Microwave coupling device for iris apertures, comprising a plurality of conductor loops

A method of using a probe head in an electron paramagnetic resonance (EPR) measurement, the method comprising:

• providing a first microwave structure having a microwave waveguide and a second microwave structure having a microwave resonant cavity with at least one opening for an EPR sample, where the first and second microwave structures share a common wall with an iris opening;
• arranging an EPR sample at the sample holder in the microwave resonant cavity;
• and
• feeding microwave radiation into the microwave waveguide and coupling the microwave radiation into the microwave resonant cavity through the iris opening with a coupling device having three or more electrically conducting conductor loops coaxially in an array along a z-axis, with axially neighboring conductor loops being separated by a dielectric, such that magnetic field lines of the microwave radiation in front of the iris opening are parallel to the z-axis, microwave magnetic field axial propagation along the z-axis is below a cutoff-condition of the coupling device so that microwave magnetic field lines parallel to the z-axis do not enter an inner volume of the coupling device, and microwave magnetic field propagation between axially neighboring loops into the inner volume of the coupling device takes place, so that local microwave magnetic field line loops around individual conductor loops are formed and link a microwave magnetic field in the first microwave structure and a microwave magnetic field in the second microwave structure via the coupling device.