Modeling of the Electrochemical Motion Sensor Conversion Factor at High Frequencies.

Vadim Agafonov,Jian Chen,Bowen Liu,Iuliia Kompaniets

doi:10.3390/mi13020153

Abstract

The conversion factor of the electrochemical motion sensors at low frequencies is usually quite high. At the same time, it decreases significantly with the increase in frequency. Thus, increasing the conversion factor for high frequencies is essential for practical use. In this work, the theoretical model that allows establishing the basic laws governing the conversion of high-frequency signals in an electrochemical cell has been suggested. The approach was based on the fact that in the case of high frequencies, the diffusion length is less than the distance between the electrodes and the thickness of the channel and it is enough to consider the transformation of the fluid motion into electrical current only near the cathodes. It was found that the signal output current can be represented as the sum of the term which is proportional to the steady-state concentration gradient along the surface on which the cathode is located, and the term proportional to the concentration gradient normal to the surface. Both first and second terms and the total signal current have been calculated for a particular case of a four-electrode planar system. The practical conclusion is that the high frequency conversion factor increases with the interelectrode distance and the channel width decreases compared to the cathode dimension.

Highlights

Electrochemical cells with characteristic geometrical dimensions of electrode systems from one to several hundred micrometers are used as sensitive elements of motion sensors and wave fields in seismometers, accelerometers, geophones and hydrophones [1–13].The most important advantage of electrochemical sensors is a high conversion coefficient in combination with a rather simple design, the production of which on a mass scale is possible with the use of modern micromachined technologies
The obtained distribution is characterized by the presence of pronounced maximums of the current density at the edges of the electrodes because of the diffusion of active carriers on these parts of the electrodes from the area directly above the electrode and from the areas adjacent to the electrodes
High frequencies are understood as signal frequencies at which the diffusion length is significantly less than the distance between the electrodes

Summary

Introduction

The most important advantage of electrochemical sensors is a high conversion coefficient in combination with a rather simple design, the production of which on a mass scale is possible with the use of modern micromachined technologies. The fact is that at low frequencies, the conversion coefficient of electrochemical sensors is always quite high. Even the very first sensors of this type had extremely high sensitivity at low frequencies [18,19]. With an increase in frequency, the conversion coefficient of early versions of electrochemical sensors decreased dramatically, which limited the range of the first samples to a band of up to 0.5 Hz [18–22]. Thanks to the efforts of many researchers and technological advances, the sensitivity at high frequencies and the measurement range were significantly increased. When compared with other technologies (piezoelectric, electrodynamic sensors), a typical situation is when

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