, in particular wherein the coupling is preferably changeable by changing the inductance and / or the capacitance and / or the impedance and / or the geometric position of the at least one coupling element.

[0031] The invention can preferably provide in one possible embodiment that in the tuning unit only the impedance of the at least one coupling element is changed at least once compared to an original impedance or is adjustable several times, in particular reversibly, in particular without providing an additional impedance element.

[0032] If, for example, the adjustment of the impedance of the at least one coupling element compared to an original impedance or the adjustability of the impedance of the at least one coupling element is not sufficient to achieve a sufficient change in the phase mismatch / phase difference to optimize the penetration reduction, or for other reasons, the invention can further preferably provide that in addition to the at least one coupling element, the aforementioned at least one separate impedance element is / will be integrated into the tuning unit.

[0033] Preferably, the coupling element and the impedance element can be positioned separately from each other. The latter is particularly relevant if access for adjustability / adjustment at the location of the coupling element is difficult and / or the components for implementing the impedance cannot be advantageously placed at the location of the coupling element, e.g., due to space requirements, exposure to magnetic fields, the emission of magnetic fields, the ambient temperature, or cooling requirements.

[0034] This at least one impedance element can, for example, have a fixed, non-changeable / changeable impedance, in particular, thus causing a fixed offset of the total impedance of the tuning unit compared to the sole impedance of the at least one coupling element. The invention can thus, for example, provide for influencing the total impedance of the tuning unit by changing the impedance of the at least one coupling element only once compared to its original impedance or by repeatedly, in particular reversibly, changing the impedance of the at least one coupling element.

[0035] However, the invention can also provide that the at least one coupling element in the tuning unit has a fixed, non-changeable / changed impedance and that the total impedance of the tuning unit can be influenced only by at least one change in the impedance of the at least one added impedance element compared to its original impedance or by multiple, in particular reversible, changes in the impedance of the at least one impedance element.

[0036] However, the invention can also preferably provide that both in the at least one coupling element and in the at least one added impedance element, the respective impedance is changed compared to an original impedance or the respective impedance can be changed multiple times, in particular reversibly, in order to influence the overall impedance of the tuning unit.

[0037] By selecting a suitable total impedance of the tuning element, preferably by changing the impedance of the at least one impedance element and / or of the at least one coupling element, which can be done e.g. by changing its ohmic resistance and / or by changing its capacitance and / or by changing its inductance, the ratio of (ohmic) resistance and total capacitance of the tuning unit and / or the ratio of (ohmic) resistance and total inductance of the tuning unit can be influenced, which affects the phase position of the current generated in the tuning unit.

[0038] The current flowing in the tuning unit, in turn, generates a magnetic field correlated with its phase position, which, particularly in the field space of the device, acts on other coils, in particular those of the measuring coil system, preferably on the at least one compensation coil. This allows the phase position of the voltage induced in the at least one compensation coil to be influenced, thus increasing the reduction in penetration.

[0039] With the invention, a penetration reduction of greater than 100 dB can preferably be achieved.

[0040] An impedance element is understood to be an element or an arrangement of several elements which forms an impedance in the tuning unit which differs from the possibly intrinsically present impedance of the at least one coupling element or acts in addition to this in the tuning unit.

[0041] In a preferred embodiment, it is provided that the impedance element and / or the at least one coupling element is changed at least once in terms of impedance compared to an original impedance, or in the alternative example is adjustable multiple times in terms of impedance, in particular reversibly.

[0042] An adjusted impedance element / coupling element is preferably understood to be one whose adjustment produces an impedance that differs from an original impedance of the previously unadjusted impedance element and / or coupling element, in particular the originally manufactured impedance element and / or coupling element.

[0043] Such an adjusted impedance element / coupling element can thus have a static impedance after adjustment, but in particular which is adjusted relative to the original impedance in such a way that the effect of the tuning unit changed by the adjustment results in an influence on the compensation of the induction voltage generated in the receiving coil by the transmitting magnetic field, which is improved compared to the sole compensation by the interaction of the transmitting coil and the at least one compensation coil.

[0044] Such an adjusted impedance element / coupling element preferably does not have its own adjustment means for changing the impedance, but is preferably adjustable at least once by an external influence, e.g., by means of an external adjustment means. Such an adjustment means can be, for example, a laser unit, whose laser beam is used to ablate an electrically effective surface area of ​​an impedance element / coupling element.

[0045] An adjustable impedance element and / or coupling element is preferably understood to be one that itself comprises an adjusting means with which the impedance can be repeatedly adjusted / changed, in particular reversibly adjusted. Such an adjusting means can, for example, effect an adjustment / change of the impedance of the impedance element and / or the coupling element through manual or actuator-based or electronic actuation.

[0046] The invention thus makes it possible to change the impedance of the impedance element and / or of the at least one coupling element and thus to optimize the penetration reduction.

[0047] Particularly preferred is an embodiment according to which the device comprises a control system by means of which, in particular depending on the detected signal of the measuring electronics, the impedance of the at least one impedance element and / or of the at least one coupling element can be changed at least once, preferably repeatedly, e.g., iteratively. The measuring electronics preferably measures and records / stores the voltage in the measuring coil system that is induced therein by the excitation with the transmitting magnetic field. Thus, in this embodiment, the invention can ensure that, before carrying out a measurement with a sample, e.g., in a device for carrying out Magnetic Particle Imaging (MPI) or Magnetic Particle Spectroscopy (MPS), the device is optimized in advance with regard to penetration reduction, e.g.,by carrying out a measuring sequence, preferably without a sample, in particular without a sample of magnetic and / or magnetizable particles / matter, within which the impedance of the at least one impedance element and / or of the at least one coupling element is changed, e.g. iteratively, while measuring the induction voltage generated by the transmitting magnetic field in the measuring coil system in order to minimize this induction voltage, in particular before a measurement is carried out with a sample, e.g. of magnetic particles or magnetizable matter.

[0048] However, the invention can also provide that the impedance of the at least one impedance element and / or of the at least one coupling element is changed during the performance of a measurement on a sample.

[0049] It is particularly preferred that the controller can control or is controlled by an adjusting means external to the at least one impedance element and / or the at least one coupling element, by means of which the impedance of the at least one impedance element and / or the at least one coupling element can be irreversibly changed, or that the controller can control an adjusting means arranged on the at least one adjustable impedance element and / or on the at least one coupling element, by means of which the impedance of the at least one impedance element and / or the at least one coupling element can be reversibly changed. Preferably, it is provided that no mechanical movement is carried out with the adjusting means in order to effect a change, but in particular the adjusting means effects an electronic change in the impedance, e.g., by being designed as a digital potentiometer, analog switch, etc.

[0050] An irreversible change can be achieved, for example, by at least partially removing, preferably mechanically or optically induced, surface regions of the at least one impedance element and / or the at least one coupling element that influence the impedance. For example, such at least partial removal can be achieved by ablating such surface regions using a laser beam.

[0051] A reversible change can be achieved, for example, if the at least one impedance element and / or the at least one coupling element comprises a resistance element that can be changed, for example, mechanically or by physical interaction (e.g. by the effect of light or temperature), e.g. a switchable resistor cascade and / or a potentiometer whose ohmic resistance can be changed, e.g. by changing an effectively acting conductor length between two tapping contacts or a thermistor or photoresistor and / or a variable capacitor whose capacitance can be changed, e.g. by changing the area of ​​the capacitor areas between two tapping contacts and / or a coil arrangement whose inductance can be changed, e.g. by changing the immersion depth of a magnetic / magnetizable core element in the coil.

[0052] The invention can preferably also provide for the total impedance of the tuning element, in particular the impedance of the at least one impedance element and / or the at least one coupling element, to be effected by geometrically deforming the at least one impedance element and / or the at least one coupling element.

[0053] A computer program can be implemented in the controller, which controls the generation of a varying current by means of the current source and controls a measurement of the induced voltages by means of the measuring electronics, as well as the changes to be made to the impedance of the at least one impedance element and / or the at least one coupling element.

[0054] In a preferred embodiment, the at least one coupling element is formed by a coil with at least one winding, in particular precisely one winding, preferably by a coil whose axial length is smaller than the axial length of the transmitting coil. In another preferred embodiment, the at least one coupling element is formed by an electrically conductive surface. This can, in particular, also effect a capacitive coupling. Such a conductive surface as a coupling element can thus effect an inductive coupling and / or a capacitive coupling, in particular by acting as a conductor loop.

[0055] The conductive surface can preferably be perforated in regions or at least partially removed, e.g. by means of laser radiation or mechanically, in order to change the impedance and / or to define a current path.

[0056] Preferably, the invention provides at least two electrically conductive surfaces as coupling elements in the tuning unit, which are electrically conductively connected by at least one impedance element.

[0057] The at least one coupling element can also combine both of the aforementioned embodiments, i.e., it can have both an inductive and a capacitive coupling effect, in particular by means of a conductor of a winding that is at least partially flat or an electrically conductive surface that comprises a current path between two connection regions of the at least one impedance element.

[0058] In a preferred embodiment, it is provided that the distance between a tuning unit, in particular from its geometric center, to a compensation coil, in particular to one of at least two compensation coils, in particular to its geometric center, is smaller than the distance to the receiving coil, in particular to its geometric center.

[0059] By positioning the tuning unit, in particular its at least one coupling element, which is designed as a winding that encloses the coil axis by more than 180 degrees, preferably 360 degrees or more, closer to a compensation coil (compared to the receiving coil), the voltage induced in the compensation coil is influenced more strongly by the inductively and / or capacitively coupled tuning unit than the induction voltage induced in the receiving coil, so that, in particular due to this different influence of both induction voltages, a phase shift results between the induction voltages of the receiving coil and the at least one compensation coil.

[0060] By positioning the tuning unit, in particular its at least one coupling element, which is designed as a winding or as a surface that encloses the coil axis by no more than 180 degrees, further away from a compensation coil (compared to the receiving coil), the voltage induced in the compensation coil is influenced more strongly by the inductively coupled tuning unit than the induction voltage induced in the receiving coil, so that, in particular due to this different influence on both induction voltages, a phase shift results between the induction voltages of the receiving coil and the at least one compensation coil. In both variants, this allows the phase error between the induction voltages of these coils to be specifically reduced.

[0061] In another embodiment, it can also be provided that each of several compensation coils, in particular also the receiving coil, is assigned a tuning unit, in particular one arranged radially outward from the respective coil. This ensures that each tuning unit interacts at least predominantly with the closest coil due to their spatial proximity. This allows the induction voltage in the several compensation coils, in particular also in the receiving coil, to be individually influenced.

[0062] In a preferred embodiment, it is provided that the at least one coupling element, in particular the at least one coupling element designed as an inductively acting coil and / or as a capacitively acting surface, completely surrounds the coil axis of the receiving coil and / or the transmitting coil and / or the compensation coil, in particular by more than 360 degrees, preferably by a conductor wound several times around the coil axis.

[0063] In this version, the tuning unit couples directly to the near-axis transmitting magnetic field.

[0064] In another embodiment, it is also preferably provided that the at least one coupling element, in particular the at least one coupling element designed as an inductively acting coil and / or as a capacitively acting surface, does not completely surround the coil axis of the receiving coil and / or the transmitting coil and / or the compensation coil, in particular extends around the coil axis by less than 180 degrees.

[0065] In this embodiment, the tuning unit essentially couples to magnetic stray field components far from the axis. This embodiment is particularly suitable when the at least one coupling element is designed as an electrically conductive surface / foil, e.g., made of copper.

[0066] Preferably, in the aforementioned embodiments, at least the at least one coupling element, in particular the entire tuning unit, is arranged radially outwardly of the receiving coil and / or the transmitting coil and / or the compensation coil(s), in particular in an arrangement covering one compensation coil more than the receiving coil, preferably in the arrangement in which the coupling element, in particular with respect to its axial length, lies radially outwardly completely over a compensation coil.

[0067] At least one impedance element separate from the at least one coupling element can preferably also be arranged outside the effective range of the transmitting magnetic field, e.g. by being connected to the at least one coupling element by electrical conductors / lines which lead out of the effective range.

[0068] Embodiments of the invention are described below with reference to the figures. Figure 1 shows a schematic overview of a device according to the invention. It comprises at least one current source 400, which is formed, for example, by a generator and an amplifier. The current source 400 serves to generate a time-varying current through the transmitting coil 300 in order to generate a time-varying, symbolically represented magnetic field 110, to which a sample volume 102 containing a sample is exposed, which comprises, for example, magnetic or magnetizable particles or matter.

[0069] The transmitting coil 300 is shown here next to the sample only for clarity. Such an arrangement of the coil next to the sample or the sample volume can also be provided in an actual construction. Preferably, the transmitting coil surrounds the sample / sample volume in the actual arrangement. In addition to the transmitting coil 300, further transmitting coils can be provided, optionally with their own power sources, which is represented here by the dashed elements. In addition, at least one magnet, preferably a pair of magnets, in particular as a respective permanent magnet or another coil arrangement, can be provided to generate a location-dependent, static magnetic field, which assumes the value zero, in particular within the measured sample volume, at a point or along a path, preferably in the form of a line, and assumes values ​​other than zero outside of this point or this path.

[0070] The device further comprises a measuring coil system comprising a receiving coil 104 and two compensation coils 103 and 105 arranged on either side at an axial distance from it. The receiving coil 104 and the two compensation coils 103 and 105 are connected in series, with the winding direction of the two compensation coils 103, 105 being opposite to the winding direction of the receiving coil 104, so that the voltages induced in the receiving coil 104 and the two compensation coils 103, 105 by the transmitting magnetic field of the transmitting coil 300 have opposite signs. Such an arrangement is called a gradiometer arrangement. Theoretically, this is intended to cancel out the voltages induced by the transmitting magnetic field, but in practice, this does not fully work.This principle is called punch-through reduction and is intended to make the voltage induced by the magnetic field of the excited particles / matter in the measuring coil system more resolvable.

[0071] The induction voltage generated in the measuring coil system 103, 104, 105 is recorded by a measuring electronics 500, e.g. a low-noise amplifier (LNA), and can be further processed.

[0072] The device, which is suitable for magnetic particle imaging, for example, further comprises a tuning unit 100 / 101, optionally at least one further tuning unit 200 / 201. Such a tuning unit 100 / 101 comprises a coupling element 101 and a separate impedance element 100, both of which are electrically contacted, preferably connected in series. The coupling element 101 is embodied here, by way of example, as an inductively coupling coil, but can also be designed with capacitive coupling.

[0073] Here it is shown that according to the invention the tuning unit 100 / 101 is arranged closer to the compensation coil 103 than to the receiving coil 104, ie the coupling between the tuning unit 100 / 101 and the compensation coil 103 is greater than the coupling between the tuning unit and the receiving coil 104. The impedance element 100 of the tuning unit is designed here so that its impedance can be changed / tuned, e.g. as an adjustable ohmic resistor.

[0074] This allows the amplitude of the current induced in the tuning unit 100 / 101 and its phase position to be influenced. Thus, the transmitting magnetic field of the transmitting coil 300 generates a current in the tuning unit, and this in turn generates a magnetic field that couples more strongly to the compensation coil 103 than to the receiving coil 104 and the further compensation coil 105, so that any existing phase mismatch between the voltages induced in the receiving coil 104 and the compensation coil 103 can be reduced. This allows the reduction in pass-through to be significantly improved compared to the prior art, in particular to over 100 dB. The invention preferably provides that the voltage induced in the receiving coil system 103, 104, 105 and detected by the measuring electronics 500 is analyzed and transmitted to the controller 600 (data acquisition), which e.g.a microcomputer (PC), by generating and applying a control signal to an actuator or electronics for adjusting an actuating element of the adjustable impedance element 100, the impedance of which is changed in order to automatically minimize the aforementioned phase mismatch. This can be done, for example, iteratively. The invention can preferably also provide a user interface (UI), e.g., on the microcomputer of the controller 600.

[0075] To minimize disruptive influences on the measurement signal, the controller 600 preferably acts galvanically isolated on the impedance element(s) 100 / 200. To minimize disruptive influences on the measurement signal, the control signals are preferably time-controlled such that a measurement signal can be detected at least temporarily without a control signal being transmitted to an impedance element at the same time.

[0076] The adjustment of the impedance of an impedance element 100 can thus be carried out reversibly, but designs are also possible in which the impedance is changed irreversibly.

[0077] Figures 2 show possibilities for forming the voting units 100 / 101.

[0078] Figure 2A, for example, shows a tuning unit with a coupling element 101, which is designed as a coil with multiple windings, and an adjustable / tunable impedance element 100, which is connected in series with the windings. Symbolically shown, for example, is the design of an adjusting means 106 present on the impedance element 100.

[0079] Figure 2B shows a tuning unit with a coupling element 101, which is designed as a coil with a single winding, and an adjustable / tunable impedance element 100, which is connected in series with the winding. The embodiments of Figures 2A and 2B are preferably provided such that the at least one winding of the coupling element 101 is wound completely around the coil axis of the transmitting coil 300 and / or receiving coil 104 and / or the compensation coil 103. The axis can be the same for all coils, but this need not be the case.

[0080] Figure 2C shows an embodiment of a tuning unit 100 / 101 in which the coupling element 101 is also designed as a coil with a single winding to which the impedance element 100 is connected, but here the winding frames a surface area which is not penetrated by the coil axis of the transmitting coil 300 and / or receiving coil 104 and / or the compensation coil 103, rather the winding is arranged such that it does not completely surround a coil, preferably a compensation coil 103, in particular radially outwardly, in particular extends less than 180 degrees around the coil axis.

[0081] Figure 2D shows an embodiment of a tuning unit 100 / 101 in which the coupling element 101 is also designed as a coil. The coil is formed by a closed current path in an electrically conductive surface, e.g., a copper foil. The current path is in series with the impedance element 100. The current path is defined here by local recesses in the surface, in particular by the notch close to the impedance element, which separates both contacts of the impedance element.

[0082] Such recesses can also serve to change the impedance of the coupling element, possibly irreversibly. For this purpose, an external adjusting means 107, e.g., realized by a laser beam, can be used. Likewise, local elongated recesses or material removals (100 left), local point-shaped recesses or material removals (100 right), or local thickness reductions (100 top) can cause an impedance change of the coupling element compared to its original impedance, thereby causing an irreversible change in the impedance of the coupling element 101. In this embodiment, the separately shown impedance element 100 can also be omitted.

[0083] Figure 3 shows a section of the capacitive coupling of a tuning unit to a coil, in this case simplified to a transmitting coil, although coupling to a receiving coil or compensation coil, or to multiple coils, is also possible. The tuning unit comprises at least two, here in particular three, coupling elements 101, each of which is designed as an electrically conductive surface and serves for capacitive coupling to the coil. Preferably, at least two coupling elements, preferably two coupling elements 101 from each possible pairing of two coupling elements 101, are connected by means of a preferably adjustable or adjusted impedance element 100.

[0084] Figure 4 shows a section of a device according to the invention, in which a tuning unit 100 / 101 is assigned to each of the coils in the measuring coil system 103, 104, 105. Here, too, it is provided that by measuring and evaluating the induced voltage by means of the measuring electronics 500 and the controller 600, an automatic change in the impedances of the respective impedance elements 100 takes place in order to optimize the penetration reduction.

[0085] The adjustable impedance elements 100 can in all possible embodiments of the invention preferably be formed by at least one of the following features: as fixed ohmic resistors, as fixed inductors, as fixed capacitors or as fixed semiconductor elements, as adjustable ohmic resistors, as adjustable inductors, as adjustable capacitors or as an adjustable semiconductor element, as potentiometers, discretely switchable resistance cascades, discretely switchable inductance cascades, discretely switchable capacitance cascades, temperature-dependent resistors, light-dependent resistors, voltage-dependent capacitance from a semiconductor element.

[0086] To achieve multiple and reproducible changes in impedance, an arrangement of semiconductor switches that connect the above elements into a circuit or bridge them is particularly preferred. Also particularly suitable as "digital potentiometers" are commercially available components that contain a chain of resistors and a number of semiconductor switches to change the effective resistance in response to a control signal.

[0087] Preferably, components are used which produce the same effect for both polarities of the voltage applied to the impedance element or for both directions of the current flowing through the impedance element.

[0088] In the case of voltage-dependent capacitance, this can be approximately achieved by designing for a control voltage (U_Bias) greater than the maximum value of the voltage applied to the impedance element. In the case of semiconductor switches and digital potentiometers (which themselves contain semiconductor switches), this can be approximately achieved by selecting components for bipolar operation.

[0089] Not shown is a potentially required power supply, possibly a bipolar power supply of a suitable magnitude. To avoid interference, a low-noise, galvanically isolated power supply is particularly advantageous, e.g., using galvanically isolated voltage converters with low noise emissions and coupling capacitance, or using batteries or accumulators.

[0090] Also not shown are special control variants where interference can be avoided, or at least reduced, by means of galvanic isolation (e.g. commercially available optocouplers).

Claims

Patent claims 1 . Device for exciting a sample, in particular a magnetic or at least magnetizable sample, in particular particles, by means of at least one time-varying, in particular oscillating, magnetic field (110), comprising a. a current source (400) for generating a time-varying current, b. a transmitting coil (300) acting on a sample volume (102) for receiving a sample, for generating a time-varying transmitting magnetic field (110) as a function of the current generated in the transmitting coil (300) by the current source (400) connected to the transmitting coil (300), c.a measuring coil system (103, 104, 105) with a receiving coil (104) for generating an induction voltage that can be induced in the receiving coil (104) as a function of a sample magnetic field and the transmitting magnetic field (110), and with at least one compensation coil (103, 105) that is connected in series with the receiving coil (104) in reverse polarity for at least partially compensating the induction voltage generated in the receiving coil (104) by the transmitting magnetic field (110), d. at least one measuring electronics unit (500) with which the induction voltage generated in the measuring coil system (103, 104, 105) can be measured, in particular stored and evaluated, e. at least one tuning unit (100 / 101, 200 / 201) which is electrically connected in a contactless manner to at least one coupling element (101). the measuring coil system (103, 104, 105) and / or the transmitting coil (300) is coupled and with which the at least partial compensation of the induction voltage generated in the receiving coil (300) by the transmitting magnetic field (103) can be influenced, characterized in that f. the tuning unit (100 / 101) comprises an element which a) has its impedance changed at least once compared to an original impedance, or b) has its impedance adjustable multiple times, in particular reversibly.

2. Device according to claim 1, characterized in that the element is the at least one coupling element (101) of the tuning unit (100 / 101) and / or at least one impedance element (100) present in the tuning unit (100 / 101) in addition to the at least one coupling element (101), in particular which is electrically connected in series or parallel with the at least one coupling element (101).

3. Device according to one of the preceding claims, characterized in that it comprises a control (600) by means of which, in particular depending on the detected signal of the measuring electronics (500), the impedance of the at least one impedance element (100) and / or of the at least one coupling element (101) can be changed at least once, preferably repeatedly.

4. Device according to one of the preceding claims, characterized in that the control (600) comprises an actuating means (107) external to the at least one impedance element (100) and / or to the at least one coupling element (101). can be controlled or is controlled by means of which the impedance of the at least one impedance element (100) and / or of the at least one coupling element (101) can be irreversibly changed, or b. an adjusting means (106) arranged on the at least one adjustable impedance element (100) and / or on the at least one adjustable coupling element (101) can be controlled, with which the impedance of the at least one impedance element (100) and / or of the at least one coupling element (101) can be reversibly changed.

5. Device according to one of the preceding claims, characterized in that the at least one coupling element (101) is formed by a. a coil with at least one winding, in particular exactly one winding, preferably by a coil whose axial length is smaller than the axial length of the transmitting coil and / or b. an electrically conductive surface, in particular whose axial length is smaller than the axial length of the transmitting coil, preferably wherein the conductive surface is perforated in regions or at least partially removed to change the impedance and / or to define a current path, preferably wherein at least two electrically conductive surfaces are electrically conductively connected by an impedance element.

6. Device according to one of the preceding claims, characterized in that the distance between the tuning unit (100 / 101), in particular from its geometric center, to a compensation coil (104, 105), in particular to one of at least two compensation coils (104, 105), in particular to its geometric center, is smaller than the distance to the receiving coil (103), in particular to its geometric center.

7. Device according to one of the preceding claims, characterized in that each of several compensation coils (104, 105), in particular also the receiving coil (103), is assigned a tuning unit (100 / 101), in particular which is arranged radially outside of the respective coil (103, 104, 105).

8. Device according to one of the preceding claims, characterized in that the at least one coupling element (101), in particular the at least one coupling element (101) designed as an inductively acting coil and / or as a capacitively acting surface, a. completely surrounds the coil axis of the receiving coil (103) and / or the transmitting coil (300) and / or the at least one compensation coil (104, 105), in particular by more than 360 degrees, preferably by a conductor wound several times around the coil axis, or b. does not completely surround it, in particular by extending around the coil axis by less than 180 degrees.

9. Method for reducing the induction voltage generated by the transmitting magnetic field (103) in the measuring coil system (103, 104, 105) of a device according to one of the preceding claims 1 to 8, characterized in that by changing the impedance of at least one element of the tuning unit (100 / 101) a phase mismatch between the induction voltages generated by the transmitting magnetic field (110) in the receiving coil (103) and the at least one compensation coil (104, 105) is reduced.

10. The method according to claim 9, characterized in that the impedance of the at least one impedance element (100) and / or of the at least one coupling element (101) in the tuning unit (100 / 101) is adjusted at least once with respect to an original impedance, in particular irreversibly, or several times and / or reversibly, in particular iteratively, in particular until a maximized penetration reduction is achieved.

11. Method according to one of the preceding claims, characterized in that the control signals of the controller (600) are supplied to the at least one element by means of a galvanically isolated method and / or the control signals of the controller (600) are temporally controlled such that a measurement signal can be detected at least temporarily without a control signal being transmitted to the at least one element at the same time.

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