Sensitivity Improvement to Eddy Current Displacement Sensor in Full Maglev LVAD

Abstract

Eddy current displacement sensors in full-maglev left ventricular assist devices (LVADs) suffer from low sensitivity resulting from the use of a stator titanium alloy frame. The aim of this study was to develop a methodology to improve the sensitivity of eddy current displacement sensors and formulate a mathematical model of coil impendence to illustrate the impact of the addition of a titanium alloy frame between the sensor coils and the measured conductor. An equivalent mutual inductance model in the circuit was established for LVADs with and without a titanium alloy frame stator wall. Comparing the differences in excitation frequency and measured metal conductivity considering the relation of inductance with displacement enabled the development of methods to improve the sensitivity of the sensor when a titanium frame is added to the stator. An experiment was conducted to collect and analyze data to ascertain the relation between impedance and rotor displacement considering different excitation frequencies, stators with and without a titanium alloy frame, and the copper ring. Relatively high sensitivity was acquired when titanium frames of 0.25-mm thickness were applied to both the stator and rotor with an additional copper ring attached to the rotor frame at an excitation frequency of 475 kHz.