MAGNETIC FIELD SENSOR AND SENSOR ASSEMBLY

Abstract

The present invention relates to a magnetic field sensor for detecting a magnetic field, comprising: a magnetoelectric sensor element which can mechanically oscillate, the sensor element having at least one first layer made of a magneto-restrictive material, a second layer made of a piezoelectric material, and at least one electrode made of an electrically conductive material, more particularly metal; and electronics. The magnetic field sensor, more particularly the electronics, is designed to induce mechanical oscillations of the sensor element by means of an excitation signal, to receive the mechanical oscillations of the sensor element and to convert said mechanical oscillations into a reception signal, to produce the excitation signal from the reception signal, and to determine a variable related to the magnetic field on the basis of the reception signal.

Claims

1-13. (canceled)

14. A magnetic field sensor for detecting a magnetic field, comprising a magnetoelectric sensor element which can mechanically oscillate, the sensor element having at least: one first layer made of a magnetostrictive material, a second layer made of a piezoelectric material, and at least one electrode made of an electrically conductive material, and electronics, wherein the magnetic field sensor is designed to induce mechanical oscillations of the sensor element by means of an excitation signal, and to receive the mechanical oscillations of the sensor element and to convert said mechanical oscillations into a reception signal, produce the excitation signal from the reception signal, and determine a variable related to the magnetic field on the basis of the reception signal.

15. The magnetic field sensor according to claim 14, wherein the sensor element is a MEMS sensor element.

16. The magnetic field sensor according claim 14, wherein the sensor element can be induced to resonant oscillations.

17. The magnetic field sensor according to claim 14, wherein the magnetic field sensor is designed to produce the excitation signal from the reception signal such that there is a specifiable phase shift between the excitation signal and the reception signal.

18. The magnetic field sensor according to claim 14, wherein the electronics comprise a phase control unit.

19. The magnetic field sensor according to claim 14, wherein the sensor element comprises at least two electrically insulated electrodes which are applied to the second layer in particular in different regions.

20. The magnetic field sensor according to claim 14, wherein the electronics are designed to alternately execute a first and a second operating mode; the electronics are designed to induce mechanical oscillations of the sensor element in the first operating mode by means of an excitation signal, and to interrupt the excitation of the sensor element in the second operating mode, to receive the mechanical oscillations of the sensor element and to convert said mechanical oscillations into a reception signal, and to determine a variable related to the magnetic field (B) and/or a damping on the basis of the reception signal.

21. The magnetic field sensor according to claim 14, wherein the variable related to the magnetic field is the magnetic flux density, the magnetic susceptibility or the magnetic permeability.

22. A sensor assembly for determining and/or monitoring at least one process variable and/or characteristic of a medium in a container comprising a magnetic field sensor according to at least one of the preceding claims.

23. The sensor assembly according to claim 22, comprising a device for producing a magnetic field in the region of the magnetic field sensor.

24. The sensor assembly according to claim 22, wherein the magnetic field sensor and/or the device for producing the magnetic field is arranged and/or designed such that the magnetic field can be influenced as a function of a value for the process variable and/or characteristic of the medium, and wherein the sensor assembly is designed to determine and/or monitor the process variable and/or characteristic on the basis of the variable related to the magnetic field.

25. The sensor assembly according to at least one of claim 22, comprising a sensor device which is designed and/or arranged such that at least one magnetic property of a component of the sensor device is dependent on the process variable and/or characteristic and that the magnetic field of the magnetic field device can be influenced by means of the sensor device as a function of the process variable and/or characteristic.

26. The sensor assembly according to claim 22, wherein the process variable and/or characteristic of the medium is the temperature, the pressure, the conductivity, or a flow rate of the medium.

Description

[0033] The invention is explained in greater detail with reference to the following figures. Illustrated are:

[0034] FIG. 1: two possible embodiments of a magnetoelectric sensor element;

[0035] FIG. 2: preferred embodiments of electronics of a magnetic field sensor according to the invention; and

[0036] FIG. 3: a preferred embodiment of a sensor assembly according to the invention.

[0037] In the figures, identical elements are provided with the same reference signs.

[0038] FIG. 1 shows two preferred embodiments of a magnetoelectric sensor element 1. The sensor element 1 from FIG. 1a has a first layer 2 made of a piezoelectric material and a second layer 3 made of a magnetostrictive material which are arranged one above the other and are mechanically coupled to one another. The sensor element 1 has a layer structure, for example in the form of a MEMS component. In other embodiments, further layers or moreover a substrate can be present.

[0039] An electrode 4 made of an electrically conductive material is applied along the surface O on the first layer 2 made of the piezoelectric material and serves for detecting a reception signal from the sensor element 1 in the form of an electrical voltage. A second electrode can be provided either by the second layer 3 made of the magnetostrictive material, since magnetostrictive materials are typically electrically conductive. The electrical voltage between the electrode 4 and the second layer 3 can then be tapped. However, it is also conceivable (but not mandatory) to provide a separate additional electrode 5, as shown in FIG. 1a, and to tap the electrical voltage between the electrodes 4 and 5.

[0040] In contrast to the embodiment shown in FIG. 1a, the sensor element 1 from FIG. 1b comprises two electrodes 4a and 4b, the first electrode 4a being an excitation electrode and the second electrode 4b being a reception electrode. The two electrodes 4a and 4b are electrically insulated from one another and applied in different regions of the surface O of the first layer 2 made of the piezoelectric material.

[0041] FIG. 2 shows various embodiments of a magnetic field sensor 6 according to the invention with a magnetoelectric sensor element 1 and electronics 7. The sensor element 1 is induced to mechanical oscillations by means of the excitation signal A, and the mechanical oscillations of the sensor element 1 are received and converted into a reception signal E.

[0042] The electronics 7 shown schematically in FIG. 2a optionally comprise an A/D and a D/A converter, but other embodiments can also comprise analogous electronics 7.

[0043] Furthermore, the electronics 7 comprise a unit 8, by means of which a specifiable target phase shift ?? between the excitation signal A and the reception signal E can be set in order to be able to produce the excitation signal A from the reception signal E. The unit 8 can be, for example, a phase control unit, more particularly a phase control unit based on the principle of a lock-in amplifier, a phase shifter, or a ring buffer.

[0044] Another possible embodiment of electronics 7 according to the invention is the subject matter of FIG. 2b. In this variant, the phase shift ?? is set by means of an adaptive filter 8a. As in the case of FIG. 2a, the reception signal E first passes through an analog-digital converter before it is supplied to the adaptive filter 8a. The filter characteristic of the adaptive filter is adjusted appropriately in order to set the phase shift ??. Adjustment of the filter characteristic can be performed, for example, by a phase control unit 9, by means of which a center frequency f.sub.m of the adaptive filter 8a is regulated such that the specifiable phase shift ?? is present between the excitation signal A and the reception signal E. The phase control unit 9, in turn, can be based on the principle of a lock-in amplifier, for example.

[0045] The use of an adaptive filter 8a for setting the phase shift ?? allows for an adjustment regardless of disruptive influences, such as, for example, external vibrations, and is hence particularly robust, in particular as regards external vibrations.

[0046] The excitation signal A passes through a digital-analog converter before it is guided from the electronics 7 to the sensor element 1. Furthermore, here, the magnetic field sensor 6 comprises an optional switching element 10 in order to allow the execution of a first and second operating mode, wherein the sensor element 1 is induced to mechanical oscillations in the first operating mode (switching element 10 closed) and excitation is interrupted in the second operating mode (switching element 10 open).

[0047] FIG. 3 finally relates to a preferred embodiment of a sensor assembly 11 according to the invention for determining and/or monitoring a process variable and/or characteristic of a medium M in a container 12. For the example shown herein, a sensor device 13 is arranged within the container 12 (here a tank) and is fastened to the wall of the container 12. The sensor device 13 comprises a component 15 for which at least one magnetic property is dependent on the process variable and/or characteristic of the medium M and which is designed in the present case in the form of a thin, elongate element. For example, this component 15 can be an element made of a ferromagnetic or magnetostrictive material. In the present case, the component 15 is arranged on a carrier 14. However, this is not mandatory, which is why the carrier 14 is shown in dashed lines.

[0048] The sensor assembly 11 further comprises a magnetic field device 16 for producing a magnetic field B in the region of the sensor device 13, at least part of the medium M and in the region of a detection device 17 which comprises a magnetic field sensor 6 according to the invention. The magnetic field B thus penetrates the detection device 17, the sensor device 13 and the medium M. The magnetic field B is influenced by the sensor device 13 or by the component 15, so that the process variable and/or characteristic of the medium M can be determined and/or monitored on the basis of the magnetic field B detected by the detection device 17, or on the basis of a detected variable related to the magnetic field B.