# US 12,181,546 B2 · Magnetic field sensor and method for measuring a magnetic field > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,181,546 B2 - Document ID: US12181546B2 - Status: Granted - Kind: B2 - Application number: 18/166,848 - Filed: 2023-02-09 - Published: 2023-08-24 - Granted: 2024-12-31 - Earliest claimed: 2022-02-18 - Assignees: Robert Bosch GmbH - Applicants: Robert Bosch GmbH - Inventors: Andreas Brenneis; Janine Riedrich-Moeller; Robert Roelver; Tino Fuchs - Web page: https://patentgrep.com/patent/US12181546B2 ## CPC - G01R 33/3692: {involving signal transmission without using electrically conductive connections, e.g. wireless communication or optical communication of the MR signal or an auxiliary signal other than the MR signal} - G01R 33/26: using optical pumping - G01N 21/6404: {Atomic fluorescence} - G01N 24/10: by using electron paramagnetic resonance (G01N24/12 takes precedence) - G01R 33/323: {Detection of MR without the use of RF or microwaves, e.g. force-detected MR, thermally detected MR, MR detection via electrical conductivity, optically detected MR} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q) ## Abstract A method for measuring a magnetic field includes radiating a microwave field having a first frequency into at least one measuring location in a crystal, which comprises optically excitable color center defects at the measuring location, radiating excitation light and detecting resulting fluorescence light, applying a deformation force which results in local mechanical strain, wherein an applied first deformation force is selected such that the first frequency corresponds to a resonance frequency of the color center defects under the action of the first deformation force without the magnetic field to be measured and the detected fluorescence light becomes minimal. The method further includes placing the sensor into the magnetic field to be measured to bring about a shift in the resonance frequency and varying the applied deformation force to compensate the shift in the resonance frequency until a minimum fluorescence signal is again acquired at a second deformation force. ## Claims ### Claim 1 A method for measuring a magnetic field using a sensor, the method, comprising: radiating a microwave field having a first frequency into at least one measuring location in a crystal, which comprises optically excitable color center defects at least at the at least one measuring location; radiating excitation light into the at least one measuring location and detecting resulting fluorescence light from the at least one measuring location; applying a deformation force to the crystal which results in local mechanical strain at least in an area of the at least one measuring location, the applying of the deformation force including applying a first deformation force that is selected such that the first frequency corresponds to a resonance frequency of the color center defects under the application of the first deformation force without the magnetic field to be measured and the detected fluorescence light becomes minimal; placing the sensor into the magnetic field to be measured in order to bring about a shift in the resonance frequency; and varying the deformation force applied to the crystal to compensate for the shift in the resonance frequency until a minimum fluorescence signal is again acquired at a second deformation force. ### Claim 2 (depends on 1) The method according to claim 1, further comprising: determining the field strength of the magnetic field to be measured on the basis of a difference between the first and the second deformation forces. ### Claim 3 (depends on 1) The method according to claim 1, further comprising: radiating microwave fields having two or more frequencies, wherein each of the two or more frequencies corresponds to a resonance frequency of the color center defects for an alignment axis of the color center defects in the crystal under the action of the first deformation force without the magnetic field to be measured; varying the deformation force after introduction into the magnetic field until a minimum fluorescence signal is again acquired for each of the radiated frequencies at a third deformation force; and determining the field strength of the magnetic field to be measured in the direction of the alignment axis assigned to the radiated frequency on the basis of a difference between the first and the third deformation forces. ### Claim 4 A magnetic field sensor for measuring a magnetic field, comprising: a crystal, which comprises optically excitable color center defects at least at one or more measuring locations; a fluorescence module configured to optically excite the color center defects at the one or more measuring locations and acquiring a resulting fluorescence light signal from the one or more measuring locations; an actuator configured to produce mechanical strains at least at the one or more measuring locations in the crystal by applying a defined variable deformation force; a microwave generator configured to produce a microwave field with a predetermined frequency at the one or more measuring locations; and a measurement module configured to control the actuator depending on the acquired fluorescence signal and to detect the deformation force applied by the actuator at least at a fluorescence minimum. ### Claim 5 (depends on 4) The magnetic field sensor according to claim 4, wherein the measurement module is further configured to: control the actuator to apply a first deformation force, which is selected such that the first frequency corresponds to a resonance frequency of the color center defects under the action of the first deformation force without the magnetic field to be measured and the detected fluorescence light is minimal; and control the actuator to vary the applied deformation force if the detected fluorescence light is no longer minimal due to the action of an external magnetic field until a minimum fluorescence signal is again acquired at a second deformation force. ### Claim 6 (depends on 5) The magnetic field sensor according to claim 5, wherein the measurement module is further configured to determine the field strength of the magnetic field to be measured on the basis of a difference between the first and the second deformation forces. ### Claim 7 (depends on 4) The magnetic field sensor according to claim 4, wherein the crystal is partly or entirely configured as a crystal membrane. ### Claim 8 (depends on 7) The magnetic field sensor according to claim 7, wherein the crystal membrane defines recesses that alter the deformation and/or strain properties of the crystal membrane. ### Claim 9 (depends on 4) The magnetic field sensor according to claim 4, wherein the crystal is partly or entirely configured as a crystal bending beam, which is rigidly attached on one or on both sides. ### Claim 10 (depends on 4) The magnetic field sensor according to claim 4, wherein the fluorescence module comprises: at least one excitation light source configured to radiate excitation light into the one or more measuring locations; and at least one photodetector configured to detect fluorescence light at one or more of the measuring locations, wherein the crystal is configured as an optical waveguide that guides excitation light to the one or more measuring locations and/or guides fluorescence light away from the one or more measuring locations to the at least one photodetector. ### Claim 11 (depends on 4) The magnetic field sensor according to claim 4, wherein the actuator comprises a piezoelectric actuator or an electrostatic actuator. ### Claim 12 (depends on 4) The magnetic field sensor according to claim 4, further comprising: a carrier substrate on which the crystal is mounted such that a recess is formed between the carrier substrate and the one or more measuring locations, wherein the actuator is disposed on the crystal such that deflection of the crystal by the actuator is possible at least in portions of the crystal. ### Claim 13 (depends on 12) The magnetic field sensor according to claim 12, wherein at least part of the fluorescence module is accommodated in the recess. ### Claim 14 (depends on 1) A computing unit comprising at least one memory having stored program instructions executed by the computing unit to carry out the method according to claim 1. ### Claim 15 (depends on 1) A computer program comprising program instructions executed by a computing unit to carry out the method according to claim 1. ### Claim 16 (depends on 15) A non-transitory machine-readable storage medium on which the computer program according to claim 15 is stored.