There is necessity to detect remotely small physiological changes in a human in order to measure the human’s condition including physiological stress levels and viability.
Neural inputs to the heart’s sinoatrial node accelerate or decelerate the heart rate over varying time scales depending on the respiration (RESP) rate and the balance of tone of the two branches of autonomic nervous system (ANS). At worst, just a heartbeat indicates the presence of vital activity. This method is particularly useful for the detection of people under rubble.
But small physiological changes, which associated with heart motion and breathing activity, can be difficult to detect with sufficient accuracy remotely using radar systems because of non-linear response in derived motion signals and drifting of signal characteristics with temperature due to temperature-dependent properties of associated electronics.
The present invention (US8378879B2, priority from 2009, by Johns Hopkins University) has been made in view of the above problems and provides an apparatus and methods.
The present invention is directed to an apparatus for sensing motion comprising a transmitter, a frequency control, a first receiver for receiving the reflected transmitted carrier signal, a second receiver for receiving the reflected transmitted carrier signal.
The second receiver being placed out of phase by less than a wavelength of the carrier signal from the first receiver. Means for subtracting produce an error signal.
When motion is sensed by the apparatus, the error signal moves from zero thereby causing a corrective signal to be generated.
The present invention is also directed for reducing distortion and drift in radar returns.