Magnetostrictive amorphous sensor for the detection of human respiration

Abstract A simple sensor for the detection of respiratory and cardiac activity is based on changes in the circumference of the human thorax. The sensor consists of magnetostrictive amorphous ribbons glued to the convex side of a prebent nonmagnetic layer. As a result, elongation is transferred into compressive stress, which reduces the ribbon's permeability, and a proportional voltage signal, respectively. The paper discusses major practical problems which result from the material's nonlinear behaviour, the sensor's individual transfer function, its undefined pre-stress and the elasticity of the applied sensor belt. In an effective way, overall linearization can be attained by means of wide-range calibration functions stored in a computer file. Alternatively, scaling by means of a spirometer yields quantitative evaluations, but restricted to respiration.