Abstract
We have developed a non-contact monitoring system to measure heart and respiratory rates, in aged care settings, using low-power 24 GHz microwave radars in accordance with the guideline for electromagnetic wave protection. Two Doppler radars are placed on a bed base under the mattress and detect the small vibration on the surface of a human body caused by respiratory movements and heartbeats. This system has the feature in which two radars output spectra are combined to improve the measurement accuracy. The main challenge was noise associated with irregular movements such as limb movement and turning over in bed mix with respiration and heart rate signals, making it difficult to separate and extract the target signal. A respiratory signal maximum value and a heart beat signal maximum value were set beforehand, and we introduced automatic gain control (AGC), a waveform compression method applied to radar output signals whereby each individual wave with the amplitude greater than the maximum value was adjusted to below the maximum value. Moreover, by judging output electric power strength of the radar signal we have distinguished the heart and respiratory rates of time zone with no body movement as data with high reliability or more.
In addition, we evaluated actual operability for residents in a nursing home for seniors, the utility of the noncontact monitoring was confirmed. The early detection of changes in health condition and reduction of the primary caregiver's physical and mental load, is very important for aged care in the home or in institutions. Our unconstrained, safe, and noninvasive method is ideal as a new monitoring system for aged care settings.
