An electromagnetic distance measuring system

A new accurate method to determine the myocardial deformation during the cardiac cycle in vivo is described. The system is based upon the mutual inductance principle, yet with transducers which consist of three perpendicular coils, yielding a spherical radiation and sensing characteristic. Thus the system is invariant with regard to rotational movements of the transducers. Residual angle dependences of the transducers can cause deviations of the recorded distance up to 4%. The output voltage is linear with the distance, with an accuracy better than 1%. The frequency response is set to 100 Hz (-3 dB). Zero drift doesn't exceed 0.5% after 24 hours. Measurements are not restricted to radiation propagating media, thus they can be performed in air, inside or outside of any biological object. For studies of regional myocardial performance in the left ventricle spherical transducers were designed with a diameter of 1.5 mm and a measuring range between 5 and 25 mm and flat surface transducers (5 mm diameter, 1.5 mm height) with a measuring range between 15 and 200 mm.