A study of the use of microwave input impedance for local measurement of human body

The possibilities of electrical measurement of the human body in the direction of depth using microwaves are discussed both theoretically and experimentally. By measuring the input impedance of an open-ended coaxial probe radiating into bilayered medium, both the depth of fat layer and the electrical surface impedance of muscle layer can be estimated. From the calculated input impedance using a full-wave method the reflected component on muscle layer surface is isolated by the approximate analysis. Theoretical results indicate that the phase shift depending on frequency and the modulus of this reflected component are useful to estimate the thickness of fat layer and the electrical properties of muscle, respectively. The experimental results show a reasonable agreement with the theoretical relationship between the phase shift and the fat thickness, indicating that further improvement is needed to utilize the modulus data slightly changing with electrical properties of muscle.