A microwave interferometer system for the displacement measurements of biological subject

Abstract

AbstractThe microwave displacement meter based on the principle of phase interferometer has a high sensitivity in detection. However, in the conventional system the measurable displacement width is limited to the order of one half‐wavelength of the microwave, and quantitative information cannot be obtained without calibration. In the system proposed in this paper, a twophase microwave Doppler sensor (10.525 GHz) is used for detecting the reflected signal from the object as a vector, and the displacement is measured directly from the phase. While the high sensitivity of the phase interferometric method is maintained, the measurable width is improved significantly and quantitative measurement is possible. However, in the present method, the offset caused by the existence of unwanted reflectors other than the object can be a problem. Since this is dependent on the measurement environment, the problem is especially severe for biological measurement. In this paper, this offset is calculated by estimation and is shown to be removable. Next, a recurrence formula is derived that is used for calculating the displacement from the phase of the signal vector. the prototype system can measure the displacement width of 36 cm with the resolution of 90 μm. As an example of biological measurement, two‐dimensional body movement measurement in the balancing function test is presented. Finally, the accuracy and resolution of the present method are studied.