A non-invasive, partial-body exposure method for measuring the complex permittivity of biological substances at microwave frequencies

A non-invasive and selective (partial-body) exposure technique for measuring the complex permittivity of biological substances at microwave frequencies is described. For this purpose a Gaussian-beam launcher is used to irradiate selectively the test-material at the particular position of interest; and a reflectometric bridge arrangement is used to measure the amplitude and phase of the reflected beam wave. Using the measured data and the theoretically formulated expression for the reflection coefficient, the real and the imaginary parts of the permittivity are computed. Results obtained by the present method for materials such as acrylic plastic, bakelite hylam, human skullbone (in vitro measurements on the occipital region) and for the midportion of the palm (in vivo measurement) are compared, with those results due to other methods. The suitability of this technique for noncontact in vivo and in vitro measurements of the permittivity in biological experiments is discussed. © 1978 IFMBE.