A method based on passive acoustic sensors for detection of vital signs in closed structures

The paper deals with the problem of non intrusive detection of concealed people by means of passive acoustic sensors To this aim, the authors present hereinafter a new method capable of detecting and recognizing vital signs, typical of human beings, thanks to the use of a suitable data acquisition system, based on a geophones network, and a proper digital signal processing algorithm. In particular, the passive sensors are mandated to (i) detect the reduced-amplitude vibrations on a solid structure generated by people´s heartbeat, breathing and associated (voluntary and involuntary) motions and (ii) convert them in a signal whose power spectrum proves to be significant in two different frequency bands, referred to as audio and infrasonic band. With regard to the processing algorithm, it is based on adaptive filter and estimates the so-called pseudo period of the received signal to single out the desired detection of vital signs. Preliminary results, carried out in a number of numerical and experimental tests, confirm the effectiveness of the proposed approach and measurement strategies.