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This paper presents a detailed technical characterization of a micromachined millimeter-wave near-field probe developed for skin cancer diagnosis. The broadband probe is optimized for frequencies from 90 to 104 GHz and consists of a dielectric-rod waveguide, which is metallized and tapered towards the tip to achieve high resolution by concentrating the electric field in a small sample area. Several probes with different tip sizes were fabricated from high-resistivity silicon by micromachining and were successfully characterized using silicon test samples with geometry-defined tailor-made permittivity. The probes show a high responsivity for samples with permittivities in the range of healthy and cancerous skin tissue at 100 GHz (from to , loss tangent of approximately 1.26). The sensing depth was determined by simulations and measurements from 0.3 to 0.4 mm, which is adapted for detecting early-stage skin tumors before they metastasize. The lateral resolution was determined to 0.2 mm for a tip size of 0.6 0.3 mm, which allows for resolving small skin tumors and inhomogeneities within a tumor.

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This paper presents for the first time measurement data on in-vivo dermatological experiments verifying the performance of a millimeter-wave medical probe designed for skin-cancer diagnosis. The probe consists of a micromachined silicon-core dielectric-rod waveguide, which is metallized and tapered at its tip as a compromise for high field concentration at the probe-to-skin interface, high sensitivity, high resolution, and an interaction volume depth adapted to diagnosing early-stage melanoma. The in-vivo dermatological tests on humans comprise: (1) measurement at different skin sites; (2) measurements of skin burns; (3) scanning the profile of benign skin neoplasma; (4) standardized dermatological tests with skin-irritant in 5 concentrations on 5 test persons, including monitoring of the healing process and reference measurements using a commercial transepidermal water loss instrument. All tests were successfully completed and show that millimeter-wave sensors are well capable of detecting physiologic changes of the skin and experimental skin reactions.Index Terms -microwave sensor, millimeter-wave sensor medical diagnosis, dielectric rod, micro machining, MEMS.

The probe has the potential to discriminate between normal and pathological skin tissue. Further, improved information, compared to the optical histological inspection can be obtained, i.e. the complex permittivity characterization is obtained with a high resolution, due to the highly reduced measurement area of the probe tip.