CROSS-REFERENCE TO RELATED APPLICATION

This application is a national stage application, filed under 35 U.S.C. § 371, of International Patent Application No. PCT/EP2019/079992, filed on Nov. 1, 2019, which claims the benefit of German Patent Application No. 10 2018 127 394.0, filed Nov. 2, 2018.

TECHNICAL FIELD

The present disclosure relates to a device for generating and controlling a magnetic field strength, and to a method for generating and controlling a magnetic field strength.

BACKGROUND

Magnetic fields and associated specific magnetic field strengths are usually generated by means of coil arrangements. The problem is that, in doing so, external magnetic fields cannot be taken into account. These can only be eliminated via magnetic shielding.

An equally difficult object is to generate reference values of physical variables. Such reference values are very important in science and technology. This is immediately obvious with respect to time, yet reference values are also very important as base values for other physical variables, such as current strength, voltage, magnetic field, electric field and the like.

The reference value for time is the second, which is defined as 9,192,631,770 times the period of the radiation corresponding to the transition between the two hyperfine levels of the ground state of atoms of the cesium isotope133Cs. Reference value transmitters for presetting the duration of a second are known through so-called “atomic clocks.”

For the length, a reference value for the meter can be derived from the definition that one meter is equal to the length of the distance that light travels in a vacuum during 1/299792458th of a second. Such reference value is therefore traced back to the reference value for time.

Current strength is defined by the fact that 1 A is the strength of the time-constant electric current that would produce a force of 2·10−7Newtons per meter of conductor length in a vacuum between two parallel, infinitely long, straight conductors of a negligibly small, circular cross-section and the distance of 1 m between such conductors. From this, it is not possible to find a direct solution for providing a reference value for current strength that is both economical and practical. This also applies, for example, to voltage, magnetic field and electric field.

Finally, the measurement of magnetic flux densities is a basic function of sensor technology, whereby the goal is to further improve the resolution and robustness of corresponding sensors.

From DE 10 2015 208 151 A1 and DE 10 2017 205 099 A1, methods are known with which the fluorescence intensity of a diamond material with a nitrogen-vacancy center is evaluated in order to be able to deduce the magnetic field acting on the nitrogen-vacancy center and the electric current of a conductor causing such magnetic field. Thereby, two different excitations, specifically an optical and a microwave excitation of the nitrogen vacancy center, are used, which makes the corresponding device expensive and complex.

From A. Wickenbrock et al. “Microwave-free magnetometry with nitrogen-vacancy centers in diamond,” Appl. Phys. Lett. 109, 053505 (2016), the measurement of magnetic fields without the use of microwaves is known. However, the problem exists that the flux density must be precisely adjusted.

Within the framework of the present disclosure, the magnetic field is distinguished between magnetic field strength (magnetic intensity) and magnetic flux density. Strictly speaking, the magnetic flux density B depends on the magnetic intensity H according to the relation B=μ0μrH, where μ0is the vacuum permeability and μris the relative permeability. Thereby, the magnetic flux density is measured, while a magnetic field with a certain field strength is generated when current flows through a conductor, in particular a coil.

SUMMARY

It is the object of the present disclosure to provide a device and a method with which a magnetic field strength can be generated and controlled. Preferably, this is to eliminate one or more of the aforementioned disadvantages. Preferentially, this is to allow a reference value of a physical variable to be generated relatively simply and economically. In particular, the device is also to be very small and used in mobile form. Furthermore, it would be advantageous if the device could also be used to measure magnetic flux densities with high resolution and, in particular, highly robustly.

Such object is achieved with the device as claimed and the method as claimed.

On the part of the inventor, it was recognized that this object can be achieved in a surprising way by the fact that the magnetic field strength is traced back to a resonance extreme value in the luminescence, which is dependent on it in a material, or in the photocurrent, as the case may be. Since this dependence is very well known and also very stable, corresponding magnetic field strengths can be controlled very reliably and reproducibly. More precisely, the magnetic field strength essentially depends on the magnetic flux density B triggering the resonance extreme value at the location of the luminescence or the photocurrent center, as the case may be, and thus advantageously exclusively depends on natural constants that do not require calibration. For example, the resonance point represents a pole of the inverted luminescence value as a function of the magnetic flux density B. Due to this point-shaped resonance point in relation to the parameter of the magnetic flux density B, the smallest deviations of the magnetic flux B lead to a very high signal sensitivity, such that the magnetic field strength can be generated very accurately, independent of other influences. From the literature (see, for example, J. Lepper, “Der Zusammenhang von Elektronenemission und Lumineszenzerscheinungen angeregter Kristalle,”Z. Naturforschg. 10a, 47-52 (1955), it is known that there is a close relationship between the luminescence and the photocurrent.

The device for generating and controlling a magnetic field strength is characterized by:a first material that generates a luminescence and/or a photocurrent upon physical excitation, wherein the luminescence or the photocurrent, as the case may be, has an extreme value (in the form of a resonance) with respect to a magnetic field at at least one magnetic flux density,means for generating the physical excitation,means for magnetic field generation, wherein the first material is exposed to the generated magnetic field, wherein the magnetic field strength is adjustable,means for measuring the luminescence or the photocurrent, as the case may be, with a detection signal that represents the strength of the detected luminescence signal or photocurrent signal, as the case may be,means for control, which are adapted to output a control signal for controlling the means for magnetic field generation and to control the magnetic field strength as a function of the detection signal, such that the detection signal assumes an extreme value.

“Means for generating the physical excitation” means any means by which the physical excitation can be generated. In doing so, it does not matter that the magnitude of the physical excitation is actually variable. It is sufficient if the physical excitation can be generated such that the resonance occurs in the luminescence or the photocurrent, as the case may be. In a preferred further development, the magnitude of the excitation, for example its frequency, can be tuned discretely or continuously over at least a certain range by the means for generating the physical excitation.

To determine the extreme value, there may preferentially be means for detecting the first and/or the second derivative of the detection signal as a function of the magnetic flux density. While maxima or minima, as the case may be, in the detection signal can be determined via zero points in the first derivative, extreme values in the first derivative can be controlled via zero points in the second derivative. The second variant is highly advantageous, because at that point control can take place with the highest sensitivity. “Extreme value in the detection signal” thus means not only a maximum or minimum, as the case may be, in the detection signal, but also a maximum or minimum in the first derivative of the detection signal; “extreme value in the detection signal” is thus preferentially to be read as “extreme value in the detection signal or in the first derivative of the detection signal.”

In an advantageous further development, means are provided for generating a physical variable as a function of the control signal. This allows reference values to be produced very accurately and reproducibly. Thereby, a strict distinction is made between “physical variable,” which refers to the reference value, and “physical excitation,” which refers to a specific physical variable that is used to generate the luminescence or the photocurrent, as the case may be, in the material.

In an advantageous further development, it is provided that the physical variable is a variable from the group consisting of electric current, electric voltage, magnetic field (magnetic flux density B or magnetic field strength H), electric field, time and frequency. Such reference values are needed particularly often and for different fields of application.

In an advantageous further development, it is provided that the means for generating the physical variable comprises at least one element selected from the following group: Current mirror, source impedance, coil, capacitor, transconductance amplifier and operational amplifier. Then, reference values for electric current, electric voltage, magnetic field, electric field, time and frequency can be generated.

In an advantageous further development, it is provided that furthermore there are:a further material that generates a luminescence and/or a photocurrent upon a further physical excitation, wherein the luminescence or the photocurrent, as the case may be, has an extreme value (in the form of a resonance) with respect to a magnetic field at at least one magnetic flux density,further means of generating the further physical excitation,further means for magnetic field generation, wherein the further material is exposed to the generated magnetic field, wherein the magnetic field strength is adjustable, wherein the further means for magnetic field generation is adapted to expose the further material to the same or a different magnetic field as the first material,further means for measuring the luminescence or the photocurrent, as the case may be, of the further material with a further detection signal, which represents the strength of the detected further luminescence signal or the further photocurrent signal, as the case may be. At that point, gradients in a magnetic field can be determined very easily. Instead of a combination of this further material and the further means, any combination thereof or even the further material or any of the further means alone may be used. A plurality of further materials and/or a plurality of further means can also be used.

The “physical excitation” can be identical to the “further physical excitation,” such that the “means for generating the physical excitation” can also be identical to the “further means for generating the further physical excitation.” Moreover, the “means for magnetic field generation” can be identical to the “further means for magnetic field generation.”

In an advantageous further development, it is provided that the first material and/or the further material has a crystal structure with at least one vacancy, wherein the first material or the further material, as the case may be, is preferably diamond, silicon carbide or silicon and the vacancy is a color center, in particular a nitrogen vacancy center or a nitrogen vacancy center in conjunction with a europium vacancy center, a vanadium vacancy center or a manganese vacancy center. When using diamond, the use of ST1 and L2 centers is also conceivable. Preferably, it is a fluorescent material. Such materials have very well-known resonance points in their luminescence. At this point, reference should be made to A. Zaitsev, “Optical Properties of Diamond,” 2001, Springer, Berlin, where numerous suitable color centers in diamond are indicated. The disclosure content of such publication with respect to color centers in diamond is hereby incorporated by reference in its entirety.

In an advantageous further development, it is provided that the means for generating the physical excitation or the further means for generating the physical excitation, as the case may be, provide an electrical or an electromagnetic excitation, preferably an excitation in the optical range and/or in the microwave range, in particular a LASER excitation or an LED excitation or an excitation by means of ionizing radiation. This makes it very easy to excite a luminescence or a photocurrent, as the case may be, and the means can be kept very compact. By using microwave excitation, fine structures in the luminescence or photocurrent spectrum can be resolved, further improving the accuracy of the generated reference value.

If electrical excitation (for example with electrical contacts) is used instead of electromagnetic excitation, then LEDs can be omitted for optical excitation, for example, which makes the corresponding sensor system much more compact. In addition, it would be possible to greatly increase the spatial resolution of a corresponding sensor. More specifically, excitation could be limited to a much smaller area by electrical contacts and, unlike optical detection, signals would not be obtained from the entire material. Until now, electrical excitation had failed because the NV center in diamond was ionized; however, this can be prevented by raising the Fermi level, for example, by phosphorus doping in diamond.

In an advantageous further development, it is provided that electrical contacts are transparent on the first material and/or the further material. For example, so-called “transparent conducting oxides (TCO),” such as indium tin oxide (“ITO”), fluorine tin oxide, aluminum zinc oxide or antimony tin oxide, could be used. Such contacts can be used both within the framework of reading the photocurrent and for electrical excitation.

Exemplary methods of electrical excitations of color centers in diamond are known, for example, from DE 43 22 830 A1 and from B. Burchard “Elektronische und optoelektronische Bauelemente und Bauelemente Grundstrukturen auf Diamantbasis,” Dissertation, Hagen, 1994. In particular, the excitation of luminescence can be carried out by PIP or PIN diodes. In this regard, exemplary reference should also be made to B. Tegetmeyer et al., “Charge state modulation of nitrogen vacancy centers in diamond by applying a forward voltage across a p-i-n junction” Diamond and Related Materials, Volume 65, May 2016, pages 42-46 and B. Tegetmeyer et al., “Electroluminescence from silicon vacancy centers in diamond p-i-n diodes” Diamond and Related Materials Volume 65, May 2016, pages 42-46. Excitation via PN diodes is also conceivable. With the exemplary use of diamond and a PIP diode, when a sufficiently high voltage is applied to the PIP diode, a first doped region, for example a p+ doped region, injects charge carriers—in this case holes—into the intrinsic region. There, they are accelerated by the electric field of the applied voltage and excite the color centers by impacts, whereupon they start to glow. Excitation via injection of electrons and holes, for example in PIN diodes, is more efficient. By means of bandgap engineering or the use of other materials, direct transitions can also be created, but then other color centers must be used, since color centers always exist in a manner specific to the material. It is conceivable to couple LEDs, such as those described above, only capacitively or by means of transformers or otherwise in a manner galvanically isolated to an AC signal source. This is particularly advantageous for CMOS integration.

In an advantageous further development, it is provided that the means for magnetic field generation or the further means for magnetic field generation, as the case may be, comprise at least one coil, which can be excited by an electric current, wherein there is preferably a magnetic conductor, in particular in the form of a yoke with an air gap, wherein the first material and/or the further material are arranged in the air gap. This allows the magnetic field to be produced very easily and at the same time very homogeneously over the first material or the further material, as the case may be. Helmholtz coil arrangements can also be used, possibly combined with one or more yoke elements in order to achieve a concentration, wherein once again an air gap can be used.

In an advantageous further development, the means for measuring luminescence and/or the further means for measuring luminescence comprise a photodetector, and preferably a filter that attenuates the physical excitation. This makes it very easy to measure luminescence, wherein miniaturization is readily possible.

In an advantageous further development, it is provided that the means for measuring the photocurrent and/or the further means for measuring the photocurrent are formed in such a manner that a voltage is applied between two electrical contacts on the first material and the further material, as the case may be, and the photocurrent is measured in series, wherein the measurement is carried out, for example, with a lock-in amplifier or simply via the voltage drop across a known resistor. Photocurrent measurement could also be carried out using photodiodes and/or CCD elements and/or avalanche photodiodes and/or SPADs (single photon avalanche photodiodes). Another simple device for measuring the photocurrent is known from DE 10 2010 060 527 B3. When using such technology, the controllers must be clocked. They are then preferably implemented in whole or in part in switched-capacitor technology. At that point, the measurement of the photocurrent can be done particularly easily. In particular, the corresponding device can be set up in a particularly compact manner.

In an advantageous further development, it is provided that the means for control are formed as a continuous linear controller, preferably as a PI or PID controller. This enables particularly precise control to the extreme value of the resonance, which further improves the accuracy and stability of the reference value.

In an advantageous further development, it is provided that at least one high-pass filter exists for filtering the detection signal and/or the further detection signal. At that point, a high-frequency useful signal imposed on the magnetic field can be determined, by which a broadband information transmission is enabled. In addition, a magnetic background field can also be analyzed very precisely.

In an advantageous further development, it is provided that there is at least one low-pass filter for filtering the control signal. This low-pass filter can exist separately; however, the means for control can also provide such a low-pass filter function. This prevents high-frequency components from flowing into the control and not being present in the detection signal or only being present in a modified form.

In an advantageous further development, it is provided that the magnitude of the lower cut-off frequency of the high-pass filter is greater than the magnitude of the upper cut-off frequency of the low-pass filter or the means for control, as the case may be. At that point, the broadband information transmission or the analysis of the background magnetic field, as the case may be, is possible very precisely, wherein, in particular, disturbances in the control of the operating point of the magnetic flux density B acting on the material are prevented. The device can then be used for typically highly broadband reception of useful signals by means of naturally or artificially modulated electromagnetic radiation by evaluating the signal of the magnetic flux density. Naturally modulated radiation can be, for example, electromagnetic fields generated during the transport of nerve signals in organisms. The invention proposed herein, if suitably designed to detect such biologically modulated signals, can find particular application in medical technology. The device and method are therefore particularly suitable for electroencephalography.

In an advantageous further development, it is provided that the means for magnetic field generation have at least two, preferably three, magnetic regions that have different magnetic resistances, such that at least two, preferably three, material regions of the first material or of the further material, as the case may be, are exposed to different magnetic fields, wherein each material region is assigned its own means for measuring the luminescence or the photocurrent, as the case may be, with a respective detection signal that represents the strength of the detected luminescence signal or photocurrent signal, as the case may be, wherein the means for control are adapted to output a control signal for the control of the means for magnetic field generation and to control the magnetic field strength as a function of the detection signal in such a manner that the detection signal of a material region assumes an extreme value. This effectively prevents the means for control from “running out” of the resonance point. Preferably, the different magnetic resistances are adjusted so that the resulting deviation in the magnetic flux density B is not greater than the statistical value Sigma in the signal curve approximated as a Gaussian function at the resonance point. In particular, the magnetic resistances are to be adapted so that the resulting magnetic flux densities differ in the range of 0.5 to 3 mT, preferably 1-2 mT. At that point, a particularly stable control is achieved.

In an advantageous further development, it is provided that the means for magnetic field generation and/or the further means for magnetic field generation have magnetic shielding against external magnetic fields. At that point, the generated magnetic field strength is independent of external magnetic fields.

In an advantageous further development, it is provided that the means for generating the magnetic field are adapted to supply an external magnetic field to the material. At that point, such external magnetic fields can be analyzed particularly easily.

In an advantageous further development, it is provided that the means for generating the physical excitation are adapted to undertake a modulation of the physical excitation, wherein means exist for correlating the modulation of the physical excitation with the detection signal. Thus, there is a very precise and stable generation of the magnetic field strength.

A method for generating and controlling a magnetic field strength includes the use:of a first material that generates a luminescence and/or a photocurrent upon physical excitation, wherein the luminescence or the photocurrent, as the case may be, has an extreme value (in the form of a resonance) with respect to a magnetic field at at least one magnetic flux density,of means for generating the physical excitation,of means for magnetic field generation, wherein the first material is exposed to the generated magnetic field, wherein the magnetic field strength is adjustable, andof means for measuring the luminescence or the photocurrent, as the case may be, with a detection signal that represents the strength of the detected luminescence signal or photocurrent signal, as the case may be,wherein a control signal is output for controlling the means for magnetic field generation in order to control the magnetic field strength as a function of the detection signal such that the detection signal assumes an extreme value.

A receiver in accordance with the disclosure receives electromagnetic waves modulated with a useful signal with at least one color center, wherein the color center has a luminescence and wherein the luminescence is dependent on a magnetic flux density at the location of the color center, wherein the receiver is adapted to demodulate the useful signal via such luminescence and/or wherein the color center is an antenna for the modulated electromagnetic waves. This allows a broadband receiver to be provided, particularly for encrypted communications.

A color center may be used as an antenna as a sub-device for receiving and/or demodulating a modulated electromagnetic signal, in particular a modulated message or measurement signal.

Finally, a color center may be used as an antenna as a sub-device for receiving and/or demodulating a biologically modulated electromagnetic signal, in particular a modulated nerve signal.

In an advantageous further development, it is provided that the device in accordance with the invention is used.

The features and further advantages of the present invention will become apparent below from the description of preferred exemplary embodiments in connection with the figures.

