Measuring Electrolyte Impedance and Noise Simultaneously by Triangular Waveform Voltage and Principal Component Analysis.

Shanzhi Xu,Peng Wang,Yonggui Dong

doi:10.3390/s16040576

Abstract

In order to measure the impedance variation process in electrolyte solutions, a method of triangular waveform voltage excitation is investigated together with principal component analysis (PCA). Using triangular waveform voltage as the excitation signal, the response current during one duty cycle is sampled to construct a measurement vector. The measurement matrix is then constructed by the measurement vectors obtained from different measurements. After being processed by PCA, the changing information of solution impedance is contained in the loading vectors while the response current and noise information is contained in the score vectors. The measurement results of impedance variation by the proposed signal processing method are independent of the equivalent impedance model. The noise-induced problems encountered during equivalent impedance calculation are therefore avoided, and the real-time variation information of noise in the electrode-electrolyte interface can be extracted at the same time. Planar-interdigitated electrodes are experimentally tested for monitoring the KCl concentration variation process. Experimental results indicate that the measured impedance variation curve reflects the changing process of solution conductivity, and the amplitude distribution of the noise during one duty cycle can be utilized to analyze the contact conditions of the electrode and electrolyte interface.

Highlights

With the rapid development of impedance biosensors, the planar-interdigitated electrode (IDT)has been widely used in the research of solution impedance measurement, in applications such as water quality monitoring [1,2,3], pathogen concentration detection [4,5,6], and the identification of different substances by taste sensors [7,8]
When measuring solution impedance, the nonlinear polarization of the electrode-electrolyte interface causes current waveform distortion to a certain degree, and higher order harmonics will appear in the response current signals [10,11]
The triangular waveform signal is digitally generated by a direct digital synthesizer (DDS) implemented in a field-programmable gate array (FPGA), and transformed to analog triangular waveform voltage utr by a digital-to-analog (D/A) converter

Summary

Introduction

With the rapid development of impedance biosensors, the planar-interdigitated electrode (IDT). Has been widely used in the research of solution impedance measurement, in applications such as water quality monitoring [1,2,3], pathogen concentration detection [4,5,6], and the identification of different substances by taste sensors [7,8]. Sinusoidal waveform voltage excitation is commonly used in impedance measurement with IDT. The response current to a sinusoidal voltage excitation will be a standard sinusoidal signal at the same frequency. When measuring solution impedance, the nonlinear polarization of the electrode-electrolyte interface causes current waveform distortion to a certain degree, and higher order harmonics will appear in the response current signals [10,11]. The noise originating from the electrode interface, such as thermal

Methods

Results

Discussion

Conclusion