Integrated magnetometer and method for detecting a magnetic field
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-12-04
- Publication Date
- 2026-03-25
AI Technical Summary
Conventional magnetoresistive sensor arrays for detecting magnetic security features on documents face a trade-off between sensitivity and interference from external magnetic fields when measuring magnetic field strength or gradients, with magnetic field sensors being highly sensitive but prone to interference, and gradient sensors being less sensitive and less affected by interference.
An integrated magnetometer that combines a magnetic field sensor and a gradient sensor on a single chip, utilizing magnetoresistive elements to measure both high-resolution magnetic field and gradient signals, allowing for interference-free signal recovery by integrating the outputs.
The integrated solution provides optimized signal quality and accuracy by combining the advantages of both sensor types without increasing space or cost, enabling high-resolution measurements immune to external interference.
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Abstract
Description
[Technical Field]
[0001] The present disclosure relates to an integrated magnetometer and method for detecting magnetic fields. In particular, the present disclosure relates to a sensor for detecting ferromagnetic or superparamagnetic structures on the surface of a material. [Background technology]
[0002] High-sensitivity magnetometers are needed, for example, when conducting security checks on banknotes to detect very weak magnetic materials contained in some magnetic security features on banknotes. Such security features can include, for example, magnetic pigments in printing color pigments or metal safety wire, both of which are specially designed magnetic features. For this purpose, anisotropic magnetoresistive (AMR) sensors can be used due to their high sensitivity and low noise. However, the electrical signal generated is still very weak.
[0003] Traditionally, banknote line sensor arrays have a reading width of approximately 10 mm per channel. Currently, there is a market effort to increase the resolution in order to be able to resolve more of the magnetic details of banknotes. Due to the increasing number of counterfeit banknotes and the increasing quality of banknotes among counterfeiters, smaller magnetic security mechanisms are expected. Naturally, the higher the resolution of the banknote's magnetic image, the more accurate the mechanism's verification must be.
[0004] For example, a banknote validation system may require 112 channels with a total scan length of 196 mm, which corresponds to a resolution of 1.75 mm per channel.
[0005] Generally, magnetoresistive sensors (also referred to in this application as magnetic sensors) measure the direction and strength of magnetic fields. Such configurations and methods are used in the technical fields of determining magnetic materials, such as magnetic markings on banknotes, and angle and position detection using magnetometers.
[0006] The sensor utilizes the magnetoresistance effect, which is the tendency of a material (e.g., ferromagnetic) to change the value of its electrical resistance in an externally applied magnetic field. In particular, in multi-element or multi-layer systems, giant magnetoresistance (GMR), tunneling magnetoresistance (TMR), colossal magnetoresistance (CMR), and extraordinary magnetoresistance (EMR) can be found, while only one layer is required for anisotropic magnetoresistance (AMR).
[0007] Magnetic sensors offer exceptional accuracy and robustness against difficult environmental conditions, playing an important role in a variety of applications, such as manufacturing and transportation applications. More specifically, sensors based on the magnetoresistive effect are important components due to their low inherent measurement error and high stability. In addition, favorable temperature characteristics and robustness against harsh environmental conditions lead to the relevance of magnetoresistive sensors in many important applications.
[0008] The strength of a magnetic field is usually expressed by the magnetic flux density B. The gradient of magnetic flux density results from the change in B per unit distance along the direction where the change in B is greatest. Because B is a vector and typically a function of all three spatial dimensions, the gradient is a tensor containing all partial derivatives of the three spatial B field components with respect to spatial coordinates. In practice, to measure the gradient, two magnetic field sensors are used, measuring the magnetic flux density at two different locations separated by a well-defined distance. The difference between the two measured magnetic flux density values is then calculated and divided by the distance. The distance is chosen so that the B field varies linearly with distance, i.e., by choosing a distance small compared to the distance between each of the sensors and the magnetic field source. Summary of the Invention [Problem to be solved by the invention]
[0009] When reading magnetic security structures on documents such as banknotes, conventional magnetoresistive sensor arrays are known to detect the absolute strength of the magnetic field or to detect local magnetic field gradients. Different sensor designs exist for each technique. Magnetic field sensors that detect the absolute strength of the magnetic field have the advantage of being highly sensitive, especially over long distances. However, magnetic field sensors have the disadvantage that their output signal can be corrupted by external magnetic fields.
[0010] On the other hand, gradient sensors are not affected by disturbing magnetic fields because they predetermine differential measurements, but they have the disadvantage of being much less sensitive than magnetic field sensors, especially as the distance from the magnetic object to be detected increases.
[0011] Therefore, known banknote sensors require a choice between these two concepts and accepting the drawbacks of each. [Means for solving the problem]
[0012] At least one of the above objects is solved by the subject matter of the independent claims. Advantageous embodiments of the invention are the subject matter of the dependent claims.
[0013] In this disclosure, an electronic design for a low-field AMR or one of the other magnetoresistive effects, for example, tunneling magnetoresistance (TMR), sensor is provided. The TMR sensor can be implemented with an application-specific integrated circuit (ASIC), greatly improving sensitivity. The integrated magnetometer according to this disclosure combines a gradient sensor and a magnetic field sensor in one sensor chip. This solution allows for the measurement of high-resolution magnetic field and gradient signals, and integration of these signals provides a lower-resolution, but interference-free, recovered magnetic field signal. Thus, the advantages of both operating modes can be used together without their respective disadvantages.
[0014] In particular, the present disclosure provides an integrated magnetometer comprising at least one magnetic field sensor unit comprising a first transducer element for generating a first electrical output signal in response to a detected magnetic field, and at least one gradient sensor unit comprising at least a pair of second transducer elements arranged to detect magnetic fields at two different positions and to generate second electrical output signals in response to the detected magnetic field gradient, wherein the first and second transducer elements are formed on a common substrate and surrounded by a unitary protective housing.
[0015] This concept allows for optimized signal quality and information retrieval. Furthermore, integrating the magnetic field sensor with the gradient sensor does not increase the space required, and therefore the cost, of the gradient sensor chip. Separate sensor types are not required for measuring the magnetic field and the gradient. This simplifies and reduces the cost of manufacturing, warehousing, and transporting the sensors.
[0016] Advantageously, the first transducer element and / or the pair of second transducer elements comprise at least one magnetoresistive element. As mentioned above, magnetoresistive elements have the advantage of low inherent measurement error, high sensitivity, and high stability. In addition, magnetoresistive elements have favorable temperature characteristics and robustness against harsh environmental conditions. Furthermore, the magnetoresistive elements can be connected to form a voltage divider or Wheatstone bridge topology for extracting electrical signals and compensating for temperature effects.
[0017] Advantageously, a transducer element configuration responsive to a uniform magnetic field is positioned in the space between two transducer elements forming a sensing configuration sensitive to local magnetic field differences. Therefore, no additional space is required compared to conventional gradient sensors. Furthermore, particularly accurate measurements can be made when the output signal of the gradient sensor is used to correct the output signal of the magnetic field sensor.
[0018] To enable identification of two or more magnetic features at once, the integrated magnetometer advantageously has two or more output channels. To achieve such multi-channel measurement, at least one first transducer element is disposed between two second transducer elements of at least one pair of second transducer elements, the first and second transducer elements are aligned to form a first transducer group, and at least one additional transducer group is disposed on a common substrate. Each group corresponds to one output signal channel.
[0019] According to a preferred embodiment, the first transducer element comprises two magnetoresistive elements positioned adjacent to each other and electrically connected to form a half-bridge. The half-bridge circuit topology has the advantage that a full bridge can be completed with an additional constant resistor, so that the measurement signal is derived from the bridge voltage. Such a measurement bridge has high sensitivity and precision.
[0020] Similarly, the two second transducer elements of the at least one gradient sensor unit may each comprise one magnetoresistive element positioned spaced apart from each other and electrically connected to form a half bridge.
[0021] According to a further advantageous example of the present disclosure, the magnetometer comprises a plurality of terminals for connecting the integrated magnetometer to external components, a first terminal connected to the magnetic field sensor unit and a second terminal connected to the gradient sensor unit, the first terminals being arranged in a pattern corresponding to the pattern of the second terminals rotated 180 degrees around the central axis of the substrate. In other words, the pin assignment of the sensor housing can be selected so that when only one operation mode is used, the operation mode can be selected by soldering to a PCB rotated 180 degrees. This simplifies production and inventory management, as only one type of chip can be adapted to three completely different measurement structures.
[0022] According to a further advantageous embodiment, the housing is a surface mount technology (SMT) compatible housing. Surface mount technology (SMT) is a method of manufacturing electronic circuits in which components are mounted or placed directly on the surface of a circuit carrier, such as a printed circuit board (PCB). Electronic devices formed in this manner are called surface mounted devices (SMD). In industry, surface mount technology has largely replaced through-hole technology construction methods in which components with leads are fitted into holes in the circuit board. Both technologies can be used on the same substrate, with through-hole technology being used for components that are not suitable for surface mounting, such as large transformers and power semiconductors with heat sinks. Important advantages of SMT in manufacturing include reduced substrate costs, reduced material processing costs, and control of the manufacturing process. This reduces the number of traces, the size of the board, and the number of drill holes. In the context of this disclosure, SMD housings are primarily used because their small and flat dimensions reduce the distance between the chip surface and the object to be measured. Furthermore, SMD components can be positioned particularly accurately at short distances from each other, which is advantageous for achieving uninterrupted readings along the linear array of sensors.
[0023] Advantageously, the substrate further comprises electronic components for protecting the sensor and / or for performing signal processing. Such additional integration reduces space requirements and can increase accuracy.
[0024] The present invention further relates to a method for detecting a magnetic field using at least one integrated magnetometer according to the present invention, the method comprising the steps of measuring the magnetic field strength at a first position of the integrated magnetometer to generate an absolute output signal, simultaneously measuring the magnetic field strength at a second position and a third position of the integrated magnetometer to calculate a differential signal, and evaluating the absolute and differential signals to generate a combined output signal.
[0025] According to an advantageous embodiment of the present invention, the magnetic field to be detected is movable relative to the integrated magnetometer. For example, the present invention can be used in conjunction with a banknote or other document authentication system, where the magnetic security feature of the banknote (or other document) is detected by a scanner. Naturally, the present disclosure may be used in many other application environments, such as position sensing, current sensing, flow sensing and measurement, or any other application where accurate detection of a magnetic field is required. Another application of the present invention can be found in the field of material testing, for example, magnetic flaw detection of metallic (not necessarily ferromagnetic) materials. A magnetic flaw detection sensor array can include an integrated pre-magnetized magnet that generates eddy currents in the conductive metal material. Such eddy currents are affected by defects, which alter the magnetic field and allow flaws to be detected by the magnetic sensor.
[0026] Furthermore, the present invention can be advantageously used for other material testing purposes. For example, such a line of magnetic sensors can generally be used to detect ferromagnetic or conductive objects, such as metal particles in food or metal objects in letters (letter bombs). The detection of magnetic particles (microbeads) in biology, medicine, or analysis is also possible with this system.
[0027] Furthermore, the absolute signal and the differential signal can be compared with each other to generate a quality signal indicating the quality of the measurement. In this way, for example, the presence of a disturbing magnetic field or a non-optimal installation of the magnetometer can be detected and eliminated. In particular, according to an advantageous example of the present disclosure, the combined output signal is a restored magnetic field signal that is corrected by canceling interference.
[0028] As mentioned above, the magnetic field to be detected can be generated by a magnetic security feature on a document. In such cases, it is advantageous to simultaneously detect more than one security feature. This can be achieved by providing multiple groups formed by first and second transducer elements and measuring multiple signal channels.
[0029] This high level of integration makes it possible, for example, to implement high-resolution line sensors in the smallest possible footprint. This is an important step for next-generation linear sensor arrays for applications in banknotes, horizontal applications, and linear applications. In addition, this approach is readily applicable to next-generation TMR sensors that have higher sensitivity, higher resistance (lower power consumption), and can be integrated directly onto ASICs.
[0030] The accompanying drawings are incorporated into and constitute a part of the specification to illustrate several embodiments of the present invention. These drawings, together with the description, serve to explain the principles of the invention. The drawings are merely intended to illustrate preferred and alternative examples of how the invention can be made and used, and should not be construed as limiting the invention to only the embodiments shown and described.
[0031] Furthermore, several aspects of the embodiments can be taken individually or in different combinations to form a solution according to the invention. Further features and advantages will become apparent from the following more detailed description of various embodiments of the invention, which are illustrated in the accompanying drawings, in which like reference numerals indicate like elements. [Brief explanation of the drawings]
[0032] [Figure 1] FIG. 1 is a schematic diagram illustrating the operation of a magnetic gradient sensor. [Figure 2] 1 is a schematic diagram illustrating the operation of a magnetic field sensor. [Figure 3] FIG. 1 is a schematic diagram of a two-channel magnetic gradient sensor. [Figure 4] FIG. 1 is a schematic diagram of a conventional three-channel magnetic gradient sensor. [Figure 5] FIG. 1 is a schematic diagram of a conventional three-channel magnetic field sensor. [Figure 6] 1 is a schematic layout diagram of an integrated magnetometer according to the present disclosure. [Figure 7] FIG. 7 is a circuit diagram of the integrated magnetometer shown in FIG. [Figure 8] 7 is a schematic diagram illustrating the magnetic field sensing mode of operation of the magnetometer shown in FIG. 6. [Figure 9] FIG. 7 is a schematic diagram illustrating the gradient-sensing mode of operation of the magnetometer shown in FIG. 6. DETAILED DESCRIPTION OF THE INVENTION
[0033] In the following, the invention will be explained in more detail with reference to the drawings. Referring to Figure 1, a schematic diagram of the detection of a moving (ferro)magnetic marking on a banknote by a magnetic gradient sensor is shown. In particular, a banknote 100 having a magnetic security feature 102 moves relative to a magnetic gradient sensor 104. The security feature 102 is generally referred to as a magnetic field source and has north and south poles and magnetic flux lines 106. As mentioned above, the magnetic source 102 can be attached to any other movable object for different measurement applications, for example, determining its position. However, in the following, a banknote validation system scenario will be described as an example of how an integrated magnetometer according to the invention works and how it can be used.
[0034] 1 shows the measurement signal δ as a function of time t as a curve 108. In particular, δ(t) is the difference between the measurements of the two transducer elements 112A, 112B. Diagrams A, B, and C show the respective positions of the magnetic source 102 relative to the magnetic gradient sensor 104 at specific instants while the banknote 100 is moving in the direction of the arrow 110. Without loss of generality, this direction is assumed to be along the y-direction, although the banknote 100 is spaced apart from the magnetic gradient sensor 104 in the z-direction. The corresponding Cartesian magnetic field components H y and H z The direction of is shown diagrammatically in FIG.
[0035] For example, the banknote 100 may move in direction 110 at a speed of 1 m / s to 10 m / s. The magnetic gradient sensor 104 has two transducer elements 112A and 112B. Each of the transducer elements 112A and 112B detects magnetic flux in the y-direction. When the magnetic source 102 is at position A shown in FIG. 1, only the transducer element 112A on the left side of the magnetic gradient sensor 104 measures magnetic flux as indicated by arrow 114, resulting in a maximum difference being measured in the negative direction.
[0036] As the banknote 100 containing the magnetic source 102 moves further in direction 110, the measurable magnetic flux of the left transducer element 112A decreases while the measurable magnetic flux of the right transducer element 112B increases. Since the measurement signal δ(t) represents the difference between the signals of the two transducer elements 112A, 112B, a configuration for position B where the magnetic source 102 is symmetrical with respect to the transducer elements 112A, 112B yields a zero signal.
[0037] Finally, a further (positive) maximum in curve 108 is seen for position C, where right transducer element 112B is closest to magnetic source 102.
[0038] The advantage of such gradient measurements is that the disturbance magnetic fields inherent in differential measurements do not impair measurement accuracy, however the signal amplitude is lower than for magnetic field sensors that detect the absolute value of the magnetic flux density.
[0039] 2 shows a banknote authentication system (corresponding to the system shown in FIG. 1) with a magnetic field sensor 116 instead of the magnetic gradient sensor 104. The magnetic field sensor 116 has only one transducer element 118 that outputs a signal H(t) indicative of the absolute value of the magnetic flux in the y-direction. Curve 120 shows the progression of the signal over time t while the banknote 100 is moving along the direction 110. As can be seen in comparison with FIG. 1, the measurable signal amplitude is higher. However, a problem with magnetic field sensors is their sensitivity to external magnetic disturbances, which directly affect the measured signal.
[0040] Furthermore, Figure 3 shows another embodiment of the magnetic gradient sensor shown in Figure 1. In Figure 3, a top view of the magnetic gradient sensor 104 is shown together with a side view according to Figure 1. The distance between the first transducer element 112A and the second transducer element 112B is indicated as Δy. The distance Δy limits the resolution of the gradient sensor in the scanning direction, i.e., the direction 110 in which the banknote 100 is moving (see Figure 1).
[0041] In the illustrated example, there is not only one pair of transducer elements 112A, 112B, but also a second pair of transducer elements 122A, 122B. The distance Δx between the transducer elements 112, 122 determines the minimum lateral resolution between two magnetic features located along the x-direction. The output signals of the two pairs of transducer elements 112, 122 form channels, each containing information about a specific region in the x-direction.
[0042] Of course, the number of channels is not limited to one or two, and three or more channels are also possible. FIGS. 4 and 5 show examples of three-channel magnetic sensors. In particular, FIG. 4 shows a three-channel magnetic gradient sensor 400. The magnetic gradient sensor 400 includes three pairs of transducer elements 412A, 412B. The transducer elements 412A, 412B of each pair are connected in series by a conductive lead 424. A central node 426 of the connection between the first transducer element 412A and the second transducer element 412B is connected to a contact pad 428. The central node 426 can be connected to signal processing components (not shown) via the contact pad 428. In particular, as described above with reference to FIG. 1, a differential signal is generated for each pair of transducer elements.
[0043] FIG. 5 illustrates a three-channel magnetic field sensor 500 according to the principles described with reference to FIG. 2. Note that the transducer element 512 can be formed as a pair of magnetoresistive elements 512A, 512B, which are positioned directly adjacent to each other and therefore experience essentially the same magnetic flux at any given time. Unlike FIG. 4, where both resistors 412A, 412B respond similarly to an external magnetic field, the resistors 512A, 512B are designed to respond to a uniform magnetic field with opposite resistance changes, so that in this case, a uniform magnetic field across both resistors will produce a strong output signal from the voltage divider configuration.
[0044] When using AMR magnetoresistive elements, such opposite responses of the two resistors can be achieved by providing different tilt directions for the barber poles arranged in the nickel-iron strip.For GMR and TMR elements, different pinning directions for the pinned layers are used.
[0045] From a signal evaluation perspective, the magnetoresistive elements 512A, 512B can be treated as a half-bridge (or voltage divider). In the connection between the first transducer element 512A and the second transducer element 512B, a central node 526 is connected to a contact pad 528 via a conductive lead 534. Through the contact pad 528, the central node 526 can be connected to signal processing components (not shown).
[0046] However, the configurations shown in Figures 4 and 5 suffer from the aforementioned drawbacks inherent in using separate chips to measure the magnetic gradient or field. In contrast, an improved magnetometer 600 in accordance with the present invention will be described with reference to Figures 6 and 7.
[0047] Figure 6 shows an arrangement of an integrated magnetometer 600 according to the present invention, which combines the advantages of magnetic gradient sensing and magnetic field sensing in one integrated chip with a common substrate, overcoming the problems of known magnetic sensors. Figure 7 shows the corresponding equivalent circuit diagram of the integrated magnetometer 600.
[0048] The integrated magnetometer 600 is designed to detect a two-channel magnetic mechanism where two separate parts of the mechanism are separated by a channel distance 602. The channel distance 602 may be, for example, 1.75 mm. The integrated magnetometer 600 includes magnetic field sensors 604, 606 in each of the two channels, each of which has two magnetoresistive elements R as transducer elements. H1 , R H2 and R H3 , R H4 The first magnetic field sensor 604 includes two magnetoresistive elements R H1 , R H2 are arranged closely adjacent to each other, and the two magnetoresistive elements R of the second magnetic field sensor 606 H3 , R H4 are arranged closely adjacent to each other. Therefore, the magnetoresistive elements of each magnetic field sensor are essentially subjected to the same magnetic flux to be measured. oH1The voltage measured at may be evaluated to generate a first output signal indicative of the absolute value of the magnetic field strength.
[0049] Furthermore, the integrated magnetometer 600 includes magnetic gradient sensors 608, 610 for each of the two channels, each of which includes two magnetoresistive elements R G1 , R G2 and R G3 , R G4 The first magnetic gradient sensor 608 includes two magnetoresistive elements R G1 , R G2 are spaced apart from each other by a distance Δy, and the two magnetoresistive elements R of the second magnetic field sensor 610 G3 , R G4 The magnetic gradient sensors are also spaced apart by a distance Δy. Thus, the magnetoresistive element of each magnetic gradient sensor operates as a gradient sensor, as described above with reference to FIG. 1. oG1 The voltage measured at the magnetoresistive element R can be evaluated to generate a second output signal indicative of the gradient of the magnetic field strength. G1 , R G2 and R G3 , R G4 Advantageously, this output signal, using respectively, is not corrupted by the presence of disturbing magnetic fields. On the other hand, the strong first output signals of the magnetic field sensors 604,606 may be corrected by taking into account the differential output signals of the gradient sensors 608,610.
[0050] In accordance with the present disclosure, all transducer elements, interconnecting conductive leads 612, and contact pads 614 are integrated on one common substrate 616 and covered by a common protective layer and / or housing 618. In other words, integrated magnetometer 600 combines a gradient sensor and a magnetic field sensor on one sensor chip.
[0051] To meet various needs regarding the width and number of channels, channels can be combined to achieve a channel width that is an integer multiple of the channel distance. In the simplest case, the output signals of adjacent channels can be mixed by connecting them directly. However, it is also possible to generate individual half-bridge signals or paired differential signals similar to a full Wheatstone bridge.
[0052] In practice, evaluation is often simplified by using a larger channel width and fewer channels distributed across the entire length of the sensor array. In such cases, the individual outputs of one or more integrated magnetometers can be directly connected to each other. Alternatively, two separate groups of channels with opposite signal polarities, each using one or more connected channel outputs, can be used to generate a differential signal. To achieve the required identical or opposite signal polarities for this purpose, the direction of the auxiliary magnetic field required for MR sensor operation can be selected accordingly, or adjacent integrated magnetometers can be operated with the same or opposite supply voltages.
[0053] This solution allows the measurement of high-resolution magnetic field and gradient signals, the integration of which provides a lower-resolution but interference-free reconstructed magnetic field signal, thus allowing the advantages of both modes of operation to be used together without their drawbacks.
[0054] Furthermore, as can be seen in Figure 6, the pin assignments on the sensor housing have been selected so that when only one operating mode is used, it is possible to select between the operating modes by soldering the terminals to a PCB rotated 180 degrees. In particular, the terminals belonging to the magnetic field sensors (UoH2, UoH1, GND, and VccH) enclosed in solid lines in Figure 6 are arranged in a pattern corresponding to the terminals belonging to the gradient sensors (UoG2, UoG1, GND, and VccG) enclosed in dashed lines.
[0055] In summary, this concept enables optimized signal quality and information retrieval. Integrating the magnetic field sensor with the gradient sensor does not increase the space required compared to using the gradient sensor alone. Separate sensor types are not required for magnetic field and gradient measurements. This simplifies and reduces the costs of manufacturing, warehousing, and transporting the sensors. The pin assignment of the SMT package makes it possible to change the operating mode without modifying the PCB. This makes it easy to adapt the sensor module to customer requirements, increasing flexibility in development and manufacturing.
[0056] The concepts of the present invention are particularly suitable for magnetoresistive transducer elements, for example AMR or TMR transducers.
[0057] As previously mentioned, the substrate 616 may include additional electronic elements such as protection components, e.g., ESD protection diodes, preamplifiers, and / or digitizer circuitry. In accordance with the present disclosure, at least three magnetoresistive transducer elements are arranged such that both a high-resolution magnetic field signal and a robust gradient magnetic field signal are obtained, and integration of these signals provides a lower-resolution, interference-free, reconstructed magnetic field signal. Furthermore, comparison of both signals provides information about the quality of the measurement.
[0058] The operation of the integrated magnetometer 600 will now be described in more detail with reference to FIGS.
[0059] Figure 8 shows a mode of operation in which only the magnetoresistive magnetic field sensors 604, 606 (only one sensor is visible in the cross section of Figure 8) are measuring the magnetic field of a moving magnetic source 620. Schematically, magnetic flux lines 622 are shown with a tangential component (dashed arrows) and a component along the sensing surface of the magnetoresistive transducer element (i.e., along the y-direction, solid arrows).
[0060] 2, a maximum signal can be measured when the magnetic flux lines 622 are parallel to the sensing surfaces of the magnetic field sensors 604, 606. When the magnetic flux lines are perpendicular to the sensing surface of the magnetic field sensor 604, the curve H(t) (reference numeral 624) has an H value of zero.
[0061] As shown in Figure 9, the magnetic gradient sensor 608 has two magnetoresistive transducer elements 608A, 608B separated by a distance Δy in the scan direction. The gradient measurement produces an output signal that is the difference between the voltage measured across the magnetoresistive element 608B and the voltage measured across the other magnetoresistive element 608A. Thus, the magnetoresistive transducer elements 608A, 608B measure local differences in the magnetic field distribution. The distance Δy determines the resolution in the scan direction and may be, for example, 0.75 mm.
[0062] In summary, the present invention provides a device for detecting ferromagnetic or superparamagnetic structures on a material surface using magnetic field-sensitive sensor elements. Such magnetic field-sensitive sensor elements are assembled on a common carrier substrate. A spatially small array of sensor elements responds to a uniform magnetic field, thereby generating a sensor signal that is initially approximately proportional to a component of the magnetic field generated by the magnetic field-generating structure. A second sensor element configuration responds to the magnetic field difference between two spatially small, spaced-apart sensor elements. The uniform magnetic field-responsive sensor element configuration is disposed in the space between the two sensor elements to form a sensor configuration sensitive to local magnetic field differences. Specifically, each sensor element can include two resistors connected in a voltage divider configuration, and the magnetoresistive effect is used to generate the signal. Additionally, separate supply voltage terminals can be provided for the sensor element arrays that respond to uniform and local field differences. An exemplary terminal assignment for the sensor package can be provided, which allows for alternating between measuring local field differences and uniform fields with a 180 degree rotated placement on the carrier plate.
Claims
1. An integrated magnetometer (600), The aforementioned integrated magnetometer (600) - A first supply voltage terminal (VccH) and a first transducer element (R) for generating a first electrical output signal in response to the detected magnetic field. Ｈ１ , R Ｈ２ ;R Ｈ３ , R Ｈ４ At least one magnetic field sensor unit (604, 606) comprising, - A second supply voltage terminal (VccG) and at least one pair of second transducer elements (R) arranged to detect the magnetic field at two different positions and generate a second electrical output signal in response to the detected magnetic field. Ｇ１ , R Ｇ２ ;R Ｇ３ , R Ｇ４ The system comprises at least one gradient sensor unit (608, 610) equipped with, The second supply voltage terminal (VccG) is separate from the first supply voltage terminal (VccH), The first transducer element and the second transducer element are formed on a common substrate (616) and surrounded by a common protective layer and / or housing (618). Integrated magnetometer (600).
2. The first transducer element (R Ｈ１ , R Ｈ２ ; R Ｈ３ , R Ｈ４ ) and / or the pair of second transducer elements (R Ｇ１ , R Ｇ２ ; R Ｇ３ , R Ｇ４ ) include at least one magnetoresistive element. The integrated magnetometer according to claim 1.
3. The at least one first transducer element (R Ｈ１ , R Ｈ２ ;R Ｈ３ , R Ｈ４ ) is the two second transducer elements (R) of the at least one pair of second transducer elements. Ｇ１ , R Ｇ２ ;R Ｇ３ , R Ｇ４ ) are placed between them, The first transducer element and the second transducer element are aligned to form a first transducer group. The integrated magnetometer according to claim 1.
4. At least one additional group of transducers is arranged on the common substrate. The integrated magnetometer according to claim 3.
5. The first transducer element (R Ｈ１ , R Ｈ２ ;R Ｈ３ , R Ｈ４ ) comprises two magnetoresistive elements positioned adjacent to each other and electrically connected to form a half-bridge, The integrated magnetometer according to claim 1.
6. The two second transducer elements (R) of the at least one gradient sensor unit Ｇ１ , R Ｇ２ ;R Ｇ３ , R Ｇ４ Each of the following comprises a magnetoresistive element that is positioned spaced apart from each other and electrically connected to form a half-bridge. The integrated magnetometer according to claim 1.
7. The integrated magnetometer (600) further includes multiple terminals for connecting to external components, The first terminal is connected to the magnetic field sensor unit, and the second terminal is connected to the gradient sensor unit. The first terminal is arranged in a pattern corresponding to the pattern of the second terminal, which is rotated 180 degrees around the central axis of the substrate. The integrated magnetometer according to claim 1.
8. The integrated magnetometer according to claim 1, wherein the housing (618) is a surface mount technology (SMT) compliant housing.
9. The substrate (616) further comprises electronic components for protecting the sensor and / or electronic components for performing signal processing. The integrated magnetometer according to claim 1.
10. The integrated magnetometer (600) comprises a plurality of magnetic field sensor units (604, 606) and a plurality of gradient sensor units (608, 610), The first transducer elements (RH1, RH2; RH3, RH4) of the plurality of magnetic field sensor units (604, 606) and the second transducer elements (RG1, RG2; RG3, RG4) of the plurality of gradient sensor units (608, 610) are formed on a single common substrate (616). The integrated magnetometer according to claim 1.
11. The magnetic field sensor unit (604, 606) comprises four transducer elements (RH1, RH2; RH3, RH4) as the first transducer element, and The gradient sensor unit (608, 610) is equipped with four transducer elements (RG1, RG2; RG3, RG4) as the second transducer element. The integrated magnetometer according to claim 10.
12. The integrated magnetometer (600) is configured to correct the first electrical output signal of the magnetic field sensor unit (604, 606) using the second electrical output signal of the gradient sensor unit (608, 610). An integrated magnetometer according to any one of claims 1 to 11.
13. The integrated magnetometer (600) is a magnetometer for security checking of banknotes. The integrated magnetometer according to claim 12.