Millimeter wave silicon micromachined waveguide probe as an aid for skin diagnosis--results of measurements on phantom material with varied water content

Millimeter-Wave Substrate Integrated Waveguide Probe for Skin Cancer Detection

This article presents an efficient and low-cost near-field probe, designed for early-stage skin cancer detection. Thanks to a tapered section, the device can achieve a sharp concentration of electric field at its tip. Moreover, the adoption of substrate integrated waveguide (SIW) technology ensures an easy and cheap fabrication process. The probe is realized on a high dielectric constant substrate (Rogers RO3210) that provides a good impedance matching with the skin, thus allowing to use the device in direct contact with it. This feature is essential to ensure that the proposed system can be adopted as a practical and effective tool for a fast scanning of many suspected skin regions. The probe is designed to operate at around 40 GHz in order to achieve the penetration depth required to detect small cancer lumps in the skin, while preventing the fields from interacting with the underlying biological tissues. Furthermore, the concept of detection depth is defined with the goal of introducing a metric that is more suitable than the penetration depth to express the notion of the maximum distance from the skin surface at which a tumor can be detected. Thanks to a differential imaging algorithm, the probe is capable of working on every different skin types and body region. The proposed device has a lateral sensitivity and detection depth of 0.2 and 0.55 mm respectively. The probe was designed and tested through simulations in CST Microwave Studio, as well as fabricated and validated through measurements on an artificial human skin phantom.

Millimeter-wave emissivity as a metric for the non-contact diagnosis of human skin conditions

A half‐space electromagnetic model of human skin over the band 30–300 GHz was constructed and used to model radiometric emissivity. The model showed that the radiometric emissivity rose from 0.4 to 0.8 over this band, with emission being localized to a layer approximately one millimeter deep in the skin. Simulations of skin with differing water contents associated with psoriasis, eczema, malignancy, and thermal burn wounds indicated radiometry could be used as a non‐contact technique to detect and monitor these conditions. The skin emissivity of a sample of 30 healthy volunteers, measured using a 95 GHz radiometer, was found to range from 0.2 to 0.7, and the experimental measurement uncertainty was ±0.002. Men on average were found to have an emissivity 0.046 higher than those of women, a measurement consistent with men having thicker skin than women. The regions of outer wrist and dorsal forearm, where skin is thicker, had emissivities 0.06–0.08 higher than the inner wrist and volar forearms where skin is generally thinner. Recommendations are made to develop a more sophisticated model of the skin and to collect larger data sets to obtain a deeper understanding of the signatures of human skin in the millimeter wave band. Bioelectromagnetics. 38:559–569, 2017. © 2017 The Authors. Bioelectromagnetics published by Wiley Periodicals, Inc.

Application of the planar-scanning technique to the near-field dosimetry of millimeter-wave radiators

The planar-scanning technique was applied to the experimental measurement of the electric field and power flux density (PFD) in the exposure area close to the millimeter-wave (MMW) radiator. In the near-field region, the field and PFD were calculated from the plane-wave spectrum of the field sampled on a scan plane far from the radiator. The measurement resolution was improved by reducing the spatial interval between the field samples to a fraction of half the wavelength and implementing multiple iterations of the fast Fourier transform. With the reference to the results from the numerical calculation, an experimental evaluation of the planar-scanning measurement was made for a 50 GHz radiator. Placing the probe 1 to 3 wavelengths from the aperture of the radiator, the direct measurement gave the near-field data with significant differences from the numerical results. The planar-scanning measurement placed the probe 9 wavelengths away from the aperture and effectively reduced the maximum and averaged differences in the near-field data by 70.6% and 65.5%, respectively. Applied to the dosimetry of an open-ended waveguide and a choke ring antenna for 60 GHz exposure, the technique proved useful to the measurement of the PFD in the near-field exposure area of MMW radiators.