Measurement of energy transmission efficiency of transcutaneous energy transformer in NaCl solution for ventricular assist devices by reducing common-mode current in the range of 200–1500 kHz

Abstract

The air-core transcutaneous energy transmission system (TETS) uses magnetic fields to transfer energy wirelessly to a ventricular assist device; the energy is transferred from a coil placed on the surface of the body (primary coil) to one inside the body. Accurate measurement of efficiency of the TETS is difficult because of the large common-mode (CM) current which flows through the ground line and the low sampling rate of the measurement equipment. In this study, a CM choke coil and a floating type measurement equipment were used to reduce the CM current flowing through the ground. Furthermore, the value of the efficiency obtained from measurements made using a floating oscilloscope with a high sampling rate was compared with the theoretical estimate of the efficiency when the transformer was kept immersed in NaCl solution to imitate the human biological tissue. In the range of 200–1500 kHz, it was possible to effectively suppress the CM current in the NaCl solution; the ratio of the primary current I1 to the CM current Icm obtained in the improved method was 21% less compared to the corresponding ratio in the conventional method. At the frequency of 500 kHz, in the NaCl solution, the maximum measured value of efficiency was 91.82%, whereas the theoretical estimate was 93.50%. The measured efficiency in the improved measurement method is in good agreement with the theoretical efficiency.