An amplitude and phase detector for dielectric spectroscopy systems

• Main Authors: Ye. Antonenko, V. Kozheshkurt, D. Shtoda, V. Katrich
• Format: Article
• Language: English
• Published: Akademperiodyka 2020-09-01
• Series: Радиофизика и электроника
• Subjects: amplitude and phase detector; dielectrometry; impedance; impedance spectroscopy; phase difference; three voltmeter method
• Online Access: http://re-journal.org.ua/sites/default/files/file_attach/2020-3/10.pdf

Subject and Purpose. The objective of the work is to investigate a possibility for the three voltmeter method application to measuring the phase and amplitude difference between two signals in dielectrometry and impedance spectroscopy systems. For the three voltmeter method implementation, two functional schemes – with addition or subtraction of signals – are chosen to consider. Methods and Methodology. The current state of dielectric spectroscopy as a method enabling measurements of the relative component content in binary solutions and suspensions is surveyed, with emphasis on special merits of this method in the analysis of biochemical properties of liquids. Calculation formulas of the modulus and the real and imaginary parts of the measuring cell impedance are presented for the procedure of measuring cell replacement by an equivalent circuit. The circuit equivalent parameters enable calculating the conductivity and permittivity of the investigated liquid. It is noted that the calculation formulas of the equivalent capacitance and impedance of the measuring cell do not incorporate effect of the adsorption of substance molecules and particles in proximity to the electrode surface, which can be responsible for conductivity and permittivity errors. Results. A prototype of the amplitude and phase detector has been performed, its technical characteristics tested. Buffer cascades are added at the inputs of the detectors, which provides a –70 dB decoupling level between the measuring and reference channels. A two-stage detection scheme has been used, involving logarithmic and peak detectors. It has been shown that the two-stage detection reduces the ripple level of the measured signal at low frequencies. Good reasons for the signal subtraction scheme in dielectrometry systems have been presented. Conclusion. A scheme of a broadband, 1 Hz to 100 MHz, amplitude and phase detector has been proposed for dielectric spectroscopy systems. The phase difference measurement accuracy has been experimentally assessed. A detector calibration method has been suggested, reducing an absolute error of phase difference measurements down to ± 0.1°.