2-Dimensional near-field millimeter-wave scanning with micromachined probe for skin cancer diagnosis

This paper reports for the first time on the 2-dimensional scanning performance of a micromachined millimeter-wave (100 GHz) near-field probe with a substantially reduced tip size which is designed for skin cancer diagnosis. Furthermore, it introduces a novel concept of creating inhomogeneous test samples with tailor-made and locally altered permittivity which mimick skin tissue with small anomalies and are used for characterizing the probe. A probe prototype with a tip size of 300 × 600 μm² and test samples with permittivity in the range of cancerous and healthy skin tissue were fabricated by micromachining and used for evaluating the sensitivity and resolution of the probe. This paper reports for the first time on 2-dimensional scanning performance, resolution, repeatability, long-term stability, and sensitivity, which are important for qualifying such measurement probes for medical applications. The resolution of the prototype, which is important for early detection of small tumor speckles, was found to be better than 200 μm, i.e. 1/6 of the medium-normalized wavelength. The reproducibility of the probe setup including operator uncertainty is 1.36% (1σ) and the long term stability of reference measurements is 0.59% (1σ) over 8 hours.