A COMMERCIAL-OFF-THE-SHELF FREQUENCY MODULATED CONTINUOUS WAVE RADAR FOR VITAL SIGN MONITORING

Abstract

Objective: Radar systems are capable of retrieving remotely micro-movements with very high precision. Millimeter-wave radars are already used in several medical applications (e.g. sleep disorders, heart beat rate, patient monitoring) and have shown promising results towards a remote Doppler cardiogram or arterial pulse wave measurements techniques. In this work, we tested a 122 GHz commercial-off-the-shelf (COTS) Frequency Modulated Continuous Wave (FMCW) radar for vital (respiratory and cardiac) signals monitoring. This required the setting up of a very precise experimental bench and the investigation of a robust data processing procedure. Design and method: An experimental bench (see Figure 1-a) has been set up with a high precision Newport linear actuator: a small target can be then displaced with less than 3 μm accuracy. Such system can replicate the thorax displacements due to the respiratory and cardiac activity. Two different motions were simulated: a ‘large’ 8 mm displacement at 0.15 Hz (a.k.a. respiratory) and a ‘small’ 0.5 mm at 1 Hz (a.k.a. cardiac). Furthermore, a shaker system can be used to reproduce completely arbitrary movements, even from real acquired Electrocardiogram (ECG) data. In this case, however, a reference measurement system would be necessary to determine the accuracy. Results: A first measurement set was dedicated to evaluate the accuracy of the radar system: around 50 acquisitions for each type of displacements were carried out. The accuracy of the radar measurements results in the order of ∼10 μm (see Figure 2). A second measurement set tested the dynamic resolution: in this case, a 0.4 Hz sinusoidal signal and a 0.8 Hz pulsation mix were fed to the shaker system. The radar is capable of retrieving both signal signatures (see Figure 3), with errors due to the combination of sharp pulse rise and low radar sampling frequency Conclusions: We show that a COST radar is able to retrieve vital signs chest displacements with a good accuracy in both amplitude and dynamics, thus representing a valid option for a remotely continuous cardiovascular monitoring. Next objectives are In Vivo measurements with an in-house radar system and measurements of blood pulse waves.