Electrolyte impedance measurement by triangular waveform voltage and principal component analysis

In order to measure the minor impedance changing process in low concentrated electrolyte solutions, a method of triangular waveform voltage excitation is investigated together with principal component analysis (PCA). The immersed planar-interdigitated electrode (IDT) is excited by a triangular waveform voltage signal. The response current during one duty cycle is sampled to construct a measurement vector. The measurement matrix is then constructed by the measured vectors obtained at different measurements. After processed by PCA, the time-varying information of solution impedance is obtained from the principal components. Since the measurement results are independent on the equivalent circuit models, the noise-induced problems encountered during equivalent impedance calculation are therefore avoided. Two kinds of commonly used planar-interdigitated electrodes, i.e. Au electrode on Si substrate and Au electrode on PCB substrate, are experimentally tested in low concentrated KCl solutions. Experimental results indicate that minor solution conductivity changes can be effectively measured by the proposed method.