Ĭlassic sensing device used in most of these achievements is a solid-state interdigitated electrodes (IDE) sensor which is stimulated by a sinusoidal wave. This paper focuses on electrical measurements of liquid mixtures in order to extract the impedance modeled as an parallel dipole. In order to face this complex challenge, instrumentation solutions are constantly developed. The quantification and qualification of liquid properties such as ionic concentration, permittivity, or pH are of major interest for the fluid identification in several domains like medicine, biology, or chemistry. We discussed and identified the sources of measurement errors as circuit parasitic capacitances, switching clock feedthrough, charge injection, bandwidth, and control-current quality. Experiments on water-glycerol mixtures validate the proposed sensing approach to measure the permittivity and the conductivity simultaneously. The results show excellent linearity and prove the repeatability of the measurements. Conductivities of saline NaCl and KCl solutions, being first calibrated by commercial equipment, are characterized by a system prototype.
The system interface is portable and only a small number of electrical components are used to generate the expected signal. This concept extends the Triangular Waveform Voltage (TWV) signal generation technique and is implemented by a system which consists in a closed-loop current-controlled oscillator and only requires DC power to operate. The principle consists in the generation of a current square wave and its application to the sensor to create a triangular output voltage which contains both the conductivity and permittivity parameters in a single periodic segment.
We present a methodology and a circuit to extract liquid resistance and capacitance simultaneously from the same output signal using interdigitated sensing electrodes.