Evanescent Microwave Microscopy of Porcine Skin Tissue

This thesis describes the application of a custom designed λ/4 resonant coaxial probe to measurements of the complex permittivity of in vitro freshly excised porcine skin tissue. The dielectric properties of the organic material within the near field of the tip of the probe frustrates the electric field and measurably changes the resonant frequency and quality factor Q of the coaxial sensor, where the change in resonant frequency and quality factor of a tuned resonance is measured as a function of tip-sample separation. The design of the probe enables better spatial resolution than previously developed probes. The following studies were performed: (1) measurement of the complex permittivity of porcine tissue over a range of frequencies revealed values consistent with published literature; (2) the change in quality factor from the probe measurements was compared to a visual microscope analysis of histological slices from the same skin location, indicating that subsurface structures such as capillary beds, ducts of exocrine sweat glands, and vein lumen ducts can be detected; and (3) measurements of the dielectric properties of a puncture wound and several burn lesions of varying severity revealed easily detectable changes, indicating that the probe has potential for evaluating and monitoring skin conditions. In addition, a new quantitative two point relationship between the real and imaginary parts of the materials complex permittivity related to the resonant frequency and quality factor shift using the method of images is developed, presented, and used in the above described skin studies. The two-point model describing the probe tip-sample interaction is capable of producing quantitative complex permittivity values for organic and biological materials