Modified Digital Correlation Technique for Accurate Phase Measurement in Multi-Frequency Bio-Impedance Analysis

Abstract

In bio-impedance analysis (BIA), high-frequency low-amplitude alternating current (AC) signals can incur time delays due to the capacitive nature of human cell membranes, and the characteristics of human tissues can be assessed from these delays in terms of phase changes. To accurately measure the phase changes, this work proposes a modified digital correlation-based phase measurement method. The accuracy of the general correlation technique is improved through digital direct synthesis (DDS) and digital correlation of unipolar square input signals. The proposed method is established through memory management and frequency adjustment. The result shows that, compared to the existing methods, the proposed method needs fewer hardware components, has better accuracy of 0.2° and higher frequency compatibility from 5 kHz to 1 MHz, and requires lower cost (140 USD). The method can be applied for the BIA of all types of tissues (recently used in COVID detection and care) and for the applications where efficient phase measurement is required.