Measurement of High-Frequency Patient Leakage Current From a Transmitting Coil in a Transcutaneous Energy Transmission System for Ventricular Assist Device

The transcutaneous energy transmission system (TETS) has been studied for wireless power supply in ventricular assist devices embedded in the body. To be approved as a medical device, it is necessary to measure the high-frequency patient leakage current (
I_p
) and to suppress it to a safety limit below 10 mA. However, it is difficult to suppress because the terminal voltage and the frequency of the transmitting coil are extremely high (500 V and 400 kHz). In this study, we propose an original measurement method for
I_p
in TETS and measure the
I_p
. Furthermore, the suppression method of
I_p
is investigated using a high-frequency isolation transformer (HFIT) and an insulation sheet for transmitting coils. Consequently, an
I_p
of 17.14 mA is obtained when the HFIT without countermeasures and an insulation silicone sheet is used (Type A), whereas an
I_p
of 7.68 mA is obtained when using two series-connected HFITs and an expanded polystyrene sheet with a thickness of 3.58 mm (Type B). Thus, it is possible to drastically suppress
I_p
below 10 mA. Additionally, we define the combined capacitance
C
_Com
based on the series connection of the capacitance of the insulation transformer
C_p
and that of the insulation sheet
C_c
and calculate the theoretical
I_p
. The theoretical
I_p
decreases from 20.8 mA for Type A to 5.6 mA for type B. The calculation results of
I_p
are mostly in agreement with the measurement results, indicating that a reduction in
C
_Com
is important for suppressing
I_p
of the TETS.