• 专利附录
  • 专利说明
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    • 专利摘要:
    An NMR probe head comprising a piezoelectric actuator (12) driven tunable capacitor having a dielectric (5) enclosing a cavity (15) and connected to an electrode (8) at a first electrical potential of the capacitor, wherein in the cavity a capacitor piston (7) with electrically conductive surface which is linearly displaceable by applying a sawtooth-shaped electrical voltage to the piezoelectric actuator is characterized in that the piezoelectric actuator is arranged outside the cavity in extension of the capacitor piston axis (a), that one with the dielectric connected sliding bushing (9) is provided with a through bore (16) in which a piston actuating rod (8) is operated, which actuates the displaceable in the cavity capacitor piston and is connected to the piezoelectric actuator such that it moves the capacitor piston linearly when applying the sawtooth voltage,and that the sliding bush exerts a decelerating friction on the piston actuating rod during the linear displacement of the condenser piston and only allows a sliding of the piston actuating rod during the steep flanks of the sawtooth voltage. Thus, the disadvantages of the prior art can be avoided, the NMR probe remains compact and the material costs and the production cost are reduced.
    公开号:CH707750B1
    申请号:CH00252/14
    申请日:2014-02-24
    公开日:2018-02-28
    发明作者:Guy Baumann Daniel
    申请人:Bruker Biospin Ag；
    IPC主号:
    专利说明:

    Description: [0001] The invention relates to an NMR (= nuclear magnetic resonance) probe head with at least one tunable capacitor in the HF (= high-frequency) resonant circuit of the NMR probe head, which is motor-driven by means of a piezoelectric actuator, wherein the capacitor has a dielectric which has a dielectric resonator Cavity at least partially surrounds and is connected to at least one electrode, at which a first and possibly another electrical potential of the capacitor can be tapped, and wherein in the cavity within the dielectric under the action of the piezoelectric actuator outside the cavity in extension of the Is arranged axis of the capacitor piston, is arranged by applying a sawtooth-shaped electrical voltage to the piezoelectric actuator linearly displaceable condenser pistons with electrically conductive surface.
    Such an arrangement is known from US 2008/0 117 560 A1 (= reference [10]).
    Background of the Invention NMR methods are used to analyze sample compositions or to determine the structure of substances in samples. NMR spectroscopy is a powerful method of instrumental analysis. In these NMR methods, the sample is exposed to a strong static magnetic field Bo in a z-direction, and orthogonal high-frequency electromagnetic pulses in the x or y direction are irradiated to the sample. This results in an interaction with the nuclear spins of the sample material. The temporal evolution of these nuclear spins of the sample in turn generates high-frequency electromagnetic fields, which are detected in the NMR apparatus. Information about the properties of the sample can be obtained from the detected RF fields. In particular, it is possible to deduce the position and intensity of NMR lines on the chemical bonding conditions in the sample.
    The transmission and reception of RF radiation takes place with so-called RF resonators. The RF resonators are arranged in the immediate vicinity of the sample, or the sample is arranged inside the RF resonators.
    The electrical network of an NMR probe head usually consists of at least one electrical RF resonant circuit. Per one nucleus (e.g., 1H, 13C, or 1SN) which an NMR probe head can excite and detect, an RF resonant circuit is found in each NMR probe head (see Figure 2). These RF resonant circuits must each be fine-tuned to the corresponding atomic nuclei to be measured for a high-quality NMR measurement. This is usually achieved with two continuously variable capacitors (tuning and matching) per RF resonant circuit. These are preferably rotary and / or sliding capacitors.
    In addition to the continuously variable capacitors, there are also discrete variable capacitors (switchable capacitors) with which you can switch the RF resonant circuits from one nuclear magnetic resonance to another. It is important that the electronic components (NMR coils, fixed and variable capacitors) of the RF resonant circuits have as small a distance as possible from each other and that the electrical leads have the shortest possible paths. Of course, the distances may only be so small that the dielectric strength of the HF resonant circuits is still guaranteed. This ensures that the electrical losses are minimal and the qualities of the HF resonant circuits are as high as possible. Since in an NMR measurement, the sample to be examined is always pushed into the magnetic center of the NMR magnet, not only the NMR coils, but the RF resonant circuits as a whole including the variable capacitors as close to the sample to be examined in NMR Sample head can be accommodated. The problem now lies in the accessibility of the variable capacitors, which usually come to lie several decimetres in the NMR magnet with a magnetic hole of a few centimeters in diameter and which must be tuned frequently (for example, after each sample change before the actual NMR measurement).
    Thus, the user of the NMR apparatus can vote the corresponding nuclear magnetic resonance of the RF resonant circuits on the variable capacitors, the capacitors must be easily adjustable with built NMR probe head. This is e.g. indirectly via adjustable rods, the ends of which are attached to the variable electronic components and the other ends are guided at a convenient location for the user outside of the NMR magnet. The adjustment rods are pushed and / or rotated according to the variable capacitor type. Frequently, in addition to the adjusting rods motors, universal joints, flexible shafts (1,2), gear and / or worm gear are used. Motors with corresponding sensors allow automatic tuning of the HF resonant circuits (3, 4).
    Disadvantages of these solutions are: [0008] 1. Elaborate and error-prone mechanics (e.g., universal joint and gears). 2. Hysteresis (compliance and play) in mechanics. This complicates in particular the automatic tuning. 3. Drift and slip-stick movements resulting from thermal expansions. This leads to an unwanted detuning of the HF resonant circuits during the NMR experiment. 4. Since it must be ensured that each individual adjustment strand is statically determined or stress-free, the construction and assembly of such a correspondingly complex and demanding. 5. Electric motors (3) can not be directly coupled to the variable capacitors or housed in the area of the bore of the magnetic resonance magnet because the stray magnetic field of the magnetic resonance magnet is so high that the electric motors are damaged (eg demagnetizing the permanent magnets) and The torque of the engine is greatly reduced or even eliminated. 6. With a cryo-NMR probe head, an elaborate vacuum feedthrough also has to be realized for each adjustment line. Because of the magnetic stray field of the NMR magnet, lack of space, Ausgasproblematik and poor heat dissipation in vacuum conventional electric motors are difficult to be housed within or in the vacuum of a cryo-NMR probe head.
    In the field of variable capacitors (cylinder volume with a diameter of about 40mm) offers the (cryo) NMR probe head little space to accommodate up to twelve electric motors (diameter about 10mm). The electric motors are therefore mounted in the region of the NMR probe head outside the NMR magnet or magnetic hole and must be connected to e.g. a coupling element (shafts, rods, gears, universal joints) are coupled to the variable capacitors.
    OBJECT OF THE INVENTION The present invention is based on the object of modifying an NMR probe head of the type defined at the outset with the simplest possible technical measures in such a way that the disadvantages listed above are largely avoided, without a reduction in the quality of the NMR spectroscopy. Produce measurements, the NMR probe head is to remain particularly compact and the material costs and manufacturing costs are reduced.
    BRIEF DESCRIPTION OF THE INVENTION This object is achieved in an astonishingly simple and effective manner in that, in a generic NMR probe head with the features defined at the beginning, a sliding bushing mechanically connected to the dielectric is provided with a through bore in which a piston actuating rod runs on the one hand can actuate the displaceable in the cavity condenser piston and on the other hand mechanically connected to the piezoelectric actuator such that upon application of the sawtooth electrical voltage to the piezoelectric actuator, the piston actuating rod moves the condenser piston linearly, and that the sliding bush is such that it has a decelerating friction on the piston actuating rod during the linear displacement of the condenser piston exerts and allows only during the steep edges of the applied sawtooth voltage slipping of the piston actuating rod.
    Compared to motorized variable capacitors according to the prior art (7, 8, 9, 10), the present invention has, inter alia, the advantage that with an already known and well-proven design of a variable capacitor together with only a single piezoelectric actuator, if necessary, a mass element and a suitable sliding bushing, simply an extremely compact motorized variable capacitor can be realized, which can be installed in larger numbers within an NMR probe head in the region of the magnetic center of an NMR magnet. In addition, this NMR probe can be used in vacuo and / or at cryogenic temperatures. All the above-listed disadvantages and difficulties of the prior art can be eliminated with this motorized variable capacitor modified according to the invention.
    PREFERRED EMBODIMENTS OF THE INVENTION Particularly preferred is an embodiment of the NMR probe head according to the invention, in which a mass element of the mass m is fastened to the piezoelectric actuator on its side facing away from the piston actuating rod such that, when a sawtooth-shaped electrical voltage is applied to the piezoelectric actuator is moved with this in the direction of its polarization and generated due to its mass m additional inertial forces. The additional mass m has the advantage that the motorized variable capacitor becomes more efficient and therefore can be operated with smaller voltages in order to achieve equal steps As as without mass m. Using the relationship below, which describes the step size As of the motorized variable capacitor assuming that the slope of the steep ramp edge is °°, this can be illustrated:
    Assuming that the masses mK (mass of the condenser piston) and mKs (mass of the piston actuating rod) are much smaller than the masses mA (mass of the actuator) and m, can be almost equal with corresponding mass m and half sawtooth voltage or half deflection AI of the actuator large step As to be executed, as without mass m and full sawtooth voltage or full deflection AI:
    As = ((m + 1 / 2mA) / (m + mK + rriKs + mA)) AI
    Also preferred is an embodiment in which at least the outer surfaces of the condenser piston and the piston actuating rod are constructed of electrically conductive material and carry an electrical connection of the capacitor, to which a second electrical potential of the capacitor can be tapped. This has the advantage that the second electrical potential of a variable capacitor according to FIG. 1 does not need to be tapped directly on the capacitor piston, which is always positioned within the dielectric, but in a region of the piston actuating rod which is fully off or on retracted state of the capacitor piston is always outside the dielectric, can be tapped. The length of the piston actuating rod outside the dielectric and in the fully extended state must therefore be longer than the required travel of the condenser piston.
    A further development of this embodiment provides that at least the outwardly directed surfaces of the sliding bush are also constructed of electrically conductive material and form an electrical contact to the piston actuating rod, so that the second electrical potential of the capacitor can be tapped on the slide bushing. Compared to the embodiment in which only the condenser piston and the piston actuating rod are electrically conductive, this embodiment with an additional electrically conductive sliding bush has the further advantage that with a shortest possible electrical conductor - the travel of the condenser piston or the piston actuator rod must not be taken into account - the second electrical potential can be tapped at a stationary or at a static part of the variable capacitor. So that the electrical losses are minimal and the grades of an RF resonant circuit are correspondingly high, one should always make sure that the RF resonant circuits can be realized with the shortest possible electrical conductors. In addition, since the electrical conductor does not move with the condenser piston or the piston actuating rod, but always remains in place, the electrical conductor is not stressed mechanically and is not in danger of being fatigue fractured.
    A further preferred embodiment of the inventive NMR probe head is characterized in that the capacitor is fixed mechanically rigidly on the NMR probe head via the slide bushing. Smallest positional changes of electronic components (e.g., fixed, continuously and discretely adjustable capacitors and coils) and electrical circuits of the RF resonant circuits can detune them and massively change the performance of an NMR probe head. It is therefore important that the electronic components, e.g. variable capacitors, as rigid as possible with the NMR probe head can be connected so that they maintain their position in the NMR probe head in each operating state possible. In addition, the NMR probe head and its RF resonant circuits are exposed during a NMR measurement to a strong magnetic field of typically several tesla from the NMR magnet. Since currents flow during an NMR measurement through the HF resonant circuits or through the electronic components and electrical conductors, these also affect Lorentz forces. The mechanical attachment interface of the variable capacitor to secure it in the NMR probe head is the slide bushing. The dielectric as a mounting interface should be avoided because of its fragility, if possible.
    Particularly advantageous is also a class of embodiments of the invention, which are characterized in that a mechanical hollow body is provided, which receives the piezoelectric actuator in its cavity and mechanically clamped in the polarization direction. Piezoelectric actuators usually have no mounting interfaces, such as. Threaded holes. With a hollow body according to FIG. 5, which is provided at both ends which hold or clamp the actuator, each with a mounting interface (for example, each with a threaded hole) and the actuator receives and clamped as described above, the assembling of a motorized variable Condensers massively simplified. The actuator, which is tensioned by the hollow body provided with at least one mounting interface or a threaded hole, only needs to be screwed to the piston actuating rod of a variable capacitor, which has an external thread at the end.
    If you still need an additional mass m, it can be attached or screwed on the free end of the hollow body. The tensile stiffness and the yield strength of the hollow body in the direction of action or polarization direction of the actuator should be selected so that the actuator can still expand sufficiently. The clamping is realized by the cavity in the polarization direction or in the effective direction of the actuator has a corresponding undersize with respect to the length of the piezoelectric actuator. One way to bring the actuator into the undersized cavity is to cool the actuator and heat the hollow body and then assemble it with play. As soon as the hollow body and the actuator are again at ambient temperature, the hollow body holds or braces the actuator.
    In preferred developments of this class of embodiments, the force acting through the mechanical hollow body on the piezoelectric actuator mechanical stress is chosen so large that the piezoelectric actuator is always suitable in operation loaded on pressure. Since the piezoelectric actuators should preferably be subjected to minimal tensile stress both in static and in dynamic operation, because otherwise the probability of crack formation in the actuator increases and thus the service life of the actuator decreases, it is advantageous if the piezoelectric actuators always work during operation are loaded with a suitable pressure. This can also be achieved with the hollow body. The bias of the actuator through the hollow body is then to be chosen so that the actuator is always suitably loaded both in unipolar and bipolar operation to pressure. The actuator is then always biased over the entire possible effective range and minimally loaded on train. In contrast to unipolar operation (E field only in the direction of the polarization direction of the actuator) of a piezoelectric actuator undergoes a piezoelectric actuator in bipolar operation and negative voltages (E field against the polarization direction of the actuator). A negative voltage causes the piezoelectric actuator to be shorter than its dead length.
    Further advantageous variants provide that the mechanical hollow body is constructed in one piece with the mass element. The assembling of a motorized variable capacitor with an additional mass m can be further simplified if the hollow body and the additional mass m are integral. The one-piece hollow body with additional mass and actuator can be easily prefabricated as an assembly and then only needs to the piston actuating rod of a variable capacitor, which has an external thread at the end to be screwed.
    Further preferred embodiments of the invention are characterized in that the moving parts of the capacitor, in particular the condenser piston, the piston actuating rod, the piezoelectric actuator and the mass element by choosing the shape of its cross section, preferably by a triangular cross-section of at least the piston actuating rod and the Through hole of the sliding bush are secured against rotation about the axis of the condenser piston. If the cross-sections of the through-hole and the piston-actuating rod are circular, then the moving parts of the condenser may rotate uncontrollably during operation. This can lead to entangle and twist the two electrical leads for the electrical supply of the piezoelectric actuator. This should be avoided, otherwise the electrical leads may be damaged. With a non-circular cross-section (e.g., triangular) of the through-hole and the piston-actuating rod, the rotational freedom of the moving parts is blocked, and thus they are secured against rotation.
    Finally, particularly preferred is also an embodiment of the inventive NMR probe head, in which the slide bushing comprises a mechanically rigid part and an elastic part. The sliding bush of the capacitor should be able to take up to four functions at the same time. The dielectric should be attached directly to the sliding bushing. In addition, the second electrical potential of the capacitor according to FIG. 1 should be able to be tapped on the sliding bush and, moreover, the variable capacitor is fastened via the sliding bush to the NMR probe head. In addition to the up to three attachment functions of the sliding bush, the sliding bushing also assumes the play-free bearings and optionally also the electrically conductive contacting of the movable part or the piston actuating rod of the capacitor. The more compliant the bearing bushing is, the less accurate the diameter of the piston actuating rod can be. However, the more compliant or more resilient the bushing is, the less suitable it is to take up to three attachment functions, particularly the attachment of the capacitor to the NMR probe head. Therefore, it is advantageous if the slide bushing has a mechanically stiff and an elastic region.
    An advantageous development of this embodiment is characterized in that the elastic part of the sliding bush is formed Spannzangenförmig, the piston actuating rod clamped and generates a mechanical friction and optionally an electrically conductive contact between the sliding bush and piston actuating rod. In practice, the mechanical frictional force between the slide bushing and the piston actuating rod will affect the pitch of the motorized variable capacitor. The more elastic the resilient guide part of the slide bush, the less will diameter fluctuations of the piston actuating rod affect the clamping force or the mechanical frictional force, and thus the step size and possibly also the electrical contacting become more reproducible. Therefore, the spring constant of the elastic guide member should be as small as possible, so that the slope of the spring characteristic is as flat as possible. This can be achieved, for example, by forming the elastic part of the sliding bush in a collet-like manner.
    Alternatively or additionally, in another development, the mechanically rigid part can be constructed in one piece with the elastic collet-shaped part of the slide bushing. This has the advantage that such a one-piece sliding bush can be produced particularly easily. For the mechanical production of such a sliding bushing, one starts first from a cylinder of suitable material with a stepped and coaxial bore according to FIGS. 6a and 6b. In the next manufacturing step, the cylinder is provided with a certain number of slots from the cylinder side with the smaller diameter. In this way, results in a certain number of collet fingers of the collet. The slots should be distributed radially along and evenly around the diameter of the slide bushing. About the wall thickness of the hollow cylinder, the length of the collet fingers or the slot depth and the selected elastic modulus E of the material, the rigidity and the clamping force of the collet can be adjusted. Of course, the small diameter of the stepped bore in the cylinder should be undersized with respect to the piston actuator rod diameter and already have the ideal diameter matched to the diameter of the piston actuator rod.
    Further advantages of the invention will become apparent from the description and the drawings. Likewise, according to the invention, the above-mentioned features and those which are still further developed can each be used individually for themselves or for several in any desired combinations. The embodiments shown and described are not to be understood as exhaustive enumeration, but rather have exemplary character for the description of the invention.
    DETAILED DESCRIPTION OF THE INVENTION AND DRAWING [0026] The invention is illustrated in the drawing and will be explained in more detail by means of exemplary embodiments. Show it:
    1 shows an embodiment of the inventive NMR probe head in a schematic vertical section with motorized variable capacitor.
    Fig. 2 is an electrical schematic of a prior art RF resonant circuit with NMR probe head;
    FIG. 3a shows the dynamics of the motorized variable capacitor according to FIG. 1 during the flat edge of a sawtooth voltage; FIG.
    Fig. 3b as Fig. 3a, but during the steep slope of the sawtooth voltage;
    4 shows a variant of the invention with two electrodes on the dielectric of the variable capacitor;
    FIG. 5 as in FIG. 1a, but with a piezoelectric actuator of the motorized variable capacitor mechanically strained by a mass element; FIG.
    6a shows a one-piece slide bushing with a through hole of diameter d, which is formed like a collet, in a schematic cross section; and
    Fig. 6b as Fig. 6a, but in a schematic longitudinal section.
    Fig. 1 illustrates schematically an embodiment of the inventive NMR probe head, as described in detail below.
    In Fig. 2 is a simple electrical circuit diagram of an RF resonant circuit of an NMR probe head according to the prior art with a transmitting and receiving coil 1 of the inductance L, a coaxial cable 2 with an electrical impedance of 50 ohms, a continuously variable capacitor 3 with capacity Gr for tuning and a continuously variable capacitor 4 with capacitance CM for matching shown. The variable capacitors 3 and 4 for the tuning and matching of at least one RF resonant circuit can be realized here as a linearly adjustable capacitors.
    A preferred construction of such a linearly adjustable capacitor in an inventive NMR probe head with a dielectric 5, which encloses a cavity 15 at least partially, and with a piezoelectric actuator 12 and a mass element 13 with the mass m is shown in Fig. 1 , At an electrode 6 or on a condenser piston 7 - the electrically conductive surface area of the condenser piston forms an electrode - a first or a further electrical potential of the capacitor is tapped. The capacitor piston 7 is contacted via an electrically conductive piston actuating rod 8, which is connected to the capacitor piston 7 in an electrically conductive manner. If the sliding sleeve 9 provided according to the invention is likewise electrically conductively short-circuited with the through-bore 16 and electrically connected to the condenser piston 7 via the electrically conductive piston actuating rod 8, then the desired electrical potential on the condenser piston 7 can be easily tapped on the sliding sleeve 9.
    There are some further variants to realize variable capacitors: FIG. 4 shows an embodiment of a variable capacitance NMR probe head according to the invention with two electrodes 6, 19 on the dielectric 5. This variable capacitor is contacted at the two electrodes 6, 19. In this variable capacitor, the piston actuating rod 8 and the slide bushing 9 are preferably made of an electrically non-conductive material.
    By means of the adjusting rods, universal joints, flexible shafts, gear and / or worm manual or motorized displacement of the piston actuating rod 8 and the condenser 7 along the axis a of the piston actuating rod 8, the capacitance of the variable capacitor can be adjusted within a certain range ,
    The variable capacitor in Fig. 1 is mechanically fastened via the sliding bushing 9 on the NMR probe head. It will also often be designed so that the piston actuating rod 8 is clamped by a suitably shaped sliding bushing 9 with a certain force FK, and therefore for the displacement of the condenser piston 7, a frictional force Fr has to be overcome. This has the advantage that the piston actuating rod 8 or the condenser piston 7 - even with temperature fluctuations or thermal expansions of the adjusting strand - during the NMR experiment in position remains and does not move. The effective direction of the clamping force FK is indicated in FIGS. 1, 3 a, 3 b, 4 and 5 in each case by opposing arrows 11.
    It is now of great advantage that directly to the piston actuating rod 8, a suitable motor for moving the condenser piston 7 is mounted. Such a motorized variable capacitor significantly reduces the material cost and manufacturing expense of an NMR probe head. Suitable motors or actuators that can be placed in the stray field or directly into the magnetic center of an NMR magnet are piezoelectric motors. Piezoelectric actuators generate the driving force in such motors [5, 6]. Piezoelectric actuators have the property that they stretch positively or negatively stretch when an electrical voltage is applied in its polarization direction or in the opposite direction or normal to it. A magnetic field does not affect this property of such a piezoelectric actuator.
    A motorized variable capacitor can be realized in the following manner: Is to the piston actuating rod 8 of guided in a sliding bush 9 under friction and adjustable condenser piston 7 in the adjustment along the axis A acting piezoelectric actuator 12 and the latter a mass element 13 with the Mass m with respect to the piston actuating rod 8, which is frictionally guided in the bushing 9, fixed, resulting in a motorized discretely adjustable variable capacitor (see about Fig. 1). By applying a sawtooth-shaped voltage to the piezoelectric actuator 12 in its polarization direction 14 of the capacitor piston 7 per sawtooth performs a step .DELTA.Ι (see Fig. 3a, 3b).
    In the following, the operation of the motorized variable capacitor, assuming that 1. the piezoelectric actuator 12 is massless, 2. and the slope of the steep sawtooth edge 18 is infinite, will be described. During the flat edge 17 of the sawtooth voltage, the actuator 12 with the length I is stretched by ΔΙ and thus the mass m is displaced by ΔΙ. However, the condenser piston 7 with the mass mK and piston actuating rod 8 with the mass mKs remain in place, since the friction 10 between the slide bushing 9 and the piston actuating rod 8 is not overcome. At the time of the steep edge 18 of the sawtooth voltage, the masses experience very high accelerations, since the actuator 12 assumes its original length I again at a point in time. In addition, since at this time the friction between the slide bushing 9 and the piston actuating rod 8 does not matter anymore (friction against the inertial forces negligible), the piston actuating rod 8 slides through the slide bushing 9 and the condenser piston 7 performs a step Δ3. By repeating this process, any distances can be covered. By changing the electrical polarity of the sawtooth voltage, the direction of movement of the condenser piston can be changed.
    The step Δ3 is smaller than the deflection ΔΙ of the piezoelectric actuator and depends on the masses of the mass m 13, the condenser piston 7 mK and the piston actuating rod 8 mKs:
    As = (m / (m + rriK + mKs)) ΔΙ In reality, however, the mass of the actuator 12 mA is not negligible and also has an influence on increment As:
    As = ((m + 1/2 mA) / (m + m + mKs + mA)) ΔΙ If the masses mK and mKS are negligibly small compared to the mass mA of the actuator 12, the mass m 13 can be dispensed with , since still reasonable steps Δ3 (max ΔΙ / 2) can be carried out.
    In a nuclear magnetic resonance probe head, the moving direction of a variable capacitor is mostly vertical. In this installation position, the weight of the movable part of the variable capacitor must not exceed the friction between sliding bushing 9 and piston actuating rod 8. It should also be noted that the second assumption above does not quite correspond to reality either. Since the slope of the steep slope of the sawtooth voltage will never really be °°, in reality, in addition to the masses and the friction between the sliding bushing 9 and the piston actuating rod 8, the elasticity of the entire variable capacitor and loads in the direction of movement of the piston actuating rod 8, the effective step size Δδ influence. Therefore, the step size As, in contrast to the idealized case, will no longer be the same in both directions of movement, if the variable capacitor is not operated horizontally.
    The sliding bushing 9 can be designed in one or more parts in different embodiments of the invention.
    In FIGS. 6a and 6b, by way of example, a special one-piece slide bush 9 'is shown with a stepped through-bore 16 formed in the manner of a collet chuck. This one-piece slide bushing 9 'with the total height h has an annular and a mechanically rigid portion with the inner diameter D and the cross-section b x s, at which by a number of slots 23 the same amount collet fingers are formed. These collet fingers are distributed radially along and uniformly around the diameter d of the one-piece slide bushing 9 '. The diameter d is undersized with respect to the diameter of the piston actuating rod 8, so that the bearing surfaces 22 of the sliding bushing 9 'clamp the piston actuating rod 8 and generate a mechanical friction between the bearing surfaces 22 and the piston actuating rod 8. About the wall thickness b, the length of the collet fingers or the slot depth t and the selected elastic modulus E of the material, the rigidity of the collet can be adjusted.
    The sliding bushing 9, 9 'may be made of electrically conductive or non-conductive (e.g., ceramic Si3N4) material. By the shape of the cross section (e.g., rectangular) of the piston actuating rod 8 and the through hole 16, the movable part of the variable condenser consisting of the condenser piston 7, the piston actuating rod 8, the actuator 12 and the mass member 13 can be secured against rotation.
    Another embodiment of a motorized variable capacitor is shown in FIG. The variable capacitor of FIG. 1 is extended here by a mechanical hollow body 20. The mechanical hollow body 20 is designed such that it has a cavity 21, which can receive the piezoelectric actuator 12.
    By the cavity 21, which has a corresponding undersize in the polarization direction 14 with respect to the length I of the piezoelectric actuator, the piezoelectric actuator 12 is braced so that it is minimally loaded during operation to train. This reduces the risks of cracking in the piezoelectric actuator 12 and a spot break of the piezoelectric actuator 12 and thus increases its life. This variant of a motorized variable capacitor can also be realized by combining the mechanical hollow body 20 and the mass element 13 and manufacturing it in one piece.
    The piezoelectric actuator 12 may consist of a monolithic block of piezoelectric material of length I and two applied electrodes with the distance I or n, usually glued together slices of piezoelectric material with the thickness l / n and with two electrodes applied be constructed with the distance l / n (piezoelectric stack actuators). The individual disks are glued together in such piezoelectric stack actuators and the individual electrodes must be electrically connected to each other. The stack actuators are more complex to produce, but have the advantage that they require much smaller electrical voltages Vpp (typically Vpp = 50 ... 200 V) for elongation ΔΙ than monolithic piezoelectric actuators.
    Compared with already known motorized variable capacitors [7, 8, 9], the present invention has the advantage that with an already known and proven many times construction of a variable capacitor together with only one piezoelectric actuator 12, if necessary, a mass element 13 and a suitable sliding bush 9, 9 'simply an extremely compact motorized variable capacitor can be realized, which can be installed in larger numbers within an NMR probe head in the region of the magnetic center of an NMR magnet. In addition, this NMR probe can be used in vacuo and / or at cryogenic temperatures. All of the above enumerated disadvantages and difficulties can be eliminated with this modified motorized variable capacitor according to the invention.
    REFERENCE SIGNS LIST: (1) Transmitting and receiving coil L of an NMR probe head (2) Coaxial cable 50 ohms (3) Continuously variable capacitor CT (tuning) (4) Continuously variable capacitor CM (matching) (5) Dielectric of Variable capacitor (6) Electrode: Electrically conductive layer (capacitor surface and electrical contact) (7) Adjustable condenser piston (electrically conductive): The lateral surface of the condenser piston is the (second) electrode of the variable capacitor (8) Piston actuating rod: Coupling interface of the adjustable capacitor (7 ) for adjusting strand (eg adjusting rods, universal joint and / or motor) (9, 9 ') Sliding bushing (mechanical fastening & electrical contacting) (11) Direction of action (opposite arrows) of the clamping force FK of the sliding bushing
    (12) Piezoelectric (or piezostrictive) actuator with the length I (13) Mass element with mass m (14) Polarization direction of the piezoelectric actuator (15) At least partially by the dielectric (5) enclosed cavity (16) Through hole of the slide bushing (9, 9 ' ) (17) Flat edge of the sawtooth voltage (18) Steep edge of the sawtooth voltage (19) Further electrode on the dielectric (5) (20) Mechanical hollow body with the appropriate dimensions for receiving the piezoelectric actuator (12), which this in its polarization direction ( 14) braced or biased
    权利要求:
    Claims (12)
    [1]
    (21) Cavity of mechanical hollow body (20) (22) Bearing rods for piston actuating rod (8) (23) Slots of one-piece sliding sleeve (9 ') (a) Longitudinal axis of piston actuating rod (8) Reference List [1] Agilent ProTune: http://www.chem.agilent.com/Library/datasheets/Public/5991-0043EN.pdf [2] Jeol auto-tune: http://www.jeolusa.com/PRODUCTS/Analyticallnstruments/NuclearMagneticResonance/Probes/tabid / 381 / Default, aspx [3] BrukerATM: http://www.bruker-biospin.com/cryoprobe_atm.html [4] Agilent ProTune-PZT: http://www.chem.agilent.com/en-US/ products-services / Instruments-Instruments / Nuclear-Magnetic-Resonance / ProTune-PZT / Pages / default.aspx [5] US-A 5,568,004 [б] US-A 4,894,579 [7] US-A 3,213,340 [8] US-A No. 3,447,047 [9] US Pat. No. 7,061,745 B2 [10] US 2008/0 117 560 A1 Patent claims
    1. NMR probe head with at least one by means of a piezoelectric actuator (12) motor-driven tunable capacitor in the RF resonant circuit of the NMR probe head, wherein the capacitor has a dielectric (5) which encloses a cavity (15) at least partially and with at least an electrode (6, 19) is connected, at which an electrical potential of the capacitor can be tapped, and wherein in the cavity within the dielectric (5) under the action of the piezoelectric actuator (12), outside the cavity (15) in extension the axis (a) of the capacitor piston (7) is arranged by applying a sawtooth-shaped electrical voltage to the piezoelectric actuator (12) linearly displaceable condenser pistons (7) is arranged with electrically conductive surface, characterized in that mechanically with the dielectric (5 ) connected sliding bush (9, 9 ') is provided with a through hole (16), in which a Ko 1), which on the one hand can actuate the condenser piston (7) displaceable in the cavity (15) and, on the other hand, is mechanically connected to the piezoelectric actuator (12), and in that the sliding bush (9; 9 ') is adapted to exert a decelerating friction on the piston-actuating rod (8) during the linear displacement of the condenser piston (7) and to allow the piston-actuating rod (8) to slide through only during the steep flanks of the applied sawtooth voltage.
    [2]
    2. NMR probe head according to claim 1, characterized in that on the piezoelectric actuator (12) on its side facing away from the piston actuating rod (8) side a mass element (13) of the mass m is fixed such that it upon application of a sawtooth electrical voltage to the piezoelectric actuator (12) is moved with this in the direction of its polarization and generated due to its mass m additional inertial forces.
    [3]
    3. NMR probe head according to one of the preceding claims, characterized in that at least the outer surfaces of the piston actuating rod (8) are constructed of electrically conductive material and the condenser piston (7) and the piston actuating rod (8) carry an electrical connection of the capacitor to which a second electrical potential of the capacitor can be tapped.
    [4]
    4. NMR probe head according to claim 3, characterized in that at least the outwardly directed surfaces of the slide bushing (9, 9 ') are also constructed of electrically conductive material and form an electrical contact to the piston actuating rod (8), so that the second electrical Potential of the capacitor on the slide bushing (9, 9 ') can be tapped.
    [5]
    5. NMR probe head according to one of the preceding claims, characterized in that the capacitor via the sliding bushing (9, 9 ') is mechanically fixed rigidly in the NMR probe head.
    [6]
    6. NMR probe head according to one of the preceding claims, characterized in that a mechanical hollow body (20) is provided which receives in its cavity (21) the piezoelectric actuator (12) and mechanically clamped in the polarization direction thereof.
    [7]
    7. NMR probe head according to claim 6, characterized in that the by the mechanical hollow body (20) acting on the piezoelectric actuator (12) mechanical stress is chosen so large that the piezoelectric actuator (12) is always loaded in operation on pressure ,
    [8]
    8. NMR probe head according to claim 6 or 7, characterized in that the mechanical hollow body (20) is constructed in one piece with the mass element (13).
    [9]
    9. NMR probe head according to one of claims 2 to 8, characterized in that the moving parts of the capacitor, in particular the condenser piston (7), the piston actuating rod (8), the piezoelectric actuator (12) and the mass element (13) Choice of the shape of its cross section, preferably by a triangular cross-section of at least the piston actuating rod (8) and the through hole (16) of the sliding bush (9; 9 '), secured against rotation about the axis (a) of the condenser piston (7).
    [10]
    10. NMR probe head according to one of the preceding claims, characterized in that the sliding bushing (9, 9 ') comprises a mechanically rigid part and an elastic part.
    [11]
    11. NMR probe head according to claim 10, characterized in that the elastic part of the slide bushing (9, 9 ') is formed like a collet, the piston actuating rod (8) clamped and a mechanical friction and optionally an electrically conductive contact between slide bushing (9; ') and piston actuating rod (8) produced.
    [12]
    12. NMR probe head according to claim 10 or 11, characterized in that the mechanically rigid part is constructed in one piece with the elastic part of the slide bush (9; 9 ').
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    同族专利:
    公开号 | 公开日
    GB2512208A|2014-09-24|
    GB201404043D0|2014-04-23|
    CH707750A2|2014-09-15|
    DE102013204131B3|2014-02-06|
    GB2512208B|2017-05-24|
    US9500726B2|2016-11-22|
    US20140253124A1|2014-09-11|
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    法律状态:
    2019-10-31| PFA| Name/firm changed|Owner name: BRUKER SWITZERLAND AG, CH Free format text: FORMER OWNER: BRUKER BIOSPIN AG, CH |
    优先权:
    申请号 | 申请日 | 专利标题
    DE102013204131.4A|DE102013204131B3|2013-03-11|2013-03-11|Nuclear magnetic resonanceprobe head has sliding bush that exerts decelerating friction at piston actuating rod for linear displacement of capacitor piston while steep flanks in sawtooth shape via piston actuating rod|
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