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A method for the non-contact measurement of two-dimensional displacement of chest surface by breathing and heartbeat using an airborne ultrasound

Vital-signs measurement systems, which have sensors that are brought into contact with or close to the body, are used for many applications. However, these systems are not suitable in some cases, namely when continuous monitoring is required or a subject cannot wear sensors. We have studied non-contact measurement of respiration and heart rate using an airborne ultrasound. In the proposed method, an M-sequence modulated ultrasound is transmitted to the chest of the subject, then the received signal is correlated with the transmitted M-sequence to detect the reflected echo with high signal-to-noise ratio. The time of flight (TOF) of the reflected echo indicates the distance to the chest surface. Therefore, the chest displacement due to breathing and heartbeat can be measured from the variation of TOFs. In this paper, the proposed measurement is demonstrated for subjects in a supine position without clothes. In the experiment, two cross-correlation functions were obtained by using one loudspeaker and two microphones to form the airborne B-mode image. Two-dimensional displacement of the chest surface due to breathing and heartbeat could be measured from the variation of airborne B-mode images.