The potential of EMFi sensors in heart activity monitoring

The unobtrusive monitoring of patients and people’s general physiological state using wearable sensors hasattracted a lot of attention in recent years. Our research group has studied the possibilities of using EMFi(Electromechanical film) sensors for monitoring tiny mechanical movements caused by the activity of the heart.The EMFi material, originally developed and patented by the Technical Research Centre of Finland in 1987[1], is a plastic film which converts mechanical energy to an electrical signal and vice versa. It is basicallyflexible and thin biaxially oriented polypropylene film coated with electrically conductive layers, which arepermanently polarized. EMFi has a static charge corresponding to hundreds of Volts. Changes in the pressureacting on the film generate a charge on its electrically conductive surfaces and this charge can be measured as acurrent or voltage signal, often with a charge amplifier. Thus the EMFi acts as a sensitive movement sensor. Thesensitivity is an order of magnitude better than the one obtained with usual piezo materials.As a result of high intrinsic resistance and bubble structure the charge persists for a long time. Adisadvantage is that storing or using the sensors in temperatures above 50