Fig. 1: magnetic field strength of the microwave in the TE102 cavity with two dielectric rings

Fig. 2.b: EPR signals of Mn with none, one and two dielectric rings

Fig. 2.a: EPR signals of Tempol with none, one and two dielectric rings

Improved sensitivity for solid and liquid samples through dielectric rings in the resonator

For a lot of EPR applications the sensitivity of the measurement tool is vital for good results, e.g. low dose dosimetry. In this application note it is described how the sensitivity of the MS5000 was enhanced by a factor of 4 for solids and factor 2 for liquid samples by concentrating the magnetic field of the microwave at the sample location through dielectric rings.

In the MS5000 a rectangular cavity with a TE102 mode at 9.2…9.6 GHz is used, which is ideal for multifunctional use. By inserting two dielectric rings (e » 30) the magnetic field of the microwave can be concentrated at the sample location and hence the fill factor rises. Figure 1 shows the simulated magnetic field strength in the cavity.

Since also the electric field is concentrated, the coupling of the cavity with liquid samples can be difficult, but since the accuracy of the coupling has been improved in the MS5000 recently, it is possible to couple up to 100 µl with the dielectric rings.

Figure 2.a and 2.b demonstrates the improved sensitivity on Mn (solid) and Tempol (liquid) for one and two dielectric rings. It becomes obvious that the sensitivity is improved by a factor of 4 for solids and a factor 2 for liquids.