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    • 专利摘要:
    Sensor (1) for a gradient magnetometer. In order to be able to determine individual components of the gradient tensensor with an improved spatial resolution compared to conventional sensors, it is provided according to the invention that the sensor (1) comprises a straight-line beam (2) which, in its longitudinal direction (x), is seen in an initial region (3). and an end region (4) is fixed and can oscillate freely therebetween, the sensor (1) further comprising at least one conducting means (5) arranged on and connected to the beam (2), in order to ensure a current flow in the form of moving charge carriers between the starting region ( 3) and the end region (4), wherein the at least one conducting means (5) can be acted upon by an alternating voltage in order to excite a vibration mode of the beam (2) by utilizing the Lorentz force (F1) when the beam (2 ) is in a magnetic field.
    公开号:AT515000A1
    申请号:T821/2013
    申请日:2013-10-23
    公开日:2015-05-15
    发明作者:Franz Dr Keplinger；Michael Dr Stifter
    申请人:Tech Universität Wien；
    IPC主号:
    专利说明:

    SENSOR AND METHOD FOR DETERMINING AN INDIVIDUAL COMPONENT OF A GRADIENT TENSOR OF A MAGNETIC FIELD
    FIELD OF THE INVENTION
    The present invention relates to a sensor for a gradient magnetometer, to an array of such sensors, and to a gradient magnetometer comprising a sensor or an arrangement according to the invention.
    Furthermore, the present invention relates to a method for determining a single component of a gradient subtraction of a magnetic field.
    Finally, the present invention relates to the use of a sensor according to the invention or an arrangement according to the invention of such sensors.
    STATE OF THE ART
    The measurement of a gradient of a magnetic field plays a role in various fields of technology and science. For example, it serves to position a gear in an ABS sensor for a vehicle or to accurately measure the earth's magnetic field.
    The strength of the magnetic field can be described by the magnetic flux density B. Its gradient results from the change of B per unit distance in the direction of the largest change in B. Since B is a vectorial quantity which is itself generally a function of all three spatial coordinates, the gradient is basically a tensor consisting of all the partial derivatives of three spatial B-field components according to the spatial coordinates.
    In practice, two magnetic field sensors, e.g. Hall sensors, used to measure the size of B at two different locations spaced at a well-defined distance. Then the difference of the measured values for B is formed and divided by the distance. The distance should be selected to ensure that the B-field varies linearly within the distance. This is achieved in that the distance between the sensors is small compared to the distance between the positions of the sensors and the source of the magnetic field.
    This two-sensor method has the fundamental, unavoidable drawback that there are not completely identical sensors, i. the sensors will always have at least slightly different characteristics, so the difference in the measured B fields is extremely susceptible to error.
    In addition, the sensors have only a limited sensitivity, which makes it necessary to place the two sensors relatively far apart in order to be able to detect differences in B, which of course reduces the spatial resolution. This can not be avoided even if only one sensor is used, which is positioned one behind the other at the two different locations for the B measurement.
    OBJECT OF THE INVENTION
    It is therefore an object of the present invention to provide a sensor or the like. to provide a method for the determination of individual components of a magnetic field gradient sensor which avoids the above-mentioned disadvantages. In particular, an improved spatial resolution should be achieved.
    PRESENTATION OF THE INVENTION
    The present invention is based on the finding that a rectilinear beam which is fixed at its start and end portion in its longitudinal direction and can oscillate therebetween can be excited to vibrate in a magnetic field by utilizing the Lorentz force to oscillate with a mode of vibration of the cantilever Vibration mode directly proportional to a single component of the gradient magnetic field sensor; the magnetic flux density B is.
    To enable excitation of the mode of vibration by means of Lorentzian force, at least one electrical conducting means is provided, which is arranged on and connected to the beam to allow a flow of current in the form of moving charge carriers between the start and end regions. If the charge carriers move in a magnetic field, the Lorentz force acts on them. Due to the coupling between the at least one guide means and the beam, the Lorentz force also acts thereon. If now the at least one conducting means is subjected to an alternating voltage and the bar is in a magnetic field, an oscillation of the bar is excited on account of the resulting oscillating Lorentz force. Basically, the beam behaves like a vibrating string, which is fixed at both ends. Accordingly, there are modes of vibration of the beam which can be excited by utilizing a resonance. This basically works regardless of whether the B-field is zero on average or not, more specifically, whether the gradient is superimposed by a DC or non-zero DC field.
    Therefore, in a sensor for a gradient magnetometer, according to the present invention, it is provided that the sensor comprises a rectilinear beam which is fixed in its longitudinal direction and freely swingable in an initial region and an end region, the sensor further comprising at least one conductive member disposed on and connected to the beam To allow current flow in the form of moving charge carriers between the initial region and the end region, wherein the at least one guide means is acted upon by an AC voltage to excite a mode of vibration of the beam by utilizing the Lorentz force when the beam is in a magnetic field.
    Basically, vibrations of the beam with amplitudes in different directions are conceivable. Accordingly, by determining these different amplitudes, it is generally possible to determine different individual components of the gradient tensiometer. In this case, the relevant component of the gradient tensensor is a B-field component derived in part according to that spatial coordinate which corresponds to the longitudinal direction of the beam. Which spatial B-field component is involved depends on the spatial direction along which the amplitude is measured.
    Specifically, the direction of the respective amplitude results from the cross product between the direction of the (alternating) current and the relevant B-field component.
    Simple detection is achieved by allowing for vibrations of an amplitude in a preferred direction. In particular, in order to enable vibrations having an amplitude in a preferred direction, it is provided in a preferred embodiment of the sensor according to the invention that the beam has a length longitudinally between the initial region and the end region such that the beam has a width in a first direction normal to the longitudinal direction and in a second direction, which is normal to the longitudinal direction and the first direction, a height, wherein the height is smaller than the width and the width is smaller than the length. On the one hand, since the beam has pronounced dimensions mainly in one dimension, it is also achieved that the electrical current in the conducting means is essentially one-dimensional. On the other hand, the dimensioning of the beam has strong different axial area moments of inertia umbzw. Both cause especially vibrations with an amplitude in the second direction to be excited.
    This behavior becomes particularly pronounced when one or more orders of magnitude lie between the dimensions of the beam along the different spatial directions. Therefore, in a preferred embodiment of the sensor according to the invention, it is provided that the width is at least ten times greater, preferably at least thirty times greater than the height and the length at least ten times greater, preferably at least thirty times greater than the width. The ratios of the axial area moments of inertia with respect to the different directions are therefore in a ratio of at least 1: 100, corresponding to the square width to length or height to width ratio, respectively.
    In order to be able to produce sensors with a well-defined structure and well-defined mechanical properties of the beam, it is provided in a preferred embodiment of the sensor according to the invention that the beam is made of preferably monocrystalline silicon. This enables, for example, production based on a silicon wafer in a so-called silicon-on-insulator (SOI) method known per se.
    An embodiment which is advantageous in terms of production technology is provided in that a conductor track, preferably of gold, is provided as the guide means. The track runs along the longitudinal direction of the beam accordingly. Therefore, in a preferred embodiment of the sensor according to the invention, it is provided that the at least one conducting means comprises a conductor track fixed on a surface of the beam.
    In order to ensure protection of the at least one conducting means against external influences, it is provided in a further preferred embodiment of the sensor according to the invention that the at least one conducting means is integrated in the beam. In this case, the at least one guiding means can be embodied, for example, as a micromechanical structure made of metal, in particular aluminum.
    In order to prevent the at least one conducting means from being mechanically damaged or garzerstört by the vibrations of the beam, it is provided in a particularly preferred embodiment of the sensor according to the invention that the beam and the at least one guide means are integrally executed. That in this case, the beam is itself at least partially electrically conductive.
    Basically, the forces that occur due to the gradient along the beam are, of course, relatively small. In order to increase the effect to be measured, a second sensor or a second bar may be provided which runs parallel to the first bar. To ensure that both beams oscillate at the same frequency, the two beams are mechanically coupled together. This arrangement has increased sensitivity to a component of the magnetic field gradient with a partial derivative in that spatial direction corresponding to the longitudinal direction of the beam (hereinafter referred to as component of the magnetic field gradient "along" the longitudinal direction) for a single sensor. Therefore, an arrangement of a plurality of sensors according to the invention is provided according to the invention, wherein at least two sensors are mechanically coupled to one another in order to force the same oscillation frequency upon excitation of a vibration of the beams of these at least two sensors. A further advantage of this arrangement is that, by spacing the two beams in a direction normal to the longitudinal direction, preferably in the first direction, a sensitivity of the device to a component of a magnetic field gradient along this direction, ie the detection of a component of the magnetic field gradient a partial derivative in this direction.
    In a manufacturing technology particularly advantageous embodiment of the arrangement according to the invention, it is provided that exactly two sensors are provided, the beams are interconnected by means of at least one coupling element, wherein the arrangement has an essentially H-shape. The arrangement need not have perfect symmetry, i. For example, the at least one coupling element need not be perfectly centered with respect to the length of the beams. Moreover, in order to ensure the function of the sensors, it is not necessary that the cross section of the beam normal to the longitudinal direction be homogeneous over the entire length of the beams. Accordingly, it is generally assumed that no symmetrical arrangement.
    From a manufacturing point of view, it is particularly advantageous if the beams of the two sensors are arranged offset from one another only in the first or second direction. Such an arrangement is easily generated by means of the already mentioned SOI technology. Accordingly, it is provided in a preferred embodiment of the arrangement according to the invention that the bars of the two sensors are parallel to each other and are substantially spaced apart from each other only in the first direction. Of course, manufacturing-related imperfections can not be excluded in practice, i. it may of course be that there is a slight spacing with respect to the second direction as well. However, these imperfections are not a departure from the claimed embodiment.
    The SOI technology allows the bars of the two sensors as well as the at least one connecting element connecting the beams to be easily manufactured in one piece.
    Thus, there are no additional steps for fixing the at least one coupling element to the beam. In addition, a very well-defined arrangement is obtained. Accordingly, it is provided in a preferred embodiment of the arrangement according to the invention that the two beams and the at least one coupling element are made in one piece.
    In order to prevent buckling of the beams or the H-shaped arrangement due to a thermal expansion, it is provided in a particularly preferred embodiment of the inventive arrangement that each beam is fixed in its initial region and in its end region to each of its anchoring element designed as a cantilever. Dielectric anchors are themselves thermally expanded and arranged in an H-shaped configuration so as to compensate for the thermal expansion of the H-shaped structure, thereby preventing buckling.
    In a production technology particularly advantageous embodiment of the arrangement according to the invention, it is provided that each beam and the associated Ankerelemente are made in one piece. Preferably, in this case also, the SOI technology is used for the production.
    Accordingly, according to the invention there is provided a gradient magnetometer comprising a sensor according to the invention or an inventive arrangement of a plurality of sensors, wherein for each sensor at least one read-out means is provided for determining an amplitude of the oscillation of the beam of the sensor To determine the respective sensor. In this case, the amplitude in the second direction does not necessarily have to be measured; in principle, the amplitude can also be measured in another, arbitrary direction, in particular in the first direction. In addition, amplitudes in multiple directions per bar can be determined simultaneously, e.g. both the amplitude in the first direction and the amplitude in the second direction. In this case, it is of course advisable to provide a separate read-out means for each sensor or bar for each amplitude to be measured.
    In order to determine the amplitude / n, different readout means can be used. A read-out means that is particularly easy to realize is a capacitive read-out element. This can be formed by the beam itself and an electrode arranged under the beam.
    Preferably, the electrode extends at least partially parallel to the beam when it is not vibrating and at an initial position. The electrode and the beam in principle form a capacitor with a certain capacity, which depends on the distance between the electrode and the beam. Swinging bar, the capacity changes depending on its deflection or on the amplitude of the oscillation. Accordingly, from the measurement of the capacitance change on the amplitude and thus on the size or on the amount of the component of the
    Magnetic field gradient tensor are closed. Accordingly, in a preferred embodiment of the gradient magnetometer according to the invention it is provided that a capacitive read-out element is provided as the respective at least one read-out means.
    Of course, other methods known per se for measuring the amplitude of a vibration of the respective beam are also applicable. Accordingly, in a preferred embodiment of the gradient magnetimagnetometer according to the invention, it is provided that a piezoelectric or piezo-resistive or optical read-out element is provided as the respective at least one read-out means.
    As already described, to determine a single component of the gradient sensor of B, a vibration mode of the beam is excited and the amplitude of the excited vibration mode is measured. Optimal resonant excitation is achieved by having the AC voltage or AC having a frequency f i, where f i is a frequency of a mode of vibration of the beam. The magnitude of the component of the gradient sensor of B is obtained by multiplying the measured amplitude by a proportionality factor. It should be noted that in principle both symmetric and antisymmetric modes of oscillation can be excited, in principle determining the size of the tensor component in both cases. When the gradient is superimposed by a non-zero field, the excitation of an antisymmetric mode may be advantageous for determining the size of the component of the gradient sensor of B to facilitate discrimination between the DC field component and the gradient tensor component.
    The said connection between the
    Gradient tensensor component and amplitude follows from the Euler-Bernoulli beam theory on the mechanical behavior of the loaded beam found in standard textbooks, such as, e.g. in Stephen P. Timoshenko, James M. Gere, "Theory of Elastic Stability", 2nd Ed., McGraw-Hill (1985) or KurtMagnus, Karl Popp, "Vibrations", 7th Edition, Vieweg + Teubner Verlag (2005). In this way, the deflection w (x) of a bridge which extends with a length 1 along the direction x (corresponding to the longitudinal direction) is fixed at its ends and can swing freely therebetween. For the displacement w (x) in a general direction a, which is normal to the direction x, the following expression results: w (x) = q / (E * Ja ') * (x4 / 24-x3l / 12 + x2l2 / 24), where q is a uniform load that causes the deflection of the beam, E the elastic modulus of the beam and Yes < the axial area moment of inertia with respect to a normal direction a 'normal to the direction x and normal to the general direction a. Assuming that - in a first symmetric mode of vibration - the greatest deflection occurs in the middle of the beam, this formula can be used for the position in the middle of the beam, i. at x = 1/2, to obtain the amplitude Aa of the vibration of the beam in the general direction a:
    Aa = w (1/2) = (q * l4) / (384 * E * Yes').
    The uniform load q, which causes the deflection of the beam, is generated in the present case by the Lorentz force FL, and therefore it is valid
    Aa = (FL * l3) / (384 * E * Yes <)
    In the presence of a gradient sensor, the Lorentz force F1 basically results as the product of the gradient of B. with the magnetic moment, which in turn results from the current flow in the conductor and the magnetic field. For the amplitude Aa, which is the maximum displacement in the general direction a, i. 'normal to the direction x and normal to the normal direction a', the Lorentz force FL is due to the tensor component 3Ba- / 3x responsible, i.
    Aa = 3BaV3x * m * l3 / (384 * E * Yes <).
    Similarly, the tensor component 3Ba </ 3x = Aa * (384 * E * JaO / (m * l3).
    In general it can therefore be said that the tensor component 3Ba '/ 3x is proportional to the amplitude Aa with a proportionality factor (X, which depends on E, Ja, m and 1, ie: 3Ba' / 3x = Aa * CX (E, Yes', m, 1).
    It should be noted that this general form is true even if torsions and concomitant changes in the shear modulus of the beam or the oscillating structure can not be neglected. The factor (X can in this case be determined completely analogously to the above representation from the Euler-Bernoulli beam theory.
    Therefore, in a method for determining a single component of a gradient magnetic field sensor using a sensor according to the invention, the method comprises the steps of: exciting a, preferably antisymmetric, vibration mode of the beam of the sensor by utilizing the Lorentz force; Conducting means having an alternating voltage 'at a frequency f ±, where f is a frequency of a mode of oscillation of the beam; - determining an amplitude of the excited vibration; Calculation of the size of the component according to the following formula: K = Aa * CC (E, Ja ', m, 1), where K is the component of the magnetic flux density in a normal direction normal to the direction of the measured amplitude Aa and normal to the longitudinal direction , is partially derived in the longitudinal direction, and α is a proportionality factor, which is the modulus of elasticity E of the beam, the axial area moment of inertia Ja &lt; of the beam with respect to the normal direction, the magnetic moment m resulting from the current flow in the conducting means and the surface enclosed by the current flow, and the length 1 of the beam.
    For example, to determine that component of the gradient tensensor that is the B-field component in the first direction partially derived longitudinally ("SBy / Sx"), in a preferred embodiment of the method of the invention, the amplitude is measured in the second direction and that the component of the gradient tensensor is determined according to the following formula K = Az * (X (E, Jy, m, 1), where K is the component of the magnetic flux density in the first direction partially derived in the longitudinal direction, Az measured along the second direction Amplitude and Jy the axial area moment of inertia of the beam with respect to the first direction, α is of course again
    Proportionality factor, where E again clearly denotes the modulus of elasticity of the beam, m the magnetic moment resulting from the current flow in the conducting means and the area enclosed by the current flow, and 1 the length of the beam.
    The method can be used analogously with an inventive
    Arrangement of sensors according to the invention are used.
    Therefore, in a preferred embodiment of the method according to the invention, simultaneously with the excitation of the vibration of the beam of the sensor, a vibration of the beam of a second sensor which is mechanically coupled to the sensor is excited by utilizing the Lorentz force by the at least one guide means of the second Sensor is applied with an AC voltage with the same frequency fi, and that the amplitudes of the excited vibration of the two bars are determined.
    As already stated, the use of the arrangement according to the invention also makes it possible to detect a component of the magnetic field gradient with a partial conduction in that direction normal to the longitudinal direction, in which the two beams are spaced from one another. Thus, if the two bars are spaced in the first direction, the B-field component in the first direction can be determined to be partially derived in the first direction ("3By / 3y"). Is this
    If the component of the gradient tensensor is not equal to zero, then, when a respective symmetrical oscillation mode of the beams is excited, the beams will oscillate out of phase. Therefore, in a preferred embodiment of the method according to the invention, it is further provided that it is also determined whether the vibration of the two beams is in phase or in antiphase.
    From a metrological point of view, the occurrence of antiphase oscillations of the beams is of great advantage, as it allows very easily and without additional computational effort to generate a difference signal of the readout means, with the aid of which the amplitudes are measured. For example, the realization of a differential capacitor would be possible with a capacitive readout of the amplitudes.
    In the foregoing, it has been assumed that the AC voltages applied to the conducting means of the two beams and the resulting AC currents in the conducting means are in-phase, respectively. In order to force the beams to move in phase in opposite directions and thus to improve measurement possibilities, even in cases where the beams would in principle oscillate in phase, it is provided in a preferred embodiment of the method according to the invention that the two alternating voltages are opposite in phase.
    Finally, it should be noted that the Sensorbzw invention. the inventive method also allows the determination of B-field components. For example, in the first direction, if there is only a non-zero DC magnetic flux density field, but not a non-zero gradient stressor component, then by biasing a single beam symmetric vibration mode, the corresponding B-field component ("By") can be determined in the same way as above for the gradient tensensor component determination portrayed. In this case, it is only to be considered that in this case the Lorentz force F1, which causes the uniform load acting on the beam, results in the product of the current i in the conducting means, the length 1 of the bar and the said B-field component. Correspondingly, the B-field component is proportional to the measured amplitude, which generally gives the following formal relationship:
    Ba '= Aa * β (E, Ja', i, l), where Ba 'is the B-field component in the normal direction a' and β is a proportionality factor that depends on E, Yes <, i and 1 •. For the B-field component in the first direction, y is thus:
    By = Az * β (E, Jy, i, l), in the case discussed above, where the deflection of the beam in the middle of the beam is considered to be the same, β (E, Jy, i, l) = (38.4 * E * Jy) / (i * l4).
    When an H-shaped arrangement and rectified AC voltages according to the invention are used, when a symmetrical oscillation mode of the two beams is excited, an in-phase oscillation occurs when in the first direction there is only a DC non-zero magnetic flux density field. Of course, in this case too, in order to improve the measurement, anti-phase alternating currents could be applied.
    Therefore, according to the present invention, there is provided the use of a sensor or assembly according to the invention for determining a single component of a gradient magnetic field sensor and / or determining a single component of the magnetic flux density.
    BRIEF DESCRIPTION OF THE FIGURES
    The invention will now be explained in more detail with reference to exemplary embodiments. The drawings are exemplary and should be the
    Although set out the idea of the invention, it does not restrict or even reproduce it in any way.
    Showing:
    Fig. 1 is an axonometric view of a sensor according to the invention
    Fig. 2 is a schematic sectional view of the sensor according to the invention with an illustration of a symmetrical vibration mode
    Fig. 3 is a schematic sectional view analogous to Fig. 2, showing an antisymmetric oscillation mode
    4 shows an axonometric view of an inventive H-shaped arrangement of two sensors according to the invention
    Fig. 5 is a schematic axonometric view of the arrangement of Fig. 4 with an illustration of in-phase, symmetric vibration modes
    Fig. 6 is a schematic axonometric view analogous to Fig. 5 with an illustration of antiphase, symmetric vibrational modes
    7 is a plan view auf.eine H-shaped according to the invention
    Arrangement with armature elements designed as cantilevers
    Fig. 8 is a sectional view taken along section line A-A in Fig.7
    WAYS FOR CARRYING OUT THE INVENTION
    Fig. 1 shows an axonometric view of a sensor 1 according to the invention for determining individual
    Components of a gradient sensor of a magnetic field or a magnetic flux density B. The sensor 1 comprises a beam 2 which extends along a longitudinal direction x with a length 1. Relative to the longitudinal direction, the beam 2 is fixed in an initial region 3 and an end region 4 and can oscillate freely between the initial region 3 and the end region 4, similar to a clamped string.
    In the exemplary embodiment shown, the beam has, normally in the longitudinal direction x, a substantially rectangular cross section with a width 7 and a height 8, cf. Fig.2. The width 7 is measured along a first direction y, the height 8 along a second direction z, with the directions x, y and z mutually normal. However, embodiments with a different cross-sectional shape are also conceivable, the cross-sectional shape need not necessarily be angular, but for example could also be elliptical.
    In this case, the length 1 is significantly greater than the width 7 and the width 7 is significantly greater than the height 8. Accordingly, greatly different axial area moments of inertia result around the different directions x, y and z, so that the beam can preferably be deflected in the second direction or oscillates with amplitudes in the direction. The representation of FIG. 1 is not true to scale. Typical dimensions are 2500 μm for the length 1, 500 μm for the width 7 and 5 μm for the height 8.
    On a surface 6 of the beam 2, a trace 5 as an electrical conducting means is arranged to allow a current flow in the form of moving charge carriers between the starting region 3 and the end region 4. Due to the dominant dimension of the beam 2 in the longitudinal direction x, the track 5 on the surface 6 can be approximated as a one-dimensional element with extension in the direction x.
    For determination of individual components of a gradient sensor of B, the track 5 is subjected to an AC voltage when the sensor 1 is in the magnetic field. Due to the resulting AC current 16 in the track 5, the Lorentz force FL acts on the carriers moving in the track 5 and in FIG Sequence on the beam 2. Since it is an alternating current, the Lorentz force Fl temporally alters its sign and thus causes an alternating deflection or oscillation of the beam 2. By choosing a suitable frequency fi of the alternating current 16, vibration modes of the beam 2 can be resonant be excited.
    Fig. 2 illustrates the situation for a flux density B perpendicular to the drawing plane and a symmetric vibrating mode of the beam 2. B is parallel to the direction y, or has a component in the first direction y, By, which is non-zero, ie By Φ 0. The amplitude of the oscillation mode is given as the maximum deflection of the beam 2 parallel to the direction z, with the deflection in FIG. 2 is indicated by the dashed or dotted line. The maximum deflection in direction z or the amplitude Az is directly proportional to By. For the ability to use the single sensor 1 to determine a component K of the gradient sensor of B, it is critical that an amplitude Aa be measured in a general direction-a. The component K to be determined is then partially derived from the magnetic flux density B in a normal direction normal to the direction of the measured amplitude Aa and normal to the longitudinal direction x, the longitudinal direction x, that is, "3Ba '/ 3x · &quot;. The component K is proportional to the amplitude Aa with a proportionality factor o, the modulus of elasticity E of the beam 2, the axial plane moment of inertia Ja 'of the beam 2 with respect to the normal direction a', the magnetic moment m, which results from the
    Alternating current 16 or current flow in the conducting means or in the conductor track 5 and the surface enclosed by the flow of current, and depends on the length 1 of the beam 2, specifically: K = 3Ba- / 3x = Aa * a (E, Ja, m, 1) .
    Neglecting torsions and assuming that, according to a first symmetrical mode of vibration, the maximum deflection of the beam 2 with respect to its longitudinal extension x in the center, i. at 1 / 2auftritt, results for the proportionality factor
    Ct (E, Yes ', m, l) = (384 * E * Yes') / (m * l3).
    Thus, the amplitude Az of a vibration mode is proportional to the corresponding partial derivative of By according to a spatial coordinate corresponding to the longitudinal direction x. That 9By / 3x is directly proportional to Az, and in the case of a first symmetric mode, K = 9By / ax = (Az * 384 * E * Jy) / (m * l3), where Jy is the axial moment of inertia of beam 2 with respect to the first direction y is. The spatial resolution of the measurement of K in the direction x is thus determined by the length 1 of the beam 2.
    When the gradient is superimposed on a non-zero DC field, the excitation of an antisymmetric mode of vibration to determine the size of the component of the gradient tensensor of B may be advantageous to simplify a distinction between the DC field component and the gradient tensor component. In the embodiment of Fig. 3, accordingly, the amplitude Az of the illustrated antisymmetric oscillation mode of the beam 2 is measured to close immediately to the size of K and 3 By / dx, respectively.
    4 shows an arrangement 9 according to the invention consisting of the sensor 1 and a second sensor 10 with a second bar 12 and a second conductor track 18, wherein the second sensor 10 basically corresponds to the first sensor 1 in construction. The second strip conductor 18 can also be subjected to an alternating voltage, whereby a second alternating current 17 sets (see FIG. 5), so that in a magnetic field the second bar 12 can be excited to oscillate.
    The two beams 2, 12 are connected to each other via a coupling element 11, whereby an H-shape of the arrangement 9gergibt. In this case, the two sensors 1, 10 and the beams 2, 12 are arranged parallel to each other and spaced apart only in the first direction y. The coupling element 11 ensures that both bars 2, 12 oscillate at the same frequency.
    The first sensor 1 of Figs. 1 to 3 and the arrangement 9 of Fig. 4 with the first sensor 1, the second sensor 10 and the coupling element 11 may e.g. made of preferably monocrystalline silicon. The conductor tracks 5, 18 may be made of gold, for example. The sensor 1bzw. The arrangement 9 can be produced by means of the silicone-on-insulator (SOI) technology known per se.
    On the one hand, the coupling of the two sensors 1, 10 achieves an increased sensitivity to components of the gradient tensensor along the longitudinal direction x, that is to say components of the gradient sensor with a partial derivation according to a spatial coordinate which corresponds to the direction x '. On the other hand, by spacing the two beams 2, 12 in the first direction, yy, a sensitivity of the array 9 to components of the gradient tensensor along the first direction y is automatically achieved.
    Fig. 5 shows first the case of a DC magnetic field with a B-component in the first direction y not equal to 0, ie By Φ0. Analogous to Fig. 2, both beams 2, 12 swing with a symmetric vibration mode with the amplitude Az Az in the second direction z. The two bars swing 2, 12gleichphasig. The two alternating voltages or the first alternating current 16 and the second alternating current 17 not only have the same frequency fi but are also in-phase.
    On the other hand, Fig. 6 shows the case with a non-zero gradient component along the first direction, namely 3By / 3y Φ 0, for clarity the effect of the non-zero dc By field is not represented, which corresponds to a mean dwindling DC field By = 0. Again, the two AC voltages and the two AC currents 16, 17, respectively, are in-phase and again oscillate the two beams 2, 12 each with a symmetric mode having the amplitude Az in the second direction z. Due to the gradient sensor component 3By / 3y Φ0, in this case, however, there is an out-of-phase Vibration of the beams2, 12.
    In addition to the unambiguous identification of the presence of the gradient tensensor component 3By / 3y, the antiphase deflection of the two bars 2, 12 offers the metrological advantage that a differential signal can be obtained from the measurements of the amplitudes Az without much effort. In this case, the measurement of the amplitude (n) can be carried out with a wide variety of readout means, which may include, for example, capacitive, piezoelectric, piezoresistive or optical readout elements.
    7 shows a plan view of an arrangement 9 according to the invention with in-phase alternating currents 16, 17. The bars 2, 12 are fixed in their initial areas 3, 19 and end areas 4, 20 to an anchor element 14 in each case. Everybody is concrete
    Beams 2, 12 connected both in its initial region 3, 19 and in its end region 4, 20 via a respective connecting portion 15 with one anchor element 14 each. Like the beams 2, 12, the anchor elements 14 are subject to thermal expansion. By virtue of the anchor elements 14 being designed as cantilevers and arranged correspondingly, the thermal expansion of the anchor elements 14 causes no thermally induced bulges of the beams 2, 12 to occur. In this sense, the thermal expansion of the anchoring elements 14 compensates for the thermal expansion of the beams 2, 12 and assembly 9. Advantageously, beams 2, 12, coupling element 11, connecting sections 15 and anchor elements 14 can be made in one piece, preferably using SOI technology for manufacturing ,
    FIG. 8 shows a section according to the section line A-A in FIG. 7. In this case, capacitive read-out elements 13 for determining the deflection of the beams 2, 12 in the second direction z or for determining the amplitude Az of the beams 2, 12 can be seen. The readout elements 13 are indicated by the dotted lines. The read-out elements 13 are formed in each case by one of the beams 2, 12 together with the latter. Conductive means or together associated interconnect 5, 18 and an under the respective bars 2, 12 arranged electrode 21, which may be embodied, for example, as a conductor track. With the amplitude Az, the distance between the beam 2, 12 and the associated electrode 21 changes, thereby changing the capacitive coupling between the respective electrode 21 and the respective conductor track 5, 18 and the resulting capacitance, respectively. The capacitance change is therefore a direct measure of the amplitude Az. REFERENCE LIST; 1 sensor 2 bar 3 initial area of the bar in the longitudinal direction 4 end area of the bar in the longitudinal direction 5 conductor 6 surface 7 width of the bar 8 height of the bar 9 arrangement of sensors 10 second sensor 11 coupling element 12 bar of the second sensor 13 capacitive read-out element 14 anchor element 15 connecting portion 16 Alternating current 17 Second alternating current 18 Second conductor 19 Initial region of the second beam 20 End region of the second beam 21 Electrode x longitudinal direction y First direction or direction along the width of the second
    Balkens z second direction or direction along the height of
    beam
    Fl Lorentz force
    Az amplitude in z direction
    Jy axial area moment of inertia of the beam with respect to the y-direction E modulus of elasticity of the beam 1 length of the beam m magnetic moment K component of a gradient sensor B magnetic flux density
    Aa amplitude measured in the general direction a general direction a 'normal direction axial area moment of inertia of the beam with respect to the normal direction
    权利要求:
    Claims (22)
    [1]
    1. Sensor (1) for a gradient magnetometer, the sensor (1) comprising a rectilinear beam (2) which is fixed in its longitudinal direction (x) in an initial region (3) and an end region (4) and can swing free between them Sensor (1) further comprising at least one conducting means (5) arranged on and connected to the beam (2) to allow a flow of current in the form of moving charge carriers between the starting region (3) and the end region (4), the at least one conducting means (5) with an alternating voltage can be applied to excite a vibrational mode of the beam (2) by utilizing the Lorentz force (Fl) when the beam (2) is in a magnetic field.
    [2]
    2. Sensor (1) according to claim 1, characterized in that the beam (2) in the longitudinal direction (x) between the initial region (3) and the end region (4) has a length (1) that the beam (2) in one first direction (y) has a width (7) normal to the longitudinal direction (x) and a height (8) in a second direction (z) normal to the longitudinal direction (x) and the first direction (y) (8) is smaller than the width (7) and the width (7) is smaller than the length (1).
    [3]
    Sensor (1) according to claim 2, characterized in that the width (7) is at least ten times greater, preferably at least thirty times greater than the height (8), and the length (1) is at least ten times greater, preferably at least thirty times greater than the width ( 7).
    [4]
    4. Sensor (1) according to one of claims 1 to 3, characterized in that the beam (2) is made of preferably monocrystalline silicon.
    [5]
    A sensor (1) according to any one of claims 1 to 4, characterized in that the at least one guide means comprises a conductor track (5) fixed on a surface (6) of the beam (2).
    [6]
    6. Sensor (1) according to one of claims 1 to 4, characterized in that the at least one conducting means (5) in the bar (2) is integrated.
    [7]
    7. Sensor (1) according to claim 6, characterized in that the beam (2) and the at least one conducting means (5) are made in one piece.
    [8]
    An assembly (9) of a plurality of sensors (1) according to any one of claims 1 to 7, wherein at least two sensors (1) are mechanically coupled to each other to force the same frequency of vibration upon excitation of vibration of the beams (2) of said at least two sensors (1) ,
    [9]
    Arrangement (9) according to claim 8, characterized in that there are exactly two sensors (1, 10), the beams (2, 12) of which are interconnected by means of at least one coupling element (11), the arrangement being substantially H-shaped having.
    [10]
    An assembly (9) according to claim 9, characterized in that the beams (2, 12) of the two sensors (1, 10) are parallel to each other and are substantially spaced apart only in the first direction (y).
    [11]
    Arrangement according to one of claims 9 to 10, characterized in that the two beams (2, 12) and the at least one coupling element (11) are made in one piece.
    [12]
    Arrangement according to one of claims 9 to 11, characterized in that each beam (2, 12) is fixed in its initial region (3) and in its end region (4) to a respective armature element (14) designed as a cantilever.
    [13]
    Arrangement according to claim 12, characterized in that each beam (2, 12) and the associated anchor elements (14) are made in one piece.
    [14]
    14. A gradient magnetometer comprising a sensor (1) according to one of claims 1 to 7 or an arrangement (9) of a plurality of sensors (1, 10) according to any one of claims 8 to 13, wherein for each sensor (1, 10) at least one read-out means is provided, to determine an amplitude (Aa, Az) of the oscillation of the beam (2, 12) of the respective sensor (1, 10).
    [15]
    15. gradient magnetometer according to claim 14, characterized in that as the respective at least one read-out means, a capacitive read-out element (13) is provided.
    [16]
    16. Gradient magnetometer according to claim 14, characterized in that as the respective at least one read-out means a piezoelectric or piezoresistive or optical read-out element is provided.
    [17]
    Method for determining a single component (K) of a magnetic field gradient sensor using a sensor (1) according to one of claims 1 to 7, comprising the following steps: - exciting a preferably antisymmetric oscillation mode of the beam (2) of the sensor (1) by utilizing the Lorentz force (FL) by applying to the at least one conducting means (5) an alternating voltage of a frequency fi, where fi is a frequency of a mode of oscillation of the beam (2); - determining an amplitude (Aa) of the excited oscillation; Calculating the size of the component (K) according to the following formula: K = Aa * a (E, Ja, m, 1), where K is the component of the magnetic flux density (B) in a normal direction (a ') normal to the Direction of the measured amplitude Aa and normal to the longitudinal direction (x), partially derived in the longitudinal direction (x), and α is a proportionality factor determined by the modulus of elasticity E of the beam (2), the axial plane moment of inertia Ja &lt; of the beam (2) with respect to the normal direction (a '), the magnetic moment m, which results from the current flow in the conducting means (5) and the surface enclosed by the current flow, and the length 1 of the beam (2).
    [18]
    Method according to claim 17, characterized in that the amplitude in the second direction (z) is measured and that the component (K) of the gradient tensensor is determined according to the following formula K = Az * a (E, Jy, m, 1), where K is the component of the magnetic flux density (B) in the first direction (y) partially derived from the longitudinal direction (x), Az the measured along the second direction (z) '. Amplitude and Jy the axial plane moment of inertia of the beam (2) with respect to the first direction (y).
    [19]
    A method according to any one of claims 17 to 18, characterized in that, simultaneously with the excitation of the vibration of the beam (2) of the sensor (1), vibration of the beam (12) of a second sensor (10) mechanically coupled to the sensor (1) is excited by utilizing the Lorentz force (FL) by applying to the at least one conducting means (5) of the second sensor (10) an alternating voltage of the same frequency fi and that the amplitudes (Aa, Az) of the excited vibration of the two bars 2, 12) are determined.
    [20]
    A method according to claim 19, characterized in that it is further determined whether the vibration of the two beams (2, 12) is in phase or in antiphase.
    [21]
    A method according to any one of claims 19 to 20, characterized in that the two AC voltages are in phase opposition.
    [22]
    22. Use of a sensor according to one of claims 1 to 7 or an arrangement according to one of claims 8 to 13 for determining a single component (K) of a gradient magnetic field sensor and / or for determining a single component of the magnetic flux density (B).
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    同族专利:
    公开号 | 公开日
    EP3060933B1|2018-04-25|
    WO2015058229A1|2015-04-30|
    EP3060933A1|2016-08-31|
    AT515000B1|2016-09-15|
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    FR2942883B1|2009-03-06|2011-05-13|Commissariat Energie Atomique|GRADIENT SENSOR OF PERMANENT MAGNET MAGNETIC FIELD COMPONENT|FR3073284B1|2017-11-08|2020-11-13|Commissariat Energie Atomique|MAGNETIC FIELD GRADIENT SENSOR WITH REDUCED VIBRATION SENSITIVITY|
    法律状态:
    2020-08-15| MM01| Lapse because of not paying annual fees|Effective date: 20191023 |
    优先权:
    申请号 | 申请日 | 专利标题
    ATA821/2013A|AT515000B1|2013-10-23|2013-10-23|Gradient magnetometer and method for determining a single component of a gradient sensor of a magnetic field|ATA821/2013A| AT515000B1|2013-10-23|2013-10-23|Gradient magnetometer and method for determining a single component of a gradient sensor of a magnetic field|
    PCT/AT2014/050254| WO2015058229A1|2013-10-23|2014-10-23|Gradient magnetometer and method for determining an individual component of a gradient tensor of a magnetic field|
    EP14803034.9A| EP3060933B1|2013-10-23|2014-10-23|Gradient magnetometer and method for determining an individual component of a gradient tensor of a magnetic field|
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