Design and evaluation of a fast Fourier transform-based nonlinear dielectric spectrometer

Abstract

Nonlinear dielectric spectroscopy of micro-organism is carried out by applying a moderate electrical field to an aqueous sample through two metal electrodes. Several ad hoc nonlinear spectrometers were proposed in the literature. However, these designs barely compensated the nonlinear distortion derived from the electrode-electrolyte interfaces (EEI). Moreover, the contribution of the suspension is masked by the effect of the nonlinearity introduced by the electrode contacts. Conversely, the nonlinear capability of a commercial tetrapolar analyzer has not been fully investigated. In this paper a new nonlinear tetrapolar spectrometer is proposed based on a commercial linear apparatus and ad hoc control and signal processing software. The system was evaluated with discrete electronic phantoms and showed that it can measure nonlinear properties of aqueous suspension independently of the presence of EEI (ANOVA test, p>0.001). It was also tested with real aqueous samples. The harmonics observed in the current that circulates through the sample reveals useful information about the transfer function of the sample. The total harmonic distortion was computed for linear mediums. Values lower than -60 dB suggest that the system has enough capability to perform nonlinear microbiological analysis. Design specifications, sources of interference, and equipment's limitations are discussed.

Evaluation of the Nonlinear Response of KCl Solution to High-Amplitude Stimulation Using a Four-Point Cylindrical Gold Electrode

“…To administer a sinusoidal voltage with a low frequency and a high amplitude, we utilized the Instek-AFG. The harmonics of the device across the whole range of amplitudes fall below −60 dBc, making it appropriate for NLDS. , …”

“…Initially, we used a circuit phantom, specifically that presented by Treo and Felice, 13 to assess the accuracy of our method. We utilized this phantom to measure the current harmonic generated by it and subsequently compared the obtained data with the simulation conducted in Spice.…”

“…The harmonics of the device across the whole range of amplitudes fall below −60 dBc, making it appropriate for NLDS. 12,13 A sinusoidal voltage signal with a frequency of 23 Hz is applied to the outer electrodes. Subsequently, the voltage of the two central electrodes and the voltage across the series resistance are measured separately, both with and without the use of the amplifier.…”

Nonlinear Impedance of Whole Cells Near an Electrode as a Probe of Mitochondrial Activity

“…Surprisingly, low voltage, lower frequency (~100 Hz) sinusoidal excitation has been found to generate harmonics in whole cells, but the origin of the harmonics and the connection with membrane protein activity has not been well-elucidated [ 7 , 14 , 15 , 16 ]. We have previously reported that 4-probe nonlinear dielectric spectroscopy is sensitive to the metabolic state of budding yeast [ 7 ], but this previous work did not explore if the harmonics originated from the bulk of the suspension [ 17 ] or from the electrode interfacial region [ 16 ]. This information is important for understanding the relationship between metabolism and the applied electric field.…”