An Improved Measurement System for Electrical Bioimpedance Spectroscopy

Electrical bioimpedance spectroscopy offers abundant information for medical research and clinical practice, exhibiting vast potential across a wide range of applications. That acquires information about impedance changes at multiple frequencies by injecting a low electrical current into the object being measured and analyzing the resultant voltage response. The aim of this paper is to develop a bioimpedance spectroscopy system which can measure bioimpedance information continuously and reliably. The bioimpedance spectroscopy system was designed to measure the impedance
$(\left\vert \boldsymbol{Z}\right\vert)$
and the phase angle
$(\theta)$
with a maximum frequency of up to 1 MHz. The in-phase/quadrature-phase (IQ) demodulation was employed to derive impedance information of the object by demodulating voltage response, and the improved impedance calibration circuit effectively minimizes errors arising from the measurement signal passing the high-pass filter, leading to a notable improvement in the accuracy of impedance measurements within the system. Tests are performed in the range of 10 kHz to 100 kHz, which is suitable for bioimpedance spectroscopy. The measurement system was calibrated using pure resistors with resistance values ranging from
$\mathbf{51}\boldsymbol{\Omega}$
to
$\mathbf{20}\ \mathbf{k}\boldsymbol{\Omega}$
and the calibration error was within 3 %. Additionally, this measurement system was evaluated against a high-precision commercial impedance analyzer (Agilent 4294A). Employing a carrot as the impedance model, the amplitude and phase errors were observed to be less than 2 %. This indicates the stability and accuracy of our measurement system in bioimpedance analysis.