A Goertzel Filter-Based System for Fast Simultaneous Multi-Frequency EIS

Abstract

Bioimpedance measurement is a non-invasive, radiation-free, and inexpensive method for measuring the electrical properties of biological tissues. In applications where transients occur, the commonly used swept sinewave is replaced with broadband signals such as multisine. This makes the signal generation and the extraction of the real and imaginary parts of the impedance challenging. In this brief, an alternative to traditional fast Fourier transform (FFT) or coherent demodulation is presented. Based on the Goertzel filter, this alternative is simpler and requires very few digital resources. Its robustness to the harmonic fold back phenomenon, enables simple ternary current pulses to be used for excitation. The developed digital architecture is capable of simultaneous demodulation of 16 frequencies with an accuracy of 97% and 96% on the magnitude and phase measurement respectively. Employing a ternary sequence allows the use of a low power H-bridge current driver. The analog front-end and demodulation algorithm were implemented in an ASIC using a 180-nm CMOS technology. The system was tested on an isolated pig heart distinguishing edema from non-edema tissue by impedance changes.

Development of a Biosensor for fast point-of-care Blood Analysis of Troponin

“…The electrode array was designed based on upgrading previous work with the tau biosensor [10], where a four microband printed-circuit board electrode was used. In this work, the four microband array was designed with a glass substrate to reduce the cost per unit and allow the sensors to be disposable.…”

“…A full EIS measurement cycle takes 0.23 seconds over the 14 frequency points. The speed can be improved by using simultaneous multi-frequency measurement instead of single frequency sweep, such as the method proposed in [10]. However, the measurement frequency range in [10] is limited between 10 kHz and 1 MHz.…”

“…The electrodes spacing can adjust the sensitivity at different distances above the electrodes to allow the maximin sensitivity of the analytical layer. Only one report on a tetrapolar EIS biosensor could be found for detecting the Alzheimer's disease-related tau protein, and the biosensor achieved a very low sensitivity (LOD = 1.37 pg/ml) and very good specificity [10]. To date, no tetrapolar EIS biosensors have been reported for cardiac troponin I detection.…”

Bioimpedance Sensors: A Tutorial

“…using undersampling [220]. Another approach is based on the Groetzel filter [221]- [223]. This essentially converts the discrete time Fourier transform (DTFT) equation into a recursive filter, that can be implemented by a second order infinite impulse response structure that is split into two parts [221].…”