A NONCONTACTING SENSOR SYSTEM FOR RESPIRATORY AIR-FLOW DETECTION

A new system for non-contacting respiratory air flow detection is pres ented. Airborne ultrasound is being used to detect variations in the v elocity of sound caused by air flow. Two opposing ultrasonic waves are reflected by the face of the subject to be investigated, and variatio ns in the differential transit times, or phase shifts, are recorded. D ue to the non-reciprocity of flow, it is possible to obtain specificit y against other influences, such as movements of the subject. Experime ntally, an operating frequency in the range 40-200 kHz has been found feasible. In the prototype system, continuous waves emitted by standar d piezoelectric transducers operating at 40 kHz and of slightly differ ent frequencies are used for identification of the opposing waves. A l inear flow dependence has been verified, with adequate resolution. The function has also been verified on human subjects. A wide range of hi gh-priority clinical applications can be foreseen for the system.