An MNP machine provides a magnetic bias field to a sample space; drive coils bracketing the sample space; pickup coils coupled through amplifiers to a computer; and a radio frequency (RF) stimulus coil driven at an electron paramagnetic resonance (EPR) frequency of MNPs in the bias field. The computer is configured to provide a MNP Brownian motion spectrum from the signals or magnetic particle images. A method of imaging MNP concentrations in a subject includes applying a magnetic bias field having a gradient; applying RF at an EPR frequency of the MNPs in the magnetic bias field; sweeping either magnetic bias field strength or radio frequency to sweep a surface of resonance through the subject; observing EPR resonances of the MNPs; rotating the magnetic bias field relative to the subject; repeating sweeping the surface of resonance through the subject; and reconstructing a three-dimensional model of MNP concentrations of the subject.

An MNP machine provides a magnetic bias field to a sample space; drive coils bracketing the sample space; pickup coils coupled through amplifiers to a computer; and a radio frequency (RF) stimulus coil driven at an electron paramagnetic resonance (EPR) frequency of MNPs in the bias field. The computer is configured to provide a MNP Brownian motion spectrum from the signals or magnetic particle images. A method of imaging MNP concentrations in a subject includes applying a magnetic bias field having a gradient; applying RF at an EPR frequency of the MNPs in the magnetic bias field; sweeping either magnetic bias field strength or radio frequency to sweep a surface of resonance through the subject; observing EPR resonances of the MNPs; rotating the magnetic bias field relative to the subject; repeating sweeping the surface of resonance through the subject; and reconstructing a three-dimensional model of MNP concentrations of the subject.

A sensing probe may be formed of a diamond material comprising one or more spin defects that are configured to emit fluorescent light and are located no more than 50 nm from a sensing surface of the sensing probe. The sensing probe may include an optical outcoupling structure formed by the diamond material and configured to optically guide the fluorescent light toward an output end of the optical outcoupling structure. An optical detector may detect the fluorescent light that is emitted from the spin defects and that exits through the output end of the optical outcoupling structure after being optically guided therethrough. A mounting system may hold the sensing probe and control a distance between the sensing surface of the sensing probe and a surface of a sample while permitting relative motion between the sensing surface and the sample surface.

A sensing probe may be formed of a diamond material comprising one or more spin defects that are configured to emit fluorescent light and are located no more than 50 nm from a sensing surface of the sensing probe. The sensing probe may include an optical outcoupling structure formed by the diamond material and configured to optically guide the fluorescent light toward an output end of the optical outcoupling structure. An optical detector may detect the fluorescent light that is emitted from the spin defects and that exits through the output end of the optical outcoupling structure after being optically guided therethrough. A mounting system may hold the sensing probe and control a distance between the sensing surface of the sensing probe and a surface of a sample while permitting relative motion between the sensing surface and the sample surface.

Certain aspects of the present disclosure provide methods and apparatus for closed-loop control of a system using one or more electron paramagnetic resonance (EPR) sensors located on-site. With such EPR sensors, a change can be applied to the system, the EPR sensors can measure the effect(s) of the change, and then adjustments can be made in real-time. This feedback process may be repeated continuously to control the system.

Certain aspects of the present disclosure provide methods and apparatus for closed-loop control of a system using one or more electron paramagnetic resonance (EPR) sensors located on-site. With such EPR sensors, a change can be applied to the system, the EPR sensors can measure the effect(s) of the change, and then adjustments can be made in real-time. This feedback process may be repeated continuously to control the system.

A synthetic diamond material comprises a surface, wherein the surface comprises a first surface region comprising a first concentration of quantum spin defects. A second surface region has a predetermined area and is located adjacent to the first surface region, the second region comprising a second concentration of quantum spin defects. The first concentration of quantum spin defects is at least ten times greater than the second concentration of quantum spin defects, and at least one of the first or second surface regions comprises chemical vapour deposition, CVD, synthetic diamond. A method of producing the synthetic diamond material is also disclosed.

A synthetic diamond material comprises a surface, wherein the surface comprises a first surface region comprising a first concentration of quantum spin defects. A second surface region has a predetermined area and is located adjacent to the first surface region, the second region comprising a second concentration of quantum spin defects. The first concentration of quantum spin defects is at least ten times greater than the second concentration of quantum spin defects, and at least one of the first or second surface regions comprises chemical vapour deposition, CVD, synthetic diamond. A method of producing the synthetic diamond material is also disclosed.

A magnetometer includes an electron spin defect body including a plurality of lattice point defects. A microwave field transmitter is operable to apply a microwave field to the electron spin defect body. An optical source is configured to emit input light of a first wavelength that excites the plurality of lattice point defects of the electron spin defect body from a ground state to an excited state. A first optical fiber has an input end optically coupled to the optical source and an output end. The output end is attached to a first face of the electron spin defect body and is arranged to direct the input light into the first face of the electron spin defect body. A second optical fiber has an output end and an input end. A photodetector is optically coupled to the output end of the second optical fiber.

A coupling device is provided for coupling microwave radiation from a first microwave structure, in particular a microwave waveguide, into a second microwave structure, in particular a microwave resonant cavity, wherein the first and second microwave structures share a common wall, through an iris opening in said wall in front of which the coupling device is positioned on the side of the first microwave structure, in particular wherein the coupling device is of a basically cylindrical shape, characterized in that the coupling device comprises N electrically conducting conductor loops, with N≥3, preferably 3≤N≤20, that the conductor loops are arranged coaxially in an array along a z-axis, and that axially neighboring conductor loops are separated by a dielectric. The inventive coupling device allows for a larger coupling coefficient, and in particular allows for a larger dynamic range.