Abstract:
A magnetic revolution counter for the unambiguous determination of a definable number of revolutions of a rotating element to be determined. The aim of creating such a revolution counter allowing a determination of any arbitrarily definable number of revolutions, for example up to values of N&gt;4000 or more as defined, and enabling a cost-effective and small design, is achieved in that a plurality of sensor elements ( 30   a  to  30   e ) are provided, which are formed by closed loops having magnetic domains attached and guiding the same, containing at least one ferromagnetic, respectively soft magnetic, layer. The loops have tapered protuberances directed toward the loop interior, wherein the number of protuberances provided per loop is determined in a defined manner deviating from loop to loop, and electric contact arrangements are provided, which allow the detection of any changes in the electric resistance of predetermined loop sections after a completed change of location of magnetic domains due to the effect of the outer rotating magnetic field in predetermined loop sections, and wherein the said resistance values can be supplied to an analysis unit for the purpose of allocating the number of revolutions of the rotating element.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a magnetic revolution counter for unambiguous determination of a pre-specifiable number of revolutions to be determined for a rotating element that can be used advantageously in numerous engineering fields, especially in automotive engineering. 
     Sensors for determining an angular position according to various physical principles are widespread. It is common to them that the sensor signal is periodic after 360°, i.e. that the sensor cannot differentiate between 10° and 370°. Therefore, for tasks in which the angle must be determined beyond 360°, such as is the case e.g. with the steering wheel in an automobile, such sensors are combined with another sensor that is able to detect the number of revolutions. It is then possible to differentiate between 10° and 370° using a combination with a revolution counter. Solutions for determining the number of revolutions are known in which the number of revolutions (for instance between 1 . . . 5) can be suggested mechanically using the course of a spiral having N spiral arms. Other solutions use mechanical gears connected to two angle sensors. The angle can be determined, even e.g. from 0 to 5-360°, from knowing the structure of the gear and the angular position of two magnets that are connected to the various wheels of the gear. Common to all of these solutions is that they require a mechanical element, that is, they are not contactless and are therefore not wear-free. However, a contact-free solution is required for many applications, particularly in an automobile. This contact-free solution could be created in that the angular position is determined at every point in time (continuously) and in this manner it is possible to differentiate a transition of 359° to 360° from angle 0°. This requires that the sensor and an associated memory element be continuously supplied with energy. This conflicts with the automotive engineering requirement that determining the absolute angle in the range of for example, 0° to for instance 5-360° must be successful even if e.g. the onboard electronics are disconnected from the battery. 
     The Posital Company developed contact-free counting of the number of revolutions that satisfies these requirements in principle (Company announcement: “Kraftwerk im Encoder . . . ” [Power Source in the Encoder . . . ], www.posital.com). In this case, a Hall sensor is used for determining the angle (0-360°). The number of revolutions is measured there using a so-called Wiegand wire. This wire has special magnetic properties that ensure that after every revolution, due to the sudden movement of a magnetic domain wall through a wire that is a few millimeters long, there is a brief but sufficiently intense voltage pulse that can be inscribed in a FeRAM (ferroelectric random access memory), even without the FeRAM being connected to the battery. This solution thus satisfies the requirement for determining the number of revolutions in a wear-free and contact-free manner and also counts revolutions up to the maximum storage capacity of the FeRAM used without the current supply being applied. However, the automobile industry rejects this type of solution because cost-effective production and packaging is not possible due to the macroscopic size of the Wiegand wire and because there are problems with electromagnetic compatibility due to the high ohmic input of the FeRAMs. 
     Another sensor element for counting revolutions that satisfies the aforesaid requirements is known from EP 1 740 909 B1 (WO 2005/106395). This sensor element is in the shape of an extended spiral having N windings and comprises a stack of layers that has the “giant magneto-resistance effect” (GMR). The GMR stratified system in this sensor element essentially comprises a hard magnetic layer, which defines the reference direction, and a soft magnetic layer, these being separated by a non-magnetic intermediate layer. The outer rotating magnetic field to be detected is strong enough to change the magnetization direction of the soft magnetic layer due to the movement of the domain walls, but it is too weak to change the magnetization direction of the hard magnetic layer, which runs parallel to the straight sections of the extended spiral. The sensor element thus reacts to a rotating magnetic field with a change in resistance, whole and half revolutions being registered in the form of 2N+1 resistance values within the countable range of 0 to N revolutions. Each resistance value is therefore bijectively assigned to a half integer or whole integer revolution value. The magnetic structure remains unchanged if the magnetic field does not rotate. Given rotation, the magnetization directions change, regardless of whether the resistance value is read out or not. This means that the system even registers all changes in the rotating magnetic field when it has no current or power, and a current supply is needed only for read-out, that is, for determining the resistance. 
     One disadvantage of such an arrangement is that, due to the memory geometry used, each revolution requires a complete spiral winding, and the spiral must be very large geometrically when counting a large number of revolutions. This means that the probability increases that defects that occur during the manufacture of the spiral will lead to failure and thus to a reduction in the yield. In addition, the chip surface area increases in size, and thus the costs for such a sensor also increase. Moreover, when there is a large number of spiral windings, the design provided in EP 1 740 909 B1 automatically leads to problems in determining the number of revolutions. The usable swing in voltage, which initially results from one revolution, is scaled at 1/number of spiral windings. This swing in voltage is clearly too small for a reliable evaluation for N&gt; to &gt;&gt;10. One alternative, which is provided in the aforesaid patent, does permit the full magneto-resistance swing at higher rates of revolution, but still has the disadvantage of a long spiral, and the advantage of the large swing is offset in that, instead of two electrical contacts, all spiral parts that form an unclosed circuit are provided with four electrical contacts and must be read out and processed electrically. When N=100, this is four hundred contacts, and thus the circuitry is very complex. 
     In addition to the attempts described in the foregoing to develop revolution counters based on moving domain walls, there are also proposals for creating a magnetic logic device using moving domain walls, even if these proposals are in a search field that is not as closely related to the invention. In this case, magnetic domains are moved by closed or branching magnetic strips such that logical functions such as AND, NOT, and XOR can be created, in addition to intersections and branches. Thus, in Science Vol. 296, 14 Jun. 2002, pages 2003-2006, Allwood et al. propose a sub-μm ferro-magnetic NOT gate and shift register in which the logical information can be inscribed in the logical construct using locally flowing currents and can be read out again only by means of a TMR effect. In this publication, domain walls are moved by rotating magnetic fields that act as the clock for the magnetic logic device. US patent 2007/0030718 A1 by these authors describes the use of such a magnetic logic device in which the magnetic domain walls are moved using electrical current pulses. The same authors provide another proposal for constructing a magnetic memory (US 2007/0047156 A1) using magnetic domains. For this, the identical loop-like structures described in the foregoing are placed above one another, with the same number of cusps that are required for attaining the maximum storage capacity sought in the foregoing. Each structure comprises a loop of a magnetic material that includes cusp-shaped protuberances that protrude into the interior of the loop. Only one of the cusps that projects into the interior is elongated and, in a special embodiment, has a geometry that differs in its width from the other cusps. The information is inscribed in the memory using this cusp by generating a magnetic domain. Each cusp has a branch that leads outward, and disposed on its end is a magneto-resistive element for reading out the information. A rotating magnetic field that the loops detect homogeneously acts as clock and power supply for transporting the domains and in a special embodiment acts as serial data channel. The basic principal of this arrangement is variable generation of domains whose number equals the information specifically to be stored. 
     The object of the present invention is to create a magnetic sensor system for a revolution counter, which magnetic sensor system permits any desired pre-specifiable number of revolutions to be determined, for instance up to values of N&gt;4000 or pre-specifiably more, and that thus if desired goes far beyond previously known solutions and that at the same time enables a cost-effective and structurally small embodiment that does not suffer from the disadvantages of the prior art. In addition, the proposed solution should overcome significant disadvantages of prior proposed solutions, specifically the large number of contacts (see EP 1 740 909 B1) (at least 4·N, where N is the number of countable revolutions), which number thus increases linearly with the number of the desired count of revolutions, and thus when determining 256 revolutions has 1000 contacts, and the long length of the spiral (2·N·1) where 1 is the longitudinal extension (typically 200 μm) of the spiral, as depicted in the aforesaid EP document. 
     SUMMARY OF THE INVENTION 
     This object is attained in accordance with the essence of the invention, wherein, depending on the number of revolutions to be measured for an element to be detected (for instance a shaft) that is provided with a magnet system, the magnetic field of which permits the detection of all provided sensor elements, a plurality of such elements is provided. The sensor elements are formed by closed loops that are covered by magnetic domains and that guide them, which loops include at least one ferromagnetic and one soft magnetic layer, said loops having tapered protuberances oriented into the interior of the loop, the number of protuberances provided per loop being defined and varying from loop to loop. Electrical contact arrangements are provided on the loops, which contact arrangements permit the changes in the electrical resistance of pre-specifiable loop segments to be determined after magnetic domains have changed location due to the effect of the outer rotating magnetic field of the magnet system in the pre-specified loop segments, and it being possible to supply these resistance values to an evaluation unit for the purpose of correlating the number of revolutions of the rotating element. 
     The basic idea of the present invention is based on the fact that every revolution of the object to be monitored is linked to a 360° revolution of a magnetic field at the site of a revolution counter and that this 360° revolution of the magnetic field leads to a change in the position of magnetic domains that move in an inventive arrangement of defined, different loops having tapered protuberances oriented into the interior of the loop. In a binary arrangement, as is described in greater detail below, each loop includes as many adjacent domains as revolutions that this loop is intended to count. Thus, in each embodiment, a fixed and defined pre-specifiable number of domains per loop is to be inscribed that then remains the same throughout the service life of the revolution counter or until it is reformatted, even if the entire arrangement is without current. 
     The measuring tasks underlying the invention and thus the use of the proposed revolution counter are used in two basic configurations. Either the number of revolutions of a shaft that is accessible from the side are to be determined (de-central arrangement or hollow shaft sensor arrangement) or the sensor may be placed at the end of the shaft (central arrangement). 
     The following exemplary embodiments and figures shall be used to explain the foregoing and the invention in greater detail. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1   a  illustrates the basic principle of a de-central sensor arrangement (hollow shaft sensor); 
         FIG. 1   b  illustrates the basic principle of a central sensor arrangement; 
         FIG. 2  depicts an exemplary stack of layers that can be employed for using the GMR or TMR effect; 
         FIG. 3  depicts a first exemplary inventive loop having two inwardly oriented tapered protuberances; 
         FIG. 4  depicts an example of a special layout for erasing domains that are present in an exemplary loop; 
         FIG. 5  depicts an example for a special layout for defined inscription of a pre-specified number of domains in an exemplary loop; 
         FIG. 6  is a schematic depiction of a loop arrangement for counting four revolutions having six cusp-like, inwardly oriented protuberances and four domains; 
         FIG. 7  depicts examples of contact arrangements for a coprime loop configuration; 
         FIGS. 8 and 9  depict examples of contact arrangements in a loop configuration constructed according to the binary principle; 
         FIG. 10  depicts examples of contact arrangements for eliminating the hysteresis problem; 
         FIG. 11   a  depicts an exemplary contact arrangement, with some detail, for a coprime loop embodiment using a GMR layer system; 
         FIG. 11   b  depicts an example of a contact arrangement, with some detail, for a coprime loop embodiment using a TMR layer system; 
         FIG. 11   c   1 - 11   c   4  depict more complete variants of how the contacts are attached to a special loop without hysteresis suppression when using a GMR layer system; 
         FIG. 11   d   1 - 11   d   4  depict more complete variants of how the contacts are attached to a special loop with hysteresis suppression when using a GMR layer system; 
         FIGS. 12 and 13  depict special embodiments within the loop structure for domain transport in only one loop direction; 
         FIGS. 14   a  and  14   b  are examples of arrangement variants for a plurality of loops that are embodied according to the coprime principle; 
         FIGS. 15   a  and  15   b  are examples of arrangement variants for a plurality of loops that are embodied according to the binary principle; and 
         FIG. 16  is an exemplary loop configuration having an uneven number of tapered protuberances oriented into the loop interior. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1   a  and  1   b  depict two basic arrangements in which the inventive revolution counter that is described in greater detail below can be used.  FIG. 1   a  depicts a cross-section through an entire system with a de-central arrangement (hollow shaft sensor arrangement), comprising a shaft  01  with a magnet system  20  that is attached to the circumference and that includes an Si substrate  10  and  10   a  (advantageously also including an evaluation unit), on which is disposed an inventive revolution counter  11  or  11   a . Acting from the outside at the site of the revolution counter  11  is a magnetic field, here in the form of a permanent magnet combination  20  that when it passes produces a 360° revolution in the direction of the magnetic field at the site of the revolution counter  11 . The revolution counters  11  and  11   a  are arranged geometrically such that the magnetic field for the magnets  20  can always act only on one of the two. In this case, when the shaft  01  rotates, a plurality of permanent magnets being disposed on its circumference at a location in the example, the revolution counter  11  experiences a 360° revolution of a magnetic field at the site of the revolution counter  11 . In this case the sensor is only exposed to the magnetic field across a small angular area. Since the condition of the domains, which are described in greater detail below, changes in this angular area, this angular area must be “blocked” during the measurement. This can happen in that a second sensor  11   a  having an evaluation unit is attached such that whenever the shaft  01  rotates, only one revolution counter is exposed to the rotating magnetic field. Since, in accordance with the known prior art, revolution counters are fundamentally operated connected to an angular sensor, which is not depicted in greater detail here, it is possible to know the site of the rotating magnetic field from the signal of the angular sensor and thus to know which of the revolution counters is supplying a valid or invalid signal, i.e., that only the signals from the revolution counter that is disposed in the moving magnetic field is read. 
     In an embodiment using a second principle and mentioned in the foregoing, a permanent magnet  20  is attached to the end face of a shaft  01 .  FIG. 1   b  depicts a cross-section through an entire system that has a central arrangement and that comprises a Si substrate, advantageously with an evaluation unit  10  on which the inventive revolution counter  11  is disposed. A magnetic field of a permanent magnet  20  that is disposed on the end of the shaft  01  acts from outside at the site of the sensor  11 , the permanent magnet  20  being embodied such that the entire revolution counter is covered by the aforesaid magnetic field, as the field lines in the example are intended to indicate. When the shaft  01  rotates 360°, the revolution counter  11  also experiences a magnetic field that rotates 360°. In this embodiment, as well, there are angular areas in which the inscribed domain configuration described below is subjected to a change and then supplies invalid information about the number of revolutions. However, if this area is less than 90° per half revolution, then for this configuration a second inventive revolution counter that is not depicted in  FIG. 1   b  and that is arranged on the Si substrate rotated 90° with respect to the sensor  11  can ensure that a valid signal is always available from one of the two revolution counters. Using a normal angular sensor in accordance with the prior art it is then possible to determine and establish which of the two revolution counters supplies the valid signal. 
     In the inventive revolution counter  11 , the domain walls themselves move in an arrangement of a plurality of loops, described in greater detail below, which arrangement is produced for instance by a structuring process and in each of which loops a defined number of domain walls is inscribed by an initialization process, which is also described below. These different loops are configured such that for instance the first repetition of the arrangement of all of the domain walls present in the different loops does not occur until after, for example N=4096 or more so that the revolution counter always supplies unambiguous values up to the pre-specifiable maximum number of revolutions. 
     The present specific domain configurations can be determined using a number of electrical contacts on the loops based on magneto-resistive effects, e.g. the GMR (giant magneto-resistance) effect or the TMR (tunneling magneto-resistance) effect and this makes it possible to find the number of revolutions of a magnetic field that the domain walls move in the closed loops. This determination of the domain configuration uses the known effect that the resistance in a GMR or TMR stack is a function of the relative direction of magnetization of the layer in which the domains move compared to a reference direction defined by a hard magnetic layer. 
     The resistance is low when the direction of magnetization is the same in the reference layer and in the sensor layer and it increases (6-10)% (in the case of the GMR effect) or (100-500)% in the case of the TMR effect, when the direction of the two magnetizations is anti-parallel. 
       FIG. 2  depicts an example of a stack of layers that is to be employed for exploiting the GMR or TMR effect.  FIG. 2  depicts a cross-section of a packet of layers that is known per se. The current flows in the direction of the indicated magnetization arrows (in the layer plane), and the electrical resistance is determined using electrical contacts (not shown here) that are attached at a great distance from one another (100-500 μm). In the present invention, if a TMR stack is employed, the 2.5 nm-thick copper layer depicted in  FIG. 2  is replaced with a 1-2 nm-thick Al 2 O 3  or MgO layer. The current then flows vertically through the stack of layers from bottom to top or vice versa. In general, the TMR stack occupies a surface area of a few to a few multiples of 10 to 100 μm 2 . It is not necessary to provide additional embodiments for special designs of GMR or TMR stacks of layers at this point because these belong to the known prior art. Therefore only the following explanation will be provided: 
     A Ni 81 Fe 19  layer (permalloy=Py) acts as the actual sensor layer in which the magnetic domains move, the 0.5 nm-thick Co layer only increasing the GMR or TMR effect. A combination of a so-called artificial anti-ferromagnet (CoFe/0.8 nm Ru/CoFe) in combination with an anti-ferromagnet (in  FIG. 2 : IrMn, otherwise also NiMn or PtMn) acts as the hard magnetic layer. The 0.8 nm-thick Ru layer ensures that the magnetic moments of the two CoFe layers are anti-parallel and cancel one another out. The IrMn in combination with a CoFe layer produces a so-called unidirectional anistropy. This defines the magnetic preferred direction. It can be homogeneous in the entire wafer and thus also in the inventively formed loops; using suitable local heat treatment and simultaneously the effects of magnetic fields, the reference direction can also be defined in a non-uniform manner locally, for example, rotated 90° with respect to the previous preferred direction. This provides, for example, advantages with respect to establishing the reference direction in the sense of aforesaid valid ranges for the measurement signal. 
     For the certain movement of the domains in the sensor layer, a minimum field H min  is necessary that is a function of the geometry (height and width of the sensor layer) and magnetization of the material of the magnetically soft layer that is structured in the inventive loop shape described below. At the same time, the proposed principle requires that the number of domains inside the loop does not change while the revolution counter is in use. This means that the magnetic field acting on the revolution counter must always be less than a magnetic field H nuc  at which nucleation of a magnetic area occurs and thus two additional domain walls are generated, which is, however, easily satisfied by selecting the magnetic field of the rotating permanent magnet  20  (see  FIGS. 1   a  and  1   b ) that is acting on the revolution counter. 
     The basic principle for counting the number of revolutions can be attained in different ways. In the proposed invention, proposed shapes are based either on loops having cusps that are oriented inward and have a structure that permits binary-type counting or on loops having inwardly-oriented cusps that are constructed such that they each attain a coprime number of revolutions in every loop. With these two variants it is possible with a relatively small number of loops to attain a large number of countable revolutions (in the described embodiment N&gt;=4096) revolutions and convert them to user-friendly signals with relatively straightforward circuitry. There are typically &lt;=12 loops for binary variants and &lt;6 loops for coprime variants. 
     To facilitate understanding, the basic principle of the present invention shall be explained for one of the inventive loops for counting two revolutions using  FIG. 3 . As will be explained in the following, this loop has two inwardly oriented tapered protuberances A. In the initial configuration (top left depiction in  FIG. 3 ) the loop and its two cusps are initially produced without any domain walls. Then a configuration like that in the depiction in the top right of  FIG. 3  is produced by means of a configuration line, not shown in this figure. This configuration corresponds to the ¼ revolution. The domain walls D that move through the loop from quarter revolution to quarter revolution and after exactly two revolutions are back in the initial configuration are depicted by small black rectangles in the individual depictions in  FIG. 3 . The central bold-face arrow indicates the direction of the permanent magnet to be detected (not shown here; see component  20  in  FIGS. 1   a  and  1   b ) and thus of the rotating component. The thinner arrows in the depictions in  FIG. 3  indicate the local direction of magnetization in the sensor loop layer. 
     Comparing the condition in  FIG. 3  (R=number of revolutions) for R=−0.25 and R=0.25, that is for exactly half a revolution, it is evident that one domain wall requires one 180° revolution of the magnetic field for moving through the cusp. For the two cusps provided here, then, one revolution of the magnetic field is needed for moving across the two cusps. One additional revolution by the magnetic field, that is, in this case moving the domains along the depicted loop area without cusps, is required to go through the entire loop and return to the initial position. 
     Thus, it follows for the inventive structure of the provided loop n, which is dimensioned for counting n whole-number 360° revolutions, that this loop includes 2n−2 cusps that project into the interior of the loop (n should be &gt;=2). Thus a 180° revolution can be detected by each of these cusps. Therefore, generalizing this case with 2n−2 cusps, exactly n−1 complete revolutions can be detected. The movement of the domains through the loop area without cusps results in another revolution, so that this arrangement is for exactly n complete revolutions. Therefore after n revolutions the configuration of the domains for R=0 and R=n is identical (where R is the number of revolutions of a permanent magnet in one direction [regardless of whether this is clockwise (cw) or counter-clockwise (ccw)]). Inventively combining a plurality of loops that all have this property (see in advance  FIGS. 14 and 15 ) makes it possible to unambiguously determine a greater number of revolutions. Using the proposed arrangement it is even possible to attain revolution counts&gt;4000 in miniaturized form but still with acceptable technical complexity. 
     Depending on the object, two basic variants of loop combinations are possible, specifically an arrangement with a binary construction or a coprime arrangement. How this should be construed shall be explained in the following. However, other designs, which may however be more complex, are also within the scope of the invention if they provide an unambiguous allocation of domains moved in loops having inwardly oriented tapered protuberances. 
     The initial configuration for the system constructed in a binary fashion proposed in accordance with the invention as the first option is characterized in that for n revolutions the loop includes exactly n magnetic domain walls that are all disposed adjacent to one another. In the framework of the invention, the cusps are to be embodied as sharp as possible so that the ratio of width to length for the cusps is at least 1:3 and the curvature radius for the cusps is itself as small as technologically feasible. 
       FIG. 6  provides a counting scheme for the binary counter variant having n=4. The loop depicted here should be able to detect four revolutions and thus, given the above condition, is provided with six cusps (2n−2), and four domains that are disposed adjacent to one another are inscribed. For the evaluation, the electrical resistances in the adjacent areas of the cusps marked with a circle are compared. The resistances to the right and to the left are equal or unequal depending on whether a domain is disposed in the cusp or not, and they can thus be assigned to the logical value, ZERO or ONE, that is entered in the loop. 
     Thus, in the framework of the invention it is possible to inscribe the required number of domains at a pre-specifiable location within the loop that is desired as the initial zero position for counting revolutions. At R=0, the magnetic domain walls are preferably disposed at the initial position indicated in  FIG. 6  (top left) in order to begin counting at zero. If a non-volatile memory is provided in the evaluation unit advantageously present for reading out the various loops, any other initial condition may also be used that corresponds to the “zero position” and that is defined (referenced) as zero using the evaluation unit. 
     The initial configuration described in the foregoing may now be adjusted for the invention for instance as described in the following, for which purpose  FIG. 4  provides a schematic depiction of one possible embodiment using a special loop: 
       FIG. 4  depicts a loop for n=4 (total revolution 4·360°) having a narrow electric conductor across the loop. In the plane of the loop, with a current flow in the narrow part of the conductor to the right, the narrow conductor produces a magnetic field upward (see arrow  42 ). First all of any domains present in the loops are erased, i.e. the loops are rendered domain-free. In addition, disposed on the loop  30 , depicted individually in  FIG. 4 , is an additional conductor  40 . It covers the loop  30  at a location and has only a slight width there. Thus the current density is high at the location  41  and therefore the magnetic field (see arrow  42 ) that acts beneath the conductor  40  at the site of the loop  30  on the location  41  is strong. The erasure process now occurs in that the rotating magnetic field, here produced by the permanent magnet  20 , is rotated exactly n times over the loop for one full revolution. For this, a magnetic field H is needed in the limits H min &lt;H&lt;H nuc , as described in the foregoing. During the erasure process for the loop, the current produces a magnetic field H&gt;H nuc  beneath the conductor at the site of the loop of a magnitude such that the magnetization there is parallel to the magnetic field acting on the sensor layer, regardless of the previous orientation. In accordance with  FIG. 4 , the magnetic field having the strength H is rotated at least 4 times (for the loop n times for n revolutions) in one direction (cw or ccw). The revolution is stopped when the direction of the magnetic field from the permanent magnet  20  that is acting on the loop  30  coincides with the direction of the magnetic field  42  that is produced by the conductor  40  in the loop. The revolution of the magnetic field moves all of the domains present in the loop to the site of the large magnetic field. It is erased there. 
     The return of the conductor  40 , which in one advantageous embodiment is returned to another location across the loop, also, should have a width such that the magnetic field that acts below in the plane of the loop does not impede the transport of the domains through the rotating permanent magnets. This can typically be attained in that the return is approximately 5 times as wide as the narrow part of the conductor  40  that produces the strong magnetic field. In accordance with one such approach, the first loop depicted in  FIG. 3  (top left), for instance, has been shifted to a configuration that has no domain walls. 
     For other loop configurations, and other numbers of domains, the foregoing formatting process occurs analogously, without it being necessary to present it here in greater detail, because it is within the freedom of choice for the person of average skill in the art. 
     The desired starting configuration is distinguished by the direction of the magnetization in the left cusp (see loop, upper right of  FIG. 3 , to stay with the example). 
     Now a desired domain configuration can be inscribed using another additional current conductor that in  FIG. 5  has an exemplary geometry and that is shown separately in  FIG. 5  for the sake of clarity.  FIG. 5  depicts one of a number of potential and possible embodiments of the additional current conductor  60 , which in the example is guided via the ends of four inwardly oriented cusps for the loop  30 . The electrical current I flowing through the additional current conductor  60  (see arrow  61 ) produces the magnetic field H I , and positioned parallel thereto is a DC field having the strength H M , where H I  and H M &gt;H nuc . 
     The current flows through the additional current conductor  60 , which in the example is embodied tapered in the area of the ends of adjacent cusps in the loop  30  and thus produces a high current density and therefore a strong magnetic field H I . If a magnetic field H M  having the strength H Min &lt;H M &lt;H nuc  is parallel to the flowing current, the magnetizations in the cusps that are disposed under the narrow area of the additional current conductor  60  are remagnetized in the direction of the magnetic field H I  and the resulting domains are transported out of the cusps through the magnetic field H M . The resultant configuration is comparable to the condition R=−0.25 depicted in  FIG. 3 . 
     Other layouts for erasing and inscribing domains are possible and will follow from the specific conditions under which the inventive loops are produced. In addition, such circuits for erasing and inscribing do not limit the invention, since once the required number of domains per provided loop has been inscribed it can be removed again without having a negative impact on the functionality of the revolution counter, since when the revolution counter is used properly a number of domains inscribed per loop always remains in the loop. 
     There is greater freedom for selecting the initial configuration for the other aforementioned basic second embodiment, specifically for counting with loops that count a coprime number n. In this case, in a first possible embodiment it is only necessary for at least 2 domains to be in the loop, but no more than 2n−2 domains, and for the arrangement of the domains to agree with the initial configuration only after n entire revolutions. We turn now to the special description of a configuration having two adjacent domain walls as a starting configuration, as described below, but this shall not be construed as a limitation in general. 
     First the revolution counter constructed using the binary principle shall be described in more detail in the following. 
     According to the considerations described in the foregoing, in this case loops are to be constructed that indicate a periodic behavior for n=2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, and 4096 in order to depict N=4096. 
     This can be accomplished as follows: 
     The width of an inventive loop perpendicular to the direction in which the domain runs should be constant at all locations and for instance should be between 100 and 200 nm. The loop itself is created e.g. using a stack of layers that has the giant magneto-resistance (GMR) effect. Such a stack of layers may have, for example, a typical structure of the type that follows: 
     3 nm Ta/5 nm Ni 81 Fe 19  like others/1 nm Co 90 Fe 10 /2 nm Cu/3 nm Co 90 Fe 10 /0.8 nm Ru/3 nm Co 90 Fe 10 /10 nm IrMn/5 nm Ta. 
     The 5 nm Ni 81 Fe 19  like others/1 nm Co 90 Fe 10  sandwich acts as a soft magnetic layer through which the domain walls run. For the instant application, in contrast to known GMR layer systems for angular sensors, it is practical to make the NiFe layer significantly thicker (typically 15-20 nm) in order to ensure that the so-called shape anisotropy is high, the shape anisotropy essentially being determined by the thickness/width ratio and by the magnetization of the sandwich layer. Naturally, instead of using a Py layer, it is within the framework of the invention to use a layer made of a different soft magnetic alloy, for instance a CoFeNi, with a layer thickness between 5 . . . 35 nm. 
     A high anisotropy compels that the magnetization in the NiFe layer, with the exception of the domains themselves, can always be only parallel to the edge. Thus there are only two stable conditions for the directions of the magnetization of the sensor layer that are oriented anti-parallel to one another. A high shape anisotropy is furthermore responsible for the fact that the magnetization does not switch spontaneously until there are relatively strong magnetic fields of typically 20-80 mT. 
     According to the adjustment in the initial configuration, as described using  FIGS. 4 and 5 , in the example in accordance with  FIG. 6  four domains are disposed in the loop n=4 exactly at the locations marked in  FIG. 6  (top left). The conditions after ½, 1, 1.5, 2, 4 revolutions, depicted in  FIG. 6 , result if a rotating magnetic field (not shown) acts on the entire loop. It is clearly evident that in this configuration the initial condition is re-attained after exactly four revolutions. The same can be attained for any desired loop that is to count n revolutions. There must be exactly 2n−2 cusps that are oriented inward for this loop. In the initial configuration, exactly n domains are inscribed using the attached additional current conductor  60  (see  FIG. 5 ). For binary counting, this means loops with n=2, 4, 8, 16, 32, 64, 128, 256, . . . , the length of the tapered inscribing conductor  60  being adjusted for each and increasing as n rises. 
     For reading out the loops, first the binary case and the situation for n=4 should be considered: 
     Without excluding other possibilities for the configuration, it is possible to provide e.g. a contact structure suggested in  FIG. 8 .  FIG. 8  provides an example of the arrangement of contacts K 1  through K 4  to the right and left adjacent to an inwardly oriented cusp. Such a contact structure permits the determination of the resistances R 12 , R 34  of the loop segments, which for the sake of simplicity are depicted in  FIG. 8  without the required roundings, to the right and left of the first cusp. If there is a domain wall in the area of the cusp identified with a circle, then the two areas disposed to the right and the left adjacent to the cusp are either both high impedance or are both low impedance. The logical ZERO is assigned to this condition. If there is no domain wall in the area of the cusp, then one of the two areas is low impedance and the other is high impedance. The logical ONE is assigned to this condition. As is evident when compared with  FIG. 6 , for R=0, 0.5, 1, and 1.5 the result for this loop where n=4 is r 4 =ZERO. The result for R=2, 2.5, 3, and 3.5 is r 4 =ONE. R=4 is a repeat of R=0, i.e. the result after n revolutions in the loop in question is ZERO for the first n/2 revolutions and ONE for the subsequent n/2 revolutions. Then the entire process repeats periodically. 
     The number of calculated revolutions in an arrangement of loops where n=2, 4, 8, . . . N then results from the equation:
 
 R=r   2 ·2 1   +r   4 ·2 2   +r   8 ·2 3   +r   16 ·2 4   +r   32 ·2 5   +r   64 ·2 6   + . . . +r   s ·2 S  or expressed generally:
 
     
       
         
           
             R 
             = 
             
               
                 ∑ 
                 
                   i 
                   = 
                   1 
                 
                 S 
               
               ⁢ 
               
                 
                   r 
                   
                     2 
                     i 
                   
                 
                 · 
                 
                   2 
                   i 
                 
               
             
           
         
       
     
     S is selected such that the number of revolutions to be counted is N=2 S . 
     The other inventive embodiment, specially mentioned in the foregoing, draws on the coprime nature of the loops used. Thus, if loops are constructed that e.g. re-attain their initial configuration after exactly 3, 4, 5, 7, and 11 revolutions, the entire arrangement does not re-attain its initial configuration e.g. until after 3*4*5*7*11=4620 revolutions. Thus even a large number N of revolutions can be counted in loops having a coprime number of different revolutions to be counted. The advantage of such an arrangement is that in it the number of the cusps projecting into the interior of the loops can be kept much smaller than in the aforesaid binary configuration, so that the geometric extension of the loops can be scaled down even further. However, this advantage is offset in that the loops are read out in a different manner. While in the binary counting loops it is only necessary to determine the loop conditions “ZERO” or “ONE”, the exact domain condition for each loop must be determined in the configuration with “coprime” loops. This means e.g. for the loop in which n=4 that it must be calculated whether the loop has experienced 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4=0 revolutions. This can be accomplished in that at least 2n contacts must be given to the loop n, it being possible to resolve the problem described in the foregoing with these contacts, as is depicted in the example in  FIG. 7 .  FIG. 7  illustrates a counting scheme for the variant of the coprime loop embodiment and n=4 as the whole number representing the 360° revolutions that can be counted using this loop. 
     In this special example, an initial configuration has been selected in which four domains were inscribed at the beginning, depicted by the solid circles in  FIG. 7 . As the table below indicates, all eight possible values are logically different and can therefore be assigned via an appropriate circuit to the conditions 0, 0.5, . . . 3.5. 
     If a domain wall is between the contacts (here numbered 1 . . . 8), the resistance value between the first six aforesaid pairs (1-2 through 6-7) is equal and is different for pairs 7-8 and 8-1, because there has been a 180° loop revolution between these last two said pairs. If there is no domain wall between them, the resistance for 1-2 through 6-7 is not equal and is equal for 7-8 and 8-1. 
     The following truth table results: 
     
       
         
               
               
               
               
               
               
               
               
               
               
             
           
               
                   
               
               
                 R 
                 0 
                 0.5 
                 1 
                 1.5 
                 2 
                 2.5 
                 3 
                 3.5 
                 4 = 0 
               
               
                   
               
             
             
               
                 1-2 
                 Zero 
                 One 
                 One 
                 One 
                 One 
                 One 
                 Zero 
                 Zero 
                 Zero 
               
               
                 2-3 
                 Zero 
                 Zero 
                 One 
                 One 
                 One 
                 One 
                 Zero 
                 Zero 
                 Zero 
               
               
                 3-4 
                 Zero 
                 Zero 
                 Zero 
                 One 
                 One 
                 One 
                 One 
                 Zero 
                 Zero 
               
               
                 4-5 
                 Zero 
                 Zero 
                 Zero 
                 Zero 
                 One 
                 One 
                 One 
                 One 
                 Zero 
               
               
                 5-6 
                 One 
                 Zero 
                 Zero 
                 Zero 
                 Zero 
                 One 
                 One 
                 One 
                 One 
               
               
                 6-7 
                 One 
                 One 
                 Zero 
                 Zero 
                 Zero 
                 Zero 
                 One 
                 One 
                 One 
               
               
                 7-8 
                 One 
                 One 
                 One 
                 Zero 
                 Zero 
                 Zero 
                 Zero 
                 One 
                 One 
               
               
                 8-1 
                 One 
                 One 
                 One 
                 One 
                 Zero 
                 Zero 
                 Zero 
                 Zero 
                 One 
               
               
                   
               
             
          
         
       
     
     Configuring the initial situation differently is also within the framework of the invention, and would result in a different truth table. The only requirement for the initial configuration in this case of counting n whole 360° revolutions and the coprime arrangement is that the loop n contains less than 2n but at least two domains and the domains are arranged such that a configuration or a position of the domains does not recur until after n revolutions. Each of these configurations permits the bijective calculation of the number of revolutions R between 0 and n. Each initial configuration is precisely linked to exactly one truth table that can be determined prior to the beginning of the counting process using the geometry of the aforesaid additional elements (erasing and inscribing component). 
     From the information presented in the foregoing, it is evident that a revolution counter with the binary variant construction requires a plurality of the inventively provided loops and cusps, but fewer electrical contacts for reading out and assigning logical conditions than in a loop arrangement that uses the coprime principle in which the situation is exactly the opposite—in other words fewer loops and cusps, but more contacts. 
     Because the placement of the contacts that are to be attached for reading out the resistance values is completely different depending on which structure described in the foregoing is selected for the loops (binary, coprime) and because there are additional problems associated with unambiguous signal assignment in this regard, some basic suggestions shall be considered in the following.  FIGS. 8 through 11 , which provide examples of possible configurations for providing electrical contacts, shall be used to better illustrate these situations and additional variants. 
       FIG. 8  is an example of a loop in which n=4 and there is binary evaluation. In this case the electrical resistances R 12  and R 34  are measured at the contacts K 1  through K 4 . As  FIG. 9  indicates, combining contacts K 2  and K 3  simplifies the circuit. The resistance values are assigned to the logical conditions in a logic circuit that is outside the invention and can be created in the manner desired, as stated in the foregoing. 
     As discussed in the foregoing, the movement of the domains is associated with a hysteresis, and the result of this is that in general one sensor alone is not always able to supply the correct information about the number of revolutions. For the example of the hollow shaft sensor, this problem can be resolved in a simple manner using a second sensor, as depicted in  FIG. 1   a . There are a number of options for resolving the hysteresis issue for the central arrangement in accordance with  FIG. 1   b . The most simple solution, but also the most expensive solution, is to use a second sensor that is rotated 90°. The signal from an additionally present angular sensor then decides from which revolution counter the valid signal can be obtained. In the case of binary counting this can be omitted if a solution like the example in  FIG. 10  is used. The left-hand side of  FIG. 10  depicts an arrangement of contacts K 1  . . . K 8 , four contacts (K 1  . . . K 4 ) being arranged on a horizontal part of the second conductor and four contacts (K 55  . . . K 8 ) being arranged on a vertical part of the conductor. The right-hand part of  FIG. 10  depicts an example of an alternative arrangement for the contacts. In this case, the contacts for the binary evaluation are at K 1  through K 4  for the 0° sensor, the sensor rotated 90° is integrated in the loop and is represented by the contacts K 5  through K 8 . However, in such a solution it must be noted that, if a GMR stack of layers is used, the reference layer must not be vertical on the series of conductors in which the resistance is measured. For the loop depicted in  FIG. 10  this could mean that the reference direction is at an angle, preferably a 45° angle, to the straight lines in which the resistance is determined. Another possibility is for the reference to have a uniform direction in a first step, in this case without any general limitations, e.g. parallel to the bar R 12 , and in a subsequent step for the loop to be heated, e.g. via the contacts K 5  through K 8 , until the reference direction experiences a local revolution, typically 1T, under the effect of the local temperature when a magnetic field of sufficient magnitude is applied. 
     When using loops with a coprime number for the revolutions to be measured, the principle for arranging the contacts in  FIG. 10  can be used analogously with the difference that in this case contacting must occur at all cusps. 
       FIG. 11   a  initially illustrates basic attachment of contacts using a GMR stack of layers, from which the entire inventive loop arrangement is then to be produced based on the foregoing, and  FIG. 11   b  illustrates the use of the TMR stack of layers, which is also possible. Further below there is more detail about the latter regarding dimensioning. As is illustrated in  FIG. 11   a , the electrical contacts for determining the resistance and thus the direction of magnetization are to the left (K 1  and K 2 ) and right (K 3  and K 4 ) of a cusp and the direction of the reference magnetization goes from left to right or vice versa. If the domain (or domains) in the entire loop are to be localized, contacts must be attached in all horizontal areas, as is depicted in  FIG. 11   c   1 . Each pair of contacts then detects the changes in resistance from one contact area to the other that are caused by domain migration due to a 180° revolution of the magnetic field. The distances between the contacts (e.g. K 1  and K 2 ) should ideally be the same in the case of GMR layer systems. Contacts may be combined, as illustrated in  FIG. 11   c   3 , in order to keep the number of contacts that are to be electrically connected as low as possible. 
     If the cusps do not all go from one side of the loop into the interior, the contact arrangements should be attached as depicted e.g. in  FIG. 11   c   2  such that domain migrations can even be detected when the outer magnetic field rotates 180°. This means that on all horizontal areas of the loops contacts are attached to the right and left of the cusps that point up or down. If one or a plurality of cusps points into the interior of the loop from the right-hand and/or left-hand side, one side of the cusp must be provided with the contacts. It is also possible in this case to combine contacts and thus reduce the number of contacts, as depicted in  FIG. 11   c   4 . 
     If there is a desire to eliminate the effects that are linked to hysteresis, contacts K 5  through K 8  must be attached in addition to contacts K 1  through K 4 , as depicted in  FIG. 11   a . The reference direction (see bolded arrow in  FIG. 11   d   1 ) must then ideally be rotated 45° or must be fixed locally using suitable measures (see aforesaid local thermal influence) such that it runs parallel to the areas to be measured. The contact arrangements that result from this are depicted as examples in  FIGS. 11   d   1  through  11   d   4  for the variants: all cusps go out from one side/from different sides of the loop and contacts for these variants may be combined. The illustrated variants are only used as examples and do not limit the invention with respect to the type of contact connections. Regardless of the specific position, it is common to all of these depicted solutions that without combining contacts 4n contacts are needed for one loop for n revolutions. If the effects of hysteresis are also to be suppressed, 8n contacts are needed. Possible combining of contacts reduces their total number, as indicated in the examples in the figures described here. 
     In addition to the variants described in the foregoing, specifically the structure of the loops as a GMR stack of layers as indicated in the aforesaid, it is also possible in the framework of the invention to form the loop using only one ferro-magnetic layer that bears the domain walls. The magnetic condition of the ferro-magnetic layer, specifically the direction of the magnetization in the one direction or in the opposing direction, but always parallel to the conductor direction, can then be read by a locally attached TMR stack ( FIG. 11   b ), which also defines the reference direction. The one contact for the TMR element is then attached directly to the TMR stack (upper electrode). The second contact, as the lower electrode, can be formed by the ferro-magnetic layer and therefore its contacting (not shown) can be at any desired location on the conductor. The same suggested layout as already described for the GMR stack of layers applies for the ferro-magnetic layer for the loop-like embodiment with inwardly projecting cusps and corners that are always rounded (this also being intended to include the loop areas outside of the cusps when there is a change in direction in the loop configuration), the radius of curvature of which is supposed to be greater than three times the loop width. Due to technical drafting constraints, the aforesaid roundings are only indicated in  FIGS. 3 ,  4 ,  7 ,  13 ,  14 , and  15 . 
     If the TMR effect is used for reading the magnetization condition of the conductors, then, with no general limitation, the contact K 1  should be used as the upper electrode for R 12 , contact K 4  for R 34 , contact K 5  for R 56 , and contact K 8  for R 78  (see  FIG. 10 ). A common contact can be used for the lower electrode for all TMR elements. In contrast to the contacts K 1 , K 4 , K 5 , and K 8 , in which a TMR stack is disposed between the magnetic layer that carries the domain wall movement, e.g. an approx. 10 nm-thick Ni 81 Fe 19  layer, and the contact, the common contact can be disposed directly on the NiFe layer. However, there may also be a TMR stack between this contact and the NiFe layer. In this case, however, the contact surface for this contact should be significantly larger with respect to the NiFe layer. In contrast, ideally contact surfaces with nearly identical sizes should be used for contacts K 1 , K 3 , K 5 , and K 7  ( FIG. 11   b ), since the resistance in these TMR elements is indirectly proportional to the surface area. 
     When using the TMR effect, it should be noted that it is the surface area that the contact has with the sensor layer that is critical for the magnitude of the resistance, not the distance between the contacts, that is, the distance between contacts K 1  and K 2  is not critical for R 12 . The size of the contact should be uniform throughout for the simplest possible evaluation. 
     For special applications of the inventive revolution counter, such as e.g. in a gas or water pipe, there is a requirement that the counter must only count up. This can be attained when the normally constant width of loops described in the aforesaid have a structure as depicted in the segment in  FIG. 12 .  FIG. 12  is a schematic depiction of a local change in width that leads to the domains being able to move through this geometrical construct only in one direction. Such a geometry means that in a field range H min &lt;H&lt;H Diode  the domains can be moved only in one direction. These types of geometrical structures are to be provided for such an application in all of the straight-line areas, as depicted in  FIG. 13 .  FIG. 13  also illustrates an example of an arrangement of the constructs with a “diode” function in a loop where n=2. 
     For better understanding of how the aforesaid loop arrangements can be configured for revolution counters,  FIGS. 14   a  and  14   b ,  15   a  and  15   b  depict top-views of the examples of different layouts for the inventive loop arrangements, but this shall not limit the invention. 
     The drawings in  FIG. 14  depict two possible examples of arrangements of loops for a revolution counter that is constructed and working using the principle of coprime loops for N=4620 with five individual loops  30   a  through  30   e  for n=3, 4, 5, 7, and 11, having 4, 6, 8, 12, or 20 inwardly oriented cusps, depending on the loop. As discussed in the foregoing, it is not important whether the individual loops are nested in one another ( FIG. 14   a ) or are adjacent to one another, or whether some are adjacent to one another, on the substrate ( 10 , see  FIG. 1   a  or  1   b ), as long as all of the loop areas can be covered by the field of the rotating outer magnet  20  (see also  FIGS. 1   a  and  1   b ). 
       FIGS. 15   a  and  15   b  illustrate two possible examples of arrangements of loops for a revolution counter constructed and working using the binary principle for N=128, having 7 individual loops  31   a  through  31   g  for n=2, 4, 8, 16, 32, 64, and 128, with respect to 2, 6, 14, 30, 62, 126, or 254 inwardly oriented cusps, depending on the loop. As discussed in the foregoing, in this example reducing the complexity for attaching the necessary contacts, which are to be provided here on one cusp-like protuberance depicted with the length L in the drawings in  FIG. 14 , is offset by the increased number of loops compared to the coprime variant in accordance with the drawings in  FIG. 14 . 
     But the coprime variant offers another additional advantage that shall be explained in the following. A first possible embodiment of this variant that detects only the site of the inscribed domains. However, in another design of the invention, the principle of measuring the resistances at each cusp also permits the following embodiment for the loops. A description follows: 
     Each domain requires one 180° revolution of the magnet to pass through a cusp. When there is an uneven number of cusps, for instance three cusps as depicted in  FIG. 16 , for reasons of symmetry the number of domains disposed in the loop is also uneven. In addition, after a half-integer number (number of cusps divided by two plus one), each domain is back in its initial position, that is, at a count of n 360° revolutions in half-steps, thus after 2.5 revolutions in the example. If the magnetization configuration is compared, in  FIG. 16  for e.g. 0 and 2.5, after 2.5 revolutions the domain D depicted here is back in its initial position. However, all of the magnetization directions at 2.5 revolutions are oriented opposing those from 0 revolutions. This results from the fact that the number of direction changes is uneven due to the uneven number of domains. Thus, there is no problem distinguishing between the configuration for 0 and for 2.5, as here due to the use of GMR or TMR layer stacks, which are also sensitive to the direction of magnetization of the domains. As is evident from  FIG. 16 , it is only at five revolutions that both the position of the domains and also all directions of magnetization match. Therefore given an uneven number of cusps and the requirement for a coprime configuration it is possible to use fewer cusps per loop, which further simplifies layout, even for the coprime variant. This means that compared to an even number of cusps this type of solution has the advantage of reducing contacts and loop surface area and even loop length. Thus in a combination of just five loops, e.g. 2.5 revolutions (R), 3.5 R, 4.5 R, 5.5 R, and 6.5 R, 45045 revolutions are registered (5*7*9*11*13). When the number of cusps is uneven, there is the requirement that such a loop includes at least one domain and at most as many domains as cusps provided in the loop. 
     As long as the coprime relationship is maintained between the loops in the entire arrangement for counting 360° revolutions, it is entirely possible to provide a combination of loops that have an even and uneven number of cusps, which therefore is expressly under the present invention. 
     As is evident from the specific exemplary embodiments and variants that have been described, the choice depends on the specific object for the revolutions that are actually to be counted, given the advantages of the binary and coprime variants. 
     It is within the framework of the invention to arrange the revolution counters identified and described in the foregoing together or alone on a substrate with an evaluation unit or to connect them thereto, and also to provide the aforesaid angular sensor there, for instance embodied as an AMR (anistropic magneto-resistance). The evaluation unit may advantageously be formed by a CMOS circuit that may already include a Hall angular sensor. 
     Since all of the types of the arrangements that have been described as examples can be attached for instance to a CMOS chip with no problem in accordance with the arrangement examples described in  FIGS. 14 and 15 , the small size with which it is possible to produce a revolution counter in accordance with the present invention is evident compared to comparable revolution counters according to the prior art. 
     Another significant advantage of the present invention is comprised in that domain conditions that change when an outer magnetic field that when rotating changes their position, can even be detected subsequently if the voltage is interrupted and thus a revolution that occurs with no current, for instance revolution of a steering wheel, can be bijectively displayed. 
     All of the features that can be found in the specification, exemplary embodiments, and drawings can be essential to the invention individually as well as in any combination with one another.