Enhancing the Precision of AD5940 Segmental Bioimpedance Measurements through Self-Calibration

Bioimpedance spectroscopy offers potential advancements in patient care through continuous monitoring in several medical conditions. Researchers attempted to develop wearable devices for segmental bioimpedance measurement but commercially available sensors had limitations regarding maximum frequency range and minimum measurable impedance values. Custom analog front-ends were typically designed, complicating the system and increasing the final device’s size. Recently, the AD5940 system-on-chip for bioimpedance measurement has entered the market, reporting a wider range of frequencies and impedances. However, in specific cases like calf bioimpedance measurement the AD5940 chip exhibits systematic errors in both magnitude and phase measurements. This study investigates the necessary calibration for this chip to measure small impedance values and compares its performance with the widely used commercial device, Impedimed SFB7. Three devices were used: the AD5940 evaluation board, a custom PCB, and the SFB7 device. Measurements before and after calibration were conducted on three RRC boards simulating human calf tissue. The calibration significantly improved the performance of the AD5940 and Volum devices, reducing the error to less than 1%. These findings highlight the potential of the AD5940 chip for home-based patient care applications.