Frequency modulation function. The solid line denotes the instantaneous frequency of the emitted signal (1) and the dashed line that of a signal reflected by a target with time of flight .
Setup of the human subject experiments. (a) Measuring (constant) breathing and cardiac rates from signal reflected by the patient’s chest. (b) Measuring two targets simultaneously: A small ceramic pendulum is placed halfway between the radar and the subject. (c) Monitoring uneven respiration using signal reflected by the patient’s hand. The rest of the patient’s body is shielded by a fine copper mesh screen.
Amplitude and phase shift of effective radar cross section of a human subject, proportional units. Left: time-domain plots. Right: Frequency-domain plots. (a) Respiration-filtered signal. peaks in both amplitude and phase frequency curves correspond to 15 breaths per minute. (b) Cardiac-filtered radar data. Frequency peaks at correspond to the heart rate of . Note the shorter time-domain display window: .
All plots use arbitrary units. (a) MFMR used to measure the patient’s vital signs and the oscillation frequency of a pendulum. Top: Denoised pendulum signal, (frequencies above cut off). Bottom: Human subject signal filtered to amplify respiration ( band filter) and cardiac motion ( band filter). (b) Radar reflection off the subject’s hand vs pressure belt signal. Coached breathing pattern: five deep breaths at , a breathhold, six breaths at . The signals derived from the radar and from the respiration monitor belt clearly mirror each other.
MFMR prototype characteristics. Low radiated power means that signal power density at distances or more is below , which is typical to common household appliances and does not pose significant health risks (Ref. 17).
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