Noncontact imaging of materials using evanescent microwave magnetic dipole probe and modulated scatterers

A near-field magnetic-dipole probe suitable for non-contact imaging of materials was described and the effects of resonator coupling strength, operation frequency, and the probe wire tip geometry on the conductivity resolution of the probe are experimentally determined. Using a simplified circuit model of the resonator, we were able to interpret the system's output and predict the magnitude of reflected wave and relate it to the properties of the samples under investigation. Thus, the probe was calibrated to perform quantitative conductivity measurement. It has been shown that we have detected metal nonuniformities with 1% accuracy and 5×10-3σ and 2×10 -2σ conductivity resolution at 2 GHz operation frequency for the critical and over-coupling probes, respectively. We also discussed the calibration results of probes with different coupling strength over a 0.91 Ω/square sample. It has been shown that resonator probe has 100 times higher conductivity resolution than that of the transmission line probe. Furthermore, we characterized and compared the calibration results of probes with tip wires of different diameters. We also reported its applications in imaging high-frequency electromagnetic properties of magnetic metallic samples. The probe was calibrated to perform quantitative conductivity measurements in uniformity of the electromagnetic properties of damascene copper on silicon, and its subsequently sulfidized and annealed surface, and magnetized ferromagnetic materials.;Moreover, we discussed a new technique that combined aspects of the "freespace" imaging with the super resolution of near-field scanning probes by using an array of local scatterers near a sample. The local scatterers generated the near-fields waves upon illumination with a microwave beam. These near-fields interacted with the nearby material and affected the reflection coefficient (or more generally, scattering parameters) of scatterers in the array. Different scatterers were mechanically modulated at different base frequencies. Thus, the free-space reflected waves from the array were spatially modulated according to the local sample properties and the corresponding scatterer's modulation frequency. We discussed applications of this technique in imaging a dielectric sample at 10 GHz using an array of micromotors and a layer of carbon nanotubes at 100 GHz using an atomic force microscope tip as the local scatterer.