A Novel Method for Estimating the Fractional Cole Impedance Model Using Single-Frequency DC-Biased Sinusoidal Excitation

The Cole model is a widely used fractional circuit model in electrical bioimpedance applications for evaluating the content and status of biological tissues and fluids. Existing methods for estimating the Cole impedance parameters are often based onmulti-frequency data obtained from stepped-sine measurements fitted using a complex nonlinear least square (CNLS) algorithm. Newly emerged numerical methods from the magnitude of electrical bioimpedance data-only do not need CNLS fitting, but they still requiremulti-frequency stepped-sine data. This study proposes a novel approach to estimating the Cole impedance parameters that combines a numerical and time-domain fitting method based on asingle-frequency DC-biased sinusoidal current excitation. First, the transient and steady-state voltage responses along with the current excitation are acquired in electrical bioimpedance measurement. From the sampled data, a numerical method is applied to provide the initial estimation of the Cole impedance parameters, which are then used in a time-domain iterative fitting algorithm. The accuracy of the algorithm proposed is tested with noisy electrical bioimpedance simulations. The maximum relative error of the estimated Cole impedance parameters is 1% considering 2% (34 dB) additive Gaussian noise. Experimental measurements performed on a 2R-1C circuit and some fruit samples show a mean difference less than 1% and 5%, respectively, compared to the Cole impedance parameters estimated from a commercial electrical bioimpedance analyzer performing stepped-sine measurements and CNLS fitting. This is the first method that allows estimating the Cole impedance parameters fromsingle-frequency electrical bioimpedance data. The approach presented could find broad use in many applications, including single-frequency body impedance analysis.

Automated summary

The study introduces a novel approach to estimating Cole impedance parameters using numerical and time-domain fitting methods with single-frequency current excitation. Experimental results show high accuracy and potential for various applications.