Design and Application of Special Microwave Interferometers for Non-Invasive Studies of Biological Effects

Special microwave interferometers have been designed to make non-contact measurements of the movements associated with various physiological functions such as respiration, pulse, muscle action, reflexes, involuntary tremors, etc. For each interferometer the factors affecting resolution across a large moving surface, sensitivity to small amplitude displacement and maintenance of calibration have been studied and accurate direct measurement of surface displacement has been achieved with very low incident microwave power levels. Interferometers based on three port circulators are most sensitive but those based on magic tee hybrids are easier to operate. Movement of the chest, hands, legs and eyeball have been studied and potential for accurate correlation with EEG, ECG, or EMG records are evident.