Design of millimeter-wave probe for diagnosis of human skin

Millimeter-wave reflectometry is a potentially interesting method to determine properties of human skin tissue. With this method an open-ended waveguide probe is pressed against the skin which then measures the reflection coefficient in the millimeter-wave frequency range. Ideally, the probe is put perpendicular on the skin. In practice, the angle between probe and skin surface will deviate from the exact 90 degrees. This could influence the measurement results. Also the pressure of the probe on the skin will vary in practice, which could also influence the results. The sensitivity for these kind of parameter variations determines the suitability for use under practical circumstances as may occur in home-care situations. In this paper, the sensitivities of three types of probes for these parameters are investigated in order to determine the most suitable candidate among three types of probes. These are the flanged probe with Teflon plug, the flanged probe without Teflon plug, and the unflanged probe with Teflon plug. The latter turns out to be the best candidate as regards sensitivity for practical circumstances.