A portable electrochemical impedance spectroscopy (EIS) system has been developed based on FPGA for bio-detection. FPGA is a programmable signal processing chip, which cooperates with DAC module to generate the sweep excitation signal, controls ADC module to perform dual channel acquisition of voltage of a peripheral circuit, performs FFT and parameter calculation and transmits the result to PC for data processing. Based on FPGA internal programming, the system greatly reduces the size and achieves a single multi-frequency measurement, which enhances integration and portability of the system. The measurements of the electrical equivalent circuit by using the EIS system is compared with a high-precision commercial ZX70A impedance analyzer in the range of limited frequency of 100 Hz - 500 kHz. The result shows that the maximum relative error of amplitude and the maximum absolute error of phase are 2.42% and 0.936°, respectively. Finally, the EIS system is used to measure electrical impedance change during egg heating. The result shows that the impedance amplitude of egg decreases linearly with the increase of heating time and electrical characteristics of raw eggs and heated eggs are significantly different. These results verified that the developed EIS system achieve portable high-precision measurement of biological tissue.

Contact impedance has an important effect on micro electrical impedance tomography (EIT) sensors compared to conventional macro sensors. In the present work, a complex contact impedance effect ratio ξ is defined to quantitatively evaluate the effect of the contact impedance on the accuracy of the reconstructed images by micro EIT. Quality of the reconstructed image under various ξ is estimated by the phantom simulation to find the optimum algorithm. The generalized vector sampled pattern matching (GVSPM) method reveals the best image quality and the best tolerance to ξ. Moreover, the images of yeast cells sedimentary distribution in a multilayered microchannel are reconstructed by the GVSPM method under various mean magnitudes of contact impedance effect ratio |ξ|. The result shows that the best image quality that has the smallest voltage error UE = 0.581 is achieved with measurement frequency f = 1 MHz and mean magnitude |ξ| = 26. In addition, the reconstructed images of cells distribution become improper while f <; 10 kHz and mean value of |ξ| > 2400.

A 10-parameter Electrical Equivalent Circuit (10-parameter EEC) has been proposed to evaluate the electrochemical characterizations which are resistance, reactance and relaxation frequency of Lithium-ion battery (LIB) slurry under different components weight ratio of three samples composed of PVDF-NMP solution, Carbon Black (CB) absent slurry and CB present slurry. The 10-parameter EEC is constructed by combining the internal structure of LIB slurry and the electrochemical responses of three samples. Four conclusions are clarified by fitting Electrochemical Impedance Spectroscopy (EIS) Nyquist and Bode plots with the 10-parameter EEC. Firstly, the standard deviation S of the 10-parameter EEC <S_10-p> = 14.3% is lower than that of a conventional 8-parameter EEC <S_8-p> = 30.6% by ΔS = 16.3%. Secondly, the resistance of electric double layer (EDL) R_dl is firstly increased and then decreased as LiCoO₂ particles weight ratio wt_LiCoO2 is increased, which is well explained by LiCoO₂-PVDF ratio effect. Thirdly, the resistances of PVDF-NMP solution R_SO and conductive path R_p are the resistances of LiCoO₂-NMP interface dispersion and PVDF-NMP solution dispersion in LIB slurry. Lastly, relaxation frequencies of LiCoO₂-NMP interface dispersion f_relax,high and PVDF-NMP solution dispersion f_relax,low obtained from EIS experiment can be represented by those of f_relax1 and f_relax2 calculated from the 10-parameter EEC.

Particle dispersion behaviors in Lithium Ion Battery (LIB) are clarified by Electrochemical Impedance Spectroscopy (EIS) method based on the dielectric characteristics of cathode slurry, which are Carbon Black (CB) aggregation, CB-bare LiCoO₂ particles, CB path and CB-coated LiCoO₂ particles. The experimental particle dispersion behaviors are evaluated by numerical simulation. In the experiments, cathode slurry is stirred under different rotational speed n; meanwhile, in the simulation, medium conductivities σ_m and particle conductivities σ_p in cathode slurry model are changed. Herein, CB aggregation and CB path are verified by σ_m, while CB-bare LiCoO₂ particles and CB-coated LiCoO₂ particles are verified by σ_p. Compared with σ_p, σ_m plays important roles in determining particle dispersion behaviors because σ_m has the similar functions as n to change characteristic resistances R_cL and R_cH and characteristic frequencies f_cL and f_cH. Therefore, compared with CB-coated LiCoO₂ particles, CB path dominates the conductivity of cathode slurry in LIB. Furthermore, the dielectric characteristics of NMP solution, CB-NMP slurry and LiCoO₂-NMP slurry are investigated to clarify how each component of cathode slurry contribute to the whole Nyquist plot. The results show that the straight line is caused by adding CB, while low frequency semi-circle is caused by CB-bare LiCoO₂ particles. Electrical impedance spectroscopy (EIS) method, Lithium ion battery (LIB).