Sensor system

A sensor system comprises a mat (20) for placement over a patient's mattress including a number of sensors (10) located in the mat. The sensors include a sensor housing (12), a sound vibration sensing element in the form of a PVDF membrane (13), and means for amplifying sensed sounds. The PVDF membrane is coated/covered with a typically latex, impedance matching layer (14). The sensor automatically provides for auscultation, in which the patient's own weight, from the patient lying on the bed, compresses their thorax against the membrane, compressing also the patient's clothing, bed sheet and mattress cover material between the two. The recoil in the mattress opposes the body mass, thus compressing the membrane against the thorax. The impedance matching layer on top of the membrane transmits fine breath sounds through to the membrane as the latex does not weaken or attenuate the fine breath sounds but transmits them to the PVDF membrane. However being flexible, it is not uncomfortable to lie on.