Patent Description:
The current technology of highly sensitive magnetic field measurement relays mainly in the use of Superconducting Quantum Interference Devices (SQUIDs). In terms of sensitivity, a second option was proposed a few years ago with the implementation of a Spin Exchange Relaxation-Free (SERF) magnetometer. Both technologies have found applications where the measurement of weak magnetic fields is relevant. For example, in the medical industry, the SQUIDs magnetometers have allowed the measurement of small cerebral currents, promoting the development of the magnetoencephalography. SERF magnetometers have been built to target the same application, demonstrating reduced sensitivity compared with the state of the art (SQUIDs). The drawback of using SQUIDs is the needing of cooling the system down close to absolute zero. This requires complex, expensive and large equipment, and restricts the applications where the sensors can effectively operate. In addition, SQUIDs and SERF magnetometers need to operate in a magnetic-free environment. In practice, the magnetometers have to be installed inside a room shielded with a Faraday cage.

The publication "<NPL>) reviews the recent progress in high-sensitivity nanoscale magnetometry based on nitrogen-vacancy (NV) centres in diamond. <FIG> of this publication shows a magnetic sensor with a single sensor pixel for the detection of a weak magnetic field.

The publication "<NPL>) describes another single-pixel magnetic sensor based on nitrogen-vacancy (NV) centres in diamond. The publication "<NPL>) describes a light-trapping diamond waveguide geometry to enhance ODMR detection efficiency using NV colour centres.

An objective of the present invention is to provide a sensor that can be manufactured at low costs and allows measuring the strength of the magnetic field simultaneously or consecutively for different locations.

An embodiment of the present invention relates to a sensor comprising a sensor element for measuring a magnetic field, the sensor element comprising a set of at least two first input ports, a set of at least two exit ports each of which is connected to one of the first input ports via a corresponding first beam path, a set of at least two second input ports each of which is connected to a second beam path, wherein the first beam paths extend through a common plane located inside the sensor element, said plane comprising a plurality of magneto-optically responsive defect centers, wherein the second beam paths also extend through said common plane, but are angled with respect to the first beam paths such that a plurality of intersections between the first and second beam paths is defined, and wherein each intersection forms a sensor pixel located at at least one of said magneto-optically responsive defect centers. The sensor further comprises a set of detectors each of which is individually assigned to one of said exit ports, an evaluation unit connected to said set of detectors and configured to evaluate detection signals of the detectors in order to generate one or more measurement values, a first emitter unit which is capable of generating a first radiation and activating at least one of the first beam paths by injecting the first radiation, a second emitter unit which is capable of generating a second radiation and activating at least one of the second beam paths by injecting the second radiation, a control unit configured to control the first and second emitter unit, and a microwave generator capable of generating a microwave field at the intersection points of the beam paths.

The sensor according to the above embodiment provides a plurality of sensor pixels that are arranged in the same common plane. The pixels can be read out consecutively or for instance line-wise simultaneously in order to characterize the magnetic field in two-dimensions. The position of the sensor pixels in the common plane is defined by the positions of the intersections. There is no need for additional fabrication steps to define the pixel positions.

The first beam paths are preferably parallel, and the second beam paths are preferably parallel. The first beam paths may be perpendicular to the second beam paths.

Planes of intersections (e.g. two-dimensional arrays) may be stacked in order to provide a three-dimensional sensor. The stack of planes may be located in the same sensor element (e.g. the same diamond plate with Nitrogen-Vacancy defect centers) or in a stack of sensor elements (e.g. a stack of diamond plates with Nitrogen-Vacancy defect centers).

The measurement values may characterize the magnetic field strength. The evaluation of the detected radiation preferably includes evaluating the absorption of the first radiation in the respective first beam path since the absorption of the first radiation may correlate to the magnetic field strength at the location of the activated sensor pixel, i.e., the location where the first radiation is intersected by the second radiation.

The microwave generator may be configured to change the microwave frequency over time. For instance, the microwave generator may periodically increase or decrease the microwave frequency in a ramp-wise fashion.

The control unit is preferably configured to control the second emitter unit such that maximally one of the second beam paths is provided with the second radiation in each moment of time.

In an exemplary embodiment, the control unit may be configured to control the first emitter unit to input the first radiation into the first beam paths consecutively, i.e., into only one first beam path at each moment in time. The evaluation unit may evaluate the detection signals of the detectors also consecutively in order to generate measurement values for a single first beam path at each moment in time.

In another exemplary embodiment, the control unit may be configured to control the first emitter unit to input the first radiation into all of the first beam paths simultaneously. The evaluation unit may be configured to evaluate the detection signals of the detectors simultaneously in order to generate measurement values for all first beam paths simultaneously.

The sensor may comprise a printed circuit board located on top of the sensor element or below the sensor element. The printed circuit board may provide at least one antenna. The antenna may be a magnetic coil. The microwave generator is preferably configured to provide a microwave signal to said at least one antenna or coil to generate a microwave field in the sensor element. The sensor may also comprise means for temperature stabilization.

The printed circuit board may comprise a plurality of antennae or coils which are each assigned to one of the intersections. This allows providing each of the intersections with an individual microwave field that is generated by the individually assigned antenna or coil.

The sensor may comprise a carrier on which the sensor element is mounted. The carrier may also carry one or more of the other elements mentioned above, for instance the detectors, the evaluation unit, the first emitter unit, the second emitter unit, the control unit and/or the microwave generator.

The carrier may provide at least one groove that carries a fiber. The fiber may connect one of the input ports with the first or second emitter unit, or connect one of the exit ports with one of the detectors.

At least one of the first and second emitter units may comprise emitter elements (e. lasers or photodiodes) that are each individually assigned to one of the input ports. Such individually assigned emitter elements may be mounted on the carrier.

Further, at least one lens may be mounted on the carrier between one of the input ports and the fibre, between one of the emitter elements and the respective input port, or between one of the exit ports and the respective detector, for instance in order to reduce coupling losses.

At least one of the first or second beam paths may be provided with a waveguide that is integrated in the sensor element and guides the radiation through said common plane.

Additionally, or alternatively, the sensor may comprise a pixel position control unit that is capable of varying the positions and/or directions of the beam paths and therefore capable of varying the positions of the intersections (= positions of the sensor pixels).

The pixel position control unit may comprise integrated micro-mechanical control components that change the positions of the input and output ports, and/or movable lenses or mirrors that influence the beam paths. The pixel position control unit or parts thereof may be carried by the carrier.

The sensor element preferably consists of or comprises a diamond plate having Nitrogen-Vacancy defect centers. The first radiation is preferably infrared (e.g. near infrared) radiation and the second radiation is preferably green radiation. The Nitrogen-Vacancy defect centers may be distributed homogeneously or inhomogeneously. For instance, the concentration of the defect centers may be higher in vicinity to pixels or intersections of laser beams than remote from them.

The sensor element may comprise reflection sections (e.g. reflection coatings on the input or output ports) that reflect portions of the first or second radiation in order that the radiation passes the respective beam paths at least twice.

Another embodiment of the present invention relates to a method of measuring a magnetic field, for instance using a sensor as described above, the method comprising the steps of injecting a first radiation into at least one of the first beam paths, injecting a second radiation into at least one of the second beam paths, generating a microwave field at least at the intersection point where the at least one of the first beam paths and at the least one of the second beam paths intersect, detecting the first radiation upon passing the corresponding exit port or ports, and evaluating the detected radiation and generating one or more measurement values that describe the magnetic field at the intersection or intersections where the first and second radiation intercept.

If the first radiation is simultaneously injected into all of the first beam paths, and the second radiation is injected into a single one of the second beam paths, measurement values may be generated simultaneously for each of the sensor pixels that belong to the activated second beam path.

The steps of evaluating the detected radiation and generating one or more measurement values preferably includes measuring the absorption of the first radiation after passing the first beam path.

In order that the manner in which the above-recited and other advantages of the invention are obtained will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are therefore not to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail by the use of the accompanying drawings in which.

The preferred embodiments of the present invention will be best understood by reference to the drawings. It will be readily understood that the present invention, as generally described and illustrated in the figures herein, could vary in a wide range. Thus, the following more detailed description of the exemplary embodiments of the present invention, as represented in the figures, is not intended to limit the scope of the invention, as claimed, but is merely representative of presently preferred embodiments of the invention.

<FIG> shows a top view of an exemplary embodiment of a sensor according to the present invention. The sensor comprises a sensor element <NUM>, a set of detectors <NUM>, an evaluation unit <NUM>, a first emitter unit <NUM>, a second emitter unit <NUM>, a control unit <NUM>, and a microwave generator <NUM>.

The first emitter unit <NUM> is configured to generate a first radiation R1 and the second emitter unit <NUM> is configured to generate a second radiation R2. The first radiation R1 is preferably infrared laser light and the second radiation R2 is preferably green laser light.

The sensor element <NUM> consists of or at least comprises a diamond plate. The diamond plate incorporates a plurality of magneto-optically responsive defect centers which are very small and therefore not explicitly illustrated in <FIG>.

The sensor element <NUM> also comprises a set of first input ports I1 and a set of exit ports E. Each of the exit ports E is connected to one of the first input ports I1 via a corresponding first beam path B1.

A set of second input ports I2 is connected to second beam paths B2 which may terminate at an absorbing layer or at absorbing terminal pads <NUM> as shown in <FIG>. Alternatively, one could couple the green laser beams in optical fibres and dissipate that energy far from the sensor.

The first beam paths B1 are parallel and extend through a common plane CP located inside the sensor element <NUM>. The magneto-optically responsive defect centers mentioned above are also located in said common plane CP and may therefore influence radiation that passes the first beam paths B1.

The second beam paths B2 are also parallel and also extend through the common plane CP, but are angled with respect to the first beam paths B1. The first and second beam paths B1/B2 therefore define a plurality of intersections. Each intersection between one of the first and second beam paths B1/B2 forms a sensor pixel P.

In the exemplary embodiment of <FIG> the first beam paths B1 are perpendicular to the second beam paths B2 such that intersections form grid or a two-dimensional array of sensor pixels P.

The concentration of the magneto-optically responsive defect centers inside the diamond plate preferably exceeds <NUM><NUM><NUM> m-<NUM> in order to make sure that each of the sensor pixels P is positioned at or within the influence of at least one of the magneto-optically responsive defect centers. At each sensor pixel P, a magnetic field may be sensed at the respective pixel position when the first and second radiation R1/R2 interact with one or more magneto-optically responsive defect centers under the influence of a microwave field that is generated by the microwave generator <NUM>.

Each of the detectors <NUM> is individually assigned to one of the exit ports E and allows measuring the first radiation R1 and in particular the absorption of the first radiation R1. The absorption is caused by the magneto-optically responsive defect centers that are activated by the second radiation R2 and the microwave field of the microwave generator <NUM>. Since the absorption also depends on the strength of the external magnetic field, the detection signals DS of the detectors characterize the magnetic field.

The evaluation unit <NUM> is connected to the detectors <NUM> and configured to evaluate the detection signals DS of the detectors <NUM> in order to generate measurement values M that indicate the strength of the magnetic field for the activated sensor pixels P. The evaluation of the detection signals DS preferably includes evaluating the absorption of the first radiation R1 after passing the respective first beam path since the degree of absorption depends on the strength of the external magnetic field and the frequency of the applied microwaves and therefore describes the magnetic field strength.

During operation of the sensor, the first emitter unit <NUM> generates the first radiation R1 and activates at least one of the first beam paths B1 by injecting the first radiation R1. The second emitter unit <NUM> generates the second radiation R2 and activates one of the second beam paths B2 by injecting the second radiation R2. To this end, the first and second emitter unit are controlled by the control unit <NUM>.

For instance, the control unit <NUM> may control both the first and the second emitter unit such that maximally one of the first beam paths B1 and one of the second beam paths B2 is provided with the first or second radiation R1/R2 in each moment of time. In other words, each of the sensor pixels P may be addressed individually. The two-dimensional array of sensor pixels P may then be read out pixel-wise by sequentially providing each of the intersections with both the first and second radiation R1/R2. The evaluation unit <NUM> may then output sequentially measurement values M individually for each sensor pixel P.

Alternatively, the control unit <NUM> may control the first emitter unit <NUM> to input the first radiation R1 into all of the first beam paths B1 simultaneously. In the latter case, the evaluation unit <NUM> may evaluate the detection signals DS of the detectors <NUM> simultaneously in order to generate simultaneously one measurement value M per first beam path B1. The two-dimensional array of sensor pixels P may then be read out line-wise by sequentially providing each of the second beam paths B2 with the second radiation R2. The evaluation unit <NUM> may output in parallel measurement values M individually for each line of activated sensor pixels P.

In the first exemplary embodiment of <FIG>, the microwave generator <NUM> generates a large microwave field that covers all of the sensor pixels. To this end, the microwave generator <NUM> may comprise a large magnetic antenna <NUM>. The antenna <NUM> may be a magnetic coil that generates a microwave field in response to an electric microwave current.

In the exemplary embodiment of <FIG>, the sensor element <NUM> comprises four sensor pixels P. At each sensor pixel P, a magnetic field may be sensed at the respective pixel position when the first and second radiation R1/R2 interact with one or more magneto-optically responsive defect centers and the external microwave field that is generated by the microwave generator <NUM>.

<FIG> depicts a second exemplary embodiment of a sensor according to the present invention. In <FIG>, the microwave generator <NUM> generates individual fields for each of the intersections. To this end, the microwave generator <NUM> may comprise an individual magnetic antenna <NUM> (for instance a magnetic coil that generates a microwave field in response to an electric microwave current) for each of the sensor pixels P.

<FIG> depicts a cross-section of parts of the first embodiment of <FIG>. The sensor element <NUM> is mounted on a carrier <NUM>. The carrier <NUM> is preferably a silicon substrate which provides V-grooves <NUM>. The V-grooves <NUM> may carry fibers <NUM> that connect input ports I1/I2 with the first or second emitter unit <NUM>/<NUM> or the exit ports E with one of the detectors <NUM>.

In order to reduce coupling losses, lenses <NUM> may be located between the fibers <NUM> and the sensor element <NUM>.

The detectors <NUM> and the emitter units <NUM>/<NUM> which are not depicted in <FIG> may also be placed on the carrier <NUM> in order to form a photonic chip that provides the described sensing or measuring capability. Alternatively, one or more of the latter components may be located elsewhere.

<FIG> also shows a printed circuit board <NUM> that is located on top of the sensor element <NUM> and carries the antenna <NUM>. The antenna <NUM> is part of the microwave generator <NUM> that generates the microwave field in the sensor element <NUM>.

The sensor element <NUM> may be provided with integrated waveguides that guide the radiation through the sensor element in order to make sure that the amplitude of the radiation R1/R2 is constant (or almost constant) at all intersections or sensor pixels P.

<FIG> depicts a cross-section of parts of the second embodiment of <FIG>. In contrast to the embodiment shown in <FIG>, the printed circuit board <NUM> provides four antennae <NUM> that are individually assigned to the sensor pixels P in <FIG>. The microwave generator <NUM> may therefore generate individual microwave fields in each of the sensor pixels P.

In the exemplary embodiments of <FIG>, the evaluation unit <NUM> may evaluate the signal strength of the detection signals DS in order to determine absorption values that indicate the absorption of the first radiation R1. The absorption values correlate with the strength of the magnetic field in the area of the activated sensor pixel P and therefore allow calculating the strength of the magnetic field for each sensor pixel P.

Alternatively, the evaluation unit may determine the absorption of both radiations R1 and R2 to allow the calculation of the strength of the magnetic field for each sensor pixel. Further possible ways of evaluating the detection signals DS in order to calculate measurement values M that describe the magnetic field are described in the above cited publications "Magnetometry with nitrogen-vacancy defects in diamond" and "Nitrogen-Vacancy Centers in Diamond: Nanoscale Sensors for Physics and Biology".

In summary, exemplary embodiments of the invention may have one or more of the following features or characteristics:.

The various embodiments and aspects of embodiments of the invention disclosed herein are to be understood not only in the order and context specifically described in this specification, but to include any order and any combination thereof. Whenever the context requires, all words used in the singular number shall be deemed to include the plural and vice versa. Whenever the context requires, all options that are listed with the word "and" shall be deemed to include the word "or" and vice versa, and any combination thereof.

In the drawings and specification, there have been disclosed a plurality of embodiments of the present invention. The applicant would like to emphasize that each feature of each embodiment may be combined with or added to any other of the embodiments in order to modify the respective embodiment and create additional embodiments. These additional embodiments form a part of the present disclosure.

Claim 1:
Sensor comprising a sensor element (<NUM>) for measuring a magnetic field, the sensor element (<NUM>) comprising
- a set of at least two first input ports (I1),
- a set of at least two exit ports (E) each of which is connected to one of the first input ports (I1) via a corresponding first beam path (B1),
- a set of at least two second input ports (<NUM>) each of which is connected to a second beam path (B2),
- wherein the first beam paths (B1) extend through a common plane (CP) located inside the sensor element (<NUM>), said plane (CP) comprising a plurality of magneto-optically responsive defect centers,
- wherein the second beam paths (B2) also extend through said common plane (CP), but are angled with respect to the first beam paths (B1) such that a plurality of intersections between the first and second beam paths (B2) is defined, and
- wherein each intersection forms a sensor pixel (P) located at at least one of said magneto-optically responsive defect centers,
wherein the sensor further comprises
- a set of detectors (<NUM>) each of which is individually assigned to one of said exit ports,
- an evaluation unit (<NUM>) connected to said set of detectors (<NUM>) and configured to evaluate detection signals (DS) of the detectors (<NUM>) in order to generate one or more measurement values (M),
- a first emitter unit (<NUM>) which is capable of generating a first radiation (R1) and activating at least one of the first beam paths (B1) by injecting the first radiation (R1),
- a second emitter unit (<NUM>) which is capable of generating a second radiation (R2) and activating at least one of the second beam paths (B2) by injecting the second radiation (R2),
- a control unit (<NUM>) configured to control the first and second emitter unit (<NUM>, <NUM>), and
- a microwave generator (<NUM>) capable of generating a microwave field at the intersection points of the beam paths (B1, B2).